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Archive for the ‘Gene Regulation’ Category

Natural Killer Cell Response: Treatment of Cancer

Curator: Larry H. Bernstein, MD, FCAP

 

Molecular mechanisms of natural killer cell activation in response to cellular stress

C J Chan1,2,3, M J Smyth1,2,3,4,5 and L Martinet1,2,4,5        Edited by M Piacentini

Cell Death and Differentiation (2014) 21, 5–14;    http://www.nature.com/cdd/journal/v21/n1/full/cdd201326a.htm

Protection against cellular stress from various sources, such as nutritional, physical, pathogenic, or oncogenic, results in the induction of both intrinsic and extrinsic cellular protection mechanisms that collectively limit the damage these insults inflict on the host. The major extrinsic protection mechanism against cellular stress is the immune system. Indeed, it has been well described that cells that are stressed due to association with viral infection or early malignant transformation can be directly sensed by the immune system, particularly natural killer (NK) cells. Although the ability of NK cells to directly recognize and respond to stressed cells is well appreciated, the mechanisms and the breadth of cell-intrinsic responses that are intimately linked with their activation are only beginning to be uncovered. This review will provide a brief introduction to NK cells and the relevant receptors and ligands involved in direct responses to cellular stress. This will be followed by an in-depth discussion surrounding the various intrinsic responses to stress that can naturally engage NK cells, and how therapeutic agents may induce specific activation of NK cells and other innate immune cells by activating cellular responses to stress.

 

  • Stress induces specific intrinsic and extrinsic physiological mechanisms within cells that lead to their identification as functionally abnormal
  • Sources of cellular stress can be nutritional, physical, pathogenic, or oncogenic
  • Intrinsic responses to cellular stress include activation of the DNA-damage response, tumor-suppressor genes, and senescence
  • The extrinsic response to cellular stress is activation of the immune system, such as natural killer cells
  • Intrinsic responses to cellular stress can directly upregulate factors that can activate the immune system, and the immune system been shown to be indispensable for the efficacy of some chemotherapy

Further critical determinants of intrinsic responses to stress and cell death that can activate the immune system must be identified

  • Identification of the different cellular pathways and molecular determinants controlling the immunogenicity of different cancer therapies is required
  • How can we harness the ability of therapeutic agents to activate both the intrinsic and extrinsic responses to cellular stress to achieve more specific and safer approaches to cancer treatment?

Any insult to a cell that leads to its abnormal behavior or premature death can be defined as a source of stress. As the turnover and maintenance of cells in all multi-cellular organisms is tightly regulated, it is essential that stressed cells be rapidly identified to avoid widespread tissue damage and to maintain tissue homeostasis. Various intrinsic cellular mechanisms exist within cells that become activated when they are exposed to stress. These include activation of DNA-damage response proteins, senescence programs, and tumor-suppressor genes.1 Extrinsic mechanisms also exist that combat cellular stress, through the upregulation of mediators that can activate different components of the immune system.2 Although frequently discussed separately, much recent evidence has indicated that intrinsic and extrinsic responses to cellular stress are intimately linked.3

As the link between cell intrinsic and extrinsic responses to stress have been uncovered, these observations are now being harnessed therapeutically, particularly in the context of cancer.4 Indeed, various chemotherapeutic agents and radiotherapy are critically dependent on the immune system to elicit their full therapeutic benefit.5, 6 The mechanisms by which this occurs may be twofold: (i) the induction of intrinsic cellular stress mechanisms activates innate immunity and (ii) the release and presentation of tumor-specific antigens engages an inflammatory adaptive immune response.

NK cells are the major effector lymphocyte of innate immunity found in all the primary and secondary immune compartments as well as various mucosal tissues.7 Through their ability to induce direct cytotoxicity of target cells and produce pro-inflammatory cytokines such as interferon-gamma, NK cells are critically involved in the immune surveillance of tumors8, 9, 10 and microbial infections.11, 12 The major mechanism that regulates NK cell contact-dependent functions (such as cytotoxicity and recognition of targets) is the relative contribution of inhibitory and activating receptors that bind to cognate ligands.

Under normal physiological conditions, NK cell activity is inhibited through the interaction of their inhibitory receptors with major histocompatibility complex (MHC) class I.13, 14 However, upon instances of cellular stress that are frequently associated with viral infection and malignant transformation, ligands for activating receptors are often upregulated and MHC class I expression may be downregulated. The upregulation of these activating ligands and downregulation of MHC class I thus provides a signal for NK cells to become activated and display effector functions. Activating receptors are able to provide NK cells with a strong stimulus in the absence of co-stimulation due to the presence of adaptor molecules such as DAP10, DAP12, FcRγ, and CD3ζ that contain immunoreceptor tyrosine-based activating motifs (ITAMs).15, 16,17 By contrast, inhibitory receptors contain inhibitory motifs (ITIMs) within their cytoplasmic tails that can activate downstream targets such as SHP-1 and SHP-2 and directly antagonize those signaling pathways activated through ITAMs.18, 19, 20 The specific details of individual classes of inhibitory and activating receptors and their ligands are summarized in Figure 1 and have been extensively reviewed elsewhere.14, 21 Instead, this review will more focus on the relevant activating receptors that are primarily involved in the direct regulation of NK cell-mediated recognition of cellular stress: natural killer group 2D (NKG2D) and DNAX accessory molecule-1 (DNAM-1).

Figure 1.

Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the authorNK cell receptors and their cognate ligands. Major inhibitory and activating receptors on NK cells and their cognate ligands on targets are depicted. BAT3, human leukocyte antigen (HLA)-B-associated transcript 3; CRTAM, class I-restricted T-cell-associated molecule; HA, hemagglutinin; HLA-E, HLA class I histocompatibility antigen, alpha chain E; IgG, immunoglobulin G; LFA-1, leukocyte function-associated antigen-1; LLT1, lectin-like transcript 1; TIGIT, T cell immunoglobulin and ITIM domain

Full figure and legend (185K)

NK Cell-Mediated Recognition of Cellular Stress by NKG2D and DNAM-1

NKG2D is a lectin-like type 2 transmembrane receptor expressed as a homodimer in both mice and humans by virtually all NK cells.22, 23 Upon interaction with its ligands, NKG2D can trigger NK cell-mediated cytotoxicity against their targets. The ligands for NKG2D are self proteins related to MHC class I molecules.24 In humans, these ligands consist of the MHC class I chain-related protein (MIC) family (e.g., MICA and MICB) and the UL16-binding protein (ULBP1-6) family.25, 26 In mice, ligands for NKG2D include the retinoic acid early inducible (Rae) gene family, the H60 family, and mouse ULBP-like transcript-1 (MULT-1).27, 28, 29 NKG2D ligands are generally absent on the cell surface of healthy cells but are frequently upregulated upon cellular stress associated with viral infection and malignant transformation.3, 30 Indeed, NKG2D ligand expression has been found on many transformed cell lines, and NKG2D-dependent elimination of tumor cells expressing NKG2D ligands has been well documented in vitro and in tumor transplant experiments.25, 30, 31, 32, 33 In humans, NKG2D ligands have been described on different primary tumors34, 35 and specific NKG2D gene polymorphisms are associated with susceptibility to cancer.36 Finally, blocking NKG2D through gene inactivation or monoclonal antibodies leads to an increased susceptibility to tumor development in mouse models,37, 38demonstrating the key role played by NKG2D in immune surveillance of tumors. NKG2D can also contribute to shape tumor immunogenicity, a process called immunoediting, as demonstrated by the frequent ability of tumor cells to avoid NKG2D-mediated recognition through NKG2D ligand shedding, as discussed later in this review.38, 39, 40

DNAM-1 is a transmembrane adhesion molecule constitutively expressed on T cells, NK cells, macrophages, and a small subset of B cells in mice and humans.41, 42, 43 DNAM-1 contains an extracellular region with two IgV-like domains, a transmembrane region and a cytoplasmic region containing tyrosine- and serine-phosphorylated sites that is able to initiate downstream activation cascades.41, 44 There is accumulating evidence showing that DNAM-1 not only promotes adhesion of NK cells and CTLs but also greatly enhances their cytotoxicity toward ligand-expressing targets.41, 45, 46, 47, 48, 49, 50 The ligands for DNAM-1 are the nectin/nectin-like family members CD155 (PVR, necl-5) and CD112 (PVRL2, nectin-2).45, 46 Like NKG2D ligands, DNAM-1 ligands are frequently expressed on virus-infected and transformed cells.51, 52DNAM-1 ligands, especially CD155, are overexpressed by many types of solid and hematological malignancies and blocking DNAM-1 interactions with its ligands reduces the ability of NK cells to kill tumor cells in vitro.41, 49, 53, 54, 55, 56, 57 Further evidence of the role of DNAM-1 in tumor immune surveillance is provided by studies using experimental and spontaneous models of cancer in vivo showing enhanced tumor spread in the absence of DNAM-1.47, 48, 49, 50, 58

As NKG2D and DNAM-1 ligands are frequently expressed on stressed cells, many studies have sought to determine the mechanisms that underpin these observations. The guiding hypothesis for these studies is that cell-intrinsic responses to stress are directly linked to cell-extrinsic responses that can trigger rapid NK cell surveillance and elimination of stressed cells. Indeed, major cell-intrinsic responses to cellular stress can directly lead to NK cell-activating ligand upregulation and are outlined in the following sections.

The DNA-Damage Response

Cellular stress caused by the activation of the DNA-damage response leads to downstream apoptosis or cell-cycle arrest. The activation of DNA-damage checkpoints occurs when there are excessive DNA strand breaks and replication errors, thereby representing an important tumorigenesis barrier that can slow or inhibit the progression of malignant transformation.59, 60 Two major transducers of the DNA-damage response are the PI3-kinase-related protein kinases ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related). ATM and ATR can modulate numerous signaling pathways such as checkpoint kinases (Chk1 and Chk2, which inhibit cell-cycle progression and promote DNA repair) and p53 (which mediates cell-cycle arrest and apoptosis).61

In addition to the induction of cell-cycle arrest and apoptosis, activation of the DNA-damage response has been shown to promote the expression of several activating ligands that are specific for NK cell receptors, primarily those of the NKG2D receptor. These findings have shown a critical direct link between cellular transformation, apoptosis, and surveillance by the immune system.62 The first evidence of this link between DNA damage and immune cell activation was provided by Raulet and colleagues who showed that NKG2D ligands were upregulated by genotoxic stress and stalled DNA replication conditions known to activate either ATM or ATR.63 These observations have now been extended by several other studies that have defined further DNA-damaging conditions (e.g., genotoxic drugs/chemotherapy, deregulated proliferation, or oxidative stress) that can promote NKG2D ligand upregulation.64, 65, 66, 67

The role of the DNA-damage response in controlling NKG2D ligand expression and subsequent NK cell activation has also been demonstrated in the context of anti-viral immunity, specifically in Abelson murine leukemia virus infection.68 This pathogen was shown to induce activation-induced cytidine deaminase (AID) expression outside the germinal center, resulting in generalized hypermutation, DNA-damage checkpoint activation, and Chk1 phosphorylation. The genotoxic activity of virally induced AID not only restricted the proliferation of infected cells but also induced the expression of NKG2D ligands. More recently, another member of APOBEC-AID family of cytidine deaminases, A3G, has been shown to promote the recognition of HIV-infected cells by NK cells after DNA-damage response activation.69 In this study, viral protein Vpr-mediated repair processes, which generate nicks, gaps, and breaks of DNA, activate an ATM/ATR DNA-damage response that leads to NKG2D ligand expression.

The DNA-damage sensors ATM and ATR have also been shown to regulate other key NK cell-activating ligands such as the DNAM-1 ligand, CD155.58, 65, 70 For example, in the Eμ-myc spontaneous B-cell lymphoma model, activation of the DNA-damage response leads to the upregulation of CD155 in the early-stage transformed B cells, subsequently activating spontaneous tumor regression in an NK cell- and T-cell-dependent manner.58 The DNA-damage response can also regulate the expression of the death receptor DR5.71 The engagement of DR5 by the effector molecule TRAIL, which is expressed by NK cells and T cells, can induce apoptosis of target cells and has been shown to have a key role in immune surveillance against tumors.72 Collectively, these results suggest that the detection of DNA damage, primarily through ATM and ATR, may represent a conserved protection mechanism governing the immunogenicity of infected or transformed cells, leading to direct recognition by NK cells (Figure 2).

Figure 2.

Figure 2 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the authorOverview of the molecular pathways leading to NK cell recognition of intrinsic cellular stress. Oncogenic transformation and viral infection can activate intrinsic cellular responses to stress. These responses include activation of the DNA-damage response, senescence, tumor suppressors, and the presentation and/or release of HSPs that, in turn, can activate NK cells through various receptor–ligand interactions. Senescent cells can also release pro-inflammatory cytokines that can recruit NK cells and other innate immunity, such as macrophages. CCL2, C-C motif chemokine ligand 2; CXCL11, C-X-C motif chemokine ligand 11; DR, death receptor 5; IFN, interferon; IL, interleukin; LFA-1, leukocyte function-associated antigen-1; TRAIL, tumor necrosis factor-related apoptosis-inducing ligand

Full figure and legend (146K)

As a result of these studies, many therapeutic agents known to induce DNA damage have been evaluated for their ability to increase the immunogenicity of cancer cells for a more targeted therapeutic approach using NK cells.64, 65 For example, treatment of multiple myeloma cells with doxorubicin, melphalan, or bortezomib can lead to DNAM-1 and NKG2D ligand upregulation.65Indeed, many chemotherapeutic agents commonly used, especially in hematological malignancies, can trigger the DNA-damage pathway. Therefore, it is reasonable to speculate that there is a general role of ATM and ATR in the induction of NK cell activation as a therapeutic effect of these agents.

Senescence

Cellular senescence is generally defined as a growth-arrest program in mammalian cells that limits their lifespan.73 The major type of cellular senescence is replicative senescence that occurs due to telomere shortening. However, it is now generally accepted that premature senescence can also occur due to oncogene activation (oncogene-induced senescence) and/or the loss/gain of tumor-suppressor gene function, in the absence of telomere shortening.74 Thus, premature senescence is an important barrier against malignant transformation.59 Upon engagement of the senescence program, although cells are in growth arrest, they remain metabolically active and can produce many pro-inflammatory cytokines, as well as upregulate adhesion molecules and activating ligands to alert the immune system.75, 76, 77Activation of the immune system, in particular innate immunity, has a critical role in the clearance of senescent cells.78, 79, 80, 81More specifically, in a model of hepatocellular carcinoma, it has been shown that reactivation of p53 can induce a senescence program, resulting in tumor regression through the activation of NK cells, macrophages, and neutrophils. Of note, intercellular adhesion molecule (ICAM)-1, which can trigger both adhesion and cytotoxicity of NK cells,82 and interleukin-15, a cytokine that can promote NK cell effector function,83 were both upregulated in senescent tumors. More recently, the potential contribution of NK cells was also shown in the clearance of senescent hepatic stellate cells, a mechanism important in limiting liver fibrosis in response to a fibrogenic agent.80 ICAM-1, NKG2D ligands (MICA and ULPB2), and DNAM-1 ligands (CD155) were all upregulated on senescent hepatic stellate cells.

The specific mechanisms linking the senescence program to immune activation are not yet fully understood. However, the intracellular molecular mechanisms that govern induction of senescence may provide possible indications. Both replicative senescence and premature senescence (e.g., oncogene-induced senescence) have been shown to have common molecular determinants, such as the activation of the DNA-damage response pathway (e.g., ATM and ATR) and downstream activation of p53 and p16INK4A.1, 59, 84, 85, 86 Activation of the DNA-damage response would presumably initiate the upregulation of NK cell-activating ligands as previously discussed. However, how senescence may be linked to the induction of pro-inflammatory cytokine release is a more compelling question and requires further investigation (Figure 2). Nevertheless, induction of pro-inflammatory cytokines is an important protective mechanism in order to recruit immune cells that can rapidly recognize and remove senescent cells. Interestingly, activation of NK cells by senescent cells has been observed in a clinical context when multiple myeloma cells were treated with chemotherapy and genotoxic agents.65 In this setting, NKG2D and DNAM-1 ligands were both upregulated through a mechanism that required activation of the DNA-damage pathway initiated by ATM and ATR.65

Tumor Suppressors: p53

p53 is a potent tumor suppressor and central regulator of apoptosis, DNA repair, and cell proliferation, that is activated in response to DNA damage, oncogene activation, and other cellular stress.87 The number of identified cellular functions that p53 regulates has greatly increased over the past few years, and there is now a vast array of evidence that shows that p53 can be induced by viral infection88 to limit pathogen spread by inducing apoptosis.89, 90 Furthermore, p53 not only acts as an intrinsic barrier against tumorigenesis or pathogenic spread but can also lead to increased cellular immunogenicity. For example, p53 reactivation in a hepatocellular carcinoma can promote tumor regression mediated by innate immunity.78 A direct link between p53 expression and immune cell recognition was recently provided by Textor et al.91 where expression of p53 in lung cancer cell lines strongly upregulated the NKG2D ligands ULBP1 and 2, resulting in NK cell activation. Subsequently, p53-responsive elements were found to directly regulate ULBP1 and 2 expression, the deletion of which abolished the capacity of p53 to mediate ULBP1 and 2 upregulation. Another recent report that used a pharmacological activator of p53 confirmed the ability of p53 to directly induce ULBP2 expression that was independent of ATM/ATR.92 However, it has also been shown that miR34a and miR34C microRNAs (miRNAs) induced by p53 can target ULBP2 mRNA and reduce its cell-surface expression, suggesting that p53 may have a dual role in regulating ULBP2 expression.93 Finally, early work showed that NKG2D ligands can be upregulated by ATR/ATM in the total absence of p53 in tumor cell lines,62, 63 suggesting the existence of ATM/ATR-dependent and p53-independent pathways that regulate NKG2D ligand expression in response to cellular stress.

In addition to regulating NK cell ligand expression, genetic reactivation of p53 in tumors can also induce a wide array of pro-inflammatory mediators ranging from adhesion receptor (ICAM-1) expression to the production of various chemokines (CXCL11 and monocyte chemoattractant protein-1) and cytokines (interleukin-15).78 Furthermore, recent studies in anti-viral immunity indicate that several interferon-inducible genes and Toll-like receptor-3 expression are direct transcriptional targets of p53 and that p53 contributes to production of type I interferon by virally infected cells.94, 95, 96 All together, these studies suggest that p53 accumulation could represent a key determinant of the immunogenicity of stressed cells that are infected or undergoing malignant transformation through its ability to regulate innate immune activation.

Oncogenes

Malignant transformation is a complex process that frequently involves the activation of one or more oncogenes in addition to the inactivation or mutation of tumor-suppressor genes (e.g., p53). Oncogene activation is a powerful inducer of cellular stress that is able to activate intrinsic cellular programs that lead to cell apoptosis or senescence (e.g., activation of the DNA-damage response and p53).1 In addition, many recent reports have also shown that major oncogenes can activate extrinsic responses to cellular stress through inducing the upregulation of NK cell-activating ligands.63, 97, 98 This suggests that oncogene activation can represent a key cellular event in alerting the immune system to ongoing cellular transformation (Figure 3).

Figure 3.

Figure 3 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the authorMolecular mechanisms that regulate the cell surface expression of NKG2D ligands. The major group of NK cell-activating ligands that are upregulated by intrinsic cellular responses to stress are those that bind the NKG2D receptor. Activation of the DNA-damage response, senescence, oncogenes, tumor suppressors, or sensing of deregulated proliferation can induce NKG2D ligand gene transcription and increase mRNA translation, leading to extracellular protein expression. MMP, matrix metalloproteases

Full figure and legend (183K)

The enhanced expression of the proto-oncogene Myc has been described as a critical event leading to cellular transformation and is a frequently found genetic alteration in cancer.99 In a recent study, again using the Eμ-myc model, Medzhitov and colleagues demonstrated the ability of c-Myc to alert NK cells to early oncogenic transformation through the upregulation of Rae-1.97 In this study, the induction of Rae-1 was dependent on the direct regulation of Rae-1 transcription by Myc through its interaction with the Raet1 epsilon gene. Collectively, these results provide a possible direct molecular mechanism to explain the increased susceptibility of NKG2D gene-targeted mice to lymphoma development in the Eμ-myc model.38

Recent evidence suggests that several oncogenic mutations of Ras (H-Ras, N-Ras, and K-Ras) can also regulate NKG2D ligand expression in both mice and humans.98 Interestingly, in this case, NKG2D ligands were regulated through MAPK/MEK and PI3K pathways downstream of oncogenic H-RasV12. The activation of PI3K pathways, and more particularly the p110α subunits by virus-encoded proteins, has also been shown to induce the Rae-1 family of ligands.100 As many viruses can manipulate the PI3K pathway101 and tumors often bear Ras and p110α oncogene mutations,102 collectively, this data suggests that there is the existence of a common molecular mechanism by which NK cells sense cellular stress mediated by PI3K-dependent regulation of NKG2D ligands.

Interestingly, whereas Myc was involved in the transcriptional regulation of NKG2D ligands, PI3K can increase NKG2D ligand expression by increasing the translation of Rae-1 mRNA.98 This involved the induction of eIF4E, a protein that enhances the translation of mRNA.103 As number of tumors and viruses can upregulate host translation initiation machinery through the overexpression of eIF4E,104, 105 this may represent an important means by which NK cells can discriminate tumor- and virus-infected cells from normal cells.

Heat-Shock Proteins (HSPs)

HSPs are highly conserved intracellular chaperone molecules that are present in most prokaryotic and eukaryotic cells that mediate protection against cellular damage under conditions of stress. HSPs are distributed in most intracellular compartments of cells where they support the correct folding of nascent polypeptides, prevent protein aggregation, and assist in protein transport across membranes.106 Many tumors display overexpression of HSPs as a response to cellular stress induced by oncogenic transformation.107, 108 HSPs can also be mobilized to the plasma membrane, or even released from cells, under conditions of stress.109

Although intracellular HSPs can promote cell survival by interfering with different apoptosis components, many studies have reported that membrane-bound or soluble HSPs can directly stimulate innate immunity.110 A major immunostimulatory function of HSPs is to promote the presentation of tumor-specific antigens by MHC class I to CD8 T cells.111, 112, 113 Soluble and membrane-bound HSPs can also induce antigen-presenting cell maturation and the resultant secretion of pro-inflammatory cytokines.114, 115, 116Finally, HSPs may directly activate NK cells as HSP70, when overexpressed on tumor cells, can induce a selective dose-dependent increase in NK cell-mediated cytotoxicity in vitro.117 NK cells may directly recognize HSP70 through a 14-amino-acid oligomer (TKD) that is localized in the C-terminal domain of the protein through CD94.118, 119 Tumor-specific HSP70 that is either presented at the cell surface or secreted on exosomes can also enhance NK cell activity against diverse types of cancer in vivo.120, 121 Most importantly, hepatocellular carcinoma cells that are treated with various chemotherapeutic agents can become more susceptible to NK cell-mediated cytotoxicity through their release of HSP-containing exosomes, giving the aforementioned findings a therapeutic context.122 Collectively, these results suggest that HSP translocation to the plasma membrane or secretion during cellular stress may represent a potent danger signal that can stimulate NK cell activity, particularly in the context of cancer.

 

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Microbe meets cancer

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Microbes Meet Cancer

Understanding cancer’s relationship with the human microbiome could transform immune-modulating therapies.

By Kate Yandell | April 1, 2016  http://www.the-scientist.com/?articles.view/articleNo/45616/title/Microbes-Meet-Cancer

 © ISTOCK.COM/KATEJA_FN; © ISTOCK.COM/FRANK RAMSPOTT  http://www.the-scientist.com/images/April2016/feature1.jpg

In 2013, two independent teams of scientists, one in Maryland and one in France, made a surprising observation: both germ-free mice and mice treated with a heavy dose of antibiotics responded poorly to a variety of cancer therapies typically effective in rodents. The Maryland team, led by Romina Goldszmidand Giorgio Trinchieri of the National Cancer Institute, showed that both an investigational immunotherapy and an approved platinum chemotherapy shrank a variety of implanted tumor types and improved survival to a far greater extent in mice with intact microbiomes.1 The French group, led by INSERM’s Laurence Zitvogel, got similar results when testing the long-standing chemotherapeutic agent cyclophosphamide in cancer-implanted mice, as well as in mice genetically engineered to develop tumors of the lung.2

The findings incited a flurry of research and speculation about how gut microbes contribute to cancer cell death, even in tumors far from the gastrointestinal tract. The most logical link between the microbiome and cancer is the immune system. Resident microbes can either dial up inflammation or tamp it down, and can modulate immune cells’ vigilance for invaders. Not only does the immune system appear to be at the root of how the microbiome interacts with cancer therapies, it also appears to mediate how our bacteria, fungi, and viruses influence cancer development in the first place.

“We clearly see shifts in the [microbial] community that precede development of tumors,” says microbiologist and immunologist Patrick Schloss, who studies the influence of the microbiome on colon cancer at the University of Michigan.

But the relationship between the microbiome and cancer is complex: while some microbes promote cell proliferation, others appear to protect us against cancerous growth. And in some cases, the conditions that spur one cancer may have the opposite effect in another. “It’s become pretty obvious that the commensal microbiota affect inflammation and, through that or through other mechanisms, affect carcinogenesis,” says Trinchieri. “What we really need is to have a much better understanding of which species, which type of bug, is doing what and try to change the balance.”

Gut feeling

In the late 1970s, pathologist J. Robin Warren of Royal Perth Hospital in Western Australia began to notice that curved bacteria often appeared in stomach tissue biopsies taken from patients with chronic gastritis, an inflammation of the stomach lining that often precedes the development of stomach cancer. He and Barry J. Marshall, a trainee in internal medicine at the hospital, speculated that the bacterium, now called Helicobacter pylori, was somehow causing the gastritis.3 So committed was Marshall to demonstrating the microbe’s causal relationship to the inflammatory condition that he had his own stomach biopsied to show that it contained no H. pylori, then infected himself with the bacterium and documented his subsequent experience of gastritis.4 Scientists now accept that H. pylori, a common gut microbe that is present in about 50 percent of the world’s population, is responsible for many cases of gastritis and most stomach ulcers, and is a strong risk factor for stomach cancer.5 Marshall and Warren earned the 2005 Nobel Prize in Physiology or Medicine for their work.

H. pylori may be the most clear-cut example of a gut bacterium that influences cancer development, but it is likely not the only one. Researchers who study cancer in mice have long had anecdotal evidence that shifts in the microbiome influence the development of diverse tumor types. “You have a mouse model of carcinogenesis. It works beautifully,” says Trinchieri. “You move to another institution. It works completely differently,” likely because the animals’ microbiomes vary with environment.

IMMUNE INFLUENCE: In recent years, research has demonstrated that microbes living in and on the mammalian body can affect cancer risk, as well as responses to cancer treatment. Although the details of this microbe-cancer link remain unclear, investigators suspect that the microbiome’s ability to modulate inflammation and train immune cells to react to tumors is to blame.
See full infographic: WEB | PDF
© AL GRANBERG

Around the turn of the 21st century, cancer researchers began to systematically experiment with the rodent microbiome, and soon had several lines of evidence linking certain gut microbes with a mouse’s risk of colon cancer. In 2001, for example, Shoichi Kado of the Yakult Central Institute for Microbiological Research in Japan and colleagues found that a strain of immunocompromised mice rapidly developed colon tumors, but that germ-free versions of these mice did not.6 That same year, an MIT-based group led by the late David Schauer demonstrated that infecting mice with the bacterium Citrobacter rodentium spurred colon tumor development.7 And in 2003, MIT’s Susan Erdman and her colleagues found that they could induce colon cancer in immunocompromised mice by infecting them with Helicobacter hepaticus, a relative of? H. pylori that commonly exists within the murine gut microbiome.8

More recent work has documented a similar link between colon cancer and the gut microbiome in humans. In 2014, a team led by Schloss sequenced 16S rRNA genes isolated from the stool of 90 people, some with colon cancer, some with precancerous adenomas, and still others with no disease.9 The researchers found that the feces of people with cancer tended to have an altered composition of bacteria, with an excess of the common mouth microbes Fusobacterium or Porphyromonas. A few months later, Peer Bork of the European Molecular Biology Laboratory performed metagenomic sequencing of stool samples from 156 people with or without colorectal cancer. Bork and his colleagues found they could predict the presence or absence of cancer using the relative abundance of 22 bacterial species, including Porphyromonas andFusobacterium.10 They could also use the method to predict colorectal cancer with about the same accuracy as a blood test, correctly identifying about 50 percent of cancers while yielding false positives less than 10 percent of the time. When the two tests were combined, they caught more than 70 percent of cancers.

Whether changes in the microbiota in colon cancer patients are harbingers of the disease or a consequence of tumor development remained unclear. “What comes first, the change in the microbiome or tumor development?” asks Schloss. To investigate this question, he and his colleagues treated mice with microbiome-altering antibiotics before administering a carcinogen and an inflammatory agent, then compared the outcomes in those animals and in mice that had received only the carcinogenic and inflammatory treatments, no antibiotics. The antibiotic-treated animals had significantly fewer and smaller colon tumors than the animals with an undisturbed microbiome, suggesting that resident bacteria were in some way promoting cancer development. And when the researchers transferred microbiota from healthy mice to antibiotic-treated or germ-free mice, the animals developed more tumors following carcinogen exposure. Sterile mice that received microbiota from mice already bearing malignancies developed the most tumors of all.11

Most recently, Schloss and his colleagues showed that treating mice with seven unique combinations of antibiotics prior to exposing them to carcinogens yielded variable but predictable levels of tumor formation. The researchers determined that the number of tumors corresponded to the unique ways that each antibiotic cocktail modulated the microbiome.12

“We’ve kind of proven to ourselves, at least, that the microbiome is involved in colon cancer,” says Schloss, who hypothesizes that gut bacteria–driven inflammation is to blame for creating an environment that is hospitable to tumor development and growth. Gain or loss of certain components of the resident bacterial community could lead to the release of reactive oxygen species, damaging cells and their genetic material. Inflammation also involves increased release of growth factors and blood vessel proliferation, potentially supporting the growth of tumors. (See illustration above.)

Recent research has also yielded evidence that the gut microbiota impact the development of cancer in sites far removed from the intestinal tract, likely through similar immune-modulating mechanisms.

Systemic effects

In the mid-2000s, MIT’s Erdman began infecting a strain of mice predisposed to intestinal tumors withH. hepaticus and observing the subsequent development of colon cancer in some of the animals. To her surprise, one of the mice developed a mammary tumor. Then, more of the mice went on to develop mammary tumors. “This told us that something really interesting was going on,” Erdman recalls. Sure enough, she and her colleagues found that mice infected with H. hepaticus were more likely to develop mammary tumors than mice not exposed to the bacterium.13The researchers showed that systemic immune activation and inflammation could contribute to mammary tumors in other, less cancer-prone mouse models, as well as to the development of prostate cancer.

MICROBIAL STOWAWAYS: Bacteria of the human gut microbiome are intimately involved in cancer development and progression, thanks to their interactions with the immune system. Some microbes, such as Helicobacter pylori, increase the risk of cancer in their immediate vicinity (stomach), while others, such as some Bacteroides species, help protect against tumors by boosting T-cell infiltration.© EYE OF SCIENCE/SCIENCE SOURCE
http://www.the-scientist.com/images/April2016/immune_2.jpg

 

 

© DR. GARY GAUGLER/SCIENCE SOURCE  http://www.the-scientist.com/images/April2016/immune3.jpg

At the University of Chicago, Thomas Gajewski and his colleagues have taken a slightly different approach to studying the role of the microbiome in cancer development. By comparing Black 6 mice coming from different vendors—Taconic Biosciences (formerly Taconic Farms) and the Jackson Laboratory—Gajewski takes advantage of the fact that the animals’ different origins result in different gut microbiomes. “We deliberately stayed away from antibiotics, because we had a desire to model how intersubject heterogeneity [in cancer development] might be impacted by the commensals they happen to be colonized with,” says Gajewski in an email to The Scientist.

Last year, the researchers published the results of a study comparing the progression of melanoma tumors implanted under the mice’s skin, finding that tumors in the Taconic mice grew more aggressively than those in the Jackson mice. When the researchers housed the different types of mice together before their tumors were implanted, however, these differences disappeared. And transferring fecal material from the Jackson mice into the Taconic mice altered the latter’s tumor progression.14

Instead of promoting cancer, in these experiments the gut microbiome appeared to slow tumor growth. Specifically, the reduced tumor growth in the Jackson mice correlated with the presence of Bifidobacterium, which led to the greater buildup of T?cells in the Jackson mice’s tumors. Bifidobacteriaactivate dendritic cells, which present antigens from bacteria or cancer cells to T?cells, training them to hunt down and kill these invaders. Feeding Taconic mice bifidobacteria improved their response to the implanted melanoma cells.

“One hypothesis going into the experiments was that we might identify immune-suppressive bacteria, or commensals that shift the immune response towards a character that was unfavorable for tumor control,” says Gajewski.  “But in fact, we found that even a single type of bacteria could boost the antitumor immune response.”

http://www.the-scientist.com/images/April2016/immune4.jpg

 

Drug interactions

Ideally, the immune system should recognize cancer as invasive and nip tumor growth in the bud. But cancer cells display “self” molecules that can inhibit immune attack. A new type of immunotherapy, dubbed checkpoint inhibition or blockade, spurs the immune system to attack cancer by blocking either the tumor cells’ surface molecules or the receptors on T?cells that bind to them.

CANCER THERAPY AND THE MICROBIOME

In addition to influencing the development and progression of cancer by regulating inflammation and other immune pathways, resident gut bacteria appear to influence the effectiveness of many cancer therapies that are intended to work in concert with host immunity to eliminate tumors.

  • Some cancer drugs, such as oxaliplatin chemotherapy and CpG-oligonucleotide immunotherapy, work by boosting inflammation. If the microbiome is altered in such a way that inflammation is reduced, these therapeutic agents are less effective.
  • Cancer-cell surface proteins bind to receptors on T cells to prevent them from killing cancer cells. Checkpoint inhibitors that block this binding of activated T cells to cancer cells are influenced by members of the microbiota that mediate these same cell interactions.
  • Cyclophosphamide chemotherapy disrupts the gut epithelial barrier, causing the gut to leak certain bacteria. Bacteria gather in lymphoid tissue just outside the gut and spur generation of T helper 1 and T helper 17 cells that migrate to the tumor and kill it.

As part of their comparison of Jackson and Taconic mice, Gajewski and his colleagues decided to test a type of investigational checkpoint inhibitor that targets PD-L1, a ligand found in high quantities on the surface of multiple types of cancer cells. Monoclonal antibodies that bind to PD-L1 block the PD-1 receptors on T?cells from doing so, allowing an immune response to proceed against the tumor cells. While treating Taconic mice with PD-L1–targeting antibodies did improve their tumor responses, they did even better when that treatment was combined with fecal transfers from Jackson mice, indicating that the microbiome and the immunotherapy can work together to take down cancer. And when the researchers combined the anti-PD-L1 therapy with a bifidobacteria-enriched diet, the mice’s tumors virtually disappeared.14

Gajewski’s group is now surveying the gut microbiota in humans undergoing therapy with checkpoint inhibitors to better understand which bacterial species are linked to positive outcomes. The researchers are also devising a clinical trial in which they will give Bifidobacterium supplements to cancer patients being treated with the approved anti-PD-1 therapy pembrolizumab (Keytruda), which targets the immune receptor PD-1 on T?cells, instead of the cancer-cell ligand PD-L1.

Meanwhile, Zitvogel’s group at INSERM is investigating interactions between the microbiome and another class of checkpoint inhibitors called CTLA-4 inhibitors, which includes the breakthrough melanoma treatment ipilimumab (Yervoy). The researchers found that tumors in antibiotic-treated and germ-free mice had poorer responses to a CTLA-4–targeting antibody compared with mice harboring unaltered microbiomes.15 Particular Bacteroides species were associated with T-cell infiltration of tumors, and feedingBacteroides fragilis to antibiotic-treated or germ-free mice improved the animals’ responses to the immunotherapy. As an added bonus, treatment with these “immunogenic” Bacteroides species decreased signs of colitis, an intestinal inflammatory condition that is a dangerous side effect in patients using checkpoint inhibitors. Moreover, Zitvogel and her colleagues showed that human metastatic melanoma patients treated with ipilimumab tended to have elevated levels of B. fragilis in their microbiomes. Mice transplanted with feces from patients who showed particularly strong B. fragilis gains did better on anti-CTLA-4 treatment than did mice transplanted with feces from patients with normal levels of B. fragilis.

“There are bugs that allow the therapy to work, and at the same time, they protect against colitis,” says Trinchieri. “That is very exciting, because not only [can] we do something to improve the therapy, but we can also, at the same time, try to reduce the side effect.”

And these checkpoint inhibitors aren’t the only cancer therapies whose effects are modulated by the microbiome. Trinchieri has also found that an immunotherapy that combines antibodies against interleukin-10 receptors with CpG oligonucleotides is more effective in mice with unaltered microbiomes.1He and his NCI colleague Goldszmid further found that the platinum chemotherapy oxaliplatin (Eloxatin) was more effective in mice with intact microbiomes, and Zitvogel’s group has shown that the chemotherapeutic agent cyclophosphamide is dependent on the microbiota for its proper function.

Although the mechanisms by which the microbiome influences the effectiveness of such therapies remains incompletely understood, researchers once again speculate that the immune system is the key link. Cyclophosphamide, for example, spurs the body to generate two types of T?helper cells, T?helper 1 cells and a subtype of T?helper 17 cells referred to as “pathogenic,” both of which destroy tumor cells. Zitvogel and her colleagues found that, in mice with unaltered microbiomes, treatment with cyclophosphamide works by disrupting the intestinal mucosa, allowing bacteria to escape into the lymphoid tissues just outside the gut. There, the bacteria spur the body to generate T?helper 1 and T?helper 17 cells, which translocate to the tumor. When the researchers transferred the “pathogenic” T?helper 17 cells into antibiotic-treated mice, the mice’s response to chemotherapy was partly restored.

Microbiome modification

As the link between the microbiome and cancer becomes clearer, researchers are thinking about how they can manipulate a patient’s resident microbial communities to improve their prognosis and treatment outcomes. “Once you figure out exactly what is happening at the molecular level, if there is something promising there, I would be shocked if people don’t then go in and try to modulate the microbiome, either by using pharmaceuticals or using probiotics,” says Michael Burns, a postdoc in the lab of University of Minnesota genomicist Ran Blekhman.

Even if researchers succeed in identifying specific, beneficial alterations to the microbiome, however, molding the microbiome is not simple. “It’s a messy, complicated system that we don’t understand,” says Schloss.

So far, studies of the gut microbiome and colon cancer have turned up few consistent differences between cancer patients and healthy controls. And the few bacterial groups that have repeatedly shown up are not present in every cancer patient. “We should move away from saying, ‘This is a causal species of bacteria,’” says Blekhman. “It’s more the function of a community instead of just a single bacterium.”

But the study of the microbiome in cancer is young. If simply adding one type of microbe into a person’s gut is not enough, researchers may learn how to dose people with patient-specific combinations of microbes or antibiotics. In February 2016, a team based in Finland and China showed that a probiotic mixture dubbed Prohep could reduce liver tumor size by 40 percent in mice, likely by promoting an anti-inflammatory environment in the gut.16

“If it is true that, in humans, we can alter the course of the disease by modulating the composition of the microbiota,” says José Conejo-Garcia of the Wistar Institute in Philadelphia, “that’s going to be very impactful.”

Kate Yandell has been a freelance writer living Philadelphia, Pennsylvania. In February she became an associate editor at Cancer Today.

GENETIC CONNECTION

The microbiome doesn’t act in isolation; a patient’s genetic background can also greatly influence response to therapy. Last year, for example, the Wistar Institute’s José Garcia-Conejo and Melanie Rutkowski, now an assistant professor at the University of Virginia, showed that a dominant polymorphism of the gene for the innate immune protein toll-like receptor 5 (TLR5) influences clinical outcomes in cancer patients by changing how the patients’ immune cells interact with their gut microbes (Cancer Cell, 27:27-40, 2015).

More than 7 percent of people carry a specific mutation in TLR5 that prevents them from mounting a full immune response when exposed to bacterial flagellin. Analyzing both genetic and survival data from the Cancer Genome Atlas, Conejo-Garcia, Rutkowski, and their colleagues found that estrogen receptor–positive breast cancer patients who carry the TLR5 mutation, called the R392X polymorphism, have worse outcomes than patients without the mutation. Among patients with ovarian cancer, on the other hand, those with the TLR5 mutation were more likely to live at least six years after diagnosis than patients who don’t carry the mutation.

Investigating the mutation’s contradictory effects, the researchers found that mice with normal TLR5produce higher levels of the cytokine interleukin 6 (IL-6) than those carrying the mutant version, which have higher levels of a different cytokine called interleukin 17 (IL-17). But when the researchers knocked out the animals’ microbiomes, these differences in cytokine production disappeared, as did the differences in cancer progression between mutant and wild-type animals.

“The effectiveness of depleting specific populations or modulating the composition of the microbiome is going to affect very differently people who are TLR5-positive or TLR5-negative,” says Conejo-Garcia. And Rutkowski speculates that many more polymorphisms linked to cancer prognosis may act via microbiome–immune system interactions. “I think that our paper is just the tip of the iceberg.”

References

  1. N. Iida et al., “Commensal bacteria control cancer response to therapy by modulating the tumor microenvironment,” Science, 342:967-70, 2013.
  2. S. Viaud et al., “The intestinal microbiota modulates the anticancer immune effects of cyclophosphamide,” Science, 342:971-76, 2013.
  3. J.R. Warren, B. Marshall, “Unidentified curved bacilli on gastric epithelium in active chronic gastritis,”Lancet, 321:1273-75, 1983.
  4. B.J. Marshall et al., “Attempt to fulfil Koch’s postulates for pyloric Campylobacter,” Med J Aust, 142:436-39, 1985.
  5. J. Parsonnet et al., “Helicobacter pylori infection and the risk of gastric carcinoma,” N Engl J Med, 325:1127-31, 1991.
  6. S. Kado et al., “Intestinal microflora are necessary for development of spontaneous adenocarcinoma of the large intestine in T-cell receptor β chain and p53 double-knockout mice,” Cancer Res, 61:2395-98, 2001.
  7. J.V. Newman et al., “Bacterial infection promotes colon tumorigenesis in ApcMin/+ mice,” J Infect Dis, 184:227-30, 2001.
  8. S.E. Erdman et al., “CD4+ CD25+ regulatory T lymphocytes inhibit microbially induced colon cancer in Rag2-deficient mice,” Am J Pathol, 162:691-702, 2003.
  9. J.P. Zackular et al., “The human gut microbiome as a screening tool for colorectal cancer,” Cancer Prev Res, 7:1112-21, 2014.
  10. G. Zeller et al., “Potential of fecal microbiota for early-stage detection of colorectal cancer,” Mol Syst Biol, 10:766, 2014.
  11. J.P. Zackular et al., “The gut microbiome modulates colon tumorigenesis,” mBio, 4:e00692-13, 2013.
  12. J.P. Zackular et al., “Manipulation of the gut microbiota reveals role in colon tumorigenesis,”mSphere, doi:10.1128/mSphere.00001-15, 2015.
  13. V.P. Rao et al., “Innate immune inflammatory response against enteric bacteria Helicobacter hepaticus induces mammary adenocarcinoma in mice,” Cancer Res, 66:7395, 2006.
  14. A. Sivan et al., “Commensal Bifidobacterium promotes antitumor immunity and facilitates anti-PD-L1 efficacy,” Science, 350:1084-89, 2015.
  15. M. Vétizou et al., “Anticancer immunotherapy by CTLA-4 blockade relies on the gut microbiota,”Science, 350:1079-84, 2015.

……..

 

Microbially Driven TLR5-Dependent Signaling Governs Distal Malignant Progression through Tumor-Promoting Inflammation

Melanie R. Rutkowski, Tom L. Stephen, Nikolaos Svoronos, …., Julia Tchou,  Gabriel A. Rabinovich, Jose R. Conejo-Garcia
Cancer cell    12 Jan 2015; Volume 27, Issue 1, p27–40  http://dx.doi.org/10.1016/j.ccell.2014.11.009
Figure thumbnail fx1
  • TLR5-dependent IL-6 mobilizes MDSCs that drive galectin-1 production by γδ T cells
  • IL-17 drives malignant progression in IL-6-unresponsive tumors
  • TLR5-dependent differences in tumor growth are abrogated upon microbiota depletion
  • A common dominant TLR5 polymorphism influences the outcome of human cancers

The dominant TLR5R392X polymorphism abrogates flagellin responses in >7% of humans. We report that TLR5-dependent commensal bacteria drive malignant progression at extramucosal locations by increasing systemic IL-6, which drives mobilization of myeloid-derived suppressor cells (MDSCs). Mechanistically, expanded granulocytic MDSCs cause γδ lymphocytes in TLR5-responsive tumors to secrete galectin-1, dampening antitumor immunity and accelerating malignant progression. In contrast, IL-17 is consistently upregulated in TLR5-unresponsive tumor-bearing mice but only accelerates malignant progression in IL-6-unresponsive tumors. Importantly, depletion of commensal bacteria abrogates TLR5-dependent differences in tumor growth. Contrasting differences in inflammatory cytokines and malignant evolution are recapitulated in TLR5-responsive/unresponsive ovarian and breast cancer patients. Therefore, inflammation, antitumor immunity, and the clinical outcome of cancer patients are influenced by a common TLR5 polymorphism.

see also… Immune Influence

In recent years, research has demonstrated that microbes living in and on the mammalian body can affect cancer risk, as well as responses to cancer treatment.

By Kate Yandell | April 1, 2016

http://www.the-scientist.com/?articles.view/articleNo/45644/title/Immune-Influence

Although the details of this microbe-cancer link remain unclear, investigators suspect that the microbiome’s ability to modulate inflammation and train immune cells to react to tumors is to blame. Here are some of the hypotheses that have come out of recent research in rodents for how gut bacteria shape immunity and influence cancer.

HOW THE MICROBIOME PROMOTES CANCER

Gut bacteria can dial up inflammation locally in the colon, as well as in other parts of the body, leading to the release of reactive oxygen species, which damage cells and DNA, and of growth factors that spur tumor growth and blood vessel formation.

http://www.the-scientist.com/images/April2016/ImmuneInfluence1_640px.jpg

http://www.the-scientist.com/images/April2016/ImmuneInfluence2_310px1.jpg

Helicobacter pylori can cause inflammation and high cell turnover in the stomach wall, which may lead to cancerous growth.

HOW THE MICROBIOME STEMS CANCER

Gut bacteria can also produce factors that lower inflammation and slow tumor growth. Some gut bacteria (e.g., Bifidobacterium)
appear to activate dendritic cells,
which present cancer-cell antigens to T cells that in turn kill the cancer cells.

http://www.the-scientist.com/images/April2016/ImmuneInfluence3_310px1.jpg

http://www.the-scientist.com/images/April2016/ImmuneInfluence4_310px1.jpg

Read the full story.

 

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Validation of FoundationOne Heme in New Study: Integrated genomic DNA/RNA profiling of hematologic malignancies in the clinical setting

Reporter: Aviva Lev-Ari, PhD, RN

 

Integrated genomic DNA/RNA profiling of hematologic malignancies in the clinical setting

  1. Jie He1,
  2. Omar Abdel-Wahab2,
  3. Michelle K. Nahas1,
  4. Kai Wang1,
  5. Raajit K. Rampal3,
  6. Andrew M. Intlekofer4,
  7. Jay Patel3,
  8. Andrei Krivstov5,
  9. Garrett M. Frampton1,
  10. Lauren E. Young1,
  11. Shan Zhong1,
  12. Mark Bailey1,
  13. Jared R. White1,
  14. Steven Roels1,
  15. Jason Deffenbaugh1,
  16. Alex Fichtenholtz1,
  17. Timothy Brennan1,
  18. Mark Rosenzweig1,
  19. Kimberly Pelak1,
  20. Kristina M. Knapp5,
  21. Kristina W. Brennan1,
  22. Amy L. Donahue1,
  23. Geneva Young1,
  24. Lazaro Garcia1,
  25. Selmira T. Beckstrom1,
  26. Mandy Zhao1,
  27. Emily White1,
  28. Vera Banning1,
  29. Jamie Buell1,
  30. Kiel Iwanik1,
  31. Jeffrey S. Ross1,
  32. Deborah Morosini1,
  33. Anas Younes4,
  34. Alan M. Hanash6,
  35. Elisabeth Paietta7,
  36. Kathryn Roberts8,
  37. Charles Mullighan8,
  38. Ahmet Dogan9,
  39. Scott A. Armstrong5,
  40. Tariq Mughal1,
  41. Jo-Anne Vergilio1,
  42. Elaine Labrecque1,
  43. Rachel Erlich1,
  44. Christine Vietz1,
  45. Roman Yelensky1,
  46. Philip J. Stephens1,
  47. Vincent A. Miller1,
  48. Marcel R. M. van den Brink10,
  49. Geoff A. Otto1,
  50. Doron Lipson1, and
  51. Ross L. Levine2,*
Author Affiliations
  1. * Corresponding author; email: leviner@mskcc.org

Key Points

  • Novel clinically-available comprehensive genomic profiling of both DNA and RNA in hematologic malignancies.

  • Profiling of 3696 clinical hematologic tumors identified somatic alterations that impact diagnosis, prognosis, and therapeutic selection.

Abstract

The spectrum of somatic alterations in hematologic malignancies includes substitutions, insertions/deletions (indels), copy number alterations (CNAs) and a wide range of gene fusions; no current clinically available single assay captures the different types of alterations. We developed a novel next-generation sequencing-based assay to identify all classes of genomic alterations using archived formalin-fixed paraffin-embedded (FFPE), blood and bone marrow samples with high accuracy in a clinically relevant timeframe, which is performed in our CLIA-certified CAP-accredited laboratory. Targeted capture of DNA/RNA and next-generation sequencing reliably identifies substitutions, indels, CNAs and gene fusions, with similar accuracy to lower-throughput assays which focus on specific genes and types of genomic alterations. Profiling of 3696 samples identified recurrent somatic alterations that impact diagnosis, prognosis and therapy selection. This comprehensive genomic profiling approach has proved effective in detecting all types of genomic alterations, including fusion transcripts, which increases the ability to identify clinically-relevant genomic alterations with therapeutic relevance.

  • Submitted August 16, 2015.
  • Accepted February 28, 2016.

SOURCE

http://www.bloodjournal.org/content/early/2016/03/10/blood-2015-08-664649?sso-checked=true

Foundation Medicine Shares Results From Validation of FoundationOne Heme in New Study

In addition to the concordance analysis, genomic profiling of the 76 test samples using FoundationOne Heme also identified 126 additional somatic alterations including clinically relevant genomic alterations in KRAS, TET2, EZH2, and DNMT3A.

Importantly, the study also showed that the molecular information supplied by the test can help accurately match patients with a particular targeted therapy.

In the study Foundation Medicine shared clinical data from genomic profiling of 3,696 hematologic malignancies submitted to its CLIA-certified, NYS-approved lab.

More than 90 percent of the specimens — 3,433 out of 3696 — were successfully characterized. The test identified at least one driver alteration in 95 percent of the tumor specimens, and results showed that 77 percent of the cases harbored at least one alteration linked to a commercially available targeted therapy or one that is in clinical development, the MSKCC researchers reported.

In addition, 61 percent of the cases harbored at least one alteration with known prognostic relevance in that tumor type.

In discussion of the results, the study authors argued that clinical merit of the test was underscored by the demonstrated ability to identify genetic lesions with prognostic and therapeutic relevance in specific diseases.

For example, the authors wrote, “In the case of B-cell ALL … the challenge has been that the critical genes … can be altered by whole gene/intragenic deletions, DNA base-pair substitutions, and larger indels, as well as chromosomal, intergenic, and cryptic rearrangements, which lead to expression of fusion transcripts.”

“Currently, most centers use an amalgam of DNA, FISH, and gene-specific RNA approaches to identify a subset of the most critical genetic lesions in B-ALL. Our assay provides a single profiling platform that can reliably identify all known actionable disease alleles relevant to B-ALL to improve diagnosis and risk-adapted therapy for B-ALL patients,” they wrote.

SOURCE

https://www.genomeweb.com/sequencing-technology/foundation-medicine-shares-results-validation-foundationone-heme-new-study?utm_source=SilverpopMailing&utm_medium=email&utm_campaign=Daily%20News:%20Foundation%20Medicine%20Shares%20Results%20From%20Validation%20of%20FoundationOne%20Heme%20in%20New%20Study%20-%2003/25/2016%2012:25:00%20PM

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Protein binding to RNAs in brain

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Regulatory consequences of neuronal ELAV-like protein binding to coding and non-coding RNAs in human brain

 Claudia Scheckel, 

Neuronal ELAV-like (nELAVL) RNA binding proteins have been linked to numerous neurological disorders. We performed crosslinking-immunoprecipitation and RNAseq on human brain, and identified nELAVL binding sites on 8681 transcripts. Using knockout mice and RNAi in human neuroblastoma cells, we showed that nELAVL intronic and 3′ UTR binding regulates human RNA splicing and abundance. We validated hundreds of nELAVL targets among which were important neuronal and disease-associated transcripts, including Alzheimer’s disease (AD) transcripts. We therefore investigated RNA regulation in AD brain, and observed differential splicing of 150 transcripts, which in some cases correlated with differential nELAVL binding. Unexpectedly, the most significant change of nELAVL binding was evident on non-coding Y RNAs. nELAVL/Y RNA complexes were specifically remodeled in AD and after acute UV stress in neuroblastoma cells. We propose that the increased nELAVL/Y RNA association during stress may lead to nELAVL sequestration, redistribution of nELAVL target binding, and altered neuronal RNA splicing.

DOI: http://dx.doi.org/10.7554/eLife.10421.001

 

eLife digest

When a gene is active, its DNA is copied into a molecule of RNA. This molecule then undergoes a process called splicing which removes certain segments, and the resulting ‘messenger RNA’ molecule is then translated into protein. Many messenger RNAs go through alternative splicing, whereby different segments can be included or excluded from the final molecule. This allows more than one type of protein to be produced from a single gene.

Specialized RNA binding proteins associate with messenger RNAs and regulate not only their splicing, but also their abundance and location within the cell. These activities are crucially important in the brain where forming memories and learning new skills requires thousands of proteins to be made rapidly. Many members of a family of RNA binding proteins called ELAV-like proteins are unique to neurons. These proteins have also been associated with conditions such as Alzheimer’s disease, but it was not known which messenger RNAs were the targets of these proteins in the human brain.

Scheckel, Drapeau et al. have now addressed this question and used a method termed ‘CLIP’ to identify thousands of messenger RNAs that directly bind to neuronal ELAV-like proteins in the human brain. Many of these messenger RNAs coded for proteins that are important for the health of neurons, and neuronal ELAV-like proteins were shown to regulate both the alternative splicing and the abundance of these messenger RNAs.

The regulation of RNA molecules in post-mortem brain samples of people with or without Alzheimer’s disease was then compared. Scheckel, Drapeau et al. unexpectedly observed that, in the Alzheimer’s disease patients, the neuronal ELAV-like proteins were very often associated with a class of RNA molecules known as Y RNAs. These RNA molecules do not code for proteins, and are therefore classified as non-coding RNA. Moreover, massive shifts in the binding of ELAV-like proteins onto Y RNAs were observed in neurons grown in the laboratory that had been briefly stressed by exposure to ultraviolet radiation.

Scheckel, Drapeau et al. suggest that the strong tendency of neuronal ELAV-like proteins to bind to Y RNAs in conditions of short- or long-term stress, including Alzheimer’s disease, might prevent these proteins from associating with their normal messenger RNA targets. This was supported by finding that some messenger RNAs targeted by neuronal ELAV-like proteins showed altered regulation after stress. Such changes to the normal regulation of these messenger RNAs could have a large impact on the proteins that are produced from them.

Together, these findings link Y RNAs to both neuronal stress and Alzheimer’s disease, and suggest a new way that a cell can alter which messenger RNAs are expressed in response to changes in its environment. The next step is to explore what causes the shift in neuronal ELAV-like protein binding from messenger RNAs to Y RNAs and how it might contribute to disease.

DOI:http://dx.doi.org/10.7554/eLife.10421.002

 

RNA binding proteins (RBPs) associate with RNAs throughout their life cycle, regulating all aspects of RNA metabolism and function. More than 800 RBPs have been described in human cells (Castello et al., 2012). The unique structure and function of neurons, and the need to rapidly adapt RNA regulation in the brain both within and at sites distant from the nucleus, are consistent with specialized roles for RBPs in the brain. Indeed, mammalian neurons have developed their own system of RNA regulation (Darnell, 2013), and RBP:mRNA interactions are thought to regulate local protein translation at synapses, perhaps underlying learning and long-term memory (McKee et al., 2005).

Numerous RBPs have been linked to human neurological disorders (reviewed in Richter and Klann (2009)). For example, FUS, TDP-43 and ATXN2 mutations have been found in familial amyotrophic lateral sclerosis patients (Elden et al., 2010; Vance et al., 2009; Sreedharan et al., 2008), TDP-43has additionally been associated with frontotemporal lobar degeneration, Alzheimer’s Disease (AD) and Parkinson’s Disease (PD) (Baloh, 2011), STEX has been linked to amyotrophic lateral sclerosis 4 (Chen et al., 2004), and spinal muscular atrophy can be caused by mutations in SMN (Clermont et al., 1995).

The neuronal ELAV-like (ELAVL) and NOVA RBPs are targeted by the immune system in paraneoplastic neurodegenerative disorders (Buckanovich et al., 1996; Szabo et al., 1991). Mammalian ELAVL proteins include the ubiquitously expressed paralog ELAVL1 (also termed HUA or HUR) and the three neuron-specific paralogs, ELAVL2, 3 and 4 (also termed HUB, C, and D, and collectively referred to as nELAVL; Ince-Dunn et al., 2012). nELAVL proteins are expressed exclusively in neurons in mice (Okano and Darnell, 1997), and they are important for neuronal differentiation and neurite outgrowth in cultured neurons (Akamatsu et al., 1999; Kasashima et al., 1999; Mobarak et al., 2000; Anderson et al., 2000; Antic et al., 1999; Aranda-Abreu et al., 1999). Redundancy between the three nELAVL isoforms complicates in vivo studies of their individual functions. Nevertheless, even haploinsuffiency of Elavl3 is sufficient to trigger cortical hypersynchronization, and Elavl3 and Elavl4 null mice display defects in motor function and neuronal maturation, respectively (Akamatsu et al., 2005; Ince-Dunn et al., 2012).

ELAVL proteins have been shown to regulate several aspects of RNA metabolism. In vitro and in tissue culture cells, nELAVL proteins have been implicated in the regulation of stabilization and/or translation of specific mRNAs, as well as in the regulation of splicing and polyadenylation of select transcripts [reviewed in Pascale et al. (2004)]. A more comprehensive approach was taken by immunoprecipitating an overexpressed isoform of ELAVL4 in mice, although such RNA immunoprecipitation experiments cannot distinguish between direct and indirect targets (Bolognani et al., 2010). Recently, direct binding of nELAVL to target RNAs in mouse brain was demonstrated by high-throughput sequencing of RNA isolated by crosslinking immunoprecipitation (HITS-CLIP; Ince-Dunn et al., 2012); these data, coupled with transcriptome profiling of Elavl3/4 KO mice, demonstrated that nELAVL directly regulates neuronal mRNA abundance and alternative splicing by binding to U-rich elements with interspersed purine residues in 3’UTRs and introns in mouse brain (Ince-Dunn et al., 2012).

While genome-wide approaches have been applied to studying nELAVL proteins in mice, the targets of nELAVL in the human brain remain largely unknown. This is of particular importance, as nELAVL proteins have been implicated in neurological disorders such as AD (Amadio et al., 2009; Kang et al., 2014) and PD (DeStefano et al., 2008; Noureddine et al., 2005). Hence, to advance our understanding of the function of nELAVL in humans and its link to human disease, we set out to investigate nELAVL:RNA interactions in the human brain.

To globally identify transcripts directly bound by nELAVL in human neurons, we generated a genome wide RNA binding map of nELAVL in human brain using CLIP. CLIP allows the identification of functional RNA-protein interactions in vivo by using UV-irradiation of intact tissues to covalently crosslink and then purify RNA-protein complexes present in vivo (Licatalosi and Darnell, 2010; Ule et al., 2003). This method has been adopted for a variety of RBPs (Darnell, 2010; 2013; Moore et al., 2014). Here, we systemically identified tens of thousands of reproducible nELAVL binding sites in human brain and showed that nELAVL binds transcripts that are important for neurological function and that have been linked to neurological diseases such as AD. We validated the functional consequences of nELAVL binding in mice and cultured human neuroblastoma cells and showed that the loss of nELAVL affected mRNA abundance and alternative splicing of hundreds of transcripts. We further investigated RNA regulation in AD brains, and found that numerous transcripts were differentially spliced in AD, which correlated with differential nELAVL binding in some cases. Remarkably, we observed the most significant increase in nELAVL binding in AD on a class of non-coding RNAs, Y RNAs. We recapitulated these findings in human neuroblastoma cells, showing that nELAVL binding is linked to Y ribonucleoprotein (RNP) remodeling acutely during UV-induced stress, and chronically in AD.

 

Article

Figure 1.

Figure 1.Identification of nELAVL targets in human brain.

(A) Illustration depicting the brain area analyzed by CLIP and RNAseq. The image was generated using BodyParts3D/Anatomography service by DBCLS, Japan. (B) SDS-PAGE separation of radiolabeled nELAVL-RNP complexes. nELAVL-RNP complexes from 40 mg of human brain were specifically immunoprecipitated with Hu-antiserum, compared to control serum (compare lane #4 to #1), which is dependent on UV irradiation (compare lane #4 to #2). Wide-range nELAVL-RNP complexes collapse to a single band in the presence of high RNAse concentration (lane #3). RNAse dilutions: + 19.23 Units/µl; +++ 3846 Units/µl. As in studies of mouse nELAVL (Ince-Dunn et al., 2012), higher molecular weight bands were present in nELAVL CLIP autoradiograms, which correspond at least in part to nELAVL multimers. (C) Shown is the most enriched motif in the top 500 nELAVL peaks, determined with MEME-ChiP. (D) Pie chart of the genomic peak distribution of 75,592 nELAVL peaks (p < 0.01; present in at least 5 individuals). (E) nELAVL binding correlates with mRNA abundance. nELAVL binding (CLIP tags within binding sites per transcript) was compared to mRNA abundance (RNAseq tags per transcript). Only expressed genes with peaks are shown and the correlation coefficient is indicated. The top 1000 targets were identified as genes with highest normalized nELAVL binding (binding sites were normalized for mRNA abundance and summarized per gene). (F) Subnetwork of direct protein-protein interactions of top nELAVL targets. The 1000 top nELAVL target genes and six additional genes highly associated with AD (APP, BACE1, MAPT, PICALM, PSEN1 and PSEN2) were clustered using the organic layout algorithm in yEd. Genes with no direct interactions with other target genes were excluded, leaving 172 nodes from the top nELAVL target list (green) and 5 AD associated genes (blue) in this subnetwork. The size of the nodes is proportional to the connectivity degree. Six clusters (gray circles) containing at least 10 nodes were identified, and subjected to enrichment analysis (see Supplementary file 1F).

DOI: http://dx.doi.org/10.7554/eLife.10421.003

 

Figure 2.

Figure 2.nELAVL mediated regulation is conserved in mouse and human.

(A) Overlap of nELAVL targets in human and mouse. Human nELAVL targets (n = 8681) were intersected with mouse targets identified by RIP (Bolognani et al., 2010) or HITS-CLIP (Ince-Dunn et al., 2012). 538 genes were identified as nELAVL targets by RIP and were expressed in human brain. 1978 expressed genes had HITS-CLIP nELAVL clusters that were present in at least 3 samples (biological complexity (BC) ≥ 3). Both overlaps (n = 500 and n = 1835) were highly significant (p = 6.5e-74 and p = 2.3e-287; hypergeometric test), compared to expressed transcripts (n = 14,737). (B) Only few nELAVL binding sites are conserved between mice and human, which are predominantly present within 3’UTRs. The genomic distribution of all human nELAVL binding sites (total) and nELAVL binding sites conserved in mouse is shown. The number of nELAVL binding sites (n) within each category is indicated. (C) UCSC Genome Browser images illustrating the 3’UTRs of RAB6B, HCN3, and KCNMB2 and their normalized nELAVL binding profile in human brain. The maximum PeakHeight is indicated by numbers in the right corner. (D) The mRNA levels of transcripts with nELAVL 3’UTR binding decrease in Elavl3/4 knockout (KO) mice. Shown are the mRNA expression fold changes (knockout/wildtype) of RAB6B, HCN3, and KCNMB2. *p< 0.01 (two-tailed t test; Ince-Dunn et al., 2012). (E) UCSC Genome Browser images showing pink cassette exons in the DST, NRXN1, and CELF2 genes and their normalized nELAVL binding profiles in human brain. The maximum PeakHeight is indicated by numbers in the right corner. (F) nELAVL binding adjacent to a cassette exon in the DST gene prevents exon inclusion. Downstream nELAVL binding promotes the inclusion of cassette exons in the NRXN1 and CELF2 genes. The change in alternative exon inclusion (delta inclusion (ΔI): wildtype – Elavl3/4 KO) is shown. * significantly changing (analyzed by Aspire2;Ince-Dunn et al., 2012).

DOI: http://dx.doi.org/10.7554/eLife.10421.010

 

Figure 3.

Figure 3.nELAVL proteins regulate mRNA abundance of human brain targets.

(A) nELAVL depletion causes mRNA level changes in IMR-32 neuroblastoma cells. The mRNA abundance change was plotted against average mRNA abundance. Significantly changing transcripts (FDR < 0.05; n = 784) are colored in blue. Shown are only expressed genes (n = 12,743), and ELAVL1/2/3/4 transcripts are indicated. (B) nELAVL with exclusively 3’UTR binding decrease upon nELAVL RNAi depletion. Box plots represent the distribution of mRNA level differences between mock and nELAVL RNAi. We compared genes with exclusively 3’UTR (n = 2346) or intronic (n = 1693) binding that were expressed in IMR-32 cells. nELAVL binding was defined as CLIP tags within binding sites per transcript. Transcripts with exclusively 3’UTR binding were less abundant upon nELAVL RNAi compared to remaining transcripts (p = 3.8e-15; two-tailed t-test). In contrast, mRNA levels of transcripts with exclusively intron binding were even slightly increased compared to remaining transcripts (p = 1.7e-4; two-tailed t-test). (C) Transcripts with nELAVL 3’UTR binding decrease upon nELAVL RNAi. Cumulative fraction curves for genes with no 3’UTR nELAVL binding in human brain, 3’UTR binding, and top 3’UTR targets. Top targets were identified as 1000 genes with highest normalized nELAVL 3’UTR binding (binding sites were normalized for mRNA abundance before summarized per gene). 952 of the top 1000 targets were expressed in IMR-32 cells. A curve displacement to the left indicates a downregulation of mRNA abundance upon nELAVL RNAi. p values were calculated with a one-sided KS test, comparing (top) targets to non-targets. (D) Many transcripts that are decreasing upon nELAVL depletion are top nELAVL 3’UTR targets. The mRNA abundance change (nELAVL/mock RNAi) of transcripts expressed in IMR-32 cells and in human brain (n = 12,242) was plotted against average mRNA abundance. Significantly changing transcripts (FDR<0.05; n = 743) are colored in blue and additionally boxed if they are top nELAVL 3’UTR targets. Transcripts shown in E/F are indicated. (E) UCSC Genome Browser images illustrating the 3’UTRs of APPBP2, ATXN3, andSHANK2 and their normalized nELAVL binding profile in human brain. The maximum PeakHeight is indicated by numbers in the right corner. (F) The mRNA abundance of top nELAVL 3’UTR targets decreases upon nELAVL RNAi. Shown are the mRNA level changes (nELAVL/mock RNAi) of APPBP2, ATXN3, and SHANK2. * FDR<0.05 (derived from edgeR).

DOI: http://dx.doi.org/10.7554/eLife.10421.012

 

Figure 4.

Figure 4.nELAVL regulates splicing of human brain targets.

(A) Analysis of splicing changes upon nELAVL RNAi. Shown is the exon inclusion fraction of cassette exons that are expressed in IMR-32 cells and in human brain (n = 7903). Significantly changing exons (FDR<0.05 and ΔI>0.1) are colored in light blue (n = 473), and additionally boxed in dark blue if adjacent (+/- 2.5 kb) to intronic nELAVL binding sites (n = 155). Significantly changing exons shown in (B/C) are boxed in pink. The two alternative events withinPICALM correspond to the same alternative exon with two different 3’ splice sites. (B) UCSC Genome Browser images depicting cassette exons in pink in the BIN1, PICALM, and APP genes and their normalized nELAVL binding profiles in human brain. The maximum PeakHeight is indicated by numbers in the right corner. (C) nELAVL binding downstream of cassette exons in BIN1 and PICALM promotes exon inclusion, whereas intronic nELAVL binding ofAPP prevents exon inclusion downstream and upstream. The change in alternative exon inclusion (ΔI: mock –nELAVL RNAi) is shown. *FDR< 0.0005; **FDR< 1e-4; ***FDR<1e-16 (GLM likelihood ratio test). (D) Normalized nELAVL binding map of nELAVL regulated exons. Only exons that changed significantly upon nELAVL RNAi (FDR<0.05 and ΔI>0.1) and that are adjacent (+/- 2.5 kb) to intronic nELAVL binding sites (n = 155) were included. Red and blue peaks represent binding associated with nELAVL-dependent exon inclusion and exclusion, respectively.

 

RNA regulation changes in AD

nELAVL has previously been linked to neurological diseases and we observed that nELAVL regulated the mRNA abundance and splicing of multiple disease-associated genes. We examined nELAVL binding in a set of genes with disease associated 3’UTR single nucleotide polymorphisms (SNPs) (Bruno et al., 2012). We found that these genes were enriched among nELAVL 3’UTR targets (n = 200; p = 0.001; hypergeometric test), and that nELAVL binding sites directly overlapped with 45 disease associated SNPs, including SNPs associated with autism, schizophrenia, depression, AD, and PD (Figure 5—figure supplement 1, Supplementary file 3A).

nELAVL proteins have been implicated in AD (Amadio et al., 2009; Kang et al., 2014), and among the validated nELAVL regulated RNAs were also several AD-related transcripts, which led us to investigate additional AD-linked genes (hereafter termed AD genes; n = 96; Supplementary file 3B). Indeed, we found that the top nELAVL targets were enriched among AD genes (n = 11; p = 0.03; hypergeometric test; contained in Supplementary file 3B) as well as among AD risk loci identified in a genome-wide association study (GWAS) in AD (Naj et al., 2011) (n = 77; p = 1.7e-14; hypergeometric test; Supplementary file 3C). To investigate if nELAVL mediated regulation of AD related and other transcripts might be affected in AD, we performed nELAVL CLIP and RNAseq on AD subject brains, age-matched to control subjects (Figure 5—figure supplement 2, Supplementary file 1A/B and 3D). Importantly, ELAVL3/4 mRNA levels were similar between control and AD samples and ELAVL2 showed only a slight decrease in transcript abundance in AD brains (Supplementary file 1B), which allowed us to compare nELAVL binding profiles between control and AD brains. We did not detect many significant changes in nELAVL binding nor mRNA abundance (Figure 5A/B, Supplementary file 1B and 3D), probably due to the variation between human samples, the small sample size, and the potential heterogeneity of AD. We did however observe that 150 transcripts were differentially spliced in the 9 AD subjects (FDR<0.05 and ΔI>0.1; Figure 5C, Supplementary file 3E). Two of these transcripts, BIN1 and PTPRD, have previously been linked to AD (Tan et al., 2013; Ghani et al., 2012), suggesting that the differential splicing of these two transcripts as well as other RNAs might be linked to AD.

Figure 5.RNA regulation changes in AD.

(A) nELAVL binding changes in AD. The nELAVL peak binding change (AD/Control) was plotted against average nELAVL peak binding. Significantly changing peaks (FDR<0.05; n = 52) are colored in blue, and peaks within AD genes are colored in pink (1811 peaks within 69 genes). Shown are only peaks that are bound in control or AD brain (n = 115,393). (B) mRNA abundance changes in AD. The mRNA abundance change (AD/Control) was plotted against average mRNA abundance. Significantly changing transcripts (FDR<0.05; n = 3) are colored in blue, and AD transcripts are colored in pink (n = 89). Shown are only transcripts that are expressed in control or AD brain (n = 14,875). (C) Analysis of splicing changes in AD. Shown is the inclusion fraction of expressed cassette exons in control and AD subjects (n = 8163). Exons within AD genes are colored in pink (n = 79). Significantly changing exons (FDR<0.05 and ΔI>0.1) are colored in light blue (n = 170), and additionally boxed in pink if within AD genes (n = 2). (D) BIN1 is alternatively spliced in AD. UCSC Genome Browser image illustrating a cassette exon in the BIN1 gene and normalized nELAVL binding profiles in control and AD brain. The maximum PeakHeight is indicated by numbers in the right corner. Bar graphs depict the difference in alternative exon inclusion (ΔI: Control – AD) and nELAVL peak binding (AD/Control) in control and AD brain. Corresponding FDR values derived from edgeR are shown. The inclusion of the exon is promoted by nELAVL (see Figure 4), and exon inclusion as well as nELAVL peak binding are reduced in AD subjects.

DOI: http://dx.doi.org/10.7554/eLife.10421.015

 

As shown above (Figure 4), nELAVL depletion in IMR-32 cells was associated with the reduced inclusion of an alternative exon of BIN1, suggesting that nELAVL binding promotes the inclusion of this exon. Precisely this exon was differentially spliced in AD subjects, with AD subjects showing a reduced exon inclusion rate compared to control subjects (Figure 5D). Along with the differential exon inclusion, we observed that nELAVL peak binding was fourfold decreased in AD subjects (log2 fold change = -2.35; p = 0.16; Figure 5D). These results are consistent with nELAVL-mediated dysregulation of this exon in AD subjects, with decreased binding leading to decreased exon inclusion. In conclusion, while we did not detect global nELAVL binding and mRNA abundance changes in AD subjects, we observed that splicing of 150 transcripts was affected, which in some cases might be linked to nELAVL dysregulation.

Non-coding Y RNAs are bound by nELAVL in AD

The largest fold changes in nELAVL binding in AD (relative to the age-matched control population) occurred on a specific class of non-coding RNAs, Y RNAs (Wolin et al., 2013). Y RNAs are 100 nt long structured RNAs usually found in complex with RO60 (also known as TROVE2; Figure 6A; modified from Chen and Wolin, 2004). RO60 is believed to act as a sensor of RNA quality, targeting defective RNAs for degradation (Sim and Wolin, 2011). RO60 was initially identified as an autoantigen targeted in systemic lupus (Lerner et al., 1981) and some subjects with the paraneoplastic encephalopathy syndrome harbor both anti-RO and anti-nELAVL (Hu) autoantibodies (Manley et al., 1994). Four canonical Y RNAs, Y1/3/4/5, have been characterized in humans, but numerous slightly divergent copies of these Y RNAs, especially Y1 and Y3, are distributed throughout the human genome (Perreault et al., 2005).

Figure 6.

Figure 6.Non-coding Y RNAs are bound by nELAVL in AD.

(A) Secondary structures of Y1 and Y3. Binding sites of nELAVL and Ro are indicated. Modified from (Chen and Wolin, 2004). (B) The nELAVL binding motif (UUUUUU, allowing a G at any position) is enriched in nELAVL-bound Y RNAs compared to non-bound Y RNAs (p = 1.1e-7; Fisher’s exact test). Y RNAs were scanned for (T)6, allowing a G at any position. nELAVL-bound Y RNAs: nELAVL CLIP tags in at least two samples; n = 320. (C) nELAVL binding of Y RNAs increases in AD compared to control samples (p = 4.47e-51; paired one-sided Wilcoxon rank sum test). The axes depict nELAVL Y RNA binding (nELAVL CLIP tags per Y RNA) in control and AD subjects. Y RNAs with nELAVL binding motif are colored in green. (D) Y RNA levels do not change in AD. Y RNA abundance (RNAseq tags per Y RNA) in AD subjects was plotted against Y RNA abundance in control subjects.

DOI: http://dx.doi.org/10.7554/eLife.10421.018

 

Surprisingly, we observed nELAVL binding to a total of 320 Y RNAs, although Y RNA copies other than the canonical four Y1/3/4/5 genes had previously been considered to be non-functional and were labeled ‘pseudogenes’ (Supplementary file 3F). We found that 237 of the 320 nELAVL bound Y RNAs were Y3-like RNAs (Supplementary file 3F), and that nELAVL bound Y RNAs showed an enrichment of the nELAVL binding motif (202 Y RNAs contained UUUUUU, allowing a G at any one position), which is also present in the canonical hY3 RNA (Figure 6A/B). We examined the 118 nELAVL bound Y RNAs that did not fit this consensus in more detail. 91 of these Y RNAs (77%) contained either a 5mer version of the motif or the motif with an A or C instead of a G, and we found U/G rich stretches in the remaining 27 Y RNAs (Supplementary file 3F). In addition, some Y RNAs with a strong binding motif did not show any evidence of nELAVL binding. In general, these Y RNAs showed a lower expression compared to nELAVL bound Y RNA, which may explain the absence of detectable nELAVL binding (Figure 6—figure supplement 1).

We next explored nELAVL/Y RNA binding in AD brain. We observed a drastic increase in nELAVL/Y RNA association in AD subjects (Figure 6C), while Y RNA levels remained largely unchanged (Figure 6D). This suggests that Y RNPs undergo nELAVL-dependent remodeling in AD. Interestingly, we did observe a high variability in nELAVL/Y RNA association between AD samples (Figure 6—figure supplement 2), with three of them showing a very strong nELAVL/Y RNA association. Efforts to relate this difference to the expression of stress-related genes, post-mortem interval, age, extent of disease and cause of death were not conclusive, and the cause for the variation in nELAVL binding to Y RNAs among AD subjects remains elusive.

Y RNPs are remodeled during UV stress

The observation of increased nELAVL/Y RNA association in AD raised the possibility that Y RNP remodeling is associated with neuronal stress. Y RNP remodeling has previously been linked to UV-induced stress (Sim et al., 2009), and both bacterial (Chen et al., 2000; Wurtmann and Wolin, 2010) and mouse cells (Chen et al., 2003) show an increased sensitivity to UV stress in the absence of RO60. ELAVL binding can be modulated in response to stress in cultured cells (Bhattacharyya et al., 2006), and ELAVL proteins, which shuttle between nucleus and cytoplasm in response to environmental cues, preferentially accumulate in cytoplasmic stress granules upon stress (Gallouzi et al., 2000; Fan and Steitz, 1998b). We therefore examined the effect of acute UV stress on Y RNP remodeling in IMR-32 cells. IMR-32 cells were exposed to a low dose of UV stress (not sufficient to induce RNA:protein crosslinking) and allowed to recover for 24 h before being analyzed by nELAVL CLIP. We found that nELAVL bound 132 Y RNAs in neuroblastoma cells (Supplementary file 3F), that Y RNAs showed an enrichment of the nELAVL binding motif (Figure 7A) or at least contained a degenerate version of it (Supplementary file 3F), and that non-bound Y RNAs with a motif show a very low expression (Figure 7—figure supplement 1). Moreover, nELAVL binding on Y RNAs was dynamic and increased in UV stressed cells compared to non-stressed cells (Figure 7B and Figure 7—figure supplement 2), while their abundance did not change upon UV irradiation (Figure 7C). To assess whether Y RNA levels were affected by nELAVL, we depleted nELAVL by RNAi three days prior to the UV exposure, and analyzed Y RNA levels by RNAseq. Y RNA abundance was not affected by nELAVL depletion in UV stressed IMR-32 cells (Figures 7D). These results indicate that increased nELAVL binding to Y RNAs is not a function of Y RNA levels, and that nELAVL binding during stress is not required for Y RNA stability.

 

Figure 7.

Figure 7.Y RNPs are remodeled during UV stress.

(A) The nELAVL binding motif (UUUUUU, allowing a G at any position) is enriched in nELAVL-bound Y RNAs compared to non-bound Y RNAs (p = 6.2e-6; Fisher’s exact test). Y RNAs were scanned for (T)6, allowing a G at any position. nELAVL-bound Y RNAs: nELAVL CLIP tags in at least two samples; n = 132. (B) nELAVL binding of Y RNAs increases during UV stress compared to non-stressed cells (p = 8.23e-29; paired one-sided Wilcoxon rank sum test). The axes depict nELAVL Y RNA binding (nELAVL CLIP tags per Y RNA) in control and UV stressed cells. Y RNAs with nELAVL binding motif are colored in green. (C) Y RNA levels do not change upon UV stress. Y RNA abundance (RNAseq tags per Y RNA) in UV stressed cells was plotted against Y RNA abundance in non-stressed control cells. (D) nELAVL is binding is not required for Y RNA stability. Comparison of Y RNA abundance between mock andnELAVL RNAi treated UV stressed cells.

DOI: http://dx.doi.org/10.7554/eLife.10421.021

…..

Figure 8.nELAVL/Y RNA correlates with loss of nELAVL-mediated splicing.

(A) Samples with high nELAVL/Y RNA association show decreased nELAVL binding on mRNA targets. Columns represent significantly changing nELAVL binding sites. Shown are changes in AD subjects with and without Y RNA association (AD_Y and AD_nY) and changes upon UV treatment. The number of nELAVL binding sites (n) within each category is indicated. (B) Identification of nELAVL-dependent UV-induced splicing changes. Comparison of the differential inclusion rate of expressed cassette exons upon UV stress between mock and nELAVL RNAi treated IMR-32 cells (n = 9397). Significant UV-induced splicing changes that do not change upon UV stress in nELAVL RNA treated cells are boxed in dark blue (FDR<0.05 and ΔI>0.1; n = 260). (C) Many exons that are alternatively spliced upon nELAVL RNAi treatment also change during UV stress in an nELAVL-dependent manner. Shown is the inclusion rate of expressed cassette exons in IMR-32 cells that were subjected to mock or nELAVL RNAi (n = 9397). nELAVL RNAi induced splicing changes are colored in light blue (n = 553), and are additionally boxed in dark blue if they are UV-induced in an nELAVL-dependent manner (n = 68). The plot is related to Figure 4A but contains additional cassette exons expressed in UV stressed cells. (D) nELAVL binding adjacent to exons that are alternatively spliced upon nELAVL RNAi and UV treatment decreases only in AD subjects with an increased Y RNA association. Displayed is the change in nELAVL peak binding. nELAVL peak binding changes were not significant except for CBFA2T2(boxed in pink). * FDR<0.05 (derived from edgeR). (E) UCSC Genome Browser images depicting an overview and an enlarged view of a cassette exon within the CBFA2T2 gene that is alternatively spliced in nELAVL RNAi and UV-treated IMR-32 cells. The nELAVL binding track in human brain and RNAseq tracks in mock and nELAVL RNAi treated non-stressed and UV-stressed IMR-32 cells are shown.

DOI: http://dx.doi.org/10.7554/eLife.10421.026

…….

Figure 9.Y RNA overexpression is linked to nELAVL sequestration from mRNA targets.

(A) Validation of Y RNA overexpression. Shown are RNA expression fold changes of Y3wt or Y3mut infected IMR-32 cells compared to non-infected IMR-32 cells assessed by qPCR. Y RNAs expression increased while control mRNAs (ACTB, GAPDH, ELAVL4) were not affected. Error bars represent SEM. p values were calculated with a two-tailed t-test (ns: not significant; * p<0.05). (B) The expression of endogenous Y3-like Y RNAs increases upon Y3wt but not Y3mut infection. Box plots represent the distribution of endogenous Y3-like and non-Y3-like Y RNA expression fold changes upon Y3wt or Y3mut infection. Y3-like Y RNAs show a slight increase in abundance upon Y3wt compared to non-Y3-like Y RNAs (p = 0.057; one-tailed t-test). In contrast, the mRNA abundance of Y3-like Y RNAs does not change upon Y3mut infection, when compared to non-Y3 like Y RNAs (p = 0.602; one-tailed t-test). (C) Identification of Y3 dependent splicing changes. Shown is the exon inclusion fraction of cassette exons that are expressed in IMR-32 cells subjected to Y3wt or Y3mut infection (n = 10,189). Exons changing significantly between Y3wt and Y3mut infection (FDR<0.05 and ΔI>0.1) are colored in light blue (n = 191). (D) Exons that are alternatively spliced upon Y3wt infection are enriched for nELAVL bound exons. Bar graph representing total expressed exons (n = 10,189), exons that change in either Y3wt (n = 240; blue points in the left panel of Figure 9—figure supplement 4) or Y3mut (n = 151; blue points in the right panel of Figure 9—figure supplement 4) infected cells compared to non-infected cells, and exons that change in Y3wt compared to Y3mut infected cells (n = 191; blue points in Figure 9C). Exons that are alternatively spliced upon Y3wt infection compared to either non-infected (p = 0.037; hypergeometric test) or Y3mut infected cells (p = 0.069; hypergeometric test) are enriched for nELAVL bound exons.

DOI: http://dx.doi.org/10.7554/eLife.10421.029

………

In contrast to the mRNA abundance changes, only few splicing changes overlapped between Y3wt and Y3mut infection when compared to non-infected cells (17% of Y3wt induced changes overlapped with Y3mut induced changes). Most of the observed splicing changes are therefore likely to be specific to Y RNA overexpression. Importantly, we observed an enrichment of nELAVL bound exons and of nELAVL RNAi dependent exons among the exons that changed upon Y3wt but not Y3mut overexpression (Figure 9C/D and Figure 9—figure supplement 4, 5). The relatively small enrichment is consistent with the modest increase in total Y3-like Y RNAs. These results suggest that Y RNA overexpression results in nELAVL sequestration from some of its intronic targets and consequent splicing changes, and partially recapitulates the stress induced nELAVL sequestration due to increased nELAVL/Y RNA association seen in AD patients and UV treated IMR-32 cells.

Discussion

nELAVL proteins are abundant neuron-specific RNA binding proteins which have been suggested to regulate various neurological processes and have been linked to neurodegenerative disorders including AD and PD. Yet the RNA targets of nELAVL in human brain were completely unknown. Here, we generated a comprehensive genome-wide RNA binding map of nELAVL in human brain, identifying 75,592 significant binding events within 8681 transcripts. We observed a significant overlap between these binding sites and disease-associated 3’UTR SNPs, and the potential disruption of nELAVL-mediated RNA regulation at these sites might contribute to disease manifestation. Most deleterious variants to date have been identified by exome sequencing while as many as 50% of disease-causing mutations are thought to affect splicing (Ward and Cooper, 2009). With whole genome sequencing being increasingly available, non-coding variants are also increasingly detected, some of which may be linked to disease. As the majority of nELAVL binding occurs in introns and 3’UTRs, we expect that many binding sites will overlap with prospective disease-associated non-coding variants. The overlap between deleterious variants and nELAVL binding sites, and the observation that nELAVL binding at individual sites diverged between mice and human, underscores the importance of this study and illustrates the caveat of relying solely on mouse models when studying human disease. Considering the widespread nature of nELAVL binding in human brain and that RNA dysregulation has been linked to numerous neurological disorders, we believe that this binding map will be a valuable resource for the scientific community.

To analyze the functional consequences of nELAVL binding, we used two different loss-of-function models: Elavl3/4 KO mice and nELAVL RNAi depletion in neuroblastoma cells. Due to the incomplete RNAi depletion of nELAVL in neuroblastoma cells, and potential differences in mRNA abundance and therefore nELAVL binding between the different samples, it is likely that we validated only a fraction of nELAVL-regulated transcripts. Despite these technical limitations we demonstrated that nELAVL impacts mRNA abundance and/or splicing of hundreds of targets. Among the nELAVL regulated transcripts were many transcripts implicated in human disease, including AD, which led us to investigate RNA regulation in AD subjects. Due to the relatively small sample size and the heterogeneity between these samples, likely due to both differences between individuals and sample preservation during postmortem collection, we did not detect many reproducible changes in mRNA abundance or nELAVL binding between AD and non-AD subjects. However, we found that 150 transcripts were differentially spliced in AD subjects, which in some cases coincided with differential nELAVL binding. Unexpectedly, the most significant binding change in AD was a dramatic increase in nELAVL binding to a class of non-coding RNAs, termed Y RNAs. This change was evident on a specific subset of Y RNAs harboring the nELAVL binding site. nELAVL/Y RNA binding also increased during UV stress in human neuroblastoma cells, while the abundance of Y RNAs remained constant in AD subjects and upon UV exposure. The increased nELAVL/Y RNA association correlated with decreased nELAVL binding at a subset of intronic binding sites, and was associated with similar splicing changes as induced by nELAVL depletion, suggesting that nELAVL/Y RNP remodeling during acute and chronic stress sequesters nELAVL from its mRNA targets. We provided further evidence for a Y RNA dependent nELAVL sequestration by overexpressing Y3 RNAs harboring either a wild type or mutated nELAVL binding site. Exons that were differentially spliced upon Y RNA overexpression were enriched for nELAVL bound exons, indicating nELAVL sequestration, which was dependent on an intact nELAVL binding site in the Y RNA.

nELAVL 3’UTR binding has been implicated in increasing mRNA abundance in vivo (Ince-Dunn et al., 2012). We described numerous nELAVL 3’UTR targets in brain, and were able to validate many of these targets, including disease-associated transcripts, indicating that nELAVL 3’UTR binding is important for the regulation of mRNA abundance in human brain. While ELAVL binding is frequently reported to result in an increase in mRNA abundance, we found several cases where nELAVL binding seemed to have an opposing effect. ELAVL proteins can compete or collaborate with miRNAs as well as RBPs like AUF1, CUGBP1 and TIA1 to regulate its targets (Bhattacharyya et al., 2006;Kawai et al., 2006; Lal et al., 2004; Young et al., 2009; Yu et al., 2013; Kim et al., 2009). The ultimate outcome of nELAVL 3’UTR binding might therefore vary between individual transcripts.

nELAVL has also been shown to regulate splicing in mouse brain by binding to intronic sequences (Ince-Dunn et al., 2012). We observed many instances of intronic nELAVL binding events adjacent to alternative exons in brain, and confirmed that nELAVL regulates many of these exons in mice and neuroblastoma cells. In contrast to the position-dependent splicing observed for other RBPs (Licatalosi and Darnell, 2010), we observed that upstream nELAVL binding was associated with both exon skipping and inclusion. While nELAVL binding was observed within 25-50 nucleotides upstream of skipped exons, coinciding with the branch point sequence, nELAVL binding peaked within the proximal 25 nucleotides upstream of included exons, overlapping the polypyrimidine tract. Binding of auxiliary splicing factors, including nELAVL, to the branch point sequence usually interferes with spliceosome assembly and thus leads to exon skipping (Licatalosi and Darnell, 2010). Polypyrimidine tract binding however can lead to both exon inclusion and skipping (Licatalosi et al., 2012; Wei et al., 2012), presumably depending on the recruitment of splicing enhancers or silencers. Our data indicates that upstream nELAVL binding can both interfere with the assembly of the spliceosome as well as promote splicing, most likely by recruiting splicing enhancers.

Splicing defects have been associated with many neurological diseases (Licatalosi and Darnell, 2006), and among the nELAVL-regulated transcripts we describe here are numerous transcripts related to disease, including AD. For example, intronic nELAVL binding of the gene encoding the amyloid precursor protein, APP, was associated with skipping of exons 7 and 8. Both exons have previously been shown to be alternatively spliced and encode for the Kunitz protease inhibitory (KPI) motif, a domain that has been linked to APP processing (Ben Khalifa et al., 2012). Remarkably, KPI domain containing isoforms of APP have been shown to be increased in AD (Zhang et al., 2012), indicating that APP splicing might contribute to AD pathogenesis, and that nELAVL binding in human brain might be important to regulate the inclusion of the KPI domain. nELAVL regulates the splicing of two more AD-related transcripts, PICALM and BIN1, by promoting the inclusion of alternative exons 13 and 6a, respectively. Both proteins have been implicated in APP trafficking and both exons lie within domains mediating protein-protein interactions (Tan et al., 2013; Treusch et al., 2011). Moreover, inclusion of the alternative exon 13 in PICALM has been linked to an AD-associated SNP (Parikh et al., 2014), and we observed in this study that exon 6a of BIN1 shows a higher inclusion rate in controls compared to AD subjects. Since nELAVL binding promotes the inclusion of this exon, and control subjects show higher nELAVL binding, we propose that the altered splicing of BIN1 in AD subjects might be due to differential nELAVL binding. In fact, several nELAVL-regulated exons have been shown to be differentially spliced in AD subjects, further strengthening the link between nELAVL dysregulation and AD.

While Y RNAs have not been linked to AD before, they have been implicated in various types of stress responses. The RNA binding protein RO60 usually associates with Y RNAs and is required for their stabilization (Chen et al., 2000; 2003; Labbé et al., 1999; Wolin et al., 2013; Xue et al., 2003). Besides RO60, Y RNPs contain several other RBPs such as ZBP1, MOV10, and Y-box proteins, and have been found to be remodeled upon stress (Sim et al., 2012). Our data suggests that nELAVL becomes increasingly associated with specific Y RNAs during both UV-induced stress and AD. ELAVL proteins can shuttle between nucleus and cytoplasm in response to environmental cues and preferentially accumulate in cytoplasmic stress granules upon cellular stress (Fan and Steitz, 1998a;Gallouzi et al., 2000), and ELAVL binding to the CAT-1 transcript is modulated in response to stress in cultured cells (Bhattacharyya et al., 2006). Interestingly, while we found that nELAVL specifically associates with Y RNAs during AD and acute UV stress, the nucleocytoplasmic distribution of nELAVL, RO60, and Y RNAs was not affected by UV stress. Because Y RNA levels remained constant, we propose that Y RNP complexes are specifically remodeled during AD and acute stress, which is not likely due to a change in nucleocytoplasmic protein/RNA distribution. These results are consistent with previous observations that stress induced shuttling might be limited to ELAVL1 (Burry and Smith, 2006). Our observation of Y RNP remodeling in two very different systems of neuronal stress suggests that differential nELAVL/Y RNA association may be a widespread phenomenon and a focus of future studies.

In addition to the four canonical human Y RNAs, hY1/3/4/5, hundreds of additional Y RNA genes are distributed throughout the human genome (Perreault et al., 2005). The apparent lack of promoters upstream led to a premature designation of these Y RNAs as pseudogenes. Surprisingly, we found that hundreds of these Y RNA copies are expressed in human brain and neuroblastoma cells, although it remains unclear if these Y RNAs can still associate with RO60, because the RO60 binding site in many Y RNA copies is mutated (Perreault et al., 2005). We observed that numerous Y RNA copies were more strongly associated with nELAVL in AD brain and acutely stressed cells, yet nELAVL binding did not affect their levels, indicating a function for this interaction other than Y RNA stabilization. While the outcome of nELAVL/Y RNA remains to be elucidated, our work revealed an aspect of nELAVL/Y RNA association related to stoichiometry. Hundreds of Y RNAs are bound by nELAVL in AD and UV-stress, which corresponds to up to 5% of all nELAVL CLIP tags. This shift of nELAVL binding may distort the normal stoichiometry of nELAVL interactions with its mRNA targets. Indeed, non-coding RNAs have previously been shown to affect RBP-RNA stoichiometry and therefore the biological function of other RNAs or RBPs (Borah et al., 2011; Cazalla et al., 2010;Hansen et al., 2013). Our data indicate that the binding of nELAVL to Y RNAs during stress may lead to a redistribution of nELAVL binding and/or competition of nELAVL from other RNAs. Consistently, we found that high nELAVL/Y RNA association was associated with a general decrease in nELAVL binding at a subset of binding sites, especially within introns, and consequential splicing changes were reminiscent of splicing changes provoked by nELAVL depletion. Consistently, splicing changes induced by Y RNA overexpression showed an enrichment of nELAVL binding that was dependent on the presence of the ELAVL binding motif in Y RNAs. Hence we propose that the increased association of nELAVL and Y RNAs during stress causes sequestration of nELAVL from its mRNA targets.

Taken together, our data indicate that nELAVL becomes strongly associated with Y RNAs in some AD subjects as well as in cells subjected to UV stress, and this is linked to a sequestration of nELAVL from some of its intronic targets, partially recapitulating splicing changes induced by nELAVL depletion. Our results are consistent with a hypothesis that a relatively subtle and perhaps long-term effect of Y RNA binding on normal nELAVL stoichiometry may underlie subtle and long-term changes in nELAVL biology. Perhaps analogously, the sequestration of the RBP, TDP-43, has previously been linked to neurodegenerative disorders (Lee et al., 2012). While the underlying mechanisms of TDP-43 and nELAVL sequestration are distinct, relatively subtle and long-term rearrangement of RNA:protein stoichiometry and interactions might be a recurrent theme of neurodegeneration.

 

 

 

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Dopamine-β-Hydroxylase Functional Variants

Curator: Larry H. Bernstein, MD, FCAP

 

 

Deep sequencing identifies novel regulatory variants in the distal promoter region of the dopamine-β-hydroxylase gene.

OBJECTIVE:

Dopamine-β-hydroxylase (DBH), an enzyme that converts dopamine into norepinephrine, is a drug target in cardiovascular and neuropsychiatric disorders. We aimed to identify functional variants in this gene by deep sequencing and enzyme phenotyping in an Indian cohort.

MATERIALS AND METHODS:

Targeted resequencing of 12 exons and 10 kb upstream sequences of DBH in healthy volunteers (n=50) was performed using the Ion Personal Genome Machine System. Enzyme quantity and activity in their sera samples were determined by ELISA and ultra performance liquid chromatography, respectively. The association of markers with phenotypes was determined using Matrix eQTL. Global P-values for haplotypes generated using UNPHASED 3.1.5 were graphed using GrASP v.082 beta.

RESULTS:

Of the 49 variants identified, nine were novel (minor allele frequency≥0.01). Though individual markers associated with enzyme quantity did not withstand multiple corrections, a novel distal promoter block driven by rs113249250 (global P=1.5×10) was associated. Of the nine single nucleotide polymorphisms (SNPs) associated with enzyme activity, rs3025369, rs1076151 and rs1611115, all from the upstream region, withstood false discovery rate correction (false discovery rate=0.03, 0.03 and 2.9×10, respectively). Conditioning for rs1611115 identified rs1989787 also to affect activity. Importantly, we report an association of a novel haplotype block distal to rs1076151 driven by rs3025369 (global P=8.9×10) with enzyme activity. This regulatory SNP explained 4.9% of the total 46.1% of variance in DBH activity caused by associated SNPs.

CONCLUSION:

This first study combining deep sequencing and enzyme phenotyping identified yet another regulatory SNP suggesting that regulatory variants may be central in the physiological or metabolic role of this gene of therapeutic and pharmacological relevance.

 

 

Correlation of plasma dopamine beta-hydroxylase activity with polymorphisms in DBH gene: a study on Eastern Indian population.

Plasma dopamine beta-hydroxylase activity (plDbetaH) is tightly regulated by the DBH gene and several genetic polymorphisms have been found to independently exert their influence. In the present investigation, association of four DBH polymorphisms, DBH-STR, rs1611115, rs1108580, and rs2519152 with plDbetaH was examined in blood samples from 100 unrelated individuals belonging to the state of West Bengal, Eastern India. Genotypes obtained after PCR amplification and restriction digestion were used for statistical analyses. plDbetaH was measured using a photometric assay and its correlation with the genetic polymorphisms was analyzed using analysis of variance and linear regression. Moderate linkage disequilibrium (LD) was observed between DBH-STR and rs1611115, while rs1108580 and rs2519152 were in strong LD. ‘T’ allele of rs1611115 showed strong negative correlation with plDbetaH, whereas DBH-STR, rs1108580 and rs2519152 had no major effect. Four haplotypes showed significant influence on plDbetaH. This is the first report on the effect of genetic polymorphisms on plDbetaH from the Indian sub-continent. rs1611115 was the only polymorphism that showed substantial control over plDbetaH. Other polymorphisms which did not show individual effects could possibly be part of larger haplotype blocks that carry the functional polymorphisms controlling plDbetaH.
Polymorphisms and low plasma activity of dopamine-beta-hydroxylase in ADHD children.
Attention-deficit Hyperactivity disorder (ADHD) is a multifactorial disorder clinically characterized by inattentiveness, impulsivity and hyperactivity. The occurrence of this disorder is between 3 and 6% of the children population, with boys predominating over girls at a ratio of 3:1 or more. The research of some candidate genes (DRD4, DAT, DRD5, DBH, 5HTT, HTR1B and SNAP25) brought consistent results confirming the heredity of ADHD syndromes. Dopamine-beta-hydroxylase (DBH) is an enzyme responsible for the conversion of dopamine into noradrenaline. Alteration of the dopamine/noradrenaline levels can result in hyperactivity. The DBH protein is released in response to stimulation. DBH activity, derived largely from sympathetic nerves, can be measured in human plasma. Patients with ADHD showed decreased activities of DBH in serum and urine. Low DBH levels correlate indirectly with the seriousness of the hyperkinetic syndrome in children [19,20]. In the DBH gene, the G444A, G910T, C1603T, C1912T, C-1021T, 5 -ins/del and TaqI polymorphisms occur frequently and may affect the function of gene products or modify gene expression and thus influence the progression of ADHD. This article reviews the DBH itself and polymorphisms in the DBH gene that influence the DBH activity in the serum and the CSF level of DBH. All those are evaluated in connection with ADHD.
Candidate gene studies of attention-deficit/hyperactivity disorder.
A growing body of behavioral and molecular genetics literature has indicated that the development of attention-deficit/hyperactivity disorder (ADHD) may be attributed to both genetic and environmental factors. Family, twin, and adoption studies provide compelling evidence that genes play a strong role in mediating susceptibility to ADHD. Molecular genetic studies suggest that the genetic architecture of ADHD is complex, while the handful of genome-wide scans conducted thus far is not conclusive. In contrast, the many candidate gene studies of ADHD have produced substantial evidence implicating several genes in the etiology of the disorder. For the 8 genes for which the same variant has been studied in 3 or more case-control or family-based studies, 7 show statistically significant evidence of association with ADHD based on pooled odds ratios across studies: the dopamine D4 receptor gene (DRD4), the dopamine D5 receptor gene (DRD5), the dopamine transporter gene (DAT), the dopamine beta-hydroxylase gene (DBH), the serotonin transporter gene (5-HTT), the serotonin receptor 1B gene (HTR1B), and the synaptosomal-associated protein 25 gene (SNAP25). Recent pharmacogenetic studies have correlated treatment nonresponse with particular gene markers, while preclinical studies have increased our understanding of gene expression paradigms and potential analogs for human trials. This literature review discusses the relevance and implications of genetic associations with ADHD for clinical practice and future research
Lack of significant association between -1021C–>T polymorphism in the dopamine beta hydroxylase gene and attention deficit hyperactivity disorder.
Recent trends in medications for attention deficit hyperactivity disorder (ADHD) suggest that norepinephrine (NE) deficiency may contribute to the disease etiology. Dopamine beta hydroxylase (DBH) is the key enzyme which converts dopamine to NE and since DBH gene is considered a major quantitative trait locus for plasma DBH activity, genetic polymorphism may lead to altered NE neurotransmission. Several polymorphisms including a 5′ flanking -1021C–>T polymorphism, was reported to be associated with changed DBH activity and an association between -1021C–>T polymorphism with ADHD was observed in Han Chinese children. We have carried out family-based studies with three polymorphisms in the DBH gene, -1021C–>T polymorphism, exon 2*444g/a and intron 5 TaqI RFLP, to explore their association with Indian ADHD cases. Allele and genotype frequency of these polymorphisms in ADHD cases were compared with that of their parents and a control group. Haplotypes obtained were analyzed for linkage disequilibrium (LD). Haplotype-based haplotype relative risk analysis and transmission disequilibrium test showed lack of significant association between transmission of the polymorphisms and ADHD. A haplotype comprising of allele 1 of all polymorphisms showed a slight positive trend towards transmission from parents to ADHD probands. Strong LD was observed between *444g/a and TaqI RFLP in all the groups. However, low D’ values and corresponding log of odds scores in the control group as compared to the ADHD families indicated that, the incidence of the two polymorphisms being transmitted together could be higher in ADHD families.
Association of the dopamine beta hydroxylase gene with attention deficit hyperactivity disorder: genetic analysis of the Milwaukee longitudinal study.
Attention deficit hyperactivity disorder (ADHD) is a highly heritable and common disorder that partly reflects disturbed dopaminergic function in the brain. Recent genetic studies have shown that candidate genes involved in dopamine signaling and metabolism contribute to ADHD susceptibility. We have initiated genetic studies in a unique cohort of 158 ADHD and 81 control adult subjects who have been followed longitudinally since childhood in the Milwaukee study of ADHD. From this cohort, genetic analysis was performed in 105 Caucasian subjects with ADHD and 68 age and ethnicity-matched controls for the DRD4 exon 3 VNTR, the SLC6A3 (DAT1) 3′ UTR VNTR, dopamine beta hydroxylase (DBH) TaqI A polymorphism, and the DBH GT microsatellite repeat polymorphism that has been quantitatively associated with serum levels of DBH activity, but not previously studied in ADHD. Results indicate a significant association between the DBH TaqI A1 allele and ADHD (P = 0.018) with a relative risk of 1.33. The DBH GT repeat 4 allele, which is associated with high serum levels of DBH, occurred more frequently in the ADHD group than controls, but the difference did not reach statistical significance. Associations were not found with the SLC6A3 10 repeat or DRD4 7 repeat alleles. These results indicate that the DBH TaqI A allele, or another polymorphism in linkage disequilibrium with this allele, may confer increased susceptibility towards ADHD.
Polymorphisms of the dopamine transporter gene: influence on response to methylphenidate in attention deficit-hyperactivity disorder.
Attention deficit-hyperactivity disorder (ADHD) is a very common and heterogeneous childhood-onset psychiatric disorder, affecting between 3% and 5% of school age children worldwide. Although the neurobiology of ADHD is not completely understood, imbalances in both dopaminergic and noradrenergic systems have been implicated in the origin and persistence of core symptoms, which include inattention, hyperactivity, and impulsivity. The role of a genetic component in its etiology is strongly supported by genetic studies, and several investigations have suggested that the dopamine transporter gene (DAT1; SLC6A3 locus) may be a small-effect susceptibility gene for ADHD. Stimulant medication has a well-documented efficacy in reducing ADHD symptoms. Methylphenidate, the most prescribed stimulant, seems to act mainly by inhibiting the dopamine transporter protein and dopamine reuptake. In fact, its effect is probably related to an increase in extracellular levels of dopamine, especially in brain regions enriched in this protein (i.e. striatum). It is also important to note that dopamine transporter densities seem to be particularly elevated in the brain of ADHD patients, decreasing after treatment with methylphenidate. Altogether, these observations suggest that the dopamine transporter does play a major role in ADHD. Among the several polymorphisms already described in the SLC6A3 locus, a 40 bp variable number of tandem repeats (VNTR) polymorphism has been extensively investigated in association studies with ADHD. Although there are some negative results, the findings from these reports indicate the allele with ten copies of the 40 bp sequence (10-repeat allele) as the risk allele for ADHD. Some investigations have suggested that this polymorphism can be implicated in dopamine transporter gene expression in vitro and dopamine transporter density in vivo, even though it is located in a non-coding region of the SLC6A3 locus. Despite all these data, few studies have addressed the relationship between genetic markers (specifically the VNTR) at the SLC6A3 locus and response to methylphenidate in ADHD patients. A significant effect of the 40 bp VNTR on response to methylphenidate has been detected in most of these reports. However, the findings are inconsistent regarding both the allele (or genotype) involved and the direction of this influence (better or worse response). Thus, further investigations are required to determine if genetic variation due to the VNTR in the dopamine transporter gene is able to predict different levels of clinical response and palatability to methylphenidate in patients with ADHD, and how this information would be useful in clinical practice.
Pharmacogenomics in psychiatry: the relevance of receptor and transporter polymorphisms.
The treatment of severe mental illness, and of psychiatric disorders in general, is limited in its efficacy and tolerability. There appear to be substantial interindividual differences in response to psychiatric drug treatments that are generally far greater than the differences between individual drugs; likewise, the occurrence of adverse effects also varies profoundly between individuals. These differences are thought to reflect, at least in part, genetic variability. The action of psychiatric drugs primarily involves effects on synaptic neurotransmission; the genes for neurotransmitter receptors and transporters have provided strong candidates in pharmacogenetic research in psychiatry. This paper reviews some aspects of the pharmacogenetics of neurotransmitter receptors and transporters in the treatment of psychiatric disorders. A focus on serotonin, catecholamines and amino acid transmitter systems reflects the direction of research efforts, while relevant results from some genome-wide association studies are also presented. There are many inconsistencies, particularly between candidate gene and genome-wide association studies. However, some consistency is seen in candidate gene studies supporting established pharmacological mechanisms of antipsychotic and antidepressant response with associations of functional genetic polymorphisms in, respectively, the dopamine D2 receptor and serotonin transporter and receptors. More recently identified effects of genes related to amino acid neurotransmission on the outcome of treatment of schizophrenia, bipolar illness or depression reflect the growing understanding of the roles of glutamate and γ-aminobutyric acid dysfunction in severe mental illness. A complete understanding of psychiatric pharmacogenomics will also need to take into account epigenetic factors, such as DNA methylation, that influence individual responses to drugs.
Pharmacogenetics of psychotropic drug response.

OBJECTIVE:

Molecular genetic approaches provide a novel method of dissecting the heterogeneity of psychotropic drug response. These pharmacogenetic strategies offer the prospect of identifying biological predictors of psychotropic drug response and could provide the means of determining the molecular substrates of drug efficacy and drug-induced adverse events.

METHOD:

The authors discuss methods issues in executing pharmacogenetic studies, review the first generation of pharmacogenetic studies of psychotropic drug response, and consider future directions for this rapidly evolving field.

RESULTS:

Pharmacogenetics has been most commonly used in studies of antipsychotic drug efficacy, antidepressant drug response, and drug-induced adverse effects. Data from antipsychotic drug studies indicate that polymorphisms within the serotonin 2A and dopamine receptor 2 genes may influence drug efficacy in schizophrenia. Moreover, a growing body of data suggests a relationship between the serotonin transporter gene and clinical effects of the selective serotonin reuptake inhibitors used to treat depression. A significant relationship between genetic variation in the cytochrome P450 system and drug-induced adverse effects may exist for certain medications. Finally, a number of independent studies point to a significant effect of a dopamine D(3) receptor polymorphism on susceptibility to tardive dyskinesia.

CONCLUSIONS:

Initial research into the pharmacogenetics of psychotropic drug response suggests that specific genes may influence phenotypes associated with psychotropic drug administration. These results remain preliminary and will require further replication and validation. New developments in molecular biology, human genomic information, statistical methods, and bioinformatics are ongoing and could pave the way for the next generation of pharmacogenetic studies in psychiatry.

OBJECTIVE: Molecular genetic approaches provide a novel method of dissecting the heterogeneity of psychotropic drug response. These pharmacogenetic strategies offer the prospect of identifying biological predictors of psychotropic drug response and could provide the means of determining the molecular substrates of drug efficacy and drug-induced adverse events. METHOD: The authors discuss methods issues in executing pharmacogenetic studies, review the first generation of pharmacogenetic studies of psychotropic drug response, and consider future directions for this rapidly evolving field. RESULTS: Pharmacogenetics has been most commonly used in studies of antipsychotic drug efficacy, antidepressant drug response, and drug-induced adverse effects. Data from antipsychotic drug studies indicate that polymorphisms within the serotonin 2A and dopamine receptor 2 genes may influence drug efficacy in schizophrenia. Moreover, a growing body of data suggests a relationship between the serotonin transporter gene and clinical effects of the selective serotonin reuptake inhibitors used to treat depression. A significant relationship between genetic variation in the cytochrome P450 system and drug-induced adverse effects may exist for certain medications. Finally, a number of independent studies point to a significant effect of a dopamine D3 receptor polymorphism on susceptibility to tardive dyskinesia. CONCLUSIONS: Initial research into the pharmacogenetics of psychotropic drug response suggests that specific genes may influence phenotypes associated with psychotropic drug administration. These results remain preliminary and will require further replication and validation. New developments in molecular biology, human genomic information, statistical methods, and bioinformatics are ongoing and could pave the way for the next generation of pharmacogenetic studies in psychiatry.

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Tracking protein expression

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Protein Counting in Single Cancer Cells

Stephanie M. Schubert, Stephanie R. Walter, Mael Manesse, and David R. Walt*
Analytical Chemistry  Anal. Chem., 2016, 88 (5), pp 2952–2957   http://dx.doi.org:/10.1021/acs.analchem.6b00146

 

Abstract Image

 

 

The cell is the basic unit of biology and protein expression drives cellular function. Tracking protein expression in single cells enables the study of cellular pathways and behavior, but requires methodologies sensitive enough to detect low numbers of protein molecules with a wide dynamic range to distinguish unique cells and quantify population distributions. This study presents an ultrasensitive and automated approach for quantifying phenotypic responses with single cell resolution using single molecule array (Simoa) technology. We demonstrate how prostate specific antigen (PSA) expression varies over several orders of magnitude between single prostate cancer cells, and how PSA expression shifts with genetic drift. Single cell Simoa intduces a straightforward process that is capable of detecting both high and low protein expression levels. This technique could be useful for understanding fundamental biology and may eventually enable both earlier disease detection and targeted therapy.

 

Quanterix’s proprietary Simoa™ technology (named for single molecule array) is based upon the isolation of individual immunocomplexes on paramagnetic beads using standard ELISA reagents. The main difference between Simoa and conventional immunoassays lies in the ability to trap single molecules in femtoliter-sized wells, allowing for a “digital” readout of each individual bead to determine if it is bound to the target analyte or not.

The digital nature of the technique allows an average of 1000x sensitivity increase over conventional assays with CVs <10%.

 

 

A. Single protein molecules are captured and labeled on beads using standard ELISA reagents.

 

B. Tens of thousands of beads – with or without immunoconjugate – are mixed with enzyme substrate and loaded into individual femtoliter-sized wells.

 

C. The microwells are sealed with oil.

 

D. Fluorophore concentration in the small sample volume of wells containing the target analyte rapidly reach detectable limits using conventional fluorescence imaging and can be digitally counted.

E. The percentage of beads containing labelled immunocomplexes can be computed at low concentration because they follow a Poisson distribution; at higher concentrations the intensity of the aggregate signal provides an analog measurement.

 

 

Clin Chem Lab Med. 2015 Oct 23. pii: /j/cclm.ahead-of-print/cclm-2015-0733/cclm-2015-0733.xml. http://dx.doi.org:/10.1515/cclm-2015-0733. [Epub ahead of print]
Assessing the commutability of reference material formats for the harmonization of amyloid beta measurements.

The cerebrospinal fluid (CSF) amyloid-β (Aβ42) peptide is an important biomarker for Alzheimer’s disease (AD). Variability in measured Aβ42 concentrations at different laboratories may be overcome by standardization and establishing traceability to a reference system. Candidate certified reference materials (CRMs) are validated herein for this purpose.

METHODS:

Commutability of 16 candidate CRM formats was assessed across five CSF Aβ42 immunoassays and one mass spectrometry (MS) method in a set of 48 individual clinical CSF samples. Promising candidate CRM formats (neat CSF and CSF spiked with Aβ42) were identified and subjected to validation across eight (Elecsys, EUROIMMUN, IBL, INNO-BIA AlzBio3, INNOTEST, MSD, Simoa, and Saladax) immunoassays and the MS method in 32 individual CSF samples. Commutability was evaluated by Passing-Bablok regression and the candidate CRM termed commutable when found within the prediction interval (PI). The relative distance to the regression line was assessed.

RESULTS:

The neat CSF candidate CRM format was commutable for almost all method comparisons, except for the Simoa/MSD, Simoa/MS and MS/IBL where it was found just outside the 95% PI. However, the neat CSF was found within 5% relative distance to the regression line for MS/IBL, between 5% and 10% for Simoa/MS and between 10% and 15% for Simoa/MSD comparisons.

CONCLUSIONS:

The neat CSF candidate CRM format was commutable for 33 of 36 method comparisons, only one comparison more than expected given the 95% PI acceptance limit. We conclude that the neat CSF candidate CRM can be used for value assignment of the kit calibrators for the different Aβ42 methods.

 

 

Nature Neuroscience18, 1559–1561(2015)    http://dx.doi.org:/10.1038/nn.4117

Cerebral β-amyloidosis is induced by inoculation of Aβ seeds into APP transgenic mice, but not into App−/− (APP null) mice. We found that brain extracts from APP null mice that had been inoculated with Aβ seeds up to 6 months previously still induced β-amyloidosis in APP transgenic hosts following secondary transmission. Thus, Aβ seeds can persist in the brain for months, and they regain propagative and pathogenic activity in the presence of host Aβ.

 

Induced amyloid lesions are partly congophilic and surrounded by activated microglia and dystrophic boutons.

Induced amyloid lesions are partly congophilic and surrounded by activated microglia and dystrophic boutons.

(a) Congo red-positive amyloid deposits induced in the dentate gyrus were surrounded by Iba1-positive microglia (black). (b) Congo red-positive plaque with surrounding hypertrophic microglial cell bodies and processes at higher magnification

 

Glial fibrillary acidic protein is a body fluid biomarker for glial pathology in human disease

Brain Research  Volume 1600, 10 March 2015, Pages 17–31    doi:10.1016/j.brainres.2014.12.027

Highlights

• Reviewing 45 years of Glial fibrillary acidic protein (Gfap).
•Gfap discovered in multiple sclerosis brain tissue.
•From Gfap genetics to post-translational modifications.
•Ninety-nine ways to quantify Gfap and related immune phenomena.
•Emergence of Gfap as a body fluid biomarker in human disease.

This review on the role of glial fibrillary acidic protein (GFAP) as a biomarker for astroglial pathology in neurological diseases provides background to protein synthesis, assembly, function and degeneration. Qualitative and quantitative analytical techniques for the investigation of human tissue and biological fluid samples are discussed including partial lack of parallelism and multiplexing capabilities. Pathological implications are reviewed in view of immunocytochemical, cell-culture and genetic findings. Particular emphasis is given to neurodegeneration related to autoimmune astrocytopathies and to genetic gain of function mutations. The current literature on body fluid levels of GFAP in human disease is summarised and illustrated by disease specific meta-analyses. In addition to the role of GFAP as a diagnostic biomarker for chronic disease, there are important data on the prognostic value for acute conditions. The published evidence permits to classify the dominant GFAP signatures in biological fluids. This classification may serve as a template for supporting diagnostic criteria of autoimmune astrocytopathies, monitoring disease progression in toxic gain of function mutations, clinical treatment trials (secondary outcome and toxicity biomarker) and provide prognostic information in neurocritical care if used within well defined time-frames.

 

The GFAP isoforms. A schematic drawing of the protein structures of the GFAP ...

 

Modelled structure of GFAP. Reprinted with permission from Biswas et al. (2011).

 

CSF and Plasma Amyloid-b Temporal Profiles and Relationships with Neurological Status and Mortality after Severe Traumatic Brain Injury

http://www.quanterix.com/literature/publications/neurology/item/482-csf-and-plasma-amyloid-b-temporal-profiles-and-relationships-with-neurological-status-and-mortality-after-severe-traumatic-brain-injury

by Stefania Mondello, Andras Burk, Pal Barzo, Jeff Randall, Gail Provuncher, David Hanlon, David Wilson, Firas Kobeissy & Andreas Jeromin

 

The role of amyloid-b (Ab) neuropathology and its significant changes in biofluids after traumatic braininjury (TBI) is still debated. We used ultrasensitive digital  ELISA approach to assess amyloid-b1-42 (Ab42) concentrations and time-course in cerebrospinal fluid (CSF) and in plasma of patients with severe TBI and
investigated their relationship to injury characteristics, neurological status and clinical outcome. We found decreased CSF Ab42 levels in TBI patients acutely after injury with lower levels in patients who died 6 months post-injury than in survivors. Conversely, plasma Ab42 levels were significantly increased in TBI
with lower levels in patients who survived. A trend analysis showed that both CSF and plasma Ab42 levels strongly correlated with mortality. A positive correlation between changes in CSF Ab42 concentrations and neurological status as assessed by Glasgow Coma Scale (GCS) was identified. Our results suggest that determination of Ab42 may be valuable to obtain prognostic information in patients with severe TBI as well as in monitoring the response of the brain to injury.
Plasma tau levels in Alzheimer’s disease
Henrik Zetterberg, David Wilson, Ulf Andreasson, Lennart Minthon, Kaj Blennow, Jeffrey Randall and Oskar Hansson
Alzheimer’s Research & Therapy 2013; 5:9   http://dx.doi.org:/10.1186/alzrt163

Efforts to find reliable blood biomarkers for Alzheimer’s disease (AD) in a highly warranted clinical laboratory test have met with little success. There is no clear change in plasma β-amyloid in AD, and assays for the axonal injury marker tau have been hampered by a lack of analytical sensitivity for accurate measurement in blood samples [1]. Here, the results of a novel ultra-sensitive assay for tau in peripheral blood are reported.

We have developed an ultra-sensitive assay for tau in peripheral blood [2]. In brief, the assay is based on digital array technology [3] and uses the Tau5 monoclonal antibody for capture (Covance, Princeton, NJ, USA) and HT7 and BT2 monoclonal antibodies for detection (Pierce, now part of Thermo Fisher Scientific Inc., Waltham, MA, USA). This combination reacts with both normal and phosphorylated tau with epitopes in the mid-region of the molecule, making the assay sensitive to all known tau isoforms. The calibrator was recombinant tau 381 (EMD Millipore Corporation, Billerica, MA, USA). To minimize matrix effects, all samples were diluted 1:4 in phosphate-buffered saline with 2% bovine serum albumin diluent prior to assay. The limit of detection of the assay, which requires 30 μL of plasma, is 0.02 pg/mL [2], which is more than 1,000-fold more sensitive than conventional immunoassays.

Here, we assess the association of plasma tau levels with AD in a cross-sectional study of 54 patients with AD dementia [4], 75 patients with mild cognitive impairment (MCI) [5], and 25 cognitively normal controls (Table 1). All participants were recruited at the specialized memory clinic at Skåne University Hospital in Malmö, Sweden, and underwent extensive clinical evaluation, including cerebrospinal fluid (CSF) sampling by lumbar puncture, in addition to venipuncture and collection of blood in ethylenediaminetetraacetic acid (EDTA) tubes for plasma preparation by centrifugation within 15 minutes from sampling. Plasma samples were aliquoted into cryo tubes and stored at -80°C pending analysis, which was performed on one occasion by using one batch of reagents with an average coefficient of variation of 9.7% for triplicate measurements of each sample. The patients with MCI were cognitively stable for an average of 101 months (n = 36) or developed AD dementia (n = 35) or other types of dementias – vascular dementia (n = 3) and semantic dementia (n = 1) – during follow-up. The study was approved by the regional ethics committee at Lund University and complied with the Declaration of Helsinki. Informed consent was obtained from all study participants.
Tau levels in plasma were significantly higher in AD patients compared with both controls and MCI patients (Figure 1a). MCI patients who developed AD during follow-up had tau levels similar to those of patients with stable MCI and cognitively normal controls (Figure 1b). There was no correlation between tau levels in plasma and CSF in any diagnostic group (Figure 1c).
https://static-content.springer.com/image/art%3A10.1186%2Falzrt163/MediaObjects/13195_2013_Article_139_Fig1_HTML.jpg

Figure 1

Elevated tau levels in plasma from patients with Alzheimer’s disease (AD). (a) Plasma levels of tau are elevated in patients with AD compared with cognitively normal controls and patients with mild cognitive impairment (MCI). (b) MCI patients who developed AD (MCI-AD) during follow-up had baseline tau levels similar to those of patients with stable MCI (SMCI). (c) There was no correlation between tau levels in plasma and cerebrospinal fluid (CSF) in any diagnostic group. Thin horizontal lines in panels (a) and (b) indicate medians. A nonparametric Kruskal-Wallis test followed by Mann-Whitney was performed to test for statistical significance. Spearman’s rank correlation coefficient was used to assess the relationship between plasma and CSF tau concentrations in panel (c), where open circles, gray squares, and black triangles represent AD, MCI, and controls, respectively.

The results of this study have several important implications. First, plasma tau levels are elevated in AD but with overlapping ranges across diagnostic groups. This overlap diminishes the utility of plasma tau as a diagnostic test. However, further studies are needed to evaluate plasma tau as a first-in-line screening tool (for example, in the primary care setting and perhaps together with other markers in a biomarker panel). Second, normal plasma tau levels in the MCI stage of AD suggest that plasma tau is a late marker, requiring substantial axonal injury before increasing to abnormal levels. In this context, other neurodegenerative diseases (for example, Creutzfeldt-Jakob disease) as well as acute conditions (for example, stroke and brain trauma) should be tested. Third, the lack of correlation of tau levels in plasma and CSF suggests that steady-state concentrations of tau in these two body fluids are differentially regulated. In our earlier study of patients with hypoxic brain injury following cardiac arrest, tau was rapidly (within 24 hours) cleared from blood in patients with good neurological outcome [2], indicating potent clearance mechanisms for this marker in the bloodstream. This may obscure any correlation with CSF tau levels, which stay elevated for weeks following an acute neurological insult [6].

Researchers Use CRISPR-based Method to Track RNA In Vivo

A research team led by researchers from the University of California has modified the CRISPR/Cas9 system to demonstrate the ability to track specific RNA sequences and processes in vivo.

As described in a paper published today in Cell, the investigators were able to use their system to visualize specific RNA molecules accumulating in stress granules — dense aggregations of proteins and RNA that form in the cytosol in response to cellular stress and have been linked to neurodegenerative disorders such as amyotrophic lateral sclerosis.

They also found that they could use Cas9 to target an mRNA without altering mRNA abundance or the amount of translated protein.

“We are just beginning to see the implications of genome engineering using the CRISPR technology, but many diseases, including cancer and autism, are linked to problems with another fundamental biological molecule: RNA,” Gene Yeo, senior study author and an associate professor at the University of California, San Diego, said in a statement.

The researchers began their project based on a modification attempted in the lab of co-author Jennifer Doudna from the University of California, Berkeley. Inthat study, the researchers found that it was possible to design a protospacer adjacent motif (PAM) as part of an oligonucleotide (PAMmer) which binds to the single-stranded RNA, allowing Cas9 to efficiently recognize and cleave RNA rather than DNA (RCas9). The researchers determined that with a few further modifications, they could use this method to not only recognize RNA instead of DNA but actually track its movements through cells.

Previously, researchers have attempted to use molecular beacons to track RNA sequences, however, these are limited to imaging applications and are difficult to deliver into cells. Researchers have also attempted to use aptamers to enable RNA tracking in living cells, but these are limited in the number of RNA sequences that they can recognize.

CRISPR/Cas9, however, has thus far proved extremely useful in the genome engineering field and the research team thought that it would be an ideal base to create a better RNA tracking tool.

To prove their concept, the team tested whether a dead Cas9 (dCas9) that was tagged with the fluorescent protein mCherry and contained a nuclear localization signal could be co-exported from the nucleus with a messenger RNA in the presence of a single-guide RNA (sgRNA) and PAMmer designed to recognize that specific mRNA.

The experiment succeeded and the researchers were also able to observe accumulation of ACTB, CCNA2, and TFRC mRNAs in RNA granules that correlated with fluorescence in situ hybridization visualization using image analysis software.

Once they had established that their method was effective, the researchers showed that they could use the sgRNA and PAMmer targeting sequences to track mRNA trafficking to stress granules.

The researchers demonstrated that they could take time-resolved measurements of ACTB mRNA trafficking to stress granules over a period of 30 minutes. They noted in the paper that RCas9 was capable of measuring the association of CCNA2 and TFRC mRNA trafficking to stress granules, as well.

Based on their results, the investigators believe they have established RCas9 as a means to track RNA in living cells in a programmable manner that doesn’t require genetically encoded tags.

“One potential application of this technique is to track RNA transport in diseased neurons over time in order to identify the molecular features of these diseases and support the developments of therapies,” David Nelles, first author on the study and a researcher at the University of California, San Diego, said in a statement. “Just as CRISPR-Cas9 is making genetic engineering accessible to any scientists with access to basic equipment, RNA-targeted Cas9 may support countless other efforts for studying the role of RNA processing in disease or for identifying drugs that reverse defects in RNA processing.”

 

Programmable RNA Tracking in Live Cells with CRISPR/Cas9

David A. Nelles, Mark Y. Fang, Mitchell R. O’Connell, Jia L. Xu, Sebastian J. Markmiller, Jennifer A. Doudna, Gene W. Yeo
Publication stage: In Press Corrected Proof
Figure thumbnail fx1

Clustered regularly-interspaced short palindromic repeats (CRISPRs) form the basis of adaptive immune systems in bacteria and archaea by encoding CRISPR RNAs that guide CRISPR-associated (Cas) nucleases to invading genetic material (Wiedenheft et al., 2012). Cas9 from the type II CRISPR system ofS. pyogenes has been repurposed for genome engineering in eukaryotic organisms (Hwang et al., 2013, Li et al., 2013a, Mali et al., 2013, Nakayama et al., 2013, Sander and Joung, 2014, Yang et al., 2014) and is rapidly proving to be an efficient means of DNA targeting for other applications such as gene expression modulation (Qi et al., 2013) and imaging (Chen et al., 2013). Cas9 and its associated single-guide RNA (sgRNA) require two critical features to target DNA: a short DNA sequence of the form 5′-NGG-3′ (where “N” = any nucleotide) known as the protospacer adjacent motif (PAM) and an adjacent sequence on the opposite DNA strand that is antisense to the sgRNA. By supporting DNA recognition with specificity determined entirely by a short spacer sequence within the sgRNA, CRISPR/Cas9 provides uniquely flexible and accessible manipulation of the genome. Manipulating cellular RNA content, in contrast, remains problematic. Whereas there exist robust means of attenuating gene expression via RNAi and antisense oligonucleotides, other critical aspects of post-transcriptional gene expression regulation such as subcellular trafficking, alternative splicing or polyadenylation, and spatiotemporally restricted translation are difficult to measure in living cells and are largely intractable.

Analogous to the assembly of zinc finger nucleases (Urnov et al., 2010) and transcription activator-like effector nucleases (TALEN) to recognize specific DNA sequences, efforts to recognize specific RNA sequences have focused on engineered RNA-binding domains. Pumilio and FBF homology (PUF) proteins carry well-defined modules capable of recognizing a single base each and have supported successful targeting of a handful of transcripts for imaging and other manipulations (Filipovska et al., 2011, Ozawa et al., 2007, Wang et al., 2009). PUF proteins can be fused to arbitrary effector domains to alter or tag target RNAs, but PUFs must be redesigned and validated for each RNA target and can only recognize eight contiguous bases, which does not allow unique discrimination in the transcriptome. Molecular beacons are self-quenched synthetic oligonucleotides that fluoresce upon binding to target RNAs and allow RNA detection without construction of a target-specific protein (Sokol et al., 1998). But molecular beacons must be microinjected to avoid the generation of excessive background signal associated with endosome-trapped probes and are limited to imaging applications. An alternative approach to recognition of RNA substrates is to introduce RNA aptamers into target RNAs, enabling specific and strong association of cognate aptamer-binding proteins such as the MS2 coat protein (Fouts et al., 1997). This approach has enabled tracking of RNA localization in living cells over time with high sensitivity (Bertrand et al., 1998) but relies upon laborious genetic manipulation of the target RNA and is not suitable for recognition of arbitrary RNA sequences. Furthermore, insertion of exogenous aptamer sequence has the potential to interfere with endogenous RNA functions. Analogous to CRISPR/Cas9-based recognition of DNA, programmable RNA recognition based on nucleic acid specificity alone without the need for genetic manipulation or libraries of RNA-binding proteins would greatly expand researchers’ ability to modify the mammalian transcriptome and enable transcriptome engineering.

Although the CRISPR/Cas9 system has evolved to recognize double-stranded DNA, recent in vitro work has demonstrated that programmable targeting of RNAs with Cas9 is possible by providing the PAM as part of an oligonucleotide (PAMmer) that hybridizes to the target RNA (O’Connell et al., 2014). By taking advantage of the Cas9 target search mechanism that relies on PAM sequences (Sternberg et al., 2014), a mismatched PAM sequence in the PAMmer/RNA hybrid allows exclusive targeting of RNA and not the encoding DNA. The high affinity and specificity of RNA recognition by Cas9 in cell-free extracts and the success of genome targeting with Cas9 indicate the potential of CRISPR/Cas9 to support programmable RNA targeting in living cells.

To assess the potential of Cas9 as a programmable RNA-binding protein in live cells, we used a modified sgRNA scaffold with improved expression and Cas9 association (Chen et al., 2013) with a stabilized PAMmer oligonucleotide that does not form a substrate for RNase H. We measured the degree of nuclear export of a nuclear localization signal-tagged nuclease-deficient Cas9-GFP fusion and demonstrate that the sgRNA alone is sufficient to promote nuclear export of Cas9 without influencing the abundance of the targeted mRNA or encoded protein. In order to evaluate whether RNA-targeting Cas9 (RCas9) signal patterns correspond with an established untagged RNA-labeling method, we compared distributions of RCas9 and fluorescence in situ hybridization (FISH) targeting ACTB mRNA. We observed high correlation among FISH and RCas9 signal that was dependent on the presence of a PAMmer, indicating the importance of the PAM for efficient RNA targeting. RNA trafficking and subcellular localization are critical to gene expression regulation and reaction to stimuli such as cellular stress. To address whether RCas9 allows tracking of RNA to oxidative stress-induced RNA/protein accumulations called stress granules, we measured ACTB, TFRC, and CCNA2 mRNA association with stress granules in cells subjected to sodium arsenite. Finally, we demonstrated the ability of RCas9 to track trafficking of ACTB mRNA to stress granules over time in living cells. This work establishes the ability of RCas9 to bind RNA in live cells and sets the foundation for manipulation of the transcriptome in addition to the genome by CRISPR/Cas9.

Thumbnail image of Figure 1. Opens large image

http://www.cell.com/cms/attachment/2050893021/2059121638/gr1.jpg

Figure 1

Targeting mRNA in Living Cells with RCas9

(A) Components required for RNA-targeting Cas9 (RCas9) recognition of mRNA include a nuclear localization signal-tagged nuclease-inactive Cas9 fused to a fluorescent protein such as GFP, a modified sgRNA with expression driven by the U6 polymerase III promoter, and a PAMmer composed of DNA and 2′-O-methyl RNA bases with a phosphodiester backbone. The sgRNA and PAMmer are antisense to adjacent regions of the target mRNA whose encoding DNA does not carry a PAM sequence. After formation of the RCas9/mRNA complex in the nucleus, the complex is exported to the cytoplasm.

(B) RCas9 nuclear co-export with GAPDH mRNA. The RCas9 system was delivered to U2OS cells with a sgRNA and PAMmer targeting the 3′ UTR of GAPDH or sgRNA and PAMmer targeting a sequence from λ bacteriophage that should not be present in human cells (“N/A”). Cellular nuclei are outlined with a dashed white line. Scale bars represent 5 microns.

(C) Fraction of cells with cytoplasmic RCas9 signal. Mean values ± SD (n = 50).

(D) A plasmid carrying the Renilla luciferase open reading frame with a β-globin 3′ UTR containing a target site for RCas9 and MS2 aptamer. A PEST protein degradation signal was appended to luciferase to reveal any translational effects of RCas9 binding to the mRNA.

(E) RNA immunoprecipitation of EGFP after transient transfection of the RCas9 system in HEK293T cells targeting the luciferase mRNA compared to non-targeting sgRNA and PAMmer or EGFP alone. Mean values ± SD (n = 3).

(F and G) Renilla luciferase mRNA (F) and protein (G) abundances were compared among the targeting and non-targeting conditions. Mean values ± SD (n = 4).

p values are calculated by Student’s t test, and one, two, and three asterisks represent p values less than 0.05, 0.01, and 0.001, respectively. See also Figure S1.

Correlation of RNA-Targeting Cas9 Signal Distributions with an Established Untagged RNA Localization Measurement

 Tracking RNA Trafficking to Stress Granules over Time
Effective RNA recognition by Cas9 in living cells while avoiding perturbation of the target transcript relies on careful design of the PAMmer and delivery of Cas9 and its cognate guide RNA to the appropriate cellular compartments. Binding of Cas9 to nucleic acids requires two critical features: a PAM DNA sequence and an adjacent spacer sequence antisense to the Cas9-associated sgRNA. By separating the PAM and sgRNA target among two molecules (the PAMmer oligonucleotide and the target mRNA) that only associate in the presence of a target mRNA, RCas9 allows recognition of RNA while avoiding the encoding DNA. To avoid unwanted degradation of the target RNA, the PAMmer is composed of a mixed 2′OMe RNA and DNA that does not form a substrate for RNase H. Further, the sgRNA features a modified scaffold that removes partial transcription termination sequences and a modified structure that promotes association with Cas9 (Chen et al., 2013). Other CRISPR/Cas systems have demonstrated RNA binding in bacteria (Hale et al., 2009, Sampson et al., 2013) or eukaryotes (Price et al., 2015), although these systems cannot discriminate RNA from DNA targets, feature RNA-targeting rules that remain unclear, or rely on large protein complexes that may be difficult to reconstitute in mammalian cells.

In this work, we demonstrate RCas9-based recognition of GAPDH, ACTB,CCNA2, and TFRC mRNAs in live cells. Because the U6-driven sgRNA is largely restricted to the nucleus, the NLS-tagged dCas9 allows association with its sgRNA and subsequent interaction with the target mRNA before nuclear co-export with the target mRNA. As an initial experiment, we evaluated the potential of RNA recognition with Cas9 by targeting GAPDH mRNA and evaluating degree of nuclear export of dCas9-mCherry (Figure 1B). Robust cytoplasmic localization of dCas9-mCherry in the presence of a sgRNA-targeting GAPDH mRNA compared to nuclear retention in the presence of a non-targeting sgRNA indicated that Cas9 association with the mRNA was sufficiently stable to support co-export from the nucleus.

RCas9 as an RNA-imaging reagent requires that RNA recognition by RCas9 does not interfere with normal RNA metabolism. Here, we show that RCas9 binding within the 3′ UTR of Renilla luciferase does not affect its mRNA abundance and translation (Figures 1F and 1G). The utility of RCas9 for imaging and other applications hinges on the recognition of endogenous transcripts, so we evaluated the influence of RCas9 targeting on GAPDH and ACTB mRNAs and observed no significant differences among the mRNA and protein abundances by western blot analysis and qRT-PCR (Figure S1). These results indicate that RCas9 targeting these 3′ UTRs does not perturb the levels of mRNA or encoded protein.

We also evaluated the ability of RCas9 to reveal RNA localization by comparing RCas9 signal patterns to FISH. We utilized a FISH probe set composed of tens of singly labeled probes targeting ACTB mRNA and compared FISH signal distributions to a single dCas9-GFP/sgRNA/PAMmer that recognizes the ACTBmRNA. Our findings indicate that the sgRNA primarily determines the degree of overlap among the FISH and RCas9 signals whereas the PAMmer plays a significant but secondary role. Importantly, in contrast to other untagged RNA localization determination methods such as FISH and molecular beacons, RCas9 is compatible with tracking untagged RNA localization in living cells and can be delivered rapidly to cells using established transfection methods. We also note that the distribution of ACTB mRNA was visualized using a single EGFP tag per transcript, and higher-sensitivity RNA tracking or single endogenous RNA molecule visualization may be possible in the future with RCas9 targeting multiple sites in a transcript or with a multiply tagged dCas9 protein.

Stress granules are translationally silent mRNA and protein accumulations that form in response to cellular stress and are increasingly thought to be involved with neurodegeneration (Li et al., 2013b). There are limited means that can track the movement of endogenous RNA to these structures in live cells (Bertrand et al., 1998). In addition to ACTB mRNA, we demonstrate that RCas9 is capable of measuring association of CCNA2 and TFRC mRNA trafficking to stress granules (Figure 3A). Upon stress induction with sodium arsenite, we observed that 50%, 39%, and 23% of stress granules featured overlapping RCas9 foci when targeting ACTB, TFRC, and CCNA2 mRNAs, respectively (Figure 3C). This result correlates with the expression levels of these transcripts (Figure S3) asACTB is expressed about 8 and 11 times more highly than CCNA2 and TFRC, respectively. We also observed that RCas9 is capable of tracking RNA localization over time as ACTB mRNA is trafficked to stress granules over a period of 30 min (Figure 3B). We noted a dependence of RCas9 signal accumulation in stress granules on stressor concentration (Figure 3D). This approach for live-cell RNA tracking stands in contrast to molecular beacons and aptamer-based RNA-tracking methods, which suffer from delivery issues and/or require alteration of the target RNA sequence via incorporation of RNA tags.

Future applications of RCas9 could allow the measurement or alteration of RNA splicing via recruitment of split fluorescent proteins or splicing factors adjacent to alternatively spliced exons. Further, the nucleic-acid-programmable nature of RCas9 lends itself to multiplexed targeting (Cong et al., 2013) and the use of Cas9 proteins that bind orthogonal sgRNAs (Esvelt et al., 2013) could support distinct activities on multiple target RNAs simultaneously. It is possible that the simple RNA targeting afforded by RCas9 could support the development of sensors that recognize specific healthy or disease-related gene expression patterns and reprogram cell behavior via alteration of gene expression or concatenation of enzymes on a target RNA (Delebecque et al., 2011, Sachdeva et al., 2014). Efforts toward Cas9 delivery in vivo are underway (Dow et al., 2015,Swiech et al., 2015, Zuris et al., 2015), and these efforts combined with existing oligonucleotide chemistries (Bennett and Swayze, 2010) could support in vivo delivery of the RCas9 system for targeted modulation of many features of RNA processing in living organisms.

RNA is subject to processing steps that include alternative splicing, nuclear export, subcellular transport, and base or backbone modifications that work in concert to regulate gene expression. The development of a programmable means of RNA recognition in order to measure and manipulate these processes has been sought after in biotechnology for decades. This work is, to our knowledge, the first demonstration of nucleic-acid-programmed RNA recognition in living cells with CRISPR/Cas9. By relying upon a sgRNA and PAMmer to determine target specificity, RCas9 supports versatile and unambiguous RNA recognition analogous to DNA recognition afforded by CRISPR/Cas9. The diverse applications supported by DNA-targeted CRISPR/Cas9 range from directed cleavage, imaging, transcription modulation, and targeted methylation, indicating the utility of both the native nucleolytic activity of Cas9 as well as the range of activities supported by Cas9-fused effectors. In addition to providing a flexible means to track this RNA in live cells, future developments of RCas9 could include effectors that modulate a variety of RNA-processing steps with applications in synthetic biology and disease modeling or treatment.

Study Unlocks Multiple Functions of CRISPR/Cas9 by Varying Guide RNAs

https://www.genomeweb.com/genetic-research/study-unlocks-multiple-functions-crisprcas9-varying-guide-rnas

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Genetic link to sleep and mood disorders

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Scientists identify molecular link between sleep and mood

A poor night’s sleep is enough to put anyone in a bad mood, and although scientists have long suspected a link between mood and sleep, the molecular basis of this connection remained a mystery. Now, new research has found several rare genetic mutations on the same gene that definitively connect the two.

Sleep goes hand-in-hand with mood. People suffering from depression and mania, for example, frequently have altered sleeping patterns, as do those with seasonal affective disorder (SAD). And although no one knows exactly how these changes come about, in SAD sufferers they are influenced by changes in light exposure, the brain’s time-keeping cue. But is mood affecting sleep, is sleep affecting mood, or is there a third factor influencing both? Although a number of tantalizing leads have linked the circadian clock to mood, there is “no definitive factor that proves causality or indicates the direction of the relationship,” says Michael McCarthy, a neurobiologist at the San Diego Veterans’ Affairs Medical Center and the University of California (UC), San Diego.

To see whether they could establish a link between the circadian clock, sleep, and mood, scientists in the new study looked at the genetics of a family that suffers from abnormal sleep patterns and mood disorders, including SAD and something called advanced sleep phase, a condition in which people wake earlier and sleep earlier than normal. The scientists screened the family for mutations in key genes involved in the circadian clock, and identified two rare variants of the PERIOD3 (PER3) gene in members suffering from SAD and advanced sleep phase. “We found a genetic change in people who have both seasonal affective disorder and the morning lark trait” says lead researcher Ying-Hui Fu, a neuroscientist at UC San Francisco. When the team tested for these mutations in DNA samples from the general population, they found that they were extremely rare, appearing in less than 1% of samples.

Fu and her team then created mice that carried the novel genetic variants. These transgenic mice showed an unusual sleep-wake cycle and struggled less when handled by the researchers, a typical sign of depression. They also had lower levels of PER2, a protein involved in circadian rhythms, than unmutated mice, providing a possible molecular explanation for the unusual sleep patterns in the family. Fu says this supports the link between the PER3 mutations and both sleep and mood. “PER3’s role in mood regulation has never been demonstrated directly before,” she says. “Our results indicate that PER3 might function in helping us adjust to seasonal changes,” by modifying the body’s internal clock.

To investigate further, the team studied mice lacking a functional PER3 gene. They found that these mice showed symptoms of SAD, exhibiting more severe depression when the duration of simulated daylight in the laboratory was reduced. Because SAD affects between 2% and 9% of people worldwide, the novel variants can’t explain it fully. But understanding the function of PER3 could yield insights into the molecular basis of a wide range of sleep and mood disorders, Fu says.

Together, these experiments show that the PERIOD3 gene likely plays a key role in regulating the sleep-wake cycle, influencing mood and regulating the relationship between depression and seasonal changes in light availability, the team reports today in the Proceedings of the National Academy of Sciences. “The identification of a mutation in PER3 with such a strong effect on mood is remarkable,” McCarthy says. “It suggests an important role for the circadian clock in determining mood.”

The next step will be to investigate how well these results generalize to other people suffering from mood and sleep disorders. “It will be interesting to see if other rare variants in PER3 are found, or if SAD is consistently observed in other carriers,” McCarthy says. That could eventually lead to new drugs that selectively target the gene, which McCarthy says, “could be a strategy for treating mood or sleep disorders.”

 

http://dx.doi.org:/10.1126/science.aaf4095

 

 

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Breast Cancer Extratumor Microenvironment has Effect on Progression

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Tumor Microenvironment Diversity Predicts Breast Cancer Outcomes

GEN News Highlights   Feb 17, 2016   http://www.genengnews.com/gen-news-highlights/tumor-microenvironment-diversity-predicts-breast-cancer-outcomes/81252378/

 

Intratumor heterogeneity, it is known, can complicate cancer treatments. Now it appears the same may be true of tumor microenvironment heterogeneity. According to a new study from the Institute of Cancer Research (ICR), London, breast cancers that develop within an “ecologically diverse” breast cancer microenvironment are particularly likely to progress and lead to death.

The study took an unusual approach: It combined ecological scoring methods with genome-wide profiling data. This approach, besides showing clinical utility in the evaluation of breast cancer outcomes, demonstrated that even so contextual a discipline as genomics can benefit from being placed within a larger context. In this case, the context is essentially Darwinian, albeit at a small scale.

Natural selection is typically studied at the level of ecosystems consisting of animals and plants. In the current study, however, it was assessed at the level of the tumor microenvironment, which consists of cancer cells, immune system lymphocytes, and stromal cells.

The ICR scientists, led by Yinyin Yuan, Ph.D., presented their work February 16 in the journal PLoS Medicine, in an article entitled “Microenvironmental Heterogeneity Parallels Breast Cancer Progression: A Histology–Genomic Integration Analysis.” The article describes how the scientists developed a tumor ecosystem diversity index (EDI), a scoring system that indicates the degree of microenvironmental heterogeneity along three spatial dimensions in solid tumors. EDI scores take account of “fully automated histology image analysis coupled with statistical measures commonly used in ecology.”

“[EDI] was compared with disease-specific survival, key mutations, genome-wide copy number, and expression profiling data in a retrospective study of 510 breast cancer patients as a test set and 516 breast cancer patients as an independent validation set,” wrote the authors. “In high-grade (grade 3) breast cancers, we uncovered a striking link between high microenvironmental heterogeneity measured by EDI and a poor prognosis that cannot be explained by tumor size, genomics, or any other data types.”

By using the EDI, the ICR team was able to identify several particularly aggressive subgroups of breast cancer. In fact, the EDI was a stronger predictor of survival than many established markers for the disease.

The ICR researchers also looked at the EDI in addition to genetic factors. For example, the researchers found that the prognostic value of EDI was enhanced with the addition of TP53 mutation status. By integrating EDI data and genome-wide profiling data, the researchers identified losses of specific genes on 4p14 and 5q13 that were enriched in grade 3 tumors. These tumors, which showed high microenvironmental diversity, substratified patients into poor prognostic groups.

“Our findings show that mathematical models of ecological diversity can spot more aggressive cancers,” said Dr. Yuan. “By analyzing images of the environment around a tumor based on Darwinian natural selection principles, we can predict survival in some breast cancer types even more effectively than many of the measures used now in the clinic.

“In the future, we hope that by combining cell diversity scores with other factors that influence cancer survival, such as genetics and tumor size, we will be able to tell apart patients with more or less aggressive disease so we can identify those who might need different types of treatment.”

“This ingenious study…teaches us a valuable lesson,” added Paul Workman, Ph.D., chief executive of the ICR. “[We] should always remember that cancer cells are not developing and growing in isolation, but are part of a complex ecosystem that involves normal human cells, too. By better understanding these ecosystems, we aim to create new ways to diagnose, monitor and treat cancer.”

 

Microenvironmental Heterogeneity Parallels Breast Cancer Progression: A Histology–Genomic Integration Analysis

 

Background

The intra-tumor diversity of cancer cells is under intense investigation; however, little is known about the heterogeneity of the tumor microenvironment that is key to cancer progression and evolution. We aimed to assess the degree of microenvironmental heterogeneity in breast cancer and correlate this with genomic and clinical parameters.

Methods and Findings

We developed a quantitative measure of microenvironmental heterogeneity along three spatial dimensions (3-D) in solid tumors, termed the tumor ecosystem diversity index (EDI), using fully automated histology image analysis coupled with statistical measures commonly used in ecology. This measure was compared with disease-specific survival, key mutations, genome-wide copy number, and expression profiling data in a retrospective study of 510 breast cancer patients as a test set and 516 breast cancer patients as an independent validation set. In high-grade (grade 3) breast cancers, we uncovered a striking link between high microenvironmental heterogeneity measured by EDI and a poor prognosis that cannot be explained by tumor size, genomics, or any other data types. However, this association was not observed in low-grade (grade 1 and 2) breast cancers. The prognostic value of EDI was superior to known prognostic factors and was enhanced with the addition of TP53 mutation status (multivariate analysis test set, p = 9 × 10−4, hazard ratio = 1.47, 95% CI 1.17–1.84; validation set, p = 0.0011, hazard ratio = 1.78, 95% CI 1.26–2.52). Integration with genome-wide profiling data identified losses of specific genes on 4p14 and 5q13 that were enriched in grade 3 tumors with high microenvironmental diversity that also substratified patients into poor prognostic groups. Limitations of this study include the number of cell types included in the model, that EDI has prognostic value only in grade 3 tumors, and that our spatial heterogeneity measure was dependent on spatial scale and tumor size.

Conclusions

To our knowledge, this is the first study to couple unbiased measures of microenvironmental heterogeneity with genomic alterations to predict breast cancer clinical outcome. We propose a clinically relevant role of microenvironmental heterogeneity for advanced breast tumors, and highlight that ecological statistics can be translated into medical advances for identifying a new type of biomarker and, furthermore, for understanding the synergistic interplay of microenvironmental heterogeneity with genomic alterations in cancer cells.

Background

The human body contains millions of cells, all of which grow, divide, and die in an orderly fashion to build tissues during early life and to replace worn-out or dying cells and repair injuries during adult life. Sometimes, however, normal cells acquire genetic changes (mutations) that allow them to divide uncontrollably and to move around the body (metastasize), resulting in cancer. Because any cell in the body can acquire the mutations needed for cancer development, there are many types of cancer. For example, breast cancer, the most common cancer in women, begins when the cells in the breast that normally make milk become altered. Moreover, different types of cancer progress and evolve differently—some cancers grow quickly and kill their “host” soon after diagnosis, whereas others can be successfully treated with drugs, surgery, or radiotherapy. The behavior of individual cancers depends both on the characteristics of the cancer cells within the tumor and on the interactions between the cancer cells and the normal stromal cells (the connective tissue cells of organs) and other cells (for example, immune cells) that surround and feed cancer cells (the tumor microenvironment).

Why Was This Study Done?

Although recent studies have highlighted the importance of the tumor microenvironment for disease-related outcomes, little is known about how the heterogeneity of the tumor microenvironment—the diversity of non-cancer cells within the tumor—affects outcomes. Mathematical modeling suggests that tumors with heterogeneous and homogeneous microenvironments have different growth patterns and that heterogeneous microenvironments are more likely to be associated with aggressive cancers than homogenous microenvironments. However, the lack of methods to quantify the spatial variability and cellular composition across solid tumors has prevented confirmation of these predictions. Here, the researchers develop a computational system for quantifying microenvironmental heterogeneity in breast cancer based on tumor morphology (shape and form) in histological sections (tissue samples taken from tumors that are examined microscopically). They then use this system to analyze the associations between clinical outcomes, molecular changes, and microenvironmental heterogeneity in breast cancer.

What Did the Researchers Do and Find?

The researchers used automated image analysis and statistical analysis to develop the ecosystem diversity index (EDI), a numerical measure of microenvironmental heterogeneity in solid tumors. They compared the EDI with prognosis (likely outcome), key mutations, genome-wide copy number (tumor cells often contain abnormal numbers of copies of specific genes), and expression profiling data (the expression of several key proteins is altered in tumors) in a test set of 510 samples from patients with breast cancer and in a validation set of 516 additional samples. Among high-grade breast cancers (grade 3 cancers; the grade of a cancer indicates what the cells look like; high-grade breast cancers have a poor prognosis), but not among low-grade breast cancers (grades 1 and 2), a high EDI (high microenvironmental heterogeneity) was associated with a poor prognosis. Specifically, patients with grade 3 tumors and a high EDI had a ten-year disease-specific survival rate of 51%, whereas the remaining patients with grade 3 tumors had a ten-year survival rate of 70%. Notably, the combination of a high EDI with specific DNA alterations—mutations in a gene called TP53 and loss of genes on Chromosomes 4p14 and 5q13—improved the accuracy of prognosis among patients with grade 3 breast cancer and stratified them into subgroups with disease-specific five-year survival rates of 35%, 9%, and 32%, respectively.

What Do These Findings Mean?

These findings establish a method for measuring the spatial heterogeneity of the microenvironment of solid tumors and suggest that the measurement of tumor microenvironmental heterogeneity can be coupled with information about genomic alterations to provide an accurate way to predict outcomes among patients with high-grade breast cancer. The association between EDI, specific genomic alterations, and outcomes needs to be confirmed in additional patients. However, these findings suggest that microenvironmental heterogeneity might provide an additional biomarker to help clinicians identify those patients with advanced breast cancer who have a particularly bad prognosis. The ability to identify these patients is important because it will help clinicians target aggressive treatments to individuals with a poor prognosis and avoid the overtreatment of patients whose prognosis is more favorable. Finally, and more generally, these findings describe a new way to investigate the interactions between the tumor microenvironment and genomic alterations in cancer cells.

Additional Information

This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at http://dx.doi.org/10.1371/journal.pmed.1001961.

Citation: Natrajan R, Sailem H, Mardakheh FK, Arias Garcia M, Tape CJ, Dowsett M, et al. (2016) Microenvironmental Heterogeneity Parallels Breast Cancer Progression: A Histology–Genomic Integration Analysis.
PLoS Med 13(2): e1001961.     http://dx.doi.org:/10.1371/journal.pmed.1001961
Fig 1. In silico tumor dissection pipeline for quantifying spatial diversity in the tumor ecosystem.
Fig 1. In silico tumor dissection pipeline for quantifying spatial diversity in the tumor ecosystem. (A) Flow diagram depicting the overall study design. (B) Schematic of our pipeline for quantifying spatial diversity in pathological samples. H&E sections are morphologically classified and divided into regions to be spatially scored. The number of clusters k in the regional scores is indicative of the number of sub-populations of cell types in the tumor regions. (C) Examples of tumor regions with low and high diversity scores using the Shannon diversity index, accounting for cancer cells (outlined in green), lymphocytes (blue), and stromal cells (red). Cell classification is automated by image analysis. (D) The 3-D landscape of cell diversity scores on an example H&E section; the x- and y-axes are the geometric axes of the image, and the z-axis is cell diversity computed on a region-by-region basis. (E) The distribution of regional scores in a tumor from the METABRIC study with two regional clusters identified using Gaussian mixture clustering (grey shading: histogram; dashed black line: density; solid black lines: mixture components/clusters).
Fig 2. Application of EDI to 1,026 breast tumors from the METABRIC study.
Fig 2. Application of EDI to 1,026 breast tumors from the METABRIC study. (A) The frequencies of EDI scores in breast tumors. (B) H&E staining, distribution of classified cells (green: cancer; blue: lymphocyte; red: stromal cells), and the heatmap of regional diversity scores for a tumor with the highest EDI score (EDI = 5). (C) Representative regions from each of the clusters k1–k5 are shown in a tumor with EDI = 5, with cluster k1 having the lowest diversity score and k5 the highest. By mapping regional clusters to the H&E image, we can begin to interpret these clusters with different cell diversity. We observed predominantly cancer cells in k1, increasingly more stromal cells and ductal in situ carcinoma cells (DCIS) in k2, and a vessel in k3. Cluster k4 features extensive stromal lymphocytes between ductal in situ carcinoma components, while k5 shows tumor-infiltrating lymphocytes (TIL) associated with invasive carcinoma cells.
Fig 3. Reproducibility, stability, and independence of the EDI-high group in 507 grade 3 breast tumors.
Fig 3. Reproducibility, stability, and independence of the EDI-high group in 507 grade 3 breast tumors. (A) Kaplan–Meier curves of disease-specific survival to illustrate the prognosis of EDI-high samples compared to other grade 3 samples in two independent patient cohorts. Shown below the graph are the number of patients (the number of disease-specific events) per group for EDI-low (grey) and EDI-high (red). (B) Agreement of the EDI subtyping between 100% data and resampling with progressively fewer tumor regions in 200 repeats. (C) Distribution of known subtypes in grade 3 tumors stratified by EDI; asterisks mark subtypes enriched in the EDI-high group. (D) Kaplan–Meier curves illustrating the duration of disease-specific survival according to tumor size (left) and improvement of stratification with the addition of EDI information (right).
Accumulating evidence suggests that the interactions of cancer cells and stromal cells within their microenvironment govern disease progression, metastasis, and, ultimately, the evolution of therapeutic resistance [1–3]. Recent reports have highlighted the significance of the contribution of stromal gene expression and morphological structure as powerful prognostic determinants for a number of tumor types, emphasizing the importance of the tumor microenvironment in disease-related outcomes [4–7]. In breast cancer, a number of studies have demonstrated the prognostic correlation of individual cell types, including the immune cell infiltrate that predicts response to therapy [8–10], and the high percentage of tumor stroma that predicts poor prognosis in triple-negative disease but good prognosis in estrogen receptor (ER)–positive disease [11,12]. Nevertheless, different types of cells coexist with varying degrees of heterogeneity within a tumor. This fundamental feature of human tumors and the combinatorial effects of cell types have been largely ignored, and the collective implications for clinical outcome remain elusive. Consistent observations from mathematical models have highlighted that tumors with diverse microenvironments show growth patterns dramatically different from those of tumors with homogeneous environments [13] and are more likely to be associated with aggressive cancer phenotypes [2] that select for cell migration and eventual metastasis by allowing cancer cells to evolve more rapidly [14]. These observations highlight the need to understand the collective physiological characteristics and heterogeneity of tumor microenvironments. However, there is a lack of methods to quantify the high spatial variability and diverse cellular composition across different solid tumors. Moreover, the interplay of genomic alterations in cancer cells and microenvironmental heterogeneity and its subsequent role in treatment response have not been explored. Our aims were (i) to develop a computational system for quantifying microenvironmental heterogeneity based on tumor morphology in routine histological sections, (ii) to define the clinical implications of microenvironmental heterogeneity, and (iii) to integrate this histologybased index with RNA gene expression and DNA copy number profiling data to identify molecular changes associated with microenvironmental heterogeneity.
The Ecosystem Diversity Index To characterize the tumor ecosystem based on cell compositions, we developed a new index to be used in conjunction with our image analysis tool [16]. First, we used our automated morphological classification method [16] to identify and classify cells into cancer, lymphocyte, or stromal cell classes in H&E sections (Fig 1B). We next divided sections into smaller spatial regions and quantified the diversity of the tumor ecosystem in a tumor region j using the Shannon diversity index: dj ¼ Sm i pi logpi ; ð1Þ where m is the number of cell types and pi is the proportion of the ith cell type (Fig 1B and 1C). A high value of the Shannon diversity index dj reports a heterogeneous environment populated by many cell types, whilst a low value indicates a homogeneous environment (Fig 1C). Compared to other methods such as the Simpson index, the Shannon diversity index accounts for rare species and, hence, is less dominated by main species [17]. Subsequently, we derived the ecosystem diversity index (EDI) by applying unsupervised clustering that identifies the optimum number of clusters in the dataset in an unbiased manner, in order to group tumor regions and quantify the degree of spatial heterogeneity. Let D = d1,d2,…,dn be the Shannon index for n regions in a tumor. We used Gaussian mixture models to fit data D: D SK k¼1okNðmk; s2 kÞ: ð2Þ where μk, ,s2 k, and ωk are the mean, variance, and weight of a Gaussian distribution k, and K is the number of clusters. The Bayesian information criterion was then used to select the best number of clusters K [18]. We used K = 1–5 as the range of K to avoid small EDI groups (S1 Text). The final value of K thus is a measurement of heterogeneity and the score of EDI for a tumor.
Fig 5. The relationship between ecological heterogeneity and cancer genomic aberrations in 507 grade 3 tumors. (A) Genome-wide copy number aberrations in grade 3 breast tumors and genomic coordinates of genes with copy number aberrations enriched in the EDI-high group. Lengths of black lines denote level of enrichment significance with copy number gains (above the horizontal line) or losses (below the horizontal line). (B) Kaplan–Meier curves illustrating the duration of disease-specific survival in grade 3 breast cancer patients according to copy number loss of the 4p14 region (left) and the EDI-high group with additional information of 4p14 copy number loss (right). (C) Kaplan–Meier curves illustrating the duration of disease-specific survival according to copy number loss of the 5q13 region (left) and the EDI-high group with additional information of 5q13 copy number loss (right).
This study has a number of limitations. The motivation for our computational development was to use a data-driven model and measure the degree of spatial heterogeneity in tumor pathological specimens. In this model, only three major cell types in breast tumors were considered. Further sub-classification of the different types of stromal and immune cells by immunohistochemistry may add additional discriminatory value to our model. For dissecting spatial heterogeneity, we chose to use square regions with equal sizes. We found that EDI was correlated with the size of the region chosen for calculation of the Shannon diversity index, and as such the spatial heterogeneity is scale dependent. This phenomenon has been well described in a number of studies in ecology that show that a scale needs to be chosen that is appropriate for the ecological process under study [38,39], further highlighting the analogy between tumor studies and ecology. Similar to the recent observation that breast cancer subclonal heterogeneity is correlated with tumor size [35], we also found an association between microenvironmental heterogeneity and tumor size; hence, EDI may have more limited value in smaller tumors. However, small tumors were present in the EDI-high group, and addition of EDI within tumors grouped by size further stratified their prognosis. We found that EDI was prognostic only in grade 3 tumors in our study, which could be a limitation, given the possible discordance in grading between pathologists.
The identification of additional biomarkers in subgroups of patients that identify them as high risk is important for patient management and to avoid overtreatment for low-risk patients. We envision that the use of our measure of microenvironment heterogeneity, together with key genomic alterations, will enable the diagnosis of patients at very high risk of relapse and facilitate the enrollment of these patients into additional clinical trials for novel therapies or treatment intensification. Our novel computational approach provides a fully automated tool that is relatively easy to implement. Integration of this measure with genomic profiling provides additional prognostic information independent of known clinical parameters. The results of this study highlight the possibility of a grade-3-specific prognostic tool that may aid in further classification of high-grade breast cancer patients beyond standard assays such as ER and HER2 status.

 

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RNA Modification

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

New RNA Modification Added to Epitranscriptomic Library   

GEN News Highlights  Feb 17, 2016    http://www.genengnews.com/gen-news-highlights/new-rna-modification-added-to-epitranscriptomic-library/81252376/

 

http://www.genengnews.com/Media/images/GENHighlight/109124_web3461772372.jpg

 

In 1956, Francis Crick—co-discoverer of DNA’s helical structure—postulated what is now considered to be a central doctrine of the biological sciences stating that “The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid.” What Crick was suggesting was that DNA makes RNA and, in turn, RNA makes protein.

In the time since the initial proposal of the central dogma, scientists have come to understand that there are not only instances of reverse information flow from RNA to DNA, but chemical alterations to RNA structures that can have a profound effect on gene regulation. The discovery of these alterations has added a critical dimension to how scientists view the genetic code and recently spawned an entirely new field of study within molecular biology: the epitranscriptome.

Now, a recent study by scientists at the University of Chicago and Tel Aviv University has revealed evidence that provides a promising new lever in the control of gene expression. The researchers describe a small chemical modification to RNA that can significantly boost the conversion of genes to proteins.

The findings from this study were published recently in Nature through an article entitled “The dynamic N1-methyladenosine methylome in eukaryotic messenger RNA.”

“Epigenetics, the regulation of gene expression beyond the primary information encoded by DNA, was thought until recently to be mediated by modifications of proteins and DNA,” explained co-senior study author Gidi Rechavi, Ph.D., chair in oncology at Tel Aviv University’s Sackler Faculty of Medicine and head of the Cancer Research Center at Sheba Medical Center. “The new findings bring RNA to a central position in epigenetics.”

“This discovery further opens the window on a whole new world of biology for us to explore,” added co-senior study author Chuan He, Ph.D., professor in the department of chemistry and investigator within the Howard Hughes Medical Institute at the University of Chicago. “These modifications have a major impact on almost every biological process.”

Previously, Dr. He’s laboratory discovered the first RNA demethylase that reverses the most prevalent mRNA methylation N6-methyladenosine (m6A), implying that the addition and removal of the methyl group could dramatically affect these messengers and the outcome of gene expression—as also seen for DNA and histones—which subsequent research found to be true.

In the current study, the investigators described a second functional mRNA methylation, N1-methyladenosine (m1A). Like m6A, the small modification is evolutionarily conserved and common, present in humans, rodents, and yeast. However, its location and effect on gene expression reflect a new form of epitranscriptome control.

“The discovery of m1A is extremely important, not only because of its own potential in affecting biological processes but also because it validates the hypothesis that there is not just one functional modification,” Dr. He stated. “There could be multiple modifications at different sites where each may carry a distinct message to control the fate and function of mRNA.”

From their findings, the research team estimates that that m1A may be present on transcripts of more than one out of three expressed human genes—suggesting that m1A, like m6A, may be a mechanism by which cells rapidly boost the expression of hundreds or thousands of specific genes.

“mRNA is the perfect place to regulate gene expression because they can code information from transcription and directly impact translation—you can add a consensus sequence to a group of genes and use a modification of the sequence to readily control several hundred transcripts simultaneously,” Dr. He said. “If you want to rapidly change the expression of several hundred or a thousand genes, this offers the best way.”

The scientists were excited by their findings and have plans for future studies that will examine the role of m1A methylation in human development, for diseases such as diabetes and cancer, and its potential as a target for therapeutic uses.

“This study represents a breakthrough discovery in the exciting, nascent field of the ‘epitranscriptome,’ which is how RNAs are regulated, akin to the genome and the epigenome,” commented Christopher Mason, Ph.D., associate professor at Weill Cornell Medicine, who was not affiliated with the study. “What is important about this work is that m6A was recently found to enrich at the ends of genes, and now we know that m1A is what is helping regulate the beginning of genes, and this opens up many questions about revealing the ‘epitranscriptome code’ just like the histone code or the genetic code.”

 

The dynamic N1-methyladenosine methylome in eukaryotic messenger RNA

Dan DominissiniSigrid NachtergaeleSharon Moshitch-MoshkovitzNitzan Kol, et al.
Nature(2016 10 Feb )      http://dx.doi.org:/10.1038/nature16998      http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16998.html

Gene expression can be regulated post-transcriptionally through dynamic and reversible RNA modifications. A recent noteworthy example is N6-methyladenosine (m6A), which affects messenger RNA (mRNA) localization, stability, translation and splicing. Here we report on a new mRNA modification, N1-methyladenosine (m1A), that occurs on thousands of different gene transcripts in eukaryotic cells, from yeast to mammals, at an estimated average transcript stoichiometry of 20% in humans. Employing newly developed sequencing approaches, we show that m1A is enriched around the start codon upstream of the first splice site: it preferentially decorates more structured regions around canonical and alternative translation initiation sites, is dynamic in response to physiological conditions, and correlates positively with protein production. These unique features are highly conserved in mouse and human cells, strongly indicating a functional role for m1A in promoting translation of methylated mRNA.

 

Figure 1: Development of m1A-seq to map a newly identified constituent of mammalian mRNA.

Development of m1A-seq to map a newly identified constituent of mammalian mRNA.

http://www.nature.com/nature/journal/vaop/ncurrent/carousel/nature16998-f1.jpg

a, Chemical structures of m1A and m6A. Methyl groups (-CH3) are in red and the positive charge (+) on m1A is in blue. b, LC-MS/MS quantitation of m1A, m6A and Ψ in human and mouse mRNA isolated from the indicated cell types. …

 

Figure 3: m1A occurs in GC-rich sequence contexts and in genes with structured 5′ UTRs.

m1A occurs in GC-rich sequence contexts and in genes with structured 5′ UTRs.

http://www.nature.com/nature/journal/vaop/ncurrent/carousel/nature16998-f3.jpg

a, Sequence frequency logo for a set of 192 adenosines in peak areas that have a higher mismatch rate in immunoprecipitation relative to input (FC ≥ 6) in HepG2 demonstrates the GC-rich context of m1A. b, Length-adjusted minimum free energy…

 

Figure 5: m1A in mRNA is a dynamic modification that responds to changing physiological and stress conditions, and varies between tissues.

m1A in mRNA is a dynamic modification that responds to changing physiological and stress conditions, and varies between tissues.

http://www.nature.com/nature/journal/vaop/ncurrent/carousel/nature16998-f5.jpg

a, LC-MS/MS quantification of m1A (left, grey) and m6A (right, black) in mRNA of untreated and glucose-starved (upper panels) or heat shock-treated (lower panels) HepG2 cells, presented as percentage of unmodified A. Mean values ± s.e.m…

 

RNA modification discovery suggests new code for control of gene expression

A new cellular signal discovered by a team of scientists at the University of Chicago and Tel Aviv University provides a promising new lever in the control of gene expression.    Gene expression study

The study, published online Feb. 10 in the journal Nature, describes a small chemical modification that can significantly boost the conversion of genes to proteins. Together with other recent findings, the discovery enriches a critical new dimension to the “Central Dogma” of molecular biology: the epitranscriptome.

“This discovery further opens the window on a whole new world of biology for us to explore,” said Chuan He, the John T. Wilson Distinguished Service Professor in Chemistry, Howard Hughes Medical Institute investigator and senior author of the study. “These modifications have a major impact on almost every biological process.”

The central dogma of molecular biology describes the cellular pathway where genetic information from DNA is copied into temporary RNA “transcripts,” which provide the recipe for the production of proteins. Since Francis Crick first postulated the theory in 1956, scientists have discovered a multitude of modifications to DNA and proteins that regulate this process.

Only recently, however, have scientists focused on investigating dynamic modifications that specifically target the RNA step. In 2011, He’s group discovered the first RNA demethylase that reverses the most prevalent mRNA methylation N6-methyladenosine, or m6A, implying that the addition and removal of the methyl group could dramatically affect these messengers and impact the outcome of gene expression, as also seen for DNA and histones. Subsequently, scientists discovered that the dynamic and reversible methylation of m6A dramatically controlled the metabolism and function of most cellular messenger RNA, and thus, the production of proteins.

In the new Nature study, researchers from UChicago and Tel Aviv University describe a second functional mRNA methylation, N1-methyladenosine, or m1A. Like m6A, the small modification is evolutionarily conserved and common, and present in humans, rodents and yeast, the authors found. But its location and effect on gene expression reflect a new form of epitranscriptome control and suggest an even larger cellular “control panel.”

“The discovery of m1A is extremely important, not only because of its own potential in affecting biological processes, but also because it validates the hypothesis that there is not just one functional modification,” He said. “There could be multiple modifications at different sites where each may carry a distinct message to control the fate and function of mRNA.”

The researchers estimated that m1A was present on transcripts of more than one out of three expressed human genes. Methylated genes exhibited enhanced translation compared to unmethlyated genes, producing protein levels nearly twice as high in all cell types. This increase suggests that m1A, like m6A, may be a mechanism by which cells rapidly boost the expression of hundreds or thousands of specific genes, perhaps during important processes such as cell division, differentiation or under stress.

“mRNA is the perfect place to regulate gene expression, because they can code information from transcription and directly impact translation; you can add a consensus sequence to a group of genes and use a modification of the sequence to readily control several hundred transcripts simultaneously,” He said. “If you want to rapidly change the expression of several hundred or a thousand genes, this offers the best way.”

However, despite their complementary effects, m1A and m6A exert their influence on mRNA through different pathways. While studies have found that m6A localizes predominantly to the tail of messenger RNA molecules, increasing their translation and turnover rate, m1A was found largely near the start codon of mRNA transcripts, where protein translation begins. The different mechanisms could allow for finer tuning of post-transcriptional gene expression, or the selective activation of particular genes in different physiological situations.

“This study represents a breakthrough discovery in the exciting, nascent field of the ‘epitranscriptome,’ which is how RNAs are regulated, akin to the genome and the epigenome,” said Christopher Mason, associate professor at Weill Cornell Medicine, who was not affiliated with the study. “What is important about this work is that m6A was recently found to enrich at the ends of genes, and now we know that m1A is what is helping regulate the beginning of genes, and this opens up many questions about revealing the ‘epitranscriptome code’ just like the histone code or the genetic code.”

Future studies will examine the role of m1A methylation in human development, diseases such as diabetes and cancer, and its potential as a target for therapeutic uses.


Citation: “The dynamic N1-methyladenosine methylome in eukaryotic messenger RNA,” Nature, Feb. 10, 2016, by Chuan He, Dan Dominissini, Sigrid Nachtergaele, Qing Dai, Dali Han, Wesley Clark, Guanqun Zheng, Tao Pan and Louis Dore from the University of Chicago, and Sharon Moshitch-Moshkovitz, Eyal Peer, Nitkan Kol, Moshe Shay Ben-Haim, Ayelet Di Segni, Mali Salmon-Divon, Oz Solomon, Eran Eyal, Vera Hershkovitz, Ninette Amariglio and Gideon Rechavi from Tel Aviv University. DOI: 10.1038/nature16998

Funding: National Institutes of Health, Howard Hughes Medical Institute, Flight Attendant Medical Research Institute, Israel Science Foundation, Israeli Centers of Excellence Program, Ernest and Bonnie Beutler Research Program, Chicago Biomedical Consortium, Damon Runyon Cancer Research Foundation and Kahn Family Foundation.

– See more at: http://news.uchicago.edu/article/2016/02/16/rna-modification-discovery-suggests-new-code-control-gene-expression#sthash.HX6wUgKW.dpuf

RNA modifications and epitranscriptomics conference   
University of Chicago, Chicago, Illinois, US   September 8-9, 2016
The meeting is aimed at bringing in students and postdocs as well as faculty involved in RNA modification and epitranscriptome research.  In addition to talks, there will be a poster session and reception.

Topics

  • M6A mRNA methylation
  • Biological functions of m6A RNA methylation
  • Dynamic RNA modifications

Registration will open on March 1, 2016

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Methylation and cancer epigenomics

Larry H. Bernstein, MD, FCAP, Curator

LPBI

UPDATED 12/12/2022

2015 DNA methylation research grant winners

https://www.diagenode.com/landingPages/display/dna-methylation-grant-applications

 

Persistency of Transgene Expression Mediated by Lentiviral Gene Delivery in Pluripotent Cell Lines

Suleiman Alhaji
Ph.D. Student, University Putra, Malaysia

My general objectives are to (1) determine the duration of reporter gene expression from pluripotent cell lines transduced by lentivirus and (2) to assess the epigenetic effects on the provirus. More specifically, I plan to (1) produce LV carrying Green Fluorescent Protein (GFP) reporter gene, (2) obtain and maintain the required cell lines including establishing primary mouse fibroblast as a control, 3) measure the duration of GFP expression from pluripotent and control cell lines transduced with the lentivirus, (4) exclude the loss of the integrated provirus as the factor for GFP silencing in transduced non-pluripotent cell lines, and (5) study the effects of epigenetics on the GFP gene and the regulatory sequence of the provirus.

Transgene integration by lentiviral (LV) vector in the host cell’s genome would theoretically generate a prolonged or permanent transgene expression. However, several citations have reported a decline in transgene expression in early progenitor cells and stem cells transduced by LV. We hypothesized that prolonged transgene expression can be achieved if the transgene is introduced into the cells before epigenetic markers are established in the genome, i.e during the pluripotency period. Therefore, the proposed study seeks to determine if this phenomenon would occur in pluripotent cell lines, focusing on mouse induced pluripotent stem (iPS) cells as the target cell, in a gene therapy context.

Two epigenetic analyses that will be performed on the promoter and transgene of the provirus are DNA methylation and chromatin modification. For DNA methylation profiling, the genomic DNA of the cell will be treated with bisulfite prior to PCR and sequencing of the proviral DNA. The cells may also be analyzed for 5-hmC using 5-hmC monoclonal antibody (C15200200-200) or hMeDIP Kit (C02010031) to assess the level of hydroxymethylation. We may also consider using Diagenode’s MethylCap kit (C02020010) to fractionate the methylated DNA by CpG density.

For the chromatin modification analysis, the cells will be treated with trichostatin A (TSA) before chromatin immunoprecipitation (ChIP) analysis by chromatin IP – bisulfite – sequencing (ChIP-Bis-Seq) and as well Combining chromatin IP and DNA methylation profiles in one assay using the Premium Bisulfite kit, Diagenode. We may also perform pull-down methylated DNA analysis by using specific antibodies such as (1) H3K4 monoclonal antibody (C1541065) (2) H3K4 polyclonal antibody (C15410037) (3) H3K9 polyclonal antibody (C15410004). Beads only will be used as a control.

 

Epigenome-wide methylation pattern discovery for irradiated skin in radiotherapy

Maxwell Johnson, Ph.D.
Research Fellow, University of Southern California, Department of Plastic and Reconstructive Surgery

Radiotherapy is utilized in neoadjuvant, definitive, and palliative treatment of a wide variety of cancers. From a reconstructive perspective, however, irradiated fields pose significant challenges as the tissue is often stiff, brittle, and heals poorly. Little is known about the mechanism by which irradiation produces these changes. The objective of our research is to reveal the epigenetic changes that occur in irradiated skin in order to identify potential targets for therapy. We aim to translate our findings into interventional studies in both cell culture and a mouse model to assess their efficacy in vitro and in vivo.

We have access to a bank of paired samples of irradiated and non-irradiated tissues from patients who have undergone reconstructive procedures after cancer treatment. We have used the Illumina Infinium Human Methylation450 BeadChip array to assess epigenome-wide methylation status of eight paired samples, and have identified a signature methylation pattern for irradiated skin. We would like to utilize the Diagenode Premium WGBS Kit for bisulfite sequencing of additional paired samples for two purposes. First, we would like to confirm the findings of our BeadChip array utilizing a more robust method of assessing epigenome-wide methylation status. Second, we would like to assess methylation status at loci that are not evaluated by the BeadChip array. Using this information, we plan to identify loci with the greatest change in methylation status between irradiated and non-irradiated samples. By comparing these loci to literature, we intend to identify genes that are known to have an effect on wound healing. We then plan to design interventional studies to assess the effects of modulating the expression of these genes and/or supplementing gene products in cell culture and a mouse model. We would like to utilize the Diagenode Bisulfite Kit to confirm methylation status at target genes in these additional studies.

 

Next-generation sequencing based methylome study of primary breast tumours

Rajbir Batra, Ph.D. Researcher
Cancer Research UK Cambridge Institute, University of Cambridge

Breast cancer is one of the leading causes of cancer death in women, and is unanimously considered a heterogeneous disease displaying distinct therapeutic responses and outcomes. While recent advances have led to the refinement of the molecular classification of the disease, the epigenetic landscape has received less attention.

We are delighted to win the DNA methylation research grant award and intend to use it to conduct a next-generation sequencing based methylome study of primary breast tumours. DNA methylation markers will also be investigated in Patient Derived Tumour Xenografts (PDTXs) and in circulating tumour DNA (ctDNA) to identify potential prognostic and predictive methylation biomarkers in breast cancer.

 

 2015 Feb 1; 29(3): 238–249.
PMCID: PMC4318141
PMID: 25644600

Chromatin signatures of cancer

Abstract

Changes in the pattern of gene expression play an important role in allowing cancer cells to acquire their hallmark characteristics, while genomic instability enables cells to acquire genetic alterations that promote oncogenesis. Chromatin plays central roles in both transcriptional regulation and the maintenance of genomic stability. Studies by cancer genome consortiums have identified frequent mutations in genes encoding chromatin regulatory factors and histone proteins in human cancer, implicating them as major mediators in the pathogenesis of both hematological malignancies and solid tumors. Here, we review recent advances in our understanding of the role of chromatin in cancer, focusing on transcriptional regulatory complexes, enhancer-associated factors, histone point mutations, and alterations in heterochromatin-interacting factors.

Keywords: cancer, chromatin, histone proteins

Fifteen years ago, in their paper “The Hallmarks of Cancer,”  laid out a conceptual framework for the properties of cancer cells. Cancer development is a complex process involving diverse tissue types of distinct developmental origins, cell–cell interactions, and a myriad of signaling pathways. Digesting decades worth of research,  extracted fundamental properties common to many cancer types. Some aspects of their six hallmarks of cancer (resisting apoptosis, self-sufficiency in growth signals, insensitivity to anti-growth signals, invasive metastasis, unlimited cellular proliferation, and sustained angiogenesis) can be viewed in the light of deregulated gene expression at the level of transcription. Indeed, many signal transduction pathways perturbed in cancer ultimately modulate the activity of transcriptional regulators (). Moreover, genomic instability is recognized as an enabling characteristic of cancer (). Thus, transcriptional control and structural maintenance of the genome at the level of chromatin are likely suspects in the hunt for culprits underlying cancer development.

The eukaryotic genome is packaged into a structure called chromatin that, at its most basic level, comprises the four core histones H2A, H2B, H3, and H4 wrapped inside ∼147 base pairs (bp) of DNA to form the nucleosome core particle (). Additionally, histone H1 functions as an internucleosome linker and is involved in the compaction of chromatin (). The N-terminal tails of the core histones protrude out from the nucleosome and are subject to a diverse array of post-translational modifications that alter chromatin structure and dynamics (). Large families of proteins containing domains such as bromodomain, chromodomain, plant homeodomain (PHD) finger, Tudor domains, PWWP domains, and YEATS domains bind these modifications to effect diverse downstream chromatin-based processes (). Considering the importance of chromatin in regulating eukaryotic gene expression and maintaining genome stability, it is perhaps not wholly unexpected that recent genome-wide sequencing studies have uncovered cancer-associated mutations in genes encoding chromatin regulatory factors and enzymes (Fig. 1).

An external file that holds a picture, illustration, etc.
Object name is 238fig1.jpg

Chromatin proteins mutated in cancer. A summary of cancer mutations that affect post-translational modifications of the histone H3 N-terminal tail. Protein classes are indicated by the fill color for the ovals ([red] methyltransferase; [green] demethylase; [orange] deacetylase; [blue] histone), whereas mutational status is indicated by the outline color ([gray] loss of function; [purple] overexpressed/hyperactive). Dashed lines indicate the residue of histone H3 that is expected to be modified due to the indicated cancer mutations.

The emerging picture of chromatin function in cancer is multifaceted and involves a complex interplay of chromatin-modifying enzymes. A recent review from  highlights the diverse mutations in genes involved in histone lysine methylation pathways associated with human cancer. In some instances, alterations in chromatin itself, such as histone H3.3 Lys27-to-methionine mutations in pediatric glioma, are highly context-specific to a single cancer type (). In other cases, mutations of related pathway component genes such as MLL3, MLL4, and UTX within the COMPASS (complex of proteins associated with Set1) family occur in a range of cancers, suggesting a broader tumor suppressor role (). As more cancer genomes are sequenced, perhaps one of the most stirring observations is co-occurrence as well as mutual exclusivity of mutations between related cancer types. These mutational signatures promise insight into not only cancer development but also the molecular signaling pathways underlying normal development. Paradoxically, whereas basic developmental biology research has supplied us with a rich understanding of the signal transduction pathways involved in cancer, the recent intense focus on cancer genomics may provide a better understanding of the interplay between cell signaling and chromatin during normal tissue development.

Mutations of Trithorax (Trx)/COMPASS and Polycomb-repressive complex 2 (PRC2) in cancer

The Trx and PCRC2 complexes were identified as factors controlling the developmentally regulated expression of the homeotic gene (Hox) clusters in Drosophila melanogaster (). Trx is essential for maintaining Hox gene activation, whereas PRC2 acts as a transcriptional repressor to prevent ectopic Hox expression. Genetically, these two complexes act in opposition to each other, suggesting that they converge on a common pathway (). Although the importance of Trx and PRC2 in developmental gene regulation has been established for some time (), the biochemical activity of these proteins remained elusive until ∼12 years ago. The first clues to the function of these complexes stemmed from the presence of a SET histone methyltransferase domain protein in both the Trx and PRC2 complexes. Studies in yeast revealed that Trx is a member of the COMPASS family of protein complexes that catalyzes methylation of histone H3 Lys4 (H3K4) (). Biochemical experiments and Drosophila genetics demonstrated that the Enhancer of Zeste [E(Z)] subunit of PRC2 is a histone methyltransferase specific for H3K27 (). Consistent with Trx’s and PRC2’s respective roles as activators and repressors of transcription, histone H3K4 trimethylation (H3K4me3) is associated with active promoters, whereas histone H3K27me3 is associated with transcriptional silencing ().

The first link between Trx function and cancer was made when it was observed that childhood mixed-lineage leukemias (MLLs) contain a translocation occurring at chromosome 11q23 involving the MLL1 gene, one of the two mammalian Trx homologs (). These translocations remove the C-terminal portion of MLL1, containing its catalytic SET histone methyltransferase domain, and create an in-frame fusion to generate gain-of-function chimeric proteins (). Recent work has elucidated the molecular mechanism underlying the oncogenic activity of these MLL1 fusions. A number of the most common MLL1 gene translocation partners, including AF4, AF9, ENL, and ELL, are components of the macromolecular complex called the super elongation complex (SEC) (). SEC associates with positive transcriptional elongation factor B (PTEF-b), a cyclin-dependent kinase (CDK) that promotes RNA polymerase II elongation by phosphorylating its C-terminal domain and other basal factors within the preinitiation complexes (). Thus, MLL1-SEC fusion proteins cause aberrant activation of MLL1 targets through misregulation of transcription elongation. MLL1 is required for normal hematopoietic stem cell function (), and MLL1 fusions likely result in altered stem cell properties that promote tumor formation.

Whereas MLL1 gene mutations involve a characteristic chromosomal translocation in a specific tumor type, PRC2 appears to a have a more complex role in cancer. Frequent point mutations of the EZH2 gene are observed in non-Hodgkin lymphoma (follicular and diffuse large B-cell lymphoma) (). These affect the EZH2 catalytic site and convert Tyr641 (Y641) to a variety of other amino acids, with asparagine being the most common substitution. In vitro, these mutants are unable to methylate an unmodified histone peptide (). However, subsequent studies revealed that these mutations are not inactive but rather possess an altered activity. Remarkably, EZH2 Y641 mutants show increased activity toward the di- and trimethylated states (). Thus, tumor cells with Y641 mutations in the EZH2 gene contain increased H3K27me3. This finding is intriguing because H3K27 monomethylation (H3K27me1), H3K27 dimethylation (H3K27me2), and H3K27me3 were recently shown to have distinct enrichment patterns across the genome, with H3K27me2 being implicated in the suppression of enhancer function (). In addition to Y641, the A677G EZH2 mutant exhibits a similar increase in H3K27me3 accompanied by a decrease in H3K27me2 (). In contrast, a recently characterized A687V mutant displayed both increased H3K27me3 and H3K27me2 (). Remarkably, a Drosophila mutation of E(Z) that mimics the Trx loss-of-function phenotype has also been shown to possess hyperactive methyltransferase activity (). The E(Z) Trx mimic mutation [E(z)(Trm)] converts Arg741 (Arg727 in human EZH2) to lysine (R741K), suggesting that this position may also be important for regulating PRC2 catalytic activity (). The activating nature of these mutations makes PRC2 an attractive target for therapeutic intervention. Recently, a small molecule inhibitor of EZH2, GSK126, was shown to specifically inhibit the growth of B-cell lymphomas containing activating EZH2 mutations, whereas tumor lines with wild-type EZH2 were largely unaffected ().

While EZH2 activating mutations are common in non-Hodgkin lymphoma, loss of PRC2 activity is associated with cancer development in other contexts. Inactivating mutations of the PRC2 components EZH2SUZ12, and EED are detected in T-cell acute lymphoblastic leukemia (T-ALL) (Fig. 2). Removal of the H3K27 methyl mark is catalyzed by the Jumonji domain containing demethylases UTX/KDM6A and JMJD3/KDM6B (). A recent study explored whether disruption of UTX and JMJD3 activity might provide a therapeutic benefit for T-ALL by increasing H3K27me3 levels (). Surprisingly, UTX and JMJD3 have strikingly distinct roles in T-ALL. UTX acts as a tumor suppressor, as mice with a NOTCH1-driven model of T-ALL succumb to disease more rapidly on a UTX mutant genetic background (). In contrast, JMJD3 is highly expressed in T-ALL versus normal T cells and is required for leukemogenesis, as mice with JMJD3 mutant T-ALL show improved survival rates. GSK-J4, an inhibitor of KDM6-type demethylases (), causes cell cycle arrest and apoptosis in T-ALL cells but not myeloid leukemia or normal hematopoietic progenitors (). Remarkably, GSK-J4 treatment results in gene expression changes that resemble knockdown of JMJD3 but are inversely correlated with the changes observed for UTX knockdown. Chromatin immunoprecipitation (ChIP) combined with sequencing (ChIP-seq) revealed a significant overlap between JMJD3 and NOTCH1 targets, including genes with known oncogenic function such as HEY1, NRARP, and HES1. Strikingly, these genes gain H3K27me3 and are repressed upon JMJD3 depletion or GSK-J4 treatment. It is unclear why GSK-J4 appears to inhibit JMJD3 but not UTX functional activity in T-ALL, but perhaps the molecule has a higher affinity for JMJD3 in vivo. Recent studies have also suggested that GSK-J4 may also target KDM5-type demethylases but with an affinity five to 10 times lower than JMJD3 and UTX (). Despite these caveats, GSK-J4 appears to be a promising drug for modulating chromatin modifications and perhaps a chemotherapeutic agent.

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Drugging the histone H3K27 methyl/acetyl switch in cancer. (A) Antagonism between H3K27 methylation and acetylation machinery. H3K27 methylation and acetylation are mutually exclusive, and the PRC2 and CBP/p300 complexes act in opposition to one another. In addition, deacetylation of H3K27ac by the HDAC1/2–NURD complex promotes PRC2-mediated repression, whereas demethylation of H3K27me3 by UTX within COMPASS or JMJD3 is required for acetylation to occur. (B) In NOTCH-driven T-ALL, the histone H3K27 demethylases UTX and JMJD3 have distinct functions. UTX acts as a tumor suppressor by activating genes such as FBXW7 that negatively regulate the NOTCH pathway. In contrast, JMJD3 exists in a complex with NOTCH and is responsible for activation of oncogenic NOTCH targets. Inhibition of JMJD3 with the small molecule GSK-J4 promotes PRC2-mediated H3K27me3 at NOTCH target genes, resulting in their silencing. (C) MPNSTs often carry mutations in the genes encoding the components of both the RAS pathway inhibitor NF1 and the PRC2 component SUZ12. In this cell type, PRC2 functions to suppress RAS target genes. Reduced H3K27 methylation by PRC2 results in increased H3K27ac, increased recruitment of BRD4, and amplification of the RAS transcriptional signature. Inhibition of BRD4 with JQ1 in combination with dampening of the RAS pathway with the MEK inhibitor PD-0325901 suppresses RAS targets, resulting in tumor regression.

Loss of PRC2 components EED and SUZ12 is often detected in combination with mutation of NF1 and CDKN2A genes in malignant peripheral nerve sheath tumors (MPNSTs) (Fig. 2). In addition to loss of H3K27me3, PRC2 mutant MPNSTs also display increased H3K27 acetylation (H3K27ac) levels, an effect observed for loss of PRC2 in multiple contexts (). Histone H3K27 methylation and acetylation are mutually exclusive modifications that correlate with gene silencing and activation, respectively. Strong evidence suggests that complexes responsible for implementing these modifications act in opposition to one another (). A recent study examined whether these increased acetylation levels in MPNSTs could serve as a therapeutic target. Bromodomain-containing protein 4 (BRD4) is a member of the bromodomain and extraterminal (BET) family of chromatin-associated proteins that bind to acetylated histone H3 and H4 via tandem bromodomains (). The small molecule JQ1 binds to the BRD4 bromodomains and evicts the protein from chromatin (). JQ1 has shown promise as a potential chemotherapeutic agent in a number of cancers in part due to regulation of the c-Myc oncogene by BRD4 (). BRD4 localizes to enhancers containing H3K27ac, and the effects of JQ1 may involve disruption of enhancer activity (). As PRC2 mutant MPNSTs display increased H3K27ac levels, BRD4 is an attractive target in this context. Indeed, loss of SUZ12 and NF1 (a negative regulator of the oncogenic RAS pathway) in MPNSTs renders them sensitive to treatment with JQ1 in combination with inhibition of the RAS pathway by the MEK inhibitor PD-0325901 (). Interestingly, the RAS pathway and PRC2 appear to synergize in MPNSTs, as SUZ12 loss promotes cell proliferation in NF1 mutant cells but not wild-type cells, and, moreover, SUZ12 loss enhances the RAS transcriptional signature (). MEK inhibition has been shown to inhibit PRC2 activity in embryonic stem cells, suggesting a potential negative feedback loop (). It will be important to determine the molecular details of the connection between RAS/MEK signaling and PRC2 activity and examine whether this link is conserved in multiple types of cancer.

PRC2 gene mutations in cancer highlight both the biochemical complexity of chromatin-modifying pathways and the rich potential for therapeutic intervention. In PRC2 loss-of-function cancer models, inhibition of BRD4, which binds to increased acetylated histones in PRC2 mutant cells, as well as inhibition of H3K27me3 demethylases show therapeutic effects. In contrast, drugs inhibiting EZH2 activity are more appropriate for non-Hodgkin lymphomas carrying hyperactive EZH2 mutations. Thus, the search for therapeutic targets should take into consideration cross-regulation between histone modification pathways (i.e., methylation and acetylation) as well as effectors of those pathways, such as bromodomain and chromodomain proteins that bind to modified histones. These studies also highlight the importance of determining the precise mutational status of individuals to determine what pathways should be targeted for treatment.

Misregulation of enhancer chromatin in cancer

Enhancers are noncoding DNA elements that play an essential role in transcriptional regulation by conferring tissue-specific gene expression patterns (). Although enhancers have been intensely studied for several decades, their precise mode of action is not fully understood. Enhancers can act across very long ranges of intervening DNA to activate a specific promoter (). Enhancer–promoter communication involves the formation of chromatin loops mediated by cohesin complexes and other trans-acting factors (). However, the mechanisms that restrict enhancer activity to a single promoter in the presence of multiple promoter choices are unclear.

Enhancers carry a unique chromatin structure characterized by the presence of 3K4me1 (). In addition, histone H3K27ac distinguishes active enhancers from poised enhancers (). Promoters typically contain H3K4me3 implemented by the Set1A/B and MLL1/2 COMPASS-like complexes, whereas MLL3/4 COMPASS catalyzes H3K4me1 at enhancers (). Acetylation of H3K27 is mediated by the acetyltransferases CREBBP (CBP) and EP300 (p300) (). Besides H3K4me1 methylase activity, MLL3/4 complexes also contain the H3K27 demethylase KDM6A (UTX), raising the possibility that removal of H3K27 methyl marks by the MLL3/4 complex facilitates acetylation by CBP and p300 ().

Recent genome-wide studies have identified mutations in genes for the regulators of enhancer chromatin in cancer (). Mutations of the H3K4 monomethylases MLL3 and MLL4 as well as their cofactor, UTX, within the COMPASS family have been identified in a range of malignancies, including the pediatric brain cancer medulloblastoma (), non-Hodgkin lymphoma (), and bladder cancer (). MLL4 is particularly frequently mutated in non-Hodgkin lymphomas and often co-occurs with mutations in the histone acetyltransferase gene CREBBP and activating mutations of EZH2 (). Mutations of EP300 and CREBBP have been found to co-occur with UTX in bladder cancer (). MEF2B, a transcription factor involved in recruiting CREBBP and EP300 to target sites in chromatin, is frequently mutated in non-Hodgkin lymphoma (). Intriguingly, the majority of these mutations result in single amino acid changes at one of four positions (K4, Y69, N81, and D83) (), and a subset of these mutations results in increased MEF2B transcriptional activation activity by loss of binding to the corepressor CABIN1 () Another enhancer-associated factor, LIM domain-binding protein 1 (LDB1), is mutated in medulloblastoma (). LDB1 is involved in the formation of chromatin loops in both Drosophila and mammalian cells and participates in enhancer–promoter communication ().

A large body of evidence implicates enhancer malfunction in cancer, and much remains to be learned about the molecular mechanisms of this process (). For instance, how does mutation in genes for factors such as EP300 and CREBBP that are thought to function globally at most enhancers play a role in cancer development? Inappropriate enhancer–promoter communication is known to play a role in the pathogenesis of some cancers. For instance, the classical chromosomal translocation found in Burkitt’s lymphoma places the c-Myc gene under the regulation of the immunoglobulin heavy chain enhancer, thus boosting its expression in B cells, resulting in lymphomagenesis. Recent studies of acute myeloid leukemia with a chromosomal translocation near the GATA2 and EVI1 genes revealed that this inversion allows a GATA2 enhancer to inappropriately activate EVI1 expression (). This raises the possibility that mutation in genes for enhancer-associated factors may lead to defective enhancer–promoter restriction, perhaps allowing for promiscuous activation of oncogenic gene products ().

Histone gene mutations in cancer

Mutations and translocations in genes encoding chromatin regulatory proteins such as the MLL family within COMPASS have been linked with oncogenesis for many years (); however, cancer-associated mutations of histone genes themselves were only recently identified. Genome sequencing studies of aggressive pediatric brainstem glioma uncovered point mutations in histone H3 (). These mutations convert Lys27 to methionine (H3K27M) or Gly34 to arginine or valine (H3G34R/V), occurring primarily in the replication-independent histone H3.3 (H3F3A) and, to lesser extent, the replication-dependent histone H3.1 (HIST1H3B) (). Strikingly, these mutations occur in only a single copy of the multiple histone H3 genes, suggesting that they have gain-of-function activity. Mutations of H3K27M and H3G34R/V define distinct subtypes of glioma, as they occur in distinct regions of the brain and display unique molecular characteristics ().

Histological examination of tumors harboring the H3K27M mutation revealed a dramatic reduction in the levels of H3K27me3 (). Further molecular studies revealed that H3K27M as well as other histone lysine-to-methionine mutants act as dominant inhibitors of histone lysine methylation pathways in tissue culture (). Histone H3K27M expression in Drosophila recapitulates the phenotype observed for depletion of the PRC2 component E(Z) and mirrors the phenotype of replacing all histone H3s with a H3K27R mutant (). In contrast, the H3K34R/V mutations do not dominantly inhibit bulk H3K27me3 or H3K36me3 in trans but do block methylation of H3K36 in cis ().

The precise mechanism of H3K27M action is still unclear. In vitro methyltransferase assays and immunoprecipitation followed by Western blotting suggest that H3K27M interacts strongly with EZH2 (). However, using an unbiased proteomic approach, we failed to detect increased enrichment of PRC2 subunits relative to wild-type H3.3 control (). In contrast, we found increased association of the bromodomain protein BRD4, which is consistent with increased histone acetylation levels observed in H3K27M mutant cells (). It is also intriguing that mutations in genes encoding for the PRC2 components do not appear to be prevalent in these pediatric gliomas.

Recent studies of chondroblastoma and giant cell tumors of bone revealed additional histone H3.3 gene mutations associated with distinct disease phenotypes (). Remarkably, 95% of chondroblastoma samples analyzed carried a mutation of the H3.3 gene at Lys36 to methionine (H3.3K36M) in the H3F3B gene, whereas 92% of giant cell tumors of bone harbored mutations of H3.3 Gly34 to tryptophan or leucine (). Similar to H3.3K27M, H3.3K36M can dominantly inhibit methylation of H3K36 ().

Histone gene mutations in cancer are not restricted to histone H3. Recent work in follicular lymphoma identified mutations in a number of histone H1 genes (). Whereas histone H2A, H2B, H3, and H4 constitute the nucleosome core, histone H1 acts as a linker histone and is involved in chromatin compaction. Like H3 gene mutations, H1 gene mutations are primarily single amino acid substitutions; however, instead of occurring at a few specific positions, the H1 gene mutations are scattered throughout the H1 globular domain (). Molecular analysis of one of these mutants, H1S102F, revealed that it has a reduced capacity to associate with chromatin () and binding to DNA methyltransferase 3B (DNMT3B) (). This suggests that histone H1 may lead to defective chromatin compaction and cause transcriptional misregulation or result in genomic instability. It will be important to examine the molecular function of histone H1 gene mutations in B-cell lymphoma in more detail.

Analysis of mutations that co-occur or are mutually exclusive to histone H3 gene mutations have been insightful. For instance, in pediatric glioblastoma, mutations of histone H3K27M, H3G34R/V, and isocitrate dehydrogenase 1 (IDH1) are mutually exclusive and occur in tumors with different molecular signatures, neuroanatomic locations, and prognostic outcome (). H3K27M mutants lose H3K27 methylation, whereas H3G34V/R mutants display DNA CpG hypomethylation, and IDH1 mutants have a CpG hypermethylation phenotype (). Mutations of the IDH1 gene are particularly prevalent in glioma but are also detected in leukemias (). IDH1 alterations occur in the substrate-binding site at position Arg132, and most mutations convert this residue to histidine (IDH1 R132H), although other substitutions have also been detected (). Under normal circumstances, IDH1 converts isocitrate to α-ketoglutarate and nicotinamide adenine dinucleotide phosphate (NADP+) to NADPH. However, the mutant IDH1 R132H enzyme generates the 2-hydroxyglutarate in place of α-ketoglutarate (). This metabolite inhibits α-ketoglutarate-dependent enzymes (including Jumonji-containing histone demethylases) as well as TET family methylcytosine dioxygenases thought to be involved in the process of DNA demethylation by converting 5-methylcytosine to 5-hydroxy-methylcytosine (). Thus, cells with the mutant IDH1 gene display CpG hypermethylation as well as increased histone lysine methylation. Interestingly, histone H3G34R/V gene mutations show an opposite effect on CpG methylation (). It is also notable that H3G34R/V gene mutations tend to co-occur with mutations of the histone H3.3 chaperone genes ATRX and DAXX, suggesting that altered histone incorporation into chromatin may play a role in these cancers ().

Recently, mutations in the gene for BMP receptor ACVR1/ALK2 were detected in pediatric glioma with H3K27M mutations (). These point mutations convert ACVR1 into a constitutively active form, and several cancer-associated mutations are identical to those found in the rare but devastating bone formation disorder fibrodysplasia ossificans progressiva (FOP) (). Interestingly, ACVR1 mutations tend to overlap with H3.1K27M mutations. Mutations of H3.3K27M are more prevalent than H3.1K27M in pediatric gliomas (), and these mutational types have distinct properties, as patients with H3.1K27M show an early disease onset with tumors located in the pons, whereas H3.3K27M tumors are located at multiple brain regions along the midline (). Determining the biological significance of these mutational signatures will be important to understanding pediatric glioma and may shed light onto other developmental disorders, such as FOP.

Maintenance of genome stability through heterochromatin

In eukaryotic cells, chromosomal structures such as pericentromeric regions and telomeres are associated with blocks of condensed heterochromatin (). Heterochromatin is characterized by histone hypoacetylation and methylation of histone H3 at Lys9, which serves as a binding substrate for the chromodomain protein heterochromatin protein-1 (HP-1) (Fig. 3). These features are essential for normal chromosome function and establish a transcriptionally repressed state (). Maintenance of heterochromatic silencing is dependent on both histone H3K9 methyltransferases and HP-1 proteins (Fig. 3). Moreover, heterochromatin is epigenetically stable through a self-reinforcing circuit by which HP-1 associates with the DNA replication machinery and recruits H3K9 histone methyltransferase complexes ().

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Maintenance of genome stability through the heterochromatin pathway. Centromeric heterochromain is essential for normal segregation of chromosomes during mitosis, and defects in this pathway result in aneuploidy. H3K9me3 and binding of HP-1 are hallmarks of heterochromatin. At pericentromeric heterochromatin, SETDB1 monomethylates H3K9, whereas Suv39 converts H3K9me1 to H3K8me2/3. Disruption of Suv39 function results in aneuploidy and lymphoma development in mice. Active deacetylation is also important for centromeric heterochromatin. Treatment of cells with the class I and II histone deacetylase inhibitor TSA results in abnormal mitosis. Similarly, Suv39 and SETDB1 are essential for telomeric heterochromatin. At telomeres, disruption of Suv39 results in loss of H3K9me2/3 and a depletion of HP-1 recruitment. However, Suv39 mutant telomeres contain increased H3K9me1 mediated by SETDB1 and exhibit abnormal telomere lengthening. Overexpression of SETDB1 has been reported in some cancers. Whereas centromeres depend on type I and II HDACs, the sirtuin deacetylase SIRT6 is essential at telomeres. Lack of SIRT6 in mice results in telomere fusions and premature senescence. In other contexts, SIRT6 functions as a tumor suppressor.

Heterochromatin plays an essential role in genomic stability at multiple levels. Mice doubly mutant for the H3K9 methyltransferases Suv39h1 and Suv39h2 lack H3K9 methylation at pericentric heterochromatin, exhibit aneuploidy and male germline meiosis defects, and develop B-cell lymphomas (). Mutations in the gene for the H3K9 methyl-binding protein HP1 also disrupt genomic stability through both aberrant centromere and telomere function. HP1 mutant flies display defective chromosome segregation as well as telomere fusions (). Interestingly, cells mutant for Suv39h1 and Suv39h2 exhibit abnormally elongated telomeres (). These mutant telomeres have reduced H3K9me2/3 and loss of HP-1 binding but display increased H3K9me1 (). This is consistent with the function of SETDB1 as a H3K9 monomethyltransferase, whereas Suv39h1/2 act as H3K9 di- and trimethylases (). Intriguingly, studies suggest that amplification of SETDB1 may play a role in development of human cancer as well as in a zebrafish model of melanoma (). It remains to be examined whether these oncogenic effects may be mediated through abnormal telomere lengthening.

Maintenance of histone hypoacetylation is also important for heterochromatin function. Treatment of cells with the class I and II histone deacetylase inhibitor trichostatin A (TSA) results in loss of HP1 binding to pericentric regions and relocalization of these domains to the nuclear periphery (). TSA also causes abnormal mitotic structures consistent with a defect in centromere function (). SIRT6, a histone deacetylase specific for histone H3K9, is essential for maintenance of telomeric heterochromatin (). SIRT6 mutant mice display genomic instability and exhibit a premature aging phenotype (). Human cells depleted for SIRT6 display telomere hyperacetylation, chromosome end-to-end fusions, and premature senescence that can be rescued by overexpression of telomerase (). While Sirt6-null mice exhibit premature aging and early death, they do not develop spontaneous tumors (). However, immortalized Sirt6-null mouse embryonic fibroblasts (MEFs) are able to form tumors in immunocompromised mice even in the absence of transformation with an activated oncogene (). Moreover, SIRT6 is frequently deleted in human cancer, and a conditional mutant mouse model revealed it to act as a tumor suppressor in an intestinal cancer model in vivo ().

Recent work has linked heterochromatin function to the regulation of DNA replication. Methylation of histone H3K9 and K36 have been linked to DNA replication in fission yeast (). The mammalian Jumonji domain protein KDM4A/JMJD2A is a histone lysine demethylase specific for methylated H3K9 and K36 (). Studies in Caenorhabditis elegans and mammalian cells revealed that KDM4A overexpression positively regulates S-phase progression, whereas depletion slowed DNA replication and induced cell death (). Moreover these effects were dependent on HP1 levels, implying that KDM4A influences cell cycle in part by removing H3K9me3 and evicting HP1. A follow-up study revealed that KDM4A is amplified in human cancers, and overexpression in tissue culture results in focal copy number gains during DNA replication (). However, these copy number gains are transient and become resolved during entry into G2/M through an as-yet-undetermined mechanism (). These copy gains are suppressed by increasing the cellular concentration of the H3K9 methyltransferase Suv39h1 or HP1-γ. Interestingly, expression of the mutant histones H3.3K9M or H3.3K36M, which inhibit bulk methylation of H3K9 and H3K36, respectively, also results in copy number gains. Recent work has shown that H3.3K9M disrupts heterochromatic transcriptional silencing in D. melanogaster (). Whereas the function of H3K9 methylation in heterochromatin is well established, studies by Whetstine and colleagues () implicate H3K36 methylation in a pathway involving heterochromatin machinery that controls mammalian DNA replication. In yeast, H3K36 methylation restricts nucleosome dynamics over transcribed regions and prevents “cryptic” transcription (). Perhaps a similar mechanism is involved in restricting access of DNA replication machinery.

Concluding remarks

The role of chromatin proteins in cancer is complex and highly context-specific. Relatively few chromatin modifiers seem capable of independently causing cancer development; they are typically mutated in combination with essential tumor suppressors and cell cycle regulators such as p53 and CDKN2A. Although some chromatin regulators, such as the MLL3/4-UTX of the COMPASS family, may play a broad tumor suppressor role in various cancers, many mutant chromatin proteins are highly tissue-specific. Moreover, in the case of PRC2, both hyperactivating and loss-of-function mutations are found in cancers of distinct origins. Whereas B-cell lymphomas tend to acquire hyperactivating mutations of the EZH2 gene in combination with loss of MLL4, other cancer types, such as T-ALL and MPNST, harbor inactivating mutations in genes encoding for PRC2 components EZH2, EED, and SUZ12. These differences likely reflect tissue-specific functions for PRC2. Thus, it is important to determine the precise molecular consequence of altered chromatin proteins, particularly in the case of point mutations that may cause either loss of function or gain of function. As the majority of cancer-associated mutations in chromatin protein-encoding genes have yet to be functionally characterized, biochemical analysis of these mutants may lead to exciting new avenues of research.

The rapid proliferation of next-generation genome sequencing promises to reveal not only novel mutations involved in cancer but also co-occurring and mutually exclusive mutations. These will likely connect developmental signaling pathways to their downstream chromatin effector proteins. In the instance of the NF1 mutant MPNST, PRC2 appears to dampen the RAS signaling pathway. Similarly, in T-ALL, PRC2 antagonizes the NOTCH1 signal transduction pathway, whereas the H3K27 demethylase JMJD3 directly associates with NOTCH1 to remove PRC2-deposited H3K27me3. Interestingly, recent studies have identified activating mutations in the gene for the BMP receptor ACVR1/ALK2 in combination with histone H3.1K27M gene mutations, suggesting a potential connection between BMP–SMAD1/5/8 signaling and PRC2-mediated repression. Thus, future collaborative efforts between clinicians, geneticists, biochemists, and developmental biologists may shed light onto both the mechanisms underlying cancer development and the connection between cell signaling pathways and the chromatin signatures of cancer.

Acknowledgments

We are grateful to the members of the Shilatifard laboratory for conversation and discussion during the writing of this review. Studies in A.S.’s laboratory are supported by grants R01CA150265, R01GM069905, and R01CA89455 to A.S.

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