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New studies link cell cycle proteins to immunosurveillance of premalignant cells

Posted in Apoptosis, Biological Networks, Biological Networks, Gene Regulation and Evolution, Cancer - General, CANCER BIOLOGY & Innovations in Cancer Therapy, Cancer-Immune Interactions, Cell Biology, Signaling & Cell Circuits, Circulating Tumor Cells (CTC), Disease Biology, DNA repair, Efficacy of Anti-Tumor T Cells, Exosomes, Exosomes: Natural Carriers for siRNA Delivery, Immune Modulatory, Immuno-Oncology & Genomics, Immunology, KRAS Mutation, Modulating Macrophages in Cancer Immunotherapy, NK Cell-Based Cancer Immunotherapy, TP53 - Germline mutations, tagged CDKI, cell cycle, cell cycle arrest, cell cycle protein, cellular senescence, DNA repair or transcription factor genes, Immunology, immunosuppression, immunosurveillance, NF-kB, p21, p53, premalignant, transcriptional, transcriptional regulation, tumor suppressors on December 16, 2021| Leave a Comment »

New studies link cell cycle proteins to immunosurveillance of premalignant cells

Curator: Stephen J. Williams, Ph.D.

The following is from a Perspectives article in the journal Science by Virinder Reen and Jesus Gil called “Clearing Stressed Cells: Cell cycle arrest produces a p21-dependent secretome that initaites immunosurveillance of premalignant cells”. This is a synopsis of the Sturmlechener et al. research article in the same issue (2).

Complex organisms repair stress-induced damage to limit the replication of faulty cells that could drive cancer. When repair is not possible, tissue homeostasis is maintained by the activation of stress response programs such as apoptosis, which eliminates the cells, or senescence, which arrests them (1). Cellular senescence causes the arrest of damaged cells through the induction of cyclin-dependent kinase inhibitors (CDKIs) such as p16 and p21 (2). Senescent cells also produce a bioactive secretome (the senescence-associated secretory phenotype, SASP) that places cells under immunosurveillance, which is key to avoiding the detrimental inflammatory effects caused by lingering senescent cells on surrounding tissues. On page 577 of this issue, Sturmlechner et al. (3) report that induction of p21 not only contributes to the arrest of senescent cells, but is also an early signal that primes stressed cells for immunosurveillance.Senescence is a complex program that is tightly regulated at the epigenetic and transcriptional levels. For example, exit from the cell cycle is controlled by the induction of p16 and p21, which inhibit phosphorylation of the retinoblastoma protein (RB), a transcriptional regulator and tumor suppressor. Hypophosphorylated RB represses transcription of E2F target genes, which are necessary for cell cycle progression. Conversely, production of the SASP is regulated by a complex program that involves super-enhancer (SE) remodeling and activation of transcriptional regulators such as nuclear factor κB (NF-κB) or CCAAT enhancer binding protein–β (C/EBPβ) (4).

Senescence is a complex program that is tightly regulated at the epigenetic and transcriptional levels. For example, exit from the cell cycle is controlled by the induction of p16 and p21, which inhibit phosphorylation of the retinoblastoma protein (RB), a transcriptional regulator and tumor suppressor. Hypophosphorylated RB represses transcription of E2F target genes, which are necessary for cell cycle progression. Conversely, production of the SASP is regulated by a complex program that involves super-enhancer (SE) remodeling and activation of transcriptional regulators such as nuclear factor κB (NF-κB) or CCAAT enhancer binding protein–β (C/EBPβ) (4).

Sturmlechner et al. found that activation of p21 following stress rapidly halted cell cycle progression and triggered an internal biological timer (of ∼4 days in hepatocytes), allowing time to repair and resolve damage (see the figure). In parallel, C-X-C motif chemokine 14 (CXCL14), a component of the PASP, attracted macrophages to surround and closely surveil these damaged cells. Stressed cells that recovered and normalized p21 expression suspended PASP production and circumvented immunosurveillance. However, if the p21-induced stress was unmanageable, the repair timer expired, and the immune cells transitioned from surveillance to clearance mode. Adjacent macrophages mounted a cytotoxic T lymphocyte response that destroyed damaged cells. Notably, the overexpression of p21 alone was sufficient to orchestrate immune killing of stressed cells, without the need of a senescence phenotype. Overexpression of other CDKIs, such as p16 and p27, did not trigger immunosurveillance, likely because they do not induce CXCL14 expression.In the context of cancer, senescent cell clearance was first observed following reactivation of the tumor suppressor p53 in liver cancer cells. Restoring p53 signaling induced senescence and triggered the elimination of senescent cells by the innate immune system, prompting tumor regression (5). Subsequent work has revealed that the SASP alerts the immune system to target preneoplastic senescent cells. Hepatocytes expressing the oncogenic mutant NRAS^G12V (Gly¹²→Val) become senescent and secrete chemokines and cytokines that trigger CD4⁺ T cell–mediated clearance (6). Despite the relevance for tumor suppression, relatively little is known about how immunosurveillance of oncogene-induced senescent cells is initiated and controlled.

Source of image: Reen, V. and Gil, J. Clearing Stressed Cells. Science Perspectives 2021;Vol 374(6567) p 534-535.

References

2. Sturmlechner I, Zhang C, Sine CC, van Deursen EJ, Jeganathan KB, Hamada N, Grasic J, Friedman D, Stutchman JT, Can I, Hamada M, Lim DY, Lee JH, Ordog T, Laberge RM, Shapiro V, Baker DJ, Li H, van Deursen JM. p21 produces a bioactive secretome that places stressed cells under immunosurveillance. Science. 2021 Oct 29;374(6567):eabb3420. doi: 10.1126/science.abb3420. Epub 2021 Oct 29. PMID: 34709885.

Genomics-based cure for diabetes on-the-way

Posted in Chemical Biology and its relations to Metabolic Disease, Chemical Genetics, Genome Biology, Reproductive Andrology, Embryology, Genomic Endocrinology, Preimplantation Genetic Diagnosis and Reproductive Genomics, tagged Adox, bivalent modification, cell reprogramming, chip, Diabetes, endocrine cells, epigenetic, ES cells, FACS, glucagon, glucose, histone acetylation, histone methylation, histone modification, homeostasis, Insulin, Islets of Langerhans, α cells, β cells, long noncoding RNA, monovalent modification, pancreatic islets, pluripotent cells, qRT-PCR, RNA sequencing, Therapy, transcriptional, transcriptome, type 1 diabetes, type 2 diabetes on March 4, 2013| 5 Comments »

Reporter: Ritu Saxena, Ph.D.

Diabetes currently affects more than 336 million people worldwide, with healthcare costs by diabetes and its complications of up to $612 million per day in the US alone. The islets of Langerhans, miniature endocrine organs within the pancreas, are essential regulators of blood glucose homeostasis and play a key role in the pathogenesis of diabetes. Islets of Langerhans are composed of several types of endocrine cells. The α- and β-cells are the most abundant and also the most important in that they secrete hormones (glucagon and insulin, respectively) crucial for glucose homeostasis (Bosco D, et al, Diabetes, May 2010;59(5):1202-10).

Diabetes is a ‘bihormonal’ disease, involving both insulin deficiency and excess glucagon. For decades, insulin deficiency was considered to be the sole reason for diabetes; however, recent studies emphasize excess glucagon as an important part of diabetes etiology. Thus, insulin-secreting β cells and glucagon-secreting α cells maintain physiological blood glucose levels, and their malfunction drives diabetes development. Increasing the number of insulin-producing β cells while decreasing the number of glucagon-producing α cells, either in vitro in donor pancreatic islets before transplantation into type 1 diabetics or in vivo in type 2 diabetics, is a promising therapeutic avenue. A huge leap has been taken in this direction by the researchers at the University of Pennsylvania (Philadelphia, PA) in collaboration with Oregon Health and Science University (Portland, OR), USA by demonstrating that α to β cell reprogramming could be promoted by manipulating the histone methylation signature of human pancreatic islets. In fact, the treatment of cultured pancreatic islets with a histone methyltransferase inhibitor leads to colocalization of both glucagon and insulin and glucagon and insulin promoter factor 1 (PDX1) in human islets and colocalization of both glucagon and insulin in mouse islets. The research findings were published in the Journal of Clinical Investigation.

Study design: First step was to study and analyze the epigenetic and transcriptional landscape of human pancreatic human pancreatic α, β, and exocrine cells using ChIP and RNA sequencing. Study design for determination of the transcriptome and differential histone marks included the dispersion and FACS to of human islets to obtain cell populations highly enriched for α, β, and exocrine (duct and acinar) cells. Then, chromatin was prepared for ChIP analysis using antibodies for histone modifications, H3K4me3 (represents gene activation) and H3K27me3 (represents gene repression). RNA-Sequencing analysis was then performed to determine mRNA and lncRNA. Sample purity was confirmed using qRT-PCR of insulin and glucagon expression levels of the individual α and β cell population revealing high sample purity.

Results:

Long noncoding transcripts: Long noncoding RNA molecules have been implicated as important developmental regulators, cell lineage allocators, and contributors to disease development. The authors discovered 12 cell–specific and 5 α cell–specific noncoding (lnc) transcripts, indicative of the valuable research resource represented from transcriptome data. Recently discovered lncRNA molecules in islets are regulated during development and dysregulated in type 2 diabetic islets.
Monovalent histone modification landscapes shared among three cell types: Monovalent H3K4me3-enriched regions, indicative of gene activation, were identified and compared in α, β, and exocrine cells. Strikingly, the vast majority of monovalently H3K4me3-marked genes were shared among the 3 pancreatic cell lineages (83%–95%), reflecting both their related function in protein secretion and common embryonic descent. Similarly, a high degree of overlap was observed in H3K27me3 modification patterns in all the three cell types (73%–83%).
Bivalent histone modifications (H3K4me3 and H3K27me3) were high in α cells: Bernstein colleagues observed bivalent marks to be common in undifferentiated cells, such as ES cells and pluripotent progenitor cells, and in most cases, one of the histone modification marks was lost during differentiation, accompanying lineage specification (Bernstein BE, et al, Cell, 21 Apr 2006; 125(2):315-26). α cells exhibited many more genes bivalently marked, followed by β cells and exocrine cells. Bivalent state was remarkably similar to that of hESC, suggesting a more plastic epigenomic state for α cells.
Monovalent histone modifications were high in β cells: Thousands of the genes that were in bivalent state in α cells were in a monovalent state, carrying only the activating or repressing mark.
Inhibition of histone methyltransferases led to partial cell-fate conversion: Adenosine dialdehye (Adox), a drug that interferes with histone methylation and decreases H3K27me3, when administered in human islet tissue, led to decrease of H3K27me3 enrichment at the 3 gene loci that are originally expressed bivalently in α cells and monovalently in β cells: MAFA, PDX1 and ARX. Adox resulted in the occasional cooccurrence of glucagon and insulin granules within the same islet cell, which was not observed in untreated islets. Thus, inhibition of histone methyltransferases leads to partial endocrine cell-fate conversion.

Conclusion: α cells have been reprogrammed into β cell fate in various mouse models. The reason, as proposed by the authors, might be the presence of more bivalently marked genes that confers a more plastic epigenomic state of the cells that probably drives them to the β cell fate. Therefore, using epigenomic information of different cell types in pancreatic islets and harnessing it for subsequent manipulation of their epigenetic signature could be utilized to reprogram cells and hence provide a path for diabetes therapy.

Source: Bramswig NC, et al, Epigenomic plasticity enables human pancreatic α to β cell reprogramming. J Clin Invest, 22 Feb 2013. pii: 66514.

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