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Posts Tagged ‘PTEN’


Author: Ziv Raviv PhD

 

Part A: Introduction to the PI3K/Akt pathway

Background

Akt/Protein kinase B (PKB) is a cytosolic serine/threonine kinase that promotes cell survival by inactivation of targets of the apoptotic pathways [1], and is implicated in the execution of many other cellular processes including:  cell proliferation, angiogenesis, glucose metabolism [2], protein translation, and gene transcription, all are mediated by extracellular and intracellular signals. In many cancers Akt is overexpressed and has central role in cancer progression and cancer cell survival [3,4], what makes it an attractive target for cancer therapy.

The Akt signaling pathway

Upstream signaling:

The Akt signaling pathway is initiated by growth factors leading to the recruiting and activation of phosphoinositol-3-kinase (PI3K) on receptor tyrosine kinases (RTKs). PI3K is then translocated to the cell membrane where it phosphorylates inositol ring at the D3 position of phosphatidylinositol  to form phosphatidylinositol (3,4,5)-triphosphate (PIP3). PIP3 serves to anchor Akt to the plasma membrane where it is phosphorylated at Thr308 by PDK1 and is further completely activated by mTOR by phosphorylation of Ser473. In certain circumstances activated Ras can also activate PI3K.

Downstream signaling:

Upon activation Akt is transducing its signals to downstream substrates to induce various intracellular processes, among them are: Activation of mTOR and its downstream effector S6K – to facilitate activation of translation; Phosphorylation of Bad – that inhibits apoptosis ; Phosphorylation of the tumor suppressor gene FOXO1 – inducing its ubiquitination and subsequent degradation by the proteasome;  Inhibition by phosphorylation of glycogen synthase kinase 3 (GSK-3) – which results in increase of glycogen synthesis.   Regulation of cell growth and survival is executed also by blocking apoptosis by Akt-associated survivin (BRC5) upregulation and via the NF-κB pathway by activation of IκB kinase (IKK).

  • Watch a Video on Akt Signaling Pathway

Figure 1: The Akt signaling pathway

AKT_cClick on image to enlarge

Taken from: Targeting the PI3K-AKT-mTOR pathway: progress, pitfalls, and promises. Workman P et al. Curr Opin Pharmacol. 2008 Aug;8(4):393-412

Negative regulation:

PI3K-dependent Akt activation is negatively regulated by the tumor suppressor protein PTEN, which works essentially opposite to PI3K, namely,  PTEN acts as a phosphatase and dephosphorylates PIP3 back to PIP2. This step removes Akt from its membrane anchoring through PIP3 resulting in substantial decreased rate of Akt activation and consequently inactivation of Akt-depended downstream pathways. In addition, PIP3 can also be dephosphorylated by the SHIP family of inositol phosphatases form PIP2.

Involvement of Akt  in cancer

The PI3K/Akt pathway is frequently altered and deregulated in many human malignancies. Hyper-activation of AKT kinases is one of the most common molecular findings in human malignancies and account for malignant transformation. Mechanisms for Akt pathway activation include loss of tumor suppressor PTEN function, amplification or mutation of PI3K, amplification or mutation of Akt, activation of growth factor receptors, inactivation of the translation repressor protein 4E-BP1 [5], and exposure to carcinogens [3 ,4]. For instance, heterozygous deletion of PTEN in mice elicits spontaneous tumors attributed mainly to activation of Akt. In addition, the production PIP3 by PI3K is over-activated in a wide range of tumor types. On the other hand, Akt knockout mice demonstrate that Akt is required for both cancer cell survival and oncogenic transformation. That activation of Akt is oncogenic, could be explained by preventing normal apoptosis of cells, thereby enabling accumulation of more oncogenic mutations in these cells. In addition, activation of Akt can also abrogate cell cycle checkpoints and can overcome G2/M cell-cycle arrest mediated by DNA mismatch repair. Thus, cells in which Akt is activated can accumulate mutations because the G2 cell-cycle point is abrogated and survive and continue to divide because of the anti-apoptotic activity of Akt. It is, therefore, proposed that this dual activity of Akt activation may explain the frequent activation of Akt in human malignancies [6].

Taken together, Akt activation has an effective role in cancer and through its downstream substrates Akt controls many cancer related cellular processes such as cell metabolism, growth and survival, proliferation, and motility, all of which contribute to tumor initiation and progression. Therefore, this pathway is an attractive therapeutic target for cancer treatment because it serves as a convergence point for many growth stimuli. Moreover, activation of the PI3/Akt pathway confers resistance to many chemotherapeutic drags [6], and is a poor prognostic factor for many types of cancers. Therefore, small molecule agents that block PI3K/Akt signaling might block many aspects of the tumor-cell phenotype [7,8]. Indeed, the Akt pathway is a major target for anticancer drug development by pharmaceutical companies.

  • The below Part B review the efforts to develop targeted Akt therapies for cancer.

 

Part B: Clinically available/in clinical development PI3K/Akt/mTOR inhibitors 

As described in Part Athe PI3/Akt cascade is a major intracellular signaling route conferring pro-survival signals to the cell. In cancer, there are many conditions where the PI3K/Akt pathway is deregulated, an attribute that is contributing to cancer formation and propagation. Given that Akt servers as convergence point to many pro-survival signals together with it being deregulated frequently in cancers, make Akt as a valuable target for developing anti-cancer therapy.

In addition, Akt shortens patient survival by allowing cancer cells to escape the cytotoxic effects of standard chemotherapy drugs. The importance of the Akt pathway in cancer thus is also evident from its significant role in the resistance of tumors to chemotherapies. A considerable route in developing anti- Akt based therapies is thus combining Akt inhibitors with standard chemotherapy rather than the using of Akt inhibitors as single agents.

Even in targeted therapies for cancer, such those that target receptor tyrosine kinases (RTKs) and other signaling pathways, it has been demonstrated that when applying a targeted agent such as trastuzumab  (Herceptin) a compensation reaction of increasing of downstream and parallel signaling pathways components, among them Akt, occurs in response, which enables cancer cells to be spared the effects of these targeted drugs. Therefore a multi-targeting approach with selective inhibitors would be useful, and inhibiting Akt directly will restore sensitivity to agents such as trastuzumab.

(i) Inhibitors that are in clinical use

Temsirolimus (CCI-779; marked as Torisel by Pfizer), an analog of sirolimus (rapamycin), is an immunophilin-binding antibiotic that blocks the initiation of the translation of mRNA by inhibiting mammalian target of rapamycin (mTOR) in a highly specific manner. Rapamycin itself is toxic and found in the clinic however as an immunosuppressant to prevent rejection in organ transplantation. Temsirolimus acts by interacting with mTOR, preventing the phosphorylation of eIF4E-BP1 and p70S6K, and thereby inhibiting the initiation of the translation of mRNA. The main mechanism of temsirolimus is inhibition of proliferation by G1 phase arrest induction, yet without inducing apoptosis. Temsirolimus was introduced only recently to treat renal cell carcinoma (RCC). In this cancer type HIF-1a levels are accumulated since its degradation is reduced significantly due to mutations of von Hippel Lindau tumor-suppressor gene and the activation of mTOR only worsen that accumulation of HIF1-a, which is its downstream effector. Therefore by blocking mTOR function temsirolimus is reducing the accumulation of HIF-1a. Temsirolimus has been generally well tolerated by advanced RCC patients that could be attributed to its high specificity toward mTOR. However, temsirolimus is associated with a small, but significant increased risk of developing a fatal adverse event. Nevertheless, temsirolimus benefit the overall patient population with the approved indications, including RCC. In the pivotal phase III study, temsirolimus demonstrated median overall survival (OS) in previously untreated patients of 10.9 months in patients with advanced RCC with poor prognostic risk, compared with 7.3 months for interferon-alpha. Temsirolimus remains the only treatment that shows a significant improvement in OSin treatment-naive, poor-risk patients with advanced RCC. Temsirolimus approved cancer indications are RCC and mantle cell lymphoma (MCL), and many other cancer conditions are found in advanced clinical development processes, including various solid tumors, diffused tumors (leukemias and lymphomas), and even in soft tissue sarcomas (STS).

Everolimus (RAD001; marketed by Novartis  as Afinitor) is an ester derivative of rapamycin and is also an inhibitor mTOR.  The drug inhibits oncogenic signaling in tumor cells and angiogenic signaling in vascular endothelial cells. Key features of everolimus include good tolerability, unique mechanism of action, G1 arrest, and induction of apoptosis. In vitro studies have demonstrated a cooperative effect between everolimus and gefitinib in various cancer cell lines. Treatment of human cancer cell lines with everolimus results in a decrease in p-4E-BP1, p-p70S6K, and p-S6 levels while increasing p-AKT levels. The rise of p-AKT is accompanied with a parallel increase in downstream p-GSK-3a/ß, suggesting feedback activation of the AKT pathway. Thus AKT activation could revert the antitumor activity of everolimus. Gefitinib completely prevents everolimus-induced p-AKT increase and markedly enhances the everolimus mediated decrease in p-4E-BP1 and p-p70S6K.

Everolimus is approved for the treatment of RCC, progressive pancreatic neuroendocrine tumors, breast cancer in post-menopausal women with advanced hormone receptor (HR)-positive/HER2-negative. In addition the drug is used as a preventive drug of organ rejection after renal transplantation. As with the case of temsirolimus, everolimus has also a slight increase of mortality risk over other drugs.

Cancer indications that are now in clinical development for treatment by everolimus, some of which are in advanced clinical studies, include various forms of leukemias and lymphomas such as AML, ALL CML, T-cell leukemia, diffuse large B-cell lymphoma (DLBCL), non-Hodgkin’s lymphoma (NHL), and MCL. Everolimus is particularly applicable to the treatment of leukemia because mTOR-related messengers, particularly PI3K, AKT, p70S6K kinase and 4E-BP1, are known to be both constitutively activated in hematologic malignancies and interfere with the activity of current anti-leukemia therapy. Solid tumors such as lung, breast, prostate, and colorectal at various stages, as well as brain cancers and STS are also in developmental stages for everolimus treatment.

(ii) Inhibitors that are in advanced clinical development (phase II/III)

Perifosine (KRX-0401) by AEterna Zentaris – among Akt inhibitors under development for cancer therapy, perifosine is found in advanced stages of clinical development and is moving toward phase III clinical trials. It belongs to alkylphosphocholines (ALP) – phospholipid-like molecules – which disrupt lipid-mediated signal transduction pathways that are necessary for tumor cell growth and survival. ALP induce apoptotic cell death in a variety of tumor cell lines. Perifosine primarily acts on the cell membrane where it inhibits signaling that could explain its capability to inhibit Akt, as Akt interaction with PIP3 in the cytosolic face of the plasma cell membrane is essential to its activation. In addition to Akt, perifosine inhibits also JNK and NF-kB, both are also associated with apoptosis, cell growth, differentiation, and survival. In addition to its potential efficacy as a single agent, perifosine may provide synergistic effects when combined with established cancer treatments such as radiotherapy, chemotherapy, tyrosine kinase inhibitors such as commercially available EGFR inhibitors, and endocrine therapies.

Many clinical trials were/are conducted with perifosine in various cancer conditions and settings. Especially successive phase II studies engaged perifosine were with colorectal cancer (CRC), where patients with metastatic disease treated with the combination of capecitabine and perifosine had more than doubled the median time to progression (TTP) of the disease, which led to an ongoing phase III study. Other solid cancer indications phase II studies employing perifosine that had encouraging results include metastatic RCC (mRCC) and non-small lung cancer (NSLC). Perifosine is also exmined in clinical trials with hematological cancers. Advanced stages clinical studies were conducted in multiple myeloma (MM), where patients treated with the combination of perifosine + bortezomib (proteasome inhibitor) and dexamethasone, in which after, a phase III study was conducted on that basis. However, that phase III study was terminated in March 2013 upon recommendation by data safety monitoring board to discontinue the experiment since it was highly unlikely that the trial would achieve a significant difference in progression-free survival (PFS).  Another potential benefit for perifosine has been documented in Waldenström’s macroglobulinemia (WM).  In addition, perifosine is examined in other hematologic cancers such as in AML, CLL and lymphomas.

MK-2206 – MK-2206 by Merck is an allosteric inhibitor of Akt that is currently widely examined in tens of clinical experimentation where some of them are in phase II status.  In preclinical experiments, MK-2206, demonstrated synergistic activity when combined with other targeted therapies, such as erlotinib in NSCLC cell lines, and lapatinib in breast cancer cell lines and in xenograft mice bearing ovarian cancer, MK-2206 treatment led to substantial growth inhibition and sustained inhibition of Akt.

Several phase II research studies employing MK-2206 are in progress, among them found a multicenter study with advanced ovarian cancer resistant to platinum therapy, and another multicenter study with breast cancer patients. Phase I/II study is conducted also for CLL patients. Many others phase I studies are in progress, among them trails testing the combinations of MK-2206 with other targeted drugs as well as chemotherapy. For instance an ongoing phase I study is evaluating the addition of MK-2206 to trastuzumab in patients with solid tumors HER2 positive, or another study is conducted to evaluate MK-2206 in combination with trastuzumab and lapatinib for the treatment of HER2 positive, advanced solid tumors. MK-2206 is testing also in advanced NSCLC with the combination of gefitinib in one study and with erlotinib in another. In another relatively large phase I study, patients with advanced solid tumors were randomized to MK-2206 either given with carboplatin and paclitaxel, docetaxel, or erlotinib. Another study with patients bearing locally advanced or metastatic solid tumors or metastatic breast cancer examined MK-2206 given with and paclitaxel (Taxol). Finally MK-2206 and selumetinib administration was tested in phase I studies in patients with advanced CRC. Other cancer indications that are investigated MK-2206 as single agent or in combination with chemotherapy in phase I studies include prostate cancer,  head and neck cancer, large B cell lymphoma, leukemias such as AML, and melanoma.

Ridaforolimus (AP23573/MK-8669,; Taltorvic by Merck) – Ridaforolimus is an oral mTOR inhibitor found in several clinical trials. A compressive phase III experiment was conducted with ridaforolimus in metastatic STS and metastatic bone sarcomas (SUCCEED – Sarcoma Multi-Center Clinical Evaluation of the Efficacy of Ridaforolimus) by Merck and Ariad Pharmaceuticals that had presented positive data at the beginning showing that patients that have received ridaforolimus had a median progression-free survival (PFC) – the primary endpoint of the study – of 17.7 weeks compared with 14.6 weeks for those received placebo. However, FDA’s oncologic drugs advisory committee (ODAC) panel (March 2012) did not approved the use of ridaforolimus as maintenance therapy for patients with metastatic soft-tissue sarcoma or bone sarcoma. The committee did not think that a significant difference was observed between the groups in terms of OS and although patients did experience a longer disease-free period before their cancer returned when receiving ridaforolimus, the delay was not significant. There was also a concern regarding side effects. In a complete response letter, (June 2012) the FDA did not approve the SUCCEED application in its present form, therefore, Merck formally withdrawn the marketing authorization application for ridaforolimus for sarcoma. However, Merck still continue experimenting ridaforolimus in other cancer indications. A phase II study is conducted in breast cancer patients examining ridaforolimus alone, ridaforolimus + dalotuzumab, or ridaforolimus + Exemestane. Another phase II study is conducted in female adult patients harboring recurrent or persistent endometrial cancer. A third Phase II study is examining ridaforolimus in patients with taxane-resistant androgen-independent prostate cancer. Many phase I experiments are conducted with ridaforolimus among them: experiment in pediatric patients with solid tumors treated with dalotuzumab given alone or in combination with ridaforolimus; Bicalutamide and ridaforolimus in men with prostate cancer; Combinations of carboplatin/paclitaxel/ridaforolimus in endometrial and ovarian tumors; Safety study examining ridaforolimus  in patients with progressive or recurrent glioma, and others. Given the consequences as with the SUCCEED experiment; it remains to see whether ridaforolimus alone or in combinations would be approved and be valid in the clinical arena.

RX-0201 (Archexin) by Rexahn Pharmaceuticals is an antisense oligonucleotide directed toward Akt1 mRNA. RX-0201 was demonstrated to significantly downregulated the expression of AKT1 at both the mRNA and protein levels. In addition combined treatment of RX-0201with several cytotoxic drugs resulted in an additive growth inhibition of Caki-1 clear cell carcinoma cells. In addition, preclinical experiments demonstrated that RX-0201 given at nano-molars as a single agent induced substantial growth inhibition in various types of human cancer cells. Furthermore, in vivo studies using nude mice xenografts have resulted in significant inhibition of tumor growth and tumor formation treated with RX-0201. Therefore RX-0201 was further tested in phase I studies in patients with solid tumors. The only dose limiting toxicity (DLT) observed was Grade 3 fatigue. Phase II studies of RX-0201 were approved thus in advanced RCC. Furthermore, another phase II study was completed last year with encouraging results.  This phase II trial was conducted in metastatic pancreatic cancer, assessing the combination of RX-0201 and gemcitabine. The study enrolled 31 patients and the primary endpoint was overall survival following 4 cycles of therapy with a 6-month follow-up. The study demonstrated that treatment with RX-0201 in combination with gemcitabine resulted in a median survival of 9.1 months compared to the published survival data of 5.65 months for gemcitabine given alone. The most frequently side effects were constipation, nausea, abdominal pain, and pyrexia, regardless of relatedness.

BKM120 – by Novartis is an oral selective class-I PI3K inhibitor, induces its inhibition in an ATP-competitive manner, thereby inhibiting the production of the secondary messenger PIP3 and activation of downstream signaling pathway. BKM120 was shown to induce pro-apoptotic effects in vitro and anti-tumor activity in vivo. BKM120 is enrolled in many clinical trials at all levels for several cancer indications. Phase I experiments are performed with the following cancers: CRC in combination with panitumumab; RCC; breast cancer (HR+/HER2+); breast cancer (triple negative, recurrent); ovarian cancer; and leukemias.  Phase II trials include: endometrial cancer; metastatic NSCLC; malignant melanoma (Braf V600 mutated); prostate; and glioblastoma multiforme (GBM).

A phase III study is currently enrolled with postmenopausal breast cancer patients with HR+/HER2- (local, advanced or metastatic), examining BKM120 in combination with fulvestrant. In preliminary clinical experiments activity was observed with BKM120 in patients with breast cancer, as a single agent or in combination with letrozole, or trastuzumab. In this phase III study, postmenopausal women with HR+/HER2- breast cancer whom were treated with aromatase inhibitor (AI), and are refractory to endocrine and mTOR inhibition (mTORi) combination therapy, are randomized to receive continuous BKM120 or placebo daily, with fulvestrant. The rational for this experiment is that the use of PI3K inhibition may overcome resistance to mTORi in breast cancer by targeting the PI3K pathway upstream.  The primary endpoint of the trail is PFS and the secondary endpoint is OS. Other secondary endpoints are overall response rate and clinical benefit rate, safety, pharmacokinetics of BKM120, and patient-reported quality of life.

CAL-101 (Idelalisib) – by Gilead Sciences is an orally bio-available, small molecule inhibitor of PI3K delta proposed for the treatment hematologic malignancies. In preclinical efficacy studies, CAL-101 inhibited the PI3K pathway and decreased cellular proliferation in primary CLL and AML cells, and in a range of NHL cell lines. The delta form of PI3K is expressed primarily in blood-cell lineages, including cells that cause or mediate hematologic malignancies, inflammation, autoimmune diseases and allergies. Therefore, CAL-101 as specific inhibitor of the PI3K-delta is expected to have therapeutic effects in these diseases without inhibiting PI3K signaling that is critical to the normal function of healthy cells. A variety of studies have shown that inhibition of other PI3K forms can cause significant toxicities, particularly with respect to glucose metabolism, which is essential for normal cell activity. CAL-101 was shown to block constitutive PI3K signaling, resulting in decreased phosphorylation of Akt and other downstream effectors, an increase in PARP and caspase cleavage, and an induction of apoptosis across a broad range of immature and mature B-cell malignancies. Importantly, CAL-101 does not promote apoptosis in normal T cells or NK cells, nor does it diminish antibody-dependent cellular cytotoxicity (ADCC) but decreased activated T-cell production of various inflammatory and anti-apoptotic cytokines. These findings provide rationale for the clinical development of CAL-101 as a first-in-class targeted therapy for CLL and related B-cell proliferative disorders. Indeed several clinical trials are currently enrolled for Hodgkin’s lymphoma, NHL, and CLL. Phase III clinical trials for CLL are now recruiting patients aimed to examine CAL-101 in combination with Bendamustine and Rituximab in one study;  CAL-101 + Rituximab;  and the combinations of CAL-101 with Ofatumumab in third phase III study. Both Rituximab and Ofatumumab are monoclonal Abs for CD20, which is primarily found on the surface of B cells. In addition, another phase III study of CAL-101 in combination with Bendamustine and Rituximab for indolent NHLs is also now recruiting patients.

(iii) Other Akt pathway inhibitors in clinical development.

There are dozens of agents targeting Akt pathway that are found at preclinical and clinical development. The various inhibitors are targeting various elements of the Akt pathway including: Akt itself, PI3K, mTOR, and PDK1. Most of these agents are small molecules inhibitors, some are extracts while others are synthetic, but also include an antisense oligonucleotide (RX-0201 to Akt).

The list below describes shortly agents which currently reached phase II stage and their relevant indications:

XL-147 – sponsored by Sanofi, small molecule-pan PI3K inhibitor for breast cancer and endometrial cancer.

XL-765 – also of Sanofi, inhibitor of the activity of PI3K and mTOR, for HR+/HER2- breast cancer patients.

BN108 – by Bionovo, an aqueous extract of Anemarrhena asphodeloides, is an orally available dual inhibitor, that induces apoptotic cancer cell death by rapid inactivation of both Akt and mTOR pathways, for breast cancer.

GDC-0068 – by Genentech, is an orally available small molecule pan-Akt inhibitor, for prostate cancer.

BEZ235 – by Novartis is a dual ATP-competitive PI3K and mTOR inhibitor, prevents PI3K signaling and inhibits growth of cancer cells with activating PI3K mutations. Phase II study is recruiting patients with metastatic or unresectable malignant PEComa (perivascular epithelioid cell tumors), other phase II include endometrial cancer indications and metastatic HR+/HER2-breast cancer patients.

BAY 80-6946 – is a pan class I PI3K inhibitor by BayerPhase II for NHL, currently recruiting.

Nelfinavir  – by ViiV Healthcare is an HIV protease inhibitor found to downregulate Akt phosphorylation by inhibiting proteasomal activity and inducing the unfolded protein response (UPR). HIV-1 protease inhibitor was found induces growth arrest and apoptosis of human prostate cancer cells in vitro and in vivo in conjunction with blockade of androgen receptor, STAT3 and AKT signaling. A phase I/II trial is enrolled for patients with locally advanced CRC to test Nelfinavir in combination with chemo/radiotherapy.

Triciribine  Triciribine phosphate monohydrate (TCN-PM) is a specific AKT inhibitor used also in the basic research arena but undergo also several clinical studies. Currently a phase II sponsored by Cahaba Pharmaceuticals is recruiting, to examine triciribine with paclitaxel in patients with locally advanced breast cancer. And a phase I/II experiment of combination with carboplatin in ovarian patients is planned.

GSK2110183 – by GlaxoSmithKline  is an oral panAkt inhibitor. Phase II is recruiting subjects with solid tumors and hematologic malignancies.

(iv) Conclusive remarks

Given the broaden arsenal of agents targeting Akt that are in pre-clinical and clinical development, it is extremely important to figure out how to use them optimally and to elucidate carefully which of them have the greatest potential to proceed into advanced stages of clinical trials and to clinical approval.  One of the various considerations in developing valid Akt inhibitors for the clinic use should be choosing a relevant cancer in which Akt has a central role in its development/propagation (e.g. mRCC). Since there is cross-talk between the Akt pathway to other pathways especially by involvement of RTKs (e.g. VEGFR), there is a rational to apply Akt inhibitions in cancer indications that had good results with inhibition of RTKs where combinations of Akt with agents such as sunitinib, could results in a synergistic anti-cancer effect. The combinations of Akt inhibitors with RTKs inhibitors could also overcome the compensate reaction to agents such as Herceptin that confer resistance. It is important to introduce efficient Akt inhibitor on the background of existing anti-cancer chemotherapies where Akt inhibitors can complement these therapies by circumvent frequent resistance to these drugs. Finally, the developing of biomarkers for a validation of the efficacy of candidate Akt inhibitor to be developed in further advance clinical studies for specific cancer indications is essentially needed, to ensure that accurate efforts would be invested at the most validate Akt inhibitors. Such biomarkers could be levels of phosphorylated Akt in blood or mRNA levels to be monitored upon treatment with Akt inhibitors and the correlation to the efficacy of these inhibitors, and that is besides of their prognostic value. The status of mutations of PI3K and PTEN could also serve as a marker for the efficiency of Akt inhibitors and how to use them optimally.

 

References

1. Song G, Ouyang G, Bao S (2005) The activation of Akt/PKB signaling pathway and cell survival. J Cell Mol Med 9 (1):59-71

2. Gonzalez E, McGraw TE (2009) The Akt kinases: isoform specificity in metabolism and cancer. Cell Cycle 8 (16):2502-2508

3. Vivanco I, Sawyers CL (2002) The phosphatidylinositol 3-Kinase AKT pathway in human cancer. Nat Rev Cancer 2 (7):489-501

4. Altomare DA, Testa JR (2005) Perturbations of the AKT signaling pathway in human cancer. Oncogene 24 (50):7455-7464

5. She QB, Halilovic E, Ye Q, Zhen W, Shirasawa S, Sasazuki T, Solit DB, Rosen N (2010) 4E-BP1 is a key effector of the oncogenic activation of the AKT and ERK signaling pathways that integrates their function in tumors. Cancer Cell 18 (1):39-51

6. Kim D, Dan HC, Park S, Yang L, Liu Q, Kaneko S, Ning J, He L, Yang H, Sun M, Nicosia SV, Cheng JQ (2005) AKT/PKB signaling mechanisms in cancer and chemoresistance. Front Biosci 10:975-987

7. Pal SK, Reckamp K, Yu H, Figlin RA (2010) Akt inhibitors in clinical development for the treatment of cancer. Expert Opin Investig Drugs 19 (11):1355-1366

8. Hsieh AC, Truitt ML, Ruggero D (2011) Oncogenic AKTivation of translation as a therapeutic target. Br J Cancer 105 (3):329-336

9. Alexander W (2011) Inhibiting the Akt pathway in cancer treatment. P T.  April; 36(4): 225–227

10. LoPiccolo J, Blumenthal GM, Bernstein WB, Dennis PA.(2008) Targeting the PI3K/Akt/mTOR pathway: effective combinations and clinical considerations. Drug Resist Updat.  Feb-Apr;11(1-2):32-50

11. Weigelt B and Downward J (2012) Genomic Determinants of PI3K Pathway Inhibitor Response in Cancer. Front Oncol. 2012;2:109

12. Janna Elizabeth Hutz. Genetic analysis of the PI3k/AKT/mTOR signaling pathway. udini.proquest.com

Resources

New medicine Oncology KnowledgeBASE (nmOK)

ClinicalTrials.gov

Related articles on this Open Access Online Scientific Journal

AKT signaling variable effects. Reporter: Larry H Bernstein, MD

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Long Noncoding RNA Network regulates PTEN Transcription

Author: Larry H Bernstein, MD, FCAP

Scientists Find Surprising New Influence On Cancer Genes

A pseudogene long noncoding RNA networkregulates PTEN transcription and translation in human cells
Per Johnsson, A Ackley, L Vidarsdottir, Weng-Onn Lui, M Corcoran, D Grandér, and KV Morris
a new study led by scientists at The Scripps Research Institute (TSRI) shows how
  • pseudogenes can regulate the activity of a cancer-related gene called PTEN.
The study also shows that pseudogenes can be targeted to control PTEN’s activity.

Mol Cancer. 2011; 10: 38.   Published online 2011 April 13. doi:  10.1186/1476-4598-10-38    PMCID: PMC3098824

New Type of Gene That Regulates Tumour Suppressor PTEN Identified

Feb. 24, 2013 — Researchers at Karolinska Institutet in Sweden have identified a new so-called pseudogene that regulates the tumour-suppressing PTEN gene.
They hope that this pseudogene will be able to control PTEN to

  1. reverse the tumour process,
  2. make the cancer tumour more sensitive to chemotherapy and
  3. prevent the development of resistance.

The findings, which are published in the scientific journal Nature Structural and Molecular Biology, can be of significance in

    • the future development of cancer drugs.

The development of tumours coincides with the activation of several cancer genes as well as the inactivation of other tumour-suppressing genes owing to

  1. damage to the DNA and
  2. to the fact that
    • the cancer cells manage to switch off the transcription of tumour-suppressor genes.

To identify what might be regulating this silencing, the researchers studied PTEN,

    • one of the most commonly inactivated tumour-suppressor genes.

It has long been believed that the switching-off process is irreversible, but the team has now shown that

  • silenced PTEN genes in tumour cells can be ‘rescued’ and
  • re-activated by a ‘pseudogene’,
    • a type of gene that, unlike normal genes,
    • does not encode an entire protein.

“We identified a new non-protein encoding pseudogene, which

  • determines whether the expression of PTEN
    • is to be switched on or off,”

says research team member Per Johnsson, at Karolinska Institutet’s Department of Oncology-Pathology. “What makes this case spectacular is that the gene

  • only produces RNA,
  • the protein’s template.

It is this RNA that, through a sequence of mechanisms,

    • regulates PTEN.

Pseudogenes have been known about for many years, but

  • it was thought that they were only junk material.”

No less than 98 per cent of human DNA consists of non-protein encoding genes (i.e. pseudogenes), and by studying these formerly neglected genes the researchers

  • have begun to understand that they are very important and
    • can have an effect without encoding proteins.

Using model systems, the team has shown that the new pseudogene can

  • control the expression of PTEN and
    • make tumours more responsive to conventional chemotherapy.

Pre Johnssom suggests “we might one day be able to re-programme cancer cells

  • to proliferate less,
  • become more normal, and that
  • resistance to chemotherapy can hopefully be avoided.

“We also believe that our findings can be very important for the future development of cancer drugs.  The human genome conceals no less than 15,000 or so pseudogenes, and it’s not unreasonable to think

  • that many of them are relevant to diseases such as cancer.”

The study was conducted in collaboration with scientists at The Scripps Research Institute, USA, and the University of New South Wales, Australia, and was made possible with

  • grants from the Swedish Childhood Cancer Foundation, the Swedish Cancer Society, the Cancer Research Funds of Radiumhemmet, Karolinska Institutet’s KID programme for doctoral studies, the Swedish Research Council, the Erik and Edith Fernström Foundation for Medical Research, the National Institute of Allergy and Infectious Diseases, the National Cancer Institute and the National Institutes of Health.

The functional role of long non-coding RNA in human carcinomas
EA Gibb, CJ Brown, and WL Lam
Long non-coding RNAs (lncRNAs) are emerging as new players in the cancer paradigm demonstrating potential roles in both oncogenic and tumor suppressive pathways. These novel genes are frequently

    • aberrantly expressed in a variety of human cancers,

however the biological functions of the vast majority remain unknown. Recently, evidence has begun to accumulate describing the molecular mechanisms by which these RNA species function, providing insight into

    • the functional roles they may play in tumorigenesis.

In this review, we highlight the emerging functional role of lncRNAs in human cancer.

One of modern biology’s great surprises was the discovery that the human genome encodes only ~20,000 protein-coding genes, representing <2% of the total genome sequence [1,2]. However, with the advent of

  • tiling resolution genomic microarrays and
  • whole genome and transcriptome sequencing technologies
    • it was determined that at least 90% of the genome is actively transcribed [3,4].

The human transcriptome was found to be more complex than

  • a collection of protein-coding genes and their splice variants; showing
    • extensive antisense,
    • overlapping and non-coding RNA (ncRNA) expression [5-10].

Although initially argued to be spurious transcriptional noise, recent evidence suggests that the proverbial “dark matter” of the genome

  • may play a major biological role in cellular development and metabolism [11-17].

One such player, the newly discovered long non-coding RNA (lncRNA) genes, demonstrate

  1. developmental and tissue specific expression patterns, and
  2. aberrant regulation in a variety of diseases, including cancer [18-27].

NcRNAs are loosely grouped into two major classes based on transcript size; small ncRNAs and lncRNAs [28-30].

  1. Small ncRNAs are represented by a broad range of known and newly discovered RNA species, with many being associated
    • with 5′ or 3′ regions of genes [4,31,32].

This class includes the well-documented miRNAs, RNAs ~22 nucleotides (nt) long involved in the specific regulation of both

  1. protein-coding, and
  2. putatively non-coding genes,
    • by post-transcriptional silencing or infrequently
    • by activation [33-35].

miRNAs serve as major

  1. regulators of gene expression and as
  2. intricate components of the cellular gene expression network [33-38].

Another newly described subclass are the transcription initiation RNAs (tiRNAs), which are

  • the smallest functional RNAs at only 18 nt in length [39,40].
  1. small ncRNAs classes, including miRNAs, have established roles in tumorigenesis, an intriguing association between
  2. the aberrant expression of ncRNA satellite repeats and cancer has been recently demonstrated [41-46].

Types of human non-coding RNAs

In contrast to miRNAs, lncRNAs, the focus of this article, are

    • mRNA-like transcripts ranging in length from 200 nt to ~100 kilobases (kb) lacking significant open reading frames.

Many identified lncRNAs are transcribed by RNA polymerase II (RNA pol II) and are polyadenylated, but this is not a fast rule [47,48].
There are examples of lncRNAs, such as the

  • antisense asOct4-pg5 or the
  • brain-associated BC200,
    • which are functional, but not polyadenylated [49-51].
  1. lncRNA expression levels appear to be lower than protein-coding genes [52-55], and some
  2. lncRNAs are preferentially expressed in specific tissues [21].

Novel lncRNAs may contribute a significant portion of the aforementioned ‘dark matter’ of the human transcriptome [56,57]. In an exciting report
by Kapranov et.al., it was revealed the bulk of the relative mass of RNA in a human cell, exclusive of the ribosomal and mitochondrial RNA,
is represented by non-coding transcripts with no known function
[57].

Like miRNAs and protein-coding genes, some

  • transcriptionally active lncRNA genes display
  • histone H3K4 trimethylation at their 5′-end and
  • histone H3K36 trimethylation in the body of the gene [8,58,59].

The small number of characterized human lncRNAs have been associated with a spectrum of biological processes, for example,

  • epigenetics,
  • alternative splicing,
  • nuclear import,
    1. as structural components,
    2. as precursors to small RNAs and
    3. even as regulators of mRNA decay [4,60-70].

Furthermore, accumulating reports of misregulated lncRNA expression across numerous cancer types suggest that

    • aberrant lncRNA expression may be a major contributor to tumorigenesis [71].

This surge in publications reflects the increasing attention to this subject  and a number of useful lncRNA databases have been created .
In this review we highlight the emerging

    • functional role of aberrant lncRNA expression, including
    • transcribed ultraconserved regions (T-UCRs), within human carcinomas.

Publications describing cancer-associated ncRNAs. Entries are based on a National Library of Medicine Pubmed search using the terms
“ncRNA” or “non-coding RNA” or “noncoding RNA” or non-protein-coding RNA” with cancer and annual (Jan.1-Dec.31) date limitations. …
Publically available long non-coding RNA online databases

The definition ‘non-coding RNA’ is typically used to describe transcripts where

    • sequence analysis has failed to identify an open reading frame.

There are cases where ‘non-coding’ transcripts were found to encode short, functional peptides [72]. Currently, a
universal classification scheme to define lncRNAs does not exist. Terms such as

  • large non-coding RNA,
  • mRNA-like long RNA, and
  • intergenic RNA

all define cellular RNAs, exclusive of rRNAs,

    • greater than 200 nt in length and having no obvious protein-coding capacity [62].

This has led to confusion in the literature as to exactly which transcripts should constitute a lncRNA. One subclass of lncRNAs is called
large or long intergenic ncRNAs (lincRNAs). These lncRNAs are

  1. exclusively intergenic and are
  2. marked by a chromatin signature indicative of transcription [8,58].

RNA species that are bifunctional preclude categorization into either group of

  • protein-coding or
  • ncRNAs as

their transcripts function both at the RNA and protein levels [73].

The term ‘lncRNA‘ is used only to describe transcripts with no protein-coding capacity. In the meantime, and for the purposes of this review,
we will consider lncRNAs as a blanket term to encompass

  1. mRNA-like ncRNAs,
  2. lincRNAs, as well as
  3. antisense and intron-encoded transcripts,
  4. T-UCRs and
  5. transcribed pseudogenes.

Discovery of LncRNAs

The earliest reports describing lncRNA predated the discovery of miRNAs, although the term ‘lncRNA‘ had not been coined at the time .
One of the first lncRNA genes reported was the imprinted H19 gene, which was quickly followed by the discovery of the

  • silencing X-inactive-specific transcript (XIST) lncRNA gene, which
    • plays a critical function in X-chromosome inactivation [74,75].

The discovery of the first miRNA lin-14 dramatically redirected the focus of ncRNA research from long ncRNAs to miRNAs [76], and
the discovery of miRNAs revealed RNA could

  1. regulate gene expression and
  2. entire gene networks could be affected by ncRNA expression and

Within the last decade miRNAs were discovered to be associated with cancer. At the time of this writing there are approximately
1049 human miRNAs described in miRBase V16 [80,81] with the potential of

    • affecting the expression of approximately 60% of protein -coding genes [82,83].

Conversely, the variety and dynamics of lncRNA expression was not to be fully appreciated until the introduction of whole transcriptome sequencing.
With the advent of the FANTOM and ENCODE transcript mapping projects, it was revealed that the mammalian genome is extensively transcribed,
although a large portion of this represented non-coding sequences [3,84]. Coupled with the novel functional annotation of a few lncRNAs, this discovery
promoted research focusing on lncRNA discovery and characterization. Recent reports have described new lncRNA classes such as lincRNAs and T-UCRs [8,58,85].
Current estimates of the lncRNA gene content in the human genome ranges from ~7000 – 23,000 unique lncRNAs, implying this class of ncRNA will
represent an enormous, yet undiscovered, component of normal cellular networks that may be disrupted in cancer biology [62].

Emerging Role of Long Non-Coding RNA in Tumorigenesis

A role for differential lncRNA expression in cancer had been suspected for many years, however, lacked strong supporting evidence [86]. With advancements
in cancer transcriptome profiling and accumulating evidence supporting lncRNA function, a number of differentially expressed lncRNAs have been associated
with cancer. LncRNAs have been implicated to

  • regulate a range of biological functions and
  • the disruption of some of these functions, such as
    • genomic imprinting and transcriptional regulation,
    • plays a critical role in cancer development.

Here we describe some of the better characterized lncRNAs that have been associated with cancer biology.

Human cancer-associated lncRNAs

Imprinted lncRNA genes

Imprinting is a process whereby the copy of a gene inherited from one parent is epigenetically silenced [87,88]. Intriguingly, imprinted regions often
include multiple maternal and paternally expressed genes with a high frequency of ncRNA genes. The imprinted ncRNA genes are implicated in the
imprinting of the region by a variety of mechanisms including

  • enhancer competition and chromatin remodeling [89].

A key feature of cancer is the loss of this imprinting resulting in altered gene expression [90,91]. Two of the best known imprinted genes
are in fact lncRNAs.

H19

The H19 gene encodes a 2.3 kb lncRNA that is expressed exclusively from the maternal allele. H19 and its reciprocally imprinted protein-coding neighbor
the Insulin-Like Growth Factor 2 or IGF2 gene at 11p15.5 were among the first genes, non-coding or otherwise, found to demonstrate genomic imprinting [74,92].

The expression of H19 is high during vertebrate embryo development, but is

  • downregulated in most tissues shortly after birth with the exception of skeletal tissue and cartilage [20,93,94].
  • Loss of imprinting and subsequent strong gene expression has been well-documented in human cancers. Likewise,
  • loss of imprinting at the H19 locus resulted in high H19 expression in cancers of the esophagus, colon, liver, bladder and with hepatic metastases [95-97].

H19 has been implicated as having both oncogenic and tumor suppression properties in cancer. H19 is upregulated in a number of human cancers, including
hepatocellular, bladder and breast carcinomas, suggesting an oncogenic function for this lncRNA [97-99]. In colon cancer H19 was shown to be directly activated
by the oncogenic transcription factor c-Myc, suggesting

  • H19 may be an intermediate functionary between c-Myc and downstream gene expression [98].

Conversely, the tumor suppressor gene and transcriptional activator p53 has been shown to

  • down-regulate H19 expression [100,101].

H19 transcripts also serve as a precursor for miR-675, a miRNA involved in the regulation of developmental genes [102].
miR-675 is processed from the first exon of H19 and functionally

  • downregulates the tumor suppressor gene retinoblastoma (RB1) in human colorectal cancer, further implying an oncogenic role for H19 [103].

There is evidence suggesting H19 may also play a role in tumor suppression [104,105]. Using a mouse model for colorectal cancer, it was shown that
mice lacking H19 manifested an increased polyp count compared to wild-type [106]. Secondly, a mouse teratocarcinoma model demonstrated larger
tumor growth when the embryo lacked H19, and finally in a hepatocarcinoma model, mice developed cancer much earlier when H19 was absent [107].
The discrepancy as to whether H19 has oncogenic or tumor suppressive potential may be due in part to the bifunctional nature of the lncRNA or may
be context dependent. In either case, the precise functional and biological role of H19 remains to be determined.

XIST – X-inactive-specific transcript

The 17 kb lncRNA XIST is arguably an archetype for the study of functional lncRNAs in mammalian cells, having been studied for nearly two decades.
In female cells, the XIST transcript plays a critical role in X-chromosome inactivation by

  • physically coating one of the two X-chromosomes, and is necessary for the
  • cis-inactivation of the over one thousand X-linked genes [75,108-110].

Like the lncRNAs HOTAIR and ANRIL, XIST associates with polycomb-repressor proteins, suggesting

    • a common pathway of inducing silencing utilized by diverse lncRNAs.

Discovery of Molecular Mechanisms of Traditional Chinese Medicinal Formula Si-Wu-Tang Using Gene Expression Microarray and Connectivity Map
by Zhining Wen, Zhijun Wang, Steven Wang, Ranadheer Ravula, Lun Yang, …et al.
PLoS ONE (2011); 6:(3), Publisher: PLoS, Pages: 14    http.//dx.doi.org/10.1371/journal.pone.0018278        PubMed: 21464939
http://dx.plos.org/Wen Z, Wang Z, Wang Z, et al./discovery of molecular mechanisms of traditional chinese medicinal formula…/
To pursue a systematic approach to discovery of mechanisms of action of traditional Chinese medicine (TCM), we used

  • microarrays,
  • bioinformatics and the
  • Connectivity Map (CMAP)
    • to examine TCM-induced changes in gene expression.

We demonstrated that this approach can be used to elucidate new molecular targets using a model TCM herbal formula Si-Wu-Tang (SWT) which is

  • widely used for women’s health.

The human breast cancer MCF-7 cells treated with 0.1 µM estradiol or 2.56 mg/ml of SWT

  • showed dramatic gene expression changes, while
  • no significant change was detected for ferulic acid, a known bioactive compound of SWT.

Pathway analysis using

  • differentially expressed genes related to the treatment effect
  • identified that expression of genes in the nuclear factor erythroid 2-related factor 2 (Nrf2) cytoprotective pathway
  • was most significantly affected by SWT,
    • but not by estradiol or ferulic acid.
  • The Nrf2-regulated genes
    • HMOX1,
    • GCLC,
    • GCLM,
    • SLC7A11 and
    • NQO1 were
  • upreguated by SWT in a dose-dependent manner, which was validated by real-time RT-PCR. Consistently,
  • treatment with SWT and its four herbal ingredients resulted in an 
  • increased antioxidant response element (ARE)-luciferase reporter activity in MCF-7 and HEK293 cells.

Furthermore, the gene expression profile of differentially expressed genes related to SWT treatment was used to compare with those of

  • 1,309 compounds in the CMAP database.

The CMAP profiles of estradiol-treated MCF-7 cells showed an excellent match with SWT treatment,

  • consistent with SWT’s widely claimed use for women’s diseases and indicating a phytoestrogenic effect.

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Author and Curator: Ritu Saxena, Ph.D.

 

Introduction

Nitric oxide (NO) is a lipophilic, highly diffusible and short-lived molecule that acts as a physiological messenger and has been known to regulate a variety of important physiological responses including vasodilation, respiration, cell migration, immune response and apoptosis. Jordi Muntané et al

NO is synthesized by the Nitric Oxide synthase (NOS) enzyme and the enzyme is encoded in three different forms in mammals: neuronal NOS (nNOS or NOS-1), inducible NOS (iNOS or NOS-2), and endothelial NOS (eNOS or NOS-3). The three isoforms, although similar in structure and catalytic function, differ in the way their activity and synthesis in controlled inside a cell. NOS-2, for example is induced in response to inflammatory stimuli, while NOS-1 and NOS-3 are constitutively expressed.

Regulation by Nitric oxide

NO is a versatile signaling molecule and the net effect of NO on gene regulation is variable and ranges from activation to inhibition of transcription.

The intracellular localization is relevant for the activity of NOS. Infact, NOSs are subject to specific targeting to subcellular compartments (plasma membrane, Golgi, cytosol, nucleus and mitochondria) and that this trafficking is crucial for NO production and specific post-translational modifications of target proteins.

Role of Nitric oxide in Cancer

One in four cases of cancer worldwide are a result of chronic inflammation. An inflammatory response causes high levels of activated macrophages. Macrophage activation, in turn, leads to the induction of iNOS gene that results in the generation of large amount of NO. The expression of iNOS induced by inflammatory stimuli coupled with the constitutive expression of nNOS and eNOS may contribute to increased cancer risk. NO can have varied roles in the tumor environment influencing DNA repair, cell cycle, and apoptosis. It can result in antagonistic actions including DNA damage and protection from cytotoxicity, inhibiting and stimulation cell proliferation, and being both anti-apoptotic and pro-apoptotic. Genotoxicity due to high levels of NO could be through direct modification of DNA (nitrosative deamination of nucleic acid bases, transition and/or transversion of nucleic acids, alkylation and DNA strand breakage) and inhibition of DNA repair enzymes (such as alkyltransferase and DNA ligase) through direct or indirect mechanisms. The Multiple actions of NO are probably the result of its chemical (post-translational modifications) and biological heterogeneity (cellular production, consumption and responses). Post-translational modifications of proteins by nitration, nitrosation, phosphorylation, acetylation or polyADP-ribosylation could lead to an increase in the cancer risk. This process can drive carcinogenesis by altering targets and pathways that are crucial for cancer progression much faster than would otherwise occur in healthy tissue.

NO can have several effects even within the tumor microenvironment where it could originate from several cell types including cancer cells, host cells, tumor endothelial cells. Tumor-derived NO could have several functional roles. It can affect cancer progression by augmenting cancer cell proliferation and invasiveness. Infact, it has been proposed that NO promotes tumor growth by regulating blood flow and maintaining the vasodilated tumor microenvironment. NO can stimulate angiogenesis and can also promote metastasis by increasing vascular permeability and upregulating matrix metalloproteinases (MMPs). MMPs have been associated with several functions including cell proliferation, migration, adhesion, differentiation, angiogenesis and so on. Recently, it was reported that metastatic tumor-released NO might impair the immune system, which enables them to escape the immunosurveillance mechanism of cells. Molecular regulation of tumour angiogenesis by nitric oxide.

S-nitrosylation and Cancer

The most prominent and recognized NO reaction with thiols groups of cysteine residues is called S-nitrosylation or S-nitrosation, which leads to the formation of more stable nitrosothiols. High concentrations of intracellular NO can result in high concentrations of S-nitrosylated proteins and dysregulated S-nitrosylation has been implicated in cancer. Oxidative and nitrosative stress is sensed and closely associated with transcriptional regulation of multiple target genes.

Following are a few proteins that are modified via NO and modification of these proteins, in turn, has been known to play direct or indirect roles in cancer.

NO mediated aberrant proteins in Cancer

Bcl2

Bcl-2 is an important anti-apoptotic protein. It works by inhibiting mitochondrial Cytochrome C that is released in response to apoptotic stimuli. In a variety of tumors, Bcl-2 has been shown to be upregulated, and it has additionally been implicated with cancer chemo-resistance through dysregulation of apoptosis. NO exposure causes S-nitrosylation at the two cysteine residues – Cys158 and Cys229 that prevents ubiquitin-proteasomal pathway mediated degradation of the protein. Once prevented from degradation, the protein attenuates its anti-apoptotic effects in cancer progression. The S-nitrosylation based modification of Bcl-2 has been observed to be relevant in drug treatment studies (for eg. Cisplatin). Thus, the impairment of S-nitrosylated Bcl-2 proteins might serve as an effective therapeutic target to decrease cancer-drug resistance.

p53

p53 has been well documented as a tumor suppressor protein and acts as a major player in response to DNA damage and other genomic alterations within the cell. The activation of p53 can lead to cell cycle arrest and DNA repair, however, in case of irrepairable DNA damage, p53 can lead to apoptosis. Nuclear p53 accumulation has been related to NO-mediated anti-tumoral properties. High concentration of NO has been found to cause conformational changes in p53 resulting in biological dysfunction.. In RAW264.7, a murine macrophage cell line, NO donors induce p53 accumulation and apoptosis through JNK-1/2.

HIF-1a

Hypoxia-inducible factor 1 (HIF1) is a heterodimeric transcription factor that is predominantly active under hypoxic conditions because the HIF-1a subunit is rapidly degraded in normoxic conditions by proteasomal degradation. It regulates the transciption of several genes including those involved in angiogenesis, cell cycle, cell metabolism, and apoptosis. Hypoxic conditions within the tumor can lead to overexpression of HIF-1a. Similar to hypoxia-mediated stress, nitrosative stress can stabilize HIF-1a. NO derivatives have also been shown to participate in hypoxia signaling. Resistance to radiotherapy has been traced back to NO-mediated HIF-1a in solid tumors in some cases.

PTEN

Phosphatase and tensin homolog deleted on chromosome ten (PTEN), is again a tumor suppressor protein. It is a phosphatase and has been implicated in many human cancers. PTEN is a crucial negative regulator of PI3K/Akt signaling pathway. Over-activation of PI3K/Akt mediated signaling pathway is known to play a major role in tumorigenesis and angiogenesis. S-nitrosylation of PTEN, that could be a result of NO stress, inhibits PTEN. Inhibition of PTEN phosphatase activity, in turn, leads to promotion of angiogenesis.

C-Src

C-src belongs to the Src family of protein tyrosine kinases and has been implicated in the promotion of cancer cell invasion and metastasis. It was demonstrated that S-nitrosylation of c-Src at cysteine 498 enhanced its kinase activity, thus, resulting in the enhancement of cancer cell invasion and metastasis.

Reference:

Muntané J and la Mata MD. Nitric oxide and cancer. World J Hepatol. 2010 Sep 27;2(9):337-44. http://www.ncbi.nlm.nih.gov/pubmed/21161018

Wang Z. Protein S-nitrosylation and cancer. Cancer Lett. 2012 Jul 28;320(2):123-9. http://www.ncbi.nlm.nih.gov/pubmed/22425962

Ziche M and Morbidelli L. Molecular regulation of tumour angiogenesis by nitric oxide. Eur Cytokine Netw. 2009 Dec;20(4):164-70.http://www.ncbi.nlm.nih.gov/pubmed/20167555

Jaiswal M, et al. Nitric oxide in gastrointestinal epithelial cell carcinogenesis: linking inflammation to oncogenesis. Am J Physiol Gastrointest Liver Physiol. 2001 Sep;281(3):G626-34. http://www.ncbi.nlm.nih.gov/pubmed/11518674

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Reporter: Aviva Lev-Ari, PhD, RN

 

PTEN Mutations as a Cause of Constitutive Insulin Sensitivity and Obesity

Aparna Pal, M.R.C.P., Thomas M. Barber, D.Phil., M.R.C.P., Martijn Van de Bunt, M.D., Simon A. Rudge, Ph.D., Qifeng Zhang, Ph.D., Katherine L. Lachlan, M.R.C.P.C.H., Nicola S. Cooper, M.R.C.P., Helen Linden, M.R.C.P., Jonathan C. Levy, M.D., F.R.C.P., Michael J.O. Wakelam, Ph.D., Lisa Walker, D.Phil., M.R.C.P.C.H., Fredrik Karpe, Ph.D., F.R.C.P., and Anna L. Gloyn, D.Phil.

N Engl J Med 2012; 367:1002-1011  September 13, 2012DOI: 10.1056/NEJMoa1113966

BACKGROUND

Epidemiologic and genetic evidence links type 2 diabetes, obesity, and cancer. The tumor-suppressor phosphatase and tensin homologue (PTEN) has roles in both cellular growth and metabolic signaling. Germline PTEN mutations cause a cancer-predisposition syndrome, providing an opportunity to study the effect of PTENhaploinsufficiency in humans.

METHODS

We measured insulin sensitivity and beta-cell function in 15 PTENmutation carriers and 15 matched controls. Insulin signaling was measured in muscle and adipose-tissue biopsy specimens from 5 mutation carriers and 5 well-matched controls. We also assessed the effect of PTEN haploinsufficiency on obesity by comparing anthropometric indexes between the 15 patients and 2097 controls from a population-based study of healthy adults. Body composition was evaluated by means of dual-emission x-ray absorptiometry and skinfold thickness.

RESULTS

Measures of insulin resistance were lower in the patients with aPTEN mutation than in controls (e.g., mean fasting plasma insulin level, 29 pmol per liter [range, 9 to 99] vs. 74 pmol per liter [range, 22 to 185]; P=0.001). This finding was confirmed with the use of hyperinsulinemic euglycemic clamping, showing a glucose infusion rate among carriers 2 times that among controls (P=0.009). The patients’ insulin sensitivity could be explained by the presence of enhanced insulin signaling through the PI3K-AKT pathway, as evidenced by increased AKT phosphorylation. The PTEN mutation carriers were obese as compared with population-based controls (mean body-mass index [the weight in kilograms divided by the square of the height in meters], 32 [range, 23 to 42] vs. 26 [range, 15 to 48]; P<0.001). This increased body mass in the patients was due to augmented adiposity without corresponding changes in fat distribution.

CONCLUSIONS

PTEN haploinsufficiency is a monogenic cause of profound constitutive insulin sensitization that is apparently obesogenic. We demonstrate an apparently divergent effect of PTEN mutations: increased risks of obesity and cancer but a decreased risk of type 2 diabetes owing to enhanced insulin sensitivity. (Funded by the Wellcome Trust and others.)

Supported by grants from the Wellcome Trust (095101/Z/10Z, to Dr. Gloyn), the Medical Research Council (G0700222, to Dr. Gloyn; and G0800467, to Drs. Pal and Gloyn), the National Institute for Health Research Oxford Biomedical Research Centre (to Drs. Pal, Karpe, and Gloyn), the Biotechnology and Biological Sciences Research Council (to Drs. Rudge, Zhang, and Wakelam), and the European Union Seventh Framework Program LipodomicNet (202272, for adipocyte signaling work, to Drs. Wakelam and Karpe).

Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.

We thank the clinicians Trevor R.P. Cole, Louise Izatt, Carole McKeown, Eamonn R. Maher, and Mary Porteous for referring patients for this study; the research nurses Beryl Barrow and Jane Cheeseman for assistance with collecting clinical data; Amy Barrett for analysis of PTEN expression; Sandy Humphries for analysis of apolipoprotein B; Tim James and colleagues at the John Radcliffe Hospital, Oxford, for analysis of glucose and insulin; the NIHR Cambridge Biomedical Research Centre Core Biochemical Assay Laboratory for analysis of leptin and adiponectin; Leanne Hodson and Barbara Fielding for access to control dual-emission x-ray absorptiometry scans and phenotypic data on postmenopausal controls; and Jonathan Clark and Izabella Niewczas for providing lipid standards for the mass-spectrometry analysis.

SOURCE INFORMATION

From the Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford (A.P., T.M.B., M.V.B., J.C.L., F.K., A.L.G.); the Oxford National Institute for Health Research Biomedical Research Centre (A.P., J.C.L., F.K., A.L.G.) and the Oxford Regional Genetics Centre (H.L., L.W.), Churchill Hospital, Oxford; the Inositide Laboratory, the Babraham Institute, Babraham, Cambridge (S.A.R., Q.Z., M.J.O.W.); Wessex Clinical Genetics Service, University Hospital Southampton, Southampton (K.L.L.); the Department of Human Genetics and Genomic Medicine, Faculty of Medicine, University of Southampton, Southampton (K.L.L.); and West Midlands Regional Clinical Genetics Service, Birmingham Women’s Hospital, Birmingham (N.S.C.) — all in the United Kingdom.

Address reprint requests to Dr. Gloyn at the Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Headington, Oxford OX3 7LE, United Kingdom, or atanna.gloyn@drl.ox.ac.uk.

 Source:

 

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