PTEN功能调节的研究进展

PTEN是具有蛋白与脂质磷酸酯酶活性的双特异性磷酸酯酶,能特异地使磷脂酰肌醇3,4,5三磷酸3′位脱磷酸,抑制PI3K/Akt信号转导途径,从而在细胞的生长、分化、凋亡、迁移等方面起着重要的调控作用。PTEN的异常与多种人类肿瘤如子宫内膜瘤、前列腺癌、乳腺癌等的发生、侵袭及转移密切相关。在细胞中,PTEN功能受到蛋白表达、磷酸化、氧化以及膜定位等因素的调节。该文就PTEN调节的分子机制作一综述。     

Sequence-dependent synergistic inhibition of human glioma cell lines by combined temozolomide and miR-21 inhibitor gene therapy

Down-regulation of microRNA-21 (miR-21) can induce cell apoptosis and reverse drug resistance in cancer treatments. In this study, we explored the most effective schedule of the miR-21 inhibitor (miR-21i) and Temozolomide (TMZ) combined treatment in human glioma cells. Three tumor cell lines, U251 phosphatase and tensin homologue (PTEN) mutant, LN229 (PTEN wild-type), and U87 (PTEN loss of function), were subjected to evaluate the antitumor effects of deigned treatments (a predose of miR-21i for 4/8 h and then a subsequent TMZ treatment, a predose of TMZ for 4/8 h and then a subsequent miR-21i treatment, or a concomitant treatment) in vitro. A synergistic antiproliferative and proapoptotic activity was only obtained in U251 and U87 cells when a predose was administered for 4 h before the treatment of the other therapeutic agent, while the best antitumor effect in LN229 cells was achieved by using the concomitant treatment. Our data indicate that the effect of sequence and timing of administration is dependent on the PTEN status of cell lines. The best suppression effect was achieved by a maximal inhibition of STAT3 and phosphorylated STAT3, in PTEN loss of function cells. Our results reveal that both the sequence and the timing of administration are crucial in glioma combination therapy.     

Advances of AKT pathway in human oncogenesis and as a target for anti-cancer drug discovery

AKT (also known as PKB) plays a central role in a variety of cellular processes including cell growth, motility and survival in both normal and tumor cells. The AKT pathway is also instrumental in epithelial mesenchymal transitions (EMT) and angiogenesis during tumorigenesis. AKT functions as a cardinal nodal point for transducing extracellular (growth factors including insulin, IGF-1 and EGF ) and intracellular (such as mutated/activated receptor tyrosine kinases, PTEN, Ras and Src) signals. It is positively regulated by phosphatidylinositol 3-kinase and inhibited by phosphatase PTEN. Deregulation of the PI3K/PTEN/AKT pathway is one of the most common altered pathways in human malignancy. In the past few years, significant advances have been made in the understanding of AKT signaling in human oncogenesis and the development of small molecule inhibitor of AKT pathway. Here, we will discuss the regulation and function of AKT as well as targeting AKT for anti-cancer drug discovery.     

The complexity of PTEN: mutation, marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-beta regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P(3) to generate PtdIns(4,5)P(2). PTEN serves to counter-balance the effects of phosphoinositide 3' kinase, which normally adds a phosphate to PtdIns(4,5)P(2) to generate PtdIns(3,4,5)P(3). PtdIns(3,4,5)P(3) recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P(3) inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.     

The complexity of PTEN: mutation,marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-β regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P₃ to generate PtdIns(4,5)P₂. PTEN serves to counter-balance the effects of phosphoinositide 3′ kinase, which normally adds a phosphate to PtdIns(4,5)P₂ to generate PtdIns(3,4,5)P₃. PtdIns(3,4,5)P₃ recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P₃ inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.     

Targeting survivin in cancer: the cell-signalling perspective

Survivin, a prominent anticancer target, is ubiquitously expressed in a plethora of cancers and the evolving complexity in functional regulation of survivin is yet to be deciphered. However, pertaining to the recent studies, therapeutic modulation of survivin is critically regulated by interaction with prominent cell-signalling pathways [HIF-1α, HSP90, PI3K/AKT, mTOR, ERK, tumour suppressor genes (p53, PTEN), oncogenes (Bcl-2, Ras)] and a wide range of growth factors (EGFR, VEGF, among others). In our article we discuss, in detail, an overview of the recent developments in the pharmacological modulation of survivin via cell-signalling paradigms and antisurvivin therapeutics, along with an outlook on therapeutic management of survivin in drug-resistant cancers.     

Inhibition of the phosphatase PTEN protects mice against oleic acid-induced acute lung injury

Background and purpose

Injury to the lung parenchyma is a constitutional feature shared by many lung diseases. The protein, phosphatase and tensin homologue deleted on chromosome Ten (PTEN) is a major suppressor of phosphoinositide-3 kinase/Akt signalling, a vital survival pathway in lung parenchymal cells. Based on this, we hypothesized that PTEN inhibition in vivo would enhance cell tolerance to stress thereby preventing acute lung injury.

Experimental approach

We evaluated the ability of a PTEN inhibitor, potassium bisperoxo (1,10-phenanthroline) oxovanadate [bpV(phen)], to prevent acute lung injury induced by oleic acid (OA) in adult C57BL/6 mice. Lung assessments included bronchoalveolar lavage, tissue morphology, immunostaining for markers of cell death, cell identity, phospho-Akt and phospho-ERK levels and oximetry.

Key results

OA induced acute lung injury in a dose- and time-dependent manner. No injury was observed in the vehicle control or bpV(phen) treatment groups. PTEN inhibition by bpV(phen) increased lung tissue levels of phospho-Akt and ERK and but not focal adhesion kinase. This occurred in conjunction with a statistically significant reduction in protein content, lactate dehydrogenase, as well as tumour necrosis factor-α and chemokines in bronchoalveolar lavage fluid when compared with OA treatment alone. The incidence of alveolar lesions, consistent with acute lung injury, and terminal uridine deoxynucleotidyl transferase dUTP nick end labelling (TUNEL)-positive cells was also significantly reduced. Importantly, PTEN suppression maintained pulmonary function.

Conclusions and implications

Treatment with bpV(phen) significantly reduced the severity of acute lung injury in mice indicating that additional investigation is warranted to understand the important role that this phosphatase may play in the lung.     

PTEN: its deregulation and tumorigenesis

The tumor suppressor phosphatase and tensin homolog (PTEN) functions as a phosphoinositide 3-phosphatase, that antagonizes phosphatidylinositol 3-kinase action, and negatively regulates cell proliferation and survival signals. Inactivation of PTEN by loss-of-function mutations gives rise to deregulated hyperproliferation of cells, leading to oncogenic transformation. Recent studies have identified a number of upstream regulatory factors for PTEN and unveiled that the impairment in the PTEN regulatory system potentially becomes a causal factor for oncogenic transformation of cells. This article will review the PTEN inactivation mechanism which is linked to human tumorigenesis, particularly focusing on recent research progress in PTEN regulators.     

Inhibition of endothelial nitric oxide synthase by the lipid phosphatase PTEN

PTEN (phosphatase and tensin homologue deleted on chromosome 10) is a lipid phosphatase that functions as a negative regulator of the phosphoinositide-3-kinase (PI3K) pathway. The present study sought to examine in depth the interaction between PTEN and eNOS activity. Co-expression of eNOS and PTEN in COS-7 cells significantly decreased NO production compared to eNOS alone, while co-expression of eNOS and the dominant negative mutant PTEN(C124A) significantly increased NO production. Upon examination of the putative eNOS phosphorylation sites, phosphorylation of S116, T497, S617, S635 and S1179 was decreased by PTEN co-expression, while the dominant negative PTEN(C124A) produced an increase in phosphorylation of all sites except S116 and S635. A myristoylation-deficient eNOS construct with little dependence on phosphorylation state (G2AeNOS) was not significantly affected by co-expression with either PTEN or PTEN(C124A). Likewise, an eNOS construct with a triple phospho-null mutation (S617A, S635A and S1179A) was also unaffected by co-expression with either PTEN or PTEN(C124A). Purified PTEN or PTEN(C124A) failed to interact with purified eNOS in vitro, arguing against a direct interaction between PTEN and eNOS. When the PTEN constructs were expressed in human aortic endothelial cells (HAECs), PTEN significantly decreased NO production and PTEN(C124A) increased it, and both S617 and S1179 were altered by co-expression with the PTEN constructs. Increased expression of PTEN in endothelial cells did not influence superoxide production. We conclude that PTEN is a regulator of eNOS function both when expressed in COS-7 cells and in human endothelial cells, and does so via its effects on the PI3K/Akt pathway.     

Phosphatase and tensin homolog deleted on chromosome 10 suppression is an important process in peroxisome proliferator-activated receptor-gamma signaling in adipocytes and myotubes

Peroxisome proliferator-activated receptor-gamma (PPARgamma) activation enhances insulin sensitivity in type 2 diabetes mellitus. However, downstream mediators of PPARgamma activation in adipocytes and myotubes, the most important cell types involved in glucose homeostasis, remained unclear. Here we show by using two synthetic PPARgamma agonists (rosiglitazone and KR-62776, a novel PPARgamma agonist) that phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a key downstream mediator of PPARgamma signaling. The PPARgamma agonists down-regulated PTEN expression, resulting in glucose uptake increase in differentiated 3T3-L1 adipocytes and C2C12 skeletal muscle cells. In both cells, PTEN knockdown increased glucose uptake, whereas overexpression abolished the agonist-induced effects. The effects of PPARgamma agonists on PTEN expression and glucose uptake disappeared by pretreatment with a PPARgamma antagonist or by knockdown of PPARgamma expression. In vivo treatment of the agonists to C57BL/6J-ob/ob mice resulted in the reduction of PTEN level in both adipose and skeletal muscle tissues and decreased plasma glucose levels. Thus, these results suggest that PTEN suppression is a key mechanism of the PPARgamma-mediated glucose uptake stimulation in insulin-sensitive cells such as adipocytes and skeletal muscle cells, thereby restoring glucose homeostasis in type 2 diabetes.     

Targeting PDK1 in cancer

Abnormal activation of phosphoinositide 3-kinase (PI3K) signalling is very common in cancer, leading to deregulation of several intracellular processes normally controlled by this enzyme, including cell survival, growth, proliferation and migration. Mutations in the gene encoding the tumour suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN), which leads to uncontrolled activation of the PI3K pathway, are reported in different cancers. Among the downstream effectors of PI3Ks, 3- phosphoinositide-dependent protein kinase 1 (PDK1) and protein kinase B (PKB)/Akt have a key role in several cancer types. More recent data indicate that alteration of PDK1 is a critical component of oncogenic PI3K signalling in breast cancer, suggesting that inhibition of PDK1 can inhibit breast cancer progression. PDK1 has an essential role in regulating cell migration especially in the context of PTEN deficiency. Downregulation of PDK1 levels inhibits migration and experimental metastasis of human breast cancer cells. PDK1 activates a large number of proteins, including Akt, some PKC isoforms, S6K and SGK. Data also reveal that PDK1 is oncogenic and this is dependent on PI3K pathway. Therefore, accumulating evidence demonstrates that PDK1 is a valid therapeutic target and suggests that PDK1 inhibitors may be useful to prevent cancer progression and abnormal tissue dissemination. This review will focus on published data on the role of PDK1 in cancer and approaches used to inhibit PDK1.     

Redox regulation of PTEN by S-nitrosothiols

PTEN (phosphatase with sequence homology to tensin) is a phosphatidylinositol 3,4,5-trisphosphate phosphatase that regulates many cellular processes. Activity of the enzyme is dependent on the redox state of the active site cysteine such that oxidation by H2O2 leads to inhibition. Because S-nitrosothiols are known to modify enzymes containing reactive cysteines, we hypothesized that S-nitrosothiols would oxidize PTEN and inhibit its phosphatase activity. In the present study, we show that S-nitrosocysteine (CSNO), S-nitrosoglutathione (GSNO), and S-nitroso-N-acetylpenicillamine (SNAP) reversibly oxidized recombinant PTEN. In addition, CSNO led to concentration- and time-dependent oxidation of endogenous cellular PTEN. However, in contrast, GSNO and SNAP were effective only when coincubated with cysteine, suggesting that these nitrosothiols must react with cysteine to form CSNO, which can be transferred across cell membranes. Oxidation of cellular PTEN resulted from thiol modification and led to reversible inhibition of phosphatase activity. Although oxidation of PTEN by H2O2 led to formation of an intramolecular disulfide, oxidation of PTEN by CSNO seemed to lead to formation of a mixed disulfide. Glutathionylation of cellular proteins by incubating cells with diamide or incubating cellular extracts with GSSG oxidized PTEN in a manner similar to that of CSNO. Overall, these data demonstrate for the first time that S-nitrosothiols oxidatively modify PTEN, leading to reversible inhibition of its phosphatase activity, and suggest that the oxidized species is a mixed disulfide.     

Cancer risk following growth hormone use in childhood: implications for current practice.

The therapeutic use of growth hormone (GH) has caused concern, as it is anabolic and mitogenic, and its effector hormone, insulin-like growth factor (IGF)-I is anti-apoptotic. As both hormones can cause proliferation of normal and malignant cells, the possibility that GH therapy may induce cancer, increase the risk of tumour recurrence in those previously treated for a malignancy, or increase the risk of cancer in those with a predisposition, has resulted in concerns over its use. There are theoretical and epidemiological reasons that suggest GH and IGF-I may be important in tumour formation and proliferation. Malignant tumours have been induced in animals exposed to supraphysiological doses of GH, whereas hypophysectomy appears to protect animals from carcinogen-induced neoplasms. In vitro, proliferation and transformation of normal haemopoetic and leukaemic cells occurs with supraphysiological doses of GH, but not with physiological levels. IGF, IGF binding proteins (IGFBP) and IGFBP proteases influence the proliferation of cancer cells in vitro; however, GH is probably not involved in this process. Epidemiological studies have suggested an association between levels of IGF-I and cancer, and an inverse relationship between IGFBP-3 and cancer; however, these associations have been inconsistent. A number of studies have been undertaken to determine the risk of the development of cancer in children treated with GH, either de novo, or the recurrence of cancer in those previously treated for a malignancy. Despite early concerns following a report of a cluster of cases of leukaemia in recipients of GH, there appears to be no increased risk for the development of leukaemia in those treated with GH unless there is an underlying predisposition. Even in children with a primary diagnosis of cancer, subsequent GH use does not appear to increase the risk of tumour recurrence. However, a recent follow-up of pituitary GH recipients has suggested an increase in colorectal cancer. In addition, follow-up of oncology patients has suggested an increase in second neoplasms in those who also received GH therapy. These studies emphasise the importance of continued surveillance both internationally with established databases and also nationally through single-centre studies.     

Exosomal miR-9 Released from HIV Tat Stimulated Astrocytes Mediates Microglial Migration

Chronic neuroinflammation still remains a common underlying feature of HIV-infected patients on combined anti-retroviral therapy (cART). Previous studies have reported that despite near complete suppression of virus replication by cART, cytotoxic viral proteins such as HIV trans-activating regulatory protein (Tat) continue to persist in tissues such as the brain and the lymph nodes, thereby contributing, in part, to chronic glial activation observed in HIV-associated neurological disorders (HAND). Understanding how the glial cells cross talk to mediate neuropathology is thus of paramount importance. MicroRNAs (miR) also known as regulators of gene expression, have emerged as key paracrine signaling mediators that regulate disease pathogenesis and cellular crosstalk, through their transfer via the extracellular vesicles (EV). In the current study we have identified a novel function of miR-9, that of mediating microglial migration. We demonstrate that miR-9 released from Tat-stimulated astrocytes can be taken up by microglia resulting in their migratory phenotype. Exposure of human astrocytoma (A172) cells to HIV Tat resulted in induction and release of miR-9 in the EVs, which, was taken up by microglia, leading in turn, increased migration of the latter cells, a process that could be blocked by both an exosome inhibitor GW4869 or a specific target protector of miR-9. Furthermore, it was also demonstrated that EV miR-9 mediated inhibition of the expression of target PTEN, via its binding to the 3’UTR seed sequence of the PTEN mRNA, was critical for microglial migration. To validate the role of miR-9 in this process, microglial cells were treated with EVs loaded with miR-9, which resulted in significant downregulation of PTEN expression with a concomitant increase in microglial migration. These findings were corroborated by transfecting microglia with a specific target protector of PTEN, that blocked miR-9-mediated downregulation of PTEN as well as microglial migration. In vivo studies wherein the miR-9 precursor-transduced microglia were transplanted into the striatum of mice, followed by assessing their migration in response to a stimulus administered distally, further validated the role of miR-9 in mediating microglial migration. Collectively, our findings provide evidence that glial crosstalk via miRs released from EVs play a vital role in mediating disease pathogenesis and could provide new avenues for development of novel therapeutic strategies aimed at dampening neuropathogenesis.     

Treatment of PTEN-Null Breast Cancer by a Synthetic Lethal Approach Involving PARP1 Gene Silencing

The loss of the phosphatase and tensin homolog (PTEN) deleted from chromosome 10 is frequently observed in a variety of human cancers and appears to be an ideal target in synthetic lethality–based treatment. In this study, the synthetic lethal interaction between PTEN loss and the gene silencing of poly [ADP-ribose] polymerase 1 (PARP1) was examined in human triple-negative breast cancer cells (PTEN-null MDA-MB-468 and PTEN-positive MDA-MB-231 cells). Polycation liposomes previously developed by us were employed to deliver the small interfering ribonucleic acid (siRNA) targeted toward PARP1 (siPARP1) into the cancer cells. The silencing of the PARP1 gene exerted a cytocidal effect on the MDA-MB-468 cells but had no effect on the MDA-MB-231 cells and the human umbilical vein endothelial cells employed as normal cells. The simultaneous knockdown of PARP1 and PTEN in the MDA-MB-231 cells resulted in the significant inhibition of cell growth. The data suggest that the effects of the PARP1 knockdown on the cells were dependent on the PTEN status. A significant increase in the DNA breaks and the extent of apoptosis, possibly due to the failure of DNA repair, was observed upon PARP1 knockdown in the MDA-MB-468 cells compared with the case in the MDA-MB-231 cells. Our findings suggest that the synthetic lethal approach via PARP1 gene silencing holds promise for the treatment of patients with PTEN-null breast cancer.     

抑癌基因PTEN与肿瘤血管生成研究进展

PTEN是具有磷酸脂酶活性的抑癌基因,是双特异蛋白磷酸酶家族(DSPs)的成员,同时具有脂质磷酸酶和蛋白酪氨酸磷酸酶活性。而在肿瘤增殖,侵袭,迁移的过程中,肿瘤血管生成作为肿瘤发生发展中一个关键因素已越来越受到人们的关注。抑癌基因PTEN可以参与PI3K/Akt信号通路,调控缺氧诱导因子1,基质金属蛋白酶,血管内皮生长因子,钠氢交换调控因子1等血管生成相关信号以及一些机体氧化产物来影响肿瘤血管生成。根据近年来PTEN基因与肿瘤血管生成关系最新研究信息,该文综述了其目前的研究现状。     

Tumour re-differentiation effect of retinoic acid: a novel therapeutic approach for advanced thyroid cancer

Although well-differentiated thyroid carcinomas are usually curable by the combined effects of surgery, radioiodine ablation and thyroid stimulating hormone (TSH) suppressive therapy, recurrence develops in 20-40% of patients. During tumour progression, cellular de-differentiation occurs in up to 30% of cases and is usually accompanied by more aggressive growth, metastasis spread and loss of iodide uptake. The therapeutic options for de-differentiated thyroid cancer are limited and generally not efficient. Retinoic acids (RA) are biologically active metabolites of vitamin A that regulate growth and differentiation of many cell types, by binding to specific nuclear receptors: the retinoic acid receptors (RAR) and the retinoid X receptors (RXR). Recent studies have shown that RA can induce in vitro re-differentiation of thyroid carcinoma cell lines, as suggested by increased expression of the sodium/iodide symporter (NIS), type I iodothyronine deiodinase, alkaline phosphatase and by the increment of cellular (131)I uptake. In addition to re-differentiating effects, RA also exert anti-proliferative actions, as the inhibition of mitosis and the induction of apoptosis. Previous clinical studies have shown that iodide uptake may be re-stimulated after RA in about 20-50% of patients with radioiodine non-responsive thyroid carcinoma. Longer follow-up of patients demonstrated that, besides iodide uptake increment, RA can induce tumour regression or at least tumour growth stabilisation. The therapy is generally well tolerated and the most frequent side effects are dryness of skin and mucosa, and hypertriglyceridemia. This paper describes the recent advances in the field of thyroid cancer therapy and reviews the use of RA as a promising novel therapeutic tool.     

Multiple mechanisms underlie metastasis suppressor function of NM23-H1 in melanoma

nm23-h1 was the first metastasis suppressor gene to be identified in humans, with early studies demonstrating its ability to inhibit the metastatic potential of breast carcinoma and melanoma cell lines. This report outlines recent findings from our laboratory indicating that the metastasis suppressor function of NM23-H1 in human melanoma involves a spectrum of molecular mechanisms. Analysis of NM23-H1-dependent profiles of gene expression in human melanoma cell lines has identified a host of target genes that appear to mediate suppression of directional motility. Of particular interest is a subset of motility-suppressing genes whose regulation by NM23-H1 is independent of its known kinase and 3??C5?? exonuclease activities. In parallel, we have recently observed that NM23-H1 expression appears to be required for genomic stability and for optimal repair of DNA damage produced by ultraviolet radiation and other agents. Thus, NM23-H1 might oppose not only the motile and invasive characteristics of metastatic cells but also the acquisition of mutations that drive malignant progression to the metastatic phenotype itself.