PLZF mediates the PTEN/AKT/FOXO3a signaling in suppression of prostate tumorigenesis.
ABSTRACT: Promyelocytic leukemia zinc finger (PLZF) protein expression is closely related to the progression of human cancers, including prostate cancer (PCa). However, the according context of a signaling pathway for PLZF to suppress prostate tumorigenesis remains greatly unknown. Here we report that PLZF is a downstream mediator of the PTEN signaling pathway in PCa. We found that PLZF expression is closely correlated with PTEN expression in a cohort of prostate cancer specimens. Interestingly, both PTEN rescue and phosphoinositide 3-kinase (PI3K) inhibitor LY294002 treatment increase the PLZF expression in prostate cancer cell lines. Further, luciferase reporter assay and chromatin immunoprecipitation assay demonstrate that FOXO3a, a transcriptional factor phosphorylated by PI3K/AKT, could directly bind to the promoter of PLZF gene. These results indicate that PTEN regulates PLZF expression by AKT/FOXO3a. Moreover, our animal experiments also demonstrate that PLZF is capable of inhibiting prostate tumorigenesis in vivo. Taken together, our study defines a PTEN/PLZF pathway and would shed new lights for developing therapeutic strategy of prostate cancer.
Project description:BACKGROUND:4%-9% of prostate cancers harbor homozygous deletions of the androgen-induced tumor suppressor gene, promyelocytic leukemia zinc finger (PLZF, ZBTB16). PLZF loss induces an in vitro phenotype of castration resistance and enzalutamide resistance. The association of low expression of PLZF and clinical outcomes is unclear. METHODS:We assessed PLZF mRNA expression in patients diagnosed with primary prostate cancer during prospective follow-up of the Health Professionals Follow-up Study (HPFS; n = 254) and the Physicians' Health Study (PHS; n = 150), as well as in The Cancer Genome Atlas (n = 333). We measured PTEN status (using copy numbers and IHC) and transcriptional activation of the MAPK pathway. Patients from HPFS and PHS were followed for metastases and prostate cancer-specific mortality (median, 15.3 years; 113 lethal events). RESULTS:PLZF mRNA expression was lower in tumors with PLZF deletions. There was a strong, positive association between intratumoral androgen receptor (AR) signaling and PLZF expression. PLZF expression was also lower in tumors with PTEN loss. Low PLZF expression was associated with higher MAPK signaling. Patients in the lowest quartile of PLZF expression compared with those in the highest quartile were more likely to develop lethal prostate cancer, independent of clinicopathologic features, Gleason score, and AR signaling (odds ratio, 3.17; 95% confidence interval, 1.32-7.60). CONCLUSIONS:Low expression of the tumor suppressor gene PLZF is associated with a worse prognosis in primary prostate cancer. IMPACT:Suppression of PLZF as a consequence of androgen deprivation may be undesirable. PLZF should be tested as a predictive marker for resistance to androgen deprivation therapy.
Project description:PLZF is a transcription repressor, which plays a critical role in development, spermatogenesis and oncogenesis. Down-regulation of PLZF has been found in various tumor cell lines. There has been virtually no tissue study on the expression of PLZF in prostate cancer (PCa). PCa is a heterogeneous disease, most of which are indolent and non-lethal. Currently there are no biomarkers that distinguish indolent from aggressive PCa; therefore there is an urgent need for such markers to provide clinical decision support. This study aimed to investigate the expression of PLZF by immunohistochemistry in different grade as well as metastatic PCa and to correlate the alteration of PLZF expression with PCa aggressiveness. We studied a total of 83 primary PCa from biopsies, 43 metastatic PCa and 8 paired primary and metastatic PCa from radical prostatectomies with lymph node dissection. Our results demonstrated that PLZF was strongly expressed in almost all (~100%) benign luminal cells (n=77) and low grade (Gleason pattern 3) PCa (n=70) and weak or absent (100%) in basal cells (n=70). Decreased or lost expression of PLZF was evidenced in 26% of high-grade (Gleason 4 and 5) primary PCa (n=70) and 84% metastatic PCa (n=43). The primary high grade PCa in the prostatectomies shared similar PLZF loss/decrease and histomorphology to that of paired parallel lymph node metastases. These data demonstrated that down-regulation of PLZF is an important molecular process for tumor progression and loss of PLZF expression detected by routine immunohistochemistry is a promising and valuable biomarker for PCa aggressiveness and metastasis in the personalized care of PCa.
Project description:Growth factor receptor-binding protein 10 (GRB10) is a well-known adaptor protein and a recently identified substrate of the mammalian target of rapamycin (mTOR). Depletion of GRB10 increases insulin sensitivity and overexpression suppresses PI3K/Akt signaling. Because the major reason for the limited efficacy of PI3K/Akt-targeted therapies in prostate cancer (PCa) is loss of mTOR-regulated feedback suppression, it is therefore important to assess the functional importance and regulation of GRB10 under these conditions. On the basis of these background observations, we explored the status and functional impact of GRB10 in PCa and found maximum expression in phosphatase and tensin homolog (PTEN)-deficient PCa. In human PCa samples, GRB10 inversely correlated with PTEN and positively correlated with pAKT levels. Knockdown of GRB10 in nontumorigenic PTEN null mouse embryonic fibroblasts and tumorigenic PCa cell lines reduced Akt phosphorylation and selectively activated a panel of receptor tyrosine kinases. Similarly, overexpression of GRB10 in PTEN wild-type PCa cell lines accelerated tumorigenesis and induced Akt phosphorylation. In PTEN wild-type PCa, GRB10 overexpression promoted mediated PTEN interaction and degradation. PI3K (but not mTOR) inhibitors reduced GRB10 expression, suggesting primarily PI3K-driven regulation of GRB10. In summary, our results suggest that GRB10 acts as a major downstream effector of PI3K and has tumor-promoting effects in prostate cancer.-Khan, M. I., Al Johani, A., Hamid, A., Ateeq, B., Manzar, N., Adhami, V. M., Lall, R. K., Rath, S., Sechi, M., Siddiqui, I. A., Choudhry, H., Zamzami, M. A., Havighurst, T. C., Huang, W., Ntambi, J. M., Mukhtar, H. Proproliferatve function of adaptor protein GRB10 in prostate carcinoma.
Project description:Pten plays a crucial role in the stem cell maintenance in a few organs. Pten defect also causes the premature oocytes and ovary aging. We and other groups have found that the phosphatidylinositol-3-OH kinase (PI3K)-Akt signaling regulates the proliferation and differentiation of spermatogonial stem cells (SSCs). PTEN functions as a negative regulator of the PI3K pathway. Thus, we thought that the fate of SSCs might be controlled by Pten.We report that promyelocytic leukaemia zinc finger (PLZF) and undifferentiated embryonic cell transcription factor 1 (UTF1), both of which are germ cell-specific transcriptional factors, are regulated by Pten. Conditional deletion of Pten leads to reduction in PLZF expression but induction of UTF1, which is associated with SSCs depletion and infertility in males with age.Our data demonstrate that Pten is required for the long-term maintenance of SSCs and precise regulation of spermatogenesis in mouse. The finding of a Pten-regulated GFRα1(+)/PLZF(-)/UTF1(+) progenitor population provides a new insight into the precise mechanisms controlling SSC fate.
Project description:Prostate carcinogenesis involves alterations in several signaling pathways, the most prominent being the PI3K/AKT pathway. This pathway is constitutively active and drives prostate cancer (PCa) progression to advanced metastatic disease. PTEN, a critical tumor and metastasis suppressor gene negatively regulates cell survival, proliferation, migration and angiogenesis via the PI3K/Akt pathway. PTEN is mutated, downregulated/dysfunctional in many cancers and its dysregulation correlates with poor prognosis in PCa. Here, we demonstrate that microRNA-4534 (miR-4534) is overexpressed in PCa and show that miR-4534 is hypermethylated in normal tissues and cell lines compared to PCa tissues/cells. miR-4534 exerts its oncogenic effects partly by downregulating the tumor suppressor PTEN gene. Knockdown of miR-4534 impaired cell proliferation, migration/invasion and induced G0/G1 cell cycle arrest and apoptosis in PCa. Suppression of miR-4534 and its effects on tumor growth was confirmed in a xenograft mouse model. We performed parallel experiments in non-cancer RWPE1 cells by overexpessing miR-4534 followed by functional assays. Overexpression of miR-4534 induced pro-cancerous characteristics in this non-cancer cell line. Statistical analyses revealed that miR-4534 has potential to independently distinguish malignant from normal tissues and positively correlated with poor overall and PSA recurrence free survival. Taken together, our results show that depletion of miR-4534 in PCa induces a tumor suppressor phenotype partly through induction of PTEN. These results have important implications for identifying and defining the role of new PTEN regulators such as microRNAs in prostate tumorigenesis. Understanding aberrantly overexpressed miR-4534 and its downregulation of PTEN will provide mechanistic insight and therapeutic targets for PCa therapy.
Project description:The androgen receptor (AR) and the phosphoinositide 3-kinase (PI3K)/protein kinase B/mammalian target of rapamycin (mTOR) signaling are two of the major proliferative pathways in a number of tissues and are the main therapeutic targets in various disorders, including prostate cancer (PCa). Previous work has shown that there is reciprocal feedback regulation of PI3K and AR signaling in PCa, suggesting that cotargeting both pathways may enhance therapeutic efficacy. Here we show that proteins encoded by two androgen-regulated genes, kallikrein related peptidase 4 (KLK4) and promyelocytic leukemia zinc finger (PLZF), integrate optimal functioning of AR and mTOR signaling in PCa cells. KLK4 interacts with PLZF and decreases its stability. PLZF in turn interacts with AR and inhibits its function as a transcription factor. PLZF also activates expression of regulated in development and DNA damage responses 1, an inhibitor of mTORC1. Thus, a unique molecular switch is generated that regulates both AR and PI3K signaling. Consistently, KLK4 knockdown results in a significant decline in PCa cell proliferation in vitro and in vivo, decreases anchorage-independent growth, induces apoptosis, and dramatically sensitizes PCa cells to apoptosis-inducing agents. Furthermore, in vivo nanoliposomal KLK4 siRNA delivery in mice bearing PCa tumors results in profound remission. These results demonstrate that the activities of AR and mTOR pathways are maintained by KLK4, which may thus be a viable target for therapy.
Project description:Although prostate cancer is clinically manageable during the early stages of progression, metastatic progression severely compromises the prognosis and leads to mortality. Constitutive activation of STAT3 has been connected to prostate cancer malignancy, and abolishing the STAT3 activity may diminish tumor growth and metastasis. However, its suppressor genes and pathways have not been well established. In this study, we show that promyelocytic leukemia zinc finger (PLZF) has a putative tumor-suppressor function in prostate cancer by inhibiting phosphorylation of STAT3. Compared with a benign prostate, high-grade prostate cancer patient tissue was negatively correlated with PLZF expression. PLZF depletion accelerated proliferation and survival, migration, and invasion in human prostate cancer cells. Mechanistically, we demonstrated a novel role of PLZF as the transcriptional regulator of the tyrosine phosphatase SHP-1 that inhibits the oncogenic JAKs-STAT3 pathway. These results suggest that the collapse of PLZF expression by the CCL3 derived from fibroblasts accelerates the cell migration and invasion properties of prostate cancer cells. Our results suggest that increasing PLZF could be an attractive strategy for suppressing prostate cancer metastasis as well as for tumor growth.
Project description:PTEN is frequently mutated in prostate cancer. The tumor suppressor function of PTEN is attributed to its lipid phosphatase activity that counters PI3K action. Here, we report a PTEN-ARID4B-PI3K axis in which PTEN inhibits expression of ARID4B, while ARID4B is a transcriptional activator of the PI3K subunit genes PIK3CA and PIK3R2 that are crucial for activation of the PI3K/AKT pathway. Reciprocal binding of ARID4B and histone H1 to the PIK3CA and PIK3R2 promoters modulates chromatin condensation, suggesting a mechanism by which ARID4B activates these promoters. Functional analyses reveals that ARID4B is required for prostate tumorigenesis when PTEN is deficient. The biological significance is further substantiated by the existence of a PTEN/ARID4B/PIK3CA three-gene signature that improves the predictive power for prostate cancer recurrence in patients. In summary, we identify ARID4B as a master regulator in the PTEN-PI3K pathway, thus providing a potential therapeutic target for prostate cancer carrying PTEN mutations.
Project description:Whole-exome sequencing of metastatic castration-resistant prostate cancer (mCRPC) reveals that 5% to 7% of tumors harbor promyelocytic leukemia zinc finger (PLZF) protein homozygous deletions. PLZF is a canonical androgen-regulated putative tumor suppressor gene whose expression is inhibited by androgen deprivation therapy (ADT). Here, we demonstrate that knockdown of PLZF expression promotes a CRPC and enzalutamide-resistant phenotype in prostate cancer cells. Reintroduction of PLZF expression is sufficient to reverse androgen-independent growth mediated by PLZF depletion. PLZF loss enhances CRPC tumor growth in a xenograft model. Bioinformatic analysis of the PLZF cistrome shows that PLZF negatively regulates multiple pathways, including the MAPK pathway. Accordingly, our data support an oncogenic program activated by ADT. This acquired mechanism together with the finding of genetic loss in CRPC implicates PLZF inactivation as a mechanism promoting ADT resistance and the CRPC phenotype.
Project description:<b>Rationale:</b> The overall success rate of prostate cancer (PCa) diagnosis and therapy has been improved over the years. However, genomic and phenotypic heterogeneity remains a major challenge for effective detection and treatment of PCa. Efforts to better classify PCa into functional subtypes and elucidate the molecular mechanisms underlying prostate tumorigenesis and therapy resistance are warranted for further improvement of PCa outcomes. <b>Methods:</b> We generated <i>Cre</i> <sup>+</sup>;<i>Runx2-</i>cTg;<i>Pten</i> <sup>p/+</sup> (<i>Runx2-Pten</i> double mutant) mice by crossbreeding <i>Cre</i> <sup>+</sup>;<i>Runx2-</i>cTg males with <i>Pten</i> conditional (<i>Pten</i> <sup>p/p</sup>) females. By using Hematoxylin and Eosin (H&E) staining, SMA and Masson's Trichrome staining, we investigated the effect of PTEN haploinsufficiency in combination with Runx2 overexpression on prostate tumorigenesis. Moreover, we employed immunohistochemistry (IHC) to stain Ki67 for cell proliferation, cleaved caspase 3 for apoptosis and AKT phosphorylation for signaling pathway in prostate tissues. Chromatin immunoprecipitation coupled quantitative PCR (ChIP-qPCR), reverse transcription coupled quantitative PCR (RT-qPCR), western blot (WB) analyses and immunofluorescence (IF) were conducted to determine the underlying mechanism by which RUNX2 regulates CXCR7 and AKT phosphorylation in PCa cells. <b>Results:</b> We demonstrated that mice with prostate-specific <i>Pten</i> heterozygous deletion and <i>Runx2</i> overexpression developed high-grade prostatic intraepithelial neoplasia (HGPIN) and cancerous lesions at age younger than one year, with concomitant high level expression of Akt phosphorylation and the chemokine receptor Cxcr7 in malignant glands. RUNX2 overexpression induced CXCR7 transcription and membrane location and AKT phosphorylation in PTEN-deficient human PCa cell lines. Increased expression of RUNX2 also promoted growth of PCa cells and this effect was largely mediated by CXCR7. CXCR7 expression also positively correlated with AKT phosphorylation in PCa patient specimens. <b>Conclusions:</b> Our results reveal a previously unidentified cooperative role of RUNX2 overexpression and PTEN haploinsufficiency in prostate tumorigenesis, suggesting that the defined RUNX2-CXCR7-AKT axis can be a viable target for effective treatment of PCa.