Low Expression of the Androgen-Induced Tumor Suppressor Gene PLZF and Lethal Prostate Cancer.
ABSTRACT: 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: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:A common treatment of advanced prostate cancer involves the deprivation of androgens. Despite the initial response to hormonal therapy, eventually all the patients relapse. In the present study, we sought to determine whether dietary polyunsaturated fatty acid (PUFA) affects the development of castration-resistant prostate cancer. Cell culture, patient tissue microarray, allograft, xenograft, prostate-specific Pten knockout and omega-3 desaturase transgenic mouse models in conjunction with dietary manipulation, gene knockdown and knockout approaches were used to determine the effect of dietary PUFA on castration-resistant Pten-null prostate cancer. We found that deletion of Pten increased androgen receptor (AR) expression and Pten-null prostate cells were castration resistant. Omega-3 PUFA slowed down the growth of castration-resistant tumors as compared with omega-6 PUFA. Omega-3 PUFA decreased AR protein to a similar extent in tumor cell cytosolic and nuclear fractions but had no effect on AR messenger RNA level. Omega-3 PUFA treatment appeared to accelerate AR protein degradation, which could be blocked by proteasome inhibitor MG132. Knockdown of AR significantly slowed down prostate cancer cell proliferation in the absence of androgens. Our data suggest that omega-3 PUFA inhibits castration-resistant prostate cancer in part by accelerating proteasome-dependent degradation of the AR protein. Dietary omega-3 PUFA supplementation in conjunction with androgen ablation may significantly delay the development of castration-resistant prostate cancer in patients compared with androgen ablation alone.
Project description:Studies of ETS-mediated prostate oncogenesis have been hampered by a lack of suitable experimental systems. Here we describe a new conditional mouse model that shows robust, homogenous ERG expression throughout the prostate. When combined with homozygous Pten loss, the mice developed accelerated, highly penetrant invasive prostate cancer. In mouse prostate tissue, ERG markedly increased androgen receptor (AR) binding. Robust ERG-mediated transcriptional changes, observed only in the setting of Pten loss, included the restoration of AR transcriptional output and upregulation of genes involved in cell death, migration, inflammation and angiogenesis. Similarly, ETS variant 1 (ETV1) positively regulated the AR cistrome and transcriptional output in ETV1-translocated, PTEN-deficient human prostate cancer cells. In two large clinical cohorts, expression of ERG and ETV1 correlated with higher AR transcriptional output in PTEN-deficient prostate cancer specimens. We propose that ETS factors cause prostate-specific transformation by altering the AR cistrome, priming the prostate epithelium to respond to aberrant upstream signals such as PTEN loss.
Project description:Overexpression of the histone acetyltransferase p300 is implicated in the proliferation and progression of prostate cancer, but evidence of a causal role is lacking. In this study, we provide genetic evidence that this generic transcriptional coactivator functions as a positive modifier of prostate tumorigenesis. In a mouse model of PTEN deletion-induced prostate cancer, genetic ablation of p300 attenuated expression of the androgen receptor (AR). This finding was confirmed in human prostate cancer cells in which PTEN expression was abolished by RNA interference-mediated attenuation. These results were consistent with clinical evidence that the expression of p300 and AR correlates positively in human prostate cancer specimens. Mechanistically, PTEN inactivation increased AR phosphorylation at serine 81 (Ser81) to promote p300 binding and acetylation of AR, thereby precluding its polyubiquitination and degradation. In support of these findings, in PTEN-deficient prostate cancer in the mouse, we found that p300 was crucial for AR target gene expression. Taken together, our work identifies p300 as a molecular determinant of AR degradation and highlights p300 as a candidate target to manage prostate cancer, especially in cases marked by PTEN loss.
Project description:Alteration of the PTEN/PI3K pathway is associated with late-stage and castrate-resistant prostate cancer (CRPC). However, how PTEN loss is involved in CRPC development is not clear. Here, we show that castration-resistant growth is an intrinsic property of Pten null prostate cancer (CaP) cells, independent of cancer development stage. PTEN loss suppresses androgen-responsive gene expressions by modulating androgen receptor (AR) transcription factor activity. Conditional deletion of Ar in the epithelium promotes the proliferation of Pten null cancer cells, at least in part, by downregulating the androgen-responsive gene Fkbp5 and preventing PHLPP-mediated AKT inhibition. Our findings identify PI3K and AR pathway crosstalk as a mechanism of CRPC development, with potentially important implications for CaP etiology and 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:Androgen receptor (AR) variants are associated with resistance to anti androgen therapy both in human prostate cancer cell lines and clinical samples. These observations support the hypothesis that AR isoform accumulation is a consequence of selective therapeutic pressure on the full length AR. The Pten deficient prostate cancer model proceeds with well-defined kinetics including progression to castration resistant prostate cancer (CRPC). While surgical castration and enzalutamide treatments yield an initial therapeutic response, Pten-/-epithelia continue to proliferate yielding locally invasive primary tumor pathology. That most epithelium remains AR positive, but ligand independent, suggests the presence of oncogenic AR variants. To address this hypothesis, we have used a panel of recently described Pten-/- tumor cell lines derived from both from hormone intact (E4, E8) and castrated Pten mutants (cE1, cE2) followed by RACE PCR to identify and characterize three novel truncated, amino terminus containing AR variants (mAR-Va, b, c). Variants appear not only conserved throughout progression but are correlated with nearly complete loss of full length AR (AR-FL) at castrate androgen levels. The overexpression of variants leads to enhanced transcriptional activity of AR while knock down studies show reduced transcriptional output. Collectively, the identification of truncated AR variants in the conditional PTEN deletion model supports a role for maintaining the CRPC phenotype and provides further therapeutic applications of this preclinical model.
Project description:Prostate cancer is characterized by a dependence upon androgen receptor (AR) signaling, and androgen deprivation therapy (ADT) is the accepted treatment for progressive prostate cancer. Although ADT is usually initially effective, acquired resistance termed castrate-resistant prostate cancer (CRPC) develops. PTEN and TP53 are two of the most commonly deleted or mutated genes in prostate cancer, the compound loss of which is enriched in CRPC. To interrogate the metabolic alterations associated with survival following ADT, we used an orthotopic model of Pten/Tp53 null prostate cancer. Metabolite profiles and associated regulators were compared in tumors from androgen-intact mice and in tumors surviving castration. AR inhibition led to changes in the levels of glycolysis and tricarboxylic acid (TCA) cycle pathway intermediates. As anticipated for inhibitory reciprocal feedback between AR and PI3K/AKT signaling pathways, pAKT levels were increased in androgen-deprived tumors. Elevated mitochondrial hexokinase 2 (HK2) levels and enzyme activities also were observed in androgen-deprived tumors, consistent with pAKT-dependent HK2 protein induction and mitochondrial association. Competitive inhibition of HK2-mitochondrial binding in prostate cancer cells led to decreased viability. These data argue for AKT-associated HK2-mediated metabolic reprogramming and mitochondrial association in PI3K-driven prostate cancer as one survival mechanism downstream of AR inhibition.
Project description:To examine the impact of common somatic mutations in prostate cancer (PCa) on androgen receptor (AR) signaling, mouse models were designed to perturb sequentially the AR, ETV1, and PTEN pathways. Mice with "humanized" AR (hAR) alleles that modified AR transcriptional strength by varying polyglutamine tract (Q-tract) length were crossed with mice expressing a prostate-specific, AR-responsive ETV1 transgene (ETV1(Tg)). While hAR allele did not grossly affect ETV1-induced neoplasia, ETV1 strongly antagonized global AR regulation and repressed critical androgen-induced differentiation and tumor suppressor genes, such as Nkx3-1 and Hoxb13. When Pten was varied to determine its impact on disease progression, mice lacking one Pten allele (Pten(+/-) ) developed more frequent prostatic intraepithelial neoplasia (PIN). Yet, only those with the ETV1 transgene progressed to invasive adenocarcinoma. Furthermore, progression was more frequent with the short Q-tract (stronger) AR, suggesting that the AR, ETV1, and PTEN pathways cooperate in aggressive disease. On the Pten(+/-) background, ETV1 had markedly less effect on AR target genes. However, a strong inflammatory gene expression signature, notably upregulation of Cxcl16, was induced by ETV1. Comparison of mouse and human patient data stratified by the presence of E26 transformation-specific ETS fusion genes highlighted additional factors, some not previously associated with prostate cancer but for which targeted therapies are in development for other diseases. In sum, concerted use of these mouse models illuminates the complex interplay of AR, ETV1, and PTEN pathways in pre-cancerous neoplasia and early tumorigenesis, disease stages difficult to analyze in man.