[Show abstract][Hide abstract] ABSTRACT: Metastatic prostate cancers generally rely on androgen receptor (AR) signaling for growth and survival, even following systemic androgen deprivation therapy (ADT). However, recent evidence suggests that some advanced prostate cancers escape ADT by utilizing signaling pro-grams and growth factors that bypass canonical AR ligand-mediated mechanisms. We utilized an in vitro high-throughput RNAi screen to identify pathways in androgen-dependent prostate cancer cell lines whose loss of function promotes androgen ligand-independent growth. We identified 40 genes where knockdown promoted proliferation of both LNCaP and VCaP prostate cancer cells in the absence of androgen. Of these, 14 were down-regulated in primary and metastatic prostate cancer, including two subunits of the protein phosphatase 2 (PP2A) holoen-zyme complex: PPP2R1A, a structural subunit with known tumor-suppressor properties in sev-eral tumor types; and PPP2R2C, a PP2A substrate-binding regulatory subunit that has not been previously identified as a tumor suppressor. We demonstrate that loss of PPP2R2C promotes androgen ligand depletion-resistant prostate cancer growth without altering AR expression or canonical AR-regulated gene expression. Furthermore, cell proliferation induced by PPP2R2C loss was not inhibited by the AR antagonist MDV3100, indicating that PPP2R2C loss may pro-mote growth independently of known AR-mediated transcriptional programs. Immunohisto-chemical analysis of PPP2R2C protein levels in primary prostate tumors determined that low PPP2R2C expression significantly associated with an increased likelihood of cancer recurrence and cancer-specific mortality. These findings provide insights into mechanisms by which pros-tate cancers resist AR-pathway suppression, and support inhibiting PPP2R2C complexes or the growth pathway(s) activated by PPP2R2C as a therapeutic strategy.
Molecular Cancer Research 03/2013; · 4.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Continued androgen receptor (AR) signaling is an established mechanism underlying castration-resistant prostate cancer (CRPC), and suppression of androgen receptor signaling remains a therapeutic goal of CRPC therapy. Constitutively active androgen receptor splice variants (AR-Vs) lack the androgen receptor ligand-binding domain (AR-LBD), the intended target of androgen deprivation therapies including CRPC therapies such as abiraterone and MDV3100. While the canonical full-length androgen receptor (AR-FL) and AR-Vs are both increased in CRPCs, their expression regulation, associated transcriptional programs, and functional relationships have not been dissected. In this study, we show that suppression of ligand-mediated AR-FL signaling by targeting AR-LBD leads to increased AR-V expression in two cell line models of CRPCs. Importantly, treatment-induced AR-Vs activated a distinct expression signature enriched for cell-cycle genes without requiring the presence of AR-FL. Conversely, activation of AR-FL signaling suppressed the AR-Vs signature and activated expression programs mainly associated with macromolecular synthesis, metabolism, and differentiation. In prostate cancer cells and CRPC xenografts treated with MDV3100 or abiraterone, increased expression of two constitutively active AR-Vs, AR-V7 and ARV567ES, but not AR-FL, paralleled increased expression of the androgen receptor-driven cell-cycle gene UBE2C. Expression of AR-V7, but not AR-FL, was positively correlated with UBE2C in clinical CRPC specimens. Together, our findings support an adaptive shift toward AR-V-mediated signaling in a subset of CRPC tumors as the AR-LBD is rendered inactive, suggesting an important mechanism contributing to drug resistance to CRPC therapy.
Cancer Research 06/2012; 72(14):3457-62. · 9.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The review highlights recently discovered mechanisms that sustain castration-resistant prostate cancer (CRPC) growth and describes advances in CRPC therapeutics.
Recent reports have shed new light on the molecular processes underlying CRPC survival during androgen deprivation therapy (ADT). This study summarizes recent findings and comments on their clinical relevance. Included in this review is a discussion on molecular mechanisms that regulate androgen receptor (AR) signaling in normal prostate epithelium and CRPC, biologically significant differences in the androgen-regulated transcriptional programs of androgen-dependent prostate cancer and CRPC, and recent discoveries involving de-novo androgen production and transport. We review the status and results of current clinical trials and finally, discuss the implications of evidence suggesting a declining importance of AR signaling in prostate cancers with PTEN loss.
Advances in the understanding of AR signaling in CRPC have identified novel drug targets and improved the rational design of targeted therapy, while illuminating a subset of prostate cancers that may progress to become completely independent of the AR signaling program.
Current opinion in oncology 02/2012; 24(3):251-7. · 4.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Merkel cell polyomavirus (MCV or MCPyV) is a recently discovered human polyomavirus that is implicated in the pathogenesis of Merkel cell carcinoma (MCC). Although the transmission route for MCV is not yet known, other polyomaviruses, such as BKV, cause non-malignant pathology in the urinary tract. Like MCC, prostate cancer predominantly affects the elderly. Furthermore, prostate cancers and premalignant precursors exhibit chronic inflammation, which suggests a possible infectious involvement. We therefore examined whether MCV might participate in the pathogenesis of prostate cancer.
To determine the presence of MCV RNA in prostate cancer and surrounding stroma or normal prostate tissue.
RNA was extracted from 28 patient-matched cancerous and 28 benign prostate epithelial samples, and six additional cancer-adjacent stromal samples. All tissues were laser-capture micro-dissected. DNA and RNA from a sequence-verified MCV-containing MCC tumor served as a positive control. Quantitative reverse-transcription PCR was used to assess the presence or absence of MCV T antigen transcript.
No MCV T antigen was detected in prostate carcinomas, patient-matched benign samples, or tumor-adjacent stroma, with appropriate sensitivity of the assay demonstrated by an MCC tumor.
MCV infection appears unlikely to be a significant factor in prostate carcinogenesis and there is no evidence of the prostate serving as a reservoir for MCV.
Journal of clinical virology: the official publication of the Pan American Society for Clinical Virology 02/2009; 44(2):164-6. · 3.12 Impact Factor