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Vav3 enhances androgen receptor splice variant activity and is critical for castration-resistant prostate cancer growth and survival.

ABSTRACT: Advanced or metastatic prostate cancer is treated by androgen deprivation; however, patients inevitably relapse with castration-resistant prostate cancer (CRPC). CRPC remains dependent on androgen receptor (AR) signaling, which may include constitutive, ligand-independent action of naturally occurring AR splice variants. For example, the AR splice variant AR3 (also termed AR-V7) is expressed in CRPC and is linked to poor prognosis. Vav3, a Rho GTPase guanine nucleotide exchange factor, is an AR coactivator that is up-regulated in human prostate cancer compared with benign tissue and in preclinical models of CRPC. Vav3 confers castration-resistant growth to androgen-dependent human prostate cancer cells. Despite the importance of AR coactivators in promoting CRPC, the potential role of these regulatory proteins in modulating AR splice variant activity is unknown. We examined the contributions of Vav3 to AR activity in two CRPC cell lines that naturally express relatively high levels of Vav3 and AR3. Vav3 or AR3 knockdown greatly attenuated cell proliferation, soft agar growth, and ligand-independent AR activity. Vav3 potently enhanced the transcriptional activity of AR3 and another clinically relevant AR splice variant, ARv567es. Vav3 knockdown resulted in lowered nuclear AR3 levels, whereas total AR3 levels remained similar. Conversely, overexpression of Vav3 resulted in increased nuclear AR3. Coimmunoprecipitation revealed that AR3 and Vav3 interact. These novel data demonstrating physical and functional interactions between Vav3, a unique AR coactivator, and an AR splice variant provide insights into the mechanisms by which Vav3 exploits and enhances AR signaling in the progression to CRPC.

SUBMITTER: Peacock SO

PROVIDER: S-EPMC3517715 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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Vav3 enhances androgen receptor splice variant activity and is critical for castration-resistant prostate cancer growth and survival.

Peacock Stephanie O SO Fahrenholtz Cale D CD Burnstein Kerry L KL

Molecular endocrinology (Baltimore, Md.) 20120928 12

Advanced or metastatic prostate cancer is treated by androgen deprivation; however, patients inevitably relapse with castration-resistant prostate cancer (CRPC). CRPC remains dependent on androgen receptor (AR) signaling, which may include constitutive, ligand-independent action of naturally occurring AR splice variants. For example, the AR splice variant AR3 (also termed AR-V7) is expressed in CRPC and is linked to poor prognosis. Vav3, a Rho GTPase guanine nucleotide exchange factor, is an AR ...[more]

PMID: 23023561

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Project description:ImportanceWe previously showed that detection of androgen receptor splice variant 7 (AR-V7) in circulating tumor cells (CTCs) from men with castration-resistant prostate cancer (CRPC) was associated with primary resistance to enzalutamide and abiraterone therapy, but the relevance of AR-V7 status in the context of chemotherapy is unknown.ObjectiveTo investigate whether AR-V7-positive patients would retain sensitivity to taxane chemotherapy and whether AR-V7 status would have a differential impact on taxane-treated men compared with enzalutamide- or abiraterone-treated men.Design, setting, and participantsWe examined CTCs for AR-V7 mRNA using a reverse-transcription polymerase chain reaction assay. From January 2013 to July 2014, we prospectively enrolled patients with metastatic CRPC initiating taxane chemotherapy (docetaxel or cabazitaxel) at a single academic institution (Johns Hopkins). Our prespecified statistical plan required a sample size of 36 taxane-treated men.Main outcomes and measuresWe evaluated associations between AR-V7 status and prostate-specific antigen (PSA) response rates, PSA progression-free survival (PSA PFS), and clinical and/or radiographic progression-free survival (PFS). After incorporating updated data from our prior study of 62 patients treated with enzalutamide or abiraterone, we also investigated the interaction between AR-V7 status (positive or negative) and treatment type (taxane vs enzalutamide or abiraterone).ResultsOf 37 taxane-treated patients enrolled, 17 (46%) had detectable AR-V7 in CTCs. Prostate-specific antigen responses were achieved in both AR-V7-positive and AR-V7-negative men (41% vs 65%; P = .19). Similarly, PSA PFS (hazard ratio [HR], 1.7, 95% CI, 0.6-5.0; P = .32) and PFS (HR, 2.7, 95% CI, 0.8-8.8; P = .11) were comparable in AR-V7-positive and AR-V7-negative patients. A significant interaction was observed between AR-V7 status and treatment type (P < .001). Clinical outcomes were superior with taxanes compared with enzalutamide or abiraterone therapy in AR-V7-positive men, whereas outcomes did not differ by treatment type in AR-V7-negative men. In AR-V7-positive patients, PSA responses were higher in taxane-treated vs enzalutamide- or abiraterone-treated men (41% vs 0%; P < .001), and PSA PFS and PFS were significantly longer in taxane-treated men (HR, 0.19 [95% CI, 0.07-0.52] for PSA PFS, P = .001; HR, 0.21 [95% CI, 0.07-0.59] for PFS, P = .003).Conclusions and relevanceDetection of AR-V7 in CTCs from men with metastatic CRPC is not associated with primary resistance to taxane chemotherapy. In AR-V7-positive men, taxanes appear to be more efficacious than enzalutamide or abiraterone therapy, whereas in AR-V7-negative men, taxanes and enzalutamide or abiraterone may have comparable efficacy. Circulating tumor cell-based AR-V7 detection may serve as a treatment selection biomarker in CRPC.

Project description:BACKGROUND:Liquid biopsies have demonstrated that the constitutively active androgen receptor splice variant-7 (AR-V7) associates with reduced response and overall survival from endocrine therapies in castration-resistant prostate cancer (CRPC). However, these studies provide little information pertaining to AR-V7 expression in prostate cancer (PC) tissue. METHODS:Following generation and validation of a potentially novel AR-V7 antibody for IHC, AR-V7 protein expression was determined for 358 primary prostate samples and 293 metastatic biopsies. Associations with disease progression, full-length androgen receptor (AR-FL) expression, response to therapy, and gene expression were determined. RESULTS:We demonstrated that AR-V7 protein is rarely expressed (<1%) in primary PC but is frequently detected (75% of cases) following androgen deprivation therapy, with further significant (P = 0.020) increase in expression following abiraterone acetate or enzalutamide therapy. In CRPC, AR-V7 expression is predominantly (94% of cases) nuclear and correlates with AR-FL expression (P ? 0.001) and AR copy number (P = 0.026). However, dissociation of expression was observed, suggesting that mRNA splicing remains crucial for AR-V7 generation. AR-V7 expression was heterogeneous between different metastases from a patient, although AR-V7 expression was similar within a metastasis. Moreover, AR-V7 expression correlated with a unique 59-gene signature in CRPC, including HOXB13, a critical coregulator of AR-V7 function. Finally, AR-V7-negative disease associated with better prostate-specific antigen (PSA) responses (100% vs. 54%, P = 0.03) and overall survival (74.3 vs. 25.2 months, hazard ratio 0.23 [0.07-0.79], P = 0.02) from endocrine therapies (pre-chemotherapy). CONCLUSION:This study provides impetus to develop therapies that abrogate AR-V7 signaling to improve our understanding of AR-V7 biology and to confirm the clinical significance of AR-V7. FUNDING:Work at the University of Washington and in the Plymate and Nelson laboratories is supported by the Department of Defense Prostate Cancer Research Program (W81XWH-14-2-0183, W81XWH-12-PCRP-TIA, W81XWH-15-1-0430, and W81XWH-13-2-0070), the Pacific Northwest Prostate Cancer SPORE (P50CA97186), the Institute for Prostate Cancer Research, the Veterans Affairs Research Program, the NIH/National Cancer Institute (P01CA163227), and the Prostate Cancer Foundation. Work in the de Bono laboratory was supported by funding from the Movember Foundation/Prostate Cancer UK (CEO13-2-002), the US Department of Defense (W81XWH-13-2-0093), the Prostate Cancer Foundation (20131017 and 20131017-1), Stand Up To Cancer (SU2C-AACR-DT0712), Cancer Research UK (CRM108X-A25144), and the UK Department of Health through an Experimental Cancer Medicine Centre grant (ECMC-CRM064X).

Dataset Information

Vav3 enhances androgen receptor splice variant activity and is critical for castration-resistant prostate cancer growth and survival.

Publications

Vav3 enhances androgen receptor splice variant activity and is critical for castration-resistant prostate cancer growth and survival.

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