Abstract 1069: Vav3 enhances androgen receptor splice variant activity and is critical for castration resistant prostate cancer growth and survival.

Abstract

Abstract Advanced or metastatic prostate cancer is treated by androgen deprivation; however, patients inevitably relapse with castration resistant prostate cancer (CRPC) that grows independently of androgen. However, CRPC remains dependent on androgen receptor (AR) signaling, which includes 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 as compared to benign tissue as well as in pre–clinical models of CRPC. Vav3 confers castration–resistant growth to androgen–dependent human prostate cancer cells and increased expression has been linked to increased clinical biochemical relapse. 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. Furthermore, Vav3 enhanced AR splice variant activity through a distinctly different mechanism than Vav3 coactivation of full length AR. Vav3 knockdown resulted in lowered nuclear AR3 levels while total AR3 protein and mRNA levels remained static. Conversely, overexpression of Vav3 resulted in increased nuclear AR3. Co–immunoprecipitation 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. Citation Format: Stephanie Peacock, Cale D. Fahrenholtz, Kerry L. Burnstein. Vav3 enhances androgen receptor splice variant activity and is critical for castration resistant prostate cancer growth and survival. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1069. doi:10.1158/1538-7445.AM2013-1069