RhoGDIα Downregulates Androgen Receptor Signaling in Prostate Cancer Cells

INTRODUCTIONTreatment of primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state due to aberrant activation of androgen receptor (AR). Understanding the mechanisms leading to the aberrant activation of AR is critical to develop effective therapy. We have previously identified Rho GDP Dissociation Inhibitor alpha (GDI) as a novel suppressor in prostate cancer. In this study, we examine the effect of GDI on AR signaling in prostate cancer cells. METHODSGDI was transiently or stably transfected into several prostate cancer cell lines including LNCaP, C4-2, CWR22Rv1, and DU145. The regulation of AR expression by GDI was analyzed by qRT-PCR and Western blot. AR activity was measured by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Immunofluorescence assay was performed to study AR nuclear translocation. The interaction between GDI and AR was examined by co-immunoprecipitation assays. RESULTSIn this study, we have identified GDI as a negative regulator of AR signaling pathway. Overexpression of GDI downregulates AR expression at both mRNA and protein levels. Overexpression of GDI is able to prevent AR nuclear translocation and inhibit transactivation of AR target genes. Co-immunoprecipitation assays showed that GDI physically interacts with the N-terminal domain of AR. CONCLUSIONSGDI suppresses AR signaling through inhibition of AR expression, nuclear translocation, and recruitment to androgen-responsive genes. GDI regulatory pathway may play a critical role in regulating AR signaling and prostate cancer growth and progression. Prostate 73: 1614-1622, 2013. (c) 2013 Wiley Periodicals, Inc.