Hsp70 Binds to the Androgen Receptor N-terminal Domain and Modulates the Receptor Function in Prostate Cancer Cells

The androgen receptor (AR) is a key driver and therapeutic target in androgen-sensitive prostate cancer, castration resistant prostate cancer (CRPC), and CRPC resistant to abiraterone and enzalutamide, two second generation inhibitors of AR signaling. Since current AR inhibitors target a functioning C-terminal ligand binding domain (LBD), the identification and characterization of co-factors interacting with the N-terminal domain (NTD) of AR may lead to new approaches to target AR signaling in CRPC. Using a pulldown approach coupled with proteomics, we have identified Hsp70 as a co-factor for the NTD of AR in prostate cancer cells. Hsp70 inhibition using siRNA or small molecules indicated that Hsp70 played an important role in the expression and transactivation of endogenous AR. Prostate specific antigen (PSA) promoter/enhancer-driven luciferase assays showed that Hsp70 was also required for transactivation of AR mutant lacking LBD. Furthermore, clonogenic assays showed that an Hsp70 inhibitor, either alone or in synergy with enzalutamide, can inhibit the proliferation of 22Rv1, a widely-used enzalutamide-resistant CRPC prostate cancer cell line. These findings suggest that Hsp70 is a potential therapeutic target for the treatment of enzalutamide-resistant CRPC.