Coordinated action of hypoxia-inducible factor-1α and β-catenin in androgen receptor signaling.

The androgen receptor (AR) acts as a ligand-dependent transcriptional factor and plays a critical role in the development and progression of androgen-dependent and castration-resistant prostate cancer. Castration results in hypoxia in prostate cancer cells, and hypoxia enhances transcriptional activity of AR through hypoxia-inducible factor (HIF)-1α at low serum androgen levels mimicking the castration-resistant stage. However, HIF-1α is necessary but not sufficient for hypoxia-activated AR transactivation, and the molecular mechanism that regulates AR function in castration-resistant prostate cancer remains unclear. Here, we report that β-catenin is required for HIF-1α-mediated AR transactivation in hypoxic LNCaP prostate cancer cells under low androgen conditions. HIF-1α and β-catenin coordinately enhanced AR N-terminal and C-terminal interaction. β-Catenin accumulated in the nucleus in the HIF-1α protein-positive cells of LNCaP xenografts in castrated mice. In LNCaP cells, when HIF-1α was knocked down or was exogenously expressed in the cytoplasm, hypoxia-induced nuclear localization of β-catenin was inhibited. β-Catenin formed a complex with HIF-1α both in the nucleus and in the cytoplasm. Hypoxia increased the amount of a complex composed of AR and β-catenin, and knockdown of HIF-1α attenuated the recruitment of AR and β-catenin to the androgen response elements (AREs) of androgen-responsive genes. Furthermore, together with β-catenin, HIF-1α bound to the AREs in the presence of androgen. These results demonstrate that (i) HIF-1α and β-catenin coordinately enhance AR transactivation by accelerating N-terminal and C-terminal interaction; (ii) HIF-1α promotes nuclear translocation of β-catenin in hypoxia; and (iii) AR, HIF-1α, and β-catenin form a ternary complex on AREs.