Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
J Biol Chem. 2012 Sep 28;287(40):33594-606. doi: 10.1074/jbc.M112.388298. Epub 2012 Aug 3.
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.
雄激素受体（AR）作为配体依赖性转录因子，在雄激素依赖性和去势抵抗性前列腺癌的发展和进展中发挥关键作用。去势导致前列腺癌细胞缺氧，并且在低血清雄激素水平下通过低氧诱导因子（HIF）-1α模拟去势抵抗阶段增强 AR 的转录活性。然而，HIF-1α对于缺氧激活的 AR 反式激活是必要的，但不是充分的，并且调节去势抵抗性前列腺癌中 AR 功能的分子机制尚不清楚。在这里，我们报告在低雄激素条件下，β-连环蛋白对于缺氧 LNCaP 前列腺癌细胞中 HIF-1α介导的 AR 反式激活是必需的。HIF-1α 和 β-连环蛋白共同增强 AR N 端和 C 端相互作用。在去势小鼠的 LNCaP 异种移植中，HIF-1α 蛋白阳性细胞中β-连环蛋白积累在核内。在 LNCaP 细胞中，当 HIF-1α 被敲低或在细胞质中外源表达时，缺氧诱导的β-连环蛋白核内定位被抑制。β-连环蛋白与 HIF-1α 在核内和细胞质中形成复合物。缺氧增加了由 AR 和 β-连环蛋白组成的复合物的量，并且敲低 HIF-1α 减弱了 AR 和 β-连环蛋白募集到雄激素反应元件（AREs）的雄激素反应基因。此外，在存在雄激素的情况下，HIF-1α 与 β-连环蛋白一起结合到 AREs 上。这些结果表明：（i）HIF-1α 和 β-连环蛋白通过加速 N 端和 C 端相互作用共同增强 AR 反式激活；（ii）HIF-1α 在缺氧时促进β-连环蛋白的核内易位；（iii）AR、HIF-1α 和 β-连环蛋白在 ARE 上形成三元复合物。
