Department of Urology, University of Michigan Comprehensive Cancer Center, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS One. 2011;6(9):e25187. doi: 10.1371/journal.pone.0025187. Epub 2011 Sep 26.
Although androgen receptor (AR) function has been extensively studied, regulation of the AR gene itself has been much less characterized. In this study, we observed a dramatic reduction in the expression of androgen receptor mRNA and protein in hyperproliferative prostate epithelium of keratin 5 promoter driven E2F1 transgenic mice. To confirm an inhibitory function for E2F1 on AR transcription, we showed that E2F1 inhibited the transcription of endogenous AR mRNA, subsequent AR protein, and AR promoter activity in both human and mouse epithelial cells. E2F1 also inhibited androgen-stimulated activation of two AR target gene promoters. To elucidate the molecular mechanism of E2F-mediated inhibition of AR, we evaluated the effects of two functional E2F1 mutants on AR promoter activity and found that the transactivation domain appears to mediate E2F1 repression of the AR promoter. Because DNMT1 is a functional intermediate of E2F1 we examined DNMT1 function in AR repression. Repression of endogenous AR in normal human prostate epithelial cells was relieved by DNMT1 shRNA knock down. DNMT1 was shown to be physically associated within the AR minimal promoter located 22 bps from the transcription start site; however, methylation remained unchanged at the promoter regardless of DNMT1 expression. Taken together, our results suggest that DNMT1 operates either as a functional intermediary or in cooperation with E2F1 inhibiting AR gene expression in a methylation independent manner.
尽管雄激素受体 (AR) 的功能已得到广泛研究，但 AR 基因本身的调控却知之甚少。在这项研究中，我们观察到在角化细胞 5 启动子驱动的 E2F1 转基因小鼠过度增殖的前列腺上皮细胞中，雄激素受体 mRNA 和蛋白的表达明显减少。为了证实 E2F1 对 AR 转录的抑制作用，我们表明 E2F1 抑制了人源和鼠源上皮细胞中内源性 AR mRNA、随后的 AR 蛋白和 AR 启动子活性的转录。E2F1 还抑制了雄激素刺激的两个 AR 靶基因启动子的激活。为了阐明 E2F 介导的 AR 抑制的分子机制，我们评估了两个功能性 E2F1 突变体对 AR 启动子活性的影响，发现转录激活结构域似乎介导了 E2F1 对 AR 启动子的抑制。因为 DNMT1 是 E2F1 的一个功能性中间产物，我们研究了 DNMT1 在 AR 抑制中的功能。正常人类前列腺上皮细胞中内源性 AR 的抑制作用通过 DNMT1 shRNA 敲低得到缓解。DNMT1 被证明与转录起始位点 22 个碱基对处的 AR 最小启动子内物理相关；然而，无论 DNMT1 的表达如何，启动子处的甲基化保持不变。总之，我们的结果表明，DNMT1 作为一种功能性中间物或与 E2F1 合作，以不依赖甲基化的方式抑制 AR 基因表达。
