Jia Li, Coetzee Gerhard A
Department of Urology and Preventive Medicine, Norris Cancer Center, USC Keck School of Medicine, Los Angeles, California 90089, USA.
Cancer Res. 2005 Sep 1;65(17):8003-8. doi: 10.1158/0008-5472.CAN-04-3679.
It is widely suspected that androgen-independent prostate cancer growth depends on androgen receptor signaling via ill-defined mechanisms. Prostate-specific antigen (PSA) expression is often used to measure androgen receptor activity in cells and prostate cancer progression in patients. In the present study, we have compared androgen receptor activity using PSA and human male germ cell-associated kinase (hMAK), as read-outs in androgen-dependent LNCaP and androgen-independent C4-2B cells. As expected, very little PSA and hMAK expression were detected in LNCaP cells in the absence of androgens, whereas substantial expression of PSA was observed only in C4-2B cells under the same conditions. The addition of dihydrotestosterone to the culture medium increased the expression of both genes in both cell types. Comprehensive chromatin immunoprecipitation analysis of the entire PSA locus and an androgen-response element in hMAK unexpectedly revealed that androgen receptor was not occupying any site in the absence of dihydrotestosterone in either cell type. In line with the expression data, and in the absence of dihydrotestosterone, histone acetylation and RNA polymerase II occupancy was substantial at the PSA locus in C4-2B but not in LNCaP cells. In the presence of dihydrotestosterone, androgen receptor was found to occupy mainly the enhancer region of PSA in both cell types, accompanied with increases in histone acetylation and RNA polymerase II occupancy. Although the androgen receptor was not directly involved in the androgen-independent expression of PSA in C4-2B cells, small interfering RNA knock-down of androgen receptor significantly reduced PSA expression in both the presence and absence of dihydrotestosterone. In contrast, hMAK expression was decreased only in the presence of dihydrotestosterone after androgen receptor knock-down. We conclude that androgen-independent expression of PSA in C4-2B cells does not rely on the direct occupancy of the androgen receptor at the PSA locus, but is nevertheless affected indirectly via unknown androgen receptor-dependent mechanism(s) that influence the expression from some but not all androgen receptor target genes.
人们普遍怀疑雄激素非依赖性前列腺癌的生长依赖于雄激素受体信号传导，但其机制尚不明确。前列腺特异性抗原（PSA）的表达常被用于衡量细胞中的雄激素受体活性以及患者前列腺癌的进展情况。在本研究中，我们比较了使用PSA和人类男性生殖细胞相关激酶（hMAK）作为雄激素依赖性LNCaP细胞和雄激素非依赖性C4-2B细胞中雄激素受体活性的读出指标。不出所料，在无雄激素的情况下，LNCaP细胞中几乎检测不到PSA和hMAK表达，而在相同条件下，仅在C4-2B细胞中观察到大量的PSA表达。向培养基中添加二氢睾酮可增加两种细胞类型中这两个基因的表达。对整个PSA基因座和hMAK中的一个雄激素反应元件进行全面的染色质免疫沉淀分析，意外地发现，在无二氢睾酮的情况下，两种细胞类型中的雄激素受体均未占据任何位点。与表达数据一致，在无二氢睾酮的情况下，C4-2B细胞中PSA基因座处的组蛋白乙酰化和RNA聚合酶II占据情况显著，但LNCaP细胞中并非如此。在有二氢睾酮存在的情况下，发现雄激素受体主要占据两种细胞类型中PSA的增强子区域，同时伴随着组蛋白乙酰化和RNA聚合酶II占据情况的增加。尽管雄激素受体不直接参与C4-2B细胞中PSA的雄激素非依赖性表达，但雄激素受体的小干扰RNA敲低在有和无二氢睾酮的情况下均显著降低了PSA表达。相反，雄激素受体敲低后，仅在有二氢睾酮存在时hMAK表达降低。我们得出结论，C4-2B细胞中PSA的雄激素非依赖性表达不依赖于雄激素受体在PSA基因座上的直接占据，但仍然通过未知的雄激素受体依赖性机制受到间接影响，这些机制影响部分而非全部雄激素受体靶基因的表达。
