Sadar M D, Gleave M E
Department of Cancer Endocrinology, British Columbia Cancer Agency, Vancouver, Canada.
Cancer Res. 2000 Oct 15;60(20):5825-31.
Androgens are potent differentiation agents that regulate prostate-specific antigen (PSA) gene expression via the androgen receptor (AR) that binds to androgen response elements (AREs) on the PSA gene to initiate transcription. However, in the absence of androgens, PSA gene expression can become elevated. This suggests that either the AR can be activated in the absence of androgen to elevate PSA gene expression through AREs on the PSA gene or that another transcription factor acting on the PSA promoter is stimulated. We have previously shown in vivo that butyrate, a differentiation agent that causes cell cycle arrest, increases serum PSA levels in castrated animals. Therefore, to determine the mechanism of butyrate induction of PSA, we used the LNCaP human prostate cancer cell line. Northern analyses and transfection experiments using a PSA reporter plasmid demonstrated induction of PSA gene expression by butyrate in LNCaP cells. Application of the antiandrogen bicalutamide blocked the induction of PSA mRNA by butyrate, suggesting a mechanism dependent on the AR. Consistent with this conclusion, electromobility shift assays showed increased AR-ARE complex formation with nuclear extracts from butyrate-treated cells. In addition, other reporter gene constructs that contain AREs were also induced by butyrate. Western blot analysis showed an increase in nuclear levels of AR protein in cells exposed to butyrate, whereas whole cell levels remained unchanged, suggesting that butyrate causes nuclear translocation of the AR. Thus, the differentiation agent butyrate causes ligand-independent activation of the AR to increase expression of the differentiation marker PSA in human prostate cancer cells.
雄激素是强效分化因子，可通过雄激素受体（AR）调节前列腺特异性抗原（PSA）基因的表达，该受体与PSA基因上的雄激素反应元件（ARE）结合以启动转录。然而，在没有雄激素的情况下，PSA基因表达可能会升高。这表明，要么AR可以在没有雄激素的情况下被激活，通过PSA基因上的ARE来提高PSA基因表达，要么作用于PSA启动子的另一种转录因子受到刺激。我们之前在体内研究中发现，丁酸盐作为一种导致细胞周期停滞的分化剂，可使去势动物的血清PSA水平升高。因此，为了确定丁酸盐诱导PSA的机制，我们使用了LNCaP人前列腺癌细胞系。Northern分析和使用PSA报告质粒的转染实验表明，丁酸盐可诱导LNCaP细胞中PSA基因的表达。抗雄激素药物比卡鲁胺的应用可阻断丁酸盐对PSA mRNA的诱导作用，提示其机制依赖于AR。与此结论一致，电泳迁移率变动分析显示，丁酸盐处理细胞的核提取物中AR-ARE复合物的形成增加。此外，其他含有ARE的报告基因构建体也被丁酸盐诱导。蛋白质印迹分析显示，暴露于丁酸盐的细胞中AR蛋白的核水平增加，而全细胞水平保持不变，这表明丁酸盐可导致AR的核转位。因此，分化剂丁酸盐可导致AR的非配体依赖性激活，从而增加人前列腺癌细胞中分化标志物PSA的表达。
