Yang X, Chen M-W, Terry S, Vacherot F, Bemis D L, Capodice J, Kitajewski J, de la Taille A, Benson M C, Guo Y, Buttyan R
Department of Urology, Columbia University Medical Center, New York, NY 10032, USA.
Oncogene. 2006 Jun 8;25(24):3436-44. doi: 10.1038/sj.onc.1209366. Epub 2006 Feb 13.
beta-Catenin, a component of the Wnt signaling pathway, is a coactivator of human androgen receptor (hAR) transcriptional activity. Here, we show that Wnt signaling also influences androgen-mediated signaling through its ability to regulate hAR mRNA and protein in prostate cancer (PCa) cells. Three functional LEF-1/TCF binding sites lie within the promoter of the hAR gene as shown by CHIP assays that captured beta-catenin-bound chromatin from Wnt-activated LNCaP cells. Chimeric reporter vectors that use the hAR gene promoter to drive luciferase expression confirmed that these LEF-1/TCF binding elements are able to confer robust upregulation of luciferase expression when stimulated by Wnt-1 or by transfection with beta-catenin and that dominant-negative TCF or mutations within the dominant TCF-binding element abrogated the response. Semi-quantitative and real time RT-PCR assays confirmed that Wnt activation upregulates hAR mRNA in PCa cells. In contrast, hAR protein expression was strongly suppressed by Wnt activation. The reduction of hAR protein is consistent with evidence that Wnt signaling increased phosphorylation of Akt and its downstream target, MDM2 that promotes degradation of hAR protein through a proteasomal pathway. These data indicate that the hAR gene is a direct target of LEF-1/TCF transcriptional regulation in PCa cells but also show that the expression of the hAR protein is suppressed by a degradation pathway regulated by cross-talk of Wnt to Akt that is likely mediated by Wnt-directed degradation of the B regulatory subunit of protein phosphatase, PP2A.
β-连环蛋白是Wnt信号通路的一个组成部分，是人类雄激素受体（hAR）转录活性的共激活因子。在此，我们表明Wnt信号通路还通过调节前列腺癌细胞（PCa）中hAR的mRNA和蛋白质，影响雄激素介导的信号传导。如染色质免疫沉淀（CHIP）分析所示，hAR基因启动子内有三个功能性淋巴样增强因子1（LEF-1）/T细胞因子（TCF）结合位点，该分析从Wnt激活的LNCaP细胞中捕获了与β-连环蛋白结合的染色质。使用hAR基因启动子驱动荧光素酶表达的嵌合报告载体证实，当受到Wnt-1刺激或转染β-连环蛋白时，这些LEF-1/TCF结合元件能够使荧光素酶表达强烈上调，而显性负性TCF或显性TCF结合元件内的突变则消除了这种反应。半定量和实时逆转录-聚合酶链反应（RT-PCR）分析证实，Wnt激活可上调PCa细胞中hAR的mRNA。相反，Wnt激活强烈抑制hAR蛋白表达。hAR蛋白的减少与以下证据一致：Wnt信号通路增加了蛋白激酶B（Akt）及其下游靶点小鼠双微体2（MDM2）的磷酸化，MDM2通过蛋白酶体途径促进hAR蛋白的降解。这些数据表明，hAR基因是PCa细胞中LEF-1/TCF转录调控的直接靶点，但也表明hAR蛋白的表达受到Wnt与Akt相互作用调节的降解途径的抑制，这种相互作用可能是由Wnt介导的蛋白磷酸酶2A（PP2A）的B调节亚基的降解所介导的。
