Hayes S A, Zarnegar M, Sharma M, Yang F, Peehl D M, ten Dijke P, Sun Z
Department of Surgery, Stanford University School of Medicine, California 94303, USA.
Cancer Res. 2001 Mar 1;61(5):2112-8.
The androgen-signaling pathway is important in the growth and progression of prostate cancer. Androgen ablation therapy, which may result in programmed cell death, is often used to treat advanced prostate cancer. The growth-promoting effects of androgen are mediated mostly through the androgen receptor (AR). Transforming growth factor beta (TGF-beta) plays critical roles in controlling prostate cell proliferation, differentiation, and apoptosis. Normal transcripts and proteins of TGF-beta receptors are frequently lost in prostate cancer cells, especially in advanced stages of the disease. However, the mechanisms by which TGF-beta inhibits proliferation and induces apoptosis in prostate cancer cells is not clear. We investigated the molecular mechanism by which TGF-beta inhibits transcriptional activation mediated by AR. Using transient transfection systems, we demonstrated that Smad3 specifically represses transcriptional activation mediated by AR on two natural androgen-responsive promoters. This repression is transmitted through TGF-beta signaling and can be regulated by other Smad proteins. A protein-protein interaction between AR and Smad3 was identified in vitro and in vivo, and the transcription activation domain of AR and the MH2 of Smad3 were identified as being responsible for binding. Additional functional experiments showed that the repression of AR by Smad3 is mediated solely through the MH2 domain. These results provide fresh insight for understanding the mechanism by which TGF-beta regulates the androgen-signaling pathway in prostate cancer cells.
雄激素信号通路在前列腺癌的生长和进展中起着重要作用。雄激素剥夺疗法可能导致程序性细胞死亡，常用于治疗晚期前列腺癌。雄激素的促生长作用主要通过雄激素受体（AR）介导。转化生长因子β（TGF-β）在控制前列腺细胞增殖、分化和凋亡中起关键作用。TGF-β受体的正常转录本和蛋白在前列腺癌细胞中经常缺失，尤其是在疾病的晚期。然而，TGF-β抑制前列腺癌细胞增殖并诱导其凋亡的机制尚不清楚。我们研究了TGF-β抑制AR介导的转录激活的分子机制。利用瞬时转染系统，我们证明Smad3特异性抑制AR在两个天然雄激素反应性启动子上介导的转录激活。这种抑制通过TGF-β信号传导传递，并且可以由其他Smad蛋白调节。在体外和体内鉴定出AR与Smad3之间的蛋白质-蛋白质相互作用，并且确定AR的转录激活结构域和Smad3的MH2负责结合。额外的功能实验表明，Smad3对AR的抑制仅通过MH2结构域介导。这些结果为理解TGF-β调节前列腺癌细胞中雄激素信号通路的机制提供了新的见解。
