Smad6/7 as Sex Steroid Hormone Receptor Corepressors

描述（由申请人提供）：去势和抗雄激素已用于预防所有阶段的前列腺癌生长。然而，通过化学或手术去势的雄激素戒断只能减缓肿瘤进展，因为前列腺癌最终变得不依赖于肿瘤，恢复生长并杀死患者。这表明其他生长因子也参与了这一过程。TGF-β是少数几类内源性细胞生长抑制剂之一。对TGF-β的反应性丧失被认为是肿瘤形成的主要因素。在前列腺癌中，TGF-β途径通常无活性，TGF-β受体表达丧失。我们的初步研究发现：1）TGF-β拮抗剂Smad 7直接与雄激素受体（AR）相互作用，抑制AR诱导的基因转录。重要的是，Smad 7与组蛋白去乙酰化酶（HDAC）免疫共沉淀，表明其作为转录抑制因子的潜在作用。2)另一种拮抗剂Smad 6与Tip 6 O和RIP 140雄激素受体共激活剂相互作用，也抑制AR介导的基因表达。我们的研究结果表明，拮抗剂Smads和AR/共激活剂之间的相互作用作为一种新的串扰TGF-β和雄激素之间的机制，因为Smad 7和Smad 6的表达打开TGF-β信号。在前列腺癌中，TGF-β信号传导缺陷导致Smad 7和Smad 6两者的缺陷，这可能反过来关闭拮抗剂Smads下调AR增强的基因表达和前列腺细胞增殖的能力。因此，我们假设拮抗剂Smads与AR及其共激活因子如RIP 140的相互作用调节AR转录活性并抑制AR诱导的前列腺细胞生长。串扰机制的表征将有助于理解TGF-β介导的前列腺癌生长抑制。我们将追求以下具体目标：1）表征Smad 7与AR以及Smad 6与AR辅激活因子RIP 140的相互作用。2)检测Smad 7和Smad 6在雄激素诱导的细胞反应中的功能。3)确定Smad 7和Smad 6诱导AR活性改变的分子机制。4)在裸鼠中表征Smad 7和Smad 6对前列腺癌进展的作用。我们相信，TGF-β和雄激素之间的串扰机制的表征将使得能够开发用于治疗前列腺癌的基于TGF-β的治疗策略，并改善前列腺患者的抗雄激素治疗。

DESCRIPTION (provided by applicant): Castration and antiandrogens have been used to prevent prostate cancer growth at all stages. However, androgen withdrawal by chemical or surgical castration only slows tumor progression as prostate cancer eventually becomes hormone-independent, resumes growth and kills the patient. This suggests other growth factors are involved in the process. TGF-beta is one of few classes of endogenous inhibitors of cell growth. Loss of responsiveness to TGF-beta is believed to be a major factor in tumor formation. In prostate cancer, the TGF-beta pathway is often inactive with loss expression of TGF-beta receptor. In our preliminary studies, we find that: 1) Smad7, a TGF-beta antagonist, directly interacts with androgen receptor (AR) and inhibits AR-induced gene transcription. Importantly, Smad7 was immunocoprecipitated with histone deacetylase (HDAC), indicating its potential role as a transcription repressor. 2) Smad6, the other antagonist, interacts with Tip6O and RIP 140 androgen receptor coactivators and also inhibits AR-mediated gene expression. Our findings suggest the interaction between antagonist Smads and AR/coactivators serve as a novel cross-talk mechanism between TGF-beta and androgen, since expression of Smad7 and Smad6 are turned on by TGF-beta signaling. In prostate cancers, defect TGF-beta signaling results in deficiency of both Smad7 and Smad6, which may in turn shut down the antagonist Smads capability in down-regulating AR-enhanced gene expression and prostate cell proliferation. Therefore, we hypothesize that the interaction of antagonist Smads with AR and its coactivators such as RIP 140, regulates AR transcription activity and inhibits AR-induced prostate cell growth. Characterization of the cross-talk mechanisms will be helpful in understanding TGF-beta mediated inhibition of prostate cancer growth. We will pursue the following specific aims:1) Characterize the interactions of Smad7 with AR and Smad6 with an AR coactivator, RIP140. 2) Examine function of Smad7and Smad6 on androgen-induced cellular response. 3) Determine the molecular mechanism underlying Smad7 and Smad6 induced alternation of AR activity. 4) Characterize the effects Smad7 and smad6 on prostate cancer progression in nude mice. We believe that characterization of the cross-talk mechanism between TGF-beta and androgen would enable development of a TGF-beta based therapeutic strategy for the treatment of prostate cancer and improve anti-androgen treatment for prostate patients.