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各个阶段的前列腺癌生长。然而，通过化学或手术去势来撤除雄激素只会减缓肿瘤进展，因为前列腺癌最终会变得不依赖激素，恢复生长并杀死患者。这表明该过程还涉及其他生长因子。 TGF-β 是少数几类细胞生长内源抑制剂之一。对 TGF-β 反应性的丧失被认为是肿瘤形成的主要因素。在前列腺癌中，TGF-β 通路通常不活跃，并且 TGF-β 受体表达缺失。在我们的初步研究中，我们发现：1）Smad7，一种TGF-β拮抗剂，直接与雄激素受体（AR）相互作用并抑制AR诱导的基因转录。重要的是，Smad7 与组蛋白脱乙酰酶 (HDAC) 进行免疫共沉淀，表明其作为转录阻遏蛋白的潜在作用。 2) 另一种拮抗剂 Smad6 与 Tip6O 和 RIP 140 雄激素受体共激活剂相互作用，并抑制 AR 介导的基因表达。我们的研究结果表明，拮抗剂 Smad 和 AR/共激活剂之间的相互作用是 TGF-β 和雄激素之间的一种新型串扰机制，因为 Smad7 和 Smad6 的表达是由 TGF-β 信号传导开启的。在前列腺癌中，TGF-β信号传导缺陷会导致Smad7和Smad6缺乏，这可能反过来会关闭拮抗剂Smads下调AR增强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 及其共激活剂（如 RIP 140）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 Smad7 与 AR 以及 Smad6 与 AR 共激活剂 RIP140 的相互作用。 2)考察Smad7和Smad6对雄激素诱导的细胞反应的功能。 3)确定Smad7和Smad6诱导AR活性交替的分子机制。 4) 表征 Smad7 和 smad6 对裸鼠前列腺癌进展的影响。我们相信，TGF-β 和雄激素之间的串扰机制的表征将有助于开发基于 TGF-β 的前列腺癌治疗策略，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.