REGULATION OF ACTIVIN FUNCTION BY SMAD7

激活素是细胞因子的TGF-β超家族的成员，并且表现出多种多样的生物活性。 激活素功能调控的研究不仅对了解激活素的生理活性具有重要意义，而且有助于在激活素功能修饰对患者有益的情况下进一步研究其潜在的临床应用。 我们的初步研究表明，Smad 7是一个新的细胞内调节激活素信号。 本研究的目的是探讨Smad 7调控激活素活性的分子机制以及Smad 7在转录水平上的表达调控。 本研究的主要目的是：（1）研究Smad 7调控激活素信号通路的分子机制。 我们将确定Smad 7与激活素I型受体ALK-4的相互作用是否是Smad 7抑制活性所必需的。我们将使用一系列Smad 7和ALK-4的结构突变体来确定这两种蛋白的相互作用结构域。此外，我们将研究Smad 7/ALK-4相互作用的调节激活素I型受体的磷酸化。(2)确定Smad 7对激活素介导的抗增殖活性的调节作用。 我们将使用肝细胞和前列腺癌细胞作为模型系统，以确定Smad 7对这些细胞中激活素的生长抑制活性的调节作用。 我们将确定激活素介导的细胞周期控制机制的调节机制。 然后，我们将确定Smad 7的异位表达是否能够调节激活素对这些细胞的调节作用。(3)研究激活素信号对Smad 7转录的调控。 我们将确定在这些细胞中激活素是否上调Smad 7 mRNA。如果激活素能够在转录水平上调节Smad 7的表达，我们将表征Smad 7的启动子，并确定启动子内介导激活素反应的DNA元件。总之，这些研究将在细胞和分子水平上提供关于Smad 7对激活素功能的调节作用的有价值的信息。

Activin is a member of the TGF-beta superfamily of cytokines and exhibits a large variety of biological activities. Studies on the regulation of activin function are not only important for understanding the physiological activities of activin, but also helpful for future research on potential clinical application when modification of activin function is beneficial to the patient. Our preliminary studies showed that Smad7 is a novel intracellular regulator of activin signaling. The objective of this proposal is to determine the molecular mechanisms underlying the regulation of activin activity by Smad7 and the regulation of Smad7 expression at the transcriptional level. We will pursue the following specific aims: (1) To characterize the molecular mechanism by which Smad7 regulates activin signaling. We will determine if the interaction of Smad7 with activin type I receptor ALK-4 is required for the inhibitory activity of Smad7. We will use a series of structural mutants of Smad7 and ALK-4 to determine the interaction domains of these two proteins. Furthermore, we will examine the regulation of Smad7/ALK-4 interaction by the phosphorylation of the activin type I receptor. (2) To determine the regulatory effect of Smad7 on activin-mediated anti-proliferative activity. We will use hepatocytes and prostate cancer cells as a model system to determine the regulatory effect of Smad7 on the growth-inhibitory activity of activin in these cells. We will determine the mechanism underlying the activin-mediated regulation of cell cycle control machinery. We will then determine if ectopic expression of Smad7 is able to modulate this regulatory role of activin on these cells. (3) To determine the regulation of Smad7 transcription by activin signaling. We will determine if Smad7 mRNA is upregulated by activin in these cells. If activin were able to regulate Smad7 expression at the transcriptional level, we will characterize the promoter of Smad7 and identify the DNA element within the promoter that mediates the activin response. In conclusion, these studies would provide valuable information on the regulatory effect Smad7 on activin function at both the cellular and molecular levels.