Novel functions of RGS3

描述(申请人提供)：G蛋白信号转导调节蛋白RGS3是一种GTP酶激活蛋白(GAP)，能结合异源三聚体G蛋白的G-α亚基并加速其GTP酶活性。我们和其他人已经证明，通过这个机制，RGS3调节GQ和GI偶联受体对血管紧张素II、内皮素-1、卡巴胆碱、促性腺激素释放激素和鞘氨醇-1磷酸的信号。我们的新数据提示：a)RGS3与以前被认为与G蛋白/RGS轴无关的Smad转录因子--转化生长因子-2信号的转导分子相互作用；b)RGS3抑制Smad介导的基因转录；c)RGS3在T淋巴细胞中大量存在，其在T细胞中的表达被转化生长因子-2进一步诱导。在T细胞中，G蛋白信号与多种趋化因子的迁移有关，而转化生长因子-2信号在多个水平上调控T细胞的增殖和分化。内源性RGS3在T细胞中的功能尚未被研究。根据我们的初步数据，我们假设：(I)RGS3是一种多功能蛋白质，除了调节G蛋白信号外，还调节转化生长因子-2的信号，以及(Ii)内源性RGS3通过调节G蛋白和转化生长因子-2信号来控制T细胞的迁移、增殖和分化。为了验证这些假设，我们提出了三个特定的目标：(I)研究RGS3及其突变体过表达导致RGS3/Smad相互作用的分子性质和功能后果；(Ii)研究内源性RGS3对EL4 T胸腺瘤细胞株G蛋白和转化生长因子-2信号的调节；以及(Iii)利用RGS3基因敲除小鼠的T细胞，研究RGS3如何在转化生长因子-2和趋化因子的作用下控制T细胞的迁移、增殖和分化。这项研究的基本意义在于潜在地发现了RGS3作为转化生长因子-2信号调节因子的一种新的、非规范的功能。这项研究的实际意义在于了解与T细胞免疫反应异常相关的疾病。 公共卫生相关性：适当的T淋巴细胞功能对适应性免疫至关重要，而T细胞功能异常会导致自身免疫和炎症性疾病，如哮喘、多发性硬化症、类风湿性关节炎、I型糖尿病等。因此，明确T细胞活化和分化的分子机制可能有助于更好地理解这些疾病的发病机制。

DESCRIPTION (provided by applicant): Regulator of G protein signaling RGS3 is a GTPase-activating protein (GAP) that binds G-alpha subunits of heterotrimeric G proteins and accelerates their GTPase activity. We and others have shown that through this mechanism, RGS3 regulates the signaling of Gq- and Gi-coupled receptors to angiotensin II, endothelin-1, carbachol, gonadotropin-releasing hormone and sphingosine-1 phosphate. Our new data suggest that a) RGS3 interacts with the transducers of TGF-2 signaling, Smad transcription factors that were previously thought to be unrelated to G protein / RGS axis; b) RGS3 inhibits Smad-mediated gene transcription; and c) RGS3 is abundant in T-lymphocytes and its expression in T cells is further induced by TGF-2 treatment. In T cells, G protein signaling is associated with migration towards various chemokines, whereas TGF-2 signaling controls proliferation and differentiation of T cells at multiple levels. The function of endogenous RGS3 has not been investigated in T cells. Based on our preliminary data, we hypothesize that (i) RGS3 is a multifunctional protein that, in addition to regulating G protein signaling, also modulates the signaling of TGF-2, and (ii) endogenous RGS3 controls T cell migration, proliferation and differentiation through the regulation of both G protein- and TGF-2 signaling. To test these hypotheses, we propose three specific aims: (i) investigate the molecular nature and functional consequences of RGS3 / Smad interaction by overexpression of RGS3 and its mutants, (ii) investigate the regulation of G protein- and TGF-2 signaling by endogenous RGS3 in EL4 T thymoma cell line; and (iii) examine how RGS3 controls T cell migration, proliferation and differentiation in response to TGF-2 and chemokines, using T cells from RGS3-knockout mouse. The fundamental significance of this study relates to a potential discovery of a novel, non-canonical function of RGS3 as a regulator of TGF-2 signaling. The practical importance of this study relates to understanding the diseases associated with abnormal immune responses of T cell. PUBLIC HEALTH RELEVANCE: Appropriate function of T lymphocytes is critical for the adaptive immunity, whereas abnormal function of T cells leads to autoimmune and inflammatory diseases such as asthma, multiple sclerosis, rheumatoid arthritis, type I diabetes and others. Therefore, defining the molecular mechanisms of T cell activation and differentiation may lead to a better understanding the pathogenesis of these diseases.