Regulation of heterotrimeric G proteins by non-receptor activators

描述(申请人提供)：异三聚体G蛋白是卓越的信号转导分子，促进人类的感觉和生理激素调节。传统的G蛋白信号通路是由细胞表面的G蛋白偶联受体(GPCRs)激活的。最近，异源三聚体G蛋白调节的新机制得到了重视。不是GPCRs的酶通过非传统方式激活G蛋白，并调节以前未归因于G蛋白控制的途径。这些新的G蛋白激活剂的原型是Ric-8蛋白。哺乳动物Ric-8A同源物通过刺激GDP对GTP交换的催化作用来激活G蛋白α亚基。RIC-8蛋白可能调节G蛋白对不对称(成体干细胞)和正常细胞分裂(G蛋白αI)、神经传递(G蛋白αQ)和嗅觉(G蛋白α1)的信号调节。果蝇RIC-8似乎是异源三聚体G蛋白正确表达和质膜定位所必需的，这一发现可能是对发散G蛋白信号通路的这种表面调控的基础。这项建议的目的是详细了解哺乳动物Ric-8同源物(A和B)对G蛋白生理的独特调节。该建议的目的是：(1)验证Ric-8B蛋白作为鸟嘌呤核苷酸交换催化剂激活G蛋白αS亚基的假设，(2)在哺乳动物中验证这一假设，即G蛋白在细胞膜上的定位需要Ric-8蛋白。(3)检验哺乳动物Ric-8A同源物负责激活G蛋白依赖的(不对称)细胞分裂的假设(4)定义G蛋白亚基与Ric-8A或Ric-8B之间真实的细胞相互作用。为定义这些相互作用而开发的技术还将用于发现Ric-8蛋白与G蛋白以外的其他蛋白之间的新相互作用。RIC-8蛋白是一种新的G蛋白激活剂。许多药物通过干预来改变GPCR介导的G蛋白激活过程。阐明Ric-8蛋白调节G蛋白的新机制可能会使在G蛋白的Ric-8激活水平上进行干预的新的治疗方法成为可能。此外，为理解Ric-8和G蛋白控制正常和缺陷干细胞分裂的机制(S)提供基础知识将有助于：(1)干细胞用于修复受损组织的治疗性使用；(2)干细胞衍生癌症的治疗。 公共卫生相关性：异三聚体G蛋白激活是药物干预的主要目标。确定Ric-8蛋白激活G蛋白的独特机制将使设计改变G蛋白激活后果的新疗法成为可能。这项研究还将确定Ric-8对G蛋白导向的干细胞分裂的控制，并为利用干细胞进行组织修复和根除因有缺陷的干细胞分裂而产生的癌症做出贡献。

DESCRIPTION (provided by applicant): Heterotrimeric G proteins are eminent signal transducing molecules that facilitate human sensation and hormone-regulation of physiology. Traditional G protein signaling pathways are activated by the action of G protein coupled receptors (GPCRs) present on the surface of cells. Recently, new mechanisms of heterotrimeric G protein regulation have been appreciated. Enzymes that are not GPCRs activate G proteins by non-traditional means and regulate pathways not previously attributed to G protein control. Prototypes of these new G protein activators are the Ric-8 proteins. The mammalian Ric-8A homolog activates G protein alpha subunits by stimulating catalysis of GDP for GTP exchange. Ric-8 proteins likely modulate G protein signaling regulation of asymmetric (adult stem cell) and normal cell division (G protein alpha i), aspects of neurotransmission (G protein alpha q), and olfaction (G protein alpha olf). Perhaps underlying this seeming regulation of divergent G protein signaling pathways is the finding that Drosophila RIC-8 appears to be required for the proper expression and plasma membrane localization of heterotrimeric G proteins. The goal of this proposal is to understand in detail, the unique regulation of G protein physiology by both mammalian Ric-8 homologs (A and B). The aims of the proposal are to: (1) examine the hypothesis that Ric-8B proteins activate G protein alpha s subunits by serving as guanine nucleotide exchange catalysts, (2) test the hypothesis in mammals, that Ric-8 proteins are required globally for G protein localization at the cell plasma membrane. (3) test the hypothesis that the mammalian Ric-8A homolog is responsible for activating G protein alpha i- dependent (asymmetric) cell division (4) define the authentic cellular interactions between the compendium of G protein subunits and Ric-8A or Ric-8B. The technology developed to define these interactions will also be used to uncover novel interactions between Ric-8 proteins and other proteins in addition to G proteins. Ric-8 proteins are new G protein activators. Many pharmaceuticals intervene to alter the process of GPCR-mediated G protein activation. Elucidation of the novel mechanisms by which Ric-8 proteins regulate G proteins may enable the engineering of new classes of therapeutics that intervene at the level of Ric-8 activation of G proteins. Furthermore, contributing basic knowledge towards understanding the mechanism(s) by which Ric-8 and G proteins control normal and defective stem cell division could profit: (1) the therapeutic use of stem cells to repair damaged tissues and (2) treatment of stem cell derived cancers. PUBLIC HEALTH RELEVANCE: Heterotrimeric G protein activation is a primary target of pharmaceutical intervention. Defining the unique mechanisms by which Ric-8 proteins activate G proteins will enable the design of new classes of therapeutics that alter the consequences of G protein activation. This research will also define Ric-8 control of G protein-directed stem cell division and contribute efforts to use stem cells for tissue repair and the eradication of cancers derived from defectively dividing stem cells.