Regulation of heterotrimeric G proteins by non-receptor activators

描述（由申请人提供）：异三聚体G蛋白是促进人类感觉和生理激素调节的重要信号转导分子。传统的G蛋白信号通路是由存在于细胞表面的G蛋白偶联受体（gpcr）激活的。近年来，异源三聚体G蛋白调控的新机制得到了重视。非gpcr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ric8蛋白。哺乳动物的Ric-8A同源物通过刺激GDP催化GTP交换来激活G蛋白α亚基。ric8蛋白可能调节G蛋白的不对称（成体干细胞）和正常细胞分裂（G蛋白α i），神经传递（G蛋白α q）和嗅觉（G蛋白α olf）方面的信号调节。也许在这种对不同G蛋白信号通路的看似调控的基础上，发现果蝇的RIC-8似乎是异源三聚体G蛋白的正确表达和质膜定位所必需的。本文的目的是详细了解两种哺乳动物ric8同源物（A和B）对G蛋白生理的独特调控。本研究的目的是：(1)验证ricc - 8b蛋白通过作为鸟嘌呤核苷酸交换催化剂激活G蛋白α - s亚基的假设；(2)在哺乳动物中验证ricc -8蛋白是G蛋白在细胞膜定位所必需的假设。(3)验证哺乳动物的Ric-8A同源物负责激活G蛋白α - i依赖性（不对称）细胞分裂的假设；(4)确定G蛋白亚基集合与Ric-8A或Ric-8B之间的真实细胞相互作用。用于定义这些相互作用的技术也将用于发现ric8蛋白与G蛋白以外的其他蛋白之间的新相互作用。ric8蛋白是一种新的G蛋白激活剂。许多药物干预改变gpcr介导的G蛋白活化过程。阐明ric8蛋白调控G蛋白的新机制，可能有助于设计出干预ric8活化G蛋白水平的新型治疗药物。此外，为理解ric8和G蛋白控制正常和缺陷干细胞分裂的机制提供基础知识可以：(1)干细胞用于修复受损组织的治疗和(2)干细胞衍生癌症的治疗。

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.