Role of XLalphas as a novel alpha-subunit of Gs in hormone signaling

描述（由申请人提供）：XLocs和Gsa（刺激性G蛋白（Gsa）的α亚基）是源自相同基因座GNAS的两种相关蛋白质。XLas与刺激性G蛋白（Gsa）的α亚基的不同之处在于具有独特序列的大的N-末端结构域。它在其他方面与后者相同，并包含大多数对Gsa功能重要的结构域。因此，XLas被预测为刺激性G蛋白的新α亚基。然而，由于其独特的N-末端结构域，XLas在其生物学作用和调控方面可能与Gsa有很大不同。当引入到内源性缺乏Gsa和XLas的细胞（Gnas-T细胞）中时，XLas可以介导受体刺激的cAMP产生，但在几种其他细胞系和组织中不能证明受体与XLas的偶联，这表明XLas的作用可以是细胞特异性的。其中XLas被消融的动物模型已经确定XLas对于许多生物过程是必不可少的，包括出生后对进食、能量和葡萄糖代谢以及脂肪细胞生物学的适应。然而，这些体内研究无法证明XLas作为类似于Gsa的信号蛋白的作用。因此，XLas的生物学作用目前仍不清楚。我们的主要目标是确定XLas作为一种新的α亚基，可以取代Gsa在体内的作用。在具体目标1中，我们建议通过研究甲状旁腺激素在肾近端小管中的作用来解决XLAS是否可以在体内替代Gsa，作为体内环境，从而可以精确地研究XLAS和Gsa的作用。在具体目标2中，我们建议确定XLas是否参与PTH抗性的时间发展，如在假性甲状旁腺功能减退症患者中所见，这是一种由破坏Gsa活性和/或表达的突变引起的疾病。为了实现我们的目标，我们将研究近端肾小管PTH的反应性在各种转基因和敲除小鼠品系由我们或我们的合作者产生。这些研究将揭示XLas和Gsa在近端肾小管PTH作用中的相互作用，并预计将提高对通常涉及G蛋白偶联受体的激素反应的理解。最终，考虑到这种信号通路在正常生理和人类疾病中的重要性，我们的研究可能会导致确定新的靶点，用于开发新药和诊断工具。

DESCRIPTION (provided by applicant): XLocs and Gsa, the alpha subunit of the stimulatory G protein (Gsa), are two related proteins derived from the same gene locus, GNAS. XLas differs from the alpha subunit of the stimulatory G protein (Gsa) by a large N-terminal domain with unique sequence. It is otherwise identical to the latter and comprises most of the domains shown to be functionally important for Gsa. Thus, XLas is predicted to act as a novel alpha subunit of the stimulatory G protein. However, owing to its unique N-terminal domain, XLas could importantly differ from Gsa with respect to its biological roles and regulation. When introduced into cells endogenously lacking Gsa and XLas (Gnas^"'" cells), XLas can mediate receptor-stimulated cAMP generation, but receptor coupling to XLas could not be demonstrated in several other cell lines and tissues, suggesting that the actions of XLas can be cell-specific. The animal models in which XLas is ablated have established that XLas is essential for many biological processes, including postnatal adaptation to feeding, energy and glucose metabolism, and adipocyte biology. However, these in vivo studies were unable to demonstrate a role for XLas as a signaling protein that is similar to Gsa. Thus, the biological roles of XLas currently remain unclear. Our main objective is to determine the role of XLas as a novel alpha subunit that can replace Gsa in vivo. In Specific Aim 1, we propose to address whether XLas can substitute for Gsa in vivo by studying the actions of parathyroid hormone in the renal proximal tubule as an in vivo setting whereby the roles of XLos and Gsa can be studied precisely. In Specific Aim 2, we propose to determine whether XLas is involved in the temporal development of PTH-resistance as seen in patients with pseudohypoparathyroidism, a disorder caused by mutations disrupting Gsa activity and/or expression. For accomplishing our aims, we will investigate proximal tubular PTH responsiveness in various transgenic and knockout mouse strains generated by us or by our collaborators. These studies will reveal the interacting roles of XLas and Gsa in the proximal tubular PTH actions and are predicted to improve the understanding of hormone responses that typically involve G protein-coupled receptors. Ultimately, given the importance of this signaling pathway in normal physiology and human disease, our investigations may lead to the identification of novel targets for development of new drugs and diagnostic tools.