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

描述（由申请人提供）：xlos和Gsa（刺激G蛋白（Gsa）的α亚基）是来自同一基因位点GNAS的两个相关蛋白。XLas与刺激G蛋白（Gsa）的α亚基的区别在于具有独特序列的大n端结构域。它在其他方面与后者相同，并且包含对Gsa具有重要功能的大多数域。因此，XLas被预测为刺激G蛋白的一个新的α亚基。然而，由于其独特的n端结构域，XLas在生物学作用和调控方面可能与Gsa有很大的不同。当引入内源性缺乏Gsa和XLas的细胞（Gnas^“'”细胞）时，XLas可以介导受体刺激的cAMP生成，但在其他几种细胞系和组织中无法证明受体与XLas的偶联，这表明XLas的作用可能是细胞特异性的。切除XLas的动物模型已经证实，XLas在许多生物过程中都是必不可少的，包括出生后对喂养的适应、能量和葡萄糖代谢以及脂肪细胞生物学。然而，这些体内研究无法证明XLas作为信号蛋白的作用类似于Gsa。因此，XLas的生物学作用目前尚不清楚。我们的主要目的是确定XLas作为一种新的α亚基在体内可以取代Gsa的作用。在Specific Aim 1中，我们提出通过研究甲状旁腺激素在肾近端小管中的作用，在体内精确研究XLos和Gsa的作用，来研究XLas是否可以在体内替代Gsa。在Specific Aim 2中，我们建议确定XLas是否参与假性甲状旁腺功能低下患者pth耐药的时间发展，假性甲状旁腺功能低下是一种由破坏Gsa活性和/或表达的突变引起的疾病。为了实现我们的目标，我们将研究由我们或我们的合作者产生的各种转基因和敲除小鼠株近端管状甲状旁腺激素的反应性。这些研究将揭示XLas和Gsa在近端管状甲状旁腺激素作用中的相互作用，并有望提高对通常涉及G蛋白偶联受体的激素反应的理解。最终，考虑到这一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新药物和诊断工具开发的新靶点的确定。

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.