XLas Relative to Gsa in Bone and Mineral Ion Metabolism

描述（由申请人提供）：G¿s对PTH和PTHrP的作用至关重要。编码g¿s （GNAS）的基因也产生XL¿s，它在各种组织中表达，包括成骨细胞和肾细胞。XL´s可以模仿G´s，通过刺激cAMP的产生来响应PTH，尽管它也被预测有独特的作用。GNAS突变在几种人类疾病中被发现，这些疾病通过PTH/PTHrP受体（PTHR）损害信号传导。大多数突变同时影响G′s和XL′s。对小鼠和人类的研究表明，XL¿s在生理和人类疾病中发挥重要作用，但XL¿s的作用仍然知之甚少。我们最近的研究为XL¿s的细胞作用提供了新的见解，加上我们从XL¿s敲除（XLKO）小鼠中获得的发现，这些使我们假设XL¿s是调节体内钙和磷代谢所必需的。在本提案的目的1中，我们将讨论在出生后早期发育过程中，pth介导的肾近端小管中XL¿s是否必要。我们将确定a) PTH在XLKO小鼠近端小管中的作用是否受损，b)通过转基因重建近端小管中XL¿s的表达是否挽救XLKO小鼠的PTH抗性表型。在Aim 2中，我们将研究XL¿s是否允许PTH作用在肾近端小管中持续，这可以解释XLKO小鼠PTH耐药表型。因此，我们将确定a) XLKO小鼠近端小管中PTHR内化是否增强；b) XLKO小鼠的PTH抗性表型是否可以通过持续活性的PTHR突变体或近端小管过表达G¿s来挽救；c) XL¿s与dynamin的相互作用是否影响PTH的作用。这些研究将为PTH和XL在肾近端小管中的作用提供新的见解，这些将适用于这些蛋白在肾近端小管中的作用

DESCRIPTION (provided by applicant): G¿s is critical for the actions of PTH and PTHrP. The gene encoding G¿s (GNAS) also gives rise to XL¿s, which is expressed in various tissues including osteoblastic and renal cells. XL¿s can mimic G¿s by stimulating cAMP generation in response PTH, although it is also predicted to have unique actions. Mutations in GNAS are found in several human diseases that impair signaling through the PTH/PTHrP receptor (PTHR). Most of these mutations affect both G¿s and XL¿s. Studies in mice and humans indicate that XL¿s plays important roles in physiology and human disease, but the actions of XL¿s remain poorly understood. Our recent studies have provided novel insights into the cellular actions of XL¿s, and together with our findings obtained from XL¿s knockout (XLKO) mice, these led us to hypothesize that XL¿s is necessary for the regulation of calcium and phosphorus metabolism in vivo. In Aim 1 of the current proposal, we will address whether XL¿s is necessary for PTH-mediated actions in the renal proximal tubule during early postnatal development. We will determine a) whether proximal tubular actions of PTH in XLKO mice are impaired and b) whether the PTH resistance phenotype in XLKO mice is rescued by transgenically reconstituting XL¿s expression in the proximal tubule. In Aim 2, we will address whether XL¿s allows PTH actions to be sustained in the renal proximal tubule, which could explain the PTH resistance phenotype in XLKO mice. We will thus determine a) whether PTHR internalization is enhanced in the proximal tubule of XLKO mice; b) whether the PTH resistance phenotype in XLKO mice can be rescued by a mutant PTHR with sustained activity or by overexpressing G¿s in the proximal tubule; and c) whether the interaction of XL¿s with dynamin influences PTH actions. These studies will provide novel insights into the actions of PTH and XL¿s in the renal proximal tubule, and these will be applicable to the actions of these proteins in skeletal tissues. Our results will also help reveal the roles of XL¿s in other systems, in addition to improving our knowledge of the mechanisms underlying the diseases caused by GNAS mutations. Given that XL¿s can activate the ubiquitous cAMP signaling pathway, our results will likely have even broader implications for human health and disease. PUBLIC HEALTH RELEVANCE: XL¿s is a variant of G¿s, which is important for the actions of parathyroid hormone. Mutations in the gene making these two proteins cause different human diseases that affect the bone and mineral metabolism. Unlike G¿s, functional roles of XL¿s are unknown. We aim to determine the role XL¿s in mediating the actions of parathyroid hormone to learn more about the mechanisms underlying those diseases.