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，XL？s在各种组织中表达，包括成骨细胞和肾细胞。XL可以通过刺激cAMP产生来模拟G，尽管它也被预测具有独特的作用。在几种人类疾病中发现了GNAS突变，这些疾病损害了通过PTH/PTHrP受体（PTHR）的信号传导。大多数这些突变影响G和XL。对小鼠和人类的研究表明，XL在生理学和人类疾病中起着重要作用，但XL的作用仍然知之甚少。我们最近的研究为XL的细胞作用提供了新的见解，再加上我们从XL基因敲除（XLKO）小鼠中获得的发现，这些使我们假设XL是调节体内钙和磷代谢所必需的。在当前提案的目标1中，我们将讨论在出生后早期发育过程中，XL s是否对肾近端小管中PTH介导的作用是必要的。我们将确定a）XLKO小鼠中PTH的近端肾小管作用是否受损，以及B）XLKO小鼠中的PTH抗性表型是否通过转基因重建近端肾小管中XL的表达而得到拯救。在目标2中，我们将讨论XL s是否允许PTH作用在肾近端小管中持续，这可以解释XLKO小鼠中的PTH抗性表型。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小鼠中PTH抗性表型是否可以通过具有持续活性的突变PTHR或通过近端小管中过表达G？来拯救;以及c）XL？与发动蛋白的相互作用是否影响PTH作用。这些研究将为PTH和XL在肾近曲小管中的作用提供新的见解，这些研究将适用于这些蛋白质在肾近曲小管中的作用。 骨骼组织我们的研究结果也将有助于揭示XL在其他系统中的作用，此外， 提高我们对GNAS突变引起的疾病的潜在机制的认识。鉴于XL？s可以激活普遍存在的cAMP信号通路，我们的研究结果可能对人类健康和疾病有更广泛的意义。

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.