Sodium Channel Biogenesis

描述(申请人提供)：上皮钠通道(ENaCs)表达在对醛固酮敏感的远端肾单位，它们是肾脏重吸收钠的最终部位，在调节细胞外液容量和血压方面起着关键作用。ENaCs也在整个呼吸道和肺泡中表达，它们介导钠的重吸收，并在调节呼吸道和肺泡液的容量方面发挥关键作用。通道组装似乎是一个低效的过程，内质网内的质量控制机制在防止错误折叠的通道亚基从内质网退出方面发挥着重要作用，同时促进正确组装的寡聚通道退出并输送到细胞表面。通道亚基也经历翻译后处理，包括被蛋白水解酶切割。目标1中拟议的研究将确定ER内针对ENaC亚基降解的质量控制机制。在目标2中提出的研究将定义ENaC亚基的处理和蛋白酶对通道活性的调节。目标3中拟议的研究将确定棕榈酰化在调节ENaC中的作用。这些研究应该产生关于ENaC生物发生和翻译后处理的新信息，从而提供对Na通道的细胞和表面池以及通道门控的额外水平的控制。公共卫生相关性：上皮钠通道在调节细胞外液容量、血压以及呼吸道和肺泡液容量方面起着关键作用。我们建议的研究将涉及钠通道的生物发生和翻译后处理的细胞机制。增强的ENaC蛋白分解有助于在利德尔综合征和囊性纤维化中观察到的通道活性的增加，并可能有助于肾病综合征中发生的钠滞留的增加。在基础水平上，我们的研究与理解ER相关降解(ERAD)的过程相关。我们建议的研究特别与寡聚整膜蛋白相关，因为它们对ERAD的细胞需求可能随着它们的四级结构的获得而演变。

DESCRIPTION (provided by applicant): Epithelial Na+ channel (ENaCs) are expressed in the aldosterone-sensitive distal nephron where they serve as the final site of renal Na+ reabsorption and have a key role in the regulation of extracellular fluid volume and blood pressure. ENaCs are also expressed throughout the airway and in alveoli, where they mediate Na+ reabsorption and have a critical role in regulating the volume of airway and alveolar fluids. Channel assembly appears to be an inefficient process, and quality control mechanisms within the ER have an important role in preventing exit of misfolded channel subunits from the ER while promoting the exit of properly assembled oligomeric channels for delivery to the cell surface. Channel subunits also undergo post- translational processing that includes cleavage by proteases. Proposed studies in Aim 1 will define quality control mechanisms within the ER that targets ENaC subunits for degradation. Proposed studies in Aim 2 will define the processing of ENaC subunits and regulation of channel activity by proteases. Proposed studies in Aim 3 will define the role of palmitoylation in the regulation of ENaC. These studies should generate new information regarding ENaC biogenesis and post-translational processing that provide additional levels of control of the cellular and surface pool of Na+ channels and of channel gating. PUBLIC HEALTH RELEVANCE: Epithelial Na+ channels have key roles in the regulation of extracellular fluid volume, blood pressure and the volume of airway and alveolar fluids. Our proposed studies will address cellular mechanisms that are involved in the biogenesis and post-translational processing of Na+ channels. Enhanced ENaC proteolysis contributes to the increase in channel activity observed in Liddle's syndrome and in cystic fibrosis, and may contribute to the increase in Na+ retention that occurs in nephrotic syndrome. At a basic level, our studies are relevant to understanding the process of ER associated degradation (ERAD). Our proposed studies are particularly relevant to oligomeric integral membrane proteins, as their cellular requirements for ERAD may evolve upon the acquisition of their quaternary structure.