Sodium Channel Biogenesis

描述（由申请方提供）：上皮Na+通道（ENaCs）在醛固酮敏感性远端肾单位中表达，在那里它们作为肾Na+重吸收的最终位点，并在细胞外液量和血压的调节中起关键作用。ENaC也在整个气道和肺泡中表达，在那里它们介导Na+重吸收，并且在调节气道和肺泡流体的体积中具有关键作用。通道组装似乎是一个低效的过程，ER内的质量控制机制在防止错误折叠的通道亚基从ER中退出，同时促进正确组装的寡聚通道退出以递送至细胞表面方面具有重要作用。通道亚基还经历翻译后加工，包括被蛋白酶切割。目标1中提出的研究将定义ER中靶向ENaC亚基降解的质量控制机制。目标2中提出的研究将定义ENaC亚基的加工和蛋白酶对通道活性的调节。目标3中提出的研究将确定棕榈酰化在ENaC调节中的作用。这些研究应该产生新的信息ENaC生物发生和翻译后加工，提供额外的水平的控制细胞和表面池的Na+通道和通道门控。公共卫生相关性：上皮细胞Na+通道在调节细胞外液容量、血压以及气道和肺泡液容量方面具有关键作用。我们提出的研究将解决涉及Na+通道的生物发生和翻译后加工的细胞机制。增强的ENaC蛋白水解有助于在Liddle综合征和囊性纤维化中观察到的通道活性的增加，并且可能有助于在肾病综合征中发生的Na+潴留的增加。在基本水平上，我们的研究与理解ER相关降解（ERAD）的过程有关。我们提出的研究是特别相关的寡聚体膜蛋白，因为它们的细胞ERAD的要求可能会演变后，收购其四级结构。

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.