ENaC Regulation by Nedd4-2 and SGK

描述（由申请人提供）：上皮Na+通道ENaC在肾集管和其他上皮中形成Na+吸收的途径（1,2）。特异性ENaC突变导致细胞表面通道过度表达，导致遗传形式的高血压（Liddle综合征）。醛固酮和其他类固醇激素通过改变ENaC在细胞表面的表达来调节Na+的吸收。因此，了解ENaC表面表达的控制机制为Na+稳态的分子机制和高血压的发病机制提供了重要的新见解。先前的研究发现Nedd4和Nedd4-2通过靶向降解通道降低ENaC表面表达。这种通路的缺陷导致了利德尔综合征。相反，血清和糖皮质激素调节激酶（SGK），醛固酮的下游介质，增加ENaC表面表达。我们的初步研究提出了新的假设，即这两种途径不是独立的，而是汇聚在一个共同的途径来调节Na+的吸收。本项目的目的是验证SGK通过Nedd4-2结合和磷酸化部分调节ENaC表面表达的假设，并了解其中的机制。在第一个具体目标中，我们将检验SGK磷酸化Nedd4-2的假设。我们将确定被磷酸化的特定残基，并将测试磷酸化是否会改变Nedd4-2的功能。在具体目标二中，我们将验证SGK与Nedd4-2结合的假设。我们将确定介导这种相互作用的序列，并测试结合的功能作用。特定形式的高血压是由Nedd4家族成员ENaC调节缺陷（Liddle综合征）和矿皮质激素和糖皮质激素信号传导缺陷（如糖皮质激素可修复的醛固酮增多症）引起的。因此，我们的工作将为这些形式的高血压提供新的认识。此外，通过阐明负责血压控制的途径和蛋白质，这项工作可能为原发性高血压的分子原因提供重要的新见解。

DESCRIPTION (provided by applicant): The epithelial Na+ channel, ENaC, forms the pathway for Na+ absorption in the kidney collecting duct and other epithelia (1, 2). Specific ENaC mutations lead to excessive channel expression at the cell surface, resulting in a genetic form of hypertension (Liddle's syndrome). Aldosterone and other steroid hormones regulate Na+ absorption by altering the expression of ENaC at the cell surface. Thus, understanding the mechanisms that control ENaC surface expression wifi provide critical new insights into the molecular mechanisms of Na+ homeostasis, and the pathogenesis of hypertension. Previous work found that Nedd4 and Nedd4-2 reduce ENaC surface expression by targeting the channel for degradation. A defect in this pathway is responsible for Liddle's syndrome. Conversely, serum and glucocorticoid-regulated kinase (SGK), a down-stream mediator of aldosterone, increases ENaC surface expression. Our preliminary studies suggest the novel hypothesis that these two pathways are not independent, but that they converge in a common pathway to regulate Na+ absorption. The goal of this project is to test the hypothesis that SGK modulates ENaC surface expression in part through Nedd4-2 binding and phosphorylation, and to understand the mechanisms involved. In the first specific aim, we will test the hypothesis that SGK phosphorylates Nedd4-2. We will identify the specific residues that are phosphorylated, and will test whether phoshorylation alters Nedd4-2 function. In specific aim two, we will test the hypothesis that SGK binds to Nedd4-2. We will identify the sequences that mediate this interaction, and test the functional role of binding. Specific forms of hypertension are caused by defects in ENaC regulation by Nedd4 family members (Liddle's syndrome) and defects in mineralocorticoid and glucocorticoid signaling signalling (e.g. glucocorticoid-remediable aldosteronism). Thus, our work will provide a new understanding of these forms of hypertension. In addition, by elucidating the pathways and proteins responsible for blood pressure control, this work may provide important new insights into the molecular causes of essential hypertension.