Trafficking and Regulation of the Epithelial Na+ Channel

描述（由申请人提供）：维持细胞外液体积稳态对于血液动力学稳定性是必不可少的，并且肾钠处理的异常与心血管疾病和高血压有关。肾中钠排泄的最终调节发生在远端肾单位中，经由通过阿米洛利敏感性上皮Na+通道（ENaC）的传导转运。上皮细胞顶膜中ENaC的表达和活性不仅在肾集合管中，而且在气道上皮和结肠中是Na+重吸收的限速步骤。ENaC功能的缺失已在盐敏感性高血压、肾性盐耗和囊性纤维化的遗传形式中得到证实。本研究的长期目标是了解调节上皮细胞顶膜中ENaC表达的因素以及激素、生理条件和其他通道（如囊性纤维化跨膜调节因子CFTR）控制ENaC功能的机制。ENaC功能的主要控制是通过调节Na+重吸收细胞膜中活性通道的数量来实现的。通道通过蛋白水解裂解激活。通道顶端表达的控制是通道向膜的递送、通过内吞作用的回收以及通道的再循环和降解之间的平衡的功能。在应答细胞系和天然组织（包括肾和肺）中的多次观察表明，通道活性的调节与组成完全活性通道的3个单独亚基的非协调调节相关。目前的实验将定义的结合伙伴和网格蛋白介导的内吞作用的通道，内吞途径和调节通道再循环到顶端膜内的各个亚基的命运的监管网站。设计实验以确定通道亚基的非协调调节是否发生在内吞途径中，并且是否与已被蛋白水解激活的野生型和切割通道的差异处理有关。该研究旨在确定在高血压等疾病状态下可能受到异常调节的调节机制。

DESCRIPTION (provided by applicant): Maintenance of.extracellular fluid volume homeostasis is essential for hemodynamic stability, and abnormalities of renal sodium handling have been linked to cardiovascular disease and hypertension, Ultimate regulation of sodium excretion in the kidney occurs in the distal nephron via conductive transport through the amiloride sensitive epithelial Na+channel (ENaC). ENaC expression and activity in the apical membrane of epithelial cells is the rate limiting step in Na+reabsorption not only in the kidney collecting duce, but in airway epithelia and colon as well. Abnormalities of ENaC function have been demonstrated in hereditary forms of salt-sensitive hypertension, renal salt wasting, and cystic Fibrosis. The long term goal of this research is to understand the factors that regulate ENaC expression in the apical membrane of epithelial cells and the mechanisms by which hormones, physiologic conditions and other channels (such as the cystic fibrosis trahsmembrane regulator CFTR) control ENaC function. Major control of ENaC function is exerted by regulation of the number of active channels in the membrane of Na+ reabsorbing cells. Channels are activated by proteolytic cleavage. Control of apical expression of the channel is a function of delivery of the channel to the membrane, retrieval through endocytosis, and the balance between recycling and degradation of the channel. Multiple observations in responsive cell lines and native tissues including kidney and lung have demonstrated that modulation of channel activity is associated with non-coordinate regulation of the 3 separate subunits which make up the fully active channel. The current experiments will define the binding partners and regulatory sites of clathrin-mediated endocytosis of the channel, the fate of the individual subunits within the endocytic pathways and the regulation of channel recycling to the apical membrane. Experiments are designed to determine if non-coordinate regulation of channel subunits takes place in the endocytic pathway and is related to differential handling of wild type and cleaved channels which have.been activated by proteolysis. The research aims to identify regulatory mechanisms which may be subject to abnormal regulation in disease states such as hypertension.