This research career award is designed to develop the scientific skills of the primary investigator (PI), within the context of studying the regulation of the epithelial sodium channel (ENaC) by serine proteases in airways. Prior to the award, the PI has studied airway epithelial processes that mediate mucociliary clearance, have been at the forefront of cystic fibrosis (CF) and epithelial cell biology for a number of years. Recently, the PI and collaborators have begun to describe the impact that endogenous serine proteases activity located on cell surfaces has on ENaC function. With this award, the PI will identify specific components of this regulatory system (protease, anti-protease) and will elucidate the mechanism by which serine proteases regulate ENAC. Importantly, based on prior observations that specific properties of airway surface liquid effect ENaC function, the PI will test whether this exo-protease mediates ENaC responses to airway surface liquid tonicity and volume. Because of the tight link between ENaC function, airway surface liquid volume, and mucociliary clearance, these studies are expected to provide important information regarding how human airways respond to their local environment in a way that facilitates the maintenance of lung defense. Also, because ENaC hyperactivity underlies CF lung disease, insights gained in this area may be translated into new therapeutic approaches for this lethal genetic disease. The career development plan that will be followed includes training in specialized research techniques, such as immunohistochemistry, in situ hybridization, a broad range of biochemical techniques, and single ion channel kinetic analysis. Also, focused coursework and participation in an array of scientific meetings and seminars will be included. The PI's long term goals are to provide important new insights into the basic elements of airway defense, CF lung disease, and to bring these findings to the development of novel therapies for CF lung disease.