The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a multifunctional protein that both transports Cl- across the apical plasma membrane of epithelial cells and regulates ion transport by other proteins, such as the Epithelial Sodium Channel, ENaC. A cardinal feature of Cystic Fibrosis (CF) is hyperactivity of Na+ transport via ENaC in the airway epithelia, although the mechanism by which this results from the absence of CFTR is not known. Efforts at pharmacologic repair of mutant CFTR function, such as the use of Sodium 4- Phenylbutyrate (4PBA) to correct trafficking of the most common mutant CFTR, ?F508-CFTR, have concentrated on assessing restoration of a mutant CFTR's Cl- transport function. These studies have often ignored the influence of 4PBA or other CFTR "correctors" on ENaC trafficking and/or function. Our proposed studies will address whether pharmacologic repair, or correction of ?F508-CFTR trafficking will promote appropriate regulation of ENaC in the CF airway. This is a key issue in the implementation of pharmacologic strategies to improve ?F508 CFTR trafficking and function. Our hypothesis is that 4PBA induces modulations of molecular chaperone expression in epithelial cells that result in altered intracellular trafficking and functional expression of CFTR and ENaC. Because 4PBA also improves the intracellular trafficking of a number of mutant proteins in diseases besides CF, this hypothesis may also be germane to developing pharmacologic therapies for a number of other protein conformational diseases. 4PBA causes altered expression of the cytosolic chaperones Hsc70 and Hsp70, as well as a novel luminal endoplasmic reticular protein of 29 kDa, ERp29. Our data suggest that specifically altered expression of these chaperones modulates CFTR, ?F508 and ENaC trafficking and functional expression. The present proposal will build on these preliminary data and test this hypothesis with studies directed at the following Specific Aims:
Specific Aim 1 : To determine the mechanism by which Hsc70 and Hsp70 modulate CFTR, ?F508 and ENaC trafficking in epithelial cells.
Specific Aim 2 : To determine the mechanism by which ERp29, a novel 4-phenylbutyrate-regulated luminal endoplasmic reticular protein, regulates the trafficking of CFTR, ?F508 and ENaC in epithelial cells.
The major mechanim by which the lung and airway defends itself from the environment depends on proper ion transport in the respiratory epithelia. Such ion transport is aberrant in Cystic Fibrosis, leading to significant morbidity and mortality. These data will promote better understanding of the regulation of channels responsible for ion transport in Cystic Fibrosis and other diseases of the airway, and inform development of novel, mechanism-based therapies for Cystic Fibrosis.
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