title: Hsc70 negatively regulates epithelial sodium channel trafficking at multiple sites in epithelial cells.
abstract: The epithelial sodium channel (ENaC) plays an important role in homeostasis of blood pressure and of the airway surface liquid, and excess function of ENaC results in refractory hypertension (in Liddle's syndrome) and impaired mucociliary clearance (in cystic fibrosis). The regulation of ENaC by molecular chaperones, such as the 70-kDa heat shock protein Hsc70, is not completely understood. Our previously published data suggest that Hsc70 negatively affects ENaC activity and surface expression in Xenopus oocytes; here we investigate the mechanism by which Hsc70 acts on ENaC in epithelial cells. In Madin-Darby canine kidney cells stably expressing epitope-tagged αβγ-ENaC and with tetracycline-inducible overexpression of Hsc70, treatment with 5 μg/ml doxycycline increased total Hsc70 expression 20%. This increase in Hsc70 expression led to a decrease in ENaC activity and surface expression that corresponded to an increased rate of functional ENaC retrieval from the cell surface. In addition, Hsc70 overexpression decreased the association of newly synthesized ENaC subunits. These data support the hypothesis that Hsc70 inhibits ENaC functional expression at the apical surface of epithelia by regulating ENaC biogenesis and ENaC trafficking at the cell surface.
authors.affiliation: Division of Pulmonary Medicine and Cystic Fibrosis Center, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania; and.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Chanoux
authors.forename: Calla B
authors.initials: CB
authors.lastname: Shubin
authors.forename: Amal
authors.initials: A
authors.lastname: Robay
authors.forename: Laurence
authors.initials: L
authors.lastname: Suaud
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Rubenstein
mesh_terms: D000818:Animals; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D061985:Madin Darby Canine Kidney Cells; D055503:Protein Multimerization; D021381:Protein Transport; D013997:Time Factors; D014162:Transfection
chemical_list: D053503:Epithelial Sodium Channels; D050883:HSC70 Heat-Shock Proteins
keywords: ENaC; chaperone; epithelia; heat shock protein; trafficking