title: Rescue of DeltaF508-CFTR by the SGK1/Nedd4-2 signaling pathway.
abstract: The most common mutation in cystic fibrosis (CF) is DeltaF508, which is associated with failure of the mutant cystic fibrosis transmembrane conductance regulator (CFTR) to traffic to the plasma membrane. By a still unknown mechanism, the loss of correctly trafficked DeltaF508-CFTR results in an excess of the epithelial sodium channel (ENaC) on the apical plasma membrane. ENaC trafficking is known to be regulated by a signaling pathway involving the glucocorticoid receptor, the serum- and glucocorticoid-regulated kinase SGK1, and the ubiquitin E3 ligase Nedd4-2. We show here that dexamethasone rescues functional expression of DeltaF508-CFTR. The half-life of DeltaF508-CFTR is also dramatically enhanced. Dexamethasone-activated DeltaF508-CFTR rescue is blocked either by the glucocorticoid receptor antagonist RU38486 or by the phosphatidylinositol 3-kinase inhibitor LY294002. Co-immunoprecipitation studies indicate that Nedd4-2 binds to both wild-type- and DeltaF508-CFTR. These complexes are inhibited by dexamethasone treatment, and CFTR ubiquitination is concomitantly decreased. We further show that knockdown of Nedd4-2 by small interfering RNA also corrects DeltaF508-CFTR trafficking. Conversely, knockdown of SGK1 by small interfering RNA completely blocks dexamethasone-activated DeltaF508-CFTR rescue. These data suggest that the SGK1/Nedd4-2 signaling pathway regulates both CFTR and ENaC trafficking in CF epithelial cells.
authors.affiliation: Department of Anatomy, Physiology, and Genetics, Uniformed Services University School of Medicine, Bethesda, Maryland 20814, USA. hcaohuy@usuhs.mil
authors.forename: Hung
authors.initials: H
authors.lastname: Caohuy
authors.forename: Catherine
authors.initials: C
authors.lastname: Jozwik
authors.forename: Harvey B
authors.initials: HB
authors.lastname: Pollard
mesh_terms: D001692:Biological Transport; D019921:Biotinylation; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D056827:Endosomal Sorting Complexes Required for Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053503:Epithelial Sodium Channels / Q000378:metabolism; D005938:Glucocorticoids / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009154:Mutation; D000075702:Nedd4 Ubiquitin Protein Ligases; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D003907:Dexamethasone; D056827:Endosomal Sorting Complexes Required for Transport; D004791:Enzyme Inhibitors; D053503:Epithelial Sodium Channels; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; D017346:Protein Serine-Threonine Kinases; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases; C093349:cystic fibrosis transmembrane conductance regulator delta F508; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human