title: Serum and glucocorticoid-regulated kinase modulates Nedd4-2-mediated inhibition of the epithelial Na+ channel.
abstract: The epithelial Na+ channel (ENaC) forms the pathway for Na+ absorption across epithelia, including the kidney collecting duct, where it plays a critical role in Na+ homeostasis and blood pressure control. Na+ absorption is regulated in part by mechanisms that control the expression of ENaC at the apical cell surface. Nedd4 family members (e.g. Nedd4, Nedd4-2) bind to the channel and decrease its surface expression by catalyzing its ubiquitination and degradation. Conversely, serum and glucocorticoid-regulated kinase (SGK), a downstream mediator of aldosterone, increases the expression of ENaC at the cell surface. Here we show that SGK and human Nedd4-2 (hNedd4-2) converge in a common pathway to regulate epithelial Na+ absorption. Consistent with this model, we found that SGK bound to hNedd4-2 and hNedd4. A PY motif in SGK mediated the interaction and was required for SGK to stimulate ENaC. SGK phosphorylated hNedd4-2 (but not hNedd4), altering hNedd4-2 function; phosphorylation reduced the binding of hNedd4-2 to alphaENaC, and hence, the hNedd4-2-mediated inhibition of Na+ absorption. These data suggest that SGK regulates epithelial Na+ absorption in part by modulating the function of hNedd4-2.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA. psynder@blue.weeg.uiowa.edu
authors.forename: Peter M
authors.initials: PM
authors.lastname: Snyder
authors.forename: Diane R
authors.initials: DR
authors.lastname: Olson
authors.forename: Brittany C
authors.initials: BC
authors.lastname: Thomas
mesh_terms: D000818:Animals; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000502:physiology*; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D008025:Ligases / Q000502:physiology*; D000075702:Nedd4 Ubiquitin Protein Ligases; D009687:Nuclear Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D008025:Ligases; D000075702:Nedd4 Ubiquitin Protein Ligases; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D012964:Sodium; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human