Interaction of Serum- and Glucocorticoid Regulated Kinase 1 (SGK1) with the WW-Domains of Nedd4-2 Is Required for Epithelial Sodium Channel Regulation |
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Authors: | Dominik Wiemuth J. Shaun Lott Kevin Ly Ying Ke Paul Teesdale-Spittle Peter M. Snyder Fiona J. McDonald |
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Affiliation: | 1. Department of Physiology, University of Otago, Dunedin, New Zealand.; 2. School of Biological Sciences, University of Auckland, Auckland, New Zealand.; 3. School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.; 4. Departments of Internal Medicine and of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.;Abramson Research Center, United States of America |
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Abstract: | BackgroundThe epithelial sodium channel (ENaC) is an integral component of the pathway for Na+ absorption in epithelial cells. The ubiquitin ligases Nedd4 and Nedd4-2 bind to ENaC and decrease its activity. Conversely, Serum- and Glucocorticoid regulated Kinase-1 (SGK1), a downstream mediator of aldosterone, increases ENaC activity. This effect is at least partly mediated by direct interaction between SGK and Nedd4-2. SGK binds both Nedd4 and Nedd4-2, but it is only able to phosphorylate Nedd4-2. Phosphorylation of Nedd4-2 reduces its ability to bind to ENaC, due to the interaction of phosphorylated Nedd4-2 with 14-3-3 proteins, and hence increases ENaC activity. WW-domains in Nedd4-like proteins bind PY-motifs (PPXY) present in ENaC subunits, and SGK also has a PY-motif.Principal FindingHere we show that single or tandem WW-domains of Nedd4 and Nedd4-2 mediate binding to SGK and that different WW-domains of Nedd4 and Nedd4-2 are involved. Our data also show that WW-domains 2 and 3 of Nedd4-2 mediate the interaction with SGK in a cooperative manner, that activated SGK has increased affinity for the WW-domains of Nedd4-2 in vitro, and a greater stimulatory effect on ENaC Na+ transport compared to wildtype SGK. Further, SGK lacking a PY motif failed to stimulate ENaC activity in the presence of Nedd4-2.ConclusionsBinding of Nedd4-2 WW-domains to SGK is necessary for SGK-induced ENaC activity. |
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