Interaction of serum- and glucocorticoid regulated kinase 1 (SGK1) with the WW-domains of Nedd4-2 is required for epithelial sodium channel regulation.
BACKGROUND
The 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.


RESULTS
Here 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.


CONCLUSIONS
Binding of Nedd4-2 WW-domains to SGK is necessary for SGK-induced ENaC activity.
Wiemuth
Dominik
D
Department of Physiology, University of Otago, Dunedin, New Zealand.
Lott
J Shaun
JS
Ly
Kevin
K
Ke
Ying
Y
Teesdale-Spittle
Paul
P
Snyder
Peter M
PM
McDonald
Fiona J
FJ
D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D056827:Endosomal Sorting Complexes Required for Transport / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D004789:Enzyme Activation; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D000075702:Nedd4 Ubiquitin Protein Ligases; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D014364:Tryptophan; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D000099184:Serum-Glucocorticoid Regulated Kinases
D056827:Endosomal Sorting Complexes Required for Transport; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; D010446:Peptide Fragments; D017346:Protein Serine-Threonine Kinases; D014364:Tryptophan; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases