Nedd4-2 isoforms ubiquitinate individual epithelial sodium channel subunits and reduce surface expression and function of the epithelial sodium channel.
We previously reported the existence of multiple isoforms of human Nedd4-2 (Am J Physiol Renal Physiol 285: F916-F929, 2003). When overexpressed in M-1 collecting duct epithelia, full-length Nedd4-2 (Nedd4-2), Nedd4-2 lacking the NH(2)-terminal C2 domain (Nedd4-2DeltaC2), and Nedd4-2 lacking WW domains 2 and 3 (Nedd4-2DeltaWW2,3) variably reduce benzamil-sensitive Na(+) transport. We investigated the effect of each of the Nedd4-2 isoforms on cell surface expression and ubiquitination of ENaC subunits. We find that alphaENaC when transfected alone or with beta and gammaENaC is expressed at the cell surface and this membrane expression is variably reduced by coexpression with each of the Nedd4-2 isoforms. Nedd4-2 reduces the half-life of ENaC subunits and enhances the ubiquitination of alpha, beta, and gammaENaC subunits when expressed alone or together suggesting that each subunit is a target for Nedd4-2-mediated ubiquitination. As has been reported recently, we confirm that the surface-expressed pool of ENaC is multi-ubiquitinated. Inhibitors of the proteasome increase ubiquitination of ENaC subunits and stimulate Na(+) transport in M-1 cells consistent with a role for the ubiquitin-proteasome pathway in regulating Na(+) transport in the collecting duct.
Raikwar
Nandita S
NS
Department of Internal Medicine, E300 GH, University of Iowa College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA.
Thomas
Christie P
CP
D000256:Adenoviridae / Q000235:genetics; D002460:Cell Line; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels / Q000096:biosynthesis* / Q000187:drug effects / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism*; D005822:Genetic Vectors; D006207:Half-Life; D006801:Humans; D007536:Isomerism; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D000075702:Nedd4 Ubiquitin Protein Ligases; D011956:Receptors, Cell Surface / Q000096:biosynthesis; D012964:Sodium / Q000378:metabolism; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D011956:Receptors, Cell Surface; D025801:Ubiquitin; D012964:Sodium; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; D044767:Ubiquitin-Protein Ligases