title: Nedd4-2 catalyzes ubiquitination and degradation of cell surface ENaC.
abstract: Epithelial Na(+) absorption is regulated by Nedd4-2, an E3 ubiquitin-protein ligase that reduces expression of the epithelial Na(+) channel ENaC at the cell surface. Defects in this regulation cause Liddle syndrome, an inherited form of hypertension. Previous work found that Nedd4-2 binds to ENaC via PY motifs located in the C termini of alpha-, beta-, and gammaENaC. However, little is known about the mechanism by which Nedd4-2 regulates ENaC surface expression. Here we found that Nedd4-2 catalyzes ubiquitination of alpha-, beta-, and gammaENaC; Nedd4-2 overexpression increased ubiquitination, whereas Nedd4-2 silencing decreased ubiquitination. Although Nedd4-2 increased both mono/oligoubiquitinated and multiubiquitinated forms of ENaC, monoubiquitination was sufficient for Nedd4-2 to reduce ENaC surface expression and reduce ENaC current. Ubiquitination was disrupted by Liddle syndrome-associated mutations in ENaC or mutation of the catalytic HECT domain in Nedd4-2. Several findings suggest that the interaction between Nedd4-2 and ENaC is localized to the cell surface. First, Nedd4-2 bound to a population of ENaC at the cell surface. Second, Nedd4-2 catalyzed ubiquitination of cell surface ENaC. Third, Nedd4-2 selectively reduced ENaC expression at the cell surface but did not alter the quantity of immature ENaC in the biosynthetic pathway. Finally, Nedd4-2 induced degradation of the cell surface pool of ENaC. Together, the data suggest a model in which Nedd4-2 binds to and ubiquitinates ENaC at the cell surface, which targets surface ENaC for degradation, and thus, reduces epithelial Na(+) transport.
authors.affiliation: Departments of Internal Medicine and Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
authors.forename: Ruifeng
authors.initials: R
authors.lastname: Zhou
authors.forename: Saumil V
authors.initials: SV
authors.lastname: Patel
authors.forename: Peter M
authors.initials: PM
authors.lastname: Snyder
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D008954:Models, Biological; D009154:Mutation; D000075702:Nedd4 Ubiquitin Protein Ligases; D011485:Protein Binding / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D025801:Ubiquitin; D012964:Sodium; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; D044767:Ubiquitin-Protein Ligases