Nedd4-2 catalyzes ubiquitination and degradation of cell surface ENaC.
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.
Mesh Terms:
Amino Acid Motifs, Cell Line, Cell Membrane, Endosomal Sorting Complexes Required for Transport, Epithelial Sodium Channel, Gene Silencing, Humans, Ion Transport, Models, Biological, Mutation, Protein Binding, Protein Processing, Post-Translational, Protein Structure, Tertiary, Sodium, Ubiquitin, Ubiquitin-Protein Ligases
Amino Acid Motifs, Cell Line, Cell Membrane, Endosomal Sorting Complexes Required for Transport, Epithelial Sodium Channel, Gene Silencing, Humans, Ion Transport, Models, Biological, Mutation, Protein Binding, Protein Processing, Post-Translational, Protein Structure, Tertiary, Sodium, Ubiquitin, Ubiquitin-Protein Ligases
J. Biol. Chem.
Date: Jul. 13, 2007
PubMed ID: 17502380
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