USP2‐45 regulates ENaC endocytosis

The epithelial sodium channel (ENaC) is important for the maintenance of Na + and volume homeostasis. Defects in its regulation cause hypertension and contribute to the pathogenesis of cystic fibrosis. ENaC surface expression is regulated by ubiquitination of each ENaC subunit. Previous work indicates that Nedd4‐2 catalyzes ENaC ubiquitination, which has two distinct effects on ENaC trafficking; ubiquitination increases ENaC endocytosis and increases its degradation in lysosomes, both which contribute to a reduction in ENaC surface expression. Recent work suggests that ENaC can be deubiquitinated by a ubiquitin‐specific protease, USP2‐45. Here we tested the hypothesis that USP2‐45 regulates ENaC trafficking. When coexpressed in HEK293T cells, we found that USP2‐45 produced a dose‐dependent increase in surface expression ofα, β, and γENaC, and reversed the Nedd4‐2 mediated decrease in ENaC surface expression. USP2‐45 coprecipitated with the cell surface pool of ENaC and decreased the rate of ENaC endocytosis. Moreover, USP2‐45 blunted the effect of Nedd4‐2 on ENaC endocytosis. In contrast, USP2‐45 had no effect on degradation of the surface pool of ENaC. Thus, USP2‐45 increases ENaC surface expression through a selective effect on ENaC endocytosis. This suggests a model in which USP2‐45 deubiquitinates ENaC at the cell surface but not in endosomes. Funded by the NIH.