Deubiquitylating enzyme USP2 counteracts Nedd4-2–mediated downregulation of KCNQ1 potassium channels

BackgroundKCNQ1 (Kv7.1), together with its KCNE β subunits, plays a pivotal role both in the repolarization of cardiac tissue and in water and salt transport across epithelial membranes. Nedd4/Nedd4-like (neuronal precursor cell–expressed developmentally downregulated 4) ubiquitin–protein ligases interact with the KCNQ1 potassium channel through a PY motif located in the C terminus of KCNQ1. This interaction induces ubiquitylation of KCNQ1, resulting in a reduced surface density of the channel. It was reported recently that the epithelial sodium channel is regulated by the reverse process—deubiquitylation—mediated by USP2 (ubiquitin-specific protease 2).ObjectiveIn this article, we investigated whether deubiquitylation may regulate KCNQ1 channel complexes.MethodsIn this study, we used electrophysiology, biochemistry, and confocal microscopy.ResultsElectrophysiological investigations of KCNQ1/KCNE1 proteins coexpressed with USP2-45 or USP2-69 isoforms and Nedd4-2 in Xenopus laevis oocytes and mammalian cells revealed that both USP2 isoforms counter the Nedd4-2–specific downregulation of IKs. Biochemical studies showed that the total and surface-expressed KCNQ1 protein was more abundant when coexpressed with USP2 and Nedd4-2 as compared with Nedd4-2 alone. Western blotting revealed partial protection against covalent attachment of ubiquitin moieties on KCNQ1 when USP2 was coexpressed with Nedd4-2. Coimmunoprecipitation assays suggested that USP2 can bind to KCNQ1 independently of the PY motif. Immunocytochemistry confirmed that USP2 restores the membrane localization of KCNQ1.ConclusionThese results demonstrate that USP2 can be a potent regulator of KCNQ1 surface density. USP2, which is well expressed in many tissues, may therefore be important in controlling the KCNQ1 channel dynamics in vivo.