αB-Crystallin Interacts with Nav1.5 and Regulates Ubiquitination and Internalization of Cell Surface Nav1.5

Abstract

Na v 1.5, the pore-forming ␣ subunit of the cardiac voltagegated Na ؉ channel complex, is required for the initiation and propagation of the cardiac action potential. Mutations in Na v 1.5 cause cardiac arrhythmias and sudden death. The cardiac Na ؉ channel functions as a protein complex; however, its complete components remain to be fully elucidated. A yeast two-hybrid screen identified a new candidate Na v 1.5-interacting protein, ␣B-crystallin. GST pull-down, co-immunoprecipitation, and immunostaining analyses validated the interaction between Na v 1.5 and ␣B-crystallin. Whole-cell patch clamping showed that overexpression of ␣B-crystallin significantly increased peak sodium current (I Na ) density, and the underlying molecular mechanism is the increased cell surface expression level of Na v 1.5 via reduced internalization of cell surface Na v 1.5 and ubiquitination of Na v 1.5. Knock-out of ␣B-crystallin expression significantly decreased the cell surface expression level of Na v 1.5. Co-immunoprecipitation analysis showed that ␣B-crystallin interacted with Nedd4-2; however, a catalytically inactive Nedd4-2-C801S mutant impaired the interaction and abolished the up-regulation of I Na by ␣B-crystallin. Na v 1.5 mutation V1980A at the interaction site for Nedd4-2 eliminated the effect of ␣B-crystallin on reduction of Na v 1.5 ubiquitination and increases of I Na density. Two disease-causing mutations in ␣B-crystallin, R109H and R151X (nonsense mutation), eliminated the effect of ␣B-crystallin on I Na . This study identifies ␣B-crystallin as a new binding partner for Na v 1.5. ␣B-Crystallin interacts with Na v 1.5 and increases I Na by modulating the expression level and internalization of cell surface Na v 1.5 and ubiquitination of Na v 1.5, which requires the protein-protein interactions between ␣B-crystallin and Na v 1.5 and between ␣B-crystallin and functionally active Nedd4-2.Na v 1.5 is the pore-forming ␣ subunit of the major cardiac voltage-gated Na ϩ channel complex. It generates the sodium current (I Na ) 4 that plays an essential role in the initiation and propagation of the cardiac action potential (1-3). Mutations in the SCN5A gene (encoding Na v 1.5) cause several inherited arrhythmias, including atrial fibrillation, Brugada syndrome, long QT syndrome, progressive cardiac conduction defect disease, sick sinus syndrome, and dilated cardiomyopathy (4). Na v 1.5 exists in vivo in a multiprotein complex, which interacts with the actin cytoskeleton and the extracellular matrix to provide an important functional link between channel complexes, cardiac structure, and electrical functioning (5, 6). Several proteins have been reported to bind to Na v 1.5 (5-7). We have previously reported a small protein, MOG1, with a function in nucleocytoplasmic protein transport that interacts directly with Na v 1.5, promotes trafficking of Na v 1.5 to the cell surface, and increases peak I Na density (4, 6). Specifically, MOG1 facilitates export of Na v 1.5 from the endoplasmic reticulum as well as targeting of Na v 1.5...

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Small GTPases SAR1A and SAR1B regulate the trafficking of the cardiac sodium channel Nav1.5

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“…Transfected cells were used for preparation of plasma membrane protein extracts using EZ-Link Sulfo-NHS-SS-Biotin (Pierce) as described previously [12, 18, 19]. Forty-eight hours after HEK293 cells were transiently co-transfected with 5 μg pcDNA3- SCN5A and 10 μg Flag-SAR1A constructs or the vector pcDNA3 using 20 μL lipofectamine 2000 (Invitrogen) respectively.…”

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