SUMOylation of the Cardiac Sodium Channel Na V 1.5 Modifies Inward Current and Cardiac Excitability

Background Decreased peak sodium current (I Na ) and increased late sodium current (I Na,L ), through the cardiac sodium channel Na V 1.5 encoded by SCN5A , cause arrhythmias. Many Na V 1.5 post-translational modifications have been reported by us and others. A recent report concluded that acute hypoxia increases I Na,L by increasing a Small Ubiquitin-like MOdifier (SUMOylation) at K442-Na V 1.5. Objective To determine whether and by what mechanisms SUMOylation alters I Na , I Na,L and cardiac electrophysiology. Methods SUMOylation of Na V 1.5 was detected by immunoprecipitation and immunoblotting. I Na was measured by patch clamp with/without SUMO1 overexpression in HEK293 cells expressing wild type (WT) or K442R-Na V 1.5 and in neonatal rat cardiac myocytes (NRCMs). SUMOylation effects were studied in vivo by electrocardiograms and ambulatory telemetry using Scn5a heterozygous knockout (SCN5A +/- ) mice and the de-SUMOylating protein SENP2 (AAV9-SENP2) or the SUMOylation inhibitor anacardic acid. Na V 1.5 trafficking was detected by immunofluorescence. Results Na V 1.5 was SUMOylated in HEK293 cells, NRCMs and human heart tissue. HyperSUMOylation at Na V 1.5-K442 increased I Na in NRCMs and in HEK cells overexpressing WT but not K442R-Na v 1.5. SUMOylation did not alter other channel properties including I Na,L . AAV9-SENP2 or anacardic acid treatment of SCN5A +/- mice decreased I Na , prolonged QRS duration, and produced heart block and ventricular arrhythmias. SUMO1 overexpression enhanced membrane localization of Na V 1.5. Conclusion SUMOylation of K442-Na v 1.5 increases peak I Na without changing I Na,L , at least in part by altering membrane abundance. Our findings do not support SUMOylation as a mechanism for changes in I Na,L . Na v 1.5 SUMOylation may modify arrhythmic risk in disease states and represents a potential target for pharmacological manipulation.