Abstract 5345: Cell Membrane Expression of Cardiac Sodium Channel Nav1.5 is Regulated by α-Actinin-2 Interactions
Cardiac voltage-gated Na+ channels play a critical role in heart excitability and conduction. They are composed of one α-subunit (Nav1.5) and several auxiliary β-subunits. This complex is thought to interact with several cytoskeleton proteins. Na+ Channel dysfunctions cause a wide range of diseases, including cardiac arrhythmia, sudden cardiac death. In this study, we used yeast two-hybrid screening to identify cardiac Na+ channel-associated proteins that might be involved in channel function and expression. We found that α-actinin-2, a major sarcomeric F-actin cross-linking protein, interacts directly with the cytoplasmic III–IV linker of Nav1.5. The interaction was further demonstrated by both in vitro His6 pull-down and co-immunoprecipitation assays in both tsA201 cells with co-expression of Nav1.5 and α-actinin-2 and native tissue. Co-expression of α-actinin-2 with Nav1.5 in tsA201 cells increased sodium current densities. Biotinylation assay revealed that α-actinin-2 increased cell-surface expression of Nav1.5, which may be the underlying mechanism by which α-actinin-2 increased sodium current densities. Moreover, we demonstrate that the spectrin-like repeats of α-actinin-2 are essential for binding Nav1.5 III–IV linker. Finally, immunostaining revealed that in human heart, Nav1.5 and α-actinin-2 co-localized at the Z line and the plasma membrane, indicating that α-actinin-2 in the heart might function as an anchoring protein by connecting Nav1.5 to the actin cytoskeleton, and that this interaction is crucial for stabilizing Nav1.5 expression at the cell surface. Our data suggest that the interaction between α-actinin-2 and Na+ channels might play an important role in the physiolopathology of these channels.