Physical and functional interaction of Snapin with Cav1.3 calcium channel impacts channel protein trafficking in atrial myocytes

The L-type Ca2+ channel (LTCC) Cav1.3 plays a critical role in generating electrical activity in atrial myocytes and cardiac pacemaker cells. However, the molecular and functional basis of Cav1.3 modulation in atrial myocytes has not yet been fully understood. By using the yeast two-hybrid system (Y2H), a Cav1.3-associated protein was screened, which was identified as Snapin. Physical interaction and co-localization between Snapin and Cav1.3 were then confirmed in both the heterologous expression system and mouse atrial myocytes. Direct interaction between them was additionally addressed in a GST pull down assay. Furthermore, both total and membrane expressions of Cav1.3 were significantly impaired by Snapin overexpression, resulting in the ubiquitin-proteasomal degradation of Cav1.3 and a consequent reduction of the densities of whole-cell ICa-L. Snapin-induced down-regulation of Cav1.3 was reversed by SNAP-23 competitively. What is more important is that the depressed-expression of Cav1.3 paralleled with enhanced-expression of Snapin was documented in atrial samples from atrial fibrillation (AF) patients. Our results provide the evidence of a direct regulatory role of Snapin on Cav1.3 channels in atrial myocytes, and highlight a potential role of Snapin in the regulation of Cav1.3 in atrial arrhythmogenesis.