Snapin, a new regulator of receptor signaling, augments α1A-adrenoceptor-operated calcium influx through TRPC6

Activation of G(q)-protein-coupled receptors, including the alpha(1A)-adrenoceptor (alpha(1A)-AR), causes a sustained Ca2+ influx via receptor-operated Ca2+ (ROC) channels, following the transient release of intracellular Ca2+. Transient receptor potential canonical (TRPC) channel is one of the candidate proteins constituting the ROC channels, but the precise mechanism linking receptor activation to increased influx of Ca2+ via TRPCs is not yet fully understood. We identified Snapin as a protein interacting with the C terminus of the alpha(1A)-AR. In receptor-expressing PC12 cells, co-transfection of Snapin augmented alpha(1A)-AR-stimulated sustained increases in intracellular Ca2+ ([Ca2+](i)) via ROC channels. By altering the Snapin binding C-terminal domain of the alpha(1A)-AR or by reducing cellular Snapin with short interfering RNA, the sustained increase in [Ca2+](i) in Snapin-alpha(1A)-AR co-expressing PC12 cells was attenuated. Snapin co-immunoprecipitated with TRPC6 and alpha(1A)-AR, and these interactions were augmented upon alpha(1A)-AR activation, increasing the recruitment of TRPC6 to the cell surface. Our data suggest a new receptor-operated signaling mechanism where Snapin links the alpha(1A)-AR to TRPC6, augmenting Ca2+ influx via ROC channels.