Snapin, a New Regulator of Receptor Signaling, Augments α1A-Adrenoceptor-operated Calcium Influx through TRPC6*

Activation of Gq-protein-coupled receptors, including the α1A-adrenoceptor (α1A-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 α1A-AR. In receptor-expressing PC12 cells, co-transfection of Snapin augmented α1A-AR-stimulated sustained increases in intracellular Ca2+ ([Ca2+]i) via ROC channels. By altering the Snapin binding C-terminal domain of the α1A-AR or by reducing cellular Snapin with short interfering RNA, the sustained increase in [Ca2+]i in Snapin-α1A-AR co-expressing PC12 cells was attenuated. Snapin co-immunoprecipitated with TRPC6 and α1A-AR, and these interactions were augmented upon α1A-AR activation, increasing the recruitment of TRPC6 to the cell surface. Our data suggest a new receptor-operated signaling mechanism where Snapin links the α1A-AR to TRPC6, augmenting Ca2+ influx via ROC channels.

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