CAP-1A is a novel linker that binds clathrin and the voltage-gated sodium channel Na(v)1.8

The voltage-gated sodium channel Na(v)1.8 produces a tetrodotoxin-resistant current and plays a key role in nociception. Annexin II/p11 binds to Na(v)1.8 and facilitates insertion of the channel within the cell membrane. However, the mechanisms responsible for removal of specific channels from the cell membrane have not been studied. We have identified a novel protein, clathrin-associated protein-1A (CAP-1A), which contains distinct domains that bind Na(v)1.8 and clathrin. CAP-1A is abundantly expressed in DRG neurons and colocalizes with Na(v)1.8 and can form a multiprotein complex with Na(v)1.8 and clathrin. Coexpression of CAP-1A and Na(v)1.8 in DRG neurons reduces Na(v)1.8 current density by approximately 50% without affecting the endogenous or recombinant tetrodotoxin-sensitive currents. This effect of CAP-1A is blocked by bafilomycin A1 treatment of transfected DRG neurons. CAP-1A thus is the first example of an adapter protein that links clathrin and a sodium channel and may regulate Na(v)1.8 channel density at the cell surface.