Inhibition of recombinant N-type CaV channels by the γ2 subunit involves unfolded protein response (UPR)-dependent and UPR-independent mechanisms

Abstract

Auxiliary γ subunits are an important component of high-voltage-activated calcium (CaV) channels, but their precise regulatory role remains to be determined. In the current report, we have used complementary approaches including molecular biology and electrophysiology to investigate the influence of the γ subunits on neuronal CaV channel activity and expression. We found that coexpression of γ2 or γ3 subunits drastically inhibited macroscopic currents through recombinant N-type channels (CaV2.2/ β3/α2δ) in HEK-293 cells. Using inhibitors of internalization, we found that removal of functional channels from the plasma membrane is an improbable mechanism of current regulation by γ. Instead, changes in current amplitude could be attributed to two distinct mechanisms. First, γ subunit expression altered the voltage dependence of channel activity. Second, γ subunit expression reduced N-type channel synthesis via activation of the endoplasmic reticulum unfolded protein response. Together, our findings (1) corroborate that neuronal γ subunits significantly downregulate CaV2.2 channel activity, (2) uncover a role for the γ2 subunit in CaV2.2 channel expression through early components of the biosynthetic pathway, and (3) suggest that, under certain conditions, channel protein misfolding could be induced by interactions with the γ subunits, supporting the notion that Ca V channels constitute a class of difficult-to-fold proteins. Copyright © 2007 Society for Neuroscience.