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Inhibition of Recombinant N-Type Ca V Channels by the γ 2 Subunit Involves Unfolded Protein Response (UPR)-Dependent and UPR-Independent Mechanisms

2007; Society for Neuroscience; Volume: 27; Issue: 12 Linguagem: Inglês

10.1523/jneurosci.4566-06.2007

1529-2401

Alejandro Sandoval, Arturo Andrade, Aaron M. Beedle, Kevin P. Campbell, Ricardo Felix,

Endoplasmic Reticulum Stress and Disease

Auxiliary γ subunits are an important component of high-voltage-activated calcium (Ca V ) 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 Ca V channel activity and expression. We found that coexpression of γ 2 or γ 3 subunits drastically inhibited macroscopic currents through recombinant N-type channels (Ca V 2.2/β 3 /α 2 δ) 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 Ca V 2.2 channel activity, (2) uncover a role for the γ 2 subunit in Ca V 2.2 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.