β1- and β3- voltage-gated sodium channel subunits modulate cell surface expression and glycosylation of Na(v)1.7 in HEK293 cells

Voltage-gated sodium channels (Na(v)s) are glycoproteins composed of a pore-forming α-subunit and associated β-subunits that regulate Na(v) α-subunit plasma membrane density and biophysical properties. Glycosylation of the Na(v) α-subunit also directly affects Na(v)s gating. β-subunits and glycosylation thus comodulate Na(v) α-subunit gating. We hypothesized that β-subunits could directly influence α-subunit glycosylation. Whole-cell patch clamp of HEK293 cells revealed that both β1- and β3-subunits coexpression shifted V(½) of steady-state activation and inactivation and increased Na(v)1.7-mediated I(Na) density. Biotinylation of cell surface proteins, combined with the use of deglycosydases, confirmed that Na(v)1.7 α-subunits exist in multiple glycosylated states. The α-subunit intracellular fraction was found in a core-glycosylated state, migrating at ~250 kDa. At the plasma membrane, in addition to the core-glycosylated form, a fully glycosylated form of Na(v)1.7 (~280 kDa) was observed. This higher band shifted to an intermediate band (~260 kDa) when β1-subunits were coexpressed, suggesting that the β1-subunit promotes an alternative glycosylated form of Na(v)1.7. Furthermore, the β1-subunit increased the expression of this alternative glycosylated form and the β3-subunit increased the expression of the core-glycosylated form of Na(v)1.7. This study describes a novel role for β1- and β3-subunits in the modulation of Na(v)1.7 α-subunit glycosylation and cell surface expression.