LRP1 influences trafficking of N-type calcium channels via interaction with the auxiliary αδ-1 subunit.

Voltage-gated Ca (Ca) channels consist of a pore-forming α1 subunit, which determines the main functional and pharmacological attributes of the channel. The Ca1 and Ca2 channels are associated with auxiliary β- and αδ-subunits. The molecular mechanisms involved in αδ subunit trafficking, and the effect of αδ subunits on trafficking calcium channel complexes remain poorly understood. Here we show that αδ-1 is a ligand for the Low Density Lipoprotein (LDL) Receptor-related Protein-1 (LRP1), a multifunctional receptor which mediates trafficking of cargoes. This interaction with LRP1 is direct, and is modulated by the LRP chaperone, Receptor-Associated Protein (RAP). LRP1 regulates αδ binding to gabapentin, and influences calcium channel trafficking and function. Whereas LRP1 alone reduces αδ-1 trafficking to the cell-surface, the LRP1/RAP combination enhances mature glycosylation, proteolytic processing and cell-surface expression of αδ-1, and also increase plasma-membrane expression and function of Ca2.2 when co-expressed with αδ-1. Furthermore RAP alone produced a small increase in cell-surface expression of Ca2.2, αδ-1 and the associated calcium currents. It is likely to be interacting with an endogenous member of the LDL receptor family to have these effects. Our findings now provide a key insight and new tools to investigate the trafficking of calcium channel αδ subunits.