Abstract
Voltage-gated Ca2+ (CaV) channels consist of a pore-forming α1 subunit, which determines the main functional and pharmacological attributes of the channel. The CaV1 and CaV2 channels are associated with auxiliary β- and α2δ-subunits. The molecular mechanisms involved in α2δ subunit trafficking, and the effect of α2δ subunits on trafficking calcium channel complexes remain poorly understood. Here we show that α2δ-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 α2δ binding to gabapentin, and influences calcium channel trafficking and function. Whereas LRP1 alone reduces α2δ-1 trafficking to the cell-surface, the LRP1/RAP combination enhances mature glycosylation, proteolytic processing and cell-surface expression of α2δ-1, and also increase plasma-membrane expression and function of CaV2.2 when co-expressed with α2δ-1. Furthermore RAP alone produced a small increase in cell-surface expression of CaV2.2, α2δ-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 α2δ subunits.
Highlights
Voltage-gated Ca2+ (CaV) channels are multi-subunit complexes, containing a pore-forming α1 subunit, which determines the main functional and pharmacological attributes of the channel[1]
We found that α2δ-1 co-immunoprecipitated with cell surface Flag-LRP1-m4, only in cells co-transfected with LRP1-m4 and Receptor-Associated Protein (RAP), and was not detectable without RAP (Fig. 2c, lower panel, lane 4 compared to lane 3)
We show that the calcium channel auxiliary subunit α2δ- 1 is a ligand for LRP1, which, when combined with its chaperone protein RAP, promotes the trafficking, cell surface expression, mature glycosylation and proteolytic cleavage of α2δ- 1
Summary
Voltage-gated Ca2+ (CaV) channels are multi-subunit complexes, containing a pore-forming α1 subunit, which determines the main functional and pharmacological attributes of the channel[1]. We have shown the Von Willebrand Factor A (VWA) domain of α2δsubunits to be crucial for the trafficking of the associated α1 subunits to the plasma membrane[4], and for their ability to increase calcium currents and transmitter release[4,10]. Both α2δ-1 and α2δ-2 bind to the anti-epileptic and anti-hyperalgesic drugs gabapentin and pregabalin[8,11].
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