The inhibition of functional expression of calcium channels by prion protein demonstrates competition with α ₂δ for GPI-anchoring pathways

Abstract

It has been shown recently that PrP (prion protein) and the calcium channel auxiliary α ₂δ subunits interact in neurons and expression systems [Senatore, Colleoni, Verderio, Restelli, Morini, Condliffe, Bertani, Mantovani, Canovi, Micotti, Forloni, Dolphin, Matteoli, Gobbi and Chiesa (2012) Neuron 74, 300–313]. In the present study we examined whether there was an effect of PrP on calcium currents. We have shown that when PrP is co-expressed with calcium channels formed from Ca _V2.1/β and α ₂δ-1 or α ₂δ-2, there is a consistent decrease in calcium current density. This reduction was absent when a PrP construct was used lacking its GPI (glycosylphosphatidylinositol) anchor. We have reported previously that α ₂δ subunits are able to form GPI-anchored proteins [Davies, Kadurin, Alvarez-Laviada, Douglas, Nieto-Rostro, Bauer, Pratt and Dolphin (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 1654–1659] and show further evidence in the present paper. We have characterized recently a C-terminally truncated α ₂δ-1 construct, α ₂δ-1ΔC, and found that, despite loss of its membrane anchor, it still shows a partial ability to increase calcium currents [Kadurin, Alvarez-Laviada, Ng, Walker-Gray, D’Arco, Fadel, Pratt and Dolphin (2012) J. Biol. Chem. 1287, 33554–33566]. We now find that PrP does not inhibit Ca _V2.1/β currents formed with α ₂δ-1ΔC, rather than α ₂δ-1. It is possible that PrP and α ₂δ-1 compete for GPI-anchor intermediates or trafficking pathways, or that interaction between PrP and α ₂δ-1 requires association in cholesterol-rich membrane microdomains. Our additional finding that Ca _V2.1/β1b/α ₂δ-1 currents were inhibited by GPI–GFP, but not cytosolic GFP, indicates that competition for limited GPI-anchor intermediates or trafficking pathways may be involved in PrP suppression of α ₂δ subunit function.

Abstract

PrP, but not GPI-anchorless PrP, suppresses Ca _V2.1/β/α ₂δ-1 or α ₂δ-2 calcium channel currents. However, PrP does not inhibit Ca _V2.1/β currents formed with anchorless α ₂δ-1, rather than full-length α ₂δ-1. The results of the present study suggest that α ₂δ subunits and PrP may compete for GPI-anchor pathways.