Protein kinase C-mediated phosphorylation and a2d-1 interdependently regulate NMDA receptor trafficking and activity

Abstract

N-methyl-D-aspartate receptors (NMDARs) are important for synaptic plasticity associated with many physiological functions and neurologic disorders. Protein kinase C (PKC) activation increases the phosphorylation and activity of NMDARs, and a2d-1 is a critical NMDAR-interacting protein and controls synaptic trafficking of NMDARs. In this study, we determined the relative roles of PKC and a2d-1 in the control of NMDAR activity. We found that a2d-1 coexpression significantly increased NMDAR activity in HEK293 cells transfected with GluN1/GluN2A or GluN1/GluN2B. PKC activation with phorbol 12-myris-tate 13-acetate (PMA) increased receptor activity only in cells coexpressing GluN1/GluN2A and a2d-1. Remarkably, PKC inhibition with Gӧ6983 abolished a2d-1-coexpression-induced potentiation of NMDAR activity in cells transfected with GluN1/ GluN2A or GluN1/GluN2B. Treatment with PMA increased the a2d-1–GluN1 interaction and promoted a2d-1 and GluN1 cell surface trafficking. PMA also significantly increased NMDAR activity of spinal dorsal horn neurons and the amount of a2d-1-bound GluN1 protein complexes in spinal cord synaptosomes in wild-type mice, but not in a2d-1 knockout mice. Furthermore, inhibiting a2d-1 with pregabalin or disrupting the a2d-1–NMDAR interaction with the a2d-1 C-terminus peptide abolished the potentiating effect of PMA on NMDAR activity. Additionally, using quantitative phosphoproteomics and mutagenesis analyses, we identified S929 on GluN2A and S1413 (S1415 in humans) on GluN2B as the phosphorylation sites responsible for NMDAR potentiation by PKC and a2d-1. Together, our findings demonstrate the interdependence of a2d-1 and PKC phosphorylation in regulating NMDAR trafficking and activity. The phosphorylation-dependent, dynamic a2d-1–NMDAR interaction constitutes an important molecular mechanism of synaptic plasticity.