Dual regulation of voltage- and ligand-gated calcium channels by collapsin response mediator protein 2

Abstract

Synaptic transmission is coordinated by a litany of protein-protein interactions that rely on the proper localization and function of pre- and post-synaptic Ca2+ channels. The axonal guidance/specification collapsin response mediator protein-2 (CRMP-2) was identified as a potential partner of the pre-synaptic N-type voltage-gated Ca2+ channel (CaV2.2). CRMP-2 bound directly to CaV2.2 in two regions; the channel domain I-II intracellular loop and the distal C-terminus. Both proteins co-localized within presynaptic sites in hippocampal neurons. Overexpression in hippocampal neurons of a CRMP-2 protein fused to EGFP caused a significant increase in Ca2+ channel current density whereas lentivirus-mediated CRMP-2 knockdown abolished this effect. Cell surface biotinylation studies showed an increased number of CaV2.2 at the cell surface in CRMP-2–overexpressing neurons. Both activity- and CRMP-2-phosphoryation altered the interaction between CaV2.2 and CRMP-2. I identified a CRMP-2-derived peptide (called CBD3) that bound CaV2.2 and effectively disrupted the interaction between CaV2.2 and CRMP-2. CBD3 peptide fused to the HIV TAT protein (TAT-CBD3) decreased neuropeptide release from sensory neurons and excitatory synaptic transmission in dorsal horn neurons, and reversed neuropathic hypersensitivity produced by an antiretroviral drug. Unchecked Ca2+ influx via N-methyl-D-aspartate receptors (NMDARs) has been linked to activation of neurotoxic cascades culminating in cell death (i.e. excitotoxicity). CRMP-2 was suggested to affect NMDAR trafficking and possibly involved in neuronal survival following excitotoxicity. Based upon these studies, I hypothesized that a peptide from CRMP2 could preserve neurons in the face of excitotoxic challenges. Lentiviral–mediated CRMP2 knockdown or treatment with TAT-CBD3 blocked neuronal death following glutamate exposure likely via blunting toxicity from NMDAR-mediated delayed calcium deregulation. TAT-CBD3 induced internalization of the NMDAR subunit NR2B in dendritic spines without altering somal surface expression. TAT-CBD3 reduced NMDA-mediated Ca2+-influx and currents in cultured neurons. The presented work validates CRMP-2 as a novel modulator of pre- and post-synaptic Ca2+ channels and provides evidence that the TAT-CBD3 peptide could be useful as a potential therapeutic for both chronic neuropathic pain and excitotoxicity following stroke or other neuronal insults.