Protein Kinase CE Activity Regulates mGluR5 Surface Expression in the Rat Nucleus Accumbens

Type 5 metabotropic glutamate receptors (mGluR5) activate protein kinase C (PKC) via coupling to Gaq/11 protein signaling. We have previously demonstrated that the epsilon isoform of PKC (PKC epsilon) is a critical downstream target of mGluR5 in regulating behavioral and biochemical responses to alcohol. Recent evidence suggests that PKC-mediated phosphorylation of mGluR5 can lead to receptor desensitization and internalization. We therefore sought to examine the specific involvement of PKC epsilon in the regulation of mGluR5 surface expression in the nucleus accumbens (NAc), a key regulator of alcohol-associated behaviors. Coronal brain sections from male Wistar rats were analyzed for either colocalization of mGluR5 and PKC epsilon via immunohistochemistry or changes in mGluR5 surface expression and PKC epsilon phosphorylation following local application of PKC epsilon translocation activator or inhibitor peptides and/or an orthosteric mGluR5 agonist. We observed colocalization of mGluR5 and PKC epsilon in the NAc. We also showed that intra-NAc infusion of the PKC epsilon translocation inhibitor EV1-2 increased mGluR5 surface expression under baseline conditions. Stimulation of mGluR5 with an orthosteric agonist DHPG, dose dependently increased ERK1/2 and PKC epsilon phosphorylation as well as mGluR5 internalization in acute NAc slices. Finally, we observed that activation of PKC epsilon translocation with Tat-WERACK peptide mediates agonist-independent mGluR5 internalization, whereas PKC epsilon translocation inhibitor EV1-2 prevents agonist-dependent internalization of mGluR5 in NAc slice preparations. These findings suggest that the subcellular localization of mGluR5 in the NAc is regulated by PKC epsilon under basal and stimulation conditions, which may influence the role of mGluR5-PKC epsilon signaling in alcohol-related behaviors. (C) 2016 Wiley Periodicals, Inc.