Group I metabotropic glutamate receptors (mGluR), including mGluR1 and mGluR 5 (mGluR1/5), are coupled to Gq and modulate activity-dependent synaptic plasticity. Direct activation of mGluR1/5 causes protein translation-dependent long-term depression (LTD). Although it has been established that intracellular Ca2+ and the Gq-regulated signaling molecules are required for mGluR1/5 LTD, whether and how Ca2+ regulates Gq signaling and upregulation of protein expression remain unknown. Through pharmacological inhibition, we tested the function of the Ca2+ sensor calmodulin (CaM) in intracellular signaling triggered by the activation of mGluR1/5. CaM inhibitor N-[4-aminobutyl]-5-chloro-2-naphthalenesulfonamide hydrochloride (W13) suppressed the mGluR1/5-stimulated activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p70-S6 kinase 1 (S6K1) in hippocampal neurons. W13 also blocked the mGluR1/5 agonist-induced synaptic depression in hippocampal slices and in anesthetized mice. Consistent with the function of CaM, inhibiting the downstream targets Ca2+/CaM-dependent protein kinases (CaMK) blocked ERK1/2 and S6K1 activation. Furthermore, disruption of the CaM–CaMK–ERK1/2 signaling cascade suppressed the mGluR1/5-stimulated upregulation of Arc expression. Altogether, our data suggest CaM as a new Gq signaling component for coupling Ca2+ and protein upregulation and regulating mGluR1/5-mediated synaptic modification. © 2016 Wiley Periodicals, Inc.
This study suggests a working model for the function of calmodulin in regulating the mGluR1/5-mediated ERK1/2–p70–S6 kinase 1 signaling cascade, which is required for the upregulation of certain plasticity-related proteins and synaptic long-term depression.