Agonist-induced internalization of mGluR1alpha is mediated by caveolin.

Agonist-induced internalization of metabotropic glutamate receptors (mGluRs) plays an important role in neuronal signaling. Although internalization of mGluRs has been reported to be mediated by clathrin-dependent pathway, studies describing clathrin-independent pathways are emerging. Here, we report that agonist-induced internalization of mGluR1alpha is mediated by caveolin. We show that two caveolin-binding motifs of mGluR1alpha interact with caveolin1/2. Using cell surface-immunoprecipitation and total internal reflection fluorescence imaging, we found that agonist-induced internalization of mGluR1alpha is regulated by caveolin-binding motifs of the receptor in heterologous cells. Moreover, in the cerebellum, group I mGluR agonist dihydroxyphenylglycol increased the interaction of phosphorylated caveolin with mGluR1alpha. This interaction was blocked by methyl-beta-cyclodextrin, known to disrupt caveolin/caveolae-dependent signaling by cholesterol depletion. Methyl-beta-cyclodextrin also blocked the agonist-induced internalization of mGluR1alpha. Thus, these findings represent the evidence for agonist-induced internalization of mGluR1alpha via caveolin and suggest that caveolin might play a role in synaptic metaplasticity by regulating internalization of mGluR1alpha in the cerebellum.