title: Phosphorylation-independent regulation of metabotropic glutamate receptor signaling by G protein-coupled receptor kinase 2.
abstract: The accepted paradigm for G protein-coupled receptor kinase (GRK)-mediated desensitization of G protein-coupled receptors involves GRK-mediated receptor phosphorylation followed by the binding of arrestin proteins. Although GRKs contribute to metabotropic glutamate receptor 1 (mGluR1) inactivation, beta-arrestins do not appear to be required for mGluR1 G protein uncoupling. Therefore, we investigated whether the phosphorylation of serine and threonine residues localized within the C terminus of mGluR1a is sufficient to allow GRK2-mediated attenuation of mGluR1a signaling. We find that the truncation of the mGluR1a C-terminal tail prevents mGluR1a phosphorylation and that GRK2 does not contribute to the phosphorylation of an mGluR1 splice variant (mGluR1b). However, mGluR1a-866Delta- and mGluR1b-stimulated inositol phosphate formation is attenuated following GRK2 expression. The expression of the GRK2 C-terminal domain to block membrane translocation of endogenous GRK2 increases mGluR1a-866Delta- and mGluR1b-stimulated inositol phosphate formation, presumably by blocking membrane translocation of GRK2. In contrast, expression of the kinase-deficient GRK2-K220R mutant inhibits inositol phosphate formation by these unphosphorylated receptors. Expression of the GRK2 N-terminal domain (residues 45-185) also attenuates both constitutive and agonist-stimulated mGluR1a, mGluR1a-866Delta, and mGluR1b signaling, and the GRK2 N terminus co-precipitates with mGluR1a. Taken together, our observations indicate that attenuation of mGluR1 signaling by GRK2 is phosphorylation-independent and that the interaction of the N-terminal domain of GRK2 with mGluR1 contributes to the regulation of mGluR1 G protein coupling.
authors.affiliation: Cell Biology Research Group, the John P. Robarts Research Institute, Department of Pharmacology and Toxicology, University of Western Ontario, Canada.
authors.forename: Gurpreet Kaur
authors.initials: GK
authors.lastname: Dhami
authors.forename: Pieter H
authors.initials: PH
authors.lastname: Anborgh
authors.forename: Lianne B
authors.initials: LB
authors.lastname: Dale
authors.forename: Rachel
authors.initials: R
authors.lastname: Sterne-Marr
authors.forename: Stephen S G
authors.initials: SS
authors.lastname: Ferguson
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010766:Phosphorylation; D011956:Receptors, Cell Surface / Q000502:physiology*; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D011956:Receptors, Cell Surface; D018094:Receptors, Metabotropic Glutamate; D019204:GTP-Binding Proteins