title: G Protein-coupled receptor kinase 2 regulator of G protein signaling homology domain binds to both metabotropic glutamate receptor 1a and Galphaq to attenuate signaling.
abstract: Heterotrimeric guanine nucleotide-binding (G) protein-coupled receptor kinases (GRKs) are cytosolic proteins that contribute to the adaptation of G protein-coupled receptor signaling. The canonical model for GRK-dependent receptor desensitization involves GRK-mediated receptor phosphorylation to promote the binding of arrestin proteins that sterically block receptor coupling to G proteins. However, GRK-mediated desensitization, in the absence of phosphorylation and arrestin binding, has been reported for metabotropic glutamate receptor 1 (mGluR1) and gamma-aminobutyric acid B receptors. Here we show that GRK2 mutants impaired in Galphaq/11 binding (R106A, D110A, and M114A), bind effectively to mGluR1a, but do not mediate mGluR1a adaptation. Galphaq/11 is immunoprecipitated as a complex with mGluR1a in the absence of agonist, and either agonist treatment or GRK2 overexpression promotes the dissociation of the receptor/Galphaq/11 complex. However, these mGluR1a/Galphaq/11 interactions are not antagonized by the overexpression of either GRK2 mutants defective in Galphaq/11 binding or RGS4. We have also identified a GRK2-D527A mutant that binds Galphaq/11 in an AlF4(-)-dependent manner but is unable to either bind mGluR1a or attenuate mGluR1a signaling. We conclude that the mechanism underlying GRK2 phosphorylation-independent attenuation of mGluR1a signaling is RH domain-dependent, requiring the binding of GRK2 to both Galphaq/11 and mGluR1a. This serves to coordinate GRK2 interactions with Galphaq/11 and to disrupt receptor/Galphaq/11 complexes. Our findings indicate that GRK2 regulates receptor/G protein interactions, in addition to its traditional role as a receptor kinase.
authors.affiliation: Cell Biology Research Group, Robarts Research Institute, London, Ontario N6A 5K8, Canada.
authors.forename: Gurpreet K
authors.initials: GK
authors.lastname: Dhami
authors.forename: Lianne B
authors.initials: LB
authors.lastname: Dale
authors.forename: Pieter H
authors.initials: PH
authors.lastname: Anborgh
authors.forename: Katharine E
authors.initials: KE
authors.lastname: O'Connor-Halligan
authors.forename: Rachel
authors.initials: R
authors.lastname: Sterne-Marr
authors.forename: Stephen S G
authors.initials: SS
authors.lastname: Ferguson
mesh_terms: D001665:Binding Sites; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D009154:Mutation; D010766:Phosphorylation; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins