title: Phosphorylation-independent desensitization of GABA(B) receptor by GRK4.
abstract: Agonist-promoted desensitization of the heterodimeric metabotropic GABA(B) receptor was investigated. Whereas no desensitization was observed in HEK293 cells heterologously expressing the receptor, GABA and the synthetic agonist baclofen induced a robust desensitization in cerebellar granule cells endogenously expressing the receptor. Taking advantage of this cell-specific desensitization phenotype, we identified GRK4 as the kinase involved in the neuronal desensitization. Transfection of small interference RNA directed against GRK4 significantly reduced GRK4 levels in cerebellar granule cells and strongly inhibited the agonist-promoted desensitization. Reciprocally, transfection of GRK4 in HEK293 cells restored agonist-promoted desensitization, confirming that this kinase is sufficient to support desensitization. Surprisingly, this desensitization occurred in the absence of ligand-induced receptor phosphorylation and could be promoted by GRK4 mutants deleted of their kinase domain. Taken together, these results suggest that GRK4 plays a central role in the agonist-promoted desensitization of GABA(B) receptor and that it does so through an atypical mechanism that challenges the generally accepted model linking the kinase activity of GRKs to their role in receptor desensitization.
authors.affiliation: Département de Biochimie, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, Quebec, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Perroy
authors.forename: Lynda
authors.initials: L
authors.lastname: Adam
authors.forename: Riad
authors.initials: R
authors.lastname: Qanbar
authors.forename: Sébastien
authors.initials: S
authors.lastname: Chénier
authors.forename: Michel
authors.initials: M
authors.lastname: Bouvier
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D002531:Cerebellum / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism; D054771:G-Protein-Coupled Receptor Kinase 4; D006801:Humans; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000378:metabolism*
chemical_list: D018080:Receptors, GABA-B; D017346:Protein Serine-Threonine Kinases; D054771:G-Protein-Coupled Receptor Kinase 4; C517855:GRK4 protein, human