title: G protein-coupled receptor kinase GRK2 is a phospholipid-dependent enzyme that can be conditionally activated by G protein betagamma subunits.
abstract: G protein-coupled receptor kinases (GRKs) mediate agonist-dependent phosphorylation of G protein-coupled receptors (GPRs) and initiate homologous receptor desensitization. Previously, we reported that charged phospholipids directly interacted with the two GRK isoforms, GRK2 and GKR3, via a pleckstrin homology (PH) domain to regulate GRK activity (DebBurman, S. K., Ptasienski, J., Boetticher, E., Lomasney, J. W., Benovic, J. L., and Hosey, M. M. (1995) J. Biol. Chem. 270: 5742-5747). Here, evidence is provided to support the hypothesis that charged phospholipids are required for agonist-dependent phosphorylation of receptors by GRK2. In the absence of charged phospholipids, the purified human m2 muscarinic acetylcholine receptor (hm2mAChR) reconstituted in pure phosphatidylcholine vesicles or in a noninhibitory detergent was not a substrate for GRK2. However, these receptor preparations were stoichiometrically phosphorylated in an agonist-dependent manner upon addition of charged phospholipids. The known ability of G protein betagamma subunits to stimulate mAChR phosphorylation also was found to be absolutely dependent on the presence of charged phospholipids, including phosphatidylinositol 4,5-bisphosphate (PIP2). Phospholipids also regulated GRK-mediated phosphorylation of casein, a nonreceptor-soluble substrate. Among lipids tested, lipid inositol phosphates, PIP2 and phosphatidylinositol 4-monophosphate, were found to be the most potent activators of GRK2 and were the only lipids that regulated GRK2 in a complex biphasic manner. At low micro concentrations, PIP2 activated GRK2 via an interaction with the GRK pleckstrin homology domain; however, at high micro concentrations, PIP2 inhibited GRK2, apparently via another mechanism. PIP2-mediated inhibition could be partly relieved by increasing ATP. The results support the hypothesis that GRK2 is a lipid-dependent protein kinase that requires charged phospholipids for enzyme activation, for regulation by Gbetagamma subunits, and potentially for membrane association.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, and Institute of Neuroscience, Northwestern University Medical School, Chicago, Illinois 60611, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: DebBurman
authors.forename: J
authors.initials: J
authors.lastname: Ptasienski
authors.forename: J L
authors.initials: JL
authors.lastname: Benovic
authors.forename: M M
authors.initials: MM
authors.lastname: Hosey
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D006224:Cricetinae; D003412:Cricetulus; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D054770:G-Protein-Coupled Receptor Kinase 3; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism; D013329:Structure-Activity Relationship; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; C037178:phosphatidylinositol 4-phosphate; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D012243:Rhodopsin; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517848:GRK3 protein, human; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins