title: Tyrosine phosphorylation of G-protein-coupled-receptor kinase 2 (GRK2) by c-Src modulates its interaction with Galphaq.
abstract: G-protein-coupled-receptor kinase 2 (GRK2) plays a key role in the modulation of G-protein-coupled-receptor (GPCR) signaling by both phosphorylating agonist-occupied GPCRs and by directly binding to activated Galphaq subunits, inhibiting downstream effectors activation. The GRK2/Galphaq interaction involves the N-terminal region of the kinase that displays homology to regulators of G-protein signaling (RGS) proteins. We have previously reported that upon GPCR stimulation, GRK2 can be phosphorylated by c-Src on tyrosine residues that are present in the RGS-homology (RH) region of this kinase. Here, we demonstrate that c-Src kinase activity increases the interaction between GRK2 and Galphaq. Tyrosine phosphorylation of GRK2 appears to be critically involved in the modulation of this interaction since the stimulatory effect of c-Src is not observed with a GRK2 mutant with impaired tyrosine phosphorylation (GRK2 Y13,86,92F), whereas a mutant that mimics GRK2 tyrosine phosphorylation in these residues displays an increased interaction with Galphaq. As evidence for a physiological role of this modulatory mechanism, activation of the muscarinic receptor M1, a Galphaq-coupled receptor, promotes an increase in GRK2/Galphaq co-immunoprecipitation that parallels the enhanced GRK2 phosphorylation on tyrosine residues. Moreover, c-Src activation enhances inhibition of the Galphaq/phospholipase Cbeta signaling pathway in intact cells, in a GRK2-tyrosine-phosphorylation-dependent manner. Our results suggest a feedback mechanism by which phosphorylation of GRK2 by c-Src increases both GRK2 kinase activity towards GPCRs and its specific interaction with Galphaq subunits, leading to a more rapid switch off of Galphaq-mediated signaling.
authors.affiliation: Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale 8A, 66030 Santa Maria Imbaro, Chieti, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Mariggiò
authors.forename: Carlota
authors.initials: C
authors.lastname: García-Hoz
authors.forename: Susana
authors.initials: S
authors.lastname: Sarnago
authors.forename: Antonio
authors.initials: A
authors.lastname: De Blasi
authors.forename: Federico
authors.initials: F
authors.lastname: Mayor
authors.forename: Catalina
authors.initials: C
authors.lastname: Ribas
mesh_terms: D000081247:CSK Tyrosine-Protein Kinase; D002460:Cell Line; D054769:G-Protein-Coupled Receptor Kinase 2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*; D051552:beta-Adrenergic Receptor Kinases / Q000378:metabolism*; D019061:src-Family Kinases
chemical_list: D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; C496567:GRK2 protein, human; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11