title: Agonist dose-dependent phosphorylation by protein kinase A and G protein-coupled receptor kinase regulates beta2 adrenoceptor coupling to G(i) proteins in cardiomyocytes.
abstract: Adrenoceptors receptors (ARs) play a pivotal role in regulating cardiovascular response to catecholamines during stress. beta(2)ARs, prototypical G protein-coupled receptors (GPCRs), expressed in animal hearts, display dual coupling to both G(s) and G(i) proteins to control the adenylyl cyclase-cAMP dependent protein kinase A (PKA) pathway to regulate contraction responses. Here, we showed that the beta(2)AR coupling to G(i) proteins was agonist dose-dependent and occurred only at high concentrations in mouse cardiac myocytes. Both the beta(2)AR-induced PKA activity, measured by fluorescence resonance energy transfer (FRET) imaging, and the increase in myocyte contraction rate displayed sensitivity to the G(i) inhibitor pertussis toxin (PTX). Further studies revealed that activated beta(2)ARs underwent PKA phosphorylation at a broad range of agonist concentrations. Disruption of the PKA phosphorylation sites on the beta(2)AR blocked receptor/G(i) coupling. However, a sufficient beta(2)AR/G(i) coupling was also dependent on the G protein-coupled receptor kinase (GRK)-mediated phosphorylation of the receptors, which only occurred at high concentrations of agonist (> or = 100 nm). Disruption of the GRK phosphorylation sites on the beta(2)AR blocked receptor internalization and coupling to G(i) proteins, probably by preventing the receptor's transportation to access G(i) proteins. Furthermore, neither PKA nor GRK site mutated receptors displayed sensitivity to the G(i)-specific inhibitor, G(i)CT. Together, our studies revealed distinct roles of PKA and GRK phosphorylation of the beta(2)AR for agonist dose-dependent coupling to G(i) proteins in cardiac myocytes, which may protect cells from overstimulation under high concentrations of catecholamines.
authors.affiliation: Department of Molecular and Integrative Physiology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Ruijie
authors.initials: R
authors.lastname: Liu
authors.forename: Biswarathan
authors.initials: B
authors.lastname: Ramani
authors.forename: Dagoberto
authors.initials: D
authors.lastname: Soto
authors.forename: Vania
authors.initials: V
authors.lastname: De Arcangelis
authors.forename: Yang
authors.initials: Y
authors.lastname: Xiang
mesh_terms: D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D031541:Fluorescence Resonance Energy Transfer; D054768:G-Protein-Coupled Receptor Kinases / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D005786:Gene Expression Regulation; D051379:Mice; D032342:Muscle Cells / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D032383:Myocytes, Cardiac / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*
chemical_list: D018343:Receptors, Adrenergic, beta-2; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D054768:G-Protein-Coupled Receptor Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go
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