Phosphodiesterase-4 influences the PKA phosphorylation status and membrane translocation of G-protein receptor kinase 2 (GRK2) in HEK-293beta2 cells and cardiac myocytes.
Membrane-recruitment of GRK2 (G-protein receptor kinase 2) provides a fundamental step in the desensitization process controlling GPCRs (G-protein-coupled receptors), such as the beta2AR (beta2-adrenergic receptor). In the present paper, we show that challenge of HEK-293beta2 [human embryonic kidney cells stably overexpressing the FLAG-tagged beta2AR-GFP (green fluorescent protein)] cells with the beta-adrenoceptor agonist, isoprenaline, causes GRK2 to become phosphorylated by PKA (cAMP-dependent protein kinase). This action is facilitated when cAMP-specific PDE4 (phosphodiesterase-4) activity is selectively inactivated, either chemically with rolipram or by siRNA (small interfering RNA)-mediated knockdown of PDE4B and PDE4D. PDE4-selective inhibition by rolipram facilitates the isoprenaline-induced membrane translocation of GRK2, phosphorylation of the beta2AR by GRK2, membrane translocation of beta-arrestin and internalization of beta2ARs. PDE4-selective inhibition also enhances the ability of isoprenaline to trigger the PKA phosphorylation of GRK2 in cardiac myocytes. In the absence of isoprenaline, rolipram-induced inhibition of PDE4 activity in HEK-293beta2 cells acts to stimulate PKA phosphorylation of GRK2, with consequential effects on GRK2 membrane recruitment and GRK2-mediated phosphorylation of the beta2AR. We propose that a key role for PDE4 enzymes is: (i) to gate the action of PKA on GRK2, influencing the rate of GRK2 phosphorylation of the beta2AR and consequential recruitment of beta-arrestin subsequent to beta-adrenoceptor agonist challenge, and (ii) to protect GRK2 from inappropriate membrane recruitment in unstimulated cells through its phosphorylation by PKA in response to fluctuations in basal levels of cAMP.
Li
Xiang
X
Molecular Pharmacology Group, Division of Biochemistry & Molecular Biology, IBLS, Wolfson Link Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, Scotland, UK.
Huston
Elaine
E
Lynch
Martin J
MJ
Houslay
Miles D
MD
Baillie
George S
GS
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D054769:G-Protein-Coupled Receptor Kinase 2; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010766:Phosphorylation; D021381:Protein Transport; D020889:Rolipram / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases / Q000378:metabolism*
D017868:Cyclic AMP-Dependent Protein Kinases; C496567:GRK2 protein, human; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C517360:PDE4B protein, human; C517376:PDE4D protein, human; D020889:Rolipram; D007545:Isoproterenol