Article: article from journal or magazin.
Characterization of the phosphorylation sites involved in G protein-coupled receptor kinase- and protein kinase C-mediated desensitization of the alpha1B-adrenergic receptor.
Journal of Biological Chemistry
Catecholamines as well as phorbol esters can induce the phosphorylation and desensitization of the alpha1B-adrenergic receptor (alpha1BAR). In this study, phosphoamino acid analysis of the phosphorylated alpha1BAR revealed that both epinephrine- and phorbol ester-induced phosphorylation predominantly occurs at serine residues of the receptor. The findings obtained with receptor mutants in which portions of the C-tail were truncated or deleted indicated that a region of 21 amino acids (393-413) of the carboxyl terminus including seven serines contains the main phosphorylation sites involved in agonist- as well as phorbol ester-induced phosphorylation and desensitization of the alpha1BAR. To identify the serines invoved in agonist- versus phorbol ester-dependent regulation of the receptor, two different strategies were adopted, the seven serines were either substituted with alanine or reintroduced into a mutant lacking all of them. Our findings indicate that Ser394 and Ser400 were phosphorylated following phorbol ester-induced activation of protein kinase C, whereas Ser404, Ser408, and Ser410 were phosphorylated upon stimulation of the alpha1BAR with epinephrine. The observation that overexpression of G protein-coupled kinase 2 (GRK2) could increase agonist-induced phosphorylation of Ser404, Ser408, and Ser410, strongly suggests that these serines are the phosphorylation sites of the alpha1BAR for kinases of the GRK family. Phorbol ester-induced phosphorylation of the Ser394 and Ser400 as well as GRK2-mediated phosphorylation of the Ser404, Ser408, and Ser410, resulted in the desensitization of alpha1BAR-mediated inositol phosphate response. This study provides generalities about the biochemical mechanisms underlying homologous and heterologous desensitization of G protein-coupled receptors linked to the activation of phospholipase C.
Amino Acid Sequence, Animals, COS Cells, Carcinogens/pharmacology, Cyclic AMP-Dependent Protein Kinases/metabolism, G-Protein-Coupled Receptor Kinase 5, Molecular Sequence Data, Mutagenesis, Site-Directed, Peptide Mapping, Phorbol Esters/pharmacology, Phosphorylation, Protein Kinase C/metabolism, Protein Structure, Secondary, Protein-Serine-Threonine Kinases, Receptor Protein-Tyrosine Kinases/metabolism, Receptors, Adrenergic, alpha-1/genetics, Receptors, Adrenergic, alpha-1/metabolism, Serine/metabolism, beta-Adrenergic Receptor Kinases
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