Phosphorylation of chick heart muscarinic cholinergic receptors by the beta-adrenergic receptor kinase.
Previous studies have demonstrated that muscarinic cholinergic receptors (mAChR) become markedly phosphorylated when intact cardiac cells are stimulated with a muscarinic agonist. This process appears to be related to the process of receptor desensitization. However, the mechanism of agonist-induced phosphorylation of mAChR is not known. In situ phosphorylation studies suggested that agonist-induced phosphorylation of mAChR may involve the participation of a receptor-specific kinase and/or require agonist occupancy. These observations regarding phosphorylation and desensitization of mAChR are similar to observations made for beta-adrenergic receptors. Recent studies have indicated that homologous desensitization of beta-adrenergic receptors may be due to the phosphorylation of these receptors by a novel protein kinase that only recognizes the agonist-occupied form of the receptors. As muscarinic receptors are structurally homologous to beta-adrenergic receptors, we have initiated studies to identify the protein kinase responsible for the phosphorylation of muscarinic receptors by determining whether the chick heart muscarinic receptor would serve as a substrate for the beta-adrenergic receptor kinase (beta-AR kinase). We report that the purified and reconstituted chick heart muscarinic receptor serves as an excellent substrate in vitro for the beta-AR kinase. Phosphorylation of mAChR receptors by the beta-AR kinase was only observed in the presence of a muscarinic receptor agonist and was prevented in the presence of antagonist. Both the extent of phosphorylation (3-4 mol of P/mol of receptor) and the phosphoamino acid composition of the mAChR after incubation in vitro with beta-AR kinase were similar to the characteristics of agonist-induced phosphorylation of mAChR in situ.(ABSTRACT TRUNCATED AT 250 WORDS)
Kwatra
M M
MM
Department of Biological Chemistry and Structure, University of Health Sciences, Chicago Medical School, Illinois 60064.
Benovic
J L
JL
Caron
M G
MG
Lefkowitz
R J
RJ
Hosey
M M
MM
D000818:Animals; D002645:Chickens; D017868:Cyclic AMP-Dependent Protein Kinases; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D051552:beta-Adrenergic Receptor Kinases
D011976:Receptors, Muscarinic; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases