Cross talk between m3-muscarinic and beta(2)-adrenergic receptors at the level of receptor phosphorylation and desensitization.
In this study we investigated cross talk between m3-muscarinic and beta(2)-adrenergic receptors coexpressed in Chinese hamster ovary (CHO-m3/beta(2)) cells, focusing on two possible mechanisms of regulation. The first mechanism is based on recent in vitro studies demonstrating that G protein-coupled receptor kinase (GRK) activity, the protein kinase responsible for beta(2)-adrenergic receptor homologous phosphorylation and desensitization, may be regulated by calcium/calmodulin and membrane phosphatidylinositol 4, 5-bisphosphate. Stimulation of the phospholipase C signaling pathway via m3-muscarinic receptors in CHO-m3/beta(2) cells increased intracellular free calcium by approximately 10 fold and membrane phosphatidylinositol 4,5-bisphosphate levels decreased by approximately 74%. However, despite these changes the ability of endogenous kinases, possibly the GRKs, to phosphorylate the beta(2)-adrenergic receptor was not altered. The second mechanism investigated involves a direct heterologous phosphorylation of the beta(2)-adrenergic receptor after muscarinic receptor stimulation. Activation of m3-muscarinic receptors did mediate heterologous phosphorylation of beta(2)-adrenergic receptors in a GRK-independent fashion, via protein kinase C. Heterologous beta(2)-adrenergic receptor phosphorylation correlated with receptor desensitization as measured by a loss in guanine-nucleotide sensitive-high affinity agonist binding and reduction in maximal cAMP response. This receptor cross talk may have a profound physiological importance in a wide variety of cell types, for example smooth muscle, where these two receptors are known to be coexpressed.
Budd
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DC
Department of Cell Physiology and Pharmacology, University of Leicester, Leicester, United Kingdom.
Challiss
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Young
K W
KW
Tobin
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D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015151:Immunoblotting; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010766:Phosphorylation; D020239:Receptor Cross-Talk; D043587:Receptor, Muscarinic M3; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D051552:beta-Adrenergic Receptor Kinases
D019269:Phosphatidylinositol 4,5-Diphosphate; D043587:Receptor, Muscarinic M3; D018343:Receptors, Adrenergic, beta-2; D011976:Receptors, Muscarinic; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D002118:Calcium