Phosphorylation Sites on Two Domains of the β2-Adrenergic Receptor Are Involved in Distinct Pathways of Receptor Desensitization

• Published in: The Journal of biological chemistry 1989-07, Vol.264 (21), p.12657-12665
• Main Authors: Hausdorff, W P, Bouvier, M, O'Dowd, B F, Irons, G P, Caron, M G, Lefkowitz, R J
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell receptors; Cell structures and functions; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine)
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)63907-9

Continuous exposure of cells to neurotransmitter or hormone agonists often results in a rapid desensitization of the cellular response. For example, pretreatment of Chinese hamster fibroblasts (CHW cells) expressing β2-adrenergic receptors (β2AR) with low (nanomolar) concentrations of isoproterenol, a β-adrenergic agonist, causes decreases in the sensitivity of the cellular adenylyl cyclase response to the agonist, without changing the maximal responsiveness. In contrast, exposure of CHW cells to high (micromolar) concentrations of isoproterenol results in decreases in both sensitivity and the maximal responsiveness to agonist. To explore the role(s) of receptor phosphorylation in these processes, we expressed in CHW cells three mutant β2AR genes encoding receptors lacking putative phosphorylation sites for the cAMP-dependent protein kinase A and/or the cAMP-independent β2AR kinase. Using these mutants we found that exposure of cells to low concentrations of agonist appears to preferentially induce phosphorylation at protein kinase A sites. This phosphorylation correlates with the decreased sensitivity to agonist stimulation of the adenylyl cyclase response. At higher agonist concentrations phosphorylation on both the β2AR kinase and protein kinase A sites occurs, and only then is the maximal cyclase responsiveness elicited by agonist reduced. We conclude that low or high concentrations of agonist elicit phosphorylation of β2AR on distinct domains, with different implications for the functional coupling of the receptors with effector molecules.