Cross-regulation between G-protein-mediated pathways. Activation of the inhibitory pathway of adenylylcylclase increases the expression of beta 2-adrenergic receptors

• Published in: The Journal of biological chemistry 1991-06, Vol.266 (18), p.11915-11922
• Main Authors: Hadcock, J R, Port, J D, Malbon, C C
• Format: Article
• Language: English
• Subjects: Adenosine - metabolism; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases - metabolism; Animals; Blotting, Western; Cells, Cultured; Cricetinae; Cross Reactions; Down-Regulation; Electrophoresis, Polyacrylamide Gel; Enzyme Activation; GTP-Binding Proteins - metabolism; Isoproterenol - pharmacology; Phenylisopropyladenosine - pharmacology; Precipitin Tests; Radioligand Assay; Receptors, Adrenergic, beta - drug effects; Receptors, Adrenergic, beta - metabolism; RNA, Messenger - metabolism; Up-Regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)99045-9

Cross-regulation from the stimulatory (Gs alpha)-mediated) to the inhibitory (Gi alpha-mediated) pathways controlling adenylylcyclase has been described (Hadcock, J. R., Ros, M., Watkins, D. C., and Malbon, C. C. (1990) J. Biol. Chem. 265, 14784-14790). The extent to which cross-regulation occurs from inhibitory to stimulatory pathways for adenylylcyclase was explored. Persistent activation of the inhibitory pathway of adenylylcyclase by the A1-adenosine receptor agonist (-)-N6 (R-phenylisopropyl) adenosine (PIA) in hamster smooth muscle DDT1 MF-2 cells enhanced the stimulatory pathway of adenylylcyclase and its activation by the beta 2-adrenergic receptor agonist isoproterenol. PIA treatment (48 h) of cells increased isoproterenol-stimulated adenylylcyclase by 2-fold. In addition, the ED50 for stimulation of adenylylcyclase by isoproterenol decreased 50-fold to approximately 1 nM. Persistent activation of cells with PIA increased beta 2-adrenergic receptor number in a time- and dose-dependent manner. The steady-state levels of beta 2-adrenergic receptors (radioligand binding and immunoblotting) and receptor mRNA levels increased by more than 70%, while the half-life of the receptor (24 h) was unaltered. Both A1-adenosine receptor binding and Gi alpha 2 levels declined by half in cells persistently activated with PIA. Although Gi alpha 2 mRNA levels and the relative rate of synthesis of Gi alpha 2 protein upon persistent activation of the inhibitory pathway were found to increase, a decrease in the half-life of Gi alpha 2 from approximately 75 h in naive cells to approximately 40 in cells provides the basis for the decline in Gi alpha 2 levels. The steady-state level of mRNA and half-life of Gs alpha protein were unaltered in persistently activated cells. Thus, activation of the inhibitory pathway of adenylylcyclase cross-regulates the stimulatory, hormone-sensitive adenylylcyclase system by: (i) up-regulating beta 2-adrenergic receptors and enhancing the activation of the stimulatory adenylylcyclase pathway and (ii) down-regulating elements of the inhibitory adenylylcyclase pathway (Gi alpha 2 and A1-adenosine receptor binding).