Cross-regulation between G-protein-mediated pathways. Activation of the inhibitory pathway of adenylylcylclase increases the expression of beta 2-adrenergic receptors.
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).
Hadcock
J R
JR
Department of Pharmacology, Diabetes and Metabolic Diseases Research Program, School of Medicine, State University of New York, Stony Brook 11794-8651.
Port
J D
JD
Malbon
C C
CC
D000241:Adenosine / Q000378:metabolism; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D006224:Cricetinae; D003429:Cross Reactions; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000378:metabolism; D011869:Radioligand Assay; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D015854:Up-Regulation
D000067956:Adenylyl Cyclase Inhibitors; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D010660:Phenylisopropyladenosine; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000241:Adenosine; D007545:Isoproterenol