Synergistic activation of the type I adenylyl cyclase by Ca2+ and Gs-coupled receptors in vivo.
The type I adenylyl cyclase is directly stimulated by Ca2+ and calmodulin in vivo (Choi, E. J., Wong, S. T., Hinds, T. R. and Storm, D. R. (1992) J. Biol. Chem. 267, 12440-12442; Wu, Z., Wong, S. T., and Storm, D. R. (1993) J. Biol. Chem. 268, 23766-23768). In this study, we examined the sensitivity of the type I adenylyl cyclase expressed in HEK-293 cells to beta-adrenergic agonists or glucagon when intracellular Ca2+ was elevated by Ca2+ ionophore or carbachol. Although previous studies have shown that this enzyme can be directly stimulated by activated Gs in vitro, we demonstrate that it is not stimulated by Gs-coupled receptors in vivo. However, the enzyme was stimulated by Gs-coupled receptors in vivo when it was activated by intracellular Ca2+. For example, the Ca2+ ionophore A23187 stimulated the enzyme 3 +/- 0.5-fold (n = 9) and isoproterenol alone did not stimulate the enzyme, but the combination of the two stimulated type I adenylyl cyclase 13 +/- 2-fold (n = 9) in vivo. Similarly, 500 nM glucagon alone did not stimulate the enzyme but the combination of A23187 and glucagon activated the enzyme 90 +/- 8-fold (n = 4). Synergistic stimulation of type I adenylyl cyclase activity was also obtained with combinations of carbachol and isoproterenol or glucagon. This phenomenon was not observed with a mutant enzyme that is insensitive to Ca2+ and calmodulin, suggesting that conformational changes caused by binding of calmodulin to the type I adenylyl cyclase enhance binding or coupling to activated Gs. These data illustrate that this adenylyl cyclase can couple Ca2+ and neurotransmitter signals to generate optimal cAMP levels, a property of the enzyme that may be important for its role in learning and memory in mammals.
Wayman
G A
GA
Department of Pharmacology, University of Washington, Washington 98195.
Impey
S
S
Wu
Z
Z
Kindsvogel
W
W
Prichard
L
L
Storm
D R
DR
D000262:Adenylyl Cyclases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000196:embryology; D047428:Protein Kinase Inhibitors; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018027:Receptors, Glucagon / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D002147:Calmodulin; D047428:Protein Kinase Inhibitors; D011943:Receptors, Adrenergic, beta; D011956:Receptors, Cell Surface; D018027:Receptors, Glucagon; D011994:Recombinant Proteins; D000001:Calcimycin; D002217:Carbachol; D005934:Glucagon; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium