Wayman G A, Impey S, Storm D R
Department of Pharmacology, University of Washington, Seattle 98195, USA.
J Biol Chem. 1995 Sep 15;270(37):21480-6. doi: 10.1074/jbc.270.37.21480.
Type III adenylyl cyclase is stimulated by beta-adrenergic agonists and glucagon in vitro and in vivo, but not by Ca2+ and calmodulin. However, the enzyme is stimulated by Ca2+ and calmodulin in vitro when it is concomitantly activated by the guanyl nucleotide stimulatory protein Gs (Choi, E. J., Xia, Z., and Storm, D. R. (1992a) Biochemistry 31, 6492-6498). Here, we examined regulation of type III adenylyl cyclase by Gs-coupled receptors and intracellular Ca2+ in vivo. Surprisingly, intracellular Ca2+ inhibited hormone-stimulated type III adenylyl cyclase activity. Submicromolar concentrations of intracellular free Ca2+, which stimulated type I adenylyl cyclase, inhibited glucagon- or isoproterenol-stimulated type III adenylyl cyclase. Inhibition of type III adenylyl cyclase by intracellular Ca2+ was not mediated by Gi, cAMP-dependent protein kinase, or protein kinase C. However, an inhibitor of CaM kinases antagonized Ca2+ inhibition of the enzyme, and coexpression of constitutively activated CaM kinase II completely inhibited isoproterenol-stimulated type III adenylyl cyclase activity. We propose that Ca2+ inhibition of type III adenylyl cyclase may serve as a regulatory mechanism to attenuate hormone-stimulated cAMP levels in some tissues.
III型腺苷酸环化酶在体外和体内均受到β-肾上腺素能激动剂和胰高血糖素的刺激，但不受Ca2+和钙调蛋白的刺激。然而，当该酶同时被鸟苷酸刺激蛋白Gs激活时，在体外它会受到Ca2+和钙调蛋白的刺激（Choi, E. J., Xia, Z., and Storm, D. R. (1992a) Biochemistry 31, 6492 - 6498）。在此，我们在体内研究了Gs偶联受体和细胞内Ca2+对III型腺苷酸环化酶的调节。令人惊讶的是，细胞内Ca2+抑制了激素刺激的III型腺苷酸环化酶活性。刺激I型腺苷酸环化酶的亚微摩尔浓度的细胞内游离Ca2+，抑制了胰高血糖素或异丙肾上腺素刺激的III型腺苷酸环化酶。细胞内Ca2+对III型腺苷酸环化酶的抑制作用不是由Gi、cAMP依赖性蛋白激酶或蛋白激酶C介导的。然而，CaM激酶的一种抑制剂拮抗了Ca2+对该酶的抑制作用，组成型激活的CaM激酶II的共表达完全抑制了异丙肾上腺素刺激的III型腺苷酸环化酶活性。我们提出，Ca2+对III型腺苷酸环化酶的抑制作用可能作为一种调节机制，在某些组织中减弱激素刺激的cAMP水平。
