Zeilig C E, Johnson R A, Sutherland E W, Friedman D L
J Cell Biol. 1976 Nov;71(2):515-34. doi: 10.1083/jcb.71.2.515.
The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine. Additional fluctuations in cAMP levels were observed during S phase. Two specific effects of cAMP on cell cycle traverse were found. Elevation of cAMP levels in S phase or G-2 caused arrest of cells in G-2 for as long as 10 h and lengthened M. However, once cells reached metaphase, elevation of cAMP accelerated the completion of mitosis. Stimulation of mitosis was also observed after addition of CaCl2. The specificity of the effects of cAMP was verified by demonstrating that: (a) intracellular cAMP was increased after exposure to methylisobutylxanthine (MIX) before any observed effects on cycle traverse; (b) submaximal concentrations of MIX potentiated the effects of isoproterenol; and (c) effects of MIX and isoproterenol were mimicked by 8-Br-cAMP. MIX at high concentrations inhibited G-1 traverse, but this effect did not appear to be mediated by cAMP. Isoproterenol slightly stimulated G-1 traverse and partially prevented the MIX-induced delay. Moreover, low concentrations of 8-Br-cAMP (0.10-100 muM) stimulated G-1 traverse, whereas high concentrations (1 mM) inhibited. Both of these effects were also observed with the control, Br-5'-AMP, at 10-fold lower concentrations.
通过测定同步化的HeLa细胞中细胞内cAMP水平的波动，并测试实验性改变的水平对细胞周期进程的影响，研究了3':5'-单磷酸腺苷（cAMP）在细胞周期调控中的作用。cAMP水平在有丝分裂期间最低，在G-1晚期或S期早期最高。当用秋水仙酰胺或高浓度胸苷使细胞在这些点积累时获得的结果支持了这些发现。在S期还观察到cAMP水平的其他波动。发现cAMP对细胞周期进程有两种特定作用。S期或G-2期cAMP水平的升高导致细胞在G-2期停滞长达10小时，并延长M期。然而，一旦细胞进入中期，cAMP的升高会加速有丝分裂的完成。添加CaCl2后也观察到有丝分裂的刺激。通过证明以下几点验证了cAMP作用的特异性：（a）在观察到对周期进程有任何影响之前，暴露于甲基异丁基黄嘌呤（MIX）后细胞内cAMP增加；（b）亚最大浓度的MIX增强了异丙肾上腺素的作用；（c）8-溴-cAMP模拟了MIX和异丙肾上腺素的作用。高浓度的MIX抑制G-1期进程，但这种作用似乎不是由cAMP介导的。异丙肾上腺素轻微刺激G-1期进程并部分防止MIX诱导的延迟。此外，低浓度的8-溴-cAMP（0.10 - 100μM）刺激G-1期进程，而高浓度（1 mM）则抑制。在浓度低10倍的对照物5'-溴-AMP中也观察到了这两种作用。
