Rechler M M, Bruni C B, Podskalny J M, Carchman R A
J Supramol Struct. 1976;4(2):199-204. doi: 10.1002/jss.400040207.
The addition of serum to density-inhibited human fibroblast cultures induced a wave of DNA synthesis, measured as [3H] thymidine incorporation into acid-precipitable material, beginning after 8-12 hr and reaching maximum levels of 16-24 hr. Addition of dibutyryl-3':5'-cyclic AMP (DBcAMP) together with serum inhibited [3H] thymidine incorporation by 75-95%. When DBcAMP was added for the first 4 hr of serum stimulation and then removed, the wave of DNA synthesis was not delayed. This suggested that serum could induce DNA synthesis even though cyclic AMP concentrations were maintained at high levels by DBcAMP during this initial period. These results are inconsistent with the hypothesis that it is the immediate transient reduction in 3':5'-cyclic AMP concentration following the addition of serum that triggers DNA synthesis. By contrast, DBcAMP added 8 hr after serum inhibited [3H] thymidine incorporation to the same extent as DBcAMP added at the same time as serum. This indicated that a step essential for DNA synthesis and occurring late in G1 was inhibited by high concentrations of 3':5'-cyclic AMP.
向密度抑制的人成纤维细胞培养物中添加血清会诱导一波DNA合成，这通过[³H]胸苷掺入酸沉淀物质来衡量，在8 - 12小时后开始，并在16 - 24小时达到最高水平。将二丁酰-3':5'-环磷酸腺苷（DBcAMP）与血清一起添加会使[³H]胸苷掺入减少75 - 95%。当在血清刺激的前4小时添加DBcAMP然后去除时，DNA合成波并未延迟。这表明即使在这个初始阶段DBcAMP使环磷酸腺苷浓度维持在高水平，血清仍可诱导DNA合成。这些结果与以下假设不一致，即添加血清后3':5'-环磷酸腺苷浓度的立即短暂降低触发了DNA合成。相比之下，在血清添加8小时后添加的DBcAMP对[³H]胸苷掺入的抑制程度与与血清同时添加的DBcAMP相同。这表明高浓度的3':5'-环磷酸腺苷抑制了DNA合成中一个在G1期后期发生的关键步骤。
