Saijo M, Ui M, Enomoto T
Department of Physiological Chemistry, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Biochemistry. 1992 Jan 21;31(2):359-63. doi: 10.1021/bi00117a007.
We have investigated the amount of DNA topoisomerase II and phosphorylation of the enzyme in Swiss 3T3 cells during the transition from cell quiescence to proliferation. A relatively high level of phosphorylation was observed with proliferating cells while no or a very low level of phosphorylation was observed with quiescent cells. Phosphoamino acid analysis of the phosphorylated topoisomerase II revealed that the phosphorylated aminoacyl residue was serine. When quiescent cells were stimulated to grow by the addition of serum, DNA synthesis began to increase at 9 h after serum addition, reaching a maximum at 15 h and then declining. The amount of topoisomerase II began to increase at 6 h and reached a maximum at 22-27 h, corresponding to the G2 phase. The phosphorylation of topoisomerase II measured by pulse-labeling gradually increased from 6 to 18 h and reached a maximum at 22 h when the amount of the enzyme was maximum. The level of phosphorylation measured by continuous-labeling increased gradually up to 12 h and markedly up to 28 h, and then declined. The increase in the rate of phosphorylation in the G2 phase was affected by inhibiting DNA synthesis, but the increase in the amount of the enzyme was not. Thus, it was suggested that the regulation of phosphorylation of topoisomerase II differs from that of the amount of the enzyme.
我们研究了瑞士3T3细胞从静止状态转变为增殖状态过程中DNA拓扑异构酶II的含量及其磷酸化情况。增殖细胞中观察到相对较高水平的磷酸化，而静止细胞中未观察到或仅有非常低水平的磷酸化。对磷酸化拓扑异构酶II进行的磷酸氨基酸分析表明，磷酸化的氨酰基残基是丝氨酸。当通过添加血清刺激静止细胞生长时，DNA合成在添加血清后9小时开始增加，在15小时达到最大值，然后下降。拓扑异构酶II的含量在6小时开始增加，在22 - 27小时达到最大值，对应于G2期。通过脉冲标记测量的拓扑异构酶II的磷酸化从6小时到18小时逐渐增加，在22小时酶含量达到最大值时达到峰值。通过连续标记测量的磷酸化水平在12小时前逐渐增加，在28小时显著增加，然后下降。G2期磷酸化速率的增加受到DNA合成抑制的影响，但酶含量的增加不受影响。因此，提示拓扑异构酶II磷酸化的调节与酶含量的调节不同。
