TOPOISOMERAS-SPECIFIC DRUG SENSITIVITY IN RELATION TO CELL-CYCLE PROGRESSION
TOPOISOMERAS-SPECIFIC DRUG SENSITIVITY IN RELATION TO CELL-CYCLE PROGRESSION
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DOI：
10.1128/mcb.7.9.3119
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发表时间：
1987-09-01
影响因子：
5.3
通讯作者：
ROSS, WE
中科院分区：
文献类型：
--
作者：
CHOW, KC;ROSS, WE
DNA拓扑异构酶Ⅱ是一种重要的核酶，它催化双链DNA的断裂和重封，在许多遗传过程中起着重要作用。它还介导DNA切割活性和临床上重要的抗癌剂如依托泊苷的细胞毒性。我们已经研究了拓扑异构酶II的活性在第一个细胞周期的静止BALB/c 3 T3细胞血清刺激后。依托泊苷介导的DNA断裂频率在体内被用作拓扑异构酶II活性的参数，酶含量通过免疫印迹法测定。密度逮捕A31细胞表现出更低的敏感性，依托泊苷的影响比积极增殖的细胞。然而，在血清刺激的静止细胞，有一个显着的药物敏感性增加，在S期开始，并达到高峰前有丝分裂。在此期间的最大药物敏感性是2.5倍以上的对数期细胞。这种药物敏感性的增加与免疫印迹法测定的细胞内拓扑异构酶II含量的增加有关。拓扑异构酶II介导的药物敏感性的诱导中止1小时内暴露的细胞蛋白质合成抑制剂放线菌酮，但DNA合成抑制剂aphidicolin没有效果。与细胞对药物诱导的DNA裂解的敏感性相反，最大的细胞毒性发生在S期。依托泊苷治疗前暴露于放线菌酮3小时导致细胞毒性几乎完全丧失。我们的研究结果表明，拓扑异构酶II的活性波动与细胞周期的进展，高峰活动发生在G2期。拓扑异构酶II的这种增加是蛋白质合成依赖性的，并且可能反映了高的酶周转率。最大药物诱导的DNA切割和细胞毒性之间的解离表明，拓扑异构酶介导的DNA断裂可能是必要的，但不足以产生细胞毒性，并且在S期特别表达的其他因子可能也很重要。
The nuclear enzyme DNA topoisomerase II catalyzes the breakage and resealing of duplex DNA and plays an important role in several genetic processes. It also mediates the DNA cleavage activity and cytotoxicity of clinically important anticancer agents such as etoposide. We have examined the activity of topoisomerase II during the first cell cycle of quiescent BALB/c 3T3 cells following serum stimulation. Etoposide-mediated DNA break frequency in vivo was used as a parameter of topoisomerase II activity, and enzyme content was assayed by immunoblotting. Density-arrested A31 cells exhibited a much lower sensitivity to the effects of etoposide than did actively proliferating cells. Upon serum stimulation of the quiescent cells, however, there was a marked increase in drug sensitivity which began during S phase and reached its peak just before mitosis. Maximal drug sensitivity during this period was 2.5 times greater than that of log-phase cells. This increase in drug sensitivity was associated with an increase in intracellular topoisomerase II content as determined by immunoblotting. The induction of topoisomerase II-mediated drug sensitivity was aborted within 1 h of exposure of cells to the protein synthesis inhibitor cycloheximide, but the DNA synthesis inhibitor aphidicolin had no effect. In contrast to the sensitivity of cells to drug-induced DNA cleavage, maximal cytotoxicity occurred during S phase. A 3-h exposure to cycloheximide before etoposide treatment resulted in nearly complete loss of cytotoxicity. Our findings indicate that topoisomerase II activity fluctuates with cell cycle progression, with peak activity occurring during the G2 phase. This increase in topoisomerase II is protein synthesis dependent and may reflect a high rate of enzyme turnover. The dissociation between maximal drug-induced DNA cleavage and cytotoxicity indicates that the topoisomerase-mediated DNA breaks may be necessary but are not sufficient for cytotoxicity and that other factors which are particularly expressed during S phase may be important as well.