Cortés F, Morgan W F, Wolff S
Laboratory of Radiobiology and Environmental Health, University of California, San Francisco 94143.
Mutat Res. 1987 Dec;192(4):277-82. doi: 10.1016/0165-7992(87)90069-8.
There are conflicting reports on the effect of exogenous thymidine (dThd) on the frequency of sister-chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) cells. Thymidine has been reported either to increase or to have no effect on SCE frequency under similar experimental conditions. To resolve this controversy, we have carried out a series of experiments to examine the effect of dThd on CHO cells cultured with 5-bromodeoxyuridine (BrdUrd). In addition, we have examined the effect of dThd on CHO cells cultured with 5-chlorodeoxyuridine (CldUrd), a much more potent inducer of SCEs than BrdUrd. The addition of 100 microM dThd to the culture medium caused a consistent decrease in the yield of SCEs in cells grown in BrdUrd for two cell cycles. The decrease was even greater when cells were grown in dThd and CldUrd. Analysis of twin and single SCEs indicated that dThd must be present during the first cell cycle to reduce the frequency of SCEs. Because excess dThd is thought to have an effect when DNA replicates on a template substituted with a halogenated nucleoside, dThd at concentrations from 100 microM to 9 mM was added to cultures for the second cell cycle after a first cell cycle in BrdUrd. In this experiment, the presence of dThd increased SCE frequency in a dose-dependent manner. The results suggest that if dThd competes with halogenated nucleosides and thus decreases their incorporation into DNA, SCEs are suppressed in the subsequent cell cycle, whereas if excess dThd creates a dNTP pool imbalance, SCEs can be increased.
关于外源性胸苷（dThd）对中国仓鼠卵巢（CHO）细胞姐妹染色单体交换（SCE）频率的影响，存在相互矛盾的报道。在相似的实验条件下，已报道胸苷对SCE频率要么有增加作用，要么无影响。为解决这一争议，我们进行了一系列实验，以研究dThd对用5-溴脱氧尿苷（BrdUrd）培养的CHO细胞的影响。此外，我们还研究了dThd对用5-氯脱氧尿苷（CldUrd）培养的CHO细胞的影响，CldUrd是一种比BrdUrd更强效的SCE诱导剂。向培养基中添加100微摩尔/升的dThd，会使在BrdUrd中生长两个细胞周期的细胞中SCE的产量持续下降。当细胞在dThd和CldUrd中生长时，这种下降更为明显。对双SCE和单SCE的分析表明，必须在第一个细胞周期中存在dThd才能降低SCE频率。由于当DNA在被卤代核苷取代的模板上复制时，过量的dThd被认为会产生影响，所以在第一个细胞周期在BrdUrd中培养后，向第二个细胞周期的培养物中添加浓度为100微摩尔/升至9毫摩尔/升的dThd。在这个实验中，dThd的存在以剂量依赖的方式增加了SCE频率。结果表明，如果dThd与卤代核苷竞争，从而减少它们掺入DNA，那么在随后的细胞周期中SCE会受到抑制，而如果过量的dThd导致dNTP池失衡，SCE则可能增加。
