Study on abnormality of DNA recombination in LEC strain rat

1.经SV40大T抗原诱导的LEC系(LEC)大鼠永生化细胞系比WKAH系(WKAH)大鼠永生化细胞系对X射线更敏感，但对紫外线辐射不敏感。LEC大鼠细胞系DNA合成对X射线和紫外线的耐受性强于WKAH大鼠。放射诱导的细胞周期从G1期延迟到S期(G1期停滞)，而在LEC细胞中未观察到此现象。照射后WKAH细胞P53蛋白条带强度增加，而LEC细胞P53蛋白条带强度无明显变化。LEC细胞对引起DNA双链断裂(DSB)的博莱霉素(BLM)和交联剂丝裂霉素C的敏感性是WKAH大鼠细胞的2~3倍，而对烷化剂乙基亚硝脲和N-甲基-N‘-亚硝胺稍敏感。虽然BLM诱导的DNA双链断裂在LEC和WKAH细胞中的初始产量没有差异，但LEC细胞的DNA双链断裂的修复过程明显慢于WKAH细胞，这一结果表明增强的细胞敏感性与DNA合成的抗性表型对DNA损伤剂的抵抗是分开的。LEC中辐射抗性DNA的合成被认为是由于缺乏从G1期到S期的短暂细胞周期停滞。此外，DNA双链断裂修复异常可能与DNA重组过程异常有关。LEC大鼠可以提供一个有用的动物模型，以帮助理解辐射诱导的DNA损伤修复过程的机制，包括DNA重组和细胞周期的调节。

1. Immortalized cell lines from LEC strain (LEC) rats by SV40 large T antigen were more sensitive to X-irradiation than the cell lines from WKAH strain (WKAH) rats, but not to UV-irradiation.2. DNA synthesis in the cell lines of LEC rats was more resistant to X- and UV-irradiation than that of WKAH rats.3. The radiation-induced delay in the progression from the G1 phase to S phase (G1 arrest) was observed in WKAH cells, but not in LEC cells. The intensities of the p53 protein bands increased following irradiation in WKAH cells, but not in LEC cells.4. LEC rat cells were 2-to 3-fold more sensitive to bleomycin (BLM) that induces DNA double-strand breaks (dsbs), and to cross-linking agent, mitomycin C,than WKAH rat cells, while they were slightly sensitive to alkylating agents, ethyl nitrosourea and N-methyl-N'-nitrosoguanidine. Although no difference was observed in the initial yields of DNA dsbs induced by BLM between LEC and WKAH cells, the repair process of DNA dsbs was significantly slower in LEC cells than WKAH cells.These results showed that the enhanced cellular sensitivity is segregated from the resistant phenotype of DNA synthesis to DNA-damaging agents. The radioresistant DNA synthesis in LEC cells is thought to be due to the deficiency in the transient cell cycle arrest from the G1 to S phases. Furthermore, it is suggested that abnormality in the repair of DNA dsbs might be associated with the abnormality of DNA recombination process. LEC rat could provide a useful animal model to assist in an understanding of the mechanism of the repair process of the radiation-induced DNA damage including DNA recombination and regulation of the cell cycle.