Camptothecin (CPT) is an anticancer drug that promotes DNA breakage at replication forks and the formation of lesions that activate the processes of homologous recombination (HR) and nonhomologous end joining. We have taken advantage of the CPT-induced damage response by coupling it to gene repair directed by synthetic oligonucleotides, a process in which a mutant base pair is converted into a wild-type one. Here, we show that pretreating DLD-1 cells with CPT leads to a significant stimulation in the frequency of correction of an integrated mutant enhanced green fluorescent protein gene. The stimulation is dose-dependent and coincident with the formation of double-strand DNA breaks. Caffeine, but not vanillin, blocks the enhancement of gene repair suggesting that, in this system, HR is the pathway most responsible for elevating the frequency of correction. The involvement of HR is further proven by studies in which wortmannin was seen to inhibit gene repair at high concentrations but not at lower levels that are known to inhibit DNA-PK activity. Taken together, our results suggest that DNA damage induced by CPT activates a cellular response that stimulates gene repair in mammalian cells.

译文

喜树碱(CPT)是一种抗癌药,可促进复制叉处的DNA断裂和损伤的形成,从而激活同源重组(HR)和非同源末端连接的过程。我们通过将CPT诱导的损伤反应与合成寡核苷酸指导的基因修复相结合来利用CPT诱导的损伤反应,在该过程中,突变碱基对被转化为野生型。在这里,我们显示用CPT对DLD-1细胞进行预处理可显着刺激整合突变增强型绿色荧光蛋白基因的校正频率。刺激是剂量依赖性的,并且与双链DNA断裂的形成同时发生。咖啡因而不是香草醛阻止了基因修复的增强,这表明在该系统中,HR是最主要的途径来提高校正频率。研究表明,渥曼青霉素在抑制DNA-PK活性的高浓度下抑制基因修复,但在较低水平上却不抑制基因修复,这进一步证实了HR的参与。综上所述,我们的结果表明,CPT诱导的DNA损伤会激活细胞反应,从而刺激哺乳动物细胞中的基因修复。

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