Dolling J A, Boreham D R, Brown D L, Raaphorst G P, Mitchel R E
Department of Biology, University of Ottawa, Ontario, Canada.
Mutat Res. 1999 Mar 10;433(2):127-36. doi: 10.1016/s0921-8777(98)00069-x.
Cis-diamminedichloroplatinum II (cisplatin) is a DNA inter- and intrastrand crosslinking agent which can sensitize prokaryotic and eukaryotic cells to killing by ionizing radiation. The mechanism of radiosensitization is unknown but may involve cisplatin inhibition of repair of DNA damage caused by radiation. Repair proficient wild type and repair deficient (rad52, recombinational repair or rad3, excision repair) strains of the yeast Saccharomyces cerevisiae were used to determine whether defects in DNA repair mechanisms would modify the radiosensitizing effect of cisplatin. We report that cisplatin exposure could sensitize yeast cells with a competent recombinational repair mechanism (wild type or rad3), but could not sensitize cells defective in recombinational repair (rad52), indicating that the radiosensitizing effect of cisplatin was due to inhibition of DNA repair processes involving error free RAD52-dependent recombinational repair. The presence or absence of oxygen during irradiation did not alter this radiosensitization. Consistent with this result, cisplatin did not sensitize cells to mutation that results from lesion processing by an error prone DNA repair system. However, under certain circumstances, cisplatin exposure did not cause radiosensitization to killing by radiation in repair competent wild type cells. Within 2 h after a sublethal cisplatin treatment, wild type yeast cells became both thermally tolerant and radiation resistant. Cisplatin pretreatment also suppressed mutations caused by exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a response previously shown in wild type yeast cells following radiation pretreatment. Like radiation, the cisplatin-induced stress response did not confer radiation resistance or suppress MNNG mutations in a recombinational repair deficient mutant (rad52), although thermal tolerance was still induced. These results support the idea that cisplatin adducts in DNA interfere with RAD52-dependent recombinational repair and thereby sensitize cells to killing by radiation. However, the lesions can subsequently induce a general stress response, part of which is induction of RAD52-dependent error free recombinational repair. This stress response confers radiation resistance, thermal tolerance, and mutation resistance in yeast.
顺二氯二氨合铂（II）（顺铂）是一种DNA链间和链内交联剂，可使原核和真核细胞对电离辐射杀伤敏感。放射增敏机制尚不清楚，但可能涉及顺铂对辐射引起的DNA损伤修复的抑制。使用酿酒酵母的修复 proficient 野生型和修复缺陷型（rad52，重组修复；或rad3，切除修复）菌株来确定DNA修复机制的缺陷是否会改变顺铂的放射增敏作用。我们报告，暴露于顺铂可使具有完整重组修复机制的酵母细胞（野生型或rad3）敏感，但不能使重组修复缺陷的细胞（rad52）敏感，这表明顺铂的放射增敏作用是由于抑制了涉及无差错RAD52依赖性重组修复的DNA修复过程。照射期间氧气的存在与否并未改变这种放射增敏作用。与此结果一致，顺铂不会使细胞对由易错DNA修复系统处理损伤导致的突变敏感。然而，在某些情况下，暴露于顺铂不会使修复 proficient 的野生型细胞对辐射杀伤产生放射增敏作用。在亚致死性顺铂处理后2小时内，野生型酵母细胞变得耐热且抗辐射。顺铂预处理还抑制了暴露于N-甲基-N'-硝基-N-亚硝基胍（MNNG）引起的突变，这种反应先前在辐射预处理后的野生型酵母细胞中已显示。与辐射一样，顺铂诱导的应激反应在重组修复缺陷突变体（rad52）中不会赋予抗辐射能力或抑制MNNG突变，尽管仍会诱导耐热性。这些结果支持这样的观点，即DNA中的顺铂加合物会干扰RAD52依赖性重组修复，从而使细胞对辐射杀伤敏感。然而，这些损伤随后可诱导一种普遍的应激反应，其中一部分是诱导RAD52依赖性无差错重组修复。这种应激反应赋予酵母抗辐射、耐热和抗突变能力。
