The role of mismatch repair and recombination in cellular responses to the DNA damaging anticancer drug Cisplatin

Abstract

Cisplatin (cis-diamminedichloroplatinum(ll)) is a successful DNA-damaging anticancer drug used in the treatment of testicular, ovarian and other tumors. In the past decade, several mutually non-exclusive hypotheses have been presented to explain the cytotoxic and organotropic effects of this compound. In this work we have focused on the opposing effects of mismatch repair and recombination in mediating cisplatin cytotoxicity. Recombination mutants showed strikingly high sensitivity to cisplatin, while mismatch repair mutants showed low sensitivity and resistance to the drug. These results further illustrated that while recombination promotes cellular survival following cisplatin damage, mismatch repair, in contrast, promotes cisplatin toxicity. The mismatch repair protein MutS recognized cisplatin-DNA adducts with 2-fold higher affinity than adducts of oxaliplatin, a cisplatin analog that does not elicit resistance in mismatch repair mutants. MutS recognized the major cisplatin DNA-adduct, the 1,2-d(GpG) intrastrand crosslink, with equal affinity as a G/T mismatch in the same sequence context. Furthermore, MutS inhibited RecA catalyzed strand exchange reaction at the level of joint molecule formation when the substrate was platinated DNA. In the cell, mismatch repair could potentiate cisplatin toxicity by inhibiting the high levels of recombination that are required for cisplatin survival. Microarray analysis of gene expression following cisplatin damage showed that in contrast to wild type and methylation dam mutant, the methylation-mismatch repair double mutant did not show induction of any significant SOS DNA damage response.

(cont.) Yet, this strain showed abrogated sensitivity in comparison to the dam mutant and high survival rate. The low damage response in the dam mutS mutants might allow for adduct tolerance and survival. Finally, genetic studies with yeast deficient in the meiosis specific mismatch repair proteins MSH4 and MSH5 showed both mutants to be resistant to cisplatin indicating that these proteins are involved in potentiating cisplatin toxicity. Taken together, these results further elucidate the role of recombination and mismatch repair in modulation of the cellular responses to cisplatin. Furthermore, because of the specific roles of these DNA metabolic pathways in meiotic cells, these results provide the framework in which the organotropic effects of cisplatin can be viewed from a molecular perspective.