P53 modulates the effect of loss of DNA mismatch repair on the sensitivityof human colon cancer cells to the cytotoxic and mutagenic effects of cisplatin

This study examined how the DNA mismatch repair (MMR) system and p53 intera ct to maintain genomic integrity in the presence of the mutagenic stress in duced by cisplatin (DDP). Sensitivity to the cytotoxic and mutagenic effect of DDP was assessed using a panel of sublines of the MMR-deficient HCT116 colon carcinoma cells in which MMR function had been restored by transfer o f a copy of MLH1 on chromosome 3 or in which p53 function had been disabled by expression of HPV-16 E6, Loss of p53 function by expression of E6 in MM R-proficient HCT116+ch3 cells conferred only 1.1-2.0-fold resistance to a p anel of commonly used chemotherapeutic agents, whereas disruption of p53 in MMR-deficient HCT116 cells resulted in substantial levels of resistance to some agents (paclitaxel, 1.9-fold; gemcitabine, 2.7-fold; 6-thioguanine, 3 .3-fold; and etoposide, 4.4-fold) but sensitization to other agents (topote can, 2.5-fold; and DDP, 3.3-fold). Loss of MMR or p53 alone had only a mino r effect on sensitivity to the mutagenic effect of DDP as measured by the a ppearance of variants resistant to 6-thioguanine, etoposide, topotecan, gem citabine, and paclitaxel in the population 10 days later (1.0-2.4-fold), wh ereas loss of both p53 and MMR had a more profound effect (1.7-6.5-fold), L oss of both p53 and MMR increased the basal frequency insertion/deletion mu tations detected by a shuttle vector-based assay to a greater extent than l oss of either alone. In association with DDP-induced injury, loss of p53 or MMR alone resulted in 1.2- and 1.7-fold more mutations, whereas loss of bo th resulted in a 5.1-fold increase in mutant frequency, Examination of the impact of loss of p53 and/or MMR on the DDP-induced cell cycle checkpoint a ctivation, p53 induction, ability of the cell to tolerate adducts in its DN A, and the rate of disappearance of platinum from genomic DNA indicated the effects of the loss of p53 and/or MMR on all of these parameters, suggesti ng a multifactorial etiology for the changes in sensitivity to the cytotoxi c and mutagenic effects of DDP, These results indicate that p53 and MMR can cooperate to control sensitivity to the cytotoxic effect of DDP and to lim it its mutagenic potential in the colon cancer cells.