Influence of mismatch repair system and p53 on celi cycle perturbation, apoptosis and chromosomal damage induced by bleomycin

The antibiotic bleomycin (BLM) is an anticancer drug used for the treatment of a variety of tumors. Similarly to ionizing radiations, its cytotoxic activity is mainly related to the generation of oxygen radicals and, for this reason, BLM is classified as a radiomimetic agent. Here we describe the influence or either the mismatch repair system (MMR) or p53 on cell cycle alterations, apoptosis and chromosomal damage induced by BLM. The MMR-deficient colon carcinoma cell line HCTI16 and its MMR-proficient subline HCTlI6/3-6, both expressing wild-type p53,were transfected with a vector encoding a dominant-negative p53 mutant, or with an empty vector. Four transfected clones having the following phenotypes: MMR-proficient/p53 wild-type, MMR-proficient/p53 mutant, MMR-deficient/p53 wild-type and MMR-deficient/p53 mutant were selected and subjected to BLM treatment. Loss of p53 alone resulted in abrogation of BLM-induced G1 arrest and a higher accumulation of cells in the G2/M phase. Inactivation of p53 was also associated with increased cell sensitivity to apoptosis and chromosomal damage induced by the drug. Loss of MMR function alone was associated with increased cell resistance to G2/M arrest, apoptosis and chromosomal damage caused by bleomycin. Disabling both p53 and MMR function led to abrogation of BLM-induced G1 arrest and to impairment of drug-induced apoptosis, which was however less pronounced than that observed in the MMR deficient/p53 wild-type clone. Chromosomal damage in BLM-treated MMR-deficient clones was lower than in MMR-proficient ones both at 3 and 48 hours after treatment. In conclusion, our data show that the functional status of both the MMR system and p53 influences cellular responses to bleomycin, being MMR-proficient/p53 mutant cells the most sensitive and MMR-deficient/p53 wild-type cells the most resistant to the drug