Role of the mismatch repair system and p53 in the clastogenicity and cytotoxicity induced by bleomycin

Mutat Res. 2006 Feb 22;594(1-2):63-77. doi: 10.1016/j.mrfmmm.2005.07.011. Epub 2005 Sep 1.


The mismatch repair (MMR) system and p53 protein play a pivotal role in maintaining genomic stability and modulate cell chemosensitivity. Aim of this study was to examine the effects of either MMR-deficiency or p53 inactivation, or both, on cellular responses to bleomycin. The MMR-deficient colon carcinoma cell line HCT116 and its MMR-proficient subline HCT116/3-6, both expressing wild-type p53, were transfected with an expression vector encoding a dominant-negative p53 mutant, or with the empty vector. Four transfected clones, having the following phenotypes, MMR-proficient/p53 wild-type, MMR-proficient/p53 mutant, MMR-deficient/p53 wild-type, MMR-deficient/p53 mutant, were subjected to treatment with bleomycin. Loss of MMR function alone was associated with increased resistance to apoptosis, chromosomal damage and inhibition of colony formation caused by bleomycin. Loss of p53 alone resulted in abrogation of G1 arrest and increased sensitivity to apoptosis and chromosomal damage induced by the drug, but did not affect clonogenic survival after bleomycin treatment. Disabling both p53 and MMR function led to abrogation of G1 arrest and to a moderate impairment of drug-induced apoptosis. Chromosomal damage was reduced in the MMR-deficient/p53 mutant clone with respect to the MMR-proficient/p53 wild-type one, when evaluated 48 h after bleomycin treatment, but was comparable in both clones 96 h after drug exposure. Clonogenic survival of the MMR-deficient/p53 mutant clone was similar to that of the MMR-deficient/p53 wild-type one. The effects of MMR-deficiency on cellular responses to bleomycin were confirmed using the MMR-proficient lymphoblastoid cell line TK6 and its MMR-deficient subline MT1, both expressing wild-type p53. In conclusion, our data show that loss of MMR and p53 function exerts opposite and independent effects on apoptosis and chromosomal damage induced by bleomycin. Moreover, inactivation of MMR confers resistance to the cytotoxic activity of the anticancer agent in cells expressing either wild-type or mutant p53.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibiotics, Antineoplastic / toxicity*
  • Base Pair Mismatch / drug effects
  • Base Pair Mismatch / genetics*
  • Bleomycin / toxicity*
  • Cell Line, Transformed
  • Cell Line, Tumor
  • Cyclin-Dependent Kinase Inhibitor p21 / biosynthesis
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • DNA Damage / drug effects
  • DNA Repair / drug effects*
  • HCT116 Cells
  • Humans
  • Mutagens / toxicity*
  • Tumor Suppressor Protein p53 / biosynthesis
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / physiology*


  • Antibiotics, Antineoplastic
  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Mutagens
  • Tumor Suppressor Protein p53
  • Bleomycin