Increased sensitivity to chromatid aberration induction by bleomycin and neocarzinostatin results from alterations in a DNA damage response pathway.
DNA damage response pathways coordinate the cellular response to DNA damage. To investigate the roles of tumor suppressor genes in these pathways, human lymphoblastoid cells (wild-type, p53-/-, ATM-/-) were treated for 1 h with 0-3 microg/ml of the radiomimetic compound bleomycin (BLM), and cells treated in G(2) were analyzed for chromatid aberrations. BLM-induced aberration frequencies were significantly increased, to the greatest extent in the ATM-/- cells and, to a lesser extent, in the p53-/- cells compared to wild-type cells. These observations are consistent with p53 and ATM acting in a damage response pathway activated by DNA strand breaks. The consequences of disrupting this pathway were further investigated by studies using wortmannin, a PI-3 kinase and DNA repair inhibitor. Wortmannin significantly increased the BLM-induced aberration frequencies in all but the ATM-/- cells, elevating the sensitivity of p53-/- cells to ATM-/- levels and that of wild-type cells to intermediate levels. These differential sensitivities suggest that the ATM phenotype is the result of dual cellular defects, one involving p53 and the other a wortmannin-sensitive component. Similar studies in Brca1+/- and Brca2+/- human lymphoblasts showed no increased sensitization to BLM in the absence of inhibitor, and differential sensitization by wortmannin. To determine if there was any substrate specificity for p53- and ATM-mediated DNA damage responses, chromatid aberrations were assessed in wild-type, p53-/-, and ATM-/- cells exposed to 0-0.4 microg/ml neocarzinostatin (NCS) for 1 h. In contrast to results with BLM, the p53-/- cells exhibited a low sensitivity to NCS-induced aberrations, similar to wild-type, while ATM-/- cells remained highly sensitive. This suggests that the response to BLM- and NCS-induced lesions involves different mechanisms.
Allio
T
T
Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709, USA.
Preston
R J
RJ
D064007:Ataxia Telangiectasia Mutated Proteins; D001761:Bleomycin / Q000494:pharmacology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002842:Chromatids / Q000187:drug effects*; D002869:Chromosome Aberrations; D004249:DNA Damage; D004268:DNA-Binding Proteins; D016158:Genes, p53; D006801:Humans; D008938:Mitosis; D009153:Mutagens / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D025521:Tumor Suppressor Proteins; D009353:Zinostatin / Q000494:pharmacology*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009153:Mutagens; D025521:Tumor Suppressor Proteins; D001761:Bleomycin; D009353:Zinostatin; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases