A comparison of the roles of p53 mutation and AraC inhibition in the enhancement of bleomycin-induced chromatid aberrations in mouse and human cells.

Previous studies have shown that p53 is involved in the repair of bleomycin-induced DNA damage, and that the frequency of bleomycin-induced chromatid aberrations is elevated in G(2)-treated p53 null transgenic mouse embryo fibroblasts (MEF) as compared to isogenic controls. To further characterize p53-mediated DNA repair, we studied the effect of p53 status on the ability of the DNA repair inhibitor 1-ss-D-arabinofuranosylcytosine (AraC) to sensitize MEF to bleomycin-induced chromatid aberrations. Both p53+/+ and p53-/- MEF were treated in G(2) with 0 to 7.5 microg/ml bleomycin in the presence or absence of AraC (5x10(-5) M). The frequency of bleomycin-induced chromatid aberrations was significantly higher in p53-/- cells than wild-type cells in the absence of AraC. AraC treatment significantly increased the frequency of bleomycin-induced chromatid aberrations in p53+/+ MEF to the levels in p53-/- (no AraC) but had no effect in p53-/- MEF. These results suggest that an AraC-sensitive DNA repair component is altered or absent in p53-/- cells. Similar results were observed in p53-mutant WTK1 and wild-type TK6 human lymphoblast cells exposed to 0 to 3 microg/ml bleomycin in G(2). However, AraC did cause a small increase in bleomycin sensitivity in WTK1 cells. This difference from the p53-/- MEF response may be due to differences in p53-mutant phenotype. To determine whether mutation of p53 alters DNA replication fidelity, p53+/+ and p53-/- MEF were exposed to 0 to 1 microg/ml mitomycin C (MMC). MMC did not induce chromosome aberrations in either cell line treated in G(2) but did with the same effectiveness in both cell lines treated in S-phase. Thus, p53 deficiency does not affect DNA replication fidelity or the repair of MMC-induced DNA damage.