Defective repair of DNA single- and double-strand breaks in the bleomycin- and X-ray-sensitive Chinese hamster ovary cell mutant, BLM-2.
Using filter elution techniques, we have measured the level of induced single- and double-strand DNA breaks and the rate of strand break rejoining following exposure of two Chinese hamster ovary (CHO) cell mutants to bleomycin or neocarzinostatin. These mutants, designated BLM-1 and BLM-2, were isolated on the basis of hypersensitivity to bleomycin and are cross-sensitive to a range of other free radical-generating agents, but exhibit enhanced resistance to neocarzinostatin. A 1-h exposure to equimolar doses of bleomycin induces a similar level of DNA strand breaks in parental CHO-K1 and mutant BLM-1 cells, but a consistently higher level is accumulated by BLM-2 cells. The rate of rejoining of bleomycin-induced single- and double-strand DNA breaks is slower in BLM-2 cells than in CHO-K1 cells. BLM-1 cells show normal strand break repair kinetics. The level of single- and double-strand breaks induced by neocarzinostatin is lower in both BLM-1 and BLM-2 cells than in CHO-K1 cells. The rate of repair of neocarzinostatin-induced strand breaks is normal in BLM-1 cells but retarded somewhat in BLM-2 cells. Thus, there is a correlation between the level of drug-induced DNA damage in BLM-2 cells and the bleomycin-sensitive, neocarzinostatin resistant phenotype of this mutant. Strand breaks induced by both of these agents are also repaired with reduced efficiency by BLM-2 cells. The neocarzinostatin resistance of BLM-1 cells appears to be a consequence of a reduced accumulation of DNA damage. However, the bleomycin-sensitive phenotype of BLM-1 cells does not apparently correlate with any alteration in DNA strand break induction or repair, as analysed by filter elution techniques, suggesting an alternative mechanism of cell killing.
Robson
C N
CN
Department of Clinical Oncology, University of Newcastle upon Tyne, Great Britain.
Harris
A L
AL
Hickson
I D
ID
D000818:Animals; D001761:Bleomycin / Q000633:toxicity; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair; D005260:Female; D009154:Mutation; D010053:Ovary; D014965:X-Rays; D009353:Zinostatin / Q000633:toxicity
D001761:Bleomycin; D009353:Zinostatin