High induction of poly(ADP-ribose) polymerase activity in bleomycin-resistant HeLa cells

Poly(ADP-ribose) polymerase activity was measured in bleomycin (BLM)-resistant HeLa (HeLa-BLMr) and the parental HeLa cells after BLM treatment. HeLa-BLMr cells, which had been subcultured in growth medium containing 1 micrograms/ml of BLM, showed a 3.75-fold higher enzyme activity than did HeLa cells, but this activity was decreased to the same level as that of HeLa cells after 48 h of BLM-free cultivation. When HeLa and HeLa-BLMr cells after a 48-h cultivation in BLM-free growth medium were treated with BLM, the enzyme activity was induced at a higher level (2.5-3.8 times) in HeLa-BLMr than in HeLa cells and was inhibited markedly in HeLa-BLMr and slightly in HeLa cells by nicotinamide, an inhibitor of this enzyme. The BLM-induced cell killing by nicotinamide was highly potentiated (about 18 times) in HeLa-BLMr as compared to HeLa cells.