Differential effects of luminol, nickel, and arsenite on the rejoining of ultraviolet light and alkylation‐induced DNA breaks

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Abstract
When Chinese hamster ovary cells were treated with ultraviolet (UV) light or methyl methanesulfonate (MMS), a large number of DNA strand breaks could be detected by alkaline elution. These strand breaks gradually disappeared if the treated cells were allowed to recover in a drug‐free medium. The presence of nickel or arsenite during the recovery incubation retarded the disappearance of UV‐induced strand breaks, whereas the disappearance of MMS‐induced strand breaks was retarded by the presence of arsenite or of luminol, a new inhibitor for poly(ADP‐ribose) synthetase. Luminol, however, had no apparent effect on the repair of UV‐induced DNA strand breaks, and nickel had no effect on the repair of MMS‐induced DNA strand breaks. When UV‐ or MMS‐treated cells were incubated in cytosine arabinofuranoside (AraC) plus hydroxyurea (HU), a large amount of low molecular weight DNA was detected by alkaline sucrose sedimentation. The molecular weight of these DNAs increased if the cells were further incubated in a drug‐free medium. This rejoining of breaks in cells pretreated with UV plus AraC and HU was inhibited by nickel and by arsenite, but not by luminol. The rejoining of breaks in cells pretreated with MMS plus AraC and HU was inhibited by luminol and by arsenite, but not by nickel. These results suggest that different enzymes may be used in DNA resynthesis and/or ligation during the repairing of UV‐ and MMS‐induced DNA strand breaks, and that nickel, luminol, and arsenite may have differential inhibitory effects on these enzymes.