Different effects of tert-butylhydroperoxide-induced peroxynitrite-dependent and -independent DNA single-strand breakage on PC12 cell poly(ADP-ribose) polymerase activity

The short-chain lipid hydroperoxide analogue tert-butyl-hydroperoxide induc es peroxynitrite-dependent and -independent DNA single strand breakage in P C12 cells. U937 cells that do not express constitutive nitric oxide synthas e respond to tert-butylhydroperoxide treatment with peroxynitrite-independe nt DNA cleavage. Under experimental conditions leading to equivalent strand break frequencies, the analysis of poly(ADP-ribose) polymerase activity sh owed an increase in PC12 cells but not in U937 cells. The enhanced poly(ADP -ribose) polymerase activity observed in PC12 cells was paralleled by a sig nificant decline in NAD(+) content and both events were prevented by treatm ents suppressing formation of peroxynitrite. Although DNA breaks were rejoi ned at similar rates in the two cell lines, an inhibitor Of poly(ADP-ribose ) polymerase delayed DNA repair in PC12 cells but had hardly any effect in U937 cells. The results obtained using the latter cell type were confirmed with an additional cell line (Chinese hamster ovary cells) that does not ex press nitric oxide synthase. Collectively, our data suggest that tert-butyl -hydroperoxide-induced peroxynitrite-independent DNA strand scission is far less effective than the DNA cleavage generated by endogenous peroxynitrite in stimulating the activity of poly(ADP-ribose) polymerase.