DNA repair by PARP-1 is disrupted by GzmA. (A) GzmA-induced DNA nicks, radiolabeled with Klenow, in HeLa cells are enhanced by inhibiting PARP-1 using the chemical inhibitor 1,5 dihydroxyisoquinoline (DIQ) and reduced by overexpressing WT PARP-1. (B) DNA damage in response to MNNG or GzmA and PFN, assessed by comet assay, is reduced by overexpressing WT PARP. Overexpression of K498A PARP-1 significantly reduces GzmA-mediated DNA damage compared with overexpression of WT PARP-1, but has a similar effect as WT PARP-1 in response to the alkylating agent. Representative comet assay images (B) and the mean and SD of the comet tail moment (C) from 3 independent experiments are shown.