Human neutrophil peptide defensins induce single strand DNA breaks in target cells

Abstract

To investigate whether target cell DNA injury participates in cytolysis by human neutrophil defensins (HNP), we analyzed HNP-treated cells for single strand breaks by the alkaline unwinding assay and the activation of ADPribose polymerase, a DNA repair enzyme. Strand breaks and ADP-ribosylation were first detected in K562 and Raji targets 6–8 hr after incubation with HNP and increased to maximal levels by 18 hr. DNA was not degraded into nucleosome-sized fragments. To assess the impact of DNA injury on cytolysis, we increased strand breakage by coincubating targets with HNP and two inhibitors of ADPribose polymerase, 3-aminobenzamide, or nicotin-amide. Concurrently with inhibiting polymerase activity and increasing DNA injury, these agents significantly enhanced HNP-mediated cytolysis. Enhancement occurred only at time points (over 6 hr) and in targets (only nucleated targets) where HNP-induced DNA injury could be occurring. These data indicate that neutrophil defensins can induce DNA injury in targets and suggest such injury may be involved in target cell death.