Introduction: Reactive oxygen species (ROS) are essential for neutrophil extracellular trap (NET) formation or NETosis. Nevertheless, how ROS induces NETosis is unknown. Neutrophil activation induces excess ROS production and a meaningless genome-wide transcription to facilitate chromatin decondensation.

Methods and Results: Here we show that the induction of NADPH oxidase-dependent NETosis leads to extensive DNA damage, and the subsequent translocation of proliferating cell nuclear antigen (PCNA), a key DNA repair protein, stored in the cytoplasm into the nucleus. During the activation of NETosis (e.g., by phorbol myristate acetate, Escherichia coli LPS, Staphylococcus aureus (RN4220) or Pseudomonas aeruginosa), preventing the DNA-repair-complex assembly leading to nick formation that decondenses chromatin causes the suppression of NETosis (e.g., by inhibitors to, or knockdown of, Apurinic endonuclease APE1, poly ADP ribose polymerase PARP and DNA ligase). The remaining repair steps involving polymerase activity and PCNA interactions with DNA polymerases β/δ do not suppress agonist-induced NETosis.

Conclusions: Therefore, excess ROS produced during neutrophil activation induces NETosis by inducing extensive DNA damage (e.g., oxidizing guanine to 8-oxoguanine), and the subsequent DNA repair pathway, leading to chromatin decondensation.