Phosphorylation of histone H2AX on Ser 139 and activation of ATM during oxidative burst in phorbol ester-treated human leukocytes.

Oxidative burst is a defense mechanism used by specialized phagocytes such as granulocytes or monocytes to kill the invading microorganisms through generation of superoxide anions. Oxidative burst also results in DNA damage of the phagocytes. Phagocytes are terminally differentiated cells, some of very short life-span cells. We could find no reports whether oxidative burst-mediated DNA damage triggers in such cells histone H2AX-Ser139 phosphorylation and activation of Ataxia Telangiectasia Mutated (ATM), the signals otherwise used to activate DNA repair and checkpoint pathways in proliferating cells. We now present the evidence that induction of oxidative stress in human peripheral blood leukocytes by phorbol myristate acetate (PMA) was associated with intense phosphorylation of histone H2AX and with ATM activation, seen already 60 min after exposure to PMA. The modifications of H2AX and ATM in individual granulocytes, monocytes and lymphocytes were detected prior to caspases activation and thus were unrelated to induction of apoptosis. A large intercellular variation in response was observed, and only a fraction of cells in these subpopulations showed H2AX and ATM modifications. The data are compatible with the earlier observations of DNA damage during oxidative burst and suggest that even in terminally differentiated cells that have a short life-span, DNA damage triggers recruitment of the DNA repair machinery. The observed H2AX phosphorylation in lymphocytes may reflect their DNA damage by the superoxide ions propagating from the neighboring granulocytes and/or monocytes.