H2O2 induces DNA repair in mononuclear cells: Evidence for association with cytosolic Ca2+ fluxes

Cellular DNA repair systems are induced whenever DNA is damaged. Reactive o xygen species (ROS) are generated, in vivo, in the tissues as a result of r egular cellular metabolism or after exposure to oxidizing agents, such as u ltraviolet (UV) irradiation. It has been suggested that ROS mediate DNA dam age. The objectives of the study were as follows: (1) to investigate whethe r hydrogen peroxide (H2O2), the commonly occurring cellular ROS, induces DN A repair as a response to the damage it probably causes; (2) to evaluate wh ether H2O2-induced DNA repair, if present, is signaled through a Ca2+-depen dent pathway via the tyrosine kinase signal transduction. H2O2 was found to induce DNA repair in human peripheral blood mononuclear cells (PBMCs) in a dose-dependent manner. The recovery of RNA synthesis, which occurred after DNA repair, confirmed that transcribable DNA was repaired. The inhibition of tyrosine kinase activity by genistein reduced the DNA repair significant ly. Furthermore, H2O2 caused a dose-dependent significant rise in cytosolic calcium ((Ca2+)i). H2O2 also induced a small rise in (Ca2+)i of cytosolic Ca2+-depleted cells, probably reflecting the release of Ca2+ from internal stores. Genistein inhibited both Ca2+ influx and Ca2+ release from internal stores. In summary, H2O2 induced a DNA repair synthesis that was in part C a2+ dependent and signaled via tyrosine kinase. The changes in DNA repair p aralleled changes in (Ca2+)i. The H2O2-induced (Ca2+)i rise was mostly the result of influx, but to some degree it was also due to the translocation o f Ca2+ from internal stores.