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 oxygen species (ROS) are generated, in vivo, in the tissues as a result of regular cellular metabolism or after exposure to oxidizing agents, such as ultraviolet (UV) irradiation. It has been suggested that ROS mediate DNA damage. The objectives of the study were as follows: (1) to investigate whether hydrogen peroxide (H₂O₂), the commonly occurring cellular ROS, induces DNA repair as a response to the damage it probably causes; (2) to evaluate whether H₂O₂-induced DNA repair, if present, is signaled through a Ca²⁺-dependent 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 significantly. 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 Ca²⁺ dependent and signaled via tyrosine kinase. The changes in DNA repair paralleled 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 of Ca²⁺ from internal stores.