The role of calcium in human lymphocyte DNA repair ability

DNA repair ability is reduced in a variety of pathologic conditions. In addition, in some of these diseases a disturbance in cellular Ca homeostasis occurs or cytosolic (Ca²⁺) responses to various stimuli are impaired. The leading environmental cause for genomal DNA damage is ultraviolet (UV) irradiation. The aims of the present study were (1) to evaluate a possible dependence of UV-induced DNA repair ability on cytosolic Ca²⁺ in human lymphocytes and (2) to assess the direct effect of UV irradiation on Ca²⁺ homeostasis in these cells. UV-induced DNA repair ability in lymphocytes was maximal at 1 mmol/L CaCl₂ in the medium. Suppression of DNA repair ability occurred after elevation or reduction of cellular (Ca²⁺) when various methods were used, including changes in Ca²⁺ concentration in the medium, cellular Ca²⁺ depletion by ethyleneglycol-bis(βaminoethylether)-N,N,N',N'-tetraacetic acid, excessive Ca²⁺ concentration induced by ionophore, and shortening of Ca²⁺ presence time during repair synthesis. UV irradiation caused an immediate and significant rise in cytosolic (Ca²⁺) that was the result of both enhanced Ca²⁺ uptake and inhibition of plasma membrane Ca-adenosine triphosphotase activity. The tyrosine kinase inhibitor genistein inhibited both UV-induced DNA repair and UV-induced cytosolic (Ca²⁺) elevation. These results emphasize the importance of a precise cellular Ca²⁺ level regulation for the optimal DNA repair process, UV irradiation, by inducing cellular Ca²⁺ rise, may activate DNA repair as soon as DNA is damaged.