Characteristics of DNA Repair Induced by DNA Polymerase Β in Hepatoma Cells after Γ-Ray Irradiation.

AIM:To investigate the effects of DNA repair induced by DNA polymerase β in hepatoma cells after γ-ray irradiation.METHODS:Cell nuclei were prepared from mouse model (SMMC LTNM), in which human hepatoma cells are transplanted on nude mice. The nuclei were then irradiated with (60)Co-γ rays at different dose levels or dose rates. A selective inhibitor test was then used to detect the effects of the radiation on DNA repair using N-ethylmaleimide (NEM) and ddTTP as selective inhibitors to DNA polymerases γ and β respectively.RESULTS:(3)H-TTP incorporation into irradiated nuclei or calf thymus DNA was significantly higher than that the rate at which it is incorporated into non-irradiated nuclei when either DNA polymerase β or γ was inhibited. When both NEM and ddTTP are present, the (3)H-TTP incorporation in irradiated DNA was not significantly different from the non-irradiated nuclei. Furthermore, (3)H-TTP incorporation into DNA of SMMC-LTNM hepatoma nuclei was higher than that of normal hepatocyte nuclei (P < 0.01). This suggests that DNA repair induced by DNA polymerase β was more active in hepatoma cell nuclei than in normal hepatocyte nuclei.CONCLUSION:DNA polymerase β may be more responsive to DNA damage in some tumor cells than that in normal cells, which may facilitate the cells to repair DNA damages from radiation more efficiently.