The influence of XPD, APE1, XRCC1, and NBS1 polymorphic variants on DNA repair in cells exposed to X-rays

To confirm the influence of XPD polymorphism on repair, we established stably-transfected HCT116 (colon carcinoma) cells which over-expressed the wild-type or variant XPD protein. Cells over-expressing Asp312Asn XPD showed a higher level of DNA breaks shortly after irradiation and more efficient repair than cells over-expressing the wild-type gene XPD312Asp, and an earlier inhibition of cell cycle transit but faster recovery from this inhibition. Polymorphisms in DNA repair genes therefore influence not only DNA repair capacity but also cell proliferation, and may serve as markers of individual repair capacity and susceptibility to environmental and occupational carcinogens.