DNA repair and survival in human lens epithelial cells with extended Lifespan

Purpose. Ultraviolet-B radiation (290-320 nm) produces cataracts in animals and has been associated with human cataract formation in several epidemiol ogical studies. WB radiation decreases the long-term cell survival and chan ges the pattern of protein synthesis in cultured lens epithelial cells. How ever, the relationship between DNA photoproduct formation and long term cel l survival in human lens epithelial cells is not known. In the present work , we used human lens epithelial cells with extended lifespan (HLE B-3 cells ) to examine the kinetics of DNA repair and cell survival after UVB exposur e. Methods. Cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6-4) phot oproducts were analyzed by radioimmunoassay . Long-term survival of the cel ls was determined by measuring their ability form colonies when plated at l ow density. Results. HLE B-3 cells were repair competent after UVB (302 nm) exposure. E xcision repair of the (6-4) photoproduct was more efficient than that of th e cyclobutane dimer. Ninety five percent of the (6-4) photoproducts were re paired 24 h after 400 J/m(2) WE exposure, whereas 50% of the cyclobutane di mers were repaired during this time. When cells were split for the clonogen ic assay immediately after irradiation, only 10% of the cells formed coloni es following 7 days of culture in the serum-containing medium. When cells w ere split for the clonogenic assay after a 48 hour incubation in serum-cont aining medium, the colony-forming ability of the irradiated cells increased to 60% following culture in a serum-containing medium. Conclusions. These results indicate a close correlation between the repair of cyclobutane dimers and the increase in the longterm survival of the cell s as measured by their colony-forming ability. The extended lifespan human lens epithelial cells HLE B-3 may be a useful model to investigate the mech anism and regulation of UVB-induced DNA repair in human lens cells.