Removal of UV-induced DNA lesions in mouse epidermis soon after irradiation.

Induction and removal of cyclobutane thymine dimers and (6-4)photoproducts were studied in epidermal DNA isolated from UV-exposed hairless mice. For the detection of DNA damage, lesion-specific monoclonal antibodies were used in an immunoslotblot assay. Following the exposure of mice to 3.0 kJ m-2 UV-B, substantial removal of both thymine dimers (66%) and (6-4)photoproducts (77%) was observed at 24 h after irradiation. No removal, however, was detected at 4 h after irradiation. In contrast, immunofluorescence data obtained previously showed a rapid initial dimer removal after irradiation with 1.0 kJ m-2 UV-B (A.A. Vink, R.J.W. Berg, F.R. De Gruijl, L. Roza and R.A. Baan, Carcinogenesis, 12 (1991) 861-864). Reinvestigation of the removal of dimers and (6-4)-photoproducts shortly after three different UV doses showed a rapid decreases of both lesions at 2 h after irradiation with 1.0 kJ m-2. The results obtained after irradiations with 2.0 and 3.0 kJ m-2 UV-B suggest a saturation of repair already at 2.0 kJ m-2. Cyclobutane dimers were found to be removed at a lower rate than (6-4)photoproducts.