Repair of UV-B-induced damage in human keratinocytes

The incidence of skin cancers has been increased during the last decades with the steepest gradient compared to other cancers under investigation. Cumulative W-exposure has been shown to be one of the main risk factors in developing (non-melanocytic) cutaneous malignancies, but the elucidation of molecular mechanisms leading to skin cancer is far of being complete. However, a number of investigations refer to the importance of enzymatic repair of UV induced DNA lesions as a key position in the initiation of skin cancer. This is dramatically documented for patients suffering from Xeroderma pigmentosum, a syndrome characterized by a deficiency in nucleotide excision repair (NER), who show a 5000 fold higher risk for developing skin cancer. We therefore investigated the repair of induced DNA lesions in human keratinocytes (HaCaT), by measuring unscheduled DNA repair-synthesis (BrdU-method) and using monoclonal antibodies against cyclobutane pyrimidine dimers (CPD) and pyrimidine-pyrimidone (6-4) photoproducts ((6-4)PP). Fluorescence microscopy and flow cytometry was used to examine the repair kinetics of both UV induced lesions. We report about remarkable differences in repair kinetics for the two photolesions under investigation. The meaning of measurements of repair kinetics as a significant and individual risk estimator for developing skin cancers is discussed.