Influence of Hyperthermia on UV-induced DNA-Damage

Heat shock proteins are involved in the protection of human keratinocytes from the deleterious effects of ultraviolet radiation (UV). This protection can be demonstrated by a reduced rate of apoptosis in cells that overexpress heat shock proteins (e.g. after sublethal heat stress). DNA damage is a major mechanism of the cytotoxic effects of UV and in the current project we adressed the question whether heat shock is able to reduce UV-induced DNA-lesions. The most common UV-induced DNA lesion, T-T dimers, was quantified by ELISA using a specific monoclonal antibody. Single and double strand breaks were determined by single cell electrophoresis (Comet assay). Normal human cell cultures (keratinocytes, melanocytes, fibroblasts) and the squamous cell carcinoma derived cell line A431 were used for this experiments. We found that heat treatment prior to UV exposure leads to an enhanced removal of T-T dimers within the first 6 hours compared to untreated controls. With prolonged incubation the curves flatten and no difference between preheated and control cell can be observed after 24 h. Similar results were obtained for keratinocytes, melanocytes, and fibroblasts. The comet assay was performed with A431 and we found no no influence of heat treatment on UV- induced tail length. Heat treatment, however, was able to inhibit H 2 O2 induced DNA damage. This results show that heat preconditioning is able to slightly improve DNA repair. This effect is transient. We conclude that therapeutic strategies that aim at heat shock protein induction for the protection of epidermal cells from UV radiation are safe with regard to DNA damage.