MELANIN REDUCES ULTRAVIOLET-INDUCED DNA-DAMAGE FORMATION AND KILLING RATE IN CULTURED HUMAN-MELANOMA CELLS

Epidermal melanin pigment is believed to prevent development of ultrav iolet (UV) - induced skin cancer by shielding cell nuclei and reducing DNA damage formation. It has not been experimentally proved, however, whether melanin reduces UV-induced DNA damage, because published expe riments have been inconclusive. The present study was carried out to d etermine whether intracellular melanin protected cultured cells agains t UV-induced DNA damage and killing. Three human melanoma cell lines c ontaining different amounts of melanin were used. Absorption spectrum, subcellular localization of melanin, and melanin concentration were e xamined in the three cell lines. Two types of DNA damage, cyclobutane pyrimidine dimers and (6-4)photoproducts, were detected by an enzyme-l inked immunosorbent assay (ELISA) with monoclonal antibodies specific for these photolesions. We found that melanin reduced the induction ra tes of both types of DNA damage in pigmented cells irradiated with low doses of UV in a melanin concentration-dependent manner. Almost no di fferences in repair capacity for the two types of photolesions were ob served among the three melanoma cell lines. We also found that the mor e highly melanotic melanoma cell lines were more UV resistant than the less melanotic melanoma cell lines. These results suggest that intrac ellular melanin plays an important role in preventing UV-induced cell killing by reducing the formation of two types of DNA damage.