Solar and UVC-induced mutation in human cells and inhibition by deoxynucleosides

Optimum conditions were established for quantitating the induction of hypoxanthine guanine phosphoribosyl transferase-deficient (HGPRT-) mutants in HeLa cells and in a human amelanotic melanoma cell line (MM96L). Compared at a fluence of equal toxicity (D37, fluence required to decrease cell survival to 37% of unirradiated control), noon sunlight in summer was slightly more mutagenic in MM96L than in HeLa cells (17 and 12 HGPRT- mutants per 10(6) survivors respectively). UVC (predominantly 254 nm) exhibited similar mutagenicity as equitoxic sunlight in HeLa but was 8-fold more effective in MM96L than equitoxic sunlight. Addition of a mixture of deoxyguanosine (20 microM), deoxyadenosine (20 microM), deoxycytidine (100 microM) and thymidine (20 microM) to the culture medium during the 7-day expression period following irradiation gave a 3-fold reduction in the UVC-induced mutation frequency of MM96L but not HeLa cells. The results suggest that these melanocytic cells are highly susceptible to mutagenesis by short wavelength UV, in a mechanism sensitive to deoxynucleosides.