A ROLE FOR ULTRAVIOLET-A IN SOLAR MUTAGENESIS

It is well established that exposure to solar UVB (290-329 nm) gives r ise to mutations in oncogenes and tumor suppressor genes that initiate the molecular cascade toward skin cancer. Although UVA (320-400 nm) h as also been implicated in multistage photocarcinogenesis, its potenti al contribution to sunlight mutagenesis remains poorly characterized. We have determined the DNA sequence specificity of mutations induced b y UVB (lambda > 290 nm), and by UVA (lambda > 350 nm), at the adenine phosphoribosyltransferase locus of Chinese hamster ovary cells. This h as been compared to results previously obtained for simulated sunlight (lambda greater than or equal to 310 nm) and 254-nm UVC in the same g ene. We demonstrate that T --> G transversions, a generally rare class of mutation, are induced at high frequency (up to 50%) in UVA-exposed cells. Furthermore, this event comprises a substantial proportion of the stimulated sunlight-induced mutant collection (25%) but is signifi cantly less frequent (P < 0.05) in cells irradiated with either UVB (9 %) or UVC (5%). We conclude that the mutagenic specificity of broad-sp ectrum solar light in rodent cells is not determined entirely by the U VB component and that UVA also plays an important role.