Cell survival and shuttle vector mutagenesis induced by ultraviolet A and ultraviolet B radiation in a human cell line

Although it is known that sunlight is carcinogenic, few molecular data are available concerning the mutagenic effects of ultraviolet (UV) B (290-320 nm) and UVA (320-400 nm) radiation in human cells. To analyze the biologic effects of UVA and UVB, we irradiated the 293 human cell line, derived from adenovirus-transformed human embryonic kidney cells, in which we had stably introduced a shuttle vector harboring the lacZ' bacterial gene as the mutagenesis target. Identical cell survival occurred after UVA doses 700-fold higher than UVB. This is comparable to the UVA/UVB ratio that reaches the basal cell layer of the? skin after sunlight exposure with UVB sunscreen. The frequency of UVA- and UVB-induced mutations increased with the UV dose as cell survival decreased. At cell survival levels greater than 10%, UVA and UVB induced similar frequencies of mutations in the episomal lacZ' gene, whereas for cell survival lower than 10%, UVA induced twice as many mutations as UVB. Sequence analysis of 81. independent lacZ' mutants (36 UVA- and 45 UVB-induced) revealed specific characteristics for some UV-induced mutations, particularly for UVB. Mutations at A/T base pairs were induced more frequently by UVA than by UVB. The UVA-induced mutation spectrum that we have observed in human cells may help to elucidate the mechanism of skin carcinogenesis.