Differential effectiveness of solar UVB subcomponents in causing cell death, oncogenic transformation and micronucleus induction in human hybrid cells

Abstract

Purpose : (1) To determine the biological effectiveness of two solar ultraviolet (UVB) spectra with different lower wavelength thresholds for oncogenic transformation and micronucleus induction in CGL1 cells; (2) to investigate whether the action spectra for short- and long-term effects are similar; and (3) to investigate possible links between transformation and other delayed effects. Material and methods : Two spectra were derived from a solar UV simulator by using two filters: the first transmitted radiation with 5 > 284 nm, the second with 5 > 293 nm. The resulting spectra have the same UVA, but different UVB components (5 between 284 and 320 nm, 19 W m m 2, and 5 between 293 and 320 nm, 13 W m m 2) . CGL1 cells were irradiated with 466 J m m 2 with 5 > 284 nm and 1582 J m m 2 with 5 > 293 nm. These doses were approximately equilethal. The endpoints examined were oncogenic transformation, and centromere-positive and -negative micronucleus frequencies in the directly irradiated cells and in transtheir progeny. Results : At equilethal doses, the oncogenic transformation frequency in the directly irradiated cells was greater by a factor of at least 7 for 5 > 284 nm irradiation compared with 5 > 293 nm. The micronucleus induction frequency was also significantly higher with the 5 > 284 spectrum. Consistent with our previous findings, no delayed micronucleus formation was found in the progeny of cells exposed to 5 > 293 nm, while a threefold elevation above controls was seen in the progeny of cells exposed to 5 > 284 nm irradiation. This was also the case for formation of micronuclei with a centromere. Conclusions : It was found that: (1) for equilethal doses the 5 > 284 nm spectrum was more biologically effective than the 5 > 293 nm spectrum for induction of oncogenic transformation and micronucleus formation; and (2) the higher effectiveness of the 5 > 284 nm spectrum found at equilethal doses for delayed effects in the progeny of irradiated cells resembles that found for transformation. The results suggest that the UVB action spectrum for cell killing is different from that of some delayed effects, and from that of transformation.