JY or MS1418 cells (3 × 106) were starved for 24 h in a mixture of RPMI 1640 and DMEM (1:1, v/v) containing 0.5% FBS. Cells were irradiated with UVA (80 kJ/m2), UVB (8 kJ/m2), or UVC (60 J/m2) and then harvested by centrifugation at time points as indicated. After lysis and sonication, samples containing equal amounts of protein were separated by 8% SDS-PAGE and analyzed by Western immunoblotting using anti-phospho-ERKs antibody as described under “Materials and Methods.” Nonirradiated cells were used as a negative control. A shows that UVA–, UVB-, or UVC-induced phosphorylation of ERKs was induced in MS1418 cells but was markedly less in JY cells. B, intensity of bands was quantitated with Image-QuanNT™ software. Each value indicates the mean and S.D. from three independent experiments and is expressed as percentage of increase in phosphorylation compared with control.