Protection against UV-induced cytotoxicity by forced expression of DDB2. (A, B, C) Sensitivity to UV is presented for stable cell lines indicated or for (D, E, F) HR18 cells which express DDB2. The protein levels of DDB2, DDB1, and β-actin are shown in the insets. The plotted values represent means ± S.D. of experiments performed in triplicates. IC50 values were also indicated in A and D.