723Original Article Overexpression of Damaged-DNA-Binding Protein 2 (DDB2) Potentiates UV Resistance in Hamster V79 Cells

(DDB2). Although the function of DDB is unclear, mutation on DDB2 is associated with cellular sensitivity to a variety of genotoxic agents including UV. It has been suggested that DDB2 may play a role in UV-induced DNA repair. However, evidence that DDB2 involves in DNA repair and UV sensi-tivity is lacking. Methods: To examine the role of DDB2, we established DDB2-overexpressing hamster V79 cell lines, V79ddb2, by stable transfection with full-length open reading frame of human ddb2 cDNA. Cells were irradiated with UV and determined its DNA repair activity by testing the remaining photoproducts on the chro-matin and measuring the plasmid reactivation, respectively. UV induced cytotoxicity was determined by the colorimetric assay (MTT assay), and apoptotic cells exhibiting morphological features of chromatin condensation and nuclear fragmentation were counted after 4-diamidino-2-phenylindole (DAPI) staining. Results: DDB activity was increased in DDB2-overexpressing cell lines. Analysis o