Induction of UV-damage recognition protein by cisplatin treatment

The biological functions of DNA damage recognition proteins are not well understood. Using the band shift assay, we detected in nuclear extracts from human carcinoma cell lines damage recognition protein which bound selectively to UV-damaged double-stranded DNA. No consistent correlation was found between steady-state levels of the UV-damage recognition protein and either cisplatin cytotoxicity or DNA repair activity. However, cisplatin treatment caused accumulation of the UV-damage recognition protein. The cisplatin-responsive induction of UV-damage recognition protein in the nucleus was higher in cisplatin-resistant cell lines than in their parental counterparts. These results imply that the level of inducibility in response to treatment, but not the constitutive binding activity, of UV-damage recognition protein correlates with cisplatin resistance. Inhibition of UV-damage recognition protein expression by actinomycin and cycloheximide suggests that induction of UV-damage recognition protein requires de novo RNA and protein synthesis, rather than post-translational modification of pre-existing protein. The increased level of UV-damage recognition protein after cisplatin treatment could be a direct response to adduct formation, since it correlated with the number of Pt-DNA adducts. However, it could also be a secondary effect of DNA replication inhibition following DNA damage, since inhibition of DNA synthesis by aphidicolin and hydroxyurea caused the same induction of UV-damage recognition protein. Inducibility of UV-damage recognition protein binding activity by Pt drug treatment suggests involvement of this protein in drug resistance, although a direct link between its function and DNA repair or damage tolerance has not been demonstrated.