CISPLATIN-MODIFIED DNA-BINDING PROTEINS IN A NUCLEAR EXTRACT OF RAT-LIVER CELLS

A mobility shift DNA-binding assay showed that cisplatin-modified DNA- binding proteins are present in the nuclear extract of rat-liver cells (Ac2F cells). The major binding proteins of 22.5, 23, 96.5 and 112 kD a were identified in vitro. The binding activity of the 23 kDa protein was markedly enhanced in the cells that were cultured in the presence of cisplatin, and was inhibited by addition of cycloheximide to the c ulture. Our previous work [Hibino et al. (1994) Biochem. Biophys. Res. Commun. 202, 749-756] has shown that an Mg2+-dependent endo-exonuclea se activity endogenous to Ac2F-cell nuclei is enhanced in the presence of cisplatin. Thus, the results of the present study imply that speci fic binding of the nuclear proteins to cisplatin-DNA lesions in rat-li ver cells is involved in the mechanism of enhancement of this nuclease activity.