Transcription factor Y-box binding protein 1 binds preferentially to cisplatin-modified DNA and interacts with proliferating cell nuclear antigen

The Y-box binding protein (YB-1) binds to inverted CCAAT box sequences that are present in the promoter region of many genes. We previously showed tha t YB-T is overexpressed in human cancer cell lines that are resistant to ci splatin and that the depletion of YB-l by transfection of a vector expressi ng YB-1 antisense RNA increases the sensitivity of human cancer cells to ci splatin. To determine whether YB-1 can bind to cisplatin-modified DNA, we f used YB-1 cDNA to glutathione S-transferase (GST) cDNA and purified the res ulting GST fusion protein. When,ve tested the fusion protein with unmodifie d or cisplatin-modified oligonucleotides, we found that GST-YB-I bound more strongly to cisplatin-modified oligonucleotides, as did GST fusion protein s of high mobility group 1 (HMG1), HMG2, and xeroderma pigmentosum group A protein. When we assayed the ability of proliferating cell nuclear antigen (PCNA) to interact with the GST fusion proteins, we observed binding to YB- 1 but not to HMG1, HMG2, or xeroderma pigmentosum group A. Subsequent exper iments demonstrated that YB-1 and PCNA interact directly via the COOH-termi nal region of YB-I. Using immunochemical coprecipitation methods, we observ ed binding of YB-l and PCNA in vivo. These results suggest that YB-1 can fu nction as a recognition protein for cisplatin-damaged DNA and that it may b e important in DNA repair or in directing the cellular response to DNA dama ge.