Objectives: The Y-box binding protein (YB-1) is a member of highly conserved cold shock protein family of transcription factors that play a critical role in cell proliferation and growth, DNA replication, cell cycle, and drug resistance to anticancer agents as well as malignancy. In our previous clinical studies, nuclear localization of YB-1 is associated with drug resistance against anticancer agents in oral cancer. However, the mechanism of nuclear localization and the association of drug resistance with YB-1 level are unclear. To investigate the further function of YB-1 in oral cancer at molecular basis, we isolated the associated protein with YB-1 using the yeast Two-Hybrid system. Methods: We screened the human oral epidermoid carcinoma cell (KB) cDNA library with the bait of full length YB-1, and isolated B23 protein, which is known as a stress-responsive protein as an YB-1 associated protein. The interaction of YB-1 with B23 was confirmed by in vitro pull down assay. KB cell and oral squamous cell carcinoma (SAS) cell were stimulated with cisplatin or UV. After stimulation, subcellular localization of YB-1 and B23 were detected by indirect immunofluorescence microscopy. Expression of YB-1 and B23 mRNA in cisplatin-resistant KB cell and their parental cell were measured by northern blot analysis. Results: We isolated B23 as YB-1 associated protein and confirm the interaction of them in vitro. YB-1 and B23 co-localized in the nucleus under the DNA damaging stimulation like UV or cisplatin, and their mRNA level were up-regulated in the in cisplatin-resistant KB cell. These results suggest the functional interaction between YB-1 and B23 in oral carcinoma. Conclusion: The expression of YB-1 protein in the nucleus may be considered a useful marker and also may reflect the sensitivity of oral carcinoma to chemotherapy.

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