Down-regulation of MDR1 by epigenetic alteration in human epithelial ovarian cancer cells

Abstract

e16556 Background: Ovarian cancer is one of the most lethal malignancies in women. Despite recent studies of many oncogenes and tumor-suppressor genes concerning about its progression, the details of ovarian cancer biology still remains to be unclear. P-glycoprotein (P-gp) encoded by the MDR1 gene is a membrane protein that can export many kinds of antineoplastic agents from cells, and overexpression of P-gp has been reported to be implicated in treatment failure in cancer. DNA methylation, a major epigenetic process, can affect every step in carcinogenesis as well as genetic alterations. The contribution of such epigenetic alteration to the expression of MDR1 remains largely unexplored in human ovarian cancer. Methods: In this study, we evaluated the DNA methylation status of the MDR1 gene by methylation-specific PCR. Then, the expression of MDR-1 mRNA and protein in primary epithelial ovarian cancer specimens were evaluated by real-time RT-PCR and immunohistochemistry using anti-mouse P-gp F4 monoclonal antibody, respectively. The correlation between these results and clinicopathological features was examined. Results: MDR1 was hypermethylated in 12 of 12 (100%) ovarian cancer cell lines, and 5 of 13 (38%) primary ovarian cancers by methylation-specific PCR analysis. MDR1 mRNA expression was subsequently found to be lost in ovarian cancer cell lines with methylation by both real-time RT-PCR and immunohistochemistry. Thus, MDR1expression was associated with the DNA methylation status of the MDR1 gene. Conclusions: In conclusion, MDR1 was frequently hypermethylated in human ovarian cancers. Our results suggest that epigenetic regulation might play a role in the expression of MDR1 and clinical treatment outcomes in human ovarian cancer. No significant financial relationships to disclose.