Evidence exists that sex steroids such as estrogens affect epithelial ovarian cancer. The expression profiles of the estrogen receptors (ER) and ERβ in particular have not been fully described. Therefore, in our present study, we examined the methylation status of the promoters 0K and 0N, and the expression of ERβ isoforms in human epithelial ovarian carcinoma. We then correlated methylation status with ER expression status. Twelve ovarian carcinoma cell lines, six primary cultures of ovarian surface epithelial cells (OSE), and 64 cases of ovarian carcinoma tissues were examined. Bisulfite sequencing and quantitative reverse transcription-polymerase chain reaction were used to evaluate methylation status and expression of ERβ isoforms. The relative abundance of exon 0N, ERβ1, ERβ2, and ERβ4 mRNA was significantly lower in ovarian cancer cell lines and tissues than in their corresponding normal counterparts. However, ERβ5 mRNA level was relatively higher in the cancers, in clear cell adenocarcinoma in particular, than in the normal ovary. Bisulfite sequencing analysis demonstrated that the two promoters of the ERβ gene exhibited distinct methylation patterns. Promoter 0N was unmethylated in OSE, rarely methylated in normal ovarian tissues, and extensively methylated in ovarian cancer cell lines and tissues (11/15 cell lines and 18/32 cancer tissues were extensively methylated). The promoter 0K was, however, unmethylated in both normal and malignant ovarian cells and tissues. A significant correlation between promoter 0N hypermethylation and the loss of exon 0N, ERβ1, ERβ2, and ERβ4 mRNA expression was detected in ovarian carcinoma cells and tissues. Treatment of ovarian carcinoma cells with 5-aza-2′ deoxycytidine resulted in reexpression of the ERβ gene. The results of our present study suggest that ERβ is inactivated mainly through aberrant DNA methylation. This process may play an important role in the pathogenesis of epithelial ovarian cancer.
ASJC Scopus subject areas
- Cancer Research