Evidence exists that sex
steroids such as
estrogens affect
epithelial ovarian cancer. The expression profiles of the
estrogen receptors (ER) and
ERbeta 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
ERbeta 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
ERbeta isoforms. The relative abundance of exon 0N, ERbeta1, ERbeta2, and ERbeta4
mRNA was significantly lower in
ovarian cancer cell lines and tissues than in their corresponding normal counterparts. However, ERbeta5
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
ERbeta 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, ERbeta1, ERbeta2, and ERbeta4
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
ERbeta gene. The results of our present study suggest that
ERbeta is inactivated mainly through aberrant DNA methylation. This process may play an important role in the pathogenesis of
epithelial ovarian cancer.