Differential expression of estrogen receptor-alpha and -beta messenger RNAs as a potential marker of ovarian carcinogenesis

Although estrogen receptor (ER)-alpha is expressed in both benign and malig nant ovarian tumors, the role of ER in ovarian carcinogenesis of epithelial tumors is still unknown, In view of the recent characterization of ER-beta , a second form of ER that seems to be highly expressed in ovaries, we reex amined this issue by studying the relative expression of ER-alpha and -beta in human ovarian tumor progression, We developed a competitive PCR assay based on coamplification of the two ER s in target nucleotide sequences displaying a high homology (exons 3 and 4) . Coamplification experiments with varying amounts of plasmids containing E R-alpha and -beta cDNAs showed that this assay was reliable for discriminat ing as Little as a 2-fold difference in the initial ER-alpha:ER-beta cDNA r atio. The relative expression of ER-alpha compared with ER-beta mRNAs was s tudied in human ovarian cancer cell lines (n = 5) and in normal ovaries (n = 6), then in human benign and malignant tumor samples including ovarian cy sts (n = 24), borderline tumors (n = 3), and cancers (n = 10), In normal ov aries, ER-beta mRNA was the predominant ER form, whereas in ovarian cancer cell lines ER-alpha mRNA was markedly increased as compared with ER-beta. I n benign and borderline tumors, ER-beta mRNA was detected in 78% of tumors, whereas ER-alpha mRNA was detected in 29%, In ovarian carcinomas, both ER- alpha and -beta mRNAs were expressed in 80% of tumors. The ER-alpha:ER-beta mRNA ratio was >1 in only one cyst sample (4%), In contrast, the ER-alpha: ER-beta mRNA ratio was markedly increased in ovarian cancers because 60% sh owed an ER-alpha: ER-beta mRNA >1, In situ hybridization experiments showed overlapping tissular distribution of ER-beta and -alpha expression in canc ers and cysts, with a main localization in the epithelium and only a low le vel of expression in stromal cells. In summary, we found an increase in the ER-alpha:ER-beta mRNA ratio in ovar ian carcinomas as compared with normal ovaries and cysts. These data sugges t that overexpression of ER-alpha relative to ER-beta mRNA may be a marker of ovarian carcinogenesis.