Role of estrogen receptor beta in endometrial carcinogenesis

Proc Amer Assoc Cancer Res, Volume 47, 2006 434 The role of estrogen receptor (ER) beta (β) in endometrial carcinoma is less well known. Hence it was our aim to determine the expression of ERβ and two of its C-terminal isoforms ERβ1 and ERβ2/βcx in endometrioid carcinoma and compare it to the levels in normal proliferative endometrium at the transcript and the protein level. Methods: Tissue was obtained after an informed consent from cases of endometrioid carcinoma (n=26). Proliferative endometrium samples (n=22) were obtained from hysterectomies for leiomyomas. Semi-quantitative RT-PCR was used to analyze transcript levels. Immunohistochemistry was used to detect protein levels. For ERβ2/βcx protein analysis, we raised a polyclonal antibody (DC-1) to its unique C-terminus and characterized it for its specificity to recognize the full-length protein. The antibodies to detect total ERβ (Clone 14C8), ERα (Clone ID5), ERβ1 (Clone EMR02) and PR (Clone hPRa2 + hPRa3) were procured commercially. The Allred scoring system was used to give the immunohistochemical scores. The statistical tests employed for comparison of the expression of the receptors between the groups was Student's t-test and Mann Whitney U-test. For comparison of the inter-relationship of the expression of the receptors within each group, Pearson's correlation, Spearman's Rank correlation and Linear Regression analysis were employed. Results and summary: The total ERβ and PR transcript levels were significantly downregulated in endometrioid carcinoma as compared to proliferative endometrium (p=0.01). The protein expressions of all the receptors were also downregulated in carcinoma compared to normal endometrium (p<0.01) with the exception of ERβ1 isoform (p=0.383). A significant decrease of the ERβ2/ERβcx transcript was observed with higher grade tumors (p=0.041) whereas the other receptors expression did not correlate with grade of carcinoma. A correlation was also observed of increased total ERβ protein expression to increasing depth of myoinvasion (p=0.034) A significant association of ERα and ERβ (total) was observed in both non-neoplastic as well as neoplastic endometrium indicating that they may be regulated in similar fashion (p≤0.001). The expression of ERβ1 and ERβ2/βcx isoform was associated in the non-neoplastic endometrium (p≤0.02), but not in the neoplastic endometrium. By logistic regression analysis, ERα was seen to be the major receptor that effects PR expression in non-neoplastic as well as the neoplastic groups. In neoplastic endometrium the effect of the ERβ isoforms was less in comparison to ERα(R square change=0.243 versus ≤ 0.08 for ERβ and its isoforms). The co-expression of ERβ2/βcx with ERα is believed to inhibit the function of the later through a dominant negative effect, which was not observed in any of the groups. Conclusion: Thus downregulation of total ERβ occurs in endometrioid carcinomas, which may have important consequences on cellular proliferation.