Expression of Estrogen Receptor-beta and Its Variants in Normal Mammary and Tumor Tissues

Kim, Ki Suk; Heo, Min Kyu; Kim, Seung Il; Park, Byeong Woo

Abstract

PURPOSE
Since the discovery of estrogen receptor-beta(ER-beta, five C-terminal variants of ER-beta were identified. We designed this study to investigate the pattern and clinical implications of ER-betaand its splicing variants expression in normal and malignant mammary tissues. METHODS: Using reverse transcription polymerase chain reaction (RT-PCR), we examined the expression levels of ER-alpha and ER-betaand its five splicing variants (beta1, beta2, beta3, beta4, beta5) in 50 paired normal and cancer tissues. We measured the densities of RT-PCR products using Tina version 2.10 (Raytest, Germany). Firstly, the incidence and intensity of ER-alpha and ER-beta and its five splicing variants were compared. Then the expression of ER-betamRNA splicing variants was also analyzed with regard to the ER-alphaprotein expression measured by immuno-histochemical staining and the menopausal status of the patients. Chi-square test and paired samples t-test were used for statistical analysis. Differences were considered to be significant with a p-value of less than 0.05. RESULTS: The expression of ER-betamRNA variants in normal breast and cancer tissues were as follows: ER-beta2 (100%/100%), ER-beta4 (76%/74%), ER-beta5 (32%/58%), and ER-beta1 (14%/16%). ER-beta3 was not detected at all. In terms of intensity, we observed a significant decrease of ER-beta2 (P<0.001) and an increase of ER-beta5 (P=0.004) in the mRNA expression levels among breast cancers compared to the corresponding normal breast tissues. Compared to the corresponding normal tissues, a significant decrease of ER-beta2 in cancer tissues was observed in patients with ER-alpha-positive (P<0.001), with age over 50 (P=0.01), and under 50 (P=0.04) as well, but not in patients with ER-alpha-negative (P=0.48). ER-beta4 also significantly decreased in patients with ER-alpha-positive (P=0.004) and with age over 50 (P=0.07). ER-beta5 showed a significant increment only in patient aged over 50 (P=0.04). CONCLUSION: ER-alpha mRNA expression significantly increases but ER-beta mRNA expression decreases in the cancer tissues compared to the corresponding normal tissues. Among ER-beta variant forms, ER-beta2 is predominant in both normal and malignant mammary tissues and ER-beta4, ER-beta5, and ER-beta1 in descending order but ER-beta3 does not express in mammary tissues. The decrease of ER-beta2 and ER-beta4 expression is prominent in cancer tissue especially in ER-alpha-positive cancers, which suggests that ER-beta2 and ER-beta4 may possess a regulatory function in mammary carcinogenesis. Further investigations to verify the roles of ER-beta variants are mandatory.