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

Purpose : Since the discovery of estrogen receptor-β (ER-β), five C-terminal variants of ER-β were identified. We designed this study to investigate the pattern and clinical implications of ER-β and 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-α and ER-β and its five splicing variants (β1, β2, β3, β4, β5) 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-α and ER-β and its five splicing variants were compared. Then the expression of ER-β mRNA splicing variants was also analyzed with regard to the ER-α protein 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-β mRNA variants in normal breast and cancer tissues were as follows: ER-β2 (100%/100%), ER-β4 (76%/74%), ER-β5 (32%/58%), and ER-β1 (14%/16%). ER-β3 was not detected at all. In terms of intensity, we observed a significant decrease of ER-β2 (P<0.001) and an increase of ER-β5 (P=0.004) in the mRNA expression levels among breast cancers compared to the correstponding normal breast tissues. Compared to the corresponding normal tissues, a significant decrease of ER-β2 in cancer tissues was observed in patients with ER-α-positive (P