Ovarian clear cell adenocarcinoma (OCCA) is an aggressive ovarian malignancy with a poor prognosis. The role of estrogen receptor β (ERβ) in the development of OCCA remains to be clarified. To investigate the action of ERβ in the proliferation and invasion of OCCA cells, the ES-2 cell line was stably transfected with full-length human ERβ cDNA, and clones were screened and identified using RT-PCR and western blot assay. ERβ stable transfectants, referred to as ESβ1 and ESβ2 cells, were compared with mock transfectant ESVE and parental ES-2 cells with respect to their growth, motility and ability to activate target genes. ESβ1 and ESβ2 cells expressed ERβ mRNA and protein, whereas ES-2 and ESVE cells were ERβ negative. ERβ transfectants exhibited distinct characteristics from ES-2 and ESVE cells including proliferative properties and the ability to express cyclin D1 in the presence of 17β-estradiol (E2). ERβ inhibited ES-2 cell proliferation, which was determined using the MTT assay, BrdU labeling method and by the down-regulation of cyclin D1 gene expression. Moreover, exogenous ERβ expression resulted in a significant inhibition of ES-2 cell motility in an in vitro invasion assay. ERβ reduced the expression of MMP2 mRNA and the activity of MMP2 enzymatic activity in a ligand-dependent manner. In summary, ERβ may inhibit the proliferation and invasion of ES-2 cells and may be an important regulator in OCCA carcinogenesis.

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