Objective      To investigate the role of estrogen receptor β1 (ERβ1)

in epithelial-mesenchymal transition (EMT) of breast cancer cells by regulating the expression of E-cadherin (E-cad)

and to explore the effects of ERβ1 on the invasion and migration of breast cancer cells.       Methods      The recombinant eukaryotic vector containing ERβ1 cDNA or specific siRNA targeting ERβ1 was transfected to human breast cancer cells MDA-MB-231 to interfere the expression of ERβ1. RT-PCR and Western blotting were used to detect the expression of ERβ1 and E-cad on mRNA and protein levels. Moreover

invasion and migration assays in vitro were applied to assess the influence of ERβ1 expression interference on malignant biological behavior of breast cancer.       Results      When ERβ1 was over-expressed

ERβ1 and E-cad showed increased expression at mRNA (0.823±0.028  vs  0.554±0.044

P

=0.025; 0.944±0.04  vs  0.724±0.28

P

=0.026) and protein (1.331±0.019  vs  0.463±0.019

P=0.001; 1.428±0.005  vs  0.500±0.010

P

0.01) levels

and the cells showed decrease of invasion (45.8±7.4  vs  70.4±13.3

P

=0.039) and migration (75.6±8.8  vs  111.8±15.1

P

=0.021) abilities. When ERβ1 was down-regulated

ERβ1 and E-cad showed decreased expression at mRNA (0.314±0.029  vs  0.554±0.044

P

=0.030; 0.444±0.042  vs  0.724±0.28

P

=0.001) and protein (0.353±0.017  vs  0.463±0.019

P

=0.032; 0.397±0.034  vs  0.500±0.010

P=0.024) levels

and the cells showed increase of invasion (193±22.6  vs  70.4±13.3

P

0.05) and migration (264.2±53.7  vs 111.8±15.1

P=0.002) abilities.       Conclusion      ERβ1 may participate in EMT of breast cancer and further influence the invasion and metastasis of breast cancer.