Objective To explore the effect of exogenous estrogen receptor β1 (ERβ1) gene on the expression of p53 as well as the changes of apoptosis in MDA-MB-231 cell line and to investigate the biological role of ERβ1 in breast cancer. Methods Recombinant eukaryotic expressing vector containing ERβ1 cDNA was transfected into human breast cancer cell MDA-MB-231 by using cationic liposome LipofectamineTM 2000. The expression levels of p53 and ERβ1 in mRNA and protein were evaluated by real-time PCR and Western blot, respectively. Cell growth curve was used to detect the changes of cell proliferation ability. Cell apoptosis was detected by flow cytometry. Results After transfected with vector containing ERβ1 cDNA, proliferation ability of MDA-MB-231 cell decreased and the expression levels of both ERβ1 and p53 in both mRNA and protein increased (Plt;0.01). Rate of cell apoptosis increased in ERβ1 upregulation groups （Plt;0.01）. Conclusion ERβ1 can induce apoptosis and inhibit the growth of MDA-MB-231 cells by upregulating p53 expression.
