Abstract:

Objective

To study the relationship of ERβ (estrogen receptor β)protein and its isoform (ERβcx ) with tamoxifen resistance in human breast cancer.

Methods

(1) Tamoxifen-sensitive MCF-7 cells and tamoxifen-resistance MCF-7 cells were cultured. A demethylation drug named 5-Aza-2-deoxycytidine (5-AZA- CdR) was used to treat human breast cancer MCF-7 cells to obtain MCF-7^5-AZA-CdR cells. Western blot method was used to detect the expressions of ERβ and ERβcx proteins in the three groups. (2) Fully-developed MCF-7 cells in log phase growth were seeded at 2. 5×10³ cells/well in 96-well tissue culture plates. The experimental groups included tamoxifen-treated MCF-7 cells (MCF-7 cells+ TAM group) and tamoxifen-treated MCF-7^5-AZA-CdR cells (MCF-75-AZA-CdR cells +TAM group), and the control group was MCF-7 cells without any treatment. MTT assay was used to observe the cell proliferation of the three groups. Statistical analysis was done using one-way analysis of variance and repeated measures.

Results

(1) The expression of ERβ protein in the tamoxifen-sensitive MCF-7 cells was higher than in the tamoxifen-resistant MCF-7 cells (P=0.000), but there was no statistical difference in ERβcx protein expression between the two groups (P=0.366). The expressions of both ERβ and ERβcx proteins in the MCF-7^5-AZA-CdR cells were the highest among the three groups, (both P=0.000). (2) Compared with the control group of MCF-7 cells, tamoxifen significantly reduced the cell proliferation in the MCF-7 cells+TAM group and the MCF-7^5-AZA-CdR cells +TAM group, and the effect of tamoxifen inhibiting cell growth in the MCF-7^5-AZA-CdR cells+TAM group was greater than in the MCF-7 cells+TAM group (P=0.000).

Conclusion

The ERβ expression in the tamoxifen-sensitive MCF-7 cells is high. The expressions of both ERβ and ERβcx proteins in the MCF-7^5-AZA-CdR cells are high. The effect of tamoxifen inhibiting cell growth is high in the tamoxifen treated MCF-7^5-AZA-Cdr cells.

Key words: breast neoplasms, estrogen receptor β, estrogen receptor βcx, tamoxifen, drug-resistance