Figure 3

Increased cell viability, invasiveness and metastasis of ERα36⁺ breast cancer cells treated with tamoxifen. (A) Assay for cell viability of ERα36⁺ cells sorted from parental MCF-7 breast cancer cells treated with E2 (1 nM) or 4-OHT (1 μM). Ethanol was used as a vehicle control. Each point indicates mean value (± SEM) from three experiments. ^*P < 0.05. (B, C) The proliferation of MCF-7/ERα36 and MDA-MB436/shControl cells promoted by 4-OHT. MCF-7/mock and MDA-MB436/shERα36 cells were used as control low ERα36-expressing cells. All cells were treated with 4-OHT (1 μM) for five days and cell number was determined daily. Each point indicates mean (± SEM) of results from three experiments. ^*P < 0.05. (D) Equal rate of growth shown by orthotopically xenografted tumors formed by MCF-7/ERα36 cells after E2 or tamoxifen treatment (n = 5 each group). ^*P < 0.05. (E) Elevated invasiveness of MCF-7/ERα36 cells after treatment with E2 (1nM) or 4-OHT (1 μM) in a Transwell assay. Each point indicates mean (± SEM) of results from three experiments. ^*P < 0.05. (F) Increased migration of MCF-7/ERα36 cells observed with E2 (1nM) or 4-OHT (1 μM) treatment. The distance of tumor cells at the leading edge was recorded and measured by Cell Observer. Ethanol was used as a solvent control. ^*P < 0.05. (G, H) Pulmonary metastasis of 4T1, mouse breast cancer cell in E2 or tamoxifen-treated animals. Lung metastasis in mice was examined using 4T1-ERα36^+/− (G) and MCF-7/ERα36 cells (H). Quantitation of metastatic nodules as means ± SEM (n = 6 mice/each group). Statistical significance was determined by two-tailed Student's t test .