Overexpression of TMEM47 Induces Tamoxifen Resistance in Human Breast Cancer Cells

Background: Tamoxifen (TAM) is the eminent first-line drug for endocrine therapy of hormone receptor positive premenopausal breast cancer and reduces the risk of recurrence by similar to 50%. However, many patients developed TAM resistance and their diseases recurred. Our previous study on transcriptome profile of TAM resistant breast cancer cells revealed that the TMEM47 is one of the most significantly differentially expressed genes. The mechanism of how TMEM47 is involved in TAM resistance was not known. Methods: We constructed a mammal breast cancer cell line, in which TMEM47 was stably overexpressed (TMEM47-OE/MCF-7), to further verify the role of TMEM47 in TAM resistance. siRNA targeting TMEM47 was transfected into TAMR / MCF-7 cells by Liposome. TMEM47 expression was validated on mRNA and protein level by qRT-PCR and western blotting. We tested the cytotoxicity of TAM in the cells. Apoptosis was detected by flow cytometry. Results: Compared to the MCF7 cells, TMEM47 mRNA was significantly up regulated more than 6 folds in the TAMR/MCF7 cells and so its protein. TMEM47 expression level in TMEM47-OE/MCF-7 was similar as in the TAMR/MCF-7 cells. The 50% inhibitory concentration (IC50) value (mean +/- SD) of TAM in MCF-7, TAMR/MCF-7 and TMEM47-OE/MCF-7 cells was 1.58 +/- 0.19, 2.74 +/- 0.24 and 3.12 +/- 0.32 mu gamma/mL, respectively. The apoptosis rates of TAMR/MCF-7 and TMEM47-OE/MCF-7 cell lines were significantly lower than that of MCF-7 cells. After 24 and 48 hours TAM treatments, cell viability was significantly inhibitied in TMEM47 knockdown TAMR/MCF7 cells (P < 0.01). Consistant with the decreased cell viability, the apoptosis rate in TMEM47 knockdown TAMR/MCF-7 cells was significantly increased. Conclusions: Our results suggest that overexpression of TMEM47 in MCF-7 cells acquired TAM resistance to those cells, and knockdown of TMEM47 in TAMR/MCF-7 cells reversed their resistance to TAM. TMEM47 might confer TAM resistance on MCF-7 cells through the inhibition of apoptosis.