IFITM1 knockdown increases cell death in AI-resistant breast cancer cells. (A) MCF-7:5C cells were transfected with control siRNA (siCon), IFITM1 siRNA (siIFITM1) or PLSCR1 siRNA (siPLSCR1) for 24, 48 and 72 hours and cell extracts were subject to Western blotting analysis to assess IFITM1 and PLSCR1 protein expression. (B) MCF-7:5C cells were transfected with siCon, siIFITM1 (left panel) or siPLSCR1 (right panel) for 24 hours and then treated with 1 nM E2 for an additional 72 hours. Cell proliferation was measured by the MTT assay. All the illustrated data are expressed as mean values of three independent experiments. Standard deviations are shown. *P <0.05 versus control; #P <0.05 versus E2 treatment. (C) MCF-7:5C cells were transfected with siCon or siIFITM1 and after 24 hours were exposed to E2 (1 nM) for an additional 96 hours. Cells were then stained with annexin V-FITC and PI for detection of apoptosis as described in Methods. (D) Cells were treated as described above in (C) and were analyzed by Western blotting to assess IFITM1, p21, Bax, p53, Noxa and PARP protein expression. Membranes were stripped and reprobed for β-actin, which was used as a loading control. The protein levels for p21, Bax and Noxa were quantified using the ImageJ software (downloaded from the NIH website) and normalized as the ratio relate to β-actin. *P <0.05; **P <0.01. AI, aromatase inhibitor; E2, 17β-estradiol; FITC, fluorescein isothiocyanate; IFITM1, interferon induced transmembrane protein1; IFNAR1, IFN alpha Type 1 receptor; MTT, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide; NIH, National Institutes of Health; PARP, poly ADP ribose polymerase; PI, propidium iodide; PLSCR1, phospholipid scramblase 1.