Activation of interferon signaling pathway in parental MCF-7 and AI-resistant MCF-7:5C cells in response to INFα. (A) MCF-7 (left panel) and MCF-7:5C (right panel) cells were incubated with IFNα (1000 U/ml) for the indicated time points. The cell extracts were examined by Western blotting using anti-PLSCR1, anti-IFITM1, anti-STAT1, anti-phospho-STAT1 (Y701), anti-IFNAR1, anti-STAT2, anti-phospho-STAT2 (Tyr690) and anti-β-actin. (B) Cellular localization of IFITM1 and PLSCR1 in MCF-7 and MCF-7:5C cells following IFNα treatment. Cells were treated for 24 hours with IFNα (1000 U/ml) and then analyzed for immunofluorescence staining of IFITM1 and PLSCR1 (original magnification 200×). (C) MCF-7 and MCF-7:5C cells were treated with IFNα (1000 U/ml) for 24, 48, 72 and 96 hours and 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; **P <0.01. AI, aromatase inhibitor; IFITM1, interferon induced transmembrane protein1; IFNAR1, IFN alpha Type 1 receptor; MTT, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide; PLSCR1, phospholipid scramblase 1; STAT1,2, Signal transducer and activator of transcription 1,2.