RNAi leads to specific down-regulation of PML and a corresponding loss of IFN-α–mediated growth inhibition. (A) Immunoblot analysis of PML induction by IFN (500 U/mL) in parental 8226 cells (left), 8226 cells transfected with control siRNA targeting luciferase (siluc, middle), and 8226 cells transfected with siRNA targeting PML (siPML, right). Protein loading control was measured by GAPDH blotting. (B) Fluorescence microscopy image of PML NB induction. Cells in left panels were untreated and, in right panels, treated with IFN-α. (C) MTS proliferation assay comparing the effect of IFN-α on 8226 cells transfected with siluc or siPML. Data are expressed as percentage of optical density (OD) value of IFN-treated versus untreated cells as described in “Materials and methods,” with untreated cells representing 100% proliferation, and are averaged values of 5 independent experiments performed in triplicate (± SD). (D) Trypan blue viability assay of the same experiment as in panel C. The data are average of 3 independent experiments performed in triplicate (± SD).