Knockdown of expression of HO-1 in CML cells is followed by apoptosis. (A) K562 cells were left untreated (Control) or were transfected with a control siRNA against luciferase or an siRNA specific for HO-1 as indicated. 8 hours after transfection, the percentage of apoptotic cells (provided for each condition) was determined by combined annexin V/propidium iodide staining and FACS analysis. PI, propidium iodide. (B) K562 cells were incubated in control medium (Co) or were transfected with control siRNA against Luciferase (Luc) or with a HO-1-specific siRNA (HO-1) at 100 nM or 200 nM. 8 hours after transfection, expression of HO-1 was determined by Western blotting. Expression of β-actin is shown as loading control. (C) The effects are shown for 3 different siRNAs (nos. 1–3) specific for HO-1 on viability of K562 cells compared with untransfected cells (Co) or cells transfected with a control siRNA (Luc). Results represent the mean (± SD) of 3 independent experiments. *P < .05 compared with control (Co).