Expression of MCL-1 in primary CML cells and CML-derived cell lines. (A,B) Immunocytochemistry performed with bone marrow mononuclear cells (BMMCs) and an antibody against MCL-1. (A) A typical staining result in normal BMMCs (top) and BMMCs in a patient with CML (bottom). An Olympus BX50 microscope (Olympus, Tokyo, Japan) was used; magnification, × 400; camera, Olympus DP11 (Olympus); software, Adobe Photoshop (Adobe Systems, San Jose, CA). (B) Semiquantitative analysis of immunostaining data (percentage of MCL-1⁺⁺ cells and of MCL-1⁺ cells) in patients with CML (n = 4, ▪) and normal BMMCs (n = 4, Co; □); results represent the mean ± SD from 4 donors; ^*P is less than .05. (C,D) Western blot analysis of expression of MCL-1 in primary CML cells after exposure to STI571 (1 μM) or control medium (control) for 24 hours. Panel C shows a representative experiment with molecular weight markers (kDa) and panel D a densitometric evaluation of MCL-1 expression (relative to β-actin) in primary CML cells with results (given as percent of control) representing the mean ± SD from 3 donors. (E,F) Northern blot analysis of expression of mcl-1 mRNA in primary CML cells exposed to control medium (control) or STI571 (1 μM) for 12 hours. Panel E shows a typical experiment in one donor and panel F a densitometric evaluation of data with results (given as percent of control) representing the mean ± SD from 3 donors; ^*P < .05. (G,H) Dose-dependent (G) and time-dependent (H) effects of STI571 on expression of the MCL-1 protein (top), cell viability (percent trypan blue-positive cells), and percentage of apoptotic cells (bottom) in K562 cells. Results represent the mean ± SD from 3 independent experiments. MCL-1 protein expression was determined by Western blotting; β-actin served as a loading control.