BCR/ABL-dependent expression of MCL-1 in Ton.B210-X cells. (A) Ton.B210-X cells were induced to express BCR/ABL by addition of doxycycline (1 μg/mL, 16 hours). Thereafter, RNA was subjected to Northern blotting. Expression of bcr/abl mRNA was determined using a c-abl-specific cDNA probe. The β-actin loading control is also shown. (B,C) Analysis of mcl-1 mRNA expression in Ton.B210-X cells after induction of BCR/ABL. Panel B shows a typical experiment and panel C a densitometric evaluation of data (corrected for β-actin) with results given as percent of control and representing the mean ± SD of 3 independent experiments; ^*P < .05. (D) Immunocytochemical detection of MCL-1 in unstimulated Ton.B210-X cells (control), Ton.B210-X cells after exposure to doxycycline (BCR/ABL), BCR/ABL⁺ Ton.B210-X cells stained with anti-MCL-1 antibody that had been preincubated with MCL-1-blocking peptide (BCR/ABL⁺ blocking peptide), and BCR/ABL⁺ Ton.B210-X cells preincubated with STI571 (1 μM) for 24 hours prior to staining with the anti-MCL-1 antibody (BCR/ABL⁺ STI571). An Olympus BX50 microscope (Olympus, Tokyo, Japan) was used; magnification, × 400; camera, Olympus DP11 (Olympus); software, Adobe Photoshop.