Effect of bcr-abl expression and inhibition on Mo7e cell signaling and apoptosis.

(A) Mo7e cells and Mo7e cells expressing bcr-abl (MBA) were grown in the continual presence of 200 U/mL GM-CSF. Equal-density cultures were harvested, and lysates were examined for distinctions in phosphotyrosine levels, activated signaling cascades, and antiapoptotic proteins. For the detection of bcr-abl, equal-protein aliquots (200 μg) from Mo7e or MBA cell lysates were immunoprecipitated with anti-bcr and immunoblotted with anti-abl. The remaining blots were derived from cell lysates (40 μg), prepared as described in “Materials and methods.” (B) Mo7e or MBA cells were treated with STI-571 (at the indicated concentrations) for 24 hours before cell growth and survival were estimated by MTT staining. Results represent the average ± SEM of 4 determinations. (C) Induction of apoptosis was determined by measuring caspase 3 activation (appearance of a 14-kd band) and PARP cleavage (85-kd band) in Mo7e or MBA cells after incubation with STI-571 for 0 to 24 hours. Similar results were obtained in experiments in which GM-CSF (200 U/mL) or IL-3 (100 ng/mL) was included in the cell culture media (data not shown).