Effect of STI571 on tyrosine phosphorylation, PARP proteolysis, and bcl-xL expression in K562 and K562-R cells.

(A) K562 (left) or K562-R cells (right) were treated with STI571 or PD180970 (1 μM) for 30 minutes before equal protein cell lysates (30 μg) were analyzed for tyrosine phosphorylation by immunoblotting. (B, top) K562 and K562-R cells were treated with 5 μM STI571 for the interval noted prior to analysis of PARP cleavage by immunoblotting as a measure of activation of caspase cascades. Intact (116 kDa) and cleaved (85 kDa) PARP are shown. (B, bottom) Lysates from untreated (control) and STI571 treated (5 μM, 24 hours) K562 or K562-R cells were analyzed for bcl-xL levels by immunoblotting. Equal protein loads were monitored by probing β-actin on the same membrane.