Inhibitory effects of BCC peptides on the growth of p185^(BCR-ABL)-expressing Ba/F3 cells in the presence and absence of STI571. (A) Coexpression of p185^(BCR-ABL) and GFP or p185^(BCR-ABL) and BCC-GFP in Ba/F3 cells. Expression levels and phosphorylation state were assessed by Western blot analysis using the indicated antibodies. Tubulin was used as a loading control. (For schematic representation of the proviruses used in this experiment see Figure 1.) (B) Factor-independent growth of Ba/F3 cells expressing the indicated transgenes. (C) Effect of 1 μM STI571 on IL-3–independent growth of Ba/F3 cells expressing p185^(BCR-ABL) and GFP or BCC-GFP or BCC-FLAG. (Left) Without STI571. (Right) With STI571. (D) Autophosphorylation of p185^(BCR-ABL) in the presence and absence of BCC-GFP. Effect of increasing concentrations of STI571 on BCR-ABL autophosphorylation detected by the relationship between the amount of ABL and phosphorylated ABL detected by α-ABL and α-pABL, respectively. (E) IC₅₀ for STI571 of Ba/F3 cell expressing p185^(BCR-ABL) in the absence or presence of BCC-GFP. Data presented in panels B, C, and E are the mean of 3 independent experiments ± SD.