Treatment of wild-type P210^BCR-ABL–expressing cells with 10 μM STI571 overnight reverses the IL-3 independence and decreases phosphotyrosine levels but does not affect P210^BCR-ABL expression.

(A) Western blots of whole cell lysates showing expression of P210^BCR-ABL and phosphotyrosine expression in pK1 control, untreated P210^BCR-ABL, K1176R, or P210^BCR-ABLcells treated overnight with 10, 5, 1, 0.5, or 0 μM STI571. The BCR-ABL–specific band is indicated by an asterisk. Expression of grb2 was used as a loading control. (B) P210^BCR-ABL 32D cells were allowed to proliferate in triplicate in media containing (▴, ▵) or free (●, ○) from WEHI as a source of IL-3 and were treated with (▴, ●) or without (▵, ○) 10 μM STI571, as indicated. Cell viability was determined by trypan blue exclusion. The 32D cells expressing P210^BCR-ABL proliferate in the absence of IL-3, but die if treated with STI571. However, cells treated with STI571 remain viable if supplemented with IL-3 showing that STI571 is not toxic at the levels used.