Effect of imatinib on BCR/ABL tyrosine phosphorylation in parental and transduced K562 cells. K562 cells overexpressing the indicated proteins were incubated with various concentrations of imatinib for 2 hours and then lysed and phosphorylation of BCR/ABL analyzed. (A) Whole-cell lysates were resolved by electrophoresis and probed by Western blotting with detection by chemifluorescence for p210 BCR/ABL using antibody to c-Abl, and for tyrosine phosphorylated p210 using antiphosphotyrosine Mabs. (B) Bands were quantitated using Typhoon and analyzed using ImageQuant software (Amersham Biosciences, Buckinghamshire, United Kingdom). The ratios of tyrosine phosphorylated and total p210 for each treatment were calculated after correction for background. Data are expressed relative to the value for each cell line in the absence of drug.