BCR-ABL expression in Baf/BCR-ABL clones.

Western blots probed with anti-Abl (upper part of the filters) and anti-actin (lower part of the filters) antibodies. (A) Lane 1: Baf/BCR-ABL-s. Lanes 2-5: 4 Baf/BCR-ABL clones resistant to 1 μmol/L STI571. Lanes 6, 7: 2 Baf/BCR-ABLclones resistant to 3 μmol/L STI571. Note that one tenth the protein was loaded onto the latter 2 lanes to enable resolution of the 210-kd Bcr-Abl band without saturation of the image. Densitometric Bcr-Abl/actin ratio for each sample showed an average 7-fold Bcr-Abl overexpression in the clones resistant to 1 μmol/L STI571 and 34-fold in those resistant to 3 μmol/L in comparison with the level of expression in the sensitive parental line. (B) Modulation of Bcr-Abl expression in Baf/BCR-ABL cells grown for 3 days in the presence (+) or absence (−) of IL-3, STI571, or both. The P210/actin ratios indicate that the removal of STI571 leads to a weak reduction in the level of Bcr-Abl protein and that the effect is significantly enhanced by the addition of IL-3. These results were reproduced in 4 identical experiments. (C) BCR-ABL mRNA levels in Baf/BCR-ABL-r1 cells after 3- and 7-day withdrawal of STI571 from the culture.