Effects of STI571 and ATRA on the levels tyrosine phosphorylation of c-Abl and c-kit.

NB4 cells seeded at an initial concentration of 2 × 10⁵/mL were treated with STI571 (5 × 10⁻⁶ M), ATRA (10⁻⁷ M), or the combination of the 2 compounds for the indicated amount of time (A) or for 16 hours (B). In (A), cell extracts (50 μg protein/lane) were subjected to Western blot analysis with c-Abl, c-kit, or β-actin antibodies. In (B), cell extracts were immunoprecipitated (ip) with c-Abl or c-kit antibodies. The immunoprecipitates were run on a 6% polyacrylamide gel and subjected to Western blot analysis (WB) with antiphosphotyrosine antibodies (p-Tyr Ab), c-Abl, or c-kit antibodies. The results are representative of 2 independent experiments.