Effect of NS-187 on intracellular phosphorylation of CrkL and ERK. NS-187 inhibits the phosphorylation of CrkL and ERK in cells expressing wt Bcr-Abl or the E255K Bcr-Abl mutant but not in cells expressing the T315I Bcr-Abl mutant. K562 (A-B), BaF3/wt (C-D), BaF3/E255K (E-F), or BaF3/T315I (G-H) cells were incubated for 1.5 hours with the indicated concentrations of each compound. Cells were then lysed and subjected to Western blot analysis with antiphosphotyrosine antibody (A-H), anti-CrkL antibody (A,C,E,G), or anti-ERK1 antibody (B,D,F,H). The phosphorylated forms of CrkL (p) migrate more slowly than the unphosphorylated forms.