Effect of MEK-1/2 inhibitor treatment on MAPK phosphorylation in CML and normal CD34⁺ cells. CD34⁺ cells from a CML patient and a healthy control were exposed to 25 μM U0126 for 16 hours in the presence or absence of 1 μM imatinib in medium containing low concentrations of GF. Whole-cell lysates were prepared, electrophoresed on 10% SDS-PAGE, and Western blotted with antibodies to dual phosphorylated p42/44 MAPK (P-MAPK) and total p42/44 MAPK (MAPK). Results of representative experiments are shown. C indicates control cells; I, the presence of 1 μM imatinib; U, the presence of 25 μM U0126; U + I, the presence of both.