VEGF promoter activity in K562 cells treated with imatinib mesylate (STI571). The different VEGF promoter constructs used in transient transfection assays are shown. The relative light units (RLU/μg protein) was measured 24 hours after transfection of 20 μg of the different reporter genes in the absence (-) or in the presence (+) of 5 μM imatinib is shown. The results are representative of 4 independent experiments performed in duplicate ± SE. The percentage of inhibition in the presence of imatinib is indicated.