Activation of TCF-dependent transcriptional activity by Flt3-ITD. (A) Activation of TCF-dependent promoters. SW387 cells were transiently transfected with wild-type (Top; ▪) or mutant (Fop; □) TCF-response reporter constructs. Cells were either cotransfected with Flt3-ITD or Flt3-WT. TCF reporter–specific luciferase expression was detected with a dual luciferase assay as described in detail in “Materials and methods.” The results of 2 independent experiments (mean and SD) are shown. (B) Induction of c-myc mRNA by Flt3-ITD mutations. 32D/Flt3-WT (□) and 32D/Flt3-ITD cells (▪) were grown in IL-3–containing medium. At time point 0, cells were washed twice and resuspended in serum-free medium with FL. At the indicated time points, samples were taken for RNA preparation and subsequent analyses of c-myc mRNA expression. The graph represents the relative c-myc mRNA expression (mean of independent experiments ± SD). (C) The effects of Flt3-ITD on the c-myc promoter were analyzed in 32D/Flt3-WT and 32D/Flt3-ITD cells. The ratio of normalized luciferase activity between del2 and del4 is shown. The TCF-binding elements contained in del2 are deleted in del4. □ indicates no GF; ▨, FL; and ▪, IL-3. The results of 2 independent experiments (mean and SD) are shown.