Elevated expression of Flt3 by transduction of Meis1 confers a survival and proliferative advantage to the NUP98-HOX cells. (A) Quantitative RT-PCR showing the levels of Meis1, Flt3, and FL transcripts in the NA10 and ND13 preleukemic cells before and after Meis1 or Flt3 transduction. Levels are shown as fold changes relative to the parental lines. The error bars represent standard deviation from 2 independent experiments. (B) Western blot analysis showing an increase of Flt3 protein levels in the NUP98-HOX cells upon transduction with the Flt3 or Meis1 retroviruses. Both bands represent Flt3; the top band is the glycosylated form. The levels of Meis1 and GAPDH are also shown. The transduced cells were sorted for GFP/YFP expression and at least 85% of the tested cells were double positive. (C) Ex vivo dose-response growth curves where bm cells harvested from diseased NA10/Meis1 mice were grown in 10% FBS and 0, 10, or 50 ng/mL FL in the presence or absence of Flt3 inhibitor AG1295 for a period of 5 days. The error bars represent the standard deviation from 3 independent experiments.