Pim2-PRα–induced leukemia is sensitive to ATRA. (A) Colony assays on methylcellulose were performed using freshly isolated BM cells from PRα or Pim2-PRα diseased mice, in the presence or absence of ATRA (1μM). The bars represent the colony growth of PRα and Pim2-PRα cells in the presence of ATRA calculated as percentage of control (ethanol treated). The results shown are the mean of 3 independent experiments ± SD. The significance in growth reduction between 2 groups PRα and Pim2-PRα was calculated by t test (P = .42). (B) MMP-9 expression is increased upon ATRA treatment for 48 hours in PRα as well as Pim2-PRα BM cells assessed by real-time RT-PCR. MMP-9 primers were used as described earlier.²⁴  Results shown here are the mean of 2 independent experiments ± SD. The significance was calculated using t test; P values are indicated in the figure. (C) Cytospin morphology of BM cells incubated with ATRA (1μM) for 48 hours from PRα or Pim2-PRα mice (Wright-Giemsa stain, original magnification ×40).