FLT3-ITD Cooperates with MOZ-TIF2 in Leukemogenesis in a Murine Bone Marrow Transplantation Model.

MOZ-TIF2 is expressed as a consequence of the chromosomal inversion inv(8)(p11q13) and is associated with AML FAB subtypes M4 and M5. Mice transplanted with MOZ-TIF2 succumb to monoclonal or oligoclonal leukemias with a long median disease latency, indicating that cooperating mutations are required for MOZ-TIF2 mediated leukemogenesis. The presence of a FLT3-ITD mutation in a patient with inv(8)(p11q13) has previously been reported, suggesting FLT3-ITD as a candidate cooperating mutation. Here we report that FLT3-ITD functionally cooperates with MOZ-TIF2 in co-transduction experiments in both a serial replating and murine bone marrow transplantation assay to induce AML that is transplantable to secondary recipients. At limit dilution, both MOZ-TIF2 and FLT3-ITD retroviruses are present, demonstrating cooperative effect. Moreover, tyrosine to phenylalanine mutations of FLT3-ITD residues 589 and 591, which we have previously reported to abrogate Stat5 signaling, also abolish the ability of FLT3-ITD to cooperate with MOZ-TIF2 both in vivo and in vitro. Furthermore, a constitutively active Stat5 mutant supports factor independent serial replating activity of MOZ-TIF2 in vitro. These data suggest a multi-step transformation model in which constitutive downstream Stat5 signaling by FLT3-ITD cooperates with MOZ-TIF2 in AML induction, and indicate that FLT3-ITD potentiates the properties of self-renewal in hematopoietic progenitors through activation of STAT5.