Gene expression changes induced by overexpression of MN1 and MN1VP16 in murine bone marrow cells

Myeloid differentiation is blocked in acute myeloid leukemia (AML), but the molecular mechanisms are not well characterized. MN1 is overexpressed in some AML patients and confers resistance to all-trans retinoic acid (ATRA)-induced differentiation. To understand the role of MN1 as a transcriptional regulator in myeloid differentiation, we fused transcriptional activation (VP16) or repression (M33) domains with MN1 and characterized these cells in vivo. Transcriptional activation of MN1 target genes induced myeloproliferative disease with long latency and differentiation potential to mature neutrophils. A large proportion of differentially expressed genes between leukemic MN1 and differentiation-permissive MN1VP16 cells belonged to the immune response pathway like Irf8 and Ccl9. As MN1 is a co-factor of MEIS1 and RARA, we compared chromatin occupancy between MN1, MEIS1 and RARA. Immune response genes that were upregulated in MN1VP16 cells were co-targeted by MN1 and MEIS1, but not RARA, suggesting that myeloid differentiation is blocked through transcriptional repression of shared target genes of MN1 and MEIS1. Constitutive expression of Irf8 or its target gene Ccl9 identified these genes as potent inhibitors of MN1-induced leukemia. Our data show that MN1 prevents activation of the immune response pathway, and suggest that restoration of Irf8 signalling as a novel therapeutic target in AML.

6