3011 – UNIQUE ROLES OF KMT2A FAMILY MEMBERS IN HEMATOPOIESIS AND LEUKEMIA

The KMT2 family (MLL1-4 also known as KMT2A-D) of histone methyltransferases are responsible for modifying histone H3 lysine 4 at enhancers and promoters, but the precise gene- and tissue-specific activities are not yet clear. The founding member, KMT2A or MLL1 was demonstrated to be essential for the development and maintenance of hematopoietic stem cells. In contrast, our previous study showed that loss of Mll2, but not Mll1, had a significant impact on the survival of leukemia cells by maintaining multiple leukemia survival pathways including NF-κB targets, integrin ß3, and IL-3 receptor alpha (IL-3Ra). Here, we further define the relative roles of KMT2A/B in normal versus leukemic hematopoiesis. We demonstrate MLL2 globally regulates GPI-anchored protein biogenesis during myeloid and B-cell differentiation, but does not do so in hematopoietic stem and progenitor cells (HSPCs). In contrast to Mll1, we show that Mll2 loss does not impact steady-state or regenerative hematopoiesis in vivo. Further, global H3K4me2/3 levels are unaffected by Mll2 deletion in primary HSPCs, yet ∼20% of H3K4me2/3 is reduced in AML cells upon Mll2 deletion. These data suggest a gained dependency on MLL2 for H3K4-methylation in leukemia. Integrating RNAseq and spike-in ChIP seq data, we found that only ∼16% of genes downregulated 72 hrs after Mll2 deletion also exhibited reduced H3K4me3, suggesting that MLL2 regulates genes both through its enzymatic activity and through other mechanisms. Our data suggest that targeting MLL2 in AML may have little impact on normal hematopoiesis, while effectively blocking leukemia survival. We extend these findings to human HSPCs, leukemia lines, and AML specimens and show that conserved pathways are regulated by MLL2. Overall, these results provide a rationale to target MLL2 for AML treatment. The KMT2 family (MLL1-4 also known as KMT2A-D) of histone methyltransferases are responsible for modifying histone H3 lysine 4 at enhancers and promoters, but the precise gene- and tissue-specific activities are not yet clear. The founding member, KMT2A or MLL1 was demonstrated to be essential for the development and maintenance of hematopoietic stem cells. In contrast, our previous study showed that loss of Mll2, but not Mll1, had a significant impact on the survival of leukemia cells by maintaining multiple leukemia survival pathways including NF-κB targets, integrin ß3, and IL-3 receptor alpha (IL-3Ra). Here, we further define the relative roles of KMT2A/B in normal versus leukemic hematopoiesis. We demonstrate MLL2 globally regulates GPI-anchored protein biogenesis during myeloid and B-cell differentiation, but does not do so in hematopoietic stem and progenitor cells (HSPCs). In contrast to Mll1, we show that Mll2 loss does not impact steady-state or regenerative hematopoiesis in vivo. Further, global H3K4me2/3 levels are unaffected by Mll2 deletion in primary HSPCs, yet ∼20% of H3K4me2/3 is reduced in AML cells upon Mll2 deletion. These data suggest a gained dependency on MLL2 for H3K4-methylation in leukemia. Integrating RNAseq and spike-in ChIP seq data, we found that only ∼16% of genes downregulated 72 hrs after Mll2 deletion also exhibited reduced H3K4me3, suggesting that MLL2 regulates genes both through its enzymatic activity and through other mechanisms. Our data suggest that targeting MLL2 in AML may have little impact on normal hematopoiesis, while effectively blocking leukemia survival. We extend these findings to human HSPCs, leukemia lines, and AML specimens and show that conserved pathways are regulated by MLL2. Overall, these results provide a rationale to target MLL2 for AML treatment.