H3K79 Methylation Profiles Define Murine and Human MLL-AF4 Leukemias

Abstract

Summary We created a mouse model where conditional expression of an Mll-AF4 fusion oncogene induces B-precursor acute lymphoblastic (ALL) or acute myeloid leukemias (AML). Gene expression profile analysis of the ALL cells demonstrated significant overlap with human MLL-rearranged ALL. ChIP-chip analysis demonstrated histone H3 Lysine 79 (H3K79) methylation profiles that correlated with Mll-AF4 associated gene expression profiles in murine ALLs, and in human MLL-rearranged leukemias. Human MLL-rearranged ALLs could be distinguished from other ALLs by their H3K79 profiles and suppression of the H3K79 methyltransferase DOT1L inhibited expression of critical MLL-AF4 target genes. We have thus demonstrated that ectopic H3K79 methylation is a distinguishing feature of murine and human MLL-AF4 ALLs and is important for maintenance of MLL-AF4 driven gene expression. Significance The t(4;11) encodes an MLL-AF4 fusion protein, and predicts a particularly poor prognosis when found in acute lymphoblastic leukemias (ALL). Recent studies suggest certain MLL-fusion proteins enhance gene expression by recruitment of the histone H3 lysine79 (H3K79) methyltransferase DOT1L. We demonstrate that H3K79 methylation is enhanced at many loci in leukemia cells from a murine model of Mll-AF4 and in human MLL-AF4 leukemia cells and this elevation is correlated with enhanced gene expression. Furthermore, suppression of H3K79 methylation leads to inhibition of gene expression in MLL-AF4 cells. These data demonstrate that inhibition of DOT1L may be a therapeutic approach in this disease, and that this mouse model should be useful for assessment of therapeutic approaches for MLL-rearranged ALL.

Catalytic site remodelling of the DOT1L methyltransferase by selective inhibitors

“…Aberrant mono-and dimethylation of H3K79 by DOT1L is an essential step in the development of MLL-rearranged mixed lineage leukaemia, an acute form of the disease that, in infants, constitutes 70% of acute lymphoid and over 35% of acute myeloid leukemias [10][11][12][13] . MLL-rearranged mixed lineage leukaemia is driven by chromosomal translocations that result in an oncogenic fusion protein comprising the amino terminal region of MLL and the carboxy terminus of one of B70 translocation partners 14 , and pharmacological targeting of MLL translocation complexes was recently shown to reverse oncogenic activity of MLL fusion proteins in leukemia 15 .…”

Prognostic significance of FLT3 mutational status and expression levels in MLL-AF4+ and MLL-germline acute lymphoblastic leukemia

“…Most of our understanding of transformation by MLL-AF4 has come from murine models [2][3][4]26,27 and human stem cell systems. 1,[28][29][30][31][32][33] These have provided important insights into the likely mode of action of MLL-AF4, but the in vivo leukemias produced in these studies do not recapitulate the actual human disease phenotype and latency, and therefore MLL-AF4 leukemogenesis remains particularly difficult to model.…”

“…Existing murine models of MLL-AF4 acute leukemia have shown an extraordinary long latency period before overt disease develops, suggesting that additional genetic insults are required to generate leukemia. [1][2][3][4] Gene expression profiling showed that the FMS-related tyrosine kinase-3 (FLT3) is highly expressed in MLL-rearranged acute lymphoblastic leukemia (ALL), 5 leading to the characterization of FLT3 mutations as potential secondary cooperating events. 6 Accordingly, Ono et al 7 and Yamaguchi et al 8 have reported that constitutively activating FLT3 mutations cooperate with MLL-ENL and MLL-AF4, respectively, to induce leukemia in murine models.…”

DOT1L Inhibitor EPZ-5676 Displays Synergistic Antiproliferative Activity in Combination with Standard of Care Drugs and Hypomethylating Agents inMLL-Rearranged Leukemia Cells

“…In this manner, DOT1L is recruited to gene locations normally under the control of MLL (Okada et al, 2005;Mueller et al, 2007;Monroe et al, 2011). DOT1L catalyzes the specific methylation of histone H3 at lysine 79 (H3K79), and this site-specific marking of histone H3 leads to transcriptional activation (Milne et al, 2005;Okada et al, 2005;Guenther et al, 2008;Krivtsov et al, 2008;Mueller et al, 2009;Thiel et al, 2010;Monroe et al, 2011;Nguyen et al, 2011). It has therefore been speculated that DOT1L enzymatic activity represents an oncogenic driver of MLL-r leukemia, and that inhibition of the DOT1L enzyme would represent a cogent approach to therapeutic intervention for MLL-r patients.…”