The MLL-AF9 and MLL-AF4 oncofusion proteins bind a distinct enhancer repertoire and target the RUNX1 program in MLLr AML

In MLL-rearranged (MLLr) leukemias the N terminal part of the MLL gene can be fused to over 60 different partner genes. Here, we investigate the genome wide binding of the MLL-AF9 and MLL-AF4 fusion proteins and their epigenetic signatures in order to define a core set of MLLr targets. We uncover both common as well as specific MLL-AF9 and MLL-AF4 target genes, which are all marked by H3K79me2, H3K27ac, and H3K4me3. Apart from promoter binding, we also identify MLL-AF9 and MLL-AF4 binding at specific subsets of non overlapping active distal regulatory elements. Despite this differential enhancer binding MLL-AF9 and MLL-AF4 still share a common gene program, which represents part of the RUNX1 gene program and constitutes of CD34+ and monocyte specific genes. Comparing these datasets revealed several zinc finger transcription factors as potential MLL-AF9 co-regulators. Together these results suggest that MLL-fusions collaborate with specific subsets of TFs to aberrantly regulate the RUNX1 gene program in 11q23 AMLs. Overall design: Genome-wide (ChIP-seq) binding of MLL, AF9, AF4, H3K4me3, H3K27ac, H3K79me2 and RUNX1 in THP-1 and MV4-11 AML cell lines. Expression Profiling (RNA-seq) of THP-1 and MV4-11 cell lines, as well as 5 MLL-AF9 positive patient blasts.