ABSTRACT
Overexpression of the BRE (brain and reproductive organ-expressed) gene defines a distinct pediatric and adult acute myeloid leukemia (AML) subgroup. Here we identify a promoter enriched for active chromatin marks in BRE intron 4 causing strong biallelic expression of a previously unknown C-terminal BRE transcript. This transcript starts with BRE intron 4 sequences spliced to exon 5 and downstream sequences, and if translated might code for an N terminally truncated BRE protein. Remarkably, the new BRE transcript was highly expressed in over 50% of 11q23/KMT2A (lysine methyl transferase 2A)-rearranged and t(8;16)/KAT6A-CREBBP cases, while it was virtually absent from other AML subsets and normal tissues. In gene reporter assays, the leukemia-specific fusion protein KMT2A-MLLT3 transactivated the intragenic BRE promoter. Further epigenome analyses revealed 97 additional intragenic promoter marks frequently bound by KMT2A in AML with C-terminal BRE expression. The corresponding genes may be part of a context-dependent KMT2A-MLLT3-driven oncogenic program, because they were higher expressed in this AML subtype compared with other groups. C-terminal BRE might be an important contributor to this program because in a case with relapsed AML, we observed an ins(11;2) fusing CHORDC1 to BRE at the region where intragenic transcription starts in KMT2A-rearranged and KAT6A-CREBBP AML.
Subject(s)
Gene Rearrangement , Leukemia, Myeloid, Acute/genetics , Nerve Tissue Proteins/genetics , Protein Interaction Domains and Motifs/genetics , Transcriptional Activation , Translocation, Genetic , Cell Line , Chromosomes, Human, Pair 11 , Chromosomes, Human, Pair 16 , Epigenesis, Genetic , Exons , Gene Expression Regulation, Leukemic , Histone-Lysine N-Methyltransferase/genetics , Histones/metabolism , Humans , Introns , Myeloid-Lymphoid Leukemia Protein/genetics , Nuclear Proteins/genetics , Promoter Regions, GeneticABSTRACT
In 11q23 leukemias, the N-terminal part of the mixed lineage leukemia (MLL) gene is fused to >60 different partner genes. In order to define a core set of MLL rearranged targets, we investigated the genome-wide binding of the MLL-AF9 and MLL-AF4 fusion proteins and associated epigenetic signatures in acute myeloid leukemia (AML) cell lines THP-1 and MV4-11. We uncovered both common as well as specific MLL-AF9 and MLL-AF4 target genes, which were all marked by H3K79me2, H3K27ac and H3K4me3. Apart from promoter binding, we also identified 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 direct a common gene program, which represents part of the RUNX1 gene program and constitutes of CD34+ and monocyte-specific genes. Comparing these data sets identified several zinc finger transcription factors (TFs) as potential MLL-AF9 co-regulators. Together, these results suggest that MLL fusions collaborate with specific subsets of TFs to deregulate the RUNX1 gene program in 11q23 AMLs.
Subject(s)
Chromosomes, Human, Pair 11/genetics , Core Binding Factor Alpha 2 Subunit/metabolism , Enhancer Elements, Genetic , Gene Expression Regulation, Neoplastic , Leukemia, Myeloid, Acute/genetics , Myeloid-Lymphoid Leukemia Protein/metabolism , Oncogene Proteins, Fusion/metabolism , Adult , Core Binding Factor Alpha 2 Subunit/genetics , Female , High-Throughput Nucleotide Sequencing/methods , Humans , Infant , Leukemia, Myeloid, Acute/metabolism , Leukemia, Myeloid, Acute/pathology , Male , Middle Aged , Myeloid-Lymphoid Leukemia Protein/genetics , Neoplasm Staging , Oncogene Proteins, Fusion/genetics , Prognosis , Promoter Regions, GeneticABSTRACT
The ETS transcription factor ERG has been implicated as a major regulator of both normal and aberrant hematopoiesis. In acute myeloid leukemias harboring t(16;21), ERG function is deregulated due to a fusion with FUS/TLS resulting in the expression of a FUS-ERG oncofusion protein. How this oncofusion protein deregulates the normal ERG transcription program is unclear. Here, we show that FUS-ERG acts in the context of a heptad of proteins (ERG, FLI1, GATA2, LYL1, LMO2, RUNX1 and TAL1) central to proper expression of genes involved in maintaining a stem cell hematopoietic phenotype. Moreover, in t(16;21) FUS-ERG co-occupies genomic regions bound by the nuclear receptor heterodimer RXR:RARA inhibiting target gene expression and interfering with hematopoietic differentiation. All-trans retinoic acid treatment of t(16;21) cells as well as FUS-ERG knockdown alleviate the myeloid-differentiation block. Together, the results suggest that FUS-ERG acts as a transcriptional repressor of the retinoic acid signaling pathway.
