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RUNX1 and CBFβ-SMMHC transactivate target genes together in abnormal myeloid progenitors for leukemogenesis

ABSTRACT: Inversion of chromosome 16 is a consistent finding in patients with acute myeloid leukemia subtype M4 with eosinophilia (AML M4Eo), which generates a CBFB-MYH11 fusion gene. It is generally considered that CBFβ-SMMHC, the fusion protein encoded by CBFB-MYH11, is a dominant negative repressor of RUNX1. However, recent findings challenge the RUNX1-repression model for CBFβ-SMMHC mediated leukemogenesis. To definitively address the role of Runx1 in CBFB-MYH11 induced leukemia, we crossed conditional Runx1 knockout mice (Runx1f/f) with conditional Cbfb-MYH11 knockin mice (Cbfb+/56M). Upon Mx1-Cre activation in hematopoietic cells induced by poly (I:C) injection, all Mx1-CreCbfb+/56M mice developed leukemia in 5 months while no leukemia developed in Runx1f/fMx1-CreCbfb+/56M mice, and this effect was cell autonomous. Importantly, the abnormal myeloid progenitors (AMPs), a leukemia initiating cell population induced by Cbfb-MYH11 in the bone marrow, decreased and disappeared in Runx1f/fMx1-CreCbfb+/56M mice. RNA-seq analysis of AMP cells showed that genes associated with proliferation, differentiation blockage and leukemia initiation, were differentially expressed between Mx1-CreCbfb+/56M and Runx1f/fMx1-CreCbfb+/56M mice. In addition, with chromatin immunocleavage sequencing (ChIC-seq) assay, we observed a significant enrichment of RUNX1/CBFβ-SMMHC target genes in Runx1f/fMx1-CreCbfb+/56M cells, especially among down-regulated genes, suggesting that RUNX1 and CBFβ-SMMHC mainly function together as activators of gene expression through direct target gene binding. These data indicate that Runx1 is indispensable for Cbfb-MYH11 induced leukemogenesis by working together with CBFβ-SMMHC to regulate critical genes associated with the generation of a functional AMP population.

ORGANISM(S): Mus musculus

PROVIDER: GSE152573 | GEO | 2020/10/06

REPOSITORIES: GEO

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Project description:Different mechanisms for CBF-MYH11 function in acute myeloid Leukemia (AML) with inv(16) have been proposed such as tethering of RUNX1 outside the nucleus, interference with transcription factor complex assembly and recruitment of histone deacetylases, all resulting in transcriptional repression of RUNX1 target genes. Here, through genome-wide CBF-MYH11 binding site analysis and quantitative interaction proteomics we found that CBF-MYH11 localizes to RUNX1 occupied promoters where it interacts with TAL1, FLI1 and TBP associated factors (TAFs) in the context of the hematopoietic transcription factors ERG, GATA2 and PU.1/SPI1 and the co regulators EP300 and HDAC1. Transcriptional analysis revealed that upon fusion protein knock down a subset of the CBF-MYH11 target genes show increased expression, confirming a role in transcriptional repression. However, the majority of CBF-MYH11 target genes, including genes implicated in hematopoietic stem cell (HSC) self-renewal such as ID1, LMO1 and JAG1, are actively transcribed and upon fusion protein knock down repressed. Together these results suggest an essential role for CBF-MYH11 in regulating expression of genes involved in maintaining a stem cell phenotype. 17 ChIP-seq samples using antibodies recognizing the indicated proteins and one RNA-seq file from ME-1 cells were analyzed. In addition 2 ChIP-seq profiles were generated using patient AML cells. A CBFβ-MYH11 inducible U937 system (U937CM) was used to examine binding patterns before (1 profile) and after (2 profiles) induction of CBFb-MYH11. In addition, expression was measured through RNA-seq analysis of the two states. The U937CM cells were maintained in the presence of tetracyclin (Tet, 1 uM) and grown in the absence of tetracycline for 3 days to induce expression of CBFβ-MYH11. Finally, a CBFb-MYH11 knock down system was developed in ME-1 cells. Two ME-1 cell lines were created, one with a stably integrated shRNA construct that targets CBFb-MYH11 (ME-1_knockdown) and one with a scrambled shRNA construct (ME-1_SCR). Expression of the shRNA constructs was induced using doxycyclin (dox; 1 mM) treatment for 3 days.

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RUNX1 and CBFβ-SMMHC transactivate target genes together in abnormal myeloid progenitors for leukemogenesis

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