Project description:In an effort to identify novel drugs targeting fusion-oncogene induced acute myeloid leukemia (AML), we performed high-resolution proteomic analysis. In AML1-ETO (AE) driven AML we uncovered a deregulation of phospholipase C (PLC) signaling. We identified PLCgamma 1 (PLCG1) as a specific target of the AE fusion protein which is induced after AE binding to intergenic regulatory DNA elements. Genetic inactivation of PLCG1 in murine and human AML inhibited AML1-ETO dependent self-renewal programs, leukemic proliferation, and leukemia maintenance in vivo. In contrast, PLCG1 was dispensable for normal hematopoietic stem- and progenitor cell function. These findings are extended to and confirmed by pharmacologic perturbation of Ca++-signaling in AML1-ETO AML cells, indicating that the PLCG1 pathway poses an important therapeutic target for AML1-ETO positive leukemic stem cells.
Project description:The AML1/ETO fusion protein, which is present in 10% to 15% of cases of acute myeloid leukemia, is known to repress myeloid differentiation genes through DNA binding and recruitment of chromatin-modifying proteins and transcription factors in target genes. ChIP-chip analysis of human hematopoietic stem/progenitor cells transduced with the AML1/ETO fusion gene enabled us to identify 1168 AML1/ETO target genes, 103 of which were co-occupied by HDAC1 and had lost the hyperacetylation at histone H4 marks and 264 of which showed a K9 trimethylation at histone H3. Enrichment of genes involved in hematopoietic differentiation and in specific signaling pathways was observed in the presence of these epigenetic modifications associated with an inactive chromatin status. Furthermore, AML1/ETO target genes had a significant correlation between the chromatin marks studied and transcriptional silencing.
Project description:Acute myeloid leukemia (AML) with the t(8;21)(q22;q22) chromosomal translocation is among the most common subtypes of AML and produces the AML1-ETO (AE) oncogenic fusion gene. AML1-ETO expression is critical to for t(8;21) AML leukemogenesis and maintenance. Post-transcriptional regulation of gene expression is often mediated through transcript 3'-untranslated regions (UTR). AML1-ETO uses the 3’UTR of the ETO gene, which is not normally expressed in hematopoietic cells. Therefore, the mechanisms regulating AML1-ETO via the 3’UTR are attractive therapeutic targets. In this study, we examine the regulation of AML1-ETO via the 3’UTR. We demonstrate that AML1-ETO primarily uses a 3.7kb isoform of the ETO 3’UTR in both t(8;21) patients and cell lines. Using a luciferase assay approach, we identify an AML1-ETO 3’UTR fragment between 2.8 and 3.4kb which is negatively regulated, increases expression upon inhibition of microRNA biogenesis, and contains a putative let-7 microRNA target site. We show that let-7b directly represses AML1-ETO through this site. An analysis of The Cancer Genome Atlas AML dataset shows that let-7b and let-7 family miRNA expression is significantly lower in t(8;21) AML than other AMLs. Finally, we demonstrate that let-7b-5p inhibits the proliferation of t(8;21) AML cell lines, rescues expression of AML1-ETO target genes, and promotes differentiation. Our findings establish AML1-ETO as a let-7b target gene and suggest that let-7 based therapeutics may be applied to t(8;21) AML.
Project description:The ETO-family transcriptional corepressors, including ETO, ETO2 and MTGR1, are all involved in leukemia-causing chromosomal translocations. In every case, an ETO-family corepressor acquires a DNA-binding domain (DBD) to form a typical transcription factor – the DBD binds to target genes, while the ETO moiety contributes essentially to its transcriptional property. A direct comparative study of these “homologous” fusion transcription factors may clarify their similarities and differences in regulating transcription and leukemogenesis. Here, we performed a side-by-side comparison between AML1-ETO and ETO2-GLIS2, the most common fusion proteins in the M2 and M7 subtypes of acute myeloid leukemia, respectively, by inducible expression of them in U937 leukemia cells. We found that, although AML1-ETO and ETO2-GLIS2 can use their own DBDs (i.e., the Runt domain of AML1 and the zinc finger domain of GLIS2) to bind DNA, they actually share a large proportion of genome-wide binding regions dependent on other cooperative transcription factors such as ETS- and CEBP-family proteins. Functionally, AML1-ETO acts as either transcriptional repressor or activator, whereas ETO2-GLIS2 mainly acts as an activator. The repressor-versus-activator functions of AML1-ETO is determined by the abundance of cooperative transcription factors/cofactors on the target genes. Through these mechanisms, AML1-ETO and ETO2-GLIS2 differentially regulate several key transcription factors that are essential for myeloid differentiation. Indeed, AML1-ETO inhibits myeloid differentiation of U937 cells, whereas ETO2-GLIS2 facilitates it. Taken together, this study is the first direct comparative study between AML1-ETO and ETO2-GLIS2 in the same cellular context, and the results provide new insights into the context-dependent transcriptional regulatory mechanisms that may underlie how these seemingly “homologous” fusion transcription factors exert distinct functions to drive different subtypes of leukemia.
Project description:The AML1/ETO fusion protein, which is present in 10% to 15% of cases of acute myeloid leukemia, is known to repress myeloid differentiation genes through DNA binding and recruitment of chromatin-modifying proteins and transcription factors in target genes. ChIP-chip analysis of human hematopoietic stem/progenitor cells transduced with the AML1/ETO fusion gene enabled us to identify 1168 AML1/ETO target genes, 103 of which were co-occupied by HDAC1 and had lost the hyperacetylation at histone H4 marks and 264 of which showed a K9 trimethylation at histone H3. Enrichment of genes involved in hematopoietic differentiation and in specific signaling pathways was observed in the presence of these epigenetic modifications associated with an inactive chromatin status. Furthermore, AML1/ETO target genes had a significant correlation between the chromatin marks studied and transcriptional silencing. ChIP-chip comparison of human hematopoietic stem/progenitor cells (HSPCs) retrovirally transduced with the AML1/ETO fusion protein with HSPCs transduced with an empty vector (Mulloy et al., Blood, 2002) using antibodies tagging the AML1/ETO fusion protein, the HDAC1 protein, as well as H4Ac and H3K9m3 chromatin modifications.
Project description:The AML1/ETO fusion protein is essential to the development of acute myeloid leukemia (AML), and is well recognized for its dominant-negative effect on the co-existing wild-type protein AML1. However, the involvement of wild-type AML1 in AML1/ETO-driven leukemogenesis remains elusive. Through chromatin immunoprecipitation sequencing, computational analysis plus a series of experimental validations, we report here that AML1 is able to orchestrate the expression of AML1/ETO targets regardless of being activated or repressed, via forming a complex with AML1/ETO and via recruiting the cofactor. 4 ChIP-seq assays were used to identify the high confidence binding regions of AML1-ETO and AML1 in t(8;21) AML Kasumi-1 cell lines. The anti-AML1 (N20) antibody targets the N-terminus of AML1 and recognizes both AML1 and AML1/ETO; the anti-AML1 (C19) antibody targets the C-terminus of AML1 and recognizes AML1 but not AML1/ETO; the anti-ETO (C20) antibody targets the C-terminus of ETO and specifically recognizes AML1/ETO. 2 ChIP-seq assays were used to identify the binding regions of AML1 in human macrophage U937 cell lines. And the total input was used as control.
Project description:AML1-ETO, a fusion protein generated by the t(8;21) translocation in acute myeloid leukemia, is a transcription factor implicated in both gene repression and activation. We now show that, in leukemic cells, AML1-ETO resides in and functions through a stable protein complex (AETFC) that contains several hematopoietic transcription factors and cofactors. In conjunction with biochemical and leukemia pathological studies, the ChIP-seq and RNA-seq analyses of the AETFC components in leukemic cells reveal that these components stabilize the complex through multivalent interactions, provide multiple DNA-binding domains for diverse target genes, colocalize genome-wide, cooperatively regulate gene expression, and contribute to leukemogenesis. RNA-seq analyses gene expression upon knockdown of each AETFC component, including AML1-ETO, HEB, E2A, LYL1, LDB1 and LMO2, and double-knockdown of HEB and E2A, in Kasumi-1 cells. ChIP-seq analyses of four AETFC components, namely AML1-ETO, HEB, E2A and LMO2, in Kasumi-1 cells.
Project description:Approximately 20% of Acute Myelogenous Leukemia (AML) cases carry the t(8;21) translocation, which involves the AML1 and ETO genes, and express the resulting AML1/ETO fusion protein that functions as a transcriptional repressor by recruiting NCoR/SMRT/HDAC complexes to DNA. We used microarrays to identify human promoters bound by AML1/ETO in U937 cells. Keywords: ChIP-chip