Supraphysiologic levels of the AML1-ETO isoform AE9a are essential for transformation

Neratinib impairs function of m6A recognition on AML1-ETO pre-mRNA and induces differentiation of t (8;21) AML cells by targeting HNRNPA3

Acute myeloid leukemia (AML) is frequently linked to genetic abnormalities, with the t (8; 21) translocation, resulting in the production of a fusion oncoprotein AML1-ETO (AE), being a prevalent occurrence. This protein plays a pivotal role in t (8; 21) AML's onset, advancement, and recurrence, making it a therapeutic target. However, the development of drug molecules targeting AML1-ETO are markedly insufficient, especially used in clinical treatment. In this study, it was uncovered that Neratinib could significantly downregulate AML1-ETO protein level, subsequently promoting differentiation of t (8; 21) AML cells. Based on "differentiated active" probes, Neratinib was identified as a functional inhibitor against HNRNPA3 through covalent binding. The further studies demonstrated that HNRNPA3 function as a putative m6A reader responsible for recognizing and regulating the alternative splicing of AML-ETO pre-mRNA. These findings not only contribute to a novel insight to the mechanism governing post-transcriptional modification of AML1-ETO transcript, but also suggest that Neratinib would be promising therapeutic potential for t (8; 21) AML treatment.

Single-cell RNA sequencing of a new transgenic t(8;21) preleukemia mouse model reveals regulatory networks promoting leukemic transformation

T(8;21)(q22;q22), which generates the AML1-ETO fusion oncoprotein, is a common chromosomal abnormality in acute myeloid leukemia (AML) patients. Despite having favorable prognosis, 40% of patients will relapse, highlighting the need for innovative models and application of the newest technologies to study t(8;21) leukemogenesis. Currently, available AML1-ETO mouse models have limited utility for studying the pre-leukemic stage because AML1-ETO produces mild hematopoietic phenotypes and no leukemic transformation. Conversely, overexpression of a truncated variant, AML1-ETO9a (AE9a), promotes fully penetrant leukemia and is too potent for studying pre-leukemic changes. To overcome these limitations, we devised a germline-transmitted Rosa26 locus AE9a knock-in mouse model that moderately overexpressed AE9a and developed leukemia with long latency and low penetrance. We observed pre-leukemic alterations in AE9a mice, including skewing of progenitors towards granulocyte/monocyte lineages and replating of stem and progenitor cells. Next, we performed single-cell RNA sequencing to identify specific cell populations that contribute to these pre-leukemic phenotypes. We discovered a subset of common myeloid progenitors that have heightened granulocyte/monocyte bias in AE9a mice. We also observed dysregulation of key hematopoietic transcription factor target gene networks, blocking cellular differentiation. Finally, we identified Sox4 activation as a potential contributor to stem cell self-renewal during the pre-leukemic stage.

Deciphering Acute Myeloid Leukemia Associated Transcription Factors in Human Primary CD34+ Hematopoietic Stem/Progenitor Cells

Hemato-oncological diseases account for nearly 10% of all malignancies and can be classified into leukemia, lymphoma, myeloproliferative diseases, and myelodysplastic syndromes. The causes and prognosis of these disease entities are highly variable. Most entities are not permanently controllable and ultimately lead to the patient's death. At the molecular level, recurrent mutations including chromosomal translocations initiate the transformation from normal stem-/progenitor cells into malignant blasts finally floating the patient's bone marrow and blood system. In acute myeloid leukemia (AML), the so-called master transcription factors such as RUNX1, KMT2A, and HOX are frequently disrupted by chromosomal translocations, resulting in neomorphic oncogenic fusion genes. Triggering ex vivo expansion of primary human CD34+ stem/progenitor cells represents a distinct characteristic of such chimeric AML transcription factors. Regarding oncogenic mechanisms of AML, most studies focus on murine models. However, due to biological differences between mice and humans, findings are only partly transferable. This review focuses on the genetic manipulation of human CD34+ primary hematopoietic stem/progenitor cells derived from healthy donors to model acute myeloid leukemia cell growth. Analysis of defined single- or multi-hit human cellular AML models will elucidate molecular mechanisms of the development, maintenance, and potential molecular intervention strategies to counteract malignant human AML blast cell growth.

Melatonin promotes differentiation and apoptosis of AML1-ETO-positive cells

INTRODUCTION

Acute Myeloid Leukemia 1-Eight-Twenty-One (AML1-ETO) is an oncogenic fusion protein that causes acute myeloid leukemia. We examined the effects of melatonin on AML1-ETO by investigating cell differentiation, apoptosis, and degradation in leukemia cell lines.

METHOD

We evaluated Kasumi-1, U937T, and primary acute myeloid leukemia (AML1-ETO-positive) cell proliferation by Cell Counting Kit-8 assay. Flow cytometry and western blotting were used to evaluate CD11b/CD14 levels (differentiation biomarkers) and the AML1-ETO protein degradation pathway, respectively. CM-Dil-labeled Kasumi-1 cells were also injected into zebrafish embryos to determine the effects of melatonin on vascular proliferation and development and to evaluate the combined effects of melatonin and common chemotherapeutic agents.

RESULTS

AML1-ETO-positive acute myeloid leukemia cells were more sensitive to melatonin than AML1-ETO-negative cells. Melatonin increased apoptosis and CD11b/CD14 expression in AML1-ETO-positive cells and decreased the nuclear/cytoplasmic ratio, together suggesting that melatonin induced cell differentiation. Mechanistically, melatonin degraded AML1-ETO by activating the caspase-3 pathway and regulating the mRNA levels of AML1-ETO downstream genes. Melatonin reduced the number of neovessels in Kasumi-1-injected zebrafish, suggesting that melatonin inhibits cell proliferation in vivo. Finally, combining drugs with melatonin inhibited cell viability.

DISCUSSION

Melatonin is a potential compound for the treatment of AML1-ETO-positive acute myeloid leukemia.

DNA hypermethylation-induced miR-182 silence targets BCL2 and HOXA9 to facilitate the self-renewal of leukemia stem cell, accelerate acute myeloid leukemia progression, and determine the sensitivity of BCL2 inhibitor venetoclax

Rationale: microRNAs (miRNAs) are frequently deregulated and play important roles in the pathogenesis and progression of acute myeloid leukemia (AML). miR-182 functions as an onco-miRNA or tumor suppressor miRNA in the context of different cancers. However, whether miR-182 affects the self-renewal of leukemia stem cells (LSCs) and normal hematopoietic stem progenitor cells (HSPCs) is unknown. Methods: Bisulfite sequencing was used to analyze the methylation status at pri-miR-182 promoter. Lineage-negative HSPCs were isolated from miR-182 knockout (182KO) and wild-type (182WT) mice to construct MLL-AF9-transformed AML model. The effects of miR-182 depletion on the overall survival and function of LSC were analyzed in this mouse model in vivo. Results: miR-182-5p (miR-182) expression was lower in AML blasts than normal controls (NCs) with hypermethylation observed at putative pri-miR-182 promoter in AML blasts but unmethylation in NCs. Overexpression of miR-182 inhibited proliferation, reduced colony formation, and induced apoptosis in leukemic cells. In addition, depletion of miR-182 accelerated the development and shortened the overall survival (OS) in MLL-AF9-transformed murine AML through increasing LSC frequency and self-renewal ability. Consistently, overexpression of miR-182 attenuated AML development and extended the OS in the murine AML model. Most importantly, miR-182 was likely dispensable for normal hematopoiesis. Mechanistically, we identified BCL2 and HOXA9 as two key targets of miR-182 in this context. Most importantly, AML patients with miR-182 unmethylation had high expression of miR-182 followed by low protein expression of BCL2 and resistance to BCL2 inhibitor venetoclax (Ven) in vitro. Conclusions: Our results suggest that miR-182 is a potential therapeutic target for AML patients through attenuating the self-renewal of LSC but not HSPC. miR-182 promoter methylation could determine the sensitivity of Ven treatment and provide a potential biomarker for it.

MicroRNA let-7b downregulates AML1-ETO oncogene expression in t(8;21) AML by targeting its 3'UTR

Background

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 (RUNX1-ETO, RUNX1-RUNX1T1) oncogenic fusion gene. AML1-ETO functions as an aberrant transcription factor which plays a key role in blocking normal hematopoiesis. Thus, the expression of AML1-ETO is critical to t(8;21) AML leukemogenesis and maintenance. Post-transcriptional regulation of gene expression is often mediated through interactions between trans-factors and cis-elements within 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 expression via the 3’UTR are attractive therapeutic targets.

Methods

We used RNA-sequencing of t(8;21) patients and cell lines to examine the 3′UTR isoforms used by AML1-ETO transcripts. Using luciferase assay approaches, we test the relative contribution of 3′UTR cis elements to AML1-ETO expression. We further use let-7b microRNA mimics and anti-let-7b sponges for functional studies of t(8;21) AML cell lines.

Results

In this study, we examine the regulation of AML1-ETO via the 3’UTR. We demonstrate that AML1-ETO transcripts primarily use a 3.7 kb isoform of the ETO 3′UTR in both t(8;21) patients and cell lines. We identify a negative regulatory element within the AML1-ETO 3′UTR. We further demonstrate that the let-7b microRNA directly represses AML1-ETO through this site. Finally, we find that let-7b inhibits the proliferation of t(8;21) AML cell lines, rescues expression of AML1-ETO target genes, and promotes differentiation.

Conclusions

AML1-ETO is post-transcriptionally regulated by let-7b, which contributes to the leukemic phenotype of t(8;21) AML and may be important for t(8;21) leukemogenesis and maintenance.

Modelling t(8;21) acute myeloid leukaemia - What have we learned?

Acute myeloid leukaemia (AML) is a heterogeneous haematopoietic malignancy caused by recurrent mutations in haematopoietic stem and progenitor cells that affect both the epigenetic regulatory machinery and signalling molecules. The t(8;21) or RUNX1‐RUNX1T1 translocation generates the RUNX1‐ETO chimeric transcription factor which primes haematopoietic stem cells for further oncogenic mutational events that in their sum cause overt disease. Significant progress has been made in generating both in vitro and in vivo model systems to recapitulate t(8;21) AML which are crucial for the understanding of the biology of the disease and the development of effective treatment. This review provides a comprehensive overview of the in vivo and in vitro model systems that were developed to gain insights into the molecular mechanisms of RUNX1‐ETO oncogenic activity and their contribution to the advancement of knowledge in the t(8;21) AML field. Such models include transgenic mice, patient‐derived xenografts, RUNX1‐ETO transduced human progenitor cells, cell lines and human embryonic stem cell model systems, making the t(8;21) as one of the well‐characterized sub‐type of AML at the molecular level.

Epigenetic Modifications in Acute Myeloid Leukemia: Prognosis, Treatment, and Heterogeneity

Leukemia, specifically acute myeloid leukemia (AML), is a common malignancy that can be differentiated into multiple subtypes based on leukemogenic history and etiology. Although genetic aberrations, particularly cytogenetic abnormalities and mutations in known oncogenes, play an integral role in AML development, epigenetic processes have been shown as a significant and sometimes independent dynamic in AML pathophysiology. Here, we summarize how tumors evolve and describe AML through an epigenetic lens, including discussions on recent discoveries that include prognostics from epialleles, changes in RNA function for hematopoietic stem cells and the epitranscriptome, and novel epigenetic treatment options. We further describe the limitations of treatment in the context of the high degree of heterogeneity that characterizes acute myeloid leukemia.

The RUNX1-ETO fusion protein trans-activates c-KIT expression by recruiting histone acetyltransferase P300 on its promoter

The oncoprotein RUNX1-ETO is the fusion product of t(8;21)(q22;q22) and constitutes one of the most common genetic alterations in acute myeloid leukemia (AML). Abnormal c-KIT overexpression is considered an independent negative prognostic factor for relapse and survival in t(8;21) AML patients. However, the molecular mechanism of high c-KIT expression in t(8;21) AML remains unknown. In this study, we detected RUNX1-ETO and c-KIT gene expression in AML-M2 patients and verified the overexpression of c-KIT in t(8;21) AML patients. We also found that c-KIT overexpression was a poor prognostic indicator in RUNX1-ETO positive AML patients, but not in RUNX1-ETO negative AML patients. We used the dual-luciferase and ChIP assays to demonstrate that the RUNX1-ETO protein epigenetically trans-activates c-KIT by binding to the c-KIT promoter and recruiting the histone acetyltransferase P300 to the c-KIT promoter, elucidating the mechanism of the abnormally increased c-KIT expression in t(8;21) AML patients. Moreover, pharmacological studies revealed that C646, a P300 inhibitor, could inhibit proliferation, induce apoptosis and arrest the cell cycle more effectively in RUNX1-ETO positive cells than in negative ones. The levels of c-KIT and RUNX1-ETO proteins were also decreased with C646 treatment in RUNX1-ETO positive cells. These findings suggested that P300 could be a therapeutic target and that C646 could be used as a potential treatment for RUNX1-ETO positive AML patients. Interestingly, using the dual-luciferase assay, we also found that the binding capacity of RUNX1-ETO9a, a truncated RUNX1-ETO isoform, to the c-KIT promoter was stronger than that of RUNX1-ETO, suggesting RUNX1-ETO9a as another valuable therapeutic target in t(8;21) AML.

Compatibility of RUNX1/ETO fusion protein modules driving CD34+ human progenitor cell expansion

Chromosomal translocations represent frequent events in leukemia. In t(8;21)+ acute myeloid leukemia, RUNX1 is fused to nearly the entire ETO protein, which contains four conserved nervy homology regions, NHR1-4. Furthermore RUNX1/ETO interacts with ETO-homologous proteins via NHR2, thereby multiplying NHR domain contacts. As shown recently, RUNX1/ETO retains oncogenic activity upon either deletion of the NHR3 + 4 N-CoR/SMRT interaction domain or substitution of the NHR2 tetramer domain. Thus, we aimed to clarify the specificities of the NHR domains. A C-terminally NHR3 + 4 truncated RUNX1/ETO containing a heterologous, structurally highly related non-NHR2 tetramer interface translocated into the nucleus and bound to RUNX1 consensus motifs. However, it failed to interact with ETO-homologues, repress RUNX1 targets, and transform progenitors. Surprisingly, transforming capacity was fully restored by C-terminal fusion with ETO's NHR4 zinc-finger or the repressor domain 3 of N-CoR, while other repression domains failed. With an inducible protein assembly system, we further demonstrated that NHR4 domain activity is critically required early in the establishment of progenitor cultures expressing the NHR2 exchanged truncated RUNX1/ETO. Together, we can show that NHR2 and NHR4 domains can be replaced by heterologous protein domains conferring tetramerization and repressor functions, thus showing that the NHR2 and NHR4 domain structures do not have irreplaceable functions concerning RUNX1/ETO activity for the establishment of human CD34+ cell expansion. We could resemble the function of RUNX1/ETO through modular recomposition with protein domains from RUNX1, ETO, BCR and N-CoR without any NHR2 and NHR4 sequences. As most transcriptional repressor proteins do not comprise tetramerization domains, our results provide a possible explanation as to the reason that RUNX1 is recurrently found translocated to ETO family members, which all contain tetramer together with transcriptional repressor moieties.

A FOXO1-induced oncogenic network defines the AML1-ETO preleukemic program

Understanding and blocking the self-renewal pathway of preleukemia stem cells could prevent acute myeloid leukemia (AML) relapse. In this study, we show that increased FOXO1 represents a critical mechanism driving aberrant self-renewal in preleukemic cells expressing the t(8;21)-associated oncogene AML1-ETO (AE). Although generally considered as a tumor suppressor, FOXO1 is consistently upregulated in t(8;21) AML. Expression of FOXO1 in human CD34⁺ cells promotes a preleukemic state with enhanced self-renewal and dysregulated differentiation. The DNA binding domain of FOXO1 is essential for these functions. FOXO1 activates a stem cell molecular signature that is also present in AE preleukemia cells and preserved in t(8;21) patient samples. Genome-wide binding studies show that AE and FOXO1 share the majority of their binding sites, whereby FOXO1 binds to multiple crucial self-renewal genes and is required for their activation. In agreement with this observation, genetic and pharmacological ablation of FOXO1 inhibited the long-term proliferation and clonogenicity of AE cells and t(8;21) AML cell lines. Targeting of FOXO1 therefore provides a potential therapeutic strategy for elimination of stem cells at both preleukemic and leukemic stages.

The full transforming capacity of MLL-Af4 is interlinked with lymphoid lineage commitment

Chromosome rearrangements involving the mixed-lineage leukemia gene (MLL) create MLL-fusion proteins, which could drive both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The lineage decision of MLL-fusion leukemia is influenced by the fusion partner and microenvironment. To investigate the interplay of fusion proteins and microenvironment in lineage choice, we transplanted human hematopoietic stem and progenitor cells (HSPCs) expressing MLL-AF9 or MLL-Af4 into immunodeficient NSGS mice, which strongly promote myeloid development. Cells expressing MLL-AF9 efficiently developed AML in NSGS mice. In contrast, MLL-Af4 cells, which were fully oncogenic under lymphoid conditions present in NSG mice, displayed compromised transformation capacity in a myeloid microenvironment. MLL-Af4 activated a self-renewal program in a lineage-dependent manner, showing the leukemogenic activity of MLL-Af4 was interlinked with lymphoid lineage commitment. The C-terminal homology domain (CHD) of Af4 was sufficient to confer this linkage. Although the MLL-CHD fusion protein failed to immortalize HSPCs in myeloid conditions in vitro, it could successfully induce ALL in NSG mice. Our data suggest that defective self-renewal ability and leukemogenesis of MLL-Af4 myeloid cells could contribute to the strong B-cell ALL association of MLL-AF4 leukemia observed in the clinic.