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Expression of mutant Asxl1 perturbs hematopoiesis and promotes susceptibility to leukemic transformation

ABSTRACT: Additional Sex Combs Like 1 (ASXL1) is frequently mutated in myeloid malignancies and clonal hematopoiesis of indeterminate potential (CHIP). Although loss of ASXL1 promotes hematopoietic transformation, there is growing evidence that ASXL1 mutations might confer an alteration of function. Here we identify that physiological expression of a C-terminal truncated Asxl1 mutant in vivo using conditional knock-in (KI) results in myeloid skewing, age-dependent anemia, thrombocytosis, and morphologic dysplasia. Although expression of mutant Asxl1 altered the functions of hematopoietic stem cells (HSCs), it maintained their survival in competitive transplantation assays and increased susceptibility to leukemic transformation by co-occurring RUNX1 mutation or viral insertional mutagenesis. KI mice displayed substantial reductions in H3K4me3 and H2AK119Ub without significant reductions in H3K27me3, distinct from the effects of Asxl1 loss. ChIP-seq analysis demonstrated opposing effects of wildtype and mutant Asxl1 on H3K4me3. These findings reveal that ASXL1 mutations confer HSCs with an altered epigenome and increase susceptibility for leukemic transformation, presenting a novel model for CHIP.

ORGANISM(S): Mus musculus

PROVIDER: GSE111067 | GEO | 2018/02/28

REPOSITORIES: GEO

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Mutant ASXL1 induces age-related expansion of phenotypic hematopoietic stem cells through activation of Akt/mTOR pathway

Project description:Somatic mutations of ASXL1 are frequently detected in age-related clonal hematopoiesis (CH). However, how ASXL1 mutations drive CH remains elusive. Using knockin (KI) mice expressing a C-terminally truncated form of ASXL1-mutant (ASXL1-MT), we examined the influence of ASXL1-MT on physiological aging in hematopoietic stem cells (HSCs). HSCs expressing ASXL1-MT display competitive disadvantage after transplantation. Nevertheless, in genetic mosaic mouse model, they acquire clonal advantage during aging, recapitulating CH in humans. Mechanistically, ASXL1-MT cooperates with BAP1 to deubiquitinate and activate AKT. Overactive Akt/mTOR signaling induced by ASXL1-MT results in aberrant proliferation and dysfunction of HSCs associated with age-related accumulation of DNA damage. Treatment with an mTOR inhibitor rapamycin ameliorates aberrant expansion of the HSC compartment as well as dysregulated hematopoiesis in aged ASXL1-MT KI mice. Our findings suggest that ASXL1-MT provokes dysfunction of HSCs, whereas it confers clonal advantage on HSCs over time, leading to the development of CH.

2021-02-08 | MSV000086816 | MassIVE

Expression of mutant Asxl1 perturbs hematopoiesis and promotes susceptibility to leukemic transformation

Project description:Expression of mutant Asxl1 perturbs hematopoiesis and promotes susceptibility to leukemic transformation

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Cancer-associated ASXL1 mutations may act as gain-of-function mutations of the ASXL1-BAP1 complex

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2015-03-11 | E-GEOD-65555 | biostudies-arrayexpress

Gene expression profiles of mutant ASXL1 knock-in HSPCs

Project description:To assess the effect of mutant ASXL1 (ASXL1-MT) on gene expression and RNA splicing in hematopoietic cells, we performed RNA-seq using HSPCs (bone marrow lineage-, c-Kit+ cells) derived from control or ASXL1-MT-KI mice.

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Cancer-associated ASXL1 mutations may act as gain-of-function mutations of the ASXL1-BAP1 complex

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Gene expression profiling of LT-HSCs and ST-HSCs conditionally expressing MLL-ENL

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Gene expression profiling of LT-HSCs and ST-HSCs conditionally expressing MLL-ENL

Project description:We have developed a new conditional transgenic mouse showing that MLL-ENL, at an endogenous-like expression level, induces leukemic transformation selectively in LT-HSCs. To investigate the molecular mechanism of leukemic transformation in LT-HSCs conditionally expressing MLL-ENL, we preliminarily performed comprehensive gene expression profiling of CreER-transduced LT-HSCs and ST-HSCs using cDNA microarray analysis. For initial screening of candidate genes invloved in the leukemic transformation, total RNA was extracted from colony-forming cells derived from LT-HSCs and ST-HSCs transduced with CreER or mock. Four samples were analyzed, and CreER-transduced LT/ST-HSC-derived cells were compared with mock-transduced LT/ST-HSC-derived cells, while CreER/mock-transduced LT-HSC-derived cells were compared with CreER/mock-transduced ST-HSC-derived cells.

2013-07-17 | E-GEOD-48539 | biostudies-arrayexpress

ASXL1 Mutations Promote Myeloid Transformation Through Loss of PRC2-Mediated Gene Repression

Project description:Recurrent somatic ASXL1 mutations occur in patients with myelodysplasia (MDS), myeloproliferative neoplasms (MPN), and acute myeloid leukemia (AML), and are associated with adverse outcome. Despite the genetic and clinical data implicating ASXL1 mutations in myeloid malignancies, the mechanisms of transformation by ASXL1 mutations are not understood. Here we identify that ASXL1 mutations result in loss of PRC2-mediated histone H3 lysine 27 (H3K27) tri-methylation. Through integration of microarray data with genome-wide histone modification ChIP-Seq data we identify targets of ASXL1 repression including the posterior HOXA cluster that is known to contribute to myeloid transformation. We demonstrate that ASXL1 associates with the Polycomb repressive complex 2 (PRC2), and that loss of ASXL1 in vivo collaborates with NRASG12D to promote myeloid leukemogenesis. To assess the genome-wide effects of ASXL1 loss on chromatin state we performed chromatin immunoprecipitation followed by next generation sequencing (CHIP-seq) for histone modifications known to be associated with PcG (histone H3 lysine 27 trimethylation (H3K27me3)) or TxG activity (histone H3 lysine 4 trimethylation (H3K4me3)) in UKE1 cells expressing empty vector (EV) or 2 independent validated shRNAs for ASXL1. This Series represents the ChIP-Seq data (not the microarray data referenced in the summary above). The related micorarray data are available in GEO as GSE38692.

2012-08-21 | E-GEOD-38861 | biostudies-arrayexpress

Expression data from bone marrow and fetal liver of Col18-wt and Col18-KO mice

Project description:Perturbations in the mechanisms controlling hematopoietic stem cells (HSCs) quiescence are believed to be at the roots of leukemic transformation. Through its ability to seize growth factors, provide docking to HSCs and modulate cell-to-cell signaling, the extracellular matrix (ECM) has been variously involved in HSCs quiescence and malignant transformation. In this context, different collagens (including Collagen VI and X) have been demonstrated to regulate HSCs growth and differentiation. Different reports suggest that Collagen XVIII (Col18), a member of the multiplexins collagen family, could play similar roles in maintaining HSCs and, potentially, in leukemic transformation, though any knowledge about its actual involvement in hematopoiesis is still lacking. Here we show that Col18 is needed to keep HSCs quiescent, and that its lack increases the risk of hematological neoplasms. We found that mice lacking Col18, in fact, have increased frequency of HSCs in both fetal liver and adult bone marrow, with a significant accumulation of myeloid precursors in the hematopoietic niches and of mature and immature myeloid cells in the blood. Along with hematopoietic deregulation, mice lacking Col18 showed a significant increase in the development of spontaneous lymphomas, a genetic predisposition to leukemic transformation, and lack of cell-to-ECM adhesion. We also confirmed that, in leukemic patients, Col18 is downregulated through genetic and epigenetic mechanisms and that such a downregulation decreases survival and contributes to a poorer prognosis. Our results demonstrate that Col18 is necessary to keep HSCs quiescent and to prevent excessive myeloid growth, and that alterations in its expression within the hematopoietic niche are likely to facilitate leukemic transformation and affect life expectancy of patients.

2017-01-22 | GSE63906 | GEO

Loss of Asxl1 Alters Mesenchymal Stem Cell Fate through H3K4me3 [ChIP-seq]

Project description:De novo ASXL1 mutations are found in patients with Bohring-Opitz syndrome (BOS), a disease with severe developmental defects and early childhood fatality. The underlying pathologic mechanisms remain largely unknown. Using Asxl1-targeted murine models, we found that Asxl1 global loss or conditional deletion in osteoblasts and their progenitors in mice leads to significant bone loss and markedly decreased numbers of marrow mesenchymal stem/progenitor cells (MSPCs) compared with wild-type (WT) littermates. Asxl1 null MSPCs display impaired self-renewal and skewed differentiation from osteoblasts towards adipocytes. ChIP-seq data identified that ASXL1 and H3K4me3 co-occupy the promoter regions of genes critical for MSPC self-renewal. Loss of Asxl1 diminished the genome enrichment of H3K4me3. Combined analysis of RNA-seq and ChIP-seq data revealed that Asxl1 loss in MSPCs altered the expression of ASXL1/H3K4me3 target genes controlling self-renewal/lineage commitment. Our study unveil a pivotal role of ASXL1 in H3K4me3-associated bone homeostasis

2018-12-08 | GSE75786 | GEO

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