DOT1L inhibitors block abnormal self-renewal induced by cohesin loss [RNA-seq]
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ABSTRACT: Acute myelogenous leukemia (AML) is a high-risk malignancy characterized by a diverse spectrum of somatic genetic alterations. The mechanisms by which these mutations contribute to leukemia development and how this informs the use of targeted therapies is critical to improving outcomes. Importantly, how to target loss-of-function mutations has been a critical challenge in precision medicine. Heterozygous inactivating mutations in cohesin complex genes contribute to AML by increasing the self-renewal capacity of hematopoietic stem and progenitor cells (HSPCs) by altering PRC2 targeting to induce HOXA9 expression, a key self-renewal transcription factor. Here we sought to delineate the mechanism underpinning the enhanced self-renewal conferred by cohesin haploinsufficiency. Using primary (HSPCs) as a model we demonstrate that a reduction in a core cohesin subunit is associated with decreased H3K27me3 and increased H3K79me2, along with increased self-renewal capacity and a leukemic transcriptional profile. Inhibition of DOT1L in cohesin-depleted HSPCs restored normal self-renewal, H3K27me3 and H3K79me2 levels, and gene expression, identifying DOT1L as a potential therapeutic target in cohesin haploinsufficient AML. Together our data further characterizes the mechanism by which cohesin mutations contribute to AML and identifies DOT1L as a potential therapeutic target for AML patients harboring cohesin mutations.
Project description:Acute myelogenous leukemia (AML) is a high-risk malignancy characterized by a diverse spectrum of somatic genetic alterations. The mechanisms by which these mutations contribute to leukemia development and how this informs the use of targeted therapies is critical to improving outcomes. Importantly, how to target loss-of-function mutations has been a critical challenge in precision medicine. Heterozygous inactivating mutations in cohesin complex genes contribute to AML by increasing the self-renewal capacity of hematopoietic stem and progenitor cells (HSPCs) by altering PRC2 targeting to induce HOXA9 expression, a key self-renewal transcription factor. Here we sought to delineate the mechanism underpinning the enhanced self-renewal conferred by cohesin haploinsufficiency. Using primary (HSPCs) as a model we demonstrate that a reduction in a core cohesin subunit is associated with decreased H3K27me3 and increased H3K79me2, along with increased self-renewal capacity and a leukemic transcriptional profile. Inhibition of DOT1L in cohesin-depleted HSPCs restored normal self-renewal, H3K27me3 and H3K79me2 levels, and gene expression, identifying DOT1L as a potential therapeutic target in cohesin haploinsufficient AML. Together our data further characterizes the mechanism by which cohesin mutations contribute to AML and identifies DOT1L as a potential therapeutic target for AML patients harboring cohesin mutations.
Project description:Elevated inflammation represents a hallmark of hematopoietic aging and leukemia development but mechanistically its impact on hematopoietic stem and progenitor cell (HSPC) maintenance remains incompletely understood. Here we identify Rad21/cohesin as a major component mediating inflammation-induced NF-kB signaling, which in turn limits self-renewal of HSPCs by induction of differentiation. Disruption of Rad21/cohesin diminishes inflammation-induced loss of self-renewal and induction of differentiation, but these effects are abrogated in NF-kB knockout (p50-/-) HSPCs. During aging, HSPCs exhibit an increased responsiveness to activate NF-kB signaling in response to inflammatory stimuli also resulting in activation of genes encoding for secreted cytokines. These cell intrinsic and extrinsic responses cooperatively enhance differentiation and loss of self-renewal of HSPCs resulting in increased selection of Rad21/cohesin deficient HSPCs exhibiting elevated self-renewal and myeloid skewed differentiation. Together, these results identify cohesin-mediated NF-kB signaling as a major axis connecting cell extrinsic increases in inflammation with the evolution of hallmark features HSC aging characterized by increases in self renewal and myeloid skewed differentiation aggravated by the concomitant selection of cohesin deficient HSPCs.
Project description:MTD project_description Inflammation and decreased stem cell function characterize organism aging, yet the relationship between these factors remains incompletely understood. This study shows that aged hematopoietic stem and progenitor cells exhibit increased ground-stage NF-κB activity, which enhances their responsiveness to undergo differentiation and loss of self-renewal in response to inflammation. The study identifies Rad21/cohesin as a critical mediator of NF-κB signals, by increasing chromatin accessibility of inter-/intra-genic and enhancer regions. Rad21/NF-κB are required for normal differentiation, but limit self-renewal of hematopoietic stem cells (HSCs) during aging and inflammation in an NF-κB dependent manner. HSCs from aged mice fail to downregulate Rad21/cohesin and inflammation/differentiation inducing signals in the resolution phase after acute inflammation. and The inhibition of cohesin/NF-κB is sufficient to revert the hypersensitivity of aged HSPCs to inflammation-induced differentiation. During aging, myeloid-biased HSCs with disrupted and naturally occurring reduced expression of Rad21/cohesin are increasingly selected over lymphoid-biased HSCs. Together, Rad21/cohesin mediated NF-κB signaling limits HSPC function during aging and selects for cohesin deficient HSCs with myeloid skewed differentiation.
Project description:High-resolution proteomic analysis of acute myeloid leukemia (AML) stem cells identified phospholipase C- and Ca++-signaling pathways to be differentially regulated in AML1-ETO (AE) driven leukemia. Phospholipase C gamma 1 (Plcg1) could be identified as a direct target of the AE fusion. Genetic Plcg1 inactivation abrogated disease initiation by AE, reduced intracellular Ca++-release and inhibited AE-driven self-renewal programs. In AE-induced leukemia, Plcg1 deletion significantly reduced disease penetrance, number of leukemia stem cells and abrogated leukemia development in secondary recipient hosts. In human AE-positive leukemic cells inactivation of Plcg1 reduced colony formation and AML development in vivo. In contrast, Plcg1 was dispensable for maintenance of murine and human hematopoietic stem- and progenitor cells (HSPCs). Pharmacologic inhibition of Ca++-signaling downstream of Plcg1 resulted in impaired proliferation and self-renewal capacity in AE-driven AML. Thus, the Plcg1 pathway represents a novel specific vulnerability of AE-driven leukemia and poses an important new therapeutic target.
Project description:The histone 3 lysine 79 (H3K79) methyltransferase Dot1l has been implicated in the development of leukemias bearing translocations that involve the Mixed Lineage Leukemia (MLL) gene. We identified the MLL-fusion targets in a murine MLL-AF9 leukemia model, and conducted epigenetic profiling for H3K79me2, H3K4me3, H3K27me3 and H3K36me3. Histone methylation patterns are highly abnormal on MLL-AF9 fusion target loci, defining a distinct epigenetic lesion involving H3K79. Conditional inactivation of Dot1l leads to specific down-regulation of direct MLL-AF9 targets and an MLL-translocation associated gene expression signature, while global transcription levels remain largely unaffected. This correlated with a greater sensitivity of leukemic blasts towards loss of Dot1l compared to normal hematopoietic cells. Development of in vivo leukemia was absolutely dependent on Dot1l. Chromatin immunoprecipitation followed by Solexa sequencing for H3K4me3, H3K27me3, H3K36me3, H3K79me2 and biotinylated MLL-AF9 in HSC, GMP and LSC.
Project description:ERG is an Ets-transcription factor required for normal blood stem cell development. High ERG expression in acute myeloid leukemia (AML) and acute T-cell lymphoblastic leukemia (T-ALL) is associated with a stem cell signature and poor prognosis. In murine over-expression models, human ERG is a potent oncogene that induces both T-ALL and AML. However the functional and molecular consequences of high ERG expression in normal hematopoietic stem/progenitors (HSPCs), and how this contributes to leukemia development, are unknown. Here we show that retroviral transduction of ERG into human CD34+ cells and maintenance of ERG at levels present in high ERG AML results in altered myeloid and T cell differentiation and an increase in the self-renewal capacity of transduced progenitors but not the more primitive stem cell compartment. Integrated analysis of genome-wide expression in high ERG CD34+ and ERG binding profiles in HSPCs revealed that these functional characteristics were accompanied by an expression signature that was enriched in normal HSCs, high ERG AMLs, early T-cell precursor (ETP)-ALLs and leukemic stem cell signatures associated with poor clinical outcome. The proliferative advantage of high ERG progenitors may provide a cellular context for the acquisition and propagation of mutations that contribute to the pathogenesis of leukaemia. RNA sequencing in ERG overexpressing human CD34+ cells
Project description:Somatic mutations in DNA methyltransferase 3A (DNMT3A) are frequently observed in patients with hematological malignancies. Hematopoietic stem/progenitor cells (HSPCs) with mutated DNMT3A demonstrate increased self-renewal activity and skewed lineage differentiation. However, the molecular mechanisms underlying these changes remain largely unexplored. In this study, we show that Dnmt3a loss leads to the upregulation of endogenous retroviruses (ERVs) in HSPCs, subsequently activating the cGAS-STING pathway and triggering inflammatory responses in these cells. Both genetic and pharmacological inhibition of STING effectively corrects the increased self-renewal activity and differentiation skewing induced by Dnmt3a deficiency in mice. Notably, targeting STING showed inhibited acute myeloid leukemia (AML) development in a Dnmt3a-KO; Flt3-ITD AML model, comparable to AC220, an FDA-approved FLT3-ITD inhibitor. A patient-derived xenograft (PDX) model further demonstrated that targeting STING effectively alleviates the leukemic burden of DNMT3A-mutant AML. Collectively, our findings highlight a critical role for STING in hematopoietic disorders induced by DNMT3A mutations and propose STING as a potential therapeutic target for preventing the progression of DNMT3A mutation-associated leukemia.
Project description:Mixed lineage leukemia (MLL) gene rearrangements trigger aberrant epigenetic modification and gene expression in hematopoietic stem and progenitor cells, which generates one of the most aggressive subtypes of leukemia with an apex self-renewal. It remains a challenge to directly inhibit rearranged MLL itself because of its multiple fusion partners and the poorly annotated downstream genes of MLL fusion proteins; therefore, novel therapeutic targets are urgently needed. We discovered that a long noncoding RNA (lncRNA) LAMP5-AS1 can promote higher degrees of H3K79 methylation, followed by upregulated expression of the self-renewal genes in the HOXA cluster, which are responsible for leukemia stemness in context of MLL rearrangements. Mechanistically, LAMP5-AS1 facilitated the methyltransferase activity of DOT1L by directly binding its Lys-rich region of catalytic domain, thus promoting the global patterns of H3K79 dimethylation and trimethylation in cells. These observations supported that LAMP5-AS1 upregulated H3K79me2/me3 and the transcription of DOT1L ectopic target genes. This is the first study that a lncRNA regulates the self-renewal program and differentiation block in MLL leukemia cells by facilitating the methyltransferase activity of DOT1L and global H3K79 methylation, showing its potential as a therapeutic target for MLL leukemia.