Propagation of trimethylated H3K27 regulated by polycomb protein EED is required for embryogenesis, hematopoietic maintenance, and tumor suppression

YY1 Knockdown Relieves the Differentiation Block and Restores Apoptosis in AML Cells

In this study we analyzed the expression of Yin and Yang 1 protein (YY1), a member of the noncanonical PcG complexes, in AML patient samples and AML cell lines and the effect of YY1 downregulation on the AML differentiation block. Our results show that YY1 is significantly overexpressed in AML patient samples and AML cell lines and that YY1 knockdown relieves the differentiation block. YY1 downregulation in two AML cell lines (HL-60 and OCI-AML3) and one AML patient sample restored the expression of members of the CEBP protein family, increased the expression of extrinsic growth factors/receptors and surface antigenic markers, induced morphological cell characteristics typical of myeloid differentiation, and sensitized cells to retinoic acid treatment and to apoptosis. Overall, our data show that YY1 is not a secondary regulator of myeloid differentiation but that, if overexpressed, it can play a predominant role in myeloid differentiation block.

Caf1 regulates the histone methyltransferase activity of Ash1 by sensing unmodified histone H3

Histone modifications are one of the many key mechanisms that regulate gene expression. Ash1 is a histone H3K36 methyltransferase and is involved in gene activation. Ash1 forms a large complex with Mrg15 and Caf1/p55/Nurf55/RbAp48 (AMC complex). The Ash1 subunit alone exhibits very low activity due to the autoinhibition, and the binding of Mrg15 releases the autoinhibition. Caf1 is a scaffolding protein commonly found in several chromatin modifying complexes and has two histone binding pockets: one for H3 and the other for H4. Caf1 has the ability to sense unmodified histone H3K4 residues using the H3 binding pocket. However, the role of Caf1 in the AMC complex has not been investigated. Here, we dissected the interaction among the AMC complex subunits, revealing that Caf1 uses the histone H4 binding pocket to interact with Ash1 near the histone binding module cluster. Furthermore, we showed that H3K4 methylation inhibits AMC HMTase activity via Caf1 sensing unmodified histone H3K4 to regulate the activity in an internucleosomal manner, suggesting that crosstalk between H3K4 and H3K36 methylation. Our work revealed a delicate mechanism by which the AMC histone H3K36 methyltransferase complex is regulated.

Epigenetic regulation of embryonic ectoderm development in stem cell differentiation and transformation during ontogenesis

Dynamic chromatin accessibility regulates stem cell fate determination and tissue homeostasis via controlling gene expression. As a histone-modifying enzyme that predominantly mediates methylation of lysine 27 in histone H3 (H3K27me1/2/3), Polycomb repressive complex 2 (PRC2) plays the canonical role in targeting developmental regulators during stem cell differentiation and transformation. Embryonic ectoderm development (EED), the core scaffold subunit of PRC2 and as an H3K27me3-recognizing protein, has been broadly implicated with PRC2 stabilization and allosterically stimulated PRC2. Accumulating evidences from experimental data indicate that EED-associating epigenetic modifications are indispensable for stem cell maintenance and differentiation into specific cell lineages. In this review, we discuss the most updated advances to summarize the structural architecture of EED and its contributions and underlying mechanisms to mediating lineage differentiation of different stem cells during epigenetic modification to expand our understanding of PRC2.

Critical Roles of Polycomb Repressive Complexes in Transcription and Cancer

Polycomp group (PcG) proteins are members of highly conserved multiprotein complexes, recognized as gene transcriptional repressors during development and shown to play a role in various physiological and pathological processes. PcG proteins consist of two Polycomb repressive complexes (PRCs) with different enzymatic activities: Polycomb repressive complexes 1 (PRC1), a ubiquitin ligase, and Polycomb repressive complexes 2 (PRC2), a histone methyltransferase. Traditionally, PRCs have been described to be associated with transcriptional repression of homeotic genes, as well as gene transcription activating effects. Particularly in cancer, PRCs have been found to misregulate gene expression, not only depending on the function of the whole PRCs, but also through their separate subunits. In this review, we focused especially on the recent findings in the transcriptional regulation of PRCs, the oncogenic and tumor-suppressive roles of PcG proteins, and the research progress of inhibitors targeting PRCs.

Loss of microglial EED impairs synapse density, learning, and memory

The embryonic ectoderm development (EED) is a core component of the polycomb-repressive complex 2 (PRC2) whose mutations are linked to neurodevelopmental abnormalities, intellectual disability, and neurodegeneration. Although EED has been extensively studied in neural stem cells and oligodendrocytes, its role in microglia is incompletely understood. Here, we show that microglial EED is essential for synaptic pruning during the postnatal stage of brain development. The absence of microglial EED at early postnatal stages resulted in reduced spines and impaired synapse density in the hippocampus at adulthood, accompanied by upregulated expression of phagocytosis-related genes in microglia. As a result, deletion of microglial Eed impaired hippocampus-dependent learning and memory in mice. These results suggest that microglial EED is critical for normal synaptic and cognitive functions during postnatal development.

Mechanisms of Polycomb group protein function in cancer

Cancer arises from a multitude of disorders resulting in loss of differentiation and a stem cell-like phenotype characterized by uncontrolled growth. Polycomb Group (PcG) proteins are members of multiprotein complexes that are highly conserved throughout evolution. Historically, they have been described as essential for maintaining epigenetic cellular memory by locking homeotic genes in a transcriptionally repressed state. What was initially thought to be a function restricted to a few target genes, subsequently turned out to be of much broader relevance, since the main role of PcG complexes is to ensure a dynamically choregraphed spatio-temporal regulation of their numerous target genes during development. Their ability to modify chromatin landscapes and refine the expression of master genes controlling major switches in cellular decisions under physiological conditions is often misregulated in tumors. Surprisingly, their functional implication in the initiation and progression of cancer may be either dependent on Polycomb complexes, or specific for a subunit that acts independently of other PcG members. In this review, we describe how misregulated Polycomb proteins play a pleiotropic role in cancer by altering a broad spectrum of biological processes such as the proliferation-differentiation balance, metabolism and the immune response, all of which are crucial in tumor progression. We also illustrate how interfering with PcG functions can provide a powerful strategy to counter tumor progression.

Expression and Function of Nicotinic Acetylcholine Receptors in Induced Regulatory T Cells

A contribution of the cholinergic system to immune cell function has been suggested, though the role of nicotine and its receptors in T cells, especially regulatory T (Treg) cells, is unclear. We herein investigated the expression and function of nicotinic acetylcholine receptors (nAChRs) in murine-induced Treg (iTreg) cells. Upon differentiation of naive BALB/c T cells into iTreg cells and other T-cell subsets, the effect of nicotine on cytokine production and proliferation of iTreg cells was examined. The expression of nAChRs and its regulatory mechanisms were comparatively analyzed among T-cell subsets. Stimulation-induced transforming growth factor-β1 (TGF-β1) production of iTreg cells was suppressed by nicotine, whereas interleukin (IL)-10 production and proliferation was not affected. α2-, α5-, α9-, and β2-nAChRs were differentially expressed in naive, Th1, Th2, Th9, Th17, and iTreg cells. Among these cell types, the α9-nAChR was particularly upregulated in iTreg cells via its gene promoter, but not through tri-methylation at the 4th lysine residue of the histone H3-dependent mechanisms. We conclude that the immunoregulatory role of Treg cells is modified by the cholinergic system, probably through the characteristic expression of nAChRs.

KDM4B promotes acute myeloid leukemia associated with AML1-ETO by regulating chromatin accessibility

Epigenetic alterations of chromatin structure affect chromatin accessibility and collaborate with genetic alterations in the development of cancer. Lysine demethylase 4B (KDM4B) has been identified as a JmjC domain-containing epigenetic modifier that possesses histone demethylase activity. Although recent studies have demonstrated that KDM4B positively regulates the pathogenesis of multiple types of solid tumors, the tissue specificity and context dependency have not been fully elucidated. In this study, we investigated gene expression profiles established from clinical samples and found that KDM4B is elevated specifically in acute myeloid leukemia (AML) associated with chromosomal translocation 8;21 [t(8;21)], which results in a fusion of the AML1 and the eight-twenty-one (ETO) genes to generate a leukemia oncogene, AML1-ETO fusion transcription factor. Short hairpin RNA-mediated KDM4B silencing significantly reduced cell proliferation in t(8;21)-positive AML cell lines. Meanwhile, KDM4B silencing suppressed the expression of AML1-ETO-inducible genes, and consistently perturbed chromatin accessibility of AML1-ETO-binding sites involving altered active enhancer marks and functional cis-regulatory elements. Notably, transduction of murine KDM4B orthologue mutants followed by KDM4B silencing demonstrated a requirement of methylated-histone binding modules for a proliferative surge. To address the role of KDM4B in leukemia development, we further generated and analyzed Kdm4b conditional knockout mice. As a result, Kdm4b deficiency attenuated clonogenic potential mediated by AML1-ETO and delayed leukemia progression in vivo. Thus, our results highlight a tumor-promoting role of KDM4B in AML associated with t(8;21).

The language of chromatin modification in human cancers

The genetic information of human cells is stored in the context of chromatin, which is subjected to DNA methylation and various histone modifications. Such a 'language' of chromatin modification constitutes a fundamental means of gene and (epi)genome regulation, underlying a myriad of cellular and developmental processes. In recent years, mounting evidence has demonstrated that miswriting, misreading or mis-erasing of the modification language embedded in chromatin represents a common, sometimes early and pivotal, event across a wide range of human cancers, contributing to oncogenesis through the induction of epigenetic, transcriptomic and phenotypic alterations. It is increasingly clear that cancer-related metabolic perturbations and oncohistone mutations also directly impact chromatin modification, thereby promoting cancerous transformation. Phase separation-based deregulation of chromatin modulators and chromatin structure is also emerging to be an important underpinning of tumorigenesis. Understanding the various molecular pathways that underscore a misregulated chromatin language in cancer, together with discovery and development of more effective drugs to target these chromatin-related vulnerabilities, will enhance treatment of human malignancies.

Polycomb Gene Silencing Mechanisms: PRC2 Chromatin Targeting, H3K27me3 'Readout', and Phase Separation-Based Compaction

Modulation of chromatin structure and/or modification by Polycomb repressive complexes (PRCs) provides an important means to partition the genome into functionally distinct subdomains and to regulate the activity of the underlying genes. Both the enzymatic activity of PRC2 and its chromatin recruitment, spreading, and eviction are exquisitely regulated via interactions with cofactors and DNA elements (such as unmethylated CpG islands), histones, RNA (nascent mRNA and long noncoding RNA), and R-loops. PRC2-catalyzed histone H3 lysine 27 trimethylation (H3K27me3) is recognized by distinct classes of effectors such as canonical PRC1 and BAH module-containing proteins (notably BAHCC1 in human). These effectors mediate gene silencing by different mechanisms including phase separation-related chromatin compaction and histone deacetylation. We discuss recent advances in understanding the structural architecture of PRC2, the regulation of its activity and chromatin recruitment, and the molecular mechanisms underlying Polycomb-mediated gene silencing. Because PRC deregulation is intimately associated with the development of diseases, a better appreciation of Polycomb-based (epi)genomic regulation will have far-reaching implications in biology and medicine.

Small Molecule Approaches for Targeting the Polycomb Repressive Complex 2 (PRC2) in Cancer

The polycomb repressive complex 2 (PRC2) is composed of three core subunits, enhancer of zeste 2 (EZH2), embryonic ectoderm development (EED), and suppressor of zeste 12 (SUZ12), along with a number of accessory proteins. It is the key enzymatic protein complex that catalyzes histone H3 lysine 27 (H3K27) methylation to mediate epigenetic silencing of target genes. PRC2 thus plays essential roles in maintaining embryonic stem cell identity and in controlling cellular differentiation. Studies in the past decade have reported frequent overexpression or mutation of PRC2 in various cancers including prostate cancer and lymphoma. Aberrant PRC2 function has been extensively studied and proven to contribute to a large number of abnormal cellular processes, including those that lead to uncontrolled proliferation and tumorigenesis. Significant efforts have recently been made to develop small molecules targeting PRC2 function for potential use as anticancer therapeutics. In this review, we describe recent approaches to identify and develop small molecules that target PRC2. These various strategies include the inhibition of the function of individual PRC2 core proteins, the disruption of PRC2 complex formation, and the degradation of its subunits.

Redox and global interconnected proteome changes in mice exposed to complex environmental hazards surrounding Doñana National Park

Natural environments are receiving an increasing number of contaminants. Therefore, the evaluation and identification of early responses to pollution in these complex habitats is an urgent and challenging task. Doñana National Park (DNP, SW Spain) has been widely used as a model area for environmental studies because, despite its strictly protected core, it is surrounded by numerous threat sources from agricultural, mining and industrial activities. Since many pollutants often induce oxidative stress, redox proteomics was used to detect redox-based variations within the proteome of Mus spretus mice captured in DNP and the surrounding areas. Functional analysis showed that most differentially oxidized proteins are involved in the maintenance of homeostasis, by eliciting mechanisms to respond to toxic substances and oxidative stress, such as antioxidant and biotransformation processes, immune and inflammatory responses, and blood coagulation. Furthermore, changes in the overall protein abundance were also analysed by label-free quantitative proteomics. The upregulation of phase I and II biotransformation enzymes in mice from Lucio del Palacio may be an alert for organic pollution in the area located at the heart of DNP. Metabolic processes involved in protein turnover (proteolysis, amino acid catabolism, new protein biosynthesis and folding) were activated in response to oxidative damage to these biomolecules. Consequently, aerobic respiratory metabolism increased to address the greater ATP demands. Alterations of cholesterol metabolism that could cause hepatic steatosis were also detected. The proteomic detection of globally altered metabolic and physiological processes offers a complete view of the main biological changes caused by environmental pollution in complex habitats.

An Allosteric PRC2 Inhibitor Targeting EED Suppresses Tumor Progression by Modulating the Immune Response

Aberrant activity of polycomb repressive complex 2 (PRC2) is involved in a wide range of human cancer progression. The WD40 repeat-containing protein EED is a core component of PRC2 and enhances PRC2 activity through interaction with H3K27me3. In this study, we report the discovery of a class of pyrimidone compounds, represented by BR-001, as potent allosteric inhibitors of PRC2. X-ray co-crystallography showed that BR-001 directly binds EED in the H3K27me3-binding pocket. BR-001 displayed antitumor potency in vitro and in vivo. In Karpas422 and Pfeiffer xenograft mouse models, twice daily oral dosing with BR-001 resulted in robust antitumor activity. BR-001 was also efficacious in syngeneic CT26 colon tumor-bearing mice; oral dosing of 30 mg/kg of BR-001 led to 59.3% tumor growth suppression and increased frequency of effector CD8⁺ T-cell infiltrates in tumors. Pharmacodynamic analysis revealed that CXCL10 was highly upregulated, suggesting that CXCL10 triggers the trafficking of CD8⁺ T cells toward tumor sites. Our results demonstrate for the first time that inhibition of EED modulates the tumor immune microenvironment to induce regression of colon tumors and therefore has the potential to be used in combination with immune-oncology therapy. SIGNIFICANCE: BR-001, a potent inhibitor of the EED subunit of the PRC2 complex, suppresses tumor progression by modulating the tumor microenvironment.

PRC2 is high maintenance

As the process that silences gene expression ensues during development, the stage is set for the activity of Polycomb-repressive complex 2 (PRC2) to maintain these repressed gene profiles. PRC2 catalyzes a specific histone posttranslational modification (hPTM) that fosters chromatin compaction. PRC2 also facilitates the inheritance of this hPTM through its self-contained "write and read" activities, key to preserving cellular identity during cell division. As these changes in gene expression occur without changes in DNA sequence and are inherited, the process is epigenetic in scope. Mutants of mammalian PRC2 or of its histone substrate contribute to the cancer process and other diseases, and research into these aberrant pathways is yielding viable candidates for therapeutic targeting. The effectiveness of PRC2 hinges on its being recruited to the proper chromatin sites; however, resolving the determinants to this process in the mammalian case was not straightforward and thus piqued the interest of many in the field. Here, we chronicle the latest advances toward exposing mammalian PRC2 and its high maintenance.

Discovery of selective activators of PRC2 mutant EED-I363M

Many common disease-causing mutations result in loss-of-function (LOF) of the proteins in which they occur. LOF mutations have proven recalcitrant to pharmacologic intervention, presenting a challenge for the development of targeted therapeutics. Polycomb repressive complex 2 (PRC2), which contains core subunits (EZH2, EED, and SUZ12), regulates gene activity by trimethylation of histone 3 lysine 27. The dysregulation of PRC2 catalytic activity by mutations has been implicated in cancer and other diseases. Among the mutations that cause PRC2 malfunction, an I363M LOF mutation of EED has been identified in myeloid disorders, where it prevents allosteric activation of EZH2 catalysis. We describe structure-based design and computational simulations of ligands created to ameliorate this LOF. Notably, these compounds selectively stimulate the catalytic activity of PRC2-EED-I363M over wildtype-PRC2. Overall, this work demonstrates the feasibility of developing targeted therapeutics for PRC2-EED-I363M that act as allosteric agonists, potentially correcting this LOF mutant phenotype.

PICOT binding to the polycomb group protein, EED, alters H3K27 methylation at the MYT1 PRC2 target gene

PICOT is a ubiquitous protein that has no functional redundant ortholog and is critical for mouse embryonic development. It is involved in the regulation of signal transduction in T lymphocytes and cardiac muscle, and in cellular iron metabolism and biogenesis of Fe/S proteins. However, very little is known about the physiological role of PICOT and its mechanism of action, and on its upstream regulators or downstream target molecules. In attempt to identify new PICOT interaction partners, we adopted the yeast two-hybrid system and screened a Jurkat T cell cDNA library using the full-length human PICOT cDNA as a bait. We found that PICOT interacts with embryonic ectoderm development (EED), a Polycomb Group (PcG) protein that serves as a core component of the Polycomb repressive complex 2 (PRC2) and contributes to the regulation of chromatin remodeling and cell differentiation. Using bead immobilized GST-PICOT and GST-EED fusion proteins in a pull-down assay and reciprocal coimmunoprecipitation studies we demonstrated that the interaction between PICOT and EED also occurs in human Jurkat T cells. In addition, immunofluorescence staining of Jurkat T cells revealed partial colocalization of PICOT and EED, predominantly in the cell nuclei. A pull-down assay using the GST-EED fusion protein and lysates of cells expressing different Myc-tagged truncation products of PICOT revealed that binding of EED is mediated by each of the two C-terminal PICOT homology domains and suggests that simultaneous interaction via both domains increases the binding affinity. Furthermore, PICOT knock-down in Jurkat T cells resulted in a reduced histone H3 lysine 27 trimethylation (H3K27me3) at the PRC2 target gene, myelin transcription factor 1 (MYT1), suggesting that PICOT binding to EED alters PRC2-regulated transcriptional repression, and potentially contributes to the epigenetic regulation of chromatin silencing and remodeling.

Polycomb complexes in normal and malignant hematopoiesis

Di Carlo et al. discuss how the regulation/dysregulation of Polycomb group proteins contributes to hematopoiesis and hematological disorders.

Epigenetic mechanisms are crucial for sustaining cell type–specific transcription programs. Among the distinct factors, Polycomb group (PcG) proteins are major negative regulators of gene expression in mammals. These proteins play key roles in regulating the proliferation, self-renewal, and differentiation of stem cells. During hematopoietic differentiation, many PcG proteins are fundamental for proper lineage commitment, as highlighted by the fact that a lack of distinct PcG proteins results in embryonic lethality accompanied by differentiation biases. Correspondingly, proteins of these complexes are frequently dysregulated in hematological diseases. In this review, we present an overview of the role of PcG proteins in normal and malignant hematopoiesis, focusing on the compositional complexity of PcG complexes, and we briefly discuss the ongoing clinical trials for drugs targeting these factors.

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

Nagase and Inoue et al. generated a novel Asxl1 mutant mouse model to mimic clonal hematopoiesis and myelodysplastic syndromes caused by ASXL1 mutations and elucidated the effects of mutant versus wild-type ASXL1 on hematopoiesis, gene expression, and chromatin state.

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. In this study, 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 morphological 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. Chromatin immunoprecipitation followed by next-generation sequencing analysis demonstrated opposing effects of wild-type 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.

Therapeutic potential of GSK-J4, a histone demethylase KDM6B/JMJD3 inhibitor, for acute myeloid leukemia

PURPOSE

Acute myeloid leukemia (AML) is a heterogeneous disease with poor outcomes. Despite increased evidence shows that dysregulation of histone modification contributes to AML, specific drugs targeting key histone modulators are not applied in the clinical treatment of AML. Here, we investigated whether targeting KDM6B, the demethylase of tri-methylated histone H3 lysine 27 (H3K27me3), has a therapeutic potential for AML.

METHODS

A KDM6B-specific inhibitor, GSK-J4, was applied to treat the primary cells from AML patients and AML cell lines in vitro and in vivo. RNA-sequencing was performed to reveal the underlying mechanisms of inhibiting KDM6B for the treatment of AML.

RESULTS

Here we observed that the mRNA expression of KDM6B was up-regulated in AML and positively correlated with poor survival. Treatment with GSK-J4 increased the global level of H3K27me3 and reduced the proliferation and colony-forming ability of primary AML cells and AML cell lines. GSK-J4 treatment significantly induced cell apoptosis and cell-cycle arrest in Kasumi-1 cells, and displayed a synergistic effect with cytosine arabinoside. Notably, injection of GSK-J4 attenuated the disease progression in a human AML xenograft mouse model in vivo. Treatment with GSK-J4 predominantly resulted in down-regulation of DNA replication and cell-cycle-related pathways, as well as abrogated the expression of critical cancer-promoting HOX genes. ChIP-qPCR validated an increased enrichment of H3K27me3 in the transcription start sites of these HOX genes.

CONCLUSIONS

In summary, our findings suggest that targeting KDM6B with GSK-J4 has a therapeutic potential for the treatment of AML.

Detection of Nuclear Protein Profile Changes by Human Metapneumovirus M2-2 Protein Using Quantitative Differential Proteomics

Human metapneumovirus (hMPV) is a leading cause of lower respiratory infection in pediatric populations globally. This study examined proteomic profile changes in A549 cells infected with hMPV and two attenuated mutants with deleted PDZ domain-binding motif(s) in the M2-2 protein. These motifs are involved in the interruption of antiviral signaling, namely the interaction between the TNF receptor associated factor (TRAF) and mitochondrial antiviral-signaling (MAVS) proteins. The aim of this study was to provide insight into the overall and novel impact of M2-2 motifs on cellular responses via an unbiased comparison. Tandem mass tagging, stable isotope labeling, and high-resolution mass spectrometry were used for quantitative proteomic analysis. Using quantitative proteomics and Venn analysis, 1248 common proteins were detected in all infected samples of both technical sets. Hierarchical clustering of the differentiated proteome displayed distinct proteomic signatures that were controlled by the motif(s). Bioinformatics and experimental analysis confirmed the differentiated proteomes, revealed novel cellular biological events, and implicated key pathways controlled by hMPV M2-2 PDZ domain-binding motif(s). This provides further insight for evaluating M2-2 mutants as potent vaccine candidates.

Acquired expression of CblQ367P in mice induces dysplastic myelopoiesis mimicking chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a hematological malignancy characterized by uncontrolled proliferation of dysplastic myelomonocytes and frequent progression to acute myeloid leukemia (AML). We identified mutations in the Cbl gene, which encodes a negative regulator of cytokine signaling, in a subset of CMML patients. To investigate the contribution of mutant Cbl in CMML pathogenesis, we generated conditional knockin mice for Cbl that express wild-type Cbl in a steady state and inducibly express Cbl^Q367P , a CMML-associated Cbl mutant. Cbl^Q367P mice exhibited sustained proliferation of myelomonocytes, multilineage dysplasia, and splenomegaly, which are the hallmarks of CMML. The phosphatidylinositol 3-kinase (PI3K)-AKT and JAK-STAT pathways were constitutively activated in Cbl^Q367P hematopoietic stem cells, which promoted cell cycle progression and enhanced chemokine-chemokine receptor activity. Gem, a gene encoding a GTPase that is upregulated by Cbl^Q367P , enhanced hematopoietic stem cell activity and induced myeloid cell proliferation. In addition, Evi1, a gene encoding a transcription factor, was found to cooperate with Cbl^Q367P and progress CMML to AML. Furthermore, targeted inhibition for the PI3K-AKT and JAK-STAT pathways efficiently suppressed the proliferative activity of Cbl^Q367P -bearing CMML cells. Our findings provide insights into the molecular mechanisms underlying mutant Cbl-induced CMML and propose a possible molecular targeting therapy for mutant Cbl-carrying CMML patients.