Leukemogenesis In Acute Myeloid Leukemia Research Articles

Mutant NPM1 marginally impacts ribosome footprint in acute myeloid leukemia cells.

NPM1-mutated acute myeloid leukemia (AML) is the most frequent AML subtype. As wild-type NPM1 is known to orchestrate ribosome biogenesis, it has been hypothesized that altered translation may contribute to leukemogenesis and leukemia maintenance in NPM1-mutated AML. However, this hypothesis has never been investigated. We reasoned that if mutant NPM1 (NPM1c) directly impacts translation in leukemic cells, loss of NPM1c would result in acute changes in the ribosome footprint. Here, we performed ribosome footprint profiling (Ribo-seq) and bulk messenger RNA (mRNA) sequencing in two NPM1-mutated cell lines engineered to express endogenous NPM1c fused to the FKBP (F36V) degron tag (degron cells). Incubation of degron cells with the small compound dTAG-13 enables highly specific degradation of NPM1c within 4hours. As expected, RNA-sequencing data showed early loss of homeobox gene expression following NPM1c degradation, confirming the reliability of our model. In contrast, Ribo-seq data showed negligible changes in the ribosome footprint in both cell lines, implying that the presence of NPM1c does not influence ribosome abundance and positioning on mRNA. While it is predictable that NPM1c exerts its leukemogenic activity at multiple levels, ribosome footprint does not seem influenced by the presence of mutant NPM1.

Dotting Out AML by Targeting Fibrillarin.

Dysregulated biomolecular condensates, formed through multivalent interactions among proteins and nucleic acids, have been recently identified to drive tumorigenesis. In acute myeloid leukemia (AML), condensates driven by RNA-binding proteins alter transcriptional networks. Yang and colleagues performed a CRISPR screen and identified fibrillarin (FBL) as a new driver in AML leukemogenesis. FBL depletion caused cell cycle arrest and death in AML cells, with minimal impact on normal cells. FBL's phase separation domains are essential for pre-rRNA processing, influencing AML cell survival by regulating ribosome biogenesis and the translation of oncogenic proteins like MYC. Therapeutically, the chemotherapeutic agent CGX-635 targets FBL, inducing its aggregation, impairing pre-rRNA processing, and reducing AML cell survival. This highlights FBL's phase separation as a therapeutic vulnerability in AML. These findings suggest that targeting the phase separation properties of RNA-binding proteins could offer a novel and effective strategy for AML treatment. Further research into condensate dynamics in cancer and development of condensate-modulating drugs holds significant promise for future cancer therapies.

Inhibiting AGTR1 reduces AML burden and protects the heart from cardiotoxicity in mouse models.

Clinical treatment of acute myeloid leukemia (AML) largely relies on intensive chemotherapy. However, the application of chemotherapy is often hindered by cardiotoxicity. Patient sequence data revealed that angiotensin II receptor type 1 (AGTR1) is a shared target between AML and cardiovascular disease (CVD). We found that inhibiting AGTR1 sensitized AML to chemotherapy and protected the heart against chemotherapy-induced cardiotoxicity in a human AML cell-transplanted mouse model. These effects were regulated by the AGTR1-Notch1 axis in AML cells and cardiomyocytes from mice. In mouse cardiomyocytes, AGTR1 was hyperactivated by AML and chemotherapy. AML leukemogenesis increased the expression of the angiotensin-converting enzyme and led to increased production of angiotensin II, the ligand of AGTR1, in an MLL-AF9-driven AML mouse model. In this model, the AGTR1-Notch1 axis regulated a variety of genes involved with cell stemness and chemotherapy resistance. AML cell stemness was reduced after Agtr1a deletion in the mouse AML cell transplant model. Mechanistically, Agtr1a deletion decreased γ-secretase formation, which is required for transmembrane Notch1 cleavage and release of the Notch1 intracellular domain into the nucleus. Using multiomics, we identified AGTR1-Notch1 signaling downstream genes and found decreased binding between these gene sequences with Notch1 and chromatin enhancers, as well as increased binding with silencers. These findings describe an AML/CVD association that may be used to improve AML treatment.

Leukemia and Lymphoma: An update of acute myeloid leukemia after Whole genome sequencing (WG)

Leukemia, known for several centuries, is a cancer of the blood and bone marrow. It starts when the DNA of a single cell in the bone marrow mutates and develops abnormal growth, which spill into blood stream. Based on the types, leukemia is classified in several groups for diagnosis and treatment. With the discovery of whole genome sequences (WGS), scientists are attempting to find out accurate diagnosis and treatment. Primary Acute myeloid leukemia (AML) samples are feasible and can detect novel, clinically relevant mutations including the clonal heterogeneity of this disease and clonal evolution that occurs over time. Some of the novel mutations are highly recurrent (>20% of patients), but there appears to be a continuum of mutation frequency down to rare (<5%) or even singleton mutations that may be relevant for the biology of this disease. Large cohorts of well-annotated samples are needed to establish mutation frequencies, implicate biological pathways, and demonstrate genotype: phenotype correlations. Recent advances in genomic techniques have unraveled the molecular complexity of AML leukemogenesis, which in turn have led to refinement of risk stratification and personalized therapeutic strategies for patients with AML

Data-driven modeling of core gene regulatory network underlying leukemogenesis in IDH mutant AML

Acute myeloid leukemia (AML) is characterized by uncontrolled proliferation of poorly differentiated myeloid cells, with a heterogenous mutational landscape. Mutations in IDH1 and IDH2 are found in 20% of the AML cases. Although much effort has been made to identify genes associated with leukemogenesis, the regulatory mechanism of AML state transition is still not fully understood. To alleviate this issue, here we develop a new computational approach that integrates genomic data from diverse sources, including gene expression and ATAC-seq datasets, curated gene regulatory interaction databases, and mathematical modeling to establish models of context-specific core gene regulatory networks (GRNs) for a mechanistic understanding of tumorigenesis of AML with IDH mutations. The approach adopts a new optimization procedure to identify the top network according to its accuracy in capturing gene expression states and its flexibility to allow sufficient control of state transitions. From GRN modeling, we identify key regulators associated with the function of IDH mutations, such as DNA methyltransferase DNMT1, and network destabilizers, such as E2F1. The constructed core regulatory network and outcomes of in-silico network perturbations are supported by survival data from AML patients. We expect that the combined bioinformatics and systems-biology modeling approach will be generally applicable to elucidate the gene regulation of disease progression.

Small extracellular vesicles derived from acute myeloid leukemia cells promote leukemogenesis by transferring miR-221-3p.

Small extracellular vesicles (sEV) transfer cargos between cells and participate in various physiological and pathological processes through their autocrine and paracrine effects. However, the pathological mechanisms employed by sEV-encapsulated microRNA (miRNA) in acute myeloid leukemia (AML) are still obscure. In this study, we aimed to investigate the effects of AML cell-derived sEV (AML-sEV) on AML cells and delineate the underlying mechanisms. We initially used high-throughput sequencing to identify miR-221-3p as the miRNA prominently enriched in AML-sEV. Our findings revealed that miR-221-3p promoted AML cell proliferation and leukemogenesis by accelerating cell cycle entry and inhibiting apoptosis. Furthermore, Gbp2 was confirmed as a target gene of miR-221-3p by dual luciferase reporter assays and rescue experiments. Additionally, AML-sEV impaired the clonogenicity, particularly the erythroid differentiation ability, of hematopoietic stem and progenitor cells. Taken together, our findings reveal how sEV-delivered miRNA contribute to AML pathogenesis, which can be exploited as a potential therapeutic target to attenuate AML progression.

Inflammatory recruitment of healthy hematopoietic stem and progenitor cells in the acute myeloid leukemia niche

Inflammation in the bone marrow (BM) microenvironment is a constitutive component of leukemogenesis in acute myeloid leukemia (AML). Current evidence suggests that both leukemic blasts and stroma secrete proinflammatory factors that actively suppress the function of healthy hematopoietic stem and progenitor cells (HSPCs). HSPCs are also cellular components of the innate immune system, and we reasoned that they may actively propagate the inflammation in the leukemic niche. In two separate congenic models of AML we confirm by evaluation of the BM plasma secretome and HSPC-selective single-cell RNA sequencing (scRNA-Seq) that multipotent progenitors and long-lived stem cells adopt inflammatory gene expression programs, even at low leukemic infiltration of the BM. In particular, we observe interferon gamma (IFN-γ) pathway activation, along with secretion of its chemokine target, CXCL10. We show that AML-derived nanometer-sized extracellular vesicles (EVAML) are sufficient to trigger this inflammatory HSPC response, both in vitro and in vivo. Altogether, our studies indicate that HSPCs are an unrecognized component of the inflammatory adaptation of the BM by leukemic cells. The pro-inflammatory conversion and long-lived presence of HSPCs in the BM along with their regenerative re-expansion during remission may impact clonal selection and disease evolution.

Evaluation of apoptosis stimulating protein of TP53-1 (ASPP1/PPP1R13B) to predict therapy resistance and overall survival in acute myeloid leukemia (AML)

ASPP1 (PPP1R13B) belongs to a family of p53-binding proteins and enhances apoptosis by stimulation of p53-transactivation of selected proapoptotic target genes. It is preferentially expressed in hematopoietic stem cells (HSC) and together with p53 preserves the genomic integrity of the HSC pool. Consequently, dysfunction of ASPP1 has been associated with malignant transformation and development of acute lymphoblastic leukemias and lymphomas - whereas methylation of the promoter region is linked to reduced transcription and ultimately attenuated expression of ASPP1. The role of ASPP1 in AML is not known. We now show that impaired regulation of PPP1R13B contributes to the biology of leukemogenesis and primary therapy resistance in AML. PPP1R13B mRNA expression patterns thereby define a distinct prognostic profile - which is not reflected by the European leukemia net (ELN) risk score. These findings have direct therapeutic implications and we provide a strategy to restore ASPP1 protein levels using hypomethylating agents to sensitize cells towards proapoptotic drugs. Prospective clinical trials are warranted to investigate the role of ASPP1 (PPP1R13B) as a biomarker for risk stratification and as a potential therapeutic target to restore susceptibility to chemotherapy.

A Comprehensive Metabolism-Related Gene Signature Predicts the Survival of Patients with Acute Myeloid Leukemia.

(1) Background: Acute myeloid leukemia (AML) is a clonal malignancy with heterogeneity in genomics and clinical outcome. Metabolism reprogramming has been increasingly recognized to play an important role in the leukemogenesis and prognosis in AML. A comprehensive prognostic model based on metabolism signatures has not yet been developed. (2) Methods: We applied Cox regression analysis and the least absolute shrinkage and selection operator (LASSO) normalization to establish a metabolism-related prognostic gene signature based on glycolysis, fatty acid metabolism, and the tricarboxylic acid cycle gene signatures. The Cancer Genome Atlas-Acute Myeloid Leukemia-like (TCGA-LAML) cohort was set as the training dataset for model construction. Three independent AML cohorts (GSE37642, GSE10358, and GSE12417) combined from Gene Expression Omnibus (GEO) datasets and the Beat-AML dataset were retrieved as two validation sets to test the robustness of the model. The transcriptome data and clinic information of the cohorts were enrolled for the analysis. (3) Results: Divided by the median value of the metabolism risk score, the five-year overall survival (OS) of the high-risk and low-risk groups in the training set were 8.2% and 41.3% (p < 0.001), respectively. The five-year OS of the high-risk and low-risk groups in the combined GEO cohort were 25.5% and 37.3% (p = 0.002), respectively. In the Beat-AML cohort, the three-year OS of the high-risk and low-risk groups were 16.2% and 40.2% (p = 0.0035), respectively. The metabolism risk score showed a significantly negative association with the long-term survival of AML. Furthermore, this metabolism risk score was an independent unfavorable factor for OS by univariate analysis and multivariate analysis. (4) Conclusions: Our study constructed a comprehensive metabolism-related signature with twelve metabolism-related genes for the risk stratification and outcome prediction of AML. This novel signature might contribute to a better use of metabolism reprogramming factors as prognostic markers and provide novel insights into potential metabolism targets for AML treatment.

Super-Enhancer-Driven IGF2BP2 and IGF2BP3 Promote DDX21 Expression in Acute Myeloid Leukemia

Background : Acute myeloid leukemia (AML) is a hematological malignancy with a median overall survival (OS) of 8.5 months and a 5-year OS rate of 24.0%. Considering that relapse and drug resistance are major obstacles affecting the survival of AML patients, it is urgent to investigate the deeper pathogenesis of AML. Epigenetic modifications are extensively involved in the leukemogenesis of AML, especially N6-methyladenosine (m 6A) RNA methylation and super-enhancers (SEs). However, the relationship between m 6A and SEs in AML has not been elucidated. Methods : Chromatin immunoprecipitation (ChIP) sequencing data from Gene Expression Omnibus (GEO) cohort were analyzed to search SE-related genes. The mechanisms of m 6A-binding proteins IGF2BP2 and IGF2BP3 on DDX21 were explored via methylated RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP) and luciferase reporter assays. The potential roles of DDX21 in AML were verified through functional assays in vitro and in vivo. Results: Two SE-associated genes, IGF2BP2 and IGF2BP3, were identified in AML. There were high enrichment of H3K27ac, H3K4me1 and BRD4 in IGF2BP2 and IGF2BP3. BRD4 inhibitor JQ1 or BRD4 knockdown could lead to the suppression of IGF2BP2/3 expression, indicating the activation by SE machinery on the transcription of IGF2BP2/3. As m 6A-binding proteins, IGF2BP2 and IGF2BP3 enhanced the stability of DDX21 mRNA in an m 6A-dependent manner. DDX21 was highly expressed in AML patients, and elevated DDX21 expression suggested a poor survival. Functionally, DDX21 deficiency inhibited proliferation, facilitated apoptosis and arrested cell cycle of AML cells in vitro . I n vivo, knockdown of DDX21 substantially reduced tumor load and prolonged survival of recipient mice. Conclusions: Dysregulation of SE-IGF2BP2/IGF2BP3-DDX21 axis promotes the progression of AML, which paves the way to develop more effective therapeutic strategies.

ARHGAP4 promotes leukemogenesis in acute myeloid leukemia by inhibiting DRAM1 signaling.

Rho GTPase-activating protein 4 (ARHGAP4) is an important Rho family GTPase-activating protein that is strongly associated with the onset and progression of some tumors. We found that ARHGAP4 mRNA and protein are overexpressed in human acute myeloid leukemia (AML) patients and are associated with a poor prognosis. ARHGAP4 knockdown significantly impairs viability and colony formation capacity and induces apoptosis in AML cells. Further results demonstrate that ARHGAP4 deletion impairs AML progression in vivo. Interestingly, DRAM1 signaling is significantly activated in AML cells with ARHGAP4 knockdown. Our results also indicated that ARHGAP4 might function in AML cells by binding with p53 to inhibit DRAM1. Moreover, knockdown of DRAM1 rescues the defects of ARHGAP4 in AML cells. This newly described role of the ARHGAP4/DRAM1 axis in regulating AML progression may have important therapeutic implications.

Abstract A39: Role of LARP1 in the leukemogenesis of Acute Myeloid Leukemia

Abstract Mammalian target of rapamycin (mTOR) is a strong driver of tumorigenesis in multiple types of tumors, however targeting mTOR for cancer therapy has yielded only limited success. This may be explained in part by signaling redundancy with other pathways, such as CDK9 mTOR-Like (CTORC) complexes, recently described by our group. One of the binders common to mTORC1 and CTORC2 is La related protein 1 (LARP1). LARP1 influences ribosome biogenesis by regulating translation of 5'terminal oligopyrimidine tract (5’ TOP) containing mRNAs, which often encode ribosomal proteins and translation factors. Here, we validate LARP1 as common target of mTORC1 and CTORC2 as well as investigate its influence on leukemogenesis. To explore LARP1’s role in leukemogenesis we utilized CRISPR/CAS9 technology to create OCI-AML5 and U937 LARP1 knockout (KO) cells. Loss of LARP1 expression significantly diminished proliferation potential of AML cell lines both in vitro as well as in vivo when implanted into the flank of athymic nude mice as xenografts. Additionally, primary CD34+ leukemia cells were transfected with LARP1 targeting or scrambled siRNA and leukemic progenitor growth was assessed in methocellulose colony formation assays. We observed suppression of leukemic progenitors colony forming ability in LARP1 siRNA transfected cells, compared to the Ctrl siRNA transfected cells. We also determined enhanced sensitivity of Larp1 KO cell lines to standard chemotherapy agents such Azacitidine, Cytarabine and Venetoclax. We employed polysome profiling to compare global translation levels between Larp1 KO and control U937 cells. Our polysomal profiling results show that KO of LARP1 in U937 cells reduces global translation and ribosome biogenesis as expected as we observed a suppression of both monosomal and polysomal peaks. In summary, Larp1 is important for leukemogenesis and influences their response to treatment with currently used chemotherapy agents. These observations together suggest that LARP1 is a promising target for development of novel antileukemia approaches. Citation Format: Dominik A Nahotko, Aneta H Baran, Mariafausta Fischietti, Elspeth M Beauchamp, Leonidas C Platanias. Role of LARP1 in the leukemogenesis of Acute Myeloid Leukemia [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A39.

Core-binding factor fusion downregulation of ADAR2 RNA editing contributes to AML leukemogenesis

AbstractAdenosine-to-inosine RNA editing, which is catalyzed by adenosine deaminases acting on RNA (ADAR) family of enzymes, ADAR1 and ADAR2, has been shown to contribute to multiple cancers. However, other than the chronic myeloid leukemia blast crisis, relatively little is known about its role in other types of hematological malignancies. Here, we found that ADAR2, but not ADAR1 and ADAR3, was specifically downregulated in the core-binding factor (CBF) acute myeloid leukemia (AML) with t(8;21) or inv(16) translocations. In t(8;21) AML, RUNX1-driven transcription of ADAR2 was repressed by the RUNX1-ETO additional exon 9a fusion protein in a dominant-negative manner. Further functional studies confirmed that ADAR2 could suppress leukemogenesis specifically in t(8;21) and inv16 AML cells dependent on its RNA editing capability. Expression of 2 exemplary ADAR2-regulated RNA editing targets coatomer subunit α and component of oligomeric Golgi complex 3 inhibits the clonogenic growth of human t(8;21) AML cells. Our findings support a hitherto, unappreciated mechanism leading to ADAR2 dysregulation in CBF AML and highlight the functional relevance of loss of ADAR2-mediated RNA editing to CBF AML.

The Role of Hottip Lncrna m6a Modification in AML Genome Organization and Leukemogenesis

Acute myeloid leukemia (AML) is one of the most common and fatal forms of hematopoietic malignancies with the dysregulation of HOX genes. MLLr+ AML is characterized by aberrant expression of HOX genes and the HOX cofactor MEIS1. HOTTIP, a HOXA-associated long non-coding RNA (lncRNA), is significantly up-regulated in MLLr+ AML. Aberrant overexpression of Hottip dramatically perturbs hematopoietic stem cell (HSC) self-renewal leading to mouse AML-like disease through maintaining a leukemic profiling. Recent studies show that N6-methyladenosine (m6A), as the most prevalent internal modification in eukaryotic coding and non-coding RNAs, plays important roles in normal and malignant hematopoiesis. There are several potential m6A modified sites in HOTTIP exon regions and 3'UTR region by re-analyzing m6A-methylated RNA immunoprecipitation sequencing (m6A-meRIP-seq) data in leukemia. However, it is still unclear whether HOTTIP m6A modification plays a critical role in AML genome organization and AML leukemogenesis. Our HOTTIP ChIRP-MASS Spectrometry (ChIRP-MS) data shows that HOTTIP directly interacts with m6A methyltransferase METTL3/METTL14 and CTCF/cohesin chromatin organization proteins in MOLM13 AML cells. To investigate whether HOTTIP lncRNA is methylated by METTL3, we perform m6A-eCLIP-seq and METTL3-eCLIP-seq in MOLM13 cells. Our data indicates that there are several m6A modified sites co-bound with METTL3 in HOTTIP exon and 3'UTR regions. Our m6A-eCLIP-qPCR data further confirms that depletion of METTL3 significantly decreases HOTTIP m6A modification levels at HOTTIP RNA m6A core motif GGACU regions (g1, g2 and g3) by comparing shScramble and shMETTL3 cells. It suggests that HOTTIP lncRNA contains specific m6A modified sites methylated by METTL3. Next, to further examine whether and which HOTTIP m6A sites is required for the interaction of HOTTIP RNA with CTCF protein, we have performed in vitro RNA methylation and RNA binding protein assay by synthesizing biotinylated HOTTIP RNA fragments in g1, g2 and g3 regions. Subsequently, these biotin-HOTTIP-g1/g2/g3 RNAs are methylated with METTL3/METTL14 recombinant proteins and then incubated with GST control or GST-CTCF fusion in vitro. Our data shows that m6A modification of HOTTIP-g2 or HOTTIP-g3 RNA fragment enhances its interaction with GST-CTCF protein, suggesting that HOTTIP m6A modification plays a critical role in coordinating with CTCF-mediated genome organization. To investigate the function of HOTTIP m6A modification in AML leukemogenesis, we have generated CRISPR-dCas13-ALKBH5 (dALK) system to specifically demethylate HOTTIP m6A sites (g1, g2 and g3) by co-transfecting gRNA vector and the catalytically inactive Cas13 (dCas13) fused with m6A demethylase AlkB homolog 5 (ALKBH5) vector. Targeting dALK to specific m6A site in HOTTIP lncRNA results in site-specific loss of m6A modification. Although loss of HOTTIP m6A modification never affects the stability and transcription of HOTTIP in dALK clones, loss of HOTTIP m6A modification significantly affects the transcription of leukemic signature genes HOXA9/13 and WNT target (β-catenin and MYC etc) in dALK-g2 or dALK-g3 cells. Additionally, our HOTTIP ChIRP-qPCR shows that loss of HOTTIP m6A modification affects HOTTIP binding at WNT target loci (β-catenin and MYC loci) in dALK-g2 or dALK-g3 cells. Critically, our data find that loss of HOTTIP m6A modification significantly impairs cell proliferation and cell cycle in dALK-g2 or dALK-g3 cells compared with ctrl cells. To further elucidate whether HOTTIP m6A modification is required for AML leukemogenesis in vivo, we xenograft ctrl and dALK clones into NOD-scid IL2Rgammanull (NSG) mice. Our data indicates that mice transplanted with ctrl or dALK-g1 cells dies around 40 days after transplantation, while those receiving dALK-g2 or dALK-g3 cells survives significantly longer up to 55 days. Critically, we also find that ctrl recipient mice have significantly higher human CD45+ cell chimerism in the BM than mice receiving dALK-g2 or dALK-g3 AML cells. Thus, loss of the specific HOTTIP m6A modification site reduces the AML leukemic burden in vivo. In summary, this research will provide a prospective insight for the role of HOTTIP-m6A-CTCT axis in AML genome organization and leukemogenesis.

Deletion of Micro RNA-15/16 Clusters Promotes Leukemic Initiation in AML Via the Deregulation of Hematopoietic Progenitors

The microRNA 15a/16-1 cluster on chromosome 13 is commonly lost in chronic lymphocytic leukemia (CLL). Even though this deletion is considered to be a CLL-associated genomic aberration, loss of miR-15/16 occurs in 79% of primary acute myeloid leukemia (AML) and in patients with myelodysplastic syndrome (MDS) that transformed into AML. A second highly homologous locus, miR-15b/16-2, is present in both human and mice, and deletion of either miR-15/16 cluster in mice leads to CLL. Unexpectedly, when both loci are deleted, only 23% of miR-15/16 double knock out (DKO) mice develop various non-Hodgkin's lymphomas, whereas 77% develop AML. Consistent with this, DKO mice have an expanded Gr-1+CD11b+ granulocytic population in both bone marrow (BM) and spleen. These observations led us to hypothesize that the miR-15/16 clusters can act coordinately to regulate lineage determination and proliferation in early hematopoiesis. Their loss might influence leukemogenesis in CLL and AML by altering the number and function of hematopoietic stem cells (HSCs) and/or their downstream lineages and potentially increasing a population of preleukemic stem cells. To test this, using flow cytometry, we analyzed the numbers and frequency of HSCs and progenitors in DKO and C57BL/6 (B6) mice. We discovered major changes in HSCs and the common myeloid progenitors (CMP) but similar numbers of common lymphoid progenitors. Therefore, we focused on the myeloid lineage, finding that CD16/32-CD34- megakaryocyte/erythroid progenitors (MEP) were significantly increased in the Lin- cKit+ compartment of DKO mice (44.9% vs 29.8% P = 0.01), but CD16/32+CD34+ granulocyte-macrophage progenitors (GMP) were decreased (19.1% vs 40.1% P = 0.01). This was surprising since we also found that a GMP progeny population, CD11b+Gr-1+ cells, was enriched in DKO compared to B6 BM (60-70% vs 40%). To determine if this was a result of a differentiation defect in an earlier progenitor, we assessed the frequency of Lin-Sca1+cKit+ (LSK) populations, finding that DKO mice had significantly more CD150+CD48-CD34- LT-HSCs among LSK cells (14.3% vs 7.8% P = 0.03), and fewer CD150-CD48+ multipotent progenitors (MPP) (58.5% vs 68.6% P = 0.04). Of note, there was an increased absolute count for all progenitors analyzed, possibly due to an increase in BM cells and/or disproportional increases of certain cell types. Since the observed myeloproliferative phenotype could be due to 1) an absolute increase of progenitor cells; 2) malfunctioning progenitor cells that aberrantly differentiate and proliferate; 3) or both, we tested whether DKO LSK cells had distinct functional characteristics in vitro. Methylcellulose replating of LT-HSC and MPP in the presence of SCF, IL-3, and IL-6 indicated that DKO LT-HSC gave rise to consistently fewer colonies as compared to B6 LT-HSC (21.5 vs 37.2 colonies/100 cells plated P = 0.02). Unexpectedly, we found the opposite for MPP, as DKO MPP consistently exhibited higher colony-forming activity than B6 MPP (16.6 vs 5.1 colonies/100 cells plated P = 0.04) over the course of serial replating experiments. This was surprising in light of the significant decrease in MPP frequency we had observed by immunophenotyping. Furthermore, B6 MPP cells ceased forming colonies after 3 rounds of replating, whereas DKO MPP continued for 5 rounds, suggesting that the absence of miR-15/16 increased the self-renewal potential of the CD150-CD48+ MPP cells. This was further supported by immunophenotyping analysis showing increased LSK cells derived from DKO MPP colonies (25.8% vs 4.4% P = 0.03). In concordance with the initial observation, an increase in DKO MPP colony-derived CD11b+Gr-1+ cells was at least partly responsible for the myeloproliferative defect in the mature cell compartment (76.1% vs 56.9%P = 0.01). Together, these results suggest that in miR-15/16 DKO mice, the phenotypically defined MPP compartment contains leukemia-initiating cells. Overall, our findings reveal a novel role for the miR-15/16 clusters at the top of the hematopoietic hierarchy. Future experiments focusing on these DKO progenitors that appears to be endowed with leukemic stem cell potential may provide clues to understand how the targets of miR-15a, miR-15b and miR-16 orchestrate their effects on lineage commitment and how their absence may lead to initiation of AML and CLL. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Combination of RSK inhibitor LJH-685 and FLT3 inhibitor FF-10101 promoted apoptosis and proliferation inhibition of AML cell lines.

FLT3 mutations occurred in approximately one third of patients with acute myeloid leukemia (AML). FLT3-ITD mutations caused the constitutive activation of the RAS/MAPK signaling pathway. Ribosomal S6 Kinases (RSKs) were serine/threonine kinases that function downstream of the Ras/Raf/MEK/ERK signaling pathway. However, roles and mechanisms of RSKs inhibitor LJH-685, and combinational effects of LJH-685 and FLT3 inhibitor FF-10101 on AML cells were till unclear. Cell viability assay, CFSE assay, RT-qPCR, Colony formation assay, PI stain, Annexin-V/7-AAD double stain, Western blot, and Xenogeneic transplantation methods were used to used to investigate roles and mechanisms of LJH-685 in the leukemogenesis of AML. LJH-685 inhibited the proliferation and clone formation of AML cells, caused cell cycle arrest and induced the apoptosis of AML cells via inhibiting the RSK-YB-1 signaling pathway. MV4-11 and MOLM-13 cells carrying FLT3-ITD mutations were more sensitive to LJH-685 than that of other AML cell lines. Further studies suggested that LJH-685 combined with Daunorubicin or FF- 10101 synergistically inhibited the cell viability, promoted the apoptosis and caused cycle arrest of AML cells carrying FLT3-ITD mutations. Moreover, in vivo experiments also indicated that LJH-685 combined with FF-10101 or Daunorubicin prolonged the survival time of NSG mice and reduced the leukemogenesis of AML. Thus, these observations demonstrated combination of RSK inhibitor LJH-685 and FLT3 inhibitor FF-10101 showed synergism anti-leukemia effects in AML cell lines with FLT3-ITD mutations via inhibiting MAPK-RSKs-YB-1 pathway and provided new targets for therapeutic intervention especially for AML with FLT3-ITD mutations and Daunorubicin-resistant AML.

HIVEP3 cooperates with ferroptosis gene signatures to confer adverse prognosis in acute myeloid leukemia.

The human immunodeficiency virus type I enhancer binding protein (HIVEP) family, which contains zinc finger and acid-rich (ZAS) domains, has been demonstrated to be implicated in vital biological processes, such as cell survival, tumor necrosis factor (TNF) signaling, and tumor formation. However, its expression patterns, prognostic relevance, and functional implications in acute myeloid leukemia (AML) remain elusive. We inspected HIVEP mRNA expression levels in datasets from The Cancer Genome Atlas (TCGA) and GSE24006. Survival analyses were orchestrated using the web-based bioinformatics platforms and R studio in two AML cohorts. Prognostic value and capacity were assessed by Cox regression analyses. Association of HIVEP3 expression levels with clinical characteristics were analyzed with R and UALCAN. Subsequentially, functional enrichment analyses were operated to interpret HIVEP3 co-expressed gene clusters. A prognostic gene signature was created by the least absolute shrinkage and selection operator (LASSO) regression algorithm. Moreover, bone marrow aspirate smears of AML patients were stained for HIVEP3 by immunohistochemistry (IHC). HIVEP3 expression was examined by qRT-PCR in leukemia cell lines treated with ferroptosis compounds in vitro. Augmented transcriptional levels of HIVEP2 and 3 were noted in AML patients (p<0.001). HIVEP3 not only could confer adverse prognosis independently in AML patients, but also was associated with AML subtypes, age, cytogenetic risk, and disease-related molecules. Co-expressed gene clusters of HIVEP3 were enriched in functional pathways related to AML leukemogenesis, such as ribosome, metabolism, and calcium signaling. Combined with multiple tumorigenesis signaling pathways, we proposed an integrated LASSO model with HIVEP3 and ferroptosis regulators AIFM2 and LPCAT3, to predict the outcome for AML patients. Furthernore, altered HIVEP3 expression at the mRNA or protein level was confirmed in sorted leukemia cells and blast cells in bone marrow tissues. In vitro experiments authenticated the involvement of HIVEP3 in ferroptosis signaling pathways. Our findings suggest that HIVEP3 is a de novo independent prognostic indicator, and the crosstalk between HIVEP3 and ferroptosis signaling pathways may inspire a specific perspective on the oncological network of AML.

Prognostic implications and functional enrichment analysis of LTB4R in patients with acute myeloid leukemia

To explore the expression patterns, prognostic implications, and biological role of leukotriene B4 receptor (LTB4R) in patients with acute myeloid leukemia (AML). We collected the data of mRNA expression levels and clinical information of patients with AML from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database for mRNA expression analyses, survival analyses, Cox regression analyses and correlation analyses using R studio to assess the expression patterns and prognostic value of LTB4R. The correlation of LTB4R expression levels with clinical characteristics of the patients were analyzed using UALCAN. The co-expressed genes LTB4R were screened from Linkedomics and subjected to functional enrichment analysis. A protein-protein interaction network was constructed using STRING. GSEA analyses of the differentially expressed genes (DEGs) were performed based on datasets from TCGA-LAML stratified by LTB4R expression level. We also collected peripheral blood mononuclear cells (PBMCs) from AML patients and healthy donors for examination of the mRNA expression levels of LTB4R and immune checkpoint genes using qRT-PCR. We also examined serum LTB4R protein levels in the patients using ELISA. The mRNA expression level of LTB4R was significantly increased in AML patients (4.898±1.220 vs 2.252±0.215, P < 0.001), and an elevated LTB4R expression level was correlated with a poor overall survival (OS) of the patients (P=0.004, HR=1.74). LTB4R was identified as an independent prognostic factor for OS (P=0.019, HR=1.66) and was associated with FAB subtypes, cytogenetic risk, karyotype abnormalities and NPM1 mutations. The co- expressed genes of LTB4R were enriched in the functional pathways closely associated with AML leukemogenesis, including neutrophil inflammation, lymphocyte activation, signal transduction, and metabolism. The DEGs were enriched in differentiation, activation of immune cells, and cytokine signaling. Examination of the clinical serum samples also demonstrated significantly increased expressions of LTB4R mRNA (P=0.044) and protein (P=0.008) in AML patients, and LTB4R mRNA expression was positively correlated with the expression of the immune checkpoint HAVCR2 (r= 0.466, P=0.040). LTB4R can serve as a novel biomarker and independent prognostic indicator of AML and its expression patterns provide insights into the crosstalk of leukemogenesis signaling pathways involving tumor immunity and metabolism.

Autophagy in acute myeloid leukemia: a paradoxical role in chemoresistance.

Autophagy is a lysosomal degradation pathway that is constitutively active in almost every cell of our body at basal level. This self-eating process primarily serves to remove superfluous constituents of the cells and recycle the degraded products. Autophagy plays an essential role in cell homeostasis and can be enhanced in response to stressful conditions. Impairment in the regulation of the autophagic pathway is implicated in pathological conditions such as neurodegeneration, cardiac disorders, and cancer. However, the role of autophagy in cancer initiation and development is controversial and context-dependent. Evidence from various studies has shown that autophagy serves dual purpose and may assist in cancer progression or suppression. In the early stages of cancer initiation, autophagy acts as a quality control mechanism and prevents cancer development. When cancer is established and progresses to a later stage, autophagy helps in the survival of these cells through adaptation to stresses, including exposure to anti-cancer drugs. In this review, we highlight various studies on autophagic pathways and describe the role of autophagy in cancer, specifically acute myeloid leukemia (AML). We also discuss the prognostic significance of autophagy genes involved in AML leukemogenesis and implications in conferring resistance to chemotherapy.

Treatment with the Recombinant SLIT2 Protein Delays AML Leukemogenesis In Vivo

Accumulating evidence suggest that the axon guidance molecules SLIT and ROBO are not only implicated in physiological process but also in cancer progression. Depending on the type of cancer the SLIT-ROBO axis can either act as a tumor suppressor gene, in which case the SLIT2 promoter site is frequently hypermethylated or as an oncogene, whereby high expression is often associated with poor prognosis. In the context of acute myeloid leukemia (AML), low expression of SLIT2 has been associated with low overall survival (OS) (Golos et al., 2019), while the functional role of SLIT2 remains largely unknown. Recently, we showed that the knockdown of SLIT2 increased cell proliferation of acute promyelocytic leukemia (APL) cells resulting in a more aggressive course of disease progression in vivo using the murine transgenic APL model (Weinhäuser et al., 2020). Here, we aimed to study the functional role of SLIT2 in a more heterogeneous disease, such as AML.Using different publicly available datasets. (GSE58477, normal karyotype blasts: 62, healthy CD34 +: 10; GSE63409, LSC: 14, HSC: 5) we detected increased methylation at the SLIT2 promoter site of AML leukemic cells compared to healthy CD34 + cells suggesting SLIT2 tumor suppressive functions. In addition, we measured decreased levels of SLIT2 in the bone marrow (BM) plasma of AML patients compared to healthy donors. To assess the biological role of SLIT2, we treated AML cell lines (KASUMI1, MV411, and MOLM13) with recombinant SLIT2 (50 ng/mL) in vitro. Administration of SLIT2 reduced AML cell growth, colony formation and induced cell cycle arrest in the G1 phase for all AML cell lines. Conversely, the knockdown of SLIT2 promoted increased THP-1 and OCI-AML3 cell proliferation. Next, we determined whether the treatment with SLIT2 could delay leukemogenesis in vivo using the AML cell line MV4-11. Engraftment was monitored by luciferase bioluminescent signal and NSGS mice were either treated with recombinant SLIT2 using a dose of 25 ng/g of body weight or vehicle (control group). SLIT2 therapy resulted in a lower disease burden, decreased leukemic infiltration in the BM and spleen, reduced spleen size, and increased OS compared to the control group (p<0.05). In conclusion, we showed that SLIT2 methylation is recurrent in AML patients and that the level of SLIT2 in the plasma of AML patients is reduced. Moreover, SLIT2 treatment appears to have a cytostatic effect on different AML cell lines delaying leukemogenesis in vivo. Overall, our study reveals the therapeutic potential of SLIT2 in hematological malignancies, which could be used as an adjuvant in the clinic. DisclosuresNo relevant conflicts of interest to declare.