Mitochondrial tRNA pseudouridylation governs erythropoiesis.

Pseudouridine is the most prevalent RNA modification, and its aberrant function is implicated in various human diseases. However, the specific impact of pseudouridylation on hematopoiesis remains poorly understood. In this study, we investigated the role of tRNA pseudouridylation in erythropoiesis and its association with mitochondrial myopathy, lactic acidosis, and sideroblastic anemia syndrome (MLASA) pathogenesis. By utilizing patient-specific induced pluripotent stem cells (iPSCs) carrying a genetic PUS1 mutation and a corresponding mutant mouse model, we demonstrated impaired erythropoiesis in MLASA iPSCs and anemia in the MLASA mouse model. Both MLASA iPSCs and mouse erythroblasts exhibited compromised mitochondrial function and impaired protein synthesis. Mechanistically, we revealed that PUS1 deficiency resulted in reduced mitochondrial tRNA levels due to pseudouridylation loss, leading to aberrant mitochondrial translation. Screening of mitochondrial supplements aimed at enhancing respiration or heme synthesis showed limited effect in promoting erythroid differentiation. Interestingly, the mTOR inhibitor rapamycin facilitated erythroid differentiation in MLASA-iPSCs by suppressing mTOR signaling and protein synthesis, and consistent results were observed in the MLASA mouse model. Importantly, rapamycin treatment effectively ameliorated anemia phenotypes in the MLASA patient. Our findings provide novel insights into the crucial role of mitochondrial tRNA pseudouridylation in governing erythropoiesis and present potential therapeutic strategies for anemia patients facing challenges related to protein translation.

Loss of RNA-binding protein CELF2 promotes acute leukemia development via FAT10-mTORC1.

RNA-binding proteins (RBPs) are critical regulators for RNA transcription and translation. As a key member of RBPs, ELAV-like family protein 2 (CELF2) has been shown to regulate RNA splicing and embryonic hematopoietic development and was frequently seen dysregulated in acute myeloid leukemia (AML). However, the functional role(s) of CELF2 in hematopoiesis and leukemogenesis has not been fully elucidated. In the current study, we showed that Celf2 deficiency in hematopoietic system led to enhanced HSCs self-renewal and differentiation toward myeloid cells in mice. Loss of Celf2 accelerated myeloid cell transformation and AML development in MLL-AF9-induced AML murine models. Gene expression profiling integrated with RNA immunoprecipitation sequencing (RIP-Seq), together with biochemical experiments revealed that CELF2 deficiency stabilizes FAT10 mRNA, promotes FAT10 translation, thereby increases AKT phosphorylation and mTORC1 signaling pathway activation. Notably, combination therapy with a mTORC1 inhibitor (Rapamycin) and a MA9/DOTL1 inhibitor (EPZ-5676) reduced the leukemia burden in MLL-AF9 mice lacking Celf2 in vivo. Our study elucidated a novel mechanism by which the CELF2/FAT10-AKT/mTORC1 axis regulates the proliferation of normal blood cells and the development of AML, thus providing potential therapeutic targets for myeloid leukemia suppression.

Pseudouridine synthase 1 regulates erythropoiesis via transfer RNAs pseudouridylation and cytoplasmic translation.

Pseudouridylation plays a regulatory role in various physiological and pathological processes. A prime example is the mitochondrial myopathy, lactic acidosis, and sideroblastic anemia syndrome (MLASA), characterized by defective pseudouridylation resulting from genetic mutations in pseudouridine synthase 1 (PUS1). However, the roles and mechanisms of pseudouridylation in normal erythropoiesis and MLASA-related anemia remain elusive. We established a mouse model carrying a point mutation (R110W) in the enzymatic domain of PUS1, mimicking the common mutation in human MLASA. Pus1-mutant mice exhibited anemia at 4 weeks old. Impaired mitochondrial oxidative phosphorylation was also observed in mutant erythroblasts. Mechanistically, mutant erythroblasts showed defective pseudouridylation of targeted tRNAs, altered tRNA profiles, decreased translation efficiency of ribosomal protein genes, and reduced globin synthesis, culminating in ineffective erythropoiesis. Our study thus provided direct evidence that pseudouridylation participates in erythropoiesis in vivo. We demonstrated the critical role of pseudouridylation in regulating tRNA homeostasis, cytoplasmic translation, and erythropoiesis.

HS-SPME-GC-MS Untargeted Analysis of Normal Rat Organs Ex Vivo: Differential VOC Discrimination and Fingerprint VOC Identification.

The investigation of volatile organic compounds (VOCs) in human metabolites has been a topic of interest as it holds the potential for the development of non-invasive technologies to screen for organ lesions in vivo. However, it remains unclear whether VOCs differ among healthy organs. Consequently, a study was conducted to analyze VOCs in ex vivo organ tissues obtained from 16 Wistar rats, comprising 12 different organs. The VOCs released from each organ tissue were detected by the headspace-solid phase microextraction-gas chromatography-mass spectrometry technique. In the untargeted analysis of 147 chromatographic peaks, the differential volatiles of rat organs were explored based on the Mann-Whitney U test and fold change (FC > 2.0) compared with other organs. It was found that there were differential VOCs in seven organs. A discussion on the possible metabolic pathways and related biomarkers of organ differential VOCs was conducted. Based on the orthogonal partial least squares discriminant analysis and receiver operating characteristic curve, we found that differential VOCs in the liver, cecum, spleen, and kidney can be used as the unique identification of the corresponding organ. In this study, differential VOCs of organs in rats were systematically reported for the first time. Profiles of VOCs produced by healthy organs can serve as a reference or baseline that may indicate the presence of disease or abnormalities in the organ's function. Differential VOCs can be used as the fingerprint of organs, and future integration with metabolic research may contribute to the development of healthcare.

PHF6 maintains acute myeloid leukemia via regulating NF-κB signaling pathway.

Acute myeloid leukemia (AML) is a major hematopoietic malignancy characterized by the accumulation of immature and abnormally differentiated myeloid cells in bone marrow. Here with in vivo and in vitro models, we demonstrate that the Plant homeodomain finger gene 6 (PHF6) plays an important role in apoptosis and proliferation in myeloid leukemia. Phf6 deficiency could delay the progression of RUNX1-ETO9a and MLL-AF9-induced AML in mice. PHF6 depletion inhibited the NF-κB signaling pathways by disrupting the PHF6-p50 complex and partially inhibiting the nuclear translocation of p50 to suppress the expression of BCL2. Treating PHF6 over-expressed myeloid leukemia cells with NF-κB inhibitor (BAY11-7082) significantly increased their apoptosis and decreased their proliferation. Taken together, in contrast to PHF6 as a tumor suppressor in T-ALL as reported, we found that PHF6 also plays a pro-oncogenic role in myeloid leukemia, and thus potentially to be a therapeutic target for treating myeloid leukemia patients.

High Expression of Microtubule-associated Protein TBCB Predicts Adverse Outcome and Immunosuppression in Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is a devastating blood cancer with high heterogeneity and ill-fated outcome. Despite numerous advances in AML treatment, the prognosis remains poor for a significant proportion of patients. Consequently, it is necessary to accurately and comprehensively identify biomarkers as soon as possible to enhance the efficacy of diagnosis, prognosis and treatment of AML. In this study, we aimed to identify prognostic markers of AML by analyzing the cohorts from TCGA-LAML database and GEO microarray datasets. Interestingly, the transcriptional level of microtubule-associated protein TBCB in AML patients was noticeably increased when compared with normal individuals, and this was verified in two independent cohorts (GSE9476 and GSE13159) and with our AML patients. Furthermore, univariate and multivariate regression analysis revealed that high TBCB expression was an independent poor prognostic factor for AML. GO and GSEA enrichment analysis hinted that immune-related signaling pathways were enriched in up-regulated DEGs between two populations separated by the median expression level of TBCB. By constructing a protein-protein interaction network, we obtained six hub genes, all of which are immune-related molecules, and their expression levels were positively linked to that of TBCB. In addition, the high expression of three hub genes was significantly associated with a poor prognosis in AML. Moreover, we found that the tumor microenvironment in AML with high TBCB expression tended to be infiltrated by NK cells, especially CD56bright NK cells. The transcriptional levels of NK cell inhibitory receptors and their ligands were positively related to that of TBCB, and their high expression levels also predicted poor prognosis in AML. Notably, we found that the down-regulation of TBCB suppressed cell proliferation in AML cell lines by enhancing the apoptosis and cell cycle arrest. Finally, drug sensitivity prediction illustrated that cells with high TBCB expression were more responsive to ATRA and midostaurin but resistant to cytarabine, dasatinib, and imatinib. In conclusion, our findings shed light on the feasibility of TBCB as a potential predictor of poor outcome and to be an alternative target of treatment in AML.

R274X-mutated Phf6 increased the self-renewal and skewed T cell differentiation of hematopoietic stem cells.

The PHD finger protein 6 (PHF6) mutations frequently occurred in hematopoietic malignancies. Although the R274X mutation in PHF6 (PHF6R274X) is one of the most common mutations identified in T cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML) patients, the specific role of PHF6R274X in hematopoiesis remains unexplored. Here, we engineered a knock-in mouse line with conditional expression of Phf6R274X-mutated protein in the hematopoietic system (Phf6R274X mouse). The Phf6R274X mice displayed an enlargement of hematopoietic stem cells (HSCs) compartment and increased proportion of T cells in bone marrow. More Phf6R274X T cells were in activated status than control. Moreover, Phf6R274X mutation led to enhanced self-renewal and biased T cells differentiation of HSCs as assessed by competitive transplantation assays. RNA-sequencing analysis confirmed that Phf6R274X mutation altered the expression of key genes involved in HSC self-renewal and T cell activation. Our study demonstrated that Phf6R274X plays a critical role in fine-tuning T cells and HSC homeostasis.

High-expression of the innate-immune related gene UNC93B1 predicts inferior outcomes in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy with dismal prognosis. Identification of better biomarkers remained a priority to improve established stratification and guide therapeutic decisions. Therefore, we extracted the RNA sequence data and clinical characteristics of AML from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression database (GTEx) to identify the key factors for prognosis. We found UNC93B1 was highly expressed in AML patients and significantly linked to poor clinical features (p < 0.05). We further validated the high expression of UNC93B1 in another independent AML cohort from GEO datasets (p < 0.001) and performed quantitative PCR of patient samples to confirm the overexpression of UNC93B1 in AML (p < 0.005). Moreover, we discovered high level of UNC93B1 was an independent prognostic factor for poorer outcome both in univariate analysis and multivariate regression (p < 0.001). Then we built a nomogram model based on UNC93B1 expression, age, FAB subtype and cytogenetic risk, the concordance index of which for predicting overall survival was 0.729 (p < 0.001). Time-dependent ROC analysis for predicting survival outcome at different time points by UNC93B1 showed the cumulative 2-year survival rate was 43.7%, and 5-year survival rate was 21.9%. The differentially expressed genes (DEGs) between two groups divided by UNC93B1 expression level were enriched in innate immune signaling and metabolic process pathway. Protein-protein interaction (PPI) network indicated four hub genes (S100A9, CCR1, MRC1 and CD1C) interacted with UNC93B1, three of which were also significantly linked to inferior outcome. Furthermore, we discovered high UNC93B1 tended to be infiltrated by innate immune cells, including Macrophages, Dendritic cells, Neutrophils, Eosinophils, and NK CD56dim cells. We also found UNC93B1 had a significantly positive correlation with CD14, CD68 and almost all Toll-like receptors. Finally, we revealed negatively correlated expression of UNC93B1 and BCL2 in AML and conjectured that high-UNC93B1 monocytic AML is more resistant to venetoclax. And we found high MCL-1 expression compensated for BCL-2 loss, thus, we proposed MCL-1 inhibitor might overcome the resistance of venetoclax in AML. Altogether, our findings demonstrated the utility of UNC93B1 as a powerful poor prognostic predictor and alternative therapeutic target.

Mass cytometry analysis identifies T cell immune signature of aplastic anemia and predicts the response to cyclosporine.

Aplastic anemia (AA) is an auto-activated T cell-mediated bone marrow failure. Cyclosporine is often used to treat non-severe AA, which demonstrates a more heterogeneous condition than severe AA. The response rate to cyclosporine is only around 50% in non-severe AA. To better predict response to cyclosporine and pinpoint who is the appropriate candidate for cyclosporine, we performed phenotypic and functional T cell immune signature at single cell level by mass cytometry from 30 patients with non-severe AA. Unexpectedly, non-significant differences of T cell subsets were observed between AA and healthy control or cyclosporine-responder and non-responders. Interestingly, when screening the expression of co-inhibitory molecules, T cell trafficking mediators, and cytokines, we found an increase of cytotoxic T lymphocyte antigen 4 (CTLA-4) on T cells in response to cyclosporine and a lower level of CTLA-4 on CD8+ T cells was correlated to hematologic response. Moreover, a decreased expression of sphingosine-1-phosphate receptor 1 (S1P1) on naive T cells and a lower level of interleukin-9 (IL-9) on T helpers also predicted a better response to cyclosporine, respectively. Therefore, the T cell immune signature, especially in CTAL-4, S1P1, and IL-9, has a predictive value for response to cyclosporine. Collectively, our study implies that immune signature analysis of T cell by mass cytometry is a useful tool to make a strategic decision on cyclosporine treatment of AA.

[Screening of proliferation related lncRNAs in leukemia cell lines by lentivirus shRNA library combined with second-generation sequencing].

Long non-coding RNA (lncRNA) has become an important regulator of many cellular processes, including cell proliferation. Although studies have shown that a variety of lncRNAs play an important role in the occurrence and development of hematopoietic malignancies, a more comprehensive and unbiased method to study the function of lncRNAs in leukemia cell lines is lacking. Here, we used short hairpin RNA (shRNA) library combined with high-throughput sequencing to screen lncRNAs that may affect the proliferation of leukemia cell lines, and identified lncRNA C20orf204-203 among 74 candidate lncRNAs in this study. Further experiments showed that C20orf204-203 was localized in the cytoplasm in both K562 and THP-1 cell lines. C20orf204-203 knockdown decreased the proliferation of K562 and THP-1 cell lines accompanied with the increased proportion of early apoptotic cells. We observed the increased mRNA level of BAD gene while decreased protein level of TP53 and BCL2. The expression of Caspase 3 decreased and Caspase 3-cleaved protein increased in THP-1 cell line. However, their changes were inconsistent in the two cell lines. Our experimental results showed that knockdown of lncRNA C20orf204-203 in leukemia cell lines affected cell proliferation although the mechanism of action in different cell lines may differ. Importantly, our research demonstrated the feasibility of using shRNA library combined with high-throughput sequencing to study the role of lncRNA in leukemia cell lines on a large scale.

Polyclonal evolution of Fanconi anemia to MDS and AML revealed at single cell resolution.

BACKGROUND: Fanconi anemia (FA) is a rare disease of bone marrow failure. FA patients are prone to develop myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). However, the molecular clonal evolution of the progression from FA to MDS/AML remains elusive. METHODS: Herein, we performed a comprehensive genomic analysis using an FA patient (P1001) sample that transformed to MDS and subsequently AML, together with other three FA patient samples at the MDS stage. RESULTS: Our finding showed the existence of polyclonal pattern in these cases at MDS stage. The clonal evolution analysis of FA case (P1001) showed the mutations of UBASH3A, SF3B1, RUNX1 and ASXL1 gradually appeared at the later stage of MDS, while the IDH2 alteration become the dominant clone at the leukemia stage. Moreover, single-cell sequencing analyses further demonstrated a polyclonal pattern was present at either MDS or AML stages, whereas IDH2 mutated cell clones appeared only at the leukemia stage. CONCLUSIONS: We thus propose a clonal evolution model from FA to MDS and AML for this patient. The results of our study on the clonal evolution and mutated genes of the progression of FA to AML are conducive to understanding the progression of the disease that still perplexes us.

Osteopontin is required for the maintenance of leukemia stem cells in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous hematopoietic disorder with a poor prognosis. The clinical significance of Leukemia stem cells (LSCs) plays an important role in the generation of AML and is the main cause of the recurrence after remission. Osteopontin (OPN), an extracellular matrix protein, has been implicated in hematopoietic malignancies. However, the specific role and the underlying mechanism of AML cell autocrined OPN in leukemia maintenance remain unknown. Here, we showed that knockdown of Opn expression significantly prolonged the survival of mice with MLL-AF9 cell-induced AML and markedly reduced the tumor burden. The LSCs from the Opn-knockdown groups exhibited decreased numbers and impaired function as determined by immunophenotype, colony-forming and limiting dilution assays. Further analysis revealed that Opn prevents LSCs from undergoing apoptosis and cell cycle arrest. Repression of OPN in human AML cell lines in vitro mimics the phenotypes observed in the mouse model. Overall, our data indicated that OPN is a potent therapeutic target for eradicating LSCs in AML.

[Effect of Rheb1 in the Development of Mouse Megakaryocyte-Erythroid Progenitor Cells].

OBJECTIVE: To investigate the effect of Rheb1 in the development of mouse megakaryocyte-erythroid progenitor cells and its related mechanism. METHODS: Rheb1 was specifically knocked-out in the hematopoietic system of Vav1-Cre;Rheb1fl/fl mice(Rheb1Δ/Δ mice). Flow cytometry was used to detect the percentage of red blood cells in peripheral blood and erythroid cells in bone marrow in Vav1-Cre;Rheb1fl/fl mice and control mice. The CFC assay was used to detect the differentiation ability of Rheb1 KO megakaryocyte-erythroid progenitor cells and control cells. Real-time fluorescence quantification PCR was used to detect the relative expression of PU.1,GATA-1,GATA-2,CEBPα and CEBPß of Rheb1 KO megakaryocyte-erythroid progenitor cells and control cells. Rapamycin was added to the culture medium, and it was used to detect the changes in cloning ability of megakaryocyte-erythroid progenitor cells from wild-type mice in vitro. RESULTS: After Rheb1 was knocked out, the development and stress response ability of megakaryocyte-erythroid progenitor cells in mice were weaken and the differentiation ability of megakaryocyte-erythroid progenitor cells in vitro was weaken. Moreover, the expression of GATA-1 of megakaryocyte-erythroid progenitor cells was decreased. Further, rapamycin could inhibit the differentiative capacity of megakaryocyte-erythroid progenitor cells in vitro. CONCLUSION: Rheb1 can regulate the development of megakaryocyte-erythroid progenitor cells probably through the mTOR signaling pathway in mice.

Analysis of volatile organic compounds in exhaled breath after radiotherapy.

Radiotherapy uses high-energy X-rays or other particles to destroy cancer cells and medical practitioners have used this approach extensively for cancer treatment (Hachadorian et al., 2020). However, it is accompanied by risks because it seriously harms normal cells while killing cancer cells. The side effects can lower cancer patients' quality of life and are very unpredictable due to individual differences (Bentzen, 2006). Therefore, it is essential to assess a patient's body damage after radiotherapy to formulate an individualized recovery treatment plan. Exhaled volatile organic compounds (VOCs) can be changed by radiotherapy and thus used for medical diagnosis (Vaks et al., 2012). During treatment, high-energy X-rays can induce apoptosis; meanwhile, cell membranes are damaged due to lipid peroxidation, converting unsaturated fatty acids into volatile metabolites (Losada-Barreiro and Bravo-Díaz, 2017). At the same time, radiotherapy oxidizes water, resulting in reactive oxygen species (ROS) that can increase the epithelial permeability of pulmonary alveoli, enabling the respiratory system to exhale volatile metabolites (Davidovich et al., 2013; Popa et al., 2020). These exhaled VOCs can be used to monitor body damage caused by radiotherapy.

Distinguish oral-source VOCs and control their potential impact on breath biomarkers.

By means of glass bottle sampling followed by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS) technique, the change characteristics of volatile organic compounds (VOCs) in breaths, between before gargling and after gargling, were investigated, respectively, in 41 healthy subjects and 50 esophageal cancer patients. Using an untargeted strategy, 143 VOC chromatographic peaks were enrolled in the statistical analysis. Based on the orthogonal partial least squares discriminant analysis (OPLS-DA), the VOC variations after gargling for each breath test group were obtained according to the combined criteria of variable importance in projection (VIP > 1.5), Wilcoxon signed-rank test (P < 0.05), and fold change (FC > 2.0). When gargled, the levels of indole, phenol, 1-propanol, and p-cresol in the breath of healthy people decreased; meanwhile, for esophageal cancer patients, the declined VOCs in breath were indole, phenol, dimethyl disulfide, and p-cresol. Particularly, these substances were previously reported as breath biomarkers in some diseases such as esophageal, gastric, thyroid, breast, oral, and lung cancers, as well as certain non-cancer disorders. The present work indicates that expiratory VOCs involve the prominent oral cavity source, and in the breath biomarkers study, the potential impact that originates from oral volatiles should be considered. In view of the present results, it is also proposed that gargle pretreatment could eliminate possible interference from the oral cavity VOCs that might benefit breath biomarker investigation. Gargle pretreatment helps to distinguish oral-source VOCs and control their potential impact on breath biomarkers.

PHF6 and JAK3 mutations cooperate to drive T-cell acute lymphoblastic leukemia progression.

T-cell acute lymphoblastic leukemia (T-ALL) is a malignant hematologic disease caused by gene mutations in T-cell progenitors. As an important epigenetic regulator, PHF6 mutations frequently coexist with JAK3 mutations in T-ALL patients. However, the role(s) of PHF6 mutations in JAK3-driven leukemia remain unclear. Here, the cooperation between JAK3 activation and PHF6 inactivation is examined in leukemia patients and in mice models. We found that the average survival time is shorter in patients with JAK/STAT and PHF6 comutation than that in other patients, suggesting a potential role of PHF6 in leukemia progression. We subsequently found that Phf6 deficiency promotes JAK3M511I-induced T-ALL progression in mice by inhibiting the Bai1-Mdm2-P53 signaling pathway, which is independent of the JAK3/STAT5 signaling pathway. Furthermore, combination therapy with a JAK3 inhibitor (tofacitinib) and a MDM2 inhibitor (idasanutlin) reduces the Phf6 KO and JAK3M511I leukemia burden in vivo. Taken together, our study suggests that combined treatment with JAK3 and MDM2 inhibitors may potentially increase the drug benefit for T-ALL patients with PHF6 and JAK3 comutation.

SETD5 modulates homeostasis of hematopoietic stem cells by mediating RNA Polymerase II pausing in cooperation with HCF-1.

SETD5 mutations were identified as the genetic causes of neurodevelopmental disorders. While the whole-body knockout of Setd5 in mice leads to embryonic lethality, the role of SETD5 in adult stem cell remains unexplored. Here, a critical role of Setd5 in hematopoietic stem cells (HSCs) is identified. Specific deletion of Setd5 in hematopoietic system significantly increased the number of immunophenotypic HSCs by promoting HSC proliferation. Setd5-deficient HSCs exhibited impaired long-term self-renewal capacity and multiple-lineage differentiation potentials under transplantation pressure. Transcriptome analysis of Setd5-deficient HSCs revealed a disruption of quiescence state of long-term HSCs, a cause of the exhaustion of functional HSCs. Mechanistically, SETD5 was shown to regulate HSC quiescence by mediating the release of promoter-proximal paused RNA polymerase II (Pol II) on E2F targets in cooperation with HCF-1 and PAF1 complex. Taken together, these findings reveal an essential role of SETD5 in regulating Pol II pausing-mediated maintenance of adult stem cells.

Loss of MBD2 attenuates MLL-AF9-driven leukemogenesis by suppressing the leukemic cell cycle via CDKN1C.

Acute myeloid leukemia (AML) is a deadly cancer characterized by an expanded self-renewal capacity that is associated with the accumulation of immature myeloid cells. Emerging evidence shows that methyl-CpG-binding domain protein 2 (MBD2), a DNA methylation reader, often participates in the transcriptional silencing of hypermethylated genes in cancer cells. Nevertheless, the role of MBD2 in AML remains unclear. Herein, by using an MLL-AF9 murine model and a human AML cell line, we observed that loss of MBD2 could delay the initiation and progression of leukemia. MBD2 depletion significantly reduced the leukemia burden by decreasing the proportion of leukemic stem cells (LSCs) and inhibiting leukemia cell proliferation in serial transplantation experiments, thereby allowing leukemic blasts to transition to a more mature state reflecting normal myelopoiesis. Both gene expression analyses and bioinformatic studies revealed that MBD2 negatively modulated genes related to myeloid differentiation, and was necessary to sustain the MLL-AF9 oncogene-induced gene program. We further demonstrated that MBD2 could promote LSC cell cycle progression through epigenetic regulation of CDKN1C transcription probably by binding to its promoter region. Taken together, our data suggest that MBD2 promotes AML development and could be a therapeutic target for myeloid malignancies.

Rheb1-Deficient Neutrophils Promote Hematopoietic Stem/Progenitor Cell Proliferation via Mesenchymal Stem Cells.

Myeloid cells have been identified as hematopoietic stem cell (HSC)-regulating cells. However, the mechanisms by which myeloid cells regulate the function of HSCs are not fully defined. Our previous study indicated that the HSCs are over-expanded in Vav1-Cre;Rheb1 f l/fl mice. Here, using in vivo and in vitro models, we found that Rheb1-deficient neutrophils remodeled the bone marrow environment and induced expansion of HSCs in vivo. Further studies showed that loss of Rheb1 impaired neutrophils' ability to secrete IL-6, led mesenchymal stem cells (MSCs) to produce more SCF, and promote HSC proliferation. We further found that IL-6 suppressed SCF mRNA expression in human MSCs. Interesting, the high level of IL-6 was also related with poor survival of chronic myeloid leukemia (CML) patients, and higher expression of IL-6 in CML cells is associated with the lower expression of SCF in MSCs in patients. Our studies suggested that blocking IL-6 signaling pathway might stimulate MSCs to secrete more SCF, and to support hematopoietic stem/progenitor cells proliferation.