Correlation between differentiation plasticity and mRNA expression profiling of CD34+-derived CD14− and CD14+ human normal myeloid precursors

The Role of BMP Signaling in Osteoclast Regulation

The osteogenic effects of Bone Morphogenetic Proteins (BMPs) were delineated in 1965 when Urist et al. showed that BMPs could induce ectopic bone formation. In subsequent decades, the effects of BMPs on bone formation and maintenance were established. BMPs induce proliferation in osteoprogenitor cells and increase mineralization activity in osteoblasts. The role of BMPs in bone homeostasis and repair led to the approval of BMP2 by the Federal Drug Administration (FDA) for anterior lumbar interbody fusion (ALIF) to increase the bone formation in the treated area. However, the use of BMP2 for treatment of degenerative bone diseases such as osteoporosis is still uncertain as patients treated with BMP2 results in the stimulation of not only osteoblast mineralization, but also osteoclast absorption, leading to early bone graft subsidence. The increase in absorption activity is the result of direct stimulation of osteoclasts by BMP2 working synergistically with the RANK signaling pathway. The dual effect of BMPs on bone resorption and mineralization highlights the essential role of BMP-signaling in bone homeostasis, making it a putative therapeutic target for diseases like osteoporosis. Before the BMP pathway can be utilized in the treatment of osteoporosis a better understanding of how BMP-signaling regulates osteoclasts must be established.

From Osteoclast Differentiation to Osteonecrosis of the Jaw: Molecular and Clinical Insights

Bone physiology relies on the delicate balance between resorption and formation of its tissue. Bone resorption depends on a process called osteoclastogenesis in which bone-resorbing cells, i.e., osteoclasts, are produced by the differentiation of more undifferentiated progenitors and precursors. This process is governed by two main factors, monocyte-colony stimulating factor (M-CSF) and receptor activator of NFκB ligand (RANKL). While the former exerts a proliferating effect on progenitors/precursors, the latter triggers a differentiation effect on more mature cells of the same lineage. Bone homeostasis requires a perfect space–time coordination of the involved signals. When osteoclastogenesis is poorly balanced with the differentiation of the bone forming counterparts, i.e., osteoblasts, physiological bone remodelling can turn into a pathological state, causing the systematic disruption of bone tissue which results in osteopenia or osteolysis. Examples of these conditions are represented by osteoporosis, Paget’s disease, bone metastasis, and multiple myeloma. Therefore, drugs targeting osteoclastogenesis, such as bisphosphonates and an anti-RANKL monoclonal antibody, have been developed and are currently used in the treatment of such diseases. Despite their demonstrated therapeutic efficacy, these agents are unfortunately not devoid of side effects. In this regard, a condition called osteonecrosis of the jaw (ONJ) has been recently correlated with anti-resorptive therapy. In this review we will address the involvement of osteoclasts and osteoclast-related factors in the pathogenesis of ONJ. It is to be hoped that a better understanding of the biological mechanisms underlying bone remodelling will help in the design a medical therapeutic approach for ONJ as an alternative to surgical procedures.

Transcription Factor MafB Suppresses Type I Interferon Production by CD14+ Monocytes in Patients With Chronic Hepatitis C

Transcription factor MafB regulates differentiation and activity of monocytes/macrophage and is associated with the development of atherosclerosis and cancers. However, the role of MafB in modulation of CD14⁺ monocytes in chronic viral hepatitis was not fully elucidated. Thus, the aim of current study was to investigate the immunoregulatory function of MafB to type I interferon (IFN) secretion by CD14⁺ monocytes and its contribution to pathogenesis of chronic hepatitis C virus (HCV) infection. A total of 29 chronic hepatitis C patients and 21 healthy individuals were enrolled. Serum IFN-α1 and IFN-β was measured by ELISA, while MafB mRNA and protein expression were assessed by real-time PCR and Western blot. MafB siRNA or MafB expression plasmid was transfected into purified CD14⁺ monocytes to suppress or increase MafB expression. The function of MafB siRNA transfected CD14⁺ monocytes to HCV in cell culture (HCVcc)-infected Huh7.5 cells or CD4⁺ T cells was also investigated in direct and indirect contact co-culture system. Serum IFN-α1 and IFN-β was robustly reduced in chronic hepatitis C patients. By contrast, MafB was notably elevated in chronic hepatitis C patients and negatively correlated with serum IFN-α1. Overexpression of MafB reduced the IFN-α1 production by CD14⁺ monocytes from healthy individuals. However, MafB inhibition elevated IFN-α1 secretion by CD14⁺ monocytes and interferon regulatory factor 3 phosphorylation in chronic hepatitis C. MafB inhibition also promoted CD14⁺ monocytes-induced viral clearance in HCVcc-infected Huh7.5 cells by up-regulation of IFN-α1 and IFN-β without increasingly destroying hepatocytes, however, did not affect CD14⁺ monocytes-induced CD4⁺ T cells differentiation in chronic hepatitis C patients. The current data revealed that overexpression of MafB in chronic hepatitis C patients might suppress type I IFN production by CD14⁺ monocytes, leading to the viral persistence. MafB might be a potential therapeutic target for treatment of chronic hepatitis C.

Neutrophilic Dermatoses Associated with Myeloid Malignancies

Neutrophilic dermatoses (ND) are a group of conditions characterized by an aseptic accumulation of polymorphonuclear leukocytes in the skin. Occurrence of ND in association with myeloid malignancies, mainly myelodysplastic syndrome and myelogenous acute leukemia, is not rare and is often associated with a poor prognosis. Recent findings have improved understanding of the pathophysiology of myeloid malignancy-associated ND. We review the clinical spectrum of myeloid malignancy-associated ND with an emphasis on recently identified mechanisms. Myeloid leukemia cells retain the potential for terminal differentiation into polymorphonuclear leukocytes in the skin. Many studies suggest a clonal link between myeloid malignancies and ND. Activation of autoinflammatory pathways (NOD-like receptor family pyrin domain-containing-3, Familial Mediterranean Fever Gene) in the clonal cells of myeloid disorders may also be involved in this setting.

Physiological expression of miR-130a during differentiation of CD34+ human hematopoietic stem cells results in the inhibition of monocyte differentiation

MicroRNAs (miRNA) are small noncoding RNAs that regulate gene expression by targeting mRNAs in a sequence specific manner, thereby determining their degradation or inhibiting translation. They are involved in processes such as proliferation, differentiation and apoptosis by fine-tuning the expression of genes underlying such events. The expression of specific miRNAs is involved in hematopoietic differentiation and their deregulation contributes to the development of hematopoietic malignancies such as acute myeloid leukemia (AML). miR-130a is over-expressed in AML. Here we show that miR-130a is physiologically expressed in myeloblasts and down-regulated during monocyte differentiation. Gain- and loss-of-function experiments performed on CD34⁺ human hematopoietic stem cells confirmed that expression of miR-130a inhibits monocyte differentiation by interfering with the expression of key transcription factors HOXA10, IRF8, KLF4, MAFB and PU-1. The data obtained in this study highlight that the correct modulation of miR-130a is necessary for normal differentiation to occur and confirming that deregulation of this miRNA might underlie the differentiation block occurring in AML.

Magnesium Is a Key Regulator of the Balance between Osteoclast and Osteoblast Differentiation in the Presence of Vitamin D₃

Magnesium (Mg) is crucial for bone health. Low concentrations of Mg inhibit the activity of osteoblasts while promoting that of osteoclasts, with the final result of inducing osteopenia. Conversely, little is known about the effects of high concentrations of extracellular Mg on osteoclasts and osteoblasts. Since the differentiation and activation of these cells is coordinated by vitamin D₃ (VD3), we investigated the effects of high extracellular Mg, as well as its impact on VD3 activity, in these cells. U937 cells were induced to osteoclastic differentiation by VD3 in the presence of supra-physiological concentrations (>1 mM) of extracellular Mg. The effect of high Mg concentrations was also studied in human bone-marrow-derived mesenchymal stem cells (bMSCs) induced to differentiate into osteoblasts by VD3. We demonstrate that high extra-cellular Mg levels potentiate VD3-induced osteoclastic differentiation, while decreasing osteoblastogenesis. We hypothesize that Mg might reprogram VD3 activity on bone remodeling, causing an unbalanced activation of osteoclasts and osteoblasts.

Chromosome positioning in interphase nuclei of hematopoietic stem cell and myeloid precursor

Human myelopoiesis is an intriguing biological process during which multipotent stem cells limit their differentiation potential generating precursors that evolve into terminally differentiated cells. The differentiation process is correlated with differential gene expression and changes in nuclear architecture. In interphase, chromosomes are distinct entities known as chromosome territories and they show a radial localization that could result in a constrain of inter-homologous distance. This element plays a role in genome stability and gene expression. Here, we provide the first experimental evidence of 3D chromosomal arrangement considering two steps of human normal myelopoiesis. Specifically, multicolor 3D-FISH and 3D image analysis revealed that, in both normal human hematopoietic stem cells and myelod precursors CD14-, chromosomal position is correlated with gene density. However, we observed that inter-homologue distances are totally different during differentiation. This could be associated with differential gene expression that we found comparing the two cell types. Our results disclose an unprecedented framework relevant for deciphering the genomic mechanisms at the base of normal human myelopoiesis.

MafB promotes atherosclerosis by inhibiting foam-cell apoptosis

MafB is a transcription factor that induces myelomonocytic differentiation. However, the precise role of MafB in the pathogenic function of macrophages has never been clarified. Here we demonstrate that MafB promotes hyperlipidemic atherosclerosis by suppressing foam-cell apoptosis. Our data show that MafB is predominantly expressed in foam cells found within atherosclerotic lesions, where MafB mediates the oxidized LDL-activated LXR/RXR-induced expression of apoptosis inhibitor of macrophages (AIM). In the absence of MafB, activated LXR/RXR fails to induce the expression of AIM, a protein that is normally responsible for protecting macrophages from apoptosis; thus, Mafb-deficient macrophages are prone to apoptosis. Haematopoietic reconstitution with Mafb-deficient fetal liver cells in recipient LDL receptor-deficient hyperlipidemic mice revealed accelerated foam-cell apoptosis, which subsequently led to the attenuation of the early atherogenic lesion. These findings represent the first evidence that the macrophage-affiliated MafB transcription factor participates in the acceleration of atherogenesis.

Remodeling of nuclear landscapes during human myelopoietic cell differentiation maintains co-aligned active and inactive nuclear compartments

Background

Previous studies of higher order chromatin organization in nuclei of mammalian species revealed both structural consistency and species-specific differences between cell lines and during early embryonic development. Here, we extended our studies to nuclear landscapes in the human myelopoietic lineage representing a somatic cell differentiation system. Our longterm goal is a search for structural features of nuclei, which are restricted to certain cell types/species, as compared to features, which are evolutionary highly conserved, arguing for their basic functional roles in nuclear organization.

Results

Common human hematopoietic progenitors, myeloid precursor cells, differentiated monocytes and granulocytes analyzed by super-resolution fluorescence microscopy and electron microscopy revealed profound differences with respect to global chromatin arrangements, the nuclear space occupied by the interchromatin compartment and the distribution of nuclear pores. In contrast, we noted a consistent organization in all cell types with regard to two co-aligned networks, an active (ANC) and an inactive (INC) nuclear compartment delineated by functionally relevant hallmarks. The ANC is enriched in active RNA polymerase II, splicing speckles and histone signatures for transcriptionally competent chromatin (H3K4me3), whereas the INC carries marks for repressed chromatin (H3K9me3).

Conclusions

Our findings substantiate the conservation of the recently published ANC-INC network model of mammalian nuclear organization during human myelopoiesis irrespective of profound changes of the global nuclear architecture observed during this differentiation process. According to this model, two spatially co-aligned and functionally interacting active and inactive nuclear compartments (ANC and INC) pervade the nuclear space.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-015-0038-0) contains supplementary material, which is available to authorized users.

MafB is a downstream target of the IL-10/STAT3 signaling pathway, involved in the regulation of macrophage de-activation

In spite of the numerous reports implicating MafB transcription factor in the molecular control of monocyte-macrophage differentiation, the precise genetic program underlying this activity has been, to date, poorly understood. To clarify this issue, we planned a number of experiments that were mainly conducted on human primary macrophages. In this regard, a preliminary gene function study, based on MafB inactivation and over-expression, indicated MMP9 and IL-7R genes as possible targets of the investigated transcription factor. Bioinformatics analysis of their promoter regions disclosed the presence of several putative MARE elements and a combined approach of EMSA and luciferase assay subsequently demonstrated that expression of both genes is indeed activated by MafB through a direct transcription mechanism. Additional investigation, performed with similar procedures to elucidate the biological relevance of our observation, revealed that MafB is a downstream target of the IL-10/STAT3 signaling pathway, normally inducing the macrophage de-activation process. Taken together our data support the existence of a signaling cascade by which stimulation of macrophages with the IL-10 cytokine determines a sequential activation of STAT3 and MafB transcription factors, in turn leading to an up-regulated expression of MMP9 and IL-7R genes.

The plasticity and potential of leukemia cell lines to differentiate into dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells that orchestrate the innate and adaptive immune systems to induce immunity. DCs are significant in maintaining immune tolerance towards self-antigens, organ transplantation and allergic responses. DCs are powerful adjuvants for eliciting T-cell immunity and are therefore considered primary targets for inducing immune responses in the prevention and treatment of infectious diseases and cancer. DCs have been increasingly applied in the immunotherapy of cancer worldwide during the last decade; however, a number of the highly specialized biological characteristics of DCs remain to be elucidated. Previous studies of human DCs have been constrained by certain difficulties, therefore the majority of studies have been carried out using in vitro model systems. Suitable cell lines with dendritic-like properties may provide valuable tools for the study of DC physiology and pathology. In the current review, various human DC line differentiation models are discussed. Certain cell lines provide valuable tools for studying the specific aspects of DC biology, despite variations in cell biological and immunological features when compared with primary DCs.

Integrated analysis of microRNA and mRNA expression profiles in physiological myelopoiesis: role of hsa-mir-299-5p in CD34+ progenitor cells commitment

Hematopoiesis entails a series of hierarchically organized events that proceed throughout cell specification and terminates with cell differentiation. Commitment needs the transcription factors' effort, which, in concert with microRNAs, drives cell fate and responds to promiscuous patterns of gene expression by turning on lineage-specific genes and repressing alternate lineage transcripts. We obtained microRNA profiles from human CD34+ hematopoietic progenitor cells and in vitro differentiated erythroblasts, megakaryoblasts, monoblasts and myeloblast precursors that we analyzed together with their gene expression profiles. The integrated analysis of microRNA-mRNA expression levels highlighted an inverse correlation between microRNAs specifically upregulated in one single-cell progeny and their putative target genes, which resulted in downregulation. Among the upregulated lineage-enriched microRNAs, hsa-miR-299-5p emerged as having a role in controlling CD34+ progenitor fate, grown in multilineage culture conditions. Gain- and loss-of-function experiments revealed that hsa-miR-299-5p participates in the regulation of hematopoietic progenitor fate, modulating megakaryocytic-granulocytic versus erythroid-monocytic differentiation.

ZFP36L1 negatively regulates erythroid differentiation of CD34+ hematopoietic stem cells by interfering with the Stat5b pathway

ZFP36L1 is a member of a family of CCCH tandem zinc finger proteins (TTP family) able to bind to AU-rich elements in the 3'-untranslated region of mRNAs, thereby triggering their degradation. The present study suggests that such mechanism is used during hematopoiesis to regulate differentiation by posttranscriptionally modulating the expression of specific target genes. In particular, it demonstrates that ZFP36L1 negatively regulates erythroid differentiation by directly binding the 3' untranslated region of Stat5b encoding mRNA. Stat5b down-regulation obtained by ZFP36L1 overexpression results, in human hematopoietic progenitors, in a drastic decrease of erythroid colonies formation. These observations have been confirmed by silencing experiments targeting Stat5b and by treating hematopoietic stem/progenitor cells with drugs able to induce ZFP36L1 expression. Moreover, this study shows that different members of ZFP36L1 family act redundantly, because cooverexpression of ZFP36L1 and family member ZFP36 determines a cumulative effect on Stat5b down-regulation. This work describes a mechanism underlying ZFP36L1 capability to regulate hematopoietic differentiation and suggests a new target for the therapy of hematopoietic diseases involving Stat5b/JAK2 pathway, such as chronic myeloproliferative disorders.

c-myb supports erythropoiesis through the transactivation of KLF1 and LMO2 expression

The c-myb transcription factor is highly expressed in immature hematopoietic cells and down-regulated during differentiation. To define its role during the hematopoietic lineage commitment, we silenced c-myb in human CD34(+) hematopoietic stem/progenitor cells. Noteworthy, c-myb silencing increased the commitment capacity toward the macrophage and megakaryocyte lineages, whereas erythroid differentiation was impaired, as demonstrated by clonogenic assay, morphologic and immunophenotypic data. Gene expression profiling and computational analysis of promoter regions of genes modulated in c-myb-silenced CD34(+) cells identified the transcription factors Kruppel-Like Factor 1 (KLF1) and LIM Domain Only 2 (LMO2) as putative targets, which can account for c-myb knockdown effects. Indeed, chromatin immunoprecipitation and luciferase reporter assay demonstrated that c-myb binds to KLF1 and LMO2 promoters and transactivates their expression. Consistently, the retroviral vector-mediated overexpression of either KLF1 or LMO2 partially rescued the defect in erythropoiesis caused by c-myb silencing, whereas only KLF1 was also able to repress the megakaryocyte differentiation enhanced in Myb-silenced CD34(+) cells. Our data collectively demonstrate that c-myb plays a pivotal role in human primary hematopoietic stem/progenitor cells lineage commitment, by enhancing erythropoiesis at the expense of megakaryocyte diffentiation. Indeed, we identified KLF1 and LMO2 transactivation as the molecular mechanism underlying Myb-driven erythroid versus megakaryocyte cell fate decision.

PPARdelta is a ligand-dependent negative regulator of vitamin D3-induced monocyte differentiation

A number of reports indicate that peroxisome proliferator-activated receptor (PPAR) delta is involved in the molecular control of monocyte-macrophage differentiation. In this regard, the recent demonstration that PPARdelta is a primary response gene of 1alpha,25-dihydroxyvitamin D3 (VD), i.e. a powerful inducer of such process, allowed us to hypothesize the existence of a cross talk between PPARdelta and VD receptor pathways. To address this issue, we analyzed the effects promoted by stimulation with PPARdelta ligands and by overexpression of this nuclear receptor in monoblastic cell lines undergoing exposure to VD. The results obtained evidenced that, although promoting a weak differentiation effect by themselves, PPARdelta ligands efficiently co-operated with VD treatment. In spite of this, PPARdelta overexpression exerted a remarkable inhibitory effect on monocyte-macrophage differentiation induced by VD that was, at least partly, reverted by stimulation with a highly specific PPARdelta ligand. These data indicate that, although acting through a ligand-dependent modality, PPARdelta is a negative regulator of VD-mediated monocyte differentiation, allowing us to hypothesize a role of the investigated nuclear receptor in the differentiation block of M5 type (monoblastic) acute myeloid leukemias (AMLs). Bioinformatic analysis of a microarray database, containing the expression profiles of 285 AML cases, further supported this hypothesis demonstrating the existence of a subset of M5 type (monoblastic) AMLs that overexpress PPARdelta gene.

The vitamin D3/Hox-A10 pathway supports MafB function during the monocyte differentiation of human CD34+ hemopoietic progenitors

Although a considerable number of reports indicate an involvement of the Hox-A10 gene in the molecular control of hemopoiesis, the conclusions of such studies are quite controversial given that they support, in some cases, a role in the stimulation of stem cell self-renewal and myeloid progenitor expansion, whereas in others they implicate this transcription factor in the induction of monocyte-macrophage differentiation. To clarify this issue, we analyzed the biological effects and the transcriptome changes determined in human primary CD34(+) hemopoietic progenitors by retroviral transduction of a full-length Hox-A10 cDNA. The results obtained clearly indicated that this homeogene is an inducer of monocyte differentiation, at least partly acting through the up-regulation of the MafB gene, recently identified as the master regulator of such a maturation pathway. By using a combined approach based on computational analysis, EMSA experiments, and luciferase assays, we were able to demonstrate the presence of a Hox-A10-binding site in the promoter region of the MafB gene, which suggested the likely molecular mechanism underlying the observed effect. Stimulation of the same cells with the vitamin D(3) monocyte differentiation inducer resulted in a clear increase of Hox-A10 and MafB transcripts, indicating the existence of a precise transactivation cascade involving vitamin D(3) receptor, Hox-A10, and MafB transcription factors. Altogether, these data allow one to conclude that the vitamin D(3)/Hox-A10 pathway supports MafB function during the induction of monocyte differentiation.

Genomic expression during human myelopoiesis

Background

Human myelopoiesis is an exciting biological model for cellular differentiation since it represents a plastic process where multipotent stem cells gradually limit their differentiation potential, generating different precursor cells which finally evolve into distinct terminally differentiated cells. This study aimed at investigating the genomic expression during myeloid differentiation through a computational approach that integrates gene expression profiles with functional information and genome organization.

Results

Gene expression data from 24 experiments for 8 different cell types of the human myelopoietic lineage were used to generate an integrated myelopoiesis dataset of 9,425 genes, each reliably associated to a unique genomic position and chromosomal coordinate. Lists of genes constitutively expressed or silent during myelopoiesis and of genes differentially expressed in commitment phase of myelopoiesis were first identified using a classical data analysis procedure. Then, the genomic distribution of myelopoiesis genes was investigated integrating transcriptional and functional characteristics of genes. This approach allowed identifying specific chromosomal regions significantly highly or weakly expressed, and clusters of differentially expressed genes and of transcripts related to specific functional modules.

Conclusion

The analysis of genomic expression during human myelopoiesis using an integrative computational approach allowed discovering important relationships between genomic position, biological function and expression patterns and highlighting chromatin domains, including genes with coordinated expression and lineage-specific functions.

Dendritic cells and myeloid leukaemias: plasticity and commitment in cell differentiation

Dendritic cells (DCs) are key antigen-presenting cells (APCs), which link innate and adaptive immunity, ultimately activating antigen-specific T cells. This review examines the relationship between the acute and chronic myeloid leukaemias and cells with DC properties. DCs are non-dividing terminally differentiated cells, and ex vivo leukaemic cells or cell lines show little similarity to DCs. However, many leukaemias differentiate further in response to defined stimuli, and retain a degree of lineage plasticity. Therefore, several studies have explored the response of leukaemic cells to the in vitro regimens used to differentiate ex vivo primary DCs. Recent data suggest that the most 'dendritic-like' cells can be derived from more undifferentiated myeloid leukaemias, such as the myelomonocytic Mutz-3 cell line. These findings have important implications for understanding the developmental origins of DCs, for harnessing the APC properties of this class of tumour to stimulate the therapeutic anti-tumour immunity, and for developing useful models for the study of human DC physiology and pathology. There is a strong rationale for further exploration of this class of tumour and its relationship to the normal DC.

Tfe3 expression is closely associated to macrophage terminal differentiation of human hematopoietic myeloid precursors

The MItf-Tfe family of basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factors encodes four family members: MItf, Tfe3, TfeB and TfeC. In vitro, each protein of the family binds DNA in a homo- or heterodimeric form with other family members. Tfe3 is involved in chromosomal translocations recurrent in different tumors and it has been demonstrated, by in vivo studies, that it plays, redundantly with MItf, an important role in the process of osteoclast formation, in particular during the transition from mono-nucleated to multi-nucleated osteoclasts. Since mono-nucleated osteoclasts derive from macrophages we investigated whether Tfe3 might play a role upstream during hematopoietic differentiation. Here we show that Tfe3 is able to induce mono-macrophagic differentiation of U937 cells, in association with a decrease of cell proliferation and an increase of apoptosis. We also show that Tfe3 does not act physiologically during commitment of CD34+ hematopoietic stem cells (HSCs), since it is not able to direct HSCs toward a specific lineage as observed by clonogenic assay, but is a strong actor of terminal differentiation since it allows human primary myeloblasts' maturation toward the macrophage lineage.

Identification of a molecular signature predictive of sensitivity to differentiation induction in acute myeloid leukemia

Acute myeloid leukemia (AML) blasts are immature committed myeloid cells unable to spontaneously undergo terminal maturation, and characterized by heterogeneous sensitivity to natural differentiation inducers. Here, we show a molecular signature predicting the resistance or sensitivity of six myeloid cell lines to differentiation induced in vitro with retinoic acid or vitamin D. The identified signature was further validated by TaqMan assay for the prediction of response to an in vitro differentiation assay performed on 28 freshly isolated AML blast populations. The TaqMan assay successfully predicts the in vitro resistance or responsiveness of AML blasts to differentiation inducers. Furthermore, performing a meta-analysis of publicly available microarray data sets, we also show the accuracy of our prediction on known phenotypes and suggest that our signature could become useful for the identification of patients eligible for new therapeutic strategies.

Virally mediated MafB transduction induces the monocyte commitment of human CD34+ hematopoietic stem/progenitor cells

Upregulation of specific transcription factors is a generally accepted mechanism to explain the commitment of hematopoietic stem cells along precise maturation lineages. Based on this premise, transduction of primary hematopoietic stem/progenitor cells with viral vectors containing the investigated transcription factors appears as a suitable experimental model to identify such regulators. Although MafB transcription factor is believed to play a role in the regulation of monocytic commitment, no demonstration is, to date, available supporting this function in normal human hematopoiesis. To address this issue, we retrovirally transduced cord blood CD34+ hematopoietic progenitors with a MafB cDNA. Immunophenotypic and morphological analysis of transduced cells demonstrated the induction of a remarkable monomacrophage differentiation. Microarray analysis confirmed these findings and disclosed the upregulation of macrophage-related transcription factors belonging to the AP-1, MAF, PPAR and MiT families. Altogether our data allow to conclude that MafB is a key regulator of human monocytopoiesis.