C/EBPalpha directs monocytic commitment of primary myeloid progenitors

Transcription factor C/EBPα is required for the development of Ly6Chi monocytes but not Ly6Clo monocytes

Monocytes comprise two major subsets, Ly6Chi classical monocytes and Ly6Clo nonclassical monocytes. Notch2 signaling in Ly6Chi monocytes triggers transition to Ly6Clo monocytes, which require Nr4a1, Bcl6, Irf2, and Cebpb. By comparison, less is known about transcriptional requirements for Ly6Chi monocytes. We find transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα) is highly expressed in Ly6Chi monocytes, but down-regulated in Ly6Clo monocytes. A few previous studies described the requirement of C/EBPα in the development of neutrophils and eosinophils. However, the role of C/EBPα for in vivo monocyte development has not been understood. We deleted the Cebpa +37 kb enhancer in mice, eliminating hematopoietic expression of C/EBPα, reproducing the expected neutrophil defect. Surprisingly, we also found a severe and selective loss of Ly6Chi monocytes, while preserving Ly6Clo monocytes. We find that BM progenitors from Cebpa +37-/- mice rapidly progress through the monocyte progenitor stage to develop directly into Ly6Clo monocytes even in the absence of Notch2 signaling. These results identify a previously unrecognized role for C/EBPα in maintaining Ly6Chi monocyte identity.

From Genotype to Phenotype: How Enhancers Control Gene Expression and Cell Identity in Hematopoiesis

Blood comprises a wide array of specialized cells, all of which share the same genetic information and ultimately derive from the same precursor, the hematopoietic stem cell (HSC). This diversity of phenotypes is underpinned by unique transcriptional programs gradually acquired in the process known as hematopoiesis. Spatiotemporal regulation of gene expression depends on many factors, but critical among them are enhancers-sequences of DNA that bind transcription factors and increase transcription of genes under their control. Thus, hematopoiesis involves the activation of specific enhancer repertoires in HSCs and their progeny, driving the expression of sets of genes that collectively determine morphology and function. Disruption of this tightly regulated process can have catastrophic consequences: in hematopoietic malignancies, dysregulation of transcriptional control by enhancers leads to misexpression of oncogenes that ultimately drive transformation. This review attempts to provide a basic understanding of enhancers and their role in transcriptional regulation, with a focus on normal and malignant hematopoiesis. We present examples of enhancers controlling master regulators of hematopoiesis and discuss the main mechanisms leading to enhancer dysregulation in leukemia and lymphoma.

Stage-specific action of Runx1 and GATA3 controls silencing of PU.1 expression in mouse pro-T cells

PU.1 (encoded by Spi1), an ETS-family transcription factor with many hematopoietic roles, is highly expressed in the earliest intrathymic T cell progenitors but must be down-regulated during T lineage commitment. The transcription factors Runx1 and GATA3 have been implicated in this Spi1 repression, but the basis of the timing was unknown. We show that increasing Runx1 and/or GATA3 down-regulates Spi1 expression in pro-T cells, while deletion of these factors after Spi1 down-regulation reactivates its expression. Leveraging the stage specificities of repression and transcription factor binding revealed an unconventional but functional site in Spi1 intron 2. Acute Cas9-mediated deletion or disruption of the Runx and GATA motifs in this element reactivates silenced Spi1 expression in a pro-T cell line, substantially more than disruption of other candidate elements, and counteracts the repression of Spi1 in primary pro-T cells during commitment. Thus, Runx1 and GATA3 work stage specifically through an intronic silencing element in mouse Spi1 to control strength and maintenance of Spi1 repression during T lineage commitment.

The AML-associated K313 mutation enhances C/EBPα activity by leading to C/EBPα overexpression

Mutations in the transcription factor C/EBPα are found in ~10% of all acute myeloid leukaemia (AML) cases but the contribution of these mutations to leukemogenesis is incompletely understood. We here use a mouse model of granulocyte progenitors expressing conditionally active HoxB8 to assess the cell biological and molecular activity of C/EBPα-mutations associated with human AML. Both N-terminal truncation and C-terminal AML-associated mutations of C/EBPα substantially altered differentiation of progenitors into mature neutrophils in cell culture. Closer analysis of the C/EBPα-K313-duplication showed expansion and prolonged survival of mutant C/EBPα-expressing granulocytes following adoptive transfer into mice. C/EBPα-protein containing the K313-mutation further showed strongly enhanced transcriptional activity compared with the wild-type protein at certain promoters. Analysis of differentially regulated genes in cells overexpressing C/EBPα-K313 indicates a strong correlation with genes regulated by C/EBPα. Analysis of transcription factor enrichment in the differentially regulated genes indicated a strong reliance of SPI1/PU.1, suggesting that despite reduced DNA binding, C/EBPα-K313 is active in regulating target gene expression and acts largely through a network of other transcription factors. Strikingly, the K313 mutation caused strongly elevated expression of C/EBPα-protein, which could also be seen in primary K313 mutated AML blasts, explaining the enhanced C/EBPα activity in K313-expressing cells.

PU.1 Mimic Synthetic Peptides Selectively Bind with GATA-1 and Allow c-Jun PU.1 Binding to Enhance Myelopoiesis

BACKGROUND

Hematopoietic stem cells' commitment to myelopoiesis builds immunity to prevent infection. This process is controlled through transcription factor, especially Purine rich box 1 (PU.1) protein, which plays a central role in regulating myelopoiesis. The β3/β4 region of PU.1 accommodates a coactivator transcription factor, c-Jun, to activate myelopoiesis. However, an erythroid transcription factor, GATA-1, competes with c-Jun for the β3/β4 region, abolishing myelopoiesis and promoting erythropoiesis. This competitive regulation decides the hematopoietic stem cells' commitment towards either erythroid or myeloid lineage.

METHODS

Therefore, this study investigated the in vitro and in vivo effect of novel synthetic PU.1 β3/β4 mimic peptide analogs and peptide-loaded hydrophilic poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles.

RESULTS

The designed peptides significantly increase the expression of corresponding myeloid markers, specifically CD33 in vitro. However, the in vivo delivery of peptide-loaded PLGA nanoparticles, which have sustained release effect of peptides, increases 10.8% of granulocytes as compared to control.

CONCLUSION

The observations showed that the fabricated nanoparticles protected the loaded peptides from the harsh intracellular environment for a longer duration without causing any toxicity. These findings highlight the possibility to use these peptides and peptide-loaded nanoparticles to increase hematopoietic stem cell commitment to myeloid cells in case of opportunistic infection.

Sparsely-connected autoencoder (SCA) for single cell RNAseq data mining

Single-cell RNA sequencing (scRNAseq) is an essential tool to investigate cellular heterogeneity. Thus, it would be of great interest being able to disclose biological information belonging to cell subpopulations, which can be defined by clustering analysis of scRNAseq data. In this manuscript, we report a tool that we developed for the functional mining of single cell clusters based on Sparsely-Connected Autoencoder (SCA). This tool allows uncovering hidden features associated with scRNAseq data. We implemented two new metrics, QCC (Quality Control of Cluster) and QCM (Quality Control of Model), which allow quantifying the ability of SCA to reconstruct valuable cell clusters and to evaluate the quality of the neural network achievements, respectively. Our data indicate that SCA encoded space, derived by different experimentally validated data (TF targets, miRNA targets, Kinase targets, and cancer-related immune signatures), can be used to grasp single cell cluster-specific functional features. In our implementation, SCA efficacy comes from its ability to reconstruct only specific clusters, thus indicating only those clusters where the SCA encoding space is a key element for cells aggregation. SCA analysis is implemented as module in rCASC framework and it is supported by a GUI to simplify it usage for biologists and medical personnel.

Myeloid transformation by MLL-ENL depends strictly on C/EBP

Chromosomal rearrangements of the mixed-lineage leukemia gene MLL1 are the hallmark of infant acute leukemia. The granulocyte-macrophage progenitor state forms the epigenetic basis for myelomonocytic leukemia stemness and transformation by MLL-type oncoproteins. Previously, it was shown that the establishment of murine myelomonocytic MLL-ENL transformation, but not its maintenance, depends on the transcription factor C/EBPα, suggesting an epigenetic hit-and-run mechanism of MLL-driven oncogenesis. Here, we demonstrate that compound deletion of Cebpa/Cebpb almost entirely abrogated the growth and survival of MLL-ENL-transformed cells. Rare, slow-growing, and apoptosis-prone MLL-ENL-transformed escapees were recovered from compound Cebpa/Cebpb deletions. The escapees were uniformly characterized by high expression of the resident Cebpe gene, suggesting inferior functional compensation of C/EBPα/C/EBPβ deficiency by C/EBPε. Complementation was augmented by ectopic C/EBPβ expression and downstream activation of IGF1 that enhanced growth. Cebpe gene inactivation was accomplished only in the presence of complementing C/EBPβ, but not in its absence, confirming the Cebpe dependency of the Cebpa/Cebpb double knockouts. Our data show that MLL-transformed myeloid cells are dependent on C/EBPs during the initiation and maintenance of transformation.

Natural HDAC-1/8 inhibitor baicalein exerts therapeutic effect in CBF-AML

BACKGROUND

Although targeting histone deacetylases (HDACs) may be an effective strategy for core binding factor-acute myeloid leukemia (CBF-AML) harboring t(8;21) or inv(16), HDAC inhibitors are reported to be limited by drug-resistant characteristic. Our purpose is to evaluate the anti-leukemia effects of Baicalein on CBF-AML and clarify its underlying mechanism.

METHODS

Enzyme activity assay was used to measure the activity inhibition of HDACs. Rhodamine123 and RT-qPCR were employed to evaluate the distribution of drugs and the change of ATP-binding cassette (ABC) transporter genes. CCK8, Annexin V/PI, and FACS staining certified the effects of Baicalein on cell growth, apoptosis, and differentiation. Duolink and IP assay assessed the interaction between HDAC-1 and ubiquitin, HSP90 and AML1-ETO, and Ac-p53 and CBFβ-MYH11. AML cell lines and primary AML cells-bearing NOD/SCID mice models were used to evaluate the anti-leukemic efficiency and potential mechanism of Baicalein in vivo.

RESULTS

Baicalein showed HDAC-1/8 inhibition to trigger growth suppression and differentiation induction of AML cell lines and primary AML cells. Although the inhibitory action on HDAC-1 was mild, Baicalein could induce the degradation of HDAC-1 via ubiquitin proteasome pathway, thereby upregulating the acetylation of Histone H3 without promoting ABC transporter genes expression. Meanwhile, Baicalein increased the acetylation of HSP90 and lessened its connection to AML1/ETO, consequently leading to degradation of AML1-ETO in t(8;21)q(22;22) AML cells. In inv(16) AML cells, Baicalein possessed the capacity of apoptosis induction accompanied with p53-mediated apoptosis genes expression. Moreover, CBFβ-MYH11-bound p53 acetylation was restored via HDAC-8 inhibition induced by Baicalein contributing the diminishing of survival of CD34+  inv(16) AML cells.

CONCLUSIONS

These findings improved the understanding of the epigenetic regulation of Baicalein, and warrant therapeutic potential of Baicalein for CBF-AML.

Gefitinib and Afatinib Show Potential Efficacy for Fanconi Anemia-Related Head and Neck Cancer

PURPOSE

Fanconi anemia rare disease is characterized by bone marrow failure and a high predisposition to solid tumors, especially head and neck squamous cell carcinoma (HNSCC). Patients with Fanconi anemia with HNSCC are not eligible for conventional therapies due to high toxicity in healthy cells, predominantly hematotoxicity, and the only treatment currently available is surgical resection. In this work, we searched and validated two already approved drugs as new potential therapies for HNSCC in patients with Fanconi anemia.

EXPERIMENTAL DESIGN

We conducted a high-content screening of 3,802 drugs in a FANCA-deficient tumor cell line to identify nongenotoxic drugs with cytotoxic/cytostatic activity. The best candidates were further studied in vitro and in vivo for efficacy and safety.

RESULTS

Several FDA/European Medicines Agency (EMA)-approved anticancer drugs showed cancer-specific lethality or cell growth inhibition in Fanconi anemia HNSCC cell lines. The two best candidates, gefitinib and afatinib, EGFR inhibitors approved for non-small cell lung cancer (NSCLC), displayed nontumor/tumor IC₅₀ ratios of approximately 400 and approximately 100 times, respectively. Neither gefitinib nor afatinib activated the Fanconi anemia signaling pathway or induced chromosomal fragility in Fanconi anemia cell lines. Importantly, both drugs inhibited tumor growth in xenograft experiments in immunodeficient mice using two Fanconi anemia patient-derived HNSCCs. Finally, in vivo toxicity studies in Fanca-deficient mice showed that administration of gefitinib or afatinib was well-tolerated, displayed manageable side effects, no toxicity to bone marrow progenitors, and did not alter any hematologic parameters.

CONCLUSIONS

Our data present a complete preclinical analysis and promising therapeutic line of the first FDA/EMA-approved anticancer drugs exerting cancer-specific toxicity for HNSCC in patients with Fanconi anemia.

Transcriptional regulation of neutrophil differentiation and function during inflammation

Neutrophils are the most abundant leukocytes in innate immunity where they elicit powerful effector functions to eliminate invading pathogens and modulate the adaptive as well as the innate immune response. Neutrophil function must be tightly regulated during inflammation and infection to avoid additional tissue damage. Increasing evidence suggests that transcription factors (TFs) function as key regulators to modulate transcriptional output, thereby controlling cell fate decision and the inflammatory responses. However, the molecular mechanisms underlying neutrophil differentiation and function during inflammation remain largely uncharacterized. Here, we provide a comprehensive overview of TFs known to be crucial for neutrophil maturation and in the signaling pathways that control neutrophil differentiation and activation. We also outline how emerging genomic and single-cell technologies may facilitate further discovery of neutrophil transcriptional regulators.

Lymphatic Endothelial Cell Progenitors in the Tumor Microenvironment

Tumor lymphatics play a key role in cancer progression as they are solely responsible for transporting malignant cells to regional lymph nodes (LNs), a process that precedes and promotes systemic lethal spread. It is broadly accepted that tumor lymphatic sprouting is induced mainly by soluble factors derived from tumor-associated macrophages (TAMs) and malignant cells. However, emerging evidence strongly suggests that a subset of TAMs, myeloid-lymphatic endothelial cell progenitors (M-LECP), also contribute to the expansion of lymphatics through both secretion of paracrine factors and a self-autonomous mode. M-LECP are derived from bone marrow (BM) precursors of the monocyte-macrophage lineage and characterized by unique co-expression of markers identifying lymphatic endothelial cells (LEC), stem cells, M2-type macrophages, and myeloid-derived immunosuppressive cells. This review describes current evidence for the origin of M-LECP in the bone marrow, their recruitment tumors and intratumoral trafficking, similarities to other TAM subsets, and mechanisms promoting tumor lymphatics. We also describe M-LECP integration into preexisting lymphatic vessels and discuss potential mechanisms and significance of this event. We conclude that improved mechanistic understanding of M-LECP functions within the tumor environment may lead to new therapeutic approaches to suppress tumor lymphangiogenesis and metastasis to lymph nodes.

Dynamic control of the T-cell specification gene regulatory network

Specification of multipotent blood precursor cells in postnatal mice to become committed T-cell precursors involves a gene regulatory network of several interacting but functionally distinct modules. Many links of this network have been defined by perturbation tests and by functional genomics. However, using the network model to predict real-life kinetics of the commitment process is still difficult, partly due to the tenacity of repressive chromatin states, and to the ability of transcription factors to affect each other's binding site choices through competitive recruitment to alternative sites ("coregulator theft"). To predict kinetics, future models will need to incorporate mechanistic information about chromatin state change dynamics and more sophisticated understanding of the proteomics and cooperative DNA site choices of transcription factor complexes.

The Endless Saga of Monocyte Diversity

Cancer immunotherapy relies on either restoring or activating the function of adaptive immune cells, mainly CD8⁺ T lymphocytes. Despite impressive clinical success, cancer immunotherapy remains ineffective in many patients due to the establishment of tumor resistance, largely dependent on the nature of tumor microenvironment. There are several cellular and molecular mechanisms at play, and the goal is to identify those that are clinically significant. Among the hematopoietic-derived cells, monocytes are endowed with high plasticity, responsible for their pro- and anti-tumoral function. Indeed, monocytes are involved in several cancer-associated processes such as immune-tolerance, metastatic spread, neoangiogenesis, and chemotherapy resistance; on the other hand, by presenting cancer-associated antigens, they can also promote and sustain anti-tumoral T cell response. Recently, by high throughput technologies, new findings have revealed previously underappreciated, profound transcriptional, epigenetic, and metabolic differences among monocyte subsets, which complement and expand our knowledge on the monocyte ontogeny, recruitment during steady state, and emergency hematopoiesis, as seen in cancer. The subdivision into discrete monocytes subsets, both in mice and humans, appears an oversimplification, whereas continuum subsets development is best for depicting the real condition. In this review, we examine the evidences sustaining the existence of a monocyte heterogeneity along with functional activities, at the primary tumor and at the metastatic niche. In particular, we describe how tumor-derived soluble factors and cell-cell contact reprogram monocyte function. Finally, we point out the role of monocytes in preparing and shaping the metastatic niche and describe relevant targetable molecules altering monocyte activities. We think that exploiting monocyte complexity can help identifying key pathways important for the treatment of cancer and several conditions where these cells are involved.

C/EBPα and PU.1 exhibit different responses to RANK signaling for osteoclastogenesis

The transcription factors C/EBPα and PU.1 are upregulated by RANKL through activation of its receptor RANK during osteoclastogenesis and are critical for osteoclast differentiation. Herein we investigated the mechanisms underlying how C/EBPα and PU.1 regulate osteoclast differentiation in response to RANK signaling. We showed that C/EBPα or PU.1 overexpression could initiate osteoclastogenesis and upregulate the expressions of the osteoclast genes encoding the nuclear factor of activated T-cells, C1, cathepsin K, and tartrate-resistant acid phosphatase independently of RANKL. However, while PU.1 upregulated C/EBPα, C/EBPα could not upregulate PU.1. RANK has a unique cytoplasmic domain, 535IVVY538 motif, which is crucial for osteoclast differentiation. We demonstrated that mutational inactivation of RANK IVVY motif blocked osteoclast differentiation and significantly attenuated C/EBPα, but not PU.1, expression, indicating that RANK-IVVY-induced signaling is dispensable to PU.1 upregulation during osteoclastogenesis. However, C/EBPα or PU.1 overexpression failed to promote osteoclastogenesis in cells expressing mutated RANK IVVY motif. We noted that RANK-IVVY-motif inactivation significantly repressed osteoclast genes as compared with a vector control, suggesting that IVVY motif might also negatively regulate osteoclast inhibitors during osteoclastogenesis. Consistently, IVVY-motif inactivation triggered upregulation of RBP-J, a potent osteoclast inhibitor, during osteoclastogenesis. Notably, C/EBPα or PU.1 overexpression in cells expressing mutated RANK IVVY motif failed to control the deregulated RBP-J expression, resulting in repression of osteoclast genes. Accordingly, RBP-J silencing in the mutant cells rescued osteoclastogenesis with C/EBPα or PU.1 overexpression. In conclusion, we revealed that while PU.1 and C/EBPα are critical for osteoclastogenesis, they respond differently to RANKL-induced activation of RANK IVVY motif.

IL-32θ: a recently identified anti-inflammatory variant of IL-32 and its preventive role in various disorders and tumor suppressor activity

Interleukin-32 theta (IL-32θ) is newly identified isoform of IL-32 which plays a vital role in inflammatory responses. Like IL-32α and IL-32β, IL-32θ isoform acts as an intracellular inflammatory modulator. It results in reduction of IL-1β production by attenuating the expression of PU.1 and inhibition of monocytes differentiation into macrophages. IL-32θ hinders TNF-α expression by inhibiting p38 MAPK and inhibitor of κB (IκB) as well. It also reserved STAT3-ZEB1 pathway leading to the inhibition of epithelial-mesenchymal transition (EMT) and stemness. Hence, it can be concluded that IL-32θ is an anti-inflammatory cytokine that can act as a tumor suppressor and can play vital role in colon cancer therapies. IL-32θ also plays a crucial role in immune system responses and cellular differentiation during disease pathogenesis. To our best knowledge this is the first ever review to condense the importance, precise mode of action in disease progression and latent remedial implications of IL-32θ in several inflammatory disorders.

ABR, a novel inducer of transcription factor C/EBPα, contributes to myeloid differentiation and is a favorable prognostic factor in acute myeloid leukemia

Active BCR related (ABR) gene deactivates ras-related C3 botulinum toxin substrate 1 (RAC1), which plays an essential role in regulating normal hematopoiesis and in leukemia. BCR gene, closely related to ABR, acts as a tumor suppressor in chronic myeloid leukemia and has overlapping functions with ABR. Evidence for a putative tumor suppressor role of ABR has been shown in several solid tumors, in which deletion of ABR is present. Our results show downregulation of ABR in AML. A block of ABR prevents myeloid differentiation and leads to repression of the myeloid transcription factor C/EBPα, a major regulator of myeloid differentiation and functionally impaired in leukemia. Conversely, stable overexpression of ABR enhances myeloid differentiation. Inactivation of the known ABR target RAC1 by treatment with the RAC1 inhibitor NSC23766 resulted in an increased expression of C/EBPα in primary AML samples and in AML cell lines U937 and MV4;11. Finally, AML patients with high ABR expression at diagnosis showed a significant longer overall survival and patients who respond to azacitidine therapy showed a significant higher ABR expression. This is the first report showing that ABR expression plays a critical role in both myelopoiesis and AML. Our data indicate the tumor suppressor potential of ABR and underline its potential role in leukemia therapeutic strategies.

C/EBPα deregulation as a paradigm for leukemogenesis

Myeloid master regulator CCAAT enhancer-binding protein alpha (C/EBPα) is deregulated by multiple mechanisms in leukemia. Inhibition of C/EBPα function plays pivotal roles in leukemogenesis. While much is known about how C/EBPα orchestrates granulopoiesis, our understanding of molecular transformation events, the role(s) of cooperating mutations and clonal evolution during C/EBPα deregulation in leukemia remains elusive. In this review, we will summarize the latest research addressing these topics with special emphasis on CEBPA mutations. We conclude by describing emerging therapeutic strategies to restore C/EBPα function.

2014 Jeffrey M. Hoeg Award Lecture: Transcriptional Control of Monocyte Development

Monocytes and macrophages are key immune cells involved in the early progression of atherosclerosis. Transcription factors that control their development in the bone marrow are important therapeutic targets to control the numbers and functions of these cells in disease. This review highlights what is currently known about the transcription factors that are critical for monocyte development.

Genome-scale definition of the transcriptional programme associated with compromised PU.1 activity in acute myeloid leukaemia

Transcriptional dysregulation is associated with haematological malignancy. Although mutations of the key haematopoietic transcription factor PU.1 are rare in human acute myeloid leukaemia (AML), they are common in murine models of radiation-induced AML, and PU.1 downregulation and/or dysfunction has been described in human AML patients carrying the fusion oncogenes RUNX1-ETO and PML-RARA. To study the transcriptional programmes associated with compromised PU.1 activity, we adapted a Pu.1-mutated murine AML cell line with an inducible wild-type PU.1. PU.1 induction caused transition from leukaemia phenotype to monocytic differentiation. Global binding maps for PU.1, CEBPA and the histone mark H3K27Ac with and without PU.1 induction showed that mutant PU.1 retains DNA-binding ability, but the induction of wild-type protein dramatically increases both the number and the height of PU.1-binding peaks. Correlating chromatin immunoprecipitation (ChIP) Seq with gene expression data, we found that PU.1 recruitment coupled with increased histone acetylation induces gene expression and activates a monocyte/macrophage transcriptional programme. PU.1 induction also caused the reorganisation of a subgroup of CEBPA binding peaks. Finally, we show that the PU.1 target gene set defined in our model allows the stratification of primary human AML samples, shedding light on both known and novel AML subtypes that may be driven by PU.1 dysfunction.

IL-32θ inhibits monocytic differentiation of leukemia cells by attenuating expression of transcription factor PU.1

PU.1 is a key transcription factor regulating the myeloid differentiation. PU.1-induced monocytic differentiation into macrophage is also important for blood cancer development. Therefore, we chose THP-1 monocytic leukemia cells to investigate the function of a recently discovered IL-32θ. Genetic analyses identified differences in the sequences of IL-32θ and IL-32β. Using previously established cell lines that stably express IL-32θ and IL-32β and cell lines transiently expressing IL-32θ, we observed that expression of IL-32θ inhibited phorbol 12-myristate 13-acetate (PMA)-induced monocytic differentiation in both THP-1 and HL-60 cells. IL-32θ also suppressed expression of the macrophage cell surface markers, CD11b, CD18, and CD36. Interestingly, expression of IL-32β or IL-32θ had no effect on the expression levels of cell cycle related factors. As a result, we concluded that these isoforms did not contribute to PMA-induced cell cycle arrest. IL-32θ was found to modulate expression of PU.1, a transcription factor necessary for myeloid lineage commitment. Transient expression of PU.1 in THP-1/IL-32θ cells rescued the observed differentiation defect. Additionally, transient expression of both CCAAT-enhancer-binding protein α (C/EBPα) and PU.1 in THP-1/IL-32θ cells exhibited synergistic effects in rescuing the differentiation defect. These observations indicate that intracellular IL-32θ inhibits the differentiation of monocytes into macrophages by attenuating PU.1 expression.

The multifaceted functions of C/EBPα in normal and malignant haematopoiesis

The process of blood formation, haematopoiesis, depends upon a small number of haematopoietic stem cells (HSCs) that reside in the bone marrow. Differentiation of HSCs is characterised by decreased expression of genes associated with self-renewal accompanied by a stepwise activation of genes promoting differentiation. Lineage branching is further directed by groups of cooperating and counteracting genes forming complex networks of lineage-specific transcription factors. Imbalances in such networks can result in blockage of differentiation, lineage reprogramming and malignant transformation. CCAAT/enhancer-binding protein-α (C/EBPα) was originally identified 30 years ago as a transcription factor that binds both promoter and enhancer regions. Most of the early work focused on the role of C/EBPα in regulating transcriptional processes as well as on its functions in key differentiation processes during liver, adipogenic and haematopoietic development. Specifically, C/EBPα was shown to control differentiation by its ability to coordinate transcriptional output with cell cycle progression. Later, its role as an important tumour suppressor, mainly in acute myeloid leukaemia (AML), was recognised and has been the focus of intense studies by a number of investigators. More recent work has revisited the role of C/EBPα in normal haematopoiesis, especially its function in HSCs, and also started to provide more mechanistic insights into its role in normal and malignant haematopoiesis. In particular, the differential actions of C/EBPα isoforms, as well as its importance in chromatin remodelling and cellular reprogramming, are beginning to be elucidated. Finally, recent work has also shed light on the dichotomous function of C/EBPα in AML by demonstrating its ability to act as both a tumour suppressor and promoter. In the present review, we will summarise the current knowledge on the functions of C/EBPα during normal and malignant haematopoiesis with special emphasis on the recent work.

Understanding chronic neutropenia: life is short

The pathophysiological mechanisms underlying chronic neutropenia are extensive, varying from haematopoietic stem cell disorders resulting in defective neutrophil production, to accelerated apoptosis of neutrophil progenitors or circulating mature neutrophils. While the knowledge concerning genetic defects associated with congenital neutropenia or bone marrow failure is increasing rapidly, the functional role and consequences of these genetic alterations is often not well understood. In addition, there is a large group of diseases, including primary immunodeficiencies and metabolic diseases, in which chronic neutropenia is one of the symptoms, while there is no clear bone marrow pathology or haematopoietic stem cell dysfunction. Altogether, these disease entities illustrate the complexity of normal neutrophil development, the functional role of the (bone marrow) microenvironment and the increased propensity to undergo apoptosis, which is typical for neutrophils. The large variety of disorders associated with chronic neutropenia makes classification almost impossible and possibly not desirable, based on the clinical phenotypes. However, a better understanding of the regulation of normal myeloid differentiation and neutrophil development is of great importance in the diagnostic evaluation of unexplained chronic neutropenia. In this review we propose insights in the pathophysiology of chronic neutropenia in the context of the functional role of key players during normal neutrophil development, neutrophil release and neutrophil survival.

Primary and secondary haemostasis changes related to aging

Life expectancy has increased in many countries as a result the world's population is aging. The projections indicate that the proportion of the elderly in a few decades will increase significantly. Aging carries with it a series of physiological changes; one of them is an imbalance in the hemostatic system. Thus the levels or activity of various proteins involved, such as most coagulation factors, natural anticoagulants and the fibrinolytic system are altered so that the hemostatic balance leans toward thrombosis. Also, platelet activity suggests a state of abnormal activation (P-selectin, beta thromboglobulin and platelet factor). In this review we will systematically examine the alterations in the hemostatic components that occur during aging. Therefore, understanding these hemostatic changes could contribute to developing strategies for the proper management of health in old age.

C/EBPα in normal and malignant myelopoiesis

CCAAT/enhancer binding protein α (C/EBPα) dimerizes via its leucine zipper (LZ) domain to bind DNA via its basic region and activate transcription via N-terminal trans-activation domains. The activity of C/EBPα is modulated by several serine/threonine kinases and via sumoylation, its gene is activated by RUNX1 and additional transcription factors, its mRNA stability is modified by miRNAs, and its mRNA is subject to translation control that affects AUG selection. In addition to inducing differentiation, C/EBPα inhibits cell cycle progression and apoptosis. Within hematopoiesis, C/EBPα levels increase as long-term stem cells progress to granulocyte-monocyte progenitors (GMP). Absence of C/EBPα prevents GMP formation, and higher levels are required for granulopoiesis compared to monopoiesis. C/EBPα interacts with AP-1 proteins to bind hybrid DNA elements during monopoiesis, and induction of Gfi-1, C/EBPε, KLF5, and miR-223 by C/EBPα enables granulopoiesis. The CEBPA ORF is mutated in approximately 10 % of acute myeloid leukemias (AML), leading to expression of N-terminally truncated C/EBPαp30 and C-terminal, in-frame C/EBPαLZ variants, which inhibit C/EBPα activities but also play additional roles during myeloid transformation. RUNX1 mutation, CEBPA promoter methylation, Trib1 or Trib2-mediated C/EBPαp42 degradation, and signaling pathways leading to C/EBPα serine 21 phosphorylation reduce C/EBPα expression or activity in additional AML cases.

Epigenetic Regulation of Immunological Alterations Following Prenatal Exposure to Marijuana Cannabinoids and its Long Term Consequences in Offspring

Use of marijuana during pregnancy is fairly commonplace and can be expected increase in frequency as more states legalize its recreational use. The cannabinoids present in marijuana have been shown to be immunosuppressive, yet the effect of prenatal exposure to cannabinoids on the immune system of the developing fetus, its long term consequences during adult stage of life, and transgenerational effects have not been well characterized. Confounding factors such as co-existing drug use make the impact of cannabis use on progeny inherently difficult to study in a human population. Data from various animal models suggests that in utero exposure to cannabinoids results in profound T cell dysfunction and a greatly reduced immune response to viral antigens. Furthermore, evidence from animal studies indicates that the immunosuppressive effects of cannabinoids can be mediated through epigenetic mechanisms such as altered microRNA, DNA methylation and histone modification profiles. Such studies support the hypothesis that that parental or prenatal exposure to cannabis can trigger epigenetic changes that could have significant immunological consequences for offspring as well as long term transgenerational effects.

A Comprehensive Profile of ChIP-Seq-Based PU.1/Spi1 Target Genes in Microglia

Microglia are resident mononuclear phagocytes that play a principal role in the maintenance of normal tissue homeostasis in the central nervous system (CNS). Microglia, rapidly activated in response to proinflammatory stimuli, are accumulated in brain lesions of neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease. The E26 transformation-specific (ETS) family transcription factor PU.1/Spi1 acts as a master regulator of myeloid and lymphoid development. PU.1-deficient mice show a complete loss of microglia, indicating that PU.1 plays a pivotal role in microgliogenesis. However, the comprehensive profile of PU.1/Spi1 target genes in microglia remains unknown. By analyzing a chromatin immunoprecipitation followed by deep sequencing (ChIP-Seq) dataset numbered SRP036026 with the Strand NGS program, we identified 5,264 Spi1 target protein-coding genes in BV2 mouse microglial cells. They included Spi1, Irf8, Runx1, Csf1r, Csf1, Il34, Aif1 (Iba1), Cx3cr1, Trem2, and Tyrobp. By motif analysis, we found that the PU-box consensus sequences were accumulated in the genomic regions surrounding ChIP-Seq peaks. By using pathway analysis tools of bioinformatics, we found that ChIP-Seq-based Spi1 target genes show a significant relationship with diverse pathways essential for normal function of monocytes/macrophages, such as endocytosis, Fc receptor-mediated phagocytosis, and lysosomal degradation. These results suggest that PU.1/Spi1 plays a crucial role in regulation of the genes relevant to specialized functions of microglia. Therefore, aberrant regulation of PU.1 target genes might contribute to the development of neurodegenerative diseases with accumulation of activated microglia.

The effects of 1,25-dihydroxyvitamin D3 on in vitro human NK cell development from hematopoietic stem cells

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] is the biologically active form of vitamin D and is immunoregulatory. 1,25(OH)2D3 binds the vitamin D receptor complex present in many immune populations and can illicit transcriptional responses that vary among different immune subsets. The effects of 1,25(OH)2D3 on mature and developing human NK cells are not well characterized. In the present study, we examined the influence of 1,25(OH)2D3 using an established NK cell differentiation system. Briefly, umbilical cord blood CD34(+) cells were isolated and cultured in conditions optimal for NK cell differentiation, and varying concentrations of 1,25(OH)2D3 were administered. At physiological concentrations (10 nM), 1,25(OH)2D3 impaired NK cell development. Moreover, the NK cells that did develop under the influence of 1,25(OH)2D3 showed a significant reduction in function (cytotoxicity and cytokine production). Conversely, 1,25(OH)2D3 strongly induced hematopoietic stem cells to differentiate along a myeloid pathway, giving rise to CD14(+) cells. Mechanistically, 1,25(OH)2D3 drives hematopoietic progenitor cells to rapidly upregulate monocyte genes (i.e., C/EBP-α and CD14). There were no effects of 1,25(OH)2D3 on mature NK cytotoxicity or cytokine production. Collectively, these studies provide novel data showing the negative regulatory effect of 1,25(OH)2D3 on NK cell development.

Granulopoiesis requires increased C/EBPα compared to monopoiesis, correlated with elevated Cebpa in immature G-CSF receptor versus M-CSF receptor expressing cells

C/EBPα is required for the formation of granulocyte-monocyte progenitors; however, its role in subsequent myeloid lineage specification remains uncertain. Transduction of murine marrow with either of two Cebpa shRNAs markedly increases monocyte and reduces granulocyte colonies in methylcellulose or the monocyte to neutrophil ratio in liquid culture. Similar findings were found after marrow shRNA transduction and transplantation and with CEBPA knockdown in human marrow CD34+ cells. These results apparently reflect altered myeloid lineage specification, as similar knockdown allowed nearly complete 32Dcl3 granulocytic maturation. Cebpa knockdown also generated lineage-negative blasts with increased colony replating capacity but unchanged cell cycle parameters, likely reflecting complete differentiation block. The shRNA having the greatest effect on lineage skewing reduced Cebpa 3-fold in differentiating cells but 6-fold in accumulating blasts. Indicating that Cebpa is the relevant shRNA target, shRNA-resistant C/EBPα-ER rescued marrow myelopoiesis. Cebpa knockdown in murine marrow cells also increased in vitro erythropoiesis, perhaps reflecting 1.6-fold reduction in PU.1 leading to GATA-1 derepression. Global gene expression analysis of lineage-negative blasts that accumulate after Cebpa knockdown demonstrated reduction in Cebpe and Gfi1, known transcriptional regulators of granulopoiesis, and also reduced Ets1 and Klf5. Populations enriched for immature granulocyte or monocyte progenitor/precursors were isolated by sorting Lin-Sca-1-c-Kit+ cells into GCSFR+MCSFR- or GCSFR-MCSFR+ subsets. Cebpa, Cebpe, Gfi1, Ets1, and Klf5 RNAs were increased in the c-Kit+GCSFR+ and Klf4 and Irf8 in the c-Kit+MCSFR+ populations, with PU.1 levels similar in both. In summary, higher levels of C/EBPα are required for granulocyte and lower levels for monocyte lineage specification, and this myeloid bifurcation may be facilitated by increased Cebpa gene expression in granulocyte compared with monocyte progenitors.

Differential effects of nitrostyrene derivatives on myelopoiesis involve regulation of C/EBPα and p38MAPK activity

Bone marrow failure syndromes and MDS represent a heterogenous group of diseases, characterized by ineffective myelopoiesis, the risk of clonal evolution and a generally poor response to chemotherapy-based treatment regimen. Nitrostyrene derivatives have been studied as protein phosphatase inhibitors in various tumor models. Pharmacological studies have identified nitrostyrene as the structural core underlying a pro-apoptotic effect in tumor cells, yet their effects on normal cells, including those of the hematopoietic system, are largely unknown. In this study, utilizing umbilical cord blood-derived myeloid progenitor cells, patient-derived bone marrow cells, and a (BALB/c) mouse model; we investigated the effects of treatment with two nitrostyrene derivatives (NTS1 and NTS2) on myeloid development. We demonstrate that these compounds stimulate the expansion and differentiation of myeloid progenitors in vitro and improve myeloid reconstitution after chemotherapy-induced bone marrow depletion in vitro and in vivo. These effects were accompanied by increased C/EBPα expression and activity and inhibition of the p38MAPK signalling pathway. Together, our data suggest that nitrostyrenes improve myelopoiesis and represent potential new treatment strategies for patients suffering from bone marrow failure syndromes, hypocellular myelodysplastic syndrome and chemotherapy-induced aplasia.

Regulation of monocyte differentiation by specific signaling modules and associated transcription factor networks

Monocyte/macrophages are important players in orchestrating the immune response as well as connecting innate and adaptive immunity. Myelopoiesis and monopoiesis are characterized by the interplay between expansion of stem/progenitor cells and progression towards further developed (myelo)monocytic phenotypes. In response to a variety of differentiation-inducing stimuli, various prominent signaling pathways are activated. Subsequently, specific transcription factors are induced, regulating cell proliferation and maturation. This review article focuses on the integration of signaling modules and transcriptional networks involved in the determination of monocytic differentiation.

Distinct microRNA expression profile and targeted biological pathways in functional myeloid-derived suppressor cells induced by Δ9-tetrahydrocannabinol in vivo: regulation of CCAAT/enhancer-binding protein α by microRNA-690

Δ(9)-Tetrahydrocannabinol (THC), the major bioactive component of marijuana, has been shown to induce functional myeloid-derived suppressor cells (MDSCs) in vivo. Here, we studied the involvement of microRNA (miRNA) in this process. CD11b(+)Gr-1(+) MDSCs were purified from peritoneal exudates of mice administered with THC and used for genome-wide miRNA profiling. Expression of CD31 and Ki-67 confirmed that the THC-MDSCs were immature and proliferating. THC-induced MDSCs exhibited distinct miRNA expression signature relative to various myeloid cells and BM precursors. We identified 13 differentially expressed (>2-fold) miRNA in THC-MDSCs relative to control BM precursors. In silico target prediction for these miRNA and pathway analysis using multiple bioinformatics tools revealed significant overrepresentation of Gene Ontology clusters within hematopoiesis, myeloid cell differentiation, and regulation categories. Insulin-like growth factor 1 signaling involved in cell growth and proliferation, and myeloid differentiation pathways were among the most significantly enriched canonical pathways. Among the differentially expressed, miRNA-690 was highly overexpressed in THC-MDSCs (∼16-fold). Transcription factor CCAAT/enhancer-binding protein α (C/EBPα) was identified as a potential functional target of miR-690. Supporting this, C/EBPα expression was attenuated in THC-MDSCs as compared with BM precursors and exhibited an inverse relation with miR-690. miR-690 knockdown using peptide nucleic acid-antagomiR was able to unblock and significantly increase C/EBPα expression establishing the functional link. Further, CD11b(+)Ly6G(+)Ly6C(+) and CD11b(+)Ly6G(-)Ly6C(+) purified subtypes showed high levels of miR-690 with attenuated C/EBPα expression. Moreover, EL-4 tumor-elicited MDSCs showed increased miR-690 expression. In conclusion, miRNA are significantly altered during the generation of functional MDSC from BM. Select miRNA such as miR-690 targeting genes involved in myeloid expansion and differentiation likely play crucial roles in this process and therefore in cannabinoid-induced immunosuppression.

Sex, stroke, and inflammation: the potential for estrogen-mediated immunoprotection in stroke

Stroke is the third leading cause of death and the primary cause of disability in the developed world. Experimental and clinical data indicate that stroke is a sexually dimorphic disease, with males demonstrating an enhanced intrinsic sensitivity to ischemic damage throughout most of their lifespan. The neuroprotective role of estrogen in the female brain is well established, however, estrogen exposure can also be deleterious, especially in older women. The mechanisms for this remain unclear. Our current understanding is based on studies examining estrogen as it relates to neuronal injury, yet cerebral ischemia also induces a robust sterile inflammatory response involving local and systemic immune cells. Despite the potent anti-inflammatory effects of estrogen, few studies have investigated the contribution of estrogen to sex differences in the inflammatory response to stroke. This review examines the potential role for estrogen-mediated immunoprotection in ischemic injury.

The role of translation initiation regulation in haematopoiesis

Organisation of RNAs into functional subgroups that are translated in response to extrinsic and intrinsic factors underlines a relatively unexplored gene expression modulation that drives cell fate in the same manner as regulation of the transcriptome by transcription factors. Recent studies on the molecular mechanisms of inflammatory responses and haematological disorders indicate clearly that the regulation of mRNA translation at the level of translation initiation, mRNA stability, and protein isoform synthesis is implicated in the tight regulation of gene expression. This paper outlines how these posttranscriptional control mechanisms, including control at the level of translation initiation factors and the role of RNA binding proteins, affect hematopoiesis. The clinical relevance of these mechanisms in haematological disorders indicates clearly the potential therapeutic implications and the need of molecular tools that allow measurement at the level of translational control. Although the importance of miRNAs in translation control is well recognised and studied extensively, this paper will exclude detailed account of this level of control.

Runx1 deletion or dominant inhibition reduces Cebpa transcription via conserved promoter and distal enhancer sites to favor monopoiesis over granulopoiesis

Deletion of Runx1 in adult mice produces a myeloproliferative phenotype. We now find that Runx1 gene deletion increases marrow monocyte while reducing granulocyte progenitors and that exogenous RUNX1 rescues granulopoiesis. Deletion of Runx1 reduces Cebpa mRNA in lineage-negative marrow cells and in granulocyte-monocyte progenitors or common myeloid progenitors. Pu.1 mRNA is also decreased, but to a lesser extent. We also transduced marrow with dominant-inhibitory RUNX1a. As with Runx1 gene deletion, RUNX1a expands lineage-Sca-1+c-kit+ and myeloid cells, increased monocyte CFUs relative to granulocyte CFUs, and reduced Cebpa mRNA. Runx1 binds a conserved site in the Cebpa promoter and binds 4 sites in a conserved 450-bp region located at +37 kb; mutation of the enhancer sites reduces activity 6-fold in 32Dcl3 myeloid cells. Endogenous Runx1 binds the promoter and putative +37 kb enhancer as assessed by ChIP, and RUNX1-ER rapidly induces Cebpa mRNA in these cells, even in cycloheximide, consistent with direct gene regulation. The +37 kb region contains strong H3K4me1 histone modification and p300-binding, as often seen with enhancers. Finally, exogenous C/EBPα increases granulocyte relative to monocyte progenitors in Runx1-deleted marrow cells. Diminished CEBPA transcription and consequent impairment of myeloid differentiation may contribute to leukemic transformation in acute myeloid leukemia cases associated with decreased RUNX1 activity.

C/EBPα dysregulation in AML and ALL

The transcription factor CCAAT/enhancer binding protein a (C/EBPα) is a critical regulator of myeloid development, directing granulocyte, and monocyte differentiation. As such, it is dysregulated in more than half of patients with acute myeloid leukemia (AML). C/EBPα expression is suppressed as result of common leukemia-associated genetic and epigenetic alterations such as AML1-ETO, BCR-ABL, FLT3-ITD, or CEBPA promoter methylation. In addition, 10-15% of patients with AML with intermediate risk cytogenetics are characterized by mutations of the CEBPA gene. Two classes of mutations are described. N-terminal changes result in expression of a truncated dominant negative C/EBPαp30 isoform. C-terminal mutations are in-frame insertions or deletions resulting in alteration of the leucine zipper preventing dimerization and DNA binding. Often, patients carry both N- and C-terminal mutations each affecting a different allele, and a mouse model recapitulates the human phenotype. Patients with mutated CEBPA AML comprise a clinically distinct group with favorable outcome consistently seen in patients with biallelic mutations. In addition, C/EBP family members are aberrantly expressing from the immunoglobulin heavy chain locus in 2% of pre-B ALLs. This review summarizes the normal hematopoietic developmental pathways regulated by C/EBPα and discusses the molecular pathways involved in mutated CEBPA AML and ALL.

Post-transcriptional modulation of C/EBPα prompts monocytic differentiation and apoptosis in acute myelomonocytic leukaemia cells

CCAAT/enhancer binding protein alpha (C/EBPα) induction induces monocytic differentiation even in acute myeloid leukaemia (AML). In this study, the induction/activation of C/EBPα in myelomonocytic AML was investigated using a combination of all-trans retinoic acid (ATRA) and RAD001 (Everolimus), a mammalian target of rapamycin complex 1 (mTORC1) inhibitor. Combining these agents increased PU.1, C/EBPε and C/EBPα expression, increased the p42/p30 C/EBPα ratio, and decreased C/EBPα phosphorylation at serine 21, and was accompanied by growth inhibition, induction of CD11b expression and apoptosis in AML cell lines. Thus, agents that induce sufficient levels of C/EBPα expression might be useful in treating AML.

Knock-in of a FLT3/ITD mutation cooperates with a NUP98-HOXD13 fusion to generate acute myeloid leukemia in a mouse model

Constitutive activation of FLT3 by internal tandem duplication (ITD) is one of the most common molecular alterations in acute myeloid leukemia (AML). FLT3/ITD mutations have also been observed in myelodysplastic syndrome patients both before and during progression to AML. Previous work has shown that insertion of an FLT3/ITD mutation into the murine Flt3 gene induces a myeloproliferative neoplasm, but not progression to acute leukemia, suggesting that additional cooperating events are required. We therefore combined the FLT3/ITD mutation with a model of myelodysplastic syndrome involving transgenic expression of the Nup98-HoxD13 (NHD13) fusion gene. Mice expressing both the FLT3/ITD and NHD13 transgene developed AML with 100% penetrance and short latency. These leukemias were driven by mutant FLT3 expression and were susceptible to treatment with FLT3 tyrosine kinase inhibitors. We also observed a spontaneous loss of the wild-type Flt3 allele in these AMLs, further modeling the loss of the heterozygosity phenomenon that is seen in human AML with FLT3-activating mutations. Because resistance to FLT3 inhibitors remains an important clinical issue, this model may help identify new molecular targets in collaborative signaling pathways.

GD1a modulates GM-CSF-induced cell proliferation

Gangliosides have been extensively described to be involved in the proliferation and differentiation of various cell types, such including hematopoietic cells. Our previous studies on murine models of stroma-mediated myelopoiesis have shown that gangliosides are required for optimal capacity of stromal cells to support proliferation of myeloid precursor cells, being shed to the supernatant and selectively incorporated into myeloid cell membranes. Here we describe the effect of gangliosides on the specific granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced proliferation. For that, we used the monocytic FDC-P1 cell line, which is dependent upon GM-CSF for survival and proliferation. Cells were cultured in the presence of GM-CSF and exogenous gangliosides (GM3, GD1a or GM1) or in the absence of endogenous ganglioside synthesis by the use of a ceramide-synthase inhibitor, D-PDMP. We observed that exogenous addition of GD1a enhanced the GM-CSF-induced proliferation of the FDC-P1 cells. Also, we detected an increase in the expression of the α isoform of the GM-CSF receptor (GMRα) as well as of the transcription factor C/EBPα. On the contrary, inhibition of glucosylceramide synthesis was accompanied by a decrease in cell proliferation, which was restored upon the addition of exogenous GD1a. We also show a co-localization of GD1a and GMR by immunocytochemistry. Taken together, our results suggest for the first time that ganglioside GD1a play a role on the modulation of GM-CSF-mediated proliferative response, which might be of great interest not only in hematopoiesis, but also in other immunological processes, Alzheimer disease, alveolar proteinosis and wherever GM-CSF exerts its effects.

SHP2 tyrosine phosphatase stimulates CEBPA gene expression to mediate cytokine-dependent granulopoiesis

G-CSF signals contribute to granulocyte lineage specification. We previously found that G-CSF induces SHP2 tyrosine phosphorylation and that chemical inhibition of SHP1/SHP2 reduces CFU-G and prevents G-CSF but not M-CSF activation of ERK. We now find that SHP2 shRNA knockdown in the 32Dcl3 granulocytic line reduces ERK activation, diminishes CEBPA protein and RNA expression and promoter histone acetylation, and inhibits granulopoiesis. Exogenous, shRNA-resistant SHP2 rescues these effects of SHP2 knockdown, exogenous C/EBPα rescues granulocytic markers, and exogenous RUNX1 rescues C/EBPα. 32Dcl3 lines with knockdown of ERK1 and ERK2 retain normal levels of C/EBPα and differentiate normally in G-CSF despite also having reduced proliferation. SHP2 knockdown reduces CEBPA levels in lineage-negative murine marrow cells cultured in TPO, Flt3 ligand, and SCF, without affecting the rate of cell expansion. On transfer to IL-3, IL-6, and SCF to induce myelopoiesis, levels of granulocytic RNAs are reduced and monocyte-specific RNAs are increased by SHP2 knockdown, and there is a reduction in the percentage of CFU-G that form in methylcellulose and of granulocytes that develop in liquid culture. In summary, SHP2 is required for induction of C/EBPα expression and granulopoiesis in response to G-CSF or other cytokines independent of SHP2-mediated ERK activation.

Dysregulated gene expression during hematopoietic differentiation from human embryonic stem cells

The generation of hematopoietic cells from human embryonic stem cells (hESC) has raised the possibility of using hESC as an alternative donor source for transplantation. However, functional defects identified in hESC-derived cells limit their use for full lymphohematopoietic reconstitution. The purpose of the present study was to define and quantitate key functional and molecular differences between CD34(+) hematopoietic progenitor subsets derived from hESC and CD34(+) subsets from umbilical cord blood (UCB) representing definitive hematopoiesis. Two distinct sub-populations were generated following mesodermal differentiation from hESC, a CD34(bright) (hematoendothelial) and CD34(dim) (hematopoietic-restricted) subset. Limiting dilution analysis revealed profound defects in clonal proliferation relative to UCB particularly in B lymphoid conditions. Transcription factors normally expressed at specific commitment stages during B lymphoid development from UCB-CD34(+) cells were aberrantly expressed in hESC-derived CD34(+) cells. Moreover, strong negative regulators of lymphopoiesis such as the adaptor protein LNK and CCAAT/enhancer-binding protein-α (CEBPα), were exclusively expressed in hESC-CD34(+) subsets. Knockdown of LNK lead to an increase in hematopoietic progenitors generated from hESCs. The aberrant molecular profile seen in hESC-CD34(+) cells represents persistence of transcripts first expressed in undifferentiated hESC and/or CD326-CD56(+) mesoderm progenitors, and may contribute to the block in definitive hematopoiesis from hESC.

Bcl3 prevents acute inflammatory lung injury in mice by restraining emergency granulopoiesis

Granulocytes are pivotal regulators of tissue injury. However, the transcriptional mechanisms that regulate granulopoiesis under inflammatory conditions are poorly understood. Here we show that the transcriptional coregulator B cell leukemia/lymphoma 3 (Bcl3) limits granulopoiesis under emergency (i.e., inflammatory) conditions, but not homeostatic conditions. Treatment of mouse myeloid progenitors with G-CSF--serum concentrations of which rise under inflammatory conditions--rapidly increased Bcl3 transcript accumulation in a STAT3-dependent manner. Bcl3-deficient myeloid progenitors demonstrated an enhanced capacity to proliferate and differentiate into granulocytes following G-CSF stimulation, whereas the accumulation of Bcl3 protein attenuated granulopoiesis in an NF-κB p50-dependent manner. In a clinically relevant model of transplant-mediated lung ischemia reperfusion injury, expression of Bcl3 in recipients inhibited emergency granulopoiesis and limited acute graft damage. These data demonstrate a critical role for Bcl3 in regulating emergency granulopoiesis and suggest that targeting the differentiation of myeloid progenitors may be a therapeutic strategy for preventing inflammatory lung injury.

The Epstein-Barr virus BZLF1 protein inhibits tumor necrosis factor receptor 1 expression through effects on cellular C/EBP proteins

The Epstein-Barr virus immediate-early protein, BZLF1 (Z), initiates the switch between latent and lytic infection and plays an essential role in mediating viral replication. Z also inhibits expression of the major receptor for tumor necrosis factor (TNF), TNFR1, thus repressing TNF cytokine signaling, but the mechanism for this effect is unknown. Here, we demonstrate that Z prevents both C/EBPα- and C/EBPβ-mediated activation of the TNFR1 promoter (TNFR1p) by interacting directly with both C/EBP family members. We show that Z interacts directly with C/EBPα and C/EBPβ in vivo and that a Z mutant altered at alanine residue 204 in the bZIP domain is impaired for the ability to interact with both C/EBP proteins. Furthermore, we find that the Z(A204D) mutant is attenuated in the ability to inhibit the TNFR1p but mediates lytic viral reactivation and replication in vitro in 293 cells as well as wild-type Z. Although Z does not bind directly to the TNFR1p in EMSA studies, chromatin immunoprecipitation studies indicate that Z is complexed with this promoter in vivo. The Z(A204D) mutant has reduced interaction with the TNFR1p in vivo but is similar to wild-type Z in its ability to complex with the IL-8 promoter. Finally, we show that the effect of Z on C/EBPα- and C/EBPβ-mediated activation is promoter dependent. These results indicate that Z modulates the effects of C/EBPα and C/EBPβ in a promoter-specific manner and that in some cases (including that of the TNFR1p), Z inhibits C/EBPα- and C/EBPβ-mediated activation.

SARS spike protein induces phenotypic conversion of human B cells to macrophage-like cells

Massive aggregations of macrophages are frequently detected in afflicted lungs of patients with severe acute respiratory syndrome-associated coronavirus (SARS-CoV) infection. In vitro, ectopic expression of transcription factors, in particular CCAAT/enhancer-binding protein alpha (C/EBPα) and C/EBPβ, can convert B cells into functional macrophages. However, little is known about the specific ligands responsible for such phenotype conversion. Here, we investigated whether spike protein of SARS-CoV can act as a ligand to trigger the conversion of B cells to macrophages. We transduced SARS-CoV spike protein-displayed recombinant baculovirus (SSDRB), vAtEpGS688, into peripheral B cells and B lymphoma cells. Cell surface expression of CD19 or Mac-1 (CD11b) was determined by flow cytometry. SSDRB-mediated changes in gene expression profiles of B lymphoma cells were analyzed by microarray. In this report, we showed that spike protein of SARS virus could induce phenotypic conversion of human B cells, either from peripheral blood or B lymphoma cells, to macrophage-like cells that were steadily losing the B-cell marker CD19 and in turn expressing the macrophage-specific marker Mac-1. Furthermore, we found that SSDRB enhanced the expression of CD86, hypoxia-inducible factor-1α (HIF1α), suppressor of cytokine signaling (SOCS or STAT-induced STAT inhibitor)-3, C/EBPβ, insulin-like growth factor-binding protein 3 (IGFBP3), Krüpple-like factor (KLF)-5, and CD54, without marked influence on C/EBPα or PU.1 expression in transduced cells. Prolonged exposure to hypoxia could also induce macrophage-like conversion of B cells. These macrophage-like cells were defective in phagocytosis of red fluorescent beads. In conclusion, our results suggest that conversion of B cells to macrophage-like cells, similar to a pathophysiological response, could be mediated by a devastating viral ligand, in particular spike protein of SARS virus, or in combination with severe local hypoxia, which is a condition often observed in afflicted lungs of SARS patients.

M-CSF elevates c-Fos and phospho-C/EBPalpha(S21) via ERK whereas G-CSF stimulates SHP2 phosphorylation in marrow progenitors to contribute to myeloid lineage specification

The role of hematopoietic cytokines in lineage commitment remains uncertain. To gain insight into the contribution of cytokine signaling to myeloid lineage specification, we compared granulocyte colony-stimulating factor (G-CSF) and macrophage colony-stimulating factor (M-CSF) signaling in Ba/F3 cells expressing both the G-CSF and M-CSF receptors and in lineage-negative murine marrow cells. G-CSF and M-CSF serve as prototypes for additional cytokines that also influence immature myeloid cells. G-CSF specifically activated signal transducer and activator of transcription 3 and induced Src homology region 2 domain-containing phosphatase 2 (SHP2) phosphorylation, whereas M-CSF preferentially activated phospholipase Cgamma2, and thereby extracellular signal-regulated kinase (ERK), to stabilize c-Fos and stimulate CCAAT/enhancer-binding protein (C/EBP)alpha(S21) phosphorylation. In contrast, activation of Jun kinase or c-Jun was similar in response to either cytokine. Inhibition of ERK prevented induction of c-Fos by M-CSF and reduced C/EBPalpha phosphorylation and formation of colony-forming unit-monocytes. SHP2 inhibition reduced ERK activation in G-CSF, but not M-CSF, and reduced colony-forming unit-granulocytes, underscoring divergent pathways to ERK activation. Phorbol ester mimicked the effect of M-CSF, activating ERK independent of SHP2. In summary, M-CSF activates ERK more potently than G-CSF, and thereby induces higher levels of c-Fos and phospho-C/EBPalpha(S21), which may directly interact to favor monopoiesis, whereas G-CSF activates signal transducer and activator of transcription 3 and SHP2, potentially shifting the balance to granulopoiesis via gene induction by C/EBPalpha homodimers and via effects of SHP2 on regulators besides ERK.

Reintroduction of CEBPA in MN1-overexpressing hematopoietic cells prevents their hyperproliferation and restores myeloid differentiation

Forced expression of MN1 in primitive mouse hematopoietic cells causes acute myeloid leukemia and impairs all-trans retinoic acid-induced granulocytic differentiation. Here, we studied the effects of MN1 on myeloid differentiation and proliferation using primary human CD34(+) hematopoietic cells, lineage-depleted mouse bone marrow cells, and bipotential (granulocytic/monocytic) human acute myeloid leukemia cell lines. We show that exogenous MN1 stimulated the growth of CD34(+) cells, which was accompanied by enhanced survival and increased cell cycle traverse in cultures supporting progenitor cell growth. Forced MN1 expression impaired both granulocytic and monocytic differentiation in vitro in primary hematopoietic cells and acute myeloid leukemia cell lines. Endogenous MN1 expression was higher in human CD34(+) cells compared with both primary and in vitro-differentiated monocytes and granulocytes. Microarray and real-time reverse-transcribed polymerase chain reaction analysis of MN1-overexpressing CD34(+) cells showed down-regulation of CEBPA and its downstream target genes. Reintroduction of conditional and constitutive CEBPA overcame the effects of MN1 on myeloid differentiation and inhibited MN1-induced proliferation in vitro. These results indicate that down-regulation of CEBPA activity contributes to MN1-modulated proliferation and impaired myeloid differentiation of hematopoietic cells.

NF-kappa B p50 regulates C/EBP alpha expression and inflammatory cytokine-induced neutrophil production

NF-kappaB is a key transcriptional inducer of the inflammatory response in mature myeloid cells, and also stimulates cell survival, but its role in immature myeloid cell development has not been well characterized. C/EBPalpha is required for the development of monocytic and granulocytic myeloid cells from early progenitors, and NF-kappaB and C/EBPbeta cooperatively induce several inflammatory mediators. Having found that C/EBPalpha binds NF-kappaB p50 preferentially compared with NF-kappaB p65, we have now investigated myelopoiesis in nfkb1(-/-) mice lacking NF-kappaB p50. Absence of p50 leads to a significant reduction in the number of granulocytic progenitors, CFU-granulocyte, obtained with G-CSF or GM-CSF in vitro and reduces neutrophil production in vivo in response to G-CSF, with preservation of monopoiesis in vitro in response to cytokines or LPS. To gain insight into the mechanism underlying reduced granulopoiesis in the absence of NF-kappaB p50, we assessed the expression of several myeloid regulatory proteins in lineage-negative, immature myeloid cells. Although PU.1, C/EBPbeta, and STAT3 levels were unchanged, C/EBPalpha protein and RNA levels were reduced approximately 3-fold in the absence of NF-kappaB p50. In addition, NF-kappaB p50 and C/EBPalpha bound the endogenous C/EBPalpha promoter in a chromatin immunoprecipitation assay, and NF-kappaB p50 trans activated the C/EBPalpha promoter, alone or in cooperation with C/EBPalpha. Despite reduction of C/EBPalpha, G-CSFR and M-CSFR levels were maintained in total marrow and in lineage-negative cells. Together, these data indicate that acute inflammation not only activates mature myeloid cells, but also stimulates neutrophil production via NF-kappaB p50 induction of C/EBPalpha transcription.

BCR-ABL promotes neutrophil differentiation in the chronic phase of chronic myeloid leukemia by downregulating c-Jun expression

The mechanism that is responsible for mature neutrophil overproduction in the chronic phase (CP) of chronic myeloid leukemia (CML), a neoplastic disease of hematopoietic stem cells carrying a constitutively active tyrosine kinase BCR-ABL, remains obscure. In this study, microarray analysis revealed that c-Jun, a monopoiesis-promoting transcription factor, was downregulated in CML neutrophils. BCR-ABL directly inhibited c-Jun expression, as c-Jun downregulation in primary CML neutrophils and in the CML blast cell lines, KCL22 and K562, was reversed by the tyrosine kinase inhibitor imatinib. We established a myeloid differentiation model in KCL22 cells using zinc-inducible CCAAT/enhancer-binding protein (C/EBP)alpha (KCL22/alpha). Myeloid differentiation was observed in C/EBP-induced KCL22/alpha cells. Imatinib-induced c-Jun upregulation promoted the monocytic differentiation of KCL22/alpha cells. c-Jun knockdown in KCL22/alpha cells by a short interfering RNA redirected their differentiation from the monocytic to the neutrophilic lineage, even after imatinib treatment. A blockade of PI3K-Akt signaling with an Akt inhibitor upregulated c-Jun and induced the monocytic differentiation of KCL22, K562, and C/EBP-induced KCL22/alpha cells. Thus, BCR-ABL downregulates c-Jun expression by activating the PI3K-Akt pathway during CML-CP, thereby allowing C/EBPs to promote neutrophil differentiation.