C/EBP alpha:AP-1 leucine zipper heterodimers bind novel DNA elements, activate the PU.1 promoter and direct monocyte lineage commitment more potently than C/EBP alpha homodimers or AP-1

Leukemic stem cells activate lineage inappropriate signalling pathways to promote their growth

Acute Myeloid Leukemia (AML) is caused by multiple mutations which dysregulate growth and differentiation of myeloid cells. Cells adopt different gene regulatory networks specific to individual mutations, maintaining a rapidly proliferating blast cell population with fatal consequences for the patient if not treated. The most common treatment option is still chemotherapy which targets such cells. However, patients harbour a population of quiescent leukemic stem cells (LSCs) which can emerge from quiescence to trigger relapse after therapy. The processes that allow such cells to re-grow remain unknown. Here, we examine the well characterised t(8;21) AML sub-type as a model to address this question. Using four primary AML samples and a novel t(8;21) patient-derived xenograft model, we show that t(8;21) LSCs aberrantly activate the VEGF and IL-5 signalling pathways. Both pathways operate within a regulatory circuit consisting of the driver oncoprotein RUNX1::ETO and an AP-1/GATA2 axis allowing LSCs to re-enter the cell cycle while preserving self-renewal capacity.

Gene regulatory network analysis predicts cooperating transcription factor regulons required for FLT3-ITD+ AML growth

Acute myeloid leukemia (AML) is a heterogeneous disease caused by different mutations. Previously, we showed that each mutational subtype develops its specific gene regulatory network (GRN) with transcription factors interacting within multiple gene modules, many of which are transcription factor genes themselves. Here, we hypothesize that highly connected nodes within such networks comprise crucial regulators of AML maintenance. We test this hypothesis using FLT3-ITD-mutated AML as a model and conduct an shRNA drop-out screen informed by this analysis. We show that AML-specific GRNs predict crucial regulatory modules required for AML growth. Furthermore, our work shows that all modules are highly connected and regulate each other. The careful multi-omic analysis of the role of one (RUNX1) module by shRNA and chemical inhibition shows that this transcription factor and its target genes stabilize the GRN of FLT3-ITD+ AML and that its removal leads to GRN collapse and cell death.

A longitudinal single-cell atlas of treatment response in pediatric AML

Pediatric acute myeloid leukemia (pAML) is characterized by heterogeneous cellular composition, driver alterations and prognosis. Characterization of this heterogeneity and how it affects treatment response remains understudied in pediatric patients. We used single-cell RNA sequencing and single-cell ATAC sequencing to profile 28 patients representing different pAML subtypes at diagnosis, remission and relapse. At diagnosis, cellular composition differed between genetic subgroups. Upon relapse, cellular hierarchies transitioned toward a more primitive state regardless of subtype. Primitive cells in the relapsed tumor were distinct compared to cells at diagnosis, with under-representation of myeloid transcriptional programs and over-representation of other lineage programs. In some patients, this was accompanied by the appearance of a B-lymphoid-like hierarchy. Our data thus reveal the emergence of apparent subtype-specific plasticity upon treatment and inform on potentially targetable processes.

FOS Inhibits the Differentiation of Intramuscular Adipocytes in Goats

Goat intramuscular fat (IMF) deposition is precisely regulated by many key genes as well as transcription factors. Nevertheless, the potential of the regulators of goat IMF deposition remains undefined. In this work, we reported that the transcription factor FOS is expressed at a low level at the early differentiation stage and at a high level in late differentiation. The overexpression of FOS inhibited intramuscular adipocyte lipid accumulation and significantly downregulated the expressions of PPARγ, C/EBPβ, C/EBPα, AP2, SREBP1, FASN, ACC, HSL, and ATGL. Consistently, the knockdown of FOS, facilitated by two distinct siRNAs, significantly promoted intramuscular adipocyte lipid accumulation. Moreover, our analysis revealed multiple potential binding sites for FOS on the promoters of PPARγ, C/EBPβ, and C/EBPα. The expression changes in PPARγ, C/EBPβ, and C/EBPα during intramuscular adipogenesis were opposite to that of FOS. In summary, FOS inhibits intramuscular lipogenesis in goats and potentially negatively regulates the expressions of PPARγ, C/EBPβ, and C/EBPα genes. Our research will provide valuable data for the underlying molecular mechanism of the FOS regulation network of intramuscular lipogenesis.

Gene regulatory network analysis predicts cooperating transcription factor regulons required for FLT3-ITD+ AML growth

AML is a heterogenous disease caused by different mutations. We have previously shown that each mutational sub-type develops its specific gene regulatory network (GRN) with transcription factors interacting with multiple gene modules, many of which are transcription factor genes themselves. Here we hypothesized that highly connected nodes within such networks comprise crucial regulators of AML maintenance. We tested this hypothesis using FLT3-ITD mutated AML as a model and conducted an shRNA drop-out screen informed by this analysis. We show that AML-specific GRNs predict identifying crucial regulatory modules required for AML but not normal cellular growth. Furthermore, our work shows that all modules are highly connected and regulate each other. The careful multi-omic analysis of the role of one (RUNX1) module by shRNA and chemical inhibition shows that this transcription factor and its target genes stabilize the GRN of FLT3-ITD AML and that its removal leads to GRN collapse and cell death.

Carm1-arginine methylation of the transcription factor C/EBPα regulates transdifferentiation velocity

Here, we describe how the speed of C/EBPα-induced B cell to macrophage transdifferentiation (BMT) can be regulated, using both mouse and human models. The identification of a mutant of C/EBPα (C/EBPαR35A) that greatly accelerates BMT helped to illuminate the mechanism. Thus, incoming C/EBPα binds to PU.1, an obligate partner expressed in B cells, leading to the release of PU.1 from B cell enhancers, chromatin closing and silencing of the B cell program. Released PU.1 redistributes to macrophage enhancers newly occupied by C/EBPα, causing chromatin opening and activation of macrophage genes. All these steps are accelerated by C/EBPαR35A, initiated by its increased affinity for PU.1. Wild-type C/EBPα is methylated by Carm1 at arginine 35 and the enzyme's perturbations modulate BMT velocity as predicted from the observations with the mutant. Increasing the proportion of unmethylated C/EBPα in granulocyte/macrophage progenitors by inhibiting Carm1 biases the cell's differentiation toward macrophages, suggesting that cell fate decision velocity and lineage directionality are closely linked processes.

Identification and interrogation of the gene regulatory network of CEBPA-double mutant acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy caused by mutations in genes encoding transcriptional and epigenetic regulators together with signaling genes. It is characterized by a disturbance of differentiation and abnormal proliferation of hematopoietic progenitors. We have previously shown that each AML subtype establishes its own core gene regulatory network (GRN), consisting of transcription factors binding to their target genes and imposing a specific gene expression pattern that is required for AML maintenance. In this study, we integrate gene expression, open chromatin and ChIP data with promoter-capture Hi-C data to define a refined core GRN common to all patients with CEBPA-double mutant (CEBPAN/C) AML. These mutations disrupt the structure of a major regulator of myelopoiesis. We identify the binding sites of mutated C/EBPα proteins in primary cells, we show that C/EBPα, AP-1 factors and RUNX1 colocalize and are required for AML maintenance, and we employ single cell experiments to link important network nodes to the specific differentiation trajectory from leukemic stem to blast cells. Taken together, our study provides an important resource which predicts the specific therapeutic vulnerabilities of this AML subtype in human cells.

Transcription Factors in the Regulation of Leydig Cell Gene Expression and Function

Cell differentiation and acquisition of specialized functions are inherent steps in events that lead to normal tissue development and function. These processes require accurate temporal, tissue, and cell-specific activation or repression of gene transcription. This is achieved by complex interactions between transcription factors that form a unique combinatorial code in each specialized cell type and in response to different physiological signals. Transcription factors typically act by binding to short, nucleotide-specific DNA sequences located in the promoter region of target genes. In males, Leydig cells play a crucial role in sex differentiation, health, and reproductive function from embryonic life to adulthood. To better understand the molecular mechanisms regulating Leydig cell differentiation and function, several transcription factors important to Leydig cells have been identified, including some previously unknown to this specialized cell type. This mini review summarizes the current knowledge on transcription factors in fetal and adult Leydig cells, describing their roles and mechanisms of action.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

TFregulomeR reveals transcription factors' context-specific features and functions

Transcription factors (TFs) are sequence-specific DNA binding proteins, fine-tuning spatiotemporal gene expression. Since genomic occupancy of a TF is highly dynamic, it is crucial to study TF binding sites (TFBSs) in a cell-specific context. To date, thousands of ChIP-seq datasets have portrayed the genomic binding landscapes of numerous TFs in different cell types. Although these datasets can be browsed via several platforms, tools that can operate on that data flow are still lacking. Here, we introduce TFregulomeR (https://github.com/benoukraflab/TFregulomeR), an R-library linked to an up-to-date compendium of cistrome and methylome datasets, implemented with functionalities that facilitate integrative analyses. In particular, TFregulomeR enables the characterization of TF binding partners and cell-specific TFBSs, along with the study of TF’s functions in the context of different partnerships and DNA methylation levels. We demonstrated that TFs’ target gene ontologies can differ notably depending on their partners and, by re-analyzing well characterized TFs, we brought to light that numerous leucine zipper TFBSs derived from ChIP-seq experiments documented in current databases were inadequately characterized, due to the fact that their position weight matrices were assembled using a mixture of homodimer and heterodimer binding sites. Altogether, analyses of context-specific transcription regulation with TFregulomeR foster our understanding of regulatory network-dependent TF functions.

Gfi1-Mediated Repression of c-Fos, Egr-1 and Egr-2, and Inhibition of ERK1/2 Signaling Contribute to the Role of Gfi1 in Granulopoiesis

Gfi1 supports neutrophil development at the expense of monopoiesis, but the underlying molecular mechanism is incompletely understood. We recently showed that the G-CSFR Y729F mutant, in which tyrosine 729 was mutated to phenylalanine, promoted monocyte rather than neutrophil development in myeloid precursors, which was associated with prolonged activation of Erk1/2 and enhanced activation of c-Fos and Egr-1. We show here that Gfi1 inhibited the expression of c-Fos, Egr-1 and Egr-2, and rescued neutrophil development in cells expressing G-CSFR Y729F. Gfi1 directly bound to and repressed c-Fos and Egr-1, as has been shown for Egr-2, all of which are the immediate early genes (IEGs) of the Erk1/2 pathway. Interestingly, G-CSF- and M-CSF-stimulated activation of Erk1/2 was augmented in lineage-negative (Lin⁻) bone marrow (BM) cells from Gfi1^−/− mice. Suppression of Erk1/2 signaling resulted in diminished expression of c-Fos, Egr-1 and Egr-2, and partially rescued the neutrophil development of Gfi1^−/− BM cells, which are intrinsically defective for neutrophil development. Together, our data indicate that Gfi1 inhibits the expression of c-Fos, Egr-1 and Egr-2 through direct transcriptional repression and indirect inhibition of Erk1/2 signaling, and that Gfi1-mediated downregulation of c-Fos, Egr-1 and Egr-2 may contribute to the role of Gfi1 in granulopoiesis.

Targeting JNK pathway promotes human hematopoietic stem cell expansion

The limited number of human hematopoietic stem cells (HSCs) has restrained their widespread clinical application. Despite great efforts in recent years, the in vitro expansion of HSCs remains a challenge due to incomplete understanding of the signaling networks underlying HSC self-renewal. Here, we show that culturing human cord blood (CB) CD34⁺ cells with JNK-IN-8, an inhibitor of the JNK signaling pathway, can enhance the self-renewal of HSCs with a 3.88-fold increase in cell number. These cultured CD34⁺ cells repopulated recipient mice for 21 weeks and can form secondary engraftment that lasted for more than 21 weeks. Knockdown of c-Jun, a major downstream target in the JNK pathway, promoted the expansion of hematopoietic stem and progenitor cells (HSPCs). Our findings demonstrate a critical role of the JNK pathway in regulating HSC expansion, provide new insights into HSC self-renewal mechanism, and may lead to improved clinical application of HSCs.

Mathematical Analysis of Cytokine-Induced Differentiation of Granulocyte-Monocyte Progenitor Cells

Granulocyte-monocyte progenitor (GMP) cells play a vital role in the immune system by maturing into a variety of white blood cells, including neutrophils and macrophages, depending on exposure to cytokines such as various types of colony stimulating factors (CSF). Granulocyte-CSF (G-CSF) induces granulopoiesis and macrophage-CSF (M-CSF) induces monopoiesis, while granulocyte/macrophage-CSF (GM-CSF) favors monocytic and granulocytic differentiation at low and high concentrations, respectively. Although these differentiation pathways are well documented, the mechanisms behind the diverse behavioral responses of GMP cells to CSFs are not well understood. In this paper, we propose a mechanism of interacting CSF-receptors and transcription factors that control GMP differentiation, convert the mechanism into a set of differential equations, and explore the properties of this mathematical model using dynamical systems theory. Our model reproduces numerous experimental observations of GMP cell differentiation in response to varying dosages of G-CSF, M-CSF, and GM-CSF. In particular, we are able to reproduce the concentration-dependent behavior of GM-CSF induced differentiation, and propose a mechanism driving this behavior. In addition, we explore the differentiation of a fourth phenotype, monocytic myeloid-derived suppressor cells (M-MDSC), showing how they might fit into the classical pathways of GMP differentiation and how progenitor cells can be primed for M-MDSC differentiation. Finally, we use the model to make novel predictions that can be explored by future experimental studies.

Absence of myeloid Klf4 reduces prostate cancer growth with pro-atherosclerotic activation of tumor myeloid cells and infiltration of CD8 T cells

The microenvironment of prostate cancer often includes abundant tumor-associated macrophages (TAMs), with their acquisition of an M2 phenotype correlating with local aggressiveness and metastasis. Tumor-derived M-CSF contributes to TAM M2 polarization, and M-CSF receptor inhibition slows prostate cancer growth in model systems. As additional cytokines can direct TAM M2 polarization, targeting downstream transcription factors could avoid resistance. Klf4 and C/EBPβ each contribute to monocyte development, and reduced expression of macrophage Klf4 or C/EBPβ favors their adoption of a pro-inflammatory M1 state. We find that a Hi-Myc C57BL/6 prostate cancer line grows more slowly in syngeneic Klf4(f/f);Lys-Cre compared with Klf4(f/f) mice when inoculated subcutaneously, but grows equally rapidly in C/EBPβ(f/f);Lys-Cre and C/EBPβ(f/f) hosts. In the absence of myeloid Klf4, TAMs have reduced expression of surface mannose receptor and Fizz1 mRNA, both M2 markers. Global gene expression analysis further revealed activation of pro-inflammatory, pro-atherosclerotic pathways. Analysis of tumor-infiltrating lymphocytes (TILs) demonstrated markedly increased activated CD8 T cell numbers, and CD8 T cell depletion obviated the inhibitory effect of myeloid Klf4 deletion on prostate cancer growth. These findings suggest that reducing expression or activity of the Klf4 transcription factor in tumor myeloid cells may contribute to prostate cancer therapy.

Myeloid suppressor cells in cancer and autoimmunity

A bottleneck for immunotherapy of cancer is the immunosuppressive microenvironment in which the tumor cells proliferate. Cancers harness the immune regulatory mechanism that prevents autoimmunity from evading immunosurveillance and promoting immune destruction. Regulatory T cells, myeloid suppressor cells, inhibitory cytokines and immune checkpoint receptors are the major components of the immune system acting in concert with cancer cells and causing the subversion of anti-tumor immunity. This redundant immunosuppressive network poses an impediment to efficacious immunotherapy by facilitating tumor progression. Tumor-associated myeloid cells comprise heterogeneous populations acting systemically (myeloid-derived suppressor cells/MDSCs) and/or locally in the tumor microenvironment (MDSCs and tumor-associated macrophages/TAMs). Both populations promote cancer cell proliferation and survival, angiogenesis and lymphangiogenesis and elicit immunosuppression through different pathways, including the expression of immunosuppressive cytokines and checkpoint inhibitors. Several evidences have demonstrated that myeloid cells can express different functional programs in response to different microenvironmental signals, a property defined as functional plasticity. The opposed extremes of this functional flexibility are generally represented by the classical macrophage activation, which identifies inflammatory and cytotoxic M1 polarized macrophages, and the alternative state of macrophage activation, which identifies M2 polarized anti-inflammatory and immunosuppressive macrophages. Functional skewing of myeloid cells occurs in vivo under physiological and pathological conditions, including cancer and autoimmunity. Here we discuss how myeloid suppressor cells can on one hand support tumor growth and, on the other, limit autoimmune responses, indicating that their therapeutic reprogramming can generate opportunities in relieving immunosuppression in the tumor microenvironment or reinstating tolerance in autoimmune conditions.

LPS independent activation of the pro-inflammatory receptor Trem1 by C/EBPε in granulocytes

C/EBPε is a critical transcriptional factor for granulocyte differentiation and function. Individuals with germline mutations of C/EBPε fail to develop normal granulocytes and suffer from repeated infections. In order to gain a global view of the transcriptional machinery regulated by C/EBPε, we performed whole-genome ChIP-Seq using mouse bone marrow cells. To complement the C/EBPε DNA binding analyses, RNA-Sequencing was done in parallel using sorted mature and immature granulocytes from WT and C/EBPε KO bone marrow. This approach led to the identification of several direct targets of C/EBPε, which are potential effectors of its role in granulocytic differentiation and function. Interestingly, Trem1, a gene critical to granulocyte function, was identified as a direct C/EBPε target gene. Trem1 expression overlaps very closely with expression signature of C/EBPε during hematopoietic development. Luciferase reporter and EMSA assays revealed that C/EBPε binds to the regulatory elements of Trem1 and regulates its expression during granulocytic differentiation. In addition, we provide evidence that inflammatory stimuli (LPS) can also control the expression of Trem1 independent of C/EBPε. Overall, this study provides comprehensive profiling of the transcriptional network controlled by C/EBPε during granulopoiesis and identifies Trem1 as one of its downstream effectors involved in eliciting an immune response.

Nuclear ERK5 inhibits progression of leukemic monocytes to macrophages by regulating the transcription factor PU.1 and heat shock protein HSP70

Differentiation therapy can supplement the therapy of APL, but other subtypes of AML are treated principally with cytotoxic agents, with few lasting remissions. While the induction of monocyte followed by macrophage differentiation by vitamin D derivatives (VDDs) is dramatic in cultured AML cells of all subtypes, attempts to translate this to the clinic have not been effective. Thus, better understanding of the mechanisms underlying VDD-induced differentiation may improve this approach. The key events in this form of differentiation include increased expression of CD11b, and the transcription factor PU.1 is known to be a part of this process. We show here that in the transition of monocytes to macrophages induced by a VDD, ERK5, a member of the MAPK family of signaling molecules, prevents PU.1 expression. However, upon ERK5 inhibition PU.1 protein is stabilized by HSP70.Thus, ERK5 may be a target for manipulation of the immunoregulatory actions of macrophages in cancer.

C/EBPα represses slow myosin heavy chain 2 gene expression in developing avian myotubes

BACKGROUND

The CCAAT/enhancer binding proteins (C/EBP) comprise a family of transcription factors that regulate many cellular processes. Little is known of their function during embryonic and fetal myogenesis. Slow myosin heavy chain 2 (MyHC2) is a marker of the slow avian skeletal muscle fiber type, and slow MyHC2 gene regulation involves molecular pathways that lead to muscle fiber type diversification.

METHODS

The biological effects of C/EBPα and C/EBPβ expression were analyzed by use of a general C/EBP activity reporter and by slow MyHC2 promoter-reporter constructs transfected into specific myogenic cell lineages. The effects of C/EBPα and C/EBPβ expression were also analyzed by immunocytochemical detection of slow MyHC2. C/EBPα interaction with the slow MyHC2 promoter was assessed by electromobility shift assays.

RESULTS

C/EBPα and C/EBPβ are present in embryonic fast and fast/slow avian myogenic lineages. Overexpression of C/EBPα cDNA repressed slow MyHC2 promoter activity in embryonic myotubes and in both electrically stimulated fetal myotubes. Deletion analysis of the slow MyHC2 promoter-luciferase reporter demonstrated that the transcriptional repression mediated by C/EBPα occurs within the first 222bp upstream from exon 1 of the slow MyHC2 gene. Electromobility shift assays determined that C/EBPα can bind to a non-canonical C/EBP site within the slow MyHC2 gene, and mutation of this site reduced transcriptional repression of the slow MyHC2 gene.

CONCLUSION

C/EBPα, but not C/EBPβ, represses slow MyHC2 promoter activity via a non-canonical C/EBP binding element.

GENERAL SIGNIFICANCE

Members of the C/EBP family of transcription factors differentially regulate genes indicative of distinct muscle fiber types.

In Vivo Deletion of the Cebpa +37 kb Enhancer Markedly Reduces Cebpa mRNA in Myeloid Progenitors but Not in Non-Hematopoietic Tissues to Impair Granulopoiesis

The murine Cebpa gene contains a +37 kb, evolutionarily conserved 440 bp enhancer that directs high-level expression to myeloid progenitors in transgenic mice. The enhancer is bound and activated by Runx1, Scl, GATA2, C/EBPα, c-Myb, Pu.1, and additional Ets factors in myeloid cells. CRISPR/Cas9-mediated replacement of the wild-type enhancer with a variant mutant in its seven Ets sites leads to 20-fold reduction of Cebpa mRNA in the 32Dcl3 myeloid cell line. To determine the effect of deleting the enhancer in vivo, we now characterize C57BL/6 mice in which loxP sites flank a 688 bp DNA segment containing the enhancer. CMV-Cre mediated germline deletion resulted in diminution of the expected number of viable Enh(f/f);CMV-Cre offspring, with 28-fold reduction in marrow Cebpa mRNA but normal levels in liver, lung, adipose, intestine, muscle, and kidney. Cre-transduction of lineage-negative marrow cells in vitro reduced Cebpa mRNA 12-fold, with impairment of granulocytic maturation, morphologic blast accumulation, and IL-3 dependent myeloid colony replating for >12 generations. Exposure of Enh(f/f);Mx1-Cre mice to pIpC led to 14-fold reduction of Cebpa mRNA in GMP or CMP, 30-fold reduction in LSK, and <2-fold reduction in the LSK/SLAM subset. FACS analysis of marrow from these mice revealed 10-fold reduced neutrophils, 3-fold decreased GMP, and 3-fold increased LSK cells. Progenitor cell cycle progression was mildly impaired. Granulocyte and B lymphoid colony forming units were reduced while monocytic and erythroid colonies were increased, with reduced Pu.1 and Gfi1 and increased Egr1 and Klf4 in GMP. Finally, competitive transplantation indicated preservation of functional long-term hematopoietic stem cells upon enhancer deletion and confirmed marrow-intrinsic impairment of granulopoiesis and B cell generation with LSK and monocyte lineage expansion. These findings demonstrate a critical role for the +37 kb Cebpa enhancer for hematopoietic-specific Cebpa expression, with enhancer deletion leading to impaired myelopoiesis and potentially preleukemic progenitor expansion.

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.

Chitosan polyplex mediated delivery of miRNA-124 reduces activation of microglial cells in vitro and in rat models of spinal cord injury

Traumatic injury to the central nervous system (CNS) is further complicated by an increase in secondary neuronal damage imposed by activated microglia/macrophages. MicroRNA-124 (miR-124) is responsible for mouse monocyte quiescence and reduction of their inflammatory cytokine production. We describe the formulation and ex vivo transfection of chitosan/miR-124 polyplex particles into rat microglia and the resulting reduction of reactive oxygen species (ROS) and TNF-α and lower expression of MHC-II. Upon microinjection into uninjured rat spinal cords, particles formed with Cy3-labeled control sequence RNA, were specifically internalized by OX42 positive macrophages and microglia cells. Alternatively particles injected in the peritoneum were transported by macrophages to the site of spinal cord injury 72 h post injection. Microinjections of chitosan/miR-124 particles significantly reduced the number of ED-1 positive macrophages in the injured spinal cord. Taken together, these data present a potential treatment technique to reduce inflammation for a multitude of CNS neurodegenerative conditions.

FROM THE CLINICAL EDITOR

The treatment of spinal cord injury remains an unresolved problem. Secondary damage is often the result of inflammation caused by activated microglia and/or macrophages. In this article, the authors developed their formulation of chitosan/miR-124 polyplex particles and investigated their use in the suppression of neuronal inflammation. This exciting data may provide a new horizon for patients who suffer from spinal cord injury.

Role of Erk1/2 signaling in the regulation of neutrophil versus monocyte development in response to G-CSF and M-CSF

Lineage specification in the hematopoietic system depends on the expression of lineage specific transcription factors. However, the role of hematopoietic cytokines in this process has been controversial and little is known about the intracellular signaling mechanisms by which cytokines instruct lineage choice. G-CSF and M-CSF are two lineage-specific cytokines that play a dominant role in granulopoiesis and monopoiesis, respectively. We show here that a G-CSFR mutant in which tyrosine 729 had been mutated to phenylalanine (Y729F) promoted monocyte rather than neutrophil development in myeloid precursors, which was associated with prolonged activation of Erk1/2 and augmented activation of downstream targets c-Fos and Egr1. Inhibition of Erk1/2 activation or knockdown of c-Fos or Egr1 largely rescued neutrophil development in cells expressing G-CSFR Y729F. We also show that M-CSF, but not G-CSF, stimulated strong and sustained activation of Erk1/2 in mouse lineage marker negative (Lin(-)) bone marrow cells. Significantly, inhibition of Erk1/2 signaling in these cells favored neutrophil over monocyte development in response to M-CSF. Thus, prolonged Erk1/2 activation resulted in monocyte development following G-CSF induction whereas inhibition of Erk1/2 signaling promoted neutrophil development at the expense of monocyte formation in response to M-CSF. These results reveal an important mechanism by which G-CSF and M-CSF instruct neutrophil versus monocyte lineage choice, i.e. differential activation of Erk1/2 pathway.

ATF4 licenses C/EBPβ activity in human mesenchymal stem cells primed for adipogenesis

A well-established cascade of transcription factor (TF) activity orchestrates adipogenesis in response to chemical cues, yet how cell-intrinsic determinants of differentiation such as cell shape and/or seeding density inform this transcriptional program remain enigmatic. Here, we uncover a novel mechanism licensing transcription in human mesenchymal stem cells (hMSCs) adipogenically primed by confluence. Prior to adipogenesis, confluency promotes heterodimer recruitment of the bZip TFs C/EBPβ and ATF4 to a non-canonical C/EBP DNA sequence. ATF4 depletion decreases both cell-density-dependent transcription and adipocyte differentiation. Global profiling in hMSCs and a novel cell-free assay reveals that ATF4 requires C/EBPβ for genomic binding at a motif distinct from that bound by the C/EBPβ homodimer. Our observations demonstrate that C/EBPβ bridges the transcriptional programs in naïve, confluent cells and early differentiating pre-adipocytes. Moreover, they suggest that homo- and heterodimer formation poise C/EBPβ to execute diverse and stage-specific transcriptional programs by exploiting an expanded motif repertoire.

Regulation of the C/EBPα signaling pathway in acute myeloid leukemia (Review)

The transcription factor CCAAT/enhancer binding protein α (C/EBPα), as a critical regulator of myeloid development, directs granulocyte and monocyte differentiation. Various mechanisms have been identified to explain how C/EBPα functions in patients with acute myeloid leukemia (AML). C/EBPα expression is suppressed as a result of common leukemia-associated genetic and epigenetic alterations such as AML1-ETO, RARα-PLZF or gene promoter methylation. Recent data have shown that ubiquitination modification also contributes to its downregulation. In addition, 10-15% of patients with AML in an intermediate cytogenetic risk subgroup were characterized by mutations of the C/EBPα gene. As a transcription factor, C/EBPα can translocate into the nucleus and further regulate a variety of genes directly or indirectly, which are all key factors for cell differentiation. This review summarizes recent reports concerning the dysregulation of C/EBPα expression at various levels in human AML. The currently available data are persuasive evidence suggesting that impaired abnormal C/EBPα expression contributes to the development of AML, and restoration of C/EBPα expression as well as its function represents a promising target for novel therapeutic strategies in AML.

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.

ERK1/2 promoted proliferation and inhibited apoptosis of human cervical cancer cells and regulated the expression of c-Fos and c-Jun proteins

Small-molecule inhibitors targeted MAPK have been wildly used for some cancer therapeutics as a biologically viable model, but no one has been used for cervical caner. ERK1/2, one of MAPK kinases, is expressed high in cervical cancer tissue. The aim of the present study was to evaluate the effects of ERK1/2 inhibitor U0126 on proliferation and apoptosis of cervical cancer cells and appraise the correlated mechanism of the effects. In this study, the cell proliferation of Hela and C33A cervical cancer cells was tested by Cell Counting Kit-8 (CCK8) assay and cell counting after treated with ERK1/2 inhibitor U0126. The cell cycle and apoptosis were evaluated by flow cytometry (FCM). The protein levels of ERK1/2 and c-Fos and c-Jun were detected by Western blot. The results indicated that after down-regulating ERK1/2 proteins with the inhibitor U0126, Hela and C33A cells proliferation was inhibited, cell apoptosis was promoted, the proportions of G0/G1 stage in cell cycle increased, and G2/M stages decreased. After down-regulating ERK1/2 proteins of Hela and C33A cells, the expression levels of p-c-Fos protein decreased, while p-c-Jun protein increased. The results of this study indicated that ERK1/2 may promote the development of cervical cancer cells, suggesting ERK1/2 inhibitor may be used as an effective target for cervical cancer therapies working for. It might inhibit cervical cancer cells growth via regulating the transcription factors expression of c-Fos and c-Jun.

Transcription of inflammatory genes: long noncoding RNA and beyond

The innate immune system must coordinate elaborate signaling pathways to turn on expression of hundreds of genes to provide protection against pathogens and resolve acute inflammation. Multiple genes within distinct functional categories are coordinately and temporally regulated by transcriptional on and off switches in response to distinct external stimuli. Three classes of transcription factors act together with transcriptional coregulators and chromatin-modifying complexes to control these programs. In addition, newer studies implicate long noncoding RNA (lncRNA) as additional regulators of these responses. LncRNAs promote, fine-tune, and restrain the inflammatory program. In this study, we provide an overview of gene regulation and the emerging importance of lncRNAs in the immune system.

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.

The role of c-Jun in controlling the EPAC1-dependent induction of the SOCS3 gene in HUVECs

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EPAC1 promotes AP1-dependent transcription in HUVECs.

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Delineation of the minimal, EPAC1-responsive SOCS3 promoter in human cells.

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Phosphorylated c-Jun (Ser 63) is constitutively associated with the SOCS3 promoter.

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Phosphorylation of c-Jun on Ser63 requires activation of PKA, but not EPAC1.

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c-Jun is required for SOCS3 induction by cyclic AMP in MEFs.

The cyclic AMP sensor, EPAC1, activates AP1-mediated transcription in HUVECs. Correspondingly, induction of the SOCS3 minimal promoter by EPAC1 requires a single AP1 site that constitutively binds phosphorylated (Ser63) c-Jun in DNA-pull-down assays. c-Jun (Ser63) becomes further phosphorylated following cyclic AMP stimulation and specific activation of protein kinase A (PKA), but not through selective activation of EPAC1. Moreover, despite a requirement for c-Jun for SOCS3 induction in fibroblasts, phospho-null c-Jun (Ser63/73Ala) had little effect on SOCS3 induction by cyclic AMP in HUVECs. AP1 activation and SOCS3 induction by EPAC1 in HUVECs therefore occur independently of c-Jun phosphorylation on Ser63.

Combinatorial recruitment of CREB, C/EBPβ and c-Jun determines activation of promoters upon keratinocyte differentiation

Background

Transcription factors CREB, C/EBPβ and Jun regulate genes involved in keratinocyte proliferation and differentiation. We questioned if specific combinations of CREB, C/EBPβ and c-Jun bound to promoters correlate with RNA polymerase II binding, mRNA transcript levels and methylation of promoters in proliferating and differentiating keratinocytes.

Results

Induction of mRNA and RNA polymerase II by differentiation is highest when promoters are bound by C/EBP β alone, C/EBPβ together with c-Jun, or by CREB, C/EBPβ and c-Jun, although in this case CREB binds with low affinity. In contrast, RNA polymerase II binding and mRNA levels change the least upon differentiation when promoters are bound by CREB either alone or in combination with C/EBPβ or c-Jun. Notably, promoters bound by CREB have relatively high levels of RNA polymerase II binding irrespective of differentiation. Inhibition of C/EBPβ or c-Jun preferentially represses mRNA when gene promoters are bound by corresponding transcription factors and not CREB. Methylated promoters have relatively low CREB binding and, accordingly, those which are bound by C/EBPβ are induced by differentiation irrespective of CREB. Composite “Half and Half” consensus motifs and co localizing consensus DNA binding motifs are overrepresented in promoters bound by the combination of corresponding transcription factors.

Conclusion

Correlational and functional data describes combinatorial mechanisms regulating the activation of promoters. Colocalization of C/EBPβ and c-Jun on promoters without strong CREB binding determines high probability of activation upon keratinocyte differentiation.

Expressions of transcription factors in goldfish (Carassius auratus L.) macrophages and their progenitors

The development of macrophages is a highly regulated process requiring coordination amongst transcription factors. The presence/absence, relative levels, antagonism, or synergy of all transcription factors involved is critical to directing lineage cell fate and differentiation. While relative levels of many key myeloid transcription factors have been determined in mammalian macrophage differentiation, a similar set of studies have yet to be conducted in a teleost system. In this study, we report on the mRNA levels of transcription factors (cebpa, cjun, cmyb, egr1, gata1, gata2, gata3, lmo2, mafb, pax5, pu.1 and runx1) in sorted goldfish progenitor cells, monocytes, and macrophages from primary kidney macrophage cultures. The mRNA levels of runx1 and pu.1 were significantly higher, gata3 and pax5 mRNA levels were lower, in monocytes compared to progenitors, and the mRNA levels of cjun, egr1, gata2, gata3, mafb and pax5 were significantly decreased in macrophages compared to progenitor cells. The relative mRNA levels of the interferon regulatory factor family of transcription factors, irf1, irf2, irf5, irf7, irf8 and irf9 in sorted progenitors, monocytes and macrophages were also measured. In contrast to other irf family transcription factors examined, irf8 mRNA levels were increased in monocytes compared to progenitors by greater than three-fold, suggesting that irf8 is important for monopoiesis. Lastly, we show the differential regulation of myeloid transcription factor mRNA levels in sorted progenitor cells from 1, 2, or 3-day old cultures in response to the recombinant goldfish growth factors, rgCSF-1 and rgKITLA.

Regulation of microglial proliferation during chronic neurodegeneration

An important component of chronic neurodegenerative diseases is the generation of an innate inflammatory response within the CNS. Microglial and astroglial cells play a key role in the development and maintenance of this inflammatory response, showing enhanced proliferation and activation. We studied the time course and regulation of microglial proliferation, using a mouse model of prion disease. Our results show that the proliferation of resident microglial cells accounts for the expansion of the population during the development of the disease. We identify the pathway regulated by the activation of CSF1R and the transcription factors PU.1 and C/EBPα as the molecular regulators of the proliferative response, correlating with the chronic human neurodegenerative conditions variant Creutzfeldt-Jakob disease and Alzheimer's disease. We show that targeting the activity of CSF1R inhibits microglial proliferation and slows neuronal damage and disease progression. Our results demonstrate that microglial proliferation is a major component in the evolution of chronic neurodegeneration, with direct implications for understanding the contribution of the CNS innate immune response to disease progression.

The transcription factor PU.1 is critical for viability and function of human brain microglia

Microglia are the predominant resident immune cells of the brain and can assume a range of phenotypes. They are critical for normal brain development and function but can also contribute to many disease processes. Although they are widely studied, the transcriptional control of microglial phenotype and activation requires further research. PU.1 is a key myeloid transcription factor expressed by peripheral macrophages and rodent microglia. In this article, we report the presence of PU.1 specifically in microglia of the adult human brain and we examine its functional role in primary human microglia. Using siRNA, we achieved substantial PU.1 protein knock-down in vitro. By assessing a range of characteristic microglial proteins we found decreased viability of adult human microglia with reduced PU.1 protein expression. This observation was confirmed with PU.1 antisense DNA oligonucleotides. An important function of microglia is to clear debris by phagocytosis. We assessed the impact of loss of PU.1 on microglial phagocytosis and show that PU.1 siRNA reduces the ability of adult human microglia to phagocytose amyloid-beta1-42 peptide. These results show that PU.1 controls human microglial viability and function and suggest PU.1 as a molecular target for manipulation of human microglial phenotype.

The role of bioactive nanofibers in enamel regeneration mediated through integrin signals acting upon C/EBPα and c-Jun

Enamel formation involves highly orchestrated intracellular and extracellular events; following development, the tissue is unable to regenerate, making it a challenging target for tissue engineering. We previously demonstrated the ability to trigger enamel differentiation and regeneration in the embryonic mouse incisor using a self-assembling matrix that displayed the integrin-binding epitope RGDS (Arg-Gly-Asp-Ser). To further elucidate the intracellular signaling pathways responsible for this phenomenon, we explore here the coupling response of integrin receptors to the biomaterial and subsequent downstream gene expression profiles. We demonstrate that the artificial matrix activates focal adhesion kinase (FAK) to increase phosphorylation of both c-Jun N-terminal kinase (JNK) and its downstream transcription factor c-Jun (c-Jun). Inhibition of FAK blocked activation of the identified matrix-mediated pathways, while independent inhibition of JNK nearly abolished phosphorylated-c-Jun (p-c-Jun) and attenuated the pathways identified to promote enamel regeneration. Cognate binding sites in the amelogenin promoter were identified to be transcriptionally up-regulated in response to p-c-Jun. Furthermore, the artificial matrix induced gene expression as evidenced by an increased abundance of amelogenin, the main protein expressed during enamel formation, and the CCAAT enhancer binding protein alpha (C/EBPα), which is the known activator of amelogenin expression. Elucidating these cues not only provides guidelines for the design of synthetic regenerative strategies and opportunities to manipulate pathways to regulate enamel regeneration, but can provide insight into the molecular mechanisms involved in tissue formation.

MicroRNAs are universal regulators of differentiation, activation, and polarization of microglia and macrophages in normal and diseased CNS

MicroRNAs (miRNAs) are a class of small (∼22 nucleotides) noncoding RNAs involved in the regulation of gene expression at the post-translational level. It is estimated that 30-90% of human genes are regulated by miRNAs, which makes these molecules of great importance for cell growth, activation, and differentiation. Microglia is CNS-resident cells of a myeloid lineage that play an important role in immune surveillance and are actively involved in many neurologic pathologies. Although the exact origin of microglia remains enigmatic, it is established that primitive macrophages from a yolk sac populate the brain and spinal cord in normal conditions throughout development. During various pathological events such as neuroinflammation, bone marrow derived myeloid cells also migrate into the CNS. Within the CNS, both primitive macrophages from the yolk sac and bone marrow derived myeloid cells acquire a specific phenotype upon interaction with other cell types within the CNS microenvironment. The factors that drive differentiation of progenitors into microglia and control the state of activation of microglia and bone marrow-derived myeloid cells within the CNS are not well understood. In this review we will summarize the role of miRNAs during activation and differentiation of myeloid cells. The role of miR-124 in the adaptation of microglia and macrophages to the CNS microenvironment will be further discussed. We will also summarize the role of miRNAs as modulators of activation of microglia and microphages. Finally, we will describe the role of miR-155 and miR-124 in the polarization of macrophages towards classically and alternatively activated phenotypes.

ATXN8 -62 G/A promoter polymorphism and risk of Taiwanese Parkinson's disease

BACKGROUND AND PURPOSE

We recently reported a novel -62 G/A polymorphism within ataxin 8 (ATXN8) gene promoter region, with -62 G displaying significantly higher luciferase activity compared with -62 A. Phenotypic variability in spinocerebellar ataxia type 8 (SCA8) has been suggested, and large SCA8 repeats were found in patients with Parkinson's disease (PD). We aimed to investigate the association of ATXN8 -62 G/A polymorphism with the risk of Taiwanese PD, and identify the trans-acting factor modulating the ATXN8 promoter activity.

METHODS

A case-control study in a cohort of 569 PD cases and 547 ethnically matched controls was conducted by polymerase chain reaction (PCR) and restriction enzyme analysis. The trans-acting factor binding to the ATXN8 promoter was examined by chromatin immunoprecipitation (ChIP)-PCR assay, cDNA co-transfection and luciferase reporter assay.

RESULTS

When genotype distribution was calculated by comparing the rare AA genotype with the GG + GA genotypes (recessive model), a significant difference was found (P = 0.035, 1 df). Individuals carrying AA genotype exhibited a decreased risk of developing PD (odds ratio: 0.73; 95% CI: 0.55-0.98, P = 0.035). After stratification by age, individuals over 60 years of age carrying AA genotype demonstrated a further decrease in the risk of developing PD (odds ratio: 0.64; 95% CI: 0.43-0.96, P = 0.030). ChIP-PCR and cDNA over-expression revealed that CCAAT/enhancer-binding protein alpha binds to the ATXN8 proximal promoter to upregulate ATXN8 expression in neuroblastoma SK-N-SH cells.

CONCLUSIONS

Our data suggest that ATXN8 -62 G/A polymorphism plays a role in Taiwanese PD susceptibility.

Positive regulation of NADPH oxidase 5 by proinflammatory-related mechanisms in human aortic smooth muscle cells

NADPH oxidase Nox5 subtype expression is significantly increased in vascular smooth muscle cells (SMCs) underlying fibro-lipid atherosclerotic lesions. The mechanisms that up-regulate Nox5 are not understood. Consequently, we characterized the promoter of the human Nox5 gene and investigated the role of various proinflammatory transcription factors in the regulation of Nox5 in human aortic SMCs. The Nox5 promoter was cloned in the pGL3 basic reporter vector. Functional analysis was done employing 5' deletion mutants to identify the sequences necessary to effect high levels of expression in SMCs. Transcriptional initiation site was detected by rapid amplification of the 5'-cDNA ends. In silico analysis indicated the existence of typical NF-kB, AP-1, and STAT1/STAT3 sites. Transient overexpression of p65/NF-kB, c-Jun/AP-1, or STAT1/STAT3 increased significantly the Nox5 promoter activity. Chromatin immunoprecipitation demonstrated the physical interaction of c-Jun/AP-1 and STAT1/STAT3 proteins with the Nox5 promoter. Lucigenin-enhanced chemiluminescence, real-time PCR, and Western blot assays showed that pharmacological inhibition and the silencing of p65/NF-kB, c-Jun/AP-1, or STAT1/STAT3 reduced significantly the interferon γ-induced Ca(2+)-dependent Nox activity and Nox5 expression. Up-regulated Nox5 correlated with increases in intracellular Ca(2+), an essential condition for Nox5 activity. NF-kB, AP-1, and STAT1/STAT3 are important regulators of Nox5 in SMCs by either direct or indirect mechanisms. Overexpressed Nox5 may generate free radicals in excess, further contributing to SMCs dysfunction in atherosclerosis.

Dynamic epigenetic enhancer signatures reveal key transcription factors associated with monocytic differentiation states

Cellular differentiation is orchestrated by lineage-specific transcription factors and associated with cell type-specific epigenetic signatures. In the present study, we used stage-specific, epigenetic "fingerprints" to deduce key transcriptional regulators of the human monocytic differentiation process. We globally mapped the distribution of epigenetic enhancer marks (histone H3 lysine 4 monomethylation, histone H3 lysine 27 acetylation, and the histone variant H2AZ), describe general properties of marked regions, and show that cell type-specific epigenetic "fingerprints" are correlated with specific, de novo-derived motif signatures at all of the differentiation stages studied (ie, hematopoietic stem cells, monocytes, and macrophages). We validated the novel, de novo-derived, macrophage-specific enhancer signature, which included ETS, CEBP, bZIP, EGR, E-Box and NF-κB motifs, by ChIP sequencing for a subset of motif corresponding transcription factors (PU.1, C/EBPβ, and EGR2), confirming their association with differentiation-associated epigenetic changes. We describe herein the dynamic enhancer landscape of human macrophage differentiation, highlight the power of genome-wide epigenetic profiling studies to reveal novel functional insights, and provide a unique resource for macrophage biologists.

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.

The emerging role of C/EBPs in glucocorticoid signaling: lessons from the lung

Glucocorticoids (GCs) have been successfully used in the treatment of inflammatory diseases for decades. However, there is a relative GC resistance in several inflammatory lung disorders, such as chronic obstructive pulmonary disease (COPD), but still the mechanism(s) behind this unresponsiveness remains unknown. Interaction between transcription factors and the GC receptor contribute to GC effects but may also provide mechanisms explaining steroid resistance. CCAAT/enhancer-binding protein (C/EBP) transcription factors are important regulators of pulmonary gene expression and have been implicated in inflammatory lung diseases such as asthma, pulmonary fibrosis, cystic fibrosis, sarcoidosis, and COPD. In addition, several studies have indicated a role for C/EBPs in mediating GC effects. In this review, we discuss the different mechanisms of GC action as well as the function of the lung-enriched members of the C/EBP transcription factor family. We also summarize the current knowledge of the role of C/EBP transcription factors in mediating the effects of GCs, with emphasis on pulmonary effects, and their potential role in mediating GC resistance.

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.

Characterization of granulocyte colony stimulating factor receptor of the goldfish (Carassius auratus L.)

Granulocyte colony stimulating factor receptor (GCSFR) is a member of the class I cytokine receptor superfamily and signaling through this receptor is important for the proliferation, differentiation and activation of neutrophils and their precursors. In this study we report on the cloning and molecular characterization of goldfish GCSFR. The identified goldfish GCSFR sequence possesses the conserved Ig-like domain, the cytokine receptor homology domain (CRH), three fibronectin domains as well as several intracellular signaling motifs characteristic of other vertebrate GCSFRs. Goldfish gcsfr mRNA was highly expressed in kidney and spleen, and in primary kidney neutrophils. The neutrophils have significantly higher mRNA levels of the transcription factors pu.1 and cebpα, and down-regulated levels of transcription factors important for macrophage development such as egr1 and cjun, compared to progenitor cells from the kidney. The gcsfr mRNA was present in the kidney progenitor cells, albeit at much lower levels compared to the neutrophils, and the expression of gcsfr in progenitor cells was not affected by duration of cultivation. Furthermore, gcsfr mRNA levels were up-regulated in neutrophils after treatment with heat-killed Aeromonas salmonicida A449 or with mitogens. Our results indicate that GCSFR may be a useful marker for fish neutrophils.

The role of transcription factors in the guidance of granulopoiesis

In recent years, the prospective isolation of hematopoietic stem and progenitor cells has identified the hierarchical structure of hematopoietic development and lineage-commitment. Moreover, these isolated cell populations allowed the elucitation of the molecular mechansims associated with lineage choice and revealed the indispensable functions of transcription factors as lineage determinants. This review summarizes current concepts regarding adult murine granulopoiesis and illustrates the importance of the transcription factors C/EBPα, PU.1 and GATA-2 for the development of neutrophil, eosinophil and basophil granulocytes.

C/EBPα, C/EBPα oncoproteins, or C/EBPβ preferentially bind NF-κB p50 compared with p65, focusing therapeutic targeting on the C/EBP:p50 interaction

Canonical nuclear factor kappaB (NF-κB) activation signals stimulate nuclear translocation of p50:p65, replacing inhibitory p50:p50 with activating complexes on chromatin. C/EBP interaction with p50 homodimers provides an alternative pathway for NF-κB target gene activation, and interaction with p50:p65 may enhance gene activation. We previously found that C/EBPα cooperates with p50, but not p65, to induce Bcl-2 transcription and that C/EBPα induces Nfkb1/p50, but not RelA/p65, transcription. Using p50 and p65 variants containing the FLAG epitope at their N- or C-termini, we now show that C/EBPα, C/EBPα myeloid oncoproteins, or the LAP1, LAP2, or LIP isoforms of C/EBPβ have markedly higher affinity for p50 than for p65. Deletion of the p65 transactivation domain did not increase p65 affinity for C/EBPs, suggesting that unique residues in p50 account for specificity, and clustered mutation of HSDL in the "p50 insert" lacking in p65 weakens interaction. Also, in contrast to Nfkb1 gene deletion, absence of the RelA gene does not reduce Bcl-2 or Cebpa RNA in unstimulated cells or prevent interaction of C/EBPα with the Bcl-2 promoter. Saturating mutagenesis of the C/EBPα basic region identifies R300 and nearby residues, identical in C/EBPβ, as critical for interaction with p50. These findings support the conclusion that C/EBPs activate NF-κB target genes via contact with p50 even in the absence of canonical NF-κB activation and indicate that targeting C/EBP:p50 rather than C/EBP:p65 interaction in the nucleus will prove effective for inflammatory or malignant conditions, alone or synergistically with agents acting in the cytoplasm to reduce canonical NF-κB activation.