C/EBPepsilon is a myeloid-specific activator of cytokine, chemokine, and macrophage-colony-stimulating factor receptor genes

The function and regulation of CCAAT/enhancer binding protein ε

In recent years, studies on the structure, function, and regulation of the C/EBPε gene have become an essential topic in the field of many diseases. CCAAT/enhancer-binding protein ε (C/EBPε) is the fifth member of the transcription factor CCAAT/C/EBP family of transcription factors. It plays crucial roles in cell proliferation, differentiation, immunity, energy metabolism, and hematopoiesis. C/EBPε plays essential roles in regulating the hematopoietic system, including myeloid cell development and maturation, participation in the body’s immune responses, and prevention of infections. C/EBPε function is regulated by phosphorylation, acetylation, methylation, and other types of genes. This review related to C/EBPε structure, function and regulation provides a theoretical basis for subsequent research in this area. C/EBPε is an emerging therapeutic target and thus provides new strategies for disease prevention and control.

Assessment of DNA methylation in porcine immune cells reveals novel regulatory elements associated with cell-specific gene expression and immune capacity traits

Background

Genetics studies in the porcine immune system have enhanced selection practices for disease resistance phenotypes and increased the efficacy of porcine models in biomedical research; however limited functional annotation of the porcine immunome has hindered progress on both fronts. Among epigenetic mechanisms that regulate gene expression, DNA methylation is the most ubiquitous modification made to the DNA molecule and influences transcription factor binding as well as gene and phenotype expression. Human and mouse DNA methylation studies have improved mapping of regulatory elements in these species, but comparable studies in the pig have been limited in scope.

Results

We performed whole-genome bisulfite sequencing to assess DNA methylation patterns in nine pig immune cell populations: CD21⁺ and CD21⁻ B cells, four T cell fractions (CD4⁺, CD8⁺, CD8⁺CD4⁺, and SWC6γδ⁺), natural killer and myeloid cells, and neutrophils. We identified 54,391 cell differentially methylated regions (cDMRs), and clustering by cDMR methylation rate grouped samples by cell lineage. 32,737 cDMRs were classified as cell lowly methylated regions (cLMRs) in at least one cell type, and cLMRs were broadly enriched in genes and regions of intermediate CpG density. We observed strong correlations between differential methylation and expression across immune cell populations, with cell-specific low methylation disproportionately impacting genes exhibiting enriched gene expression in the same cell type. Motif analysis of cLMRs revealed cell type-specific enrichment of transcription factor binding motifs, indicating that cell-specific methylation patterns may influence accessibility by trans-acting factors. Lastly, cDMRs were enriched for immune capacity GWAS SNPs, and many such overlaps occurred within genes known to influence immune cell development and function (CD8B, NDRG1).

Conclusion

Our DNA methylation data improve functional annotation of the porcine genome through characterization of epigenomic regulatory patterns that contribute to immune cell identity and function, and increase the potential for identifying mechanistic links between genotype and phenotype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08773-5.

CCAAT/Enhancer-Binding Protein ε27 Antagonism of GATA-1 Transcriptional Activity in the Eosinophil Is Mediated by a Unique N-Terminal Repression Domain, Is Independent of Sumoylation and Does Not Require DNA Binding

CCAAT/enhancer binding protein epsilon (C/EBPε) is required for eosinophil differentiation, lineage-specific gene transcription, and expression of C/EBPε³² and shorter 27kD and 14kD isoforms is developmentally regulated during this process. We previously defined the 27kD isoform (C/EBPε²⁷) as an antagonist of GATA-1 transactivation of the eosinophil's major basic protein-1 (MBP1) P2-promoter, showing C/EBPε²⁷ and GATA-1 physically interact. In the current study, we used a Tat-C/EBPε²⁷ fusion protein for cell/nuclear transduction of an eosinophil myelocyte cell line to demonstrate that C/EBPε²⁷ is a potent repressor of MBP1 transcription. We performed structure-function analyses of C/EBPε²⁷ mapping its repressor domains, comparing it to C/EBPε³² and C/EBPε¹⁴, using GATA-1 co-transactivation of the MBP1-P2 promoter. Results show C/EBPε²⁷ repression of GATA-1 is mediated by its unique 68aa N-terminus combined with previously identified RDI domain. This repressor activity does not require, but is enhanced by, DNA binding via the basic region of C/EBPε²⁷ but independent of sumoylation of the RDI core "VKEEP" sumoylation site. These findings identify the N-terminus of C/EBPε²⁷ as the minimum repressor domain required for antagonism of GATA-1 in the eosinophil. C/EBPε²⁷ repression of GATA-1 occurs via a combination of both C/EBPε²⁷-GATA-1 protein-protein interaction and C/EBPε²⁷ binding to a C/EBP site in the MBP1 promoter. The C/EBPε²⁷ isoform may serve to titrate and/or turn off eosinophil granule protein genes like MBP1 during eosinophil differentiation, as these genes are ultimately silenced in the mature cell. Understanding the functionality of C/EBPε²⁷ in eosinophil development may prove promising in developing therapeutics that reduce eosinophil proliferation in allergic diseases.

Transcription factor and cytokine regulation of eosinophil lineage commitment

PURPOSE OF REVIEW

Lineage commitment is governed by instructive and stochastic signals, which drive both active induction of the lineage program and repression of alternative fates. Eosinophil lineage commitment is driven by the ordered interaction of transcription factors, supported by cytokine signals. This review summarizes key findings in the study of eosinophil lineage commitment and examines new data investigating the factors that regulate this process.

RECENT FINDINGS

Recent and past studies highlight how intrinsic and extrinsic signals modulate transcription factor network and lineage decisions. Early action of the transcription factors C/EBPα and GATA binding protein-1 along with C/EBPε supports lineage commitment and eosinophil differentiation. This process is regulated and enforced by the pseudokinase Trib1, a regulator of C/EBPα levels. The cytokines interleukin (IL)-5 and IL-33 also support early eosinophil development. However, current studies suggest that these cytokines are not specifically required for lineage commitment.

SUMMARY

Together, recent evidence suggests a model where early transcription factor activity drives expression of key eosinophil genes and cytokine receptors to prime lineage commitment. Understanding the factors and signals that control eosinophil lineage commitment may guide therapeutic development for eosinophil-mediated diseases and provide examples for fate choices in other lineages.

First description of the rs45496295 polymorphism of the C/EBPE gene in β-thalassemia intermedia patients

The C/EBPE gene, located in 14q11.2, encodes for a B/zip-type transcription factor. The C/EBPɛ is involved in terminal differentiation and functional maturity of granulocyte progenitor cells and in cell apoptosis during myeloid differentiation. A C/EBPE gene has recently been described as a candidate gene involved in clinical variability of β-thalassemia (β-thal). In this study, the C/EBPE gene was sequenced in 146 subjects divided into the severe type of β-thal major (β-TM) and moderate type of β-thal intermedia (β-TI), and a control group. The analysis identified the rs45496295 (C > T) polymorphism in the heterozygous state in 73.9% β-TI patients, which was not the case in the β-TM patients or in the control group. Thus, the T allele is consequently associated with the β-TI group (p = 10^-3). According to the Human Splicing Finder (version 3.0, Marseille, France), the presence of the rs45496295 polymorphism leads the creation of a new intronic exotic splicing enhancer (ESE) site. Moreover, the T allele of rs45496295 is associated with a lower transfusion regimen (p = 10^-3) and a higher pretransfusion hemoglobin (Hb) rate (p = .006). The comparison of several factors concerning T allele carriers and non-carriers showed that the T allele does not act on the Hb F rate. The T allele of rs45496295, associated with moderate type of β-thal, seems to modify the C/EBPɛ action, thereby preventing the hemolysis.

Macrophage ABHD5 promotes colorectal cancer growth by suppressing spermidine production by SRM

Metabolic reprogramming in stromal cells plays an essential role in regulating tumour growth. The metabolic activities of tumour-associated macrophages (TAMs) in colorectal cancer (CRC) are incompletely characterized. Here, we identify TAM-derived factors and their roles in the development of CRC. We demonstrate that ABHD5, a lipolytic co-activator, is ectopically expressed in CRC-associated macrophages. We demonstrate in vitro and in mouse models that macrophage ABHD5 potentiates growth of CRC cells. Mechanistically, ABHD5 suppresses spermidine synthase (SRM)-dependent spermidine production in macrophages by inhibiting the reactive oxygen species-dependent expression of C/EBPɛ, which activates transcription of the srm gene. Notably, macrophage-specific ABHD5 transgene-induced CRC growth in mice can be prevented by an additional SRM transgene in macrophages. Altogether, our results show that the lipolytic factor ABHD5 suppresses SRM-dependent spermidine production in TAMs and potentiates the growth of CRC. The ABHD5/SRM/spermidine axis in TAMs might represent a potential target for therapy.

ABHD5 is a co-activator of lipolysis. Here the authors show that in tumour-associated macrophages ABHD5 inhibits ROS-dependent induction of C/EBP_ɛ, which transcriptionally activates spermidine synthase, and that blocking ABHD5 delays colorectal cancer growth in mice by inhibiting spermidine production.

Quaking promotes monocyte differentiation into pro-atherogenic macrophages by controlling pre-mRNA splicing and gene expression

A hallmark of inflammatory diseases is the excessive recruitment and influx of monocytes to sites of tissue damage and their ensuing differentiation into macrophages. Numerous stimuli are known to induce transcriptional changes associated with macrophage phenotype, but posttranscriptional control of human macrophage differentiation is less well understood. Here we show that expression levels of the RNA-binding protein Quaking (QKI) are low in monocytes and early human atherosclerotic lesions, but are abundant in macrophages of advanced plaques. Depletion of QKI protein impairs monocyte adhesion, migration, differentiation into macrophages and foam cell formation in vitro and in vivo. RNA-seq and microarray analysis of human monocyte and macrophage transcriptomes, including those of a unique QKI haploinsufficient patient, reveal striking changes in QKI-dependent messenger RNA levels and splicing of RNA transcripts. The biological importance of these transcripts and requirement for QKI during differentiation illustrates a central role for QKI in posttranscriptionally guiding macrophage identity and function.

Post-transcriptional control of RNA is important in health and disease. Here, the authors show that the RNA-binding protein Quaking guides pre-mRNA splicing and transcript abundance during monocyte to macrophage differentiation, and that Quaking depletion impairs pro-atherogenic foam cell formation.

Acetylation of C/EBPε is a prerequisite for terminal neutrophil differentiation

C/EBPε, a member of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors, is exclusively expressed in myeloid cells and regulates transition from the promyelocytic stage to the myelocytic stage of neutrophil development, being indispensable for secondary and tertiary granule formation. Knowledge concerning the functional role of C/EBPε posttranslational modifications is limited to studies concerning phosphorylation and sumoylation. In the current study, using ectopic expression and ex vivo differentiation of CD34(+) hematopoietic progenitor cells, we demonstrate that C/EBPε is acetylated, which was confirmed by mass spectrometry analysis, identifying 4 acetylated lysines in 3 distinct functional domains. Regulation of C/EBPε acetylation levels by the p300 acetyltransferase and the sirtuin 1 deacetylase controls transcriptional activity, which can at least in part be explained by modulation of DNA binding. During neutrophil development, acetylation of lysines 121 and 198 were found to be crucial for terminal neutrophil differentiation and the expression of neutrophil-specific granule proteins, including lactoferrin and collagenase. Taken together, our data illustrate a critical role for acetylation in the functional regulation of C/EBPε activity during terminal neutrophil development.

Human α-defensin expression is not dependent on CCAAT/enhancer binding protein-ε in a murine model

Specific granule deficiency (SGD) is a rare congenital disorder characterized by recurrent infections. The disease is caused by inactivating mutations of the CCAAT/enhancer binding protein-ε (C/EBP-ε) gene. As a consequence, specific and gelatinase granules lack most matrix proteins. Furthermore, azurophil granules contain diminished amounts of their most abundant proteins, α-defensins, also known as human neutrophil peptides (HNPs). In accordance with this, in vitro models have demonstrated induction of HNPs by C/EBP-ε. Since mice do not express myeloid defensins, they cannot per se be used to characterize the role of C/EBP-ε in controlling HNP expression in vivo. We therefore crossed a transgenic HNP-1-expressing mouse with the Cebpe^-/- mouse to study the in vivo significance of C/EBP-ε for HNP-1 transcription and expression. Surprisingly, neither expression nor processing of HNP-1 was affected by lack of C/EBP-ε in these mice. Transduction of C/EBP-ε into primary bone marrow cells from HNP-1 mice induced some HNP-1 expression, but not to levels comparable to expression human cells. Taken together, our data infer that the HNP-1 of the transgenic mouse does not show an expression pattern equivalent to endogenous secondary granule proteins. This limits the use of these transgenic mice as a model for human conditions.

Deficiency of CCAAT/enhancer binding protein-epsilon reduces atherosclerotic lesions in LDLR-/- mice

The CCAAT/enhancer binding proteins (C/EBPs) are transcription factors involved in hematopoietic cell development and induction of several inflammatory mediators. C/EBPε is expressed only in myeloid cells including monocytes/macrophages. Atherosclerosis is an inflammatory disorder of the vascular wall and circulating immune cells such as monocytes/macrophages. Mice deficient in the low density lipoprotein (LDL) receptor (Ldlr−/−) fed on a high cholesterol diet (HCD) show elevated blood cholesterol levels and are widely used as models to study human atherosclerosis. In this study, we generated Ldlr and Cebpe double-knockout (llee) mice and compared their atherogenic phenotypes to Ldlr single deficient (llEE) mice after HCD. Macrophages from llee mice have reduced lipid uptake by foam cells and impaired phagokinetic motility in vitro compared to macrophages from llEE mice. Also, compared to llEE mice, llee mice have alterations of lipid metabolism, and reduced atheroma and obesity, particularly the males. Peritoneal macrophages of llee male mice have reduced mRNA expression of FABP4, a fatty acid binding protein implicated in atherosclerosis. Overall, our study suggests that the myeloid specific factor C/EBPε is involved in systemic lipid metabolism and that silencing of C/EBPε could decrease the development of atherosclerosis.

C/EBPε mediates nicotinamide-enhanced clearance of Staphylococcus aureus in mice

The myeloid-specific transcription factor, CCAAT/enhancer-binding protein ε (C/EBPε) is a critical mediator of myelopoiesis. Mutation of this gene is responsible for neutrophil-specific granule deficiency in humans, a condition that confers susceptibility to Staphylococcus aureus infection. We found that C/EBPε-deficient mice are severely affected by infection with S. aureus, and C/EBPε deficiency in neutrophils contributes to the infectious phenotype. Conversely, exposure to the epigenetic modulator nicotinamide (vitamin B3) increased expression of C/EBPε in WT myeloid cells. Further, nicotinamide increased the activity of C/EBPε and select downstream antimicrobial targets, particularly in neutrophils. In a systemic murine infection model as well as in murine and human peripheral blood, nicotinamide enhanced killing of S. aureus by up to 1,000 fold but had no effect when administered to either C/EBPε-deficient mice or mice depleted of neutrophils. Nicotinamide was efficacious in both prophylactic and therapeutic settings. Our findings suggest that C/EBPε is an important target to boost killing of bacteria by the innate immune system.

Proteomic analysis reveals a novel mechanism induced by the leukemic oncogene Tel/PDGFRβ in stem cells: activation of the interferon response pathways

Objective proteomic analysis offers opportunities for hypothesis generation on molecular events associated with pathogenesis in stem cells. Relative quantification mass spectrometry was employed to identify pathways affected by Tel/PDGFRβ, an oncogene associated with myeloproliferative neoplasia (MPN). Its effects on over 1800 proteins were quantified with high confidence. Of those up-regulated by Tel/PDGFRβ several were involved in the interferon gamma (IFNγ) response. To validate these observations we employed embryonic and myeloid stem cells models which revealed Tel/PDGFRβ-induced STAT1 up-regulation and activation was responsible for modulating the interferon response. A STAT1 target highly up-regulated was ICSBP, a transcriptional regulator of myeloid and eosinophilic differentiation. ICSBP interacts with CBP/p300 and Ets transcription factors, to promote transcription of additional genes, including the Egr family, key regulators of myelopoiesis. These interferon responses were recapitulated using IFNγ stimulation of stem cells. Thus Tel/PDGFRβ induces aberrant IFN signaling and downstream targets, which may ultimately impact the hematopoietic transcriptional factor network to bias myelomonocytic differentiation in this MPN.

C/EBPepsilon directs granulocytic-vs-monocytic lineage determination and confers chemotactic function via Hlx

OBJECTIVE

Mutations in the CCAAT enhancer binding protein epsilon (C/EBPepsilon) gene have been identified in the cells of patients with neutrophil specific granule deficiency, a rare congenital disorder marked by recurrent bacterial infections. Their neutrophils, in addition to lacking specific granules required for normal respiratory burst activity, also lack normal phagocytosis and chemotaxis. Although the specific granule deficiency phenotype has been replicated in C/EBPepsilon(-/-) (knockout [KO]) mice, the mechanisms by which C/EBPepsilon mutations act to decrease neutrophil function are not entirely clear.

MATERIALS AND METHODS

In order to determine the role of C/EBPepsilon in neutrophil differentiation and migration, we generated immortalized progenitor cell lines from C/EBPepsilon KO and wild-type mice and performed expression and flow cytometric analysis and functional studies.

RESULTS

Expression of lineage-specific cell surface antigens on our in vitro differentiated cell lines revealed persistent expression of monocytic markers on KO granulocytes. We verified this in primary murine peripheral blood and bone marrow cells. In addition, KO bone marrow had an increase in immature myeloid precursors at the common myeloid progenitor and granulocyte/monocyte progenitor levels, suggesting a critical role for C/EBPepsilon not only in granulocyte maturation beyond the promyelocyte stage, but also in the monocyte/granulocyte lineage decision. We found that restoration of Hlx (H2.0-like homeo box 1) expression, which was decreased in C/EBPepsilon KO cells, rescued chemotaxis, but not the other defects of C/EBPepsilon KO neutrophils.

CONCLUSIONS

We show two new regulatory functions of C/EBPepsilon in myelopoiesis: in the absence of C/EBPepsilon, there is not only incomplete differentiation of granulocytes, but myelopoiesis is disrupted with the appearance of an intermediate cell type with monocyte and granulocyte features, and the neutrophils have abnormal chemotaxis. Restoration of expression of Hlx provides partial recovery of function; it has no effect on neutrophil maturation, but can completely ameliorate the chemotaxis defect in C/EBPepsilon KO cells.

C/EBPzeta (CHOP/Gadd153) is a negative regulator of LPS-induced IL-6 expression in B cells

C/EBPzeta was originally identified as a gene induced upon DNA damage and growth arrest. It has been shown to be involved in the cellular response to endoplasmic reticulum stress. Because of sequence divergence from other C/EBP family members in its DNA-binding domain and its consequent inability to bind the C/EBP consensus-binding motif, C/EBPzeta can act as a dominant negative inhibitor of other C/EBPs. C/EBP transactivators are essential to the expression of many proinflammatory cytokines and acute phase proteins, but a role for C/EBPzeta in regulating their expression has not been described. We found that expression of C/EBPzeta is induced in response to LPS treatment of B cells at both the mRNA and protein levels. Correlating with the highest levels of C/EBPzeta expression at 48 h after LPS treatment, there is an increased association of C/EBPzeta with C/EBPbeta, and both the abundance of C/EBP DNA-binding species and IL-6 expression are downregulated. Furthermore, ectopic expression of C/EBPzeta inhibited C/EBPbeta-dependent IL-6 expression from both the endogenous IL-6 gene and an IL-6 promoter-reporter. These results suggest that C/EBPzeta functions as negative regulator of IL-6 expression in B cells and that it contributes to the transitory expression of IL-6 that is observed after LPS treatment.

Human C/EBP-epsilon activator and repressor isoforms differentially reprogram myeloid lineage commitment and differentiation

CCAAT enhancer-binding protein-epsilon (C/EBP-epsilon) is required for the terminal differentiation of neutrophils and eosinophils. Human C/EBP-epsilon is expressed as 4 isoforms (32, 30, 27, and 14 kDa) through differential RNA splicing, and alternative promoters and translational start sites. The C/EBP-epsilon(32/30) isoforms are transcriptional activators, whereas C/EBP-epsilon(27) interacts with and represses GATA-1 transactivation of eosinophil promoters. C/EBP-epsilon(14) contains only DNA-binding and -dimerization domains and may function as a dominant-negative regulator. To define functional activities for these C/EBP-epsilon isoforms in myelopoiesis, human CD34(+) progenitors were transduced with internal ribosomal entry site-enhanced green fluorescent protein retroviral vectors encoding the 32/30, 27, and 14-kDa isoforms, purified by fluorescence-activated cell sorter, and analyzed in colony-forming assays and suspension cultures. Progenitors transduced with C/EBP-epsilon(32/30) default exclusively to eosinophil differentiation and gene expression, independent of interleukin-5, and regardless of inclusion of cytokines to induce other lineages. In contrast, the putative repressor C/EBP-epsilon(27) isoform strongly inhibits eosinophil differentiation and gene expression, including GATA-1, promoting granulocyte (neutrophil)-macrophage differen-tiation. The C/EBP-epsilon(14) repressor isoform strongly inhibits eosinophil development and gene expression, promoting erythroid differentiation, an effect enhanced by erythropoietin. Thus, C/EBP-epsilon isoforms can reprogram myeloid lineage commitment and differentiation consistent with their predicted activities based on activator and repressor domains and in vitro functional activities.

IFN consensus sequence binding protein (Icsbp) is critical for eosinophil development

IFN consensus sequence binding protein (Icsbp) (IFN response factor-8) is a hematopoietic transcription factor with dual functions in myelopoiesis and immunity. In this study, we report a novel role of Icsbp in regulating the development of eosinophils. Loss of Icsbp in mice leads to a reduction of eosinophils in different tissues. During parasite infection with the nematode Nippostrongylus brasiliensis, Icsbp-deficient mice fail to mount eosinophilia despite a vigorous IL-5 response. Numbers of phenotypically defined eosinophil progenitors are decreased and those progenitors have, on a per-cell basis, reduced eosinophil differentiation potential. The transcription factor Gata1, crucial for eosinophil development, is reduced expressed in committed eosinophil progenitors in wells as mature eosinophils. These findings identify Icsbp as a novel transcription factor critical for the development of the eosinophil lineage.

The lamin B receptor under transcriptional control of C/EBPepsilon is required for morphological but not functional maturation of neutrophils

The lamin B receptor (LBR) is an integral nuclear envelope protein that interacts with chromatin and has homology to sterol reductases. Mutations in LBR result in Pelger-Huët anomaly and HEM-Greenberg skeletal dysplasia, whereas in mice Lbr mutations result in ichthyosis. To further understand the function of the LBR and its role in disease, we derived a novel mouse model with a gene-trap insertion into the Lbr locus (Lbr(GT/GT)). Phenotypically, the Lbr(GT/GT) mice are similar to ichthyosis mice. The Lbr(GT/GT) granulocytes lack a mature segmented nucleus and have a block in late maturation. Despite these changes in nuclear morphology, the innate granulocyte immune function in the killing of Staphylococcus aureus bacteria appears to be intact. Granulocyte differentiation requires the transcription factor C/EBPepsilon. We identified C/EBPepsilon binding sites within the Lbr promoter and used EMSAs and luciferase assays to show that Lbr is transcriptionally regulated by C/EBPepsilon. Our findings indicate that the Lbr(GT/GT) mice are a model for Pelger-Huët anomaly and that Lbr, under transcriptional regulation of C/EBPepsilon, is necessary for morphological but not necessarily functional granulocyte maturation.

C/EBPalpha and C/EBPvarepsilon induce the monocytic differentiation of myelomonocytic cells with the MLL-chimeric fusion gene

CCAAT/enhancer binding proteins (C/EBPs) have an important function in granulocytic differentiation, and are also involved in the leukemogenesis of acute myeloid leukemia (AML). Their involvement in myelomonocytic leukemia, however, is still unclear. Therefore, the expression and function of C/EBPs in myelomonocytic cells with MLL-fusion genes were investigated. Retinoic acid (RA) induced monocytic differentiation in the myelomonocytic cell lines with MLL-fusion genes, THP-1, MOLM-14 and HF-6 cells, accompanied by monocytic differentiation with the upregulation of C/EBPalpha and C/EBPepsilon. Monocytic differentiation by RA treatment was confirmed in primary AML cells using a clonogenic assay. When the activity of C/EBPalpha or C/EBPepsilon was introduced into HF-6 cells, their cellular growth was arrested through differentiation into monocytes with the concomitant marked downregulation of Myc. Cebpe mRNA was upregulated by the induction of C/EBPalpha-ER, but not vice versa, thus suggesting that C/EBPepsilon may have an important function in the differentiation process. Introduction of Myc isoforms into HF-6 cells partially antagonized the C/EBPs effects. These findings suggest that the ectopic expression of C/EBPepsilon, as well as C/EBPalpha, can induce the monocytic differentiation of myelomonocytic leukemic cells with MLL-fusion gene through the downregulation of Myc, thus providing insight into the development of novel therapeutic approaches.

The C/EBPβ Isoform 34-kDa LAP Is Responsible for NF-IL-6-Mediated Gene Induction in Activated Macrophages, but Is Not Essential for Intracellular Bacteria Killing

The C/ebpb gene is translated into three different protein isoforms, two transcriptional activating proteins (38-kDa Full and 34-kDa liver-enriched transcriptional activation protein (LAP)) and one transcriptional inhibitory protein, by alternative use of different AUG initiation codons within the same open reading frame. The isoform 34-kDa LAP is thought to be the most transcriptionally active form of C/EBPbeta in macrophages. To assess the function of the 34-kDa LAP in vivo, we generated knock-in mice, in which methionine 20 of C/EBPbeta, the start site for the 34-kDa LAP is replaced with an alanine. The expression of the 34-kDa LAP was abolished in C/ebpb(M20A/M20A) mice. The induction of C/EBPbeta target genes, such as inflammatory cytokines, chemokines, prostanoid synthetase, and antimicrobial peptides, was abolished in C/ebpb(M20A/M20A) macrophages, and C/ebpb(M20A/M20A) mice were susceptible to Listeria monocytogenes infection. Furthermore, the heat-killed Propionibacterium acnes-induced Th1 response, granuloma formation, and LPS shock were severely impaired. Nevertheless, impairment of intracellular bacteria killing, which is the most prominent phenotype in C/EBPbeta-deficient mice, was not observed in C/ebpb(M20A/M20A) mice. Collectively, we demonstrated that 34-kDa LAP is responsible for NF-IL6-mediated gene induction, but not essential for intracellular bacteria killing in activated macrophages.

C/EBPbeta serine 64, a phosphoacceptor site, has a critical role in LPS-induced IL-6 and MCP-1 transcription

C/EBPbeta is a member of the CCAAT/enhancer binding protein family of transcription factors and has been shown to be a critical transcriptional regulator of various proinflammatory genes, including IL-6 and MCP-1. Serine 64 in the transactivation domain of C/EBPbeta has recently been identified as a Ras-induced phosphoacceptor site. The integrity of serine 64 along with threonine 189 is important for the Ha-ras(V12)-induced transformation of NIH3T3 cells, however no target genes dependent upon serine 64 for their expression have been reported. In order to evaluate a potential role of serine 64 in C/EBPbeta-regulated cytokine expression, we expressed a form of C/EBPbeta with an alanine substitution at serine 64 (C/EBPbeta(S64A)) in P388 murine B lymphoblasts, which lack endogenous C/EBPbeta expression and are normally unresponsive to LPS for expression of IL-6 and MCP-1. In comparison to wild type C/EBPbeta, which robustly supports the LPS-induced expression of IL-6 and MCP-1, C/EBPbeta(S64A) was severely impaired in its ability to support the LPS-induced transcription of IL-6 and MCP-1. Furthermore, LPS stimulation increased the level of phosphorylation detected at serine 64. Thus, serine 64, probably through its phosphorylation, is a critical determinant of C/EBPbeta activity in the transcription of IL-6 and MCP-1.

An anti-infective peptide that selectively modulates the innate immune response

We show that an innate defense-regulator peptide (IDR-1) was protective in mouse models of infection with important Gram-positive and Gram-negative pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus and Salmonella enterica serovar Typhimurium. When given from 48 h before to 6 h after infection, the peptide was effective by both local and systemic administration. Because protection by IDR-1 was prevented by in vivo depletion of monocytes and macrophages, but not neutrophils or B- and T-lymphocytes, we conclude that monocytes and macrophages are key effector cells. IDR-1 was not directly antimicrobial: gene and protein expression analysis in human and mouse monocytes and macrophages indicated that IDR-1, acting through mitogen-activated protein kinase and other signaling pathways, enhanced the levels of monocyte chemokines while reducing pro-inflammatory cytokine responses. To our knowledge, an innate defense regulator that counters infection by selective modulation of innate immunity without obvious toxicities has not been reported previously.

Differential roles of C/EBP beta regulatory domains in specifying MCP-1 and IL-6 transcription

C/EBPbeta is a member of the CCAAT/enhancer binding protein family of transcription factors and has been shown to be a critical transcriptional regulator of various proinflammatory genes, including IL-6 and MCP-1. To examine the roles of the C/EBPbeta transactivation and regulatory domains in LPS-induced MCP-1 and IL-6 expression, we expressed various N-terminal truncations and deletions of C/EBPbeta in P388 murine B lymphoblasts, which lack endogenous C/EBPbeta expression and are normally unresponsive to LPS for expression of IL-6 and MCP-1. Unexpectedly, a region between amino acids 105 and 212 of C/EBPbeta that includes regulatory domains 1 and 2 facilitates C/EBPbeta activation of IL-6 expression, while having an inhibitory effect on MCP-1 expression. Thus, this region can mediate promoter-specific effects on cytokine and chemokine gene transcription. LIP, the naturally occurring truncated form of C/EBPbeta, largely retains these regulatory domains and stimulates IL-6 but not MCP-1 transcription.

CCAAT/enhancer-binding proteins modulate human T cell leukemia virus type 1 long terminal repeat activation

CCAAT/enhancer-binding protein (C/EBP) basic region/leucine zipper (bZIP) transcription factors have been shown to form heterodimers with cAMP-responsive element binding protein 2 (CREB-2), a transcription factor involved in regulating basal and Tax-mediated transactivation of the human T cell leukemia virus type 1 (HTLV-1) long terminal repeat (LTR). In cells of the monocyte-macrophage lineage (proposed to play a role in HTLV-1 pathogenesis as an accessory target cell), several members of the C/EBP family are expressed at high levels and may have functional impact on both basal and Tax-mediated transactivation of the HTLV-1 LTR. Basal activation of the HTLV-1 LTR was enhanced by overexpression of C/EBPbeta, C/EBPdelta, or C/EBPepsilon, whereas transactivation of the LTR by Tax was inhibited by overexpression of C/EBPalpha and C/EBPbeta. Inhibition of Tax-mediated transactivation of the HTLV-1 LTR was co-activator-independent, did not require C/EBP binding to the Tax-responsive elements, and may involve heterodimerization with CREB factors.

Aberrant expression of neutrophil and macrophage-related genes in a murine model for human neutrophil-specific granule deficiency

Neutrophil-specific granule deficiency involves inheritance of germline mutations in the CCAAT/enhancer-binding protein epsilon (C/EBPE) gene. Humans and mice lacking active C/EBPepsilon suffer frequent bacterial infections as a result of functionally defective neutrophils and macrophages. We hypothesized that these defects reflected dysregulation of important immune response genes. To test this, gene expression differences of peritoneally derived neutrophils and macrophages from C/EBPepsilon-/- and wild-type mice were determined with DNA microarrays. Of 283 genes, 146 known genes and 21 expressed sequence tags (ESTs) were down-regulated, and 85 known genes and 31 ESTs were up-regulated in the C/EBP-/- mice. These included genes involved in cell adhesion/chemotaxis, cytoskeletal organization, signal transduction, and immune/inflammatory responses. The cytokines CC chemokine ligand 4, CXC chemokine ligand 2, and interleukin (IL)-6, as well as cytokine receptors IL-8RB and granulocyte-colony stimulating factor, were down-regulated. Chromatin immunoprecipitation analysis identified binding of C/EBPepsilon to their promoter regions. Increased expression for lipid metabolism genes apolipoprotein E (APOE), scavenger receptor class B-1, sorting protein-related receptor containing low-density lipoprotein receptor class A repeat 1, and APOC2 in the C/EBPepsilon-/- mice correlated with reduced total cholesterol levels in these mice before and after maintenance on a high-fat diet. Also, C/EBPepsilon-deficient macrophages showed a reduced capacity to accumulate lipids. In summary, dysregulation of numerous, novel C/EBPepsilon target genes impairs innate immune response and possibly other important biological processes mediated by neutrophils and macrophages.

Regulation of gene-activation pathways by PIAS proteins in the immune system

The protein inhibitor of activated STAT (PIAS) family of proteins has been proposed to regulate the activity of many transcription factors, including signal transducer and activator of transcription proteins (STATs), nuclear factor-kappaB, SMA- and MAD-related proteins (SMADs), and the tumour-suppressor protein p53. PIAS proteins regulate transcription through several mechanisms, including blocking the DNA-binding activity of transcription factors, recruiting transcriptional corepressors or co-activators, and promoting protein sumoylation. Recent genetic studies support an in vivo function for PIAS proteins in the regulation of innate immune responses. In this article, we review the current understanding of the molecular basis, specificity and physiological roles of PIAS proteins in the regulation of gene-activation pathways in the immune system.

FAM20: an evolutionarily conserved family of secreted proteins expressed in hematopoietic cells

Background

Hematopoiesis is a complex developmental process controlled by a large number of factors that regulate stem cell renewal, lineage commitment and differentiation. Secreted proteins, including the hematopoietic growth factors, play critical roles in these processes and have important biological and clinical significance. We have employed representational difference analysis to identify genes that are differentially expressed during experimentally induced myeloid differentiation in the murine EML hematopoietic stem cell line.

Results

One identified clone encoded a previously unidentified protein of 541 amino acids that contains an amino terminal signal sequence but no other characterized domains. This protein is a member of family of related proteins that has been named family with sequence similarity 20 (FAM20) with three members (FAM20A, FAM20B and FAM20C) in mammals. Evolutionary comparisons revealed the existence of a single FAM20 gene in the simple vertebrate Ciona intestinalis and the invertebrate worm Caenorhabditis elegans and two genes in two insect species, Drosophila melanogaster and Anopheles gambiae. Six FAM20 family members were identified in the genome of the pufferfish, Fugu rubripes and five members in the zebrafish, Danio rerio. The mouse Fam20a protein was ectopically expressed in a mammalian cell line and found to be a bona fide secreted protein and efficient secretion was dependent on the integrity of the signal sequence. Expression analysis revealed that the Fam20a gene was indeed differentially expressed during hematopoietic differentiation and that the other two family members (Fam20b and Fam20c) were also expressed during hematcpoiesis but that their mRNA levels did not vary significantly. Likewise FAM20A was expressed in more limited set of human tissues than the other two family members.

Conclusions

The FAM20 family represents a new family of secreted proteins with potential functions in regulating differentiation and function of hematopoietic and other tissues. The Fam20a mRNA was only expressed during early stages of hematopoietic development and may play a role in lineage commitment or proliferation. The expansion in gene number in different species suggests that the family has evolved as a result of several gene duplication events that have occurred in both vertebrates and invertebrates.

Repression and coactivation of CCAAT/enhancer-binding protein epsilon by sumoylation and protein inhibitor of activated STATx proteins

CCAAT/enhancer-binding protein epsilon (C/EBPepsilon) is a neutrophil-specific transcription factor whose activity is controlled by juxtaposed activating and regulatory domains. We previously determined that the function of the major regulatory domain (RD1) in C/EBPepsilon was dependent on the integrity of a five-amino acid motif that was identical to the recognition site for members of the small ubiquitin-like modifier (SUMO) family of ubiquitin-related proteins. We show here that the SUMO attachment site (the regulatory domain motif) is necessary and sufficient both for the intrinsic inhibitory function of RD1 and for coactivation by PIASxalpha and PIASxbeta, two members of the protein inhibitor of activated STAT (PIAS) family of SUMO E3 ligases. PIASxbeta was a more potent coactivator than PIASxalpha of both full-length C/EBPepsilon and fusion proteins containing the N-terminal portion of C/EBPepsilon, whereas PIASxalpha was more active on fusion proteins containing a heterologous activation domain. Two modes of coactivation were observed, one that was dependent on the integrity of the RING finger (RF) domain and was shared by both PIASxalpha and PIASxbeta and a second mode that was independent of the RF and was only observed with PIASxbeta. Sumoylation of C/EBPepsilon was enhanced by coexpression of PIASxalpha, suggesting that this modification is associated with the enhanced activity of the target protein. These results suggest that a complex interplay of accessory factors, including SUMO and PIAS proteins, modulates the activity of C/EBPepsilon.

Phenotypic and functional alterations of peripheral blood monocytes in neutrophil-specific granule deficiency

Neutrophil-specific granule deficiency (SGD) is a rare, congenital disease characterized by atypical neutrophil structure and function, resulting in recurrent bacterial infections from early infancy. Homozygous recessive mutations in the CCAAT/enhancer-binding protein epsilon (C/EBPepsilon) gene were described in two of five SGD patients, indicating loss of C/EBPepsilon function as the primary genetic defect in this disease. C/EBPepsilon is expressed in murine and human macrophages. Macrophages from the C/EBPepsilon-deficient mice show impaired differentiation, phagocytic activity, and transcription of macrophage-specific genes. To determine if monocyte/macrophage cells are impacted in SGD, we analyzed phenotypic features of peripheral blood (PB) monocytes in a SGD individual lacking functional C/EBPepsilon. Flow cytometric analysis of PB leukocytes revealed aberrant expression of CD45, CD11b, CD14, CD15, and CD16 on cells from the SGD individual. Also, the PB CD14(+) cells from this individual, weakly stained for the monocyte-specific enzyme, nonspecific esterase, and electron microscopic examination, indicated morphologic differences between the SGD cells and those from normal controls. Serum interleukin (IL)-6 levels in the SGD individual during a severe bacterial infection were lower compared with levels in other non-SGD individuals with sepsis. In contrast, serum IL-8 levels were markedly elevated in the SGD individual compared with those of non-SGD individuals in sepsis. PB CD14(+) cells from the SGD individual expressed higher IL-8 mRNA levels compared with normal controls in response to lipopolysaccharide and interferon-gamma. These phenotypic and functional alterations of PB monocytes in the SGD individual suggest that C/EBPepsilon plays a critical role in monocyte/macrophage development of humans and is consistent with observations in the murine system. This study implicates abnormalities in monocytes/macrophages and neutrophils in the onset and development of SGD.

Convergent alteration of granulopoiesis, chemotactic activity, and neutrophil apoptosis during mouse selection for high acute inflammatory response

Neutrophil homeostasis was investigated in two mouse lines, AIRmax and AIRmin, genetically selected for high or low acute inflammatory response (AIR) and compared with unselected BALB/c mice. Mature neutrophil phenotype and functions appeared similar in the three mouse lines. However, an unprecedented phenotype was revealed in AIRmax animals characterized by a high neutrophil production in bone marrow (BM), a high number of neutrophils in blood, a high concentration of chemotactic agents in acrylamide-induced inflammatory exudates, and an increased resistance of locally infiltrated neutrophils to spontaneous apoptosis. In vitro, BM production of neutrophils and eosinophils was accompanied by an unusual high up-regulation of cytokine receptors as assessed by antibodies to CD131, which bind the common beta chain of receptors to interleukin (IL)-3, IL-5, and granulocyte macrophage-colony stimulating factor. An accelerated neutrophil maturation was also observed in response to all-trans retinoic acid. Several candidate genes can be proposed to explain this phenotype. Yet, more importantly, the results underline that genetic selection, based on the degree of AIR and starting from a founding population resulting from the intercross of eight inbred mouse lines, which display a continuous range of inflammatory responses, can lead to the convergent selection of alleles affecting neutrophil homeostasis. Similar gene combinations may occur in the human with important consequences in the susceptibility to inflammatory or infectious diseases and cancer.

Regulation of neutrophil and eosinophil secondary granule gene expression by transcription factors C/EBP epsilon and PU.1

In the bone marrow of C/EBP epsilon(-/-) mice, expression of neutrophil secondary and tertiary granule mRNAs is absent for lactoferrin (LF), neutrophil gelatinase (NG), murine cathelin-like protein (MCLP), and the cathelin B9; it is severely reduced for neutrophil collagenase (NC) and neutrophil gelatinase-associated lipocalin (NGAL). In addition, the expression of eosinophil granule genes, major basic protein (MBP), and eosinophil peroxidase (EPX) is absent. These mice express C/EBP alpha, C/EBP beta, and C/EBP delta in the bone marrow at levels similar to those of their wild-type counterparts, suggesting a lack of functional redundancy among the family in vivo. Stable inducible expression of C/EBP epsilon and C/EBP alpha in the murine fibroblast cell line NIH 3T3 activated expression of mRNAs for B9, MCLP, NC, and NGAL but not for LF. In transient transfections of C/EBP epsilon and C/EBP alpha, B9 was strongly induced with weaker induction of the other genes. C/EBP beta and C/EBP delta proteins weakly induced B9 expression, but C/EBP delta induced NC expression more efficiently than the other C/EBPs. The expression of MBP was inefficiently induced by C/EBP epsilon alone and weakly induced with C/EBP epsilon and GATA-1, but the addition of PU.1 resulted in a striking cooperative induction of MBP in NIH 3T3 cells. Mutation of a predicted PU.1 site in the human MBP promoter-luciferase reporter construct abrogated the response to PU.1. Gel-shift analysis demonstrated binding of PU.1 to this site. MBP and EPX mRNAs were absent in a PU.1-null myeloid cell line established from the embryonic liver of PU.1(-/-) mice. Restitution of PU.1 protein expression restored MBP and EPX protein expression. This study demonstrates that C/EBP epsilon is essential and sufficient for the expression of a particular subset of neutrophil secondary granule genes. Furthermore, it indicates the importance of PU.1 in the cooperative activation of eosinophil granule genes.

Early up-regulation of chemokine expression in fulminant hepatic failure

CC-chemokines recruit and activate macrophages and T lymphocytes, the major components of inflammatory infiltrates in fulminant hepatic failure (FHF). To analyse the role of CC-chemokines in the pathogenesis of FHF, this study examined serum levels and intrahepatic expression of MCP-1, MIP-1alpha, MIP-1beta, and RANTES in the livers and sera of patients with FHF and controls by ELISA, immunohistochemistry, and competitive RT-PCR. Serum levels and intrahepatic expression of all chemokines studied in FHF exceeded the levels in chronic liver diseases and normal controls. Distinct patterns of expression of each chemokine were noted on Kupffer cells, sinusoidal endothelial cells, hepatocytes, lymphocytes, and bile ducts. Intrahepatic chemokine expression correlated closely with the extent of infiltration by macrophages and T lymphocytes (r = 0.65-0.95, p < 0.001). The functional relationship between intrahepatic chemokine release and infiltration was confirmed in chemotaxis assays by inhibiting chemotaxis induced by homogenates of liver tissue obtained from FHF patients with neutralizing MCP-1, MIP-1alpha, MIP-1beta, and RANTES antibodies. The time course of CC-chemokine release was studied in the concanavalin A and the galactosamine/LPS mouse models of FHF. In both models, intrahepatic chemokine up-regulation occurred as an early event prior to hepatic infiltration and liver damage. The data indicate that an abundant intrahepatic release of CC-chemokines is an early and pivotal step in the pathogenesis of FHF.

Novel combinatorial interactions of GATA-1, PU.1, and C/EBPepsilon isoforms regulate transcription of the gene encoding eosinophil granule major basic protein

GATA-1 and the ets factor PU.1 have been reported to functionally antagonize one another in the regulation of erythroid versus myeloid gene transcription and development. The CCAAT enhancer binding protein epsilon (C/EBPepsilon) is expressed as multiple isoforms and has been shown to be essential to myeloid (granulocyte) terminal differentiation. We have defined a novel synergistic, as opposed to antagonistic, combinatorial interaction between GATA-1 and PU.1, and a unique repressor role for certain C/EBPepsilon isoforms in the transcriptional regulation of a model eosinophil granulocyte gene, the major basic protein (MBP). The eosinophil-specific P2 promoter of the MBP gene contains GATA-1, C/EBP, and PU.1 consensus sites that bind these factors in nuclear extracts of the eosinophil myelocyte cell line, AML14.3D10. The promoter is transactivated by GATA-1 alone but is synergistically transactivated by low levels of PU.1 in the context of optimal levels of GATA-1. The C/EBPepsilon(27) isoform strongly represses GATA-1 activity and completely blocks GATA-1/PU.1 synergy. In vitro mutational analyses of the MBP-P2 promoter showed that both the GATA-1/PU.1 synergy, and repressor activity of C/EBPepsilon(27) are mediated via protein-protein interactions through the C/EBP and/or GATA-binding sites but not the PU.1 sites. Co-immunoprecipitations using lysates of AML14.3D10 eosinophils show that both C/EBPepsilon(32/30) and epsilon(27) physically interact in vivo with PU.1 and GATA-1, demonstrating functional interactions among these factors in eosinophil progenitors. Our findings identify novel combinatorial protein-protein interactions for GATA-1, PU.1, and C/EBPepsilon isoforms in eosinophil gene transcription that include GATA-1/PU.1 synergy and repressor activity for C/EBPepsilon(27).

C/EBP gamma has a stimulatory role on the IL-6 and IL-8 promoters

CCAAT/enhancer-binding protein gamma (C/EBP gamma) is an ubiquitously expressed member of the C/EBP family of transcription factors that has been shown to be an inhibitor of C/EBP transcriptional activators and has been proposed to act as a buffer against C/EBP-mediated activation. We have now unexpectedly found that C/EBP gamma dramatically augments the activity of C/EBP beta in lipopolysaccharide induction of the interleukin-6 and interleukin-8 promoters in a B lymphoblast cell line. This activating role for C/EBP gamma is promoter-specific, neither being observed in the regulation of a simple C/EBP-dependent promoter nor the TNF alpha promoter. C/EBP gamma activity also shows cell-type specificity with no activity observed in a macrophage cell line. Studies with chimeric C/EBP proteins implicate the formation of a heterodimeric leucine zipper between C/EBP beta and C/EBP gamma as the critical structural feature required for C/EBP gamma stimulatory activity. These findings suggest a unique role for C/EBP gamma in B cell gene regulation and, along with our previous observation of the ability of C/EBP basic region-leucine zipper domains to confer lipopolysaccharide inducibility of interleukin-6, suggest that the C/EBP leucine zipper domain has a role in C/EBP function beyond allowing dimerization between C/EBP family members.

CCAAT/enhancer-binding proteins: structure, function and regulation

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBP alpha[bond]C/EBP zeta), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein-protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels during several physiological and pathophysiological conditions through the action of a range of factors, including hormones, mitogens, cytokines, nutrients and certain toxins. The mechanisms through which the C/EBP members are regulated during such conditions have also been the focus of several recent studies and have revealed an immense complexity with the potential existence of cell/tissue- and species-specific differences. This review deals with the structure, biological function and the regulation of the C/EBP family.

Mapping gene expression patterns during myeloid differentiation using the EML hematopoietic progenitor cell line

OBJECTIVE

The detailed examination of the molecular events that control the early stages of myeloid differentiation has been hampered by the relative scarcity of hematopoietic stem cells and the lack of suitable cell line models. In this study, we examined the expression of several myeloid and nonmyeloid genes in the murine EML hematopoietic stem cell line.

METHODS

Expression patterns for 19 different genes were examined by Northern blotting and RT-PCR in RNA samples from EML, a variety of other immortalized cell lines, and purified murine hematopoietic stem cells. Representational difference analysis (RDA) was performed to identify differentially expressed genes in EML.

RESULTS

Expression patterns of genes encoding transcription factors (four members of the C/EBP family, GATA-1, GATA-2, PU.1, CBFbeta, SCL, and c-myb) in EML were examined and were consistent with the proposed functions of these proteins in hematopoietic differentiation. Expression levels of three markers of terminal myeloid differentiation (neutrophil elastase, proteinase 3, and Mac-1) were highest in EML cells at the later stages of differentiation. In a search for genes that were differentially expressed in EML cells during myeloid differentiation, six cDNAs were isolated. These included three known genes (lysozyme, histidine decarboxylase, and tryptophan hydroxylase) and three novel genes.

CONCLUSION

Expression patterns of known genes in differentiating EML cells accurately reflected their expected expression patterns based on previous studies. The identification of three novel genes, two of which encode proteins that may act as regulators of hematopoietic differentiation, suggests that EML is a useful model system for the molecular analysis of hematopoietic differentiation.

CCAAT/enhancer-binding proteins are required for granulopoiesis independent of their induction of the granulocyte colony-stimulating factor receptor

Potential redundancy among members of the CCAAT/enhancer-binding protein (C/EBP) family in myeloid cells is indicated by the ability of C/EBPbeta to replace C/EBPalpha in vivo, by the expression of granulocyte colony-stimulating factor receptor (G-CSFR) on C/EBPalpha(-/-) cell lines, and by our finding that as with C/EBPalpha-estrogen receptor (C/EBPalpha-ER), either C/EBPbeta-ER or C/EBPdelta-ER can induce terminal granulopoiesis in 32D cl3 cells. To assess the consequences of globally inhibiting C/EBPs, we employed KalphaER, containing a Kruppel-associated box (KRAB) transrepression domain, the C/EBPalpha DNA-binding domain, and an ER ligand-binding domain. C/EBPs have a common DNA-binding consensus, and activation of KalphaER repressed transactivation by endogenous C/EBPs 50-fold and reduced endogenous G-CSFR expression. In 32D cl3 cells coexpressing exogenous G-CSFR, activation of KalphaER prevented and even reversed myeloperoxidase, lysozyme, lactoferrin, and C/EBPepsilon RNA induction by G-CSF. In contrast, induction of PU.1 and CD11b, a gene regulated by PU.1 but not by C/EBPs, was unaffected. A KalphaER variant incapable of binding DNA owing to an altered leucine zipper did not affect 32D cl3 differentiation. Transduction of KalphaER into murine hematopoietic progenitor cells suppressed the formation of granulocyte colony-forming units, even in cytokines that enable C/EBPalpha(-/-) progenitors to differentiate into neutrophils. The formation of macrophage and of granulocyte-macrophage colony-forming units were also inhibited, but erythroid burst-forming units grew normally. Thus, in 32D cl3 cells and perhaps normal progenitors, C/EBPs are required for granulopoiesis beyond their ability to induce receptors for G-CSF and other cytokines. One requisite activity may be activation of the C/EBPepsilon gene by C/EBPalpha, as either C/EBPalpha-ER or C/EBPbeta-ER rapidly elevated C/EBPepsilon RNA in 32D cl3 cells in the presence of cycloheximide but not actinomycin D.

Molecular cloning and expression of CCAAT/enhancer binding proteins in Japanese flounder Paralichthys olivaceus

The findings of this study represent the first report, to the authors' knowledge, of CCAAT/enhancer binding protein (C/EBP) cDNA sequence in a fish species. C/EBP epsilon of Japanese flounder was 1861 bp in length (ORF of 822 bp) encoding for 274 amino acids, with a calculated molecular weight of 30 kDa. Japanese flounder C/EBP beta was found to be 1561 bp in length (ORF of 1041 bp), encoding for 347 amino acids and a calculated molecular weight of 39 kDa. These genes were expressed in various fish organs, tissues and secretions. C/EBP epsilon was detected by Northern blot from total RNA of head and posterior kidney, heart and spleen. However, RT-PCR also detected C/EBP epsilon in brain, spleen and peritoneal cavity fluid and peripheral blood leucocyte cDNA. C/EBP beta was detected by Northern blot analysis in the head and posterior kidney, spleen, intestine, liver, brain, heart, gill and testis and further found by RT-PCR to be detected in mucus, peritoneal cavity fluid, peripheral blood leucocytes and eye cDNA. Phylogenetic analysis placed the Japanese flounder C/EBP beta within the same cluster as previously reported C/EBP beta sequences. However, Japanese flounder C/EBP epsilon sequence data were not found to cluster with the three reported mammalian C/EBP epsilon sequences currently available. Understanding C/EBP transcriptional gene control in commercially important fish species may lead to a better control of disease.

Macrophage functional maturation and cytokine production are impaired in C/EBP epsilon-deficient mice

Members of the CCAAT/enhancer-binding protein (C/EBP) family are involved in the regulation of cellular differentiation and function of many tissues. Unlike the other members of the family, C/EBP epsilon expression is restricted to granulocytes, macrophages, and lymphocytes. C/EBP epsilon is highly conserved between human and rodents and is essential for terminal granulopoiesis in both species. To study the role that C/EBP epsilon plays in macrophages, wild-type and C/EBP epsilon-deficient (-/-) murine macrophages obtained from thioglycollate-elicited peritoneal lavages and differentiated bone marrow cells were compared. Although macrophage development occurred in both types of mice, the C/EBP epsilon -/- cells had a lower expression of macrophage markers and a morphologic and ultrastructural appearance of immaturity. Phagocytic function, measured by calculating the percentage of internalized opsonized fluorescein isothiocyanate (FITC)-labeled yeast, was significantly impaired in the C/EBP epsilon -/- macrophages compared with their wild-type counterparts. Furthermore, the differential expression of 26 macrophage-specific genes between wild-type and C/EBP-/- mice was analyzed. A subset of genes involved in differentiation, immune, and inflammatory responses was found down-regulated in the C/EBP-/- macrophages. Taken together, this study implicates the C/EBP epsilon gene as an important transcription factor required for normal function and development of macrophages.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Neutrophil specific granule deficiency and mutations in the gene encoding transcription factor C/EBP(epsilon)

Neutrophil specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of these patients display atypical bilobed nuclei; lack expression of at least one primary and all secondary and tertiary granule proteins; and possess defects in chemotaxis, disaggregation, receptor upregulation, and bactericidal activity. SGD patients suffer frequent and severe bacterial infections. Although the first of five patients worldwide was reported in the early 1970s, the molecular basis for the defect was discovered only recently. This review presents data implicating the functional loss of the myeloid transcription factor CCAAT/enhancer binding protein (C/EBP(epsilon)) as a causative agent in the development of SGD. The murine model for SGD provides evidence for defects in eosinophil granule gene expression and indicates abnormalities in macrophage maturation and function. Deficiencies in multiple myeloid lineages, in addition to neutrophils, indicate the importance of C/EBP(epsilon) in regulating important innate immune and inflammatory responses critical for host defense.

Transcriptional regulation of hemopoiesis

The regulation of blood cell formation, or hemopoiesis, is central to the replenishment of mature effector cells of innate and acquired immune responses. These cells fulfil specific roles in the host defense against invading pathogens, and in the maintenance of homeostasis. The development of hemopoietic cells is under stringent control from extracellular and intracellular stimuli that result in the activation of specific downstream signaling cascades. Ultimately, all signal transduction pathways converge at the level of gene expression where positive and negative modulators of transcription interact to delineate the pattern of gene expression and the overall cellular hemopoietic response. Transcription factors, therefore, represent a nodal point of hemopoietic control through the integration of the various signaling pathways and subsequent modulation of the transcriptional machinery. Transcription factors can act both positively and negatively to regulate the expression of a wide range of hemopoiesis-relevant genes including growth factors and their receptors, other transcription factors, as well as various molecules important for the function of developing cells. The expression of these genes is dependent on the complex interactions between transcription factors, co-regulatory molecules, and specific binding sequences on the DNA. Recent advances in various vertebrate and invertebrate systems emphasize the importance of transcription factors for hemopoiesis control and the evolutionary conservation of several of such mechanisms. In this review we outline some of the key issues frequently identified in studies of the transcriptional regulation of hemopoietic gene expression. In teleosts, we expect that the characterization of several of these transcription factors and their regulatory mechanisms will complement recent advances in a number of fish systems where identification of cytokine and other hemopoiesis-relevant factors are currently under investigation.

Dichotomy of AML1-ETO functions: growth arrest versus block of differentiation

The fusion gene AML1-ETO is the product of t(8;21)(q22;q22), one of the most common chromosomal translocations associated with acute myeloid leukemia. To investigate the impact of AML1-ETO on hematopoiesis, tetracycline-inducible AML1-ETO-expressing cell lines were generated using myeloid cells. AML1-ETO is tightly and strongly induced upon tetracycline withdrawal. The proliferation of AML1-ETO(+) cells was markedly reduced, and most of the cells eventually underwent apoptosis. RNase protection assays revealed that the amount of Bcl-2 mRNA was decreased after AML1-ETO induction. Enforced expression of Bcl-2 was able to significantly delay, but not completely overcome, AML1-ETO-induced apoptosis. Prior to the onset of apoptosis, we also studied the ability of AML1-ETO to modulate differentiation. AML1-ETO expression altered granulocytic differentiation of U937T-A/E cells. More significantly, this change of differentiation was associated with the down-regulation of CCAAT/enhancer binding protein alpha (C/EBPalpha), a key regulator of granulocytic differentiation. These observations suggest a dichotomy in the functions of AML1-ETO: (i) reduction of granulocytic differentiation correlated with decreased expression of C/EBPalpha and (ii) growth arrest leading to apoptosis with decreased expression of CDK4, c-myc, and Bcl-2. We predict that the preleukemic AML1-ETO(+) cells must overcome AML1-ETO-induced growth arrest and apoptosis prior to fulfilling their leukemogenic potential.

Expression of matrix metalloprotease and tissue inhibitor of metalloprotease genes in human anterior cruciate ligament

Women are more susceptible to anterior cruciate ligament (ACL) injuries than men performing similar athletic activities. Because tissue remodeling may affect ligament strength, we assessed expression of tissue remodeling effector genes in the human ACL. Specifically, we surveyed ACL for RNAs encoding all known matrix metalloproteases (MMPs) and tissue inhibitors of metalloproteases (TIMPs) by reverse transcription/polymerase chain reaction (RT-PCR). These experiments revealed that mRNAs encoding nine of sixteen MMPs and all four TIMPs are present in the normal ACL. The nine expressed proteases were MMPs 1-3, 7, 9, 11, 14, and 17 (collagenase 1, gelatinase A, stromelysin 1, matrilysin, gelatinase B, stromelysin 3, and membrane types 1 and 4, respectively), and MMP-18. Genes for MMPs 8, 10, 12, 13, 15, and 16 appeared not to be expressed in ACL, as their mRNAs were not detected using RT-PCR conditions that did yield positive signals from other tissues (testis or bone). We conclude that numerous genes encoding tissue remodeling effector proteins are expressedin the human ACL.

The role of C/EBP(epsilon) in the terminal stages of granulocyte differentiation

As a consequence of its characterization using both in vitro and knockout mouse models, the myeloid-specific transcription factor, CCAAT/enhancer binding protein (C/EBP)epsilon, has been identified as a critical regulator of terminal granulopoiesis and one of the causative mutations in the human disease, neutrophil-specific granule deficiency. C/EBPs are a family of transcription factors sharing numerous structural and functional features and to date include C/EBPalpha, -beta, -gamma, -delta, -epsilon, and -zeta. C/EBPalpha was the first family member isolated and characterized, its essential role in hepatocyte and adipocyte differentiation demonstrated in knockout mouse models. Subsequent analysis of the hematopoietic elements in fetal mouse liver revealed its critical role in myelopoiesis. Understanding the role of C/EBPepsilon in terminal granulopoiesis in the context of other known transcription factors is ongoing with analysis of deficient and conditionally expressing cell lines and knockout models. Mouse models with targeted gene disruptions have contributed greatly to our understanding of the transcriptional regulation of granulopoiesis. Further manipulation of these models and other conditional expression systems have bypassed some of the limitations of knockout models and helped delineate the interactions of different transcription factors in affecting granulocyte development. Phenotypic expression of the loss of C/EBPepsilon in mice is extreme, resembling absolute neutropenia with systemic infection with P. aeruginosa. Future work will need to explore the regulation of C/EBPepsilon expression, its functional interactions with other transcriptional regulators such as PU.1, and its role in monocyte differentiation and function in the mouse.

HIV-1-associated central nervous system dysfunction

Despite more than 15 years of extensive investigative efforts, a complete understanding of the neurological consequences of HIV-1 CNS infection remains elusive. Although the resources of numerous investigators have been focused on studies of HIV-1-associated CNS disease, the complex nature of the disease processes that underlie the clinical, pathological, and cellular manifestations of HIV-1 CNS infection have required a larger volume of studies than was initially envisioned. Several major areas remain as the focus of current research efforts. One of the more pressing issues facing researchers and clinicians alike is the search for correlates to the development of HIV-1-associated CNS neuropathology and the onset of HIVD. Although numerous parameters have been studied, none have been shown to be absolute predictors or markers of HIV-1-related CNS dysfunction. The identification of solid correlates of HIVD is an important goal that would permit clinical identification of individuals at risk for developing potentially crippling, life-threatening CNS abnormalities and would facilitate early treatment of nascent neurological problems. A more complete comprehension of the cellular foundations of CNS dysfunction and HIVD is also a fundamental part of strategies designed to treat or prevent HIV-1-associated CNS disease. Future investigations will strive to expand the body of knowledge concerning the complex interactions between infected and uninfected neuroglial cells and the roles of numerous cytokines, chemokines, and other soluble agents that are deregulated during HIV-1 CNS infection. In particular, a thorough understanding of the mechanisms of neurotoxicity may facilitate the development of new therapies that alleviate or eliminate the clinical consequences of CNS infection. Finally, investigators will continue to study HIVD within the context of single and combination drug therapies used in the treatment of HIV-1 infection and AIDS. As newer and more effective systemic treatments for HIV-1 infection and AIDS are introduced, the effects of these treatments on the onset, incidence, and severity of HIVD will also require intensive study. The impact of drug therapies on the ability of the CNS to act as an HIV-1 reservoir will also need to be addressed. Introduction of each new drug or drug combination will necessitate studies of drug penetration into the CNS and efficacy against the development of CNS abnormalities. Furthermore, as more effective treatments prolong the lifespan of individuals infected with HIV-1, the impact of extended survival on the occurrence and severity of HIVD will also require further investigations. The quest for answers to these and other questions will be complicated by the diversity of experimental systems used to study different aspects of HIV-1 CNS infection and HIVD. Each system has its own unique strengths and weaknesses. Clinical observations provide a continuous spectrum of symptomatic findings but reveal little about the underlying mechanisms of disease. In vivo imaging techniques, such as CT and MRI, also provide a continuum of observations, but the images are limited in their resolution. Neuropathological examinations of postmortem HIV-1-infected brains offer gross, cellular, and molecular views (including phenotypic and genotypic analyses of CNS viral isolates) of the diseased brain, but only provide a snapshot of the end-stage neurologic dysfunction. Studies that rely on animal surrogates for HIV-1, including SIV, simian-HIV (SHIV), feline immunodeficiency virus (FIV), visna virus, and HIV-1 SCID-hu models, permit experimental protocols that cannot be carried out in humans, but are limited by the fidelity with which each virus and animal model emulates the conditions and events observed in the human host. Finally, in vitro techniques, which include the use of primary cells and cell lines, adult or fetal human cell cultures, and BBB barrier model systems, are also convenient means by which aspe

C/EBPepsilon -/- mice: increased rate of myeloid proliferation and apoptosis

CCAAT/enhancer binding protein epsilon (C/EBPepsilon) is essential for terminal granulocytic differentiation. Its expression begins at the transition between the proliferative and non-proliferative compartments of myelopoiesis. We studied the effect of targeted disruption of the C/EBPepsilon gene on murine myeloid proliferation and apoptosis. Bone marrow cellularity of C/EBPepsilon -/- and wild-type mice was 95% and 65%, respectively. The C/EBPepsilon -/- mice had an expansion in the number of their CFU-GM/femur. The number of myeloid committed progenitor cells in the peripheral blood and the spleen of these mice was also increased. Bromodeoxyuridine (BrDU) pulse labeling studies demonstrated that the fraction of actively proliferating cells was two-fold higher in the bone marrow of C/EBPepsilon -/- mice. However, the number of myeloid colonies arising from purified Sca-1+/lin- early hematopoietic progenitor cells and from bone marrow mononuclear cells grown in different cytokine combinations was not significantly different between wild-type and knock-out mice. Also, long-term marrow growth, and CFU were not different between the wild-type and C/EBPepsilon -/- mice. The sensitivity to induction of apoptosis in the committed progenitor cell compartment after either withdrawal of growth factor or brief exposure to etoposide was normal. However, Gr-1 antigen-positive C/EBPepsilon -/- granulocytic cells showed an increased rate of apoptosis in comparison to their wild-type counterparts. In summary, the myeloid compartment appears to be expanded in mice lacking C/EBPepsilon. However, this is not the consequence of an intrinsic myeloproliferation but due to an indirect, possibly cytokine-mediated stimulation of myelopoiesis in vivo. C/EBPepsilon may have a role in the inhibition of apoptosis in maturing granulocytic cells.

Representational difference analysis using myeloid cells from C/EBPε deletional mice

C/EBPε is a recently cloned member of the C/EBP family of transcriptional factors. Previous studies demonstrated that the expression of this gene is tightly regulated in a tissue specific manner; it is expressed exclusively in myeloid cells. C/EBPε-deficient mice developed normally but failed to generate functional neutrophils and eosinophils, and these mice died of opportunistic infections suggesting that C/EBPε may play a central role in myeloid differentiation. To identify myelomonocytic genes regulated by the C/EBPε gene, we performed representational difference analysis (RDA), a polymerase chain reaction (PCR)-based subtractive hybridization using neutrophils and macrophages from wild-type and C/EBPε knockout mice. We identified a set of differentially expressed genes, including chemokines specific to myelomonocytic cells. Several novel genes were identified that were differentially expressed in normal myelomonocytic cells. Taken together, we have found several genes whose expression might be enhanced by C/EBPε.

Representational difference analysis using myeloid cells from C/EBPε deletional mice

C/EBPε is a recently cloned member of the C/EBP family of transcriptional factors. Previous studies demonstrated that the expression of this gene is tightly regulated in a tissue specific manner; it is expressed exclusively in myeloid cells. C/EBPε-deficient mice developed normally but failed to generate functional neutrophils and eosinophils, and these mice died of opportunistic infections suggesting that C/EBPε may play a central role in myeloid differentiation. To identify myelomonocytic genes regulated by the C/EBPε gene, we performed representational difference analysis (RDA), a polymerase chain reaction (PCR)-based subtractive hybridization using neutrophils and macrophages from wild-type and C/EBPε knockout mice. We identified a set of differentially expressed genes, including chemokines specific to myelomonocytic cells. Several novel genes were identified that were differentially expressed in normal myelomonocytic cells. Taken together, we have found several genes whose expression might be enhanced by C/EBPε.