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

Cord blood molecular biomarkers of eosinophilopoiesis: kinetic analysis of GATA-1, MBP1 and IL-5R alpha mRNA expression

Eosinophil/basophil (Eo/B) progenitor phenotype and function in cord blood (CB) are associated with atopic risk at birth and infant clinical outcomes. Molecular analyses of eosinophil-basophil differentiation events could identify clinically predictive biomarkers. To determine CB kinetic patterns of Eo/B lineage-associated gene expression (GATA-1, MBP1 and IL-5R alpha) after IL-5 stimulation, CB non-adherent mononuclear cells were isolated from random fresh and frozen samples and incubated in the presence of recombinant human interleukin-5. Some underwent CD34+ positive selection using magnetic cell separation. At various time-points, mRNA expression of GATA-1, MBP1 and IL-5R alpha (total transcripts) was determined utilizing multiplex quantitative polymerase chain reaction (Q-PCR). Relative expression levels of the IL-5R alpha soluble vs. transmembrane isoforms were also analyzed. Stimulation of the non-adherent mononuclear cells with IL-5 resulted in early up-regulation of GATA-1, peaking at 48 h, followed by decreasing expression and down-regulation by 96 h. The CD34+ enriched population demonstrated an equivalent expression pattern (r = 0.963, p = 0.0349). MBP1 mRNA expression [non-adherent mononuclear cells (NAMNCs) and CD34+ alike; r = 0.988, p = 0.012] was slowly up-regulated in response to IL-5, maximal at 96 h. Total IL-5R alpha expression appeared stable over the time-course, mediated by differential expression of the soluble and transmembrane isoforms (i.e., initial increase in the transmembrane contribution followed by a predominance of the soluble isoform by 48-72 h). Multiplex Q-PCR analysis of mRNA from CB demonstrates expression of critical eosinophil-basophil lineage-specific events that are consistent with current understanding of eosinophil differentiation and maturation. The non-adherent mononuclear cell population provides a surrogate signal for the CD34+ progenitor population.

Fractionation of mature eosinophils in GATA-reporter transgenic mice

Eosinophils contribute to the pathophysiology of allergic and infectious diseases, albeit their molecular functions remain unknown. Mature eosinophils are identified by their unique morphology and staining characteristics. However, it is difficult to fractionate living eosinophils by flow cytometry because these granulocytes express multiple cell surface markers that are shared by other cells of hematopoietic or non-hematopoietic origin. In this study, we describe a flow cytometry-based method to enumerate and fractionate eosinophils by developmental stages. To fractionate these cell types, we used transgenic mouse lines that express fluorescent proteins under control of the Gata1 gene hematopoietic regulatory region (Gata1-HRD), which is exclusively active in Gata1-expressing hematopoietic cells, including eosinophils. As expected, mature eosinophils were highly enriched in the fluorescent reporter-expressing subfraction of bone marrow myeloid cells that were negatively selected by using multiple antibodies against B220, CD4, CD8, Ter119, c-Kit and CD71. Cytochemical analyses of flow-sorted cells identified the cells in this fraction as eosinophils harboring eosinophilic granules. Additionally, expression of eosinophil-specific genes, for instance eosinophil enzymes and the IL-5 receptor alpha gene, were specifically detected in this fraction. The expression of these eosinophil-specific genes increased as the cells differentiated. This method for enrichment of bone marrow eosinophils is applicable to fractionation of eosinophils and bronchoalveolar lavage fluid from transgenic mice with atopic asthma. Thus, both pathological and developmental stages of eosinophils are efficiently fractionated by this flow cytometry-based method using Gata1-HRD transgenic reporter mice. This study, therefore, proposes a useful means to study the experimental allergic and inflammatory systems.

Eosinophil survival and apoptosis in health and disease

Eosinophilia is common feature of many disorders, including allergic diseases. There are many factors that influence the production, migration, survival and death of the eosinophil. Apoptosis is the most common form of physiological cell death and a necessary process to maintain but limit cell numbers in humans and other species. It has been directly demonstrated that eosinophil apoptosis is delayed in allergic inflammatory sites, and that this mechanism contributes to the expansion of eosinophil numbers within tissues. Among the proteins known to influence hematopoiesis and survival, expression of the cytokine interleukin-5 appears to be uniquely important and specific for eosinophils. In contrast, eosinophil death can result from withdrawal of survival factors, but also by activation of pro-apoptotic pathways via death factors. Recent observations suggest a role for cell surface death receptors and mitochondria in facilitating eosinophil apoptosis, although the mechanisms that trigger each of these death pathways remain incompletely delineated. Ultimately, the control of eosinophil apoptosis may someday become another therapeutic strategy for treating allergic diseases and other eosinophil-associated disorders.

Granulocytes: effector cells or immunomodulators in the immune response to helminth infection?

Granulocytes are effector cells in defence against helminth infections. We review the current evidence for the role of granulocytes in protective immunity against different helminth infections and note that for each parasite species the role of granulocytes as effector cells can vary. Emerging evidence also points to granulocytes as immunomodulatory cells able to produce many cytokines, chemokines and modulatory factors which can bias the immune response in a particular direction. Thus, the role of granulocytes in an immunomodulatory context is discussed including the most recent data that points to an important role for basophils under this guise.

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.

Graded repression of PU.1/Sfpi1 gene transcription by GATA factors regulates hematopoietic cell fate

GATA-1 and PU.1 are essential hematopoietic transcription factors that control erythromegakaryocytic and myelolymphoid differentiation, respectively. These proteins antagonize each other through direct physical interaction to repress alternate lineage programs. We used immortalized Gata1(-) erythromegakaryocytic progenitor cells to study how PU.1/Sfpi1 expression is regulated by GATA-1 and GATA-2, a related factor that is normally expressed at earlier stages of hematopoiesis. Both GATA factors bind the PU.1/Sfpi1 gene at 2 highly conserved regions. In the absence of GATA-1, GATA-2 binding is associated with an undifferentiated state, intermediate level PU.1/Sfpi1 expression, and low-level expression of its downstream myeloid target genes. Restoration of GATA-1 function induces erythromegakaryocytic differentiation. Concomitantly, GATA-1 replaces GATA-2 at the PU.1/Sfpi1 locus and PU.1/Sfpi1 expression is extinguished. In contrast, when GATA-1 is not present, shRNA knockdown of GATA-2 increases PU.1/Sfpi1 expression by 3-fold and reprograms the cells to become macrophages. Our findings indicate that GATA factors act sequentially to regulate lineage determination during hematopoiesis, in part by exerting variable repressive effects at the PU.1/Sfpi1 locus.

PU.1 and partners: regulation of haematopoietic stem cell fate in normal and malignant haematopoiesis

During normal haematopoiesis, cell development and differentiation programs are accomplished by switching ‘on’ and ‘off’ specific set of genes. Specificity of gene expression is primarily achieved by combinatorial control, i.e. through physical and functional interactions among several transcription factors that form sequence-specific multiprotein complexes on regulatory regions (gene promoters and enhancers). Such combinatorial gene switches permit flexibility of regulation and allow numerous developmental decisions to be taken with a limited number of regulators. The haematopoietic-specific Ets family transcription factor PU.1 regulates many lymphoid- and myeloid-specific gene promoters and enhancers by interacting with multiple proteins during haematopoietic development. Such protein–protein interactions regulate DNA binding, subcellular localization, target gene selection and transcriptional activity of PU.1 itself in response to diverse signals including cytokines, growth factors, antigen and cellular stresses. Specific domains of PU.1 interact with many protein motifs such as bHLH, bZipper, zinc fingers and paired domain for regulating its activity. This review focuses on important protein–protein interactions of PU.1 that play a crucial role in regulation of normal as well as malignant haematopoiesis. Precise delineation of PU.1 protein-partner interacting interface may provide an improved insight of the molecular mechanisms underlying haematopoietic stem cell fate regulation. Its interactions with some proteins could be targeted to modulate the aberrant signalling pathways for reversing the malignant phenotype and to control the generation of specific haematopoietic progeny for treatment of haematopoietic disorders.

FIP1L1-PDGFRalpha imposes eosinophil lineage commitment on hematopoietic stem/progenitor cells

Although leukemogenic tyrosine kinases (LTKs) activate a common set of downstream molecules, the phenotypes of leukemia caused by LTKs are rather distinct. Here we report the molecular mechanism underlying the development of hypereosinophilic syndrome/chronic eosinophilic leukemia by FIP1L1-PDGFRalpha. When introduced into c-Kit(high)Sca-1(+)Lineage(-) cells, FIP1L1-PDGFRalpha conferred cytokine-independent growth on these cells and enhanced their self-renewal, whereas it did not immortalize common myeloid progenitors in in vitro replating assays and transplantation assays. Importantly, FIP1L1-PDGFRalpha but not TEL-PDGFRbeta enhanced the development of Gr-1(+)IL-5Ralpha(+) eosinophil progenitors from c-Kit(high)Sca-1(+)Lineage(-) cells. FIP1L1-PDGFRalpha also promoted eosinophil development from common myeloid progenitors. Furthermore, when expressed in megakaryocyte/erythrocyte progenitors and common lymphoid progenitors, FIP1L1-PDGFRalpha not only inhibited differentiation toward erythroid cells, megakaryocytes, and B-lymphocytes but aberrantly developed eosinophil progenitors from megakaryocyte/erythrocyte progenitors and common lymphoid progenitors. As for the mechanism of FIP1L1-PDGFRalpha-induced eosinophil development, FIP1L1-PDGFRalpha was found to more intensely activate MEK1/2 and p38(MAPK) than TEL-PDGFRbeta. In addition, a MEK1/2 inhibitor and a p38(MAPK) inhibitor suppressed FIP1L1-PDGFRalpha-promoted eosinophil development. Also, reverse transcription-PCR analysis revealed that FIP1L1-PDGFRalpha augmented the expression of C/EBPalpha, GATA-1, and GATA-2, whereas it hardly affected PU.1 expression. In addition, short hairpin RNAs against C/EBPalpha and GATA-2 and GATA-3KRR, which can act as a dominant-negative form over all GATA members, inhibited FIP1L1-PDGFRalpha-induced eosinophil development. Furthermore, FIP1L1-PDGFRalpha and its downstream Ras inhibited PU.1 activity in luciferase assays. Together, these results indicate that FIP1L1-PDGFRalpha enhances eosinophil development by modifying the expression and activity of lineage-specific transcription factors through Ras/MEK and p38(MAPK) cascades.

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.

Biology of the eosinophil

In this review, we aim to put in perspective the biology of a multifunctional leukocyte, the eosinophil, by placing it in the context of innate and adaptive immune responses. Eosinophils have a unique contribution in initiating inflammatory and adaptive responses, due to their bidirectional interactions with dendritic cells and T cells, as well as their large panel of secreted cytokines and soluble mediators. The mechanisms and consequences of eosinophil responses in experimental inflammatory models and human diseases are discussed.

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.

E2F4 modulates differentiation and gene expression in hematopoietic progenitor cells during commitment to the lymphoid lineage

The E2F4 protein is involved in gene repression and cell cycle exit, and also has poorly understood effects in differentiation. We analyzed the impact of E2F4 deficiency on early steps in mouse hematopoietic development, and found defects in early hematopoietic progenitor cells that were propagated through common lymphoid precursors to the B and T lineages. In contrast, the defects in erythromyeloid precursor cells were self-correcting over time. This suggests that E2F4 is important in early stages of commitment to the lymphoid lineage. The E2F4-deficient progenitor cells showed reduced expression of several key lymphoid-lineage genes, and overexpression of two erythromyeloid lineage genes. However, we did not detect effects on cell proliferation. These findings emphasize the significance of E2F4 in controlling gene expression and cell fate.

Transcription factor PU.1 is expressed in white adipose and inhibits adipocyte differentiation

PU.1 transcription factor is a critical regulator of hematopoiesis and leukemogenesis. Because PU.1 interacts with transcription factors GATA-2 and C/EBPalpha, and both are involved in the regulation of adipogenesis, we investigated whether PU.1 plays a role in the regulation of adipocyte differentiation. Our data indicate that PU.1 is expressed in white adipose tissue. PU.1 protein can also be detected in cultured 3T3-L1 adipocytes. Forced expression of PU.1 in 3T3-L1 cells inhibits adipocyte differentiation, whereas deletion of the transactivation domain of PU.1 abolishes this effect. The inhibition of adipocyte differentiation by PU.1 is achieved, at least in part, through repression of the transcriptional activity of C/EBPalpha and C/EBPbeta. Furthermore, GATA-2 and PU.1 have an additive inhibitory effect on C/EBP transactivation and adipogenesis. Finally, the expression of PU.1 is increased in white adipose of obese mice.

Eosinophils: biological properties and role in health and disease

Eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, the biology of eosinophils is summarized, focusing on transcriptional regulation of eosinophil differentiation, characterization of the growing properties of eosinophil granule proteins, surface proteins and pleiotropic mediators, and molecular mechanisms of eosinophil degranulation. New views on the role of eosinophils in homeostatic function are examined, including developmental biology and innate and adaptive immunity (as well as their interaction with mast cells and T cells) and their proposed role in disease processes including infections, asthma, and gastrointestinal disorders. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized.

Role of the GATA family of transcription factors in endocrine development, function, and disease

The WGATAR motif is a common nucleotide sequence found in the transcriptional regulatory regions of numerous genes. In vertebrates, these motifs are bound by one of six factors (GATA1 to GATA6) that constitute the GATA family of transcriptional regulatory proteins. Although originally considered for their roles in hematopoietic cells and the heart, GATA factors are now known to be expressed in a wide variety of tissues where they act as critical regulators of cell-specific gene expression. This includes multiple endocrine organs such as the pituitary, pancreas, adrenals, and especially the gonads. Insights into the functional roles played by GATA factors in adult organ systems have been hampered by the early embryonic lethality associated with the different Gata-null mice. This is now being overcome with the generation of tissue-specific knockout models and other knockdown strategies. These approaches, together with the increasing number of human GATA-related pathologies have greatly broadened the scope of GATA-dependent genes and, importantly, have shown that GATA action is not necessarily limited to early development. This has been particularly evident in endocrine organs where GATA factors appear to contribute to the transcription of multiple hormone-encoding genes. This review provides an overview of the GATA family of transcription factors as they relate to endocrine function and disease.

Origin, regulation and physiological function of intestinal oeosinophils

Oeosinophils are pleiotropic multi-functional leukocytes that are typically associated with the initiation and propagation of inflammatory responses, particularly helminth infection and allergic disease. However, expanding evidence supports a broader role for oeosinophils in homoeostatic function and organ development and modulation of local immune responses via interaction with other effector cells. In this review, the biology of oeosinophils in the healthy gut is summarised. In particular, the molecular steps involved in oeosinophil development and trafficking are described, with special attention to the important role of the transcription factor GATA-1, the oeosinophil-selective cytokine IL-5 and the eotaxin subfamily of chemokines. In addition, the regulation of oeosinophil survival by inhibitory and death receptors and the expanding role for oeosinophils in health and disease are reviewed.

Mechanisms of eosinophilia in the pathogenesis of hypereosinophilic disorders

The increased numbers of activated eosinophils in the blood and tissues that typically accompany hypereosinophilic disorders result from a variety of mechanisms. Exciting advances in translating discoveries achieved from mouse models and molecular strategies to the clinic have led to a flurry of new therapeutics specifically designed to target eosinophil-associated diseases. So far, this form of hypothesis testing in humans in vivo through pharmacology generally has supported the paradigms generated in vitro and in animal models, raising hopes that a spectrum of novel therapies soon may become available to help those who have eosinophil-associated diseases.

Eosinophil trafficking in allergy and asthma

Blood eosinophilia and tissue eosinophilia are characteristic features of allergic inflammation and asthma, conditions associated with prominent production of T(H)2 cytokines IL-4, IL-5, and IL-13. In this review, we will consider recent advances in our understanding of the molecular mechanisms that promote expansion and differentiation of eosinophil progenitors in bone marrow, eosinophil recruitment in response to chemokine receptor 3 agonists eosinophil transit mediated by specific ligand-receptor interactions, and prolonged survival of eosinophils in peripheral tissues. Novel rational therapies including antiselectin and antichemokine receptor modalities designed to block eosinophil development and trafficking are discussed, together with the implications of recent clinical studies that have evaluated the efficacy of humanized anti-IL-5 mAb therapy.

Eosinophils in the pathogenesis of allergic airways disease

Eosinophils are traditionally thought to form part of the innate immune response against parasitic helminths acting through the release of cytotoxic granule proteins. However, they are also a central feature in asthma. From their development in the bone marrow to their recruitment to the lung via chemokines and cytokines, they form an important component of the inflammatory milieu observed in the asthmatic lung following allergen challenge. A wealth of studies has been performed in both patients with asthma and in mouse models of allergic pulmonary inflammation to delineate the role of eosinophils in the allergic response. Although the long-standing association between eosinophils and the induction of airway hyper-responsiveness remains controversial, recent studies have shown that eosinophils may also promote airway remodelling. In addition, emerging evidence suggests that the eosinophil may also serve to modulate the immune response. Here we review the highly co-ordinated nature of eosinophil development and trafficking and the evolution of the eosinophil as a multi-factoral leukocyte with diverse functions in asthma.

Eosinophil cationic protein (ECP) polymorphisms and association with asthma, s-ECP levels and related phenotypes

BACKGROUND

Eosinophil cationic protein (ECP) is a potent cytotoxic secretory protein with bactericidal and antiviral properties. ECP is released by activated eosinophils and regarded as a marker of eosinophilic inflammation. High levels of ECP have been reported in cases of active asthma and other allergic diseases. This study aimed to assess whether three single-nucleotide polymorphisms (SNPs) in the ECP gene (RNASE3) on chromosome 14 q24-q31 or their haplotypes are associated with asthma, allergy, or related phenotypes.

METHODS

The three SNPs -38CA, +371CG and +499CG in RNASE3 and their haplotypes were analyzed for associations with asthma, serum-ECP (s-ECP) levels, allergic sensitization (positive skin-prick test to common allergens), bronchial hyperresponsiveness (BHR) assessed by methacholine inhalation, and serum-IgE (s-IgE) levels in 177 families from Norway and the Netherlands identified through siblings with asthma.

RESULTS

Transmission disequilibrium test (TDT) demonstrated significant associations between the A-G-G haplotype and asthma as well as the specific phenotypes allergic asthma (but not non-allergic asthma), high s-ECP, high s-IgE and BHR, while the C-G-G haplotype was associated with reduced occurrence of these traits. In addition, the -38A allele was associated with high s-ECP levels and allergic asthma.

CONCLUSION

The present study suggests that the A-G-G haplotype in the RNASE3 gene influences the development of asthma, in particular, an allergic form of asthma. Furthermore, as the -38CA SNP lies in close vicinity of known intron-regulatory sites, results of SNP analysis suggest that the detected association is possibly linked to a genetic transcriptional control of s-ECP levels.

EGO, a novel, noncoding RNA gene, regulates eosinophil granule protein transcript expression

Gene expression profiling of early eosinophil development shows increased transcript levels of proinflammatory cytokines, chemokines, transcription factors, and a novel gene, EGO (eosinophil granule ontogeny). EGO is nested within an intron of the inositol triphosphate receptor type 1 (ITPR1) gene and is conserved at the nucleotide level; however, the largest open reading frame (ORF) is 86 amino acids. Sucrose density gradients show that EGO is not associated with ribosomes and therefore is a noncoding RNA (ncRNA). EGO transcript levels rapidly increase following interleukin-5 (IL-5) stimulation of CD34(+) hematopoietic progenitors. EGO RNA also is highly expressed in human bone marrow and in mature eosinophils. RNA silencing of EGO results in decreased major basic protein (MBP) and eosinophil derived neurotoxin (EDN) mRNA expression in developing CD34(+) hematopoietic progenitors in vitro and in a CD34(+) cell line model. Therefore, EGO is a novel ncRNA gene expressed during eosinophil development and is necessary for normal MBP and EDN transcript expression.

ATF4 differentially regulates transcriptional activation of myeloid-specific genes by C/EBPepsilon and C/EBPalpha

Dimerization between different basic region leucine zipper (ZIP) transcription factors is regarded as an important mechanism for integrating various extracellular signals to control specific patterns of gene expression in cells. The activating transcription factor 4 (ATF4) protein was identified as a principal partner for the myeloid-specific transcriptional factor C/EBPepsilon. Dimerization required the ZIP motif of each protein and redirected DNA binding of C/EBPepsilon and ATF4 from their respective symmetric consensus sites to asymmetric C/EBP and cAMP response element sites. The C/EBPepsilon:ATF4 heterodimer bound to the C/EBP sites in the promoters of the myeloid-specific genes encoding neutrophil elastase (NE) and the G-CSF receptor (G-CSFR). Also, the heterodimer bound a previously uncharacterized site in the promoter of the mim-1 gene at nucleotide -174. Coexpression of ATF4 and C/EBPepsilon in the presence of c-Myb synergistically activated the mim-1 and NE promoters compared with C/EBPepsilon plus c-Myb alone. Synergistic activation was not observed for the G-CSFR promoter and only occurred in the presence of c-myb with the NE or mim-1 promoters. In contrast, ATF4:C/EBPalpha dimers bound to the C/EBP sites in the G-CSFR and NE promoters, but transcriptional activation was inhibited by 30-80% in the presence or absence of c-Myb. We propose that ATF4 may regulate myeloid gene expression differentially by potentiating C/EBPepsilon but inhibiting C/EBPalpha-mediated transcriptional activation.

Differentiation of eosinophilic leukemia EoL-1 cells into eosinophils induced by histone deacetylase inhibitors

EoL-1 cells differentiate into eosinophils in the presence of n-butyrate, but the mechanism has remained to be elucidated. Because n-butyrate can inhibit histone deacetylases, we hypothesized that the inhibition of histone deacetylases induces the differentiation of EoL-1 cells into eosinophils. In this study, using n-butyrate and two other histone deacetylase inhibitors, apicidin and trichostatin A, we have analyzed the relationship between the inhibition of histone deacetylases and the differentiation into eosinophils in EoL-1 cells. It was demonstrated that apicidin and n-butyrate induced a continuous acetylation of histones H4 and H3, inhibited the proliferation of EoL-1 cells without attenuating the level of FIP1L1-PDGFRA mRNA, and induced the expression of markers for mature eosinophils such as integrin beta7, CCR1, and CCR3 on EoL-1 cells, while trichostatin A evoked a transient acetylation of histones and induced no differentiation into eosinophils. These findings suggest that the continuous inhibition of histone deacetylases in EoL-1 cells induces the differentiation into mature eosinophils.

The eosinophil

Eosinophils have been considered end-stage cells involved in host protection against parasites. However, numerous lines of evidence have now changed this perspective by showing that eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, we summarize the biology of eosinophils, focusing on the growing properties of eosinophil-derived products, including the constituents of their granules as well as the mechanisms by which they release their pleiotropic mediators. We examine new views on the role of eosinophils in homeostatic function, including developmental biology and innate and adaptive immunity (as well as interaction with mast cells and T cells). The molecular steps involved in eosinophil development and trafficking are described, with special attention to the important role of the transcription factor GATA-1, the eosinophil-selective cytokine IL-5, and the eotaxin subfamily of chemokines. We also review the role of eosinophils in disease processes, including infections, asthma, and gastrointestinal disorders, and new data concerning genetically engineered eosinophil-deficient mice. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized.

PU.1 phosphorylation correlates with hydroquinone-induced alterations in myeloid differentiation and cytokine-dependent clonogenic response in human CD34+ hematopoietic progenitor cells

The transcriptional regulatory factor PU.1 is important for the regulation of a diverse group of hematopoietic and myeloid genes. Posttranslational phosphorylation of PU.1 has been demonstrated in the regulation of a variety of promoters in normal cells. In leukemia cells, differing patterns of PU.1 phosphorylation have been described among acute myelogenous leukemia (AML) subtypes. Therefore, we hypothesized that modulation of PU.1-dependent gene expression might be a molecular mediator of alterations in myeloid cell growth and differentiation that have been demonstrated to be early events in benzene-induced leukemogenesis. We found that freshly isolated human CD34(+) hematopoietic progenitor cells (HPC) exhibit multiple PU.1-DNA binding species that represent PU.1 proteins in varying degrees of phosphorylation states as determined by phosphatase treatment in combination with electrophoretic mobility shift assay (EMSA). Maturation of granulocyte and monocyte lineages is also accompanied by distinct changes in PU.1-DNA binding patterns. Experiments reveal that increasing doses of the benzene metabolite, hydroquinone (HQ) induce a time-and dose-dependent alteration in the pattern of PU.1-DNA binding in cultured human CD34(+) cells, corresponding to hyperphosphorylation of the PU.1 protein. HQ-induced alterations in PU.1-DNA binding are concomitant with a sustained immature CD34(+) phenotype and cytokine-dependent enhanced clonogenic activity in cultured human HPC. These results suggest that HQ induces a dysregulation in the external signals modulating PU.1 protein phosphorylation and this dysregulation may be an early event in the generation of benzene-induced AML.

Towards an understanding of lineage specification in hematopoietic stem cells: a mathematical model for the interaction of transcription factors GATA-1 and PU.1

In addition to their self-renewal capabilities, hematopoietic stem cells guarantee the continuous supply of fully differentiated, functional cells of various types in the peripheral blood. The process which controls differentiation into the different lineages of the hematopoietic system (erythroid, myeloid, lymphoid) is referred to as lineage specification. It requires a potentially multi-step decision sequence which determines the fate of the cells and their successors. It is generally accepted that lineage specification is regulated by a complex system of interacting transcription factors. However, the underlying principles controlling this regulation are currently unknown. Here, we propose a simple quantitative model describing the interaction of two transcription factors. This model is motivated by experimental observations on the transcription factors GATA-1 and PU.1, both known to act as key regulators and potential antagonists in the erythroid vs. myeloid differentiation processes of hematopoietic progenitor cells. We demonstrate the ability of the model to account for the observed switching behavior of a transition from a state of low expression of both factors (undifferentiated state) to the dominance of one factor (differentiated state). Depending on the parameter choice, the model predicts two different possibilities to explain the experimentally suggested, stem cell characterizing priming state of low level co-expression. Whereas increasing transcription rates are sufficient to induce differentiation in one scenario, an additional system perturbation (by stochastic fluctuations or directed impulses) of transcription factor levels is required in the other case.

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.

Mechanism of the eosinophilic differentiation of HL-60 clone 15 cells induced by n-butyrate

n-Butyrate is one of the most powerful chemical inducers of the differentiation of human eosinophilic leukemia HL-60 clone 15 cells into mature eosinophils. We have recently reported that the mechanism by which HL-60 clone 15 cells differentiate into eosinophils by n-butyrate is that n-butyrate continuously inhibits histone deacetylase activity as a histone deacetylase inhibitor, resulting in continuous acetylation of histones. In this review, we discuss roles of histone acetyltransferase, histone deacetylase and histone deacetylase inhibitors in the differentiation of HL-60 clone 15 cells into eosinophils.

GATA-1 forms distinct activating and repressive complexes in erythroid cells

GATA-1 is essential for the generation of the erythroid, megakaryocytic, eosinophilic and mast cell lineages. It acts as an activator and repressor of different target genes, for example, in erythroid cells it represses cell proliferation and early hematopoietic genes while activating erythroid genes, yet it is not clear how both of these functions are mediated. Using a biotinylation tagging/proteomics approach in erythroid cells, we describe distinct GATA-1 interactions with the essential hematopoietic factor Gfi-1b, the repressive MeCP1 complex and the chromatin remodeling ACF/WCRF complex, in addition to the known GATA-1/FOG-1 and GATA-1/TAL-1 complexes. Importantly, we show that FOG-1 mediates GATA-1 interactions with the MeCP1 complex, thus providing an explanation for the overlapping functions of these two factors in erythropoiesis. We also show that subsets of GATA-1 gene targets are bound in vivo by distinct complexes, thus linking specific GATA-1 partners to distinct aspects of its functions. Based on these findings, we suggest a model for the different roles of GATA-1 in erythroid differentiation.

FOG-1 recruits the NuRD repressor complex to mediate transcriptional repression by GATA-1

Transcription factor GATA-1 and its cofactor FOG-1 coordinate erythroid cell maturation by activating erythroid-specific genes and repressing genes associated with the undifferentiated state. Here we show that FOG-1 binds to the NuRD corepressor complex in vitro and in vivo. The interaction is mediated by a small conserved domain at the extreme N-terminus of FOG-1 that is necessary and sufficient for NuRD binding. This domain defines a novel repression module found in diverse transcriptional repressors. NuRD is present at GATA-1/FOG-1-repressed genes in erythroid cells in vivo. Point mutations near the N-terminus of FOG-1 that abrogate NuRD binding block gene repression by FOG-1. Finally, the ability of GATA-1 to repress transcription was impaired in erythroid cells expressing mutant forms of FOG-1 that are defective for NuRD binding. Together, these studies show that FOG-1 and likely other FOG-like proteins are corepressors that link GATA factors to histone deacetylation and nucleosome remodeling.

C/EBPδ and C/EBPγ bind the CCAAT-box in the human β-globin promoter and modulate the activity of the CACC-box binding protein, EKLF

Developmental- and tissue-specific expression of globin genes is mediated by a few key elements within the proximal promoter of each gene. DNA-binding assays previously identified NF-Y, GATA-1, C/EBPbeta and C/EBPgamma as candidate regulators of beta-globin transcription via the CCAAT-box, a promoter element situated between CACC- and TATA-boxes. We have identified C/EBPdelta as an additional beta-globin CCAAT-box binding protein. In reporter assays, we show that C/EBPdelta can co-operate with EKLF, a CACC-box binding protein, to activate the beta-globin promoter, whereas C/EBPgamma inhibits the transcriptional activity of EKLF in this assay.

Possible mechanism of action of the histone deacetylase inhibitors for the induction of differentiation of HL-60 clone 15 cells into eosinophils

1 We have examined the effect of the histone deacetylase inhibitors apicidin, trichostatin A (TSA) and n-butyrate on the histone acetylation and the differentiation of human eosinophilic leukemia HL-60 clone 15 cells into eosinophils. 2 Viability of the cells incubated with apicidin (100 nm), TSA (30 nm) or n-butyrate (500 microm) did not change significantly, but higher concentrations of apicidin (> or =300 nm) or TSA (> or =100 nm) decreased the viability when examined at day 1. 3 Apicidin (100 nm) as well as n-butyrate (500 microm) induced continuous acetylations of histone H4 and lysine14 residue on histone H3, while TSA (30 nm) induced transient acetylations. 4 After 6 days incubation, eosinophilic cells stained by Luxol-fast-blue were generated by apicidin (100 nm) and n-butyrate (500 microm) but not by TSA (30 nm). Other markers for differentiation into eosinophils such as changes in intracellular structure, and expressions of integrin beta7 and major basic protein, and the inhibition of cell proliferation were also induced by apicidin and n-butyrate but not by TSA. 5 Continuous acetylation of histone H4 achieved by repeated treatment with TSA (30 nm) at an interval of 12 h for more than three times induced such changes when examined on day 6. In addition, the induction was impaired by shortening the period of incubation with apicidin (100 nm) or n-butyrate (500 microm). 6 CCAAT/enhancer binding protein was continuously activated by apicidin (100 nm) and n-butyrate (500 microm), but was transiently activated by TSA (30 nm). 7 These findings suggest that the continuous acetylation of histones H3 and H4 is necessary for the differentiation of HL-60 clone 15 cells into eosinophils.

In vitro analysis of Bombyx mori early chorion gene regulation: stage specific expression involves interactions with C/EBP-like and GATA factors

This is the first attempt to identify regulatory elements that are involved in early choriogenesis of the silkworm Bombyx mori. A new cis element in the promoter region of five early chorion genes was identified. The consensus sequence of this element matches the consensus of the C/EBP DNA binding site. Moreover, this sequence interacts with a 70 kD protein (pX2) present in follicular nuclear extracts and complex formation exhibits early developmental specificity. There is strong evidence that this factor belongs to the C/EBP family. Surprisingly, the same protein binds with the same developmental specificity to a similar sequence of a late chorion gene promoter, which has been previously defined as the binding site for a putative late specific factor, BCFII. The possibility that pX2 and BCFII are isoforms or modifications of the same protein factor, which is presumably able to bind to the highly similar sequence elements of both early and late genes, is discussed. A hypothesis involving protein-protein interactions between C/EBP (pX2/BCFII) and GATA during choriogenesis is presented to explain the temporal specificity of chorion genes.