Autoregulation enables different pathways to control CCAAT/enhancer binding protein beta (C/EBP beta) transcription

C/EBPβ: The structure, regulation, and its roles in inflammation-related diseases

Inflammation, a mechanism of the human body, has been implicated in many diseases. Inflammatory responses include the release of inflammatory mediators by activating various signaling pathways. CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor in the C/EBP family, contains the leucine zipper (bZIP) domain. The expression of C/EBPβ is mediated at the transcriptional and post-translational levels, such as phosphorylation, acetylation, methylation, and SUMOylation. C/EBPβ has been involved in inflammatory responses by mediating several signaling pathways, such as MAPK/NF-κB and IL-6/JAK/STAT3 pathways. C/EBPβ plays an important role in the pathological development of inflammation-related diseases, such as osteoarthritis, pneumonia, hepatitis, inflammatory bowel diseases, and rheumatoid arthritis. Here, we comprehensively discuss the structure and biological effects of C/EBPβ and its role in inflammatory diseases.

TET2 is recruited by CREB to promote Cebpb, Cebpa, and Pparg transcription by facilitating hydroxymethylation during adipocyte differentiation

Ten-eleven translocation proteins (TETs) are dioxygenases that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), an important epigenetic mark that regulates gene expression during development and differentiation. Here, we found that the TET2 expression was positively associated with adipogenesis. Further, in vitro and in vivo experiments showed that TET2 deficiency blocked adipogenesis by inhibiting the expression of the key transcription factors CCAAT/enhancer-binding protein beta (C/EBPβ), C/EBPα and peroxisome proliferator-activated receptor gamma (PPARγ). In addition, TET2 promoted 5hmC on the CpG islands (CGIs) of Cebpb, Cebpa and Pparg at the initial time point of their transcription, which requires the cAMP-responsive element-binding protein (CREB). At last, specific knockout of Tet2 in preadipocytes enabled mice to resist obesity and attenuated the obesity-associated insulin resistance. Together, TET2 is recruited by CREB to promote the expression of Cebpb, Cebpa and Pparg via 5hmC during adipogenesis and may be a potential therapeutic target for obesity and insulin resistance.

The Dual Role of C/EBPδ in Cancer

CCAAT/Enhancer-Binding Protein delta (C/EBPδ) is a transcription factor involved in differentiation and inflammation. While sparsely expressed in adult tissues, aberrant expression of C/EBPδ has been associated with different cancers. Initially, re-expression of C/EBPδ in cell cultures limited tumor cell proliferation, assigning it a tumor suppressor role. However, opposing observations were made in pre-clinical models and patients, suggesting that C/EBPδ not only mediates cell proliferation but dictates a broader spectrum of tumorigenesis-related effects. It is now widely accepted that C/EBPδ contributes to an inflammatory, tumor-promoting microenvironment, aids hypoxia adaption and contributes to the recruitment of blood vessels for improved nutrient supply to tumor cells and facilitated extravasation. This review summarizes the work published on this transcription factor in the field of cancer over the past decade. It points out areas in which a consensus on C/EBPδ's role appears to emerge and seek to explain seemingly contradictory results.

BCR-Associated Protein 31 Regulates Macrophages Polarization and Wound Healing Function via Early Growth Response 2/C/EBPβ and IL-4Rα/C/EBPβ Pathways

The BCR-associated protein 31 (BAP31), a transmembrane protein in the endoplasmic reticulum, participates in the regulation of immune cells, such as microglia and T cells, and has potential functions in macrophages that remain to be unexplored. In this study, we designed and bred macrophage-specific BAP31 knockdown mice to detect the polarization and functions of macrophages. The results revealed that M2 macrophage-associated genes were suppressed in mouse bone marrow–derived macrophages of Lyz2 Cre-BAP31flox/flox mice. Multiple macrophage-associated transcription factors were demonstrated to be able to be regulated by BAP31. Among these factors, C/EBPβ was the most significantly decreased and was regulated by early growth response 2. BAP31 could also affect C/EBPβ via modulating IL-4Rα ubiquitination and proteasome degradation in IL-4–stimulated macrophages. Furthermore, we found that BAP31 affects macrophages functions, including angiogenesis and skin fibrosis, during the wound healing process through IL-4Rα, as confirmed by infection with adeno-associated virus–short hairpin (sh)-IL-4Rα in Lyz2 Cre-BAP31flox/flox mice. Our findings indicate a novel mechanism of BAP31 in regulating macrophages and provide potential solutions for the prevention and treatment of chronic wounds.

Transient Delivery of A-C/EBP Protein Perturbs Differentiation of 3T3-L1 Cells and Induces Preadipocyte Marker Genes

Transformation of committed 3T3-L1 preadipocytes to lipid-laden adipocytes involves the timely appearance of numerous transcription factors (TFs); foremost among them, C/EBPβ is expressed during the early phases of differentiation. Here, we describe liposome-mediated protein transfection approach to rapidly downregulate C/EBPβ by A-C/EBP protein inhibitor. Signals from EGFP-tagged A-C/EBP protein were observed in 3T3-L1 cells within 2 h of transfections, whereas for A-C/EBP gene transfections, equivalent signals appeared in 48 h. Following transient transfections, the expression profiles of 24 marker genes belonging to pro- and anti-adipogenic, cell cycle, and preadipocyte pathways were analyzed. Expectedly, the mRNA and protein expression profiles of adipocyte marker genes showed lower expression in both A-C/EBP protein- and gene-transfected samples. Interestingly, for preadipocytes and cell fate determinant genes, striking differences were observed between A-C/EBP protein- and A-C/EBP gene-transfected samples. Preadipocyte differentiation factors Stat5a and Creb were downregulated in A-C/EBP protein samples. Five preadipocyte markers, namely, Pdgfrα, Pdgfrβ, Ly6A, CD34, and Itgb1, showed high expression in A-C/EBP protein samples, whereas only Ly6A and CD34 were expressed in A-C/EBP gene-transfected samples. Pdgfrα and Pdgfrβ, two known cell fate markers, were expressed in A-C/EBP protein-transfected samples, suggesting a possible reversal of differentiation. Our study provides evidences for the immediate and efficient knockdown of C/EBPβ protein to understand time-dependent preadipocytes differentiation.

Orchestration of Intracellular Circuits by G Protein-Coupled Receptor 39 for Hepatitis B Virus Proliferation

Hepatitis B virus (HBV), a highly persistent pathogen causing hepatocellular carcinoma (HCC), takes full advantage of host machinery, presenting therapeutic targets. Here we aimed to identify novel druggable host cellular factors using the reporter HBV we have recently generated. In an RNAi screen of G protein-coupled receptors (GPCRs), GPCR39 (GPR39) appeared as the top hit to facilitate HBV proliferation. Lentiviral overexpression of active GPR39 proteins and an agonist enhanced HBV replication and transcriptional activities of viral promoters, inducing the expression of CCAAT/enhancer binding protein (CEBP)-β (CEBPB). Meanwhile, GPR39 was uncovered to activate the heat shock response, upregulating the expression of proviral heat shock proteins (HSPs). In addition, glioma-associated oncogene homologue signaling, a recently reported target of GPR39, was suggested to inhibit HBV replication and eventually suppress expression of CEBPB and HSPs. Thus, GPR39 provirally governed intracellular circuits simultaneously affecting the carcinopathogenetic gene functions. GPR39 and the regulated signaling networks would serve as antiviral targets, and strategies with selective inhibitors of GPR39 functions can develop host-targeted antiviral therapies preventing HCC.

IKZF2 Drives Leukemia Stem Cell Self-Renewal and Inhibits Myeloid Differentiation

Leukemias exhibit a dysregulated developmental program mediated through both genetic and epigenetic mechanisms. Although IKZF2 is expressed in hematopoietic stem cells (HSCs), we found that it is dispensable for mouse and human HSC function. In contrast to its role as a tumor suppressor in hypodiploid B-acute lymphoblastic leukemia, we found that IKZF2 is required for myeloid leukemia. IKZF2 is highly expressed in leukemic stem cells (LSCs), and its deficiency results in defective LSC function. IKZF2 depletion in acute myeloid leukemia (AML) cells reduced colony formation, increased differentiation and apoptosis, and delayed leukemogenesis. Gene expression, chromatin accessibility, and direct IKZF2 binding in MLL-AF9 LSCs demonstrate that IKZF2 regulates a HOXA9 self-renewal gene expression program and inhibits a C/EBP-driven differentiation program. Ectopic HOXA9 expression and CEBPE depletion rescued the effects of IKZF2 depletion. Thus, our study shows that IKZF2 regulates the AML LSC program and provides a rationale to therapeutically target IKZF2 in myeloid leukemia.

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

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

Zinc Modulates Endotoxin-Induced Human Macrophage Inflammation through ZIP8 Induction and C/EBPβ Inhibition

Two vital functions of the innate immune system are to initiate inflammation and redistribute micronutrients in favor of the host. Zinc is an essential micronutrient used in host defense. The zinc importer ZIP8 is uniquely induced through stimulation of the NF-κB pathway by LPS in monocytes and functions to regulate inflammation in a zinc-dependent manner. Herein we determined the impact of zinc metabolism following LPS-induced inflammation in human macrophages. We observed that ZIP8 is constitutively expressed in resting macrophages and strikingly elevated following LPS exposure, a response that is unique compared to the 13 other known zinc import proteins. During LPS exposure, extracellular zinc concentrations within the physiological range markedly reduced IL-10 mRNA expression and protein release but increased mRNA expression of TNFα, IL-8, and IL-6. ZIP8 knockdown inhibited LPS-driven cellular accumulation of zinc and prevented zinc-dependent reduction of IL-10 release. Further, zinc supplementation reduced nuclear localization and activity of C/EBPβ, a transcription factor known to drive IL-10 expression. These studies demonstrate for the first time that zinc regulates LPS-mediated immune activation of human macrophages in a ZIP8-dependent manner, reducing IL-10. Based on these findings we predict that macrophage zinc metabolism is important in host defense against pathogens.

Understanding how long-acting β2 -adrenoceptor agonists enhance the clinical efficacy of inhaled corticosteroids in asthma - an update

In moderate-to-severe asthma, adding an inhaled long-acting β₂ -adenoceptor agonist (LABA) to an inhaled corticosteroid (ICS) provides better disease control than simply increasing the dose of ICS. Acting on the glucocorticoid receptor (GR, gene NR3C1), ICSs promote anti-inflammatory/anti-asthma gene expression. In vitro, LABAs synergistically enhance the maximal expression of many glucocorticoid-induced genes. Other genes, including dual-specificity phosphatase 1(DUSP1) in human airways smooth muscle (ASM) and epithelial cells, are up-regulated additively by both drug classes. Synergy may also occur for LABA-induced genes, as illustrated by the bronchoprotective gene, regulator of G-protein signalling 2 (RGS2) in ASM. Such effects cannot be produced by either drug alone and may explain the therapeutic efficacy of ICS/LABA combination therapies. While the molecular basis of synergy remains unclear, mechanistic interpretations must accommodate gene-specific regulation. We explore the concept that each glucocorticoid-induced gene is an independent signal transducer optimally activated by a specific, ligand-directed, GR conformation. In addition to explaining partial agonism, this realization provides opportunities to identify novel GR ligands that exhibit gene expression bias. Translating this into improved therapeutic ratios requires consideration of GR density in target tissues and further understanding of gene function. Similarly, the ability of a LABA to interact with a glucocorticoid may be suboptimal due to low β₂ -adrenoceptor density or biased β₂ -adrenoceptor signalling. Strategies to overcome these limitations include adding-on a phosphodiesterase inhibitor and using agonists of other Gs-coupled receptors. In all cases, the rational design of ICS/LABA, and derivative, combination therapies requires functional knowledge of induced (and repressed) genes for therapeutic benefit to be maximized.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

C/EBPβ Isoforms Expression in the Rat Brain during the Estrous Cycle

The CCAAT/enhancer-binding protein beta (C/EBPβ) is a transcription factor expressed in different areas of the brain that regulates the expression of several genes involved in cell differentiation and proliferation. This protein has three isoforms (LAP1, LAP2, and LIP) with different transcription activation potential. The role of female sex hormones in the expression pattern of C/EBPβ isoforms in the rat brain has not yet been described. In this study we demonstrate by western blot that the expression of the three C/EBPβ isoforms changes in different brain areas during the estrous cycle. In the cerebellum, LAP2 content diminished on diestrus and proestrus and LIP content diminished on proestrus and estrus days. In the prefrontal cortex, LIP content was higher on proestrus and estrus days. In the hippocampus, LAP isoforms presented a switch on diestrus day, since LAP1 content was the highest while that of LAP2 was the lowest. The LAP2 isoform was the most abundant one in all the three brain areas. The LAP/LIP ratio changed throughout the cycle and was tissue specific. These results suggest that C/EBPβ isoforms expression changes in a tissue-specific manner in the rat brain due to the changes in sex steroid hormone levels presented during the estrous cycle.

Retinoic acid promotes myogenesis in myoblasts by antagonizing transforming growth factor-beta signaling via C/EBPβ

BACKGROUND

The effects of transforming growth factor-beta (TGFβ) are mediated by the transcription factors Smad2 and Smad3. During adult skeletal myogenesis, TGFβ signaling inhibits the differentiation of myoblasts, and this can be reversed by treatment with retinoic acid (RA). In mesenchymal stem cells and preadipocytes, RA treatment can function in a non-classical manner by stimulating the expression of Smad3. Smad3 can bind to and prevent the bzip transcription factor CCAAT/enhancer-binding protein beta (C/EBPβ) from binding DNA response elements in target promoters, thereby affecting cell differentiation. In skeletal muscle, C/EBPβ is highly expressed in satellite cells and myoblasts and is downregulated during differentiation. Persistent expression of C/EBPβ in myoblasts inhibits their differentiation.

METHODS

Using both C2C12 myoblasts and primary myoblasts, we examined the regulation of C/EBPβ expression and activity following treatment with TGFβ and RA.

RESULTS

We demonstrate that treatment with RA upregulates Smad3, but not Smad2 expression in myoblasts, and can partially rescue the block of differentiation induced by TGFβ. RA treatment reduces C/EBPβ occupancy of the Pax7 and Smad2 promoters and decreased their expression. RA also inhibits the TGFβ-mediated phosphorylation of Smad2, which may also contribute to its pro-myogenic activities. TGFβ treatment of C2C12 myoblasts stimulates C/EBPβ expression, which in turn can stimulate Pax7 and Smad2 expression, and inhibits myogenesis. Loss of C/EBPβ expression in myoblasts partially restores differentiation in the presence of TGFβ.

CONCLUSIONS

TGFβ acts, at least in part, to inhibit myogenesis by upregulating the expression of C/EBPβ, as treatment with RA or loss of C/EBPβ can partially rescue differentiation in TGFβ-treated cells. This work identifies a pro-myogenic role for Smad3, through the inhibition of C/EBPβ's actions in myoblasts, and reveals mechanisms of crosstalk between RA and TGFβ signaling pathways.

CCAAT/enhancer binding protein β in relation to ER stress, inflammation, and metabolic disturbances

The prevalence of the metabolic syndrome and underlying metabolic disturbances increase rapidly in developed countries. Various molecular targets are currently under investigation to unravel the molecular mechanisms that cause these disturbances. This is done in attempt to counter or prevent the negative health consequences of the metabolic disturbances. Here, we reviewed the current knowledge on the role of C/EBP-β in these metabolic disturbances. C/EBP-β deletion in mice resulted in downregulation of hepatic lipogenic genes and increased expression of β-oxidation genes in brown adipose tissue. Furthermore, C/EBP-β is important in the differentiation and maturation of adipocytes and is increased during ER stress and proinflammatory conditions. So far, studies were only conducted in animals and in cell systems. The results found that C/EBP-β is an important transcription factor within the metabolic disturbances of the metabolic system. Therefore, it is interesting to examine the potential role of C/EBP-β at molecular and physiological level in humans.

MUC1-C oncoprotein activates ERK→C/EBPβ signaling and induction of aldehyde dehydrogenase 1A1 in breast cancer cells

Aldehyde dehydrogenase 1A1 (ALDH1A1) activity is used as a marker of breast cancer stem cells; however, little is known about the regulation of ALDH1A1 expression. Mucin 1 (MUC1) is a heterodimeric protein that is aberrantly overexpressed in most human breast cancers. In studies of breast cancer cells stably silenced for MUC1 or overexpressing the oncogenic MUC1-C subunit, we demonstrate that MUC1-C is sufficient for induction of MEK → ERK signaling and that treatment with a MUC1-C inhibitor suppresses ERK activation. In turn, MUC1-C induces ERK-mediated phosphorylation and activation of the CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor. The results further show that MUC1-C and C/EBPβ form a complex on the ALDH1A1 gene promoter and activate ALDH1A1 gene transcription. MUC1-C-induced up-regulation of ALDH1A1 expression is associated with increases in ALDH activity and is detectable in stem-like cells when expanded as mammospheres. These findings demonstrate that MUC1-C (i) activates a previously unrecognized ERK→C/EBPβ→ALDH1A1 pathway, and (ii) promotes the induction of ALDH activity in breast cancer cells.

Interaction of adenosine 3',5'-cyclic monophosphate and tumor necrosis factor-alpha on serum amyloid A3 expression in mouse granulosa cells: dependence on CCAAT-enhancing binding protein-beta isoform

TNFalpha is an inflammatory-related cytokine that has inhibitory effects on gonadotropin- and cAMP-stimulated steroidogenesis and folliculogenesis. Because ovulation is an inflammatory reaction and TNF specifically induces serum amyloid A3 (SAA3) in mouse granulosa cells, the effect of cAMP on TNF-induced SAA3 promoter activity, mRNA and protein was investigated. Granulosa cells from immature mice were cultured with TNF and/or cAMP. TNF increased SAA3 promoter activity, mRNA, and protein, which were further increased by cAMP. cAMP alone increased SAA3 promoter activity, but SAA3 mRNA and protein remained undetectable. Thus, there appeared to be different mechanisms by which TNF and cAMP regulated SAA3 expression. SAA3 promoters lacking a nuclear factor (NF)-kappaB-like site or containing its mutant were not responsive to TNF but were responsive to cAMP. Among four CCAAT-enhancing binding protein (C/EBP) sites in the SAA3 promoter, the C/EBP site nearest the NF-kappaB-like site was required for TNF-induced SAA3. The C/EBP site at -75/-67 was necessary for responsiveness to cAMP. Dominant-negative C/EBP and cAMP response element-binding protein or short interfering RNA of C/EBPbeta blocked TNF- or cAMP-induced SAA3 promoter activity. The combination of TNF and cAMP increased C/EBPbeta protein above that induced by TNF or cAMP alone. Thus, cAMP in combination with TNF specifically induced C/EBPbeta protein, leading to enhanced SAA3 expression but requiring NF-kappaB in mouse granulose cells. In addition, like TNF, SAA inhibited cAMP-induced estradiol accumulation and CYP19 levels. These data indicate SAA may play a role in events occurring during the ovulation process.

C/EBPbeta regulates transcription factors critical for proliferation and survival of multiple myeloma cells

CCAAT/enhancer-binding protein beta (C/EBPbeta), also known as nuclear factor-interleukin-6 (NF-IL6), is a transcription factor that plays an important role in the regulation of growth and differentiation of myeloid and lymphoid cells. Mice deficient in C/EBPbeta show impaired generation of B lymphocytes. We show that C/EBPbeta regulates transcription factors critical for proliferation and survival in multiple myeloma. Multiple myeloma cell lines and primary multiple myeloma cells strongly expressed C/EBPbeta, whereas normal B cells and plasma cells had little or no detectable levels of C/EBPbeta. Silencing of C/EBPbeta led to down-regulation of transcription factors such as IRF4, XBP1, and BLIMP1 accompanied by a strong inhibition of proliferation. Further, silencing of C/EBPbeta led to a complete down-regulation of antiapoptotic B-cell lymphoma 2 (BCL2) expression. In chromatin immunoprecipitation assays, C/EBPbeta directly bound to the promoter region of IRF4, BLIMP1, and BCL2. Our data indicate that C/EBPbeta is involved in the regulatory network of transcription factors that are critical for plasma cell differentiation and survival. Targeting C/EBPbeta may provide a novel therapeutic strategy in the treatment of multiple myeloma.

Aromatase expression in the ovary: hormonal and molecular regulation

Estrogens are synthesized by the aromatase enzyme encoded by the Cyp19a1 gene, which contains an unusually large regulatory region. In most mammals, aromatase expression is under the control of two distinct promoters a gonad- and a brain-specific promoter. In humans, this gene contains 10 tissue-specific promoters that are alternatively used in various cell types and tumors. Each promoter is regulated by a distinct set of regulatory sequences and transcription factors that bind to these specific sequences. The cAMP/PKA/CREB pathway is considered to be the primary signaling cascade through which the gonad Cyp19 promoter is regulated. Very interestingly, in rat luteal cells, the proximal promoter is not controlled in a cAMP dependent manner. Strikingly, these cells express aromatase at high levels similar to those found in preovulatory follicles, suggesting that alternative and powerful mechanisms control aromatase expression in luteal cells and that the rat corpus luteum represents an important paradigm for understanding alternative controls of the aromatase gene. Here, the molecular and cellular mechanisms controlling the expression of the aromatase gene in granulosa and luteal cells are discussed.

Ets-2 and C/EBP-beta are important mediators of ovine trophoblast Kunitz domain protein-1 gene expression in trophoblast

Background

The trophoblast Kunitz domain proteins (TKDPs) constitute a highly expressed, placenta-specific, multigene family restricted to ruminant ungulates and characterized by a C-terminal "Kunitz" domain, preceded by one or more unique N-terminal domains. TKDP-1 shares an almost identical expression pattern with interferon-tau, the "maternal recognition of pregnancy protein" in ruminants. Our goal here has been to determine whether the ovine (ov) Tkdp-1 and IFNT genes possess a similar transcriptional code.

Results

The ovTkdp-1 promoter has been cloned and characterized. As with the IFNT promoter, the Tkdp-1 promoter is responsive to Ets-2, and promoter-driven reporter activity can be increased over 700-fold in response to over-expression of Ets-2 and a constitutively active form of protein Kinase A (PKA). Unexpectedly, the promoter element of Tkdp-1 responsible for this up-regulation, unlike that of the IFNT, does not bind Ets-2. However, mutation of a CCAAT/enhancer binding element within this control region not only reduced basal transcriptional activity, but prevented Ets-2 as well as cyclic adenosine 5'-monophosphate (cAMP)/PKA and Ras/mitogen-activated protein kinase (MAPK) responsiveness. In vitro binding experiments and in vivo protein-protein interaction assays implicated CCAAT/enhancer binding protein-beta (C/EBP-β) as involved in up-regulating the Tkdp-1 promoter activity. A combination of Ets-2 and C/EBP-β can up-regulate expression of the minimal Tkdp-1 promoter as much as 930-fold in presence of a cAMP analog. An AP-1-like element adjacent to the CCAAT enhancer, which binds Jun family members, is required for basal and cAMP/ C/EBP-β-dependent activation of the gene, but not for Ets-2-dependent activity.

Conclusion

This paper demonstrates how Ets-2, a key transcription factor for trophoblast differentiation and function, can control expression of two genes (Tkdp-1 and IFNT) having similar spatial and temporal expression patterns via very different mechanisms.

Inhibition of collagen gene expression by interferon-gamma: novel role of the CCAAT/enhancer binding protein beta (C/EBPbeta)

By inhibiting collagen synthesis, interferon-gamma (IFN-gamma) plays a key role in maintaining connective tissue homeostasis, but the mechanisms are not well-understood. In addition to intracellular signaling through the canonical JAK-STAT transduction pathway, IFN-gamma was recently shown to regulate gene expression via the CCAAT/enhancer-binding protein beta (C/EBPbeta) as well. Because C/EBPbeta is a crucial mediator of immune and inflammatory responses, and has been implicated in regulation of collagen synthesis by tumor necrosis factor-alpha, we examined its role in the inhibitory effects of IFN-gamma. The results demonstrated that IFN-gamma caused increased C/EBPbeta expression in dermal fibroblasts and enhanced its binding to cognate DNA sequences in the alpha2(I) procollagen gene (COL1A2) promoter in vitro and in vivo. Disruption of C/EBP binding by deletion or site-directed mutagenesis abrogated the inhibition of collagen promoter activity in transient transfection assays, as did cotransfection with dominant negative C/EBPbeta, indicating a functional role of cellular C/EBPbeta in mediating the IFN-gamma response. Rapid phosphorylation of the ERK1/2 MAP kinases induced by IFN-gamma was accompanied by phosphorylation and nuclear translocation of cellular C/EBPbeta, and pretreatment of fibroblasts with ERK1/2 kinase inhibitor blocked C/EBPbeta phosphorylation, as well as inhibition of COL1A2 promoter activity, elicited by IFN-gamma. These results provide compelling evidence for a novel C/EBPbeta-dependent IFN-gamma signaling pathway responsible for inhibition of collagen gene transcription. Taken together with recent reports, the findings indicate that intracellular pathways mediating negative regulation of collagen synthesis in response to distinct inflammatory signals that converge on C/EBPbeta.

Amino-acid limitation induces transcription from the human C/EBPbeta gene via an enhancer activity located downstream of the protein coding sequence

For animals, dietary protein is critical for the nutrition of the organism and, at the cellular level, protein nutrition translates into amino acid availability. Amino acid deprivation triggers the AAR (amino acid response) pathway, which causes enhanced transcription from specific target genes. The present results show that C/EBPbeta (CCAAT/enhancer-binding protein beta) mRNA and protein content were increased following the deprivation of HepG2 human hepatoma cells of a single amino acid. Although there was a modest increase in mRNA half-life following histidine limitation, the primary mechanism for the elevated steady-state mRNA was increased transcription. Transient transfection documented that C/EBPbeta genomic fragments containing the 8451 bp 5' upstream of the transcription start site did not contain amino-acid-responsive elements. However, deletion analysis of the genomic region located 3' downstream of the protein coding sequence revealed that a 93 bp fragment contained an amino-acid-responsive activity that functioned as an enhancer. Exogenous expression of ATF4 (activating transcription factor 4), known to activate other genes through amino acid response elements, caused increased transcription from reporter constructs containing the C/EBPbeta enhancer in cells maintained in complete amino acid medium. Chromatin immunoprecipitation demonstrated that RNA polymerase II is bound at the C/EBPbeta promoter and at the 93 bp regulatory region in vivo, whereas ATF4 binds to the enhancer region only. Immediately following amino acid removal, the kinetics of binding for ATF4, ATF3, and C/EBPbeta itself to the 93 bp regulatory region were similar to those observed for the amino-acid-responsive asparagine synthetase gene. Collectively the findings show that expression of C/EBPbeta, which contributes to the regulation of amino-acid-responsive genes, is itself controlled by amino acid availability through transcription.

Highly conserved proximal promoter element harbouring paired Sox9-binding sites contributes to the tissue- and developmental stage-specific activity of the matrilin-1 gene

The matrilin-1 gene has the unique feature that it is expressed in chondrocytes in a developmental stage-specific manner. Previously, we found that the chicken matrilin-1 long promoter with or without the intronic enhancer and the short promoter with the intronic enhancer restricted the transgene expression to the columnar proliferative chondroblasts and prehypertrophic chondrocytes of growth-plate cartilage in transgenic mice. To study whether the short promoter shared by these transgenes harbours cartilage-specific control elements, we generated transgenic mice expressing the LacZ reporter gene under the control of the matrilin-1 promoter between -338 and +67. Histological analysis of the founder embryos demonstrated relatively weak transgene activity in the developing chondrocranium, axial and appendicular skeleton with highest level of expression in the columnar proliferating chondroblasts and prehypertrophic chondrocytes. Computer analysis of the matrilin-1 genes of amniotes revealed a highly conserved Pe1 (proximal promoter element 1) and two less-conserved sequence blocks in the distal promoter region. The inverted Sox motifs of the Pe1 element interacted with chondrogenic transcription factors Sox9, L-Sox5 and Sox6 in vitro and another factor bound to the spacer region. Point mutations in the Sox motifs or in the spacer region interfered with or altered the formation of nucleoprotein complexes in vitro and significantly decreased the reporter gene activity in transient expression assays in chondrocytes. In vivo occupancy of the Sox motifs in genomic footprinting in the expressing cell type, but not in fibroblasts, also supported the involvement of Pe1 in the tissue-specific regulation of the gene. Our results indicate that interaction of Pe1 with distal DNA elements is required for the high level, cartilage- and developmental stage-specific transgene expression.

The molecular scaffold kinase suppressor of Ras 1 (KSR1) regulates adipogenesis

Mitogen-activated protein kinase pathways are implicated in the regulation of cell differentiation, although their precise roles in many differentiation programs remain elusive. The Raf/MEK/extracellular signal-regulated kinase (ERK) kinase cascade has been proposed to both promote and inhibit adipogenesis. Here, we titrate expression of the molecular scaffold kinase suppressor of Ras 1 (KSR1) to regulate signaling through the Raf/MEK/ERK/p90 ribosomal S6 kinase (RSK) kinase cascade and show how it determines adipogenic potential. Deletion of KSR1 prevents adipogenesis in vitro, which can be rescued by introduction of low levels of KSR1. Appropriate levels of KSR1 coordinate ERK and RSK activation with C/EBPbeta synthesis leading to the phosphorylation and stabilization of C/EBPbeta at the precise moment it is required within the adipogenic program. Elevated levels of KSR1 expression, previously shown to enhance cell proliferation, promote high, sustained ERK activation that phosphorylates and inhibits peroxisome proliferator-activated receptor gamma, inhibiting adipogenesis. Titration of KSR1 expression reveals how a molecular scaffold can modulate the intensity and duration of signaling emanating from a single pathway to dictate cell fate.

Transcriptional repression of peroxisome proliferator-activated receptor beta/delta in murine keratinocytes by CCAAT/enhancer-binding proteins

The roles of peroxisome proliferator-activated receptors (PPARs) and CCAAT/enhancer-binding proteins (C/EBPs) in keratinocyte and sebocyte differentiation suggest that both families of transcription factors closely interact in the skin. Initial characterization of the mouse PPARbeta promoter revealed an AP-1 site that is crucial for the regulation of PPARbeta expression in response to inflammatory cytokines in the skin. We now present evidence for a novel regulatory mechanism of the expression of the PPARbeta gene by which two members of the C/EBP family of transcription factors inhibit its basal promoter activity in mouse keratinocytes. We first demonstrate that C/EBPalpha and C/EBPbeta, but not C/EBPdelta, inhibit the expression of PPARbeta through the recruitment of a transcriptional repressor complex containing HDAC-1 to a specific C/EBP binding site on the PPARbeta promoter. Consistent with this repression, the expression patterns of PPARbeta and C/EBPs are mutually exclusive in keratinocytes of the interfollicular epidermis and hair follicles in mouse developing skin. This work reveals the importance of the regulatory interplay between PPARbeta and C/EBP transcription factors in the control of proliferation and differentiation in this organ. Such insights are crucial for the understanding of the molecular control regulating the balance between proliferation and differentiation in many cell types including keratinocytes.

Ceramide- and ERK-dependent pathway for the activation of CCAAT/enhancer binding protein by interleukin-1beta in hepatocytes

Interleukin-1beta (IL-1beta) is a major inducer of liver acute-phase protein expression in response to infection. Several transcription factors, including CCAAT/enhancer binding protein (C/EBP), are known mediators in this process, although the mechanisms by which they modulate IL-1beta's action are not completely understood. Activation of sphingomyelinase (SMase) and the subsequent generation of ceramide are early steps in the IL-1beta signaling cascade. In this study, we investigate the role of ceramide in the IL-1beta regulation of C/EBP in primary hepatocytes. The C/EBP DNA binding activity was found to increase in a dose-dependent manner after stimulation with IL-1beta and exogenous addition of C2-ceramide or treatment with SMase. These changes were accompanied by an increase in the nuclear content of C/EBPbeta. Both IL-1beta and ceramide led to extracellular signal-regulated kinase 1/2 (ERK1/2) activation as early as 15 min after treatment. Furthermore, the increase of cellular ceramide content resulted in increased phosphorylation of C/EBPbeta at serine 105 at later time points. Concurrently, the cytosolic levels of C/EBPbeta decreased, suggesting that IL-1beta and ceramide induced nuclear translocation of C/EBPbeta. Ceramide-induced C/EBPbeta phosphorylation, translocation, and DNA binding were suppressed by the addition of PD98059, an inhibitor of ERK1/2 phosphorylation. These results suggest that ceramide and ERK mediate a pathway in the IL-1beta signaling cascade, which results in rapid posttranslational activation of C/EBPbeta.

Liver-enriched transcription factors in liver function and development. Part II: the C/EBPs and D site-binding protein in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation

In the first part of our review (see Pharmacol Rev 2002;54:129-158), we discussed the basic principles of gene transcription and the complex interactions within the network of hepatocyte nuclear factors, coactivators, ligands, and corepressors in targeted liver-specific gene expression. Now we summarize the role of basic region/leucine zipper protein family members and particularly the albumin D site-binding protein (DBP) and the CAAT/enhancer-binding proteins (C/EBPs) for their importance in liver-specific gene expression and their role in liver function and development. Specifically, regulatory networks and molecular interactions were examined in detail, and the experimental findings summarized in this review point to pivotal roles of DBP and C/EBPs in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation. These regulatory proteins are therefore of great importance in liver physiology, liver disease, and liver development. Furthermore, interpretation of the vast data generated by novel genomic platform technologies requires a thorough understanding of regulatory networks and particularly the hierarchies that govern transcription and translation of proteins as well as intracellular protein modifications. Thus, this review aims to stimulate discussions on directions of future research and particularly the identification of molecular targets for pharmacological intervention of liver disease.

Regulation of desmocollin gene expression in the epidermis: CCAAT/enhancer-binding proteins modulate early and late events in keratinocyte differentiation

Desmocollins (Dscs) are desmosomal cadherins that exhibit differentiation-specific patterns of expression in the epidermis. Dsc3 expression is strongest in basal cell layers, whereas Dsc1 is largely confined to upper, terminally differentiating strata. To understand better the processes by which Dsc expression is regulated in the epidermis, we have isolated Dsc3 and Dsc1 5'-flanking DNAs and analysed their activity in primary keratinocytes. In the present study, we found that transcription factors of the CCAAT/enhancer-binding protein family play a role in the regulation of expression of both Dscs and, in so doing, implicate this class of transcription factors in both early and late events in keratinocyte differentiation. We show that Dscs are differentially regulated by C/EBP (CCAAT/enhancer-binding protein) family members, with Dsc3 expression being activated by C/EBPbeta but not C/EBPalpha, and the reverse being the case for Dsc1. Expression of both Dscs is activated by another family member, C/EBPdelta. These results show for the first time how desmosomal cadherin gene expression is regulated and provide a mechanism for the control of other differentiation-specific genes in the epidermis.

Fos-related antigen 2 controls protein kinase A-induced CCAAT/enhancer-binding protein beta expression in osteoblasts

Transcription factor CCAAT/enhancer-binding protein beta (C/EBPbeta) plays an important role in hormone-dependent gene expression. In osteoblasts C/EBPbeta can increase insulin-like growth factor I (IGF-I) transcription following treatment with hormones that activate protein kinase A, but little is known as yet about the expression of C/EBPbeta itself in these cells. We initially showed that prostaglandin E2 (PGE2) rapidly enhances C/EBPbeta mRNA and protein expression, and in this study we identified a 3'-proximal region of the C/EBPbeta promoter containing a 541-bp upstream sequence that could account for this effect. PGE2-dependent activation of C/EBPbeta was blocked by expression of a mutated regulatory subunit of protein kinase A or by mutation of two previously identified cAMP-sensitive cis-acting regulatory elements within the promoter between bp -111 and -61. Nuclear protein binding to these elements was induced by PGE2, required new protein synthesis, and was sensitive to antibody to the transcription factor termed Fos-related antigen 2 (Fra-2). Fra-2 cDNA generated from rat osteoblasts by reverse transcriptase PCR was 95% homologous to human Fra-2, and PGE2 rapidly induced Fra-2 mRNA and protein expression. Consistent with these findings, over-expression of Fra-2 significantly increased C/EBPbeta promoter activity in PGE2-induced osteoblasts, whereas expression of Fra-2 lacking its activation domain had a dominant negative inhibitory effect. Together, these results reveal a significant, hormone-dependent role for Fra-2 in osteoblast function, both directly, through its ability to increase new C/EBPbeta gene expression, and indirectly, through downstream C/EBP sensitive genes.

Identification of a Myb-responsive enhancer of the chicken C/EBPβ gene

The retroviral oncogene v-myb encodes a transcription factor (v-Myb) that disrupts myelomonocytic differentiation and transforms myelomonocytic cells. It is thought that the biological effects of v-Myb are caused by deregulation of specific target genes. The CCAAT box/enhancer binding protein beta (C/EBPbeta), a member of the basic region-leucine zipper (bzip) class of transcription factors, which itself plays an important role during myelomonocytic differentiation, has previously been shown to be regulated by Myb. Here we have addressed the mechanism by which v-Myb affects C/EBPbeta expression. We have employed the mapping of DNase I hypersensitive sites (DHSs) in chromatin as a tool to detect in vivo target sites of v-Myb. Our data identify a DHS downstream of the C/EBPbeta gene that appears to be specific for v-myb-transformed myeloblasts. We have confirmed by chromatin immunoprecipitation that v-Myb is bound to this region in vivo. Furthermore, we have found that ectopic expression of v-Myb in a myelomonocytic cell line is able to induce a DHS downstream of the C/EBPbeta gene, showing for the first time that v-Myb can affect chromatin structure. Reporter gene experiments demonstrate that the downstream DHS acts as a Myb-dependent enhancing element in transiently as well as in stably transfected myelomonocytic cells. Previous work has shown that v-Myb acts on the C/EBPbeta promoter; it now appears that Myb stimulates C/EBPbeta expression by acting on the promoter as well as on an enhancer of the C/EBPbeta gene. Interestingly, the mechanisms by which Myb acts on both elements differ; while Myb activation of the promoter requires the cooperation with C/EBPbeta, activation of the enhancer by Myb is independent of C/EBPbeta. Apart from the identification of a novel Myb-dependent enhancer, our work demonstrates the potential of chromatin structure analysis for the identification of Myb target sites.

Human CCAAT/enhancer-binding protein beta gene expression is activated by endoplasmic reticulum stress through an unfolded protein response element downstream of the protein coding sequence

CCAAT/enhancer-binding protein beta (C/EBPbeta) is a member of the bZIP family of transcription factors that contribute to the regulation of a wide range of important cellular processes. The data in the present study document that transcription from the human C/EBPbeta gene is induced in response to endoplasmic reticulum stress, such as glucose deprivation, or treatment of cells with tunicamycin or thapsigargin. Transient transfection of C/EBPbeta genomic fragments linked to a luciferase reporter gene demonstrated that the C/EBPbeta promoter plays no major regulatory role. Instead, by deletion analysis it was discovered that a 46-bp region, located at a genomic site that corresponds to the 3'-untranslated region of the C/EBPbeta mRNA, harbored an element that was required for the stress response. Mutagenesis demonstrated that a cis-regulatory element located at nt +1614-1621 (5'-TGACGCAA-3') is responsible for activation of the C/EBPbeta gene. Electrophoresis mobility shift analysis revealed that proteins are bound to this element and that the amount of binding is increased following glucose deprivation. This element is homologous to a previously reported mammalian unfolded protein response element that binds XBP-1. Consistent with those data, overexpression of XBP-1 caused an increase in transcription that was mediated by the C/EBPbeta mammalian unfolded protein response element.

TBX5, a gene mutated in Holt-Oram syndrome, is regulated through a GC box and T-box binding elements (TBEs)

TBX5 is a member of the T-box gene family and encodes a transcription factor that regulates the expression of other gene(s) in the developing heart and limbs. Mutations of TBX5 cause Holt-Oram syndrome (HOS), an autosomal dominant condition characterized by congenital heart defects and limb anomalies. How TBX5 gene expression is regulated is still largely unknown. In order to identify transcription factors regulating TBX5 expression, we examined the 5'-flanking region of the human TBX5 gene. We determined that up to 300 bp of the 5'-flanking region of the TBX5 gene was necessary for promoter activity in mouse cardiomyocyte ECL2 cells. One GC box, three potential T-box-like binding elements (TBE-A, -B, and -C), and one NKX2.5 binding site were identified. Site-directed mutagenesis of the potential binding sites revealed that the GC box, TBE-B, TBE-C, and NKX2.5 are functionally positive for the expression of TBX5. DNA footprint analysis showed that these binding regions are resistant to DNaseI digestion. Electrophoretic mobility shift assays (EMSAs) further demonstrated the protein-DNA interactions at the GC box and the potential TBE-B, TBE-C, and NKX2.5 sites in a sequence-specific manner. The ability of TBX5 to regulate its own promoter was demonstrated by the ability of ectopically expressed human TBX5 to increase reporter expression. We conclude that the GC box, T-box-like binding elements, and NKX2.5 binding site play important roles in the regulation of TBX5 expression, and that TBX5 is likely to be autoregulated as part of the mechanism of its transcription.

Regulation of elastin gene transcription by interleukin-1 beta-induced C/EBP beta isoforms

We previously showed that interleukin (IL)-1beta decreases elastin gene transcription through activation of the NF-kappaB subunit p65 in neonatal rat lung fibroblasts. The present study was undertaken to further explore the molecular mechanisms responsible for the inhibitory effect of IL-1beta on elastin gene transcription. We found that cycloheximide blocked IL-1beta-induced downregulation of elastin mRNA but did not inhibit IL-1beta-induced translocation of p65 into the nucleus. IL-1beta treatment increased CCAAT/enhancer-binding protein (C/EBP)beta mRNA and protein levels including liver-enriched activating protein (LAP) and liver-enriched inhibitory protein (LIP), which was cycloheximide sensitive. C/EBPbeta isoforms bound a GCAAT-containing sequence in the proximal elastin promoter as determined by electrophoretic gel shift studies and confirmed by using specific anti-C/EBPbeta antibodies and by competition studies with oligonucleotides. Transient transfection of LIP expression vectors strongly decreased the transcriptional activity of the cotransfected elastin promoter and decreased levels of endogenous elastin mRNA. We demonstrated that IL-1beta-induced downregulation of elastin mRNA is dependent on NF-kappaB activation and C/EBPbeta expression. These results indicate that IL-1beta treatment activates NF-kappaB, which subsequently induces LIP expression and inhibition of elastin gene transcription.

Calcium channel and NMDA receptor activities differentially regulate nuclear C/EBPbeta levels to control neuronal survival

Insulin-like growth factor-1 (IGF-1) promotes the survival of cerebellar granule neurons by enhancing calcium influx through L-type calcium channels, whereas NMDA receptor-mediated calcium influx can lead to excitotoxic death. Here we demonstrate that L and NMDA receptor channel activities differentially regulate the transcription factor C/EBPbeta to control neuronal survival. Specifically, we show that L channel-dependent calcium influx results in increased CaMKIV activity, which acts to decrease nuclear C/EBPbeta levels. Conversely, NMDA receptor-mediated influx rapidly elevates nuclear C/EBPbeta and induces excitotoxic death via activation of the calcium-dependent phosphatase, calcineurin. Moderate levels of AMPA receptor activity stimulate L channels to improve survival, whereas higher levels stimulate NMDA receptors and reduce neuronal survival, suggesting differential synaptic effects. Finally, N-type calcium channel activity reduces survival, potentially by increasing glutamate release. Together, these results show that the L-type calcium channel-dependent survival and NMDA receptor death pathways converge to regulate nuclear C/EBPbeta levels, which appears to be pivotal in these mechanisms.

The role of C/EBPbeta in mammary gland development and breast cancer

The CCAAT/enhancer binding protein (C/EBP) family of bZIP transcription factors control the proliferation and differentiation of a variety of tissues. While C/EBPalpha and -delta are also expressed in the mammary gland, the multiple protein isoforms of C/EBPbeta appear to play a critical role in mammary gland development and breast cancer. Targeted deletion of all the C/EBPbeta isoforms results in a severe inhibition of lobuloalveolar development and a block to functional differentiation, as well as more subtle changes in ductal morphogenesis. The altered expression of a number of molecular markers, including the progesterone, estrogen, and prolactin receptors, the transporter proteins (NKCC1 and aquaporin 5), and several markers of skin differentiation (Sprr2A and keratin 6), suggests that germline deletion of C/EBPbeta results in an altered cell fate. Thus, C/EBPbeta appears to play a role in the specification of progenitor cell fate not only in the mammary gland, but also in a number of other tissues.

Analysis of DNase I-hypersensitive sites in the chromatin of the chicken C/EBPbeta gene reveals multiple cis-regulatory elements

CCAAT box/enhancer binding protein beta (C/EBPbeta), a member of the basic region-leucine zipper (bzip) class of transcription factors, plays important roles during differentiation of certain cell types, such as liver cells, fat cells and myelomonocytic cells. C/EBPbeta is highly expressed in these cell types, and activates specific genes during their differentiation. In the hematopoietic system, C/EBPbeta expression is restricted to the myelomonocytic lineage. To investigate the molecular basis of the cell-type specific expression of the C/EBPbeta gene in hematopoietic cells we have cloned the chicken C/EBPbeta gene and mapped DNase I hypersensitive sites (DHS) in the vicinity of the gene, using myelomonocytic as well as other cell types. We show that there are multiple nuclease-sensitive sites, most of which are cell-type specific, suggesting that they might act as cell-type specific cis-regulatory DNA elements. To study the possible function of these elements we have constructed reporter genes containing these sequences and analyzed their activity in different cell types. Our results show that several of the nuclease-sensitive regions act as cis-acting stimulatory elements in myelomonocytic but not in other cells. Taken together, our data suggest that the expression of the C/EBPbeta gene in myelomonocytic cells is controlled by multiple cell-type specific cis-acting sequences located both upstream and downstream of the gene.

Asthma and the CCAAT-enhancer binding proteins: a holistic view on airway inflammation and remodeling

Asthma is an airway disease with increasing prevalence characterized by intermittent reversible airway obstruction, airway inflammation, and airway wall remodeling. The disease is generally triggered by inhalation of allergens, but nonallergic asthma triggers are quite common. The pathogenesis of asthma is well documented, and a great deal of research has been carried out to elucidate the underlying mechanisms. A multitude of articles have focused on cells alleged to be involved in the pathogenesis, including circulating cells from the immunologic compartment (ie, eosinophils and T lymphocytes) and resident cells, such as fibroblasts, airway smooth muscle cells, and, more recently, the airway epithelium. Despite the enormous amount of research, it is still unclear what exactly causes asthma. A general feature of most studies is an enhanced activation status of asthmatic cells, suggesting a general defect with respect to regulation of cellular responses. Here we discuss the ubiquitous transcription factor family of CCAAT-enhancer binding proteins (C/EBPs) and its involvement in inflammation and proliferation. We propose that an imbalance of C/EBP isoform expression might lead to an enhanced activity of asthmatic cells and provide an overall hypothesis that both airway inflammation and remodeling can be conceived as the result of an imbalance of C/EBP isoform expression.

Ketoconazole suppresses interleukin-4 plus anti-CD40-induced IgE class switching in surface IgE negative B cells from patients with atopic dermatitis

We previously reported that antimycotic agent ketoconazole suppressed interleukin-4 production in T cells from patients with atopic dermatitis. We herein studied if ketoconazole may suppress B cell IgE class switching. Interleukin-4 plus anti-CD40-induced IgE secretion was enhanced in peripheral blood surface IgE- B cells from atopic dermatitis patients compared to those from normal donors, and the secretion was inhibited by ketoconazole. Ketoconazole suppressed interleukin-4 plus anti-CD40-induced germline and mature epsilon transcripts in surface IgE- B cells. Ketoconazole also inhibited interleukin-4 plus anti-CD40-induced activation of germline epsilon promoter in human Burkitt lymphoma Ramos cells. The regions -171/-155 bp containing CCAAT/enhancer-binding protein element and -155/-109 bp containing Stat6 and nuclear factor kappaB elements were required for the ketoconazole-induced inhibition of the germline epsilon promoter activity. Ketoconazole inhibited interleukin-4 plus anti-CD40-induced enhancer activities of CCAAT/enhancer-binding protein and nuclear factor kappaB, and those of composite elements of CCAAT/enhancer-binding protein/Stat6 or of Stat6/nuclear factor kappaB, but did not alter that of Stat6 in Ramos cells. cAMP analog reversed the inhibitory effects of ketoconazole on interleukin-4 plus anti-CD40-induced IgE secretion, germline and mature epsilon transcripts, and epsilon germline promoter activation. Interleukin-4 plus anti-CD40 increased intracellular cAMP by activating cAMP-synthesizing adenylate cyclase in surface IgE- B cells, and the increase was greater in the cells from atopic dermatitis patients than in those from normal donors. Ketoconazole suppressed interleukin-4 plus anti-CD40-induced activation of adenylate cyclase in surface IgE- B cells. These results suggest that ketoconazole may suppress interleukin-4 plus anti-CD40-induced B cell IgE class switching by inhibiting cAMP signal, and stress its prophylactic effects on allergic diseases.

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.