Sumoylation and the function of CCAAT enhancer binding protein alpha (C/EBP alpha)

Central role of SUMOylation in the regulation of chromatin interactions and transcriptional outputs of the androgen receptor in prostate cancer cells

The androgen receptor (AR) is pivotal in prostate cancer (PCa) progression and represents a critical therapeutic target. AR-mediated gene regulation involves intricate interactions with nuclear proteins, with many mediating and undergoing post-translational modifications that present alternative therapeutic avenues. Through chromatin proteomics in PCa cells, we identified SUMO ligases together with nuclear receptor coregulators and pioneer transcription factors within the AR's protein network. Intriguingly, this network displayed a significant association with SUMO2/3. To elucidate the influence of SUMOylation on AR chromatin interactions and subsequent gene regulation, we inhibited SUMOylation using ML-792 (SUMOi). While androgens generally facilitated the co-occupancy of SUMO2/3 and AR on chromatin, SUMOi induced divergent effects dependent on the type of AR-binding site (ARB). SUMOi augmented AR's pioneer-like binding on inaccessible chromatin regions abundant in androgen response elements (AREs) and diminished its interaction with accessible chromatin regions sparse in AREs yet rich in pioneer transcription factor motifs. The SUMOi-impacted ARBs divergently influenced AR-regulated genes; those associated with AR-mediated activation played roles in negative regulation of cell proliferation, while those with AR-mediated repression were involved in pattern formation. In conclusion, our findings underscore the pervasive influence of SUMOylation in shaping AR's role in PCa cells, potentially unveiling new therapeutic strategies.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Sumoylation of CCAAT-enhancer-binding protein α inhibits lung differentiation in Bronchopulmonary Dysplasia model rats

Bronchopulmonary dysplasia (BPD) is a major cause of mortality and morbidity in premature infants, characterized by alveolar simplification, surfactant deficiency, and respiratory distress. In the present study, we have investigated the functional roles of sumoylated CCAAT/enhancer binding protein alpha (C/EBPα) in the BPD rat model. A significant increase in small ubiquitin‐like modifier 1 (SUMO1) and sumoylated C/EBPα protein levels were observed in BPD rats, and the levels of the sumoylated C/EBPα were associated with the pulmonary surfactant proteins (SPs). In order to confirm the role of sumoylated C/EBPα in BPD rats, SUMO1 was knocked down by lentiviral transfection of neonatal rat lungs with SUMO1‐RNAi‐LV. We found that the expression of C/EBPα and surfactant proteins increased following SUMO1 knockdown. Furthermore, the relatively low decrease in the levels of C/EBPα sumoylation was correlated with reduced glycogen consumption. Besides, co‐immunoprecipitation assays revealed that sumoylation is involved in the regulation of the interaction between C/EBPα and TGFβ2 in the lung. In conclusion, our findings indicate that sumoylation may act as a negative regulator of the C/EBPα‐mediated transactivation in BPD rats.

Small molecules for mesenchymal stem cell fate determination

Mesenchymal stem cells (MSCs) are adult stem cells harboring self-renewal and multilineage differentiation potential that are capable of differentiating into osteoblasts, adipocytes, or chondrocytes in vitro, and regulating the bone marrow microenvironment and adipose tissue remodeling in vivo. The process of fate determination is initiated by signaling molecules that drive MSCs into a specific lineage. Impairment of MSC fate determination leads to different bone and adipose tissue-related diseases, including aging, osteoporosis, and insulin resistance. Much progress has been made in recent years in discovering small molecules and their underlying mechanisms control the cell fate of MSCs both in vitro and in vivo. In this review, we summarize recent findings in applying small molecules to the trilineage commitment of MSCs, for instance, genistein, medicarpin, and icariin for the osteogenic cell fate commitment; isorhamnetin, risedronate, and arctigenin for pro-adipogenesis; and atractylenolides and dihydroartemisinin for chondrogenic fate determination. We highlight the underlying mechanisms, including direct regulation, epigenetic modification, and post-translational modification of signaling molecules in the AMPK, MAPK, Notch, PI3K/AKT, Hedgehog signaling pathways etc. and discuss the small molecules that are currently being studied in clinical trials. The target-based manipulation of lineage-specific commitment by small molecules offers substantial insights into bone marrow microenvironment regulation, adipose tissue homeostasis, and therapeutic strategies for MSC-related diseases.

MORC2 regulates C/EBPα-mediated cell differentiation via sumoylation

The expression and activity of CCAAT/enhancer-binding protein α (C/EBPα) are involved in sumoylation modification, which is critical to divert normal cells from differentiation to proliferation. However, the role and underlying mechanism of C/EBPα in cancer is poorly understood. Human MORC2 (microrchidia family CW-type zinc-finger 2), is a member of the MORC proteins family containing a CW-type zinc-finger domain. Here, we found that MORC2 interacted with TE-III domain of C/EBPα, and the overexpression of MORC2 promoted wild-type C/EBPα sumoylation and its subsequent degradation, which didn’t significantly observe in mutant C/EBPα-K161R. Furthermore, the overexpression of MORC2 inhibited C/EBPα-mediated C2C12 cell differentiation to maintain cell cycle progression. Moreover, the striking correlation between the decreased C/EBPα expression and the increased MORC2 expression was also observed in the poor differentiation status of gastric cancer tissues. Most notably, the high expression of MORC2 is correlated  with an aggressive phenotype of clinical gastric cancer and shorter overall survival of patients. Taken together, our findings demonstrated that MORC2 expression regulated C/EBPα-mediated the axis of differentiation/proliferation via sumoylation modification, and affected its protein stability, causing cell proliferation and tumorigenesis.

Ginkgolic acid, a sumoylation inhibitor, promotes adipocyte commitment but suppresses adipocyte terminal differentiation of mouse bone marrow stromal cells

Sumoylation is a post-translational modification process having an important influence in mesenchymal stem cell (MSC) differentiation. Thus, sumoylation-modulating chemicals might be used to control MSC differentiation for skeletal tissue engineering. In this work, we studied how the differentiation of mouse bone marrow stromal cells (mBMSCs) is affected by ginkgolic acid (GA), a potent sumoylation inhibitor also reported to inhibit histone acetylation transferase (HAT). Our results show that GA promoted the differentiation of mBMSCs into adipocytes when cultured in osteogenic medium. Moreover, mBMSCs pre-treated with GA showed enhanced pre-adipogenic gene expression and were more efficiently differentiated into adipocytes when subsequently cultured in the adipogenic medium. However, when GA was added at a later stage of adipogenesis, adipocyte maturation was markedly inhibited, with a dramatic down-regulation of multiple lipogenesis genes. Moreover, we found that the effects of garcinol, a HAT inhibitor, differed from those of GA in regulating adipocyte commitment and adipocyte maturation of mBMSCs, implying that the GA function in adipogenesis is likely through its activity as a sumoylation inhibitor, not as a HAT inhibitor. Overall, our studies revealed an unprecedented role of GA in MSC differentiation and provide new mechanistic insights into the use of GA in clinical applications.

Functional roles of C/EBPα and SUMO‑modification in lung development

CCAAT enhancer binding protein alpha (C/EBPα) is a transcription factor regulating the core aspects of cell growth and differentiation. The present study investigated the level and functional role of C/EBPα during the development of the rat lung. C/EBPα protein exhibits a dynamic expression pattern. The correlation between the expression of C/EBPα protein and the content of glycogen during lung maturation was analyzed to understand the function of C/EBPα in lung differentiation. The high expression of C/EBPα coincides with the reduction of glycogen in the fetal lung. In addition, the authors identified that changes in the level of C/EBPα are associated with the secretion of pulmonary surfactant. C/EBPα is modified by small ubiquitin-related modifier (SUMO) post-translationally. The results of double immunofluorescence staining and immunoprecipitation demonstrated that SUMO-modified C/EBPα was present in the lung. The sumoylated C/EBPα gradually decreased during lung differentiation and was negatively correlated with pulmonary surfactant secretion, thereby suggesting that the SUMO modification may participate in C/EBPα-mediated lung growth and differentiation. These results indicated that C/EBPα played a role in lung development and provided the insight into the mechanism underlying SUMO-modification.

Transcriptional Regulation of Adipogenesis

Adipocytes are the defining cell type of adipose tissue. Once considered a passive participant in energy storage, adipose tissue is now recognized as a dynamic organ that contributes to several important physiological processes, such as lipid metabolism, systemic energy homeostasis, and whole-body insulin sensitivity. Therefore, understanding the mechanisms involved in its development and function is of great importance. Adipocyte differentiation is a highly orchestrated process which can vary between different fat depots as well as between the sexes. While hormones, miRNAs, cytoskeletal proteins, and many other effectors can modulate adipocyte development, the best understood regulators of adipogenesis are the transcription factors that inhibit or promote this process. Ectopic expression and knockdown approaches in cultured cells have been widely used to understand the contribution of transcription factors to adipocyte development, providing a basis for more sophisticated in vivo strategies to examine adipogenesis. To date, over two dozen transcription factors have been shown to play important roles in adipocyte development. These transcription factors belong to several families with many different DNA-binding domains. While peroxisome proliferator-activated receptor gamma (PPARγ) is undoubtedly the most important transcriptional modulator of adipocyte development in all types of adipose tissue, members of the CCAAT/enhancer-binding protein, Krüppel-like transcription factor, signal transducer and activator of transcription, GATA, early B cell factor, and interferon-regulatory factor families also regulate adipogenesis. The importance of PPARγ activity is underscored by several covalent modifications that modulate its activity and its ability to modulate adipocyte development. This review will primarily focus on the transcriptional control of adipogenesis in white fat cells and on the mechanisms involved in this fine-tuned developmental process. © 2017 American Physiological Society. Compr Physiol 7:635-674, 2017.

GEP analysis validates high risk MDS and acute myeloid leukemia post MDS mice models and highlights novel dysregulated pathways

Background

In spite of the recent discovery of genetic mutations in most myelodysplasic (MDS) patients, the pathophysiology of these disorders still remains poorly understood, and only few in vivo models are available to help unravel the disease.

Methods

We performed global specific gene expression profiling and functional pathway analysis in purified Sca1+ cells of two MDS transgenic mouse models that mimic human high-risk MDS (HR-MDS) and acute myeloid leukemia (AML) post MDS, with NRASD12 and BCL2 transgenes under the control of different promoters _MRP8NRASD12/_tethBCL-2 or _MRP8[NRASD12/hBCL-2], respectively.

Results

Analysis of dysregulated genes that were unique to the diseased HR-MDS and AML post MDS mice and not their founder mice pointed first to pathways that had previously been reported in MDS patients, including DNA replication/damage/repair, cell cycle, apoptosis, immune responses, and canonical Wnt pathways, further validating these models at the gene expression level. Interestingly, pathways not previously reported in MDS were discovered. These included dysregulated genes of noncanonical Wnt pathways and energy and lipid metabolisms. These dysregulated genes were not only confirmed in a different independent set of BM and spleen Sca1+ cells from the MDS mice but also in MDS CD34+ BM patient samples.

Conclusions

These two MDS models may thus provide useful preclinical models to target pathways previously identified in MDS patients and to unravel novel pathways highlighted by this study.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0235-8) contains supplementary material, which is available to authorized users.

miR-200c-SUMOylated KLF4 feedback loop acts as a switch in transcriptional programs that control VSMC proliferation

The regulation of vascular smooth muscle cell (VSMC) proliferation is an important issue because it has major implications for the prevention of pathological vascular conditions. Using microRNA array screen, we found the expression levels of 200 unique miRNAs in hyperplasic tissues. Among them, miR-200c expression substantially was down-regulated. The objective of this work was to assess the function of miR-200c and SUMOylated Krϋppel-like transcription factor 4 (KLF4) in the regulation of VSMC proliferation in both cultured cells and animal models of balloon injury. Under basal conditions, we found that miR-200c inhibited the expression of KLF4 and the SUMO-conjugating enzyme Ubc9. Upon PDGF-BB treatment, Ubc9 interacted with and promoted the SUMOylation of KLF4, which allowed the recruitment of transcriptional corepressors (e.g., nuclear receptor corepressor (NCoR) and HDAC2) to the miR-200c promoter. The reduction in miR-200c levels led to increased target gene expression (e.g., Ubc9 and KLF4), which further repressed miR-200c levels and accelerated VSMC proliferation. These results demonstrate that induction of a miR-200c-SUMOylated KLF4 feedback loop is a significant aspect of the PDGF-BB proliferative response in VSMCs and that targeting Ubc9 represents a novel approach for the prevention of restenosis.

CCAAT/enhancer-binding protein α negatively regulates IFN-γ expression in T cells

Humoral immunity, including Ab switching and somatic hypermutation, is critically regulated by CD4(+) T cells. T follicular helper (Tfh) cells have been recently shown to be a distinct T cell subset important in germinal center reactions. The transcriptional regulation of Tfh cell development and function has not been well understood. In this study, we report that C/EBPα, a basic region/leucine zipper transcription factor, is highly expressed in Tfh cells. Cebpa-deficient CD4(+) T cells exhibit enhanced IFN-γ expression in vitro and in vivo. T cell-specific Cebpa knockout mice, although not defective in Tfh cell generation, produce significantly increased levels of IgG2a/b and IgG3 following immunization with a protein Ag. Moreover, C/EBPα binds to the Ifng gene and inhibits T-bet-driven Ifng transcription in a DNA binding-dependent manner. Our study thus demonstrates that C/EBPα restricts IFN-γ expression in T cells to allow proper class switching by B cells.

SWI/SNF chromatin-remodeling complexes in cardiovascular development and disease

Our understanding of congenital heart defects has been recently advanced by whole exome sequencing projects, which have identified de novo mutations in many genes encoding epigenetic regulators. Notably, multiple subunits of switching defective/sucrose non-fermenting (SWI/SNF) chromatin-remodeling complexes have been identified as strong candidates underlying these defects because they physically and functionally interact with cardiogenic transcription factors critical to cardiac development, such as TBX5, GATA-4, and NKX2-5. While these studies indicate a critical role of SWI/SNF complexes in cardiac development and congenital heart disease, many exciting new discoveries have identified their critical role in the adult heart in both physiological and pathological conditions involving multiple cell types in the heart, including cardiomyocytes, vascular endothelial cells, pericytes, and neural crest cells. This review summarizes the role of SWI/SNF chromatin-remodeling complexes in cardiac development, congenital heart disease, cardiac hypertrophy, and vascular endothelial cell survival. Although the clinical relevance of SWI/SNF mutations has traditionally been focused primarily on their role in tumor suppression, these recent studies illustrate their critical role in the heart whereby they regulate cell proliferation, differentiation, and apoptosis of cardiac derived cell lines.

CCAAT/enhancer-binding protein-α suppresses lung tumor development in mice through the p38α MAP kinase pathway

The transcription factor CCAAT/enhancer-binding protein α (C/EBPα) is a basic leucine zipper transcription factor and is expressed in alveolar type II cells, alveolar macrophages and Clara cells in the lung. Although decrease or absence of C/EBPα expression in human non-small cell lung cancer suggests a possible role of C/EBPα as a lung tumor suppressor, there is no direct proof for this hypothesis. In this study, we investigated, for the first time, the role of C/EBPα in lung tumors in vivo using transgenic mice with lung epithelial specific conditional deletion of Cebpa (Cebpα(Δ/Δ) mice) and a urethane-induced lung tumor model. C/EBPα expression in the lung was dispensable, and its deletion was not oncogenic under unstressed conditions. However, at 28 wk after urethane injection, the number and size of tumors and the tumor burden were significantly higher in Cebpα(Δ/Δ) mice than in littermate control mice. Urethane-injected Cebpα(Δ/Δ) mice showed highly proliferative adenomas and adenocarcinomas in the lung, and survival time after urethane-injection was significantly shorter than that in control mice. In control mice, C/EBPα was strongly induced in the tumor tissues at 28 weeks after urethane-injection, but became weakened or absent as tumors progressed after long-term observation for over 1 year. Using intraperitoneal injection of p38 inhibitor (SB203580), we demonstrated that the induction of C/EBPα is strongly regulated by the p38 MAP kinase in murine alveolar epithelial cells. A high correlation was demonstrated between the expression of C/EBPα and p38α MAP kinase in tumor cells, suggesting that C/EBPα silencing in tumor cells is caused by down-regulation of p38α MAP kinase. In conclusion, the role of C/EBPα as a lung tumor suppressor was demonstrated for the first time in the present study, and the extinguished C/EBPα expression through p38α inactivation leads tumor promotion and progression.

Up-regulation of translation eukaryotic initiation factor 4E in nucleophosmin 1 haploinsufficient cells results in changes in CCAAT enhancer-binding protein α activity: implications in myelodysplastic syndrome and acute myeloid leukemia

NPM1 is a ubiquitously expressed nucleolar phosphoprotein, the gene for which maps to chromosome 5q35 in close proximity to a commonly deleted region associated with (del)5q, a type of myelodysplastic syndrome (MDS). This region is also a frequent target of deletions in de novo and therapy-related MDS/acute myeloid leukemia. Previous studies have shown that Npm1(+/-) mice develop an MDS-like disease that transforms to acute myeloid leukemia over time. To better understand the mechanism by which NPM1 haploinsufficiency causes an MDS phenotype, we generated factor-dependent myeloid cell lines from the bone marrow of Npm1(+/+) and Npm1(+/-) mice and demonstrated compromised neutrophil-specific gene expression in the MNPM1(+/-) cells. We attribute these observations to increased levels of the shorter, dominant negative leukemogenic isoform (p30) of CCAAT enhancer-binding protein α (C/EBPα). We show that this increase is caused, in part, by elevated levels of the activated translation initiation factor eIF4E, overexpression of which also increases translation of C/EBPαp30 in HEK293 cells. In a positive feedback loop, eIF4E expression is further elevated both at the mRNA and protein levels by C/EBPαp30 but not by the full-length C/EBPαp42. Re-expression of C/EBPαp42 or NPM1 but not C/EBPαp30 in MNPM1(+/-) cells partially rescues the myeloid phenotype. Our observations suggest that the aberrant feed-forward pathway that keeps eIF4E and C/EBPαp30 elevated in NPM1(+/-) cells contributes to the MDS phenotype associated with NPM1 deficiency.

Control of progesterone receptor transcriptional synergy by SUMOylation and deSUMOylation

Background

Covalent modification of nuclear receptors by the Small Ubiquitin-like Modifier (SUMO) is dynamically regulated by competing conjugation/deconjugation steps that modulate their overall transcriptional activity. SUMO conjugation of progesterone receptors (PRs) at the N-terminal lysine (K) 388 residue of PR-B is hormone-dependent and suppresses PR-dependent transcription. Mutation of the SUMOylation motif promotes transcriptional synergy.

Results

The present studies address mechanisms underlying this transcriptional synergy by using SUMOylation deficient PR mutants and PR specifically deSUMOylated by Sentrin-specific proteases (SENPs). We show that deSUMOylation of a small pool of receptors by catalytically competent SENPs globally modulates the cooperativity-driven transcriptional synergy between PR observed on exogenous promoters containing at least two progesterone-response elements (PRE₂). This occurs in part by raising PR sensitivity to ligands. The C-terminal ligand binding domain of PR is required for the transcriptional stimulatory effects of N-terminal deSUMOylation, but neither a functional PR dimerization interface, nor a DNA binding domain exhibiting PR specificity, are required.

Conclusion

We conclude that direct and reversible SUMOylation of a minor PR protein subpopulation tightly controls the overall transcriptional activity of the receptors at complex synthetic promoters. Transcriptional synergism controlled by SENP-dependent PR deSUMOylation is dissociable from MAPK-catalyzed receptor phosphorylation, from SRC-1 coactivation and from recruitment of histone deacetylases to promoters. This will provide more information for targeting PR as a part of hormonal therapy of breast cancer. Taken together, these data demonstrate that the SUMOylation/deSUMOylation pathway is an interesting target for therapeutic treatment of breast cancer.

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

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

Ongoing Trials in Low-Grade Lymphoma

There are many therapies available for the management of low-grade lymphoma. With follicular lymphoma, for example, combination of chemotherapy and rituximab (immuno-chemotherapy) and consecutive maintenance therapy for 2 years is the current standard of care. To date, the most widely used regimen seems to be rituximab combined with cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). Substitution of liposomal doxorubicin in place of conventional doxorubicin may improve outcomes in this indication, although evidence for its use in low-grade lymphoma is not as relevant as in aggressive lymphoma. Bendamustine, in combination with rituximab, has shown very good efficacy and tolerability in several lymphoma types, particularly follicular lymphoma and other low-grade lymphomas. Other combinations, such as those including bortezomib and lenalidomide, are under investigation in low-grade lymphoma, and the duration of rituximab maintenance therapy following bendamustine-rituximab-containing induction is being researched by the German Study Group for Indolent Lymphoma (StiL).

Differential effects of sumoylation on the activities of CCAAT enhancer binding protein alpha (C/EBPα) p42 versus p30 may contribute in part, to aberrant C/EBPα activity in acute leukemias

In this study, we have examined the role of post-translational modification of the myeloid master regulator C/EBPα by small ubiquitin-related modifier (SUMO). We have used transient transfection analysis, oligonucleotide pulldown assays and chromatin immuno-precititation in all-trans retinoic acid (ATRA)-inducible promyelocytic cell lines MPRO and NB4. We demonstrate that sumoylated wild-type p42-C/EBPα is associated with negative regulation of the myeloid specific lactoferrin (LF) gene in early myeloid cells and that a reduction in p42-C/EBPα sumoylation coincides with expression of the LF gene in maturing myeloid cells. In the acute promyelocytic leukemia cell line NB4 however, sumoylated p42 remains persistently bound to the LF promoter following ATRA-induction. This correlates with lack of lactoferrin expression in these cells. Changes in sumoylation status of C/EBPα thus appear to contribute to a switch that regulates transcriptional activity of this master regulator during normal neutrophil development. We also demonstrate that sumoylation of the AML associated dominant negative p30-C/EBPα isoform does not alter transactivation activity of the LF promoter. This may be because the p30 C/EBPα isoform binds to the LF promoter much less efficiently than its full length counterpart. Our data suggest that the activity of p42-C/EBPα in the developing neutrophil is more sensitive to changes in sumoylation than the p30 isoform. This difference may contribute to the leukemogenic potential of p30-C/EBPα.

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is critical for interleukin-4 expression in response to FcepsilonRI receptor cross-linking

Basophils mediate many of their biological functions by producing IL-4. However, it is unknown how the Il4 gene is regulated in basophils. Here, we report that CCAAT/enhancer-binding protein α (C/EBPα), a major myeloid transcription factor, was highly expressed in basophils. We show that C/EBPα selectively activated Il4 promoter-luciferase reporter gene transcription in response to IgE cross-linking, but C/EBPα did not activate other known Th2 or mast cell enhancers. We found that the PI3K pathway and calcineurin were essential in C/EBPα-driven Il4 promoter-luciferase gene transcription. Our mutation analyses revealed that C/EBPα drove Il4 promoter-luciferase activity depending on its DNA binding domain. Mutation of the C/EBPα-binding site in the Il4 promoter region abolished C/EBPα-driven Il4 promoter-luciferase activity. Our results further showed that a mutation in nuclear factor of activated T cells (NFAT)-binding sites in the Il4 promoter also negated C/EBPα-driven Il4 promoter-luciferase activity. Our study demonstrates that C/EBPα, in cooperation with NFAT, directly regulates Il4 gene transcription.

CCAAT/enhancer binding proteins alpha and beta regulate the tumor necrosis factor receptor 1 gene promoter

CCAAT/enhancer binding protein (C/EBP) transcription factors play essential roles in regulating an array of cellular processes, including differentiation, energy metabolism, and inflammation. In this report we demonstrate that both C/EBPalpha and C/EBPbeta activate the promoter driving transcription of the tumor necrosis factor receptor 1 (TNFR1). TNFR1 is the major receptor for tumor necrosis factor (TNF), a critical cytokine mediator of the inflammatory response. Although the TNFR1 protein has been shown to be regulated through post-translational modifications, very little is known about the transcriptional regulation of the TNFR1 gene. Here we have identified a specific C/EBP binding site within the TNFR1 promoter, and shown that this site is required for both C/EBPalpha and C/EBPbeta activation of the promoter in reporter gene assays. Furthermore, we show that both C/EBPalpha and C/EBPbeta are bound to the TNFR1 promoter in cells using chromatin immunoprecipitation assays. Finally, we demonstrate that reducing the level of C/EBPalpha and C/EBPbeta expression in cells using siRNA technology leads to decreased expression of the TNFR1 protein. These results suggest that the C/EBPalpha and C/EBPbeta transcription factors enhance expression of the TNFR1 protein in cells. Given that TNF and C/EBPbeta are known to activate each other's expression, C/EBPbeta may greatly amplify the initial TNF signal through a positive auto-regulatory mechanism.

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.