The zinc finger transcription factor Egr-1 potentiates macrophage differentiation of hematopoietic cells

The CD2v protein of African swine fever virus inhibits macrophage migration and inflammatory cytokines expression by downregulating EGR1 expression through dampening ERK1/2 activity

African swine fever virus (ASFV) is a highly contagious and deadly virus that leads to high mortality rates in domestic swine populations. Although the envelope protein CD2v of ASFV has been implicated in immunomodulation, the molecular mechanisms underlying CD2v-mediated immunoregulation remain unclear. In this study, we generated a stable CD2v-expressing porcine macrophage (PAM-CD2v) line and investigated the CD2v-dependent transcriptomic landscape using RNA-seq. GO terms enrichment analysis and gene set enrichment analysis revealed that CD2v predominantly affected the organization and assembly process of the extracellular matrix. Wound healing and Transwell assays showed that CD2v inhibited swine macrophage migration. Further investigation revealed a significant decrease in the expression of transcription factor early growth response 1 (EGR1) through inhibiting the activity of extracellular signal-regulated kinase 1 and 2 (ERK1/2). Notably, EGR1 knockout in swine macrophages restricted cell migration, whereas EGR1 overexpression in PAM-CD2v restored the ability of macrophage migration, suggesting that CD2v inhibits swine macrophage motility by downregulating EGR1 expression. Furthermore, we performed chromatin immunoprecipitation and sequencing for EGR1 and the histone mark H3K27 acetylation (H3K27ac), and we found that EGR1 co-localized with the activated histone modification H3K27ac neighboring the transcriptional start sites. Further analysis indicated that EGR1 and H3K27ac co-occupy the promoter regions of cell locomotion-related genes. Finally, by treating various derivatives of swine macrophages with lipopolysaccharides, we showed that depletion of EGR1 decreased the expression of inflammatory cytokines including TNFα, IL1α, IL1β, IL6, and IL8, which play essential roles in inflammation and host immune response. Collectively, our results provide new insights into the immunomodulatory mechanism of ASFV CD2v.

Antiviral activity of zinc against hepatitis viruses: current status and future prospects

Viral hepatitis is a major public health concern globally. World health organization aims at eliminating viral hepatitis as a public health threat by 2030. Among the hepatitis causing viruses, hepatitis B and C are primarily transmitted via contaminated blood. Hepatitis A and E, which gets transmitted primarily via the feco-oral route, are the leading cause of acute viral hepatitis. Although vaccines are available against some of these viruses, new cases continue to be reported. There is an urgent need to devise a potent yet economical antiviral strategy against the hepatitis-causing viruses (denoted as hepatitis viruses) for achieving global elimination of viral hepatitis. Although zinc was known to mankind for a long time (since before Christ era), it was identified as an element in 1746 and its importance for human health was discovered in 1963 by the pioneering work of Dr. Ananda S. Prasad. A series of follow up studies involving zinc supplementation as a therapy demonstrated zinc as an essential element for humans, leading to establishment of a recommended dietary allowance (RDA) of 15 milligram zinc [United States RDA for zinc]. Being an essential component of many cellular enzymes and transcription factors, zinc is vital for growth and homeostasis of most living organisms, including human. Importantly, several studies indicate potent antiviral activity of zinc. Multiple studies have demonstrated antiviral activity of zinc against viruses that cause hepatitis. This article provides a comprehensive overview of the findings on antiviral activity of zinc against hepatitis viruses, discusses the mechanisms underlying the antiviral properties of zinc and summarizes the prospects of harnessing the therapeutic benefit of zinc supplementation therapy in reducing the disease burden due to viral hepatitis.

Early Growth Response Factor 1 in Aging Hematopoietic Stem Cells and Leukemia

Aging is associated with various hematological disorders and a higher risk of myeloproliferative disorders. An aged hematopoietic system can be characterized by decreased immune function and increased myeloid cell production. Hematopoietic stem cells (HSCs) regulate the production of blood cells throughout life. The self-renewal and regenerative potential of HSCs determine the quality and quantity of the peripheral blood cells. External signals from the microenvironment under different conditions determine the fate of the HSCs to proliferate, self-renew, differentiate, or remain quiescent. HSCs respond impromptu to a vast array of extracellular signaling cascades such as cytokines, growth factors, or nutrients, which are crucial in the regulation of HSCs. Early growth response factor 1 (EGR1) is one of the key transcription factors controlling HSC proliferation and their localization in the bone marrow (BM) niche. Downregulation of Egr1 activates and recruits HSCs for their proliferation and differentiation to produce mature blood cells. Increased expression of Egr1 is implicated in immuno-aging of HSCs. However, dysregulation of Egr1 is associated with hematological malignancies such as acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and chronic myelogenous leukemia (CML). Here, we summarize the current understanding of the role of EGR1 in the regulation of HSC functionality and the manifestation of leukemia. We also discuss the alternative strategies to rejuvenate the aged HSCs by targeting EGR1 in different settings.

Inflammation in Focus: The Beginning and the End

The inflammation is an important biological response induced by various harmful stimuli, like viruses, bacterial infections, toxins, toxic compounds, tissue injury. During inflammation inflammatory cytokines and reactive oxygen species are produced. Inflammatory cytokines act on various receptors present on the plasma membrane of target cells. To initiate signaling cascade, and activate transcription factors, receptors should be internalized and enter the early endosomes, where the members of the signaling cascade can meet. The further cytoplasmic fate of the receptor plays crucial role in the progression and the course of inflammation. Usually acute inflammation removes injurious stimuli and helps to regain the normal healthy status of the organism. In contrast to this the uncontrolled chronic inflammation—stimulating other than immune cells, inducing transdifferentiation—can provide base of various serious diseases. This paper draws the attention of the long-lasting consequence of chronic inflammation, pointing out that one of the most important step in medication is to identify in time the factors initiating and maintaining inflammation.

The -172 A-to-G variation in ADAM17 gene promoter region affects EGR1/ADAM17 pathway and confers susceptibility to septic mortality with sepsis-3.0 criteria

BACKGROUND

A disintegrin and metalloproteinase 17 (ADAM17) is a proteolytic cleaving protein with a crucial function in the inflammatory responses, especially sepsis. But the clear role of ADAM17 in sepsis and the underlying mechanism remained unknown. In this study, we aim to determine the clinical association of ADAM17 -172A > G (rs12692386) promoter polymorphism with sepsis and to further explore the effect and mechanism of the early growth response 1 (EGR1)/ADAM17 pathway in inflammatory process during sepsis.

METHODS

A total of 477 sepsis patients and 750 controls were enrolled in this study to determine the association of ADAM17 -172A > G polymorphism with sepsis. The transcription factor binding to the promoter region of ADAM17 gene was predicted by bioinformatics analysis and verified by Chromatin Immunoprecipitation (ChIP) and luciferase assays. Quantitative real-time PCR and Western blot were performed to detect EGR1 and ADAM17 expression. Cytokine production was detected by enzyme-linked immunosorbent assay. The effect of EGR1/ADAM17 pathway on sepsis-induced inflammatory responses was evaluated in EGR1-silenced cells and endotoxemia mouse model.

RESULTS

The frequencies of non-survivors among the sepsis patients with the -172AG/GG genotypes and G allele were distinctly higher than those among patients with the AA genotype (53.9% vs. 39.7%, OR = 1.779, 95% CI = 1.119-2.829, P = 0.0142) and A allele (30.9% vs. 22.2%, OR = 1.570, 95% CI = 1.095-2.251, P = 0.0136). The Kaplan-Meier survival analysis indicated that the 28-day survival in septic patients with -172AG/GG genotypes of this functional ADAM17 promoter polymorphism was much worse than in the AA genotype carriers (log-rank = 5.358, P = 0.021). The results of in vitro lipopolysaccharide-stimulated and luciferase assays indicated that the -172 A-to-G variation could functionally upregulate promoter activity and transcription of ADAM17 gene via enhancing the binding affinity of its promoter region with the EGR1. The ChIP assay identified the direct interaction. Further studies demonstrated that inhibition of EGR1 significantly decreased ADAM17 expression and the pro-inflammatory cytokine secretion in vitro, and improved the survival and inflammatory response of sepsis mouse model.

CONCLUSIONS

These results provided evidence that the ADAM17 -172A > G polymorphism functionally promoted ADAM17 expression and enhanced sepsis-induced inflammatory responses via the EGR1/ADAM17 pathway, which ultimately conferred susceptibility to sepsis mortality and poor prognosis.

Low EGR1 expression predicts poor prognosis in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is resistant to conventional therapy due to the deletion of the von Hippel-Lindau (VHL) gene, and novel treatment options are urgently needed. Here, using tissue microarray analysis of 445 cancer tissues and 326 adjacent normal renal tissues obtained from patients with ccRCC, we present the early growth response-1 (EGR1) protein levels are significantly decreased in ccRCC cancer tissues. Consistently, the EGR1 mRNA expression also decreased in cancer tissues based on the transcriptomic data for 599 tumor and normal samples from The Cancer Genome Atlas. Moreover, Patients with ccRCC presenting low EGR1 expression are more prone to exhibit metastasis and a poor prognosis than those with high EGR1 expression. By multivariate Cox regression analysis, EGR1 is determined to serve as an independent prognostic factor for patients with ccRCC. Further cellular biochemical function analyses show that EGR1 may inhibit proliferation, invasion and metastasis of ccRCC. These findings will deepen our understanding of EGR1 function and shed light on precise treatment for ccRCC patients.

A Risk Prediction Model for Breast Cancer Based on Immune Genes Related to Early Growth Response Proteins Family

Early growth response proteins (EGRs), a transcriptional regulatory family comprised of EGR1, EGR2, EGR3, and EGR 4, are reportedly involved in a vast array of functions. However, EGRs, as a whole, are rarely studied in breast cancer cases. This research was performed based on public datasets. The results demonstrated that, except EGR4, the other EGRs were differentially expressed genes in breast cancer. Subsequently, this study determined the prognosis significance of the EGR family, higher expression levels of EGRs indicating better overall survival (OS) and disease-free survival (DFS), except EGR4. So we attempted to explore the potential mechanism behind the prognostic value of EGRs. At the DNA level, however, neither DNA methylation status nor genetic alterations of EGRs contributed to the prognosis significance. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that EGRs were involved in several immune-related functions. Afterward, we assessed the correlation between EGRs and the immune system before establishing a risk prediction model with a 14-gene immune signature associated with EGRs, a prognostic nomogram predicting individuals’ 1-, 3-, and 5-year survival probabilities. The risk score was an independent prognosis predictor in the breast cancer cohorts. This study evidenced EGRs’ significance for tumor immunity, demonstrating that the EGR family may be a potential immunotherapeutic target for breast cancer. The 14-gene immune signature is a promising prognostic biomarker in breast cancer.

Cellular and molecular events of inflammation induced transdifferentiation (EMT) and regeneration (MET) in mesenteric mesothelial cells

In this review we summarize the cellular and molecular events of inflammation induced epithelial-to-mesenchymal (EMT) and mesothelial-to-macrophage transition (MET) during regeneration. Since the receptor transmits the environmental stimulus, downregulating or upregulating the process on an epigenetic level, the intracellular localization of receptors (signaling organelles: early endosomes or lysosomal degradation: late endosomes) plays a crucial role in the signaling events regulating inflammation and regeneration. Therefore, we focused on the internalization of the receptors as well as the intracellular compartmentalization of signaling molecules during EMT and MET. The review draws the reader's attention to the plasticity of mesothelial cells and supports the idea that during inflammation an ambient macrophage population might derive from mesothelial cells.

Commensal microbiota drive the functional diversification of colon macrophages

Mononuclear phagocytes are a heterogeneous population of leukocytes essential for immune homeostasis that develop tissue-specific functions due to unique transcriptional programs driven by local microenvironmental cues. Single cell RNA sequencing (scRNA-seq) of colonic myeloid cells from specific pathogen free (SPF) and germ-free (GF) C57BL/6 mice revealed extensive heterogeneity of both colon macrophages (MPs) and dendritic cells (DCs). Modeling of developmental pathways combined with inference of gene regulatory networks indicate two major trajectories from common CCR2+ precursors resulting in colon MP populations with unique transcription factors and downstream target genes. Compared to SPF mice, GF mice had decreased numbers of total colon MPs, as well as selective proportional decreases of two major CD11c+CD206intCD121b+ and CD11c-CD206hiCD121b- colon MP populations, whereas DC numbers and proportions were not different. Importantly, these two major colon MP populations were clearly distinct from other colon MP populations regarding their gene expression profile, localization within the lamina propria (LP) and ability to phagocytose macromolecules from the blood. These data uncover the diversity of intestinal myeloid cell populations at the molecular level and highlight the importance of microbiota on the unique developmental as well as anatomical and functional fates of colon MPs.

Inflammation-Induced Epithelial-to-Mesenchymal Transition and GM-CSF Treatment Stimulate Mesenteric Mesothelial Cells to Transdifferentiate into Macrophages

In our previous work, we showed that during inflammation-induced epithelial-to-mesenchymal transition (EMT), mesenteric mesothelial cells express ED1 (pan-macrophage marker), indicating that they are transformed into macrophage-like cells. In this paper, we provide additional evidences about this transition by following the phagocytic activity and the TNFα production of mesenteric mesothelial cells during inflammation. Upon injection of India ink particles or fluorescent-labeled bioparticles (pHrodo) into the peritoneal cavity of rats pretreated with Freund's adjuvant, we found that mesothelial cells efficiently engulfed these particles. A similar increase of internalization could be observed by mesothelial cells in GM-CSF pretreated primary mesenteric culture. Since macrophages are the major producers of tumor necrosis factor, TNFα, we investigated expression level of TNFα during inflammation-induced EMT and found that TNFα was indeed expressed in these cells, reaching the highest level at the 5th day of inflammation. Since TNFα is one of the target genes of early growth response (EGR1) transcription factor, playing important role in monocyte-macrophage differentiation, expression of EGR1 in mesothelial cells was also investigated by Western blot and immunocytochemistry. While mesothelial cells did not express EGR1, a marked increase was observed in mesothelial cells by the time of inflammation. Parallel to this, nuclear translocation of EGR1 was shown by immunocytochemistry at the day 5 of inflammation. Caveolin-1 level was high and ERK1/2 became phosphorylated as the inflammation proceeded showing a slight decrease when the regeneration started. Our present data support the idea that under special stimuli, mesenteric mesothelial cells are able to transdifferentiate into macrophages, and this transition is regulated by the caveolin-1/ERK1/2/EGR1 signaling pathway.

The Molecular Mechanisms of Plant-Derived Compounds Targeting Brain Cancer

Glioblastoma multiforme (GBM) is one of the most aggressive and malignant forms of brain tumors. Despite recent advances in operative and postoperative treatments, it is almost impossible to perform complete resection of these tumors owing to their invasive and diffuse nature. Several natural plant-derived products, however, have been demonstrated to have promising therapeutic effects, such that they may serve as resources for anticancer drug discovery. The therapeutic effects of one such plant product, n-butylidenephthalide (BP), are wide-ranging in nature, including impacts on cancer cell apoptosis, cell cycle arrest, and cancer cell senescence. The compound also exhibits a relatively high level of penetration through the blood-brain barrier (BBB). Taken together, its actions have been shown to have anti-proliferative, anti-chemoresistance, anti-invasion, anti-migration, and anti-dissemination effects against GBM. In addition, a local drug delivery system for the subcutaneous and intracranial implantation of BP wafers that significantly reduce tumor size in xenograft models, as well as orthotopic and spontaneous brain tumors in animal models, has been developed. Isochaihulactone (ICL), another kind of plant product, possesses a broad spectrum of pharmacological activities, including impacts on cancer cell apoptosis and cell cycle arrest, as well as anti-proliferative and anti-chemoresistance effects. Furthermore, these actions have been specifically shown to have cancer-fighting effects on GBM. In short, the results of various studies reviewed herein have provided substantial evidence indicating that BP and ICH are promising novel anticancer compounds with good potential for clinical applications.

Role of early growth response 1 in arteriogenesis: Impact on vascular cell proliferation and leukocyte recruitment in vivo

Based on previous findings that early growth response 1 (Egr-1) participates in leukocyte recruitment and cell proliferation in vitro, this study was designed to investigate its mode of action during arteriogenesis in vivo. In a model of peripheral arteriogenesis, Egr-1 was significantly upregulated in growing collaterals of wild-type (WT) mice, both on mRNA and protein level. Egr-1−/− mice demonstrated delayed arteriogenesis after femoral artery ligation. They further showed increased levels of monocytes and granulocytes in the circulation, but reduced levels in adductor muscles under baseline conditions. After femoral artery ligation, elevated numbers of macrophages were detected in the perivascular zone of collaterals in Egr-1−/− mice and mRNA of leukocyte recruitment mediators was upregulated. Other Egr family members (Egr-2 to -4) were significantly upregulated only in Egr-1−/− mice, suggesting a mechanism of counterbalancing Egr-1 deficiency. Moreover, splicing factor-1, downregulated in WT mice after femoral artery ligation in the process of increased vascular cell proliferation, was upregulated in Egr-1−/− mice. αSM-actin on the other hand, significantly downregulated in WT mice, showed no differential expression in Egr-1−/− mice. While cell cycle regulator cyclin E and cdc20 were upregulated in Egr-1−/− mice, cyclin D1 expression decreased below the detection limit in collaterals, and the proliferation marker ki67 was not differentially expressed. In conclusion, compensation for deficiency in Egr-1 function in leukocyte recruitment can presumably be mediated by other transcription factors; however, Egr-1 is indispensable for effective vascular cell cycle progression in arteriogenesis.

Metallothioneins: Emerging Modulators in Immunity and Infection

Metallothioneins (MTs) are a family of metal-binding proteins virtually expressed in all organisms including prokaryotes, lower eukaryotes, invertebrates and mammals. These proteins regulate homeostasis of zinc (Zn) and copper (Cu), mitigate heavy metal poisoning, and alleviate superoxide stress. In recent years, MTs have emerged as an important, yet largely underappreciated, component of the immune system. Innate and adaptive immune cells regulate MTs in response to stress stimuli, cytokine signals and microbial challenge. Modulation of MTs in these cells in turn regulates metal ion release, transport and distribution, cellular redox status, enzyme function and cell signaling. While it is well established that the host strictly regulates availability of metal ions during microbial pathogenesis, we are only recently beginning to unravel the interplay between metal-regulatory pathways and immunological defenses. In this perspective, investigation of mechanisms that leverage the potential of MTs to orchestrate inflammatory responses and antimicrobial defenses has gained momentum. The purpose of this review, therefore, is to illumine the role of MTs in immune regulation. We discuss the mechanisms of MT induction and signaling in immune cells and explore the therapeutic potential of the MT-Zn axis in bolstering immune defenses against pathogens.

Loss of Egr1, a human del5q gene, accelerates BCR-ABL driven chronic myelogenous leukemia

There is substantial evidence that early growth response-1 (Egr1) gene, a zinc-finger transcription factor, behaves as a tumor suppressor in leukemia. This includes reports from this laboratory that constitutive Egr1 overrides leukemia conferred by deregulated c-Myc or E2F-1 in the M1 myeloid leukemic cell line by promoting differentiation. To investigate the effect of Egr1 on the initiation and progression of Chronic Myelogenous Leukemia (CML), lethally irradiated syngeneic wild type mice were reconstituted with bone marrow (BM) from either wild type or Egr1 null mice transduced with a 210-kD BCR-ABL-expressing MSCV-retrovirus (bone marrow transplantation {BMT}). Loss of Egr1 was observed to accelerate the development of BCR-ABL driven leukemia in recipient mice, resulting in the development of a more aggressive disease, a significantly shortened median survival time, and increased BCR-ABL expressing leukemic stem/progenitor cells (GFP+Lin-cKit+Sca+). Egr1 deficient progenitors expressing BCR-ABL exhibited decreased apoptosis, and increased cell viability and proliferation relative to WT counterparts. Secondary BMT of BCR-ABL BM revealed that loss of Egr1 resulted in enrichment of LSCs, consistent with shorter survival time and more aggressive disease of these mice compared to WT counterparts. Furthermore, serial re-plating colony assays indicated that loss of Egr1 increased self-renewal ability of BCR-ABL expressing BM. These novel findings on the tumor suppressor role of Egr1 in CML provide the impetus to study the effect of altering Egr1 expression in AML, where the overall five year survival rate remains low. The effect of loss of Egr1 in CML could reflect its established functions in normal hematopoiesis, maintaining quiescence of HSCs and driving terminal differentiation to the monocyte/macrophage lineage. Gain of function studies should validate these conclusions and provide further rationale for increased Egr1 as a therapeutic target in AML.

Early growth response 2 and Egr3 are unique regulators in immune system

The immune system is evolved to defend the body against pathogens and is composed of thousands of complicated and intertwined pathways, which are highly controlled by processes such as transcription and repression of cellular genes. Sometimes the immune system malfunctions and a break down in self-tolerance occurs. This lead to the inability to distinguish between self and non-self and cause attacks on host tissues, a condition also known as autoimmunity, which can result in chronic debilitating diseases. Early growth response genes are family of transcription factors comprising of four members, Egr1, Egr2, Egr3 and Egr4. All of which contain three cyc2-His2 zinc fingers. Initially, Egr2 function was identified in the regulation of peripheral nerve myelination, hindbrain segmentation. Egr3, on the other hand, is highly expressed in muscle spindle development. Egr2 and Egr3 are induced due to the antigen stimulation and this signaling is implemented through the B and T cell receptors in the adaptive immunity. T cell receptor signaling plays a key role in Egr 2 and 3 expressions via their interaction with NFAT molecules. Egr 2 and 3 play a crucial role in regulation of the immune system and their involvement in B and T cell activation, anergy induction and preventing the autoimmune disease has been investigated. The deficiency of these transcription factors has been associated to deficient Cbl-b expression, a resistant to anergy phenotype, and expression of effector and activated T cells.

Transcriptional mechanisms that control expression of the macrophage colony-stimulating factor receptor locus

The proliferation, differentiation, and survival of cells of the macrophage lineage depends upon signals from the macrophage colony-stimulating factor (CSF) receptor (CSF1R). CSF1R is expressed by embryonic macrophages and induced early in adult hematopoiesis, upon commitment of multipotent progenitors to the myeloid lineage. Transcriptional activation of CSF1R requires interaction between members of the E26 transformation-specific family of transcription factors (Ets) (notably PU.1), C/EBP, RUNX, AP-1/ATF, interferon regulatory factor (IRF), STAT, KLF, REL, FUS/TLS (fused in sarcoma/ranslocated in liposarcoma) families, and conserved regulatory elements within the mouse and human CSF1R locus. One element, the Fms-intronic regulatory element (FIRE), within intron 2, is conserved functionally across all the amniotes. Lineage commitment in multipotent progenitors also requires down-regulation of specific transcription factors such as MYB, FLI1, basic leucine zipper transcriptional factor ATF-like (BATF3), GATA-1, and PAX5 that contribute to differentiation of alternative lineages and repress CSF1R transcription. Many of these transcription factors regulate each other, interact at the protein level, and are themselves downstream targets of CSF1R signaling. Control of CSF1R transcription involves feed–forward and feedback signaling in which CSF1R is both a target and a participant; and dysregulation of CSF1R expression and/or function is associated with numerous pathological conditions. In this review, we describe the regulatory network behind CSF1R expression during differentiation and development of cells of the mononuclear phagocyte system.

Goldfish (Carassius auratus L.) as a model system to study the growth factors, receptors and transcription factors that govern myelopoiesis in fish

The process of myeloid cell development (myelopoiesis) in fish has mainly been studied in three cyprinid species: zebrafish (Danio rerio), ginbuna carp (Carassius auratus langsdorfii) and goldfish (C. auratus, L.). Our studies on goldfish myelopoiesis have utilized in vitro generated primary kidney macrophage (PKM) cultures and isolated primary kidney neutrophils (PKNs) cultured overnight to study the process of macrophage (monopoiesis) and neutrophil (granulopoiesis) development and the key growth factors, receptors, and transcription factors that govern this process in vitro. The PKM culture system is unique in that all three subpopulations of macrophage development, namely progenitor cells, monocytes, and mature macrophages, are simultaneously present in culture unlike mammalian systems, allowing for the elucidation of the complex mixture of cytokines that regulate progressive and selective macrophage development from progenitor cells to fully functional mature macrophages in vitro. Furthermore, we have been able to extend our investigations to include the development of erythrocytes (erythropoiesis) and thrombocytes (thrombopoiesis) through studies focusing on the progenitor cell population isolated from the goldfish kidney. Herein, we review the in vitro goldfish model systems focusing on the characteristics of cell sub-populations, growth factors and their receptors, and transcription factors that regulate goldfish myelopoiesis.

Monocyte to macrophage differentiation goes along with modulation of the plasmalogen pattern through transcriptional regulation

BACKGROUND

Dysregulation of monocyte-macrophage differentiation is a hallmark of vascular and metabolic diseases and associated with persistent low grade inflammation. Plasmalogens represent ether lipids that play a role in diabesity and previous data show diminished plasmalogen levels in obese subjects. We therefore analyzed transcriptomic and lipidomic changes during monocyte-macrophage differentiation in vitro using a bioinformatic approach.

METHODS

Elutriated monocytes from 13 healthy donors were differentiated in vitro to macrophages using rhM-CSF under serum-free conditions. Samples were taken on days 0, 1, 4 and 5 and analyzed for their lipidomic and transcriptomic profiles.

RESULTS

Gene expression analysis showed strong regulation of lipidome-related transcripts. Enzymes involved in fatty acid desaturation and elongation were increasingly expressed, peroxisomal and ER stress related genes were induced. Total plasmalogen levels remained unchanged, while the PE plasmalogen species pattern became more similar to circulating granulocytes, showing decreases in PUFA and increases in MUFA. A partial least squares discriminant analysis (PLS/DA) revealed that PE plasmalogens discriminate the stage of monocyte-derived macrophage differentiation. Partial correlation analysis could predict novel potential key nodes including DOCK1, PDK4, GNPTAB and FAM126A that might be involved in regulating lipid and especially plasmalogen homeostasis during differentiation. An in silico transcription analysis of lipid related regulation revealed known motifs such as PPAR-gamma and KLF4 as well as novel candidates such as NFY, RNF96 and Zinc-finger proteins.

CONCLUSION

Monocyte to macrophage differentiation goes along with profound changes in the lipid-related transcriptome. This leads to an induction of fatty-acid desaturation and elongation. In their PE-plasmalogen profile macrophages become more similar to granulocytes than monocytes, indicating terminal phagocytic differentiation. Therefore PE plasmalogens may represent potential biomarkers for cell activation. For the underlying transcriptional network we were able to predict a range of novel central key nodes and underlying transcription factors using a bioinformatic approach.

Molecular control of monocyte development

Monocyte development is a tightly regulated and multi-staged process, occurring through several defined progenitor cell intermediates. The key transcription factors, including PU.1, IRF8 and KLF4, growth factors, such as M-CSF and IL-34 and cytokines that drive monocyte development from hematopoietic progenitor cells are well defined. However, the molecular controls that direct differentiation into the Ly6C(hi) inflammatory and Ly6C(lo) monocyte subsets are yet to be completely elucidated. This review will provide a summary of the transcriptional regulation of monocyte development. We will also discuss how these molecular controls are also critical for microglial development despite their distinct haematopoetic origins. Furthermore, we will examine recent breakthroughs in defining mechanisms that promote differentiation of specific monocyte subpopulations.

The let-7/LIN-41 pathway regulates reprogramming to human induced pluripotent stem cells by controlling expression of prodifferentiation genes

Reprogramming differentiated cells into induced pluripotent stem cells (iPSCs) promotes a broad array of cellular changes. Here we show that the let-7 family of microRNAs acts as an inhibitory influence on the reprogramming process through a regulatory pathway involving prodifferentiation factors, including EGR1. Inhibiting let-7 in human cells promotes reprogramming to a comparable extent to c-MYC when combined with OCT4, SOX2, and KLF4, and persistence of let-7 inhibits reprogramming. Inhibiting let-7 during reprogramming leads to an increase in the level of the let-7 target LIN-41/TRIM71, which in turn promotes reprogramming and is important for overcoming the let-7 barrier to reprogramming. Mechanistic studies revealed that LIN-41 regulates a broad array of differentiation genes, and more specifically, inhibits translation of EGR1 through binding its cognate mRNA. Together our findings outline a let-7-based pathway that counteracts the activity of reprogramming factors through promoting the expression of prodifferentiation genes.

Molecular signatures of peripheral blood mononuclear cells during chronic interferon-α treatment: relationship with depression and fatigue

BACKGROUND

Interferon-alpha (IFN-α) treatment for infectious disease and cancer causes high rates of depression and fatigue, and has been used to investigate the impact of inflammatory cytokines on brain and behavior. However, little is known about the transcriptional impact of chronic IFN-α on immune cells in vivo and its relationship to IFN-α-induced behavioral changes.

METHOD

Genome-wide transcriptional profiling was performed on peripheral blood mononuclear cells (PBMCs) from 21 patients with chronic hepatitis C virus (HCV) either awaiting IFN-α therapy (n=10) or at 12 weeks of IFN-α treatment (n=11).

RESULTS

Significance analysis of microarray data identified 252 up-regulated and 116 down-regulated gene transcripts. Of the up-regulated genes, 2'-5'-oligoadenylate synthetase 2 (OAS2), a gene linked to chronic fatigue syndrome (CFS), was the only gene that was differentially expressed in patients with IFN-α-induced depression/fatigue, and correlated with depression and fatigue scores at 12 weeks (r=0.80, p=0.003 and r=0.70, p=0.017 respectively). Promoter-based bioinformatic analyses linked IFN-α-related transcriptional alterations to transcription factors involved in myeloid differentiation, IFN-α signaling, activator protein-1 (AP1) and cAMP responsive element binding protein/activation transcription factor (CREB/ATF) pathways, which were derived primarily from monocytes and plasmacytoid dendritic cells. IFN-α-treated patients with high depression/fatigue scores demonstrated up-regulation of genes bearing promoter motifs for transcription factors involved in myeloid differentiation, IFN-α and AP1 signaling, and reduced prevalence of motifs for CREB/ATF, which has been implicated in major depression.

CONCLUSIONS

Depression and fatigue during chronic IFN-α administration were associated with alterations in the expression (OAS2) and transcriptional control (CREB/ATF) of genes linked to behavioral disorders including CFS and major depression, further supporting an immune contribution to these diseases.

Epigenetic silencing of the oncogenic miR-17-92 cluster during PU.1-directed macrophage differentiation

This study unravels an epigenetic mechanism for the regulation of the oncogenic miRNA cluster 17-92, involving the master hematopoietic transcription factor PU.1/Egr-2 and Jarid1b.

The oncogenic cluster miR-17-92 encodes seven related microRNAs that regulate cell proliferation, apoptosis and development. Expression of miR-17-92 cluster is decreased upon cell differentiation. Here, we report a novel mechanism of the regulation of miR-17-92 cluster. Using transgenic PU.1^−/− myeloid progenitors we show that upon macrophage differentiation, the transcription factor PU.1 induces the secondary determinant Egr2 which, in turn, directly represses miR-17-92 expression by recruiting histone demethylase Jarid1b leading to histone H3 lysine K4 demethylation within the CpG island at the miR-17-92 promoter. Conversely, Egr2 itself is targeted by miR-17-92, indicating existence of mutual regulatory relationship between miR-17-92 and Egr2. Furthermore, restoring EGR2 levels in primary acute myeloid leukaemia blasts expressing elevated levels of miR-17-92 and low levels of PU.1 and EGR2 leads to downregulation of miR-17-92 and restored expression of its targets p21CIP1 and BIM. We propose that upon macrophage differentiation PU.1 represses the miR-17-92 cluster promoter by an Egr-2/Jarid1b-mediated H3K4 demethylation mechanism whose deregulation may contribute to leukaemic states.

A cryptic deletion in 5q31.2 provides further evidence for a minimally deleted region in myelodysplastic syndromes

Recurrent deletions of 5q in myeloid malignancies encompass two separate regions: deletion of 5q33, which is associated with the 5q− syndrome and haploinsufficiency of RPS14, and deletion of a more proximal locus at 5q31. We present a case with a cryptic 1.3 Mb deletion in 5q31.2 identified by array comparative genomic hybridization that places the proximal boundary of the deletion proximal and close to the candidate EGR1 gene. The patient was diagnosed initially with a myelodysplastic syndrome, with a del(20)(q11.2q13.3) as the sole abnormality identified by karyotyping. The patient progressed to acute myeloid leukemia with no change to the G-banded karyotype. The 1.3 Mb deletion on the long arm of one chromosome 5 was confirmed to have been present both at presentation with myelodysplastic syndrome and at transformation. This is an interesting case because there are few array studies identifying cryptic 5q deletions, and the study of these small deletions helps to refine the common deleted region. This case, together with previously published studies, suggests that the proximal boundary of the common deleted region may lie within the KDM3B gene.

Live in vivo imaging of Egr-1 promoter activity during neonatal development, liver regeneration and wound healing

BACKGROUND

The zinc finger transcription factor Egr-1 (Early growth response 1) is central to several growth factors and represents an important activator of target genes not only involved in physiological processes like embryogenesis and neonatal development, but also in a variety of pathophysiological processes, for example atherosclerosis or cancer. Current options to investigate its transcription and activation in vivo are end-point measurements that do not provide insights into dynamic changes in the living organism.

RESULTS

We developed a transgenic mouse (Egr-1-luc) in which the luciferase reporter gene is under the control of the murine Egr-1 promoter providing a versatile tool to study the time course of Egr-1 activation in vivo. In neonatal mice, bioluminescence imaging revealed a high Egr-1 promoter activity reaching basal levels three weeks after birth with activity at snout, ears and paws. Using a model of partial hepatectomy we could show that Egr-1 promoter activity and Egr-1 mRNA levels were increased in the regenerating liver. In a model of wound healing, we demonstrated that Egr-1 promoter activity was upregulated at the site of injury.

CONCLUSION

Taken together, we have developed a transgenic mouse model that allows real time in vivo imaging of the Egr-1 promoter activity. The ability to monitor and quantify Egr-1 activity in the living organism may facilitate a better understanding of Egr-1 function in vivo.

PML is a key component for the differentiation of myeloid progenitor cells to macrophages

IFN regulatory factor-8 (IRF-8, previously known as ICSBP) is a key transcription factor driving the differentiation of granulocyte\monocyte progenitor (GMP) cells toward monocyte\macrophage lineage. The promyelocytic leukemia (PML) gene is an immediate target gene regulated by IRF-8 in response to IFN-γ activation. PML is a multifunctional protein that has many isoforms serving as the scaffold components for nuclear bodies (NBs) engaged in numerous proteins interactions. The role of PML in the retinoic acid pathway that drives GMPs to granulopoiesis is documented in the literature. Here, we show that PML is also involved in monopoiesis by mediating some of the IRF-8 activities during the differentiation of murine-derived bone marrow macrophages (BMMs). PML silencing resulted in altered expression level of key transcription factors essential for monopoiesis that was accompanied by silencing of typical myeloid-specific genes. Interestingly, this altered expression resembled that of the GMPs and that of BMMs derived from IRF-8(-/-) mice altogether supporting the role of PML in monopoiesis. Further, PML silencing led to reduced colony-forming capacity of bone marrow cells highlighting the dual function of PML in myelopoiesis. Last, PML overexpression only partially rescued the phenotype of IRF-8(-/-) BMMs. Together, our data show that PML is an important factor for monopoiesis and not solely for granulopoiesis. This suggests that PML-NBs respond to an incoming signal that affects the fate of GMP driving cell differentiation to granulocytes or monocytes.

Krox20/EGR2 deficiency accelerates cell growth and differentiation in the monocytic lineage and decreases bone mass

Krox20/EGR2, one of the 4 early growth response genes, is a highly conserved transcription factor implicated in hindbrain development, peripheral nerve myelination, tumor suppression, and monocyte/macrophage cell fate determination. Here, we established a novel role for Krox20 in postnatal skeletal metabolism. Microcomputed tomographic analysis of 4- and 8-week-old mice revealed a low bone mass phenotype (LBM) in both the distal femur and the vertebra of Krox20(+/-) mice. This was attributable to accelerated bone resorption as demonstrated in vivo by increased osteoclast number and serum C-terminal telopeptides, a marker for collagen degradation. Krox20 haploinsufficiency did not reduce bone formation in vivo, nor did it compromise osteoblast differentiation in vitro. In contrast, growth and differentiation were significantly stimulated in preosteoclast cultures derived from Krox20(+/-) splenocytes, suggesting that the LBM is attributable to Krox20 haploinsufficiency in the monocytic lineage. Furthermore, Krox20 silencing in preosteoclasts increased cFms expression and response to macrophage colony-stimulating factor, leading to a cell-autonomous stimulation of cell-cycle progression. Our data indicate that the antimitogenic role of Krox20 in preosteoclasts is the predominant mechanism underlying the LBM phenotype of Krox20-deficient mice. Stimulation of Krox20 expression in preosteoclasts may present a viable therapeutic strategy for high-turnover osteoporosis.

The gene encoding early growth response 2, a target of the transcription factor NFAT, is required for the development and maturation of natural killer T cells

The influence of signals transmitted by the phosphatase calcineurin and the transcription factor NFAT on the development and function of natural killer T (NKT) cells is unclear. In this report, we demonstrate that the transcription factor early growth response 2 (Egr2), a target gene of NFAT, was specifically required for the ontogeny of NKT cells but not that of conventional CD4(+) or CD8(+) T cells. NKT cells developed normally in the absence of Egr1 or Egr3, which suggests that Egr2 is a specific regulator of NKT cell differentiation. We found that Egr2 was important in the selection, survival and maturation of NKT cells. Our findings emphasize the importance of the calcineurin-NFAT-Egr2 pathway in the development of the NKT lymphocyte lineage.

Early growth response genes regulate B cell development, proliferation, and immune response

Egr-1 (early growth response gene-1) is an immediate early gene encoding a zinc finger motif-containing transcription factor. Upon cross-linking of BCR, mature B cells undergo proliferation with an increase in Egr-1 message. Immature B lymphoma cells that express Egr-1 message and protein constitutively are growth inhibited when Egr-1 is down-regulated by negative signals from BCR or by antisense oligonucleotides. To test the hypothesis that Egr-1 is important for B cell development, we examined B cells from primary and secondary lymphoid organs in Egr-1(-/-) mice. Marginal zone B cell development was arrested in these mice, whereas the B cells in all other compartments were increased. To test the hypothesis that Egr-1 function may be partially compensated by other Egr family members, we developed transgenic mice expressing a dominant negative form of Egr-1, which lacks the trans activation domain but retains the DNA-binding domain, in a B cell-specific manner. There was a decrease in B lymphopoiesis in the bone marrow accompanied by a reduction in splenic immature and mature B cells as well as marginal zone B cells in the transgenic mice. Moreover, transgenic mice respond poorly to BCR cross-linking in vitro and T-independent and T-dependent Ags in vivo.

Proinflammatory role of leukocyte-derived Egr-1 in the development of murine postoperative ileus

BACKGROUND & AIMS

Early growth response gene-1 (Egr-1) is an important inflammatory transcription factor. We hypothesize that leukocyte-derived Egr-1 plays a key inflammatory role in causing postoperative ileus.

METHODS

Wild-type, Egr-1 knockout, and chimera mice (constructed by irradiation followed by injection with Egr-1(+/+) or Egr-1(-/-) bone marrow) were subjected to surgical manipulation of the gastrointestinal tract to induce ileus. Reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry quantified and localized Egr-1. Lumenal transit of nonabsorbable fluorescein isothiocyanate-labeled dextran and in vitro organ bath techniques measured functional gastrointestinal motility. Inflammatory mediator expressions were measured by Griess reaction, enzyme-linked immunosorbent assay, and multiplex Luminex assay.

RESULTS

Intestinal manipulation rapidly and significantly induced Egr-1 messenger RNA and protein within the inflamed muscularis externa. Egr-1 was colocalized early to smooth muscle and enteric neurons and later in extravasated monocytes after surgery when postoperative ileus was functionally prominent. The functional severity of postoperative ileus was significantly ameliorated in mice deficient in Egr-1(-/-) and chimera wild-type mice transplanted with Egr-1(-/-) bone marrow, whereas knockout mice with Egr-1(+/+) bone marrow again displayed significant ileus. Motility was mechanistically associated in Egr-1(-/-) gene deficiency with a down-regulation in the release of nitric oxide, prostanoids, monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, interleukin-6, interleukin-1, and granulocyte colony-stimulating factor, as well as a decrease in the recruitment of leukocytes into the manipulated muscle wall of the intestine compared with wild-type mice.

CONCLUSIONS

Leukocyte-derived Egr-1 plays an early critical inflammatory role in the initiation of the postoperative inflammatory response, which leads to a prolonged decreased in gastrointestinal motility after intestinal surgery.

The MADS transcription factor Mef2c is a pivotal modulator of myeloid cell fate

Mef2c is a MADS (MCM1-agamous–deficient serum response factor) transcription factor best known for its role in muscle and cardiovascular development. A causal role of up-regulated MEF2C expression in myelomonocytic acute myeloid leukemia (AML) has recently been demonstrated. Due to the pronounced monocytic component observed in Mef2c-induced AML, this study was designed to assess the importance of Mef2c in normal myeloid differentiation. Analysis of bone marrow (BM) cells manipulated to constitutively express Mef2c demonstrated increased monopoiesis at the expense of granulopoiesis, whereas BM isolated from Mef2cΔ/− mice showed reduced levels of monocytic differentiation in response to cytokines. Mechanistic studies showed that loss of Mef2c expression correlated with reduced levels of transcripts encoding c-Jun, but not PU.1, C/EBPα, or JunB transcription factors. Inhibiting Jun expression by short-interfering RNA impaired Mef2c-mediated inhibition of granulocyte development. Moreover, retroviral expression of c-Jun in BM cells promoted monocytic differentiation. The ability of Mef2c to modulate cell-fate decisions between monocyte and granulocyte differentiation, coupled with its functional sensitivity to extracellular stimuli, demonstrate an important role in immunity—and, consistent with findings of other myeloid transcription factors, a target of oncogenic lesions in AML.

FP prostanoid receptor-mediated induction of the expression of early growth response factor-1 by activation of a Ras/Raf/mitogen-activated protein kinase signaling cascade

FP prostanoid receptors are G-protein-coupled receptors whose physiological activator is prostaglandin-F(2alpha) (PGF(2alpha)). PGF(2alpha) has been implicated in wound healing and cardiac hypertrophy, which are both known to involve the induction of the immediate-early response gene, early growth response factor-1 (EGR-1). We hypothesized that activation of the human FP receptor by PGF(2alpha) could induce the expression of EGR-1 and found that 1 muM PGF(2alpha) produced a time-dependent induction of both mRNA and protein expression for EGR-1. This FP receptor-mediated induction of EGR-1 expression involved activation of the small GTPase Ras followed by activation of C-Raf and the mitogen-activated protein (MAP) kinase kinases 1 and 2 (MEK1/2). Thus, induction of EGR-1 expression by PGF(2alpha) was blocked using dominant-negative constructs of Ras and C-Raf and the Raf kinase inhibitor 4-(4-(3-(4-chloro-3-trifluoromethylphenyl)ureido)phenoxy)-pyridine-2-carboxyllic acid methyamide-4-methylbenzenesulfonate (BAY43-9006). Likewise, the MEK1/2 inhibitor 2'-amino-3'-methoxyflavone (PD98059) blocked the induction of EGR-1 expression by PGF(2alpha). FP receptor stimulation by PGF(2alpha) induced the phosphorylation of C-Raf, MEK1/2, and extracellular signal-regulated kinases 1 and 2, consistent with the activation of a MAP kinase signaling cascade. PGF(2alpha) was also found to induce the expression of EGR-1 in rat cardiomyocytes through the activation of endogenous FP receptors. This induction of EGR-1 expression in cardiomyocytes also involved the activation of Raf and MAP kinase signaling and was dependent on the activation of protein kinase C. This is the first report to show the regulation of EGR-1 expression after PGF(2alpha) activation of FP receptors and suggests that this could be an early event involved in wound healing and cardiac hypertrophy.

Activation of nonsteroidal anti-inflammatory drug-activated gene-1 via extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase revealed a isochaihulactone-triggered apoptotic pathway in human lung cancer A549 cells

The novel lignan isochaihulactone inhibits cell proliferation and is an effective inducer of apoptosis in a variety of carcinoma cell lines. To determine the mechanisms underlying these effects, we examined isochaihulactone-induced changes in gene expression using oligodeoxynucleotide-based microarray screening of a human lung carcinoma cell line, A549. Isochaihulactone-inducible genes included the early growth response gene-1 (EGR-1) and nonsteroidal anti-inflammatory drug-activated gene (NAG-1). Isochaihulactone increased EGR-1 and then NAG-1 mRNA and protein expression. Pure isochaihulactone induced phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. Isochaihulactone-induced increases in EGR-1 and NAG-1 expression were reduced by the mitogen-activated protein kinase kinase 1/2 inhibitor 2'-amino-3'-methoxyflavone (PD98059), and this effect was not blocked by the phosphatidylinositol 3-kinase/protein kinase B pathway inhibitor 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002). Inhibition of isochaihulactone-induced NAG-1 expression by EGR-1 small interfering RNA blocked isochaihulactone-induced apoptosis in A549 cells, suggesting that induction of EGR-1 expression decreases survival of A549 cells. RNA interference using double-stranded RNA specific for NAG-1 also inhibited isochaihulactone-induced apoptosis, and cells transfected to increased NAG-1 expression had a greater apoptotic response to isochaihulactone and reduced colony formation efficiency. In addition, treatment of nude mice with isochaihulactone increased the in vivo NAG-1 expression as examined by immunohistochemistry from tumor biopsy. Isochaihulactone treatment increased the luciferase activity of NAG-1 in A549 cells transfected with the NAG-1 promoter construct. This induction increased expression of NAG-1 that was p53-independent and Sp1-dependent. Our findings suggest that NAG-1 expression is up-regulated by isochaihulactone through an ERK-dependent pathway involving the activation of EGR-1.

Egr-1 abrogates the E2F-1 block in terminal myeloid differentiation and suppresses leukemia

Deregulated growth and blocks in differentiation collaborate in the multistage process of leukemogenesis. Previously, we have shown that ectopic expression of the zinc finger transcription factor Egr-1 in M1 myeloblastic leukemia cells promotes terminal differentiation with interleukin-6 (IL-6). In addition, we have shown that deregulated expression of the oncogene E2F-1 blocks the myeloid terminal differentiation program, resulting in proliferation of immature cells in the presence of IL-6. Here it is shown that the positive regulator of differentiation Egr-1 abrogates the E2F-1-driven block in myeloid terminal differentiation. The M1E2F-1/Egr-1 cells underwent G(0)/G(1) arrest and functional macrophage maturation following treatment with IL-6. Furthermore, Egr-1 diminished the aggressiveness of M1E2F-1 leukemias and abrogated the leukemic potential of IL-6-treated M1E2F-1 cells. Previously, we reported that Egr-1 abrogated the block in terminal myeloid differentiation imparted by deregulated c-myc, which blocks differentiation at a later stage than E2F-1, resulting in cells that have the characteristics of functionally mature macrophages that did not undergo G(0)/G(1) arrest. Taken together, this work extends and highlights the tumor suppressor role of Egr-1, with Egr-1 behaving as a tumor suppressor against two oncogenes, each blocking myeloid differentiation by a different mechanism. These findings suggest that Egr-1 and/or Egr-1 target genes may be useful tools to treat or suppress oncogene-driven hematological malignancies.

The early growth response factor-1 is involved in stem cell factor (SCF)-induced interleukin 13 production by mast cells, but is dispensable for SCF-dependent mast cell growth

The stem cell factor (SCF) plays a central role in the regulation of mast cell function and growth. However, roles of transcription factors involved in these processes remain incompletely defined. The early growth response factor-1 (Egr-1) is a member of the zinc finger transcription factor family. A role for Egr-1 in SCF-induced mast cell activation and growth was investigated in mouse bone marrow-derived mast cells (BMMC). The stimulation of BMMC with SCF induced a strong expression of Egr-1 mRNA. SCF-induced Egr-1 nuclear translocation and DNA binding were demonstrated by electrophoretic mobility shift assay (EMSA) and immunofluorescence assay. SCF-induced IL-13 expression was significantly reduced at both mRNA and protein levels in Egr-1-deficient BMMC. In addition, the synergy between IgE and SCF on IL-13 and IL-4 production was reduced in Egr-1-deficient mast cells. Interestingly, Egr-1 deficiency had little effect on SCF-induced mast cell growth. SCF-induced Egr activation likely requires tyrosine phosphorylation because a tyrosine kinase inhibitor PP2 blocked SCF-induced nuclear protein binding to Egr probe as determined by EMSA. Thus, Egr-1 is required for SCF-induced IL-13 expression, but not mast cell growth. Egr-1 represents a novel mechanism for SCF-induced mast cell activation.

Early growth response transcriptional regulators are dispensable for macrophage differentiation

Early growth response (Egr) proteins comprise a family of transcriptional regulators (Egr1-4) that modulate gene expression involved in the growth and differentiation of many cell types. In particular, Egr1 is widely believed to have an essential role in regulating monocyte/macrophage differentiation. However, Egr1-deficient mice have normal numbers of functional macrophages, an observation that has led to the hypothesis that other Egr proteins may compensate for Egr1 function in vivo. We examined whether other Egr transcription factors have a functionally redundant role in monocyte/macrophage differentiation. Egr1 and Egr3 expression was found to be induced in myeloid cells when they were differentiated into macrophages by treatment with M-CSF, whereas Egr2 was minimally induced and Egr4 was not detected. In either Egr1/Egr3 or Egr1/Egr2 double homozygous mutant mice, macrophage differentiation and function remained unimpaired. Additionally, the expression of molecules that broadly inhibit Egr function failed to block commitment to the monocytic lineage or inhibit the maturation of monocyte precursors. Finally, several hemopoietic growth factors were found to induce Egr gene expression, indicating that Egr gene expression is not cell lineage specific. Taken together, these results demonstrate that Egr transcription factors are neither essential for nor specific to monocyte/macrophage differentiation.

Recent insights into the signals that control alphabeta/gammadelta-lineage fate

During thymopoiesis, two major types of mature T cells are generated that can be distinguished by the clonotypic subunits contained within their T-cell receptor (TCR) complexes: alphabeta T cells and gammadelta T cells. Although there is no consensus as to the exact developmental stage where alphabeta and gammadelta T-cell lineages diverge, gammadelta T cells and precursors to the alphabeta T-cell lineage (bearing the pre-TCR) are thought to be derived from a common CD4- CD8- double-negative precursor. The role of the TCR in alphabeta/gammadelta lineage commitment has been controversial, in particular whether different TCR isotypes intrinsically favor adoption of the corresponding lineage. Recent evidence supports a signal strength model of lineage commitment, whereby stronger signals promote gammadelta development and weaker signals promote adoption of the alphabeta fate, irrespective of the TCR isotype from which the signals originate. Moreover, differences in the amplitude of activation of the extracellular signal-regulated kinase- mitogen-activated protein kinase-early growth response pathway appear to play a critical role. These findings will be placed in context of previous analyses in an effort to more precisely define the signals that control T-lineage fate during thymocyte development.

Induction of Krox-24 by endogenous cannabinoid type 1 receptors in Neuro2A cells is mediated by the MEK-ERK MAPK pathway and is suppressed by the phosphatidylinositol 3-kinase pathway

Neuro2a cells endogenously express cannabinoid type 1 (CB1) receptors. CB1 stimulation with HU210 activated ERK and induced the transcription factor Krox-24. A functional MEK-ERK pathway is an important requirement for CB1-mediated Krox-24 induction as blockade of MEK signaling by UO126 reduces both basal and CB1-mediated activation of Krox-24. CB1 receptor stimulation did not activate either JNK or p38 MAPK pathways or the pro-proliferation phosphatidylinositol 3-kinase (PI3K)-Akt pathway. However, serum removal or blockade of PI3K signaling by LY294002 transiently stimulated basal Krox-24 expression and increased CB1-mediated induction of Krox-24. This was consistent with a transient increase in pMEK, pERK, and pCREB levels following PI3K blockade. These data demonstrate that CB1-mediated activation of the Krox-24 transcription factor is negatively regulated through the PI3K-Akt pathway and reveals several points of signaling cross-talk between these two important kinase pathways.

De novo synthesis of early growth response factor-1 is required for the full responsiveness of mast cells to produce TNF and IL-13 by IgE and antigen stimulation

Early growth-response factor 1 (Egr-1) is a zinc-finger transcription factor that plays a regulatory role in the expression of many genes important for inflammation. Whether Egr-1 is involved in IgE-dependent mast-cell activation was investigated. We demonstrated that IgE and antigen (TNP) stimulation induced a rapid expression of Egr-1 mRNA in mouse bone marrow-derived mast cells (BMMCs). As early as 15 to 20 minutes after IgE + TNP stimulation, Egr-1 protein was detectable in the nucleus of BMMCs by immunofluorescence or electrophoretic mobility shift assay. To examine a role for Egr-1 in IgE-dependent cytokine production by mast cells, Egr-1-deficient (Egr-1-/-) BMMCs were developed from the bone marrow cells of Egr-1 knockout mice. Egr-1-/- BMMCs express similar levels of surface c-kit and IgE receptor as compared with those on Egr-1+/+ BMMCs. Importantly, IgE + TNP-induced TNF and IL-13 expression was significantly reduced at both mRNA and protein levels in Egr-1-/- BMMCs as compared with those in Egr-1+/+ BMMCs. Thus, our results suggest that de novo synthesis of Egr-1 represents a novel mechanism in FcepsilonRI signaling and is required for the full responsiveness of IgE-dependent TNF and IL-13 production by mast cells.

The interferon-inducible gene, Ifi204, is transcriptionally activated in response to M-CSF, and its expression favors macrophage differentiation in myeloid progenitor cells

The interferon-inducible (Ifi)204 gene was isolated as a macrophage-colony stimulating factor (M-CSF)-responsive gene using a gene trap approach in the myeloid interleukin-3 (IL-3)-dependent FD-Fms cell line, which differentiates in macrophages in response to M-CSF. Here, we show that Ifi204 was transcriptionally activated in response to M-CSF, and FD-Fms cells decreased their growth and committed toward a macrophage morphology; this induction was abrogated when the differentiation signal of the M-CSF receptor was blocked; the Ifi204 gene was also induced during macrophage differentiation controlled by leukemia inhibitory factor; and the Ifi204 gene is expressed in different mature monocyte/macrophage cells. Finally, we showed that enforced expression of Ifi204 strongly decreased IL-3- and M-CSF-dependent proliferation and conversely, favored macrophage differentiation of FD-Fms cells in response to M-CSF. Altogether, these results demonstrate that the Ifi204 gene is activated during macrophage development and suggest that the Ifi204 protein may act as a regulator of the balance between proliferation and differentiation. Moreover, this study suggests that other members of the Ifi family might act as regulators of hematopoiesis under the control of hemopoietic cytokines.

Egr-1 abrogates the block imparted by c-Myc on terminal M1 myeloid differentiation

Both deregulated growth and blocks in differentiation cooperate in the multistage process of leukemogenesis. Thus, understanding functional interactions between genes that regulate normal blood cell development, including cell growth and differentiation, and how their altered expression contributes to leukemia, is important for rational drug design. Previously, we have shown that the zinc finger transcription factor Egr-1 plays a role in monocytic differentiation. Ectopic expression of Egr-1 in M1 myeloblastic leukemia cells was observed to activate the macrophage differentiation program in the absence of the differentiation inducer interleukin 6 (IL-6) and to promote terminal differentiation in its presence. In addition, we have shown that deregulated expression of the proto-oncogene c-myc blocks the myeloid terminal differentiation program. Here we show that restoring expression of Egr-1 in M1 cells that express deregulated c-Myc abrogates the c-Myc block in terminal differentiation, resulting in cells that undergo functional macrophage maturation. However, there is an absence of both growth arrest and cell adhesion. In addition, Egr-1 expression diminished M1myc leukemogenicity in vivo. These findings indicate that Egr-1 can act as a tumor suppressor gene and suggest that Egr-1 or Egr-1 targets may provide important tools for differentiation therapy in certain leukemic phenotypes.

CD8 T cell responses to lymphocytic choriomeningitis virus in early growth response gene 1-deficient mice

Previous in vitro work has implicated a role for transcriptional factor early growth response gene 1 (EGR1) in regulating immune responses. However, the in vivo role of EGR1 in orchestrating T cell responses has not been studied. To investigate the importance of EGR1 in T cell immunity, we compared Ag-specific CD8 T cell responses between wild type (+/+) and EGR1-deficient (EGR1-/-) mice following an acute infection with lymphocytic choriomeningitis virus (LCMV). These studies revealed that the expansion of LCMV-specific CD8 T cells was substantially reduced in EGR1-/- mice, as compared with +/+ mice. The reduced numbers of LCMV-specific CD8 T cells in EGR1-/- mice were not due to an intrinsic T cell defect per se because purified EGR1-deficient T cells exhibited normal proliferative response to anti-CD3 stimulation in vitro, and underwent normal activation and expansion in response to LCMV upon adoptive transfer into T cell-deficient mice. Furthermore, adoptive transfer of CD8 T cells bearing a transgenic TCR into EGR1-/- mice showed that EGR1 deficiency in non-CD8 T cells impaired CD8 T cell expansion in vivo following an LCMV infection. Further investigations on accessory cells showed that bone marrow-derived dendritic cells from EGR1-/- mice did not exhibit detectable impairment to prime Ag-specific CD8 T cell responses in vivo. However, in LCMV-infected mice, EGR1 deficiency selectively impaired the maturation of CD8alpha(+ve) plasmacytoid dendritic cells. Taken together, our findings suggest that EGR1 might promote expansion of CD8 T cells during an acute viral infection by modulating the cues in the lymphoid microenvironment.

Fos modulates myeloid cell survival and differentiation and partially abrogates the c-Myc block in terminal myeloid differentiation

Previously, we have shown that Fos/Jun transcription factor complexes function as positive modulators of myeloid differentiation. Fos, which is stably induced during normal myeloid differentiation, is not induced upon differentiation of M1 myeloblastic leukemia cells. Establishing M1 cells that express a β-estradiol-conditional FosER chimera, we show that in the absence of the differentiation inducer interleukin-6 (IL-6), Fos expression in M1 myeloblasts promoted apoptotic cell death, entailing cytochrome c release and caspase-9 activation. In contrast, in the presence of IL-6, Fos-mediated apoptosis was abrogated, and Fos promoted terminal differentiation, increasing the sensitivity of M1 cells to be induced for differentiation by IL-6. Fos-mediated apoptosis was accelerated by deregulated c-Myc. Furthermore, restoring Fos expression in M1 partially abrogated the block imparted by deregulated c-Myc on the myeloid differentiation program, increased the sensitivity of the cells to be induced for differentiation, and curtailed their leukemic phenotype. These data provide evidence that Fos/Jun transcription factor complexes play a role in modulating both myeloid cell survival and differentiation and suggest that genetic lesions that alter Fos expression may cooperate with deregulated c-Myc in leukemogenesis. (Blood. 2004;103:4259-4267)

The transcription factor early growth response factor-1 (EGR-1) promotes apoptosis of neuroblastoma cells

Early growth response factor-1 (EGR-1) is an immediate early gene, which is rapidly activated in quiescent cells by mitogens or in postmitotic neurons after depolarization. EGR-1 has been involved in diverse biological functions such as cell growth, differentiation and apoptosis. Here we report that enforced expression of the EGR-1 gene induces apoptosis, as determined by flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein nick-end labelling (TUNEL) analysis, in murine Neuro2A cells. In accordance with this role of EGR-1 in cell death, antisense oligonucleotides increase cell viability in cells cultured in the absence of serum. This apoptotic activity of the EGR-1 appears to be mediated by p73, a member of the p53 family of proteins, since an increase in the amount of p73 is observed in clones stably expressing the EGR-1 protein. We also observed an increase in the transcriptional activity of the mdm2 promoter in cells overexpressing EGR-1, which is paralleled by a marked decrease in the levels of p53 protein, therefore excluding a role of this protein in mediating EGR-1-induced apoptosis. Our results suggest that EGR-1 is an important factor involved in neuronal apoptosis.

Fes tyrosine kinase promotes survival and terminal granulocyte differentiation of factor-dependent myeloid progenitors (32D) and activates lineage-specific transcription factors

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is involved in myeloid cell development and function. We have recently shown that expression of an activated allele of Fes (Fes(act)) in monocyte precursors resulted in their differentiation into functional macrophages through the activation of lineage-specific transcription factors. We now report that this kinase also plays a role in the survival and terminal differentiation of granulocyte progenitors. The expression of Fes(act) in factor-dependent 32D cells prevented their apoptotic death after interleukin-3 removal, but Fes(act)-expressing cells remained factor-dependent for proliferation. Removal of interleukin-3 from the Fes(act)-expressing cells was followed by granulocytic differentiation in the absence of granulocyte colony-stimulating factor within 4-8 days. The differentiated cells had distinctive granulocyte morphology and there was up-regulation of CD11b, Gr-1, and late differentiation markers such as lactoferrin, suggesting that this kinase induced terminal granulocytic differentiation. Concomitantly, Fes(act) down-regulated the macrophage marker F4/80, suggesting that the biological activity of Fes was coordinated in a lineage-specific manner. Further analysis showed that Fes(act) caused activation of CCAAT/enhancer-binding protein-alpha and STAT3, two transcription factors that are involved in granulocyte differentiation. Our results provide evidence that Fes may be a key component of the granulocyte differentiation machinery, and suggest a potential mechanism by which this kinase may regulate granulocyte-specific gene expression.

Expression of the zinc finger Egr1 gene during zebrafish embryonic development

Egr1 is a highly conserved zinc finger protein which plays important roles in many aspects of vertebrate development and in the adult. The cDNA coding for zebrafish Egr1 was obtained and its expression pattern was examined during zebrafish embryogenesis using whole-mount in situ hybridization. Egr1 mRNA is first detected in adaxial cells in the presomitic mesoderm between 11 and 20 h post-fertilization (hpf), spanning the 4-24 somite stages. Later, Egr1 expression is observed only in specific brain areas, starting at 21 hpf and subsequently increasing in distinct domains of the central nervous system, e.g. in the telencephalon, diencephalon and hypothalamus. Between 24 and 48 hpf, Egr1 is expressed in specific domains of the hypothalamus, mesencephalon, tegmentum, pharynx, retina, otic vesicle and heart.