Egr2 is required for Bcl-2 induction during positive selection

Gene Regulatory Programs that Specify Age-Related Differences during Thymocyte Development

T cell development is fundamental to immune system establishment, yet how this development changes with age remains poorly understood. Here, we construct a transcriptional and epigenetic atlas of T cell developmental programs in neonatal and adult mice, revealing the ontogeny of divergent gene regulatory programs and their link to age-related differences in phenotype and function. Specifically, we identify a gene module that diverges with age from the earliest stages of genesis and includes programs that govern effector response and cell cycle regulation. Moreover, we reveal that neonates possess more accessible chromatin during early thymocyte development, likely establishing poised gene expression programs that manifest later in thymocyte development. Finally, we leverage this atlas, employing a CRISPR-based perturbation approach coupled with single-cell RNA sequencing as a readout to uncover a conserved transcriptional regulator, Zbtb20, that contributes to age-dependent differences in T cell development. Altogether, our study defines transcriptional and epigenetic programs that regulate age-specific differences in T cell development.

Transcription factor EGR2 controls homing and pathogenicity of TH17 cells in the central nervous system

CD4+ T helper 17 (TH17) cells protect barrier tissues but also trigger autoimmunity. The mechanisms behind these opposing processes remain unclear. Here, we found that the transcription factor EGR2 controlled the transcriptional program of pathogenic TH17 cells in the central nervous system (CNS) but not that of protective TH17 cells at barrier sites. EGR2 was significantly elevated in myelin-reactive CD4+ T cells from patients with multiple sclerosis and mice with autoimmune neuroinflammation. The EGR2 transcriptional program was intricately woven within the TH17 cell transcriptional regulatory network and showed high interconnectivity with core TH17 cell-specific transcription factors. Mechanistically, EGR2 enhanced TH17 cell differentiation and myeloid cell recruitment to the CNS by upregulating pathogenesis-associated genes and myelomonocytic chemokines. T cell-specific deletion of Egr2 attenuated neuroinflammation without compromising the host's ability to control infections. Our study shows that EGR2 regulates tissue-specific and disease-specific functions in pathogenic TH17 cells in the CNS.

Bcl-2 Is Necessary to Counteract Bim and Promote Survival of TCRαβ+CD8αα+ Intraepithelial Lymphocyte Precursors in the Thymus

The precursors of TCRαβ+CD8αα+ intraepithelial lymphocytes (IEL) arise in the thymus through a complex process of agonist selection. We and others have shown that the proapoptotic protein, Bim, is critical to limit the number of thymic IEL precursors (IELp), as loss of Bim at the CD4+CD8+ double-positive stage of development drastically increases IELp. The factors determining this cell death versus survival decision remain largely unknown. In this study, we used CD4CreBcl2f/f mice to define the role of the antiapoptotic protein Bcl-2 and CD4CreBcl2f/fBimf/f mice to determine the role of Bcl-2 in opposing Bim to promote survival of IELp. First, in wild-type mice, we defined distinct subpopulations within PD-1+CD122+ IELp, based on their expression of Runx3 and α4β7. Coexpression of α4β7 and Runx3 marked IELp that were most dependent upon Bcl-2 for survival. Importantly, the additional loss of Bim restored Runx3+α4β7+ IELp, showing that Bcl-2 antagonizes Bim to enable IELp survival. Further, the loss of thymic IELp in CD4CreBcl2f/f mice also led to a dramatic loss of IEL in the gut, and the additional loss of Bim restored gut IEL. The loss of gut IEL was due to both reduced seeding by IELp from the thymus as well as a requirement for Bcl-2 for peripheral IEL survival. Together, these findings highlight subset-specific and temporal roles for Bcl-2 in driving the survival of TCRαβ+CD8αα+ IEL and thymic IELp.

An autonomous TCR signal-sensing switch influences CD4/CD8 lineage choice in mice

How multipotential cells initiate distinct gene expression programs in response to external cues to instruct cell fate choice remains a fundamental question in biology. Establishment of CD4 and CD8 T cell fates during thymocyte development is critically regulated by T cell receptor (TCR) signals, which in turn control expression of the CD4-determining transcription factor ThPOK. However, the mechanism whereby differential TCR signals are molecularly interpreted to promote or antagonize ThPOK expression, and thereby CD4 versus CD8 lineage fates remains unknown. Here we show, using reverse genetic and molecular approaches that an autonomous, position-independent TCR-sensing switch is embedded within the ThPOK locus. Further, using an in vivo mutagenesis approach, we demonstrate that differential TCR signals are interpreted during lineage commitment by relative binding of EGR, NFAT and Ebox factors to this bistable switch. Collectively our study reveals the central molecular mechanism whereby TCR signaling influences differential lineage choice. Ultimately, these findings may provide an important new tool for skewing T cell fate to treat cancer and autoimmune diseases.

Extracellular Vesicle-Derived microRNA-410 From Mesenchymal Stem Cells Protects Against Neonatal Hypoxia-Ischemia Brain Damage Through an HDAC1-Dependent EGR2/Bcl2 Axis

Hypoxia-ischemia brain damage (HIBD) is a neurological disorder occring in neonates, which is exacerbated by neuronal apoptosis. Mesenchymal stem cells (MSCs)-derived extracellular vesicles (EVs) have been proposed as a promising strategy for treating or preventing ischemia-related diseases. However, their mechanisms in HIBD remain unclear. Thus, we aimed to address the role of EV-derived microRNA (miR)-410 in HIBD. Neonatal HIBD mouse model was constructed using HI insult, from which neurons were isolated, followed by exposure to oxygen glucose deprivation (OGD). EVs were isolated from human umbilical cord (hUC)-derived MSCs. In silico analyses, dual-luciferase reporter gene and chromatin immunoprecipitation assays were adopted to determine relationships among miR-410, histone deacetylase 1 (HDAC1), early growth response protein 2 (EGR2), and B cell lymphoma/leukemia 2 (Bcl2). The functional roles of EV-derived miR-410 were determined using loss- and gain-of functions experiments, and by evaluating neuronal viability, cell-cycle distribution and neuronal apoptosis in vitro as well as modified neurological severity score (mNSS), edema formation, and cerebral infarction volume in vivo. hUC-MSCs-derived EVs protected against HIBD in vivo and inhibited the OGD-induced neuronal apoptosis in vitro. miR-410 was successfully delivered to neurons by hUC-MSCs-EVs and negatively targeted HDAC1, which inversely mediated the expression of EGR2/Bcl2. Upregulation of EV-derived miR-410 promoted the viability but inhibited apoptosis of neurons, which was reversed by HDAC1 overexpression. EV-derived miR-410 elevation reduced mNSS, edema formation, and cerebral infarction volume by increasing EGR2/Bcl2 expression through downregulating HDAC1 expression in vivo. In summary, EV-derived miR-410 impeded neuronal apoptosis by elevating the expression of EGR2/Bcl2 via HDAC1 downregulation, thereby providing a potential strategy for treating or preventing HIBD.

ERK Signaling Controls Innate-like CD8+ T Cell Differentiation via the ELK4 (SAP-1) and ELK1 Transcription Factors

In mouse thymocyte development, signaling by the TCR through the ERK pathway is required for positive selection of conventional naive T cells. The Ets transcription factor ELK4 (SAP-1), an ERK-regulated cofactor of the SRF transcription factor, plays an important role in positive selection by activating immediate-early genes such as the Egr transcription factor family. The role of ELK4-SRF signaling in development of other T cell types dependent on ERK signaling has been unclear. In this article, we show that ELK4, and its close relative ELK1, act cell autonomously in the thymus to control the generation of innate-like αβ CD8+ T cells with memory-like characteristics. Mice lacking ELK4 and ELK1 develop increased numbers of innate-like αβ CD8+ T cells, which populate the periphery. These cells develop cell autonomously rather than through expansion of PLZF+ thymocytes and concomitantly increased IL-4 signaling. Their development is associated with reduced TCR-mediated activation of ELK4-SRF target genes and can be partially suppressed by overexpression of the ELK4-SRF target gene EGR2. Consistent with this, partial inhibition of ERK signaling in peripheral CD8+T cells promotes the generation of cells with innate-like characteristics. These data establish that low-level ERK signaling through ELK4 (and ELK1) promotes innate-like αβ CD8+ T cell differentiation, tuning conventional versus innate-like development.

NCOR1-a new player on the field of T cell development

Nuclear receptor corepressor 1 (NCOR1) is a transcriptional corepressor that links chromatin-modifying enzymes with gene-specific transcription factors. Although identified more than 20 years ago as a corepressor of nuclear receptors, the role of NCOR1 in T cells remained only poorly understood. However, recent studies indicate that the survival of developing thymocytes is regulated by NCOR1, revealing an essential role for NCOR1 in the T cell lineage. In this review, we will briefly summarize basic facts about NCOR1 structure and functions. We will further summarize studies demonstrating an essential role for NCOR1 in controlling positive and negative selection of thymocytes during T cell development. Finally, we will discuss similarities and differences between the phenotypes of mice with a T cell-specific deletion of NCOR1 or histone deacetylase 3 (HDAC3), because HDAC3 is the predominant member of the HDAC family that interacts with NCOR1 corepressor complexes. With this review we aim to introduce NCOR1 as a new player in the team of transcriptional coregulators that control T cell development and thus the generation of the peripheral T cell pool.

Id3 Restricts γδ NKT Cell Expansion by Controlling Egr2 and c-Myc Activity

γδ NKT cells are neonatal-derived γδ T lymphocytes that are grouped together with invariant NKT cells based on their shared innate-like developmental program characterized by the transcription factor PLZF (promyelocytic leukemia zinc finger). Previous studies have demonstrated that the population size of γδ NKT cells is tightly controlled by Id3-mediated inhibition of E-protein activity in mice. However, how E proteins promote γδ NKT cell development and expansion remains to be determined. In this study, we report that the transcription factor Egr2, which also activates PLZF expression in invariant NKT cells, is essential for regulating γδ NKT cell expansion. We observed a higher expression of Egr family genes in γδ NKT cells compared with the conventional γδ T cell population. Loss of function of Id3 caused an expansion of γδ NKT cells, which is accompanied by further upregulation of Egr family genes as well as PLZF. Deletion of Egr2 in Id3-deficient γδ NKT cells prevented cell expansion and blocked PLZF upregulation. We further show that this Egr2-mediated γδ NKT cell expansion is dependent on c-Myc. c-Myc knockdown attenuated the proliferation of Id3-deficient γδ NKT cells, whereas c-Myc overexpression enhanced the proliferation of Id3/Egr2-double-deficient γδ NKT cells. Therefore, our data reveal a regulatory circuit involving Egr2-Id3-E2A, which normally restricts the population size of γδ NKT cells by adjusting Egr2 dosage and c-Myc expression.

Gli3 in fetal thymic epithelial cells promotes thymocyte positive selection and differentiation by repression of Shh

Gli3 is a Hedgehog (Hh)-responsive transcription factor that can function as a transcriptional repressor or activator. We show that Gli3 activity in mouse thymic epithelial cells (TECs) promotes positive selection and differentiation from CD4⁺ CD8⁺ to CD4⁺ CD8^- single-positive (SP4) cells in the fetal thymus and that Gli3 represses Shh Constitutive deletion of Gli3, and conditional deletion of Gli3 from TECs, reduced differentiation to SP4, whereas conditional deletion of Gli3 from thymocytes did not. Conditional deletion of Shh from TECs increased differentiation to SP4, and expression of Shh was upregulated in the Gli3-deficient thymus. Use of a transgenic Hh reporter showed that the Hh pathway was active in thymocytes, and increased in the Gli3-deficient fetal thymus. Neutralisation of endogenous Hh proteins in the Gli3^-/- thymus restored SP4 differentiation, indicating that Gli3 in TECs promotes SP4 differentiation by repression of Shh Transcriptome analysis showed that Hh-mediated transcription was increased whereas TCR-mediated transcription was decreased in Gli3^-/- thymocytes compared with wild type.

The corepressor NCOR1 regulates the survival of single-positive thymocytes

Nuclear receptor corepressor 1 (NCOR1) is a transcriptional regulator bridging repressive chromatin modifying enzymes with transcription factors. NCOR1 regulates many biological processes, however its role in T cells is not known. Here we show that Cd4-Cre-mediated deletion of NCOR1 (NCOR1 cKO^Cd4) resulted in a reduction of peripheral T cell numbers due to a decrease in single-positive (SP) thymocytes. In contrast, double-positive (DP) thymocyte numbers were not affected in the absence of NCOR1. The reduction in SP cells was due to diminished survival of NCOR1-null postselection TCRβ^hiCD69⁺ and mature TCRβ^hiCD69^- thymocytes. NCOR1-null thymocytes expressed elevated levels of the pro-apoptotic factor BIM and showed a higher fraction of cleaved caspase 3-positive cells upon TCR stimulation ex vivo. However, staphylococcal enterotoxin B (SEB)-mediated deletion of Vβ8⁺ CD4SP thymocytes was normal, suggesting that negative selection is not altered in the absence of NCOR1. Finally, transgenic expression of the pro-survival protein BCL2 restored the population of CD69⁺ thymocytes in NCOR1 cKO^Cd4 mice to a similar percentage as observed in WT mice. Together, these data identify NCOR1 as a crucial regulator of the survival of SP thymocytes and revealed that NCOR1 is essential for the proper generation of the peripheral T cell pool.

Histone deacetylase 3 is required for iNKT cell development

NKT cells are a distinct subset that have developmental requirements that often differ from conventional T cells. Here, we show that NKT-specific deletion of Hdac3 results in a severe reduction in the number of iNKT cells, particularly of NKT1 cells. In addition, there is decreased cytokine production by Hdac3-deficient NKT2 and NKT17 cells. Hdac3-deficient iNKT cells have increased cell death that is not rescued by transgenic expression of Bcl-2 or Bcl-xL. Hdac3-deficient iNKT cells have less Cyto-ID staining and lower LC3A/B expression, indicative of reduced autophagy. Interestingly, Hdac3-deficient iNKT cells also have lower expression of the nutrient receptors GLUT1, CD71 and CD98, which would increase the need for autophagy when nutrients are limiting. Therefore, Hdac3 is required for iNKT cell development and differentiation.

Nab2 maintains thymus cellularity with aging and stress

Thymic cellularity is influenced by a variety of biological and environmental factors, such as age and stress; however, little is known about the molecular genetic mechanisms that regulate this process. Immediate early genes of the Early growth response (Egr) family have critical roles in immune function and response to environmental stress. The transcription factors, Egr1, Egr2 and Egr3, play roles in the thymus and in peripheral T-cell activation. Nab2, which binds Egrs 1, 2, and 3 as a co-regulator of transcription, also regulates peripheral T-cell activation. However, a role for Nab2 in the thymus has not been reported. Using Nab2-deficient (KO) mice we found that male Nab2KO mice have reduced thymus size and decreased numbers of thymocytes, compared with age-matched wildtype (WT) mice. Furthermore, the number of thymocytes in Nab2KO males decreases more rapidly with age. This effect is sex-dependent as female Nab2KO mice show neither reduced thymocyte numbers nor accelerated thymocyte loss with age, compared to female WT littermates. Since stress induces expression of Nab2 and the Egrs, we examined whether loss of Nab2 alters stress-induced decrease in thymic cellularity. Restraint stress induced a significant decrease in thymic cellularity in Nab2KO and WT mice, with significant changes in the thymocyte subset populations only in the Nab2KO mice. Stress reduced the percentage of DP cells by half and increased the percentage of CD4SP and CD8SP cells by roughly three-fold in Nab2KO mice. These findings indicate a requirement for Nab2 in maintaining thymocyte number in male mice with age and in response to stress.

Egr2 and Egr3 in regulatory T cells cooperatively control systemic autoimmunity through Ltbp3-mediated TGF-β3 production

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease characterized by multiorgan inflammation induced by autoantibodies. Early growth response gene 2 (Egr2), a transcription factor essential for T-cell anergy induction, controls systemic autoimmunity in mice and humans. We have previously identified a subpopulation of CD4⁺ regulatory T cells, CD4⁺CD25^-LAG3⁺ cells, that characteristically express both Egr2 and LAG3 and control mice model of lupus via TGF-β3 production. However, due to the mild phenotype of lymphocyte-specific Egr2-deficient mice, the presence of an additional regulator has been speculated. Here, we show that Egr2 and Egr3 expressed in T cells cooperatively prevent humoral immune responses by supporting TGF-β3 secretion. T cell-specific Egr2/Egr3 double-deficient (Egr2/3DKO) mice spontaneously developed an early onset lupus-like disease that was more severe than in T cell-specific Egr2-deficient mice. In accordance with the observation that CD4⁺CD25^-LAG3⁺ cells from Egr2/3DKO mice completely lost the capacity to produce TGF-β3, the excessive germinal center reaction in Egr2/3DKO mice was suppressed by the adoptive transfer of WT CD4⁺CD25^-LAG3⁺ cells or treatment with a TGF-β3-expressing vector. Intriguingly, latent TGF-β binding protein (Ltbp)3 expression maintained by Egr2 and Egr3 was required for TGF-β3 production from CD4⁺CD25^-LAG3⁺ cells. Because Egr2 and Egr3 did not demonstrate cell intrinsic suppression of the development of follicular helper T cells, Egr2- and Egr3-dependent TGF-β3 production by CD4⁺CD25^-LAG3⁺ cells is critical for controlling excessive B-cell responses. The unique attributes of Egr2/Egr3 in T cells may provide an opportunity for developing novel therapeutics for autoantibody-mediated diseases including SLE.

The roles of Egr-2 in autoimmune diseases

Being a member of the early growth response (Egr) family of transcription factors, Egr-2 is expressed in a variety of cell types of the immune system. Recent findings imply that Egr-2 is important in the development and function of T helper (Th) 17 cell, regulatory T (Treg) cell, as well as dendritic cell (DC). Although these cells perform significantly in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus, multiple sclerosis, and systemic sclerosis, the roles of Egr-2 in the pathogenesis of autoimmune diseases can not be neglected. In this article, we will discuss recent findings about the important roles of Egr-2 in immune cells and the possible pathological roles of Egr-2 in autoimmune diseases.

EGR2 is critical for peripheral naïve T-cell differentiation and the T-cell response to influenza

Early growth response 2 (EGR2) transcription factor negatively regulates T-cell activation, in contrast to the positive regulation of this process by EGR1. Here, we unexpectedly found that EGR2 promotes peripheral naïve T-cell differentiation, with delayed T-cell receptor-induced proliferation in naïve T cells from Egr2 conditional knockout (CKO) mice and decreased production of IFN-γ, IL-4, IL-9, and IL-17A in cells subjected to T-helper differentiation. Moreover, genes that promote T-cell activation, including Tbx21 and Notch1, had decreased expression in Egr2 CKO T cells and are direct EGR2 target genes. Following influenza infection, Egr2 CKO mice had delayed viral clearance, more weight loss, and more severe pathological changes in the lung than did WT and Egr1 KO mice, with decreased production of effector cytokines, increased infiltration of antigen-specific memory-precursor CD8(+) T cells, and lower numbers of lung-resident memory CD8(+) T cells. Thus, unexpectedly, EGR2 can function as a positive regulator that is essential for naïve T-cell differentiation and in vivo T-cell responses to a viral infection.

Triggering receptor expressed on myeloid cells 1 (TREM-1)-mediated Bcl-2 induction prolongs macrophage survival

Triggering receptor expressed on myeloid cells 1 (TREM-1) is a superimmunoglobulin receptor expressed on myeloid cells that plays an important role in the amplification of inflammation. Recent studies suggest a role for TREM-1 in tumor-associated macrophages with relationship to tumor growth and progression. Whether the effects of TREM-1 on inflammation and tumor growth are mediated by an alteration in cell survival signaling is not known. In these studies, we show that TREM-1 knock-out macrophages exhibit an increase in apoptosis of cells in response to lipopolysaccharide (LPS) suggesting a role for TREM-1 in macrophage survival. Specific ligation of TREM-1 with monoclonal TREM-1 (mTREM-1) or overexpression of TREM-1 with adeno-TREM-1 induced B-cell lymphoma-2 (Bcl-2) with depletion of the key executioner caspase-3 prevents the cleavage of poly(ADP-ribose) polymerase. TREM-1 knock-out cells showed lack of induction of Bcl2 with an increase in caspase-3 activation in response to lipopolysaccharide. In addition overexpression of TREM-1 with adeno-TREM-1 led to an increase in mitofusins (MFN1 and MFN2) and knockdown of TREM-1 decreased the expression of mitofusins suggesting that TREM-1 contributes to the maintenance of mitochondrial integrity favoring cell survival. Investigations into potential mechanisms by which TREM-1 alters cell survival showed that TREM-1-induced Bcl-2 in an Egr2-dependent manner. Furthermore, our data shows that expression of Egr2 in response to specific ligation of TREM-1 is ERK mediated. These data for the first time provide novel mechanistic insights into the role of TREM-1 as an anti-apoptotic protein that prolongs macrophage survival.

Zfat-deficiency results in a loss of CD3ζ phosphorylation with dysregulation of ERK and Egr activities leading to impaired positive selection

The human ZFAT gene was originally identified as a susceptibility gene for autoimmune thyroid disease. Mouse Zfat is a critical transcriptional regulator for primitive hematopoiesis and required for peripheral T cell homeostasis. However, its physiological roles in T cell development remain poorly understood. Here, we generated Zfat^f/f-LckCre mice and demonstrated that T cell-specific Zfat-deletion in Zfat^f/f-LckCre mice resulted in a reduction in the number of CD4⁺CD8⁺double-positive (DP) cells, CD4⁺single positive cells and CD8⁺single positive cells. Indeed, in Zfat^f/f-LckCre DP cells, positive selection was severely impaired. Defects of positive selection in Zfat-deficient thymocytes were not restored in the presence of the exogenous TCR by using TCR-transgenic mice. Furthermore, Zfat-deficient DP cells showed a loss of CD3ζ phosphorylation in response to T cell antigen receptor (TCR)-stimulation concomitant with dysregulation of extracellular signal-related kinase (ERK) and early growth response protein (Egr) activities. These results demonstrate that Zfat is required for proper regulation of the TCR-proximal signalings, and is a crucial molecule for positive selection through ERK and Egr activities, thus suggesting that a full understanding of the precise molecular mechanisms of Zfat will provide deeper insight into T cell development and immune regulation.

The Ras GTPase-activating protein neurofibromin 1 promotes the positive selection of thymocytes

TCR-mediated activation of the Ras signaling pathway is critical for T cell development in the thymus and function in the periphery. However, which members of a family of Ras GTPase-activating proteins (RasGAPs) negatively regulate Ras activation in T cells is unknown. In this study we examined a potential function for the neurofibromin 1 (NF1) RasGAP in the T cell lineage with the use of T cell-specific NF1-deficient mice. Surprisingly, on an MHC class I-restricted TCR transgenic background, NF1 was found to promote thymocyte positive selection. By contrast, NF1 neither promoted nor inhibited the negative selection of thymocytes. In the periphery, NF1 was found to be necessary for the maintenance of normal numbers of naïve CD4⁺ and CD8⁺ T cells but was dispensable as a regulator of TCR-induced Ras activation, cytokine synthesis, proliferation and differentiation and death. These findings point to a novel unexpected role for NF1 in T cell development as well as a regulator of T cell homeostasis.

Egr2 induced during DC development acts as an intrinsic negative regulator of DC immunogenicity

Early growth response gene 2 (Egr2), which encodes a zinc finger transcription factor, is rapidly and transiently induced in various cell types independently of de novo protein synthesis. Although a role for Egr2 is well established in T-cell development, Egr2 expression and its biological function in dendritic cells (DCs) have not yet been described. Here, we demonstrate Egr2 expression during DC development, and its role in DC-mediated immune responses. Egr2 is expressed in the later stage of DC development from BM precursor cells. Even at steady state, Egr2 is highly expressed in mouse splenic DCs. Egr2-knockdown (Egr2-KD) DCs showed increased levels of major histocompatability complex (MHC) class I and II and co-stimulatory molecules, and enhanced antigen uptake and migratory capacities. Furthermore, Egr2-KD abolished SOCS1 expression and signal transducer and activator of transcription 5 (STAT5) activation during DC development, probably resulting in the enhancement of IL-12 expression and Th1 immunogenicity of a DC vaccine. DC-mediated cytotoxic T lymphocyte (CTL) activation and antitumor immunity were significantly enhanced by Egr2-KD, and impaired by Egr2 overexpression in antigen-pulsed DC vaccines. These data suggest that Egr2 acts as an intrinsic negative regulator of DC immunogenicity and can be an attractive molecular target for DC vaccine development.

Early growth response gene-2 controls IL-17 expression and Th17 differentiation by negatively regulating Batf

Early growth response gene (Egr)-2 is important for the maintenance of T cell homeostasis and controls the development of autoimmune disease. However, the underlying mechanisms are unknown. We have now discovered that Egr-2, which is induced by TGF-β and IL-6, negatively regulates the expression of IL-17, but not IL-2 or IFN-γ, in effector T cells. In the absence of Egr-2, CD4 T cells produce high levels of Th17 cytokines, which renders mice susceptible to experimental autoimmune encephalomyelitis induction. T cells lacking Egr-2 show increased propensity for Th17, but not Th1 or Th2, differentiation. Control of IL-17 expression and Th17 differentiation by Egr-2 is due to inhibition of Batf, a transcription factor that regulates IL-17 expression and Th17 differentiation. Egr-2 interacts with Batf in CD4 T cells and suppresses its interaction with DNA sequences derived from the IL-17 promoter, whereas the activation of STAT3 and expression of retinoic acid-related orphan receptor γt are unchanged in Th17 cells in the absence of Egr-2. Thus, Egr-2 plays an important role to intrinsically control Th17 differentiation. We also found that CD4 T cells from multiple sclerosis patients have reduced expression of Egr-2 and increased expression of IL-17 following stimulation with anti-CD3 in vitro. Collectively, our results demonstrate that Egr-2 is an intrinsic regulator that controls Th17 differentiation by inhibiting Batf activation, which may be important for the control of multiple sclerosis development.

Genetic association of the EGR2 gene with bipolar disorder in Korea

The early growth response gene 2 (EGR2) is located at chromosome 10q21, one of the susceptibility loci in bipolar disorder (BD). EGR2 is involved in cognitive function, myelination, and signal transduction related to neuregulin-ErbB receptor, Bcl-2 family proteins, and brain-derived neurotrophic factor. This study investigated the genetic association of the EGR2 gene with BD and schizophrenia (SPR) in Korea. In 946 subjects (350 healthy controls, 352 patients with BD, and 244 with SPR), nine single nucleotide polymorphisms (SNPs) in the EGR2 gene region were genotyped. Five SNPs showed nominally significant allelic associations with BD (rs2295814, rs61865882, rs10995315, rs2297488, and rs2297489), and the positive associations of all except rs2297488 remained significant after multiple testing correction. Linkage disequilibrium structure analysis revealed two haplotype blocks. Among the common identified haplotypes (frequency > 5%), 'T-G-A-C-T (block 1)' and 'A-A-G-C (block 2)' haplotypes were over-represented, while 'C-G-G-T-T (block 1)' haplotype was under-represented in BD. In contrast, no significant associations were found with SPR. Although an extended analysis with a larger sample size or independent replication is required, these findings suggest a genetic association of EGR2 with BD. Combined with a plausible biological function of EGR2, the EGR2 gene is a possible susceptibility gene in BD.

Skint-1 identifies a common molecular mechanism for the development of interferon-γ-secreting versus interleukin-17-secreting γδ T cells

Murine T cell development begins with the generation of a unique Vγ5(+)Vδ1(+) epidermal γδ T cell compartment and a unique, more broadly distributed Vγ6(+)Vδ1(+) subset that is an important source of interleukin-17 (IL-17). This study showed that these respective functional programs were determined by Skint-1, a thymic epithelial cell determinant. By engaging Skint-1(+) cells, Vγ5(+)Vδ1(+) thymocytes induced an Egr3-mediated pathway, provoking differentiation and the potential to produce IFN-γ while suppressing the γδ T cell lineage factor, Sox13, and a RORγt transcription factor-associated IL-17-producing capacity. Hence, the functions of the earliest T cells are substantially preprogrammed in the thymus. Additionally, the phenotype of Skint-1-selected fetal thymocytes permitted identification in the adult thymus of an analogous gene regulatory network regulated by the γδ T cell receptor. Hence, these observations describe a molecular pathway by which distinct stress-responsive lymphocyte repertoires may emerge throughout ontogeny and offer parallels with emerging perspectives on the functional selection of other lymphoid cells.

Control of early stages in invariant natural killer T-cell development

Natural killer T (NKT) cells develop in the thymus from the same precursors as conventional CD4(+) and CD8(+) αβ T cells, CD4(+)  CD8(+) double-positive cells. In contrast to conventional αβT cells, which are selected by MHC-peptide complexes presented by thymic epithelial cells, invariant NKT cells are selected by lipid antigens presented by the non-polymorphic, MHC I-like molecule CD1d, present on the surface of other double-positive thymocytes, and require additional signals from the signalling lymphocytic-activation molecule (SLAM) family of receptors. In this review, we provide a discussion of recent findings that have modified our understanding of the NKT cell developmental programme, with an emphasis on events that affect the early stages of this process. This includes factors that control double-positive thymocyte lifespan, and therefore the ability to generate the canonical Vα rearrangements that characterize this lineage, as well as the signal transduction pathways engaged downstream of the T-cell receptor and SLAM molecules.

A role for p120 RasGAP in thymocyte positive selection and survival of naive T cells

Activation of the Ras small GTP-binding protein is necessary for normal T cell development and function. However, it is unknown which Ras GTPase-activating proteins (RasGAPs) inactivate Ras in T cells. We used a T cell-specific RASA1-deficient mouse model to investigate the role of the p120 RasGAP (RASA1) in T cells. Death of CD4(+)CD8(+) double-positive thymocytes was increased in RASA1-deficient mice. Despite this finding, on an MHC class II-restricted TCR transgenic background, evidence was obtained for increased positive selection of thymocytes associated with augmented activation of the Ras-MAPK pathway. In the periphery, RASA1 was found to be dispensable as a regulator of Ras-MAPK activation and T cell functional responses induced by full agonist peptides. However, numbers of naive T cells were substantially reduced in RASA1-deficient mice. Loss of naive T cells in the absence of RASA1 could be attributed in part to impaired responsiveness to the IL-7 prosurvival cytokine. These findings reveal an important role for RASA1 as a regulator of double-positive survival and positive selection in the thymus as well as naive T cell survival in the periphery.

The Ras/MAPK pathway is required for generation of iNKT cells

iNKT cells derive from CD4(+)CD8(+) DP thymocytes, and are selected by thymocyte-thymocyte interactions through signals from their invariant Vα14-Jα18 TCR and from the costimulatory molecules SLAMF1 and SLAMF6. Genetic studies have demonstrated the contribution of different signaling pathways to this process. Surprisingly, current models imply that the Ras/MAPK pathway, one of the critical mediators of conventional αβ T cell positive selection, is not necessary for iNKT cell development. Using mice defective at different levels of this pathway our results refute this paradigm, and demonstrate that Ras, and its downstream effectors Egr-1 and Egr-2 are required for positive selection of iNKT cells. Interestingly our results also show that there are differences in the contributions of several of these molecules to the development of iNKT and conventional αβ T cells.

Early growth response gene-2 (Egr-2) regulates the development of B and T cells

Background

Understanding of how transcription factors are involved in lymphocyte development still remains a challenge. It has been shown that Egr-2 deficiency results in impaired NKT cell development and defective positive selection of T cells. Here we investigated the development of T, B and NKT cells in Egr-2 transgenic mice and the roles in the regulation of distinct stages of B and T cell development.

Methods and Findings

The expression of Egr1, 2 and 3 were analysed at different stages of T and B cell development by RT-PCT and results showed that the expression was strictly regulated at different stages. Forced expression of Egr-2 in CD2⁺ lymphocytes resulted in a severe reduction of CD4⁺CD8⁺ (DP) cells in thymus and pro-B cells in bone marrow, which was associated with reduced expression of Notch1 in ISP thymocytes and Pax5 in pro-B cells, suggesting that retraction of Egr-2 at the ISP and pro-B cell stages is important for the activation of lineage differentiation programs. In contrast to reduction of DP and pro-B cells, Egr-2 enhanced the maturation of DP cells into single positive (SP) T and NKT cells in thymus, and immature B cells into mature B cells in bone marrow.

Conclusions

Our results demonstrate that Egr-2 expressed in restricted stages of lymphocyte development plays a dynamic, but similar role for the development of T, NKT and B cells.

The essential function for serum response factor in T-cell development reflects its specific coupling to extracellular signal-regulated kinase signaling

Serum response factor (SRF) recruits members of two families of signal-regulated coactivators, the extracellular signal-regulated kinase (ERK)-regulated ternary complex factors (TCFs) and the actin-regulated myocardin-related transcription factors (MRTFs), to its target genes through its DNA-binding domain. Whether coactivator association is required for SRF function in vivo and whether particular SRF functions reflect specific coupling to one or the other signal pathway have remained largely unexplored. We show that SRF is essential for thymocyte positive selection and thymic T(reg) and NK T-cell development but dispensable for early thymocyte development and negative selection. Expression of wild-type SRF, or mutants lacking the N-terminal phosphorylation sites or C-terminal transcriptional activation domain, restores positive selection in SRF null thymocytes. In contrast, SRF.V194E, which cannot recruit TCF or MRTF family members, is inactive, although it is recruited to target genes. Fusion of a TCF C-terminal activation domain to SRF.V194E effectively restores ERK-dependent single-positive (SP) thymocyte development. The resulting SP thymocytes exhibit normal surface marker expression and proliferation following T-cell receptor cross-linking. Thus, ERK signaling through the TCF pathway to SRF is necessary and sufficient for SRF function in thymocyte positive selection.

Tenuous paths in unexplored territory: From T cell receptor signaling to effector gene expression during thymocyte selection

During the last step of alphabeta T cell development, thymocytes that have rearranged genes encoding TCR chains and express CD4 and CD8 coreceptors are selected on the basis of their TCR reactivity to escape programmed cell death and become mature CD4 or CD8 T cells. This process is triggered by intrathymic TCR signaling, that activates 'sensor' transcription factors 'constitutively' expressed in DP thymocytes. Eventually, TCR-signaled thymocytes evolve effector transcriptional circuits that control basal metabolism, migration, survival and initiation of lineage-specific gene expression. This review examines how components of the 'sensing' transcription apparatus responds to positive selection signals, and highlights important differences with mature T cell responses. In a second part, we evaluate current observations and hypotheses on the connections between sensing transcription factors and effector circuitries.

The transcription factor c-Myb primes CD4+CD8+ immature thymocytes for selection into the iNKT lineage

Type I invariant NKT cells (iNKT cells) are a subset of alphabeta T cells characterized by the expression of an invariant alpha-chain variable region 14-alpha-chain joining region 18 (V(alpha)14J(alpha)18) T cell antigen receptor (TCR) alpha-chain. The iNKT cells derive from CD4(+)CD8(+) double-positive (DP) thymocytes, and their generation requires a long half-life of DP thymocytes to allow V(alpha)14-J(alpha)18 rearrangements, expression of glycolipid-loaded CD1d on DP thymocytes, and signaling through the signaling-activation molecule SLAM-adaptor SAP pathway. Here we show that the transcription factor c-Myb has a central role in priming DP thymocytes to enter the iNKT lineage by simultaneously regulating CD1d expression, the half-life of DP cells and expression of SLAMF1, SLAMF6 and SAP.

Regulatory polymorphisms in EGR2 are associated with susceptibility to systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease induced by the combinations of environmental and genetic factors. Recently, mice in which the early growth response 2 (EGR2) gene, a zinc-finger transcription factor, is conditionally knocked out in CD2(+) T cells have been shown to develop a lupus-like autoimmune disease. Here, we evaluated if polymorphisms in the EGR2 gene influence SLE susceptibility in humans. We first analyzed the effect of SNPs in the EGR2 region on EGR2 expression, and a significant positive correlation with expression was identified in an SNP located at the 5' flanking region of EGR2 (rs10761670, R=0.23, P=0.00072). We then performed a case-control association study using three sets of SLE cohorts by genotyping 14 tag SNPs in the EGR2 gene region. A peak of association with SLE susceptibility was observed for rs10761670 [Pooled: OR = 1.23 (95% CI 1.10-1.37), P=0.00023). This SNP was also associated with susceptibility to rheumatoid arthritis (RA) [OR = 1.15 (95% CI 1.05-1.26), P = 0.0019), suggesting that EGR2 is a common risk factor for SLE and RA. Among the SNPs in complete linkage disequilibrium with rs10761670 (r(2) = 1.0), two SNPs (rs1412554 and rs1509957) affected the binding of transcription factors and transcriptional activity in vitro, suggesting that they may be candidates of causal regulatory variants in this region. Therefore, EGR2 is a genetic risk factor for SLE, in which increased gene expression may contribute to SLE pathogenesis.

Early growth response 2 regulates the survival of thymocytes during positive selection

The early growth response (Egr) transcription factor family regulates multiple steps during T-cell development. We examine here the role played by Egr2 in positive selection. In double-positive cells, Egr2 is upregulated immediately following TCR ligation, and its expression requires both the MAPK and calcineurin signaling pathways. Inducible transgenic and knockout mice were generated to cause gain- or loss-of-function of Egr2 in double-positive cells, and had reciprocal effects; more mature single-positive cells were made when Egr2 was overexpressed, and fewer when Egr2 was absent. These defects were associated with changes in the survival of positively selected cells rather than perturbation of positive selection or immediate post-selection signaling. The survival function of Egr2 at least partly depends upon its ability to activate the cytokine-mediated survival pathway, likely through negative regulation of both the IL-7R and suppressor of cytokine signaling 1 (Socs1), the molecular switch whose downregulation normally results in restored responsiveness to cytokine signaling following selection. While gain of Egr2 caused a decrease in Socs1 mRNA, loss of Egr2 resulted in downregulation of IL-7R, upregulation of Socs1, and inhibition of Stat5 phosphorylation and IL-7-mediated survival post-selection. Therefore, expression of Egr2 following positive selection links the initial TCR signaling event to subsequent survival of signaled cells.