Overexpression of the Runx3 Transcription Factor Increases the Proportion of Mature Thymocytes of the CD8 Single-Positive Lineage

Intrinsic sexual dimorphism in the placenta determines the differential response to benzene exposure

Maternal immune activation (MIA) by environmental challenges is linked to severe developmental complications, such as neurocognitive disorders, autism, and even fetal/maternal death. Benzene is a major toxic compound in air pollution that affects the mother as well as the fetus and has been associated with reproductive complications. Our objective was to elucidate whether benzene exposure during gestation triggers MIA and its impact on fetal development. We report that benzene exposure during pregnancy leads MIA associated with increased fetal resorptions, fetal growth, and abnormal placenta development. Furthermore, we demonstrate the existence of a sexual dimorphic response to benzene exposure in male and female placentas. The sexual dimorphic response is a consequence of inherent differences between male and female placenta. These data provide crucial information on the origins or sexual dimorphism and how exposure to environmental factors can have a differential impact on the development of male and female offspring.

The TOX subfamily: all-round players in the immune system

The thymocyte selection-related HMG box protein (TOX) subfamily comprises evolutionarily conserved DNA-binding proteins, and is expressed in certain immune cell subsets and plays key roles in the development of CD4+ T cells, innate lymphoid cells (ILCs), T follicular helper (Tfh) cells, and in CD8+ T-cell exhaustion. Although its roles in CD4+ T and natural killer (NK) cells have been extensively studied, recent findings have demonstrated previously unknown roles for TOX in the development of ILCs, Tfh cells, as well as CD8+ T-cell exhaustion; however, the molecular mechanism underlying TOX regulation of these immune cells remains to be elucidated. In this review, we discuss recent studies on the influence of TOX on the development of various immune cells and CD8+ T-cell exhaustion and the roles of specific TOX family members in the immune system. Moreover, this review suggests candidate regulatory targets for cell therapy and immunotherapies.

Transcriptional programming and gene regulation in WC1+ γδ T cell subpopulations

γδ T cells represent a high proportion of lymphocytes in the blood of ruminants with the majority expressing lineage-specific glycoproteins from the WC1 family. WC1 receptors are coded for by a multigenic array whose genes have variegated but stable expression among cells in the γδ T cell population. WC1 molecules function as hybrid pattern recognition receptors as well as co-receptors for the TCR and are required for responses by the cells. Because of the variegated gene expression, WC1⁺ γδ T cells can be divided into two main populations known as WC1.1⁺ and WC1.2⁺ based on monoclonal antibody reactivity with the expressed WC1 molecules. These subpopulations differ in their ability to respond to specific pathogens. Here, we showed these populations are established in the thymus and that WC1.1⁺ and WC1.2⁺ subpopulations have transcriptional programming that is consistent with stratification towards Tγδ1 or Tγδ17. WC1.1⁺ cells exhibited the Tγδ1 phenotype with greater transcription of Tbx21 and production of more IFNγ while the WC1.2⁺ subpopulation tended towards Tγδ17 programming producing higher levels of IL-17 and had greater transcription of Rorc. However, when activated both WC1⁺ subpopulations' cells transcribed Tbx21 and secreted IFNγ and IL-17 reflecting the complexity of these subpopulations defined by WC1 gene expression. The gene networks involved in development of these two subpopulations including expression of their archetypal genes wc1-3 (WC1.1⁺) and wc1-4 (WC1.2⁺) were unknown but we report that SOX-13, a γδ T cell fate-determining transcription factor, has differential occupancy on these WC1 gene loci and suggest a model for development of these subpopulations.

NR4A3 Mediates Thymic Negative Selection

Central tolerance aims to limit the production of T lymphocytes bearing TCR with high affinity for self-peptide presented by MHC molecules. The accumulation of thymocytes with such receptors is limited by negative selection or by diversion into alternative differentiation, including T regulatory cell commitment. A role for the orphan nuclear receptor NR4A3 in negative selection has been suggested, but its function in this process has never been investigated. We find that Nr4a3 transcription is upregulated in postselection double-positive thymocytes, particularly those that have received a strong selecting signal and are destined for negative selection. Indeed, we found an accumulation of cells bearing a negative selection phenotype in NR4A3-deficient mice as compared with wild-type controls, suggesting that Nr4a3 transcriptional induction is necessary to limit accumulation of self-reactive thymocytes. This is consistent with a decrease of cleaved caspase-3⁺-signaled thymocytes and more T regulatory and CD4⁺Foxp3^-HELIOS⁺ cells in the NR4A3-deficient thymus. We further tested the role for NR4A3 in negative selection by reconstituting transgenic mice expressing the OVA Ag under the control of the insulin promoter with bone marrow cells from OT-I Nr4a3 ^+/+ or OT-I Nr4a3 ^-/- mice. Accumulation of autoreactive CD8 thymocytes and autoimmune diabetes developed only in the absence of NR4A3. Overall, our results demonstrate an important role for NR4A3 in T cell development.

Endothelial transdifferentiation of human HGC-27 gastric cancer cells in vitro

Malignant tumor cells are able to transdifferentiate into other cell types in various tissues or organs. Recent studies have demonstrated the ability of cancer cells to transdifferentiate into functional endothelial cells (ECs). However, whether human gastric cancer (GC) cells are able to transdifferentiate into other cell types has remained largely elusive. Furthermore, whether HGC-27 cells are able to participate in GC angiogenesis remains to be clarified. In the present study, the HGC-27 cell line grown under hypoxic conditions for 4 days exhibited the typical ‘flagstone’ appearance, which is typical for cultured ECs. HGC-27 cells cultured on Matrigel under hypoxic conditions gradually formed net-like structures. Furthermore, the cultured HGC-27 cells expressed CD31, CD34 and von Willebrand factor, the molecular markers for ECs, under hypoxic conditions. These results indicated that HGC-27 cells, cultured under hypoxic conditions, are able to transdifferentiate into EC-like cells in vitro.

Twist2 promotes CD8+ T-cell differentiation by repressing ThPOK expression

CD4/CD8 T-cell lineage differentiation is a key process in immune system development; however, a defined regulator(s) that converts the signal from T-cell receptor and co-receptor complexes into lineage differentiation remains unclear. Here, we show that Twist2 is a critical factor in CD4/CD8 thymocyte differentiation. Twist2 expression is differentially regulated by T-cell receptor signaling, leading to differentiation into the CD4 or CD8 lineage. Forced Twist2 expression perturbed CD4⁺ thymocyte differentiation while enhancing CD8⁺ thymocyte differentiation. Furthermore, Twist2 expression produced mature CD8⁺ thymocytes in B₂m^-/- mice, while its deficiency significantly impaired CD8⁺ cells in MHC class-II^-/- and TCR transgenic mice, favoring CD8 T-cell differentiation. During CD8 lineage differentiation, Twist2 interacted with Runx3 to bind to the silencer region of the ThPOK locus, thereby blocking ThPOK expression. These findings indicate that Twist2 is a part of the transcription factor network controlling CD8 lineage differentiation.

RUNX transcription factors: orchestrators of development

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

HDAC3 restrains CD8-lineage genes to maintain a bi-potential state in CD4+CD8+ thymocytes for CD4-lineage commitment

CD4 and CD8 T cells are vital components of the immune system. We found that histone deacetylase 3 (HDAC3) is critical for the development of CD4 T cells, as HDAC3-deficient DP thymocytes generate only CD8SP thymocytes in mice. In the absence of HDAC3, MHC Class II-restricted OT-II thymocytes are redirected to the CD8 cytotoxic lineage, which occurs with accelerated kinetics. Analysis of histone acetylation and RNA-seq reveals that HDAC3-deficient DP thymocytes are biased towards the CD8 lineage prior to positive selection. Commitment to the CD4 or CD8 lineage is determined by whether persistent TCR signaling or cytokine signaling predominates, respectively. Despite elevated IL-21R/γc/STAT5 signaling in HDAC3-deficient DP thymocytes, blocking IL-21R does not restore CD4 lineage commitment. Instead, HDAC3 binds directly to CD8-lineage promoting genes. Thus, HDAC3 is required to restrain CD8-lineage genes in DP thymocytes for the generation of CD4 T cells.

Mice Deficient in Nucleoporin Nup210 Develop Peripheral T Cell Alterations

The nucleopore is an essential structure of the eukaryotic cell, regulating passage between the nucleus and cytoplasm. While individual functions of core nucleopore proteins have been identified, the role of other components, such as Nup210, are poorly defined. Here, through the use of an unbiased ENU mutagenesis screen for mutations effecting the peripheral T cell compartment, we identified a Nup210 mutation in a mouse strain with altered CD4/CD8 T cell ratios. Through the generation of Nup210 knockout mice we identified Nup210 as having a T cell-intrinsic function in the peripheral homeostasis of T cells. Remarkably, despite the deep evolutionary conservation of this key nucleopore complex member, no other major phenotypes developed, with viable and healthy knockout mice. These results identify Nup210 as an important nucleopore complex component for peripheral T cells, and raise further questions of why this nucleopore component shows deep evolutionary conservation despite seemingly redundant functions in most cell types.

Identification of lineage-specifying cytokines that signal all CD8+-cytotoxic-lineage-fate 'decisions' in the thymus

T cell antigen receptor (TCR) signaling in the thymus initiates positive selection but CD8 lineage fate is thought to be induced by cytokines after TCR signaling has ceased, although this remains controversial and unproven. We now identify four non-common gamma chain (γc) receptor-signaling cytokines (IL-6, IFN-γ, TSLP, TGF-β) that, like IL-7 and IL-15, induce expression of the lineage-specifying transcription factor Runx3d and signal the generation of CD8 T cells. Remarkably, elimination of in vivo signaling by all ‘lineage-specifying cytokines’ during positive selection eliminated Runx3d expression and completely abrogated CD8 single-positive thymocyte generation. Thus, this study proves that signaling during positive selection by lineage-specifying cytokines is responsible for all CD8 lineage fate decisions in the thymus.

Goldmine integrates information placing genomic ranges into meaningful biological contexts

Bioinformatic analysis often produces large sets of genomic ranges that can be difficult to interpret in the absence of genomic context. Goldmine annotates genomic ranges from any source with gene model and feature contexts to facilitate global descriptions and candidate loci discovery. We demonstrate the value of genomic context by using Goldmine to elucidate context dynamics in transcription factor binding and to reveal differentially methylated regions (DMRs) with context-specific functional correlations. The open source R package and documentation for Goldmine are available at http://jeffbhasin.github.io/goldmine.

Restriction of Nonpermissive RUNX3 Protein Expression in T Lymphocytes by the Kozak Sequence

The transcription factor Runx3 promotes differentiation of naive CD4(+) T cells into type-1 effector T (TH1) cells at the expense of TH2. TH1 cells as well as CD8(+) T cells express a subset-specific Runx3 transcript from a distal promoter, which is necessary for high protein expression. However, all T cell subsets, including naive CD4(+) T cells and TH2 cells, express a distinct transcript of Runx3 that is derived from a proximal promoter and that produces functional protein in neurons. Therefore, accumulation of RUNX3 protein generated from the proximal transcript needs to be repressed at the posttranscriptional level to preserve CD4(+) T cell capability of differentiating into TH2 cells. In this article, we show that expression of RUNX3 protein from the proximal Runx3 transcript is blocked at the level of translational initiation in T cells. A coding sequence for the proximal Runx3 mRNA is preceded by a nonoptimal context sequence for translational initiation, known as the Kozak sequence, and thus generates protein at low efficiencies and with multiple alternative translational initiations. Editing the endogenous initiation context to an "optimal" Kozak sequence in a human T cell line resulted in enhanced translation of a single RUNX3 protein derived from the proximal transcript. Furthermore, RUNX3 protein represses transcription from the proximal promoter in T cells. These results suggest that nonpermissive expression of RUNX3 protein is restricted at the translational level, and that the repression is further enforced by a transcriptional regulation for maintenance of diverse developmental plasticity of T cells for different effector subsets.

The nuclear receptor nr4a1 controls CD8 T cell development through transcriptional suppression of runx3

The NR4A nuclear receptor family member Nr4a1 is strongly induced in thymocytes undergoing selection, and has been shown to control the development of T_reg cells; however the role of Nr4a1 in CD8⁺ T cells remains undefined. Here we report a novel role for Nr4a1 in regulating the development and frequency of CD8⁺ T cells through direct transcriptional control of Runx3. We discovered that Nr4a1 recruits the corepressor, CoREST to suppress Runx3 expression in CD8⁺ T cells. Loss of Nr4a1 results in increased Runx3 expression in thymocytes which consequently causes a 2-fold increase in the frequency and total number of intrathymic and peripheral CD8⁺ T cells. Our findings establish Nr4a1 as a novel and critical player in the regulation of CD8 T cell development through the direct suppression of Runx3.

TCF-1 and LEF-1 act upstream of Th-POK to promote the CD4(+) T cell fate and interact with Runx3 to silence Cd4 in CD8(+) T cells

The transcription factors TCF-1 and LEF-1 are essential for early T cell development, but their roles beyond the CD4(+)CD8(+) double-positive (DP) stage are unknown. By specific ablation of these factors in DP thymocytes, we demonstrated that deficiency in TCF-1 and LEF-1 diminished the output of CD4(+) T cells and redirected CD4(+) T cells to a CD8(+) T cell fate. The role of TCF-1 and LEF-1 in the CD4-versus-CD8 lineage 'choice' was mediated in part by direct positive regulation of the transcription factor Th-POK. Furthermore, loss of TCF-1 and LEF-1 unexpectedly caused derepression of CD4 expression in T cells committed to the CD8(+) lineage without affecting the expression of Runx transcription factors. Instead, TCF-1 physically interacted with Runx3 to cooperatively silence Cd4. Thus, TCF-1 and LEF-1 adopted distinct genetic 'wiring' to promote the CD4(+) T cell fate and establish CD8(+) T cell identity.

CD4 CTL: living up to the challenge

During thymic development, thymocytes expressing a T cell receptor consisting of an alpha and beta chain (TCRαβ), commit to either the cytotoxic- or T helper-lineage fate. This lineage dichotomy is controlled by key transcription factors, including the T helper (Th) lineage master regulator, the Th-inducing BTB/POZ domain-containing Kruppel-like zinc-finger transcription factor, ThPOK, (formally cKrox or Zfp67; encoded by Zbtb7b), which suppresses the cytolytic program in major histocompatibility complex (MHC) class II-restricted CD4(+) thymocytes and the Runt related transcription factor 3 (Runx3), which counteracts ThPOK in MHC class I restricted precursor cells and promotes the lineage commitment of CD8αβ(+) cytolytic T lymphocytes (CTL). ThPOK continues to repress the CTL gene program in mature CD4(+) T cells, even as they differentiate into effector Th cell subsets. The Th cell fate however is not fixed and two recent studies showed that mature, antigen-stimulated CD4(+) T cells have the flexibility to terminate the expression of ThPOK and functionally reprogram to cytotoxic effector cells. This unexpected plasticity of CD4(+) T cells results in the post-thymic termination of the Th lineage fate and the functional differentiation of distinct MHC class II-restricted CD4(+) CTL. The recognition of CD4 CTL as a defined separate subset of effector cells and the identification of the mechanisms and factors that drive their reprogramming finally create new opportunities to explore the physiological relevance of these effector cells in vivo and to determine their pivotal roles in both, protective immunity as well as in immune-related pathology.

Whole-blood gene expression profiling in ankylosing spondylitis identifies novel candidate genes that may contribute to the inflammatory and tissue-destructive disease aspects

We performed a comprehensive gene expression analysis to identify differentially expressed genes (DEGs) between AS (ankylosing spondylitis) and health controls. A total of 1454 DEGs were obtained, including 919 up-regulated genes and 535 down-regulated genes. There were 218 interactions and 224 pairs in the conPPI network. Topological analysis showed that 11 genes had a close relationship with AS. GO (gene ontology) functional enrichment analysis of the two modules showed that the DEGs in conPPI mainly participated in the biologic process of immune response. The KEGG pathway analysis showed that most DEGs in the two modules were enriched into cell receptor signaling pathway, natural killer cell mediated cytotoxicity and primary immunodeficiency. We hypothesized that these DEGs associated with immune response DEGs might provide basic for depth understanding of the AS development.

Thpok-independent repression of Runx3 by Gata3 during CD4+ T-cell differentiation in the thymus

CD4(+) helper T cells are essential for immune responses and differentiate in the thymus from CD4(+) CD8(+) "double-positive" (DP) thymocytes. The transcription factor Runx3 inhibits CD4(+) T-cell differentiation by repressing Cd4 gene expression; accordingly, Runx3 is not expressed in DP thymocytes or developing CD4(+) T cells. The transcription factor Thpok is upregulated in CD4-differentiating thymocytes and required to repress Runx3. However, how Runx3 is controlled at early stages of CD4(+) T-cell differentiation, before the onset of Thpok expression, remains unknown. Here we show that Gata3, a transcription factor preferentially and transiently upregulated by CD4(+) T-cell precursors, represses Runx3 and binds the Runx3 locus in vivo. Accordingly, we show that high-level Gata3 expression and expression of Runx3 are mutually exclusive. Furthermore, whereas Runx3 represses Cd4, we show that Gata3 promotes Cd4 expression in Thpok-deficient thymocytes. Thus, in addition to its previously documented role in promoting CD4-lineage gene-expression, Gata3 represses CD8-lineage gene expression. These findings identify Gata3 as a critical pivot of CD4-CD8 lineage differentiation.

Comparative and functional evaluation of in vitro generated to ex vivo CD8 T cells

The generation of the cytotoxic CD8 T cell response is dependent on the functional outcomes imposed by the intrathymic constraints of differentiation and self-tolerance. Although thymic function can be partly replicated in vitro using OP9-DL1 cell cultures to yield CD8 αβ TCR-bearing cells from hematopoietic progenitor cells, a comprehensive and functional assessment of entirely in vitro generated CD8 T cells derived from bone marrow hematopoietic stem cells has not been established and remains controversial. In this study, we demonstrate that a phenotypic, molecular, and functional signature of in vitro derived CD8 T cells is akin to that of ex vivo CD8 T cells, although several significant differences were also observed. Transfer of in vitro derived CD8 T cells into syngeneic and immunodeficient host mice showed no graft-versus-host response, whereas a robust homeostatic proliferation was observed, respectively. These findings, along with a diverse and broad TCR repertoire expressed by the in vitro derived CD8 T cells, allowed for the successful generation of Ag-specific T cells to be obtained from an entirely in vitro generated CD8 T cell pool. These findings support the use of Ag-specific in vitro derived effector CD8 T cells for immune reconstitution approaches, which would be amenable to further tailoring for their use against viral infections or malignancies.

E protein transcription factors are required for the development of CD4(+) lineage T cells

The double-positive (DP) to single-positive (SP) transition during T cell development is initiated by downregulation of the E protein transcription factors HEB and E2A. Here, we have demonstrated that in addition to regulating the onset of this transition, HEB and E2A also play a separate role in CD4(+) lineage choice. Deletion of HEB and E2A in DP thymocytes specifically blocked the development of CD4(+) lineage T cells. Furthermore, deletion of the E protein inhibitors Id2 and Id3 allowed CD4(+) T cell development but blocked CD8(+) lineage development. Analysis of the CD4(+) lineage transcriptional regulators ThPOK and Gata3 placed HEB and E2A upstream of CD4(+) lineage specification. These studies identify an important role for E proteins in the activation of CD4(+) lineage differentiation as thymocytes undergo the DP to SP transition.

The many roles of TOX in the immune system

TOX is a member of an evolutionarily conserved DNA-binding protein family and is expressed in several immune-relevant cell subsets. Here, we review the key role of TOX in regulating development of CD4 T cells, natural killer cells and lymphoid tissue inducer cells, the latter responsible for the generation of lymph nodes. Although the exact molecular mechanism of action of TOX remains to be elucidated, the role of TOX in establishment of gene programs in the thymus and the potential of TOX as a regulator of E protein activity are discussed.

TOX is required for development of the CD4 T cell lineage gene program

The factors that regulate thymic development of the CD4(+) T cell gene program remain poorly defined. The transcriptional regulator ThPOK is a dominant factor in CD4(+) T cell development, which functions primarily to repress the CD8 lineage fate. Previously, we showed that nuclear protein TOX is also required for murine CD4(+) T cell development. In this study, we sought to investigate whether the requirement for TOX was solely due to a role in ThPOK induction. In apparent support of this proposition, ThPOK upregulation and CD8 lineage repression were compromised in the absence of TOX, and enforced ThPOK expression could restore some CD4 development. However, these "rescued" CD4 cells were defective in many aspects of the CD4(+) T cell gene program, including expression of Id2, Foxo1, and endogenous Thpok, among others. Thus, TOX is necessary to establish the CD4(+) T cell lineage gene program, independent of its influence on ThPOK expression.

Maintaining CD4-CD8 lineage integrity in T cells: where plasticity serves versatility

The divergence of the two αβ T cell subsets defined by the mutually exclusive expression of CD4 and CD8 glycoproteins is an important event during the intrathymic differentiation of T lymphocytes. This reviews briefly summarizes the mechanisms that promote commitment to the CD4 or CD8 lineage in the thymus, and discusses the transcription factor circuits and epigenetic mechanisms that concur to maintain lineage integrity in post-thymic cells and yet allow effector cell differentiation.

The pre-TCR signal induces transcriptional silencing of the TCRγ locus by reducing the recruitment of STAT5 and Runx to transcriptional enhancers

The mouse TCRγ locus is positively regulated by the transcription factors STAT5 and Runx. While the locus undergoes frequent rearrangements in T lymphocytes, TCRγ transcription is repressed in αβ T cells. This phenomenon, known as TCRγ silencing, depends on pre-TCR-induced thymocyte proliferation. The molecular basis for TCRγ silencing, however, is largely unknown. Here, we show that pre-TCR signaling reduces transcription and histone acetylation of the TCRγ locus irrespective of V-J rearrangements. We also demonstrate that Runx is recruited to Eγ and HsA enhancer elements of the TCRγ locus, primarily at the CD4(-)CD8(-) double-negative stage and that Runx binding to these elements decreases at later stages of thymocyte development. Importantly, anti-CD3 antibody treatment decreased IL-7R expression levels, STAT5 phosphorylation and recruitment of STAT5 and Runx to Eγ and HsA elements in RAG2-deficient thymocytes, suggesting that pre-TCR signaling triggers reduced binding of STAT5 and Runx to the enhancer elements. Furthermore, we observed that misexpression of STAT5 or Runx in the CD4(+)CD8(+) double-positive cell line DPK induces TCRγ gene transcription. Finally, we showed that TCRγ transcription is induced in αβ T cells from Runx3 transgenic mice, suggesting that Runx3 counteracts TCRγ silencing in αβ T cells in vivo. Our results suggest that pre-TCR signaling indirectly inactivates TCRγ enhancers by reducing recruitment of STAT5 and Runx and imply that this effect is an important step for TCRγ silencing in αβ T cells.

Runx3 suppresses gastric cancer metastasis through inactivation of MMP9 by upregulation of TIMP-1

Recent studies have suggested that loss of RUNX3 expression is involved with gastric tumor metastasis. However, the precise mechanism of RUNX3-mediated suppression of tumor metastasis remains elusive. We aimed to clarify the effect of RUNX3 on tumor metastasis in gastric cancer cell lines and tumors. Immunohistochemistry revealed that RUNX3 was significantly decreased in metastatic gastric cancer. Gelatin zymography and Western blot showed that instead of regulating matrix metalloproteinase 9 (MMP9) expression, RUNX3 expression inhibited MMP9 enzyme activity, and this was consistent with the upregulation of tissue inhibitor of metalloproteinases 1 (TIMP1) by RUNX3. TIMP1 siRNA treatment impaired RUNX3-mediated suppression of gastric cancer cell invasion. Reporter assays demonstrated regulation of TIMP-1 by RUNX3. Two RUNX3 binding sites were identified in the TIMP-1 promoter and direct interaction of RUNX3 with the TIMP-1 promoter was confirmed in vitro and in vivo. These findings provide evidence for RUNX3-mediated suppression of gastric cancer invasion and metastasis and define a novel molecular mechanism that for the metastasis-inhibiting activity of RUNX3. These data may be applied in the development of RUNX3 for gastric cancer metastasis diagnostics and therapeutics.

Expanding roles for ThPOK in thymic development

The role of the zinc finger transcription factor ThPOK (T-helper-inducing POZ-Kruppel-like factor) in promoting commitment of αβ T cells to the CD4 lineage is now well established. New results indicate that ThPOK is also important for the development and/or acquisition of effector functions by other T cell subsets, including several not marked by CD4 expression, i.e. double-negative invariant natural killer T (iNKT) cells, γδ cells, and even memory CD8(+) T cells. There is compelling evidence that ThPOK expression in most or all of these cases is dependent on T-cell receptor signaling and that differences in relative TCR signal strength/length may induce different levels of ThPOK expression. The developmental consequences of ThPOK expression vary according to cell type, which may partly reflect differences in ThPOK levels and/or in transcriptional networks between cell types.

Runx3 is required for full activation of regulatory T cells to prevent colitis-associated tumor formation

Inflammation is increasingly recognized as an essential component of tumorigenesis, which is promoted and suppressed by various T cell subsets acting in different ways. It was shown previously in Runx3-deficient mice that differentiation of CD8 T and NK cells is perturbed. In this study, we show that Runx3 is also required for proper differentiation and function of regulatory T cells. In Runx3-deficient mice, T cells were unable to inhibit inflammation and to suppress tumor development. As expected, recombination activating gene 2-deficient mice bearing Runx3-deficient lymphocytes spontaneously developed colon tumors. However, tumor formation was completely blocked by transfer of either regulatory T cells or CD8 T cells derived from wild-type mice to mutant mice or by housing mutant mice in a specific pathogen-free condition. These results indicate that Runx3-deficient lymphocytes and microorganisms act together to induce inflammation and consequently induce the development of colon tumors.

Down-regulation of Runx1 expression by TCR signal involves an autoregulatory mechanism and contributes to IL-2 production

Runx1 transcription factor plays multiple roles in T cell development, differentiation, and function. However, the regulatory mechanisms and functional significance of high Runx1 protein expression in resting peripheral CD4+ T cells is not well understood. Here, we demonstrate that T-cell receptor (TCR) activation down-regulates distal Runx1 transcription, resulting in a significant reduction of Runx1 protein. Interestingly, this down-regulation of distal Runx1 transcription appears to be mediated through a negative auto-regulatory mechanism, whereby Runx1 protein binds to a Runx consensus site in the distal promoter. Through the use of Runx1-overexpressing cells from transgenic mice, we demonstrate that interference with TCR-mediated Runx1 down-regulation inhibits IL-2 production and proliferation in activated CD4+ T cells. In contrast, using Runx1-deficient cells prepared from targeted mice, we show that the absence of Runx1 in unstimulated CD4+ T cells results in IL-2 derepression. In summary, we propose that high levels of Runx1 in resting CD4+ T cells functions negatively in the regulation of IL-2 transcription, and that TCR activation-mediated down-regulation of Runx1 involves negative auto-regulation of the distal Runx1 promoter and contributes to IL-2 production.

Functions of Runx in IgA class switch recombination

Runt-related (Runx) transcriptional regulators play essential roles in various cell fate determination processes, and dysfunction of these regulators causes many human diseases. Considerable insight into the functions of Runx proteins was provided mainly by studies of hematopoietic and skeletal disorders. Recently, extensive investigations have revealed new functions of these transcription factors in immune cell differentiation and functioning. In the present review, we discuss the mechanisms of selective IgA production in the intestine and report the involvement of Runx proteins in this process.

Transcriptional and epigenetic regulation of CD4/CD8 lineage choice

The helper versus cytotoxic-lineage choice of CD4(+)CD8(+) DP thymocytes correlates with MHC restriction of their T cell receptors and the termination of either CD8 or CD4 coreceptor expression. It has been hypothesized that transcription factors regulating the expression of the Cd4/Cd8 coreceptor genes must play a role in regulating the lineage decision of DP thymocytes. Indeed, progress made during the past decade led to the identification of several transcription factors that regulate CD4/CD8 expression that are as well important regulators of helper/cytotoxic cell fate choice. These studies provided insight into the molecular link between the regulation of coreceptor expression and lineage decision. However, studies initiated by the identification of ThPOK, a central transcription factor for helper T cell development, have offered another perspective on the cross-regulation between these two processes. Here, we review advances in our understanding of regulatory circuits composed of transcription factors and their link to epigenetic mechanisms, which play essential roles in specifying and sealing cell lineage identity during the CD4/CD8 commitment process of DP thymocytes.

Interplay of transcription factors in T-cell differentiation and function: the role of Runx

Over the past years, increasing numbers of distinct subsets have been discovered and identified for a T lymphocytes' entity. Differentiation and function of each T cell subset are controlled by a specific master transcription factor. Importantly, Runt-related transcription factors, particularly Runx1 and Runx3, interplay with these master regulators in various aspects of T cells' immunity. In this review article, we first explain roles of Th-Pok and Runx3 in differentiation of CD4 versus CD8 single positive cells, and later focus on cross-regulation of Th-Pok and Runx3 and their relationship with other factors such as TCR strength. Next, we provide evidences for the direct interplay of Runx1/3 with T-bet and GATA3 during Th1 versus Th2 commitment to activate or silence transcription of signature cytokine genes, IFNγ and IL4. Lastly, we explain feed-forward relationship between Runx1 and Foxp3 and discuss roles of Runx1 in regulatory T cells' suppressive activity. This review highlights an essential importance of Runx molecules in controlling various T cell subsets' differentiation and functions through molecular interplay with the master transcription factors in terms of protein-protein interaction as well as regulation of gene expression.

The network of transcription factors that underlie the CD4 versus CD8 lineage decision

Virtually all mature T cells are CD4(+)CD8(-) or CD4(-)CD8(+) and this not only is their most important surface-phenotype distinction but also has crucial functional consequences for the entire immune response. Both subsets arise from double-positive thymocytes, and much has been learned about the molecular events that govern this lineage bifurcation process. As detailed in this review, the signaling pathways and specific molecules that control this process are now being discovered. In particular, the transcription factors ThPOK (T-helper inducing POZ-Kruppel factor) and Runx3 have emerged as the crucial regulators of helper lineage commitment and the cytotoxic lineage, respectively. This article describes their antagonistic interaction that is an important mechanism of the lineage specification, as well as the hierarchy and importance of several other transcription factors and cytokine signals in the network of pathways that govern thymocyte helper/cytotoxic lineage commitment.

Gfi1 expression is controlled by five distinct regulatory regions spread over 100 kilobases, with Scl/Tal1, Gata2, PU.1, Erg, Meis1, and Runx1 acting as upstream regulators in early hematopoietic cells

The growth factor independence 1 (Gfi1) gene was originally discovered in the hematopoietic system, where it functions as a key regulator of stem cell homeostasis, as well as neutrophil and T-cell development. Outside the blood system, Gfi1 is essential for inner-ear hair and intestinal secretory cell differentiation. To understand the regulatory hierarchies within which Gfi1 operates to control these diverse biological functions, we used a combination of comparative genomics, locus-wide chromatin immunoprecipitation assays, functional validation in cell lines, and extensive transgenic mouse assays to identify and characterize the complete ensemble of Gfi1 regulatory elements. This concerted effort identified five distinct regulatory elements spread over 100kb each driving expression in transgenic mice to a subdomain of endogenous Gfi1. Detailed characterization of an enhancer 35 kb upstream of Gfi1 demonstrated activity in the dorsal aorta region and fetal liver in transgenic mice, which was bound by key stem cell transcription factors Scl/Tal1, PU.1/Sfpi1, Runx1, Erg, Meis1, and Gata2. Taken together, our results reveal the regulatory regions responsible for Gfi1 expression and importantly establish that Gfi1 expression at the sites of hematopoietic stem cell (HSC) emergence is controlled by key HSC regulators, thus integrating Gfi1 into the wider HSC regulatory networks.

The role of ThPOK in control of CD4/CD8 lineage commitment

During alphabeta T cell development, cells diverge into alternate CD4 helper and CD8(+) cytotoxic T cell lineages. The precise correlation between a T cell's CD8 and CD4 choice and its TCR specificity to class I or class II MHC was noted more than 20 years ago, and establishing the underlying mechanism has remained a focus of intense study since then. This review deals with three formerly discrete topics that are gradually becoming interconnected: the role of TCR signaling in lineage commitment, the regulation of expression of the CD4 and CD8 genes, and transcriptional regulation of lineage commitment. It is widely accepted that TCR signaling exerts a decisive influence on lineage choice, although the underlying mechanism remains intensely debated. Current evidence suggests that both duration and intensity of TCR signaling may control lineage choice, as proposed by the kinetic signaling and quantitative instructive models, respectively. Alternate expression of the CD4 and CD8 genes is the most visible manifestation of lineage choice, and much progress has been made in defining the responsible cis elements and transcription factors. Finally, important clues to the molecular basis of lineage commitment have been provided by the recent identification of the transcription factor ThPOK as a key regulator of lineage choice. ThPOK is selectively expressed in class II-restricted cells at the CD4(+)8(lo) stage and is necessary and sufficient for development to the CD4 lineage. Given the central role of ThPOK in lineage commitment, understanding its upstream regulation and downstream gene targets is expected to reveal further important aspects of the molecular machinery underlying lineage commitment.

The Runx3 transcription factor augments Th1 and down-modulates Th2 phenotypes by interacting with and attenuating GATA3

Recently, it was reported that the expression of Runt-related transcription factor 3 (Runx3) is up-regulated in CD4(+) helper T cells during Th1 cell differentiation, and that Runx3 functions in a positive feed-forward manner with the T-box family transcription factor, T-bet, which is a master regulator of Th1 cell differentiation. The relative expression levels of IFN-gamma and IL-4 are also regulated by the Th2-associated transcription factor, GATA3. Here, we demonstrate that Runx3 was induced in Th2 as well as Th1 cells and that Runx3 interacted with GATA3 and attenuated GATA3 transcriptional activity. Ectopic expression of Runx3 in vitro in cultured cells or transgenic expression of Runx3 in mice accelerated CD4(+) cells to a Th1-biased population or down-modulated Th2 responses, in part by neutralizing GATA3. Our results suggest that the balance of Runx3 and GATA3 is one factor that influences the manifestation of CD4(+) cells as the Th1 or Th2 phenotypes.

Serial OX40 engagement on CD4+ T cells and natural killer T cells causes allergic airway inflammation

RATIONALE

OX40-OX40 ligand (OX40L) interactions have been proposed to support induction of allergic airway inflammation, which may be attributable to OX40 signaling in CD4(+) helper T cells for adaptive immune responses. However, a possible involvement of natural killer T (NKT) cells in the pathogenesis suggests that the underlying mechanisms are not yet fully elucidated.

OBJECTIVES

We aimed to characterize the OX40-modulated cellular contribution to allergic airway inflammation in a mouse model of house dust mite (HDM) allergen exposure.

METHODS

Mice were sensitized to HDM and, 3 weeks later, challenged with HDM on three consecutive days through the airways. Two days after the last exposure, bronchoalveolar lavage fluids and blood samples and lung tissues were evaluated for the airway inflammation.

MEASUREMENTS AND MAIN RESULTS

The development of HDM-induced eosinophilic airway inflammation was dependent on OX40 of both CD4(+) T cells and NKT cells; OX40 engagement on CD4(+) T cells in the sensitization led to pulmonary OX40L augmentation after the allergen challenge, which stimulated pulmonary NKT cells through OX40 to provide the pathogenic cytokine milieu. This was ablated by OX40L blockade by inhalation of the neutralizing antibody during the challenge, suggesting the therapeutic potential of targeting pulmonary OX40-OX40L interactions. Moreover, OX40 expression in CD4(+) T cells, but not in NKT cells, was reciprocally regulated by the helper T cell type 1-skewing transcription factor Runx3.

CONCLUSIONS

OX40 on not only CD4(+) T cells but also NKT cells is involved in allergic airway inflammation. Notably, pulmonary blockade of OX40 ligation on NKT cells has therapeutic implications.

The transcription factor Ets1 is important for CD4 repression and Runx3 up-regulation during CD8 T cell differentiation in the thymus

The transcription factor Ets1 contributes to the differentiation of CD8 lineage cells in the thymus, but how it does so is not understood. In this study, we demonstrate that Ets1 is required for the proper termination of CD4 expression during the differentiation of major histocompatability class 1 (MHC I)–restricted thymocytes, but not for other events associated with their positive selection, including the initiation of cytotoxic gene expression, corticomedullary migration, or thymus exit. We further show that Ets1 promotes expression of Runx3, a transcription factor important for CD8 T cell differentiation and the cessation of Cd4 gene expression. Enforced Runx3 expression in Ets1-deficient MHC I–restricted thymocytes largely rescued their impaired Cd4 silencing, indicating that Ets1 is not required for Runx3 function. Finally, we document that Ets1 binds at least two evolutionarily conserved regions within the Runx3 gene in vivo, supporting the possibility that Ets1 directly contributes to Runx3 transcription. These findings identify Ets1 as a key player during CD8 lineage differentiation and indicate that it acts, at least in part, by promoting Runx3 expression.

Domain analyses of the Runx1 transcription factor responsible for modulating T-cell receptor-beta/CD4 and interleukin-4/interferon-gamma expression in CD4(+) peripheral T lymphocytes

The Runx1 transcription factor is one of the master regulators of T-lymphocyte differentiation. There have been several reports trying to assign a domain within the Runx1 protein that is responsible for gene expression in thymocytes. The Runx1 domains involved in regulating the expression of several genes in peripheral CD4(+) T cells were analysed. It was observed that Runx1 over-expression enhanced the surface expression of CD4 and CD69 molecules via its activation domain and VWRPY domain, and decreased that of T-cell receptor-beta via its activation domain. Runx1 over-expression enhanced interferon-gamma expression via its activation and VWRPY domains, and abolished interleukin-4 expression through its activation domain. Transduction of Runx1 did not down-regulate CD4 expression until 72 hr of culture, but the repression of CD4 expression became evident after 96 hr. The main region responsible for repressing CD4 expression was the inhibitory domain of Runx1. Taken together, these results lead to a proposal that the regions in Runx1 responsible for modulating gene expression are distinct in thymocytes and in peripheral CD4(+) T cells.

CD4-CD8 lineage differentiation: Thpok-ing into the nucleus

The mature alphabeta T cell population is divided into two main lineages that are defined by the mutually exclusive expression of CD4 and CD8 surface molecules (coreceptors) and that differ in their MHC restriction and function. CD4 T cells are typically MHC-II restricted and helper (or regulatory), whereas CD8 T cells are typically cytotoxic. Several transcription factors are known to control the emergence of CD4 and CD8 lineages, including the zinc finger proteins Thpok and Gata3, which are required for CD4 lineage differentiation, and the Runx factors Runx1 and Runx3, which contribute to CD8 lineage differentiation. This review summarizes recent advances on the function of these transcription factors in lineage differentiation. We also discuss how the "circuitry" connecting these factors could operate to match the expression of the lineage-committing factors Thpok and Runx3, and therefore lineage differentiation, to MHC specificity.

RUNX proteins in transcription factor networks that regulate T-cell lineage choice

Recent research has uncovered complex transcription factor networks that control the processes of T-cell development and differentiation. RUNX (runt-related transcription factor) proteins are among the many factors that have crucial roles in these networks. In this Review, we examine the mechanisms by which RUNX complexes act together with other transcription factors, such as Th-POK (T-helper-inducing POZ/Kruppel-like factor) and GATA-binding protein 3 (GATA3) in determining the CD4/CD8 lineage choice of developing thymocytes. In addition, we discuss evidence indicating that RUNX complexes are also involved in the differentiation of effector T-cell subsets and that the molecular mechanisms by which RUNX proteins regulate T-cell fate decisions are conserved between the thymus and periphery.

The zinc finger transcription factor Zbtb7b represses CD8-lineage gene expression in peripheral CD4+ T cells

How CD4-CD8 differentiation is maintained in mature T cells is largely unknown. The present study has examined the role in this process of the zinc finger protein Zbtb7b, a critical factor for the commitment of MHC II-restricted thymocytes to the CD4+ lineage. We showed that Zbtb7b acted in peripheral CD4+ T cells to suppress CD8-lineage gene expression, including that of CD8 and cytotoxic effector genes perforin and Granzyme B, and was important for the proper repression of interferon-gamma (IFN-gamma) during effector differentiation. The inappropriate expression of IFN-gamma by Zbtb7b-deficient CD4+ T cells required the activities of Eomesodermin and Runx transcription factors. Runx activity was needed for Granzyme B expression, indicating that Runx proteins control expression of the cytotoxic program. We conclude that a key function of Zbtb7b in the mature CD4+ T cell compartment is to repress CD8-lineage gene expression.

Lineage fate and intense debate: myths, models and mechanisms of CD4- versus CD8-lineage choice

Following successful gene rearrangement at alphabeta T-cell receptor (TCR) loci, developing thymocytes express both CD4 and CD8 co-receptors and undergo a life-or-death selection event, which is known as positive selection, to identify cells that express TCRs with potentially useful ligand specificities. Positively selected thymocytes must then differentiate into either CD4(+) helper T cells or CD8(+) cytotoxic T cells, a crucial decision known as CD4/CD8-lineage choice. In this Review, we summarize recent advances in our understanding of the cellular and molecular events involved in lineage-fate decision and discuss them in the context of the major models of CD4/CD8-lineage choice.

Gene expression changes in children with autism

The objective of this study was to identify gene expression differences in blood differences in children with autism (AU) and autism spectrum disorder (ASD) compared to general population controls. Transcriptional profiles were compared with age- and gender-matched, typically developing children from the general population (GP). The AU group was subdivided based on a history of developmental regression (A-R) or a history of early onset (A-E without regression). Total RNA from blood was processed on human Affymetrix microarrays. Thirty-five children with AU (17 with early onset autism and 18 with autism with regression) and 14 ASD children (who did not meet criteria for AU) were compared to 12 GP children. Unpaired t tests (corrected for multiple comparisons with a false discovery rate of 0.05) detected a number of genes that were regulated more than 1.5-fold for AU versus GP (n=55 genes), for A-E versus GP (n=140 genes), for A-R versus GP (n=20 genes), and for A-R versus A-E (n=494 genes). No genes were significantly regulated for ASD versus GP. There were 11 genes shared between the comparisons of all autism subgroups to GP (AU, A-E, and A-R versus GP) and these genes were all expressed in natural killer cells and many belonged to the KEGG natural killer cytotoxicity pathway (p=0.02). A subset of these genes (n=7) was tested with qRT-PCR and all genes were found to be differentially expressed (p<0.05). We conclude that the gene expression data support emerging evidence for abnormalities in peripheral blood leukocytes in autism that could represent a genetic and/or environmental predisposition to the disorder.