Runx3 regulates mouse TGF-beta-mediated dendritic cell function and its absence results in airway inflammation

TGFbeta-dependent gene expression profile during maturation of dendritic cells

Primary immune response to pathogens involves the maturation of antigen-presenting dendritic cells (DC). Bacterial lipopolysacharride (LPS) is a potent inducer of DC maturation, whereas the transforming growth factor beta (TGFbeta) attenuates much of this process. Here, we analyzed the global gene expression pattern in LPS-treated bone marrow derived DC during inhibition of their maturation process by TGFbeta. Exposure of DC to LPS induces a pronounced cell response, manifested in altered expression of a large number of genes. Interestingly, TGFbeta did not affect most of the LPS responding genes. Nevertheless, analysis identified a subset of genes that did respond to TGFbeta, among them the two inflammatory cytokines interleukin (IL)-12 and IL-18. Expression of IL-12, the major proinflammatory cytokine secreted by mature DC, was downregulated by TGFbeta, whereas the expression level of the proinflammatory cytokine IL-18, known to potentiate the IL-12 effect, was upregulated. Expression of the peroxisome proliferator-activated receptor gamma (PPARgamma) increased in response to TGFbeta, concomitantly with reduced expression of chemokine receptor 7 (CCR7). This finding supports the possibility that TGFbeta-dependent inhibition of CCR7 expression in DC is mediated by PPARgamma.

Transcriptional control of lung morphogenesis

The vertebrate lung consists of multiple cell types that are derived primarily from endodermal and mesodermal compartments of the early embryo. The process of pulmonary organogenesis requires the generation of precise signaling centers that are linked to transcriptional programs that, in turn, regulate cell numbers, differentiation, and behavior, as branching morphogenesis and alveolarization proceed. This review summarizes knowledge regarding the expression and proposed roles of transcription factors influencing lung formation and function with particular focus on knowledge derived from the study of the mouse. A group of transcription factors active in the endodermally derived cells of the developing lung tubules, including thyroid transcription factor-1 (TTF-1), beta-catenin, Forkhead orthologs (FOX), GATA, SOX, and ETS family members are required for normal lung morphogenesis and function. In contrast, a group of distinct proteins, including FOXF1, POD1, GLI, and HOX family members, play important roles in the developing lung mesenchyme, from which pulmonary vessels and bronchial smooth muscle develop. Lung formation is dependent on reciprocal signaling among cells of both endodermal and mesenchymal compartments that instruct transcriptional processes mediating lung formation and adaptation to breathing after birth.

Transcription factors T-bet and Runx3 cooperate to activate Ifng and silence Il4 in T helper type 1 cells

Cell differentiation involves activation and silencing of lineage-specific genes. Here we show that the transcription factor Runx3 is induced in T helper type 1 (T(H)1) cells in a T-bet-dependent manner, and that both transcription factors T-bet and Runx3 are required for maximal production of interferon-gamma (IFN-gamma) and silencing of the gene encoding interleukin 4 (Il4) in T(H)1 cells. T-bet does not repress Il4 in Runx3-deficient T(H)2 cells, but coexpression of Runx3 and T-bet induces potent repression in those cells. Both T-bet and Runx3 bind to the Ifng promoter and the Il4 silencer, and deletion of the silencer decreases the sensitivity of Il4 to repression by either factor. Our data indicate that cytokine gene expression in T(H)1 cells may be controlled by a feed-forward regulatory circuit in which T-bet induces Runx3 and then 'partners' with Runx3 to direct lineage-specific gene activation and silencing.

Runx3 regulates dendritic epidermal T cell development

The Runx3 transcription factor regulates development of T cells during thymopoiesis and TrkC sensory neurons during dorsal root ganglia neurogenesis. It also mediates transforming growth factor-beta signaling in dendritic cells and is essential for development of skin Langerhans cells. Here, we report that Runx3 is involved in the development of skin dendritic epidermal T cells (DETCs); an important component of tissue immunoregulation. In developing DETCs, Runx3 regulates expression of the alphaEbeta7 integrin CD103, known to affect migration and epithelial retention of DETCs. It also regulates expression of IL-2 receptor beta (IL-2Rbeta) that mediates cell proliferation in response to IL-2 or IL-15. In the absence of Runx3, the reduction in CD103 and IL-2Rbeta expression on Runx3(-/-) DETC precursors resulted in impaired cell proliferation and maturation, leading to complete lack of skin DETCs in Runx3(-/-) mice. The data demonstrate the requirement of Runx3 for DETCs development and underscore the importance of CD103 and IL-2Rbeta in this process. Of note, while Runx3(-/-) mice lack both DETCs and Langerhans cells, the two most important components of skin immune surveillance, the mice did not develop skin lesions under pathogen-free (SPF) conditions.

Psoriasis: genetic associations and immune system changes

Psoriasis is a common inflammatory skin disease characterized by infiltration of inflammatory cells into the epidermis and altered keratinocyte differentiation. Psoriasis is currently thought of as a T-cell mediated 'Type-1' autoimmune disease. Gene expression changes in psoriasis lesions have been well documented, and strongly support an important role for tumor necrosis factor and interferon gamma signal pathways in its pathogenesis. The strongest genetic determinant of psoriasis identified to date lies within the class I region of the multiple histocompatibility locus antigen cluster, although its low penetrance implicates a requirement for other genetic risk factors. Multiple genome-wide linkage and an increasing number of association studies have been carried out, leading to multiple linkage peaks, and the identification of potential low risk variants. A number of these variants lie within genes encoding components of the immune system. However, the functional relationships between predisposing genetic variation is unclear, and presumably involves genetic susceptibility factors affecting both immune cell activation and keratinocyte differentiation. The interaction of environmental trigger factors with genetic effects is also not understood, but provide further evidence for the complex basis of this disease.

RUNX3 negatively regulates CD36 expression in myeloid cell lines

CD36 is a member of the scavenger receptor type B family implicated in the binding of lipoproteins, phosphatidylserine, thrombospondin-1, and the uptake of long-chain fatty acids. On mononuclear phagocytes, recognition of apoptotic cells by CD36 contributes to peripheral tolerance and prevention of autoimmunity by impairing dendritic cell (DC) maturation. Besides, CD36 acts as a coreceptor with TLR2/6 for sensing microbial diacylglycerides, and its deficiency leads to increased susceptibility to Staphylococcus aureus infections. The RUNX3 transcription factor participates in reprogramming DC transcription after pathogen recognition, and its defective expression leads to abnormally accelerated DC maturation. We present evidence that CD36 expression is negatively regulated by the RUNX3 transcription factor during myeloid cell differentiation and activation. In molecular terms, RUNX3 impairs the activity of the proximal regulatory region of the CD36 gene in myeloid cells through in vitro recognition of two functional RUNX-binding elements. Moreover, RUNX3 occupies the CD36 gene proximal regulatory region in vivo, and its overexpression in myeloid cells results in drastically diminished CD36 expression. The down-regulation of CD36 expression by RUNX3 implies that this transcription factor could impair harmful autoimmune responses by contributing to the loss of pathogen- and apoptotic cell-recognition capabilities by mature DCs.

The genetics of systemic lupus erythematosus: understanding how SNPs confer disease susceptibility

The identification of genes for autoimmune diseases is just the first step towards our understanding of disease pathogenesis. In investigating how mutations, deletions or other types of polymorphic defects occur, it is important to determine the pathways and the mechanisms through which susceptibility leads to disease. In this review I touch on three examples of studies that have attempted to understand the mechanisms of genetic susceptibility in three genes identified recently for systemic lupus erythematosus: PDCD1, PTPN22 and IRF5. We are just beginning to comprehend and much needs to be done.

Identification of an N-terminal Transactivation Domain of Runx1 That Separates Molecular Function from Global Differentiation Function

RUNX1, or AML1, is a transcription factor that is the most frequent target for chromosomal gene translocations in acute leukemias. RUNX1 is essential for definitive hematopoiesis in embryos and profoundly influences adult steady-state hematopoiesis both positively and negatively. To investigate this wide range of normal activities and the pathological role of RUNX1, it is important to define the functions of different domains of the protein. RUNX1, RUNX2, and RUNX3 are highly conserved in their DNA binding runt homology domain and contain divergent sequences of unknown function N-terminal to this domain. Here we analyzed the role of the N-terminal sequence and the alpha-helix of the runt homology domain of Runx1 in DNA binding, transactivation, and megakaryocytopoiesis. Both the N terminus and the alpha-helix were found to reduce DNA binding of Runx1 and be essential for transactivation of the granulocyte-macrophage colony-stimulating factor and Ialpha1 promoters by Runx1. The N terminus of Runx1, including the alpha-helix, was also required for transactivation of a Gal4 reporter when expressed as fusion proteins with a Gal4 DNA binding domain, and the N terminus alone was capable of stimulating transcription when fused to the Gal4 DNA binding domain. The N terminus and the alpha-helix, however, were not required for megakaryocyte development from embryonic stem cells differentiated in vitro. Thus, our findings define a second transactivation domain of Runx1 that is differentially required for activation of transcription of some Runx1-dependent promoters and megakaryocytopoiesis.

T-lymphoid, megakaryocyte, and granulocyte development are sensitive to decreases in CBFbeta dosage

The family of core-binding factors includes the DNA-binding subunits Runx1-3 and their common non-DNA-binding partner CBFbeta. We examined the collective role of core-binding factors in hematopoiesis with a hypomorphic Cbfb allelic series. Reducing CBFbeta levels by 3- or 6-fold caused abnormalities in bone development, megakaryocytes, granulocytes, and T cells. T-cell development was very sensitive to an incremental reduction of CBFbeta levels: mature thymocytes were decreased in number upon a 3-fold reduction in CBFbeta levels, and were virtually absent when CBFbeta levels were 6-fold lower. Partially penetrant consecutive differentiation blocks were found among early T-lineage progenitors within the CD4- CD8- double-negative 1 and downstream double-negative 2 thymocyte subsets. Our data define a critical CBFbeta threshold for normal T-cell development, and situate an essential role for core-binding factors during the earliest stages of T-cell development.

Molecular switches and developmental potential of adult stem cells

Stem cell commitment and differentiation entails the successive loss of self-renewal and developmental potential, and results in the final restriction to a terminally differentiated mature cell type. Hematopoiesis, the development of blood cells from hematopoietic stem cells in bone marrow, is particularly well studied, and at different branching points within the hematopoietic system multiple developmental intermediates have been identified. Here we describe a Flt3+ CD11b+ multipotent progenitor that can be amplified in vitro by a specific cytokine combination to high cell numbers, and following adoptive transfer into syngeneic mice, it generates dendritic cells but also additional mature cell types. By employing gene expression profiling with DNA microarrays and knockout mouse models, we demonstrate that the helix-loop-helix (HLH) transcription factor Id2 (inhibitor of DNA binding/differentiation 2) acts as a molecular switch in development of Langerhans cells (LCs), the cutaneous contingent of dendritic cells (DCs), and of specific DC subsets and B cells.

Groucho/transducin-like Enhancer-of-split (TLE)-dependent and -independent transcriptional regulation by Runx3

Regulation of gene expression by tissue-specific transcription factors involves both turning on and turning off transcription of target genes. Runx3, a runt-domain transcription factor, regulates cell-intrinsic functions by activating and repressing gene expression in sensory neurons, dendritic cells (DC), and T cells. To investigate the mechanism of Runx3-mediated repression in an in vivo context, we generated mice expressing a mutant Runx3 lacking the C-terminal VWRPY, a motif required for Runx3 interaction with the corepressor Groucho/transducin-like Enhancer-of-split (TLE). In contrast with Runx3(-/-) mice, which displayed ataxia due to the death of dorsal root ganglia TrkC neurons, Runx3(VWRPY-/-) mice were not ataxic and had intact dorsal root ganglia neurons, indicating that ability of Runx3 to tether Groucho/TLE is not essential for neurogenesis. In the DC compartment, the mutant protein Runx3(VWRPY-) promoted normally developed skin Langerhans cells but failed to restrain DC spontaneous maturation, indicating that this latter process involves Runx3-mediated repression through recruitment of Groucho/TLE. Moreover, in CD8(+) thymocytes, Runx3(VWRPY-) up-regulated alphaE/CD103-like WT Runx3, whereas unlike wild type, it failed to repress alphaE/CD103 in CD8(+) splenocytes. Thus, in CD8-lineage T cells, Runx3 regulates alphaE/CD103 in opposing regulatory modes and recruits Groucho/TLE to facilitate the transition from activation to repression. Runx3(VWRPY-) also failed to mediate the epigenetic silencing of CD4 gene in CD8(+) T cells, but normally regulated other pan-CD8(+) T cell genes. These data provide evidence for the requirement of Groucho/TLE for Runx3-mediated epigenetic silencing of CD4 and pertain to the mechanism through which other Runx3-regulated genes are epigenetically silenced.

Alveolar Macrophage in the Driver's Seat

Although alveolar macrophages are normally quiescent to prevent damaging the alveoli, in this issue of Immunity, Takabayshi et al. (2006) demonstrate that alveolar macrophages can self-regulate their function on demand to mount an appropriate immune response.

Exclusion of RUNX3 as a tumour-suppressor gene in early-onset gastric carcinomas

Recent studies claim a critical role for RUNX3 in gastric epithelial homeostasis. However, conflicting results exist regarding RUNX3 expression in the stomach and its potential role as a tumour-suppressor gene (TSG) in gastric carcinogenesis. Our aim was to evaluate the role of RUNX3 in early-onset gastric carcinomas (EOGCs). We analysed 41 EOGCs for RUNX3 aberrations using loss of heterozygosity (LOH), fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) analyses. LOH of markers flanking RUNX3 was relatively common, indicating that loss of the gene may play a role in gastric carcinogenesis. However, FISH analysis of selected cases and a panel of 14 gastric carcinoma-derived cell lines showed widespread presence of multiple copies of centromere 1. While RUNX3 copy numbers were generally equal to or fewer than those of centromere 1, at least two copies were present in almost all cells analysed. Accordingly, a subpopulation of tumour cells in 12/37 cases showed RUNX3 protein expression. However, expression was not detected in the adjacent nontumorous mucosa of any case. Together, these observations indicate that chromosome 1 aberrations occur frequently in EOGCs and are reflected in the LOH and IHC patterns found. Our findings refute a role for RUNX3 as a TSG in EOGCs.

Towards an understanding of the transcription factor network of dendritic cell development

Dendritic cells (DCs) are antigen-presenting cells of the immune system and develop from hematopoietic stem cells through successive steps of lineage commitment and differentiation. The three major DC populations are epidermal Langerhans cells, tissue/interstitial/dermal DCs and plasmacytoid DCs. We review how gene-targeted mutations in mice have contributed to our understanding of how the various DC subpopulations develop. These studies have revealed both overlapping and distinct pathways of DC differentiation and show that there is no obvious correlation between transcription factor knockout phenotypes and a lymphoid or myeloid origin of DCs.

RUNX3: A new player in myeloid gene expression and immune response

RUNX transcription factors function as scaffolds for interaction with various coregulatory proteins during developmental processes such as hematopoiesis, neurogenesis, and osteogenesis. The current view places RUNX proteins within the TGF-beta signaling pathway, although each one exhibits cell- and tissue-specific functions. In the case of RUNX3, recent data have suggested its function as a tumor suppressor factor and highlighted its involvement in immune cell differentiation and activation. The molecular mechanisms for the pleiotropic effects of Runx3 deficiency are not completely understood. The present article will summarize the known functional activities of RUNX3, emphasizing its role in myeloid cell gene expression and its potential contribution to the migratory and adhesive capabilities of this cell lineage.

The genetics of psoriasis and autoimmunity

Psoriasis is an inflammatory/autoimmune disease and, as with many autoimmune diseases, is associated with alleles from the major histocompatibility complex (MHC). With psoriasis and autoimmune disease, the penetrance of the MHC-associated alleles is never 100%, even for monozygotic twins. This may be because development requires additional environmental and/or genetic modifiers or requires specific T-cell receptor arrangements. Families segregating single or multilocus susceptibility alleles other than the MHC have also been reported. Overlapping genetic locations of loci for different autoimmune diseases have been known for several years and are starting to reveal common genes or genetic variants. These include genes normally involved in preventing spontaneous T-cell activation or proliferation, immune synapse formation, or cytokine production via pathways such as those mediated by NFkappaB and those involved in thymic selection. Autoimmunity may also involve dysregulation of genes or pathways regulated by the RUNX family of transcription factors. RUNX is involved in hematopoietic cell development, development of T cells in the thymus, chromatin remodeling, and gene silencing. Hence, its effect on cells of the immune system may be due to variable changes in gene expression and could account for variable body surface involvement and waxing and waning of disease.

RUNX3 regulates the activity of the CD11a and CD49d integrin gene promoters

The leukocyte integrins CD11a/CD18 (LFA-1, alphaLbeta2) and CD49d (VLA-4, alpha4beta1, alpha4beta7) mediate leukocyte transendothelial migration during immune and inflammatory responses and provides co-stimulatory signals for the activation of T lymphocytes. Our previous studies demonstrate that the CD11a gene promoter directs CD11a/CD18 integrin expression, and it depends on two overlapping sequences within the MS7 element, RUNX-110 and CEBP-100, which are recognized by RUNX and C/EBP transcription factor families, respectively. Recognition of MS7 differs in lymphoid (RUNX) and myeloid (C/EBP and RUNX) cells and its in vivo occupancy is regulated in a competitive and differentiation-dependent manner. The functional relevance of these elements are illustrated by the fact that RUNX3 overexpression leads to enhanced CD11a/CD18 levels, whereas RUNX1-ETO-expressing cells exhibit a weak/absent CD11a/CD18 integrin cell surface expression. We now provide evidence that RUNX3 also transactivates the CD49d gene promoter, and that the increased expression of CD49d mRNA and CD49d integrins on mature monocyte-derived dendritic cells correlates with an up-regulation of RUNX3 mRNA. The regulation of CD49d and CD11a integrins by RUNX3 could potentially contribute to the enhancement of transendothelial migration, antigen presentation and T cell stimulatory capabilities of mature dendritic cells.

Runx3 regulates integrin alpha E/CD103 and CD4 expression during development of CD4-/CD8+ T cells

During thymic T cell development, immature CD4+CD8+ double-positive (DP) thymocytes develop either into CD4+CD8- Th cells or CD4-CD8+ CTLs. Differentially expressed primary factors inducing the fate of these cell types are still poorly described. The transcription factor Runx3/AML-2 Runx, runt [corrected] dominant factor; AML, acute myeloid leukemia is expressed specifically during the development of CD8 single-positive (SP) thymocytes, where it silences CD4 expression. Deletion of murine Runx3 results in a reduction of CD8 SP T cells and concomitant accumulation of CD4+CD8+ T cells, which cannot down-regulate CD4 expression in the thymus and periphery. In this study we have investigated the role of Runx3 during thymocyte development and CD4 silencing and have identified integrin alpha(E)/CD103 on CD8 SP T cells as a new potential target gene of Runx3. We demonstrate that Runx3 is necessary not only to repress CD4, but also to induce CD103 expression during development of CD8 SP T cells. In addition, transgenic overexpression of Runx3 reduced CD4 expression during development of DP thymocytes, leading to a reduced number of CD4 SP thymocytes and an increased number of CD8 SP thymocytes. This reversal is not caused by redirection of specific MHC class II-restricted cells to the CD8 lineage. Overexpression of Runx3 also up-regulated CD103 expression on a subpopulation of CD4 SP T cells with characteristics of regulatory T cells. Thus, Runx3 is a main regulator of CD4 silencing and CD103 induction and thus contributes to the phenotype of CD8 SP T cells during thymocyte development.

Decreased expression of TGF-beta type II receptor in bronchial glands of smokers with COPD

BACKGROUND

The role of transforming growth factor-beta1 (TGF-beta1) in chronic obstructive pulmonary disease is still controversial, but it has been proposed that it may protect from mucus hypersecretion since it is able to downregulate mucin production. A study was undertaken to investigate the expression of TGF-beta1 and its type II receptor (TGF-beta RII) in the bronchial glands of smokers with COPD.

METHODS

The expression of TGF-beta(1) and TGF-beta RII were examined immunohistochemically in the bronchial glands of 24 smokers undergoing lung resection for solitary peripheral nodules: 12 with airflow limitation (smokers with COPD) and 12 with normal lung function.

RESULTS

The expression of TGF-beta1 in bronchial glands was similar in the two groups of subjects while that of TGF-beta RII was lower in smokers with COPD than in smokers with normal lung function (p=0.004). TGF-beta RII expression was inversely correlated with the values of Reid's index, a measure of gland size (p=0.02, r=-0.50).

CONCLUSIONS

In the bronchial glands of smokers with COPD there is decreased expression of TGF-beta RII which is associated with bronchial gland enlargement. These findings support the view that the absence of TGF-beta signalling may induce structural changes in the bronchial glands which, in turn, may promote mucus hypersecretion.

Regulation of skeletal development by the Runx family of transcription factors

The Runx (runt-related protein) family of transcription factors plays important roles in different tissues and cell lineages. Runx1 determines commitment to the hematopoietic cell lineage and Runx2 determines commitment to the osteoblastic lineage. Cbfbeta is required for Runx1- and Runx2-dependent transcriptional regulation. Runx2 interacts with many other transcription factors and co-regulators in the transcriptional regulation of its target genes. Runx2 is essential for the commitment of multipotent mesenchymal cells into the osteoblastic lineage and inhibits adipocyte differentiation. Runx2 induces the gene expression of bone matrix proteins, while keeping the osteoblastic cells in an immature stage. Runx2 and Runx3 have redundant functions in chondrocytes, and they are essential for chondrocyte maturation. Runx2 directly induces Indian hedgehog (Ihh) expression and co-ordinates the proliferation and differentiation of chondrocytes. Therefore, elucidation of the signaling pathways through Runx2 and Runx3 will unravel the complex mechanism of skeletal development.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Immunoregulation of dendritic cells

The paradigm of tolerogenic/immature versus inflammatory/mature dendritic cells has dominated the recent literature regarding the role of these antigen-presenting cells in mediating immune homeostasis or self-tolerance and response to pathogens, respectively. This issue is further complicated by the identification of distinct subtypes of dendritic cells that exhibit different antigen-presenting cell effector functions. The discovery of pathogen-associated molecular patterns and toll-like receptors provides the mechanistic basis for dendritic cell recognition of specific pathogens and induction of appropriate innate and adaptive immune responses. Only recently has insight been gained into how dendritic cells contribute to establishing and/or maintaining immunological tolerance to self. Soluble and cellular mediators have been reported to effectively regulate the function of dendritic cells by inducing several outcomes ranging from non-inflammatory dendritic cells that lack the ability to induce T lymphocyte activation to dendritic cells that actively suppress T lymphocyte responses. A thorough discussion of these stimuli and their outcomes is essential to understanding the potential for modulating dendritic cell function in the treatment of inflammatory disease conditions.

PU.1 regulates the tissue-specific expression of dendritic cell-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin

Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is a cell surface C-type lectin expressed on myeloid dendritic cells and certain tissue macrophages, which mediates antigen capture for processing and presentation and participates in intercellular interactions with naive T lymphocytes or endothelial cells. In their strategy to evade immunosurveillance, numerous pathogenic microorganisms, including human immunodeficiency virus and Mycobacterium, bind to DC-SIGN in order to gain access to dendritic cells. We present evidence that PU.1 dictates the basal and cell-specific activity of DC-SIGN gene-regulatory region through in vivo occupancy of two functional Ets elements, whose integrity is required for PU.1 responsiveness and for the cooperative actions of PU.1 and other transcription factors (Myb, RUNX) on the DC-SIGN gene proximal regulatory region. In addition, protein analysis and gene profiling experiments indicate that DC-SIGN and PU.1 are coordinately expressed upon classical and alternative macrophage activation and during dendritic cell maturation. Moreover, small interfering RNA-mediated reduction of PU.1 expression results in diminished DC-SIGN cellular levels. Altogether, these results indicate that PU.1 is involved in the myeloid-specific expression of DC-SIGN in myeloid cells, a contribution that can be framed within the role that PU.1 has on the acquisition of the antigen uptake molecular repertoire by dendritic cells and macrophages.

Accelerated chemokine receptor 7-mediated dendritic cell migration in Runx3 knockout mice and the spontaneous development of asthma-like disease

The Runx3 transcription factor is a key regulator of lineage-specific gene expression in several developmental pathways and could also be involved in autoimmunity. We report that, in dendritic cells (DC), Runx3 regulates TGFbeta-mediated transcriptional attenuation of the chemokine receptor CCR7. When Runx3 is lost, i.e., in Runx3 knockout mice, expression of CCR7 is enhanced, resulting in increased migration of alveolar DC to the lung-draining lymph nodes. This increased DC migration and the consequent accumulation of activated DC in draining lymph nodes is associated with the development of asthma-like features, including increased serum IgE, hypersensitivity to inhaled bacterial lipopolysaccharide, and methacholine-induced airway hyperresponsiveness. The enhanced migration of DC in the knockout mice could be blocked in vivo by anti-CCR7 antibodies and by the drug Ciglitazone, known to inhibit CCR7 expression. The data indicate that Runx3 transcriptionally regulates CCR7 and that, when absent, the dysregulated expression of CCR7 in DC plays a role in the etiology of asthmatic conditions that recapitulate clinical symptoms of the human disease. Interestingly, human RUNX3 resides in a region of chromosome 1p36 that contains susceptibility genes for asthma and hypersensitivity against environmental antigens. Thus, mutations in RUNX3 may be associated with increased sensitivity to asthma development.

The RUNX genes: gain or loss of function in cancer

The RUNX genes have come to prominence recently because of their roles as essential regulators of cell fate in development and their paradoxical effects in cancer, in which they can function either as tumour-suppressor genes or dominant oncogenes according to context. How can this family of transcription factors have such an ambiguous role in cancer? How and where do these genes impinge on the pathways that regulate growth control and differentiation? And what is the evidence for a wider role for the RUNX genes in non-haematopoietic cancers?

Transcriptional cross-regulation of RUNX1 by RUNX3 in human B cells

RUNX transcription factors are important in development and in numerous types of human cancer. They act as either transcriptional activators or repressors and can be proto-oncogenes or tumour suppressors. Understanding their regulation and interaction may explain how RUNX factors contribute to such different and often opposing biological processes. We show that RUNX3 regulates RUNX1 expression, contributing to the mutually exclusive expression of RUNX3 and RUNX1 in human B lymphoid cell lines. RUNX3 repressed the RUNX1 P1 promoter by binding specifically to conserved RUNX sites near the transcription start of the promoter. siRNA inhibition of RUNX3 in lymphoblastoid cells resulted in increased RUNX1 expression, indicating that continuous expression of physiological levels of RUNX3 is required to maintain repression. Furthermore, expression of RUNX3 was required for efficient proliferation of B cells immortalized by Epstein-Barr virus. Cross-regulation between different RUNX family members is therefore a means of controlling RUNX protein expression and must now be considered in the interpretation of pathological changes due to loss of RUNX3 tumour suppressor function or following gene duplication or translocation events.

The interplay of dendritic cells, Th2 cells and regulatory T cells in asthma

Dendritic cells are essential for Th2 differentiation of naive CD4+ T cells in response to aeroallergens, and in recent years it has been well established that these cells play a pivotal role in the initiation phase of allergic asthma. Dendritic cells are also crucial for maintaining eosinophilic airway inflammation by controlling the recruitment and activation of primed Th2 cells in the lung. A picture is emerging wherein the balance of pathogenic Th2 cells and regulatory T cells is tuned by dendritic cells not only at the initiation but also at the effector stage of the allergic immune response.

Runx3 is involved in hair shape determination

Transcriptional regulators of the Runx family play critical roles in normal organ development and, when mutated, lead to genetic diseases and cancer. Runx3 functions during cell lineage decisions in thymopoiesis and neurogenesis and mediates transforming growth factor-beta signaling in dendritic cells. Here, we study the function of Runx3 in the skin and its appendages, primarily the hair follicle, during mouse development. Runx3 is expressed predominantly in the dermal compartment of the hair follicles as they form and during the hair cycle, as well as in the nail and sweat gland skin appendages. Distinct expression is also detected periodically in isolated cells of the epidermis and in melanocytes, populating the hair bulb. Runx3-deficient mice display a perturbation of the normal hair coat, which we show to be due to hair type and hair shape changes. Thus, one of the functions of Runx3 in skin may be to regulate the formation of the epithelial derived structural hair by affecting dermal to epidermal interactions.

Loss of Runx3 function in leukocytes is associated with spontaneously developed colitis and gastric mucosal hyperplasia

RUNX transcription factors are key regulators of lineage-specific gene expression and might be involved in autoimmune diseases. Runx3 plays a role during the development of sensory neurons and T cells and regulates transforming growth factor beta (TGF-beta) signaling in dendritic cells. Here, we report that at 4 weeks of age, Runx3 knockout (KO) mice spontaneously develop inflammatory bowel disease (IBD) characterized by leukocyte infiltration, mucosal hyperplasia, formation of lymphoid clusters, and increased production of IgA. Additionally, at a considerably older age (8 months), the KO mice also develop progressive hyperplasia of the gastric mucosa associated with disturbed epithelial differentiation and cellular hyaline degeneration. Analysis of cytokines in the colonic mucosa of Runx3 KO mice revealed a mixed T helper 1/T helper 2 response. By using immunohistochemistry and RNA in situ hybridization, Runx3 expression in the gastrointestinal tract is detected in lymphoid and myeloid populations but not in the epithelium. The data indicate that loss of leukocytic cell-autonomous function of Runx3 results in IBD and gastric lesion in the KO mice. IBD in humans is viewed as a complex genetic disorder. Several susceptibility loci were identified on different human chromosomes including the chromosomal region 1p36 where RUNX3 resides. It is thus tempting to speculate that mutations in RUNX3 may constitute an IBD risk factor in humans.

Caspase-8 serves both apoptotic and nonapoptotic roles

Knockout of caspase-8, a cysteine protease that participates in the signaling for cell death by receptors of the TNF/nerve growth factor family, is lethal to mice in utero. To explore tissue-specific roles of this enzyme, we established its conditional knockout using the Cre/loxP recombination system. Consistent with its role in cell death induction, deletion of caspase-8 in hepatocytes protected them from Fas-induced caspase activation and death. However, application of the conditional knockout approach to investigate the cause of death of caspase-8 knockout embryos revealed that this enzyme also serves cellular functions that are nonapoptotic. Its deletion in endothelial cells resulted in degeneration of the yolk sac vasculature and embryonal death due to circulatory failure. Caspase-8 deletion in bone-marrow cells resulted in arrest of hemopoietic progenitor functioning, and in cells of the myelomonocytic lineage, its deletion led to arrest of differentiation into macrophages and to cell death. Thus, besides participating in cell death induction by receptors of the TNF/nerve growth factor family, caspase-8, apparently independently of these receptors, also mediates nonapoptotic and perhaps even antiapoptotic activities.

Role of RUNX in autoimmune diseases linking rheumatoid arthritis, psoriasis and lupus

Recent studies investigating the genetic susceptibility of systemic lupus erythematosus, rheumatoid arthritis and psoriasis have revealed a potential role for the RUNX proteins in the development of autoimmune disease. A new pathway of disease pathogenesis opens new avenues of research with thousands of questions that remain to be answered. In this review I attempt to propose how the RUNX proteins might be involved in these diseases and review current knowledge on this very interesting trio of transcription factors that was previously only suspected to be involved in cancer.

Oncogenic potential of the RUNX gene family: 'overview'

Runt-related (RUNX) gene family is composed of three members, RUNX1/AML1, RUNX2 and RUNX3, and encodes the DNA-binding (alpha) subunits of the Runt domain transcription factor polyomavirus enhancer-binding protein 2 (PEBP2)/core-binding factor (CBF), which is a heterodimeric transcription factor. RUNX1 is most frequently involved in human acute leukemia. RUNX2 shows oncogenic potential in mouse experimental system. RUNX3 is a strong candidate as a gastric cancer tumor suppressor. The beta subunit gene of PEBP2/CBF is also frequently involved in chromosome rearrangements associated with human leukemia. In this Overview, I will summarize how this growing field has been formed and what are the challenging new frontiers for better understanding of the oncogenic potential of this gene family.

Structure and regulated expression of mammalian RUNX genes

The RUNX are key regulators of lineage-specific gene expression in major developmental pathways. The expression of RUNX genes is tightly regulated, leading to a highly specific spatio/temporal expression pattern and to distinct phenotypes of gene knockouts. This review highlights the extensive structural similarities between the three mammalian RUNX genes and delineates how regulation of their expression at the levels of transcription and translation are orchestrated into the unique RUNX expression pattern.

Core-binding factors in hematopoiesis and immune function

Core binding factors are heterodimeric transcription factors containing a DNA binding Runx1, Runx2, or Runx3 subunit, along with a non DNA binding CBF beta subunit. All four subunits are required at one or more stages of hematopoiesis. This review describes the role of Runx1 and CBF beta in the initiation of hematopoiesis in the embryo, and in the emergence of hematopoietic stem cells. We also discuss the later stages of hematopoiesis for which members of the core binding factor family are required, as well as the recently described roles for these proteins in autoimmunity.