Transcriptional regulation of CD1D1 by Ets family transcription factors

Invariant natural killer T cells balance B cell immunity

Invariant natural killer T (iNKT) cells mediate rapid immune responses which bridge the gap between innate and adaptive responses to pathogens while also providing key regulation to maintain immune homeostasis. Both types of important iNKT immune responses are mediated through interactions with innate and adaptive B cells. As such, iNKT cells sit at the decision-making fulcrum between regulating inflammatory or autoreactive B cells and supporting protective or regulatory B cell populations. iNKT cells interpret the signals in their environment to set the tone for subsequent adaptive responses, with outcomes ranging from getting licensed to maintain homeostasis as an iNKT regulatory cell (iNKT_reg ) or being activated to become an iNKT follicular helper (iNKT_FH ) cell supporting pathogen-specific effector B cells. Here we review iNKT and B cell cooperation across the spectrum of immune outcomes, including during allergy and autoimmune disease, tumor surveillance and immunotherapy, or pathogen defense and vaccine responses. Because of their key role as influencers, iNKT cells provide a valuable target for therapeutic interventions. Understanding the nature of the interactions between iNKT and B cells will enable the development of clinical interventions to strategically target regulatory iNKT and B cell populations or inflammatory ones, depending on the circumstance.

Hepatocyte CD1d protects against liver immunopathology in mice with schistosomiasis japonica

Schistosomiasis is a neglected tropical disease with over 250 million people infected worldwide. The main clinically important species Schistosoma mansoni (S. mansoni) and Schistosoma japonicum (S. japonicum) cause inflammatory responses against tissue-trapped eggs, resulting in formation of granulomas mainly in host liver. Persistent granulomatous response results in severe fibrosis in the liver, leading to irreversible impairment of the liver and even death of the host. CD1d, a highly conserved MHC class I-like molecule, is expressed by both haematopoietic and non-haematopoietic cells. CD1d on antigen-presenting cells (APCs) of haematopoietic origin presents pathogen-derived lipid antigens to natural killer T (NKT) cells, which enables them to rapidly produce large amounts of various cytokines and facilitate CD4⁺ T helper (Th) cell differentiation upon invading pathogens. Noteworthy, hepatocytes of non-haematopoietic origin have recently been shown to be involved in maintaining liver NKT cell homeostasis through a CD1d-dependent manner. However, whether hepatocyte CD1d-dependent regulation of NKT cell homeostasis also modulates CD4⁺ Th cell responses and liver immunopathology in murine schistosomiasis remains to be addressed. Here, we show in mice that CD1d expression on hepatocytes was decreased dramatically upon S. japonicum infection, accompanied by increased NKT cells, as well as upregulated Th1 and Th2 responses. Overexpression of CD1d in hepatocytes significantly decreased local NKT numbers and cytokines (IFN-γ, IL-4, IL-13), concomitantly with downregulation of both Th1 and Th2 responses and alleviation in pathological damage in livers of S. japonicum-infected mice. These findings highlight the potential of hepatocyte CD1d-targeted therapies for liver immunopathology control in schistosomiasis.

Bacteroides fragilis alleviates the symptoms of lupus nephritis via regulating CD1d and CD86 expressions in B cells

Emerging evidences indicated that the dysbiosis of microbiota was related to the onset of systemic lupus erythematosus (SLE). Bacteroides fragilis (B. fragilis) ATCC 25285, a human commensal, was discovered to improve inflammatory diseases. However, whether B. fragilis (ATCC 25285) has the beneficial effects on the treatment of lupus nephritis has still remained elusive. In the present study, oral treatment with B. fragilis (ATCC 25285) ameliorated the activity of MRL/lpr mice, including decreased levels of autoantibodies and symptoms of lupus nephritis. Furthermore, we demonstrated that treatment with B. fragilis (ATCC 25285) could promote CD1d expression in B cells by Est-1 pathway, while inhibit CD86 expression via SHP-2 signaling pathway to repair the immune response of B cells in MRL/lpr mice. In addition, our findings revealed a possible role of treatment with B. fragilis (ATCC 25285) in relieving intestinal inflammation in MRL/lpr mice. Meanwhile, it was uncovered that B. fragilis (ATCC 25285) restored the Th17/Treg balance in MRL/lpr mice that was consistent with the role of B. fragilis in other autoimmune diseases. Overall, the current study may highlight the potential application of B. fragilis (ATCC 25285) to treat manifestations of SLE in high-risk individuals.

Differing roles of CD1d2 and CD1d1 proteins in type I natural killer T cell development and function

MHC class I-like CD1 molecules have evolved to present lipid-based antigens to T cells. Differences in the antigen-binding clefts of the CD1 family members determine the conformation and size of the lipids that are presented, although the factors that shape CD1 diversity remain unclear. In mice, two homologous genes, CD1D1 and CD1D2, encode the CD1d protein, which is essential to the development and function of natural killer T (NKT) cells. However, it remains unclear whether both CD1d isoforms are equivalent in their antigen presentation capacity and functions. Here, we report that CD1d2 molecules are expressed in the thymus of some mouse strains, where they select functional type I NKT cells. Intriguingly, the T cell antigen receptor repertoire and phenotype of CD1d2-selected type I NKT cells in CD1D1^-/- mice differed from CD1d1-selected type I NKT cells. The structures of CD1d2 in complex with endogenous lipids and a truncated acyl-chain analog of α-galactosylceramide revealed that its A'-pocket was restricted in size compared with CD1d1. Accordingly, CD1d2 molecules could not present glycolipid antigens with long acyl chains efficiently, favoring the presentation of short acyl chain antigens. These results indicate that the two CD1d molecules present different sets of self-antigen(s) in the mouse thymus, thereby impacting the development of invariant NKT cells.

Altered Marginal Zone B Cell Selection in the Absence of IκBNS

Marginal zone (MZ) B cells reside in the splenic MZ and play important roles in T cell-independent humoral immune responses against blood-borne pathogens. IκBNS-deficient bumble mice exhibit a severe reduction in the MZ B compartment but regain an MZ B population with age and, thus, represent a valuable model to examine the biology of MZ B cells. In this article, we characterized the MZ B cell defect in further detail and investigated the nature of the B cells that appear in the MZ of aged bumble mice. Flow cytometry analysis of the splenic transitional B cell subsets demonstrated that MZ B cell development was blocked at the transitional-1 to transitional-2-MZ precursor stage in the absence of functional IκBNS. Immunohistochemical analysis of spleen sections from wild-type and bumble mice revealed no alteration in the cellular MZ microenvironment, and analysis of bone marrow chimeras indicated that the MZ B cell development defect in bumble mice was B cell intrinsic. Further, we demonstrate that the B cells that repopulate the MZ in aged bumble mice were distinct from age-matched wild-type MZ B cells. Specifically, the expression of surface markers characteristic for MZ B cells was altered and the L chain Igλ⁺ repertoire was reduced in bumble mice. Finally, plasma cell differentiation of sorted LPS-stimulated MZ B cells was impaired, and aged bumble mice were unable to respond to NP-Ficoll immunization. These results demonstrate that IκBNS is required for an intact MZ B cell compartment in C57BL/6 mice.

Harnessing the CD1 restricted T cell response for leukemia adoptive immunotherapy

Disease recurrence following chemotherapy and allogeneic hematopoietic cell transplantation is the major unmet clinical need of acute leukemia. Adoptive cell therapy (ACT) with allogeneic T lymphocytes can control recurrences at the cost of inducing detrimental GVHD. Targeting T cell recognition on leukemia cells is therefore needed to overcome the problem and ensure safe and durable disease remission. In this review, we discuss adoptive cells therapy based on CD1-restricted T cells specific for tumor associated self-lipid antigens. CD1 molecules are identical in every individual and expressed essentially on mature hematopoietic cells and leukemia blasts, but not by parenchymatous cells, while lipid antigens are enriched in malignant cells and unlike to mutate upon immune-mediated selective pressure. Redirecting T cells against self-lipids presented by CD1 molecules can thus provide an appealing cell therapy strategy for acute leukemia that is patient-unrestricted and can minimize risks for GVHD, implying potential prognostic improvement for this cancer.

The Immunology of CD1- and MR1-Restricted T Cells

CD1- and MHC-related molecule-1 (MR1)-restricted T lymphocytes recognize nonpeptidic antigens, such as lipids and small metabolites, and account for a major fraction of circulating and tissue-resident T cells. They represent a readily activated, long-lasting population of effector cells and contribute to the early phases of immune response, orchestrating the function of other cells. This review addresses the main aspects of their immunological functions, including antigen and T cell receptor repertoires, mechanisms of nonpeptidic antigen presentation, and the current evidence for their participation in human and experimental diseases.

Group 1 CD1-restricted T cells and the pathophysiological implications of self-lipid antigen recognition

T cell responses are generally regarded as specific for protein-derived peptide antigens. This is based on the molecular paradigm dictated by the T cell receptor (TCR) recognition of peptide-major histocompatibility complexs, which provides the molecular bases of the specificity and restriction of the T cell responses. An increasing number of findings in the last 20 years have challenged this paradigm, by showing the existence of T cells specific for lipid antigens presented by CD1 molecules. CD1-restricted T cells have been proven to be frequent components of the immune system and to recognize exogenous lipids, derived from pathogenic bacteria, as well as cell-endogenous self-lipids. This represents a young and exciting area of research in immunology with intriguing biological bases and a potential direct impact on human health.

Role and regulation of CD1d in normal and pathological B cells

CD1d is a nonpolymorphic, MHC class I-like molecule that presents phospholipid and glycosphingolipid Ags to a subset of CD1d-restricted T cells called invariant NKT (iNKT) cells. This CD1d-iNKT cell axis regulates nearly all aspects of both the innate and adaptive immune responses. Expression of CD1d on B cells is suggestive of the ability of these cells to present Ag to, and form cognate interactions with, iNKT cells. In this article, we summarize key evidence regarding the role and regulation of CD1d in normal B cells and in humoral immunity. We then extend the discussion to B cell disorders, with emphasis on autoimmune disease, viral infection, and neoplastic transformation of B lineage cells, in which CD1d expression can be altered as a mechanism of immune evasion and can have both diagnostic and prognostic importance. Finally, we highlight current and future therapeutic strategies that aim to target the CD1d-iNKT cell axis in B cells.

All-trans-retinoic acid and CD38 ligation differentially regulate CD1d expression and α-galactosylceramide-induced immune responses

The MHC class-I like molecule CD1d presents glycolipid antigens and thereby activates invariant natural killer-T (NKT) cells. However, little is understood regarding the regulation of its expression. All-trans-retinoic acid (RA) and CD38, which is itself a target of RA, both independently regulate the differentiation of antigen presenting cells. In the current study, we treated human THP-1 cells and murine splenic cells with RA, with and without antibody-mediated ligation of cell-surface CD38. Whereas a physiological concentration (20 nM) of RA alone rapidly and markedly increased CD1d protein in THP-1 cells, there was a marked synergy between RA and ligation of CD38 with antibody to CD38. Moreover, RA and CD38 ligation differentially regulated CD1d protein distribution between the cell surface and intracellular compartments, as, whereas RA mainly increased intracellular CD1d protein, ligation of CD38 increased CD1d protein both at the cell surface and intracellularly. By confocal microscopy, CD1d was located close to the plasma membrane but only partially overlapped with LAMP1, a late endosomes/lysosomal marker. Furthermore, RA and/or CD38 ligation increased splenocyte proliferation and differentiation after treatment with the CD1 ligand α-galactosylceramide (αGalCer), evidenced by an increase in the number of splenic dendritic cells, NKT cells, and germinal center plasmacytes. RA also differentially regulated αGalCer-induced cytokine expression, increasing IL-4 and decreasing IFNγ production by total spleen cells and the NKT cell population. Our results indicate a previously unknown mechanism in which RA and CD38 differentially yet cooperatively regulate CD1d expression and antigen-presenting function, which could be important for the enhancement of immunity.

CD1d-mediated presentation of endogenous lipid antigens by adipocytes requires microsomal triglyceride transfer protein

Obesity-induced adipose tissue (AT) dysfunction results in a chronic low-grade inflammation that predisposes to the development of insulin resistance and type 2 diabetes. During the development of obesity, the AT-resident immune cell profile alters to create a pro-inflammatory state. Very recently, CD1d-restricted invariant (i) natural killer T (NKT) cells, a unique subset of lymphocytes that are reactive to so called lipid antigens, were implicated in AT homeostasis. Interestingly, recent data also suggest that human and mouse adipocytes can present such lipid antigens to iNKT cells in a CD1d-dependent fashion, but little is known about the lipid antigen presentation machinery in adipocytes. Here we show that CD1d, as well as the lipid antigen loading machinery genes pro-saposin (Psap), Niemann Pick type C2 (Npc2), α-galactosidase (Gla), are up-regulated in early adipogenesis, and are transcriptionally controlled by CCAAT/enhancer-binding protein (C/EBP)-β and -δ. Moreover, adipocyte-induced Th1 and Th2 cytokine release by iNKT cells also occurred in the absence of exogenous ligands, suggesting the display of endogenous lipid antigen-D1d complexes by 3T3-L1 adipocytes. Furthermore, we identified microsomal triglyceride transfer protein, which we show is also under the transcriptional regulation of C/EBPβ and -δ, as a novel player in the presentation of endogenous lipid antigens by adipocytes. Overall, our findings indicate that adipocytes can function as non-professional lipid antigen presenting cells, which may present an important aspect of adipocyte-immune cell communication in the regulation of whole body energy metabolism and immune homeostasis.

Polymorphisms in the CD1d promoter that regulate CD1d gene expression are associated with impaired NKT cell development

CD1d-restricted NKT cells comprise an innate-like T cell population that exerts significant influence over early events in the developing immune response. The frequency of NKT cells is highly variable in humans and in mice, but the basis for this variability remains unclear. In this study, we report a striking deficiency of type I NKT cells in the wild-derived inbred strains PWD/PhJ, SPRET/EiJ, and CAST/EiJ. Investigation of the underlying basis for the lack of type I NKT cells revealed that one strain, PWD/PhJ, exhibited a significant impairment in thymocyte and splenocyte CD1d gene and protein expression. Accordingly, both thymocytes and bone marrow-derived dendritic cells from PWD mice exhibited a significant impairment in the ability to present α-galactosylceramide to NKT cells. The impaired PWD CD1d gene expression was due to impaired CD1d promoter activity. Fine-mapping of the promoter activity revealed that two single nucleotide substitutions at positions -331 and -164 in the proximal promoter were each sufficient to account for the diminished PWD CD1d promoter activity. Examination of the strain distribution pattern of these polymorphisms revealed that, of 19 strains analyzed, only PWD and PWK mice possessed both CD1d promoter polymorphisms. A subsequent examination of the PWK strain revealed that it also exhibited impaired thymocyte CD1d expression and very low numbers of NKT cells. Taken together, these results provide new insight into the control of CD1d gene expression, and they have implications for the evolution of CD1d and type I NKT cells.

Human CD1d knock-in mouse model demonstrates potent antitumor potential of human CD1d-restricted invariant natural killer T cells

Despite a high degree of conservation, subtle but important differences exist between the CD1d antigen presentation pathways of humans and mice. These differences may account for the minimal success of natural killer T (NKT) cell-based antitumor therapies in human clinical trials, which contrast strongly with the powerful antitumor effects in conventional mouse models. To develop an accurate model for in vivo human CD1d (hCD1d) antigen presentation, we have generated a hCD1d knock-in (hCD1d-KI) mouse. In these mice, hCD1d is expressed in a native tissue distribution pattern and supports NKT cell development. Reduced numbers of invariant NKT (iNKT) cells were observed, but at an abundance comparable to that in most normal humans. These iNKT cells predominantly expressed mouse Vβ8, the homolog of human Vβ11, and phenotypically resembled human iNKT cells in their reduced expression of CD4. Importantly, iNKT cells in hCD1d knock-in mice exert a potent antitumor function in a melanoma challenge model. Our results show that replacement of mCD1d by hCD1d can select a population of functional iNKT cells closely resembling human iNKT cells. These hCD1d knock-in mice will allow more accurate in vivo modeling of human iNKT cell responses and will facilitate the preclinical assessment of iNKT cell-targeted antitumor therapies.

A novel function of adipocytes in lipid antigen presentation to iNKT cells

Systemic low-grade chronic inflammation has been intensively investigated in obese subjects. Recently, various immune cell types, such as macrophages, granulocytes, helper T cells, cytotoxic T cells, and B cells, have been implicated in the pathogenesis of adipose tissue inflammation. However, the roles of invariant natural killer T cells (iNKT cells) and the regulation of iNKT cell activity in adipose tissue are not thoroughly understood. Here, we demonstrated that iNKT cells were decreased in number in the adipose tissue of obese subjects. Interestingly, CD1d, a molecule involved in lipid antigen presentation to iNKT cells, was highly expressed in adipocytes, and CD1d-expressing adipocytes stimulated iNKT cell activity through physical interaction. iNKT cell population and CD1d expression were reduced in the adipose tissue of obese mice and humans compared to those of lean subjects. Moreover, iNKT cell-deficient Jα18 knockout mice became more obese and exhibited increased adipose tissue inflammation at the early stage of obesity. These data suggest that adipocytes regulate iNKT cell activity via CD1d and that the interaction between adipocytes and iNKT cells may modulate adipose tissue inflammation in obesity.

CD1d induction in solid tumor cells by histone deacetylase inhibitors through inhibition of HDAC1/2 and activation of Sp1

CD1d is a MHC class-like molecule that presents glycolipids to natural killer T (NKT) cells, then regulates innate and adaptive immunity. The regulation of CD1d gene expression in solid tumors is still largely unknown. Gene expression can be epigenetically regulated by DNA methylation and histone acetylation. We found that histone deacetylase inhibitors, trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA), induced CD1d gene expression in human (A549 and NCI-H292) and mouse (TC-1 and B16/F0) cancer cells. Simultaneous knockdown of HDAC1 and 2 induced CD1d gene expression. Sp1 inhibitor mitramycin A (MTM) blocked TSA- and SAHA-induced CD1d mRNA expression and Sp1 luciferase activity. Co-transfection of GAL4-Sp1 and Fc-luciferase reporters demonstrated that TSA and SAHA induced Sp1 luciferase reporter activity by enhancing Sp1 transactivation activity. The binding of Sp1 to CD1d promoter and histone H3 acetylation on Sp1 sites were increased by TSA and SAHA. These results indicate that TSA and SAHA could up-regulate CD1d expression in tumor cells through inhibition of HDAC1/2 and activation of Sp1.

Differential requirements for the Ets transcription factor Elf-1 in the development of NKT cells and NK cells

E26 Transformation specific (Ets) family transcription factors control the expression of a large number of genes regulating hematopoietic cell development and function. Two such transcription factors, Ets-1 and myeloid Elf-1-like factor (MEF), have been shown to play critical roles in both natural killer (NK)- and NKT-cell development, but not in the development of conventional T cells. In this study, we address the role of E74-like factor 1 (Elf-1), another Ets family transcription factor that is closely related to MEF but divergent from Ets-1, in NK- and NKT-cell development using Elf-1-deficient (Elf-1(-/-)) mice. Whereas the proportion of NK cells in Elf-1(-/-) mice was normal, the proportion of NKT cells was significantly reduced in the thymus and periphery of Elf-1(-/-) mice compared with wild-type (WT) mice. Although Ets-1-deficient mice lack NKT cells altogether, Elf-1(-/-) mice exhibited only a partial block in NKT-cell development caused by a cell-intrinsic defect in the selection, survival, and maturation of NKT cells. In addition, residual NKT cells found in Elf-1(-/-) mice produced less cytokine upon antigen stimulation compared with WT NKT cells. Our data demonstrate that Elf-1 plays an important and nonredundant role in the development and function of NKT cells, but is not involved in NK-cell development.

Transcriptional regulation of Elf-1: locus-wide analysis reveals four distinct promoters, a tissue-specific enhancer, control by PU.1 and the importance of Elf-1 downregulation for erythroid maturation

Ets transcription factors play important roles during the development and maintenance of the haematopoietic system. One such factor, Elf-1 (E74-like factor 1) controls the expression of multiple essential haematopoietic regulators including Scl/Tal1, Lmo2 and PU.1. However, to integrate Elf-1 into the wider regulatory hierarchies controlling haematopoietic development and differentiation, regulatory elements as well as upstream regulators of Elf-1 need to be identified. Here, we have used locus-wide comparative genomic analysis coupled with chromatin immunoprecipitation (ChIP-chip) assays which resulted in the identification of five distinct regulatory regions directing expression of Elf-1. Further, ChIP-chip assays followed by functional validation demonstrated that the key haematopoietic transcription factor PU.1 is a major upstream regulator of Elf-1. Finally, overexpression studies in a well-characterized erythroid differentiation assay from primary murine fetal liver cells demonstrated that Elf-1 downregulation is necessary for terminal erythroid differentiation. Given the known activation of PU.1 by Elf-1 and our newly identified reciprocal activation of Elf-1 by PU.1, identification of an inhibitory role for Elf-1 has significant implications for our understanding of how PU.1 controls myeloid-erythroid differentiation. Our findings therefore not only represent the first report of Elf-1 regulation but also enhance our understanding of the wider regulatory networks that control haematopoiesis.

Human CD1D gene expression is regulated by LEF-1 through distal promoter regulatory elements

CD1d-expressing cells present lipid Ag to CD1d-restricted NKT cells, which play an important role in immune regulation and tumor rejection. Lymphoid enhancer-binding factor-1 (LEF-1) is one of the regulators of the Wnt signaling pathway, which is a powerful regulator in cellular growth, differentiation, and transformation. There is little evidence connecting Wnt signaling to CD1d expression. In this study, we have identified LEF-1 as a regulator of the expression of the gene encoding the human CD1d molecule (CD1D). We found that LEF-1 binds specifically to the CD1D promoter. Overexpression of LEF-1 in K562 or Jurkat cells suppresses CD1D promoter activity and downregulates endogenous CD1D transcripts, whereas knockdown of LEF-1 using LEF-1-specific small interfering RNA increases CD1D transcripts in K562 and Jurkat cells but there are different levels of surface CD1d on these two cell types. Chromatin immunoprecipitation showed that the endogenous LEF-1 is situated at the CD1D promoter and interacts with histone deacetylase-1 to facilitate the transcriptional repressor activity. Knockdown of LEF-1 using small interfering RNA potentiates an acetylation state of histone H3/H4, supporting the notion that LEF-1 acts as a transcriptional repressor for the CD1D gene. Our finding links LEF-1 to CD1D and suggests a role of Wnt signaling in the regulation of the human CD1D gene.

The surprising diversity of lipid antigens for CD1-restricted T cells

CD1 proteins have been conserved throughout mammalian evolution and function to present lipid antigens to T cells. Crystal structures of CD1-lipid complexes show that CD1 antigen-binding grooves are composed of four pockets and two antigen entry portals. This structural information now provides a detailed understanding of how CD1-binding grooves capture a surprisingly diverse array of lipid ligands. CD1-expressing APCs are able to acquire lipid antigens from their own pool of lipids and from exogenous sources, including microbial pathogens, bystander cells, or even the systemic circulation. CD1 proteins bind to certain antigens using high stringency loading reactions within endosomes that involve low pH, glycosidases, and lipid transfer proteins. Other antigens can directly load onto CD1 proteins using low stringency mechanisms that are independent of cellular factors. New evidence from in vivo systems shows that CD1-restricted T cells influence outcomes in infectious, autoimmune, and allergic diseases. These studies lead to a broader view of the natural function of alphabeta T cells, which involves recognition of both cellular proteins and lipids.

Oncogenic activation of the human Pygopus2 promoter by E74-like factor-1

Pygopus is a component of the T-cell factor/beta-catenin transcriptional complex essential for activation of Wnt target genes and is also required for cell regulation in the absence of Wnt signaling. Human Pygopus2 (hPygo2) is overexpressed in a high proportion of breast and epithelial ovarian malignant tumors and is required for the growth of several cell lines derived from these carcinomas. The mechanisms regulating hPygo2 gene activation, however, are unknown. Here, we have determined cis- and trans-interacting factors responsible for hPygo2 expression in cancer. The minimal region required for a maximal 109-fold activation of the hPygo2 promoter in MCF-7 breast cancer cells is 48 bp upstream of the start of transcription. Within 25 bp of the transcriptional start, there are two overlapping tandem Ets transcription factor-binding sites, which are critical for hPygo2 promoter activity. In vitro DNA pull-down assays and proteomic analyses identified the Ets family members Elk-1 and E74-like factor-1 (Elf-1) as potential hPygo2 promoter binding factors, whereas in vivo chromatin immunoprecipitation assays verified that only Elf-1 specifically bound to the hPygo2 promoter in MCF-7 cells. Modulation of elf-1 in MCF-7 cells by silencing via RNA interference or overexpression caused a corresponding decrease or increase, respectively, in hPygo2 promoter activity. Overexpression of Elf-1 in HeLa cells, in which Elf-1 is expressed at a lower level than in MCF-7 cells, caused a 4-fold increase in endogenous hPygo2 mRNA levels. These results provide new evidence that Elf-1 is involved in transcriptional activation of hPygo2. Like hPygo2, previous studies implicated Elf-1 in breast and ovarian cancer and our present findings suggest that the oncogenic requirement of hPygo2 is fulfilled, in part, by Elf-1.

ERM is expressed by alveolar epithelial cells in adult mouse lung and regulates caveolin-1 transcription in mouse lung epithelial cell lines

We previously identified an Ets cis-element in the mouse caveolin-1 promoter that is selectively activated in lung epithelial (E10), but not lung endothelial murine lung endothelial cell line (MFLM-4), cell lines and therefore appears important for differential, cell-specific caveolin-1 transcription. In the present study, we demonstrate that immunostaining of adult mouse lung detects the ETS protein Ets-related molecule (ERM PEA3) in distal lung epithelium in alveolar type I and II cells, but not in bronchial epithelium or lung endothelial cells. We tested ERM and polyomavirus enhancer activator 3 (PEA3) for their ability to increase endogenous caveolin-1 transcripts and to activate caveolin-1 promoter fragments containing the -865 Ets cis-element. Chromatin immunoprecipitation (ChIP) assays show that both ERM and PEA3 bind to the caveolin-1 promoter in murine E10, but not MFLM-4, cells. Normalized luciferase activities show that only ERM activates the caveolin-1 promoter in E10 cells, but neither protein enhances promoter activity in MFLM-4 cells. Mutation of the Ets site blocks ERM-mediated promoter activation in E10 cells. Furthermore, overexpression of ERM increases the cellular content of caveolin-1 mRNA and protein, in E10, but not MFLM-4, cells. The effects of PEA3 on the cellular content of endogenous caveolin-1 expression are variable. These results demonstrate that ERM is involved in caveolin-1 regulation in a murine lung epithelial, but not lung endothelial cell line. We conclude that transcriptional regulation of caveolin-1 differs markedly between lung epithelial and endothelial cell lines, perhaps explaining why the onset of caveolin-1 expression differs in epithelial and endothelial cells during lung development.

CD1 expression on antigen-presenting cells

CD1 proteins present self and microbial glycolipids to CD 1-restricted T cells, or in the case of CD1d, to NKT cells. The CD1 family in humans consists of group I proteins CDla, CDlb, CDlc, and CDle and the group II protein CDld. Rodents express only CDld, but as CD1d is broadly expressed and traffics to all endosomal compartments, this single CD1 family member is thereby able to acquire antigens in many subcellular compartments. A complete understanding of the CD 1 family requires an appreciation of which cells express CD1 and how CD1 contributes to the unique function of each cell type. While group I CD 1 expression is limited to thymocytes and professional APCs, CD1d has a wider tissue distribution and can be found on many nonhematopoietic cells. The expression and regulation of CD1 are presented here with particular emphasis on the function of CD1 in thymocytes, B cells, monocytes and macrophages, dendritic cells (DCs), and intestinal epithelial cells (IECs). Altered expression of CD 1 in cancer, autoimmunity, and infectious disease is well documented, and the implication of CD 1 expression in these diseases is discussed.

IFN-beta-mediated up-regulation of CD1d in bacteria-infected APCs

The expression of CD1d molecules is essential for the selection and activation of a unique subset of T cells, invariant NKT cells, which express limited TCR diversity and have been demonstrated to function in both regulatory and antimicrobial immune responses. Although it has been reported that the levels of CD1d expression can be modulated during infection, the mechanisms that mediate this effect are poorly defined. In this study, we show that infection of dendritic cells and macrophages both in vitro and in vivo with the intracellular pathogen Listeria monocytogenes leads to up-regulation of CD1d. IFN-beta is required to mediate this up-regulation in L. monocytogenes infection, as well as being sufficient to up-regulate CD1d expression in vitro. Unlike MHC class I molecules, the increased surface expression of CD1d by IFN-beta is not regulated at the transcriptional level. Confocal microscopy and metabolic labeling experiments show that the total pool of CD1d protein is increased in IFN-beta-treated cells and that increased surface expression of CD1d is not due to the redistribution of the intracellular pool of CD1d. IFN-beta treatment increases the de novo synthesis of CD1d. This change in surface CD1d expression was functionally relevant, as IFN-beta-treated dendritic cells are more efficient in stimulating invariant NKT cells than untreated controls. Taken together, these data support a role for early IFN-beta-mediated up-regulation of CD1d in NKT cell activation during infection.

Activating Transcription Factor/cAMP Response Element Binding Protein Family Member Regulated Transcription of CD1A

CD1a has a unique expression pattern among Ag-presenting molecules, expressed specifically on cortical thymocytes and APCs. As autoimmune disease, infection, and tumors can all result in alteration of CD1a expression, we are attempting to characterize the transcriptional regulation, and thus shed some light on specific expression, of CD1A. In this study, we have identified a minimal proximal promoter region required for CD1A transcription. Computer searches within this region identified numerous potential binding sites for lymphoid-specific transcription factors, including the ETS transcription factors, C/EBP, GATA, and CREB. Deletion and site-specific mutant analysis revealed a critical role of a potential cAMP response element (CRE) 965 bp upstream of the CD1A translation start site. Two activating transcription factor (ATF)/CREB family members, CREB-1 and ATF-2, are able to bind this site in vitro and in vivo. Notably, activation of ATF/CREB family members decreases CD1A transcription, while decrease in ATF-2 expression results in increased CD1A RNA level. The fact that these factors also bind the CD1A promoter in human monocytes strongly suggests a role for ATF/CREB family members in regulation of CD1A expression.

A failure to launch: fuelling cytokine secretion in iNKT cells

In this issue of Immunity, Bezbradica et al., (2006) uncover an unsuspected role for the cytokine GM-CSF in the thymic development of invariant NKT cells, a role that licenses these cells to secrete effector cytokines upon activation in the periphery.

TLR gateways to CD1 function

CD1-restricted T cells can be activated by diverse lipids derived from mammals, bacteria and protozoa. Certain lipids function as antigens, which bind to CD1 proteins and contact T cell antigen receptors. Other lipids activate CD1-restricted T cells by functioning as adjuvants. By stimulating Toll-like receptors on antigen-presenting cells, these adjuvants alter cytokine secretion, lipid antigen synthesis and CD1 protein translation. Delineation of the separate mechanisms by which adjuvants and antigens activate CD1-restricted T cells is leading to new hypotheses about the functions of individual CD1 proteins during the transition from innate to acquired immune responses.

Regulation of the human LAT gene by the Elf-1 transcription factor

Background

The LAT gene encodes an intracellular adaptor protein that links cell-surface receptor engagement to numerous downstream signalling events, and thereby plays an integral role in the function of cell types that express the gene, including T cells, mast cells, natural killer cells, and platelets. To date, the mechanisms responsible for the transcriptional regulation of this gene have not been investigated.

Results

In this study we have mapped the transcriptional start sites for the human LAT gene and localized the 5' and 3' boundaries of the proximal promoter. We find that the promoter contains both positive and negative regulatory regions, and that two binding sites for the Ets family of transcription factors have a strong, positive effect on gene expression. Each site binds the Ets family member Elf-1, and overexpression of Elf-1 augments LAT promoter activity. The promoter also contains a Runx binding site adjacent to one of the Ets sites. This site, which is shown to bind Runx-1, has an inhibitory effect on gene expression. Finally, data is also presented indicating that the identified promoter may regulate cell-type specific expression.

Conclusion

Collectively, these results provide the first insights into the transcriptional regulation of the LAT gene, including the discovery that the Ets transcription factor Elf-1 may play a central role in its expression.