Ets transcription factors regulate AIRE gene promoter

Novel Insights into the Autoimmunity from the Genetic Approach of the Human Disease

Autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic inborn error of autoimmunity that is caused by damaging germline variants in the AIRE gene and clinically manifests with multiple autoimmune diseases in patients. Studies on the function of the AIRE gene, discovered in 1997, have contributed to fundamental aspects of human immunology as they have been important in understanding the basic mechanism of immune balance between self and non-self. This chapter looks back to the discovery of the AIRE gene, reviews its main properties, and discusses the key findings of its function in the thymus. However, more recent autoantibody profilings in APECED patients have highlighted a gap in our knowledge of the disease pathology and point to the need to revisit the current paradigm of AIRE function. The chapter reviews these new findings in APECED patients, which potentially trigger new thoughts on the mechanism of immune tolerance.

Loss of AIRE-Mediated Immune Tolerance and the Skin

The core function of the immune response is to distinguish between self and foreign. The multiorgan human autoimmune disease, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED/autoimmune polyendocrine syndrome type 1) is an example of what happens in the body when central immune tolerance goes astray. APECED revealed the existence and function of the autoimmune regulator gene, which has a central role in the development of tolerance. The discovery of autoimmune regulator was the start of a new period in immunology and in understanding the role of central and peripheral tolerance, also very relevant to many skin diseases as we highlight in this review.

AIRE is induced in oral squamous cell carcinoma and promotes cancer gene expression

Autoimmune regulator (AIRE) is a transcriptional regulator that is primarily expressed in medullary epithelial cells, where it induces tissue-specific antigen expression. Under pathological conditions, AIRE expression is induced in epidermal cells and promotes skin tumor development. This study aimed to clarify the role of AIRE in the pathogenesis of oral squamous cell carcinoma (OSCC). AIRE expression was evaluated in six OSCC cell lines and in OSCC tissue specimens. Expression of STAT1, ICAM1, CXCL10, CXCL11, and MMP9 was elevated in 293A cells stably expressing AIRE, and conversely, was decreased in AIRE-knockout HSC3 OSCC cells when compared to the respective controls. Upregulation of STAT1, and ICAM in OSCC cells was confirmed in tissue specimens by immunohistochemistry. We provide evidence that AIRE exerts transcriptional control in cooperation with ETS1. Expression of STAT1, ICAM1, CXCL10, CXCL11, and MMP9 was increased in 293A cells upon Ets1 transfection, and coexpression of AIRE further increased the expression of these proteins. AIRE coprecipitated with ETS1 in a modified immunoprecipitation assay using formaldehyde crosslinking. Chromatin immunoprecipitation and quantitative PCR analysis revealed that promoter fragments of STAT1, ICAM1, CXCL10, and MMP9 were enriched in the AIRE precipitates. These results indicate that AIRE is induced in OSCC and supports cancer-related gene expression in cooperation with ETS1. This is a novel function of AIRE in extrathymic tissues under the pathological condition.

AIRE promotes androgen-independent prostate cancer by directly regulating IL-6 and modulating tumor microenvironment

Early stage prostate cancers are dependent on androgens for their growth and survival and androgen withdrawal causes them to regress. Progressive prostate cancers eventually acquire androgen independence rendering anti-androgen therapy ineffective. However, the factors leading to this have not been adequately addressed. This study shows that AIRE finds differential expression in androgen-dependent and -independent prostate cancer cells. AIRE expression is more in androgen-independent cells due to its regulation by transcription factor Elk-1. These enhanced levels of AIRE modulate the prostate tumor microenvironment by transcriptionally activating a malignancy gene IL-6 in androgen-independent cells. Additionally, AIRE prevents the cancer cells from anticancer drug-induced death and enhances their invasiveness. Moreover, AIRE by modulating the cytokine milieu skews the tumor-associated macrophage polarization towards M2 phenotype with increased CD206 and CD163 expression. Subcutaneous mouse model of prostate cancer revealed AIRE^+/+ mice forming a palpable tumor and presents lymphadenopathy however, only a small benign tumor is observed in AIRE^−/− mice and lymph nodes appear normal in size. In conclusion, our findings suggest AIRE as a probable factor in promoting prostate cancer progression.

The dual role of autoimmune regulator in maintaining normal expression level of tissue-restricted autoantigen in the thymus: A modeling investigation

The expression level of tissue-restricted autoantigens (TSA) in the thymus is crucial for the negative selection of autoreactive T cells during central tolerance. The autoimmune regulator factor (AIRE) plays an important role in the positive regulation of these TSA in medullary thymic epithelial cells and, consequently, in the negative selection of high-avidity autoreactive T cells. Recent studies, however, revealed that thymic islet cell autoantigen (ICA69) expression level in non-obese diabetic (NOD) mice, prone to developing type 1 diabetes (T1D), is reduced due to an increase in the binding affinity of AIRE to the Ica1-promoter region, which regulates ICA69 protein synthesis. This seemed to suggest that AIRE acts as a transcriptional repressor of Ica1 gene in the thymus, causing down regulation in the expression level of ICA69. To investigate this hypothesis and the apparent dual role of AIRE in negative selection, we develop a series of mathematical models of increasing complexity describing the temporal dynamics of self-reactive T cells, AIRE-mRNA and AIRE-(in)dependent thymic TSA-associated genes. The goal is to understand how changing the binding affinity of AIRE to Ica1-promoter affects both T-cell tolerance and the dual role of the transcription factor. Using stability analysis and numerical computations, we show that the model possesses a bistable switch, consisting of healthy and autoimmune states, in the expression level of Ica1 gene with respect to AIRE binding affinity, and that it can capture the experimentally observed dual role of AIRE. We also show that the model must contain a positive feedback loop exerted by T cells on AIRE expression (e.g., via lymphotoxin released by T cells) to produce bistability. Our results suggest that the expression-level of AIRE-mRNA in the healthy state is lower than that of the autoimmune state, and that negative selection is very sensitive to parameter perturbations in T-cell avidity.

Epithelial Fli1 deficiency drives systemic autoimmunity and fibrosis: Possible roles in scleroderma

Systemic sclerosis (SSc), or scleroderma, is a multisystem autoimmune disorder characterized by vasculopathy and fibrosis in the skin and internal organs, most frequently in the esophagus and lungs. Hitherto, studies on SSc pathogenesis centered on immune cells, vascular cells, and fibroblasts. Although dysregulated keratinocytes in SSc have been recently reported, the contribution of epithelial cells to pathogenesis remains unexplored. In this study, we demonstrated the induction of SSc-like molecular phenotype in keratinocytes by gene silencing of transcription factor Friend leukemia virus integration 1 (Fli1), the deficiency of which is implicated in SSc pathogenesis. Keratin 14-expressing epithelial cell-specific Fli1 knockout mice spontaneously developed dermal and esophageal fibrosis with epithelial activation. Furthermore, they developed remarkable autoimmunity with interstitial lung disease derived from thymic defects with down-regulation of autoimmune regulator (Aire). Importantly, Fli1 directly regulated Aire expression in epithelial cells. Collectively, epithelial Fli1 deficiency might be involved in the systemic autoimmunity and selective organ fibrosis in SSc. This study uncovers unidentified roles of dysregulated epithelial cells in SSc pathogenesis.

Sex bias in CNS autoimmune disease mediated by androgen control of autoimmune regulator

Male gender is protective against multiple sclerosis and other T-cell-mediated autoimmune diseases. This protection may be due, in part, to higher androgen levels in males. Androgen binds to the androgen receptor (AR) to regulate gene expression, but how androgen protects against autoimmunity is not well understood. Autoimmune regulator (Aire) prevents autoimmunity by promoting self-antigen expression in medullary thymic epithelial cells, such that developing T cells that recognize these self-antigens within the thymus undergo clonal deletion. Here we show that androgen upregulates Aire-mediated thymic tolerance to protect against autoimmunity. Androgen recruits AR to Aire promoter regions, with consequent enhancement of Aire transcription. In mice and humans, thymic Aire expression is higher in males compared with females. Androgen administration and male gender protect against autoimmunity in a multiple sclerosis mouse model in an Aire-dependent manner. Thus, androgen control of an intrathymic Aire-mediated tolerance mechanism contributes to gender differences in autoimmunity.

Estrogen turns down "the AIRE"

Genetic alterations are known drivers of autoimmune disease; however, there is a much higher incidence of autoimmunity in women, implicating sex-specific factors in disease development. The autoimmune regulator (AIRE) gene contributes to the maintenance of central tolerance, and complete loss of AIRE function results in the development of autoimmune polyendocrinopathy syndrome type 1. In this issue of the JCI, Dragin and colleagues demonstrate that AIRE expression is downregulated in females as the result of estrogen-mediated alterations at the AIRE promoter. The association between estrogen and reduction of AIRE may at least partially account for the elevated incidence of autoimmune disease in women and has potential implications for sex hormone therapy.

A highly conserved NF-κB-responsive enhancer is critical for thymic expression of Aire in mice

Autoimmune regulator (Aire) has a unique expression pattern in thymic medullary epithelial cells (mTECs), in which it plays a critical role in the activation of tissue-specific antigens. The expression of Aire in mTECs is activated by receptor activator of nuclear factor κB (RANK) signaling; however, the molecular mechanism behind this activation is unknown. Here, we characterize a conserved noncoding sequence 1 (CNS1) containing two NF-κB binding sites upstream of the Aire coding region. We show that CNS1-deficient mice lack thymic expression of Aire and share several features of Aire-knockout mice, including downregulation of Aire-dependent genes, impaired terminal differentiation of the mTEC population, and reduced production of thymic Treg cells. In addition, we show that CNS1 is indispensable for RANK-induced Aire expression and that CNS1 is activated by NF-κB pathway complexes containing RelA. Together, our results indicate that CNS1 is a critical link between RANK signaling, NF-κB activation, and thymic expression of Aire.

The AIRE -230Y Polymorphism Affects AIRE Transcriptional Activity: Potential Influence on AIRE Function in the Thymus

BACKGROUND

The autoimmune regulator (AIRE) is expressed in the thymus, particularly in thymic medullary epithelial cells (mTECs), and is required for the ectopic expression of a diverse range of peripheral tissue antigens by mTECs, facilitating their ability to perform negative selection of auto-reactive immature T-cells. The expression profile of peripheral tissue antigens is affected not only by AIRE deficiency but also with variation of AIRE activity in the thymus.

METHOD AND RESULTS

Therefore we screened 591bp upstream of the AIRE transcription start site including AIRE minimal promoter for single nucleotide polymorphism (SNPs) and identified two SNPs -655R (rs117557896) and -230Y (rs751032) respectively. To study the effect of these variations on AIRE promoter activity we generated a Flp-In host cell line which was stably transfected with a single copy of the reporter vector. Relative promoter activity was estimated by comparing the luciferase specific activity for lysates of the different reporter AIRE promoter-reporter gene constructs including AIRE-655G AIRE-230C, AIRE-655G AIRE-230T and AIRE-655A AIRE-230C. The analysis showed that the commonest haplotype AIRE-655G AIRE-230C has the highest luciferase specific activity (p<0.001). Whereas AIRE-655G AIRE-230T has a luciferase specific activity value that approaches null. Both AIRE promoter polymorphic sites have one allele that forms a CpG methylation site which we determined can be methylated in methylation assays using the M.SssI CpG methyltransferase.

CONCLUSION

AIRE-230Y is in a conserved region of the promoter and is adjacent to a predicted WT1 transcription factor binding site, suggesting that AIRE-230Y affects AIRE expression by influencing the binding of biochemical factors to this region. Our findings show that AIRE-655GAIRE-230T haplotype could dramatically alter AIRE transcription and so have an effect on the process of negative selection and affect susceptibility to autoimmune conditions.

Expression of thyrotropin receptor, thyroglobulin, sodium-iodide symporter, and thyroperoxidase by fibrocytes depends on AIRE

CONTEXT

CD34(+) fibrocytes, bone marrow-derived progenitor cells, infiltrate orbital connective tissue in thyroid-associated ophthalmopathy, a manifestation of Graves' disease. In the orbit, they become CD34(+) fibroblasts and coexist with native CD34(-) fibroblasts. Fibrocytes have been shown to express TSH receptor and thyroglobulin.

OBJECTIVE

The objective of the study was to determine whether a broader repertoire of thyroid protein expression can be detected in fibrocytes and whether a common factor is responsible.

DESIGN/SETTING/PARTICIPANTS

Fibrocytes and fibroblasts were collected and analyzed from healthy individuals and those with Graves' disease in an academic clinical practice.

MAIN OUTCOME MEASURES

Real-time PCR, Western blot analysis, gene promoter analysis, cell transfections, and flow cytometric cell sorting were performed.

RESULTS

We detect two additional thyroid proteins expressed by fibrocytes, namely sodium-iodide symporter and thyroperoxidase. The autoimmune regulator (AIRE) protein appears necessary for this expression. AIRE expression in fibrocytes results from an active AIRE gene promoter and stable AIRE mRNA. Knocking down AIRE with a targeting small interfering RNA reduces the expression of these thyroid proteins in fibrocytes as well as the transcription factors paired box-8 and thyroid transcription factor-1. When compared with an unaffected first-degree relative, levels of these proteins are substantially reduced in fibrocytes from an individual with an inactivating AIRE mutation. Levels of AIRE and the thyroid proteins are lower in orbital fibroblasts from patients with thyroid-associated ophthalmopathy than in fibrocytes. However, when mixed fibroblast populations are sorted into pure CD34(+) and CD34(-) subsets, the levels of these proteins are dramatically increased selectively in CD34(+) fibroblasts.

CONCLUSIONS

Fibrocytes express four proteins, the aggregate expression of which was previously thought to be restricted to thyroid epithelium. These proteins represent the necessary molecular biosynthetic machinery necessary for thyroid hormone production. Our findings implicate AIRE in the promiscuous expression of thyroid proteins in fibrocytes.

Regulations of gene expression in medullary thymic epithelial cells required for preventing the onset of autoimmune diseases

Elimination of potential self-reactive T cells in the thymus is crucial for preventing the onset of autoimmune diseases. Epithelial cell subsets localized in thymic medulla [medullary thymic epithelial cells (mTECs)] contribute to this process by supplying a wide range of self-antigens that are otherwise expressed in a tissue-specific manner (TSAs). Expression of some TSAs in mTECs is controlled by the autoimmune regulator (AIRE) protein, of which dysfunctional mutations are the causative factor of autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). In addition to the elimination of self-reactive T cells, recent studies indicated roles of mTECs in the development of Foxp3-positive regulatory T cells, which suppress autoimmunity and excess immune reactions in peripheral tissues. The TNF family cytokines, RANK ligand, CD40 ligand, and lymphotoxin were found to promote the differentiation of AIRE- and TSA-expressing mTECs. Furthermore, activation of NF-κB is essential for mTEC differentiation. In this mini-review, we focus on molecular mechanisms that regulate induction of AIRE and TSA expression and discuss possible contributions of these mechanisms to prevent the onset of autoimmune diseases.

The mechanism of tissue-restricted antigen gene expression by AIRE

The autoimmune regulator is a critical transcription factor for generating central tolerance in the thymus. Recent studies have revealed how the autoimmune regulator targets many otherwise tissue-restricted Ag genes to enable negative selection of autoreactive T cells.

Screening large numbers of expression patterns of transcription factors in late stages of the mouse thymus

Transcription factor families are well known to be involved in the intrinsic pathways that regulate the organogenesis, early development, and microenvironment of the thymus. However, identification of the transcription factors (TFs) involved in the late development of the thymus, particularly later than embryonic day 15.5 (E15.5), is progressing slowly. In this study, we used in situ hybridization to screen numerous expression patterns of the TFs involved in the development of the mouse thymus. More than 400 members, including unique TFs and some transcription co-factors, were tested. Among the screened TFs, 160 were found to be expressed in the thymus after E15.5, and 74 of these were expressed in restricted areas.

Aberrant transcriptional regulatory network in T cells of multiple sclerosis

To identify the molecular network of the genes deregulated in multiple sclerosis (MS), we studied gene expression profile of purified CD3(+) T cells isolated from Hungarian monozygotic MS twins by DNA microarray analysis. By comparing three concordant and one discordant pairs, we identified 20 differentially expressed genes (DEG) between the MS patient and the genetically identical healthy subject. Molecular network of 20 DEG analyzed by KeyMolnet, a comprehensive information platform, indicated the close relationship with transcriptional regulation by the Ets transcription factor family and the nuclear factor NF-kappaB. This novel bioinformatic approach proposes the logical hypothesis that aberrant regulation of the complex transcriptional regulatory network contributes to development of pathogenic T cells in MS.

Highly variable expression of tissue-restricted self-antigens in human thymus: Implications for self-tolerance and autoimmunity

Induction of T cell tolerance in the thymus (central tolerance) is essential for preventing organ-specific autoimmunity. This apparent paradox is in part explained by promiscuous expression of numerous tissue-restricted self-antigens (TRA) in medullary thymic epithelial cells (mTEC), which is highly conserved between mice and man. In animal models, the threshold of central tolerance towards such TRA is surprisingly sensitive towards minor shifts in antigen expression levels and this might also be the case in humans. To precisely assess the inter-individual variability of TRA expression in man, we determined the level of transcription of several auto-antigens in purified human mTEC and subsets thereof by quantitative RT-PCR. We detected two expression patterns: first, high variability (>20-fold) correlated with autoimmune regulator (Aire) expression and mTEC differentiation, and secondly, non-correlated low variability. Importantly, our approach revealed a significantly higher Aire-correlated insulin transcription in mTEC of carriers of the protective insulin-dependent diabetes mellitus locus 2 haplotype compared to the non-protective haplotype. The considerable, yet selective variability in thymic expression levels of target auto-antigen expression might constitute a hitherto underestimated risk factor for the susceptibility of autoimmune diseases in man.