Specific activation of human interleukin-5 depends on de novo synthesis of an AP-1 complex

Progress in the Study of Fra-2 in Respiratory Diseases

Fos-related antigen-2 (Fra-2) is a member of the activating protein-1 (AP-1) family of transcription factors. It is involved in controlling cell growth and differentiation by regulating the production of the extracellular matrix (ECM) and coordinating the balance of signals within and outside the cell. Fra-2 is not only closely related to bone development, metabolism, and immune system and eye development but also in the progression of respiratory conditions like lung tumors, asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD). The increased expression and activation of Fra-2 in various lung diseases has been shown in several studies. However, the specific molecular mechanisms through which Fra-2 affects the development of respiratory diseases are not yet understood. The purpose of this research is to summarize and delineate advancements in the study of the involvement of transcription factor Fra-2 in disorders related to the respiratory system.

Fra-2 Is a Dominant Negative Regulator of Natural Killer Cell Development

Natural killer (NK) cells play an important role in recognizing and killing pathogen-infected or malignant cells. Changes in their numbers or activation can contribute to several diseases and pathologies including systemic sclerosis (SSc), an autoimmune disease characterized by inflammation and tissue remodeling. In these patients, increased expression of the AP-1 transcription factor, Fra-2 was reported. In mice ectopic overexpression of Fra-2 (TG) leads to SSc with strong pulmonary fibrosis, pulmonary hypertension, and inflammation. Analysis of the underlying immune cell profile in the lungs of young TG mice, which do not yet show any signs of lung disease, revealed increased numbers of eosinophils and T cells but strongly reduced NK numbers. Therefore, we aimed to identify the cause of the absence of NK cells in the lungs of these mice and to determine the potential role of Fra-2 in NK development. Examination of inflammatory cell distribution in TG mice revealed similar NK deficiencies in the spleen, blood, and bone marrow. Deeper analysis of the WT and TG bone marrow revealed a potential NK cell developmental defect beginning at the preNKP stage. To determine whether this defect was cell-intrinsic or extrinsic, mixed bone marrow chimera and in vitro differentiation experiments were performed. Both experiments showed that the defect caused by Fra-2 was primarily cell-intrinsic and minimally dependent on the environment. Closer examination of surface markers and transcription factors required for NK development, revealed the expected receptor distribution but changes in transcription factor expression. We found a significant reduction in Nfil3, which is essential for the transition of common lymphoid cells to NK committed precursor cells and an AP-1 binding site in the promotor of this gene. In Summary, our data demonstrates that regulation of Fra-2 is essential for NK development and maturation, and suggests that the early NK dysfunction plays an important role in the pathogenesis of systemic sclerosis.

Pulmonary fibrosis in Fra-2 transgenic mice is associated with decreased numbers of alveolar macrophages and increased susceptibility to pneumococcal pneumonia

Idiopathic pulmonary fibrosis (IPF) is a deadly condition characterized by progressive respiratory dysfunction. Exacerbations due to airway infections are believed to promote disease progression, and presence of Streptococcus in the lung microbiome has been associated with the progression of IPF and mortality. The aim of this study was to analyze the effect of lung fibrosis on susceptibility to pneumococcal pneumonia and bacteremia. The effects of subclinical (low dose) infection with Streptococcus pneumoniae were studied in a well characterized fos-related antigen-2 (Fra-2) transgenic (TG) mouse model of spontaneous, progressive pulmonary fibrosis. Forty-eight hours after transnasal infection with S. pneumoniae, bacterial load was assessed in lung tissue, bronchoalveolar lavage (BAL), blood, and spleen. Leukocyte subsets and cytokine levels were analyzed in BAL and blood. Lung compliance and arterial blood gases were assessed. In contrast to wildtype mice, low dose lung infection with S. pneumoniae in Fra-2 TG mice resulted in substantial pneumonia including weight loss, increased lung bacterial load, and bacteremia. BAL alveolar macrophages were reduced in Fra-2 TG mice compared to the corresponding WT mice. Proinflammatory cytokines and chemokines (IL-1β, IL-6, TNF-α, and CXCL1) were elevated upon infection in BAL supernatant and plasma of Fra-2 TG mice. Lung compliance was decreased in Fra-2 TG mice following low dose infection with S. pneumoniae. Pulmonary fibrosis increases susceptibility to pneumococcal pneumonia and bacteremia possibly via impaired alveolar bacterial clearance.

Transcription factor Fra-2 and its emerging role in matrix deposition, proliferation and inflammation in chronic lung diseases

Fos-related antigen-2 (Fra-2) belongs to the activator protein 1 (AP-1) family of transcription factors and is involved in a broad variety of cellular processes, such as proliferation or differentiation. Aberrant expression of Fra-2 or regulation can lead to severe growth defects or diverse pathologies. Elevated Fra-2 expression has been described in several chronic lung diseases, such as pulmonary fibrosis, chronic obstructive pulmonary disease and asthma. However, the pathomechanisms behind the Fra-2-induced pulmonary remodelling are still not fully elucidated. Fra-2 overexpressing mice were initially described as a model of systemic sclerosis associated organ fibrosis, with predominant alterations in the lung. High levels of Fra-2 expression give rise to profound inflammation with severe remodelling of the parenchyma and the vasculature, resulting in fibrosis and pulmonary hypertension, respectively, but also alters bronchial function. In this review we discuss the central role of Fra-2 connecting inflammation, cellular proliferation and extracellular matrix deposition underlying chronic lung diseases and what we can learn for future therapeutic options.

Cytokine-induced cysteine- serine-rich nuclear protein-1 (CSRNP1) selectively contributes to MMP1 expression in human chondrocytes

Irreversible cartilage collagen breakdown by the collagenolytic matrix metalloproteinases (MMPs)-1 and MMP-13 represents a key event in pathologies associated with tissue destruction such as arthritis. Inflammation is closely associated with such pathology and occurs in both rheumatoid and osteoarthritis making it highly relevant to the prevailing tissue damage that characterises these diseases. The inflammation-induced activating protein-1 (AP-1) transcription factor is an important regulator of both MMP1 and MMP13 genes with interplay between signalling pathways contributing to their expression. Here, we have examined the regulation of MMP1 expression, and using in vivo chromatin immunoprecipitation analyses we have demonstrated that cFos bound to the AP-1 cis element within the proximal MMP1 promoter only when the gene was transcriptionally silent as previously observed for MMP13. Subsequent small interfering RNA-mediated silencing confirmed however, that cFos significantly contributes to MMP1 expression. In contrast, silencing of ATF3 (a prime MMP13 modulator) did not affect MMP1 expression whilst silencing of the Wnt-associated regulator cysteine- serine-rich nuclear protein-1 (CSRNP1) resulted in substantial repression of MMP1 but not MMP13. Furthermore, following an early transient peak in expression of CSRNP1 at the mRNA and protein levels similar to that seen for cFOS, CSRNP1 expression subsequently persisted unlike cFOS. Finally, DNA binding assays indicated that the binding of CSRNP1 to the AP-1 consensus-like sequences within the proximal promoter regions of MMP1 and MMP13 was preferentially selective for MMP1 whilst activating transcription factor 3 (ATF3) binding was exclusive to MMP13. These data further extend our understanding of the previously reported differential regulation of these MMP genes, and strongly indicate that although cFos modulates the expression of MMP1/13, downstream factors such as CSRNP1 and ATF3 ultimately serve as transcriptional regulators in the context of an inflammatory stimulus for these potent collagenolytic MMPs.

Deducing corticotropin-releasing hormone receptor type 1 signaling networks from gene expression data by usage of genetic algorithms and graphical Gaussian models

BACKGROUND

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is a hallmark of complex and multifactorial psychiatric diseases such as anxiety and mood disorders. About 50-60% of patients with major depression show HPA axis dysfunction, i.e. hyperactivity and impaired negative feedback regulation. The neuropeptide corticotropin-releasing hormone (CRH) and its receptor type 1 (CRHR1) are key regulators of this neuroendocrine stress axis. Therefore, we analyzed CRH/CRHR1-dependent gene expression data obtained from the pituitary corticotrope cell line AtT-20, a well-established in vitro model for CRHR1-mediated signal transduction. To extract significantly regulated genes from a genome-wide microarray data set and to deduce underlying CRHR1-dependent signaling networks, we combined supervised and unsupervised algorithms.

RESULTS

We present an efficient variable selection strategy by consecutively applying univariate as well as multivariate methods followed by graphical models. First, feature preselection was used to exclude genes not differentially regulated over time from the dataset. For multivariate variable selection a maximum likelihood (MLHD) discriminant function within GALGO, an R package based on a genetic algorithm (GA), was chosen. The topmost genes representing major nodes in the expression network were ranked to find highly separating candidate genes. By using groups of five genes (chromosome size) in the discriminant function and repeating the genetic algorithm separately four times we found eleven genes occurring at least in three of the top ranked result lists of the four repetitions. In addition, we compared the results of GA/MLHD with the alternative optimization algorithms greedy selection and simulated annealing as well as with the state-of-the-art method random forest. In every case we obtained a clear overlap of the selected genes independently confirming the results of MLHD in combination with a genetic algorithm. With two unsupervised algorithms, principal component analysis and graphical Gaussian models, putative interactions of the candidate genes were determined and reconstructed by literature mining. Differential regulation of six candidate genes was validated by qRT-PCR.

CONCLUSIONS

The combination of supervised and unsupervised algorithms in this study allowed extracting a small subset of meaningful candidate genes from the genome-wide expression data set. Thereby, variable selection using different optimization algorithms based on linear classifiers as well as the nonlinear random forest method resulted in congruent candidate genes. The calculated interacting network connecting these new target genes was bioinformatically mapped to known CRHR1-dependent signaling pathways. Additionally, the differential expression of the identified target genes was confirmed experimentally.

A genomic and expression study of AP-1 in primary cutaneous T-cell lymphoma: evidence for dysregulated expression of JUNB and JUND in MF and SS

Activator protein 1 (AP-1) consists of a group of transcription factors including the JUN and FOS family proteins with diverse biological functions. This study assessed the genomic and expression status of the AP-1 transcription factors in primary cutaneous T-cell lymphoma (CTCL) by using immunohistochemistry (IHC), Affymetrix expression microarray, real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and fluorescent in situ hybridization (FISH). IHC showed JUNB protein expression in tumor cells from 17 of 33 cases of Sezary syndrome (SS) and JUND protein expression in 16 of 23 mycosis fungoides cases. There was no correlation between JUNB and CD30 expression. However, 7 of 12 JUNB-positive SS cases expressed both phosphorylated and total extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK) proteins. Expression microarray showed over threefold increased expression of JUNB in three of six SS patients and similar findings were also noted after re-analysis of previously published data. Real-time RT-PCR confirmed the overexpression of JUNB in four SS cases and of JUND in three of four cases. FISH showed increased JUNB copy number in four of seven SS cases. These findings suggest that deregulation of AP-1 expression in CTCL is the result of aberrant expression of JUNB and possible JUND resulting from genomic amplification and constitutive activation of ERK1/2 MAPK in this type of lymphoma.

Multiple facets of junD gene expression are atypical among AP-1 family members

JunD is a versatile AP-1 transcription factor that can activate or repress a diverse collection of target genes. Precise control of junD expression and JunD protein-protein interactions modulate tumor angiogenesis, cellular differentiation, proliferation and apoptosis. Molecular and clinical knowledge of two decades has revealed that precise JunD activity is elaborated by interrelated layers of constitutive transcriptional control, complex post-transcriptional regulation and a collection of post-translational modifications and protein-protein interactions. The stakes are high, as inappropriate JunD activity contributes to neoplastic, metabolic and viral diseases. This article deconvolutes multiple layers of control that safeguard junD gene expression and functional activity. The activity of JunD in transcriptional activation and repression is integrated into a regulatory network by which JunD exerts a pivotal role in cellular growth control. Our discussion of the JunD regulatory network integrates important open issues and posits new therapeutic targets for the neoplastic, metabolic and viral diseases associated with JunD/AP-1 expression.

Eosinophilic inflammation: mechanisms regulating IL-5 transcription in human T lymphocytes

BACKGROUND

Interleukin (IL)-5 is a key regulator of eosinophilia in allergic inflammation and parasite infections but the mechanisms regulating IL-5 expression in activated human T lymphocytes are poorly understood. From studies on mouse cells, the activation protein (AP)-1 and GATA-3 sites in the proximal promoter region appear to be important in IL-5 regulation but the significance of an adjacent Ets/nuclear factor of activated T cell (NFAT) site has been less clear.

METHODS

Interleukin-5 transcriptional activity was measured by transfection of reporter genes into the human HSB-2 cells and normal T lymphocytes. Expression vectors encoding transcription factors were used for transactivation studies and IL-5 expression measured using reporter genes and mRNA levels. Transcription factor binding was shown with chromatin immunoprecipitation (ChIP).

RESULTS

HSB-2 cells showed high inducible expression of IL-5 mRNA. Mutation of reporter gene plasmids showed the Ets/NFAT site was of equal importance to the AP-1 and GATA-3 sites in regulating IL-5 transcription. Transactivation by Ets1 increased luciferase expression 15-fold, in the absence of stimulation, and AP-1 (c-Fos/c-Jun) and GATA-3 gave transactivations of 85-fold, and 100-fold, respectively. Synergistic interactions were demonstrated between Ets1, GATA-3 and AP-1. Dominant-negative AP-1 inhibited IL-5 transcription. Transactivation by GATA-3 and synergy between GATA-3, Ets1 and AP-1 were verified measuring IL-5 mRNA levels. Chromatin immunoprecipitation showed increased binding of Ets1 and GATA-3 to the IL-5 promoter after stimulation. The importance of the Ets1 site and of synergistic interactions between the three transcription factors were verified with primary human T cells.

CONCLUSION

Ets1, GATA-3 and AP-1 synergize to regulate IL-5 transcription in human T cells.

Lentiviral-mediated GATA-3 RNAi decreases allergic airway inflammation and hyperresponsiveness

GATA-3 is the key transcriptional factor for Th2 commitment in T cells and is strongly associated with asthma and allergic disease. We studied the silencing of the GATA-3 gene expression using RNA interference (RNAi) delivered by a lentiviral vector, to evaluate the therapeutic role of GATA-3 short hairpin RNAs (shRNAs) in a murine model of asthma. Mice were sensitized with OVA and instilled intratracheally (IT) with GATA-3 shRNAs lentiviral vector (Lenti-si-GATA-3) once, 48 hours before challenge. After three challenges with the OVA antigen, the mice were assessed for airway hyperresponsiveness (AHR) and inflammation. With infection of Lenti-si-GATA-3 in EL-4 cells, GATA-3 gene expression was abrogated and downstream Th2 cytokines, such as interleukin-4 (IL-4) and IL-5, were also significantly inhibited. IT delivery of Lenti-si-GATA-3 in OVA-immunized mice resulted in a strong inhibition of local GATA-3 gene expression. Treatment with Lenti-si-GATA-3 successfully alleviated OVA-induced airway eosinophilia and Th2 cytokine release. While evaluating AHR by means of enhanced pause (Penh) and pulmonary resistance (R(L)) using body plethysmography, it was found that the administration of Lenti-si-GATA-3 had significantly decreased AHR in OVA-immunized mice. These results suggest that inhibition of GATA-3 gene expression by shRNAs lentiviral vectors strongly attenuates antigen-induced airway inflammation and hyper-responsiveness in mice.

HDAC inhibitors TSA and sodium butyrate enhanced the human IL-5 expression by altering histone acetylation status at its promoter region

The expression of IL-5 correlated tightly with the maturation and differentiation of eosinophils, and is considered as a cytokine responsible for allergic inflammation. We report here that inhibition of HDAC activity by Trichostatin A (TSA) and sodium butyrate (NaBu), the two specific HDAC inhibitors, resulted in the elevation of both endogenous and exogenous activity of IL-5 promoter. We demonstrated that both the mRNA expression and protein production of IL-5 were stimulated by TSA and NaBu treatments. ChIP assays showed that treatments of TSA and NaBu caused hyperacetylation of histones H3 and H4 on IL-5 promoter in Jurkat cells, which consequently promoted the exogenous luciferase activity driven by this promoter. Moreover, site-directed mutagenesis studies showed that the binding sites for transcription factors NFAT, GATA3 and YY1 on IL-5 promoter were critical for the effects of TSA and NaBu, suggesting that the transcriptional activation of IL-5 gene by these inhibitors was achieved by affecting HDAC function on IL-5 promoter via transcription factors. These data will contribute to elucidating the unique mechanism of IL-5 transcriptional control and to the therapy of allergic disorders related to IL-5.

Recruitment of histone deacetylase 4 by transcription factors represses interleukin-5 transcription

The critical role of IL-5 (interleukin-5) in eosinophilic inflammation implicates it as a therapeutic target for allergic diseases. The aim of the present study was to elucidate the molecular basis for the involvement of reversible histone acetylation in IL-5 transcriptional regulation. We provide evidence that HDAC4 (histone deacetylase 4) and p300, a known HAT (histone acetyltransferase), reversibly controlled the activity of the IL-5 promoter in vivo and in vitro, with a concurrent alteration of histone H3 acetylation status at the promoter regions. The nucleo-cytoplasmic shuttling of HDAC4 was shown to play an important role in the suppressive function of HDAC4 in IL-5 gene expression. Point mutation and reporter ChIP (chromatin immunoprecipitation) studies determined that the four transcription factors binding on the IL-5 promoter, i.e. C/EBPbeta (CAAT/enhancer-binding protein beta), GATA3 (GATA binding protein 3), NFAT (nuclear factor of activated T cells) and YY1 (Yin and Yang 1), were essential for the recruitment of HDAC4. Consistent with these observations, HDAC4 was found to form protein complexes with GATA3 and YY1, and to co-exist in the nuclei with GATA3. We propose that the unique regulatory mechanism of IL-5 gene transcription involves the reversible histone modification catalysed by HDAC4 and p300, which are recruited by the transcription factors. The dynamic balance in IL-5 transcriptional regulation is achieved through interactions among HATs/HDACs, histones and transcription factors. These data contribute to understanding the molecular mechanisms of IL-5 regulation, which is crucial to the development of new therapeutic strategies for IL-5-related allergic diseases.

Dexamethasone suppresses human interleukin-5 gene promoter

Synthetic glucocorticoid dexamethasone suppressed interleukin-5 gene expression in PER-117 human T cells at the level of transcription. The conserved lymphokine element 0 in the interleukin-5 gene promoter context served as a target for dexamethasone.

A role for Ets1, synergizing with AP-1 and GATA-3 in the regulation of IL-5 transcription in mouse Th2 lymphocytes

IL-5 is a key regulator of eosinophilic inflammation and is selectively expressed by antigen-activated Th2 lymphocytes. An important role for the proximal AP-1 and GATA sites in regulating IL-5 transcription is generally accepted but the significance of an adjacent Ets/NFAT site has remained unclear. We have investigated its role using the mouse Th2 clone D10.G4.1. Transcription of IL-5 reporter gene plasmids could be induced in D10 cells by phorbol myristate acetate/cyclic adenosine monophosphate (PMA/cAMP) stimulation and significantly further enhanced by activation of the mitogen-activated protein (MAP) kinase pathways. Strong induction of IL-5 mRNA was also induced by PMA/cAMP. Mutagenesis showed that the Ets/NFAT site is of critical importance along with the AP-1 and GATA sites in regulating IL-5 transcription stimulated by PMA/cAMP and MAP kinase activation. Transactivation was used to investigate the transcription factors which could function at the three sites and possible synergistic interactions. AP-1 (c-Fos/c-Jun) strongly induced IL-5 transcription and dominant negative AP-1 constructs confirmed that AP-1 plays an important role in regulating IL-5 expression. Ets1, unlike other members of the Ets/NFAT family, synergized strongly with AP-1 suggesting that Ets1 is the family member which functions at the Ets/NFAT site. AP-1/Ets1 transactivation also stimulated IL-5 mRNA expression. Ets1 binding to the proximal promoter region, demonstrated by chromatin immunoprecipitation, was stimulated by PMA/cAMP. The absolute dependence on the binding sites for Ets1, AP-1 and GATA-3 together with the strong synergy between Ets1 and AP-1 suggest close cooperative interactions between the three transcription factors in the regulation of IL-5 expression in mouse T cells.

The conserved lymphokine element 0 is a powerful activator and target for corticosteroid inhibition in human interleukin-5 transcription

The role of eosinophilia in allergic disorders indicates hIL-5 as a potential target for therapy. The conservation of hIL-5 gene proximal elements suggests they are important in controlling expression. Corticosteroids are important in the treatment of allergy, and are powerful inhibitors of IL-5 expression. This study aimed at understanding the role of hIL-5 conserved proximal elements, and elucidating the target of corticosteroid activity, in hIL-5 gene expression. Methods used include transient transfection of PBMC and PER117 cells with hIL-5 deletion constructs, EMSA, Western Blotting, and RT-PCR. The conserved proximal CLE0/TATA elements driving a reporter gene gave similar or higher expression than a 500 bp promoter in primary human T cells and a T-cell line. Two and three copies of IL-5 CLE0 upstream of the silent IL-4 minimal promoter gave 30-45 fold increases in expression in forward orientation, but little activity in reverse orientation. Consequently, CLE0 is a powerful activator but not a classical enhancer. Deletion analysis identified CLE0 as the key element in the inhibition of IL-5 reporter constructs by dexamethasone, and RT-PCR analysis indicated that GILZ expression correlated with dexamethasone-induced inhibition of IL-5. Ectopic expression of GILZ, confirmed by western blotting, gave a 90% inhibition of promoter constructs in absence of dexamethasone. CLE0 is a powerful activator sufficient for the inducible expression of IL-5, and functions when moved upstream in a heterologous promoter. CLE0 is also the main target for IL-5 inhibition by dexamethasone, and we present evidence consistent with a role of GILZ in this.

Distal regulatory elements play an important role in regulation of the human IL-5 gene

Eosinophil infiltration of the lung is a feature of both allergic and nonallergic asthma, and IL-5 is the key cytokine regulating the production and activation of these cells. Despite many studies focusing on the IL-5 promoter in both humans and mice there is as yet no clear picture of how the IL-5 gene is regulated. The aim of this study was to determine if distal regulatory elements contribute to appropriate regulation of the human IL-5 (hIL-5) gene. Activity of the -507/+44 hIL-5 promoter was compared to expression of the endogenous IL-5 gene in PER-117 T cells. The IL-5 promoter was not sufficient to reproduce a physiological pattern of IL-5 expression. Further, functional analysis of the 5' and 3' intergenic regions revealed a number of novel regulatory elements. We have identified a conserved enhancer located approximately 6.2 kb upstream of the hIL-5 gene. This region contains two potential GATA-3-binding sites and increases expression from the hIL-5 promoter by up to ninefold.

Multiple cis-Elements Mediate the Transcriptional Activation of Human fra-1 by 12-O-Tetradecanoylphorbol-13-acetate in Bronchial Epithelial Cells

Recent studies indicate a potential role for Fra-1, a heterodimeric partner of activator protein 1 (AP1), in toxicant-induced epithelial injury, repair, and cellular transformation. Here, we have investigated the transcriptional regulation of fra-1 by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human bronchial epithelial (HBE) cells, which are the direct targets of inhaled toxins/carcinogens. In contrast to a transient induction by H2O2, TPA persistently activated fra-1 transcription, principally at the transcriptional level. A deletion analysis of the fra-1 promoter revealed that several cis-elements located between -105/+32 and -283/-105 bp mediate minimal and basal promoter activities, respectively. A region between -379 and -283 bp, which harbors a putative TPA response element, a GC box, and an Ets-like binding site, was required for high level TPA-inducible expression. Mutations in any of these cis-elements markedly reduced both basal and TPA-inducible expression. Thus, cooperative interactions between factors binding to multiple cis-elements of the -379/-283 promoter region appear to regulate TPA-induced fra-1 transcription in HBE cells. Consistent with this finding, electrophoretic mobility shift assays indicated the formation of multiple complexes consisting of the AP1-, Sp-, and ETS-specific family of transcription factors with the -379/-283 fragment. Members of the AP1 family distinctly regulated the fra-1 promoter. In particular, coexpression of c-Jun, Jun-D, and Fra-2 up-regulated fra-1 transcription. Chromatin immunoprecipitation assays revealed an enhanced recruitment of c-Jun, Jun-D, and Fra-2 to the endogenous fra-1 promoter upon TPA stimulation. These results underscore the regulatory role of c-Jun, Jun-D, and Fra-2 in TPA-inducible fra-1 expression in HBE cells in vivo.