A novel interferon-inducible domain: structural and functional analysis of the human interferon regulatory factor 1 gene promoter

BCG vaccination stimulates integrated organ immunity by feedback of the adaptive immune response to imprint prolonged innate antiviral resistance

Bacille Calmette-Guérin (BCG) vaccination can confer nonspecific protection against heterologous pathogens. However, the underlying mechanisms remain mysterious. We show that mice vaccinated intravenously with BCG exhibited reduced weight loss and/or improved viral clearance when challenged with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 B.1.351) or PR8 influenza. Protection was first evident between 14 and 21 d post-vaccination and lasted ∼3 months. Notably, BCG induced a biphasic innate response and robust antigen-specific type 1 helper T cell (TH1 cell) responses in the lungs. MyD88 signaling was essential for innate and TH1 cell responses, and protection against SARS-CoV-2. Depletion of CD4+ T cells or interferon (IFN)-γ activity before infection obliterated innate activation and protection. Single-cell and spatial transcriptomics revealed CD4-dependent expression of IFN-stimulated genes in lung myeloid and epithelial cells. Notably, BCG also induced protection against weight loss after mouse-adapted SARS-CoV-2 BA.5, SARS-CoV and SHC014 coronavirus infections. Thus, BCG elicits integrated organ immunity, where CD4+ T cells feed back on tissue myeloid and epithelial cells to imprint prolonged and broad innate antiviral resistance.

Transcriptome Analysis of Cells Exposed to Actinomycin D and Nutlin-3a Reveals New Candidate p53-Target Genes and Indicates That CHIR-98014 Is an Important Inhibitor of p53 Activity

Co-treatment with actinomycin D and nutlin-3a (A + N) strongly activates p53. Previously we reported that CHIR-98014 (GSK-3 kinase inhibitor), acting in cells exposed to A + N, prevents activation of TREM2-an innate immunity and p53-regulated gene associated with Alzheimer’s disease. In order to find novel candidate p53-target genes and genes regulated by CHIR-98014, we performed RNA-Seq of control A549 cells and the cells exposed to A + N, A + N with CHIR-98014 or to CHIR-98014. We validated the data for selected genes using RT-PCR and/or Western blotting. Using CRISPR/Cas9 technology we generated p53-deficient cells. These tools enabled us to identify dozens of candidate p53-regulated genes. We confirmed that p53 participates in upregulation of BLNK, APOE and IRF1. BLNK assists in activation of immune cells, APOE codes for apolipoprotein associated with Alzheimer’s disease and IRF1 is activated by interferon gamma and regulates expression of antiviral genes. CHIR-98014 prevented or inhibited the upregulation of a fraction of genes stimulated by A + N. Downregulation of GSK-3 did not mimic the activity of CHIR-98014. Our data generate the hypothesis, that an unidentified kinase inhibited by CHIR-98014, participates in modification of p53 and enables it to activate a subset of its target genes, e.g., the ones associated with innate immunity.

IκB kinase-ε-mediated phosphorylation triggers IRF-1 degradation in breast cancer cells

Interferon Regulatory Factors (IRFs) are key regulators of immunity, cell survival and apoptosis. IRF transcriptional activity and subcellular localization are tightly regulated by posttranscriptional modifications including phosphorylation. The IκB kinase family member IKK-ε is essential in regulating antiviral innate immunity mediated by IRFs but is now also recognized as an oncoprotein amplified and overexpressed in breast cancer cell lines and patient-derived tumors. In the present study, we report that the tumor suppressor IRF-1 is a specific target of IKK-ε in breast cancer cells. IKK-ε-mediated phosphorylation of IRF-1 dramatically decreases IRF-1 protein stability, accelerating IRF-1 degradation and quenching IRF-1 transcriptional activity. Chemical inhibition of IKK-ε activity, fully restores IRF-1 levels and function and positively correlates with inhibition of cell growth and proliferation of breast cancer cells. By using a breast cancer cell line stably expressing a dominant negative version of IRF-1 we were able to demonstrate that IKK-ε preferentially exerts its oncogenic potential in breast cancer through the regulation of IRF-1 and point to the IKK-ε-mediated phosphorylation of IRF-1 as a therapeutic target to overcome IKK-ε-mediated tumorigenesis.

Src Family Kinases Regulate Interferon Regulatory Factor 1 K63 Ubiquitination following Activation by TLR7/8 Vaccine Adjuvant in Human Monocytes and B Cells

Toll-like receptors (TLRs) play a key role in the activation of innate immune cells, in which their engagement leads to production of cytokines and co-stimulatory molecules. TLRs signaling requires recruitment of toll/IL-1R (TIR) domain-containing adaptors, such as MyD88 and/or TRIF, and leads to activation of several transcription factors, such as NF-κB, the AP1 complex, and various members of the interferon regulatory factor (IRF) family, which in turn results in triggering of several cellular functions associated with these receptors. A role for Src family kinases (SFKs) in this signaling pathway has also been established. Our work and that of others have shown that this type of kinases is activated following engagement of several TLRs, and that this event is essential for the initiation of specific downstream cellular response. In particular, we have previously demonstrated that activation of SFKs is required for balanced production of pro-inflammatory cytokines by monocyte-derived dendritic cells after stimulation with R848, an agonist of human TLRs 7/8. We also showed that TLR7/8 triggering leads to an increase in interferon regulatory factor 1 (IRF-1) protein levels and that this effect is abolished by inhibition of SFKs, suggesting a critical role of these kinases in IRF-1 regulation. In this study, we first confirmed the key role of SFKs in TLR7/8 signaling for cytokine production and accumulation of IRF-1 protein in monocytes and in B lymphocytes, two other type of antigen-presenting cells. Then, we demonstrate that TLR7 triggering leads to an increase of K63-linked ubiquitination of IRF-1, which is prevented by SFKs inhibition, suggesting a key role of these kinases in posttranslational regulation of IRF-1 in the immune cells. In order to understand the mechanism that links SFKs activation to IRF-1 K63-linked ubiquitination, we examined SFKs and IRF-1 possible interactors and proved that activation of SFKs is necessary for their interaction with TNFR-associated factor 6 (TRAF6) and promotes the recruitment of both cIAP2 and IRF-1 by TRAF6. Collectively, our data demonstrate that TLR7/8 engagement leads to the formation of a complex that allows the interaction of cIAP2 and IRF-1 resulting in IRF-1 K63-linked ubiquitination, and that active SFKs are required for this process.

HIV-1 Tat Recruits HDM2 E3 Ligase To Target IRF-1 for Ubiquitination and Proteasomal Degradation

In addition to its ability to regulate HIV-1 promoter activation, the viral transactivator Tat also functions as a determinant of pathogenesis and disease progression by directly and indirectly modulating the host anti-HIV response, largely through the capacity of Tat to interact with and modulate the activities of multiple host proteins. We previously demonstrated that Tat modulated both viral and host transcriptional machinery by interacting with the cellular transcription factor interferon regulatory factor 1 (IRF-1). In the present study, we investigated the mechanistic basis and functional significance of Tat−IRF-1 interaction and demonstrate that Tat dramatically decreased IRF-1 protein stability. To accomplish this, Tat exploited the cellular HDM2 (human double minute 2 protein) ubiquitin ligase to accelerate IRF-1 proteasome-mediated degradation, resulting in a quenching of IRF-1 transcriptional activity during HIV-1 infection. These data identify IRF-1 as a new target of Tat-induced modulation of the cellular protein machinery and reveal a new strategy developed by HIV-1 to evade host immune responses.

Current therapies have dramatically reduced morbidity and mortality associated with HIV infection and have converted infection from a fatal pathology to a chronic disease that is manageable via antiretroviral therapy. Nevertheless, HIV-1 infection remains a challenge, and the identification of useful cellular targets for therapeutic intervention remains a major goal. The cellular transcription factor IRF-1 impacts various physiological functions, including the immune response to viral infection. In this study, we have identified a unique mechanism by which HIV-1 evades IRF-1-mediated host immune responses and show that the viral protein Tat accelerates IRF-1 proteasome-mediated degradation and inactivates IRF-1 function. Restoration of IRF-1 functionality may thus be regarded as a potential strategy to reinstate both a direct antiviral response and a more broadly acting immune regulatory circuit.

Maximal Expression of the Evolutionarily Conserved Slit2 Gene Promoter Requires Sp1

Slit2 is a neural axon guidance and chemorepellent protein that stimulates motility in a variety of cell types. The role of Slit2 in neural development and neoplastic growth and migration has been well established, while the genetic mechanisms underlying regulation of the Slit2 gene have not. We identified the core and proximal promoter of Slit2 by mapping multiple transcriptional start sites, analyzing transcriptional activity, and confirming sequence homology for the Slit2 proximal promoter among a number of species. Deletion series and transient transfection identified the Slit2 proximal promoter as within 399 base pairs upstream of the start of transcription. A crucial region for full expression of the Slit2 proximal promoter lies between 399 base pairs and 296 base pairs upstream of the start of transcription. Computer modeling identified three transcription factor-binding consensus sites within this region, of which only site-directed mutagenesis of one of the two identified Sp1 consensus sites inhibited transcriptional activity of the Slit2 proximal promoter (-399 to +253). Bioinformatics analysis of the Slit2 proximal promoter -399 base pair to -296 base pair region shows high sequence conservation over twenty-two species, and that this region follows an expected pattern of sequence divergence through evolution.

STAT1 as a central mediator of IFNγ and TLR4 signal integration in vascular dysfunction

Atherosclerosis is characterized by early endothelial dysfunction and altered vascular smooth muscle cells (VSMCs) contractility. The forming atheroma is a site of excessive production of cytokines and inflammatory ligands by various cell types that mediate inflammation and immune responses. Key factors contributing to early stages of plaque development are IFNγ and TLR4. This review provides insight in the differential STAT1-dependent signal integration between IFNγ and TLR4 signals in vascular cells and atheroma interacting immune cells. This results in increased leukocyte attraction and adhesion and VSMC proliferation and migration, which are important characteristics of EC dysfunction and early triggers of atherosclerosis.

Downregulation of connective tissue growth factor by LPS/IFN-γ-induced nitric oxide is reversed by aristolochic acid treatment in glomerular mesangial cells via STAT-1α and NF-κB signaling

Aristolochic acid (AA) is a common cause of Chinese herb nephropathy. The mechanisms involved in the pathogenesis of AA nephropathy (AAN) are intricate. One well-documented effect of AA in the kidney is its pro-fibrotic activity. Nitric oxide (NO), a messenger gas generated from l-arginine, is the product of nitric oxide synthase (NOS). NO is involved in renal hemodynamics and exerts cytoprotective effects against renal injury. In the present study, the role of NO in AAN was investigated in MES-13 cells, a glomerular mesangial cell line. NO endogenously generated by the induction of inducible nitric oxide synthase (iNOS) with lipopolysaccharide (LPS)/interferon-γ (IFN-γ) significantly downregulated connective tissue growth factor (CTGF) protein expression in MES-13 cells. AA significantly suppressed LPS/IFN-γ-induced NO production and reversed CTGF expression that was downregulated by LPS/IFN-γ. AA decreased iNOS gene and protein expressions in a concentration-dependent manner. AA caused declines in LPS/IFN-γ-induced signal transducer and activator of transcription-1α (STAT-1α) phosphorylation and interferon response factor-1 (IRF-1) mRNA expression. Furthermore, AA attenuated IκB phosphorylation and reduced NF-κB translocation to the nuclear fraction. Taken together, our data indicate that AA reversed the CTGF expression inhibited by LPS/IFN-γ treatment via suppression of NO and iNOS expressions in MES-13 cells through inhibition of the JAK/STAT-1α and NF-κB signaling pathways. NO potentially exerts antifibrotic activity by down regulation of CTGF in MES-13 cells and inhibition of the iNOS gene by AA might partially account for the fibrotic effects of AA in nephropathy.

An association study of functional polymorphic genes IRF-1, IFNGR-1, and IFN-γ with disease progression, aspartate aminotransferase, alanine aminotransferase, and viral load in chronic hepatitis B and C

BACKGROUND

Investigational approaches based on genome-wide association studies have proven useful in identifying genetic predictors for many diseases, including susceptibility to chronic hepatitis B and C. In these studies, the majority of genetic variants that have shown a positive association have been identified in genes involved in the immune response. In this study IFN-γ, IFNGR-1, and IRF-1 genes were analyzed for their role in susceptibility to the development of chronic hepatitis B and chronic hepatitis C in a Turkish population.

METHODS

Polymorphic genes IRF-1 (-410, -388), IFNGR-1 (-56, -611), and IFN-γ (+874) were analyzed in a total of 400 individuals: 100 chronic hepatitis B patients, 100 hepatitis B carriers, 100 chronic hepatitis C patients, and 100 healthy controls. A single base primer extension assay was used. Correlations between genes and gender, viral load, and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were also investigated.

RESULTS

The IRF-1 gene at positions -388 and -410 were observed to be candidate gene markers for susceptibility to the development of chronic hepatitis B and C (p<0.05). IFN-γ +874 and IFNGR-1 (-56 and -611) correlated with chronic hepatitis B but not chronic hepatitis C. Correlation of functional genotype with viral load and AST and ALT levels revealed an association of IFN-γ +874 and IFNGR-1 -611 with chronic hepatitis C and IFN-γ +874 with viral load and chronic hepatitis B (p<0.05).

CONCLUSIONS

Findings suggest that IFN-γ (+874), IRF-1 (-410, -388), and IFNGR-1 (-56, -611) are candidate gene markers for determining patient susceptibility to the development of chronic hepatitis B and C.

Suppression of IP-10/CXCL10 gene expression in LPS- and/or IFN-γ-stimulated macrophages by parasite-secreted products

T helper (Th)2 polarized immune responses are characteristically dominant in helminth infections. The gene expression of interferon (IFN)-γ-inducible protein 10 (IP-10/CXCL10), which promotes Th1 responses, in mouse macrophages stimulated with lipopolysaccharide (LPS) and/or IFN-γ was suppressed by excretory/secretory (ES) products of Spirometra erinaceieuropaei plerocercoids. ES products suppressed LPS- and/or IFN-γ-induced transcriptional activities of a luciferase reporter gene under the control of a 243-bp fragment of the IP-10 gene promoter/enhancer, which contains an IFN-stimulated response element (ISRE) and two κB elements. Consistent with this result, ES products inhibited ISRE-dependent heterologous promoter activities and LPS- or IFN-γ-induced ISRE-binding activity. ES products also suppressed LPS-induced IFN-β gene expression. Furthermore, ES products suppressed nuclear factor (NF)-κB RelA (p65)-dependent transcriptional activity, whereas ES products had no effect on the κB-binding activity. These results suggest that ES products suppress the IP-10 gene expression by inhibiting the ISRE- and RelA-dependent transcriptional activities in mouse macrophages.

Antiviral protection mechanisms mediated by ginbuna crucian carp interferon gamma isoforms 1 and 2 through two distinct interferon gamma-receptors

Fish genomes possess three type II interferon (IFN) genes, ifnγ1, ifnγ2 and ifnγ-related (ifnγrel). The IFNγ-dependent STAT signalling pathway found in humans and mice had not been characterized in fish previously. To identify the antiviral functions and signalling pathways of the type II IFN system in fish, we purified the ifnγ1, ifnγ2 and ifnγrel proteins of ginbuna crucian carp expressed in bacteria and found them to elicit high antiviral activities against crucian carp hematopoietic necrosis virus. We also cloned two distinct ifnγ receptor alpha chain (ifngr1) isoforms, 1 and 2, and stably expressed them in HeLa cells by transfecting the cells with ifngr1-1 or ifngr1-2 cDNA. When receptor transfectants were treated with the ligands in a one-ligand-one-receptor manner (ifnγ1 and ifngr1-2 or ifnγ2 and ifngr1-1), the stat1 protein was phosphorylated at both serine-727 and tyrosine-701 residues. Gel shift mobility analysis and reporter assay clearly showed that the specific ligand-receptor interaction resulted in the binding of the stat1 protein to the GAS element and enhanced transcription. Therefore, the actions of ifnγ1 and ifnγ2 were found to be mediated by a specific receptor for each signalling pathway via a stat1-dependent mechanism.

NFAT regulates the expression of AIF-1 and IRT-1: yin and yang splice variants of neointima formation and atherosclerosis

AIMS

Alternative transcription and splicing of the allograft inflammatory factor-1 (AIF-1) gene results in the expression of two different proteins: AIF-1 and interferon responsive transcript-1 (IRT-1).  Here, we explore the impact of AIF-1 and IRT-1 on vascular smooth muscle cell (VSMC) activation and neointima formation, the mechanisms underlying their alternative splicing, and associations of AIF-1 and IRT-1 mRNA with parameters defining human atherosclerotic plaque phenotype.

METHODS AND RESULTS

Translation of AIF-1 and IRT-1 results in different products with contrasting cellular distribution and functions. Overexpression of AIF-1 stimulates migration and proliferation of human VSMCs, whereas IRT-1 exerts opposite effects. Adenoviral infection of angioplasty-injured rat carotid arteries with AdAIF-1 exacerbates intima hyperplasia, whereas infection with AdIRT-1 reduces neointima. Expression of these variants is modulated by changes in nuclear factor of activated T-cells (NFAT) activity.  Pharmacological inhibition of NFAT or targeting of NFATc3 with small interfering RNA (siRNA) lowers the AIF-1/IRT-1 ratio and favours an anti-proliferative outcome.  NFAT acts as a repressor on the IRT-1 transcriptional start site, which is also sensitive to interferon-γ stimulation. Expression of AIF-1 mRNA in human carotid plaques associates with less extracellular matrix and a more pro-inflammatory plaque and plasma profile, features that may predispose to plaque rupture. In contrast, expression of IRT-1 mRNA associates with a less aggressive phenotype and less VSMCs at the most stenotic region of the plaque.

CONCLUSION

Inhibition of NFAT signalling, by shifting the AIF-1/IRT-1 ratio, may be an attractive target to regulate the VSMC response to injury and manipulate plaque stability in atherosclerosis.

The DNA damage response induces IFN

This study reveals a new complexity in the cellular response to DNA damage: activation of IFN signaling. The DNA damage response involves the rapid recruitment of repair enzymes and the activation of signal transducers that regulate cell-cycle checkpoints and cell survival. To understand the link between DNA damage and the innate cellular defense that occurs in response to many viral infections, we evaluated the effects of agents such as etoposide that promote dsDNA breaks. Treatment of human cells with etoposide led to the induction of IFN-stimulated genes and the IFN-α and IFN-λ genes. NF-κB, known to be activated in response to DNA damage, was shown to be a key regulator of this IFN gene induction. Expression of an NF-κB subunit, p65/RelA, was sufficient for induction of the human IFN-λ1 gene. In addition, NF-κB was required for the induction of IFN regulatory factor-1 and -7 that are able to stimulate expression of the IFN-α and IFN-λ genes. Cells that lack the NF-κB essential modulator lack the ability to induce the IFN genes following DNA damage. Breaks in DNA are generated during normal physiological processes of replication, transcription, and recombination, as well as by external genotoxic agents or infectious agents. The significant finding of IFN production as a stress response to DNA damage provides a new perspective on the role of IFN signaling.

alpha-Viniferin suppresses the signal transducer and activation of transcription-1 (STAT-1)-inducible inflammatory genes in interferon-gamma-stimulated macrophages

alpha-Viniferin, an oligostilbene of trimeric resveratrol, has been reported to have anti-inflammatory potential in carrageenin-induced paw edema or adjuvant-induced arthritis in animal models. However, little is known about the molecular basis. In this study, alpha-viniferin at 3 - 10 microM dose-dependently inhibited interferon (IFN)-gamma-induced Ser(727) phosphorylation of the signal transducer and activation of transcription-1 (STAT-1), a pivotal transcription factor controlling IFN-gamma-targeted genes, in RAW 264.7 macrophages, and also IFN-gamma-induced activation of the extracellular signal-regulated kinase (ERK)-1, a protein kinase upstream of the Ser(727) phosphorylation of STAT-1. However, alpha-viniferin, only at a higher concentration of 10 microM, inhibited Janus kinase 2-mediated Tyr(701) phosphorylation of STAT-1 in the cells. To understand STAT-1-dependent inflammatory responses, we quantified nitric oxide (NO) or chemokines. alpha-Viniferin at 3 - 10 muM dose-dependently inhibited IFN-gamma-induced production of NO, IFN-gamma-inducible protein-10 (IP-10), or the monokine induced by IFN-gamma (MIG) in RAW 264.7 cells and also that of NO in primary macrophages-derived from C57BL/6 mice. Furthermore, alpha-viniferin diminished IFN-gamma-induced protein levels of inducible NO synthase (iNOS), attenuated mRNA levels of iNOS, IP-10, or MIG as well as inhibited promoter activity of the iNOS gene. In conclusion, this study proposes an anti-inflammatory mechanism of alpha-viniferin, down-regulating STAT-1-inducible inflammatory genes via inhibiting ERK-mediated STAT-1 activation in IFN-gamma-stimulated macrophages.

The IFN-gamma-dependent suppressor of cytokine signaling 1 promoter activity is positively regulated by IFN regulatory factor-1 and Sp1 but repressed by growth factor independence-1b and Krüppel-like factor-4, and it is dysregulated in psoriatic keratinocytes

Epidermal keratinocytes can counteract the detrimental effects of IFN-gamma by inducing the expression of suppressor of cytokine signaling (SOCS)1, which plays an important anti-inflammatory and self-protective role. To date, limited information exists on its expression and regulation in human diseased keratinocytes. In this study, we compared the expression levels of SOCS1 in keratinocytes isolated from skin affected by psoriasis with cells obtained from healthy donors, unveiling that keratinocytes are more prone than healthy cells to upregulate SOCS1 mRNA expression in response to IFN-gamma. We explored the regulatory mechanisms involved in socs1 gene transcription, and found that Sp1 and IFN regulatory factor-1 transcription factors are, respectively, responsible for the basal and IFN-gamma-induced activity of human socs1 promoter. In parallel, we demonstrated that socs1 promoter is negatively regulated by two transcriptional repressors, namely, growth factor independence-1b and Krüppel-like factor 4, which tightly control SOCS1 transcription on IFN-gamma stimulation. Interestingly, although the expression of Sp1 and IFN regulatory factor-1 activators of socs1 promoter is unaltered, growth factor independence-1b and Krüppel-like factor 4 are significantly reduced in psoriatic compared with healthy keratinocytes. This reduction and the consequent unbalanced binding of transcriptional activators and repressors to socs1 promoter after IFN-gamma stimulation might be responsible for the enhanced expression of SOCS1 in psoriatic cells. We suggest that SOCS1 exaggerated upregulation in psoriatic keratinocytes could represent a mechanism through which these cells attempt to protect themselves from IFN-gamma effects. However, the SOCS1 increased levels in psoriatic keratinocytes are not sufficient to completely inhibit the expression of proinflammatory genes.

The benzoxathiolone LYR-71 down-regulates interferon-gamma-inducible pro-inflammatory genes by uncoupling tyrosine phosphorylation of STAT-1 in macrophages

BACKGROUND AND PURPOSE

Benzoxathiolone derivatives have shown anti-inflammatory and immunomodulatory potential in acne and psoriatic disorders. However, little is known about the molecular basis for these pharmacological effects. In this study, we decided to investigate the anti-inflammatory actions of a benzoxathiolone derivative LYR-71, 6-methyl-2-propylimino-6,7-dihydro-5H-benzo[1,3]oxathiol-4-one, in interferon (IFN)-gamma-activated macrophages.

EXPERIMENTAL APPROACH

RAW 264.7 macrophages or primary macrophages, derived from bone marrow of C3H/HeJ mice, were stimulated with IFN-gamma in the presence of LYR-71. Nitric oxide (NO) or chemokine production was measured by Griess reaction or enzyme-linked immunosorbent assay. RAW 264.7 cells were used to examine the molecular mechanisms of LYR-71 in modulating IFN-gamma-induced inflammatory responses.

KEY RESULTS

LYR-71 down-regulated IFN-gamma-induced transcription of inducible NO synthase, IFN-gamma-inducible protein-10 and the monokine induced by IFN-gamma genes in macrophages. This effect was mediated by uncoupling tyrosine phosphorylation of the signal transducer and activator of transcription (STAT)-1 in response to IFN-gamma. LYR-71 directly inhibited the in vitro catalytic activity of Janus kinase (JAK)-2. Further, the inhibitory actions of LYR-71 on IFN-gamma-induced STAT-1 phosphorylation and NO production were consistently abolished in the presence of peroxyvanadate, implying another target dependent on protein tyrosine phosphatase.

CONCLUSIONS AND IMPLICATIONS

Taken together, LYR-71 could restrain IFN-gamma-induced inflammatory responses through uncoupling the tyrosine phosphorylation of STAT-1, an activation index of JAK-STAT-1 signalling, in macrophages. These results may provide a molecular mechanism underlying anti-inflammatory actions shown by benzoxathiolone derivatives.

Insertional chromatin immunoprecipitation: a method for isolating specific genomic regions

We established a novel method, insertional chromatin immunoprecipitation (iChIP), for isolation of specific genomic regions. In iChIP, specific genomic domains are immunoprecipitated with antibody against a tag, which is fused to the DNA-binding domain of an exogenous DNA-binding protein, whose recognition sequence is inserted into the genomic domains of interest. The iChIP method will be a useful tool for dissecting chromatin structure of genomic region of interest.

Molecular mechanisms underlying the pro-inflammatory synergistic effect of tumor necrosis factor alpha and interferon gamma in human microvascular endothelium

Tumor necrosis factor alpha (TNFalpha) and interferon gamma (IFNgamma) are among the most potent cytokines involved in orchestrating the inflammation response. The molecular mechanisms implicated in the synergism between cytokines are still poorly characterized. We demonstrate that both cytokines dose-dependently stimulate IFNgamma-inducible-protein-of-10-kDa (IP-10) secretion in human microvascular endothelial cells (HMEC-1), showing a potent synergism which is not restricted to IP-10, but is also evident for monokine-induced-by-IFNgamma (MIG) and IL-6 secretion. Immunofluorescence analysis reveals that TNFalpha and IFNgamma converge on a rapid phosphorylation of ERK, which however results in a different subcellular compartmentalization of the activated enzyme in response to the two cytokines. Differences in the subcellular recruitment of ERK in response to IFNgamma and TNFalpha are responsible for generating different ERK downstream signaling, which can thus synergize on the secretion of IP-10 as well as of other cytokines/chemokines. The importance of ERK activation in mediating the synergism of the two cytokines is further confirmed by the inhibitory effect of the anti-diabetic drug rosiglitazone and ERK blockers on IP-10, MIG and IL-6 secretion. A further mechanism of synergism involving the reciprocal upregulation of TNFalpha-RII and of IFNgamma-R, in response to IFNgamma and TNFalpha, respectively, was revealed by flow cytometry and quantitative real time RT-PCR analysis.

Sp2 regulates interferon-gamma-mediated socs1 gene expression

Suppressor of cytokine signalling (SOCS) proteins are inducible feedback inhibitors of Janus kinase (JAK) and signal transducers and activators of transcription signalling (STAT) pathways. Interferon (IFN)-gamma induces the expression of the socs1 gene in several cell types through several cis elements present in its promoter and their binding proteins. Socs1 expression is induced in the human keratinocytes HaCaT cell line through sequential activation of STAT1 and IRF-1. Comparison of the 5'-upstream sequences of the mouse and human socs1 genes identified conserved binding sites for IRF-1 regulatory elements. Although this response element is able to bind IRF-1 in human cells, no IFN-gamma responsiveness was observed with human socs1 promoter reporter constructs containing this element. In contrast the mouse socs1 promoter was fully responsive. The mouse promoter contains two cis-acting elements which modulate its expression and are recognized by IRF-1 and Sp2. Despite the absence of Sp2 in the 5'-upstream sequence of the human promoter, silencing of Sp2 by RNA interference clearly demonstrated that Sp2 is required for IFN-gamma-induced regulation of socs1 mRNA both in human and mouse.

Characterization of the 5'-flanking region and regulation of expression of human anion exchanger SLC26A6

SLC26A6 (putative anion transporter 1, PAT1) has been shown to play an important role in mediating the luminal Cl(-)/OH(-)(HCO(3)(-)) exchange process in the intestine. Very little is known about the molecular mechanisms involved in the transcriptional regulation of intestinal SLC26A6 gene expression in the intestine. Current studies were, therefore, designed to clone and characterize the 5'-regulatory region of the human SLC26A6 gene and determine the mechanisms involved in its regulation. A 1,120 bp (p-964/+156) SLC26A6 promoter fragment cloned upstream to the luciferase reporter gene in pGL2-basic exhibited high promoter activity when transfected in Caco2 cells. Progressive deletions of the 5'-flanking region demonstrated that -214/-44 region of the promoter harbors cis-acting elements important for maximal SLC26A6 promoter activity. Since, diarrhea associated with inflammatory bowel diseases is attributed to increased secretion of pro-inflammatory cytokines, we examined the effects of IFNgamma (30 ng/ml, 24 h) on SLC26A6 function, expression and promoter activity. IFNgamma decreased both SLC26A6 mRNA and function and repressed SLC26A6 promoter activity. Deletion analysis indicated that IFNgamma response element is located between -414/-214 region and sequence analysis of this region revealed the presence of potential Interferon Stimulated Responsive Element (ISRE), a binding site (-318/-300 bp) for interferon regulatory factor-1 transcription factor (IRF-1). Mutations in the potential ISRE site abrogated the inhibitory effects of IFNgamma. These studies provided novel evidence for the involvement of IRF-1 in the regulation of SLC26A6 gene expression by IFNgamma in the human intestine.

KAP1 regulates type I interferon/STAT1-mediated IRF-1 gene expression

Signal transducers and activators of transcription (STATs) mediate cell proliferation, differentiation, and survival in immune responses, hematopoiesis, neurogenesis, and other biological processes. Recently, we showed that KAP1 is a novel STAT-binding partner that regulates STAT3-mediated transactivation. KAP1 is a universal co-repressor protein for the KRAB zinc finger protein superfamily of transcriptional repressors. In this study, we found KAP1-dependent repression of interferon (IFN)/STAT1-mediated signaling. We also demonstrated that endogenous KAP1 associates with endogenous STAT1 in vivo. Importantly, a small-interfering RNA-mediated reduction in KAP1 expression enhanced IFN-induced STAT1-dependent IRF-1 gene expression. These results indicate that KAP1 may act as an endogenous regulator of the IFN/STAT1 signaling pathway.

The NS5A protein of hepatitis C virus represses gene expression of hRPB10alpha, a common subunit of host RNA polymerases, through interferon regulatory factor-1 binding site

The nonstructural (NS) 5A protein of hepatitis C virus (HCV) plays important roles in both viral RNA replication and modulation of the physiology of the host cell. Here we report that NS5A repressed gene expression of hRPB10alpha, a common subunit of host RNA polymerases (Pol), in hepatoma cell lines and Huh-7 cells harboring HCV replicon. Analysis of the hRPB10alpha promoter region revealed that interferon regulatory factor-1 binding element (IRF-E) was essential for its transcription. The IRF-E was responsible for the NS5A-mediated repression of the hRPB10alpha transcription and its induction by IRF-1 that is known to be induced by interferon-alpha. Electrophoretic mobility shift assay showed that IRF-1 bound to the IRF-E and the binding reduced when NS5A was expressed. NS5A appeared to negatively regulate IRF-1 expression, which might be partly responsible for the decrease of hRPB10alpha expression. NS5A expression moderately decreased promoter-independent Pol activity in vitro. Transcription of adenoviral genes that are dependent on Pol II or III and propagation of adenoviral genome were impaired in HeLa cells with stable NS5A expression. The results suggest that NS5A may partly modulate host cell transcription by the down-regulation of hRPB10alpha.

Suppression of innate immune cytokines and interferon regulatory factor-1 by endogenous interferon-alpha in response to respiratory syncytial virus in neonate mononuclear cells

Respiratory syncytial virus (RSV) infections are extremely common in early childhood but are most severe in infants in the first few months of life. Unresponsive adaptive immunity and hyporesponsive innate immunity were previously found to be the typical responses of neonate mononuclear cells (MCs) to live RSV. Investigating the mechanism of innate immune hyporesponsiveness in neonate MCs to live RSV revealed that in contrast to the previously reported low expression of interferon (IFN)-gamma, IFN-alpha expression in response to live RSV was significantly greater than that observed in adult MCs. Inhibition of live RSV-induced IFN-alpha with anti-IFN-alpha antibodies in neonate MCs led to significant increases in innate cytokine [IFN-gamma, interleukin (IL)-12, IL-18 and tumor necrosis factor (TNF)-alpha] but not adaptive immune cytokine [IL-2] production. Although MCs from adults responded to live RSV with upregulation of interferon regulatory factor-1 (IRF-1) mRNA, IRF-1 mRNA in RSV-treated neonate MCs was not detectable. However, in the presence of anti-IFN-alpha antibodies, live RSV induced detectable IRF-1 mRNA expression in neonate MCs. These data support the possibility that the severity of early life RSV-induced illnesses may occur via a mechanism in which live RSV induces IFN-alpha that in turn leads to innate immune suppression in neonate MCs.

Lycopene, quercetin and tyrosol prevent macrophage activation induced by gliadin and IFN-gamma

Oxidative stress plays an important role in inflammatory process of celiac disease. We have studied the effect of the lycopene, quercetin and tyrosol natural antioxidants on the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expression in RAW 264.7 macrophages stimulated by gliadin in association with IFN-gamma. The IFN-gamma plus gliadin combination treatment was capable of enhancing iNOS and COX-2 gene expression and nuclear factor-kappaB (NF-kappaB), interferon regulatory factor-1 (IRF-1) and signal transducer and activator of transcription-1alpha (STAT-1alpha) activation induced by reactive oxygen species generation at 24 h. Lycopene, quercetin and tyrosol inhibited all these effects. The results here reported suggest that these compounds may represent non toxic agents for the control of pro-inflammatory genes involved in celiac disease.

Sulindac, a nonsteroidal anti-inflammatory drug, selectively inhibits interferon-gamma-induced expression of the chemokine CXCL9 gene in mouse macrophages

Sulindac, a non-steroidal anti-inflammatory drug, has been shown to exert an anti-tumor effect on several types of cancer. To determine the effect of sulindac on intracellular signaling pathways in host immune cells such as macrophages, we investigated the effect of the drug on interferon gamma (IFNgamma)-induced expression of signal transducer and activator of transcription 1 (STAT1) and other genes in mouse macrophage-like cell line RAW264.7 cells. Sulindac, but not aspirin or sodium salicylate, inhibited IFNgamma-induced expression of the CXC ligand 9 (CXCL9) mRNA, a chemokine for activated T cells, whereas the interferon-induced expression of CXCL10 or IFN regulatory factor-1 was not affected by sulindac. Luciferase reporter assay demonstrated that sulindac inhibited IFNgamma-induced promoter activity of the CXCL9 gene. Surprisingly, sulindac had no inhibitory effect on IFNgamma-induced STAT1 activation; however, constitutive nuclear factor kappaB activity was suppressed by the drug. These results indicate that sulindac selectively inhibited IFNgamma-inducible gene expression without inhibiting STAT1 activation.

Signal integration between IFNgamma and TLR signalling pathways in macrophages

Macrophages are major effector cells of the innate immune system, and appropriate regulation of macrophage function requires the integration of multiple signalling inputs derived from the recognition of host factors (e.g. interferon-gamma/IFNgamma) and pathogen products (e.g. toll-like receptor/TLR agonists). The profound effects of IFNgamma pre-treatment ("priming") on TLR-induced macrophage activation have long been recognised, but many of the mechanisms underlying the priming phenotype have only recently been identified. This review summarises the known mechanisms of integration between the IFNgamma and TLR signalling pathways. Synergy occurs at multiple levels, ranging from signal recognition to convergence of signals at the promoters of target genes. In particular, the cross-talk between the IFNgamma, and LPS and CpG DNA signalling pathways is discussed.

Regulation of Stat1 protein expression by phenylalanine 172 in the coiled-coil domain

Stat1 plays an essential role in signal transduction and gene expression of various cytokines including interferons (IFNs). Although the mechanism of cytokine-induced activation of Stat1 and transcriptional regulation of Stat1 gene expression have been established, post-transcriptional regulation of Stat1 protein expression is not fully understood. Here, we report identification of a mutant of Stat1 that has decreased expression levels by using inducible translocation trap (ITT), a reporter gene-based detection system of nuclear translocation. The substitution of serine for phenylalanine 172 (F172S) in the coiled-coil domain causes marked decrease in Stat1 protein expression in various cell lines without decreasing its mRNA levels. Our results suggest that the decrease is caused by translational/post-translational mechanisms independent of proteasome machinery. These results suggest a novel potential mechanism of determination of specificity of Stat proteins and showed that the ITT system is a powerful technique to identify mutants of nuclear translocating signal transducers.

Genetic polymorphism of interferon-gamma, interferon-gamma receptor, and interferon regulatory factor-1 genes in patients with hepatitis B virus infection

The natural history of hepatitis B virus (HBV) infection is probably related to host immune factors. Interferon-gamma (IFN-gamma) plays significant roles in immune defense. This study was undertaken to investigate the association between HBV infection and single nucleotide polymorphisms (SNPs) of IFN-gamma, IFN-gamma receptor (IFNGR)-1 and 2, and interferon regulatory factor (IRF)-1 genes. Between March 2002 and December 2002, 614 Korean patients were enrolled in two different groups: an HBV clearance group (n = 201), who were hepatitis B surface antigen (HBsAg) negative with antibodies to HBsAg and hepatitis B core antigen, and an HBV persistence group (n = 413), who were repeatedly HBsAg positive. We assessed polymorphisms in the IFN-gamma gene at position +874, in the IFNGR-1 gene at positions -56 and +95, in the IFNGR-2 gene at the second position of codon 64 (Gln64Arg), and in the IRF-1 gene promoter (-410, -388), and the genotype distributions of the HBV clearance and persistence groups were compared. On the basis of unconditional logistic regression analysis with adjustment for age and sex, no statistically significant association with susceptibility to persistent HBV infection was observed with the IFN-gamma, IFNGR-1 and 2, and IRF-1 gene polymorphisms under the codominant, dominant, and recessive models.

Human LBP-32/MGR is a repressor of the P450scc in human choriocarcinoma cell line JEG-3

Steroid hormones regulate a wide range of physiologic functions in humans. The cholesterol side-chain cleavage enzyme P450scc regulates the initial step of biosynthesis of all steroid hormones. We investigated the expression of P450scc by studying a potential regulator of P450scc, LBP-32/MGR. Using a Northern blot, we found that LBP-32/MGR mRNA was expressed mainly in the human placenta. Using radiation hybrid mapping, we identified LBP-32/MGR on human chromosome 2p25. Recombinant LBP-32/MGR protein bound preferentially to a DNA fragment from the promoter of P450scc in vitro and exhibited clear nuclear localization in transfected cells. Luciferase reporter gene assays showed that LBP-32/MGR specifically repressed transcriptional activation of the human P450scc promoter. Because placental P450scc expression is essential for pregnancy and steroid biosynthesis, the placental expression and transcriptional repressor activity of LBP-32/MGR in JEG-3 cells suggest it has a role as a transcriptional modulator of steroid biosynthesis.

Proteasome Inhibition to Maximize the Apoptotic Potential of Cytokine Therapy for Murine Neuroblastoma Tumors

Human neuroblastomas possess several mechanisms of self-defense that may confer an ability to resist apoptosis and contribute to the observed difficulty in treating these tumors in the clinical setting. These molecular alterations may include defects in proapoptotic genes as well as the overexpression of prosurvival factors, such as Akt among others. As a key regulator of the turnover of proteins that modulate the cell cycle and mechanisms of apoptosis, the proteasome could serve as an important target for the treatment of neuroblastoma. The present studies provide the first evidence that bortezomib, a newly approved inhibitor of proteasome function, inhibits phosphorylation of Akt, induces the translocation of proapoptotic Bid, and potently enhances the apoptosis of murine neuroblastoma tumor cells in vitro. Furthermore, in that inhibitors of the Akt pathway can sensitize otherwise resistant TBJ/Neuro-2a cells to apoptosis induced by IFN-gamma plus TNF-alpha, we hypothesized that bortezomib also could sensitize these cells to IFN-gamma plus TNF-alpha. We demonstrate for the first time that bortezomib not only up-regulates the expression of receptors for IFN-gamma and TNF-alpha on both TBJ neuroblastoma and EOMA endothelial cell lines, but also markedly enhances the sensitivity of these cells to apoptosis induced by IFN-gamma plus TNF-alpha in vitro. Furthermore, bortezomib enhances the in vivo antitumor efficacy of IFN-gamma/TNF-alpha-inducing cytokines, including both IL-2 and IL-12 in mice bearing well-established primary and/or metastatic TBJ neuroblastoma tumors. Collectively, these studies suggest that bortezomib could be used therapeutically to enhance the proapoptotic and overall antitumor activity of systemic cytokine therapy in children with advanced neuroblastoma.

REFINEMENT: A search framework for the identification of interferon-responsive elements in DNA sequences – a case study with ISRE and GAS

Interferons (IFN) are a family of pleiotropic secreted proteins that play a key role in mediating antiviral and apoptotic responses, and in immune modulation. Interferons induce a large number of genes through activating the janus tyrosine kinase (JAK)-signal transducers and activators of transcription proteins (STAT) pathway, and the binding of transcription factors to upstream regions of the inducible genes (interferon-stimulated gene, ISG) at specific DNA regulatory elements known as interferon-stimulated response element (ISRE) and gamma-activated sequence (GAS). We have previously performed DNA micro-arrays on peripheral blood mononuclear cells (PBMC) treated with interferon-alpha in culture and showed that approximately 700 genes are significantly modulated (P < or = 0.001). In order to search for ISRE and GAS we have developed a framework called regulatory element finding with iteration and effective model refinement (REFINEMENT) using an existing program (HMMER) and a standard discriminating scoring technique. Although REFINEMENT uses existing programs, our framework itself is novel as it effectively discriminates occurrences using an iterative model refinement technique. REFINEMENT has detected either ISRE or GAS sequence in all of the genes shown to be induced at a P-value < or = 0.001. There were far more functional occurrences in ISRE than in GAS, suggesting that ISRE plays a greater role in response to interferon-alpha than GAS sequences. This method can be used to identify such sequences in any set of genes. REFINEMENT is non-commercial and is accessible at .

The role of NF-κB, IRF-1, and STAT-1α transcription factors in the iNOS gene induction by gliadin and IFN-γ in RAW 264.7 macrophages

Nitric oxide (NO) plays an important role in the pathogenesis of celiac disease. We have examined the involvement of nuclear factor-kappaB (NF-kappaB), interferon regulatory factor-1 (IRF-1), and signal transducer and activator of transcription-1alpha (STAT-1alpha) on the synergistic induction of inducible nitric oxide synthase (iNOS) gene expression by gliadin (G) in association with interferon-gamma (IFN-gamma) in RAW 264.7 macrophages. We found that IFN-gamma was efficient in enhancing the basal transcription of the iNOS promoter at 1, 6, and 24 h, whereas G had no effect. The G plus IFN-gamma association caused an increase in iNOS promoter activity which was inhibited by pyrrolidine dithiocarbammate (PDTC) at 6 and 24 h as well as by genistein (Gen) and tyrphostine B42 (TB42) at 1 h, inhibitors of NF-kappaB, IRF-1, and STAT-1alpha activation, respectively. Similarly, the IFN-gamma and G combination treatment led to a higher increase in iNOS mRNA levels at 1, 6, and 24 h compared with IFN-gamma alone. Gen and TB42 inhibited iNOS mRNA levels at 1 h, whereas PDTC inhibited iNOS mRNA levels at 6 and 24 h. In addition, the synergistic induction of iNOS gene expression by G plus IFN-gamma correlated with the induction of NF-kappaB, IRF-1, and STAT-1alpha/DNA binding activity and mRNA expression. In conclusion, our study, which provides evidence that the effect of G on iNOS gene transcription in IFN-gamma-stimulated RAW 264.7 cells can be ascribed to all three transcription factors, may contribute to lead to new insights into the molecular mechanisms governing the inflammatory process in celiac disease.

Functional characterization of core promoter elements: DPE-specific transcription requires the protein kinase CK2 and the PC4 coactivator

Downstream core promoter elements are an expanding class of regulatory sequences that add considerable diversity to the promoter architecture of RNA polymerase II-transcribed genes. We set out to determine the factors necessary for downstream promoter element (DPE)-dependent transcription and find that, against expectations, TFIID and the GTFs are not sufficient. Instead, the protein kinase CK2 and the coactivator PC4 establish DPE-specific transcription in an in vitro transcription system containing TFIID, Mediator, and the GTFs. Chromatin immunoprecipitation analyses using the DPE-dependent IRF-1 and TAF7 promoters demonstrated that CK2, and PC4 are present on these promoters in vivo. In contrast, neither PC4 nor CK2 were detected on the TAF1-dependent cyclin D promoter, which contains a DCE type of downstream element. Our findings also demonstrate that CK2 activity alters TFIID-dependent recognition of DCE sequences. These data establish that CK2 acts as a switch, converting the transcriptional machinery from functioning on one type of downstream element to another.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

Sodium butyrate suppresses interferon-gamma-, but not lipopolysaccharide-mediated induction of nitric oxide and tumor necrosis factor-alpha in microglia

In the present study, we demonstrate that sodium butyrate repressed IFN-gamma-induced expression of iNOS and TNF-alpha, but had little effect on LPS-induced expression in BV2 murine microglial cells. Sodium butyrate significantly inhibited NF-kappa B binding and NF-kappa B-mediated transcription induced by IFN-gamma, suggesting that the anti-inflammatory effect of sodium butyrate is mediated via specific inhibition of the NF-kappa B pathway. IFN-gamma is a major stimulator of innate and adaptive immune response. Thus, the specific down-regulation of IFN-gamma-induced microglial activation by sodium butyrate may provide potential therapeutic strategies for a variety of inflammatory diseases in the central nervous system.

A Single Residue Modulates Tyrosine Dephosphorylation, Oligomerization, and Nuclear Accumulation of Stat Transcription Factors

The NH(2) terminus of Stat proteins forms a versatile protein interaction domain that is believed to use discrete surfaces to mediate oligomerization and tyrosine dephosphorylation of Stat dimers. Here we show for Stat1 and Stat5a/b that these interfaces overlap and need to be reassigned to an unrelated region of the N-domain. Unexpectedly, our study showed for Stat1 that defective oligomerization of DNA-bound dimers was associated with prolonged interferon-induced nuclear accumulation. This uncoupling of DNA binding and nuclear retention was explained by the concomitant dephosphorylation deficiency that both Stat1 and Stat5a/b have in common and that for Stat1 was due to defective dephosphorylation by the phosphatase TC45. Furthermore, diminished N-domain-mediated oligomerization affected transcriptional activation by both Stat1 and Stat5a/b in a promoter-specific manner. DNA binding analysis indicated that oligomerization of Stats on DNA may be common, irrespective of the presence of multiple canonical binding sites. Accordingly, also transcription from promoters with only a single discernable gamma-activated sequence site was negatively effected by reduced tetramerization. Thus, these results indicate that defective oligomerization cannot generally be compensated for by enhanced tyrosine phosphorylation and prolonged nuclear accumulation. In addition, these data clarify the role of DNA binding in nuclear retention of Stat1.

Alternate interferon signaling pathways

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Induction of interferon regulatory factor 1 expression in human dermal endothelial cells by interferon-gamma and tumor necrosis factor-alpha is transcriptionally regulated and requires iron

Interferon regulatory factor-1 is a transcription factor that is linked to the expression of genes important in the initiation of the inflammatory response and the control of cell cycle. In this study, we determined that the generation of interferon regulatory factor-1 expression in human dermal microvascular endothelial cells was transcriptionally mediated by tumor necrosis factor-alpha or interferon-gamma via iron-dependent pathways. The induction of interferon regulatory factor-1 protein and the up-regulation of interferon regulatory factor-1 mRNA levels was inhibited when cells were pretreated with the iron chelators 2-2-dipyridyl or deferoxamine. This inhibition of interferon regulatory factor-1 expression was associated with loss of interferon regulatory factor-1 binding to the interferon-stimulated response element as assessed by electrophoretic mobility shift assay. Addition of exogenous iron with the iron chelator resulted in reconstitution of cytokine responsiveness, thus demonstrating iron as the target for the chelator effect. Both tumor necrosis factor-alpha and interferon-gamma-induced interferon regulatory factor-1 gene transcription, as assessed by the measurement of unspliced, nascent, heterogeneous nuclear RNA, and treatment with iron chelators blocked tumor necrosis factor-alpha or interferon-gamma mediated interferon regulatory factor-1 gene transcription. Iron was not essential, however, for the association of interferon regulatory factor-1 mRNA with polyribosomes, suggesting iron was not essential for interferon regulatory factor-1 protein translation. Through such inhibitory regulation on pro-inflammatory transcription factors, iron chelators may serve as anti-inflammatory agents.

Arsenic enhances the activation of Stat1 by interferon gamma leading to synergistic expression of IRF-1

Arsenic trioxide (As2O3) can induce clinical remission in patients with acute promyelocytic leukemia (APL), including those who have relapsed after treatment with all-trans-retinoic acid (RA). In vitro studies with the APL-derived NB4 cell line showed that As2O3 exerts a dose-dependent dual effect, which induces apoptosis at 1 microM, whereas at a lower concentration of 0.1 microM, a partial differentiation of APL is observed. In non-APL cells, interferon (IFN) alpha and 1 microM As2O3 act synergistically to induce apoptosis. In this report, we show that in NB4 cells and in two RA-resistant NB4-derived cell lines, NB4-R1 and NB4-R2, IFNalpha or IFNgamma combined with 0.1 microM As2O3 lead to an increased maturation effect. Moreover, IFNgamma alone is able to differentiate RA-sensitive and -resistant cells with a higher maturation effect on NB4-R2 cells. In contrast, all these cells underwent apoptosis in the presence of the cytokine and a higher concentration of As2O3. IFNgamma boosted As2O3-induced apoptosis in APL cells as tested by TUNEL, Annexin V staining and activation of caspase 3. As2O3 differently altered IFN-induced gene products; it downregulated PML/RARalpha and PML, did not alter PKR and Stat1, and upregulated interferon regulatory family (IRF)-1. Synergism by IFNgamma and arsenic on IRF-1 expression is mediated by a composite element in the IRF-1 promoter that includes an IFNgamma-activation site (GAS) overlapped by a nonconsensus site for nuclear factor kappa B (NFkappaB). Arsenic has no effect on NFkappaB, whereas it enhances the activation of Stat1 by IFNgamma in NB4 cells leading to an increase in IRF-1 expression.