Interferon regulatory factor-2 physically interacts with NF-kappa B in vitro and inhibits NF-kappa B induction of major histocompatibility class I and beta 2-microglobulin gene expression in transfected human neuroblastoma cells

The transcription factor IRF2 drives interferon-mediated CD8+ T cell exhaustion to restrict anti-tumor immunity

Type I and II interferons (IFNs) stimulate pro-inflammatory programs that are critical for immune activation, but also induce immune-suppressive feedback circuits that impede control of cancer growth. Here, we sought to determine how these opposing programs are differentially induced. We demonstrated that the transcription factor interferon regulatory factor 2 (IRF2) was expressed by many immune cells in the tumor in response to sustained IFN signaling. CD8+ T cell-specific deletion of IRF2 prevented acquisition of the T cell exhaustion program within the tumor and instead enabled sustained effector functions that promoted long-term tumor control and increased responsiveness to immune checkpoint and adoptive cell therapies. The long-term tumor control by IRF2-deficient CD8+ T cells required continuous integration of both IFN-I and IFN-II signals. Thus, IRF2 is a foundational feedback molecule that redirects IFN signals to suppress T cell responses and represents a potential target to enhance cancer control.

IRF11 enhances the inhibitory effect of IκBα on NF-κB activation in miiuy croaker

NF-κB is a typical transcription factor that regulates expression of various genes involved in inflammatory and immune responses. Therefore, it is essential that NF-κB signaling tightly regulated to maintain immune balance. Compared with those of mammals, the regulatory mechanisms of NF-κB signaling is rarely reported in teleost fish. IκBα is a prominent negative feedback regulator in the NF-κB signaling system. In this study, we determined that IRF11 enhances the inhibitory effect of IκBα on NF-κB activation in teleost fish. Overexpression of IRF11 can inhibit IκBα degradation, whereas its knockdown has the opposite effect of IκBα. Our study further indicates that IκBα was regulated via ubiquitin-proteasome degradation pathway, IRF11 inhibits IκBα in ubiquitin-proteasome degradation. This study provides a novel evidence on the regulation of innate immune signaling pathways in teleost fish and thus provides new insights into the regulatory mechanisms in mammals.

Genome-wide DNA methylation meta-analysis in the brains of suicide completers

Suicide is the second leading cause of death globally among young people representing a significant global health burden. Although the molecular correlates of suicide remains poorly understood, it has been hypothesised that epigenomic processes may play a role. The objective of this study was to identify suicide-associated DNA methylation changes in the human brain by utilising previously published and unpublished methylomic datasets. We analysed prefrontal cortex (PFC, n = 211) and cerebellum (CER, n = 114) DNA methylation profiles from suicide completers and non-psychiatric, sudden-death controls, meta-analysing data from independent cohorts for each brain region separately. We report evidence for altered DNA methylation at several genetic loci in suicide cases compared to controls in both brain regions with suicide-associated differentially methylated positions enriched among functional pathways relevant to psychiatric phenotypes and suicidality, including nervous system development (PFC) and regulation of long-term synaptic depression (CER). In addition, we examined the functional consequences of variable DNA methylation within a PFC suicide-associated differentially methylated region (PSORS1C3 DMR) using a dual luciferase assay and examined expression of nearby genes. DNA methylation within this region was associated with decreased expression of firefly luciferase but was not associated with expression of nearby genes, PSORS1C3 and POU5F1. Our data suggest that suicide is associated with DNA methylation, offering novel insights into the molecular pathology associated with suicidality.

Type I interferon signaling, regulation and gene stimulation in chronic virus infection

Type I Interferons (IFN-I) mediate numerous immune interactions during viral infections, from the establishment of an antiviral state to invoking and regulating innate and adaptive immune cells that eliminate infection. While continuous IFN-I signaling plays critical roles in limiting virus replication during both acute and chronic infections, sustained IFN-I signaling also leads to chronic immune activation, inflammation and, consequently, immune exhaustion and dysfunction. Thus, an understanding of the balance between the desirable and deleterious effects of chronic IFN-I signaling will inform our quest for IFN-based therapies for chronic viral infections as well as other chronic diseases, including cancer. As such the factors involved in induction, propagation and regulation of IFN-I signaling, from the initial sensing of viral nucleotides within the cell to regulatory downstream signaling factors and resulting IFN-stimulated genes (ISGs) have received significant research attention. This review summarizes recent work on IFN-I signaling in chronic infections, and provides an update on therapeutic approaches being considered to counter such infections.

Literature-Informed Analysis of a Genome-Wide Association Study of Gestational Age in Norwegian Women and Children Suggests Involvement of Inflammatory Pathways

Background

Five-to-eighteen percent of pregnancies worldwide end in preterm birth, which is the major cause of neonatal death and morbidity. Approximately 30% of the variation in gestational age at birth can be attributed to genetic factors. Genome-wide association studies (GWAS) have not shown robust evidence of association with genomic loci yet.

Methods

We separately investigated 1921 Norwegian mothers and 1199 children from pregnancies with spontaneous onset of delivery. Individuals were further divided based on the onset of delivery: initiated by labor or prelabor rupture of membranes. Genetic association with ultrasound-dated gestational age was evaluated using three genetic models and adaptive permutations. The top-ranked loci were tested for enrichment in 12 candidate gene-sets generated by text-mining PubMed abstracts containing pregnancy-related keywords.

Results

The six GWAS did not reveal significant associations, with the most extreme empirical p = 5.1 × 10⁻⁷. The top loci from maternal GWAS with deliveries initiated by labor showed significant enrichment in 10 PubMed gene-sets, e.g., p = 0.001 and 0.005 for keywords "uterus" and "preterm" respectively. Enrichment signals were mainly caused by infection/inflammation-related genes TLR4, NFKB1, ABCA1, MMP9. Literature-informed analysis of top loci revealed further immunity genes: IL1A, IL1B, CAMP, TREM1, TFRC, NFKBIA, MEFV, IRF8, WNT5A.

Conclusion

Our analyses support the role of inflammatory pathways in determining pregnancy duration and provide a list of 32 candidate genes for a follow-up work. We observed that the top regions from GWAS in mothers with labor-initiated deliveries significantly more often overlap with pregnancy-related genes than would be expected by chance, suggesting that increased sample size would benefit similar studies.

RelA-Induced Interferon Response Negatively Regulates Proliferation

Both oncogenic and tumor-suppressor activities are attributed to the Nuclear Factor kappa B (NF-kB) pathway. Moreover, NF-kB may positively or negatively regulate proliferation. The molecular determinants of these opposing roles of NF-kB are unclear. Using primary human mammary epithelial cells (HMEC) as a model, we show that increased RelA levels and consequent increase in basal transcriptional activity of RelA induces IRF1, a target gene. Induced IRF1 upregulates STAT1 and IRF7, and in consort, these factors induce the expression of interferon response genes. Activation of the interferon pathway down-regulates CDK4 and up-regulates p27 resulting in Rb hypo-phosphorylation and cell cycle arrest. Stimulation of HMEC with IFN-γ elicits similar phenotypic and molecular changes suggesting that basal activity of RelA and IFN-γ converge on IRF1 to regulate proliferation. The anti-proliferative RelA-IRF1-CDK4 signaling axis is retained in ER+/HER2- breast tumors analyzed by The Cancer Genome Atlas (TCGA). Using immuno-histochemical analysis of breast tumors, we confirm the negative correlation between RelA levels and proliferation rate in ER+/HER2- breast tumors. These findings attribute an anti-proliferative tumor-suppressor role to basal RelA activity. Inactivation of Rb, down-regulation of RelA or IRF1, or upregulation of CDK4 or IRF2 rescues the RelA-IRF1-CDK4 induced proliferation arrest in HMEC and are points of disruption in aggressive tumors. Activity of the RelA-IRF1-CDK4 axis may explain favorable response to CDK4/6 inhibition observed in patients with ER+ Rb competent tumors.

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

The family of interferon regulatory factors (IRFs) consists of nine members (IRF1-IRF9) in mammals. They act as transcription factors for the interferons and thus exert essential regulatory functions in the immune system and in oncogenesis. Recent clinical and experimental studies have identified critically important roles of the IRFs in cardiovascular diseases, arising from their participation in divergent and overlapping molecular programmes beyond the immune response. Here we review the current knowledge of the regulatory effects and mechanisms of IRFs on the immune system. The role of IRFs and their potential molecular mechanisms as novel stress sensors and mediators of cardiovascular diseases are highlighted.

Human papillomavirus 16-encoded E7 protein inhibits IFN-γ-mediated MHC class I antigen presentation and CTL-induced lysis by blocking IRF-1 expression in mouse keratinocytes

Human papillomavirus 16 (HPV16) infection causes 50 % or more of cervical cancers in women. The HPV16 E7 oncogene is continuously expressed in infected epithelium with its oncogenicity linked to cervical cancer. The E7 protein is an ideal target in control of HPV infection through T-cell-mediated immunity. Using HPV16 E7-transgenic mouse keratinocytes (KCs-E7) to investigate T-cell-mediated immune responses, we have shown previously that HPV16-encoded E7 protein inhibits IFN-γ-mediated enhancement of MHC class I antigen processing and T-cell-induced target cell lysis. In this study, we found that HPV16 E7 suppresses IFN-γ-induced phosphorylation of STAT1((Tyr701)), leading to the blockade of interferon regulatory factor-1 (IRF-1) and transporter associated antigen processing subunit 1 (TAP-1) expression in KCs-E7. The results of a (51)Cr release assay demonstrated that IFN-γ-treated KCs-E7 escaped from CTL recognition because HPV16 E7 downregulated MHC class I antigen presentation on KCs. Restoration of IRF-1 expression in KCs-E7 overcame the inhibitory effect of E7 protein on IFN-γ-mediated CTL lysis and MHC class I antigen presentation on KCs. Our results suggest that HPV16 E7 interferes with the IFN-γ-mediated JAK1/JAK2/STAT1/IRF-1 signal transduction pathway and reduces the efficiency of peptide loading and MHC class I antigen presentation on KCs-E7. These results may reveal a new mechanism whereby HPV16 escapes from immune surveillance in vivo.

IRF1 and NF-kB restore MHC class I-restricted tumor antigen processing and presentation to cytotoxic T cells in aggressive neuroblastoma

Neuroblastoma (NB), the most common solid extracranial cancer of childhood, displays a remarkable low expression of Major Histocompatibility Complex class I (MHC-I) and Antigen Processing Machinery (APM) molecules, including Endoplasmic Reticulum (ER) Aminopeptidases, and poorly presents tumor antigens to Cytotoxic T Lymphocytes (CTL). We have previously shown that this is due to low expression of the transcription factor NF-kB p65. Herein, we show that not only NF-kB p65, but also the Interferon Regulatory Factor 1 (IRF1) and certain APM components are low in a subset of NB cell lines with aggressive features. Whereas single transfection with either IRF1, or NF-kB p65 is ineffective, co-transfection results in strong synergy and substantial reversion of the MHC-I/APM-low phenotype in all NB cell lines tested. Accordingly, linked immunohistochemistry expression patterns between nuclear IRF1 and p65 on the one hand, and MHC-I on the other hand, were observed in vivo. Absence and presence of the three molecules neatly segregated between high-grade and low-grade NB, respectively. Finally, APM reconstitution by double IRF1/p65 transfection rendered a NB cell line susceptible to killing by anti MAGE-A3 CTLs, lytic efficiency comparable to those seen upon IFN-γ treatment. This is the first demonstration that a complex immune escape phenotype can be rescued by reconstitution of a limited number of master regulatory genes. These findings provide molecular insight into defective MHC-I expression in NB cells and provide the rational for T cell-based immunotherapy in NB variants refractory to conventional therapy.

Genome-wide mRNA expression analysis of hepatic adaptation to high-fat diets reveals switch from an inflammatory to steatotic transcriptional program

BACKGROUND

Excessive exposure to dietary fats is an important factor in the initiation of obesity and metabolic syndrome associated pathologies. The cellular processes associated with the onset and progression of diet-induced metabolic syndrome are insufficiently understood.

PRINCIPAL FINDINGS

To identify the mechanisms underlying the pathological changes associated with short and long-term exposure to excess dietary fat, hepatic gene expression of ApoE3Leiden mice fed chow and two types of high-fat (HF) diets was monitored using microarrays during a 16-week period. A functional characterization of 1663 HF-responsive genes reveals perturbations in lipid, cholesterol and oxidative metabolism, immune and inflammatory responses and stress-related pathways. The major changes in gene expression take place during the early (day 3) and late (week 12) phases of HF feeding. This is also associated with characteristic opposite regulation of many HF-affected pathways between these two phases. The most prominent switch occurs in the expression of inflammatory/immune pathways (early activation, late repression) and lipogenic/adipogenic pathways (early repression, late activation). Transcriptional network analysis identifies NF-kappaB, NEMO, Akt, PPARgamma and SREBP1 as the key controllers of these processes and suggests that direct regulatory interactions between these factors may govern the transition from early (stressed, inflammatory) to late (pathological, steatotic) hepatic adaptation to HF feeding. This transition observed by hepatic gene expression analysis is confirmed by expression of inflammatory proteins in plasma and the late increase in hepatic triglyceride content. In addition, the genes most predictive of fat accumulation in liver during 16-week high-fat feeding period are uncovered by regression analysis of hepatic gene expression and triglyceride levels.

CONCLUSIONS

The transition from an inflammatory to a steatotic transcriptional program, possibly driven by the reciprocal activation of NF-kappaB and PPARgamma regulators, emerges as the principal signature of the hepatic adaptation to excess dietary fat. These findings may be of essential interest for devising new strategies aiming to prevent the progression of high-fat diet induced pathologies.

Biomarkers of lupus nephritis determined by serial urine proteomics

Lupus nephritis is a frequent and serious complication of systemic lupus erythematosus (SLE), the treatment of which often requires the use of immunosuppressives that can have severe side effects. Here we determined the low-molecular weight proteome of serial lupus urine samples to uncover novel and predictive biomarkers of SLE renal flare. Urine from 25 flare cycles of 19 patients with WHO Class III, IV, and V SLE nephritis were obtained at baseline, pre-flare, flare and post-flare. Each sample was first fractionated to remove proteins larger than 30 kDa, then applied onto weak cation exchanger protein chips for analysis by SELDI-TOF mass spectrometry. We found 176 protein ions of which 27 were differentially expressed between specific flare intervals. On-chip peptide sequencing by integrated tandem mass spectrometry positively identified the 20 and 25 amino-acid isoforms of hepcidin, as well as fragments of alpha1-antitrypsin and albumin among the selected differentially expressed protein ions. Hepcidin 20 increased 4 months before renal flare and returned to baseline at renal flare, whereas hepcidin 25 decreased at renal flare and returned to baseline 4 months after the flare. These studies provide a beginning proteomic analysis aimed at predicting impending renal relapse, relapse severity, and the potential for recovery after SLE nephritis flare.

IRF-2 regulates NF-kappaB activity by modulating the subcellular localization of NF-kappaB

Nuclear Factor-kappa B (NF-kappaB) is a transcription factor essential to the control of cell proliferation, survival, differentiation, immune response, and inflammation. Constitutive NF-kappaB activation has been observed in a broad variety of solid tumors and hematological malignancies, which suggests that NF-kappaB signaling may perform a critical role in the development of human cancers. Interferon regulatory factor-2 (IRF-2), an antagonistic transcriptional repressor of IRF-1, evidences oncogenic potential, but little is currently known regarding the mechanism underlying the oncogenic activities of IRF-2. In this study, we report that IRF-2 recruits RelA/p65 transcription factors into the nucleus via physical interaction. While the nuclear recruitment of RelA by IRF-2 augments TNFalpha-induced NF-kappaB dependent transcription, the N-terminal truncated mutant form of IRF-2 inhibits the nuclear localization of RelA, and thus interferes with NF-kappaB activation. Furthermore, the knockdown of IRF-2 by IRF-2 siRNA attenuates TNFalpha-induced NF-kappaB dependent transcription by inhibiting the nuclear localization of RelA. Thus, these results show that IRF-2 regulates NF-kappaB activity via the modulation of NF-kappaB subcellular localization.

Characterization of vascular protein expression patterns in cerebral ischemia/reperfusion using laser capture microdissection and ICAT‐nanoLC‐MS/MS

Cerebral ischemia rapidly initiates structural and functional changes in brain vessels, including blood-brain barrier disruption, inflammation, and angiogenesis. Molecular events that accompany these changes were investigated in brain microvessels extracted using laser-capture microdissection (LCM) from Sprague-Dawley rats subjected to a 20 min transient global cerebral ischemia followed by 1, 6, or 24 h reperfusion. Proteins extracted from approximately 300 LCM captured microvessels (20-100 microm) were ICAT-labeled and analyzed by nanoLC-MS. In-house software was used to identify paired ICAT peaks, which were then sequenced by nanoLC-MS/MS. Pattern analyses using k-means clustering method classified 57 differentially expressed proteins in 7 distinct dynamic patterns. Protein function was assigned using Panther Classification system. Early reperfusion (1 h) was characterized by down-regulation of ion pumps, nutrient transporters, and cell structure/motility proteins, and up-regulation of transcription factors, signal transduction molecules and proteins involved in carbohydrate metabolism. The up-regulation of inflammatory cytokines and proteins involved in the extracellular matrix remodeling and anti-oxidative defense was observed in late reperfusion (6-24 h). The up-regulation of IL-1beta and TGF-1beta in ischemic brain vessels was confirmed by ELISA, quantitative PCR, and/or immunohistochemistry. A biphasic postischemic (1 and 24 h) BBB opening for (3)H-sucrose was evident in the same model. Differentially expressed proteins identified in brain vessels during reperfusion are likely involved in orchestrating functional vascular responses to ischemia, including the observed BBB disruption.

Macrophages and cytokines in the early defence against herpes simplex virus

Herpes simplex virus (HSV) type 1 and 2 are old viruses, with a history of evolution shared with humans. Thus, it is generally well-adapted viruses, infecting many of us without doing much harm, and with the capacity to hide in our neurons for life. In rare situations, however, the primary infection becomes generalized or involves the brain. Normally, the primary HSV infection is asymptomatic, and a crucial element in the early restriction of virus replication and thus avoidance of symptoms from the infection is the concerted action of different arms of the innate immune response. An early and light struggle inhibiting some HSV replication will spare the host from the real war against huge amounts of virus later in infection. As far as such a war will jeopardize the life of the host, it will be in both interests, including the virus, to settle the conflict amicably. Some important weapons of the unspecific defence and the early strikes and beginning battle during the first days of a HSV infection are discussed in this review. Generally, macrophages are orchestrating a multitude of anti-herpetic actions during the first hours of the attack. In a first wave of responses, cytokines, primarily type I interferons (IFN) and tumour necrosis factor are produced and exert a direct antiviral effect and activate the macrophages themselves. In the next wave, interleukin (IL)-12 together with the above and other cytokines induce production of IFN-gamma in mainly NK cells. Many positive feed-back mechanisms and synergistic interactions intensify these systems and give rise to heavy antiviral weapons such as reactive oxygen species and nitric oxide. This results in the generation of an alliance against the viral enemy. However, these heavy weapons have to be controlled to avoid too much harm to the host. By IL-4 and others, these reactions are hampered, but they are still allowed in foci of HSV replication, thus focusing the activity to only relevant sites. So, no hero does it alone. Rather, an alliance of cytokines, macrophages and other cells seems to play a central role. Implications of this for future treatment modalities are shortly considered.

IRF-2 is involved in up-regulation of nonmuscle myosin heavy chain II-A gene expression during phorbol ester-induced promyelocytic HL-60 differentiation

Transcription of the nonmuscle myosin heavy chain II-A (NMHC-A) gene is regulated by various factors, including cell type, proliferation and differentiation stage, and extracellular stimuli. We have identified an intronic region (designated 32kb-150), which is located 32 kb downstream of the transcription start sites in the human NMHC-A gene, as a transcriptional regulatory region. 32kb-150 contains an interferon-stimulated response element (ISRE). By using HeLa and NIH3T3 cells, in which NMHC-A is constitutively expressed, interferon regulatory factor (IRF)-2 was found to be the only major protein, among the IRF family proteins, that bound to the ISRE in 32kb-150 both in vitro and in intact cells. IRF-2, which is known to either repress or activate target gene expression, acts as a transcriptional activator in the context of the 32kb-150 reporter gene. The carboxyl-terminal basic region of IRF-2 serves as an activation domain in this context. This is in contrast to its acting as a repressor domain in the context of the synthetic core ISRE. Furthermore, after treatment of promyelocytic HL-60 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), which triggers differentiation into macrophages, both NMHC-A expression and IRF-2 expression were found to be up-regulated with a similar time course. TPA treatment leads to recruitment of IRF-2 to 32kb-150 of the endogenous NMHC-A gene and acetylation of the core histones surrounding this region. In addition, the ISRE in the 32kb-150 reporter gene recruits IRF-2 and mediates TPA-induced activation of a reporter gene in HL-60 cells. Together, these results indicate that IRF-2 contributes to transcriptional activation of the NMHC-A gene via 32kb-150 during TPA-induced differentiation of HL-60 cells.

Profiling gene transcription reveals a deficiency of mitochondrial oxidative phosphorylation in Trypanosoma cruzi-infected murine hearts: implications in chagasic myocarditis development

In this study, we report the host genetic responses that characterize Trypanosoma cruzi-induced myocarditis in a murine model of infection and disease development. The mRNA species from the myocardium of infected mice were assessed using cDNA microarray technology at immediate early, acute, and chronic stages of infection. The immediate early reaction of the host to T. cruzi infection was marked by up-regulation of transcripts indicative of proinflammatory and interferon-induced immune responses. Following acute infection, overexpression of transcripts for extracellular matrix (ECM) proteins, possibly initiated in response to myocardial injuries by invading and replicating parasites, was suggestive of active reparative and remodeling reactions. Surprisingly, progression to the cardiac disease phase was associated with coordinated down-regulation of a majority (>70%) of the differentially expressed genes. Among the most repressed genes were the troponins, essential for contractile function of the myofibrils, and the genes encoding components of oxidative phosphorylation (OXPHOS) pathways. Reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and biochemical assays confirmed the microarray results and provided evidence for the deficiency of OXPHOS complex IV in the chagasic murine heart. We discuss the apparent role of OXPHOS dysfunction in the cardiac hypertrophic and remodeling processes with the development of chagasic cardiomyopathy (CCM).

Regulation of lipopolysaccharide sensitivity by IFN regulatory factor-2

IFN regulatory factors (IRFs) are a family of transcription factors and include several members that regulate expression of pro- and anti-inflammatory genes. Mice with a targeted mutation in IRF-2 (IRF-2(-/-)) were studied after injection of LPS to evaluate the importance of IRF-2 in the regulation of endotoxicity. IRF-2(-/-) mice were highly refractory to LPS-induced lethality. Although hepatic TNF-alpha mRNA and circulating TNF-alpha were significantly elevated in LPS-challenged IRF-2(-/-) mice, levels of IL-1, IL-12, and IFN-gamma mRNA and protein, as well as IL-6 protein, were significantly lower than levels seen in LPS-challenged IRF-2(+/+) mice. IRF-2(-/-) mice were also more refractory to TNF-alpha challenge than were control mice, which was consistent with their diminished sensitivity to LPS, yet no significant difference in the mRNA expression of TNFRs was observed. IL-12R beta 2 mRNA levels from LPS-challenged IRF-2(-/-) mice were significantly different after 1, 6, and 8 h, suggesting that both diminished IL-12 and altered IL-12R expression contribute to the paucity of IFN-gamma produced. IRF-2 knockout mice also failed to sustain LPS-inducible levels of IRF-1 and IFN consensus sequence binding protein mRNA expression, two transacting factors required for IL-12 transcription, perhaps as a result of diminished IL-1 beta, IL-6, and IFN-gamma levels. Liver sections from IRF-2(+/+) and IRF-2(-/-) mice were analyzed 6 h after a typically lethal injection of LPS. IRF-2(-/-) mice exhibited greater numbers of apoptotic Kupffer cells than did wild-type mice, suggesting a novel anti-apoptotic role for IRF-2. Collectively, these findings reveal a critical role for IRF-2 in endotoxicity, and point to a previously unappreciated role for IRF-2 in the regulation of apoptosis.

Immediate/early response to Trypanosoma cruzi infection involves minimal modulation of host cell transcription

Host cell infection by the intracellular pathogen, Trypanosoma cruzi, involves activation of signaling pathways, cytoskeletal reorganization, and targeted recruitment of host cell lysosomes. To determine the consequences of T. cruzi invasion on host cell gene expression, high density microarrays consisting of approximately 27,000 human cDNAs were hybridized with fluorescent probes generated from T. cruzi-infected human fibroblasts (HFF) at early time points following infection (2-24 h). Surprisingly, no genes were induced > or =2-fold in HFF between 2 and 6 h post-infection (hpi) in repeated experiments while immediate repression of six host cell transcripts was observed. A significant increase in transcript abundance for 106 host cell genes was observed at 24 hpi. Among the most highly induced is a set of interferon-stimulated genes, indicative of a type I interferon (IFN) response to T. cruzi. In support of this, T. cruzi-infected fibroblasts begin to secrete IFNbeta at 18 hpi following the induction of IFNbeta transcripts. As compared with global transcriptional responses evoked by other intracellular pathogens, T. cruzi is a stealth parasite that elicits few changes in host cell transcription during the initiation of infection.

Interferon regulatory factor-1 is required for interferon-gamma-induced MHC class I genes in astrocytes

Recent studies have shown that the role of the transcription factor interferon regulatory factor-1 (IRF-1) in the expression of major histocompatibility complex (MHC) class I molecules is tissue-specific. Our previous studies indicated a role for IRF-1 in expression of MHC class I genes in cultured astrocytes in response to interferon-gamma (IFN-gamma). However, the requirement for IRF-1 in MHC class I expression has not been directly analyzed in neural tissue. To further ascertain the importance of IRF-1 in the induction of MHC class I genes in astrocytes in response to IFN-gamma, we analyzed astrocytes from mice with a targeted disruption of the IRF-1 gene (IRF-1(-/-) mice). As expected, astrocytes from wild type (IRF-1(+/+)) mice showed a coordinate increase in both IRF-1 and MHC class I gene expression in response to IFN-gamma. To the contrary, astrocytes from IRF-1(-/-) mice had greatly reduced MHC class I mRNA expression. MHC class I gene promoter activity in astrocytes was controlled entirely through a single enhancer, the MHC-IRF-E, to which IRF-1 bound in response to IFN-gamma in wild type but not in IRF-1(-/-) mouse astrocytes. In vivo, astrocytes in brains of wild type mice readily responded to IFN-gamma to express MHC class I molecules. This correlated with increased MHC class I mRNA in the brain. In contrast, brains of IRF-1(-/-) mice showed no MHC class I gene induction following exposure to IFN-gamma indicating that all cells in the central nervous system (CNS) including astrocytes with the potential to express MHC class I molecules were dependent on IRF-1. These studies conclusively demonstrate a major role for IRF-1/MHC-IRF-E interactions in controlling MHC class I gene expression in astrocytes in response to IFN-gamma.

Lineage-specific modulation of interleukin 4 signaling by interferon regulatory factor 4

Interleukin (IL)-4 is an immunoregulatory cytokine that exerts distinct biological activities on different cell types. Our studies indicate that interferon regulatory factor (IRF)-4 is both a target and a modulator of the IL-4 signaling cascade. IRF-4 expression is strongly upregulated upon costimulation of B cells with CD40 and IL-4. Furthermore, we find that IRF-4 can interact with signal transducer and activator of transcription (Stat)6 and drive the expression of IL-4-inducible genes. The transactivating ability of IRF-4 is blocked by the repressor factor BCL-6. Since expression of IRF-4 is mostly confined to lymphoid cells, these data provide a potential mechanism by which IL-4-inducible genes can be regulated in a lineage-specific manner.

The p53 paradox in the pathogenesis of tumor progression

Recent evidence suggests that the p53 molecule appears in two different forms: the mutant p53 that stimulates tumor progression, and wild type p53 that inhibits tumor progression. In addition, it has been established that tumor necrosis factor-alpha (TNF-alpha) can activate the expression of wild type p53 in concert with the nuclear transcription factor, NF-kappa B. Both TNF-alpha and NF-kappa B are also involved in the stimulation of the pathway that leads to the expression of major histocompatibility complex (MHC) class I molecules and, hence, antigen presentation to the T cells. In this paper we shall advance the hypothesis that: (i) TNF-alpha indirectly controls immune surveillance; and (ii) TNF-alpha controls DNA repair and tumor suppression through the regulation of wild type p53. Thus, it is hypothesized that elevated TNF-alpha is primarily responsible for promoting tumor progression.

Tumor necrosis factor-alpha: a continuum of liability between insulin-dependent diabetes mellitus, non-insulin-dependent diabetes mellitus and carcinoma (review)

In this review, tumor necrosis factor-alpha (TNF-alpha) is identified as the uniting principle linking the pathogenesis of insulin-dependent diabetes mellitus (IDDM), non-insulin dependent diabetes mellitus (NIDDM) and carcinoma. Elevated TNF-alpha initially increases, and then inhibits, the activity of a number of key enzymes involved in energy metabolism and major histocompatibility (MHC) class I molecule expression. These enzymes include: protein-tyrosine kinase (PTKase) and protein-tyrosine phosphatase (PTPase--enzymes involved in energy metabolism, cell proliferation and stimulation of the MHC class I molecule pathway. Of primary importance is the inhibiting effect of TNF-alpha on PTKase, since this induces insulin resistance in NIDDM and carcinoma, and PTPase, which inhibits MHC class I molecule expression. Studies have shown that IDDM is associated with an increase in PTPase activity which leads to overexpression of MHC class I molecules and a concomitant destruction of pancreatic beta cells. Conversely, carcinoma is associated with an inhibition of PTPase activity, which reduces the expression of MHC class I antigen expression on the cell surface thereby allowing malignant cells to escape immune surveillance. It will be argued that there is continuum of liability between these three conditions, initiated by the effect of TNF-alpha on these key enzymes.

Interferon regulatory factor 2 represses the Epstein-Barr virus BamHI Q latency promoter in type III latency

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) is the essential protein for maintenance of the EBV episome and establishment of latency. The BamHI Q promoter (Qp) is used for the transcription of EBNA-1 mRNA in type I and type II latency, which are EBV infection states exemplified by Burkitt's lymphoma and nasopharyngeal carcinoma. However, Qp is inactive in type III latency, and other promoters (the BamHI C promoter and/or the BamHI W promoter) are used for EBNA-1. The involvement of interferon regulatory factors (IRFs) in the regulation of Qp is suggested by the presence of an essential interferon-stimulated response element (ISRE) in the promoter. In this work, expression of IRF-2 is shown to be inversely associated with Qp status, i.e., IRF-2 levels are high in type III latency (when Qp is inactive) and low in type I latency (when Qp is active). Also, IRF-2 is identified by electrophoretic mobility shift assay as the major protein binding to the Qp ISRE in type III latency. In transient transfection assays, IRF-2 represses the activity of Qp-reporter constructs. Overexpression of IRF-2 in a type I latency cell line did not activate the endogenous Qp but marginally reduced the EBNA-1 mRNA level. Switching from type III latency (Qp inactive) to type II latency (Qp active), as produced by cell fusion, is directly associated with greatly reduced expression of IRF-2. These data strongly suggest that IRF-2 is a negative regulator of Qp and may contribute to the silencing of Qp in type III latency.

Nuclear factor-kappaB/Rel proteins: a point of convergence of signalling pathways relevant in neuronal function and dysfunction

Nuclear factor-kappaB (NF-kappaB)/Rel designates a family of transcription factors participating in the activation of a wide range of genes crucially involved in immune and inflammatory function. NF-kappaB/Rel proteins have been demonstrated recently in primary neurons and in several brain areas. Functional significance of these proteins is still not understood completely, but since certain subsets of neurons appear to contain constitutively active DNA-binding activity, it seems likely that they may participate in normal brain function. A growing body of evidence is accumulating for a specific activation of NF-kappaB/Rel proteins in the CNS, and in particular in neuronal cells, during neurodegenerative processes associated to etiologically unrelated conditions. Whether NF-kappaB activation is part of the neurodegenerative process or of protective mechanisms is a matter of debate. This issue will be reviewed here with particular attention to the available reports on the activity of NF-kappaB/Rel proteins in both experimental paradigms of neurodegeneration and post-mortem brain tissue of patients affected by various neurological diseases. We hypothesize that NF-kappaB/Rel proteins may represent the point of convergence of several signalling pathways relevant for initiating or accelerating the process of neuronal dysfunction and degeneration in many neurological diseases, including Parkinson's disease, Alzheimer's disease, CNS viral infections, and possibly others. If NF-kappaB/Rel proteins represent an integrating point of several pathways potentially contributing to neuronal degeneration, molecules that finely modulate their activity could represent a novel pharmacological approach to several neurological diseases.

p48/STAT-1α-Containing Complexes Play a Predominant Role in Induction of IFN-γ-Inducible Protein, 10 kDa (IP-10) by IFN-γ Alone or in Synergy with TNF-α

Human IFN-γ-inducible protein, 10 kDa (hIP-10) and murine IP-10 (mIP-10) genes are induced by IFN-γ alone, and synergistically induced by TNF-α and IFN-γ. Upstream regions of the human and murine genes contain conserved regulatory motifs, including an IFN-stimulated response element (ISRE), which governs response of the mIP-10 gene to IFN-γ. Trans-acting factors mediating the IFN-γ response via ISRE remain incompletely defined. We examined ISRE-binding factors in the regulation of the hIP-10 gene. The requirement of p48 for hIP-10 induction by IFN-γ, with or without TNF-α, was demonstrated using p48-deficient U2A cells. An hIP-10 promoter-reporter mutant (mISRE3) that was relatively deficient for binding a related factor, IFN regulatory factor-1 (IRF-1) but competent for binding p48, was induced as well as the wild-type hIP-10 promoter, supporting the interpretation that p48 played a necessary and sufficient role in hIP-10 transcription. Genomic in vivo footprinting revealed IFN-γ/TNF-α-inducible binding at the ISRE consistent with the presence of p48 and associated factors, but not with IRF-1. Induction of hIP-10 by TNF-α/IFN-γ also required NFκB binding sites, which were protected in vivo and bound p65 homodimeric NFκB in vitro. These results documented the essential role of p48 (complexed with STAT-1α) for induction and sustained transcription of the IP-10 gene, strongly suggesting that IRF-1 is not required for IP-10 induction by these inflammatory cytokines.

An immunological model connecting the pathogenesis of stress, depression and carcinoma

Recently there has been considerable conjecture in the literature concerning a possible relationship between stress, depression and bereavement, and carcinoma. We shall propose a causal model in which the relationship between stress, depression and carcinoma is clarified. This relationship is grounded on dysregulation of the inflammatory cytokines in stress and depression. Stress is associated with increased expression of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), and reduced expression of IL-2, interferon-gamma (IFN-gamma), major histocompatability complex (MHC) class II molecules and natural killer cell activity (NKA). Depression is associated with elevated IFN-gamma and IL-1 beta, downregulated IL-2, and reduced NKA. Most organ-related carcinomas are associated with elevated TNF-alpha, which inhibits the activity of protein tyrosine phosphatase (PTPase), the enzyme that initiates activation of the MHC class I pathway. Sustained elevation of TNF-alpha inhibits the activity of PTPase which results in diminished expression of the MHC class I antigen on the cell surface and thus, malignant cells escape immune surveillance. Therefore, stress and depression can foster tumor progression by means of inhibiting the expression of MHC class I and II molecules and through the reduction of NKA.

Interferon regulatory factor 1 is induced by interferon-gamma equally in neurons and glial cells

Class I MHC protein is induced in glia but not mature neurons by IFN-gamma. We have compared IFN-gamma signal transduction in these populations. There were identical levels of STAT1 homodimers and IRF-1 by gel-shift and IRF-1 mRNA was induced equally. However class I MHC, beta2-microglobulin and interleukin 1-beta converting enzyme mRNA levels were greatly reduced in neurons. These experiments show that there is no defect in expression of IRF-1 in response to IFN-gamma in mature mouse neurons but that insufficient class I MHC gene expression is induced for detectable cell surface protein expression.

NF-kappa B: a crucial transcription factor for glial and neuronal cell function

Transcription factors provide the link between early membrane-proximal signalling events and changes in gene expression. NF-kappa B is one of the best-characterized transcription factors. It is expressed ubiquitously and regulates the expression of many genes, most of which encode proteins that play an important and often determining role in the processes of immunity and inflammation. Apart from its role in these events, evidence has begun to accumulate that NF-kappa B is involved in brain function, particularly following injury and in neurodegenerative conditions such as Alzheimer's disease. NF-kappa B might also be important for viral replication in the CNS. An involvement of NF-kappa B in neuronal development is suggested from studies that demonstrate its activation in neurones in certain regions of the brain during neurogenesis. Brain-specific activators of NF-kappa B include glutamate (via both AMPA/KA and NMDA receptors) and neurotrophins, pointing to an involvement in synaptic plasticity. NF-kappa B can therefore be considered as one of the most important transcription factors characterized in brain to date and it might be as crucial for neuronal and glial cell function as it is for immune cells.

Active repression of major histocompatibility complex class I genes in a human neuroblastoma cell line

Human neuronal cells express neither major histocompatibility complex (MHC) class I RNA nor cell surface molecules but can be induced to do so by various cytokines. In the present studies, we report that expression of MHC class I in a neuroblastoma cell line, CHP-126, is actively repressed. This repression is mediated by the combined effects of a series of upstream silencer elements. Removal of the silencers reveals not only an active promoter element but also the presence of an active enhancer. Four silencers have been identified and shown to have distinct sequences, binding factors, and patterns of function. One element is located between -724 and -697 base pairs (bp) and corresponds to a silencer involved in tissue-specific regulation of class I gene expression. Three additional elements occur between -503 and -402 bp. One of these corresponds to a c-jun responsive element. Neither of the remaining elements corresponds to DNA sequences known to regulate expression of other genes. These data demonstrate that MHC class I expression normally is actively repressed in neuronal cells and suggest a model of rapid and specific triggering of class I in neuronal cells in response to infection.