Differential effects of TNF-alpha and IFN-gamma on gene transcription mediated by NF-kappaB-Stat1 interactions

MORA and EnsembleTFpredictor: An ensemble approach to reveal functional transcription factor regulatory networks

MOTIVATION

Our study aimed to identify biologically relevant transcription factors (TFs) that control the expression of a set of co-expressed or co-regulated genes.

RESULTS

We developed a fully automated pipeline, Motif Over Representation Analysis (MORA), to detect enrichment of known TF binding motifs in any query sequences. MORA performed better than or comparable to five other TF-prediction tools as evaluated using hundreds of differentially expressed gene sets and ChIP-seq datasets derived from known TFs. Additionally, we developed EnsembleTFpredictor to harness the power of multiple TF-prediction tools to provide a list of functional TFs ranked by prediction confidence. When applied to the test datasets, EnsembleTFpredictor not only identified the target TF but also revealed many TFs known to cooperate with the target TF in the corresponding biological systems. MORA and EnsembleTFpredictor have been used in two publications, demonstrating their power in guiding experimental design and in revealing novel biological insights.

Discovery of diarylheptanoids that activate α7 nAchR-JAK2-STAT3 signaling in macrophages with anti-inflammatory activity in vitro and in vivo

Acute inflammatory diseases, such as sepsis, are life-threatening illnesses. Regulating the α7 nicotinic acetylcholine receptor (α7 nAchR)-mediated signaling may be a promising strategy to treat sepsis. Diarylheptanoids have long been found to exhibit anti-inflammatory properties. However, the possible mechanism of diarylheptanoids has rarely been investigated. In this study, we isolated and synthesized 49 diarylheptanoids and analogues and evaluated their anti-inflammatory activities. Among them, compounds 28 and 40 markedly blocked lipopolysaccharide (LPS)-induced production of nitric oxide (NO), interleukin-1β (IL-1β) and interleukin-6 in murine RAW264.7 cells. Furthermore, compounds 28 and 40 also effectively attenuated LPS-induced sepsis, acute lung injury, and cytokines release in vivo. Mechanistically, compounds 28 and 40 significantly induced phosphorylation of janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling and suppression of nuclear factor-κB (NF-κB) pathway. Furthermore, blocking α7 nAchR could effectively abolish compounds 28 and 40-mediated activation of JAK2-STAT3 signaling as well as inhibition of NF-κB activation and NO production in LPS-exposed RAW264.7 cells. Collectively, our findings have identified a new diarylheptanoid, compound 28, as an agonist of α7 nAchR-JAK2-STAT3 signaling, which can be potentially developed as a valuable candidate for the treatment of sepsis, and provide a new lead structure for the development of anti-inflammatory agents targeting α7 nAchR-JAK2-STAT3 signaling.

IFNγ induces JAK1/STAT1/p65 NFκB-dependent interleukin-8 expression in ovarian cancer cells, resulting in their increased migration

Interferon-γ (IFNγ) is a pleiotropic cytokine that has a crucial role in immune response and tumor immunity. Because of its anti-tumor effects, IFNγ has been used in cancer treatment. However, IFNγ also has tumor-promoting functions that are less well understood. Here, we show that IFNγ induces expression of the pro-inflammatory and pro-angiogenic chemokine interleukin-8 (IL-8, CXCL8) in ovarian cancer (OC) cells. The IFNγ-induced IL-8 expression is dependent on JAK1, STAT1, and p65 NFκB, and is associated with an increased occupancy of K314/315 acetylated p65 NFκB and Ser-727 phosphorylated STAT1 at the IL-8 promoter. Neutralization of IL-8 using anti-IL-8 antibody reduces IFNγ-induced migration of OC cells, and their invasion ability in 3D spheroids. Together, these findings identify IL-8 as a novel target induced by IFNγ/JAK1/STAT1/p65 NFκB signaling, and indicate that the IFNγ-induced IL-8 contributes to IFNγ pro-tumorigenic effects in ovarian cancer cells.

Methylmercury induces neuronal cell death by inducing TNF-α expression through the ASK1/p38 signaling pathway in microglia

We recently found that tumor necrosis factor-α (TNF-α) may be involved in neuronal cell death induced by methylmercury in the mouse brain. Here, we examined the cells involved in the induction of TNF-α expression by methylmercury in the mouse brain by in situ hybridization. TNF-α-expressing cells were found throughout the brain and were identified as microglia by immunostaining for ionized calcium binding adaptor molecule 1 (Iba1). Methylmercury induced TNF-α expression in mouse primary microglia and mouse microglial cell line BV2. Knockdown of apoptosis signal-regulating kinase 1 (ASK1), an inflammatory cytokine up-regulator that is responsible for reactive oxygen species (ROS), decreased methylmercury-induced TNF-α expression through decreased phosphorylation of p38 MAP kinase in BV2 cells. Suppression of methylmercury-induced reactive oxygen species (ROS) by antioxidant treatment largely abolished the induction of TNF-α expression and phosphorylation of p38 by methylmercury in BV2 cells. Finally, in mouse brain slices, the TNF-α antagonist (WP9QY) inhibited neuronal cell death induced by methylmercury, as did the p38 inhibitor SB203580 and liposomal clodronate (a microglia-depleting agent). These results indicate that methylmercury induces mitochondrial ROS that are involved in activation of the ASK1/p38 pathway in microglia and that this is associated with induction of TNF-α expression and neuronal cell death.

The role of extracellular DNA in COVID-19: Clues from inflamm-aging

Epidemiological data convey severe prognosis and high mortality rate for COVID-19 in elderly men affected by age-related diseases. These subjects develop local and systemic hyper-inflammation, which are associated with thrombotic complications and multi-organ failure. Therefore, understanding SARS-CoV-2 induced hyper-inflammation in elderly men is a pressing need. Here we focus on the role of extracellular DNA, mainly mitochondrial DNA (mtDNA) and telomeric DNA (telDNA) in the modulation of systemic inflammation in these subjects. In particular, extracellular mtDNA is regarded as a powerful trigger of the inflammatory response. On the contrary, extracellular telDNA pool is estimated to be capable of inhibiting a variety of inflammatory pathways. In turn, we underpin that telDNA reservoir is progressively depleted during aging, and that it is scarcer in men than in women. We propose that an increase in extracellular mtDNA, concomitant with the reduction of the anti-inflammatory telDNA reservoir may explain hyper-inflammation in elderly male affected by COVID-19. This scenario is reminiscent of inflamm-aging, the portmanteau word that depicts how aging and aging related diseases are intimately linked to inflammation.

Signal Integration of IFN-I and IFN-II With TLR4 Involves Sequential Recruitment of STAT1-Complexes and NFκB to Enhance Pro-inflammatory Transcription

Atherosclerosis is a chronic inflammatory disease of the blood vessels, characterized by atherosclerotic lesion formation. Vascular Smooth Muscle Cells (VSMC), macrophages (MΦ), and dendritic cells (DC) play a crucial role in vascular inflammation and atherosclerosis. Interferon (IFN)α, IFNγ, and Toll-like receptor (TLR)4 activate pro-inflammatory gene expression and are pro-atherogenic. Gene expression regulation of many pro-inflammatory genes has shown to rely on Signal Integration (SI) between IFNs and TLR4 through combinatorial actions of the Signal Transducer and Activator of Transcription (STAT)1 complexes ISGF3 and γ-activated factor (GAF), and Nuclear Factor-κB (NFκB). Thus, IFN pre-treatment (“priming”) followed by LPS stimulation leads to enhanced transcriptional responses as compared to the individual stimuli. To characterize the mechanism of priming-induced IFNα + LPS- and IFNγ + LPS-dependent SI in vascular cells as compared to immune cells, we performed a comprehensive genome-wide analysis of mouse VSMC, MΦ, and DC in response to IFNα, IFNγ, and/or LPS. Thus, we identified IFNα + LPS or IFNγ + LPS induced genes commonly expressed in these cell types that bound STAT1 and p65 at comparable γ-activated sequence (GAS), Interferon-stimulated response element (ISRE), or NFκB sites in promoter proximal and distal regions. Comparison of the relatively high number of overlapping ISRE sites in these genes unraveled a novel role of ISGF3 and possibly STAT1/IRF9 in IFNγ responses. In addition, similar STAT1-p65 co-binding modes were detected for IFNα + LPS and IFNγ + LPS up-regulated genes, which involved recruitment of STAT1 complexes preceding p65 to closely located GAS/NFκB or ISRE/NFκB composite sites already upon IFNα or IFNγ treatment. This STAT1-p65 co-binding significantly increased after subsequent LPS exposure and correlated with histone acetylation, PolII recruitment, and amplified target gene transcription in a STAT1-p65 co-bound dependent manner. Thus, co-binding of STAT1-containing transcription factor complexes and NFκB, activated by IFN-I or IFN-II together with LPS, provides a platform for robust transcriptional activation of pro-inflammatory genes. Moreover, our data offer an explanation for the comparable effects of IFNα or IFNγ priming on TLR4-induced activation in vascular and immune cells, with important implications in atherosclerosis.

MnTE-2-PyP reduces prostate cancer growth and metastasis by suppressing p300 activity and p300/HIF-1/CREB binding to the promoter region of the PAI-1 gene

To improve radiation therapy-induced quality of life impairments for prostate cancer patients, the development of radio-protectors is needed. Our previous work has demonstrated that MnTE-2-PyP significantly protects urogenital tissues from radiation-induced damage. So, in order for MnTE-2-PyP to be used clinically as a radio-protector, it is fully necessary to explore the effect of MnTE-2-PyP on human prostate cancer progression. MnTE-2-PyP inhibited prostate cancer growth in the presence and absence of radiation and also inhibited prostate cancer migration and invasion. MnTE-2-PyP altered p300 DNA binding, which resulted in the inhibition of HIF-1β and CREB signaling pathways. Accordingly, we also found that MnTE-2-PyP reduced the expression of three genes regulated by HIF-1β and/or CREB: TGF-β2, FGF-1 and PAI-1. Specifically, MnTE-2-PyP decreased p300 complex binding to a specific HRE motif within the PAI-1 gene promoter region, suppressed H3K9 acetylation, and consequently, repressed PAI-1 expression. Mechanistically, less p300 transcriptional complex binding is not due to the reduction of binding between p300 and HIF-1/CREB transcription factors, but through inhibiting the binding of HIF-1/CREB transcription factors to DNA. Our data provide an in depth mechanism by which MnTE-2-PyP reduces prostate cancer growth and metastasis, which validates the clinical use of MnTE-2-PyP as a radio-protector to enhance treatment outcomes in prostate cancer radiotherapy.

Up-Regulation of Human Inducible Nitric Oxide Synthase by p300 Transcriptional Complex

p300, a ubiquitous transcription coactivator, plays an important role in gene activation. Our previous work demonstrated that human inducible nitric oxide synthase (hiNOS) expression can be highly induced with the cytokine mixture (CM) of TNF-α + IL-1β + IFN-γ. In this study, we investigated the functional role of p300 in the regulation of hiNOS gene expression. Our initial data showed that overexpression of p300 significantly increased the basal and cytokine-induced hiNOS promoter activities in A549 cells. Interestingly, p300 activated cytokine-induced hiNOS transcriptional activity was completely abrogated by deleting the upstream hiNOS enhancer at -5 kb to -6 kb in the promoter. Furthermore, p300 over-expression increased cytokine-induced transcriptional activity on a heterologous minimal TK promoter with the same hiNOS enhancer. Site-directed mutagenesis of the hiNOS AP-1 motifs revealed that an intact upstream (-5.3kb) AP-1 binding site was critical for p300 mediated cytokine-induced hiNOS transcription. Furthermore, our ChIP analysis demonstrated that p300 was binding to Jun D and Fra-2 proteins at -5.3 kb AP-1 binding site in vivo. Lastly, our 3C assay was able to detect a long DNA loop between the hiNOS enhancer and core promoter site, and ChIP loop assay confirmed that p300 binds to AP-1 and RNA pol II proteins. Overall, our results suggest that coactivator p300 mediates cytokine-induced hiNOS transactivation by forming a distant DNA loop between its enhancer and core promoter region.

Requirement for endogenous heat shock factor 1 in inducible nitric oxide synthase induction in murine microglia

Background

Inducible nitric oxide synthase (iNOS) makes a great contribution to host defense and inflammation. In many settings, lipopolysaccharide (LPS) induces iNOS expression through activation of the inhibitor of κB-α (IκB-α)-nuclear factor-κB (NF-κB) cascade, whereas interferon-γ (IFN-γ) acts through Janus kinase (JAK)-signal transducer and activator of transcription 1 (STAT1) signals. Heat shock factor 1 (HSF1), a major regulator of heat shock protein transcription, has been shown to regulate the production of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), but it remains obscure whether and how HSF1 affects iNOS induction.

Methods

Western blot was used to measure the protein expression. The mRNA level was measured by real-time PCR. Silence of HSF1 was achieved by small interfering RNA. Nitric oxide (NO) content and NF-κB binding activity were assayed by commercial kits. Chromatin immunoprecipitation (ChIP) was used to measure the binding activity of NF-κB and STAT1 to iNOS promoters.

Results

HSF1 inhibition or knockdown prevented the LPS- and/or IFN-γ-stimulated iNOS protein expression in cultured microglia. HSF1 inhibition blocked iNOS mRNA transcription. These inhibitory effects of HSF1 inhibition on iNOS expression were confirmed in brain tissues from endotoxemic mice. Further analysis showed that HSF1 inhibition had no effect on IκB-α degradation and NF-κB or STAT1 phosphorylation in LPS/IFN-γ-stimulated cells. The nuclear transport of active NF-κB or STAT1 was also not affected by HSF1 inhibition, but HSF1 inhibition reduced the binding of NF-κB and STAT1 to their DNA elements. In addition, HSF1 inhibition reduced NF-κB and STAT1 bindings to iNOS promoter inside the LPS/IFN-γ-stimulated cells.

Conclusions

This preventing effect of HSF1 inhibition on iNOS mRNA transcription presents the necessary role of HSF1 in iNOS induction.

cFLIP is critical for oligodendrocyte protection from inflammation

Neuroinflammation associated with degenerative central nervous system disease and injury frequently results in oligodendrocyte death. While promoting oligodendrocyte viability is a major therapeutic goal, little is known about protective signaling strategies. We report that in highly purified rat oligodendrocytes, interferon gamma (IFNγ) activates a signaling pathway that protects these cells from tumor necrosis factor alpha (TNFα)-induced cytotoxicity. IFNγ protection requires Jak (Janus kinase) activation, components of the integrated stress response and NF-κB activation. Although NF-κB activation also occurred transiently in the absence of IFNγ and presence of TNFα, this activation was not sufficient to prevent induction of the TNFα-responsive cell death pathway. Genetic inhibition of NF-κB translocation to the nucleus abrogated IFNγ-mediated protection and did not change the cell death induced by TNFα, suggesting that NF-κB activation via IFNγ induces a different set of responses than activation of NF-κB via TNFα. A promising candidate is the NF-κB target cFLIP (cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein), which is protease-deficient caspase homolog that inhibits caspase-3 activation. We show that IFNγ-mediated protection led to upregulation of cFLIP. Overexpression of cFLIP was sufficient for oligodendrocyte protection from TNFα and short hairpin RNA knockdown of cFLIP-abrogated IFNγ -mediated protection. To determine the relevance of our in vitro finding to the more complex in vivo situation, we determined the impact on oligodendrocyte death of regional cFLIP loss of function in a murine model of neuroinflammation. Our data show that downregulation of cFLIP during inflammation leads to death of oligodendrocytes and decrease of myelin in vivo. Taken together, we show that IFNγ-mediated induction of cFLIP expression provides a new mechanism by which this cytokine can protect oligodendrocytes from TNFα-induced cell death.

Data mining of atherosclerotic plaque transcriptomes predicts STAT1-dependent inflammatory signal integration in vascular disease

Atherosclerotic plaque development involves multiple extra- and intra-cellular signals engaging cells from the immune system and from the vasculature. Pro-inflammatory pathways activated by interferon gamma (IFNγ) and toll-like receptor 4 (TLR4) ligands are profoundly involved in plaque formation and have been shown to involve cross-talk in all atheroma-interacting cell types leading to increased activation of signal transducer and activator of transcription-1 (STAT1) and elevated expression of pro-inflammatory mediators. Here we demonstrate that in Gene Expression Omnibus repository (GEO) deposited microarray datasets, obtained from human coronary and carotid atherosclerotic plaques, a significant increase in expression of pro-inflammatory and immunomodulatory genes can be detected. Moreover, increased expression of multiple chemokines, adhesion molecules and matrix-remodeling molecules was commonly detected in both plaque types and correlated with the presence of putative STAT1 binding sites in their promoters, suggesting strong involvement of STAT1 in plaque development. We also provide evidence to suggest that STAT1-nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) or STAT1-interferon-regulated factor (IRF) regulatory modules are over-represented in the promoters of these inflammatory genes, which points to a possible contribution of IFNγ and TLR4 cross-talk in the process of atherogenesis. Finally, a subset of these genes encodes for secreted proteins that could serve as a basis of a non-invasive diagnostic assay. The results of our in silico analysis in vitro provide potential evidence that STAT1-dependent IFNγ-TLR4 cross-talk plays a crucial role in coronary and carotid artery plaque development and identifies a STAT1-dependent gene signature that could represent a novel diagnostic tool to monitor and diagnose plaque progression in human atherosclerosis.

The role of tumor necrosis factor-α and interferon-γ in regulating angiomotin-like protein 1 expression in lung microvascular endothelial cells

BACKGROUND

Angiogenesis in the alveolar septa is thought be a critical factor in pulmonary emphysema. Angiomotin-like protein 1 (AmotL1) is involved in angiogenesis via regulating endothelial cell function. However, the role of AmotL1 in the pathogenesis of pulmonary emphysema has not been elucidated. The objective of this study is to evaluate the expression of AmotL1 in lung tissues from a murine model with emphysema, as well as from patients with chronic obstructive pulmonary disease (COPD). Furthermore, we analyzed the regulation of AmotL1 expression by TNF-α and IFN-γ in endothelial cells in vitro.

METHODS

Nrf2 knockout mice were exposed to cigarette smoke (CS) for 4 weeks, and the down-regulated genes affecting vascularity in the whole lung were identified by microarray analysis. This analysis revealed that the mRNA expression of AmotL1 decreased in response to CS when compared with air exposure. To confirm the protein levels that were indicated in the microarray data, we determined the expression of AmotL1 in lung tissues obtained from patients with COPD and also determined the expression of AmotL1, NFκB and IκBα in cultured normal human lung microvascular endothelial cells (HLMVECs) that were stimulated by TNF-α and IFN-γ.

RESULTS

We found that the number of AmotL1-positive vessels decreased in the emphysema lungs compared with the normal and bronchial asthmatic lungs. IFN-γ pretreatment diminished the TNF-α-induced AmotL1 in the cultured HLMVECs by blocking the degradation of IκBα.

CONCLUSIONS

These results suggested that IFN-γ exhibits anti-angiogenesis effects by regulating the expression of TNF-α-induced AmotL1 via NFκB in emphysema lungs.

Tumor necrosis factor-α downregulates sodium current in skeletal muscle by protein kinase C activation: involvement in critical illness polyneuromyopathy

Sepsis is involved in the decrease of membrane excitability of skeletal muscle, leading to polyneuromyopathy. This effect is mediated by alterations of the properties of voltage-gated sodium channels (Na(V)), but the exact mechanism is still unknown. The aim of the present study was to check whether tumor necrosis factor (TNF-α), a cytokine released during sepsis, exerts a rapid effect on Na(V). Sodium current (I(Na)) was recorded by macropatch clamp in skeletal muscle fibers isolated from rat peroneus longus muscle, in control conditions and after TNF-α addition. Analyses of dose-effect and time-effect relationships were carried out. Effect of chelerythrine, a PKC inhibitor, was also studied to determine the way of action of TNF-α. TNF-α induced a reversible dose- and time-dependent inhibition of I(Na). A maximum inhibition of 75% of the control current was observed. A shift toward more negative potentials of activation and inactivation curves of I(Na) was also noticed. These effects were prevented by chelerythrine pretreatment. TNF-α is a cytokine released in the early stages of sepsis. Besides a possible transcriptional role, i.e., modification of the channel type and/or number, we demonstrated the existence of a rapid, posttranscriptional inhibition of Na(V) by TNF-α. The downregulation of the sodium current could be mediated by a PKC-induced phosphorylation of the sodium channel, thus leading to a significant decrease in muscle excitability.

Inhibition of nuclear delivery of plasmid DNA and transcription by interferon γ: hurdles to be overcome for sustained gene therapy

Sustained expression of murine interferon (IFN)-γ (Muγ) was found to be effective in preventing tumor metastasis and atopic dermatitis in mouse models. However, our preliminary experiments suggested that the time-dependent decrease in the Muγ expression was not compensated for by repeated injections of Muγ-expressing plasmid. To identify the mechanism underlying this observation, a reporter plasmid was hydrodynamically injected into mice and the levels of the plasmid, mRNA and reporter protein were measured in mice receiving a pre- or co-administration of Muγ-expressing plasmid. Co-injection of Muγ-expressing plasmid had no significant effects on transgene expression from the reporter plasmid. In contrast, pre-injection of Muγ-expressing plasmid greatly inhibited the expression of the reporter protein. Moreover, pre-injection of Muγ-expressing plasmid also reduced the amount of the reporter plasmid in the nuclear fraction of mouse liver to < 10%, and that of reporter mRNA to < 1%. The degree of reduction in the expression of reporter protein was comparable with the reduction in mRNA. These results indicate that the difficulty in regaining the expression level of IFN-γ is due to the impaired delivery of plasmid to the nucleus and to the suppression of transcription from the plasmid.

Anti-inflammatory and antioxidant effects of a hypoglycemic fructan fraction from Psacalium peltatum (H.B.K.) Cass. in streptozotocin-induced diabetes mice

ETHNOPHARMACOLOGICAL IMPORTANCE

Psacalium peltatum (H.B.K.) Cass. (Asteraceae) is used medicinally to treat diabetes, rheumatic pains, as well as gastrointestinal and kidney ailments. Previous pharmacological and chemical assays have demonstrated that an aqueous fraction from Psacalium peltatum (AP-fraction) contains a carbohydrate-type compound with hypoglycemic activity. Nevertheless, studies have not yet considered the hypoglycemic action of the AP-faction by sub-chronic administration nor on other healing properties, some of which might be associated with DM2 and other inflammatory processes.

AIM OF STUDY

To determine whether a hypoglycemic carbohydrate fraction (AP-fraction) from Psacalium peltatum roots has antioxidant and anti-inflammatory effects in streptozotocin-induced diabetes mice.

MATERIAL AND METHODS

Healthy mice received either saline, the AP-fraction with a high content of fructans, or pioglitazone (a positive control) daily by gavage. After 15 days of treatment, these animals received a single intraperitoneal administration of streptozotocin and all treatments were continued for additional 33 days. The antioxidant and anti-inflammatory properties of the AP-fraction were evaluated through the quantification of biomarkers of oxidative stress (glutathione (GSH) and malondialdehyde (MDA)) and inflammation (interleukin (IL)-6, tumor necrosis factor alpha (TNF-α), interferon-gamma (IFN-γ), and IL-10).

RESULTS

The AP-fraction reduced glycemia and the glycated hemoglobin. Furthermore, animals treated with the AP-fraction had increased GSH, while MDA was decreased in the liver and the heart, without changes in the kidneys and the pancreas. The AP-fraction significantly reduced TNF-α serum levels but did not modify IL-6; in addition, this fraction increased IFN-γ and IL-10 levels. The increase in IL-10 levels may indicate an inhibition of the production of pro-inflammatory cytokines such as TNF-α, whereas the increase in IFN-γ might be indicative of a beneficial effect on the immune system.

CONCLUSIONS

The AP-fraction hypoglycemic fructans from Psacalium peltatum roots showed antioxidant and anti-inflammatory properties in mice with streptozotocin-induced diabetes. The Psacalium peltatum hypoglycemic fructans may be valuable in preventing insulin resistance, as well as the development and progression of diabetic complications caused by chronic inflammation.

Inhibition of STAT1 accelerates bone fracture healing

Skeletal fracture healing involves a variety of cellular and molecular events; however, the mechanisms behind these processes are not fully understood. In the current study, we investigated the potential involvement of the signal transducer and activator of transcription 1 (STAT1), a critical regulator for both osteoclastogenesis and osteoblast differentiation, in skeletal fracture healing. We used a fracture model and a cortical defect model in mice, and found that fracture callus remodeling and membranous ossification are highly accelerated in STAT1-deficient mice. Additionally, we found that STAT1 suppresses Osterix transcript levels and Osterix promoter activity in vitro, indicating the suppression of Osterix transcription as one of the mechanisms behind the inhibitory effect of STAT1 on osteoblast differentiation. Furthermore, we found that fludarabine, a potent STAT1 inhibitor, significantly increases bone formation in a heterotopic ossification model. These results reveal previously unknown functions of STAT1 in skeletal homeostasis and may have important clinical implications for the treatment of skeletal bone fracture.

Francisella tularensis antioxidants harness reactive oxygen species to restrict macrophage signaling and cytokine production

Francisella tularensis is the etiologic agent of the highly infectious animal and human disease tularemia. Its extreme infectivity and virulence are associated with its ability to evade immune detection, which we now link to its robust reactive oxygen species-scavenging capacity. Infection of primary human monocyte-derived macrophages with virulent F. tularensis SchuS4 prevented proinflammatory cytokine production in the presence or absence of IFN-gamma compared with infection with the attenuated live vaccine strain. SchuS4 infection also blocked signals required for macrophage cytokine production, including Akt phosphorylation, IkappaB alpha degradation, and NF-kappaB nuclear localization and activation. Concomitant with SchuS4-mediated suppression of Akt phosphorylation was an increase in the levels of the Akt antagonist PTEN. Moreover, SchuS4 prevented the H(2)O(2)-dependent oxidative inactivation of PTEN compared with a virulent live vaccine strain. Mutation of catalase (katG) sensitized F. tularensis to H(2)O(2) and enhanced PTEN oxidation, Akt phosphorylation, NF-kappaB activation, and inflammatory cytokine production. Together, these findings suggest a novel role for bacterial antioxidants in restricting macrophage activation through their ability to preserve phosphatases that temper kinase signaling and proinflammatory cytokine production.

Interferon-gamma regulates intestinal epithelial homeostasis through converging beta-catenin signaling pathways

Inflammatory cytokines have been proposed to regulate epithelial homeostasis during intestinal inflammation. We report here that interferon-gamma (IFN-gamma) regulates the crucial homeostatic functions of cell proliferation and apoptosis through serine-threonine protein kinase AKT-beta-catenin and Wingless-Int (Wnt)-beta-catenin signaling pathways. Short-term exposure of intestinal epithelial cells to IFN-gamma resulted in activation of beta-catenin through AKT, followed by induction of the secreted Wnt inhibitor Dkk1. Consequently, we observed an increase in Dkk1-mediated apoptosis upon extended IFN-gamma treatment and reduced proliferation through depletion of the Wnt coreceptor LRP6. These effects were enhanced by tumor necrosis factor-alpha (TNF-alpha), suggesting synergism between the two cytokines. Consistent with these results, colitis in vivo was associated with decreased beta-catenin-T cell factor (TCF) signaling, loss of plasma membrane-associated LRP6, and reduced epithelial cell proliferation. Proliferation was partially restored in IFN-gamma-deficient mice. Thus, we propose that IFN-gamma regulates intestinal epithelial homeostasis by sequential regulation of converging beta-catenin signaling pathways.

Exacerbated innate host response to SARS-CoV in aged non-human primates

The emergence of viral respiratory pathogens with pandemic potential, such as severe acute respiratory syndrome coronavirus (SARS-CoV) and influenza A H5N1, urges the need for deciphering their pathogenesis to develop new intervention strategies. SARS-CoV infection causes acute lung injury (ALI) that may develop into life-threatening acute respiratory distress syndrome (ARDS) with advanced age correlating positively with adverse disease outcome. The molecular pathways, however, that cause virus-induced ALI/ARDS in aged individuals are ill-defined. Here, we show that SARS-CoV-infected aged macaques develop more severe pathology than young adult animals, even though viral replication levels are similar. Comprehensive genomic analyses indicate that aged macaques have a stronger host response to virus infection than young adult macaques, with an increase in differential expression of genes associated with inflammation, with NF-κB as central player, whereas expression of type I interferon (IFN)-β is reduced. Therapeutic treatment of SARS-CoV-infected aged macaques with type I IFN reduces pathology and diminishes pro-inflammatory gene expression, including interleukin-8 (IL-8) levels, without affecting virus replication in the lungs. Thus, ALI in SARS-CoV-infected aged macaques developed as a result of an exacerbated innate host response. The anti-inflammatory action of type I IFN reveals a potential intervention strategy for virus-induced ALI.

Severe acute respiratory syndrome coronavirus (SARS-CoV) infection causes acute lung injury that may develop into the life-threatening acute respiratory distress syndrome (ARDS) in mostly elderly individuals. Although SARS-CoV infection can be fatal, most patients recover, suggesting that protective host responses are operational to combat the viral infection. Therefore, we used age as predisposing factor to obtain insight into the pathogenesis of SARS-CoV. In this study, we show that SARS-CoV-infected aged macaques developed significantly more pathology than young adult animals, which could not be contributed to differences in viral replication. Using comparative microarray analyses, it was shown that although the nature of the host response to SARS-CoV infection was similar in aged and young adult macaques, the severity was significantly different, with aged macaques displaying an increase in differential expression of genes associated with inflammation. Interestingly, type I IFN-β mRNA levels correlated negatively with gross pathology. Therapeutic treatment of aged macaques with type I IFN reduced pathology without affecting virus replication. However, pro-inflammatory gene expression was significantly diminished. Thus, modulation of the host response by type I IFNs provides a promising outlook for novel intervention strategies.

Tumor Necrosis Factor alpha (TNFalpha) regulates CD40 expression through SMAR1 phosphorylation

CD40 plays an important role in mediating inflammatory response and is mainly induced by JAK/STAT phosphorylation cascade. TNFalpha is the key cytokine that activates CD40 during inflammation and tumorigenesis. We have earlier shown that SMAR1 can repress the transcription of Cyclin D1 promoter by forming a HDAC1 dependent repressor complex. In this study, we show that SMAR1 regulates the transcription of NF-kappaB target gene CD40. SMAR1 recruits HDAC1 and forms a repressor complex on CD40 promoter and keeps its basal transcription in check. Further, we show that TNFalpha stimulation induces SMAR1 phosphorylation at Ser-347 and promotes its cytoplasmic translocation, thus releasing its negative effect. Concomitantly, TNFalpha induced phosphorylation of STAT1 at Tyr-701 by JAK1 facilitates its nuclear translocation and activation of CD40 through p300 recruitment and core Histone-3 acetylation. Thus, TNFalpha mediated regulation of CD40 expression occurs by dual phosphorylation of SMAR1 and STAT1.

Eicosanoid release is increased by membrane destabilization and CFTR inhibition in Calu-3 cells

The antiinflammatory protein annexin-1 (ANXA1) and the adaptor S100A10 (p11), inhibit cytosolic phospholipase A2 (cPLA2α) by direct interaction. Since the latter is responsible for the cleavage of arachidonic acid at membrane phospholipids, all three proteins modulate eicosanoid production. We have previously shown the association of ANXA1 expression with that of CFTR, the multifactorial protein mutated in cystic fibrosis. This could in part account for the abnormal inflammatory status characteristic of this disease. We postulated that CFTR participates in the regulation of eicosanoid release by direct interaction with a complex containing ANXA1, p11 and cPLA2α. We first analyzed by plasmon surface resonance the in vitro binding of CFTR to the three proteins. A significant interaction between p11 and the NBD1 domain of CFTR was found. We observed in Calu-3 cells a rapid and partial redistribution of all four proteins in detergent resistant membranes (DRM) induced by TNF-α. This was concomitant with increased IL-8 synthesis and cPLA2α activation, ultimately resulting in eicosanoid (PGE2 and LTB4) overproduction. DRM destabilizing agent methyl-β-cyclodextrin induced further cPLA2α activation and eicosanoid release, but inhibited IL-8 synthesis. We tested in parallel the effect of short exposure of cells to CFTR inhibitors Inh172 and Gly-101. Both inhibitors induced a rapid increase in eicosanoid production. Longer exposure to Inh172 did not increase further eicosanoid release, but inhibited TNF-α-induced relocalization to DRM. These results show that (i) CFTR may form a complex with cPLA2α and ANXA1 via interaction with p11, (ii) CFTR inhibition and DRM disruption induce eicosanoid synthesis, and (iii) suggest that the putative cPLA2/ANXA1/p11/CFTR complex may participate in the modulation of the TNF-α-induced production of eicosanoids, pointing to the importance of membrane composition and CFTR function in the regulation of inflammation mediator synthesis.

A far-upstream Oct-1 motif regulates cytokine-induced transcription of the human inducible nitric oxide synthase gene

Transcriptional regulation of the human inducible nitric oxide synthase (hiNOS) gene is highly complex and requires an orchestrated flow of positive and negative transcription factors that bind to specific cis-acting upstream response elements. Very little specific information exists about the far-upstream region of the hiNOS gene. Oct-1 protein belongs to the Pit-Oct-Unc domain transcription factor family and is constitutively expressed in all dividing cells. It is essential for proliferation, differentiation, and other key cell processes. However, the role of Oct-1 in regulating hiNOS gene expression has not been reported. In this work, the octamer sequence 5'-ATGCAAAT-3' at -10.2 kb in the hiNOS promoter was identified as high-affinity Oct-1 binding by electrophoretic mobility shift assay in vitro and chromatin immunoprecipitation assay in vivo. Mutation of Oct-1 motif at -10.2 kb in the hiNOS promoter decreased cytokine-induced hiNOS promoter activity by 40%. Cytokine-induced hiNOS promoter activity was also significantly reduced by Oct-1 small interfering RNA targeting. Overexpression of Oct-1 increased cytokine-induced hiNOS protein expression in primary human hepatocytes. Furthermore, the Oct-1 motif at -10.2 kb of the hiNOS promoter conferred increased transcriptional activity to the heterologous thymidine kinase promoter irrespective of cytokine induction. Taken together, this work identifies a far-upstream functional Oct-1 enhancer motif at -10.2 kb in the hiNOS promoter that regulates cytokine-induced hiNOS gene transcription and further underscores tight control mechanisms regulating the expression of the hiNOS gene.

Pressure activates epidermal growth factor receptor leading to the induction of iNOS via NFkappaB and STAT3 in human proximal tubule cells

Ureteral obstruction leads to increased pressure and inducible nitric oxide synthase (iNOS) expression. This study examined the involvement of epidermal growth factor (EGF) receptor (EGFR), nuclear factor-kappaB (NFkappaB), and signal transducers and activators of transcription 3 (STAT3) in iNOS induction in human proximal tubule (HKC-8) cells in response to pressure or EGF. HKC-8 cells were subjected to 60 mmHg pressure or treated with EGF for 0-36 h. iNOS was more rapidly induced in response to EGF than pressure. The addition of EGFR, NFkappaB, and STAT3 inhibitors significantly suppressed pressure- or EGF-stimulated iNOS mRNA and protein expression. Analysis of the activated states of EGFR, NFkappaB p65, and STAT3 after exposure to both stimuli demonstrated phosphorylation within 2.5 min. Anti-EGF antibody inhibited iNOS induction in pressurized HKC-8 cells, providing evidence that endogenous EGF mediates the response to pressure. In ureteral obstruction, when pressure is elevated, phosphorylated EGFR was detected in the apical surface of the renal tubules, validating the in vitro findings. These data indicate that EGFR, NFkappaB, and STAT3 are required for human iNOS gene induction in response to pressure or EGF, indicating a similar mechanism of activation.

Wnt/beta-catenin signaling regulates cytokine-induced human inducible nitric oxide synthase expression by inhibiting nuclear factor-kappaB activation in cancer cells

The human inducible nitric oxide synthase (hiNOS) gene is regulated by nuclear factor kappaB (NF-kappaB) and has recently been shown to be a target of the Wnt/beta-catenin pathway. In this study, we tested the hypothesis that Wnt/beta-catenin signaling might regulate cytokine- or tumor necrosis factor alpha (TNFalpha)-induced hiNOS expression through interaction with NF-kappaB. A cytokine mixture of TNFalpha + interleukin (IL)-1beta + IFNgamma induced a 2- to 3-fold increase in hiNOS promoter activity in HCT116 and DLD1 colon cells, but produced a 2-fold decrease in SW480 colon cancer cells. A similar differential activity was seen in liver cancer cells (HepG2, Huh7, and Hep3B). Overexpression of beta-catenin produced a dose-dependent decrease in NF-kappaB reporter activity and decreased cytokine mixture-induced hiNOS promoter activity. Gel shift for TNFalpha-induced hiNOS NF-kappaB activation showed decreased p50 binding and decreased NF-kappaB reporter activity in the beta-catenin-mutant HAbeta18 cells. Conversely, enhanced p50 binding and increased NF-kappaB reporter activity were seen in HAbeta85 cells, which lack beta-catenin signaling. Coimmunoprecipitation confirmed that beta-catenin complexed with both p65 and p50 NF-kappaB proteins. NF-kappaB-dependent Traf1 protein expression also inversely correlated with the level of beta-catenin. Furthermore, SW480 cells stably transformed with wild-type adenomatous polyposis coli showed decreased beta-catenin protein and increased TNFalpha-induced p65 NF-kappaB binding as well as iNOS and Traf1 expression. Finally, beta-catenin inversely correlated with iNOS and Fas expression in vivo in hepatocellular carcinoma tumor samples. Our in vitro and in vivo data show that beta-catenin signaling inversely correlates with cytokine-induced hiNOS and other NF-kappaB-dependent gene expression. These findings underscore the complex role of Wnt/beta-catenin, NF-kappaB, and iNOS signaling in the pathophysiology of inflammation-associated carcinogenesis.

HDACi--targets beyond chromatin

Histone deacetylases (HDACs) play an important role in gene regulation. Inhibitors of HDACs (HDACi) are novel anti-cancer drugs, which induce histone (hyper-) acetylation and counteract aberrant gene repression. On the other hand, HDACi treatment can also result in decreased gene expression, and targeting HDACs affects more than chromatin. Recently, HDACi were shown to evoke non-histone protein acetylation, which can alter signaling networks relevant for tumorgenesis. Furthermore, HDACi can promote the degradation of (proto-) oncoproteins. Here, we summarize these findings and discuss how these substances could be beneficial for the treatment and prevention of human ailments, such as cancer and unbalanced immune functions.

Coordinate regulation of enzyme markers for inflammation and for protection against oxidants and electrophiles

An elaborate network of highly inducible phase 2 proteins protects aerobic cells against the cumulative damaging effects of reactive oxygen intermediates and toxic electrophiles, which are the major causes of malignancy and chronic degenerative diseases. Many chemical and phytochemical agents, all of which react with thiol groups, induce the phase 2 response through their reactivity with critical cysteine thiols of Keap1. We recently found that the anti-inflammatory potencies (suppression of iNOS and COX-2 expression) of a series of triterpenoids with Michael reaction centers were closely correlated with the potencies of these agents to induce the phase 2 response. We now report that representatives of seven recognized chemical classes of inducers, including isothiocyanates, bisbenzylidenes, arsenicals, heavy metals, and vicinal dithiols, showed highly correlated inducer and anti-inflammatory potencies spanning more than six orders of magnitude of concentrations in established cells and in primary mouse peritoneal macrophages. Potency measurements were expressed as the D(m) values (median effect concentration) by use of the Median Effect Equation. Whereas the phase 2 induction required the functional integrity of both the repressor Keap1 and the transcription factor Nrf2, the effectiveness of inducers in blocking the up-regulation of iNOS by inflammatory cytokines was related to the nature of the cytokine and the inducer concentration. These studies identify suppression of inflammation as a consistent property of inducers of the phase 2 response and strongly suggest that this property is a central aspect of their chemoprotective actions.

Characterization of short range DNA looping in endotoxin-mediated transcription of the murine inducible nitric-oxide synthase (iNOS) gene

The local structural properties and spatial conformations of chromosomes are intimately associated with gene expression. The spatial associations of critical genomic elements in inducible nitric-oxide synthase (iNOS) transcription have not been previously examined. In this regard, the murine iNOS promoter contains 2 NF-kappaB binding sites (nt -86 and nt -972) that are essential for maximal transactivation of iNOS by LPS. Although AP-1 is commonly listed as an essential transcription factor for LPS-mediated iNOS transactivation, the relationship between AP-1 and NF-kappaB in this setting is not well studied. In this study using a model of LPS-stimulated ANA-1 murine macrophages, we demonstrate that short range DNA looping occurs at the iNOS promoter. This looping requires the presence of AP-1, c-Jun, NF-kappaB p65, and p300-associated acetyltransferase activity. The distal AP-1 binding site interacts via p300 with the proximal NF-kappaB binding site to create this DNA loop to participate in iNOS transcription. Other geographically distant AP-1 and NF-kappaB sites are certainly occupied, but selected sites are critical for iNOS transcription and the formation of the c-Jun, p65, and p300 transcriptional complex. In this "simplified" model of murine iNOS promoter, numerous transcription factors recognize and bind to various response elements, but these locales do not equally contribute to iNOS gene transcription.

CREB, ATF, and AP-1 transcription factors regulate IFN-gamma secretion by human T cells in response to mycobacterial antigen

IFN-gamma production by T cells is pivotal for defense against many pathogens, and the proximal promoter of IFN-gamma, -73 to -48 bp upstream of the transcription start site, is essential for its expression. However, transcriptional regulation mechanisms through this promoter in primary human cells remain unclear. We studied the effects of cAMP response element binding protein/activating transcription factor (CREB/ATF) and AP-1 transcription factors on the proximal promoter of IFN-gamma in human T cells stimulated with Mycobacterium tuberculosis. Using EMSA, supershift assays, and promoter pulldown assays, we demonstrated that CREB, ATF-2, and c-Jun, but not cyclic AMP response element modulator, ATF-1, or c-Fos, bind to the proximal promoter of IFN-gamma upon stimulation, and coimmunoprecipitation indicated the possibility of interaction among these transcription factors. Chromatin immunoprecipitation confirmed the recruitment of these transcription factors to the IFN-gamma proximal promoter in live Ag-activated T cells. Inhibition of ATF-2 activity in T cells with a dominant-negative ATF-2 peptide or with small interfering RNA markedly reduced the expression of IFN-gamma and decreased the expression of CREB and c-Jun. These findings suggest that CREB, ATF-2, and c-Jun are recruited to the IFN-gamma proximal promoter and that they up-regulate IFN-gamma transcription in response to microbial Ag. Additionally, ATF-2 controls expression of CREB and c-Jun during T cell activation.

Exogenous tumour necrosis factor alpha induces suppression of autoimmune arthritis

Introduction

Our previous studies showed that arthritic Lewis (LEW) rats produced the highest levels of tumour necrosis factor (TNF)α in the recovery phase of adjuvant arthritis (AA), suggesting a correlation between high TNFα levels and reduced severity of arthritis. To further explore this correlation, we compared the TNFα secretion profile of the AA-resistant Wistar Kyoto (WKY) rats with that of LEW rats, determined the effect of exogenous TNFα on the course of AA in LEW rats, and examined various mechanisms involved in TNFα-induced disease modulation.

Methods

A cohort each of LEW and WKY rats was immunised subcutaneously with heat-killed Mycobacterium tuberculosis H37Ra (Mtb). At different time points thereafter, subgroups of rats were killed and their draining lymph node cells were tested for cytokine production. Another group of LEW rats was injected with TNFα intraperitoneally daily for a total of 10 injections, 3 before and 6 after Mtb challenge, and then observed for signs of AA. In parallel, TNFα-treated rats were examined for changes in other cytokines, in CD4+CD25+ T cell frequency, and in indoleamine 2,3-dioxygenase (IDO) mRNA expression levels.

Results

LEW rats displayed a TNFα secretion profile that was opposite to that of the WKY rats. Furthermore, TNFα treatment significantly downmodulated the severity of AA in LEW rats, and decreased the interferon (IFN)-γ secretion in response to the pathogenic determinant of the disease-related antigen. No significant alterations were observed in other parameters tested.

Conclusion

The role of endogenous TNFα in the induction and propagation of arthritis is well established. However, exogenous TNFα can downmodulate the course of AA, displaying an immunoregulatory functional attribute of this cytokine.

Airway smooth muscle cell as an inflammatory cell: lessons learned from interferon signaling pathways

The present article will describe the potential role of airway smooth muscle (ASM) in mediating both deleterious/beneficial effects of interferons (IFNs) in asthma. First described as beneficial in treating the main features of asthma, the interplay between IFNs and ASM could explain their deleterious actions recently described in a number of different studies. Through multiple mechanisms, including the suppression of steroid action, the synergistic pro-inflammatory actions when combined with other cytokines, and the modulation of calcium metabolism, IFNs are now seen as critical mediators in the pathogenesis of asthma.

Generation of Th1 and Th2 chemokines by human eosinophils: evidence for a critical role of TNF-alpha

Emerging evidence suggests a role for eosinophils in immune regulation of T cells. Thus, we sought to determine whether human eosinophils may exert their effect via differential generation of Th1 and Th2 chemokines depending on cytokines in their microenvironment and, if so, to establish the conditions under which these chemokines are produced. Eosinophils cultured with TNF-alpha plus IL-4 had increased mRNA expression and protein secretion of the Th2-type chemokines, CCL17 (thymus and activation-regulated chemokine) and CCL22 (macrophage-derived chemokine). Conversely, the Th1-type chemokines, CXCL9 (monokine induced by IFN-gamma) and CXCL10 (IFN-gamma-inducible protein-10), were expressed after stimulation with TNF-alpha plus IFN-gamma. Addition of TNF-alpha appeared to be essential for IFN-gamma-induced release of Th1-type chemokines and significantly enhanced IL-4-induced Th2-type chemokines. Inhibition of NF-kappaB completely blocked the production of both Th1 and Th2 chemokines. Activation of NF-kappaB, STAT6, and STAT1 was induced in eosinophils by TNF-alpha, IL-4, and IFN-gamma, respectively. However, there was no evidence for enhancement of these signaling events when eosinophils were stimulated with the combination of TNF-alpha plus IL-4 or TNF-alpha plus IFN-gamma. Thus, independently activated signaling cascades appear to lead to activation of NF-kappaB, STAT1, and STAT6, which may then cooperate at the promoter level to increase gene transcription. Our data demonstrate that TNF-alpha is a vital component for eosinophil chemokine generation and that, depending on the cytokines present in their microenvironment, eosinophils can promote either a Th2 or a Th1 immune response, supporting an immunoregulatory role for eosinophils.

Stat1 acetylation inhibits inducible nitric oxide synthase expression in interferon-gamma-treated RAW264.7 murine macrophages

BACKGROUND

We hypothesized that acetylation of the Stat1 regulates interferon-gamma (IFN-gamma) mediated macrophage expression of inducible nitric oxide synthase (iNOS).

METHODS

RAW 264.7 iNOS expression was induced with IFN-gamma. Deacetylase inhibitors trichostatin A (TSA) or valproic acid (VPA) were added. Stat1 and iNOS mRNA and protein were measured. Acetylated Stat1 was determined by immunoprecipitation. Chromatin immunoprecipitation assessed in vivo binding of Stat1 to the iNOS promoter.

RESULTS

IFN-gamma significantly increased nitrite, iNOS protein and iNOS mRNA, and iNOS promoter activation. (P < .01 vs control for nitrite, protein, and mRNA). TSA-mediated acetylation decreased these to levels that were not different from controls. IFN-gamma increased acetylated Stat1 by 5-fold (P < .02 vs control); TSA + IFN-gamma caused an additional 4-fold increase in acetylated Stat1 (P < .05 vs IFN alone). Stat1 binding to the iNOS promoter increased 8-fold with IFN-gamma (P < .01 vs control). In TSA + IFN-gamma, Stat1 binding was not different from controls. Although less potent than TSA, VPA also significantly decreased nitrite, iNOS protein, iNOS mRNA, Stat1 acetylation, and Stat1 binding.

CONCLUSIONS

Acetylation of Stat1 protein correlates with decreased Stat1 binding to the iNOS promoter with resultant inhibition of IFN-gamma-mediated iNOS expression. Acetylation of the Stat1 protein may downregulate iNOS expression in proinflammatory states.

Effects of IFN-gamma and Stat1 on gene expression, growth, and survival in non-small cell lung cancer cells

Stat transcription factors are activated by cytokines and can activate pathways important in oncogenesis. Although previous studies have identified an oncogenic role of Stat3 in lung cancer cells, the role of Stat1 is unclear. Using a mutant of Stat1 with constitutive activity (Stat1C), we examined the effect of persistent Stat1 activity on lung cancer cell growth, survival and gene expression. We identified no significant effect of Stat1C alone or with interferon-gamma (IFN-gamma) on lung cancer cell growth or survival. Consistent with prior reports, Stat1C expression alone elicited minimal changes in gene expression and required costimulatory IFN-gamma for full activity. Using oligonucleotide gene arrays and quantitative real-time PCR, we identified numerous proinflammatory gene products and chemokines regulated by IFN-gamma/Stat1C signaling. These results suggest the major role of IFN-gamma and Stat1 in lung cells is to direct a proinflammatory gene expression program rather than have major effects on cell growth or survival or both.

Identification of a classic cytokine‐induced enhancer upstream in the human iNOS promoter

The human inducible NOS (iNOS) promoter transcriptionally regulated by 5' flanking region extending 16 kb upstream that contains cytokine-responsive DNA motifs. In this study, we further identified a classic inducible enhancer located between -5 and -6 kb in the hiNOS upstream promoter. This 1 kb promoter sequence functions as a cytokine-inducible enhancer in an orientation- and position-independent manner in human lung A549 and liver AKN1 cells. This DNA enhancer also confers cytokine inducibility to the heterologous thymidine kinase (TK) promoter. Chromatin immunoprecipitation (ChIP) analysis was applied, and confirmed cytokine-inducible in vivo DNA-protein interactions within this enhancer region. In vivo functional binding of both NF-kappaB (p65/p50) and Stat-1alpha at the -5.8 kb human iNOS promoter site was significantly increased in A549 cells after cytokine stimulation, while only Stat-1alpha bound at the -5.2 kb site. These results identify the -5 to -6 kb promoter region as a classic transcriptional enhancer for the human iNOS gene and provide definitive in vivo evidence of specific NF-kappaB and Stat-1 nuclear protein binding that mediates transcription of the hiNOS gene under cytokine stimulation.

Inhibition of tumor necrosis factor-alpha-inducible inflammatory genes by interferon-gamma is associated with altered nuclear factor-kappaB transactivation and enhanced histone deacetylase activity

Airway smooth muscle (ASM) cells can act as effector cells in the initiation and/or perpetuation of airway inflammation in asthma by producing various inflammatory chemokines or cytokines. Previous studies from our laboratory and others showed that the combination of tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) or endogenous IFNbeta results in a synergistic induction of various pro-inflammatory genes, including CD38 and regulated upon activation normal T-cell expressed and secreted (RANTES), in ASM cells. In contrast to these studies, we found that IFNgamma (1000 U/ml) markedly inhibited TNFalpha-induced expression of interleukin (IL)-6, IL-8, and eotaxin by 66.29+/-3.33, 43.86+/-7.11, and 63.25+/-6.46%, respectively. These genes were also found to be NF-kappaB-dependent in that TNFalpha-induced expression of IL-6, IL-8, and eotaxin was dose-dependently inhibited by the selective IKKbeta inhibitor 4-(2'-aminoethyl)amino-1,8-dimethylimidazo[1,2-a]quinoxaline (BMS-345541) (1-30 microM). Using a luciferase reporter construct containing kappaB sites, we found that IFNgamma (10-1000 U/ml) inhibits NF-kappaB-dependent gene transcription in a dose-dependent manner. Moreover, IFNgamma failed to affect TNFalpha-induced IkappaKbeta phosphorylation or IkappaB degradation as well as nuclear NF-kappaB/DNA interaction. It is noteworthy that IFNgamma decreases TNFalpha-induced histone acetyl transferase (HAT) and increases histone deacetylase (HDAC) activities. Finally, trichostatin A, an HDAC inhibitor, prevents IFNgamma inhibitory action on TNFalpha-induced gene expression. Together, our data indicate that IFNgamma is a potent inhibitor of specific TNFalpha-inducible inflammatory genes by acting on NF-kappaB transactivation via the modulation of HDAC function.

Regulation of human nitric oxide synthase 2 expression by Wnt beta-catenin signaling

Nitric oxide (NO.), an important mediator of inflammation, and beta-catenin, a component of the Wnt-adenomatous polyposis coli signaling pathway, contribute to the development of cancer. We have identified two T-cell factor 4 (Tcf-4)-binding elements (TBE1 and TBE2) in the promoter of human inducible NO synthase 2 (NOS2). We tested the hypothesis that beta-catenin regulates human NOS2 gene. Mutation in either of the two TBE sites decreased the basal and cytokine-induced NOS2 promoter activity in different cell lines. The promoter activity was significantly reduced when both TBE1 and TBE2 sites were mutated (P < 0.01). Nuclear extract from HCT116, HepG2, or DLD1 cells bound to NOS2 TBE1 or TBE2 oligonucleotides in electrophoretic mobility shift assays and the specific protein-DNA complexes were supershifted with anti-beta-catenin or anti-Tcf-4 antibody. Overexpression of beta-catenin and Tcf-4 significantly increased both basal and cytokine-induced NOS2 promoter activity (P < 0.01), and the induction was dependent on intact TBE sites. Overexpression of beta-catenin or Tcf-4 increased NOS2 mRNA and protein expression in HCT116 cells. Lithium chloride (LiCl), an inhibitor of glycogen synthase kinase-3beta, increased cytosolic and nuclear beta-catenin level, NOS2 expression, and NO. production in primary human and rat hepatocytes and cancer cell lines. Treatment with Wnt-3A-conditioned medium increased beta-catenin and NOS2 expression in fetal human hepatocytes. When administered in vivo, LiCl increased hepatic beta-catenin level in a dose-dependent manner with simultaneous increase in NOS2 expression. These data are consistent with the hypothesis that beta-catenin up-regulates NOS2 and suggest a novel mechanism by which the Wnt/beta-catenin signaling pathway may contribute to cancer by increasing NO. production.