Lymphotoxin beta receptor induces interleukin 8 gene expression via NF-kappaB and AP-1 activation

Integrative analysis reveals novel insights into juvenile idiopathic arthritis pathogenesis and shared molecular pathways with associated traits

Background

Juvenile idiopathic arthritis (JIA) is an autoimmune joint disease that frequently co-occurs with other complex phenotypes, including cancers and other autoimmune diseases. Despite the identification of numerous risk variants through genome-wide association studies (GWAS), the affected genes, their connection to JIA pathogenesis, and their role in the development of associated traits remain unclear. This study aims to address these gaps by elucidating the gene-regulatory mechanisms underlying JIA pathogenesis and exploring its potential role in the emergence of associated traits.

Methods

A two-sample Mendelian Randomization (MR) analysis was conducted to identify blood-expressed genes causally linked to JIA. A curated protein interaction network was subsequently used to identify sets of single-nucleotide polymorphisms (i.e., spatial eQTL SNPs) that regulate the expression of JIA causal genes and their protein interaction partners. These SNPs were cross-referenced against the GWAS catalog to identify statistically enriched traits associated with JIA.

Results

The two-sample MR analysis identified 52 genes whose expression changes in the blood are putatively causal for JIA. These genes (e.g., HLA, LTA, LTB, IL6ST) participate in a range of immune-related pathways (e.g., antigen presentation, cytokine signalling) and demonstrate cell type-specific regulatory patterns across different immune cell types (e.g., PPP1R11 in CD4+ T cells). The spatial eQTLs that regulate JIA causal genes and their interaction partners were statistically enriched for GWAS SNPs linked with 95 other traits, including both known and novel JIA-associated traits. This integrative analysis identified genes whose dysregulation may explain the links between JIA and associated traits, such as autoimmune/inflammatory diseases (genes at 6p22.1 locus), Hodgkin lymphoma (genes at 6p21.3 [FKBPL, PBX2, AGER]), and chronic lymphocytic leukemia (BAK1).

Conclusion

Our approach provides a significant advance in understanding the genetic architecture of JIA and associated traits. The results suggest that the burden of associated traits may differ among JIA patients, influenced by their combined genetic risk across different clusters of traits. Future experimental validation of the identified connections could pave the way for refined patient stratification, the discovery of new biomarkers, and shared therapeutic targets.

Juvenile idiopathic arthritis-associated genetic loci exhibit spatially constrained gene regulatory effects across multiple tissues and immune cell types

Juvenile idiopathic arthritis (JIA) is an autoimmune, inflammatory joint disease with complex genetic etiology. Previous GWAS have found many genetic loci associated with JIA. However, the biological mechanism behind JIA remains unknown mainly because most risk loci are located in non-coding genetic regions. Interestingly, increasing evidence has found that regulatory elements in the non-coding regions can regulate the expression of distant target genes through spatial (physical) interactions. Here, we used information on the 3D genome organization (Hi-C data) to identify target genes that physically interact with SNPs within JIA risk loci. Subsequent analysis of these SNP-gene pairs using data from tissue and immune cell type-specific expression quantitative trait loci (eQTL) databases allowed the identification of risk loci that regulate the expression of their target genes. In total, we identified 59 JIA-risk loci that regulate the expression of 210 target genes across diverse tissues and immune cell types. Functional annotation of spatial eQTLs within JIA risk loci identified significant overlap with gene regulatory elements (i.e., enhancers and transcription factor binding sites). We found target genes involved in immune-related pathways such as antigen processing and presentation (e.g., ERAP2, HLA class I and II), the release of pro-inflammatory cytokines (e.g., LTBR, TYK2), proliferation and differentiation of specific immune cell types (e.g., AURKA in Th17 cells), and genes involved in physiological mechanisms related to pathological joint inflammation (e.g., LRG1 in arteries). Notably, many of the tissues where JIA-risk loci act as spatial eQTLs are not classically considered central to JIA pathology. Overall, our findings highlight the potential tissue and immune cell type-specific regulatory changes contributing to JIA pathogenesis. Future integration of our data with clinical studies can contribute to the development of improved JIA therapy.

Transcriptome analysis of turbot (Scophthalmus maximus) head kidney and liver reveals immune mechanism in response to Vibrio anguillarum infection

The diseases triggered by Vibrio anguillarum infection have created huge economic losses to the turbot (Scophthalmus maximus) farming industry. However, the immune mechanism of turbot to V. anguillarum infection has not been deeply investigated. To better understand the immune response of turbot to V. anguillarum infection, transcriptome analysis of the head kidney and liver of turbot was performed. A total of 15,948 and 11,494 differentially expressed genes (DEGs) were obtained from the turbot head kidney and liver, respectively. Transcriptome analysis revealed that the head kidney and liver of turbot have some differences in the gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis of the DEGs for the different functions of these two organs. Although there are many uncertain factors in this immune process, such as the occurrence of alternative splicing (AS) events and the differences in the protein structure of the DEGs, the NFκB signalling pathway, MKK-dependent AP-1 activation, JAK-STAT signalling pathway, the signal transmission of MHC Ⅰ and a series of DEGs including HSP90 driving NLRP3 to produce inflammatory factors (IL-1β, IL-8, TNFα, etc.) were possible important immune response pathways for turbot to V. anguillarum infection. Overall, our research has conducted a preliminary exploration of the immune mechanism of turbot in response to V. anguillarum infection.

Functional characterization of a novel tumor necrosis factor gene (TNF-New) in rock bream (Oplegnathus fasciatus)

The novel tumor necrosis factor (TNF-New or TNFN) gene has been identified only in teleost such as zebrafish, medaka (Oryzias latipes), fugu (Takifugu rubripes), and rainbow trout (Oncorhynchus mykiss). In this study, a putative TNFN gene in rock bream (named RB-TNFN) was cloned and its functional expression in the immune system was analyzed. Although it was previously reported to share a high degree of homology with mammalian lymphotoxin (LT)-β, in silico analysis revealed that RB-TNFN differed slightly from mammalian LT-β in its genomic structure, phylogenetic relationship, and predicted protein tertiary structure, whereas the genomic location of TNFN (immediately behind TNF-α) was the same as that of LT-β. In healthy rock bream, RB-TNFN gene expression was the highest in the liver and the lowest in the head kidney. In vitro, it was significantly upregulated in head kidney cells following polyinosinic:polycytidylic acid, concanavalin A, phytohemagglutinin, or calcium ionophore (CI) stimulation and in spleen cells by lipopolysaccharide (LPS), CI, and rock bream iridovirus (RBIV). In vivo, it was upregulated in the spleen, liver, and gut on day 1 and in the blood on day 3 following LPS injection, and in the blood, head kidney, and liver following RBIV vaccination. Post-RBIV infection, the vaccinated group showed a significantly higher TNFN gene expression in the head kidney and blood than the unvaccinated group. Treatment with recombinant TNFN protein (RB-rTNFN) resulted in significantly upregulated interleukin-1β expression in the head kidney, spleen, blood, liver, and peritoneal cells. It also enhanced IL-8 gene expression in the head kidney, blood, and peritoneal cells, and interferon γ gene expression in the gut and gills on day 1. TNFN and cyclo-oxygenase-2 gene expression was upregulated in peritoneal cells on day 3. Flow cytometry analysis revealed a significant increase in the peritoneal lymphocyte population after the intraperitoneal (i.p.) injection of RB-rTNFN. These results suggest that RB-TNFN mediated innate and adaptive immunity in rock bream.

Role of JAK/STAT in the Neuroinflammation and its Association with Neurological Disorders

Background:

Innate immunity is mediated by a variety of cell types, including microglia, macrophages, and neutrophils, and serves as the immune system's first line of defense. There are numerous pathways involved in innate immunity, including the interferon (IFN) pathway, TRK pathway, mitogen-activated protein kinase (MAPK) pathway, Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, interleukin (IL) pathways, chemokine pathways (CCR5), GSK signaling, and Fas signaling.

Summary:

JAK/STAT is one of these important signaling pathways and this review focused on JAK/STAT signaling pathway only. The overactivation of microglia and astrocytes influences JAK/STAT's role in neuroinflammatory disease by initiating innate immunity, orchestrating adaptive immune mechanisms, and ultimately constraining inflammatory and immunological responses. The JAK/STAT signaling pathway is one of the critical factors that promotes neuroinflammation in neurodegenerative diseases.

Key message:

Given the importance of the JAK/STAT pathway in neurodegenerative disease, this review discussed the feasibility of targeting the JAK/STAT pathway as a neuroprotective therapy for neurodegenerative diseases in near future.

Clathrin- and dynamin-dependent endocytosis limits canonical NF-κB signaling triggered by lymphotoxin β receptor

Background

Lymphotoxin β receptor (LTβR) is a member of tumor necrosis factor receptor (TNFR) superfamily which regulates the immune response. At the cellular level, upon ligand binding, the receptor activates the pro-inflammatory NF-κB and AP-1 pathways. Yet, the intracellular distribution of LTβR, the routes of its endocytosis and their connection to the signaling activation are not characterized. Here, we investigated the contribution of LTβR internalization to its signaling potential.

Methods

Intracellular localization of LTβR in unstimulated and stimulated cells was analyzed by confocal microscopy. Endocytosis impairment was achieved through siRNA- or CRISPR/Cas9-mediated depletion, or chemical inhibition of proteins regulating endocytic routes. The activation of LTβR-induced signaling was examined. The levels of effector proteins of the canonical and non-canonical branches of the NF-κB pathway, and the phosphorylation of JNK, Akt, ERK1/2, STAT1 and STAT3 involved in diverse signaling cascades, were measured by Western blotting. A transcriptional response to LTβR stimulation was assessed by qRT-PCR analysis.

Results

We demonstrated that LTβR was predominantly present on endocytic vesicles and the Golgi apparatus. The ligand-bound pool of the receptor localized to endosomes and was trafficked towards lysosomes for degradation. Depletion of regulators of different endocytic routes (clathrin-mediated, dynamin-dependent or clathrin-independent) resulted in the impairment of LTβR internalization, indicating that this receptor uses multiple entry pathways. Cells deprived of clathrin and dynamins exhibited enhanced activation of canonical NF-κB signaling represented by increased degradation of IκBα inhibitor and elevated expression of LTβR target genes. We also demonstrated that clathrin and dynamin deficiency reduced to some extent LTβR-triggered activation of the non-canonical branch of the NF-κB pathway.

Conclusions

Our work shows that the impairment of clathrin- and dynamin-dependent internalization amplifies a cellular response to LTβR stimulation. We postulate that receptor internalization restricts responsiveness of the cell to subthreshold stimuli.

Immunochip meta-analysis in European and Argentinian populations identifies two novel genetic loci associated with celiac disease

Celiac disease (CeD) is a common immune-mediated disease of the small intestine that is triggered by exposure to dietary gluten. While the HLA locus plays a major role in disease susceptibility, 39 non-HLA loci were also identified in a study of 24,269 individuals. We now build on this earlier study by adding 4125 additional Caucasian samples including an Argentinian cohort. In doing so, we not only confirm the previous associations, we also identify two novel independent genome-wide significant associations at loci: 12p13.31 and 22q13.1. By applying a genomics approach and differential expression analysis in CeD intestinal biopsies, we prioritize potential causal genes at these novel loci, including LTBR, CYTH4, and RAC2. Nineteen prioritized causal genes are overlapping known drug targets. Pathway enrichment analysis and expression of these genes in CeD biopsies suggest that they have roles in regulating multiple pathways such as the tumor necrosis factor (TNF) mediated signaling pathway and positive regulation of I-κB kinase/NF-κB signaling.

Cutting Edge: The RNA-Binding Protein Ewing Sarcoma Is a Novel Modulator of Lymphotoxin β Receptor Signaling

Lymphotoxin β receptor (LTβR) signaling is crucial for lymphoid tissue organogenesis and immune homeostasis. To identify novel regulatory mechanisms for signaling, we implemented a two-step screen that uses coexpression analysis of human fibroblasts undergoing LTβR stimulation and affinity-purification mass spectrometry for the LTβR signaling protein TNFR-associated factor 3 (TRAF3). We identify Ewing sarcoma (EWS) protein as a novel LTβR signaling component that associates with TRAF3 but not with TNFR-associated factor 2 (TRAF2). The EWS:TRAF3 complex forms under unligated conditions that are disrupted following activation of the LTβR. We conclude that EWS limits expression of proinflammatory molecules, GM-CSF, and ERK-2, promoting immune homeostasis.

Cholesterol restricts lymphotoxin β receptor-triggered NF-κB signaling

BACKGROUND

Lymphotoxin β receptor (LTβR) plays important roles in the development of the immune system and immune response. At the cellular level, ligand-bound LTβR activates the pro-inflammatory NF-κB pathway but the detailed mechanisms regulating its signaling remain unknown. Understanding them is of high importance since LTβR and its ligands are promising therapeutic targets. Here, we studied the consequences of perturbed cellular cholesterol content on LTβR-induced NF-κB signaling.

METHODS

To modulate cholesterol availability and/or level in lung carcinoma A549 and H2228, and endothelial HUVEC cells different treatment regimens with filipin, methyl-β-cyclodextrin and simvastatin were applied. LTβR localization was studied by confocal microscopy. The activity of LTβR-induced NF-κB pathway was assessed by measuring the levels of NF-κB pathway inhibitor IκBα and phosphorylation of RelA transcription factor by Western blotting. The NF-κB transcriptional response, production of chemokines and adhesion molecules were examined by qRT-PCR, ELISA, and Western blotting, respectively. Adherence of different types of primary immune cells to epithelial A549 cells and endothelial HUVECs was measured fluorometrically. Interactions of LTβR with its protein partners were investigated by immunoprecipitation.

RESULTS

We showed that filipin-mediated sequestration of cholesterol or its depletion from the plasma membrane with methyl-β-cyclodextrin impaired LTβR internalization and potentiated LTβR-dependent activation of the canonical branch of the NF-κB pathway. The latter was manifested by enhanced degradation of IκBα inhibitor, elevated RelA phosphorylation, substantial increase in the expression of NF-κB target genes encoding, among others, cytokines and adhesion molecules known to play important roles in immune response. It was followed by robust secretion of CXCL8 and upregulation of ICAM1, that favored the adhesion of immune cells (NK and T cells, neutrophils) to A549 cells and HUVECs. Mechanistically, we showed that cholesterol depletion stabilized interactions of ligand-stimulated LTβR with modified forms of TRAF2 and NEMO proteins.

CONCLUSIONS

Our results showed that the reduction of the plasma membrane content of cholesterol or its sequestration strongly potentiated signaling outcome initiated by LTβR. Thus, drugs modulating cholesterol levels could potentially improve efficacy of LTβR-based therapies. Video abstract.

The Impact of p53 on Aristolochic Acid I-Induced Gene Expression In Vivo

Exposure to aristolochic acid (AA) is linked to kidney disease and urothelial cancer in humans. The major carcinogenic component of the AA plant extract is aristolochic acid I (AAI). The tumour suppressor p53 is frequently mutated in AA-induced tumours. We previously showed that p53 protects from AAI-induced renal proximal tubular injury, but the underlying mechanism(s) involved remain to be further explored. In the present study, we investigated the impact of p53 on AAI-induced gene expression by treating Trp53(+/+), Trp53(+/-), and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for six days. The Clariom™ S Assay microarray was used to elucidate gene expression profiles in mouse kidneys after AAI treatment. Analyses in Qlucore Omics Explorer showed that gene expression in AAI-exposed kidneys is treatment-dependent. However, gene expression profiles did not segregate in a clear-cut manner according to Trp53 genotype, hence further investigations were performed by pathway analysis with MetaCore™. Several pathways were significantly altered to varying degrees for AAI-exposed kidneys. Apoptotic pathways were modulated in Trp53(+/+) kidneys; whereas oncogenic and pro-survival pathways were significantly altered for Trp53(+/-) and Trp53(-/-) kidneys, respectively. Alterations of biological processes by AAI in mouse kidneys could explain the mechanisms by which p53 protects from or p53 loss drives AAI-induced renal injury in vivo.

Acute Proteomic Changes in the Lung After WTLI in a Mouse Model: Identification of Potential Initiating Events for Delayed Effects of Acute Radiation Exposure

Radiation-induced lung injury is a delayed effect of acute radiation exposure resulting in pulmonary pneumonitis and fibrosis. Molecular mechanisms that lead to radiation-induced lung injury remain incompletely understood. Using a murine model of whole-thorax lung irradiation, C57BL/6J mice were irradiated at 8, 10, 12, and 14 Gy and assayed at day 1, 3, and 6 postexposure and compared to nonirradiated (sham) controls. Tryptic digests of lung tissues were analyzed by liquid chromatography-tandem mass spectrometry on a Waters nanoLC instrument coupled to a Thermo Scientific Q Exactive hybrid quadrupole-orbitrap mass spectrometer. Pathway and gene ontology analysis were performed with Qiagen Ingenuity, Panther GO, and DAVID databases. A number of trends were identified in the proteomic data, including protein changes greater than 10 fold, protein changes that were consistently up regulated or down regulated at all time points and dose levels interrogated, time and dose dependency of protein changes, canonical pathways affected by irradiation, changes in proteins that serve as upstream regulators, and proteins involved in key processes including inflammation, radiation, and retinoic acid signaling. The proteomic profiling conducted here represents an untargeted systems biology approach to identify acute molecular events that could potentially be initiating events for radiation-induced lung injury.

Lack of LTβR Increases Susceptibility of IPEC-J2 Cells to Porcine Epidemic Diarrhea Virus

The essential requirement of the lymphotoxin beta receptor (LTβR) in the development and maintenance of peripheral lymphoid organs is well recognized. Evidence shows that LTβR is involved in various cellular processes; however, whether it plays a role in maintaining the cellular function of intestinal porcine enterocytes (IPEC-J2), specifically during porcine epidemic diarrhea virus (PEDV) infection, remains unknown. In this study, we generated LTβR null IPEC-J2 cells using CRISPR/Cas9 to examine the importance of LTβR in cell proliferation, apoptosis, and the response to PEDV infection. Our results showed that the lack of LTβR leads to significantly decreased cell proliferation, potentially due to S phase arrest in LTβR^−/− IPEC-J2 cells. Label-free digital holographic microscopy was used to record the three-dimensional morphology of both cell types for up to 72 hours and revealed significantly increased numbers of LTβR^−/− cells undergoing apoptosis. Furthermore, we found that PEDV-infected LTβR^−/− null IPEC-J2 cells exhibited significant suppression of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) target genes (interleukin (IL)-6 and IL-8) and mucosal barrier integrity-related genes (vascular cell adhesion molecule 1 (VCAM1) and IL-22), which may explain why LTβR^−/− cells are more susceptible to PEDV infection. Collectively, our data not only demonstrate the key role of LTβR in intestinal porcine enterocytes, but also provide data for the improved understanding of the cellular response to PEDV infection.

The topology of lymphotoxin β receptor accumulated upon endolysosomal dysfunction dictates the NF-κB signaling outcome

Cytokine receptors, such as tumor necrosis factor receptor I (TNFRI) and lymphotoxin β receptor (LTβR), activate inflammatory NF-κB signaling upon stimulation. We previously demonstrated that depletion of ESCRT components leads to endosomal accumulation of TNFRI and LTβR, and their ligand-independent signaling to NF-κB. Here, we studied if other perturbations of the endolysosomal system could trigger intracellular accumulation and signaling of ligand-free LTβR. While depletion of CORVET had no effect, knockdown of HOPS or Rab7, or pharmacological inhibition of lysosomal degradation, caused endosomal accumulation of LTβR and its increased interactions with TRAF2/TRAF3 signaling adaptors. However, the NF-κB pathway was not activated under these conditions. We found that knockdown of HOPS or Rab7 led to LTβR sequestration in intraluminal vesicles of endosomes, thus precluding NF-κB signaling. This was in contrast to LTβR localization on the outer endosomal membrane after ESCRT depletion that was permissive for signaling. We propose that the inflammatory response induced by intracellular accumulation of endocytosed cytokine receptors critically depends on the precise receptor topology within endosomal compartments.

Dexamethasone inhibits inflammatory response via down regulation of AP-1 transcription factor in human lung epithelial cells

The production of inflammatory mediators by epithelial cells in inflammatory lung diseases may represent an important target for the anti-inflammatory effects of glucocorticoids. Activator protein-1 is a major activator of inflammatory genes and has been proposed as a target for inhibition by glucocorticoids. We have used human pulmonary type-II A549 cells to examine the effect of dexamethasone on the phorbol ester (PMA)/Lipopolysaccharide (LPS) induced pro-inflammatory cytokines and AP-1 factors. A549 cells were treated with and without PMA or LPS or dexamethasone and the cell viability and nitric oxide production was measured by MTT assay and Griess reagent respectively. Expression of pro-inflammatory cytokines and AP-1 factors mRNA were measured using semi quantitative RT-PCR. The PMA/LPS treated cells show significant 2-3 fold increase in the mRNA levels of pro-inflammatory cytokines (IL-1β, IL-2, IL-6, IL-8 and TNF-α), cyclo‑oxygenase-2 (COX-2) and specific AP-1 factors (c-Jun, c-Fos and Jun-D). Whereas, pretreatment of cells with dexamethasone significantly inhibited the LPS induced nitric oxide production and PMA/LPS induced mRNAs expression of above pro-inflammatory cytokines, COX-2 and AP-1 factors. Cells treated with dexamethasone alone at both the concentrations inhibit the mRNAs expression of IL-1β, IL-6 and TNF-α compared to control. Our study reveals that dexamethasone decreased the mRNAs expression of c-Jun and c-Fos available for AP-1 formation suggested that AP-1 is the probable key transcription factor involved in the anti-inflammatory activity of dexamethasone. This may be an important molecular mechanism of steroid action in asthma and other chronic inflammatory lung diseases which may be useful for treatment of lung inflammatory diseases.

The regulatory and signaling mechanisms of the ASK family

Apoptosis signal-regulating kinase 1 (ASK1) was identified as a MAP3K that activates the JNK and p38 pathways, and subsequent studies have reported ASK2 and ASK3 as members of the ASK family. The ASK family is activated by various intrinsic and extrinsic stresses, including oxidative stress, ER stress and osmotic stress. Numerous lines of evidence have revealed that members of the ASK family are critical for signal transduction systems to control a wide range of stress responses such as cell death, differentiation and cytokine induction. In this review, we focus on the precise signaling mechanisms of the ASK family in response to diverse stressors.

A Zebrafish Live Imaging Model Reveals Differential Responses of Microglia Toward Glioblastoma Cells In Vivo

Glioblastoma multiforme is the most common and deadliest form of brain cancer. Glioblastomas are infiltrated by a high number of microglia, which promote tumor growth and surrounding tissue invasion. However, it is unclear how microglia and glioma cells physically interact and if there are differences, depending on glioma cell type. Hence, we have developed a novel live imaging assay to study microglia-glioma interactions in vivo in the zebrafish brain. We transplanted well-established human glioblastoma cell lines, U87 and U251, into transgenic zebrafish lines with labelled macrophages/microglia. Our confocal live imaging results show distinct interactions between microglia and U87, as well as U251 glioblastoma cells that differ in number and nature. Importantly these interactions do not appear to be antitumoral as zebrafish microglia do not engulf and phagocytose the human glioblastoma cells. Finally, xenotransplants into the irf8-/- zebrafish mutant that lacks microglia, as well as pharmacological inhibition of the CSF-1 receptor (CSF-1R) on microglia, confirm a prominent role for zebrafish microglia in promoting human glioblastoma cell growth. This new model will be an important tool for drug screening and the development of future immunotherapeutics targeting microglia within glioma.

Context-dependent roles for lymphotoxin-β receptor signaling in cancer development

The LTα1β2 and LIGHT TNF superfamily cytokines exert pleiotropic physiological functions through the activation of their cognate lymphotoxin-β receptor (LTβR). Interestingly, since the discovery of these proteins, accumulating evidence has pinpointed a role for LTβR signaling in carcinogenesis. Early studies have shown a potential anti-tumoral role in a subset of solid cancers either by triggering apoptosis in malignant cells or by eliciting an anti-tumor immune response. However, more recent studies provided robust evidence that LTβR signaling is also involved in diverse cell-intrinsic and microenvironment-dependent pro-oncogenic mechanisms, affecting several solid and hematological malignancies. Consequently, the usefulness of LTβR signaling axis blockade has been investigated as a potential therapeutic approach for cancer. Considering the seemingly opposite roles of LTβR signaling in diverse cancer types and their key implications for therapy, we here extensively review the different mechanisms by which LTβR activation affects carcinogenesis, focusing on the diverse contexts and different models assessed.

Activation of lymphotoxin-beta receptor enhances the LPS-induced expression of IL-8 through NF-κB and IRF-1

Lymphotoxin-beta receptor (LTβR), a receptor for LIGHT and LTα1β2, is expressed on the epithelial, stromal, and myeloid cells. LTβR is known to affect the lymphoid organ development and immune homeostasis. However, its role in macrophage function has not been sufficiently elucidated. The effect of LTβR stimulation in the inflammatory activation of macrophages was investigated by treating the human macrophage-like cell line THP-1 with LTβR-specific monoclonal antibody. Interestingly, combined treatment with anti-LTβR antibody and LPS caused the synergistic induction of IL-8 expression at the transcriptional level. Analysis indicated that nuclear factor (NF)-κB activity was enhanced via the mitogen-activated protein kinase (MAPK) and glycogen synthase kinase (GSK)-3β/cAMP response element binding protein (CREB) pathways. In addition, LTβR stimulation induced the expression of interferon regulatory factor (IRF)-1, one of the major transcription factors of IL-8 gene. Down-regulation of IRF-1 expression reduced the enhancing effect caused by LTβR stimulation. This indicates that the LTβR stimulation enhances the LPS-induced expression of IL-8 via the combined action of NF-κB and IRF-1.

Lymphotoxin β receptor signaling induces IL-8 production in human bronchial epithelial cells

Asthma-related mortality has been decreasing due to inhaled corticosteroid use, but severe asthma remains a major clinical problem. One characteristic of severe asthma is resistance to steroid therapy, which is related to neutrophilic inflammation. Recently, the tumor necrosis factor superfamily member (TNFSF) 14/LIGHT has been recognized as a key mediator in severe asthmatic airway inflammation. However, the profiles and intracellular mechanisms of cytokine/chemokine production induced in cells by LIGHT are poorly understood. We aimed to elucidate the molecular mechanism of LIGHT-induced cytokine/chemokine production by bronchial epithelial cells. Human bronchial epithelial cells express lymphotoxin β receptor (LTβR), but not herpesvirus entry mediator, which are receptors for LIGHT. LIGHT induced various cytokines/chemokines, such as interleukin (IL)-6, oncostatin M, monocyte chemotactic protein-1, growth-regulated protein α and IL-8. Specific siRNA for LTβR attenuated IL-6 and IL-8 production by BEAS-2B and normal human bronchial epithelial cells. LIGHT activated intracellular signaling, such as mitogen-activated protein kinase and nuclear factor-κB (NF-κB) signaling. LIGHT also induced luciferase activity of NF-κB response element, but not of activator protein-1 or serum response element. Specific inhibitors of phosphorylation of extracellular signal-regulated kinase (Erk) and that of inhibitor κB attenuated IL-8 production, suggesting that LIGHT-LTβR signaling induces IL-8 production via the Erk and NF-κB pathways. LIGHT, via LTβR signaling, may contribute to exacerbation of airway neutrophilic inflammation through cytokine and chemokine production by bronchial epithelial cells.

Mechanistic basis for functional promiscuity in the TNF and TNF receptor superfamilies: structure of the LIGHT:DcR3 assembly

LIGHT initiates intracellular signaling via engagement of the two TNF receptors, HVEM and LTβR. In humans, LIGHT is neutralized by DcR3, a unique soluble member of the TNFR superfamily, which tightly binds LIGHT and inhibits its interactions with HVEM and LTβR. DcR3 also neutralizes two other TNF ligands, FasL and TL1A. Due to its ability to neutralize three distinct different ligands, DcR3 contributes to a wide range of biological and pathological processes, including cancer and autoimmune diseases. However, the mechanisms that support the broad specificity of DcR3 remain to be fully defined. We report the structures of LIGHT and the LIGHT:DcR3 complex, which reveal the structural basis for the DcR3-mediated neutralization of LIGHT and afford insights into DcR3 function and binding promiscuity. Based on these structures, we designed LIGHT mutants with altered affinities for DcR3 and HVEM, which may represent mechanistically informative probe reagents.

Herpesvirus entry mediator (HVEM) attenuates signals mediated by the lymphotoxin β receptor (LTβR) in human cells stimulated by the shared ligand LIGHT

Signals mediated by members of the tumor necrosis factor receptor superfamily modulate a network of diverse processes including initiation of inflammatory responses and altering cell fate between pathways favoring survival and death. Although such pathways have been well-described for the TNF-α receptor, less is known about signaling induced by the TNF superfamily member LIGHT and how it is differentially altered by expression of its two receptors LTβR and HVEM in the same cell. We used cell lines with different relative expression of HVEM and LTβR to show that LIGHT-induced signals mediated by these receptors were associated with altered TRAF2 stability and RelA nuclear translocation. Production of the inflammatory chemokine CXCL10 was primarily mediated by LTβR. Higher expression of HVEM was associated with cell survival, while unopposed LTβR signaling favored pathways leading to apoptosis. Importantly, restoring HVEM expression in cells with low endogenous expression recapitulated the phenotype of cells with higher endogenous expression. Together, our data provide evidence that relative expression of HVEM and LTβR modulates canonical NF-κB and pro-apoptotic signals stimulated by LIGHT.

Cancer cell-derived lymphotoxin mediates reciprocal tumour-stromal interactions in human ovarian cancer by inducing CXCL11 in fibroblasts

We have investigated the role of cytokine lymphotoxin in tumour-stromal interactions in human ovarian cancer. We found that lymphotoxin overexpression is commonly shared by the cancer cells of various ovarian cancer subtypes, and lymphotoxin-beta receptor (LTBR) is expressed ubiquitously in both the cancer cells and cancer-associated fibroblasts (CAFs). In monoculture, we showed that ovarian cancer cells are not the major lymphotoxin-responsive cells. On the other hand, our co-culture studies demonstrated that the cancer cell-derived lymphotoxin induces chemokine expression in stromal fibroblasts through LTBR-NF-κB signalling. Amongst the chemokines being produced, we found that fibroblast-secreted CXCL11 promotes proliferation and migration of ovarian cancer cells via the chemokine receptor CXCR3. CXCL11 is highly expressed in CAFs in ovarian cancer biopsies, while CXCR3 is found in malignant cells in primary ovarian tumours. Additionally, the overexpression of CXCR3 is significantly associated with the tumour grade and lymph node metastasis of ovarian cancer, further supporting the role of CXCR3, which interacts with CXCL11, in promoting growth and metastasis of human ovarian cancer. Taken together, these results demonstrated that cancer-cell-derived lymphotoxin mediates reciprocal tumour-stromal interactions in human ovarian cancer by inducing CXCL11 in fibroblasts. Our findings suggest that lymphotoxin-LTBR and CXCL11-CXCR3 signalling represent therapeutic targets in ovarian cancer.

Gene expression profiling in the cerebral cortex of patients with cirrhosis with and without hepatic encephalopathy

Hepatic encephalopathy (HE) is a frequent complication of liver cirrhosis and is seen as the clinical manifestation of a low-grade cerebral edema associated with oxidative-nitrosative stress. However, comprehensive data on HE-associated molecular derangements in the human brain are lacking. In the present study, we used a whole human genome microarray approach for gene expression profiling in post mortem brain samples from patients with cirrhosis with or without HE and controls without cirrhosis. Altered expression levels were found for a total of 1,012 genes in liver cirrhosis patients without and with HE, and HE-characteristic gene expression changes were identified. Genes with altered expression pattern in HE were related to oxidative stress, microglia activation, receptor signaling, inflammatory pathways, cell proliferation, and apoptosis. Despite an up-regulation of genes associated with microglia activation, pro-inflammatory cytokine messenger RNA profiles remained unchanged in the brains of patients with liver cirrhosis and HE compared with controls. Interestingly, many genes counteracting pro-inflammatory signaling and inflammatory cytokine expression were up-regulated in the cerebral cortex of patients with liver cirrhosis and HE.

CONCLUSION

Pathogenetic mechanisms of HE deduced from cell culture and animal experiments, such as oxidative stress, altered Zn(2+) homeostasis and microglia activation also apply to human brain from patients with liver cirrhosis and HE. The study also revealed a not-yet recognized increased expression of genes antagonizing proinflammatory signaling and inflammatory cytokine expression. (HEPATOLOGY 2013;57:2436-2447).

Curcumin potentiates rhabdomyosarcoma radiosensitivity by suppressing NF-κB activity

Ionizing radiation (IR) is an essential component of therapy for alveolar rhabdomyosarcoma. Nuclear factor-kappaB (NF-κΒ) transcription factors are upregulated by IR and have been implicated in radioresistance. We evaluated the ability of curcumin, a putative NF-κΒ inhibitor, and cells expressing genetic NF- κΒ inhibitors (IκBα and p100 super-repressor constructs) to function as a radiosensitizer. Ionizing radiation induced NF-κΒ activity in the ARMS cells in vitro in a dose- and time-dependent manner, and upregulated expression of NF-κΒ target proteins. Pretreatment of the cells with curcumin inhibited radiation-induced NF-κΒ activity and target protein expression. In vivo, the combination of curcumin and IR had synergistic antitumor activity against Rh30 and Rh41 ARMS xenografts. The greatest effect occurred when tumor-bearing mice were treated with curcumin prior to IR. Immunohistochemistry revealed that combination therapy significantly decreased tumor cell proliferation and endothelial cell count, and increased tumor cell apoptosis. Stable expression of the super-repressor, SR-IκBα, that blocks the classical NF-κB pathway, increased sensitivity to IR, while expression of SR-p100, that blocks the alternative pathway, did not. Our results demonstrate that curcumin can potentiate the antitumor activity of IR in ARMS xenografts by suppressing a classical NF-κΒ activation pathway induced by ionizing radiation. These data support testing of curcumin as a radiosensitizer for the clinical treatment of alveolar rhabdomyosarcoma. IMPACT OF WORK: The NF-κΒ protein complex has been linked to radioresistance in several cancers. In this study, we have demonstrated that inhibiting radiation-induced NF-κΒ activity by either pharmacologic (curcumin) or genetic (SR-IκBα) means significantly enhanced the efficacy of radiation therapy in the treatment of alveolar rhabdomyosarcoma cells and xenografts. These data suggest that preventing the radiation-induced activation of the NF-κΒ pathway is a promising way to improve the antitumor efficacy of ionizing radiation and warrants clinical trials.

Regulation of NF-κB by ubiquitination and degradation of the IκBs

The nuclear factor-κB (NF-κB) signaling pathway is a busy ground for the action of the ubiquitin-proteasome system; many of the signaling steps are coordinated by protein ubiquitination. The end point of this pathway is to induce transcription, and to this end, there is a need to overcome a major obstacle, a set of inhibitors (IκBs) that bind NF-κB and prohibit either the nuclear entry or the DNA binding of the transcription factor. Two major signaling steps are required for the elimination of the inhibitors: activation of the IκB kinase (IKK) and degradation of the phosphorylated inhibitors. IKK activation and IκB degradation involve different ubiquitination modes; the latter is mediated by a specific E3 ubiquitin ligase SCF(β-TrCP) . The F-box component of this E3, β-TrCP, recognizes the IκB degron formed following phosphorylation by IKK and thus couples IκB phosphorylation to ubiquitination. SCF(β-TrCP) -mediated IκB ubiquitination and degradation is a very efficient process, often resulting in complete degradation of the key inhibitor IκBα within a few minutes of cell stimulation. In vivo ablation of β-TrCP results in accumulation of all the IκBs and complete NF-κB inhibition. As many details of IκB-β-TrCP interaction have been worked out, the development of β-TrCP inhibitors might be a feasible therapeutic approach for NF-κB-associated human disease. However, we may still need to advance our understanding of the mechanism of IκB degradation as well as of the diverse functions of β-TrCP in vivo.

Cellular inhibitors of apoptosis are global regulators of NF-κB and MAPK activation by members of the TNF family of receptors

Tumor necrosis factor (TNF) family members are essential for the development and proper functioning of the immune system. TNF receptor (TNFR) signaling is mediated through the assembly of protein signaling complexes that activate the nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in a ubiquitin-dependent manner. The cellular inhibitor of apoptosis (c-IAP) proteins c-IAP1 and c-IAP2 are E3 ubiquitin ligases that are recruited to TNFR signaling complexes through their constitutive association with the adaptor protein TNFR-associated factor 2 (TRAF2). We demonstrated that c-IAP1 and c-IAP2 were required for canonical activation of NF-κB and MAPK by members of the TNFR family. c-IAPs were required for the recruitment of inhibitor of κB kinase β (IKKβ), the IKK regulatory subunit NF-κB essential modulator (NEMO), and RBCK1/Hoil1-interacting protein (HOIP) to TNFR signaling complexes and the induction of gene expression by TNF family members. In contrast, TNFRs that stimulated the noncanonical NF-κB pathway triggered translocation of c-IAPs, TRAF2, and TRAF3 from the cytosol to membrane fractions, which led to their proteasomal and lysosomal degradation. Finally, we established that signaling by B cell-activating factor receptor 3 induced the cytosolic depletion of TRAF3, which enabled noncanonical NF-κB activation. These results define c-IAP proteins as critical regulators of the activation of NF-κB and MAPK signaling pathways by members of the TNFR superfamily.

DISCOVERY OF HIGHLY DIFFERENTIATIVE GENE GROUPS FROM MICROARRAY GENE EXPRESSION DATA USING THE GENE CLUB APPROACH

Motivation: It is commonly believed that suitable analysis of microarray gene expression profile data can lead to better understanding of diseases, and better ways to diagnose and treat diseases. To achieve those goals, it is of interest to discover the gene interaction networks, and perhaps even pathways, underlying given diseases from such data. In this paper, we consider methods for efficiently discovering highly differentiative gene groups (HDGG), which may provide insights on gene interaction networks. HDGGs are groups of genes which completely or nearly completely characterize the diseased or normal tissues. Discovering HDGGs is challenging, due to the high dimensionality of the data.

Results: Our methods are based on the novel concept of gene clubs. A gene club consists of a set of genes having high potential to be interactive with each other. The methods can (i) efficiently discover signature HDGGs which completely characterize the diseased and the normal tissues respectively, (ii) find strongest or near strongest HDGGs containing any given gene, and (iii) find much stronger HDGGs than previous methods. As part of the experimental evaluation, the methods are applied to colon, prostate, ovarian, and breast cancer, and leukemia and so on. Some of the genes in the extracted signature HDGGs have known biological functions, and some have attracted little attention in biology and medicine. We hope that appropriate study on them can lead to medical breakthroughs. Some HDGGs for colon and prostate cancers are listed here. The website listed below contains HDGGs for the other cancers.

Availability: HDGG is implemented in C++ and runs on Unix or Windows platform. The code is available at: .

How do pleiotropic kinase hubs mediate specific signaling by TNFR superfamily members?

Tumor necrosis factor receptor (TNFR) superfamily members mediate the cellular response to a wide variety of biological inputs. The responses range from cell death, survival, differentiation, proliferation, to the regulation of immunity. All these physiological responses are regulated by a limited number of highly pleiotropic kinases. The fact that the same signaling molecules are involved in transducing signals from TNFR superfamily members that regulate different and even opposing processes raises the question of how their specificity is determined. Regulatory strategies that can contribute to signaling specificity include scaffolding to control kinase specificity, combinatorial use of several signal transducers, and temporal control of signaling. In this review, we discuss these strategies in the context of TNFR superfamily member signaling.

Tumor necrosis factor α stimulates endothelin-1 synthesis in rat hepatic stellate cells in hepatic wound healing through a novel IKK/JNK pathway

Endothelin-1 (ET-1), a potent vasoconstrictor peptide up-regulated during wound healing and fibrosis, induces myofibroblasts to contract tissue. Here we have used a liver injury model to test the hypothesis that TNFα may be an important stimulator of ET-1 production in hepatic wound healing. We examined primary rat hepatic stellate cells, isolated from either normal or injured livers and used standard methodology to measure preproET-1 mRNA and mature ET-1 peptide, specific kinases, and preproET-1 promoter activity. Chromatin immunoprecipitation analysis was used to determine basal binding of transcription factors to the preproET-1 promoter. TNFα induced preproET-1 expression in activated hepatic stellate cells in a c-Jun N-terminal kinase (JNK)/AP-1-dependent fashion. TNFα activated JNK through an IκB kinase (IKK) pathway, which activated the transcriptional factor, c-Jun, leading to preproET-1 promoter mediated ET-1 transcription. The TNFα mediated induction of ET-1 synthesis also had functional effects, specifically mediating autocrine induced stellate cell contraction. TNFα stimulated activated stellate cells to produce ET-1 via a novel IKK-JNK-dependent signaling pathway. The resulting autocrine functional effects of ET-1 are likely to be important in the wound-healing process.

Transient receptor potential vanilloid 4 activated inflammatory signals by intestinal epithelial cells and colitis in mice

BACKGROUND & AIMS

Ligand-gated calcium channels have been reported to be involved in the pathogenesis of inflammatory bowel disease. One family member, transient receptor potential vanilloid 4 (TRPV4), is activated by arachidonic acid derivatives that might be released on inflammation, yet its role in gastrointestinal inflammation has not been characterized. We investigated whether TRPV4 activation participates in intestinal inflammation and its expression and functions in the gastrointestinal tract.

METHODS

TRPV4 expression was studied in human colon samples, human intestinal epithelial cell lines (Caco-2 and T84), and inflamed colons of mice. Calcium mobilization and cytokine release were analyzed in intestinal epithelial cells exposed to the selective TRPV4 agonist 4α-phorbol-12,13-didecanoate (4αPDD). Mice were killed 3, 6, or 24 hours after intracolonic administration of 4αPDD; inflammatory parameters were measured in their colon tissues, and paracellular colonic permeability was measured by the passage of (51)Cr-EDTA from the colon lumen to the blood.

RESULTS

High levels of TRPV4 were detected in Caco-2 cells and in epithelial cells of human colon tissue samples; its expression was up-regulated in colons from inflamed mice compared with noninflamed control mice. Administration of 4αPDD to Caco-2 and T84 cells caused a dose-dependent increase in intracellular calcium concentration and chemokine release. In mice, intracolonic administration of 4αPDD caused colitis to develop 3 to 6 hours later; inflammation resolved by 24 hours. Increased colonic permeability was observed in vivo 3 hours after intracolonic administration of 4αPDD.

CONCLUSIONS

TRPV4 is expressed and functional in intestinal epithelial cells; its activation in the gastrointestinal tract causes increases in intracellular calcium concentrations, chemokine release, and colitis.

Ubiquitination and degradation of the inhibitors of NF-kappaB

The key step in NF-kappaB activation is the release of the NF-kappaB dimers from their inhibitory proteins, achieved via proteolysis of the IkappaBs. This irreversible signaling step constitutes a commitment to transcriptional activation. The signal is eventually terminated through nuclear expulsion of NF-kappaB, the outcome of a negative feedback loop based on IkappaBalpha transcription, synthesis, and IkappaBalpha-dependent nuclear export of NF-kappaB (Karin and Ben-Neriah 2000). Here, we review the process of signal-induced IkappaB ubiquitination and degradation by comparing the degradation of several IkappaBs and discussing the characteristics of IkappaBs' ubiquitin machinery.

Zinc-finger protein 91 plays a key role in LIGHT-induced activation of non-canonical NF-κB pathway

LIGHT is a member of tumor necrosis factor (TNF) superfamily, and its function is mediated through lymphotoxin-β receptor (LTβR), which is known to play important roles in inflammatory and immune responses through activation of NF-κB signaling pathways. However, molecular mechanism of LTβR ligation-induced NF-κB signaling remains incompletely understood. In this report we demonstrate that a novel zinc-finger protein 91 (ZFP91) is a critical regulator in LIGHT-induced activation of non-canonical NF-κB pathway. ZFP91 appears to be required for NF-κB2 (p100) processing to p52, nuclear translocation of p52 and RelB, and DNA-binding activity of NF-κB in LIGHT-induced activation of non-canonical NF-κB pathway. Furthermore, ZFP91 knock-down by RNA interference blocks the LIGHT-induced accumulation of NIK and p100 processing, as well as the expression of non-canonical NF-κB target genes. These data clearly indicate that ZFP91 is a key regulator in LIGHT-induced activation of non-canonical NF-κB pathway in LTβR signaling.

A loss-of-function screen reveals Ras- and Raf-independent MEK-ERK signaling during Chlamydia trachomatis infection

Chlamydiae are obligate intracellular bacterial pathogens that have a major effect on human health. Because of their intimate association with their host, chlamydiae depend on various host cell functions for their survival. Here, we present an RNA-interference-based screen in human epithelial cells that identified 59 host factors that either positively or negatively influenced the replication of Chlamydia trachomatis (Ctr). Two factors, K-Ras and Raf-1, which are members of the canonical Ras-Raf-MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase)-ERK (extracellular signal-regulated kinase) pathway, were identified as central components of signaling networks associated with hits from the screen. Depletion of Ras or Raf in HeLa cells increased pathogen growth. Mechanistic analyses revealed that ERK was activated independently of K-Ras and Raf-1. Infection with Ctr led to the Akt-dependent, increased phosphorylation (and inactivation) of Raf-1 at serine-259. Furthermore, phosphorylated Raf-1 relocalized from the cytoplasm to the intracellular bacterial inclusion in an Akt- and 14-3-3beta-dependent manner. Together, these findings not only show that Chlamydia regulates components of an important host cell signaling pathway, but also provide mechanistic insights into how this is achieved.

Signal transduction pathways linking the activation of alveolar macrophages with the recruitment of neutrophils to lungs in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem. It is predicted by the World Health Organization to become the third most common cause of death and the fifth most common cause of disability in the world by 2020. COPD is a complex inflammatory disease involving several types of inflammatory cells and multiple inflammatory mediators. Although abnormal numbers of inflammatory cells such as macrophages, dendritic cells, neutrophils, and T lymphocytes have been documented in COPD, the relationship between these cell types and the sequence of their appearance and persistence is largely unknown. Alveolar macrophages have been identified as one of the major cell types that plays a key role in orchestrating the inflammatory events associated with the pathophysiology of COPD. One of the major functions of macrophages is the secretion of chemotactic factors and this function is markedly increased on exposure to cigarette smoke (CS). This enhanced release of chemoattractants results in increased lung neutrophil infiltration, which is thought to be a key event in the development of COPD. The molecular basis for this amplified inflammatory response is not very clear, but it could be due to an alteration in signal transduction pathways within the macrophage. Based on existing literature, an attempt has been made to create a comprehensive review of the signal transduction pathways that link the activation of macrophages with the increased recruitment of neutrophils into the airways. Some of the major stimuli that activate macrophages and cause them to secrete chemotactic factors have been identified as CS, wood smoke, ozone, bacterial endotoxin, and proinflammatory cytokines such as interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. These stimuli seem to activate mainly redox-sensitive transcription factors such as nuclear factor (NF)-kappa B and activator protein (AP)-1, both of which play a major role in the synthesis and secretion of chemotactic factors such as IL-8 and leukotriene B(4) (LTB(4)). The pathways involved in the synthesis and secretion of other factors such as macrophage chemotactic protein-1 (MCP-1) and growth-related oncogene-alpha (Gro-alpha) have also been reviewed.

Differential RelA- and RelB-dependent gene transcription in LTbetaR-stimulated mouse embryonic fibroblasts

BACKGROUND

Lymphotoxin signaling via the lymphotoxin-beta receptor (LTbetaR) has been implicated in biological processes ranging from development of secondary lymphoid organs, maintenance of spleen architecture, host defense against pathogens, autoimmunity, and lipid homeostasis. The major transcription factor that is activated by LTbetaR crosslinking is NF-kappaB. Two signaling pathways have been described, the classical inhibitor of NF-kappaB alpha (IkappaBalpha)-regulated and the alternative p100-regulated pathway that result in the activation of p50-RelA and p52-RelB NF-kappaB heterodimers, respectively.

RESULTS

Using microarray analysis, we investigated the transcriptional response downstream of the LTbetaR in mouse embryonic fibroblasts (MEFs) and its regulation by the RelA and RelB subunits of NF-kappaB. We describe novel LTbetaR-responsive genes that were regulated by RelA and/or RelB. The majority of LTbetaR-regulated genes required the presence of both RelA and RelB, revealing significant crosstalk between the two NF-kappaB activation pathways. Gene Ontology (GO) analysis confirmed that LTbetaR-NF-kappaB target genes are predominantly involved in the regulation of immune responses. However, other biological processes, such as apoptosis/cell death, cell cycle, angiogenesis, and taxis were also regulated by LTbetaR signaling. Moreover, LTbetaR activation inhibited expression of a key adipogenic transcription factor, peroxisome proliferator activated receptor-gamma (pparg), suggesting that LTbetaR signaling may interfere with adipogenic differentiation.

CONCLUSION

Microarray analysis of LTbetaR-stimulated fibroblasts provided comprehensive insight into the transcriptional response of LTbetaR signaling and its regulation by the NF-kappaB family members RelA and RelB.

The lymphotoxin-beta receptor is an upstream activator of NF-kappaB-mediated transcription in melanoma cells

The pleiotropic transcription factor nuclear factor-kappaB (NF-kappaB (p50/p65)) regulates the transcription of genes involved in the modulation of cell proliferation, apoptosis, and oncogenesis. Furthermore, a host of solid and hematopoietic tumor types exhibit constitutive activation of NF-kappaB (Basseres, D. S., and Baldwin, A. S. (2006) 25, 6817-6830). However, the mechanism for this constitutive activation of NF-kappaB has not been elucidated in the tumors. We have previously shown that NF-kappaB-inducing kinase (NIK) protein and its association with Inhibitor of kappaB kinase alphabeta are elevated in melanoma cells compared with their normal counterpart, leading to constitutive activation of NF-kappaB. Moreover, expression of dominant negative NIK blocked this base-line NF-kappaB activity in melanoma cells. Of the three receptors that require NIK for activation of NF-kappaB, only the lymphotoxin-beta receptor (LTbeta-R) is expressed in melanoma. We show in this manuscript that for melanoma there is a strong relationship between expression of the LTbeta-R and constitutive NF-kappaB transcriptional activity. Moreover, we show that activation of the LTbeta-R can drive NF-kappaB activity to regulate gene expression that leads to enhanced cell growth. The inhibition by LTbeta-R shRNA resulted in decreased NF-kappaB promoter activity, decreased growth, and decreased invasiveness as compared with control. These results indicate that the LTbeta-R constitutively induces NF-kappaB activation, and this event may be associated with autonomous growth of melanoma cells.

The LT beta R signaling pathway

The lymphotoxin-beta receptor (LTbetaR, TNFRSF3) signaling pathway activates gene transcription programs and cell death important in immune development and host defense. The TNF receptor associated factors (TRAF)-2, 3 and 5 function as adaptors linking LTbetaR signaling targets. Interestingly, TRAF deficient mice do not phenocopy mice deficient in components of the LTbetaR pathway, presenting a conundrum. Here, an update of our understanding and models of the LTbetaR signaling pathway are reviewed, with a focus on this conundrum.

LIGHT, a member of the TNF superfamily, activates Stat3 mediated by NIK pathway

Stat3, a member of the signal transducers and activators of transcription (STAT) family, is a key signal transduction protein activated by numerous cytokines, growth factors, and oncoproteins that controls cell proliferation, differentiation, development, survival, and inflammation. Constitutive activation of Stat3 has been found frequently in a wide variety of human tumors and induces cellular transformation and tumor formation. In this study, we demonstrated that LIGHT, a member of tumor necrosis factor superfamily, activates Stat3 in cancer cells. LIGHT induces dose-dependent activation of Stat3 by phosphorylation at both the tyrosine 705 and serine 727 residues. The activation of Stat3 by LIGHT appears to be mediated by NIK phosphorylation. Expression of a kinase-inactive NIK mutant abolished LIGHT induced Stat3 activation. Overexpression of an active NIK induces Stat3 activation by phosphorylation at the both tyrosine 705 and serine 727 residues. Activation of Stat3 by NIK requires NIK kinase activity as showed by kinase assays. In addition, LIGHT increases the expression of Stat3 target genes including cyclin D1, survivin, and Bcl-xL, and stimulates human LNCaP prostate cancer cell growth in vitro which can be blocked by expression of a dominant-negative Stat3 mutant. Taken together, these results indicate that in addition to activating NF-kappaB/p52, LIGHT also activates Stat3. Activation of Stat3 together with activating non-canonical NF-kappaB/p52 signaling by LIGHT may maximize its effects on cellular proliferation, survival, and inflammation.

Gene expression changes in long-term culture of T-cell clones: genomic effects of chronic antigenic stress in aging and immunosenescence

The adaptive immune response requires waves of T-cell clonal expansion on contact with altered self and contraction after elimination of antigen. In the case of persisting antigen, as occurs for example in cytomegalovirus or Epstein–Barr virus infection, this critical process can become dysregulated and responding T-cells enter into a dysfunctional senescent state. Longitudinal studies suggest that the presence of increased numbers of such T-cells is a poor prognostic factor for survival in the very elderly. Understanding the nature of the defects in these T-cells might facilitate intervention to improve immunity in the elderly. The process of clonal expansion under chronic antigenic stress can be modelled in vitro using continuously cultured T-cells. Here, we have used cDNA array technology to investigate differences in gene expression in a set of five different T-cell clones at early, middle and late passage in culture. Differentially expressed genes were confirmed by real-time polymerase chain reaction, and relationships between these assessed using Ingenuity Systems evidence-based association analysis. Several genes and chemokines related to induction of apoptosis and signal transduction pathways regulated by transforming growth factor β (TGFβ), epidermal growth factor (EGF), fos and β-catenin were altered in late compared to early passage cells. These pathways and affected genes may play a significant role in driving the cellular senescent phenotype and warrant further investigation as potential biomarkers of aging and senescence. These genes may additionally provide targets for intervention.

Signaling pathways of LIGHT induced macrophage migration and vascular smooth muscle cell proliferation

The biological actions of LIGHT, a member of the tumor necrosis factor superfamily, are mediated by the interaction with lymphotoxin-beta receptor (LTbetaR) and/or herpes virus entry mediator (HVEM). Previous study demonstrated high-level expressions of LIGHT and HVEM receptors in atherosclerotic plaques. To investigate the role of LIGHT in the functioning of macrophages and vascular smooth muscle cells (VSMC) in relation to atherogenesis, we determined the effects of LIGHT on macrophage migration and VSMC proliferation. We found LIGHT through HVEM activation can induce both events. LIGHT-induced macrophage migration was associated with activation of signaling kinases, including MAPKs, PI3K/Akt, NF-kappaB, Src members, and FAK. Proliferation of VSMC was also shown relating to the activation of MAPKs, PI3K/Akt, and NF-kappaB, which consequently led to alter the expression of cell cycle regulatory molecules. Down-regulation of p21, p27, and p53, and inversely up-regulation of cyclin D and RB hyper-phosphorylation were demonstrated. In conclusion, LIGHT acts as a novel mediator for macrophage migration and VSMC proliferation, suggesting its involvement in the atherogenesis.

Intracellular signals and events activated by cytokines of the tumor necrosis factor superfamily: From simple paradigms to complex mechanisms

Tumor necrosis factor (TNF) and several related cytokines can induce opposite effects such as cell activation and proliferation or cell death. How the cell maintains the balance between these seemingly mutually exclusive pathways has long remained a mystery. TNF receptor I (TNFRI) initially emerged as a potent activator of NFkappaB and AP-1 transcription factors, while the related CD95 (Fas, Apo-1) was recognized as a prototype death receptor. Advances in research have uncovered critical molecular players in these intracellular processes. They have also revealed a much more complex picture than originally thought. Several new signaling pathways, including the alternative NFkappaB activation cascade, have been uncovered, and previously unknown modes of cross-talk between intracellular signaling molecules were revealed. It also turned out that signaling mechanisms mediated by the TNF receptor superfamily members can operate not only in the immune system but also in organ development.

Oregonin inhibits lipopolysaccharide-induced iNOS gene transcription and upregulates HO-1 expression in macrophages and microglia

Oregonin isolated from Alnus formosana is a diarylheptanoid derivative, which appears to have antioxidative and anti-inflammatory activities. In this study, our data demonstrated inhibitory actions of oregonin on the LPS-induced iNOS protein in RAW264.7 macrophages and BV-2 microglial cells. We also suggested that HO-1 induction by oregonin might contribute to this action. Oregonin is able to dose-dependently reduce NO production, iNOS protein and iNOS promoter activity stimulated by LPS in RAW264.7 and BV-2 cells. Oregonin also showed inhibition of LPS-mediated NF-kappaB promoter activity and DNA-binding ability, as well as p65 nuclear translocation and phosphorylation. However, oregonin had no effect on IKK activity. AP-1 promoter activity and p38 MAPK activation but not PKC, ERK and JNK activation induced by LPS were attenuated by oregonin. Accompanying with iNOS protein reduction, moreover, we found that oregonin was able to induce HO-1 protein level. Results using a CO donor, [Ru(CO)(3)Cl(2)](2) further showed the ability of CO in reduction of iNOS protein level induced by LPS through the blockade of NF-kappaB and AP-1. Taken together, these results provide new evidences into the anti-inflammatory actions of oregonin, which include the inhibition of iNOS gene transcription via suppressing transcriptional activity of NF-kappaB and AP-1, as well as the upregulation of anti-inflammatory molecule HO-1. The HO-1-derived CO may also be involved in the suppressive effect on iNOS gene regulation.

Proinflammatory effects of LIGHT through HVEM and LTbetaR interactions in cultured human umbilical vein endothelial cells

Members of the tumor necrosis factor (TNF) receptor (TNFR) superfamily are known to be potent mediators of immune responses. LIGHT is a member of the TNF superfamily, and its receptors have been identified as lymphotoxin beta receptor (LTbetaR), herpes virus entry mediator (HVEM), and decoy receptor 3 (DcR3). LIGHT can induce either cell death and/or NF-kappaB activation via its interaction with LTbetaR and/or HVEM. In this study, we investigated the effects of LIGHT in human umbilical vein endothelial cells (HUVECs). We demonstrated that both LTbetaR and HVEM, but not DcR3, are present in HUVECs, and LIGHT can induce the secretion of chemokines (IL-8 and GRO-alpha), cell surface expression of adhesion molecules (ICAM-1 and VCAM-1), PGI2 release, and COX-2 expression. However, the LIGHT mutein, LIGHT-R228E, which has been shown to exhibit binding specificity to LTbetaR, could not induce the secretion of GRO-alpha, PGI2, or the expression of COX-2. These results indicate that both LTbetaR and HVEM can discriminatively mediate the expression of different genes in HUVECs, and suggest that LIGHT is a proinflammatory cytokine.