Lymphotoxin-beta receptor signaling complex: role of tumor necrosis factor receptor-associated factor 3 recruitment in cell death and activation of nuclear factor kappaB

Transcriptional analysis reveals antioxidant, ion transport, and glycolysis mechanisms in Litopenaeus vannamei gills involved in the response to high alkali stress

Saline-alkali aquacultural systems have an important role in improving the economic output of the aquacultural industry. However, the survival rate of shrimp in intensive aquacultural systems is affected by alkalinity fluctuations. This study explored the ion transport and molecular responses of the whiteleg shrimp Litopenaeus vannamei to short-term high alkaline stress (96 h). The results showed that survival rate decreased significantly with time, hemolymph osmotic pressure and oxygen consumption dropped sharply after peaking at 48 h, and ammonia excretion followed a non-monotonic pattern, with an initial decline followed by a subsequent increase. Analysis of key physiological indicators revealed that urea nitrogen continued to accumulate, antioxidant (SOD and CAT) and glycolytic (PFK and LDH) enzymes were significantly activated, but ion regulatory enzymes (Na+/K+-ATPase) were severely suppressed. Gill histopathology showed typical injuries (such as gill filament shrinkage, vacuolation, and hemocytopenia). Furthermore, transcriptome analysis confirmed that high alkali stress activated insulin signaling pathway and glycolysis-related genes (e.g., upregulating PFK and GLUT expression). These results indicate that the high alkalinity causes an ion imbalance, changes the ammonia transport process, and activates the glycolysis pathway. These conclusions provide a theoretical basis for the subsequent development for the saline-alkaline aquacultural of Litopenaeus vannamei.

LUBAC enables tumor-promoting LTβ receptor signaling by activating canonical NF-κB

Lymphotoxin β receptor (LTβR), a member of the TNF receptor superfamily (TNFR-SF), is essential for development and maturation of lymphoid organs. In addition, LTβR activation promotes carcinogenesis by inducing a proinflammatory secretome. Yet, we currently lack a detailed understanding of LTβR signaling. In this study we discovered the linear ubiquitin chain assembly complex (LUBAC) as a previously unrecognized and functionally crucial component of the native LTβR signaling complex (LTβR-SC). Mechanistically, LUBAC-generated linear ubiquitin chains enable recruitment of NEMO, OPTN and A20 to the LTβR-SC, where they act coordinately to regulate the balance between canonical and non-canonical NF-κB pathways. Thus, different from death receptor signaling, where LUBAC prevents inflammation through inhibition of cell death, in LTβR signaling LUBAC is required for inflammatory signaling by enabling canonical and interfering with non-canonical NF-κB activation. This results in a LUBAC-dependent LTβR-driven inflammatory, protumorigenic secretome. Intriguingly, in liver cancer patients with high LTβR expression, high expression of LUBAC correlates with poor prognosis, providing clinical relevance for LUBAC-mediated inflammatory LTβR signaling.

MicroRNA-322 overexpression reduces neural tube defects in diabetic pregnancies

BACKGROUND

Hyperglycemia from pregestational diabetes mellitus induces neural tube defects in the developing fetus. Folate supplementation is the only effective way to prevent neural tube defects; however, some cases of neural tube defects are resistant to folate. Excess folate has been linked to higher maternal cancer risk and infant allergy. Therefore, additional interventions are needed. Understanding the mechanisms underlying maternal diabetes mellitus-induced neural tube defects can identify potential targets for preventing such defects. Despite not yet being in clinical use, growing evidence suggests that microRNAs are important intermediates in embryonic development and can serve as both biomarkers and drug targets for disease intervention. Our previous studies showed that maternal diabetes mellitus in vivo activates the inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) in the developing embryo and that a high glucose condition in vitro reduces microRNA-322 (miR-322) levels. IRE1α is an RNA endonuclease; however, it is unknown whether IRE1α targets and degrades miR-322 specifically or whether miR-322 degradation leads to neural tube defects via apoptosis. We hypothesize that IRE1α can inhibit miR-322 in maternal diabetes mellitus-induced neural tube defects and that restoring miR-322 expression in developing neuroepithelium ameliorates neural tube defects.

OBJECTIVE

This study aimed to identify potential targets for preventing maternal diabetes mellitus-induced neural tube defects and to investigate the roles and relationship of a microRNA and an RNA endonuclease in mouse embryos exposed to maternal diabetes mellitus.

STUDY DESIGN

To determine whether miR-322 reduction is necessary for neural tube defect formation in pregnancies complicated by diabetes mellitus, male mice carrying a transgene expressing miR-322 were mated with nondiabetic or diabetic wide-type female mice to generate embryos with or without miR-322 overexpression. At embryonic day 8.5 when the neural tube is not yet closed, embryos were harvested for the assessment of 3 miR-322 transcripts (primary, precursor, and mature miR-322), tumor necrosis factor receptor-associated factor 3 (TRAF3), and neuroepithelium cell survival. Neural tube defect incidences were determined in embryonic day 10.5 embryos when the neural tube should be closed if there is no neural tube defect formation. To identify which miR-322 transcript is affected by maternal diabetes mellitus and high glucose conditions, 3 miR-322 transcripts were assessed in embryos from dams with or without diabetes mellitus and in C17.2 mouse neural stem cells treated with different concentrations of glucose and at different time points. To determine whether the endonuclease IRE1α targets miR-322, small interfering RNA knockdown of IRE1α or overexpression of inositol-requiring transmembrane kinase/endoribonuclease 1α by DNA plasmid transfection was used to determine the effect of IRE1α deficiency or overexpression on miR-322 expression. RNA immunoprecipitation was performed to reveal the direct targets of inositol-requiring transmembrane kinase/endoribonuclease 1α.

RESULTS

Maternal diabetes mellitus suppressed miR-322 expression in the developing neuroepithelium. Restoring miR-322 expression in the neuroepithelium blocked maternal diabetes mellitus-induced caspase-3 and caspase-8 cleavage and cell apoptosis, leading to a neural tube defect reduction. Reversal of maternal diabetes mellitus-inhibited miR-322 via transgenic overexpression prevented TRAF3 up-regulation in embryos exposed to maternal diabetes mellitus. Activated IRE1α acted as an endonuclease and degraded precursor miR-322, resulting in mature miR-322 reduction.

CONCLUSION

This study supports the crucial role of the IRE1α-microRNA-TRAF3 circuit in the induction of neuroepithelial cell apoptosis and neural tube defect formation in pregnancies complicated by diabetes mellitus and identifies IRE1α and miR-322 as potential targets for preventing maternal diabetes mellitus-induced neural tube defects.

Integrating Single-cell RNA-seq to construct a Neutrophil prognostic model for predicting immune responses in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the most widely distributed tumor in the world, and its immunotherapy is not practical. Neutrophil is one of a tumor’s most abundant immune cell groups. This research aimed to investigate the complex communication network in the immune microenvironment (TIME) of NSCLC tumors to clarify the interaction between immune cells and tumors and establish a prognostic risk model that can predict immune response and prognosis of patients by analyzing the characteristics of Neutrophil differentiation. Integrated Single-cell RNA sequencing (scRNA-seq) data from NSCLC samples and Bulk RNA-seq were used for analysis. Twenty-eight main cell clusters were identified, and their interactions were clarified. Next, four subsets of Neutrophils with different differentiation states were found, closely related to immune regulation and metabolic pathways. Based on the ratio of four housekeeping genes (ACTB, GAPDH, TFRC, TUBB), six Neutrophil differentiation-related genes (NDRGs) prognostic risk models, including MS4A7, CXCR2, CSRNP1, RETN, CD177, and LUCAT1, were constructed by Elastic Net and Multivariate Cox regression, and patients’ total survival time and immunotherapy response were successfully predicted and validated in three large cohorts. Finally, the causes of the unfavorable prognosis of NSCLC caused by six prognostic genes were explored, and the small molecular compounds targeted at the anti-tumor effect of prognostic genes were screened. This study clarifies the TIME regulation network in NSCLC and emphasizes the critical role of NDRGs in predicting the prognosis of patients with NSCLC and their potential response to immunotherapy, thus providing a promising therapeutic target for NSCLC.

Enhanced Anti-Cancer Effects of Conditioned Medium from Hypoxic Human Adult Dermal Fibroblasts on Cervical Cancer Cells

Hypoxia regulates fibroblast function by changing intracellular signaling and secretion factors, that influence the states of nearby cells. In this work, we investigated how medium (CM) from human adult dermal fibroblasts (HDFs) cultured in normoxic and hypoxic conditions affected cervical cancer (HeLa) cells. The HeLa cells showed decreased cell viability, increased apoptosis, and cell cycle arrest in response to CM from hypoxic-cultured HDFs (H-CM) compared with CM from normoxic-cultured HDFs (N-CM). Among the proteins up-regulated (>2-fold) in H-CM compared with N-CM, lymphotoxin-beta receptor (LTBR) decreased the viability of HeLa cells. Among the intracellular proteins down-regulated (>2-fold) in HeLa cells treated with H-CM compared with N-CM, the most enriched biological process GO term and KEGG pathway were protein deubiquitination and hsa05166:HTLV-I infection, respectively. In the protein−protein interaction network of intracellular proteins with altered expression (>2-fold), 1 up-regulated (TNF) and 8 down-regulated (ESR1, MCL1, TBP, CD19, LCK, PCNA, CHEK1, and POLA1) hub proteins were defined. Among the down-regulated hub proteins, the most enriched biological process GO term and KEGG pathway were leading strand elongation and hsa05166:HTLV-I infection, respectively. This study reveals that H-CM had stronger anti-cancer effects on cervical cancer cells than N-CM and induced intracellular signaling patterns related to those enhanced anti-cancer effects.

Gene Expression in Lung Epithelial Cells Following Interaction with Pneumocystis carinii and its Specific Life Forms Yields Insights into Host Gene Responses to Infection

Pneumocystis spp. interacts with epithelial cells in the alveolar spaces of the lung. It is thought that the binding of Pneumocystis to host cell epithelium is needed for life cycle completion and proliferation. The effect of this interaction on lung epithelial cells have previously shown that the trophic form of this organism greatly inhibits p34 ^cdc2 activity, a serine/threonine kinase required for transition from G₂ to M phase in the cell cycle. To gain further insight into the host response during Pneumocystis pneumonia (PCP), we used microarray technology to profile epithelial cell (A549) gene expression patterns following Pneumocystis carinii interaction. Furthermore, we isolated separate populations of cyst and trophic forms of P. carinii, which were then applied to the lung epithelial cells. Differential expression of genes involved in various cellular functions dependent on the specific P. carinii life form in contact with the A549 cell were identified. The reliability of our data was further confirmed by Northern blot analysis on a number of selected up or down regulated transcripts. The transcriptional response to P. carinii was dominated by cytokines, apoptotic, and anti-apoptotic related genes. These results reveal several previously unknown effects of P. carinii on the lung epithelial cell and provide insight into the complex interactions of host and pathogen. This article is protected by copyright. All rights reserved.

Nasal immune gene expression in response to azelastine and fluticasone propionate combination or monotherapy

BACKGROUND

The combination of the antihistamine azelastine (AZE) with the corticosteroid fluticasone propionate (FP) in a single spray, has been reported to be significantly more effective at reducing allergic rhinitis (AR) symptoms than treatment with either corticosteroid or antihistamine monotherapy. However, the biological basis for enhanced symptom relief is not known. This study aimed to compare gene expression profiles (760 immune genes, performed with the NanoString nCounter) from peripheral blood and nasal brushing/lavage lysate samples in response to nasal spray treatment.

METHODS

Moderate/severe persistent dust mite AR sufferers received either AZE (125 μg/spray) nasal spray (n = 16), FP (50 μg/spray) nasal spray (n = 14) or combination spray AZE/FP (125 μg AZE and 50 μg FP/spray) (n = 14) for 7 days, twice daily. Self-reported symptom questionnaires were completed daily for the study duration. Gene expression analysis (760 immune genes) was performed with the NanoString nCounter on purified RNA from peripheral blood and nasal brushing/lavage lysate samples.

RESULTS

In nasal samples, 206 genes were significantly differentially expressed following FP treatment; 182 genes downregulated (-2.57 to -0.45 Log2 fold change [FC]), 24 genes upregulated (0.49-1.40 Log2 FC). In response to AZE/FP, only 16 genes were significantly differentially expressed; 10 genes downregulated (-1.53 to -0.58 Log2 FC), six genes upregulated (1.07-1.62 Log2 FC). Following AZE treatment only five genes were significantly differentially expressed; one gene downregulated (-1.68 Log2 FC), four genes upregulated (0.59-1.19 Log2 FC). Immune gene changes in peripheral blood samples following treatment were minimal. AR symptoms improved under all treatments, but improvements were less pronounced following AZE treatment.

CONCLUSION

AZE/FP, FP, and AZE had diverse effects on immune gene expression profiles in nasal mucosa samples. The moderate number of genes modulated by AZE/FP indicates alternative pathways in reducing AR symptoms whilst avoiding extensive local immune suppression.

A genome-scale screen for synthetic drivers of T cell proliferation

The engineering of autologous patient T cells for adoptive cell therapies has revolutionized the treatment of several types of cancer1. However, further improvements are needed to increase response and cure rates. CRISPR-based loss-of-function screens have been limited to negative regulators of T cell functions2-4 and raise safety concerns owing to the permanent modification of the genome. Here we identify positive regulators of T cell functions through overexpression of around 12,000 barcoded human open reading frames (ORFs). The top-ranked genes increased the proliferation and activation of primary human CD4+ and CD8+ T cells and their secretion of key cytokines such as interleukin-2 and interferon-γ. In addition, we developed the single-cell genomics method OverCITE-seq for high-throughput quantification of the transcriptome and surface antigens in ORF-engineered T cells. The top-ranked ORF-lymphotoxin-β receptor (LTBR)-is typically expressed in myeloid cells but absent in lymphocytes. When overexpressed in T cells, LTBR induced profound transcriptional and epigenomic remodelling, leading to increased T cell effector functions and resistance to exhaustion in chronic stimulation settings through constitutive activation of the canonical NF-κB pathway. LTBR and other highly ranked genes improved the antigen-specific responses of chimeric antigen receptor T cells and γδ T cells, highlighting their potential for future cancer-agnostic therapies5. Our results provide several strategies for improving next-generation T cell therapies by the induction of synthetic cell programmes.

LTβR Signaling Controls Lymphatic Migration of Immune Cells

The pleiotropic functions of lymphotoxin (LT)β receptor (LTβR) signaling are linked to the control of secondary lymphoid organ development and structural maintenance, inflammatory or autoimmune disorders, and carcinogenesis. Recently, LTβR signaling in endothelial cells has been revealed to regulate immune cell migration. Signaling through LTβR is comprised of both the canonical and non-canonical-nuclear factor κB (NF-κB) pathways, which induce chemokines, cytokines, and cell adhesion molecules. Here, we focus on the novel functions of LTβR signaling in lymphatic endothelial cells for migration of regulatory T cells (Tregs), and specific targeting of LTβR signaling for potential therapeutics in transplantation and cancer patient survival.

miR-346-3p promotes osteoclastogenesis via inhibiting TRAF3 gene

MicroRNAs (miRNAs) modulate gene expression and regulate many physiological and pathological conditions. However, their modulation and effect in osteoclastogenesis remain unknown. In this study, we investigated the role of miR-346-3p in regulating the osteoclast differentiation from RAW264.7 cells. We used the miRNA microarray assay, miR-346-3p mimic transfection, tartrate resistant acid phosphatase (TRAP) staining, bone resorption assay, qRT-PCR, and western blot. Our results showed that the expression of miR-346-3p was significantly upregulated during osteoclast differentiation. Further, by transfecting cells with miR-346-3p mimic, we observed an increased number of TRAP-positive multinucleated cells, increased pit area caused by bone resorption, and enhanced expression of osteoclast-specific genes and proteins. Conversely, miR-346-3p inhibition attenuated the osteoclast differentiation and function. Software-mediated prediction and validation using luciferase reporter assay showed that TRAF3, a negative regulator of osteoclast differentiation, was inhibited by miR-346-3p overexpression. Our results showed that miR-346-3p directly targeted TRAF3 mRNA via binding to its 3'-UTR and inhibited the expression of TRAF3 protein. Taken together, our results revealed that miR-346-3p promotes the regulation of osteoclastogenesis by suppressing the TRAF3 gene. In conclusion, miR-346-3p could be a novel therapeutic target for bone loss-related pathogenesis.

Apoptosis and genes involved in oral cancer - a comprehensive review

Oral cancers needs relentless research due to high mortality and morbidity associated with it. Despite of the comparable ease in accessibility to these sites, more than 2/3^rd cases are diagnosed in advanced stages. Molecular/genetic studies augment clinical assessment, classification and prediction of malignant potential of oral lesions, thereby reducing its incidence and increasing the scope for early diagnosis and treatment of oral cancers. Herein we aim to review the role of apoptosis and genes associated with it in oral cancer development in order to aid in early diagnosis, prediction of malignant potential and evaluation of possible treatment targets in oral cancer. An internet-based search was done with key words apoptosis, genes, mutations, targets and analysis to extract 72 articles after considering inclusion and exclusion criteria. The knowledge of genetics and genomics of oral cancer is of utmost need in order to stop the rising prevalence of oral cancer. Translational approach and interventions at the early stage of oral cancer, targeted destruction of cancerous cells by silencing or promoting involved genes should be the ideal intervention.

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.

Induction of the Epithelial-to-Mesenchymal Transition of Human Colorectal Cancer by Human TNF-β (Lymphotoxin) and its Reversal by Resveratrol

Objective: Tumor necrosis factor-beta (TNF-β), as an inflammatory mediator that has been shown to promote tumorigenesis, induces NF-κB. Natural multi-targeted agent resveratrol in turn shows anti-inflammatory and anti-cancer properties. Epithelial-to-mesenchymal transition (EMT) allows cancer cells to turn into a motile state with invasive capacities and is associated with metastasis and development of cancer stem cells (CSC). However, TNF-β-induced EMT and the anti-invasion mechanism of resveratrol on CRC are not yet completely understood. Methods: We investigated the underlying molecular mechanisms of resveratrol on TNF-β/TNF-βR-induced EMT and migration of CRC cells (HCT116, RKO, SW480) in monolayer or 3D alginate cultures. Results: TNF-β, similar to TNF-α, induced significant cell proliferation, morphological change, from an epithelial to a spindle-like mesenchymal shape with the formation of filopodia and lamellipodia associated with the expression of EMT parameters (elevated vimentin and slug, reduced E-cadherin), increased migration/invasion, and formation of CSC in all CRC cells. Interestingly, these effects were dramatically decreased in the presence of resveratrol or anti-TNF-βR with TNF-β co-treatment, inducing biochemical changes to the mesenchymal-epithelial transition (MET), with a planar cell surface and suppressed formation of CSC cells. This was associated with a significant increase in apoptosis. Furthermore, we found that resveratrol suppressed TNF-β-induced NF-κB and NF-κB-regulated gene biomarkers associated with growth, proliferation, and invasion. Finally, TNF-βR interacts directly with focal adhesion kinase (FAK) and NF-κB. Conclusion: These results suggest that resveratrol down-regulates TNF-β/TNF-βR-induced EMT, at least in part via specific suppression of NF-κΒ and FAK in CRC cells.

Network meta-analysis correlates with analysis of merged independent transcriptome expression data

BACKGROUND

Using meta-analysis, high-dimensional transcriptome expression data from public repositories can be merged to make group comparisons that have not been considered in the original studies. Merging of high-dimensional expression data can, however, implicate batch effects that are sometimes difficult to be removed. Removing batch effects becomes even more difficult when expression data was taken using different technologies in the individual studies (e.g. merging of microarray and RNA-seq data). Network meta-analysis has so far not been considered to make indirect comparisons in transcriptome expression data, when data merging appears to yield biased results.

RESULTS

We demonstrate in a simulation study that the results from analyzing merged data sets and the results from network meta-analysis are highly correlated in simple study networks. In the case that an edge in the network is supported by multiple independent studies, network meta-analysis produces fold changes that are closer to the simulated ones than those obtained from analyzing merged data sets. Finally, we also demonstrate the practicability of network meta-analysis on a real-world data example from neuroinfection research.

CONCLUSIONS

Network meta-analysis is a useful means to make new inferences when combining multiple independent studies of molecular, high-throughput expression data. This method is especially advantageous when batch effects between studies are hard to get removed.

IL-17A modulates osteoclast precursors' apoptosis through autophagy-TRAF3 signaling during osteoclastogenesis

Osteoclasts play an important role in bone remodeling. The inflammatory cytokine IL-17A could modulate the RANKL-induced osteoclastogenesis by regulating the autophagic activity. It is well accepted that protective autophagy has an anti-apoptotic effect. It is necessary to elucidate whether IL-17A can influence the apoptosis of osteoclast precursors (OCPs) through autophagy responses during osteoclastogenesis. The results showed that apoptosis of RAW264.7-derived OCPs was promoted by high levels of IL-17A, but the opposite anti-apoptotic function was shown by low levels of IL-17A. Furthermore, the enhanced apoptosis by high levels of IL-17A was reversed by overexpression of autophagy protein Beclin1; conversely, the inhibited apoptosis by low levels of IL-17A was restored by knockdown of Beclin1. It was also found that Beclin1 suppression with Beclin1 inhibitor (spautin1) could block the reduced apoptosis by low levels of IL-17A, which was recovered by TRAF3 knockdown. Moreover, the enhanced apoptosis by high levels of IL-17A decreased following the downregulation of TRAF3. Importantly, overexpression of caspase3 further attenuated osteoclastogenesis treated by high levels of IL-17A, without significantly affecting osteoclastogenesis stimulated by low levels of IL-17A. In conclusion, IL-17A modulates apoptosis of OCPs through Beclin1-autophagy-TRAF3 signaling pathway, thereby influencing osteoclastogenesis. Therefore, our study sheds lights on the improvement of clinical strategies of dental implantation or orthodontic treatment by revealing the novel targets in the bone remodeling.

The Role of Co-Stimulatory Molecules in Chagas Disease

Chagas disease, caused by Trypanosoma cruzi, is a potentially life-threatening tropical disease endemic to Latin American countries that affects approximately 8 million people. In the chronic phase of the disease, individuals are classified as belonging to the indeterminate clinical form or to the cardiac and/or digestive forms when clinical symptoms are apparent. The relationship between monocytes and lymphocytes may be an important point to help clarify the complexity that surrounds the clinical symptoms of the chronic phase of Chagas disease. The co-stimulatory signals are essential to determining the magnitude of T cell response to the antigen. The signals are known to determine the regulation of subsequent adaptive immune response. However, little is known about the expression and function of these molecules in Chagas disease. Therefore, this review aims to discuss the possible role of main pathways of co-stimulatory molecule-receptor interactions in this pathology that could be crucial to understand the disease dynamics.

IL-17A regulates the autophagic activity of osteoclast precursors through RANKL-JNK1 signaling during osteoclastogenesis in vitro

Interleukin-17A(IL-17A), a proinflammatory cytokine, may have effects on osteoclastic resorption in inflammation-mediated bone loss, including postmenopausal osteoporosis. IL-17A could alter autophagic activity among other tissues and cells, thereby causing corresponding lesions. The aim of this study was to clarify how IL-17A influenced osteoclastogenesis by regulating autophagy. The present study showed that IL-17A could facilitate osteoclast precursors (OCPs) autophagy and osteoclastogenesis at a low concentration. Furthermore, suppression of autophagy with chloroquine (CQ) or 3-MA could significantly attenuate the enhanced osteoclastogenesis by a low level of IL-17A. It was also found that a low level of IL-17A couldn't up-regulate OCPs autophagy after removal of RANKL(Receptor Activator for Nuclear Factor-κB Ligand), and JNK(c-Jun N-terminal kinase) inhibitor only inhibited autophagy at a low level of IL-17A. These results suggest that a low concentration of IL-17A is likely to promote autophagic activity via activating RANKL-JNK pathway during osteoclastogenesis.

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.

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.

Myocyte-derived Tnfsf14 is a survival factor necessary for myoblast differentiation and skeletal muscle regeneration

Adult skeletal muscle tissue has a uniquely robust capacity for regeneration, which gradually declines with aging or is compromised in muscle diseases. The cellular mechanisms regulating adult myogenesis remain incompletely understood. Here we identify the cytokine tumor necrosis factor superfamily member 14 (Tnfsf14) as a positive regulator of myoblast differentiation in culture and muscle regeneration in vivo. We find that Tnfsf14, as well as its cognate receptors herpes virus entry mediator (HVEM) and lymphotoxin β receptor (LTβR), are expressed in both differentiating myocytes and regenerating myofibers. Depletion of Tnfsf14 or either receptor inhibits myoblast differentiation and promotes apoptosis. Our results also suggest that Tnfsf14 regulates myogenesis by supporting cell survival and maintaining a sufficient pool of cells for fusion. In addition, we show that Akt mediates the survival and myogenic function of Tnfsf14. Importantly, local knockdown of Tnfsf14 is found to impair injury-induced muscle regeneration in a mouse model, affirming an important physiological role for Tnfsf14 in myogenesis in vivo. Furthermore, we demonstrate that localized overexpression of Tnfsf14 potently enhances muscle regeneration, and that this regenerative capacity of Tnfsf14 is dependent on Akt signaling. Taken together, our findings reveal a novel regulator of skeletal myogenesis and implicate Tnfsf14 in future therapeutic development.

Mechanisms of human lymphotoxin beta receptor activation on upregulation of CCL5/RANTES production

Human lymphotoxin-β receptor (LTβR), a member of the tumor necrosis factor receptor superfamily, plays an essential role in secondary lymphoid organ development, host defense, chemokine secretion, and apoptosis. In our study, LTβR activations by different stimulations were all found to induce RANTES secretion. Overexpression of LTβR or stimulation LTβR by ligands or agonistic antibody in human lung epithelial cells induced RANTES secretion However, the regulatory mechanism and the signaling cascade have not been fully elucidated. Therefore, the aim of this study was to elucidate the mechanism underlying LTβR-mediated RANTES production. Our study indicated that activation of JNK and ERK was important for the regulation of RANTES secretion. In addition, dominant negative mutants of ASK1, TAK1, and MEKK1 inhibited LTβR-induced RANTES expression. The dominant negative mutants of TRAF2, 3, and 5 also inhibited LTβR-mediated RANTES secretion. Chromatin immunoprecipitation analysis showed that LTβR activation induced the binding of c-Jun and NF-κB to the RANTES promoter. The results of this study show that LTβR activates ASK1, TAK1, and MEKK1 cascades via TRAF2, 3, and 5, resulting in the activation of JNK and ERK, which promotes the binding of c-Jun and NF-κB to the RANTES promoter, thereby increasing RANTES expression and secretion.

Phenotype-dependent alteration of pathways and networks reveals a pure synergistic mechanism for compounds treating mouse cerebral ischemia

AIM

Our previous studies have showed that ursodeoxycholic acid (UA) and jasminoidin (JA) effectively reduce cerebral infarct volume in mice. In this study we explored the pure synergistic mechanism of these compounds in treatment of mouse cerebral ischemia, which was defined as synergistic actions specific for phenotype variations after excluding interference from ineffective compounds.

METHODS

Mice with focal cerebral ischemia were treated with UA, JA or a combination JA and UA (JU). Concha margaritifera (CM) was taken as ineffective compound. Cerebral infarct volume of the mice was determined, and the hippocampi were taken for microarray analysis. Particular signaling pathways and biological functions were enriched based on differentially expressed genes, and corresponding networks were constructed through Ingenuity Pathway Analysis.

RESULTS

In phenotype analysis, UA, JA, and JU significantly reduced the ischemic infarct volume with JU being superior to UA or JA alone, while CM was ineffective. As a result, 4 pathways enriched in CM were excluded. Core pathways in the phenotype-positive groups (UA or JA) were involved in neuronal homeostasis and neuropathology. JU-contributing pathways included all UA-contributing and the majority (71.7%) of JA-contributing pathways, and 10 new core pathways whose effects included inflammatory immunity, apoptosis and nervous system development. The functions of JU group included all functions of JA group, the majority (93.1%) of UA-contributing functions, and 3 new core functions, which focused on physiological system development and function.

CONCLUSION

The pure synergism between UA and JA underlies 10 new core pathways and 3 new core functions, which are involved in inflammation, immune responses, apoptosis and nervous system development.

The miR-322-TRAF3 circuit mediates the pro-apoptotic effect of high glucose on neural stem cells

Maternal diabetes increases the risk of neural tube defects (NTDs), and caspase-dependent apoptosis and gene dysregulation are implicated in this disease process. This study investigates the role of miR-322 and its putative target gene, TNF receptor-associated factor 3 (TRAF3), in high glucose-induced apoptosis. miR-322 and TRAF3 expression were assessed in embryos of nondiabetic and diabetic dams, and in neural stem cells under high glucose conditions. Maternal diabetes in vivo and high glucose in vitro significantly down-regulated miR-322 and up-regulated TRAF3 protein expression. Overexpression of the antioxidant enzyme, superoxide dismutase 1 (SOD1), or treatment with the SOD1 mimetic Tempol, abolished the effect of maternal diabetes or high glucose on miR-322 and TRAF3 expression, respectively. A miRNA target prediction algorithm reveals 2 miR-322 binding sites the 3'-untranslated region (UTR) of TRAF3 mRNA. A RNA pull-down assay using biotin-labeled miR-322 revealed that miR-322 interacted with the 3'-UTR of TRAF3 mRNA at one specific binding site. The miR-322 mimic or TRAF3 knockdown blocked high glucose-increased TRAF3 protein expression and apoptosis, whereas the miR-322 inhibitor mimicked the effect of high glucose leading to TRAF3 up-regulation and apoptosis. This study demonstrates that both maternal diabetes and high glucose negatively regulate miR-322 through oxidative stress. miR-322 interacts with the 3'-UTR of TRAF3 and represses its translation. The miR-322-TRAF3 pathway is implicated in high glucose-induced caspase activation and apoptosis.

Epstein-Barr virus latent genes

Latent Epstein–Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.

Defining the functional boundaries of the murine α1,3-fucosyltransferase Fut7 reveals a remarkably compact locus

Fut7 encodes an α1,3-fucosyltransferase critical for biosynthesis of glycan ligands for all three selectins. Consistent with this function, Fut7 expression is limited to hematopoietic cells and high endothelial cells which express selectin ligands. Mechanisms that govern Fut7 expression are poorly defined. To begin to understand the molecular genetic basis for transcriptional regulation of Fut7, a transgenic, gain-of-function, genetic complementation approach in mice was used to define the "functional boundaries" of the murine Fut7 locus, defined here as any uninterupted stretch of genomic DNA that contains all cis-acting genetic elements essential for accurate physiologic expression. A 12.7-kb contiguous genomic interval, which lies completely between the highly conserved flanking Npdc1 and Abca2 loci on chromosome 2 and which contains the complete transcriptional unit plus ∼7.4 kb upstream of the transcriptional start site and ∼2 kb downstream of the transcriptional termination and polyadenylation sites, was used as a transgene (Tg) on a Fut7 null background. Tg+ mice exhibited restoration of Fut7 gene expression and physiologic levels of selectin ligand expression and function on neutrophils, activated T cells, and high endothelial cells and corrected the functional defects in these cells found in Fut7 null mice without leading to detectable expression of Fut7 in normally non-expressing tissues. These results demonstrate that all genetic information essential for appropriate and selective expression of Fut7 in diverse cell types and in response to distinct developmental signals is contained within this comparatively small genetic region.

Overexpression of miR-122 promotes the hepatic differentiation and maturation of mouse ESCs through a miR-122/FoxA1/HNF4a-positive feedback loop

BACKGROUND & AIMS

microRNA-122 is the only identified liver-specific miRNA and plays a crucial role in liver development, maintenance of hepatic homeostasis as well as tumourigenesis. In our previous differentiation of ESCs into hepatocytes, microRNA-122 (miR-122) was expressed at a relatively low level. Here, we aim to elucidate the effect and underlying mechanisms of miR-122 during differentiation of ESCs into hepatocytes.

METHODS

Mouse ESCs were initially induced towards HPCs by activin A, FGF-4 and sodium butyrate and were subsequently transfected with a recombinant adenovirus expressing vector pAV.Ex1d-CMV>miR-122/IRES/eGFP 9 days after induction. Cells were analysed by real-time PCR, immunofluorescence, flow cytometry, microscopy and functional assays. Furthermore, microarray analysis was performed.

RESULTS

We demonstrated that overexpression of miR-122 could effectively promote hepatic differentiation and maturation, as assessed by morphological and functional tests. The microarray analysis revealed that 323 genes were down-regulated, whereas 59 were up-regulated. Particularly, two liver-specific transcription factors, FoxA1 and HNF4a, were significantly up-regulated. Moreover, the expression of E-cadherin was dramatically increased and the proliferation of HPCs was suppressed, whereas knockdown of FoxA1 reduced E-cadherin expression and increased the proliferation of HPCs. In addition, the expression levels of FoxA1, HNF4a and E-cadherin in time-course transfection experiments with miR-122 were not significantly increased except in cells in which transfection with miR-122 occurred 9 days after induction.

CONCLUSION

Overexpression of miR-122 at an appropriate stage could promote hepatic differentiation and maturation by regulating the balance between proliferation and differentiation, as well as the balance between EMT and MET, partially through a miR-122/FoxA1/HNF4a-positive feedback loop.

SUMOylation is required for optimal TRAF3 signaling capacity

TNF receptor-associated factors (TRAFs) are multifunctional adaptor proteins involved in temporal and spatial coordination of signals necessary for normal immune function. Here, we report that TRAF3, a TRAF family member with a key role in Toll-like and TNF family receptor signaling and suppressor of lymphomagenesis, is post-translationally modified by the small ubiquitin-related modifier (SUMO). Through yeast two-hybrid and co-immunoprecipitation assays we have identified Ubc9, the SUMO conjugating enzyme, as a novel TRAF3-interacting protein. We show that Ubc9-dependent SUMOylation of TRAF3 modulates optimal association with the CD40 receptor, thereby influencing TRAF3 degradation and non-canonical NF-κB activation upon CD40 triggering. Collectively, our findings describe a novel post-translational modification of a TRAF family member and reveal a link between SUMOylation and TRAF-mediated signal transduction.

TRAF molecules in cell signaling and in human diseases

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of intracellular proteins were originally identified as signaling adaptors that bind directly to the cytoplasmic regions of receptors of the TNF-R superfamily. The past decade has witnessed rapid expansion of receptor families identified to employ TRAFs for signaling. These include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), T cell receptor, IL-1 receptor family, IL-17 receptors, IFN receptors and TGFβ receptors. In addition to their role as adaptor proteins, most TRAFs also act as E3 ubiquitin ligases to activate downstream signaling events. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-κBs (NF-κBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Compelling evidence obtained from germ-line and cell-specific TRAF-deficient mice demonstrates that each TRAF plays indispensable and non-redundant physiological roles, regulating innate and adaptive immunity, embryonic development, tissue homeostasis, stress response, and bone metabolism. Notably, mounting evidence implicates TRAFs in the pathogenesis of human diseases such as cancers and autoimmune diseases, which has sparked new appreciation and interest in TRAF research. This review presents an overview of the current knowledge of TRAFs, with an emphasis on recent findings concerning TRAF molecules in signaling and in human diseases.

Roles of tumor necrosis factor receptor associated factor 3 (TRAF3) and TRAF5 in immune cell functions

A large and diverse group of receptors utilizes the family of cytoplasmic signaling proteins known as tumor necrosis factor receptor (TNFR)-associated factors (TRAFs). In recent years, there has been a resurgence of interest and exploration of the roles played by TRAF3 and TRAF5 in cellular regulation, particularly in cells of the immune system, the cell types of focus in this review. This work has revealed that TRAF3 and TRAF5 can play diverse roles for different receptors even in the same cell type, as well as distinct roles in different cell types. Evidence indicates that TRAF3 and TRAF5 play important roles beyond the TNFR-superfamily (SF) and viral mimics of its members, mediating certain innate immune receptor and cytokine receptor signals, and most recently, signals delivered by the T-cell receptor (TCR) signaling complex. Additionally, much research has demonstrated the importance of TRAF3-mediated cellular regulation via its cytoplasmic interactions with additional signaling proteins. In particular, we discuss below evidence for the participation by TRAF3 in a number of the regulatory post-translational modifications involving ubiquitin that are important in various signaling pathways.

Sources and signals regulating type I interferon production: lessons learned from cytomegalovirus

Type I interferons (IFN-αβ) are pleiotropic cytokines critical for antiviral host defense, and the timing and magnitude of their production involve a complex interplay between host and pathogen factors. Mouse cytomegalovirus (a β-herpesvirus) is a persistent virus that induces a biphasic IFN-αβ response during the first days of infection. The cell types and molecular mechanisms governing these 2 phases are unique, with splenic stromal cells being a major source of initial IFN-αβ, requiring communication with B cells expressing lymphotoxin, a tumor necrosis factor family cytokine. Here we review the factors that regulate this lymphotoxin-IFN-αβ "axis" during cytomegalovirus infection, highlight how stroma-derived IFN-αβ contributes in other models, and discuss how deregulation of this axis can lead to pathology in some settings.

Functional genomics reveals diverse cellular processes that modulate tumor cell response to oxaliplatin

Oxaliplatin is widely used to treat colorectal cancer, as both adjuvant therapy for resected disease and palliative treatment of metastatic disease. However, a significant number of patients experience serious side effects, including prolonged neurotoxicity, from oxaliplatin treatment creating an urgent need for biomarkers of oxaliplatin response or resistance to direct therapy to those most likely to benefit. As a first step to improve selection of patients for oxaliplatin-based chemotherapy, we have conducted an in vitro cell-based small interfering RNA (siRNA) screen of 500 genes aimed at identifying genes whose loss of expression alters tumor cell response to oxaliplatin. The siRNA screen identified twenty-seven genes, which when silenced, significantly altered colon tumor cell line sensitivity to oxaliplatin. Silencing of a group of putative resistance genes increased the extent of oxaliplatin-mediated DNA damage and inhibited cell-cycle progression in oxaliplatin-treated cells. The activity of several signaling nodes, including AKT1 and MEK1, was also altered. We used cDNA transfection to overexpress two genes (LTBR and TMEM30A) that were identified in the siRNA screen as mediators of oxaliplatin sensitivity. In both instances, overexpression conferred resistance to oxaliplatin. In summary, this study identified numerous putative predictive biomarkers of response to oxaliplatin that should be studied further in patient specimens for potential clinical application. Diverse gene networks seem to influence tumor survival in response to DNA damage by oxaliplatin. Finally, those genes whose loss of expression (or function) is related to oxaliplatin sensitivity may be promising therapeutic targets to increase patient response to oxaliplatin.

Modulation of experimental autoimmune encephalomyelitis through TRAF3-mediated suppression of interleukin 17 receptor signaling

By binding to the interleukin 17 receptor (IL-17R), TRAF3 blocks formation of the IL-17R–Act1–TRAF6 complex and inhibits downstream signaling.

Interleukin 17 (IL-17) plays critical roles in the pathogenesis of various autoimmune diseases, including experimental autoimmune encephalomyelitis (EAE). How the signals triggered by this powerful inflammatory cytokine are controlled to avoid abnormal inflammatory responses is not well understood. In this study, we report that TRAF3 is a receptor proximal negative regulator of IL-17 receptor (IL-17R) signaling. TRAF3 greatly suppressed IL-17–induced NF-κB and mitogen-activated protein kinase activation and subsequent production of inflammatory cytokines and chemokines. Mechanistically, the binding of TRAF3 to IL-17R interfered with the formation of the receptor signaling activation complex IL-17R–Act1–TRAF6, resulting in suppression of downstream signaling. TRAF3 markedly inhibited IL-17–induced expression of inflammatory cytokine and chemokine genes in vivo and consequently delayed the onset and greatly reduced the incidence and severity of EAE. Thus, TRAF3 is a negative regulator of IL-17R proximal signaling.

Differential TRAF3 utilization by a variant human CD40 receptor with enhanced signaling

CD40 is required for T cell-dependent humoral immunity, but it can also contribute to the pathogenesis of autoimmunity and B cell malignancy. The TNFR-associated factor (TRAF)2 and TRAF6 adaptor proteins are positive regulators of CD40 signaling required to activate downstream kinase cascades and transcription factors. In contrast, TRAF3 can serve as a negative regulator of CD40 signaling, and CD40 signals are amplified in TRAF3(-/-) B cells. We previously reported a gain-of-function polymorphism of the human CD40 receptor, hCD40-P227A, which signals in an amplified manner to B lymphocytes. In this study, we show that hCD40-P227A binds more TRAF3 and TRAF5, as well as certain associated proteins, than wild-type-CD40. Studies in TRAF-deficient B cell lines revealed that hCD40-P227A uses TRAF3 as a positive rather than negative regulator. Although located outside of any known TRAF binding sites, the P227A polymorphism can alter TRAF binding and dramatically changes the role played by TRAF3 in CD40 signaling.

Allosteric regulation of the ubiquitin:NIK and ubiquitin:TRAF3 E3 ligases by the lymphotoxin-beta receptor

The lymphotoxin-beta receptor (LTbetaR) activates the NF-kappaB2 transcription factors, p100 and RelB, by regulating the NF-kappaB-inducing kinase (NIK). Constitutive proteosomal degradation of NIK limits NF-kappaB activation in unstimulated cells by the ubiquitin:NIK E3 ligase comprised of subunits TNFR-associated factors (TRAF)3, TRAF2, and cellular inhibitor of apoptosis (cIAP). However, the mechanism releasing NIK from constitutive degradation remains unclear. We found that insertion of a charge-repulsion mutation in the receptor-binding crevice of TRAF3 ablated binding of both LTbetaR and NIK suggesting a common recognition site. A homologous mutation in TRAF2 inhibited cIAP interaction and blocked NIK degradation. Furthermore, the recruitment of TRAF3 and TRAF2 to the ligated LTbetaR competitively displaced NIK from TRAF3. Ligated LTbetaR complexed with TRAF3 and TRAF2 redirected the specificity of the ubiquitin ligase reaction to polyubiquitinate TRAF3 and TRAF2, leading to their proteosomal degradation. Stimulus-dependent degradation of TRAF3 required the RING domain of TRAF2, but not of TRAF3, implicating TRAF2 as a key E3 ligase in TRAF turnover. The combined action of competitive displacement of NIK and TRAF degradation halted NIK turnover, and promoted its association with IKKalpha and signal transmission. These results indicate the LTbetaR modifies the ubiquitin:NIK E3 ligase, and also acts as an allosteric regulator of the ubiquitin:TRAF E3 ligase.

TRAF3 controls activation of the canonical and alternative NFkappaB by the lymphotoxin beta receptor

Components of lymphotoxin beta receptor (LTBR)-associated signaling complexes, including TRAF2, TRAF3, NIK, IKK1, and IKK2 have been shown to participate in the coupling of LTBR to NFkappaB. Here, we report that TRAF3 functions as a negative regulator of LTBR signaling via both canonical and non-canonical NFkappaB pathways by two distinct mechanisms. Analysis of NFkappaB signaling in cell lines with functionally intact NFkappaB pathway but lacking LTBR-mediated induction of NFkappaB target genes revealed an inverse association of cellular TRAF3 levels with LTBR-specific defect in canonical NFkappaB activation. Increased expression of TRAF3 correlated with its increased recruitment to LTBR-induced signaling complexes, decreased recruitment of TRAF2, and attenuated phosphorylation of IkappaB alpha and RelA. In contrast, activation of NFkappaB by TNF did not depend on TRAF3 levels. siRNA-mediated depletion of TRAF3 promoted recruitment of TRAF2 and IKK1 to activated LTBR, enabling LTBR-inducible canonical NFkappaB signaling and NFkappaB target gene expression. TRAF3 knock-down also increased mRNA and protein expression of several non-canonical NFkappaB components, including NFkappaB2/p100, RelB, and NIK, accompanied by processing of NFkappaB2/p100 into p52. These effects of TRAF3 depletion did not require LTBR signaling and were consistent with autonomous activation of the non-canonical NFkappaB pathway. Our data illustrate the function of TRAF3 as a dual-mode repressor of LTBR signaling that controls activation of canonical NFkappaB, and de-repression of the intrinsic activity of non-canonical NFkappaB. Modulation of cellular TRAF3 levels may thus contribute to regulation of NFkappaB-dependent gene expression by LTBR by affecting the balance of LTBR-dependent activation of canonical and non-canonical NFkappaB pathways.

Unconventional ligand activation of herpesvirus entry mediator signals cell survival

The herpesvirus entry mediator (HVEM; TNFRSF14) activates NF-kappaB through the canonical TNF-related cytokine LIGHT, serving as a costimulatory pathway during activation of T cells. HVEM also functions as a ligand for the Ig superfamily members B and T lymphocyte attenuator (BTLA) and CD160, both of which limit inflammatory responses initiated by T cells. Emerging evidence indicates BTLA also promotes T cell survival, but its structural differences from LIGHT intimate BTLA is unlikely to function as an activator of HVEM. We demonstrate here that BTLA, CD160, and herpes simplex virus envelope glycoprotein D (gD) function as activating ligands for HVEM, promoting NF-kappaB activation and cell survival. Membrane-expressed BTLA and CD160, as well as soluble dimeric receptor surrogates BTLA-Fc and gD-Fc specifically activated HVEM-dependent NF-kappaB. BTLA and CD160 engagement induced recruitment of TNF receptor-associated factor 2 (TRAF2), but not TRAF3, to HVEM that specifically activated the RelA but not the RelB form of NF-kappaB in a mucosal epithelial tumor cell line. Moreover, Btla(-/-) T cells survived poorly following activation but were rescued with BTLA-Fc, indicating HVEM-BTLA bidirectional signaling may serve as a critical cell-survival system for lymphoid and epithelial cells.

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.

Protein-protein interactions in TRAF3

TNF-receptor-associated factors (TRAFs) are intracellular proteins that bind to the cytoplasmic portion of TNF receptors and mediate downstream signaling. The six known TRAF proteins play overlapping yet distinct roles in controlling immune responses as well as cellular processes such as activation of NF-kappaB and JNK signaling pathways. For example, CD40 binds to TRAF2, TRAF3 and TRAF6 to control B cell differentiation, proliferation and growth. In contrast, binding of lymphotoxin-beta receptor (LTbetaR) to TRAF2 and TRAF5 propagates signals leading to activation of NF-kappaB, while binding to TRAF3 induces negative regulation of this pathway and leads to apoptosis in tumor cells. Binding recognition is mediated by specific contacts of a consensus recognition sequence in the partner with residues in a hydrophobic crevice on the TRAF molecule. Since each of these protein-protein interactions occurs within this same binding crevice, it appears that TRAF-mediated cellular mechanisms may be regulated, in part, by the level of expression or recruitment of the adaptor proteins or receptors that are competing for the crevice. The specific contacts of CD40, LTbetaR and BAFF-R have been defined in crystal structures of the complex with TRAF3. In addition, the downstream regulator TANK and the viral oncogenic protein LMP1 from the Epstein Barr virus also bind to the same TRAF crevice and these contacts have also been described crystallographically. Comparison of these five crystal structures has revealed that the recognition motifs in each of these proteins are accommodated in one TRAF3 binding crevice and that the binding interface is structurally and functionally adaptive. In this chapter, the molecular details of the interactions will be described and correlated with the functional implications for multiple TRAF3 roles in cellular regulation.

Targeting the lymphotoxin-beta receptor with agonist antibodies as a potential cancer therapy

The lymphotoxin-beta receptor (LT beta R) is a tumor necrosis factor receptor family member critical for the development and maintenance of various lymphoid microenvironments. Herein, we show that agonistic anti-LT beta R monoclonal antibody (mAb) CBE11 inhibited tumor growth in xenograft models and potentiated tumor responses to chemotherapeutic agents. In a syngeneic colon carcinoma tumor model, treatment of the tumor-bearing mice with an agonistic antibody against murine LT beta R caused increased lymphocyte infiltration and necrosis of the tumor. A pattern of differential gene expression predictive of cellular and xenograft response to LT beta R activation was identified in a panel of colon carcinoma cell lines and when applied to a panel of clinical colorectal tumor samples indicated 35% likelihood a tumor response to CBE11. Consistent with this estimate, CBE11 decreased tumor size and/or improved long-term animal survival with two of six independent orthotopic xenografts prepared from surgical colorectal carcinoma samples. Targeting of LT beta R with agonistic mAbs offers a novel approach to the treatment of colorectal and potentially other types of cancers.

Targeting lymphotoxin beta receptor with tumor-specific T lymphocytes for tumor regression

PURPOSE

One of the impediments of immunotherapy against cancer is the suppression of tumor-specific CTLs in the tumor microenvironment, partly due to the selective inhibition of the perforin pathway and the emergence of Fas-resistant tumors. Therefore, we sought to identify perforin- and Fas-independent cytotoxic pathways and explored the potential of targeting LTbetaR with tumor-specific CTLs to induce tumor rejection in vivo.

EXPERIMENTAL DESIGN

Fas-resistant tumors were examined for their susceptibility to perforin-deficient (pfp) CTLs via CTL adoptive transfer in mouse models of experimental lung metastasis. The specificity of LTbetaR, a cell surface death receptor, in causing tumor rejection by CTLs was analyzed by LTbetaR-specific neutralizing monoclonal antibody in vitro. The specificity and efficacy of LTbetaR in the suppression of established tumors was further investigated by silencing LTbetaR in tumor cells in vivo.

RESULTS

pfp CTLs exhibited significant cytotoxicity against Fas-resistant tumors in vivo. The perforin- and Fas-independent cytotoxicity was directly mediated, at least in part, by the adoptively transferred CTLs. It was observed that LTbetaR was expressed on the tumor cell surface, and LTalpha, LTbeta, and LIGHT, all of which are ligands for LTbetaR, were either constitutively expressed or activated in the tumor-specific CTLs and primary CD8(+) T cells. Blocking LTbetaR with LTbetaR-specific neutralizing monoclonal antibody decreased CTL cytotoxicity in vitro. Silencing LTbetaR using LTbetaR-specific short hairpin RNA reduced the ability of pfp CTLs to induce tumor rejection in vivo.

CONCLUSION

LTbetaR directly mediates CTL-directed tumor rejection in vivo. Targeting LTbetaR with tumor-specific CTLs is a potential therapeutic approach.

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.