NF-kappaB signal triggering and termination by tumor necrosis factor receptor 2

Tumor microenvironment as niche constructed by cancer stem cells: Breaking the ecosystem to combat cancer

BACKGROUND

Cancer stem cells (CSCs) are a distinct subpopulation of cancer cells with the capacity to constantly self-renew and differentiate, and they are the main driver in the progression of cancer resistance and relapse. The tumor microenvironment (TME) constructed by CSCs is the "soil" adapted to tumor growth, helping CSCs evade immune killing, enhance their chemical resistance, and promote cancer progression.

AIM OF REVIEW

We aim to elaborate the tight connection between CSCs and immunosuppressive components of the TME. We attempt to summarize and provide a therapeutic strategy to eradicate CSCs based on the destruction of the tumor ecological niche.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review is focused on three main key concepts. First, we highlight that CSCs recruit and transform normal cells to construct the TME, which further provides ecological niche support for CSCs. Second, we describe the main characteristics of the immunosuppressive components of the TME, targeting strategies and summarize the progress of corresponding drugs in clinical trials. Third, we explore the multilevel insights of the TME to serve as an ecological niche for CSCs.

Identification and characterization of the tumor necrosis factor receptor superfamily in the Chinese tree shrew (Tupaia belangeri chinensis)

The tumor necrosis factor receptor superfamily (TNFRSF) plays a vital role in eliciting immune responses against infections. The tree shrew, closely related to primates, is often utilized in human disease models. Here, we analyzed TNFRSF members from 11 different animal species, including the Chinese tree shrew, and identified 24 tree shrew TNFRSF (tTNFRSF) genes, which were grouped into seven subcategories with similar motifs, sequences, and gene structures. As expected, the multi-species collinearity analysis revealed that tTNFRSF genome bears a greater resemblance to humans than to mice. Transcriptome data from 28 samples across ten organ types showed high TNFRSF expression predominantly in immune organs. It was seen that TNFRSF13C co-expresses consistently with the B cell surface marker CD79A, which is consistent with its characteristics in humans. The tissue distribution and co-expression were confirmed via RT-qPCR and immunofluorescence. Evaluation of transcriptome data from 70 samples infected with six types of viruses showed that most TNFRSF genes were upregulated in tree shrew post-viral infection. TNFRSF exerts antiviral function most probably through the activation of the NF-κB pathway, subsequently causing apoptosis of infected cells. Our findings provide evolutionary and functional insights into tTNFRSF, indicating its potential utility in human viral infection models.

Inflammation, physical activity, and disease-free survival in stage III colon cancer: Cancer and Leukemia Group B-Southwest Oncology Group 80702 (Alliance)

BACKGROUND

Inflammation and insufficient physical inactivity contribute to individual-level risk of disease recurrence and death in stage III colon cancer. The extent to which increased inflammatory risk can be offset by sufficient physical activity remains unknown.

METHODS

This cohort study was nested within the Cancer and Leukemia Group B (now part of the Alliance for Clinical Trials in Oncology) and Southwest Oncology Group randomized trial. Inflammatory burden was quantified by high-sensitivity C-reactive protein, interleukin-6, and soluble tumor necrosis factor-α receptor 2 after recovery from tumor resection. Physical activity was measured during and after postoperative chemotherapy. The primary endpoint was disease-free survival.

RESULTS

The 3-year disease-free survival rate was 88.4% among patients with low inflammation and sufficient physical activity (referent group for all comparisons), 84.9% with low inflammation and insufficient physical activity (absolute risk difference = -3.5 percentage points, 95% confidence interval [CI] = -11.3 to 4.3; P = .38), 78.0% with intermediate inflammation and insufficient physical activity (absolute risk difference = -10.4 percentage points, 95% CI = -17.4 to -3.3; P = .007), and 79.7% with high inflammation and insufficient physical activity (absolute risk difference = -8.7 percentage points, 95% CI = -15.7 to -1.6; P = .022). In contrast, the 3-year disease-free survival rate was 87.3% among patients with intermediate inflammation and sufficient physical activity (absolute risk difference = -1.1 percentage points, 95% CI = -7.5 to 5.3; P = .74) and 84.4% with high inflammation and sufficient physical activity (absolute risk difference = -4.0 percentage points, 95% CI = -12.3 to 4.3; P = .34).

CONCLUSION

In this observational study of stage III colon cancer patients, physical activity was associated with improved disease-free survival despite high inflammation. Patients with intermediate or high inflammation who were physically active had disease-free survival rates that were not statistically significantly different from those with low inflammation.

Understanding the role of TNFR2 signaling in the tumor microenvironment of breast cancer

Breast cancer (BC) is the most frequently diagnosed malignancy among women. It is characterized by a high level of heterogeneity that emerges from the interaction of several cellular and soluble components in the tumor microenvironment (TME), such as cytokines, tumor cells and tumor-associated immune cells. Tumor necrosis factor (TNF) receptor 2 (TNFR2) appears to play a significant role in microenvironmental regulation, tumor progression, immune evasion, drug resistance, and metastasis of many types of cancer, including BC. However, the significance of TNFR2 in BC biology is not fully understood. This review provides an overview of TNFR2 biology, detailing its activation and its interactions with important signaling pathways in the TME (e.g., NF-κB, MAPK, and PI3K/Akt pathways). We discuss potential therapeutic strategies targeting TNFR2, with the aim of enhancing the antitumor immune response to BC. This review provides insights into role of TNFR2 as a major immune checkpoint for the future treatment of patients with BC.

The dose-response effect of aerobic exercise on inflammation in colon cancer survivors

Background

Physical activity after surgical resection for colon cancer is associated with significantly longer disease-free survival. Inflammation is hypothesized to mediate the association between physical activity and disease-free survival in colon cancer.

Methods

In this exploratory analysis of a randomized dose-response trial, 39 colon cancer survivors who completed standard therapy were stratified by cancer stage and randomized in a 1:1:1 ratio to one of three treatment groups for 24 weeks of usual-care control, 150 min/wk of moderate-intensity aerobic exercise (low-dose), or 300 min/wk of moderate-intensity aerobic exercise (high-dose). Inflammation outcomes included high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL6), and soluble tumor necrosis factor-alpha receptor 2 (sTNFαR2). Mixed models for repeated measures were used to test the hypothesis that exercise was associated with dose-response reductions in inflammation; exploratory analyses examined treatment effects by cancer stage.

Results

In the overall population, aerobic exercise was not associated with dose-response reductions in hs-CRP, IL6, or sTNFαR2. Cancer stage modified the association between randomized group and hs-CRP (P=0.022) and IL6 (P<0.001) but not sTNFαR2 (P=0.39). In stage I-II disease, compared to control, exercise was not associated with inflammation outcomes. In stage III disease, compared to control, low-dose exercise reduced hs-CRP: -35.4% (95% CI: -70.1, -0.7) and IL6: -29.6% (95% CI: -58.4, -0.8) but not sTNFαR2: 2.7% (95% CI: sTNFαR2: -15.7, 21.1); high-dose exercise was not associated with inflammation outcomes in stage III disease.

Conclusion

This exploratory analysis offers preliminary data to support the hypothesis that inflammation may mediate the association between physical activity and disease-free survival in colon cancer.

Clinical trial registration

clinicaltrials.gov, identifier NCT02250053.

Therapeutic potential of TNFR2 agonists: a mechanistic perspective

TNFR2 agonists have been investigated as potential therapies for inflammatory diseases due to their ability to activate and expand immunosuppressive CD4+Foxp3+ Treg cells and myeloid-derived suppressor cells (MDSCs). Despite TNFR2 being predominantly expressed in Treg cells at high levels, activated effector T cells also exhibit a certain degree of TNFR2 expression. Consequently, the role of TNFR2 signaling in coordinating immune or inflammatory responses under different pathological conditions is complex. In this review article, we analyze possible factors that may determine the therapeutic outcomes of TNFR2 agonism, including the levels of TNFR2 expression on different cell types, the biological properties of TNFR2 agonists, and disease status. Based on recent progress in the understanding of TNFR2 biology and the study of TNFR2 agonistic agents, we discuss the future direction of developing TNFR2 agonists as a therapeutic agents.

TNF-α impairs EP4 signaling through the association of TRAF2-GRK2 in primary fibroblast-like synoviocytes

Our previous study showed that chronic treatment with tumor necrosis factor-α (TNF-α) decreased cAMP concentration in fibroblast-like synoviocytes (FLSs) of collagen-induced arthritis (CIA) rats. In this study we investigated how TNF-α impairs cAMP homeostasis, particularly clarifying the potential downstream molecules of TNF-α and prostaglandin receptor 4 (EP4) signaling that would interact with each other. Using a cAMP FRET biosensor PM-ICUE3, we demonstrated that TNF-α (20 ng/mL) blocked ONO-4819-triggered EP4 signaling, but not Butaprost-triggered EP2 signaling in normal rat FLSs. We showed that TNF-α (0.02-20 ng/mL) dose-dependently reduced EP4 membrane distribution in normal rat FLS. TNF-α significantly increased TNF receptor 2 (TNFR2) expression and stimulated proliferation in human FLS (hFLS) via ecruiting TNF receptor-associated factor 2 (TRAF2) to cell membrane. More interestingly, we revealed that TRAF2 interacted with G protein-coupled receptor kinase (GRK2) in the cytoplasm of primary hFLS and helped to bring GRK2 to cell membrane in response of TNF-α stimulation, the complex of TRAF2 and GRK2 then separated on the membrane, and translocated GRK2 induced the desensitization and internalization of EP4, leading to reduced production of intracellular cAMP. Silencing of TRAF2 by siRNA substantially diminished TRAF2-GRK2 interaction, blocked the translocation of GRK2, and resulted in upregulated expression of membrane EP4 and intracellular cAMP. In CIA rats, administration of paroxetine to inhibit GRK2 effectively improved the symptoms and clinic parameters with significantly reduced joint synovium inflammation and bone destruction. These results elucidate a novel form of cross-talk between TNFR (a cytokine receptor) and EP4 (a typical G protein-coupled receptor) signaling pathways. The interaction between TRAF2 and GRK2 may become a potential new drug target for the treatment of inflammatory diseases.

Anti-Tumor Necrosis Factor Receptor 2 Antibody Combined With Anti-PD-L1 Therapy Exerts Robust Antitumor Effects in Breast Cancer

Breast cancer is a leading type of malignant tumor in women; however, the immunotherapy in breast cancer is still underappreciated. In this study, we demonstrated that tumor necrosis factor receptor 2 (TNFR2) is highly expressed in both breast tumor tissue and tumor-infiltrating immunosuppressive CD4⁺Foxp3⁺ regulatory T cells (Tregs). We found that TNFR2 antagonistic antibody reduced Foxp3 expression and the proliferation of Tregs and impaired the inhibitory effect of Tregs on CD4⁺CD25^– effector T (Teff) cells in a dose-dependent manner. The treatment of anti-TNFR2 antibody not only inhibited the proliferation of breast tumor cells in vitro but also suppressed the tumorigenesis of murine mammary carcinoma 4T1 cells in vivo. Mice recovered from tumor growth also developed 4T1-specific immunity. Furthermore, we demonstrated that anti-TNFR2 antibody in combination with anti-PD-L1 exhibited augmented antitumor effects than monotherapy. Anti-TNFR2 treatment also tended to increase the expression of proinflammatory cytokines in tumor tissues. In conclusion, our study suggests that TNFR2 antagonist could potentially offer a clinical benefit as a single agent or in combination with immune checkpoint blockade treatment for breast cancer immunotherapy.

LILRB3 supports acute myeloid leukemia development and regulates T-cell antitumor immune responses through the TRAF2-cFLIP-NF-κB signaling axis

Leukocyte immunoglobulin-like receptor B (LILRB), a family of immune checkpoint receptors, contributes to acute myeloid leukemia (AML) development, but the specific mechanisms triggered by activation or inhibition of these immune checkpoints in cancer is largely unknown. Here we demonstrate that the intracellular domain of LILRB3 is constitutively associated with the adaptor protein TRAF2. Activated LILRB3 in AML cells leads to recruitment of cFLIP and subsequent NF-κB upregulation, resulting in enhanced leukemic cell survival and inhibition of T-cell-mediated anti-tumor activity. Hyperactivation of NF-κB induces a negative regulatory feedback loop mediated by A20, which disrupts the interaction of LILRB3 and TRAF2; consequently the SHP-1/2-mediated inhibitory activity of LILRB3 becomes dominant. Finally, we show that blockade of LILRB3 signaling with antagonizing antibodies hampers AML progression. LILRB3 thus exerts context-dependent activating and inhibitory functions, and targeting LILRB3 may become a potential therapeutic strategy for AML treatment.

Cytokine TNF-α and its receptors TNFRI and TNFRII play a key role in the in vitro proliferative response of BLV infected animals

Bovine leukemia virus (BLV) main host cells are B lymphocytes. Infected animals can be classified into high or low proviral load (HPL or LPL respectively), regarding the number of proviral copies infected lymphocytes they carry. After infection, there is an overexpression of several cytokines, particularly TNF-α, which has a delicate regulation mediated by receptors TNFRI and TNFRII; the first one involved with apoptosis, while the other stimulates cell proliferation. The study aimed to quantify TNF-α and its receptors mRNA expression, and in which extent in vitro proliferation was affected, in peripheral blood mononuclear cells (PBMC) from BLV-infected animals with different proviral loads, after the addition or not of synthetic TNF-α (rTNF-α) for 48 h. PBMC from BLV-infected animals showed spontaneous proliferation after 48 h in culture but did not show changes in proliferation rates after 48 h incubation in the presence of the rTNF-α. TNF-α mRNA expression after 48 h culture without exogenous stimulation was significantly lower, regardless of the proviral load of the donor, compared to non-infected animals. In the LPL animals, the expression of TNF-α mRNA was significantly lower with respect to the control group while the expression of TNFRI mRNA was significantly increased. The HPL animals showed a significant decrease in the expression of TNF-α and TNFRII mRNA respect to the control group. After 48 h incubation with rTNF-α, PBMC from infected animals had different responses: TNF-α and TNFRI mRNA expression was reduced in PBMC from the LPL group compared to the BLV negative group, but no differences were observed in PBMC from the HPL group. TNFRII mRNA expression showed no differences between HPL, LPL, and BLV negative groups, though HPL animals expressed 10.35 times more TNFRI mRNA than LPL. These results support the hypothesis that LPL animals, when faced with viral reactivation, present a pro-apoptotic and anti-proliferative state. However, complementary studies are needed to explain the influence of TNFRII on the development of the HLP profile. On the other hand, exogenous stimulation studies reinforce the hypothesis that BLV infection compromises the immune response of the animals.

Effect of Exercise or Metformin on Biomarkers of Inflammation in Breast and Colorectal Cancer: A Randomized Trial

Observational studies report that physical activity and metformin are associated with improved clinical outcome in patients with cancer. Inflammation is one biological mechanism hypothesized to mediate these associations. In this phase II, multicenter, 2 × 2 factorial trial, 139 patients with breast and colorectal cancer who completed standard therapy were randomized to one of four treatment groups for 12 weeks: exercise alone, metformin alone, exercise and metformin, or control. Inflammation outcomes included high-sensitivity C-reactive protein (hs-CRP), soluble tumor necrosis factor alpha receptor two (sTNFαR2), and IL6. The primary modeling strategy evaluated the trial product estimand that was quantified using a generalized linear mixed model. Compared with control, exercise alone reduced hs-CRP [-30.2%; 95% confidence interval (CI), -50.3, -1.0] and IL6 (-30.9%; 95% CI, -47.3, -9.5) but did not change sTNFαR2 (1.0%; 95% CI, -10.4, 13.9). Compared with control, metformin alone did not change hs-CRP (-13.9%; 95% CI, -40.0, 23.4), sTNFαR2 (-10.4%; 95% CI, -21.3, 2.0), or IL6 (-22.9%; 95% CI, -42.3, 2.0). Compared with control, exercise and metformin reduced sTNFαR2 (-13.1%; 95% CI, -22.9, -1.0) and IL6 (-38.7%; 95% CI, -52.3, -18.9) but did not change hs-CRP (-20.5%; 95% CI, -44.0, 12.7). The combination of exercise and metformin was not synergistic for hs-CRP, sTNFαR2, or IL6. In survivors of breast and colorectal cancer with low baseline physical activity and without type 2 diabetes, exercise and metformin reduced measures of inflammation that are associated with cancer recurrence and mortality.

Dry eye induced by exposure to cigarette smoke pollution: An in vivo and in vitro study

Exposure to cigarette smoke (CS) pollution has previously associated with dry eye symptoms but without detailed experimental data and elucidation of the mechanism. We aimed to evaluate the effects of CS on the ocular surfaces of mice and the extraction of DMSO lipid-soluble cigarette smoke particles (DCSP) on cultured human corneal epithelial cells (HCECs), and explore to elucidate the probable mechanism. C57BL mice were exposed to CS challenging. In vivo clinical evaluations, including corneal fluorescein staining, tear film break-up time, and confocal microscopic observations, were performed before exposure and post-exposure. At the end of the in vivo study, changes in corneal and conjunctival histology, corneal ultrastructure, and conjunctival goblet cell intensity were examined, expression of TUNLE and Ki67 in tissue were also detected. In vitro, cell confluence and caspase3/7 were assessed in DCSP treated HCECs. Production of TNF-α, IL-1β and IL-6, activation of NF-κB and Ki67 were evaluated by means of ELISA and Western blot respectively in HCECs cultured with 0.6 μL/mL DCSP. We found that longer-term CS exposure induced dry eye symptoms in mice. Additionally, corneal and conjunctival epithelial damage occurred, the corneal ultrastructure changed, and the density of goblet cells decreased. Apoptosis and Ki67 increased in both the conjunctiva and the cornea of CS-exposed animals. Furthermore, although DCSP inhibited the proliferation of HCECs, expression of Ki67 increased and apoptosis was only induced significantly by 2.0 μL/mL DCSP. The release of IL-1β and IL-6, activation of NF-κB were prompted by DCSP. The results indicated that CS is toxic to the ocular surface of mice and HCECs. Longer-term CS exposure in mice stimulates ocular surface changes that resemble those observed with dry eye. The mechanism may relate to inflammation and activation of NF-κB. In this study, we established a novel animal model to study dry eye, with the experimental data and elucidation of mechanism facilitating further research.

Pathophysiological landscape of osteoarthritis

A sharp rise in osteoarthritis (OA) incidence is expected as over 25% of world population ages in the coming decade. Although OA is considered a degenerative disease, mounting evidence suggests a strong connection with chronic metabolic conditions and low-grade inflammation. OA pathology is increasingly understood as a complex interplay of multiple pathological events including oxidative stress, synovitis and immune responses revealing its intricate nature. Cellular, biochemical and molecular aspects of these pathological events along with major outcomes of the relevant research studies in this area are discussed in the present review. With reference to their published and unpublished work, the authors strongly propose synovitis as a central OA pathology and the key OA pathological events are described in connection with it. Recent research outcomes also have succeeded to establish a linkage between metabolic syndrome and OA, which has been precisely included in the present review. Impact of aging process cannot be neglected in OA. Cell senescence is an important mechanism of aging through which it facilitates development of OA like other degenerative disorders, also discussed within a frame of OA. Conclusively, the reviewers urge low-grade inflammation linked to aging and derailed immune function as a pathological platform for OA development and progression. Thus, interventions targeted to prevent inflammaging hold a promising potential in effective OA management and efforts should be invested in this direction.

Selective inhibition of Tumor necrosis factor receptor-1 (TNFR1) for the treatment of autoimmune diseases

Anti-TNF biologics have achieved great success in the treatment of autoimmune diseases and have been the most selling biologics on market. However, the anti-TNF biologics have shown some disadvantages such as poor efficacy to some patients and high risk of infection and malignancies during clinical application. Current anti-TNF biologics are antibodies or antibody fragments that bind to TNF-α and subsequently block both TNF-TNFR1 and TNF-TNFR2 signaling. Transgenic animal studies indicate that TNFR1 signaling is responsible for chronic inflammation and cell apoptosis whereas TNFR2 signaling regulates tissue regeneration and inflammation. Recent studies propose to selectively inhibit TNFR1 to enhance efficacy and avoid side effects. In this review, we introduce the biology of TNF-TNFR1 and TNF-TNFR2 signaling, the advantages of selective inhibition of TNF-TNFR1 signaling and research updates on the development of selective inhibitors for TNF-TNFR1 signaling. Antibodies, small molecules and aptamers that selectively inhibit TNFR1 have showed therapeutic potential and less side effects in preclinical studies. Development of selective inhibitors for TNFR1 is a good strategy to enhance the efficacy and reduce the side effects of anti-TNF inhibitors and will be a trend for next-generation of anti-TNF inhibitors.

Tumour Necrosis Factor Alpha in Intestinal Homeostasis and Gut Related Diseases

The intestinal epithelium constitutes an indispensable single-layered barrier to protect the body from invading pathogens, antigens or toxins. At the same time, beneficial nutrients and water have to be absorbed by the epithelium. To prevent development of intestinal inflammation or tumour formation, intestinal homeostasis has to be tightly controlled and therefore a strict balance between cell death and proliferation has to be maintained. The proinflammatory cytokine tumour necrosis factor alpha (TNFα) was shown to play a striking role for the regulation of this balance in the gut. Depending on the cellular conditions, on the one hand TNFα is able to mediate cell survival by activating NFκB signalling. On the other hand, TNFα might trigger cell death, in particular caspase-dependent apoptosis but also caspase-independent programmed necrosis. By regulating these cell death and survival mechanisms, TNFα exerts a variety of beneficial functions in the intestine. However, TNFα signalling is also supposed to play a critical role for the pathogenesis of inflammatory bowel disease (IBD), infectious diseases, intestinal wound healing and tumour formation. Here we review the literature about the physiological and pathophysiological role of TNFα signalling for the maintenance of intestinal homeostasis and the benefits and difficulties of anti-TNFα treatment during IBD.

Identification and functional characterization of grass carp (Ctenopharyngodon idella) tumor necrosis factor receptor 2 and its soluble form with potentiality for targeting inflammation

Tumor necrosis factor-alpha (TNF-α) signals through two distinct cell surface receptors, TNFR1 and TNFR2 in mammals. In the present study, grass carp Tnfr2 (gcTnfr2) was isolated and characterized. Sequence alignment and phylogenetic analysis suggested that gcTnfr2 was a homolog of goldfish and zebrafish Tnfr2. Tissue distribution assay showed gctnfr2 transcripts were expressed in all examined tissues similar to gctnfr1. To functionally characterize the newly cloned molecule, gcTnfr2 was overexpressed in COS7 cell lines and it showed the ability to mediate the recombinant grass carp Tnf (rgcTnf)-α-triggered NF-κΒ activity and gcil1b promoter activity, clarifying its role in mediating Tnf-α signaling. The recombinant soluble form of gcTnfr2 (rgcsTnfr2) was prepared and it was able to interact with rgcTnf-α with higher affinity than that of rgcsTnfr1. Moreover, grass carp soluble Tnfr2 (gcsTnfr2) were detected in the culture medium of grass carp head kidney leukocytes (HKLs) and heat-inactivated A. hydrophila challenge significantly induced its production, indicating involvement of gcsTnfr2 in inflammation response. In agreement with this notion, rgcsTnfr2 effectively antagonized the effect of rgcTnf-α on il1b mRNA expression in HKLs, suggesting anti-Tnf-α property of gcsTnfr2. To strengthen the anti-inflammatory role of soluble Tnfr2, bacteria were injected intraperitoneally in grass carp followed by rgcsTnfr2. Hematoxylin-eosin (HE) staining of head kidney, spleen and intestine showed that rgcsTnfr2 could significantly improve infection-induced histopathological changes. These results functionally identified gcTnfr2 and its soluble form, particularly highlighting the role of gcsTnfr2 against Tnf-α-triggered inflammatory signaling. In this line, rgcsTnfr2 displayed anti-inflammatory potentiality during infection, thereby providing a powerful mediator of inflammation control in fish.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Tumor Necrosis Factor Receptor Superfamily in T Cell Priming and Effector Function

The tumor necrosis factor receptor superfamily (TNFRSF) and their ligands mediate lymphoid tissue development and homeostasis in addition to key aspects of innate and adaptive immune responses. T cells of the adaptive immune system express a number of TNFRSF members that are used to receive signals at different instructive stages and produce several tumor necrosis factor superfamily (TNFSF) members as effector molecules. There is also one example of a TNFRSF member serving as a ligand for negative regulatory checkpoint receptors. In most cases, the ligands in afferent and efferent phases are membrane proteins and thus the interaction with TNFRSF members must take place in immunological synapses and other modes of cell-cell interaction. A particular feature of the TNFRSF-mediated signaling is the prominent use of linear ubiquitin chains as scaffolds for signaling complexes that activate nuclear factor κ-B and Fos/Jun transcriptional regulators. This review will focus on the signaling mechanisms triggered by TNFRSF members in their role as costimulators of early and late phases of T cell instruction and the delivery mechanism of TNFSF members through the immunological synapses of helper and cytotoxic effector cells.

TNF Receptor 2 Makes Tumor Necrosis Factor a Friend of Tumors

Tumor necrosis factor (TNF) is widely accepted as a tumor-suppressive cytokine via its ubiquitous receptor TNF receptor 1 (TNFR1). The other receptor, TNFR2, is not only expressed on some tumor cells but also on suppressive immune cells, including regulatory T cells and myeloid-derived suppressor cells. In contrast to TNFR1, TNFR2 diverts the tumor-inhibiting TNF into a tumor-advocating factor. TNFR2 directly promotes the proliferation of some kinds of tumor cells. Also activating immunosuppressive cells, it supports immune escape and tumor development. Hence, TNFR2 may represent a potential target of cancer therapy. Here, we focus on expression and role of TNFR2 in the tumor microenvironment. We summarize the recent progress in understanding how TNFR2-dependent mechanisms promote carcinogenesis and tumor growth and discuss the potential value of TNFR2 in cancer treatment.

Autocrine Tnf signaling favors malignant cells in myelofibrosis in a Tnfr2-dependent fashion

Tumor necrosis factor alpha (TNF) is increased in myelofibrosis (MF) and promotes survival of malignant over normal cells. The mechanisms altering TNF responsiveness in MF cells are unknown. We show that the proportion of marrow (BM) cells expressing TNF is increased in MF compared to controls, with the largest differential in primitive cells. Blockade of TNF receptor 2 (TNFR2), but not TNFR1, selectively inhibited colony formation by MF CD34⁺ and mouse JAK2^V617F progenitor cells. Microarray of mouse MPN revealed reduced expression of X-linked inhibitor of apoptosis (Xiap) and mitogen-activated protein kinase 8 (Mapk8) in JAK2^V617F relative to JAK2^WT cells, which were normalized by TNFR2 but not TNFR1 blockade. XIAP and MAPK8 were also reduced in MF CD34⁺ cells compared to normal BM, and their ectopic expression induced apoptosis. Unlike XIAP, expression of cellular IAP (cIAP) protein was increased in MF CD34⁺ cells. Consistent with cIAP's role in NF-κB activation, TNF-induced NF-κB activity was higher in MF vs. normal BM CD34⁺ cells. This suggests that JAK2^V617F reprograms TNF response toward survival by downregulating XIAP and MAPK8 through TNFR2. Our results reveal an unexpected pro-apoptotic role for XIAP in MF and identify TNFR2 as a key mediator of TNF-induced clonal expansion.

The Significance of Tumor Necrosis Factor Receptor Type II in CD8+ Regulatory T Cells and CD8+ Effector T Cells

Tumor necrosis factor (TNF) is a pleiotropic cytokine that has both pro-inflammatory and anti-inflammatory functions. The biological functions of TNF are mediated by two receptors, TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). TNFR1 is expressed universally on almost all cell types and has been extensively studied, whereas TNFR2 is mainly restricted to immune cells and some tumor cells and its role is far from clarified. Studies have shown that TNFR2 mediates the stimulatory activity of TNF on CD4⁺Foxp3⁺ regulatory T cells (Tregs) and CD8⁺Foxp3⁺ Tregs, and is involved in the phenotypic stability, proliferation, activation, and suppressive activity of Tregs. TNFR2 can also be expressed on CD8⁺ effector T cells (Teffs), which delivers an activation signal and cytotoxic ability to CD8⁺ Teffs during the early immune response, as well as an apoptosis signal to terminate the immune response. TNFR2-induced abolition of TNF receptor-associated factor 2 (TRAF2) degradation may play an important role in these processes. Consequently, due to the distribution of TNFR2 and its pleiotropic effects, TNFR2 appears to be critical to keeping the balance between Tregs and Teffs, and may be an efficient therapeutic target for tumor and autoimmune diseases. In this review, we summarize the biological functions of TNFR2 expressed on CD8⁺Foxp3⁺ Tregs and CD8⁺ Teffs, and highlight how TNF uses TNFR2 to coordinate the complex events that ultimately lead to efficient CD8⁺ T cell-mediated immune responses.

An Autocrine TNFα-Tumor Necrosis Factor Receptor 2 Loop Promotes Epigenetic Effects Inducing Human Treg Stability In Vitro

A crucial issue for Treg-based immunotherapy is to maintain a bona fide Treg phenotype as well as suppressive function during and after ex vivo expansion. Several strategies have been applied to harness Treg lineage stability. For instance, CD28 superagonist stimulation in vitro, in the absence of CD3 ligation, is more efficient in promoting Treg proliferation, and prevention of pro-inflammatory cytokine expression, such as IL-17, as compared to CD3/CD28-stimulated Treg. Addition of the mTOR inhibitor rapamycin to Treg cultures enhances FOXP3 expression and Treg stability, but does impair proliferative capacity. A tumor necrosis factor receptor 2 (TNFR2) agonist antibody was recently shown to favor homogenous expansion of Treg in vitro. Combined stimulation with rapamycin and TNFR2 agonist antibody enhanced hypo-methylation of the FOXP3 gene, and thus promoting Treg stability. To further explore the underlying mechanisms of rapamycin and TNFR2 agonist-mediated Treg stability, we here stimulated FACS-sorted human Treg with a CD28 superagonist, in the presence of rapamycin and a TNFR2 agonist. Phenotypic analysis of expanded Treg revealed an autocrine loop of TNFα-TNFR2 underlying the maintenance of Treg stability in vitro. Addition of rapamycin to CD28 superagonist-stimulated Treg led to a high expression of TNFR2, the main TNFR expressed on Treg, and additional stimulation with a TNFR2 agonist enhanced the production of soluble as well as membrane-bound TNFα. Moreover, our data showed that the expression of histone methyltransferase EZH2, a crucial epigenetic modulator for potent Treg suppressor function, was enhanced upon stimulation with CD28 superagonist. Interestingly, rapamycin seemed to downregulate CD28 superagonist-induced EZH2 expression, which could be rescued by the additional addition of TNFR2 agonist antibody. This process appeared TNFα-dependent manner, since depletion of TNFα using Etanercept inhibited EZH2 expression. To summarize, we propose that an autocrine TNFα-TNFR2 loop plays an important role in endorsing Treg stability.

Forward and Reverse Signaling Mediated by Transmembrane Tumor Necrosis Factor-Alpha and TNF Receptor 2: Potential Roles in an Immunosuppressive Tumor Microenvironment

Tumor necrosis factor-alpha (TNF-α) is a pleiotropic inflammatory cytokine produced mainly by activated macrophages, lymphocytes and other cell types. Two distinct forms of TNF-α have been identified: soluble TNF-α (sTNF-α) and transmembrane TNF-α (mTNF-α). mTNF-α, which is the precursor of sTNF-α, can be cleaved by the TNF-α converting enzyme (TACE) and is released as sTNF-α. sTNF-α binds primarily to TNF receptor 1 (TNFR1) and plays an important role in the inflammatory immune response, whereas mTNF-α interacts primarily with TNF receptor 2 (TNFR2) and mediates the promotion of cellular proliferation and survival and other biological effects. It has been reported that the interaction between mTNF-α and TNFR2 induces bi-directional (forward and reverse) signaling in both mTNF-α- and TNFR2-expressing cells. Increasing evidence shows that the forward and reverse signaling mediated by mTNF-α and TNFR2 might play a significant role in the tumor microenvironment. In this review, the role of the crosstalk between mTNF-α and TNFR2 in the tumor microenvironment will be discussed.

Autophagy of metallothioneins prevents TNF-induced oxidative stress and toxicity in hepatoma cells

Lysosomal membrane permeabilization (LMP) induced by oxidative stress has recently emerged as a prominent mechanism behind TNF cytotoxicity. This pathway relies on diffusion of hydrogen peroxide into lysosomes containing redox-active iron, accumulated by breakdown of iron-containing proteins and subcellular organelles. Upon oxidative lysosomal damage, LMP allows relocation to the cytoplasm of low mass iron and acidic hydrolases that contribute to DNA and mitochondrial damage, resulting in death by apoptosis or necrosis. Here we investigate the role of lysosomes and free iron in death of HTC cells, a rat hepatoma line, exposed to TNF following metallothionein (MT) upregulation. Iron-binding MT does not normally occur in HTC cells in significant amounts. Intracellular iron chelation attenuates TNF and cycloheximide (CHX)-induced LMP and cell death, demonstrating the critical role of this transition metal in mediating cytokine lethality. MT upregulation, combined with starvation-activated MT autophagy almost completely suppresses TNF and CHX toxicity, while impairment of both autophagy and MT upregulation by silencing of Atg7, and Mt1a and/or Mt2a, respectively, abrogates protection. Interestingly, MT upregulation by itself has little effect, while stimulated autophagy alone depresses cytokine toxicity to some degree. These results provide evidence that intralysosomal iron-catalyzed redox reactions play a key role in TNF and CHX-induced LMP and toxicity. The finding that chelation of intralysosomal iron achieved by autophagic delivery of MT, and to some degree probably of other iron-binding proteins as well, into the lysosomal compartment is highly protective provides a putative mechanism to explain autophagy-related suppression of death by TNF and CHX.

Endogenous Transmembrane TNF-Alpha Protects Against Premature Senescence in Endothelial Colony Forming Cells

RATIONALE

Transmembrane tumor necrosis factor-α (tmTNF-α) is the prime ligand for TNF receptor 2, which has been shown to mediate angiogenic and blood vessel repair activities in mice. We have previously reported that the angiogenic potential of highly proliferative endothelial colony-forming cells (ECFCs) can be explained by the absence of senescent cells, which in mature endothelial cells occupy >30% of the population, and that exposure to a chronic inflammatory environment induced premature, telomere-independent senescence in ECFCs.

OBJECTIVE

The goal of this study was to determine the role of tmTNF-α in the proliferation of ECFCs.

METHODS AND RESULTS

Here, we show that tmTNF-α expression on ECFCs selects for higher proliferative potential and when removed from the cell surface promotes ECFC senescence. Moreover, the induction of premature senescence by chronic inflammatory conditions is blocked by inhibition of tmTNF-α cleavage. Indeed, the mechanism of chronic inflammation-induced premature senescence involves an abrogation of tmTNF/TNF receptor 2 signaling. This process is mediated by activation of the tmTNF cleavage metalloprotease TNF-α-converting enzyme via p38 MAP kinase activation and its concurrent export to the cell surface by means of increased iRhom2 expression.

CONCLUSIONS

Thus, we conclude that tmTNF-α on the surface of highly proliferative ECFCs plays an important role in the regulation of their proliferative capacity.

The SREC-I and SREC-II associated with epidermal growth factor in scavenger receptor family are the potential regulative transmembrane receptors in Larimichthys crocea

In innate immunity, the regulation of the immunologic gene expression plays a vital role in defense against pathogenic threat. The class F scavenger receptors (SCARFs), a kind of crucial immunologic type I transmembrane receptors, mainly involve in the signal transmission and eliminating pathogens in host immune system. In this study, the SREC-I and SREC-II of SCARFs in Larimichthys crocea (designated as LycSREC1 and LycSREC2 respectively) were first identified, the potential genetic locus relationships with other species were depicted and the features of gene expression after Vibrio alginolyticus stimulation were tested. The results demonstrated that the complete ORF sequences of two candidates were 3024 bp and 2832 bp (KM884873 and KM884874) respectively including some important domains and motifs, such as EGF/EGF-like domains, TRAF2-binding consensus motif, generic motif and atipical motif. The gene location maps and genetic locus interpreted that the DNA sequences of LycSREC1 and LycSREC2 were 7603 bp and 4883 bp, and some locus had changed compared with human being, but three more crucial genetic locus were conservative among ten species. Furthermore, quantitative real-time PCR (qRT-PCR) analysis indicated that the highest mRNA expression of LycSREC1 and LycSREC2 were both in liver among eight detected tissues, and their expression were up-regulated by V. alginolyticus stimulation. All these findings would contribute to better understanding the biologic function of SCARFs in defending against pathogenic bacteria challenge and further exploring the innate immune of sciaenidae fish.

c-Jun N-terminal kinase attenuates TNFα signaling by reducing Nox1-dependent endosomal ROS production in vascular smooth muscle cells

Tumor necrosis factor-α (TNFα), a proinflammatory cytokine, causes vascular smooth muscle cell (VSMC) proliferation and migration and promotes inflammatory vascular lesions. Nuclear factor-kappa B (NF-κB) activation by TNFα requires endosomal superoxide production by Nox1. In endothelial cells, TNFα stimulates c-Jun N-terminal kinase (JNK), which inhibits NF-κB signaling. The mechanism by which JNK negatively regulates TNFα-induced NF-κB activation has not been defined. We hypothesized that JNK modulates NF-κB activation in VSMC, and does so via a Nox1-dependent mechanism. TNFα-induced NF-κB activation was TNFR1- and endocytosis-dependent. Inhibition of endocytosis with dominant-negative dynamin (DynK44A) potentiated TNFα-induced JNK activation, but decreased ERK activation, while p38 kinase phosphorylation was not altered. DynK44A attenuated intracellular, endosomal superoxide production in wild-type (WT) VSMC, but not in NADPH oxidase 1 (Nox1) knockout (KO) cells. siRNA targeting JNK1 or JNK2 potentiated, while a JNK activator (anisomycin) inhibited, TNFα-induced NF-κB activation in WT, but not in Nox1 KO cells. TNFα-stimulated superoxide generation was enhanced by JNK1 inhibition in WT, but not in Nox1 KO VSMC. These data suggest that JNK suppresses the inflammatory response to TNFα by reducing Nox1-dependent endosomal ROS production. JNK and endosomal superoxide may represent novel targets for pharmacologic modulation of TNFα signaling and vascular inflammation.

Genomic analysis of mycosis fungoides and Sézary syndrome identifies recurrent alterations in TNFR2

Mycosis fungoides and Sézary syndrome comprise the majority of cutaneous T cell lymphomas (CTCLs), disorders notable for their clinical heterogeneity that can present in skin or peripheral blood. Effective treatment options for CTCL are limited, and the genetic basis of these T cell lymphomas remains incompletely characterized. Here we report recurrent point mutations and genomic gains of TNFRSF1B, encoding the tumor necrosis factor receptor TNFR2, in 18% of patients with mycosis fungoides and Sézary syndrome. Expression of the recurrent TNFR2 Thr377Ile mutant in T cells leads to enhanced non-canonical NF-κB signaling that is sensitive to the proteasome inhibitor bortezomib. Using an integrative genomic approach, we additionally discovered a recurrent CTLA4-CD28 fusion, as well as mutations in downstream signaling mediators of these receptors.

Endoplasmic reticulum stress impairs insulin receptor signaling in the brains of obese rats

The incidence of obesity is increasing worldwide. It was reported that endoplasmic reticulum stress (ERS) could inhibit insulin receptor signaling by activating c-Jun N-terminal kinase (JNK) in the liver. However, the relationship between ERS and insulin receptor signaling in the brain during obesity remains unclear. The aim of the current study was to assess whether ERS alters insulin receptor signaling through the hyper-activation of JNK in the hippocampus and frontal cortex in the brains of obese rats. Obesity was induced using a high fat diet (HFD). The Morris water maze test was then performed to evaluate decreases in cognitive function, and western blot was used to verify whether abnormal insulin receptor signaling was induced by ERS in HFD rats exhibiting cognitive decline. In addition, to determine whether ERS activated JNK and consequently impaired insulin receptor signaling, SH-SY5Y cells were treated with the JNK inhibitor, SP600125, followed by tunicamycin or thapsigargin, and primary rat hippocampal and cortical neurons were transfected with siRNA against IRE1α and JNK. We found that the expression of phosphorylation of PKR-like kinase (PERK), phosphorylation of α subunit of translation initiation factor 2 (eIF2α), and phosphorylation of inositol-requiring kinase-1α (IRE-1α) were increased in the brains of rats with HFD when compared with control rats. The level of serine phosphorylation of insulin receptor substrate-1 (IRS-1) was also increased, while protein kinase B (PKB/Akt) was reduced. ERS was also found to inhibit insulin receptor signaling via the activation of JNK in SH-SY5Y cells, primary rat hippocampal, and cortical neurons. These results indicate that ERS was increased, thereby resulting in impaired insulin receptor signaling in the hippocampus and frontal cortex of obese rats.

Bovine leukemia virus: a major silent threat to proper immune responses in cattle

Bovine leukemia virus (BLV) infection is widespread in the US dairy industry and the majority of producers do not actively try to manage or reduce BLV incidence within their herds. However, BLV is estimated to cost the dairy industry hundreds of millions of dollars annually and this is likely a conservative estimate. BLV is not thought to cause animal distress or serious pathology unless infection progresses to leukemia or lymphoma. However, a wealth of research supports the notion that BLV infection causes widespread abnormal immune function. BLV infection can impact cells of both the innate and adaptive immune system and alter proper functioning of uninfected cells. Despite strong evidence of abnormal immune signaling and functioning, little research has investigated the large-scale effects of BLV infection on host immunity and resistance to other infectious diseases. This review focuses on mechanisms of immune suppression associated with BLV infection, specifically aberrant signaling, proliferation and apoptosis, and the implications of switching from BLV latency to activation. In addition, this review will highlight underdeveloped areas of research relating to BLV infection and how it causes immune suppression.

A TRAF2 binding independent region of TNFR2 is responsible for TRAF2 depletion and enhancement of cytotoxicity driven by TNFR1

Tumor Necrosis Factor (TNF) interacts with two receptors known as TNFR1 and TNFR2. TNFR1 activation may result in either cell proliferation or cell death. TNFR2 activates Nuclear Factor-kappaB (NF-kB) and c-Jun N-terminal kinase (JNK) which lead to transcriptional activation of genes related to cell proliferation and survival. This depends on the binding of TNF Receptor Associated Factor 2 (TRAF2) to the receptor. TNFR2 also induces TRAF2 degradation. In this work we have investigated the structural features of TNFR2 responsible for inducing TRAF2 degradation and have studied the biological consequences of this activity. We show that when TNFR1 and TNFR2 are co-expressed, TRAF2 depletion leads to an enhanced TNFR1 cytotoxicity which correlates with the inhibition of NF-kB. NF-kB activation and TRAF2 degradation depend of different regions of the receptor since TNFR2 mutants at amino acids 343-349 fail to induce TRAF2 degradation and have lost their ability to enhance TNFR1-mediated cell death but are still able to activate NF-kB. Moreover, whereas NF-kB activation requires TRAF2 binding to the receptor, TRAF2 degradation appears independent of TRAF2 binding. Thus, TNFR2 mutants unable to bind TRAF2 are still able to induce its degradation and to enhance TNFR1-mediated cytotoxicity. To test further this receptor crosstalk we have developed a system stably expressing in cells carrying only endogenous TNFR1 the chimeric receptor RANK-TNFR2, formed by the extracellular region of RANK (Receptor activator of NF-kB) and the intracellular region of TNFR2.This has made possible to study independently the signals triggered by TNFR1 and TNFR2. In these cells TNFR1 is selectively activated by soluble TNF (sTNF) while RANK-TNFR2 is selectively activated by RANKL. Treatment of these cells with sTNF and RANKL leads to an enhanced cytotoxicity.

Identification of SCARA3, SCARA5 and MARCO of class A scavenger receptor-like family in Pseudosciaena crocea

The class A scavenger receptors are important pattern recognition receptors of the innate immune system in living organisms. According to the whole-genome data of large yellow croaker (Pseudosciaena crocea), three kinds of scavenger receptors, SCARA3, SCARA5 and MARCO were cloned from the spleen, designated severally as TycSA3, TycSA5 and TycMAC. The complete cDNAs open reading frames (ORF) of TycSA3, TycSA5 and TycMAC were 1938 bp, 1677 bp and 1218 bp (GenBank accession no. KJ467772, KJ467773 and KJ467771), encoding 645, 558 and 405 amino acid (aa) residues respectively. The BLASTp analysis strongly suggested that the sequences shared high similarity with known SCARA3, SCARA5 and MARCO. The phylogenetic relationship analysis illustrated that different subtype of SRs formed their own separate branches, TycSA3 and TycSA5 were placed in SCARA3 and SCARA5 branch of Osteichthyes fish respectively with strong bootstrap support. Curiously, the TycMAC was clustered with Alligator sinensis. ClustalW analysis with amino acid sequences revealed that the proportion of identity with other species was 59-71% for TycSA3 and 55-72% for TycSA5, but the scale of TycMAC was considerable lower than those of other two genes (only approximately 38%). The SR family motifs, such as transmembrane helix region, colied coli region and collagens region in the TycSA3, TycSA5 and TycMAC were conserved. There was an optional cysteine-rich (SRCR) domain (from 457 to 557 residues) containing 6 conserved cysteines (C-482, C-495, C-526, C-536, C-546 and C-556) in TycSA5. Likewise, the SRCR domains of TycMAC (from 310 to 405 residues) also contained C-333, C-346, C-374, C-384, C-394 and C-404 cysteines residues. Particularly, there were the major TRAF2-binding consensus motif and two main motifs on internalization of receptor in TycSA3 and TycSA5. The gene structures of different species were analyzed with GeneMaper v2.5, and the number of introns and exons of TycSA3, TycSA5 and TycMAC in DNA sequences were different, for example some corresponding exon regions were divided into several smaller exon portions. Furthermore, quantitative real-time PCR (qRT-PCR) analysis indicated the highest mRNA expression of TycSA3, TycSA5 and TycMAC all appeared in spleen among eight detected tissues, and the expression of them were up-regulated in spleen after Vibrio alginolyticus injection. All these results demonstrated that class A SRs played a significant role in the defense against pathogenic bacteria infection in innate immune of sciaenidae fish.

Network dynamics determine the autocrine and paracrine signaling functions of TNF

A hallmark of the inflammatory response to pathogen exposure is the production of tumor necrosis factor (TNF) that coordinates innate and adaptive immune responses by functioning in an autocrine or paracrine manner. Numerous molecular mechanisms contributing to TNF production have been identified, but how they function together in macrophages remains unclear. Here, we pursued an iterative systems biology approach to develop a quantitative understanding of the regulatory modules that control TNF mRNA synthesis and processing, mRNA half-life and translation, and protein processing and secretion. By linking the resulting model of TNF production to models of the TLR-, the TNFR-, and the NFκB signaling modules, we were able to study TNF's functions during the inflammatory response to diverse TLR agonists. Contrary to expectation, we predicted and then experimentally confirmed that in response to lipopolysaccaride, TNF does not have an autocrine function in amplifying the NFκB response, although it plays a potent paracrine role in neighboring cells. However, in response to CpG DNA, autocrine TNF extends the duration of NFκB activity and shapes CpG-induced gene expression programs. Our systems biology approach revealed that network dynamics of MyD88 and TRIF signaling and of cytokine production and response govern the stimulus-specific autocrine and paracrine functions of TNF.

Tumor necrosis factor receptor 2 (TNFR2)·interleukin-17 receptor D (IL-17RD) heteromerization reveals a novel mechanism for NF-κB activation

TNF receptor 2 (TNFR2) exerts diverse roles in the pathogenesis of inflammatory and autoimmune diseases. Here, we report that TNFR2 but not TNFR1 forms a heteromer with interleukin-17 receptor D (IL-17RD), also named Sef, to activate NF-κB signaling. TNFR2 associates with IL-17RD, leading to mutual receptor aggregation and TRAF2 recruitment, which further activate the downstream cascade of NF-κB signaling. Depletion of IL-17RD impaired TNFR2-mediated activation of NF-κB signaling. Importantly, IL-17RD was markedly increased in renal tubular epithelial cells in nephritis rats, and a strong interaction of TNFR2 and IL-17RD was observed in the renal epithelia. The IL-17RD·TNFR2 complex in activation of NF-κB may explain the role of TNFR2 in inflammatory diseases including nephritis.

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.

The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of osteoarthritis

Osteoarthritis (OA) is the most common chronic disease of human joints. The basis of pathologic changes involves all the tissues forming the joint; already, at an early stage, it has the nature of inflammation with varying degrees of severity. An analysis of the complex relationships indicates that the processes taking place inside the joint are not merely a set that (seemingly) only includes catabolic effects. Apart from them, anti-inflammatory anabolic processes also occur continually. These phenomena are driven by various mediators, of which the key role is attributed to the interactions within the cytokine network. The most important group controlling the disease seems to be inflammatory cytokines, including IL-1β, TNFα, IL-6, IL-15, IL-17, and IL-18. The second group with antagonistic effect is formed by cytokines known as anti-inflammatory cytokines such as IL-4, IL-10, and IL-13. The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of OA with respect to inter- and intracellular signaling pathways is still under investigation. This paper summarizes the current state of knowledge. The cytokine network in OA is put in the context of cells involved in this degenerative joint disease. The possibilities for further implementation of new therapeutic strategies in OA are also pointed.

Effect of milrinone on the inflammatory response and NF-kB activation in renal ischemia-reperfusion injury in mice

BACKGROUND

Milrinone increases intracellular adenosine 3',5'-cyclic monophosphate concentration and enhances vascular relaxation. Nuclear factor-kappa B (NF-kB) plays a key role in inflammatory responses during ischemia-reperfusion (I/R) injury. We aimed to investigate the effect of milrinone on the inflammatory responses and NF-kB activation in renal I/R injury in mice.

METHODS

Thirty C57BL/6 mice were allocated into 3 groups. In group S (n = 10), only right nephrectomy was done. In group C (n = 10), the left kidney was subjected to 30 min of ischemia after right nephrectomy. In group M (n = 10), milrinone (5 µg/kg) was administered before ischemia. After 24 hours of reperfusion, the serum creatinine was measured, kidney samples were obtained for histology, and expressions of NF-kB and proinflammatory cytokines were analyzed.

RESULTS

In group C, the serum creatinine concentration was markedly elevated, compared with group S. Creatinine concentration in group M was also elevated, but it was significantly lower than that in group C. Histologic evidence of renal damage was severe in group C, but it was improved in group M. In groups C and M, expression of NF-kB, tumor necrosis factor-α (TNF-α), intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) mRNA increased significantly compared with group S (P < 0.05). But group M showed a lower expression of NF-kB, TNF-α, ICAM-1, MCP-1 and MIP-2 mRNA than group C (P < 0.05).

CONCLUSIONS

Milrinone treatment attenuates the renal inflammatory response and activation of NF-kB, resulting in improvement of renal function and tissue injury.

TNFR2 increases the sensitivity of ligand-induced activation of the p38 MAPK and NF-κB pathways and signals TRAF2 protein degradation in macrophages

Tumour necrosis factor (p55 or p60) receptor (TNFR) 1 is the major receptor that activates pro-inflammatory signalling and induces gene expression in response to TNF. Consensus is lacking for the function of (p75 or p80) TNFR2 but experiments in mice have suggested neuro-, cardio- and osteo-protective and anti-inflammatory roles. It has been shown in various cell types to be specifically required for the induction of TNFR-associated factor-2 (TRAF2) degradation and activation of the alternative nuclear factor (NF)-kappaB pathway, and to contribute to the activation of mitogen-activated protein kinases (MAPK) and the classical NF-kappaB pathway. We have investigated the signalling functions of TNFR2 in primary human and murine macrophages. We find that in these cells TNF induces TRAF2 degradation, and this is blocked in TNFR2(-/-) macrophages. TRAF2 has been previously reported to be required for TNF-induced activation of p38 MAPK. However, TRAF2 degradation does not inhibit TNF-induced tolerance of p38 MAPK activation. Neither TNF, nor lipopolysaccharide treatment, induced activation of the alternative NF-kappaB pathway in macrophages. Activation by TNF of the p38 MAPK and NF-kappaB pathways was blocked in TNFR1(-/-) macrophages. In contrast, although TNFR2(-/-) macrophages displayed robust p38 MAPK activation and IkappaBα degradation at high concentrations of TNF, at lower doses the concentration dependence of signalling was weakened by an order of magnitude. Our results suggest that, in addition to inducing TRAF2 protein degradation, TNFR2 also plays a crucial auxiliary role to TNFR1 in sensitising macrophages for the ligand-induced activation of the p38 MAPK and classical NF-kappaB pro-inflammatory signalling pathways.

A mouse model of pathological small intestinal epithelial cell apoptosis and shedding induced by systemic administration of lipopolysaccharide

The gut barrier, composed of a single layer of intestinal epithelial cells (IECs) held together by tight junctions, prevents the entrance of harmful microorganisms, antigens and toxins from the gut lumen into the blood. Small intestinal homeostasis is normally maintained by the rate of shedding of senescent enterocytes from the villus tip exactly matching the rate of generation of new cells in the crypt. However, in various localized and systemic inflammatory conditions, intestinal homeostasis can be disturbed as a result of increased IEC shedding. Such pathological IEC shedding can cause transient gaps to develop in the epithelial barrier and result in increased intestinal permeability. Although pathological IEC shedding has been implicated in the pathogenesis of conditions such as inflammatory bowel disease, our understanding of the underlying mechanisms remains limited. We have therefore developed a murine model to study this phenomenon, because IEC shedding in this species is morphologically analogous to humans. IEC shedding was induced by systemic lipopolysaccharide (LPS) administration in wild-type C57BL/6 mice, and in mice deficient in TNF-receptor 1 (Tnfr1^−/−), Tnfr2 (Tnfr2^−/−), nuclear factor kappa B1 (Nfκb1^−/−) or Nfĸb2 (Nfĸb2^−/−). Apoptosis and cell shedding was quantified using immunohistochemistry for active caspase-3, and gut-to-circulation permeability was assessed by measuring plasma fluorescence following fluorescein-isothiocyanate–dextran gavage. LPS, at doses ≥0.125 mg/kg body weight, induced rapid villus IEC apoptosis, with peak cell shedding occurring at 1.5 hours after treatment. This coincided with significant villus shortening, fluid exudation into the gut lumen and diarrhea. A significant increase in gut-to-circulation permeability was observed at 5 hours. TNFR1 was essential for LPS-induced IEC apoptosis and shedding, and the fate of the IECs was also dependent on NFκB, with signaling via NFκB1 favoring cell survival and via NFκB2 favoring apoptosis. This model will enable investigation of the importance and regulation of pathological IEC apoptosis and cell shedding in various diseases.

Release of nonmuscle myosin II from the cytosolic domain of tumor necrosis factor receptor 2 is required for target gene expression

Tumor necrosis factor-α (TNF-α) elicits its biological activities through activation of TNF receptor 1 (TNFR1, also known as p55) and TNFR2 (also known as p75). The activities of both receptors are required for the TNF-α-induced proinflammatory response. The adaptor protein TNFR-associated factor 2 (TRAF2) is critical for either p55- or p75-mediated activation of nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling, as well as for target gene expression. We identified nonmuscle myosin II (myosin) as a binding partner of p75. TNF-α-dependent signaling by p75 and induction of target gene expression persisted substantially longer in cells deficient in myosin regulatory light chain (MRLC; a component of myosin) than in cells replete in myosin. In resting endothelial cells, myosin was bound constitutively to the intracellular region of p75, a region that overlaps with the TRAF2-binding domain, and TNF-α caused the rapid dissociation of myosin from p75. At early time points after exposure to TNF-α, p75 activated Rho-associated kinase 1 (ROCK1). Inhibition of ROCK1 activity blocked TNF-α-dependent phosphorylation of MRLC and the dissociation of myosin from p75. ROCK1-dependent release of myosin was necessary for the TNF-α-dependent recruitment of TRAF2 to p75 and for p75-specific activation of NF-κB and MAPK signaling. Thus, our findings have revealed a previously uncharacterized, noncanonical regulatory function of myosin in cytokine signaling.

Distinct contributions of TNF receptor 1 and 2 to TNF-induced glomerular inflammation in mice

TNF is an important mediator of glomerulonephritis. The two TNF-receptors TNFR1 and TNFR2 contribute differently to glomerular inflammation in vivo, but specific mechanisms of TNFR-mediated inflammatory responses in glomeruli are unknown. We investigated their expression and function in murine kidneys, isolated glomeruli ex vivo, and glomerular cells in vitro. In normal kidney TNFR1 and TNFR2 were preferentially expressed in glomeruli. Expression of both TNFRs and TNF-induced upregulation of TNFR2 mRNA was confirmed in murine glomerular endothelial and mesangial cell lines. In vivo, TNF exposure rapidly induced glomerular accumulation of leukocytes. To examine TNFR-specific inflammatory responses in intrinsic glomerular cells but not infiltrating leukocytes we performed microarray gene expression profiling on intact glomeruli isolated from wildtype and Tnfr-deficient mice following exposure to soluble TNF ex vivo. Most TNF-induced effects were exclusively mediated by TNFR1, including induced glomerular expression of adhesion molecules, chemokines, complement factors and pro-apoptotic molecules. However, TNFR2 contributed to TNFR1-dependent mRNA expression of inflammatory mediators in glomeruli when exposed to low TNF concentrations. Chemokine secretion was absent in TNF-stimulated Tnfr1-deficient glomeruli, but also significantly decreased in glomeruli lacking TNFR2. In vivo, TNF-induced glomerular leukocyte infiltration was abrogated in Tnfr1-deficient mice, whereas Tnfr2-deficiency decreased mononuclear phagocytes infiltrates, but not neutrophils. These data demonstrate that activation of intrinsic glomerular cells by soluble TNF requires TNFR1, whereas TNFR2 is not essential, but augments TNFR1-dependent effects. Previously described TNFR2-dependent glomerular inflammation may therefore require TNFR2 activation by membrane-bound, but not soluble TNF.

Etanercept attenuates short-term cigarette-smoke-exposure-induced pulmonary arterial remodelling in rats by suppressing the activation of TNF-a/NF-kB signal and the activities of MMP-2 and MMP-9

The pathogenesis of cigarette-smoke-exposure-induced pulmonary vasculature impairment is unclear. Cigarette-smoke-exposure-induced the accumulation of tumour necrosis factor-alpha (TNF-α) and upregulates the expression and activities of matrix metalloproteinases (MMPs) involved in smoke-induced vascular remodelling, which are important processes in the pathogenesis of vasculature impairment. The TNF-α antagonist Etanercept is an anti-inflammatory drug with a potential role in regulating MMP expression. To determine the effect of Etanercept on short-term smoke-induced pulmonary arteriole impairment and investigate its possible mechanism, male Sprague-Dawley rats were exposed to cigarette-smoke daily for two weeks in both the absence and presence of Etanercept. Cigarette-smoke-exposure-induced elevation of mean pulmonary artery pressures and medial hypertrophy of pulmonary arterioles were partially reduced by Etanercept. Up-regulation of the expression and activities of MMP-2 and MMP-9, induced by cigarette-smoke, were also suppressed significantly by Etanercept. Furthermore, Etanercept treatment significantly attenuated cigarette-smoke-induced TNFα accumulation and activation of nuclear factor NF-kB signal. These results suggest that Etanercept have the protective effects in cigarette-smoke-induced pulmonary vascular remodelling, with the attenuation of the up-regulated expression and activities of MMP-2 and MMP-9 and activation of TNF-α/NF-kB signal pathway probably being involved as part of its mechanism. Our study might provide insight into the development of new interventions for vasculature impairment.

Tumor necrosis factor receptors: biology and therapeutic potential in kidney diseases

The major evolutionary advance represented in the human immune system is a mechanism of antigen-directed immunity in which tumor necrosis factor (TNF)-α and TNF receptors (TNFRs) play essential roles. Binding of TNF-α to the 55-kDa type I TNFR (TNFR1, TNFRSF1A, CD120a, p55) or the 75-kDa type II TNFR (TNFR2, TNFRSF1B, CD120b, p75) activates signaling pathways controlling inflammatory, immune and stress responses, as well as host defense and apoptosis. Multiple studies have investigated the role of TNFRs in the development of early and late renal failure (diabetic nephropathy, nephroangiosclerosis, acute kidney transplant rejection, renal cell carcinoma, glomerulonephritis, sepsis and obstructive renal injury). This article reviews the general characteristics, the analytical aspects and the biology of TNFRs in this domain. In addition, the potential therapeutic application of specific TNFR blockers is discussed.

Both internalization and AIP1 association are required for tumor necrosis factor receptor 2-mediated JNK signaling

OBJECTIVE

The proinflammtory cytokine tumor necrosis factor (TNF), primarily via TNF receptor 1 (TNFR1), induces nuclear factor-κB (NF-κB)-dependent cell survival, and c-Jun N-terminal kinase (JNK) and caspase-dependent cell death, regulating vascular endothelial cell (EC) activation and apoptosis. However, signaling by the second receptor, TNFR2, is poorly understood. The goal of this study was to dissect how TNFR2 mediates NF-κB and JNK signaling in vascular EC, and its relevance to in vivo EC function.

METHODS AND RESULTS

We show that TNFR2 contributes to TNF-induced NF-κB and JNK signaling in EC as TNFR2 deletion or knockdown reduces the TNF responses. To dissect the critical domains of TNFR2 that mediate the TNF responses, we examine the activity of TNFR2 mutant with a specific deletion of the TNFR2 intracellular region, which contains conserved domain I, domain II, domain III, and 2 TNFR-associated factor-2-binding sites. Deletion analyses indicate that different sequences on TNFR2 have distinct roles in NF-κB and JNK activation. Specifically, deletion of the TNFR-associated factor-2-binding sites (TNFR2-59) diminishes the TNFR2-mediated NF-κB, but not JNK activation; whereas, deletion of domain II or domain III blunts TNFR2-mediated JNK but not NF-κB activation. Interestingly, we find that the TNFR-associated factor-2-binding sites ensure TNFR2 on the plasma membrane, but the di-leucine LL motif within the domain II and aa338-355 within the domain III are required for TNFR2 internalization as well as TNFR2-dependent JNK signaling. Moreover, domain III of TNFR2 is responsible for association with ASK1-interacting protein-1, a signaling adaptor critical for TNF-induced JNK signaling. While TNFR2 containing the TNFR-associated factor-2-binding sites prevents EC cell death, a specific activation of JNK without NF-κB activation by TNFR2-59 strongly induces caspase activation and EC apoptosis.

CONCLUSIONS

Our data reveal that both internalization and ASK1-interacting protein-1 association are required for TNFR2-dependent JNK and apoptotic signaling. Controlling TNFR2-mediated JNK and apoptotic signaling in EC may provide a novel strategy for the treatment of vascular diseases.