The death domain of tumor necrosis factor receptor 1 is necessary but not sufficient for Golgi retention of the receptor and mediates receptor desensitization

The causal role of intestinal microbiome in development of pre-eclampsia

The correlation of pre-eclampsia (PE) and intestinal microbiome has been widely demonstrated in existing research, whereas their causal relationship has been rarely explored. The causal relationship between intestinal microbiome and PE risk was examined using large-scale genome-wide association studies (GWAS) summary statistics. To be specific, the causal microbial taxa for PE were identified using the two-sample Mendelian randomization (MR) method. The results were verified to be robust through comprehensive sensitive analyses, and the independence of causal relationship was ensured through novel multivariable MR analyses. The possibility of reverse relationships was ruled out through reverse-direction MR analyses. Lastly, the biofunction was explored through enrichment analysis, and a series of validations of PE results in a second GWAS were performed to confirm the results. After correction, four microbial taxa, including Streptococcus genus for PE (FDR q = 0.085), Olsenella genus for PE (FDR q = 0.085), Enterobacteriales order for PE (FDR q = 0.0134), and Akkermansia genus for PE (FDR q = 0.015), had a causal relationship to diverse joint PE (FDR q < 0.15). Moreover, when three different methods were employed on basis of the nominal significance (P < 0.05), five suggestive microbial taxa took on significance. The effect of heterogeneity and horizontal pleiotropy was excluded through sensitive analysis, and the possibility of horizontal pleiotropy of BMI was ruled out through multivariable MR analysis. The protective mechanism of the identified taxa against PE was illustrated through GO enrichment analysis and KEGG pathways. A number of microbial taxa had a causal relationship to PE. The result of this study provides more insights into intestinal microbiome in the pathology of PE.

A TNFR1-UBCH10 axis drives lung squamous cell carcinoma dedifferentiation and metastasis through a cell-autonomous signaling loop

Tumor necrosis factor receptor 1 (TNFR1), encoded by TNFRSF1A, is a critical transducer of inflammatory pathways, but its physiological role in human cancer is not completely understood. Here, we observed high expression of TNFR1 in many human lung squamous cell carcinoma (SCCs) samples and in spontaneous lung SCCs derived from kinase-dead Ikkα knock-in (KA/KA) mice. Knocking out Tnfrf1a in KA/KA mice blocked lung SCC formation. When injected via tail vein, KAL^LU+ lung SCC cells that highly expressed TNFR1/TNF, Sox2, c-Myc, Twist1, Bcl2, and UBCH10, generated dedifferentiated spindle cell carcinomas with epithelial-mesenchymal transition markers in mouse lungs. In contrast, KAL^LU+ cells with silenced TNFR1 and KAL^LU- cells that expressed low levels of TNFR1 generated well-differentiated lung SCCs and were less tumorigenic and metastatic. We identified a downstream effector of TNFR1: oncogenic UBCH10, an E2 ubiquitin-conjugating enzyme with targets including Twist1, c-Myc, and Sox2, which enhanced SCC cell dedifferentiation. Furthermore, Tg-K5.TNFR1;KA/KA mice, which expressed transgenic TNFR1 in keratin 5-positve epithelial cells, developed more poorly differentiated and metastatic lung SCCs than those found in KA/KA mice. These findings demonstrate that an overexpressed TNFR1-UBCH10 axis advances lung carcinogenesis and metastasis through a dedifferentiation mechanism. Constituents in this pathway may contribute to the development of differentiation-related therapies for lung SCC.

Monocytes transition to macrophages within the inflamed vasculature via monocyte CCR2 and endothelial TNFR2

Monocytes undergo phenotypic and functional changes in response to inflammatory cues, but the molecular signals that drive different monocyte states remain largely undefined. We show that monocytes acquire macrophage markers upon glomerulonephritis and may be derived from CCR2+CX3CR1+ double-positive monocytes, which are preferentially recruited, dwell within glomerular capillaries, and acquire proinflammatory characteristics in the nephritic kidney. Mechanistically, the transition to immature macrophages begins within the vasculature and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells, findings that are recapitulated in vitro with monocytes cocultured with TNF-TNFR2-activated endothelial cells generating CCR2 ligands. Single-cell RNA sequencing of cocultures defines a CCR2-dependent monocyte differentiation path associated with the acquisition of immune effector functions and generation of CCR2 ligands. Immature macrophages are detected in the urine of lupus nephritis patients, and their frequency correlates with clinical disease. In conclusion, CCR2-dependent functional specialization of monocytes into macrophages begins within the TNF-TNFR2-activated vasculature and may establish a CCR2-based autocrine, feed-forward loop that amplifies renal inflammation.

Regulation of Death Receptor Signaling by S-Palmitoylation and Detergent-Resistant Membrane Micro Domains-Greasing the Gears of Extrinsic Cell Death Induction, Survival, and Inflammation

Death-receptor-mediated signaling results in either cell death or survival. Such opposite signaling cascades emanate from receptor-associated signaling complexes, which are often formed in different subcellular locations. The proteins involved are frequently post-translationally modified (PTM) by ubiquitination, phosphorylation, or glycosylation to allow proper spatio-temporal regulation/recruitment of these signaling complexes in a defined cellular compartment. During the last couple of years, increasing attention has been paid to the reversible cysteine-centered PTM S-palmitoylation. This PTM regulates the hydrophobicity of soluble and membrane proteins and modulates protein:protein interaction and their interaction with distinct membrane micro-domains (i.e., lipid rafts). We conclude with which functional and mechanistic roles for S-palmitoylation as well as different forms of membrane micro-domains in death-receptor-mediated signal transduction were unraveled in the last two decades.

Single-molecule imaging reveals the oligomeric state of functional TNFα-induced plasma membrane TNFR1 clusters in cells

Ligand-induced tumor necrosis factor receptor 1 (TNFR1) activation controls nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling, cell proliferation, programmed cell death, and survival and is crucially involved in inflammation, autoimmune disorders, and cancer progression. Despite the relevance of TNFR1 clustering for signaling, oligomerization of ligand-free and ligand-activated TNFR1 remains controversial. At present, models range from ligand-independent receptor predimerization to ligand-induced oligomerization. Here, we used quantitative, single-molecule superresolution microscopy to study TNFR1 assembly directly in native cellular settings and at physiological cell surface abundance. In the absence of its ligand TNFα, TNFR1 assembled into monomeric and dimeric receptor units. Upon binding of TNFα, TNFR1 clustered predominantly not only into trimers but also into higher-order oligomers. A functional mutation in the preligand assembly domain of TNFR1 resulted in only monomeric TNFR1, which exhibited impaired ligand binding. In contrast, a form of TNFR1 with a mutation in the ligand-binding CRD2 subdomain retained the monomer-to-dimer ratio of the unliganded wild-type TNFR1 but exhibited no ligand binding. These results underscore the importance of ligand-independent TNFR1 dimerization in NF-κB signaling.

Leukocyte-Released Mediators in Response to Both Bacterial and Fungal Infections Trigger IFN Pathways, Independent of IL-1 and TNF-α, in Endothelial Cells

In sepsis, dysregulated immune responses to infections cause damage to the host. Previous studies have attempted to capture pathogen-induced leukocyte responses. However, the impact of mediators released after pathogen-leukocyte interaction on endothelial cells, and how endothelial cell responses vary depending on the pathogen-type is lacking. Here, we comprehensively characterized the transcriptomic responses of human leukocytes and endothelial cells to Gram negative-bacteria, Gram positive-bacteria, and fungi. We showed that whole pathogen lysates induced strong activation of leukocytes but not endothelial cells. Interestingly, the common response of leukocytes to various pathogens converges on endothelial activation. By exposing endothelial cells to leukocyte-released mediators, we observed a strong activation of endothelial cells at both transcription and protein levels. By adding IL-1RA and TNF-α antibody in leukocyte-released mediators before exposing to endothelial cells, we identified specific roles for IL-1 and TNF-α in driving the most, but not all, endothelial activation. We also showed for the first time, activation of interferon response by endothelial cells in response to leukocyte-released mediators, independently from IL-1 and TNF-α pathways. Our study therefore, not only provides pathogen-dependent transcriptional changes in leukocytes and endothelial cells during infections, but also reveals a role for IFN, together with IL1 and TNFα signaling, in mediating leukocyte-endothelial interaction in infections.

Extrinsically derived TNF is primarily responsible for limiting antiviral CD8+ T cell response magnitude

TNF is a pro-inflammatory cytokine produced by both lymphoid and non-lymphoid cells. As a consequence of the widespread expression of its receptors (TNFR1 and 2), TNF plays a role in many important biological processes. In the context of influenza A virus (IAV) infection, TNF has variably been implicated in mediating immunopathology as well as suppression of the immune response. Although a number of cell types are able to produce TNF, the ability of CD8⁺ T cells to produce TNF following viral infection is a hallmark of their effector function. As such, the regulation and role of CD8⁺ T cell-derived TNF following viral infection is of great interest. Here, we show that the biphasic production of TNF by CD8⁺ T cells following in vitro stimulation corresponds to distinct patterns of epigenetic modifications. Further, we show that a global loss of TNF during IAV infection results in an augmentation of the peripheral virus-specific CD8⁺ T cell response. Subsequent adoptive transfer experiments demonstrated that this attenuation of the CD8⁺ T cell response was largely, but not exclusively, conferred by extrinsic TNF, with intrinsically-derived TNF making only modest contributions. In conclusion, TNF exerts an immunoregulatory role on CD8⁺ T cell responses following IAV infection, an effect that is largely mediated by extrinsically-derived TNF.

FXYD5 Protein Has a Pro-inflammatory Role in Epithelial Cells

The FXYD proteins are a family of small membrane proteins that share an invariant four amino acid signature motif F-X-Y-D and act as tissue-specific regulatory subunits of the Na,K-ATPase. FXYD5 (also termed dysadherin or RIC) is a structurally and functionally unique member of the FXYD family. As other FXYD proteins, FXYD5 specifically interacts with the Na,K-ATPase and alters its kinetics by increasing Vmax However, unlike other family members FXYD5 appears to have additional functions, which cannot be readily explained by modulation of transport kinetics. Knockdown of FXYD5 in MDA-MB-231 breast cancer cells largely decreases expression and secretion of the chemokine CCL2 (MCP-1). A related effect has also been observed in renal cell carcinoma cells. The current study aims to further characterize the relationship between the expression of FXYD5 and CCL2 secretion. We demonstrate that transfection of M1 epithelial cell line with FXYD5 largely increases lipopolysaccharide (LPS) stimulated CCL2 mRNA and secretion of the translated protein. We have completed a detailed analysis of the molecular events leading to the above response. Our key findings indicate that FXYD5 generates a late response by increasing the surface expression of the TNFα receptor, without affecting its total protein level, or mRNA transcription. LPS administration to mice demonstrates induced secretion of CCL2 and TNFα in FXYD5-expressing lung peripheral tissue, which suggests a possible role for FXYD5 in normal epithelia during inflammation.

Regulation and dysregulation of tumor necrosis factor receptor-1

TNF is an essential regulator of the immune system. Dysregulation of TNF plays a role in the pathology of many auto-immune diseases. TNF-blocking agents have proven successful in the treatment of such diseases. Development of novel, safer or more effective drugs requires a deeper understanding of the regulation of the pro-inflammatory activities of TNF and its receptors. The ubiquitously expressed TNFR1 is responsible for most TNF effects, while TNFR2 has a limited expression pattern and performs immune-regulatory functions. Despite extensive knowledge of TNFR1 signaling, the regulation of TNFR1 expression, its modifications, localization and processing are less clear and the data are scattered. Here we review the current knowledge of TNFR1 regulation and discuss the impact this has on the host.

Endothelial TNF receptor 2 induces IRF1 transcription factor-dependent interferon-β autocrine signaling to promote monocyte recruitment

Endothelial-dependent mechanisms of mononuclear cell influx are not well understood. We showed that acute stimulation of murine microvascular endothelial cells expressing the tumor necrosis factor receptors TNFR1 and TNFR2 with the soluble cytokine TNF led to CXCR3 chemokine generation. The TNF receptors signaled through interferon regulatory factor-1 (IRF1) to induce interferon-β (IFN-β) and subsequent autocrine signaling via the type I IFN receptor and the transcription factor STAT1. Both TNFR2 and TNFR1 were required for IRF1-IFNβ signaling and, in human endothelial cells TNFR2 expression alone induced IFN-β signaling and monocyte recruitment. In vivo, TNFR1 was required for acute renal neutrophil and monocyte influx after systemic TNF treatment, whereas the TNFR2-IRF1-IFN-β autocrine loop was essential only for macrophage accumulation. In a chronic model of proliferative nephritis, IRF1 and renal-expressed TNFR2 were essential for sustained macrophage accumulation. Thus, our data identify a pathway in endothelial cells that selectively recruits monocytes during a TNF-induced inflammatory response.

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.

Group B streptococcal colonization and the risk of pre-eclampsia

To determine if there was an association between recto-vaginal group B streptococcus (GBS) colonization and pre-eclampsia, two cross-sectional studies were conducted using statewide hospital databases. The first study analysed data from the state of Florida, USA, and included 190 645 women who were discharged in 2001. This dataset was used to generate the hypothesis that GBS colonization is associated with pre-eclampsia. The second study tested the GBS hypothesis using the records of 577 153 women who delivered in 2004 or 2005 in Texas, USA. Adjusted odds ratios (aOR) for the outcome of pre-eclampsia comparing GBS-positive to GBS-negative women were calculated using logistic regression. The aOR for the association between GBS carriage and pre-eclampsia was 0·71 [95% confidence interval (CI) 0·65–0·77] in the Florida dataset. In the Texas dataset, the overall prevalence of GBS carriage was 14·1% while the overall prevalence of pre-eclampsia was 4·0%. GBS carriers were 31% less likely than non-carriers to have pre-eclampsia (aOR 0·69, 95% CI 0·66–0·72) in Texas. In two large statewide analyses, GBS carriage was inversely associated with pre-eclampsia. A sensitivity analysis revealed that misclassification of GBS status is not a likely explanation of our findings.

Tumour necrosis factor receptor trafficking dysfunction opens the TRAPS door to pro-inflammatory cytokine secretion

Cytokines are secreted from macrophages and other cells of the immune system in response to pathogens. Additionally, in autoinflammatory diseases cytokine secretion occurs in the absence of pathogenic stimuli. In the case of TRAPS [TNFR (tumour necrosis factor receptor)-associated periodic syndrome], inflammatory episodes result from mutations in the TNFRSF1A gene that encodes TNFR1. This work remains controversial, however, with at least three distinct separate mechanisms of receptor dysfunction having been proposed. Central to these hypotheses are the NF-κB (nuclear factor κB) and MAPK (mitogen-activated protein kinase) families of transcriptional activators that are able to up-regulate expression of a number of genes, including pro-inflammatory cytokines. The present review examines each proposed mechanism of TNFR1 dysfunction, and addresses how these processes might ultimately impact upon cytokine secretion and disease pathophysiology.

Emerging role for TNF-α in erectile dysfunction

INTRODUCTION

A role for cytokines in the pathophysiology of erectile dysfunction (ED) has emerged. Cytokines induce genes that synthesize other peptides in the cytokine family and several mediators, such as prostanoids, leukotrienes, nitric oxide, bradykinin, reactive oxygen species, and platelet-activating factor, all of which can affect vascular function. Consistent with the fact that the cavernosal tissue is a complex extension of the vasculature, risk factors that affect the vasculature have been shown to affect cavernosal function as well. Accordingly, the penile tissue has been recognized as an early sentinel for atherosclerosis that underlies coronary artery disease and cardiovascular diseases (CVD).

AIM

To review the literature pertaining to the role of tumor necrosis factor-alpha (TNF-α) in ED.

METHODS

PubMed search for pertinent publications on the role of cytokines, particularly TNF-α, in CVD and ED.

MAIN OUTCOME MEASURES

Clinical and experimental evidence demonstrates that TNF-α may play a role in ED.

RESULTS

TNF-α has been shown to play an important role in CVD, mainly due to its direct effects on the vasculature. In addition, high levels of TNF-α were demonstrated in patients with ED. In this review, we present a short description of the physiology of erection and the cytokine network. We focus on vascular actions of TNF-α that support a role for this cytokine as a potential candidate in the pathophysiology of ED, particularly in the context of CVD. A brief overview of its discovery, mechanisms of synthesis, receptors, and its main actions on the systemic and penile vasculature is also presented.

CONCLUSIONS

Considering that ED results from a systemic arterial defect not only confined to the penile vasculature, implication of TNF-α in the pathophysiology of ED offers a humoral linking between CVD and ED.

Targeting of tumor necrosis factor receptor 1 to low density plasma membrane domains in human endothelial cells

TNFR1 (tumor necrosis factor receptor 1) localizes to caveolae of human endothelial-derived EA.hy926 cells. Transduced TNFR1 molecules lacking amino acid residues 229-244 (spanning the transmembrane/intercellular boundary) are expressed on the cell surface equivalently to full-length TNFR1 molecules but incompletely localize to caveolae. A peptide containing this sequence pulls down CAV-1 (caveolin-1) and TNFR1 from cell lysates but fails to do so following disruption of caveolae with methyl-beta-cyclodextrin. We previously reported that methyl-beta-cyclodextrin eliminates caveolae and blocks tumor necrosis factor (TNF)-induced internalization of TNFR1 but not TNF-induced activation of NF-kappaB in EA.hy926 cells. Both CAV-1 and FLOT-2 (flotillin-2), organizing proteins of caveolae and lipid rafts, respectively, associate with caveolae in EA.hy926 cells. Small interfering RNA-mediated knockdown of CAV-1 but not FLOT-2 strikingly reduces caveolae number. Both knockdowns reduce total TNFR1 protein expression, but neither prevents TNFR1 localization to low density membrane domains, TNF-induced internalization of TNFR1, or NF-kappaB activation by TNF. Both CAV-1 and FLOT-2 knockdowns reduce TNF-mediated activation of stress-activated protein kinase (SAPK). However, both knockdowns reduce expression of TRAF2 (TNF receptor-associated factor-2) protein, and small interfering RNA targeting of TRAF2 also selectively inhibits SAPK activation. We conclude that TNFR1 contains a membrane-proximal sequence that targets the receptor to caveolae/lipid rafts. Neither TNFR1 targeting to nor internalization from these low density membrane domains depends upon CAV-1 or FLOT-2. Furthermore, both NF-kappaB and SAPK activation appear independent of both TNFR1 localization to low density membrane domains and to TNF-induced receptor internalization.

Dysregulation of innate immunity: hereditary periodic fever syndromes

The hereditary periodic fever syndromes encompass a rare group of diseases that have lifelong recurrent episodes of inflammatory symptoms and an acute phase response in common. Clinical presentation can mimic that of lymphoproliferative disorders and patients often go undiagnosed for many years. These syndromes follow an autosomal inheritance pattern, and the major syndromes are linked to specific genes, most of which are involved in regulation of the innate immune response through pathways of apoptosis, nuclear factor kappaBeta activation and cytokine production. In others, the link between the protein involved and inflammation is less clear. The recurrent inflammation can lead to complications, such as renal impairment due to amyloidosis and vasculitis, visual impairment, hearing loss, and joint destruction, depending on the specific syndrome. In recent years, treatment options for these diseases have improved significantly. Early establishment of an accurate diagnosis and start of appropriate therapy improves prognosis in these patients.

Intracellular application of TNF-alpha impairs cell to cell communication via gap junctions in glioma cells

Human gliomas are the most common class of brain neoplasm. In order to better characterize their response to inflammation, we evaluated the influence of tumor necrosis factor alpha (TNF-alpha) on the coupling behaviour and the membrane resting potential (MRP) of glioma cells (F98 glioma cell line) compared to primary astrocytes. In contrast to cultured primary astrocytes which exhibited a profound inhibition of gap junction mediated intercellular communication (GJIC), extracellular exposure of TNF-alpha to F98 glioma cells gained no effect on the functional coupling. Whereas, intracellular application of TNF-alpha into the glioma cells elicited similar effects as those found in primary astrocytes indicating a compromised accessibility of the TNF-alpha receptor in F98 cells. Western blotting, immunocytochemical staining and real time RT PCR analysis revealed a differential expression and distribution of TNF-alpha receptor 1 (TNFR1) in the glioma cells. Connexin 43 (Cx43) is the major astrocytic gap junction protein which when phosphorylated has been shown to reveal altered gating properties. Here we show that TNF-alpha increases the level of phosphorylated Cx43 in primary astrocytes but not in the F98 glioma cells. Our observations could account for the decreased regulatory effects of TNF-alpha on GJIC of F98 glioma cells.

Increased ICAM-1 expression causes endothelial cell leakiness, cytoskeletal reorganization and junctional alterations

Tumor necrosis factor (TNF)-induced ICAM-1 in endothelial cells (EC) promotes leukocyte adhesion. Here we report that ICAM-1 also effects EC barrier function. Control- or E-selectin-transduced human dermal microvascular EC (HDMEC) form a barrier to flux of proteins and to passage of current (measured as transendothelial electrical resistance or TEER). HDMEC transduced with ICAM-1 at levels comparable to that induced by TNF show reduced TEER, but do so without overtly changing their cell junctions, cell shape, or cytoskeleton organization. Higher levels of ICAM-1 further reduce TEER, increase F/G-actin ratios, rearrange the actin cytoskeleton to cause cell elongation, and alter junctional zona occludens 1 and vascular endothelial-cadherin staining. Transducing with ICAM-1 lacking an intracellular region also reduces TEER. TNF-induced changes in TEER and shape follow a similar time course as ICAM-1 induction; however, the fall in TEER occurs at lower TNF concentrations. Inhibiting NF-kappaB activation blocks ICAM-1 induction; TEER reduction, and shape change. Specific small-interfering RNA knockdown of ICAM-1 partially inhibits TNF-induced shape change. We conclude that moderately elevated ICAM-1 expression reduces EC barrier function and that expressing higher levels of ICAM-1 affects cell junctions and the cytoskeleton. Induction of ICAM-1 may contribute to but does not fully account for TNF-induced vascular leak and EC shape change.

Pathogenesis of familial periodic fever syndromes or hereditary autoinflammatory syndromes

Familial periodic fever syndromes, otherwise known as hereditary autoinflammatory syndromes, are inherited disorders characterized by recurrent episodes of fever and inflammation. The general hypothesis is that the innate immune response in these patients is wrongly tuned, being either too sensitive to very minor stimuli or turned off too late. The genetic background of the major familial periodic fever syndromes has been unraveled, and through research into the pathophysiology, a clearer picture of the innate immune system is emerging. After an introduction on fever, interleukin-1beta and inflammasomes, which are involved in the majority of these diseases, this manuscript offers a detailed review of the pathophysiology of the cryopyrin-associated periodic syndromes, familial Mediterranean fever, the syndrome of pyogenic arthritis, pyoderma gangrenosum and acne, Blau syndrome, TNF-receptor-associated periodic syndrome and hyper-IgD and periodic fever syndrome. Despite recent major advances, there are still many questions to be answered regarding the pathogenesis of these disorders.

Modeling of tumor necrosis factor receptor superfamily 1A mutants associated with tumor necrosis factor receptor–associated periodic syndrome indicates misfolding consistent with abnormal function

OBJECTIVE

To investigate the effect of mutations in the tumor necrosis factor receptor superfamily 1A (TNFRSF1A) gene on the conformation and behavior of the TNFRSF1A protein. Mutations in TNFRSF1A cause the autosomal-dominant, autoinflammatory TNFR-associated periodic syndrome (TRAPS).

METHODS

The expression of recombinant TNFRSF1A was compared in SK-HEp-1 endothelial cells and HEK 293 epithelial cells stably transfected with full-length R347A or Deltasig constructs of wild-type or TRAPS-associated mutant TNFRSF1A. TNF binding was assessed in HEK 293 cell lines expressing R347A wild-type or mutant TNFRSF1A. Homology modeling of the 3-dimensional structure of the ectodomains of wild-type and mutant TNFRSF1A was performed.

RESULTS

TRAPS-associated mutant and wild-type TNFRSF1A behaved differently and had different localization properties within the cell, as a direct result of mutations in the ectodomains of TNFRSF1A. From a structural perspective, mutants with a predicted structure similar to that of the wild-type protein (e.g., R92Q) behaved similarly to wild-type TNFRSF1A, whereas forms of TNFRSF1A with mutations predicted to drastically destabilize the protein structure (e.g., cysteine mutations) showed defects in cell surface expression and TNF binding.

CONCLUSION

The results obtained from the in vitro experiments, in combination with the modeled structures, indicate that the phenotype and clinical differences between different TRAPS-associated mutants of TNFRSF1A result from different conformations of the TNFRSF1A ectodomains.

Tumor necrosis factor receptor I from patients with tumor necrosis factor receptor-associated periodic syndrome interacts with wild-type tumor necrosis factor receptor I and induces ligand-independent NF-κB activation

OBJECTIVE

To investigate the molecular consequences of expressing mutated forms of tumor necrosis factor receptor I (TNFRI) as found in patients with TNFR-associated periodic syndrome (TRAPS).

METHODS

We cloned and expressed full-length wild-type (WT) and T50K and P46L variants of TNFRI using a new tightly regulated doxycycline-dependent expression system. This system enabled the study of molecular interactions between these receptors at both physiologic and pathophysiologic levels of expression.

RESULTS

We used chemical crosslinking on the cell surface to show that WT and mutant forms of TNFRI, derived from TRAPS patients, interact in the absence of TNF ligand. Doxycycline-controlled up-regulation of one TNFRI allele, either WT or mutant, caused down-regulation of the other allele, indicating dynamic control of cell surface assembly. We also demonstrated that increased expression of mutant TNFRI (T50K) was associated with a parallel increase in NF-kappaB p65 (RelA) subunit activation, which did not occur with increased expression of WT TNFRI.

CONCLUSION

The T50K TRAPS-related variant is capable of sustaining inappropriate NF-kappaB activation, resulting in persistent auto-inflammation in target organs such as skin, synovial membrane, and the central nervous system. We conclude that some of the inflammatory processes seen in TRAPS do not involve direct interaction of TNF with its receptors, but that other proinflammatory mechanisms capable of up-regulating TNFRI expression may cause cellular activation through the NF-kappaB signaling pathway.

Mutant forms of tumour necrosis factor receptor I that occur in TNF-receptor-associated periodic syndrome retain signalling functions but show abnormal behaviour

Tumour necrosis factor (TNF)-receptor-associated periodic syndrome (TRAPS) is a hereditary autoinflammatory disorder involving autosomal-dominant missense mutations in TNF receptor superfamily 1A (TNFRSF1A) ectodomains. To elucidate the molecular effects of TRAPS-related mutations, we transfected HEK-293 cells to produce lines stably expressing high levels of either wild-type (WT) or single mutant recombinant forms of TNFRSF1A. Mutants with single amino acid substitutions in the first cysteine-rich domain (CRD1) were produced both as full-length receptor proteins and as truncated forms lacking the cytoplasmic signalling domain (deltasig). High-level expression of either WT or mutant full-length TNFRSF1A spontaneously induced apoptosis and interleukin-8 production, indicating that the mutations in CRD1 did not abrogate signalling. Consistent with this, WT and mutant full-length TNFRSF1A formed cytoplasmic aggregates that co-localized with ubiquitin and chaperones, and with the signal transducer TRADD, but not with the inhibitor, silencer of death domain (SODD). Furthermore, as expected, WT and mutant deltasig forms of TNFRSF1A did not induce apoptosis or interleukin-8 production. However, whereas the WT full-length TNFRSF1A was expressed both in the cytoplasm and on the cell surface, the mutant receptors showed strong cytoplasmic expression but reduced cell-surface expression. The WT and mutant deltasig forms of TNFRSF1A were all expressed at the cell surface, but a proportion of the mutant receptors were also retained in the cytoplasm and co-localized with BiP. Furthermore, the mutant forms of surface-expressed deltasig TNFRSF1A were defective in binding TNF-alpha. We conclude that TRAPS-related CRD1 mutants of TNFRSF1A possess signalling properties associated with the cytoplasmic death domain, but other behavioural features of the mutant receptors are abnormal, including intracellular trafficking and TNF binding.

Deficient tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor transport to the cell surface in human colon cancer cells selected for resistance to TRAIL-induced apoptosis

Many tumor cell types are sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Incubation of TRAIL-sensitive cells with TRAIL invariably leads to resistant survivors even when high doses of TRAIL are used. Because the emergence of resistance to apoptosis is a major concern in successful treatment of cancer, and TRAIL survivors may contribute to therapeutic failure, we investigated potential resistance mechanisms. We selected TRAIL-resistant SW480 human colon adenocarcinoma cells by repeatedly treating them with high and/or low doses of TRAIL. The resulting TRAIL-resistant clones were not cross-resistant to Fas or paclitaxel. Expression of modulators of apoptosis was not changed in the resistant cells, including TRAIL receptors, cFLIP, Bax, Bid, or IAP proteins. Surprisingly, we found that DISC formation was deficient in multiple selected TRAIL-resistant clones. DR4 was not recruited to the DISC upon TRAIL treatment, and caspase-8 was not activated at the DISC. Although total cellular DR4 mRNA and protein were virtually identical in TRAIL-sensitive parental and TRAIL-resistant clones, DR4 protein expression on the cell surface was essentially undetectable in the TRAIL-resistant clones. Moreover, exogenous DR4 and KILLER/DR5 were not properly transported to the cell surface in the TRAIL-resistant cells. Interestingly, TRAIL-resistant cells were resensitized to TRAIL by tunicamycin pretreatment, which increased cell surface expression of DR4 and KILLER/DR5. Our data suggest that tumor cells may become resistant to TRAIL through regulation of the death receptor cell surface transport and that resistance to TRAIL may be overcome by the glycosylation inhibitor/endoplasmic reticulum stress-inducing agent tunicamycin.

Histamine antagonizes tumor necrosis factor (TNF) signaling by stimulating TNF receptor shedding from the cell surface and Golgi storage pool

Tumor necrosis factor (TNF) activates pro-inflammatory functions of vascular endothelial cells (EC) through binding to receptor type 1 (TNFR1) molecules expressed on the cell surface. The majority of TNFR1 molecules are localized to the Golgi apparatus. Soluble forms of TNFR1 (as well as of TNFR2) can be shed from the EC surface and inhibit TNF actions. The relationships among cell surface, Golgi-associated, and shed forms of TNFR1 are unclear. Here we report that histamine causes transient loss of surface TNFR1, TNFR1 shedding, and mobilization of TNFR1 molecules from the Golgi in cultured human EC. The Golgi pool of TNFR1 serves both to replenish cell surface receptors and as a source of shed receptor. Histamine-induced shedding is blocked by TNF-alpha protease inhibitor, an inhibitor of TNF-alpha-converting enzyme, and through the H1 receptor via a MEK-1/p42 and p44 mitogen-activated protein kinase pathway. Cultured EC with histamine-induced surface receptor loss become transiently refractory to TNF. Histamine injection into human skin engrafted on immunodeficient mice similarly caused shedding of TNFR1 and diminished TNF-mediated induction of endothelial adhesion molecules. These results both clarify relationships among TNFR1 populations and reveal a novel anti-inflammatory activity of histamine.

The p55 tumour necrosis factor receptor TNFR1 contains a trans-Golgi network localization signal in the C-terminal region of its cytoplasmic tail

It has been reported in some human cells that, in addition to a plasma membrane localization, members of the tumour necrosis factor receptor superfamily may be localized to the Golgi complex. We have shown by immunofluorescence and immunoelectron microscopy that the p55 tumour necrosis factor receptor, TNFR1, is principally localized to the trans-Golgi network in the human breast carcinoma cell line, MCF7. Chimaeras consisting of the extracellular and transmembrane domains of CD8 together with the cytoplasmic tail of TNFR1 were targeted to the trans-Golgi network in stably transfected rat fibroblastic cells. Deletions in the cytoplasmic tails of these chimaeras demonstrated the requirement for the C-terminal sequence of 23 amino acids for this targeting. The 23 amino acid sequence is mostly outside the death domain and contains both an acid patch and a dileucine motif. Interaction of this sequence with membrane traffic adaptor proteins may play an important role in controlling the responses of cells to tumour necrosis factor, since binding of signalling adaptor proteins has only been demonstrated for plasma membrane, and not Golgi-localized, TNFR1.

Restricted localization of the TNF receptor CD120a to lipid rafts: a novel role for the death domain

The TNF-alpha receptor, CD120a, has recently been shown to be localized to both plasma membrane lipid rafts and to the trans Golgi complex. Through a combination of both confocal microscopy and sucrose density gradient ultracentrifugation, we show that amino acid sequences located within the death domain (DD) of CD120a are both necessary and sufficient to promote the appropriate localization of the receptor to lipid rafts. Deletion of the DD (CD120a.Delta321-425) prevented the receptor from being targeted to lipid rafts and resulted in a uniform plasma membrane localization. A similar loss of raft localization was also observed following pairwise deletion of the six alpha-helices that comprise the DD. In all situations, the loss of the ability of CD120a to become localized to lipid rafts following mutagenesis was paralleled by a failure of the receptor to initiate apoptosis. Furthermore, introduction of the lpr mutation into CD120a (CD120a.L351N) also resulted in both a loss in the ability of the receptor to signal apoptosis and to be appropriately localized to rafts. In contrast to CD120a, CD120b, which lacks a DD, is mainly expressed in the bulk plasma membrane and to a lesser extent in lipid rafts, but is absent from the Golgi complex. However, a chimeric receptor in which the DD of CD120a was fused to the cytoplasmic domain of CD120b was predominantly localized to lipid rafts. Collectively, these findings suggest that in addition to its role in CD120a signaling, an appropriately folded and functionally active DD is required for the localization of the receptor to lipid rafts.

Endothelial activation: intracellular signaling pathways

Tumor necrosis factor (TNF) is the prototypic proinflammatory cytokine and endothelial cells are the principal cellular targets of its actions. Here I review the responses of endothelial cells to TNF, with emphasis on the induction of endothelial leukocyte adhesion molecules. I focus on the biochemistry and cell biology of signal transduction in TNF-treated endothelial cells that lead to the expression of adhesion molecules.

Role of NF-kappaB activity in apoptotic response of keratinocytes mediated by interferon-gamma, tumor necrosis factor-alpha, and tumor-necrosis-factor-related apoptosis-inducing ligand

An important step in tumorigenesis involves loss of sensitivity to various apoptotic signals by malignant cells, imbuing them with an enhanced survival phenotype. NF-kappaB also regulates epidermal thickness, susceptibility to apoptosis, and tumor formation in skin. Keratinocytes were examined for their susceptibility to apoptosis using cytokines produced during an immunologic response to tumor antigens, i.e., interferon-gamma and/or tumor necrosis factor-alpha (TNF-alpha). The role for NF-kappaB in this response was examined using a retroviral vector containing a degradation-resistant form of IkappaBalpha. Whereas interferon-gamma and TNF-alpha either alone or in combination did not induce apoptosis in keratinocytes, after infection with the retrovirus to block NF-kappaB activation they became susceptible to TNF-alpha but not Fas-induced apoptosis. Moreover, when keratinocytes with repressed NF-kappaB activity were simultaneously treated with interferon-gamma, there was a synergistic induction of apoptosis by TNF-alpha that was dependent on FADD, tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL), and caspase activation. Molecular abnormalities accompanying repressed NF-kappaB activity included failure to induce TNF-RII receptor together with enhanced levels of TRAIL death receptor 4. The ability of interferon-gamma when combined with TNF-alpha to mediate keratinocyte apoptosis included induction of TRAIL coupled with diminished capacity of keratinocytes with repressed NF-kappaB activity to increase the TRAIL decoy receptor-1, as well as lower levels of several NF-kappaB-dependent antiapoptotic proteins accompanied by enhanced caspase 8 levels. These results indicate that interferon-gamma and TNF-alpha synergistically induce keratinocyte apoptosis when concomitant induction of NF-kappaB is blocked. Participants in the apoptotic response mediated by NF-kappaB, besides cell-survival proteins, include modulation of TRAIL and both death and decoy receptors. Thus, not only does NF-kappaB signaling influence the intrinsic survival pathway for keratinocytes in normal skin, but it may also play a role in determining the apoptotic response to cytokines generated during an immune response via TRAIL produced by the keratinocytes themselves.

TNF signaling in vascular endothelial cells

Vascular endothelium is a major target of actions of the proinflammatory cytokine tumor necrosis factor (TNF). Increasingly, the intracellular pathways that are activated in response to TNF have been elucidated. Many of these pathways have proven to be cell type-specific, requiring that observations made in other cell types be confirmed or ruled out in endothelial cells (EC). In this review the authors will summarize the state of the field, emphasizing studies in cultured human EC.