Two tumour necrosis factor receptors: structure and function

Tumour necrosis factor (TNF) exerts two main effects: a beneficial one as an anti-infection, anti-tumour cytokine, and a detrimental one in the systemic inflammatory response syndrome (SIRS). Two receptors (TNF-R) mediate these effects, but their precise role in different cell types is far from solved. TNF induces receptor oligomerization, an event that is believed to connect the receptors to downstream signalling pathways. Recent research suggests that several TNF-R-associated proteins, including kinases, may initiate cytoplasmic signal transduction.     

Clinical applications of tumour necrosis factor

Tumour necrosis factor (TNF) is a polypeptide hormone produced in vivo by activated macrophages and lymphocytes. TNF has diverse effects in vivo and has a physiological role as an immune modulator, as a mediator of the immune response, both through activation of neutrophils and eosinophils, and also affects the vascular endothelium. TNF also has antiviral activity and causes alterations in lipid metabolism. In disease states excessive production of TNF may have adverse affects. TNF has been implicated as a mediator of endotoxic shock, inflammatory joint disease, immune deficiency states, allograft rejection, and in the cachexia associated with malignant disease and some parasitic infections. When used in pharmacological doses, TNF is cytotoxic to many malignant cells in vitro and in vivo. The mechanisms underlying cytotoxicity are not fully elucidated but involve both a direct toxic effect to the cell and an indirect effect on tumour vasculature. Cytotoxicity is not universal and TNF may act as a differentiating agent or growth factor for some haematological cell types. So far the clinical application of TNF has been as a treatment for cancer in Phase I and II trials in patients with advanced disease and its efficacy here is still unproven. TNF may have potential for clinical application in combination therapy for cancer. There is experimental evidence for its interaction with other biological agents and cytotoxic drugs. The use of specific antibodies to inhibit production of TNF, or other agents to antagonise the toxic effects of TNF may have clinical relevance in counteracting septic shock and the clinical manifestations of TNF in inflammatory and neoplastic disease.     

Polymorphism in the tumour necrosis factor receptor II gene is associated with circulating levels of soluble tumour necrosis factor receptors in rheumatoid arthritis

Levels of soluble tumour necrosis factor receptors (sTNFRs) are elevated in the circulation of patients with rheumatoid arthritis (RA). Although these receptors can act as natural inhibitors of tumour necrosis factor-α, levels of sTNFRs in RA appear to be insufficient to prevent tumour necrosis factor-α induced inflammation. The factors that regulate circulating levels of sTNFRs are unclear, but polymorphisms in the tumour necrosis factor receptor genes may play a role. We investigated the relationship between polymorphisms in the tumour necrosis factor receptor I (TNF-RI) and II (TNF-RII) genes and levels of sTNFRs in two groups of Caucasian RA patients: one with early (disease duration ≤2 years; n = 103) and one with established disease (disease duration ≥5 years; n = 151). PCR restriction fragment length polymorphism analysis was used to genotype patients for the A36G polymorphism in the TNF-RI gene and the T676G polymorphism in TNF-RII. Levels of sTNFRs were measured using ELISA. We also isolated T cells from peripheral blood of 58 patients with established RA with known TNF-R genotypes, and release of sTNFRs into the culture medium was measured in cells incubated with or without phytohaemagglutinin. Serum levels of the two sTNFRs (sTNF-RI and sTNF-RII) were positively correlated in both populations, and the level of each sTNFR was significantly higher in the patients with established disease (P < 0.0001). Multiple regression analyses corrected for age, sex and disease duration revealed a significant trend toward decreasing sTNF-RI and sTNF-RII levels across the TNF-RII genotypes (TT > TG > GG) of patients with established disease (P for trend = 0.01 and P for trend = 0.03, respectively). A similar nonsignificant trend was seen for early disease. No relationship with the TNF-RI A36G polymorphism was observed. sTNFRs released by isolated T cells exhibited a similar trend toward decreasing levels according to TNF-RII genotype, although only the association with levels of sTNF-RII was significant. Strong correlations were found between levels of circulating sTNFRs and levels released by T cells in vitro. Our data indicate that the T676G polymorphism in TNF-RII is associated with levels of sTNFRs released from peripheral blood T cells, and with circulating levels of sTNFR in patients with RA.     

Mechanism of tumour necrosis factor alpha mediated eosinophil survival

Prolonged eosinophil survival is an essential step in the late and chronic phases of allergic inflammation and is regulated by the eosinophil survival cytokines. Our work has demonstrated that tumour necrosis factor (TNF)-alpha enhances survival (Trypan blue exclusion test) of human peripheral blood eosinophils from mildly allergic patients in a dose-dependent manner. The survival activity of TNF-alpha was inhibited by anti-TNF-RI, anti-TNF-RII antagonist antibodies and anti-granulocyte-monocyte colony-stimulating factor (GM-CSF) neutralizing antibodies but not by anti-interleukin (IL)-3 or anti-IL-5 antibodies. Furthermore, TNF-alpha-induced GM-CSF release from eosinophils. Anti-TNF-alpha antibodies also inhibited GM-CSF release from eosinophils induced by rat mast cell sonicate, which enhances eosinophil survival. To define the signal transduction pathway involved in GM-CSF production, eosinophils were incubated either with various mitogen-activated protein kinases (MAPK) inhibitors (MEK, JNK, P38), or Cyclosporin A (calcineurin inhibitor), or MG-132 (proteasome inhibitor). Only the proteasome inhibitor significantly decreased both TNF-alpha-enhanced eosinophil survival (from 38.1+/-4.1% to 13.3+/-1.4%) and GM-CSF release (from 6.2+/-0.7 pg/ml to 0.3+/-0.1 pg/ml). TNF-alpha also induced nuclear factor-kappaB (NF-kappaB) translocation to the nucleus, an essential step in GM-CSF mRNA production. All these findings provide evidence that NF-kappaB is involved in TNF-alpha-enhanced eosinophil survival through the regulation of GM-CSF production by eosinophils.     

Expression and purification of woodchuck tumour necrosis factor alpha

The production of recombinant woodchuck cytokines is an essential prerequisite to study the immune response to hepadnavirus infection in the woodchuck model. Woodchuck tumour necrosis factor-alpha (TNF-alpha) was expressed in mammalian cells and in Escherichia coli. A test system for the biological activity of woodchuck TNF-alpha was established on basis of its cytotoxic effect to the murine fibrosarcoma cell line L929. Recombinant TNF-alpha was purified and used for the production of neutralizing antisera.     

Production of urinary tumour necrosis factors and soluble tumour necrosis factor receptors in bladder cancer patients afterbacillus Calmette-Guerin immunotherapy

Intravesical immunotherapy for bladder cancer is the most effective form of tumour immunotherapy. Following repeated instillations of bacillus Calmette-Guérin (BCG) organisms into the bladder large 0quantities of several cytokines are detected in the urine. These cytokines include interleukins IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, tumour necrosis factor α (TNFα), interferon γ (IFNγ) and also soluble intercellular adhesion molecule ICAM-1. In the work reported here we simultaneously quantified urinary levels of TNFα, TNFβ, TNF receptor I and TNF receptor II by enzyme-linked immunosorbent assay (ELISA) techniques and compared this with bioactive levels of TNF. This was undertaken with a limited number of patients throughout a course of six instillations of immuno therapy. Sequential instillations of BCG induced secretion of TNFα and TNFβ into urine. These cytokines were not always secreted simultaneously, perhaps suggesting differential regulation of their synthesis. Maximal concentrations of TNFα were 675 pg/ml and TNFβ 47 pg/ml. High levels of both species of soluble TNF receptor were readily identified in urine. Maximal levels of sTNF-RI were 6200 pg/ml (range from 0) and for sTNF-RII 7800 pg/ml (range from 0). Contrasting with earlier published observations concerning cytokine levels, the concentration of soluble receptor did not increase with repeated instillation. In apparent contrast with the ELISA data, very low levels of bioactive TNF were identified by the L929 bioassay (maximum concentration 1 U/ml) despite the elevated concen t ration of immunoreactive TNF. The large concentrations of soluble TNF receptor in patients’ urine samples could account for the apparently low bioactivity as determined by the L929 cytotoxicity assay. The precise nature of the role of TNF in BCG immunotherapy remains undetermined; however, it is thought that proinflammatory cytokines are in part responsible for the clinical efficacy of this therapeutic approach. Whether other cytokines are antogonised by soluble binding proteins remains to be determined. Furthermore, whether TNF is bioactive in the bladder wall and only neutralised in the urine also requires investigation. Received: 24 August 1994 / Accepted: 17 October 1994     

Induction of tumour necrosis factor alpha in experimental animals treated with hepatotoxicants.

Administrations of hepatotoxicants namely carbon tetrachloride (CCl4:0.4 ml in 1.2 ml of liquid paraffin) and ANIT (1 ml of 1.5% solution in liquid paraffin) in Charles foster rats (force fed) and D-galactosamine (8 mg in water per swiss albino mouse, ip) induce the release of TNF-alpha in case of CCl4 and D-galactosamine. High TNF-alpha level was observed up to 48 hr in CCl4 and up to 24 hr in D-galactosamine treated animals. Elevated levels of biochemical like ALP and SGPT are also recorded. TNF-alpha level can be measured of tissue damage and prognosis in case of hepatitis.     

Structure of CrmE, a virus-encoded tumour necrosis factor receptor

Vaccinia virus (VACV), the smallpox vaccine, encodes many proteins that subvert the host immune response. One of these, cytokine response modifier E (CrmE), is secreted by infected cells and protects these cells from apoptotic challenge by tumour necrosis factor alpha (TNFalpha). We have expressed recombinant CrmE from VACV strain Lister in Escherichia coli, shown that the purified protein is monomeric in solution and competent to bind TNFalpha, and solved the structure to 2.0 A resolution. This is the first structure of a virus-encoded tumour necrosis factor receptor (TNFR). CrmE shares significant sequence similarity with mammalian type 2 TNF receptors (TNFSFR1B, p75; TNFR type 2). The structure confirms that CrmE adopts the canonical TNFR fold but only one of the two "ligand-binding" loops of TNFRSF1A is conserved in CrmE, suggesting a mechanism for the higher affinity of poxvirus TNFRs for TNFalpha over lymphotoxin-alpha. The roles of dimerisation and pre-ligand-assembly domains (PLADs) in poxvirus and mammalian TNFR activity are discussed.     

Role of tumour necrosis factor in the tumour-necrotizing activity of agents with diverging toxicity

Summary We investigated the ability of various tumournecrotizing agents with diverging toxicity to induce tumour necrosis factor (TNF) and cytostatic activity inPropionibacterium-acnes-primed Swiss and tumour-bearing BALB/c mice, and the capacity of anti-TNF antibodies to inhibit induction of tumour necrosis by the agents. Lipid A and especially its combination with muramyl dipeptide induced high TNF levels in Swiss mice, as measured in the serum. Lower levels were induced by detoxified lipid A and the nontoxic dsRNA, polyadenylic polyuridylic acid, either alone or combined with muramyl dipeptide. The toxic agents also appeared the strongest inducers of mediators with cytostatic activity against cultured endothelial cells and MethA tumour cells. Anti-TNF antibodies partially reduced the cytostatic activity of the sera against MethA cells. Tumour-bearing BALB/c mice produced only low levels of TNF and cytostatic factors in response to all agents. Recombinant mouse TNF hardly reduced the DNA synthesis of MethA cells, unless normal mouse serum was added. Serum fromP.-acnes-treated Swiss mice and tumour-bearing BALB/c mice, that were inhibitory on their own, failed to potentiate the action of TNF. Serum from Swiss mice treated with toxic, but not detoxified, lipid A caused extensive tumour necrosis upon injection into MethA-bearing BALB/c mice. This activity was completely abolished by pre-incubation of the serum with anti-TNF. The tumour-necrotizing activity of the agents could be partially reduced by prior injection of these antibodies. Results show that the capacity of the agents to induce TNF and cytostatic activity is not related to their antitumour potential. Although TNF is likely to be a crucial mediator of the tumour-necrotizing action of the toxic as well as the nontoxic agents, it is probably not the sole mediator. Data also indicate that induction of tumour necrosis does not require induction of high and, thus toxic, TNF levels in the serum.     

Inhibition of fibronectin-activated migration of microvascular endothelial cells by interleukin-1alpha, tumour necrosis factor alpha and interferon gamma

The effect of interferon gamma (IFN) and the inflammatory cytokines tumour necrosis factor alpha (TNF) and interleukin 1alpha (IL-1) on micro- and macrovascular endothelial cell (EC) proliferation and migration was analysed. Whereas both micro- and macrovascular EC were growth-inhibited in response to the aforementioned cytokines, only microvascular EC were sensitive to TNF, IL-1 and IFN as inhibitors of fibronectin-activated cell migration. In addition, because microvascular EC play a crucial role in angiogenesis, and the formation of new capillaries depends upon the presence of angiogenic polypeptides, we evaluated the synthesis of fibroblast growth factor (FGF) type 1 and 2, Vascular Endothelial Growth Factor (VEGF) and Hepatocyte Growth Factor (HGF) in our system. Both micro- and macrovascular EC produce large amounts of FGF-2, which is mainly localized in the nucleus, and almost undetectable levels of FGF-1. In addition, the two cell types synthesize notable levels of VEGF and no HGF. Whether these findings are relevant to the different in vivo functions of EC residing different districts remains the focus of additional studies.     

The tumour necrosis factor receptor-associated periodic syndrome: current concepts

The tumour necrosis factor receptor (TNFR)-associated periodic syndrome (TRAPS) is an autosomal dominant, multisystemic, autoinflammatory disorder caused by mutations in the TNFR1 gene ( TNFRSF1A ). Traps seems to be the most common hereditary periodic fever (HPF) syndrome in some western populations, and the second most prevalent HPF worldwide, behind familial mediterranean fever (FMF). The proteins involved in susceptibility to TRAPS (TNFRSF1A) and FMF (pyrin) are both members of the death-domain-fold superfamily. Mutations affecting these proteins might cause dysregulation of innate immune responses, with a propensity to autoinflammation. Most TRAPS patients have reduced blood levels of soluble TNFRSF1A between attacks, with an inappropriately small increase during bouts of fever. The pathogenesis of the 'hyperinflammatory state' in TRAPS has been variously ascribed to a shedding defect of TNFRSF1A from the cell surface resulting in increased TNF inflammatory signalling, or impaired TNF apoptotic signalling. Some low-penetrance TNFRSF1A variants also contribute to the clinical phenotype in individuals carrying other HPF-associated mutations, and have been reported in several disorders such as Beh?et's disease and systemic lupus erythematosus. Synthetic anti-TNF agents provide a rational form of therapy for TRAPS, and have been shown to delay or indeed prevent development of systemic amyloidosis (AA type), a life-threatening complication in this condition.     

Interleukin 1 and tumour necrosis factor increase phosphorylation of fibroblast proteins

Interleukin 1 (IL1) or tumour necrosis factor (TNF) stimulated phosphorylation of a triad of 27 kDa phosphoproteins (pI 6.0, 5.7 and 5.5) in human dermal fibroblasts. The change was dependent on the dose of cytokine in the range 0.1-20 ng, was detectable between 3 and 5 min after stimulation and was maximal by 10 min. The proteins were found in the cytosol after subcellular fractionation. The 32P was removed from them by alkali, indicating the presence of phosphoserine and/or phosphothreonine. The results suggest that early changes in serine/threonine protein kinase activity may be involved in responses of fibroblasts to IL1 and TNF.     

Induction of tumour necrosis factor by staphylococcal toxic shock toxin 1

Abstract Staphylococcal toxic shock syndrome toxin 1 (TSST1) induced the release of tumour necrosis factor (TNF) from human and rabbit monocytes in vitro. Nanogram amounts of TSST1 were sufficient to induce TNF release. There was considerable variation in response between cells from different rabbits and different donors. Rabbit monocytes were slightly more sensitive to TSST1 than were human monocytes. Release of TNF in vivo could explain many of the symptoms of toxic shock syndrome.     

The significance of tumour necrosis factor serum levels in organ transplantation

This paper describes a detailed study of tumour necrosis factor release during the immediate post transplant period in recipients of liver and kidney allografts. The results show no correlation between levels of TNF and rejection in Azathioprine and steroid treated patients and give good correlation in cyclosporin A immunosuppressed patients. Treatment with monoclonal antibody Campath 1-G caused high levels of TNF production. Interleukin-1 levels were not associated with levels of TNF. Sequential measurements of TNF levels may provide an aid to early diagnosis of graft rejection.