Distinct Differences between TNF Receptor 1- and TNF Receptor 2- mediated Activation of NFκB

The Signaling Pathway of TNF Receptors: Linking Animal Models of Renal Disease to Human CKD

Chronic kidney disease (CKD) has been recognized as a global public health problem. Despite the current advances in medicine, CKD-associated morbidity and mortality remain unacceptably high. Several studies have highlighted the contribution of inflammation and inflammatory mediators to the development and/or progression of CKD, such as tumor necrosis factor (TNF)-related biomarkers. The inflammation pathway driven by TNF-α, through TNF receptors 1 (TNFR1) and 2 (TNFR2), involves important mediators in the pathogenesis of CKD. Circulating levels of TNFRs were associated with changes in other biomarkers of kidney function and injury, and were described as predictors of disease progression, cardiovascular morbidity, and mortality in several cohorts of patients. Experimental studies describe the possible downstream signaling pathways induced upon TNFR activation and the resulting biological responses. This review will focus on the available data on TNFR1 and TNFR2, and illustrates their contributions to the pathophysiology of kidney diseases, their cellular and molecular roles, as well as their potential as CKD biomarkers. The emerging evidence shows that TNF receptors could act as biomarkers of renal damage and as mediators of the disease. Furthermore, it has been suggested that these biomarkers could significantly improve the discrimination of clinical CKD prognostic models.

Cordyceps militaris induces apoptosis in ovarian cancer cells through TNF-α/TNFR1-mediated inhibition of NF-κB phosphorylation

BACKGROUND

Cordyceps militaris (L.) Fr. (C. militaris) exhibits pharmacological activities, including antitumor properties, through the regulation of the nuclear factor kappa B (NF-κB) signaling. Tumor Necrosis Factor (TNF) and TNF-α modulates cell survival and apoptosis through NF- κB signaling. However, the mechanism underlying its mode of action on the NF-κB pathway is unclear.

METHODS

Here, we analyzed the effect of C. militaris extract (CME) on the proliferation of ovarian cancer cells by confirming viability, morphological changes, migration assay. Additionally, CME induced apoptosis was determined by apoptosis assay and apoptotic body formation under TEM. The mechanisms of CME were determined through microarray, immunoblotting and immunocytochemistry.

RESULTS

CME reduced the viability of cells in a dose-dependent manner and induced morphological changes. We confirmed the decrease in the migration activity of SKOV-3 cells after treatment with CME and the consequent induction of apoptosis. Immunoblotting results showed that the CME-mediated upregulation of tumor necrosis factor receptor 1 (TNFR1) expression induced apoptosis of SKOV-3 cells via the serial activation of caspases. Moreover, CME negatively modulated NF-κB activation via TNFR expression, suggestive of the activation of the extrinsic apoptotic pathway. The binding of TNF-α to TNFR results in the disassociation of IκB from NF-κB and the subsequent translocation of the active NF-κB to the nucleus. CME clearly suppressed NF-κB translocation induced by interleukin (IL-1β) from the cytosol into the nucleus. The decrease in the expression levels of B cell lymphoma (Bcl)-xL and Bcl-2 led to a marked increase in cell apoptosis.

CONCLUSION

These results suggest that C. militaris inhibited ovarian cancer cell proliferation, survival, and migration, possibly through the coordination between TNF-α/TNFR1 signaling and NF-κB activation. Taken together, our findings provide a new insight into a novel treatment strategy for ovarian cancer using C. militaris.

The Role of the Nuclear Factor κB Pathway in the Cellular Response to Low and High Linear Energy Transfer Radiation

Astronauts are exposed to considerable doses of space radiation during long-term space missions. As complete shielding of the highly energetic particles is impracticable, the cellular response to space-relevant radiation qualities has to be understood in order to develop countermeasures and to reduce radiation risk uncertainties. The transcription factor Nuclear Factor κB (NF-κB) plays a fundamental role in the immune response and in the pathogenesis of many diseases. We have previously shown that heavy ions with a linear energy transfer (LET) of 100–300 keV/µm have a nine times higher potential to activate NF-κB compared to low-LET X-rays. Here, chemical inhibitor studies using human embryonic kidney cells (HEK) showed that the DNA damage sensor Ataxia telangiectasia mutated (ATM) and the proteasome were essential for NF-κB activation in response to X-rays and heavy ions. NF-κB’s role in cellular radiation response was determined by stable knock-down of the NF-κB subunit RelA. Transfection of a RelA short-hairpin RNA plasmid resulted in higher sensitivity towards X-rays, but not towards heavy ions. Reverse Transcriptase real-time quantitative PCR (RT-qPCR) showed that after exposure to X-rays and heavy ions, NF-κB predominantly upregulates genes involved in intercellular communication processes. This process is strictly NF-κB dependent as the response is completely absent in RelA knock-down cells. NF-κB’s role in the cellular radiation response depends on the radiation quality.

Chlorpyrifos and cypermethrin induce apoptosis in human neuroblastoma cell line SH-SY5Y

Our previous in vivo studies showed that chlorpyrifos (CPF) and cypermethrin (CM) in a mixture dermally administered, strongly inhibited cholinesterase activity in plasma and the brain and were very toxic to the rat central nervous system. In this work, the mechanisms of neurotoxicity have not been elucidated. We used human undifferentiated SH-SY5Y cells to study mechanisms of pesticide-induced neuronal cell death. It was found that chlorpyrifos (CPF) and its mixture with cypermethrin (CPF+CM) induced cell death of SH-SY5Y cells in a dose- and time-dependent manner, as shown by MTT assays. Pesticide-induced SH-SY5Y cell death was characterized by concentration-dependent down-regulation of Bcl-2 and Bcl-xL as well as an increase in the caspase 3 activation. Pan-caspase inhibitor Q-VD-OPh produced a slight but significant reversal effect of pesticide-induced toxicity indicating that the major caspase pathways are not integral to CPF- and CPF+CM-induced cell death. Furthermore, signal transduction inhibitors PD98059, SL-327, SB202190, SP600125 and mecamylamine failed to attenuate pesticides effect. Atropine exhibited minimal ability to reverse toxicity. Finally, it was shown that inhibition of TNF-α by pomalidomide attenuated CPF-/CPF+CM-induced apoptosis. Overall, our data suggest that FAS/TNF signalling pathways may participate in CPF and CPF+CM toxicity.

Enhanced apoptosis of monocytes from complication-free juvenile-onset diabetes mellitus type 1 may be ameliorated by TNF-α inhibitors

Diabetes mellitus type 1 is associated with an enhanced apoptosis of different cells and tissues, accelerating occurrence of diabetic microvascular complications. The aim of our study was to determine spontaneous apoptotic potential of the monocyte subsets in juvenile-onset complication-free diabetes mellitus type 1 and to compare them with the corresponding values of the healthy. Moreover, we wanted to assess effects of TNF-R1 blocking agents and those of general TNF-α blocker (Infliximab) on spontaneous apoptosis of monocytes. Sixty randomly selected DM1 patients (14.5 ± 3.2 years) and 30 healthy (13.5 ± 2.8 years) volunteers were enrolled in the study. Our results indicate that three monocyte subsets are distinguishable in the groups of young diabetic patients and the healthy, similarly to in the blood of adults. DM1 patients were characterized by higher values of apoptotic monocytes than the healthy. The manipulation with drugs inhibiting TNF-R1 expression diminished the pool of CD16(+) apoptotic monocytes. Infliximab reduced the apoptotic CD16(-) cells. In conclusion, diabetes mellitus type 1 is associated with greater apoptosis of three monocyte subsets which may contribute to the development of microvascular complications. TNF-α modifiers appear to ameliorate monocyte apoptosis. They may be useful for controlling excessive monocyte apoptosis in diabetic patients.

Genetic deletion of TNFRII gene enhances the Alzheimer-like pathology in an APP transgenic mouse model via reduction of phosphorylated IκBα

Tumor necrosis factor receptor II (TNFRII) is one of the TNF receptor superfamily members and our recent pathological studies show that TNFRII is deficient in the brains of Alzheimer's disease (AD). However, the mechanisms of TNFRII in AD pathogenesis remain unclear. In the present study, by using the gene-targeting approach to delete TNFRII in AD transgenic mouse model, we found that, in the brain of APP23 mice with TNFRII deletion (APP23/TNFRII(-/-)), AD-like pathology, i.e. plaque formation and microglial activation, occurs as early as 6 months of age. To test whether the increased levels of Aβ plaques was due to elevated Aβ, we measured Aβ and found that Aβ levels indeed were significantly increased at this age. Because β-secretase, BACE1, is critical enzyme for Aβ production, we have examined BACE1 and found that BACE1 is increased in both protein levels and enzymatic activity as early as 6 months of age; Having shown that BACE1 promoter region contains NF-κB binding sites, we found that cytoplasmic NF-κB was elevated and SUMO1 binding to IκBα was decreased. To further verify these findings, we have overexpressed TNFRII and identified that overexpressing TNFRII can reverse the findings from APP23/TNFRII(-/-) mice. Altogether, our results demonstrate novel roles of TNFRII in the regulation of Aβ production, suggesting a potential therapeutic strategy for AD by up-regulating TNFRII levels and elevating phosphorylated IκBα by SUMOylation.

The Anti-inflammatory Role of Endometase/Matrilysin-2 in Human Prostate Cancer Cells

Human endometase/matrilysin-2/matrix metalloproteinase-26 (MMP-26) is an endopeptidase mostly produced by human carcinoma cells. While MMPs are thought to regulate the dynamics of extracellular matrix turnover, new evidence shows that these enzymes may play a critical regulatory role in inflammation. To investigate the role of MMP-26 in inflammation, three different variants of androgen repressed human prostate cancer (ARCaP) cells were investigated in the study: parental, MMP-26 sense cDNA-transfected, and MMP-26 antisense cDNA-transfected ARCaP cells. Protein lysates and RNA from control and genetically modified cells were analyzed by Western blotting and real-time reverse transcription polymerase chain reaction on arrays of genes critical to the inflammatory response. In comparison to parental controls, up-regulation of MMP-26 expression in MMP-26 sense cDNA-transfected cells resulted in a decrease in inflammatory genes expression. Conversely, inflammatory genes were up-regulated in MMP-26 antisense cDNA-transfected cells. Therefore, modulation of MMP-26 levels significantly affects the expression of inflammatory genes, suggesting an anti-inflammatory role of MMP-26. To determine a possible mechanism of action, further analysis, at both transcript and protein levels, revealed a dramatic down-regulation of interleukin-10 receptor B (IL10RB) in MMP-26 antisense cDNA-transfected cells. The low level of IL10RB was inversely correlated with matrix metalloproteinase-9 (MMP-9) expression. Collectively, our data suggest that the deficiency of MMP-26 may promote inflammation via inhibition of IL10RB-mediated signaling. These results propose a novel anti-inflammation function of MMP-26 and could provide novel molecular insight of therapeutic targeting.

Differential regulation of TNF receptor 1 and receptor 2 in adiponectin expression following myocardial ischemia

BACKGROUND

In vitro experiments demonstrate that adiponectin, a cardioprotective cytokine, is inhibited by tumor necrosis factor-alpha (TNFα). However, the role of TNFα in post-myocardial infarction (post-MI) adiponectin reduction remains unclear. More importantly, the TNF receptor type (TNFR1 or TNFR2) responsible for TNFα-mediated suppression of adiponectin production is unknown. The current study determined the role of TNFα in post-myocardial infarction (post-MI) adiponectin reduction, and identified the receptor type responsible for TNFα-mediated suppression of adiponectin production.

METHODS AND RESULTS

Adult male wild type (WT) and three knockout variety (TNFα(-/-), TNFR1(-/-), and TNFR2(-/-)) mice were subjected to MI via coronary artery occlusion. Histological and biochemical analyses were performed 3 and 7days post-MI. In WT mice, MI significantly increased plasma TNFα, reduced adipocyte adiponectin mRNA, and decreased plasma adiponectin levels. TNFα deletion had no significant effect upon basal adiponectin level, and partially restored adiponectin expression/production post-MI (P<0.01 vs. WT). Basal adiponectin levels were significantly increased in TNFR1(-/-) (P<0.05 vs. WT), and unchanged in TNFR2(-/-) mice. Importantly, suppressed adiponectin expression/production by MI or TNFα administration was markedly decreased by TNFR1 deletion (P<0.01 vs. WT), but exacerbated by TNFR2 deletion (P<0.05 vs. WT). Mechanistically, TNFR1 knockout significantly inhibited, whereas TNFR2 knockout further enhanced TNFα-induced mRNA and protein expression of ATF3, a transcriptional factor known to significantly inhibit adiponectin expression.

CONCLUSION

Our study demonstrates that TNFα overproduction is responsible for reduced adiponectin expression/production following MI. Furthermore, we show that TNFR1/TNFR2 exerts opposite effects upon adiponectin expression/production via differential regulation of ATF3.

TNF-α type 2 receptor mediates renal inflammatory response to chronic angiotensin II administration with high salt intake in mice

Tumor necrosis factor-alpha (TNF-α) has been implicated in salt-sensitive hypertension and renal injury (RI) induced by angiotensin II (ANG II). To determine the receptor type of TNF-α involved in this mechanism, we evaluated the responses to chronic ANG II infusion (25 ng/min by implanted minipump) given with high-salt diet (HS; 4% NaCl) for 2 wk in gene knockout mice for TNF-α receptor type 1 (TNFR1KO; n = 6) and type 2 (TNFR2KO; n = 6) and compared the responses with those in wild-type (WT; C57BL/6; n = 6) mice. Blood pressure in these mice was measured by implanted radiotelemetry as well as by tail-cuff plethysmography. RI responses were assessed by measuring macrophage cell infiltration (CD68(+) immunohistochemistry), glomerulosclerosis (PAS staining), and interstitial fibrosis (Gomori's trichrome staining) in renal tissues at the end of the treatment period. The increase in mean arterial pressure induced by ANG II + HS treatment was not different in these three groups of mice (TNFR1KO, 114 ± 1 to 161 ± 7 mmHg; TNFR2KO, 113 ± 1 to 161 ± 3 mmHg; WT, 110 ± 3 to 154 ± 3 mmHg). ANG II + HS-induced RI changes were similar in TNFR1KO mice but significantly less in TNFR2KO mice (macrophage infiltration, 0.02 ± 0.01 vs. 1.65 ± 0.45 cells/mm(2); glomerulosclerosis, 26.3 ± 2.6 vs. 35.7 ± 2.2% area; and interstitial fibrosis, 5.2 ± 0.6 vs. 8.1 ± 1.1% area) compared with the RI changes in WT mice. The results suggest that a direct activation of TNF-α receptors may not be required in inducing hypertensive response to chronic ANG II administration with HS intake, but the induction of inflammatory responses leading to renal injury are mainly mediated by TNF-α receptor type 2.

TNF-α mediates macrophage-induced bystander effects through Netrin-1

Macrophage-induced bystander effects have been implicated as an important mediator of chromosomal instability and colon cancer triggered by Enterococcus faecalis, a human intestinal commensal bacteria. There is little understanding about how inflammatory cytokines mediate bystander effects, but questions in this area are important because of the pivotal contributions made by inflammatory processes to cancer initiation and progression. Here, we report that the central proinflammatory cytokine TNF-α acts as a diffusible mediator of the bystander effects induced by macrophages, an effect caused by a proliferation of macrophages that trigger epithelial cell production of Netrin-1, a neuronal guidance molecule. TNF-α-mediated bystander assays used a murine coculture system of primary colonic epithelial cells and E. faecalis-infected macrophages (in vitro), with an interleukin 10 (IL-10)-deficient mouse model of colon cancer that involves long-term colonization with E. faecalis (in vivo). In cell cocultures, we observed increased expression of the TNF-α receptor Tnfrsf1b and Netrin-1. These effects were blocked by anti-TNF-α antibody or by pretreatment with an inhibitor of NF-κB signaling. RNAi-mediated attenuation of Tnfrsf1b decreased TNF-α-induced netrin-1 production and augmented epithelial cell apoptosis in culture. Extending these observations, colon biopsies from E. faecalis-colonized IL-10(-/-) mice exhibited crypt hyperplasia and increased staining for macrophages, TNF-α, netrin-1, NF-κB, Tnfrsf1b, and the proliferation marker proliferating cell nuclear antigen while also displaying a reduction in epithelial cell apoptosis. Together, our results define a pathway for macrophage-induced bystander effects in which TNF-α triggers TNFRSF1b receptor signaling leading to increased production of Netrin-1, crypt hyperplasia, and decreased epithelial cell apoptosis. In elucidating an important commensal-associated proinflammatory mechanism in the intestinal microenvironment, our work highlights the role of Netrin-1 and a specific TNF-α receptor as candidate targets to prevent or treat colorectal cancer.

Immune-neuroendocrine integration at the adrenal gland: cytokine control of the adrenomedullary transcriptome

The bovine chromaffin cell represents an ideal model for the study of cell signaling to gene expression by first messengers. An abundance of GPCR, ionotropic, and growth factor receptors are expressed on these cells, and they can be obtained and studied as an abundant highly enriched cell population; importantly, this is true of no other postmitotic neuroendocrine or neuronal cell type. Chromaffin cells have now been shown to bear receptors for cytokines whose expression in the circulation is highly elevated in inflammation, including tumor necrosis factor, interferon, interleukin-1, and interleukin-6. The use of bovine-specific microarrays, and various biochemical measurements in this highly homogenous cell preparation reveals unique cohorts of distinct genes regulated by cytokines in chromaffin cells, via signaling pathways that are in some cases uniquely neuroendocrine. The transcriptomic signatures of cytokine signaling in chromaffin cells suggest that the adrenal medulla may integrate neuronal, hormonal, and immune signaling during inflammation, through induction of paracrine factors that signal to both adrenal cortex and sensory afferents of the adrenal gland, and autocrine factors, which determine the duration and type of paracrine secretory signaling that occurs in either acute or chronic inflammatory conditions.

Tumour necrosis factor (TNF)-mediated NF-κB activation facilitates cellular invasion of non-professional phagocytic epithelial cell lines by Trypanosoma cruzi

At the site of infection, pro-inflammatory cytokines locally produced by macrophages infected with Trypanosoma cruzi can activate surrounding non-professional phagocytes such as fibroblasts, epithelial and endothelial cells, which can be further invaded by the parasite. The effect of secreted soluble factors on the invasion of these cells remains, however, to be established. We show here that two epithelial cell lines become significantly susceptible to the infection by the Y strain of T. cruzi after tumour necrosis factor (TNF) treatment. The increase in the invasion was correlated with the increasing concentration of recombinant TNF added to cultures of HEK293T or LLC-MK2 cells. Supernatants taken from PMA-differentiated human monocytes infected with T. cruzi also increased the permissiveness of epithelial cells to subsequent infection with the parasite, which was inhibited by a TNF monoclonal antibody. Furthermore, the permissiveness induced by TNF was inhibited by TPCK, and led to significant decrease in the number of intracellular parasites, providing evidence that activation of NF-κB induced by TNF favours the invasion of the epithelial cell lines by T. cruzi through yet an unidentified mechanism. Our data indicate that soluble factors released from macrophages early in the infection favours T. cruzi invasion of non-professional phagocytic cells.

Tumor necrosis factor receptor cross-talk

Extensive research has been performed to unravel the mechanistic signaling pathways mediated by tumor necrosis factor receptor 1 (TNFR1), by contrast there is limited knowledge on cellular signaling upon activation of TNFR2. Recently published data have revealed that these two receptors not only function independently, but also can influence each other via cross-talk between the different signaling pathways initiated by TNFR1 and TNFR2 stimulation. Furthermore, the complexity of this cross-talk is also dependent on the different signaling kinetics between TNFR1 and TNFR2, by which a delicate balance between cell survival and apoptosis can be maintained. Some known signaling factors and the kinetics that are involved in the receptor cross-talk between TNFR1 and TNFR2 are the topic of this review.

Increased IkappaB alpha expression is essential for the tolerogenic property of TGF-beta-exposed APCs

IkappaB alpha is an inhibitor of the transcriptional factor NF-kappaB, and it is an essential component of the signaling pathways that lead to expression of inflammatory molecules. These include cytokines and costimulatory molecules associated with antigen presentation in an inflammatory immune response. In this study, we report that antigen-presenting cells exposed to TGF-beta induce peripheral tolerance by increasing IkappaB alpha expression. Exposure of antigen presenting cells (APCs) to TGF-beta is known to impair their ability to secrete IL-12, and such impairment correlated with reduced NF-kappaB activity as indicated by significantly reduced nuclear levels of p50, an essential subunit of NF-kappaB for IL-12 transcription. Blockade of increased nuclear IkappaB alpha in APCs by expression of small interfering RNA molecules (siRNAs) targeting IkappaB alpha transcripts prevented IL-12 impairment and the decline in nuclear p50 levels. Furthermore, such IkappaB alpha blockade also interfered with the tolerogenic property of TGF-beta-exposed APCs. However, increased expression of IkappaB alpha in APCs, independent of TGF-beta exposure, reduced nuclear p50 levels and permitted tolerance induction by APCs. Thus, our findings attribute a direct and significant role to IkappaB alpha in the tolerogenic potential of APCs. Increased IkappaB alpha expression in APCs may therefore offer a therapeutic approach to achieve antigen-specific immunomodulation.

Immunoregulatory role of TNFalpha in inflammatory kidney diseases

Tumor necrosis factor alpha (TNFalpha), a pleiotropic cytokine, plays important inflammatory roles in renal diseases such as lupus nephritis, anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis and renal allograft rejection. However, TNFalpha also plays critical immunoregulatory roles that are required to maintain immune homeostasis. These complex biological functions of TNFalpha are orchestrated by its two receptors, TNFR1 and TNFR2. For example, TNFR2 promotes leukocyte infiltration and tissue injury in an animal model of immune complex-mediated glomerulonephritis. On the other hand, TNFR1 plays an immunoregulatory function in a murine lupus model with a deficiency in this receptor that leads to more severe autoimmune symptoms. In humans, proinflammatory and immunoregulatory roles for TNFalpha are strikingly illustrated in patients on anti-TNFalpha medications: These treatments are greatly beneficial in certain inflammatory diseases such as rheumatoid arthritis but, on the other hand, are also associated with the induction of autoimmune lupus-like syndromes and enhanced autoimmunity in multiple sclerosis patients. The indication for anti-TNFalpha treatments in renal inflammatory diseases is still under discussion. Ongoing clinical trials may help to clarify the potential benefit of such treatments in lupus nephritis and ANCA-associated glomerulonephritis. Overall, the complex biology of TNFalpha is not fully understood. A greater understanding of the function of its receptors may provide a framework to understand its contrasting proinflammatory and immunoregulatory functions. This may lead the development of new, more specific anti-inflammatory drugs.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

TNF-alpha-induced apoptosis is prevented by erythropoietin treatment on SH-SY5Y cells

The growth factor erythropoietin (Epo) has shown neuronal protective action in addition to its well known proerythroid activity. Furthermore, Epo has dealt with cellular inflammation by inhibiting the expression of several proinflammatory cytokines, such as IL-1 and TNF-alpha. The action of TNF can have both apoptotic and antiapoptotic consequences due to altered balance between different cell signalling pathways. This work has focused on the apoptotic effects of this cytokine and the potential protective action of Epo. The model we used was neuroblastoma SH-SY5Y cells cultured in the presence of 25 ng/ml TNF-alpha or pretreated with 25 U/ml Epo for 12 h before the addition of TNF-alpha. Apoptosis was evaluated by differential cell count after Hoechst staining, analysis of DNA ladder pattern, and measurement of caspase activity. Despite its ability to induce NF-kappaB nuclear translocation, TNF-alpha induced cell death, which was found to be associated to upregulation of TNF Receptor 1 expression. On the other hand, cells activated by Epo became resistant to cell death. Prevention of death receptor upregulation and caspase activation may explain this antiapoptotic effect of Epo, which may be also favoured by the induction of a higher expression of protective factors, such as Bcl-2 and NF-kappaB, through mechanisms involving Jak/STAT and PI3K signalling pathways.

Tumor necrosis factor (TNF)-alpha persistently activates nuclear factor-kappaB signaling through the type 2 TNF receptor in chromaffin cells: implications for long-term regulation of neuropeptide gene expression in inflammation

Chromaffin cells of the adrenal medulla elaborate and secrete catecholamines and neuropeptides for hormonal and paracrine signaling in stress and during inflammation. We have recently documented the action of the cytokine TNF-alpha on neuropeptide secretion and biosynthesis in isolated bovine chromaffin cells. Here, we demonstrate that the type 2 TNF-alpha receptor (TNF-R2) mediates TNF-alpha signaling in chromaffin cells via activation of nuclear factor (NF)-kappaB. Microarray and suppression subtractive hybridization have been used to identify TNF-alpha target genes in addition to those encoding the neuropeptides galanin, vasoactive intestinal polypeptide, and secretogranin II in chromaffin cells. TNF-alpha, acting through the TNF-R2, causes an early up-regulation of NF-kappaB, long-lasting induction of the NF-kappaB target gene inhibitor kappaB (IkappaB), and persistent stimulation of other NF-kappaB-associated genes including mitogen-inducible gene-6 (MIG-6), which acts as an IkappaB signaling antagonist, and butyrate-induced transcript 1. Consistent with long-term activation of the NF-kappaB signaling pathway, delayed induction of neuropeptide gene transcription by TNF-alpha in chromaffin cells is blocked by an antagonist of NF-kappaB signaling. TNF-alpha-dependent signaling in neuroendocrine cells thus leads to a unique, persistent mode of NF-kappaB activation that features long-lasting transcription of both IkappaB and MIG-6, which may play a role in the long-lasting effects of TNF-alpha in regulating neuropeptide output from the adrenal, a potentially important feedback station for modulating long-term cytokine effects in inflammation.

Tumor Necrosis Factor Receptor 2–Mediated Tumor Suppression Is Nitric Oxide Dependent and Involves Angiostasis

Tumor necrosis factor (TNF) binds to two different receptors. Although most of its functions are attributed to TNF receptor 1 (TNFR1), the independent role of TNFR2 is still largely unknown. Using TNFR single or double knock-out mice, we show here that the expression of TNFR2 alone on host cells was sufficient to suppress the growth of TNF-secreting tumors in both immune competent and T/B lymphocyte-deficient severe combined immunodeficiency (SCID) mice. Histologic studies showed that TNF recruited, via TNFR2, large numbers of macrophages and efficiently inhibited angiogenesis in the tumor. In vitro, TNF activated TNFR1-deficient macrophages to produce nitric oxide (NO). Treatment of TNFR1 knock-out mice with L-NAME, a specific NO synthase inhibitor, almost completely eliminated TNF-induced angiostasis and tumor suppression. Moreover, L-NAME acted only during the first few days of tumor growth. Our results show for the first time that TNFR2 expressed on host innate immune cells is sufficient to mediate the antitumor effect of TNF, and NO is necessary for this process, possibly by inhibition of angiogenesis in the tumor.

Serum-soluble tumor necrosis factor receptor 2 (sTNF-R2) level determines clinical outcome in patients with aggressive non-Hodgkin's lymphoma

BACKGROUND

Recently investigators have worked to identify prognostic factors in non-Hodgkin's lymphoma (NHL) so an appropriate therapeutic plan can be put in action. The aim of the present study was to assess the prognostic significance of serum soluble tumor necrosis factor receptor (sTNF-R) 2 in aggressive NHL.

METHODS

One hundred and ten consecutive patients with aggressive NHL who were previously untreated (diffuse large B-cell lymphoma; 94, peripheral T-cell lymphoma; 16) were prospectively enrolled in this study between 1997 and 2002. The patients were treated with 6-8 cycles of CHOP or THP-COP regimens.

RESULTS

High serum sTNF-Rs level was associated with some poor prognostic factors and low complete remission rate. Patients with high sTNF-R1 (4 ng/mL and over) and sTNF-R2 (15 ng/mL and over) at onset had significantly lower survival rates (5 yr: 19%, 19%) than those with low sTNF-R1 (under 4 ng/mL) and sTNF-R2 (under 15 ng/mL) (62% and 69%), respectively (P < 0.0005 and 0.0001). Multivariate analysis employing sTNF-R2 and some conventional prognostic factors demonstrated that a combination of sTNF-R2 and performance status, and that of sTNF-R2, sIL-2R, and LDH were significant prognostic factors for poor overall survival and for poor event-free survival, respectively. In addition, we attempted to use sTNF-R2 in combination with the international prognostic index (IPI). The patients in the high risk group and those with high sTNF-R2 in the low-intermediate (LI)/high-intermediate (HI) risk group had significantly lower survival rates than the patients in the low risk group and those with low sTNF-R2 in LI/HI risk group (P < 0.0001).

CONCLUSIONS

The results suggest that a high serum sTNF-R2 level predicts a poor prognosis in aggressive NHL and may be a useful biomarker for selecting appropriate treatment when used in combination with the IPI.

Modulation of tumor necrosis factor by microbial pathogens

In response to invasion by microbial pathogens, host defense mechanisms get activated by both the innate and adaptive arms of the immune responses. TNF (tumor necrosis factor) is a potent proinflammatory cytokine expressed by activated macrophages and lymphocytes that induces diverse cellular responses that can vary from apoptosis to the expression of genes involved in both early inflammatory and acquired immune responses. A wide spectrum of microbes has acquired elegant mechanisms to overcome or deflect the host responses mediated by TNF. For example, modulatory proteins encoded by multiple families of viruses can block TNF and TNF-mediated responses at multiple levels, such as the inhibition of the TNF ligand or its receptors, or by modulating key transduction molecules of the TNF signaling pathway. Bacteria, on the other hand, tend to modify TNF-mediated responses specifically by regulating components of the TNF signaling pathway. Investigation of these diverse strategies employed by viral and bacterial pathogens has significantly advanced our understanding of both host TNF responses and microbial pathogenesis. This review summarizes the diverse microbial strategies to regulate TNF and how such insights into TNF modulation could benefit the treatment of inflammatory or autoimmune diseases.