Through TNF Receptor 1 Research Articles

Therapeutic CRISPR epigenome editing of inflammatory receptors in the intervertebral disc

Low back pain (LBP) ranks among the leading causes of disability worldwide and generates a tremendous socioeconomic cost. Disc degeneration, a leading contributor to LBP, can be characterized by the breakdown of the extracellular matrix of the intervertebral disc (IVD), disc height loss, and inflammation. The inflammatory cytokine TNF-α has multiple signaling pathways, including proinflammatory signaling through Tumor Necrosis Factor Receptor 1 (TNFR1), and has been implicated as a primary mediator of disc degeneration. We tested our ability to regulate the TNFR1 signaling pathway in vivo, utilizing Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) epigenome editing to slow the progression of disc degeneration in rats. Sprague-Dawley rats were treated with TNF-α and CRISPR interference (CRISPRi)-based epigenome-editing therapeutics targeting TNFR1, showing decreased behavioral pain in a disc degeneration model. Surprisingly, while treatment with the vectors alone was therapeutic, the TNF-α injection became therapeutic after TNFR1 modulation. These results suggest direct inflammatory receptor modulation as a potent strategy for treating disc degeneration.

TNFR1/p38αMAPK signaling in Nex + supraspinal neurons regulates estrogen-dependent chronic neuropathic pain

Upregulation of soluble tumor necrosis factor (sTNF) cytokine signaling through TNF receptor 1 (TNFR1) and subsequent neuronal hyperexcitability are observed in both animal models and human chronic neuropathic pain (CNP). Previously, we have shown that estrogen modulates sTNF/TNFR1 signaling in CNP, which may contribute to female prevalence of CNP. The estrogen-dependent role of TNFR1-mediated supraspinal neuronal circuitry in CNP remains unknown. In this study, we interrogated the intersect between supraspinal TNFR1 mediated neuronal signaling and sex specificity by selectively removing TNFR1 in Nex + neurons in adult mice (NexCreERT2::TNFR1f/f). We determined that mechanical hypersensitivity induced by chronic constriction injury (CCI) decreases over time in males, but not in females. Subsequently, we investigated two downstream pathways, p38MAPK and NF-κB, important in TNFR1 signaling and injury response. We detected p38MAPK and NF-κB activation in male cortical tissue; however, p38MAPK phosphorylation was reduced in NexCreERT2::TNFR1f/f males. We observed a similar recovery from acute pain in male mice following CCI when p38αMAPK was knocked out of supraspinal Nex + neurons (NexCreERT2::p38αMAPKf/f), while chronic pain developed in female mice. To explore the intersection between estrogen and inflammation in CNP we used a combination therapy of an estrogen receptor β (ER β) inhibitor with a sTNF/TNFR1 or general p38MAPK inhibitor. We determined both combination therapies lends therapeutic relief to females following CCI comparable to the response evaluated in male mice. These data suggest that TNFR1/p38αMAPK signaling in Nex + neurons in CNP is male-specific and lack of therapeutic efficacy following sTNF inhibition in females is due to ER β interference. These studies highlight sex-specific differences in pathways important to pain chronification and elucidate potential therapeutic strategies that would be effective in both sexes.

Systemic treatment with a selective TNFR2 agonist alters the central and peripheral immune responses and transiently improves functional outcome after experimental ischemic stroke

Ischemic stroke often leaves survivors with permanent disabilities and therapies aimed at limiting detrimental inflammation and improving functional outcome are still needed. Tumor necrosis factor (TNF) levels increase rapidly after ischemic stroke, and while signaling through TNF receptor 1 (TNFR1) is primarily detrimental, TNFR2 signaling mainly has protective functions. We therefore investigated how systemic stimulation of TNFR2 with the TNFR2 agonist NewSTAR2 affects ischemic stroke in mice. We found that NewSTAR2 treatment induced changes in peripheral immune cell numbers and transiently affected microglial numbers and neuroinflammation. However, this was not sufficient to improve long-term functional outcome after stroke in mice.

Exogenous IL-10 posttreatment along with TLR4 and TNFR1 blockade improves tissue antioxidant status by modulating sepsis-induced macrophage polarization.

Multi-organ dysfunction is one of the major reasons behind the high mortality of sepsis throughout the world. With the pathophysiology of sepsis remaining largely unknown, the uncontrolled reactive oxygen species (ROS) production along with the decreased antioxidants contributes to the progression toward septic shock. Being the effector cells of the innate immunity system, macrophages secrete both pro-inflammatory and anti-inflammatory mediators during inflammation. Lipopolysaccharide (LPS) binding to toll-like receptor 4 (TLR4) releases TNF-α, which initiates pro-inflammatory events through tumor necrosis factor receptor 1 (TNFR1) signaling. However, it is counteracted by the anti-inflammatory interleukin 10 (IL-10) causing decreased oxidative stress. Our study thus aimed to assess the effects of exogenous IL-10 treatment post-neutralization of TLR4 and TNFR1 (by anti-TLR4 antibody and anti-TNFR1 antibody, respectively) in an in vivo murine model of LPS-sepsis. We have also examined the tissue-specific antioxidant status in the spleen, liver, and lungs along with the serum cytokine levels in adult male Swiss albino mice to determine the functional association with the disease. The results showed that administration of recombinant IL-10 post-neutralization of the receptors was beneficial in shifting the macrophage polarization to the anti-inflammatory M2 phenotype. IL-10 treatment significantly downregulated the free radicals production resulting in diminished lipid peroxidase (LPO) levels. The increased antioxidant activities of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GRX ) conferred protection against LPS-induced sepsis. Western blot data further confirmed diminished expressions of TLR4 and TNFR1 along with suppressed stress-activated protein kinases/Jun amino-terminal kinases (SAPK/JNK) and increased SOD and CAT expressions, which altogether indicated that neutralization of TLR4 and TNFR1 along with IL-10 posttreatment might be a potential therapeutic measure for the treatment of sepsis.

Arg-GlcNAcylation on TRADD by NleB and SseK1 Is Crucial for Bacterial Pathogenesis.

Death receptor signaling is critical for cell death, inflammation, and immune homeostasis. Hijacking death receptors and their corresponding adaptors through type III secretion system (T3SS) effectors has been evolved to be a bacterial evasion strategy. NleB from enteropathogenic Escherichia coli (EPEC) and SseK1/2/3 from Salmonella enterica serovar Typhimurium (S. Typhimurium) can modify some death domain (DD) proteins through arginine-GlcNAcylation. Here, we performed a substrate screen on 12 host DD proteins with conserved arginine during EPEC and Salmonella infection. NleB from EPEC hijacked death receptor signaling through tumor necrosis factor receptor 1 (TNFR1)-associated death domain protein (TRADD), FAS-associated death domain protein (FADD), and receptor-interacting serine/threonine-protein kinase 1 (RIPK1), whereas SseK1 and SseK3 disturbed TNF signaling through the modification of TRADD Arg235/Arg245 and TNFR1 Arg376, respectively. Furthermore, mouse infection studies showed that SseK1 but not SseK3 rescued the bacterial colonization deficiency contributed by the deletion of NleBc (Citrobacter NleB), indicating that TRADD was the in vivo substrate. The result provides an insight into the mechanism by which attaching and effacing (A/E) pathogen manipulate TRADD-mediated signaling and evade host immune defense through T3SS effectors.

Role of TNF-TNF Receptor 2 Signal in Regulatory T Cells and Its Therapeutic Implications.

Tumor necrosis factor α (TNFα) is a pleiotropic cytokine which signals through TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2). Emerging evidence has demonstrated that TNFR1 is ubiquitously expressed on almost all cells, while TNFR2 exhibits a limited expression, predominantly on regulatory T cells (Tregs). In addition, the signaling pathway by sTNF via TNFR1 mainly triggers pro-inflammatory pathways, and mTNF binding to TNFR2 usually initiates immune modulation and tissue regeneration. TNFα plays a critical role in upregulation or downregulation of Treg activity. Deficiency in TNFR2 signaling is significant in various autoimmune diseases. An ideal therapeutic strategy for autoimmune diseases would be to selectively block the sTNF/TNFR1 signal through the administration of sTNF inhibitors, or using TNFR1 antagonists while keeping the TNFR2 signaling pathway intact. Another promising strategy would be to rely on TNFR2 agonists which could drive the expansion of Tregs and promote tissue regeneration. Design of these therapeutic strategies targeting the TNFR1 or TNFR2 signaling pathways holds promise for the treatment of diverse inflammatory and degenerative diseases.

Differential expression and tumor necrosis factor-mediated regulation of TNFRSF11b/osteoprotegerin production by human melanomas

Tumors escape host immune responses, in part, through the release of immunomodulatory factors and decoy receptors into their microenvironment. Several cancers express surface-bound and soluble members of the tumor necrosis factor (TNF) receptor superfamily, including TNFRSF11b/osteoprotegerin (OPG). In its physiologic role, OPG regulates bone remodeling through competition for osteoclast-activating cytokines and protects newly forming bone from T cell-mediated apoptosis. In multiple tumor types, OPG production is associated with an aggressive phenotype and increased metastasis to bone, but no study has examined OPG production in human metastatic melanoma. We demonstrate that a significant proportion of human metastatic melanomas constitutively produces OPG through a mechanism governed by membrane-bound TNF-α signaling through TNF receptor 1 (TNFR1). These observations both define a specific mechanism that regulates melanoma production of OPG and establish a new molecular target for the therapeutic regulation of OPG.

Contribution of TNF receptor 1 to retinal neural cell death induced by elevated glucose

Diabetic retinopathy (DR), a leading cause of vision loss and blindness among working-age adults, holds several hallmarks of an inflammatory disease. The increase in cell death in neural retina is an early event in the diabetic retina, preceding the loss of microvascular cells. Since tumor necrosis factor-α (TNF-α) has been shown to trigger the death of perycites and endothelial cells as well as the breakdown of the blood-retinal barrier, we set out to investigate whether TNF-α acting through tumor necrosis factor receptor 1 (TNFR1), the major receptor responsible for mediating TNF-induced cell death, could also be responsible for the early neuronal cell death observed in DR. We used retinal neural cell cultures exposed to high glucose conditions, to mimic hyperglycaemia, and evaluated the contribution of TNFR1 in neural cell death. TNFR1 was found to be present to a great extent in retinal neurons and the levels of this receptor were found to be altered in cells cultured in high glucose conditions. High glucose induced an early decrease in cell viability, an increase in apoptosis and a higher immunoreactivity for the cleaved caspase-3, indicating a high glucose-induced caspase-dependent cell death. These observations were correlated with an increase in TNF-α expression. Nonetheless, inhibiting the activation of TNFR1 was sufficient to prevent the decrease in cell viability and the increase in retinal cell death by apoptosis. In conclusion, our data indicate that TNF-α acting through TNFR1 is responsible for the high glucose-induced cell death and that blocking the activity of this receptor is an adequate strategy to avoid cell loss in such conditions.

FAT10 mediates the effect of TNF-α in inducing chromosomal instability

Tumor necrosis factor-alpha (TNF-α) plays important roles in chronic inflammation-associated tumorigenesis but the mechanisms involved remain poorly understood. Previously, we reported that high levels of FAT10 led to chromosomal instability that is mediated by an abbreviated mitotic phase. Here, we show that TNF-α induces FAT10 gene expression through TNF receptor 1 (TNFR1) and activates the NF-κB pathway in HCT116 and SW620 cells. TNF-α treatment also leads to an abbreviated mitotic phase that can be reversed by inhibiting FAT10 expression. This abbreviated mitotic phase is correlated with a TNF-α-induced reduction in the kinetochore localization of MAD2 during prometaphase which, again, can be reversed by inhibiting FAT10 gene expression. There is greater variability of chromosome numbers in HCT116 and SW620 cells treated with TNF-α than in untreated cells, which can be reversed by the introduction of short hairpin RNA (shRNA) against FAT10. The more stable chromosome numbers in HCT116 cells expressing FAT10 shRNA can revert to greater variability with the addition of a mutant FAT10 that is not recognized by the FAT10 shRNA. Upon TNF-α stimulation, higher cell death is observed when FAT10 expression is inhibited by shRNA. These data strongly suggest that FAT10 plays an important role in mediating the function of TNF-α during tumorigenesis by inducing cell cycle deregulation and chromosomal instability, and by inhibiting apoptosis.

Increased susceptibility to acute kidney injury due to endoplasmic reticulum stress in mice lacking tumor necrosis factor-α and its receptor 1

Endoplasmic reticulum (ER) stress is actively involved in acute organ injury. Since tumor necrosis factor α (TNFα) plays a role in acute kidney injury, and induces ER stress and cell death in vitro, we examined the contribution of TNFα to acute kidney ER stress induced by tunicamycin. Contrary to expectation, tunicamycin caused much more severe kidney injury in TNFα-/- than in wild-type mice. The major site of kidney injury in TNFα-/- mice was proximal tubules, which showed extensive cell vacuolation, lipid accumulation, and apoptosis. Reconstitution of TNFα-/- mice with TNFα 24 h before tunicamycin injection reversed the susceptibility. When TNFα-receptor-deficient mice were treated with tunicamycin, severe renal injury developed in TNFR1-/- but not TNFR2-/- mice, suggesting this aspect of TNFα action was through TNF receptor-1 (TNFR1). In response to tunicamycin-induced acute ER stress, kidneys from neither TNFα-/- nor TNFR1-/- mice showed a significant increase in phosphorylated eukaryotic translation initiation factor 2α (eIF2α), a key step in ER stress regulation. Moreover, proximal tubular cells from TNFR1-/- mice did not show increased eIF2α phosphorylation in response to tunicamycin and were susceptible to ER stress-induced cell death. Finally, treatment of proximal tubule cells isolated from TNFR1-/- mice with an inhibitor of eIF2α phosphatase increased the levels of phosphorylated eIF2α and substantially reduced tunicamycin-induced cell death. Thus, disruption of TNFR1 signaling leads to dysregulation of eIF2α and increased susceptibility to acute ER stress injury in the kidney.

Direct crosstalk between mast cell–TNF and TNFR1-expressing endothelia mediates local tissue inflammation

AbstractSignaling through tumor necrosis factor receptor 1 (TNFR1) controls bacterial infections and the induction of inflammatory Th1 cell–mediated autoimmune diseases. By dissecting Th1 cell–mediated delayed-type hypersensitivity responses (DTHRs) into single steps, we localized a central defect to the missing TNFR1 expression by endothelial cells (ECs). Adoptive transfer and mast cell knockin experiments into KitW/KitW-v, TNF−/−, and TNFR1−/− mice showed that the signaling defect exclusively affects mast cell–EC interactions but not T cells or antigen-presenting cells. As a consequence, TNFR1−/− mice had strongly reduced mRNA and protein expression of P-selectin, E-selectin, ICAM-1, and VCAM-1 during DTHR elicitation. In consequence, intravital fluorescence microscopy revealed up to 80% reduction of leukocyte rolling and firm adhesion in TNFR1−/− mice. As substitution of TNF−/− mice with TNF-producing mast cells fully restored DTHR in these mice, signaling of mast cell-derived TNF through TNFR1-expressing ECs is essential for the recruitment of leukocytes into sites of inflammation.

Age‐related changes to tumor necrosis factor receptors affect neuron survival in the presence of beta‐amyloid

Inflammation including local accumulations of tumor necrosis factor alpha (TNF-alpha) is a part of Alzheimer's disease pathology and may exacerbate age-related neurodegeneration. Most studies on TNF-alpha and TNF neuronal receptors are conducted by using embryonic neurons. Few studies consider age-related deficits that may occur in neurons. Age-related changes in susceptibility to TNF-alpha through TNF receptor 1 (TNFR1) and receptor 2 (TNFR2) expression could increase susceptibility to beta-amyloid (1-42, Abeta42). Evidence is conflicting about which receptor mediates survival and/or apoptosis. We determined how aging affects receptor expression in cultured adult rat cortical neurons. Old neurons were more susceptible to Abeta42 toxicity than middle-aged neurons, and the addition of TNF-alpha was neuroprotective in middle-aged neurons, but exacerbated the toxicity from Abeta42 in old neurons. These pathologic and protective responses in old and middle-aged neurons, respectively, correlated with higher starting TNFR1 and TNFR2 mRNA levels in old vs. middle-aged neurons. Middle-aged neurons treated with TNF-alpha plus Abeta42 did not show an increase in either TNFR1 or TNFR2 mRNA, but old neurons showed an up-regulation in TNFR2 mRNA and not TNFR1 mRNA. Despite these mRNA changes, surface immunoreactivity of both TNFR1 and TNFR2 increased with the dose of TNF-alpha in middle-aged neurons. However, middle-aged neurons treated with TNF-alpha plus Abeta42 showed an up-regulation in both TNFR1 and TNFR2 surface expression, whereas old neurons failed to up-regulate surface expression of either receptor. These findings support the hypothesis that age-related changes in TNF-alpha surface receptor expression contribute to the neuronal loss associated with inflammation in Alzheimer's disease.

Blockade of TNF receptor 1 reduces disease severity but increases parasite transmission during Plasmodium chabaudi chabaudi infection

Reducing host carriage of transmission-stage malaria parasites (gametocytes) is expected to decrease the population-wide burden of malaria. Some malaria disease severity is attributed to the induction of the pro-inflammatory cytokines TNF-α and lymphotoxin-alpha (LT-α), and we are interested in whether anti-malaria interventions which ameliorate the symptoms induced by those cytokines may have the capacity to alter malaria transmission. As many functions of TNF-α and LT-α are exerted through TNF receptor 1 (TNFR1), we investigated the effect TNFR1 blockade exerted on parasite transmission using the rodent malaria Plasmodium chabaudi chabaudi. We found that blocking TNFR1 simultaneously increased gametocyte density and infectivity to mosquitoes, whilst reducing disease severity (weight loss). These transmission-enhancing and severity-reducing effects of TNFR1 blockade were independent of asexual parasite load and were observed for several P. c. chabaudi genotypes. These results suggest that the effects of candidate malaria interventions on infectivity should be examined alongside effects on disease severity so that the epidemiological consequences of such interventions can be evaluated.

Regulation of TNF mediated antiapoptotic signaling in human neutrophils: role of δ-PKC and ERK1/2

TNF is implicated in the suppression of neutrophil apoptosis during sepsis. Multiple signaling pathways are involved in TNF-mediated antiapoptotic signaling; a role for the MAP kinases (MAPK), ERK1/2, and p38 MAPK has been suggested. Antiapoptotic signaling is mediated principally through TNF receptor-1 (TNFR-1), and the PKC isotype-delta (delta-PKC) is a critical regulator of TNFR-1 signaling. delta-PKC associates with TNFR-1 in response to TNF and is required for NFkappaB activation and inhibition of caspase 3. The role of delta-PKC in TNF-mediated activation of MAPK is not known. The purpose of this study was to determine whether the MAPK, ERK1/2, and p38 MAPK are involved in TNF antiapoptotic signaling and whether delta-PKC is a key regulator of MAPK activation by TNF. In human neutrophils, TNF activated both p38 MAPK and ERK1/2 principally via TNFR-1. The MEK1/2 inhibitors PD098059 and U0126, but not the p38 MAPK inhibitor SB203580, decreased TNF antiapoptotic signaling as measured by caspase 3 activity. A specific delta-PKC antagonist, V1.1delta-PKC-Tat peptide, inhibited TNF-mediated ERK1/2 activation, but not p38 MAPK. ERK1/2 inhibition did not alter recruitment of delta-PKC to TNFR-1, indicating delta-PKC is acting upstream of ERK1/2. In HL-60 cells differentiated to a neutrophilic phenotype, delta-PKC depletion by delta-PKC siRNA resulted in inhibition of TNF mediated ERK1/2 activation but not p38 MAPK. Thus, ERK1/2, but not p38 MAPK, is an essential component of TNF-mediated antiapoptotic signaling. In human neutrophils, delta-PKC is a positive regulator of ERK1/2 activation via TNFR-1 but has no role in p38 MAPK activation.

Parasite genetic diversity does not influence TNF-mediated effects on the virulence of primary rodent malaria infections

The pro-inflammatory cytokine tumour necrosis factor alpha (TNF-alpha) is associated with malaria virulence (disease severity) in both rodents and humans. We are interested in whether parasite genetic diversity influences TNF-mediated effects on malaria virulence. Here, primary infections with genetically distinct Plasmodium chabaudi chabaudi (P.c.c.) clones varied in the virulence and cytokine responses induced in female C57BL/6 mice. Even when parasitaemia was controlled for, a greater day 7 TNF-alpha response was induced by infection with more virulent P.c.c. clones. Since many functions of TNF-alpha are exerted through TNF receptor 1 (TNFR1), a TNFR-1 fusion protein (TNFR-Ig) was used to investigate whether TNFR1 blockade eliminated clone virulence differences. We found that TNFR-1 blockade ameliorated the weight loss but not the anaemia induced by malaria infection, regardless of P.c.c. clone. We show that distinct P.c.c. infections induced significantly different plasma interferon gamma (IFN-gamma), interleukin 6 (IL-6) and interleukin 10 (IL-10) levels. Our results demonstrate that regardless of P.c.c. genotype, blocking TNFR1 signalling protected against weight loss, but had negligible effects on both anaemia and asexual parasite kinetics. Thus, during P.c.c. infection, TNF-alpha is a key mediator of weight loss, independent of parasite load and across parasite genotypes.

Jun kinase modulates tumor necrosis factor–dependent apoptosis in liver cells

Tumor necrosis factor (TNF) triggers distinct pathways in liver cells through TNF receptor 1 (TNF-R1) via adapter molecules, including the intracellular cascades leading to apoptosis, nuclear factor-κB (NF-κB), and Jun kinase (JNK) activation. TNF-dependent activation of NF-κB induces the transcription of antiapoptotic genes that renders liver cells resistant against TNF-induced apoptosis. In contrast, the role of JNK during TNF-induced apoptosis is less clear, so we studied its role during this process. Hepatoma cells treated with TNF and cycloheximide undergo apoptosis, which is proceeded by a strong activation of JNK. Adenoviral vectors (adv) were tested to block TNF-dependent JNK activation selectively. An adv expressing dominant-negative (dn) TRAF2 inhibited only JNK and not ERK or NF-κB activation. However, the effect of inhibiting JNK activation with a dn TAK1 virus was also specific but was stronger than that via dn TRAF2. In further experiments, the inhibitory effect of dn TAK1 on JNK was used to define its role during TNF-dependent apoptosis. Inhibition of JNK by adv dn TAK1 resulted in an earlier and stronger induction of apoptosis. Interestingly, TAM67, a dn form of c-Jun, did not mediate the JNK-dependent effect on TNF-dependent apoptosis, indicating that other molecular targets are essential to confer this mechanism. However, the modified apoptosis pattern could be inhibited by adv expressing Bcl-2 or dn FADD. In conclusion, we define TAK1 as a kinase specifically involved in TNF-induced JNK activation in hepatoma cells and show that JNK transduces antiapoptotic signals, which modulate the strength and time course of FADD-dependent cell death involving mitochondrial permeability transfer. (H EPATOLOGY 2002;36:315-325.)

Temporary blockade of the tumor necrosis factor receptor signaling pathway impedes the spread of scrapie to the brain.

Although the transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases, their agents usually replicate and accumulate in lymphoid tissues long before infection spreads to the central nervous system (CNS). Studies of a mouse scrapie model have shown that mature follicular dendritic cells (FDCs), which express the host prion protein (PrP(c)), are critical for replication of infection in lymphoid tissues. In the absence of mature FDCs, the spread of infection to the CNS is significantly impaired. Tumor necrosis factor alpha (TNF-alpha) secretion by lymphocytes is important for maintaining FDC networks, and signaling is mediated through TNF receptor 1 (TNFR-1) expressed on FDCs and/or their precursors. A treatment that blocks TNFR signaling leads to the temporary dedifferentiation of mature FDCs, raising the hypothesis that a similar treatment would significantly delay the peripheral pathogenesis of scrapie. Here, specific neutralization of the TNFR signaling pathway was achieved through treatment with a fusion protein consisting of two soluble human TNFR (huTNFR) (p80) domains linked to the Fc portion of human immunoglobulin G1 (huTNFR:Fc). A single treatment of mice with huTNFR:Fc before or shortly after intraperitoneal injection with the ME7 scrapie strain significantly delayed the onset of disease in the CNS and reduced the early accumulation of disease-specific PrP in the spleen. These effects coincided with a temporary dedifferentiation of mature FDCs within 5 days of huTNFR:Fc treatment. We conclude that treatments that specifically inhibit the TNFR signaling pathway may present an opportunity for early intervention in peripherally transmitted TSEs.

Engagement of Tumor Necrosis Factor (TNF) Receptor 1 Leads to ATF-2- and p38 Mitogen-activated Protein Kinase-dependent TNF-α Gene Expression

Engagement of the tumor necrosis factor-alpha (TNF-alpha) receptors by the TNF-alpha ligand results in the rapid induction of TNF-alpha gene expression. The study presented here shows that autoregulation of TNF-alpha gene transcription by selective signaling through tumor necrosis factor receptor 1 (TNFR1) requires p38 mitogen-activated protein (MAP) kinase activity and the binding of the transcription factors ATF-2 and Jun to the TNF-alpha cAMP-response element (CRE) promoter element. Consistent with these findings, TNFR1 engagement results in increased p38 MAP kinase activity and p38-dependent phosphorylation of ATF-2. Furthermore, overexpression of MADD (MAP kinase-activating death domain protein), an adapter protein that binds to the death domain of TNFR1 and activates MAP kinase cascades, results in CRE-dependent induction of TNF-alpha gene expression. Thus, the TNF-alpha CRE site is the target of TNFR1 stimulation and mediates the autoregulation of TNF-alpha gene transcription.

The TNF receptor 1-associated protein TRADD signals cell death and NF-κB activation

Many diverse activities of tumor necrosis factor (TNF) are signaled through TNF receptor 1(TNFR1). We have identified a novel 34 kDa protein, designated TRADD, that specifically interacts with an intracellular domain of TNFR1 known to be essential for mediating programmed cell death. Overexpression of TRADD leads to two major TNF-induced responses, apoptosis and activation of NF-κB. The C-terminal 118 amino acids of TRADD are sufficient to trigger both of these activities and likewise sufficient for interaction with the death domain of TNFR1. TRADD-mediated cell death can be suppressed by the crmA gene, which encodes a specific inhibitor of the interleukin-1 β-converting enzyme. However, NF-κB activation by TRADD is not inhibited by crmA expression, demonstrating that the signaling pathways for TNF-induced cell death and NF-κB activation are distinct.