Tumor necrosis factor receptor signaling. A dominant negative mutation suppresses the activation of the 55-kDa tumor necrosis factor receptor

Mutations in the binding site of TNFR1 PLAD reduce homologous interactions but can enhance antagonism of wild-type TNFR1 activity

The tumour necrosis factor receptor superfamily (TNFRSF) members contain cysteine-rich domains (CRD) in their extracellular regions, and the membrane-distal CRD1 forms homologous interactions in the absence of ligand. The CRD1 is therefore termed a pre-ligand assembly domain (PLAD). The role of PLAD-PLAD interactions in the induction of signalling as a consequence of TNF-TNFR binding led to the development of soluble PLAD domains as antagonists of TNFR activation. In the present study, we generated recombinant wild-type (WT) PLAD of TNFR1 and mutant forms with single alanine substitutions of amino acid residues thought to be critical for the formation of homologous dimers and/or trimers of PLAD (K19A, T31A, D49A and D52A). These mutated PLADs were compared with WT PLAD as antagonists of TNF-induced apoptosis or the activation of inflammatory signalling pathways. Unlike WT PLAD, the mutated PLADs showed little or no homologous interactions, confirming the importance of particular amino acids as contact residues in the PLAD binding region. However, as with WT PLAD, the mutated PLADs functioned as antagonists of TNF-induced TNFR1 activity leading to induction of cell death or NF-κB signalling. Indeed, some of the mutant PLADs, and K19A PLAD in particular, showed enhanced antagonistic activity compared with WT PLAD. This is consistent with the reduced formation of homologous multimers by these PLAD mutants effectively increasing the concentration of PLAD available to bind and antagonize WT TNFR1 when compared to WT PLAD acting as an antagonist. This may have implications for the development of antagonistic PLADs as therapeutic agents.

Effect of menopausal hormone therapy on proteins associated with senescence and inflammation

BACKGROUND

Estrogen may inhibit cell senescence that contributes to age-related disorders. This study determined the effects of menopausal hormone treatments on circulating levels of markers of cell senescence.

METHODS

Growth differentiation factor 15 (GDF15), tumor necrosis factor receptor 1 (TNFR1), FAS, and macrophage inflammatory protein 1α (MIP1α) were measured in serum using multiplexed bead-based assays and compared among menopausal women participating in the Kronos Early Estrogen Prevention Study randomized to either placebo (n = 38), oral conjugated equine estrogen (oCEE, n = 37), or transdermal 17β-estradiol (tE2, n = 34). Serum levels of the senescent markers for each treatment were compared to placebo 36 months after randomization using the Wilcoxon rank sum test.

RESULTS

Serum levels of GDF15, TNFR1, and FAS, but not MIP1α, were lower in both the oCEE and tE2 groups compared to placebo. The difference in levels between treatment and placebo for GDF15, TNFR1, and FAS were greater for oCEE [-108 pg/mL (p = .008), -234 pg/mL (p = .0006), and -1374 pg/mL (p < .0001), respectively] than for tE2 [-76 pg/mL (p = .072), -105 pg/mL (p = .076), and -695 pg/mL (p = .036), respectively]. Additionally, TNFR1 showed a positive association with time past menopause (correlation = 0.255, p = .019).

CONCLUSIONS

Circulating levels of some markers of cell senescence were lower in menopausal women treated with oCEE and tE2 compared to placebo. Differences in the magnitude of effect of the two active treatments may reflect the differences in circulating levels of estrogen metabolites due to formulation and mode of delivery. These data generate new hypotheses with regard to the effects of menopause on the biology of aging.

Advances in the Potential Biomarkers of Epilepsy

Epilepsy is a group of chronic neurological disorders characterized by recurrent, spontaneous, and unpredictable seizures. It is one of the most common neurological disorders, affecting tens of millions of people worldwide. Comprehensive studies on epilepsy in recent decades have revealed the complexity of epileptogenesis, in which immunological processes, epigenetic modifications, and structural changes in neuronal tissues have been identified as playing a crucial role. This review discusses the recent advances in the biomarkers of epilepsy. We evaluate the possible molecular background underlying the clinical changes observed in recent studies, focusing on therapeutic investigations, and the evidence of their safety and efficacy in the human population. This article reviews the pathophysiology of epilepsy, including recent reports on the effects of oxidative stress and hypoxia, and focuses on specific biomarkers and their clinical implications, along with further perspectives in epilepsy research.

Inflammation: A Network in the Pathogenesis of Status Epilepticus

Status epilepticus (SE) is an abnormally prolonged or recurrent epileptic seizure that is a serious, life-threatening medical emergency. Notably, it requires prompt and aggressive treatment. SE is characterized by high mortality and morbidity. However, its pathogenesis remains unclear. Numerous studies of SE have reported widespread brain inflammation, suggesting that inflammation plays a vital role in the occurrence and development of SE. This mini review article reviews the current knowledge with regard to the role of inflammation in SE.

Targeted silencing of inhibitors of apoptosis proteins with siRNAs: a potential anti-cancer strategy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies, with a very poor prognosis. Despite significant improvements in diagnosis and treatment in recent years, the long-term therapeutic efficacy is poor, partially due to tumor metastasis, recurrence, and resistance to chemo- or radio-therapy. Recently, it was found that a major feature of tumors is a combination of unrestrained cell proliferation and impaired apoptosis. There are now 8 recognized members of the IAP-family: NAIP, c-IAP1, c-IAP2, XIAP, Survivin, Bruce, Livin and ILP-2. These proteins all contribute to inhibition of apoptosis, and provide new potential avenues of cancer treatment. As a powerful tool to suppress gene expression in mammalian cells, RNAi species for inhibiting IAP genes can be directed against cancers. This review will provide a brief introduction to recent developments of the application IAP-siRNA in tumor studies, with the aim of inspiring future treatment of HCC.

RANK receptor oligomerisation in the regulation of NFκB signalling

The interaction of receptor activator of NFκB (RANK), a member of the tumour necrosis factor receptor superfamily, with RANK ligand is crucial for the formation, function and survival of osteoclasts. The role of the cytoplasmic oligomerisation domain (pre-ligand assembly domain; PLAD or 'IVVY' motif) in the ligand-dependent activation of downstream NFκB signalling has not been studied previously. The discovery of truncating mutations of TNFRSF11A (W434X and G280X that lack the PLAD) as the cause of rare cases of osteoclast-poor osteopetrosis offered the opportunity for functional study of this region. Recapitulating the W434X mutation by transcription activator-like effector nuclease (TALEN)-mediated targeted disruption of Tnfrsf11a within the region homologous to W434X in the mouse macrophage-like cell line RAW264.7 impaired formation of osteoclast-like cells. Using overexpression studies, we demonstrated that, in contrast to WT-RANK, the absence of the PLAD in G280X-RANK and W434X-RANK prevented ligand-independent but not ligand-dependent oligomerisation. Cells expressing W434X-RANK, in which only two of the three TRAF6-binding motifs are present, continued to exhibit ligand-dependent NFκB signalling. Hence, the absence of the PLAD did not prevent ligand-induced trimerisation and subsequent NFκB activation of RANK, demonstrating that therapeutic targeting of the PLAD in the prevention of osteoporosis may not be as effective as proposed previously.

Breast carcinoma progression and tumour vascular markers related to apoptotic mechanisms

Background. In the last few years, the cancer research had tried to identify and characterize new biochemical and molecular pathways in which the inhibition induces prosurvival mechanisms. Our work describes the expression of two different members of apoptotic regulatory pathway and their relationship with a progression of breast carcinoma. Materials and Methods. We compared expression of genes related to apoptosis (DR6 and Gpm6B) in the blood of patients suffering from stage I of breast cancer in different grades (I–IV), with healthy controls. After isolation of mRNA, transcription of mRNA into the cDNA was performed. The quantification of gene expression changes in DR6 and Gpm6B was detected by RT-PCR method. Analysis at the protein level was performed by the Western blot.Results. In statistical analysis of Dr6 mRNA level changes we detected significant increase starting in Grading 1 (G1) and reached maximal level in G3.This expression on mRNA levels was similar to protein levels, which copy rising tendency with maximal value in G3. The results of Gpm6B were significantly lower.Conclusion. This result showed that antiapoptotic signalling during neovascularization is increased significantly. It would be advisable in the future to study the influence of cytostatic treatment on the expression of genes related to apoptotic pathways and their relationship with progression of breast cancer tumours.

Elevated CSF levels of TACE activity and soluble TNF receptors in subjects with mild cognitive impairment and patients with Alzheimer's disease

We recently reported that expression levels of tumor necrosis factor (TNF) receptors, TNFR1 and TNFR2, are significantly changed in the brains and cerebrospinal fluid (CSF) with Alzheimer's disease (AD). Moreover, we also found that, in an Alzheimer's mouse model, genetic deletion of TNF receptor (TNFR1) reduces amyloid plaques and amyloid beta peptides (Aβ) production through β-secretase (BACE1) regulation. TNF-α converting enzyme (TACE/ADAM-17) does not only cleave pro- TNF-α but also TNF receptors, however, whether the TACE activity was changed in the CSF was not clear. In this study, we examined TACE in the CSF in 32 AD patients and 27 age-matched healthy controls (HCs). Interestingly, we found that TACE activity was significantly elevated in the CSF from AD patients compared with HCs. Furthermore, we also assayed the CSF levels of TACE cleaved soluble forms of TNFR1 and TNFR2 in the same patients. We found that AD patients had higher levels of both TACE cleaved soluble TNFR1 (sTNFR1) and TNFR2 (sTNFR2) in the CSF compared to age- and gender-matched healthy controls. Levels of sTNFR1 correlated strongly with the levels of sTNFR2 (rs = 0.567-0.663, p < 0.01). The levels of both sTNFR1 and sTNFR2 significantly correlated with the TACE activity (rs = 0.491-0.557, p < 0.05). To examine if changes in TACE activity and in levels of cleaved soluble TNFRs are an early event in the course of AD, we measured these molecules in the CSF from 47 subjects with mild cognitive impairment (MCI), which is considered as a preclinical stage of AD. Unexpectedly, we found significantly higher levels of TACE activity and soluble TNFRs in the MCI group than that in AD patients. These results suggest that TACE activity and soluble TNF receptors may be potential diagnostic candidate biomarkers in AD and MCI.

P2X7 receptor activation ameliorates CA3 neuronal damage via a tumor necrosis factor-α-mediated pathway in the rat hippocampus following status epilepticus

BACKGROUND

The release of tumor necrosis factor-α (TNF-α) appears depend on the P2X7 receptor, a purinergic receptor. In the present study, we addressed the question of whether P2X7 receptor-mediated TNF-α regulation is involved in pathogenesis and outcome of status epilepticus (SE).

METHODS

SE was induced by pilocarpine in rats that were intracerebroventricularly infused with saline-, 2',3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP), A-438079, or A-740003 prior to SE induction. Thereafter, we performed Fluoro-Jade B staining and immunohistochemical studies for TNF-α and NF-κB subunit phosphorylations.

RESULTS

Following SE, P2X7 receptor agonist (BzATP) infusion increased TNF-α immunoreactivity in dentate granule cells as compared with that in saline-infused animals. In addition, TNF-α immunoreactivity was readily apparent in the mossy fibers, while TNF-α immunoreactivity in CA1-3 pyramidal cells was unaltered. However, P2X7 receptor antagonist (OxATP-, A-438079, and A-740003) infusion reduced SE-induced TNF-α expression in dentate granule cells. In the CA3 region, BzATP infusion attenuated SE-induced neuronal damage, accompanied by enhancement of p65-Ser276 and p65-Ser311 NF-κB subunit phosphorylations. In contrast, OxATP-, A-438079, and A-740003 infusions increased SE-induced neuronal death. Soluble TNF p55 receptor (sTNFp55R), and cotreatment with BzATP and sTNFp55R infusion also increased SE-induced neuronal damage in CA3 region. However, OxATP-, sTNFp55R or BzATP+sTNFp55R infusions could not exacerbate SE-induced neuronal damages in the dentate gyrus and the CA1 region, as compared to BzATP infusion.

CONCLUSIONS

These findings suggest that TNF-α induction by P2X7 receptor activation may ameliorate SE-induced CA3 neuronal damage via enhancing NF-κB p65-Ser276 and p65-Ser311 phosphorylations.

Detection of anti-TNFalpha activity in canine hyperimmune serum using a TNFalpha inhibition assay

BACKGROUND

Increased serum tumor necrosis factor-alpha (TNFalpha) activity has been associated with onset of serious inflammatory diseases in dogs. Development of treatment with TNFalpha-antagonists has been limited by the unavailability of suitable reagents and potency assays for TNFalpha.

OBJECTIVES

The objectives of this study were to optimize a cell-based assay to measure anti-TNFalpha activity in serum and plasma from hyperimmune (vaccinated with an Escherichia coli J5 bacterin) and unvaccinated canine donors; to use the assay to determine whether hyperimmune serum inhibits TNFalpha activity in vivo; and to determine whether soluble TNF receptor-1 (sTNFR1, a naturally occurring TNFalpha antagonist) contributes to anti-TNFalpha activity.

METHODS

Commercial plasma and serum from hyperimmune-frozen plasma (HFP) donors and unvaccinated fresh-frozen plasma (FFP) donors were used in the study. An L929-cell TNFalpha-inhibition assay (LTIA) was optimized to measure anti-TNFalpha activity. Using a rat subcutaneous pouch model of inflammation, the effects of HFP, FFP, a synthetic TNFalpha antagonist (Etanercept), and carprofen on TNFalpha activity were compared in vivo. Immunofluorescence was used to measure soluble sTNFR1 concentration.

RESULTS

Using the optimized LTIA, HFP serum but not FFP serum decreased canine TNFalpha activity (P<.01). HFP plasma and Etanercept (but not FFP plasma or carprofen) significantly decreased TNFalpha activity in pouch exudates (P<.05). A significantly higher concentration of sTNFR1 was found in HFP than FFP serum.

CONCLUSIONS

Using the LTIA, anti-TNFalpha activity is readily measured in canine serum and inflammatory exudates. sTNFR1 appears to contribute to anti-TNFalpha activity in HFP serum. These results suggest HFP should be investigated further as a potential immunotherapeutic agent for controlling canine diseases in which TNFalpha is implicated.

Peripheral lipopolysaccharide administration affects the olfactory dopamine system in mice

Peripheral administration of lipopolysaccharide (LPS) in an amount that produces acute stress has been found to affect the catecholamine systems in the brain. Acute peripheral LPS administration activated norepinephrine (NE) metabolism in the locus ceruleus (LC). Approximately 40% of murine LC neurons project to the olfactory bulb (OB) and the anterior olfactory nucleus (AON). Thus, we investigated the effects of a single intra-peritoneal (i.p.) LPS injection on catecholamine biosynthesis in the OB and AON in 8-week-old C3H/HeN male mice. In the AON, the content of dopamine (DA), but not that of NE, was highly increased 6 h after LPS injection. In the OB, the contents of DA and NE did not change; but within 2 h after a single i.p. LPS injection, the mRNA levels of IkappaB, TNF-alpha, and TNF-alpha receptor type 1 were significantly enhanced. Almost all TNF-alpha-immunoreactive cells in the OB of the LPS-injected mice were located in the granule cell layer, and unexpectedly, they were not microglia but astroglia. The number of TUNEL-positive cells identified exclusively in the granule cell layer was significantly increased at 24 h after LPS injection. Therefore, our data suggest that astroglia activated by peripherally injected LPS may release TNF-alpha, which may trigger apoptosis in the granule cell layer in the OB. The increase in DA content in the AON and the production of TNF-alpha and apoptotic cells in the OB by acute peripheral LPS administration are not likely to be related.

New implications for the QUAKING RNA binding protein in human disease

The use of spontaneously occurring mouse models has proved to be a valuable tool throughout the years to delineate the signals required for nervous system development. This is especially true in the field of myelin biology, with a large number of different models available. The quaking viable mouse models dysmyelination in the nervous system and links the QUAKING RNA binding proteins to myelination and cell fate decisions. In this Mini-Review, we highlight the biological functions attributed to this KH-type RNA binding protein and the recent achievements linking it to human disorders.

Aminopeptidase N (CD13) Regulates Tumor Necrosis Factor-α-induced Apoptosis in Human Neutrophils

Neutrophil apoptosis plays a central role in the resolution of granulocytic inflammation. We have shown previously that tumor necrosis factor-alpha (TNFalpha) enhances the rate of neutrophil apoptosis at early time points via a mechanism involving both TNF receptor (TNFR) I and TNFRII. Here we reveal a marked but consistent variation in the magnitude of the pro-apoptotic effect of TNFalpha in neutrophils isolated from healthy donors, and we show that inhibition of cell surface aminopeptidase N (APN) using actinonin, bestatin, or inhibitory peptides significantly enhanced the efficacy of TNFalpha-induced killing. Notably, an inverse correlation is shown to exist between neutrophil APN activity and the sensitivity of donor cells to TNFalpha-induced apoptosis. Inhibition of cell surface APN appears to interfere with the shedding of TNFRI, and as a consequence results in augmented TNFalpha-induced apoptosis, cell polarization, and TNFalpha-primed, formyl-methionyl-leucyl-phenylalanine-stimulated respiratory burst. Of note, actinonin and bestatin had no effect on TNFRII expression under resting or TNFalpha-stimulated conditions and did not alter CXCRI or CXCRII expression. These data suggest significant variation in the activity of APN/CD13 on the cell surface of neutrophils in normal individuals and reveal a novel mechanism whereby APN/CD13 regulates TNFalpha-induced apoptosis via inhibition of TNFRI shedding. This has therapeutic relevance for driving neutrophil apoptosis in vivo.

Novel mutations in the EDAR gene in two Pakistani consanguineous families with autosomal recessive hypohidrotic ectodermal dysplasia

BACKGROUND

Hypohidrotic ectodermal dysplasia (HED) is a human heritable disorder characterized by sparse hair, a lack of sweat glands and malformation of teeth. There are X-linked, autosomal recessive and autosomal dominant forms of this disorder. Mutations in the EDA gene cause X-linked HED and mutations in either the EDAR or the EDARADD genes cause autosomal forms of HED.

OBJECTIVES

To identify pathogenic mutations in two consanguineous Pakistani families (A and B) with 11 affected individuals demonstrating the autosomal recessive form of HED.

METHODS

Genotyping of 17 members of the two families, including eight affected and nine unaffected individuals, was carried out by using polymorphic markers D2S293, D2S1893 and D2S1891, which are closely linked to the EDAR gene on chromosome 2q11-q13. To screen for mutations in the EDAR gene, all of its exons and splice junctions were polymerase chain reaction amplified from genomic DNA and sequenced directly in an ABI Prism 310 automated sequencer.

RESULTS

Genotyping results showed linkage in both the Pakistani families to the EDAR locus. Sequence analysis of the EDAR gene identified two novel mutations in the families: a missense mutation (G382S) in family A and a 4-bp deletion (718delAAAG) in family B.

CONCLUSIONS

We describe novel mutations in the EDAR gene in two Pakistani families affected with the autosomal recessive form of HED. Our findings extend the body of evidence that supports the importance of the ectodysplasin A1 isoform receptor, a member of the tumour necrosis factor receptor family, in the development of ectodermal appendages.

Peripheral lipopolysaccharide induces apoptosis in the murine olfactory bulb

The olfactory bulb (OB) is one of the few structures in the adult mammalian CNS that contains a continuous supply of newly generated neurons in the subventricular zone. Therefore, the balance between the supply of new cells and apoptosis in the OB might determine olfactory function. Lipopolysaccharide-induced tumor necrosis factor (TNF)-alpha triggers the apoptotic cascade mediated by the TNF/TNF receptor (TNFR) pathway. The present study therefore examines the effect of the propagated innate immune reaction triggered by peripheral lipopolysaccharide on the OB of C3H/HeN mice. Within 2 h of an intraperitoneal injection of lipopolysaccharide, mRNA expression levels of the genes encoding IkappaB, TNF-alpha, and TNFR type 1 in the mouse OB were significantly enhanced. Double immunofluorescence microscopy confirmed that almost all TNF-alpha-immunopositive cells in the OB of the TNF-injected mice were located in the subependymal zone and that they overlapped cells immunostained with antibody against glial fibrillary acidic protein, but not with the antibody against F4/80, an antigenic marker of microglia. The number of TUNEL-positive cells identified exclusively in the granule cell layer was significantly increased in mice injected with lipopolysaccharide and sacrificed at 24 h thereafter. These results suggest that peripheral lipopolysaccharide causes disequilibrium between the supply and disappearance of the cells in the OB, which might lead to olfactory dysfunction.

Analysis of human tumour necrosis factor receptor 1 dominant-negative mutants reveals a major region controlling cell surface expression

Tumour necrosis factor receptor 1 (TNFR1) plays a critical role in host defence and inflammation. We have identified a membrane proximal region (aa 218-324) of TNFR1 that restricts surface expression. This was prompted by comparing the dominant-negative properties of a C-terminal truncation of TNFR1 with a point mutant that prevents signalling. C-terminal truncation (aa 218-426) generates a better dominant-negative TNFR1 mutant than inactivation of the death domain by point mutation. The increased dominant-negative activity correlates with increased cell surface expression. The membrane proximal region is the most important region of the receptor for restricting expression.

Ectodysplasin signaling in development

Ectodysplasin (Eda), a signaling molecule belonging to the tumor necrosis factor family, is required for normal development of several ectodermally derived organs in humans and mice. Two closely related isoforms of ectodysplasin, Eda-A1 and Eda-A2, have been described which bind to and activate two different receptors, Edar and X-linked Eda-A2 receptor (Xedar), respectively. Mutations in Eda, Edar or other molecules of this signaling pathway cause ectodermal dysplasias characterized by defective development of teeth, hairs, and several exocrine glands such as sweat glands presumably due to impaired NF-kappaB response. Studies with mice either lacking the functional proteins of Edar pathway or overexpressing the ligand or receptor suggest that Eda-A1-Edar signaling has multiple roles in ectodermal organ development regulating their initiation, morphogenesis, and differentiation.

In vivo identification of inducible phosphoacceptors in the IKKgamma/NEMO subunit of human IkappaB kinase

Transcription factor NF-kappaB plays a pivotal regulatory role in the genetic programs for cell cycle progression and inflammation. Nuclear translocation of NF-kappaB is controlled by an inducible protein kinase called IKK, which earmarks cytoplasmic inhibitors of NF-kappaB for proteolytic destruction. IKK contains two structurally related catalytic subunits termed IKKalpha and IKKbeta as well as a noncatalytic subunit called IKKgamma/NEMO. Mutations in the X-linked gene encoding IKKgamma can interfere with NF-kappaB signaling and lead to immunodeficiency disease. Although its precise mechanism of action remains unknown, IKKgamma is phosphorylated in concert with the induction of NF-kappaB by the viral oncoprotein Tax and the proinflammatory cytokine tumor necrosis factor alpha (TNF). We now demonstrate that TNF-induced phosphorylation of IKKgamma is blocked in cells deficient for IKKbeta but not IKKalpha. Phosphopeptide-mapping experiments with metabolically radiolabeled cells indicate that IKKbeta phosphorylates human IKKgamma at Ser-31, Ser-43, and Ser-376 following the enforced expression of either the Tax oncoprotein or the type 1 TNF receptor. Inducible phosphorylation of IKKgamma is attenuated following the deletion of its COOH-terminal zinc finger domain (amino acids 397-419), a frequent target for mutations that occur in IKKgamma-associated immunodeficiencies. As such, IKKbeta-mediated phosphorylation of IKKgamma at these specific serine targets may facilitate proper regulation of NF-kappaB signaling in the immune system.

Identification of gene function by cyclical packaging rescue of retroviral cDNA libraries

Genes regulating responses in mammalian cells are often difficult to identify by functional cloning strategies limited to a single round of selection. Here we describe a strategy, cyclical packaging rescue (CPR), which allows rapid recovery and retransmission of retroviral cDNA libraries. CPR can be used not only with immortalized cell lines such as fibroblasts and Jurkat T cells, but also with primary B lymphocytes, which can be maintained only in short-term cultures. CPR allows for multiple rounds of selection and enrichment to identify cDNAs regulating responses in mammalian cells. Using CPR, five cDNAs were functionally cloned, which conferred protection against tumor necrosis factor alpha (TNFalpha)-induced apoptosis in RelA(-/-) fibroblasts. Three of the genes, RelA, cellular FLICE-like inhibitory protein (c-FLIP), and a dominant-negative mutant of TNF receptor 1 arising through CPR afforded strong protection against apoptosis. Two of the genes identified, Dbs and Fas-associated death domain protein (FADD), previously identified as a proapoptotic molecule, afforded partial protection against TNFalpha-induced apoptosis. These results suggest that CPR is a versatile method that permits functional identification of both wild-type and dominant-negative gene products that regulate cellular responses.

Amyloid beta binds trimers as well as monomers of the 75-kDa neurotrophin receptor and activates receptor signaling

p75(NTR), a nerve growth factor co-receptor that has been implicated in apoptosis of neurons, is structurally related to Fas and the receptors for tumor necrosis factor-alpha that display ligand independent assembly into trimers. Using embryonic day 17 fetal rat cortical neurons and p75(NTR)-expressing NIH-3T3 cells, we now show that p75(NTR) exists as a trimer as well as a monomer. Furthermore, we have reported and others have confirmed that amyloid beta binds p75(NTR), and that this binding leads to apoptotic cell death. We now report that amyloid beta binds to trimers of p75(NTR) as well as to p75(NTR) monomers but not to the p140(trkA), the nerve growth factor co-receptor that mediates neuronal survival. Furthermore, amyloid beta activates p75(NTR), strongly inducing the transcription of c-Jun mRNA and stimulating the stress-activated c-Jun NH(2)-terminal kinase, as measured by phosphorylation of its substrate (glutathione S-transferase-c-Jun-(1-79)). Our data suggest that p75(NTR) may be present as a preformed trimer that binds amyloid beta to induce receptor activation, and support the hypothesis that p75(NTR) activation by amyloid beta is causally related to Alzheimer's disease.

Characterization of a CD40-dominant inhibitory receptor mutant

CD40 is an important mediator of immune and inflammatory responses. It is a costimulatory molecule for B cell proliferation and survival. Blockade of CD40 has been shown to induce tolerance and its role in other pathogenic conditions has led to the proposal that CD40 inhibition could be valuable therapeutically. As a first step to this end, we have characterized a CD40-dominant negative receptor. This inhibitory mutant lacks the identified CD40 signaling domains. It inhibits both cotransfected and endogenous CD40 activation of NF-kappaB. This mutant is specific, as it does not affect TNF or latent membrane protein 1 signaling. Its potential usefulness is illustrated by its ability to inhibit the CD40 ligand-stimulated increases of HLA and CD54 expression, molecules involved in Ag recognition and lymphocyte recruitment leading to organ rejection. The inhibitory mutant has no TNFR-associated factor 2-binding capabilities and inhibits the recruitment of TNFR-associated factor 2 to the CD40 signaling complex after stimulation. These studies show that the CD40 inhibitory receptor molecule is effective, specific, and useful both for research and potentially as a clinical tool. And furthermore, it is likely that similar dominant inhibitory receptors can be generated for all of the members of the TNFR superfamily.

Myosin ii light chain phosphorylation regulates membrane localization and apoptotic signaling of tumor necrosis factor receptor-1

Activation of myosin II by myosin light chain kinase (MLCK) produces the force for many cellular processes including muscle contraction, mitosis, migration, and other cellular shape changes. The results of this study show that inhibition or potentiation of myosin II activation via over-expression of a dominant negative or wild type MLCK can delay or accelerate tumor necrosis factor-alpha (TNF)-induced apoptotic cell death in cells. Changes in the activation of caspase-8 that parallel changes in regulatory light chain phosphorylation levels reveal that myosin II motor activities regulate TNF receptor-1 (TNFR-1) signaling at an early step in the TNF death signaling pathway. Treatment of cells with either ionomycin or endotoxin (lipopolysaccharide) leads to activation of myosin II and increased translocation of TNFR-1 to the plasma membrane independent of TNF signaling. The results of these studies establish a new role for myosin II motor activity in regulating TNFR-1-mediated apoptosis through the translocation of TNFR-1 to or within the plasma membrane.

Localization of the gD-binding region of the human herpes simplex virus receptor, HveA

During virus entry, herpes simplex virus (HSV) glycoprotein D (gD) binds to one of several human cellular receptors. One of these, herpesvirus entry mediator A (HveA), is a member of the tumor necrosis factor receptor (TNFR) superfamily, and its ectodomain contains four characteristic cysteine-rich pseudorepeat (CRP) elements. We previously showed that gD binds the ectodomain of HveA expressed as a truncated, soluble protein [HveA(200t)]. To localize the gD-binding domain of HveA, we expressed three additional soluble forms of HveA consisting of the first CRP [HveA(76t)], the second CRP [HveA(77-120t)], or the first and second CRPs [HveA(120t)]. Biosensor and enzyme-linked immunosorbent assay studies showed that gD bound to HveA(120t) and HveA(200t) with the same affinity. However, gD did not bind to HveA(76t) or HveA(77-120t). Furthermore, HveA(200t) and HveA(120t), but not HveA(76t) or HveA(77-120t), blocked herpes simplex virus (HSV) entry into CHO cells expressing HveA. We also generated six monoclonal antibodies (MAbs) against HveA(200t). MAbs CW1, -2, and -4 bound linear epitopes within the second CRP, while CW7 and -8 bound linear epitopes within the third or fourth CRPs. None of these MAbs blocked the binding of gD to HveA. In contrast, MAb CW3 recognized a discontinuous epitope within the first CRP of HveA, blocked the binding of gD to HveA, and exhibited a limited ability to block virus entry into cells expressing HveA, suggesting that the first domain of HveA contains at least a portion of the gD binding site. The inability of gD to bind HveA(76t) suggests that additional amino acid residues of the gD binding site may reside within the second CRP.

Activation of the Ikappa B kinases by RIP via IKKgamma /NEMO-mediated oligomerization

To understand the mechanism of activation of the IkappaB kinase (IKK) complex in the tumor necrosis factor (TNF) receptor 1 pathway, we examined the possibility that oligomerization of the IKK complex triggered by ligand-induced trimerization of the TNF receptor 1 complex is responsible for activation of the IKKs. Gel filtration analysis of the IKK complex revealed that TNFalpha stimulation induces a large increase in the size of this complex, suggesting oligomerization. Substitution of the C-terminal region of IKKgamma, which interacts with RIP, with a truncated DR4 lacking its cytoplasmic death domain, produced a molecule that could induce IKK and NF-kappaB activation in cells in response to TRAIL. Enforced oligomerization of the N terminus of IKKgamma or truncated IKKalpha or IKKbeta lacking their serine-cluster domains can also induce IKK and NF-kappaB activation. These data suggest that IKKgamma functions as a signaling adaptor between the upstream regulators such as RIP and the IKKs and that oligomerization of the IKK complex by upstream regulators is a critical step in activation of this complex.

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

TNF signals are mediated through two different receptors, TNFR1 and TNFR2. In endothelial cells, TNFR1 is predominantly localized in the Golgi apparatus and TNFR2 on the plasma membrane. To investigate structural features responsible for the disparate localization, endothelial cells were transfected with epitope-tagged or green fluorescent protein-fused wild type and mutant receptor molecules. Wild type receptors recapitulated the distribution of endogenous receptors. Deletions of the entire TNFR1 intracellular domain or of the C-terminal death domain (TNFR1(-DD)) allowed expression of the receptor on the plasma membrane. However, addition of the death domain to the C-terminus of TNFR2 (TNFR2(+DD)) did not lead to Golgi-retention of this chimeric receptor. Overexpressed TNFR1, TNFR2, and TNFR2(+DD) increased basal expression of a cotransfected NF-kappaB-dependent promotor-reporter gene. Overexpressed TNFR1(-DD) did not activate NF-kappaB but acted as a ligand-specific dominant negative inhibitor of TNF actions. Unexpectedly, TNF responses were also inhibited by overexpressed TNFR1 and TNFR2(+DD), but not TNFR2. We conclude that the death domain of TNFR1 is required for retention of TNFR1 in the Golgi apparatus but is not sufficient to direct Golgi retention of a TNFR2(+DD) chimera, and that overexpressed receptors that contain the death domain (TNFR1 and TNFR2(+DD)) spontaneously activate NF-kappaB while inhibiting TNF responses.

A domain in TNF receptors that mediates ligand-independent receptor assembly and signaling

A conserved domain in the extracellular region of the 60- and 80-kilodalton tumor necrosis factor receptors (TNFRs) was identified that mediates specific ligand-independent assembly of receptor trimers. This pre-ligand-binding assembly domain (PLAD) is physically distinct from the domain that forms the major contacts with ligand, but is necessary and sufficient for the assembly of TNFR complexes that bind TNF-alpha and mediate signaling. Other members of the TNFR superfamily, including TRAIL receptor 1 and CD40, show similar homotypic association. Thus, TNFRs and related receptors appear to function as preformed complexes rather than as individual receptor subunits that oligomerize after ligand binding.

Mutations in the human homologue of mouse dl cause autosomal recessive and dominant hypohidrotic ectodermal dysplasia

X-linked hypohidrotic ectodermal dysplasia results in abnormal morphogenesis of teeth, hair and eccrine sweat glands. The gene (ED1) responsible for the disorder has been identified, as well as the analogous X-linked gene (Ta) in the mouse. Autosomal recessive disorders, phenotypically indistinguishable from the X-linked forms, exist in humans and at two separate loci (crinkled, cr, and downless, dl) in mice. Dominant disorders, possibly allelic to the recessive loci, are seen in both species (ED3, Dlslk). A candidate gene has recently been identified at the dl locus that is mutated in both dl and Dlslk mutant alleles. We isolated and characterized its human DL homologue, and identified mutations in three families displaying recessive inheritance and two with dominant inheritance. The disorder does not map to the candidate gene locus in all autosomal recessive families, implying the existence of at least one additional human locus. The putative protein is predicted to have a single transmembrane domain, and shows similarity to two separate domains of the tumour necrosis factor receptor (TNFR) family.

Inhibitory effects of TNF alpha on mouse tumor Leydig cells: possible role of ceramide in the mechanism of action

TNF alpha is reported to inhibit steroidogenesis in mouse Leydig cells. In primary cells this inhibition resulted mainly from a reduced expression of Cyp-17 gene. Mouse tumor Leydig cells, MA-10, being free of macrophages and lacking Cyp-17, appear to be an excellent model to investigate those effects of TNF alpha which are independent of either macrophages or Cyp-17. We report here that TNF alpha receptors are expressed in this cell line. Treatment of the cells with TNF alpha had no effect on basal progesterone production. In contrast, LH-, 8Br-cAMP and forskolin-stimulated progesterone production was inhibited by TNF alpha. Neither enzymes involved in the conversion of cholesterol to pregnenolone nor hormone-induced hydrolysis of [14C] cholesterol-ester were affected by TNF alpha. The hormone-induced expression of StAR protein was diminished in mitochondrial fractions from TNF alpha-treated cells. Also cell permeable ceramides markedly inhibited StAR protein levels. We show further that TNF alpha was able to induce [14C]-ceramide accumulation in MA-10 cells and suggest that this sphingolipid may be considered as a transmitter of TNF alpha signals to the StAR protein.

Tumor necrosis factor-alpha mediates both apoptotic cell death and cell proliferation in a human hematopoietic cell line dependent on mitotic activity and receptor subtype expression

The TF-1 human erythroleukemic cell line exhibits opposing physiological responses toward tumor necrosis factor-alpha (TNF) treatment, dependent upon the mitotic state of the cells. Mitotically active cells in log growth respond to TNF by rapidly undergoing apoptosis whereas TNF exposure stimulates cellular proliferation in mitotically quiescent cells. The concentration-dependent TNF-induced apoptosis was monitored by cellular metabolic activity and confirmed by both DNA epifluorescence and DNA fragmentation. Moreover, these responses could be detected by measuring extracellular acidification activity, enabling rapid prediction (within approximately 1.5 h of TNF treatment) of the fate of the cell in response to TNF. Growth factor resupplementation of quiescent cells, resulting in reactivation of cell cycling, altered TNF action from a proliferative stimulus to an apoptotic signal. Expression levels of the type II TNF receptor subtype (p75TNFR) were found to correlate with sensitivity to TNF-induced apoptosis. Pretreatment of log growth TF-1 cells with a neutralizing anti-p75TNFR monoclonal antibody inhibited TNF-induced apoptosis by greater than 80%. Studies utilizing TNF receptor subtype-specific TNF mutants and neutralizing antisera implicated p75TNFR in TNF-dependent apoptotic signaling. These data show a bifunctional physiological role for TNF in TF-1 cells that is dependent on mitotic activity and controlled by the p75TNFR.

The resistance against Listeria monocytogenes and the formation of germinal centers depend on a functional death domain of the 55 kDa tumor necrosis factor receptor

The biological functions mediated by the death domain of the 55-kDa tumor necrosis factor receptor (TNFRp55) in vivo are still elusive. TNFRp55 mutants lacking a functional death domain were expressed in TNFRp55-/- and in TNFRp55+/- mice as transgenes under control of the H-2Kb promoter. Analysis of these animals revealed that signals originating from the TNFRp55 death domain are indispensable for the protection against Listeria monocytogenes, the expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in the spleen and the development of splenic germinal centers. Furthermore, the transgenic coexpression of the TNFRp55 mutants in TNFRp55+/- mice exerts a dominant negative effect on the signaling of the endogenous receptor chains in vivo.

Autocrine tumor necrosis factor (TNF) and lymphotoxin (LT) alpha differentially modulate cellular sensitivity to TNF/LT-alpha cytotoxicity in L929 cells

Tumor necrosis factor (TNF) and lymphotoxin (LT) alpha are structurally and functionally related cytokines. We expressed the TNF and LT-alpha genes in murine fibrosarcoma L929r2 cells, which can be sensitized to TNF/LT-alpha-dependent necrosis by inhibitors of transcription or translation. Autocrine production of murine TNF in L929r2 cells completely downmodulated the expression of the 55- and 75-kD TNF receptors, resulting in resistance to TNF/LT-alpha cytotoxicity. Partial downmodulation of the 55-kD receptor was observed in human TNF-producing L929r2 cells. In contrast, an unaltered TNF receptor expression was found on LT-alpha L929r2 transfectants. Hence, although similar cytotoxic effects are induced by extracellularly administered TNF and LT-alpha, endogenous expression of these cytokines fundamentally differs in the way they modulate TNF receptor expression. Unlike LT-alpha, secreted by the classical pathway, TNF is first formed as a membrane-bound protein, which is responsible for receptor downmodulation. To explore whether the different pathways for secretion of TNF and LT-alpha explain this difference, we examined the effect of membrane-bound LT-alpha expression. This was obtained by exchange of the classical signal sequence of LT-alpha for the membrane anchor of chicken hepatic lectin. Membrane retention of LT-alpha resulted indeed in receptor downmodulation and TNF/LT-alpha resistance. We conclude that membrane retention of newly synthesized TNF or LT-alpha is absolutely required for receptor downmodulation and TNF/LT-alpha resistance.

TNF-related ligands and their receptors

Multicellular organisms have the challenging task of coordinating the activities of many distinct cell types. This coordination is accomplished largely by cell-associated and soluble signalling molecules that act locally or distantly to alter target-cell physiology. The tumour necrosis factor family of cytokines are type II transmembrane proteins that are important regulators of homeostasis and have been implicated as mediators of disease. These molecules serve as ligands for a family of cell-surface receptors termed the tumour necrosis factor/nerve growth factor (TNF/NGF) receptor family. The receptors are type I transmembrane proteins capable of mediating a wide range of responses in vitro and in vivo. Signal transduction is mediated by several newly discovered cytoplasmic proteins that couple these receptors to downstream signalling events. The elucidation and use of spontaneously occurring mutants in TNF-related ligands and receptors in addition to gene-targeting experiments have begun to clarify the diverse biological effects mediated by this superfamily of cytokines.

Cooperative signaling by tumor necrosis factor receptors CD120a (p55) and CD120b (p75) in the expression of nitric oxide and inducible nitric oxide synthase by mouse macrophages

Tumor necrosis factor-alpha (TNFalpha) is recognized by the cell-surface receptors CD120a (p55) and CD120b (p75). In the present study, we have investigated the role of these receptors in the expression of NO2-, a stable metabolite of nitric oxide, and inducible nitric oxide synthase (iNOS) by mouse macrophages. Specific antibody-mediated aggregation of CD120a (p55) induced NO2- accumulation in culture supernatants and iNOS mRNA expression in macrophage lysates, whereas cross-linking of CD120b (p75) had a minimal effect. In contrast, simultaneous cross-linking of both receptors led to a marked augmentation in NO2- and iNOS mRNA expression. Antibody-mediated blockade of CD120a (p55) completely inhibited NO2- expression in response to TNFalpha, whereas blockade of CD120b (p75) reduced NO2- accumulation by approximately 50%. Specific ligation of CD120a (p55) with either (i) human TNFalpha or (ii) by incubation with mouse TNFalpha following pretreatment of macrophages with blocking concentrations of anti-CD120b (p75) antibody resulted in a similar reduction in NO2- production in response to TNFalpha. Quantification of iNOS mRNA, protein, and NO2- expression during independent and co-ligation of CD120a (p55) and CD120b (p75) indicated that iNOS mRNA and protein expression was transient in nature when CD120a (p55) was cross-linked alone but was prolonged when both receptors were simultaneously cross-linked. In addition, cross-linking both receptors also led to a potentiation of NO2- accumulation in culture supernatants that was more pronounced at later time points. These findings suggest that while cross-linking of CD120a (p55) is necessary and sufficient for iNOS mRNA and NO2- expression, CD120b (p75) participates by (i) increasing the sensitivity of the cells to TNFalpha, probably by "passing" ligand to CD120a (p55), and (ii) initiating a signaling event that results in a more sustained induction of iNOS mRNA and protein and thereby augments the production of nitric oxide.

Epstein-Barr virus-transforming protein latent infection membrane protein 1 activates transcription factor NF-kappaB through a pathway that includes the NF-kappaB-inducing kinase and the IkappaB kinases IKKalpha and IKKbeta

The Epstein-Barr virus oncoprotein latent infection membrane protein 1 (LMP1) is a constitutively aggregated pseudo-tumor necrosis factor receptor (TNFR) that activates transcription factor NF-kappaB through two sites in its C-terminal cytoplasmic domain. One site is similar to activated TNFRII in associating with TNFR-associated factors TRAF1 and TRAF2, and the second site is similar to TNFRI in associating with the TNFRI death domain interacting protein TRADD. TNFRI has been recently shown to activate NF-kappaB through association with TRADD, RIP, and TRAF2; activation of the NF-kappaB-inducing kinase (NIK); activation of the IkappaB alpha kinases (IKKalpha and IKKbeta); and phosphorylation of IkappaB alpha. IkappaB alpha phosphorylation on Ser-32 and Ser-36 is followed by its degradation and NF-kappaB activation. In this report, we show that NF-kappaB activation by LMP1 or by each of its effector sites is mediated by a pathway that includes NIK, IKKalpha, and IKKbeta. Dominant negative mutants of NIK, IKKalpha, or IKKbeta substantially inhibited NF-kappaB activation by LMP1 or by each of its effector sites.

Expression of the Epstein-Barr Virus Protein LMP1 Mediates Tumor Regression In Vivo

By stimulating the expression of murine IP-10 and Mig, CXC chemokines that inhibit neovascularization and cause damage to established tumor vasculature, human B cells immortalized with Epstein-Barr virus (EBV) can promote an effective antitumor response in athymic mice. In the present study, we examined the potential role of EBV in the induction of this antitumor response. Using a panel of EBV+ and EBV− Burkitt lymphoma (BL) cell lines, a significant correlation was detected between the expression of the EBV latency gene LMP1 and the occurrence of spontaneous tumor regression in athymic mice. Inoculation of LMP1+ and LMP1− BL cells in the same subcutaneous site resulted in tumors that completely regressed in a manner indistinguishable from that induced by EBV-immortalized B cells. EBV-converted BL30 and BL41 sublines infected with B95-8 virus expressed LMP1, generated tumors that frequently regressed spontaneously, and promoted an effective antitumor response against progressively growing tumors. In contrast, the EBV− BL30 and BL41 cell lines and the EBV-converted BL30 and BL41 infected with P3HR-1 virus did not express LMP1 protein, and generated progressively growing tumors in nude mice. When transfected with the LMP1 gene, BL41 cells produced tumors that regressed spontaneously in most cases, and could induce the regression of tumors derived from BL41 cells transfected with vector alone. Tumors induced by LMP1-expressing cells expressed murine IP-10 and Mig and displayed histological evidence of extensive tumor tissue necrosis and vascular damage. We conclude that the EBV protein LMP1 is likely responsible for the antitumor response elicited by EBV-immortalized cells in athymic mice.

Expression of the Epstein-Barr Virus Protein LMP1 Mediates Tumor Regression In Vivo

By stimulating the expression of murine IP-10 and Mig, CXC chemokines that inhibit neovascularization and cause damage to established tumor vasculature, human B cells immortalized with Epstein-Barr virus (EBV) can promote an effective antitumor response in athymic mice. In the present study, we examined the potential role of EBV in the induction of this antitumor response. Using a panel of EBV+ and EBV− Burkitt lymphoma (BL) cell lines, a significant correlation was detected between the expression of the EBV latency gene LMP1 and the occurrence of spontaneous tumor regression in athymic mice. Inoculation of LMP1+ and LMP1− BL cells in the same subcutaneous site resulted in tumors that completely regressed in a manner indistinguishable from that induced by EBV-immortalized B cells. EBV-converted BL30 and BL41 sublines infected with B95-8 virus expressed LMP1, generated tumors that frequently regressed spontaneously, and promoted an effective antitumor response against progressively growing tumors. In contrast, the EBV− BL30 and BL41 cell lines and the EBV-converted BL30 and BL41 infected with P3HR-1 virus did not express LMP1 protein, and generated progressively growing tumors in nude mice. When transfected with the LMP1 gene, BL41 cells produced tumors that regressed spontaneously in most cases, and could induce the regression of tumors derived from BL41 cells transfected with vector alone. Tumors induced by LMP1-expressing cells expressed murine IP-10 and Mig and displayed histological evidence of extensive tumor tissue necrosis and vascular damage. We conclude that the EBV protein LMP1 is likely responsible for the antitumor response elicited by EBV-immortalized cells in athymic mice.

The tumor necrosis factor signaling complex: choosing a path toward cell death or cell proliferation

Signal transduction pathways which are initiated by the tumor necrosis factor (TNF) utilize receptors which are devoid of intrinsic catalytic activity. Recently identified two families of proteins that directly associate with the cytoplasmic domains of the TNF receptor family members, have partially bridged a molecular gap within the TNF-induced signaling pathways. Clearly, there are numerous alternate routes that originate from the TNF ligand-receptor assembly and terminate on the diverse cellular responses, including proliferation, differentiation, or death. This review focuses on recent advances characterizing the TNF ligand-receptor signaling network, which allow to better understand its participation in a life-death balance within the target cell.

Induction of Dendritic Cell Differentiation by Granulocyte-Macrophage Colony-Stimulating Factor, Stem Cell Factor, and Tumor Necrosis Factor α In Vitro From Lineage Phenotypes-Negative c-kit+ Murine Hematopoietic Progenitor Cells

To elucidate the capacity of murine early hematopoietic progenitor cells (HPCs) to differentiate into dendritic cells (DCs), lineage phenotypes (Lin)−c-kit+ HPCs were highly purified from either wild-type or tumor necrosis factor (TNF) receptor p55 (TNF-Rp55)-deficient mice. Upon culture with granulocyte-macrophage colony-stimulating factor (GM-CSF) and stem cell factor (SCF) for 14 days, wild-type mouse Lin−c-kit+ HPCs did not exhibit characteristic features of DC such as sheet-like projections and veil processes. Moreover, these cells expressed a marginal level of DC markers such as DEC-205, CD86, and barely supported allogenic MLR. However, the addition of mouse TNFα generated a large number of cells with typical DC morphology, expression of high levels of Ia, DEC-205, CD86, and function of stimulating allogenic MLR. Moreover, a proportion of these mature DCs and thymic DCs expressed Thy-1 mRNA as well as Thy-1 antigen, whereas freshly isolated splenic DCs did not. These results suggested that DCs generated in our culture system phenotypically resemble thymic ones. In contrast, mouse TNFα failed to induce TNF-Rp55-deficient mice-derived Lin−c-kit+ HPCs to generate DCs with characteristic morphology, immunophenotype, and accessory function for T cells under the same culture conditions, suggesting a crucial role of TNF-Rp55 in TNFα-mediated DC differentiation from HPCs. Interestingly, human TNFα, which can bind to mouse TNF-Rp55 but not TNF-Rp75, was incapable to augment DC generation from wild-type mouse Lin−c-kit+ HPCs. Collectively, these results suggest that TNFα has a pivotal role in DC generation from murine early HPCs in collaboration with GM-CSF and SCF through the interaction of TNF-Rp55 and TNF-Rp75.

Induction of Dendritic Cell Differentiation by Granulocyte-Macrophage Colony-Stimulating Factor, Stem Cell Factor, and Tumor Necrosis Factor α In Vitro From Lineage Phenotypes-Negative c-kit+ Murine Hematopoietic Progenitor Cells

To elucidate the capacity of murine early hematopoietic progenitor cells (HPCs) to differentiate into dendritic cells (DCs), lineage phenotypes (Lin)−c-kit+ HPCs were highly purified from either wild-type or tumor necrosis factor (TNF) receptor p55 (TNF-Rp55)-deficient mice. Upon culture with granulocyte-macrophage colony-stimulating factor (GM-CSF) and stem cell factor (SCF) for 14 days, wild-type mouse Lin−c-kit+ HPCs did not exhibit characteristic features of DC such as sheet-like projections and veil processes. Moreover, these cells expressed a marginal level of DC markers such as DEC-205, CD86, and barely supported allogenic MLR. However, the addition of mouse TNFα generated a large number of cells with typical DC morphology, expression of high levels of Ia, DEC-205, CD86, and function of stimulating allogenic MLR. Moreover, a proportion of these mature DCs and thymic DCs expressed Thy-1 mRNA as well as Thy-1 antigen, whereas freshly isolated splenic DCs did not. These results suggested that DCs generated in our culture system phenotypically resemble thymic ones. In contrast, mouse TNFα failed to induce TNF-Rp55-deficient mice-derived Lin−c-kit+ HPCs to generate DCs with characteristic morphology, immunophenotype, and accessory function for T cells under the same culture conditions, suggesting a crucial role of TNF-Rp55 in TNFα-mediated DC differentiation from HPCs. Interestingly, human TNFα, which can bind to mouse TNF-Rp55 but not TNF-Rp75, was incapable to augment DC generation from wild-type mouse Lin−c-kit+ HPCs. Collectively, these results suggest that TNFα has a pivotal role in DC generation from murine early HPCs in collaboration with GM-CSF and SCF through the interaction of TNF-Rp55 and TNF-Rp75.

Sequence-specific inhibition of the tumor necrosis factor-alpha receptor I gene by oligodeoxynucleotides containing N7 modified 2'-deoxyguanosine

Tumor necrosis factor-alpha (TNF-alpha) is a highly pleiotropic cytokine produced mainly by activated macrophages. This cytokine has been found to mediate the growth of certain tumors, the replication of HIV-1, septic shock, cachexia, graft-versus-host disease, and autoimmune diseases. The binding of TNF-alpha to the p55 tumor necrosis factor receptor type I (TNFRI) is considered one of the initial steps responsible for the multiple physiologic effects mediated by TNF-alpha. The role of TNF-alpha as an inflammatory mediator through TNFRI makes both of these genes attractive targets for intervention in both acute and chronic inflammatory diseases. We have designed antisense oligodeoxynucleotides (ODNs) containing chemically modified purine and pyrimidine bases that specifically inhibit TNFRI expression and functions. These ODNs were designed to hybridize to the 3'-polyadenylation signal region of the TNFRI gene. In cell-based assays, gene-specific antisense inhibition occurred in a dose-dependent fashion at submicromolar concentrations in the presence of cellular uptake enhancing agents. Within ODN sets with a common pattern of stabilizing backbone substitution, the inhibition of the gene expression is found to be correlated with the affinity of the ODNs for their cognate mRNA target sites, providing direct evidence for an antisense mechanism of action. In addition, events triggered by the binding of TNF-alpha to TNFRI, such as the production of IL-6 and IL-8, were significantly reduced by treatment of cells with the anti-TNFRI ODN. Therefore, antisense ODNs can be used to control biologic processes mediated by TNF-alpha and may be useful as therapeutic agents to treat conditions resulting from overproduction of TNF-alpha.

Dominant negative and cooperative effects of mutant forms of prolactin receptor

In addition to a long form of 591 amino acids (aa), two other forms of PRL receptor (PRLR), differing in the length of their cytoplasmic domains, have been identified in the rat. The Nb2 form, lacking 198 aa in the cytoplasmic domain, is able to transmit a lactogenic signal similar to the long form, whereas the short form of 291 aa is inactive. The ability of PRL to activate the promoter of the beta-casein gene or the lactogenic hormone responsive element fused to the luciferase reporter was assessed in Chinese hamster ovary cells or 293 fibroblasts transiently transfected with PRLR cDNAs. The function of the short form was examined after cotransfection of both the long and short forms. These results clearly show that the short form acts as a dominant negative inhibitor through the formation of inactive heterodimers, resulting in an inhibition of Janus kinase 2 (JAK2) activation. The present study also investigates the possible participation of cytoplasmic receptors in the signal transduction pathway, using cotransfection experiments and a new approach that selectively determines the contribution of cytoplasmic receptors in the process of signal transduction. We cotransfected Chinese hamster ovary cells with two cDNA constructs: a cytoplasmic (soluble) form of the receptor with a deleted signal peptide (delta-19), which is unable to bind PRL, and a functionally inactive receptor mutant (lacking box 1), which is anchored in the plasma membrane and able to bind PRL. This approach has allowed us to show that delta-19, lacking expression at the plasma membrane, can transduce the hormonal message, at least to a limited extent (up to 30% of wild type efficiency), providing that association/activation occurs with a PRL-PRLR complex initiated at the cell surface level; box 1 of the cytoplasmic form is necessary to rescue this partial transcriptional activity of the inactive mutant. This partial recovery is also parallel to the partial activation of JAK2, indicating that the signal transduction pathway implicated JAK2. Our results provide evidence that heterodimerization of receptors can be implicated either in the positive or in negative activation of gene transcription.

Induced expression of trimerized intracellular domains of the human tumor necrosis factor (TNF) p55 receptor elicits TNF effects

The various biological activities of tumor necrosis factor (TNF) are mediated by two receptors, one of 55 kD (TNF-R55) and one of 75 kD (TNF-R75). Although the phenotypic and molecular responses elicited by TNF in different cell types are fairly well characterized, the signaling pathways leading to them are so far only partly understood. To further unravel these processes, we focused on TNF-R55, which is responsible for mediating most of the known TNF effects. Since several studies have demonstrated the importance of receptor clustering and consequently of close association of the intracellular domains for signaling, we addressed the question of whether clustering of the intracellular domains of TNF-R55 (TNF-R55i) needs to occur in structural association with the inner side of the cell membrane, where many signaling mediators are known to reside. Therefore, we investigated whether induced intracellular clustering of only TNF-R55i would be sufficient to initiate and generate a full TNF response, without the need for a full-length receptor molecule or a transmembrane region. Our results provide clear evidence that inducible forced trimerization of either TNF-R55i or only the death domain elicits an efficient TNF response, comprising activation of the nuclear factor kappaB, induction of interleukin-6, and cell killing.

Distinct domains of M-T2, the myxoma virus tumor necrosis factor (TNF) receptor homolog, mediate extracellular TNF binding and intracellular apoptosis inhibition

The myxoma virus tumor necrosis factor (TNF) receptor homolog, M-T2, is expressed both as a secreted glycoprotein that inhibits the cytolytic activity of rabbit TNF-alpha and as an endoglycosidase H-sensitive intracellular species that prevents myxoma virus-infected CD4+ T lymphocytes from undergoing apoptosis. To compare the domains of M-T2 mediating extracellular TNF inhibition and intracellular apoptosis inhibition, recombinant myxoma viruses expressing nested C-terminal truncations of M-T2 protein were constructed. One mutant, deltaL113, containing intact copies of only two cysteine-rich domains, was not secreted and was incapable of binding rabbit TNF-alpha yet retained full ability to inhibit virus-induced apoptosis of RL-5 cells. Thus, the minimal domain of intracellular M-T2 protein required to inhibit apoptosis is distinct from that required by the extracellular M-T2 for functional TNF-alpha binding and inhibition. This is the first report of a virus-encoded immunomodular protein with two distinct antiimmune properties.