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Biomedical subjects

B Beutler

Publications and source records attributed to B Beutler.

At least 55 records · Page 3Linked to original sources
PubMed1995

Chimeric tumor necrosis factor receptors with constitutive signaling activity.

Many hormone and cytokine receptors are crosslinked by their specific ligands, and multimerization is an essential step leading to the generation of a signal. In the case of the tumor necrosis factor (TNF) receptors (TNF-Rs), antibody-induced crosslinking is sufficient to trigger a cytolytic effect. However, the quaternary structural requirements for signaling--i.e., the formation of dimers, trimers, or higher-order multimers--have remained obscure. Moreover, it has not been clear whether the 55-kDa or 75-kDa TNF-R is responsible for initiation of cytolysis. We reasoned that an obligate receptor dimer, targeted to the plasma membrane, might continuously signal the presence of TNF despite the actual absence of the ligand. Such a molecule, inserted into an appropriate vector, could be used to project receptor-specific "TNF-like" activity to specific cells and tissues in vivo. Accordingly, we constructed sequences encoding chimeric receptors in which the extracellular domain of the mouse erythropoietin receptor (Epo-R) was fused to the "stem," transmembrane domain, and cytoplasmic domain of the two mouse TNF-Rs. Thus, the Epo-R group was used to drive dimerization of the TNF-R cytoplasmic domain. These chimeric proteins were well expressed in a variety of cell lines and bound erythropoietin at the cell surface. Both the 55-kDa and the 75-kDa Epo/TNF-R chimeras exerted a constitutive cytotoxic effect detected by cotransfection or clonogenic assay. Thus, despite the lack of structural homology between the cytoplasmic domains of the two TNF-Rs, a similar signaling endpoint was observed. Moreover, dimerization (rather than trimerization or higher-order multimerization) was sufficient for elicitation of a biological response.

Animals↗
PubMed1995

Adenovirus-mediated blockade of tumor necrosis factor in mice protects against endotoxic shock yet impairs pulmonary host defense.

A replication-deficient recombinant adenovirus encoding a chimeric protein capable of binding tumor necrosis factor (TNF) and lymphotoxin was given to mice. Administration of this virus (10(9) pfu intravenously) yielded high levels of the recombinant protein in plasma and afforded significant protection to a lethal challenge with lipopolysaccharide with or without D-galactosamine. However, this protein inhibitor was readily detectable in the lung and was associated with decreased neutrophil recruitment and bacterial killing after intratracheal LPS or Pseudomonas aeruginosa, respectively. These data reflect the dual role of many proinflammatory cytokines. This model of TNF inhibition is similar to the homozygous 55-kDa TNF receptor deletion; thus, adenovirus-mediated gene transfer of cytokine inhibitors in vivo is a useful tool to abrogate the function of single or multiple cytokines for investigational or therapeutic purposes.

Adenoviridae↗
PubMed1995

Lipopolysaccharide signal transduction, regulation of tumor necrosis factor biosynthesis, and signaling by tumor necrosis factor itself.

In recent years, the chain of events that connects introduction of bacterial endotoxin (lipopolysaccharide; LPS) into a mammalian host, and the syndrome of organ damage and vascular collapse that ensues, have come into sharper focus. Several of the molecules that engage LPS, and a rough outline of the signaling cascade that leads to cytokine release from mononuclear cells, have been elucidated. The principal cytokines that mediate the untoward effects of LPS have also been identified. The most important of these is tumor necrosis factor (TNF), which elicits biologic responses from virtually every type of cell to which it binds. Two distinct receptors transduce the TNF signal. Mechanisms of TNF receptor action are becoming increasing clear, and there is reason to hope that, through intervention at many distinct levels, the devastating effects of LPS might be attenuated or averted.

Animals↗
PubMed1995

Expression of the tumor necrosis factor gene by dermal fibroblasts in response to ultraviolet irradiation or lipopolysaccharide.

To examine the effects of different wavelengths of ultraviolet (UV) radiation on tumor necrosis factor (TNF) production, we took advantage of mice carrying a chloramphenicol acetyl transferase (CAT) reporter transgene bearing the entire TNF promoter and 3'-untranslated region. Aside from constitutive expression in the thymus, CAT activity was detected only in locally UVB- or UVC-irradiated skin. After UVB irradiation, markedly greater amounts of CAT activity were traced to the dermis rather than the epidermis; by contrast, almost all CAT activity was localized to the epidermis after UVC irradiation. Fibroblasts have not been shown previously to express the TNF gene, i.e., the TNF gene is highly methylated and inaccessible to exogenous modulation in 3T3 fibroblasts. However, the present report reveals that cultured dermal fibroblasts are capable of producing both CAT and TNF in response to treatment in vitro with either UVB irradiation, UVC irradiation, or lipopolysaccharide. These findings indicate that dermal fibroblasts may serve not only as a target for but also as a source of TNF.

Animals↗
PubMed1995

Comparative expression of TNF-alpha alleles from normal and autoimmune-prone MHC haplotypes.

The tumor necrosis factor-alpha (TNF-alpha, or TNF) genes of NOD mice and NZW mice are reportedly underexpressed relative to the TNF genes of control mice in lipopolysaccharide (LPS)-induced peritoneal macrophages. These findings, as well as the well-known major histocompatibility complex (MHC) linkage of the TNF genes, have prompted speculation that mutations affecting expression of the TNF-alpha loci might represent a primary cause of autoimmune diseases. Differences in expression of the TNF genes in different strains of mice might result either from effects of cis-acting mutations or from differences in the cellular environment that operate in trans. To discriminate between these possibilities, we directly examined the relative contribution made by each of two different TNF alleles (one associated with an autoimmune-prone haplotype and the other not) to the pool of TNF mRNA within the cells of F1 hybrid mice. Reverse transcription-polymerase chain reaction (RT-PCR) was used to amplify a polymorphic fragment derived from the total pool of TNF mRNA present in LPS-induced peritoneal macrophages of hybrid animals produced by crossing BALB/c to non-obese diabetic (NOD), and New Zealand black (NZB) to New Zealand white (NZW). In both types of F1 hybrid, the two alleles were represented in nearly equal quantities at the mRNA level. It may be inferred that at all pretranslational levels, the NZW and NOD TNF alleles are functionally equivalent to the control alleles that were examined. Interstrain differences in responsiveness to LPS are therefore responsible for interstrain differences in TNF gene expression.

Alleles↗
PubMed1995

MIP-1 gamma: molecular cloning, expression, and biological activities of a novel CC chemokine that is constitutively secreted in vivo.

We have identified a novel CC chemokine family member, herein termed MIP-1 gamma in view of its similarity to existing members of the MIP-1 group. The murine protein has a predicted length of 100 amino acids. Like MIP-1 alpha, recombinant MIP-1 gamma acts as a pyrogen when administered intracerebroventricularly. MIP-1 gamma and MIP-1 alpha engage the same high-affinity receptor on neutrophils, activating calcium release within seconds following cell contact. Pretreatment with either chemokine abolishes responses to the other, and to itself, suggesting utilization of a common signaling pathway. However, unlike MIP-1 alpha or any of the other CC chemokines, MIP-1 gamma is expressed constitutively by a wide variety of tissues, and circulates in the blood of healthy mice at concentrations of approximately 1 microgram/ml (90 nM). It would therefore be predicted that MIP-1 gamma occupies most of the CC chemokine receptors that exist in the intravascular compartment. As such it might, under normal circumstances, markedly influence responses to the inducible CC chemokines.

3T3 Cells↗
PubMed1995

How do tumor necrosis factor receptors work?

Quite suddenly, a new level of understanding has been attached to the TNF ligand and receptor families. Many of the proximal transducers that signal the presence of TNF or its homologs have been identified, and certain components of the distal signaling pathway have emerged as well. We lack, however, a "movie" of the events that transpire when TNF binds its receptors on the surface of a cell. The facts in hand permit an educated approximation.

Animals↗
PubMed1995

Expression of an adenovirally encoded lymphotoxin-beta inhibitor prevents clearance of Listeria monocytogenes in mice.

The lymphotoxin (LT)-beta heterotrimer was recently identified as a molecule containing LT-alpha subunits, tethered to the cell through non-covalent association with an integral plasma membrane protein, derived from the LT-beta gene. Since knockout mutations of the LT-alpha gene yield animals that lack lymph nodes, whereas animals lacking either or both of the receptors for tumor necrosis factor (TNF) and LT-alpha homotrimers have normal lymph nodes, it has been inferred that the association between the LT-beta heterotrimer and its cognate receptor is required for lymph node ontogeny. Similarly, LT-beta and its receptor are thought to be important for development of the spleen. Since LT-alpha deficient mice lack lymph nodes, it is difficult to assess the extradevelopmental contribution of LT-beta to immune competence. To this end, we employed a strategy for the conditional blockade of LT-beta heteromer activity in normal mice. The interaction between LT-beta and its receptor is essential for the destruction of intracellular Listeria monocytogenes.

Adenoviridae↗
PubMed1994

Receptor-mediated label-transfer assay (RELAY): a novel method for the detection of plasma tumor necrosis factor at attomolar concentrations.

We have exploited the extremely high binding specificity of the 55 kDa human tumor necrosis factor (TNF) receptor in an assay designed to detect TNF with sensitivity limited only by limits in the detection of 131I. Bivalent derivatives of the 55 kDa TNF receptor (referred to here as the TNF binding protein), in which the extracellular domain is coupled to an IgG heavy chain, ordinarily bind TNF with very high affinity as a result of the fact that they interact with two separate sites on the trimer surface. The TNF binding protein is radioiodinated to a high specific activity and then added to plasma at a saturating concentration, so that it binds all active TNF present in the solution. Covalent adducts between molecules of TNF and molecules of the binding protein are then produced by crosslinking with disuccinimidyl suberate (DSS). The complexes are swept out of solution using sepharose beads to which polyclonal anti-TNF antibodies have been affixed. On electrophoresis, the complex presents itself as a band of M(r) = 200 kDa (as distinct from the uncomplexed binding protein, which has a size of 120 kDa and which in any case is removed by washing). As little as 50 fg of active TNF (600,000 trimers) can be detected in a 5 ml sample of plasma using this approach, corresponding to the detection of TNF at a 200 aM concentration. Notably, no TNF is detectable in normal plasma specimens, indicating that normal plasma contains active TNF at a concentration beneath 200 aM.

Animals↗
PubMed1994

Prolonged and effective blockade of tumor necrosis factor activity through adenovirus-mediated gene transfer.

A chimeric protein capable of binding and neutralizing tumor necrosis factor (TNF) and lymphotoxin was expressed in mice transduced with a replication-incompetent adenoviral vector into which a TNF inhibitor gene had been engineered. Within 3 days following the injection of 10(9) infectious particles, the TNF inhibitor concentration exceeded 1 mg/ml of plasma; this level of expression was maintained for at least 4 weeks, and detectable TNF inhibitory activity was measured 6 weeks after injection of the recombinant virus. Introduction of the artificial gene produced a phenotypic effect comparable to homozygous deletion of the 55-kDa TNF receptor, in that animals were rendered highly susceptible to infection by Listeria monocytogenes, whereas control animals receiving a replication-incompetent virus coding for beta-galactosidase were capable of resisting Listeria challenge. Adenovirus-mediated transfer of a gene encoding a TNF inhibitor offers a practical means of imposing effective, long-term blockade of TNF activity in vivo for investigational and therapeutic purposes.

Adenoviridae↗
PubMed1994

Analysis of tumor necrosis factor promoter responses to ultraviolet light.

Ultraviolet (UV) light induces the biosynthesis of chloramphenicol acetyltransferase (CAT) in the skin of mice bearing the CATTNF reporter transgene. Moreover, nuclear run-on assays indicate that UV light induces transcription of the TNF gene in RAW 264.7 macrophages. These observations suggest that the TNF gene (and/or its mRNA product) responds to signals elicited by UV light. To identify transcriptional UV response elements within the TNF promoter, and to determine whether a posttranscriptional response might also exist, a series of reporter constructs using a CAT coding sequence attached to various portions of the TNF promoter and 3' untranslated region were devised and transfected into several cultured cell lines. All cells tested were found to be UV responsive, and in NIH 3T3 cells, induction was found to depend upon two general regions of the promoter. The more distal region encompassed nucleotides (nt) -1059 through -451 with respect to the cap site, while the more proximal region spanned nt -403 through -261. A negative element, blocking the UV response, was interposed (nt -451 through -403). As with the response to LPS, the response to UV irradiation appears to involve translational activation in macrophages. However, the UV and LPS signaling pathways have little in common with one another, as indicated by three observations. First, no difference in responsiveness was observed on comparison of TNF gene induction in macrophages derived from C3H/HeN as opposed to C3H/HeJ mice. Second, cell fusion studies showed that while the LPS signaling pathway is extinguished by fusion of RAW 264.7 cells with NIH 3T3 cells, the UV signaling pathway remained intact. Finally, induction did not depend upon the NF-kappa B binding sites that are known to be required for LPS response in macrophages, since mutation of these sites did not impair the UV response.

3T3 Cells↗
PubMed1994

Lipopolysaccharide signals activation of tumor necrosis factor biosynthesis through the ras/raf-1/MEK/MAPK pathway.

BACKGROUND: Lipopolysaccharide (LPS) is known to activate macrophages, causing the release of toxic cytokines that may provoke inflammation and shock. One of the most important and best studied of these cytokines is tumor necrosis factor (TNF). Details of the signaling pathway leading to TNF biosynthesis remain unclear. The pathway is branched in the sense that TNF gene transcription and TNF mRNA translation are both strongly stimulated by LPS. Recent evidence has indicated that MAP kinase homologs become phosphorylated in LPS-stimulated cells, suggesting their possible involvement in signal transduction. We sought to test this hypothesis. MATERIALS AND METHODS: Measurements of LPS-induced MEK and ERK2 activity were undertaken in LPS-sensitive and LPS-insensitive cells. Transfection studies, in which dominant inhibitors of ras and raf-1 were used to block signaling to the level of MAP kinase, were carried out in order to judge whether the TNF gene transcription and TNF mRNA translation are modulated through this pathway. RESULTS: In RAW 264.7 mouse macrophages, both ERK2 and MEK1 activity are induced by LPS treatment. In the same cell line, dominant negative inhibitors of ras and raf-1 block LPS-induced activation of the TNF promoter, as well as derepression of the translational blockade normally imposed by the TNF 3'-untranslated region. A constitutively active form of raf-1 (raf-BXB) was found to augment, but not replace, the LPS signal. In LPS-insensitive cells (RAW 264.7 x NIH 3T3 fusion hybrid cells and primary macrophages derived from C3H/HeJ mice), ERK2 activity was found to be refractory to induction by LPS. CONCLUSIONS: The ras/raf-1/MEK/MAPK pathway is chiefly responsible for transduction of the LPS signal to the level of the TNF gene and mRNA. raf and raf-1 lie upstream from (or actually represent) the physical branchpoints of the transcriptional and translation activation signals generated by LPS. The lesions that prevent LPS signaling in macrophages from C3H/HeJ mice, or in RAW 264.7 x NIH 3T3 fusion hybrid cells, occupy a proximal position in the signaling pathway.

3T3 Cells↗
PubMed1993

Expression of a TNF inhibitor in transgenic mice.

We previously reported that a chimeric protein consisting of the human p55 TNF receptor covalently linked to a murine IgG1 Fc heavy chain acts as an efficient TNF inhibitor, as a result of its high binding affinity for native TNF trimers of both murine and human origin. A transgenic mouse line constitutively expressing the inhibitor from a cytomegalovirus promoter was established. All organs examined expressed the transgene. TNF inhibitory activity was easily detected in plasma of transgenic animals but not in plasma of nontransgenic littermates. This founder line was not found to have any obvious phenotype. Specifically, transgenic mice born to wild-type or transgenic females were indistinguishable from nontransgenic littermates with respect to their size at birth, at three months and at six months of age, with respect to the size and morphology of their lymphoid organs and with respect to their hematocrit, white blood cell count, and differential. Although TNF is known to be constitutively expressed by cells of the thymus and trophoblast, the lack of a clear phenotype in association with the constitutive expression of a TNF inhibitor suggests that TNF may be dispensable in early development.

Animals↗
PubMed1993

Polymorphism of the mouse TNF-alpha locus: sequence studies of the 3'-untranslated region and first intron.

We have sequenced the 3'-untranslated region (3'-UTR) and first intron of six strains of Mus musculus, as well as M. spretus, M. castaneus, and M. shanghai. A marked degree of polymorphism was evident in the sequences, and among all of the strains, no two haplotypes were identical. Of particular note, insertional mutations modifying the 5'-TTATTTAT sequence in the 3'-UTR, which in its RNA form acts as a translational repressor, were observed in New Zealand White and M. spretus strains. The mutations that we have identified dictate several restriction-fragment length polymorphisms, which should be useful in following the tumor necrosis factor-encoding gene (TNF) in backcross analysis and in defining the ancestry of TNF in mice of indeterminate parentage. Moreover, the data provide a substrate for the future analysis of differences in the level of TNF expression by genetically distinct mice.

Animals↗