Biomedical subjects

W Fiers

Publications and source records attributed to W Fiers.

At least 127 records · Page 7Linked to original sources

PubMed1995

Secretion of biologically active murine interleukin-2 by Lactococcus lactis subsp. lactis.

Secretion of functional recombinant murine interleukin-2 (mIL2) by Lactococcus lactis was achieved by fusion of the sequence encoding mature mIL2 to the secretion signal leader of the lactococcal usp45 gene placed under transcriptional control of the phage T7 promoter-T7 RNA polymerase expression system. The recombinant mature mIL2 was one of only a few proteins which accumulated in the growth medium. Sequence analysis revealed correct processing at the first amino acid of the mature protein. A T-cell proliferation assay showed that the recombinant protein has the same specific biological activity as mIL2 obtained from a natural source.

Amino Acid Sequence↗

PubMed1995

Mechanism of tolerance to tumor necrosis factor: receptor-specific pathway and selectivity.

Repetitive administration of low doses of tumor necrosis factor (TNF) induces a selective tolerance to some, but not all, of its effects. The aim of the present study was to define the pathways involved in tolerance. We observed that the induction of tolerance is mediated by TNF-R55 triggering. TNF-R75 triggering or the addition of sensitizers can interfere with this induction but does not break an acquired tolerance, inasmuch as tolerant animals were also tolerant to otherwise lethal challenges with the combination of human TNF and the sensitizers interleukin-1 and RU-38486. We further defined the selectivity of the tolerance by examining changes in quantitative parameters such as interleukin-6 induction, hypothermia, and hemoconcentration. The differences between tolerant and nontolerant animals mimicked those observed after administration of human TNF vs. murine TNF and were to be found in the duration rather than in the amplitude of the induced changes. We conclude that tolerance selectively blocks the TNF-R75-mediated pathway, especially the part mimicked by interleukin-1 and RU-38486; this pathway normally leads to a state of unresponsiveness to glucocorticoids.

Animals↗

PubMed1994

Complete DNA sequence of yeast chromosome II.

In the framework of the EU genome-sequencing programmes, the complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome II (807 188 bp) has been determined. At present, this is the largest eukaryotic chromosome entirely sequenced. A total of 410 open reading frames (ORFs) were identified, covering 72% of the sequence. Similarity searches revealed that 124 ORFs (30%) correspond to genes of known function, 51 ORFs (12.5%) appear to be homologues of genes whose functions are known, 52 others (12.5%) have homologues the functions of which are not well defined and another 33 of the novel putative genes (8%) exhibit a degree of similarity which is insufficient to confidently assign function. Of the genes on chromosome II, 37-45% are thus of unpredicted function. Among the novel putative genes, we found several that are related to genes that perform differentiated functions in multicellular organisms of are involved in malignancy. In addition to a compact arrangement of potential protein coding sequences, the analysis of this chromosome confirmed general chromosome patterns but also revealed particular novel features of chromosomal organization. Alternating regional variations in average base composition correlate with variations in local gene density along chromosome II, as observed in chromosomes XI and III. We propose that functional ARS elements are preferably located in the AT-rich regions that have a spacing of approximately 110 kb. Similarly, the 13 tRNA genes and the three Ty elements of chromosome II are found in AT-rich regions. In chromosome II, the distribution of coding sequences between the two strands is biased, with a ratio of 1.3:1. An interesting aspect regarding the evolution of the eukaryotic genome is the finding that chromosome II has a high degree of internal genetic redundancy, amounting to 16% of the coding capacity.

Base Composition↗

PubMed1994

Protection by alpha 1-acid glycoprotein against tumor necrosis factor-induced lethality.

We here report that alpha 1-acid glycoprotein, a typical acute phase protein, protects mice from lethal shock induced by tumor necrosis factor (TNF) or endotoxin. The protection is observed both in normal and in galactosamine-sensitized mice. Optimal desensitization requires at least 3 mg alpha 1-acid glycoprotein administered 2 h before the lethal challenge. Under these conditions, complete inhibition of all TNF-induced metabolic changes was observed: fall in body temperature, release of liver transaminases, enhanced clotting time, and mortality. The known platelet aggregation-inhibitory activity of alpha 1-acid glycoprotein provides a possible explanation for this protective capacity.

Animals↗

PubMed1994

Modulation of the release of cytokines and reduction of the shock syndrome induced by anti-CD3 monoclonal antibody in mice by interleukin-10.

Since IL-10 was recently shown to inhibit several T cell functions in vitro, we investigated the effects of IL-10 on the cytokine release syndrome induced in mice by the 145-2C11 anti-CD3 mAb. As OKT3 in man, this mAb induces a massive polyclonal T cell activation before to induce immunosuppression. First, we found that administration of 1000 U of recombinant mouse IL-10 (mIL-10) 30 min before injection of 10 micrograms of the 145-2C11 antimouse CD3 mAb markedly reduced the systemic release of IFN-gamma and TNF. In contrast, IL-10 pretreatment did not significantly modify the release of IL-6. To determine the effect of IL-10 pretreatment on the endogenous secretion of IL-10 induced by the 145-2C11 mAb, mice were injected with human IL-10 (hIL-10) which does not cross-react in the ELISA for mIL-10 determination. While hIL-10 was as efficient as mIL-10 in reducing TNF and IFN-gamma release, it did not modify peak serum levels of IL-10. The modulation of cytokine production by mIL-10 was associated with a significant reduction of the toxicity of the 145-2C11 mAb, as assessed by the attenuation of hypothermia and by the reduced lethality in D-galactosamine-sensitize mice. We conclude that IL-10 differentially regulates the in vivo production of cytokines and decreases the systemic toxicity induced by the 145-2C11 mAb. These observations suggest potential therapeutic applications of IL-10 in organ transplantation, especially in association with anti-CD3 mAb.

Animals↗

PubMed1994

Recombinant IL-1 receptor antagonist protects against TNF-induced lethality in mice.

The possible role of induced IL-1 in a number of in vivo actions of TNF was investigated. We were particularly interested to know whether a species-specific induction of IL-1 might explain the important differences observed between murine TNF and human TNF in systems such as lethal shock and the induction of long lasting, high levels of circulating IL-6 in mice. We also studied the possible involvement of IL-1 in the sensitization to TNF observed in tumor-bearing mice or in combination with D(+)-galactosamine or RU38486, particularly because such sensitization results in the loss of species-specific differences between both TNF. Using a specific rIL-1R antagonist (IL-1ra), which inhibits the binding of IL-1 to the IL-1R type I, we were able to protect mice against a lethal murine TNF injection. However, the induction of high levels of circulating IL-6 by murine TNF was not affected, although IL-1ra almost completely blocked the induction of IL-6 by exogenously administered IL-1. Furthermore, the increased susceptibility of tumor-bearing mice to human TNF, relative to control mice, or the sensitization by co-administration of RU38486 or D(+)-galactosamine do not seem to be mediated by IL-1.

Animals↗

PubMed1994

Production of enzymatically active rat protein disulfide isomerase in Escherichia coli.

We report the development of a bacterial expression system allowing high-level synthesis of enzymatically active rat protein disulfide isomerase (rPDI). After expression of the rpdi gene under control of the inducible trc promoter (Ptrc), a significant amount of soluble, active rPDI was detected in the periplasmic contents, which were released from the cells by cold osmotic shock. However, the exported molecules were incompletely or improperly processed, while the major amount of synthesized rPDI was in fact detected in the soluble cellular fraction. Substitution of the autologous eukaryotic export signal with the nucleotide (nt) sequence encoding the signal peptide (sOmpA) of the bacterial outer membrane protein A, and expression of the sompA::rpdi fusion gene under control of both the lpp promoter (Plpp) and the lac promoter-operator (POlac), resulted in high-level production of rPDI. Furthermore, the latter was efficiently exported into the periplasmic compartment, from where it was recovered as a soluble, fully active form with the sOmpA precisely removed. The synthesis of a small 21-kDa peptide accompanying the production of rPDI was also observed. This rPDI-related peptide (rPDIf), which represented a C-terminal fragment of rPDI including the second active site, arose by internal translation initiation within rpdi. Replacement of the presumed internal start codon by CTC completely eliminated the aforementioned phenomenon and resulted in the production of a slightly mutated, enzymatically active enzyme (rPDIm).

Amino Acid Sequence↗

PubMed1994

Human tumor necrosis factor mutants with preferential binding to and activity on either the R55 or R75 receptor.

Previously, we reported that the cytotoxic activity of human (h) tumor necrosis factor (TNF) on murine (m) L929 cells requires the integrity of three loops (positions 30-36, 84-88 and 138-150) which cluster around the interface between each two subunits of the trimeric hTNF structure. The collection of hTNF mutants was further characterized by their activity on various human cell systems as well as by their binding to the two types of hTNF receptor (R), R55 and R75. It turned out that two amino acids (Leu29 and Arg32) were specifically involved in hR75 binding, as Leu29-->Ser (L29S) and Arg32-->Trp (R32W) mutant molecules had largely lost binding to hR75, but not to hR55. In order to screen for more highly R55-specific mutants, nine other amino acids were inserted at these two positions; only the substitutions L29G and L29Y showed an increased differential binding as compared to L29S, while no further improvement was found with mutations at position 32 compared to R32W. Biological assays mediated either by hR55 or hR75 confirmed the results obtained by physical binding to purified receptors. A similar substitution in mTNF, Arg32-->Tyr, also resulted in a preferential loss of binding to hR75 and a large decrease in mR75-mediated bioactivity. Except for the double mutant L29S-R32W, all other tested amino acid substitutions in the loops at positions 30-36 or 84-88 of hTNF led to a substantial loss of affinity for both receptors and a concomitant reduction of biological activity. In the loop at positions 138-150, the non-conservative replacement of Glu by Lys at position 146 (E146K) resulted in an even lower binding to R75 as compared to R32W, while binding on and bioactivity through R55 was only slightly reduced. Remarkably, a reversed differential binding was observed after substitution at position 143 in hTNF; replacing Asp by non-conservative residues such as Tyr, Phe or Asn resulted in a much larger decrease in binding to R55 than to R75. In conclusion, receptor-specific mutants such as R32W, E146K and D143N can be used to study the function either of R55 or R75 on different human cell types. In vivo, we presume that the R55-specific mutants will retain antitumor activity in the absence of R75-dependent, severe side effects.

Animals↗

PubMed1994

Molecular mechanisms of tumor necrosis factor-induced cytotoxicity. What we do understand and what we do not.

Although TNF plays an important role in several physiological and pathological conditions, the hallmark of this important cytokine has been its selective cytotoxic activity on tumor cells. Since its cloning in 1984, understanding of how TNF selectively kills tumor cells has been the subject of research in many laboratories. Here we review TNF-induced post-receptor signaling mechanisms which seem to be involved in the pathway to cytotoxicity.

Animals↗

PubMed1994

Dissociation of TNF-alpha cytotoxic and proinflammatory activities by p55 receptor- and p75 receptor-selective TNF-alpha mutants.

Human tumour necrosis factor alpha (TNF-alpha) is a pleiotropic cytokine capable of killing mammalian tumour cells in vitro and in vivo, and of enhancing the proinflammatory activity of leucocytes and endothelium, the latter effects limiting its usage as an antitumour agent in humans. Using TNF-alpha mutants with a selective capacity to bind to the TNF p55 receptor (TNFR55) or to the p75 receptor (TNFR75) we show here that these two major activities of TNF-alpha can be dissociated. The TNFR55-selective mutants (R32W, E146K and R32W-S86T) which bind poorly to TNFR75 displayed similar potency to wild-type TNF in causing cytotoxicity of a human laryngeal carcinoma-derived cell line (HEp-2) and cytostasis in a human leukaemic cell line (U937). However, these TNFR55-selective mutants exhibited lower proinflammatory activity than wild-type TNF. Specifically, TNF-alpha's priming of human neutrophils for superoxide production and antibody-dependent cell-mediated cytotoxicity, platelet-activating factor synthesis and adhesion to endothelium were reduced by up to 170-fold. Activation of human endothelial cell functions represented by human umbilical venular endothelial cell (HUVEC) adhesiveness for neutrophils, E-selectin expression, neutrophil transmigration and IL-8 secretion were also reduced by up to 280-fold. On the other hand, D143F, a TNFR75-selective mutant tested either alone or in combination with TNFR55-selective mutants, did not stimulate these activities despite being able to cause cytokine production in TNFR75-transfected PC60 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗

PubMed1994

Human interferon-beta, expressed in Saccharomyces cerevisiae, is predominantly directed to the vacuoles. Influence of modified co-expression of secretion factors and chaperones.

Expression of the human interferon-beta (hIFN-beta) gene was found to be very toxic for Saccharomyces cerevisiae. An integrative expression cassette, containing the hIFN-beta gene under control of the inducible galactokinase (GAL1) promoter in combination with the alpha-factor prepro-secretion signal, was used to study the secretion process in more detail. Specific differences were found between a vacuolar proteinase--mutant and a normal laboratory yeast strain. Cell organelle fractionation, carried out with the recombinant C13-ABYS66 strain, revealed that 99% of the hIFN-beta remained intracellular and that the majority was associated with the vacuolar fraction. The secretion efficiency in the latter strain was investigated by overexpressing chaperone molecules (HSP70 and BiP) and homologous secretion factors (SEC1 and SEC18). Only the presence of HSP70 resulted in a 5-fold increase in secreted hIFN-beta.

Adenosine Triphosphatases↗

PubMed1994

Response of interleukin-6-deficient mice to tumor necrosis factor-induced metabolic changes and lethality.

Whether interleukin (IL)-6 contributes to tumor necrosis factor (TNF)-induced lethal shock or whether, on the contrary, it is part of a protective feedback system, remains unresolved. Here, we report experiments with IL-6 gene-disrupted mice (IL-6(0/0)). We have tested the susceptibility of these to TNF-induced metabolic changes and lethality in different models, and compared the results with those obtained with IL-6+/+ wild-type mice. We studied the response to TNF in three different models: (i) murine TNF administration; (ii) TNF in galactosamine (GalN)-sensitized mice; (iii) TNF in Bacillus Calmette-Guérin-sensitized mice. We observed no significant difference between the two types of mice in any of the three models. Furthermore, IL-6(0/0) mice could be equally well desensitized (by IL-1) to TNF/GalN-induced lethality and tolerized to TNF-induced shock as IL-6+/+ mice. We also observed that, in response to turpentine, TNF or IL-1, IL-6(0/0) mice produced significantly less acute phase proteins (APP) than IL-6+/+ mice. In IL-6(0/0) mice, less corticosterone was induced by TNF than in the control mice, while the response to adrenocorticotropic hormone was the same. The results indicate that IL-6 is not contributing in a major way to the pathogenesis leading to TNF-induced shock, and that neither IL-6 nor the APP studied are essential for a protective feedback system.

Acute-Phase Proteins↗

PubMed1994

The two genes encoding yeast ribosomal protein S8 reside on different chromosomes, and are closely linked to the hsp70 stress protein genes SSA3 and SSA4.

A 7.4 kb segment of chromosome II was sequenced and analysed. This segment is part of the 25 kb insert of cosmid clone alpha 1004.10 which is located on the left arm of chromosome II. Sequence analysis revealed four open reading frames (ORFs), of which two had been characterized previously (SSA3, AAR2) and one was not identified. The other ORF was precisely 600 bp long and the deduced protein sequence predicted a very basic protein (pI = 11.1; molecular weight = 22.5 kDa). Evidence was found that the ORF is the S40 ribosomal protein gene (RPG) S8. Consensus splice signals were found in the 5' leader sequence and also potential RPG-specific sequences. Chromoblot analysis revealed a second copy of the S8 RPG on chromosome IV or VIII. This copy is also closely linked to an hsp70 protein gene, SSA4.

Amino Acid Sequence↗

PubMed1994

A bifunctional murine::human chimeric antibody with one antigen-binding arm replaced by bacterial beta-lactamase.

We here report the genetic engineering of a murine::human chimeric antibody--directed against the tumor marker human placental alkaline phosphatase--in which one antigen-binding arm (Fab) has been replaced by Escherichia coli beta-lactamase (Bla). A mutated Bla gene in which the termination codon had been replaced by GAG, was fused in-phase to the cDNA sequence encoding the hinge region, CH2 and CH3 of the human IgG3 heavy chain. The resulting BlaHG3f fusion gene was placed under control of the Simian Virus 40 late promoter, and transiently expressed in COS-1 cells together with the genes encoding the murine light and murine::human chimeric heavy chains. Approximately 200 ng/ml of correctly assembled bifunctional antibody-Bla immunoconjugates were detected in the culture supernatant. This observation indicates that Bla (with its own leader peptide) can efficiently direct secretion into the culture medium of adventitious sequences fused at its C-terminus. Furthermore, the assembly in the Fc region was not affected by steric hindrance due to a Bla moiety and an Fab arm in close proximity. The antibody-Bla immunoconjugate could be of therapeutic value for the activation of cephalosporin-based anti-cancer prodrugs at the tumor site. Moreover, the expression strategy adopted here is particularly suitable for a quick and convenient analysis of newly designed gene products in which the Bla moiety has been replaced by other enzymes or by antigen-binding fragments in order to engineer bispecific antibodies.

Alkaline Phosphatase↗

PubMed1994

Mechanism of induction of tolerance to tumour necrosis factor (TNF): no involvement of modulators of TNF bioavailability or receptor binding.

The repetitive administration of low doses of hTNF to mice induces tolerance to the lethal effects of mTNF. The underlying mechanism is unknown. In this study we have investigated whether changes in bioavailability and receptor binding could account for the observed differences. To that end we compared the pharmacokinetics of mTNF, the antibody response to TNF, the levels of soluble TNF receptors and the receptor binding of TNF in tolerant and control mice. No differences in pharmacokinetic parameters were observed. An antibody response towards hTNF occurred but the antibodies did not neutralize the mTNF used as a challenge. Furthermore, tolerance failed to protect mice against lethality induced by TNF in the presence of galactosamine, where 100- to 1000-fold lower dose of TNF is required. Also, tolerance could be induced in athymic nude mice where the antibody response is absent. These results show that the mechanism of induction of tolerance is not due to an antibody response. No differences in levels of soluble receptors or receptor binding could be observed in tolerant vs control mice. We conclude that the induction of tolerance involves mechanisms operating at the post-receptor pathways.

Animals↗

PubMed1994

Structure-activity studies of human tumour necrosis factors.

The mechanism by which tumour necrosis factors (TNF and lymphotoxin, also called TNF alpha and TNF beta respectively) exert their cytotoxic activity on many malignant cells, remains largely unknown. Furthermore, the broad array of differentiation (gene induction) and mitogenic activities towards many primary cells is still a subject of intensive investigation. TNF is an important mediator in inflammation, immune responses and infection-related phenomena and these activities contribute to the severe toxicity seen when TNF is used as an anticancer agent. The first step in the mechanism of action is the specific binding of the ligand to its receptors and dissection of the molecular mechanism involved in this interaction is the subject of this review. The reasons for the interest in this aspect are obvious: first, the development of strong antagonistic TNF analogues can be useful in dampening the potentially lethal or debilitating effects of an overproduction of the cytokine (as in septic shock or rheumatoid arthritis). Secondly, since two distinct TNF receptors exist, construction of TNF muteins that distinguish between both types may lead to derivatives of this pleiotropic agent with a more restricted biological activity pattern. Ideally, one would like to develop a TNF mutant that has retained its cytotoxic action on tumour cells without inducing the deleterious systemic toxicity. Such an optimized TNF molecule could become a potent anticancer agent.

Amino Acid Sequence↗

PubMed1994

Receptor-selective mutants of tumour necrosis factor in the therapy of cancer: preclinical studies.

The use of TNF-mutants that are selective agonists of the TNF-R55 is one strategy that is being explored to broaden the therapeutic margin of TNF. Several problems still have to be overcome before they can be used in clinical trials. Regarding the sensitizing effect of some infections and some tumours, we identified IFN-gamma as a mediator in BCG- but not in tumour-induced sensitization. In both models, the vessel wall is most probably the key tissue as alpha-LFA-1 antibodies could protect against lethality. Studies in primates showed that an unexpected feature, namely, the longer half-life of such mutants, might interfere with this strategy. Recent observations also indicate that the mechanism of tolerance-induction, another way to separate antitumour and toxic effects of TNF, might reside in the functional ablation of the TNF-R75. Using IL-60/0 knockout mice, we could not find any causal role for IL-6 in TNF-mediated lethality, this in contrast to results obtained previously with neutralizing antibodies. Finally, we identified the acute phase protein alpha 1-acid glycoprotein as a protein with protective properties towards TNF-induced lethality and liver damage.

Animals↗

PubMed1993

Expression, purification and crystallization of fully active, glycosylated human interleukin-5.

Recombinant human interleukin-5 (hIL-5) has been expressed at high levels and produced in large quantities in baculovirus infected Sf9 insect cells. The glycosylated protein was purified using immuno-affinity chromatography and gel filtration. Purified hIL-5 has been crystallized using standard vapour diffusion techniques with PEG as a coprecipitant. The crystals belong to the C2 space group and diffract to 2 A.

Animals↗