Biomedical subjects

W Declercq

Publications and source records attributed to W Declercq.

47 records · Page 3Linked to original sources

PubMed1997

Tumour necrosis factor-induced necrosis versus anti-Fas-induced apoptosis in L929 cells.

Murine fibrosarcoma L929 cells were transfected with human Fas cDNA. The mode of cell death was analysed following treatment either with tumour necrosis factor (TNF) or with agonistic antibodies to Fas. While triggering of the TNF receptors led to necrosis, clustering of the Fas antigen resulted in apoptotic cell death. N-tosyl-l-phenylalanine chloromethyl ketone and Nalpha-p-tosyl-l-lysine chloromethyl ketone, two serine protease inhibitors, has a protective effect on TNF-induced killing, while Fas-mediated cell death was rather enhanced. Lithium chloride, which had a synergistic effect on TNF cytotoxicity, did not affect Fas-mediated death, whereas staurosporine had an enhancing effect on both types of cell death. Aphidicolin and hydroxyurea, inhibitors of DNA synthesis, were able to sensitize cells to Fas-induced killing, but had no effect on TNF cytotoxicity. Finally, we demonstrate that the effect of increasing concentrations of actinomycin D or cycloheximide is very different for the two types of cell killing. We conclude that either necrosis or apoptosis can occur in the same cell type, depending on the trigger, and that, although both pathways perhaps may share some cellular components, signal transduction is different for the two types of cell death.

Adjuvants, Immunologic↗

PubMed1995

Casein kinase-1 phosphorylates the p75 tumor necrosis factor receptor and negatively regulates tumor necrosis factor signaling for apoptosis.

Cellular responses initiated by tumor necrosis factor (TNF) are mediated by two different cell surface receptors with respective molecular masses of 55 kDa (p55) and 75 kDa (p75). p55 is functional in almost every cell type and can independently transmit most biological activities of TNF. In contrast, TNF signaling via p75 seems so far largely restricted to cells of lymphoid origin, where it can induce proliferation, cytokine production, and/or apoptosis. The mechanisms that regulate TNF receptor activity are largely unknown. Here we report that the p75 of unstimulated p75-responsive PC60 T cells is phosphorylated on serine by a kinase activity present in p75 immune complexes. Several lines of evidence indicate that the latter kinase is casein kinase-1 (CK-1). Previous results have shown that the p75 TNF receptor is constitutively phosphorylated in vivo. Our data show that the latter in vivo phosphorylation is also at least partially due to CK-1. Pretreatment of cells with TNF had no detectable effect on p75 phosphorylation in vitro or in vivo. However, a specific CK-1 inhibitor potentiated TNF-induced apoptosis mediated by p75, suggesting an inhibitory role for phosphorylation by CK-1. Although in vivo p75 phosphorylation could be seen in both p75-unresponsive and p75-responsive cell lines, in vitro p75 phosphorylation in p75 coimmunoprecipitates could not be observed in cell lines that were biologically unresponsive to p75 stimulation. The latter observation further indicates a regulatory role for p75 phosphorylation in p75-mediated signaling. Taken together, our data demonstrate that the p75 TNF receptor is phosphorylated and associated with CK-1, which negatively regulates p75-mediated TNF signaling.

Apoptosis↗

PubMed1995

Both TNF receptors are required for TNF-mediated induction of apoptosis in PC60 cells.

A rat/mouse T cell hybridoma (PC60) was transfected either with human (h) TNF-R p55 (TNF-R55), p75 (TNF-R75) or both cDNAs. hTNF-R55 expression was below 50 molecules/cell, whereas the number of hTNF-R75 reached about 4000 molecules/cell. Only cells co-expressing the two types of receptor showed TNF-dependent apoptosis, in contrast to cells expressing similar levels of only one receptor type, indicating that both TNF-R55 and TNF-R75 are required. Stable co-transfection of the bcl-2 proto-oncogene largely prevented this TNF-mediated induction of apoptosis. We found that a high level of hTNF-R75 expression was essential for obtaining TNF-dependent apoptosis in PC60 cells in addition to a low number of hTNF-R55. Both receptors are signal transducing because simultaneous triggering of hTNF-R55 and hTNF-R75 by agonistic mAbs or by TNF-R-specific TNF muteins induced similar levels of apoptosis as wild-type hTNF. Apoptotic killing of only those lymphocytes expressing a high, induced level of TNF-R75, in addition to TNF-R55, may play a physiologically important role.

Animals↗

PubMed1995

Cytotoxicity in L929 murine fibrosarcoma cells after triggering of transfected human p75 tumour necrosis factor (TNF) receptor is mediated by endogenous murine TNF.

We compared the biological function of the human tumor necrosis factor receptors p55 (hTNF-R55) and p75 (hTNF-R75) expressed in the murine (m) fibrosarcoma cell line L929. Receptor-specific triggering of hTNF-R55 in transfected L929 cells by agonistic monoclonal antibodies or hTNF-R32WS86T, a hTNF-R55-specific mutant of hTNF, resulted in cytotoxicity. Specific clustering of hTNF-R75 in transfected L929 cells by agonistic monoclonal antibodies or hTNF-D143F, a hTNF-R75-specific mutant of hTNF also induced cytotoxicity, albeit at low level. In both cases, the cytotoxic activity of receptor clustering could be synergized by addition of 20 mM LiCl. Remarkably, cytotoxicity induced after R75 triggering in transfected L929 cells could be completely abolished by addition of neutralizing anti-mTNF antibodies, in contrast to cell killing seen after specific R55 clustering. No soluble mTNF could be demonstrated using a sensitive biological assay, although L929 cells were expressing low levels of mTNF-specific mRNA as shown by PCR. These data clearly demonstrate that minute amounts of endogenously produced TNF can be a key mediator in R75-mediated cytotoxicity. Presumably, the latter efficiently traps the ligand and transfers it to TNF-R55, and/or by binding it, protects the endogenously made TNF from inactivation.

Animals↗

PubMed1995

Dimerization of chimeric erythropoietin/75 kDa tumour necrosis factor (TNF) receptors transduces TNF signals: necessity for the 75 kDa-TNF receptor transmembrane domain.

We developed a transfection-based assay for evaluating human (h) Tumour Necrosis Factor receptor (TNF-R) activities in a rat/mouse T-cell hybridoma, viz. PC60. Here we report on the role of TNF-R75 cross-linking in induction of GM-CSF secretion and apoptosis. The effect of TNF-R75 dimerization, in contrast to trimerization, was analysed by replacing the extracellular domain of this receptor with the equivalent domain of the murine erythropoietin receptor (EPO-R), which dimerizes upon ligand interaction. To determine the role of the transmembrane region in signal transduction, chimeric EPO-R/TNF-R75 were constructed in which the respective transmembrane domains were interchanged. The hybrid receptors were introduced into PC60hTNFR55 cells, which already expressed functional, transfected hTNF-R55. By this approach we demonstrated that dimerized chimeric EPO-R/TNF-R75 receptors act synergistically with hTNF-R55-induced cytokine production and apoptosis as does trimerized wild-type hTNF-R75. Dimeric triggering of these hybrid receptors with EPO alone was less efficient than trimerization of hTNF-R75. Furthermore, EPO-R/TNFR75 only responded to EPO when the matching transmembrane region of TNF-R75 was present. Our results also prove that the hTNF-R75 extracellular part per se is not required for signalling. Finally, our data indicate that the expression of chimeric EPO-R/TNF-R75 in PC60hTNF-R55 cells, regardless of the presence of the TNF-R75 transmembrane region, facilitates TNF-R55-dependent signal transduction leading to apoptosis. This means that introduction of the intracellular domain of hTNF-R75, even without triggering, is sufficient to promote hTNF-R55-dependent activities in PC60 cells.

Animals↗

PubMed1994

Functional requirement of the two TNF receptors for induction of apoptosis in PC60 cells and the role of mitochondria in TNF-induced cytotoxicity.

The rat/mouse T-cell hybridoma PC60 was transfected either with hTNF-R55 cDNA, hTNF-R75 cDNA, or both. Receptor-specific stimulation was achieved using agonistic monoclonal antibodies or receptor-specific muteins of hTNF. Either hTNF-R55 or hTNF-R75 could mediate the activation of NF-kappa B and the induction of GM-CSF, IL-6, and IFN-gamma. But only in cells carrying both hTNF-R55 and hTNF-R75, was TNF able to induce apoptosis. This apoptosis could be inhibited almost completely by cotransfection with human bcl-2 cDNA. Functional cooperation was observed between liganded and unliganded receptors for the induction of apoptosis. In vitro protein kinase activity was detected only in TNF-R75 immunoprecipitates from cells in which the receptor was signaling. Direct evidence was obtained for reactive oxygen intermediates of mitochondrial origin responsible for TNF-induced cytotoxicity in L929 cells.

Animals↗

PubMed1992

Functional characterization of the human tumor necrosis factor receptor p75 in a transfected rat/mouse T cell hybridoma.

We investigated the biological role of the human tumor necrosis factor p75 (hTNF-R75), making use of the species specificity of TNF responses in murine (m) T cell lines. Several TNF-mediated activities on mouse T cells, such as cytokine induction or proliferation, showed a 100-500-fold difference in specific biological activity between mTNF and hTNF. After transfection of hTNF-R75 cDNA in a rat/mouse T cell hybridoma (PC60), however, the 100-fold lower specific biological activity of hTNF was converted to the same specific biological activity as mTNF. The TNF-mediated induction of granulocyte/macrophage colony-stimulating factor was strongly synergized by the addition of interleukin 1. In the presence of the latter cytokine, ligand-competing monoclonal antibodies against hTNF-R75 (utr-1, utr-2, utr-3) were agonistic on transfected PC60 cells. This agonistic activity was further enhanced by crosslinking with sheep anti-murine immunoglobulin antibodies. These data provide direct evidence for a functional role of TNF-R75, without ligand-dependent TNF-R55 involvement, in the induction of cytokine secretion in T cells.

Animals↗

PubMed1990

Development of a simple, sensitive and specific bioassay for interleukin-1 based on the proliferation of RPMI 1788 cells. Comparison with other bioassays for IL-1.

The IL-1-dependent proliferation of RPMI 1788, a human EBV-transformed cell line, was used to develop a biological assay system for IL-1. Preparations of rhIL-1 alpha and rhIL-1 beta, as well as rmIL-1 beta exhibited a specific biological activity (50% of the maximal response) between 5.8 x 10(8) and 8.6 x 10(8) U/mg. Remarkably, a 3-5-fold reduced specific biological activity was noticed for rm-IL-1 alpha, viz. 1.7 x 10(8) U/mg. The IL-1-dependent proliferation of RPMI 1788 cells was compared with other IL-1 test systems, such as the IL-1-mediated induction of IL-2 in EL4-NOB-1, LBRM-33-1A5 and thymocytes, and the IL-1-driven induction of cytotoxic activity by PC60 cells, the so-called CIA assay. The cytokine-dependent growth of RPMI 1788 cells is highly specific for IL-1, and no other cytokine tested induced a proliferative response. The presence of high concentrations of rmTNF, rhTNF or rhIL-6 did not interfere with the quantification of IL-1. Additionally, we evaluated the detection of IL-1 in the presence of mitogens, phorbol ester or calcium ionophore, as well as the determination of IL-1 in serum and PF samples of human and murine origin.

Animals↗

PubMed1990

Response of murine cell lines to an IL-1/IL-2-induced factor in a rat/mouse T hybridoma (PC60): differential induction of cytokines by human IL-1 alpha and IL-1 beta and partial amino acid sequence of rat GM-CSF.

We analyzed the proliferative response of the growth factor-dependent murine cell lines FDCp1, DA1-a, 32DC1, Ea3.15, 7TD1, BCL1 and of femural bone marrow cells for their sensitivity to various cytokines, viz. rhIL-1 beta, rhTNF, rhIL-2, mIL-3, rmIL-4, rmIL-5, rhIL-6, rhG-CSF and rmGM-CSF. We also tested for IL-1 and TNF-mediated cytokine secretion by several T cell lines and thymocytes. In all T cell systems, IL-1 alpha and IL-1 beta were equally active in the induction of cytokine production, except for the rat/mouse T cell hybridoma PC60. This cell line exhibited a 10-fold difference in specific activity for the induction of cytokine secretion between rhIL-1 alpha and the other human or murine IL-1 species. Furthermore, IL-1 and IL-2 synergistically induced PC60 cells to produce a factor, which was preferentially active on FDCp1-cells, provisionally called FDCp1-growth factor. SDS-PAGE analysis of partially purified FDCp1-GF showed 19 kDa and 24 kDa-associated biological activities. Amino-terminal and internal amino acid sequences of both bands were determined and on this basis, we identified FDCp1-GF as rat GM-CSF.

Amino Acid Sequence↗

PubMed1987

Recombinant tumor necrosis factor can induce interleukin 2 receptor expression and cytolytic activity in a rat x mouse T cell hybrid.

Tumor necrosis factor (TNF), an endotoxin-induced macrophage monokine, is known for its cytotoxic and cytostatic effect on some tumor cell lines. Here we show that highly purified recombinant TNF, in combination with interleukin 2 (IL2), can induce IL2 receptor expression and cytolytic activity in a rat x mouse T cell hybrid (PC60). Previously, it was shown that IL1 had a similar effect on PC60 cells. The ability of TNF to co-induce IL2 receptor expression suggests that it may play a role in the activation of certain lymphoid effector cells. This observation augments the growing list of biological activities attributed to TNF.

Animals↗

PubMedDate not supplied

TNF-induced intracellular signaling leading to gene induction or to cytotoxicity by necrosis or by apoptosis.

TNF-induced apoptosis, e.g. in murine PC60 cells, requires the TNF receptor p55 (TNF-R55) and the TNF receptor p75 (TNF-R75); the latter even does not have to be triggered. The intracellular domain of TNF-R55 can be activated in the cytosol by linking it to the trimeric CAT protein; induction of this fusion protein leads to a full TNF response. A new MAP kinase, p38, has been shown to be also activated by TNF. This activation is essential for gene induction, but not for cytotoxicity in L929 cells. TNF treatment of L929 leads to reactive oxygen formation in the mitochondria, resulting in cell death by necrosis. TNF treatment of many other cell types results in apoptosis, and this process involves activation of one or more ICE homologs (IHO). In the mouse, seven cysteine proteases of the IHO family have been cloned and partially characterized. One or more of these IHOs is involved in cell killing by proteolysis of critical substrate(s). One substrate, which may be a key effector molecule in the apoptotic process, is PITSLRE kinase.

Animals↗