Induction of apoptosis and activation of NF-κB by CD95 require different signalling thresholds
TL;DR: It is demonstrated that induction of apoptosis requires two wild‐type alleles of CD95, at the same time allowing induction of survival or proliferative pathways, which could contribute to the increased risk for lymphoma seen in ALPS type Ia patients.
Abstract: Mutations in the death domain of the death receptor CD95 (APO-1/Fas) cause lymphoproliferation and autoimmune disease in both lprcg mice and in patients with autoimmune lymphoproliferative syndrome (ALPS) type Ia. By testing lymphocytes from ALPS type Ia patients, comparing heterozygous with homozygous lprcg mice and coexpressing wild-type and mutant CD95 receptors, we demonstrate that induction of apoptosis requires two wild-type alleles of CD95. By contrast, nuclear factor-κB (NF-κB) can be fully activated in cells expressing both a mutant and a wild-type CD95 allele, suggesting different thresholds to activate the two signalling pathways. This was confirmed by testing lymphocytes from heterozygous lpr mice, which showed reduced sensitivity to CD95-mediated apoptosis but normal activation of NF-κB when compared with wild-type mice. Mutations in CD95 may eliminate the tumour-suppressive function of CD95, at the same time allowing induction of survival or proliferative pathways, which could contribute to the increased risk for lymphoma seen in ALPS type Ia patients.
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TL;DR: Although APO010 and radiation had a clear combined cytotoxic effect on tumor cells in vitro, a combined therapeutic effect was not achieved on the same cells subcutaneously grafted in mice, atAPO010 doses approximating the maximally tolerable level.
Abstract: Purpose: Various proapoptotic agents are currently being explored to improve the outcome of radiotherapy. We have evaluated whether APO010—a novel recombinant ligand of the Fas/CD95 death receptor—enhanced the cytotoxic effect of radiation on lymphoid and solid tumor cell types. Experimental Design: A Bcl-2–overexpressing T-leukemic cell line (Jurkat), a colon carcinoma cell line (HCT116), and a mesothelioma cell line were used as model systems in vitro and in a subcutaneous transplant setting in immunodeficient mice. Sensitivity to single and combined treatment was read out by apoptosis hallmarks and clonogenic survival in vitro , and by tumor growth delay using bioluminescence and palpation in vivo . Results: Whereas the three cell lines resisted apoptosis induction by irradiation and APO010 alone, combined treatment greatly enhanced their apoptotic response. In clonogenic survival assays, APO010 reduced the outgrowth of Jurkat-Bcl-2 and HCT116 cells and sensitized the mesothelioma cell line to radiation. In vivo , systemic treatment with APO010 alone caused tumor growth delay in Jurkat-Bcl-2 and HCT116 cells. However, APO010 did not improve the efficacy of radiotherapy in any of the model systems at the selected single dose, which had moderate and reversible systemic toxicity. Conclusions: Although APO010 and radiation had a clear combined cytotoxic effect on tumor cells in vitro , a combined therapeutic effect was not achieved on the same cells subcutaneously grafted in mice, at APO010 doses approximating the maximally tolerable level. These findings suggest that it will be difficult to identify a therapeutic window for this combined modality approach in a clinical setting.
32 citations
TL;DR: Several human-inherited diseases with impaired apoptosis have been identified at the genetic level: autoimmune lymphoproliferative syndrome, caspase-8 deficiency state, and X-linked lymphoprologative syndrome.
32 citations
Cites background from "Induction of apoptosis and activati..."
...The increased predisposition may result from differential signaling thresholds for heterozygous Fas mutations, with continued Fas-dependent signaling promoting growth despite impaired apoptosis induction [62]....
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TL;DR: The interaction between s-CD95 L and its receptor CD95 fails to trigger apoptosis, but instead promotes calcium-dependent cell migration, which contributes to the accumulation of inflammatory Th17 cells in damaged organs of lupus patients and favors cancer cell invasiveness.
28 citations
TL;DR: It is shown that the activation threshold for the Fas receptor is more easily overcome by multimeric FasL than by agonistic antibodies and that the increase of this threshold due to mutation in the Fas death domain can be overcome by acting on a downstream effector of the Fas signal, c-FLIP.
Abstract: Fas triggering by agonistic antibodies or by its cognate ligand, FasL, induces apoptotic cell death, whereas mutation in the Fas death domain is associated with lymphoma progression. On prolonged culture in the presence of an agonistic anti-Fas antibody, we raised a Jurkat cell line resistant to agonistic antibodies but still sensitive to soluble FasL, which carried at the heterozygous state, a point mutation into the Fas death domain. Down-modulation of c-FLIP expression reversed the blockade of the Fas pathway. We show that the activation threshold for the Fas receptor is more easily overcome by multimeric FasL than by agonistic antibodies and that the increase of this threshold due to mutation in the Fas death domain can be overcome by acting on a downstream effector of the Fas signal, c-FLIP. These findings put forward a new approach to eradicate Fas-resistant tumor cells. [Cancer Res 2007;67(1):108-15]
28 citations
Cites background from "Induction of apoptosis and activati..."
...Recently, we questioned this dogma when we found that cells expressing a heterozygous death domain–mutated Fas could still transduce nonapoptotic signals (29)....
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TL;DR: Surprisingly, c-FLIP protects mature T cells not only from apoptosis induced by the death receptors Fas and TNFR but also from TCR-mediated and spontaneous apoptosis.
Abstract: Although c-FLIP has been identified as an important player in the extrinsic (death receptor-induced) apoptosis pathway, its endogenous function in mature T lymphocytes remains undefined. c-FLIP may inhibit or promote T cell death as previous data demonstrate that the c-FLIP L isoform can promote or inhibit caspase 8 activation while the c-FLIP S isoform promotes or inhibits T cell death when overexpressed. Although the c-FLIP R isoform inhibits cell death in cell lines, its function in T cells remains unknown. To investigate the function of c-FLIP in mature T cells, we have generated several genetic mouse models with c-FLIP or its individual isoforms deleted in mature T cells. Surprisingly, we found that c-FLIP protects mature T cells not only from apoptosis induced by the death receptors Fas and TNFR but also from TCR-mediated and spontaneous apoptosis. Thus, c-FLIP plays an essential role in protecting mature T cells from a death signal induced through the TCR itself and is required for naive T cell survival. Our results demonstrate that c-FLIP functions beyond the extrinsic death pathway.
27 citations
Cites background from "Induction of apoptosis and activati..."
...Third, in the report showing that lpr mutant is partially functional, the authors clearly demonstrated that lpr mutant completely loses the capacity to induce cell death while it can activate NF- B signaling only in heterozygous (lpr/ ) mice (40)....
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...Although lpr mutation does not completely eliminate Fas signaling (40), it is unlikely that the mutant Fas still delivers a critical death signal during TCR-induced cell death in our system based on three lines of evidences....
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References
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TL;DR: The occurrence of Fas mutations together with abnormal T cell apoptosis in ALPS patients suggests an involvement of Fas in this recently recognized disorder of lymphocyte homeostasis and peripheral self-tolerance.
1,472 citations
"Induction of apoptosis and activati..." refers background in this paper
...Mutations in the DD have been shown to abrogate induction of apoptosis (Fisher et al, 1995)....
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01 Jan 1995
TL;DR: Fas expression and function were analyzed in three children with a lymphoproliferative syndrome and may provide a molecular basis for some autoimmune diseases in humans.
Abstract: Fas (also known as Apo1 and CD95) is a cell surface receptor involved in apoptotic cell death. Fas expression and function were analyzed in three children (including two siblings) with a lymphoproliferative syndrome, two of whom also had autoimmune disorders. A large deletion in the gene encoding Fas and no detectable cell surface expression characterized the most affected patient. Clinical manifestations in the two related patients were less severe: Fas-mediated apoptosis was impaired and a deletion within the intracytoplasmic domain was detected. These findings illustrate the crucial regulatory role of Fas and may provide a molecular basis for some autoimmune diseases in humans.
1,194 citations
"Induction of apoptosis and activati..." refers background in this paper
...Mutations in the DD of CD95 are naturally found both in mice (lprcg mice; Kimura & Matsuzawa, 1994) and in many patients suffering from autoimmune lymphoproliferative syndrome (ALPS) type Ia (Rieux-Laucat et al, 1995, 1999; Drappa et al, 1996; Martin et al, 1999; Straus et al, 2001)....
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TL;DR: Fas expression and function were analyzed in three children (including two siblings) with a lymphoproliferative syndrome, two of whom also had autoimmune disorders as discussed by the authors, showing that a large deletion in the gene encoding Fas and no detectable cell surface expression characterized the most affected patient.
Abstract: Fas (also known as Apo1 and CD95) is a cell surface receptor involved in apoptotic cell death. Fas expression and function were analyzed in three children (including two siblings) with a lymphoproliferative syndrome, two of whom also had autoimmune disorders. A large deletion in the gene encoding Fas and no detectable cell surface expression characterized the most affected patient. Clinical manifestations in the two related patients were less severe: Fas-mediated apoptosis was impaired and a deletion within the intracytoplasmic domain was detected. These findings illustrate the crucial regulatory role of Fas and may provide a molecular basis for some autoimmune diseases in humans.
1,193 citations
TL;DR: A number of proteins have been reported to regulate formation or activity of the DISC, the complex of proteins that forms upon triggering of CD95 that is essential for induction of apoptosis.
Abstract: CD95 (APO-1/Fas) is a prototype death receptor characterized by the presence of an 80 amino acid death domain in its cytoplasmic tail. This domain is essential for the recruitment of a number of signaling components upon activation by either agonistic anti-CD95 antibodies or cognate CD95 ligand that initiate apoptosis. The complex of proteins that forms upon triggering of CD95 is called the death-inducting signaling complex (DISC). The DISC consists of an adaptor protein and initiator caspases and is essential for induction of apoptosis. A number of proteins have been reported to regulate formation or activity of the DISC. This review discusses recent developments in this area of death receptor research.
1,096 citations
"Induction of apoptosis and activati..." refers background in this paper
...On binding of CD95 ligand (CD95L), CD95 recruits the adaptor protein FADD, the initiator caspases 8 and 10 and the apoptosis regulator c-FLIP, forming the death-inducing signalling complex (DISC; Peter & Krammer, 2003)....
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TL;DR: Results show that formation of preassociated receptor complexes is necessary for Fas signaling and dominant interference in human disease.
Abstract: Heterozygous mutations encoding abnormal forms of the death receptor Fas dominantly interfere with Fas-induced lymphocyte apoptosis in human autoimmune lymphoproliferative syndrome. This effect, rather than depending on ligand-induced receptor oligomerization, was found to stem from ligand- independent interaction of wild-type and mutant Fas receptors through a specific region in the extracellular domain. Preassociated Fas complexes were found in living cells by means of fluorescence resonance energy transfer between variants of green fluorescent protein. These results show that formation of preassociated receptor complexes is necessary for Fas signaling and dominant interference in human disease.
693 citations
"Induction of apoptosis and activati..." refers background in this paper
...&2004 EUROPEAN MOLECULAR BIOLOGY ORGANIZATION EMBO reports VOL 5 | NO 11 | 2004 scientificreport 1085 wild-type receptors (Siegel et al, 2000)....
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