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Query: UNIPROT:Q14790 (caspase-8)
 8,899 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the immune system, lymphocyte activation by antigen is followed by cell proliferation and induction of effector functions. Subsequently, physiologic cell-death signals are induced, resulting in removal of expanded effector-cell populations, to maintain homeostasis. Caspases are intracellular participants in both activation responses and cell death by apoptosis. Targets of caspases include inflammatory activators and also other members of the caspase family that mediate apoptosis. Caspase-8 and caspase-10 participate in the protease cascade following cell surface CD95 engagement by its ligand. Humans with defects in these caspases were initially evaluated for the autoimmune lymphoproliferative syndrome because of their spleen and lymph node enlargement. Although both caspase-8- and caspase-10-deficient individuals had impaired apoptosis, those with caspase-8 deficiency, who also had immunodeficiency, had additional defects in activation of lymphocytes and natural killer cells. These disorders help to define the importance and specificity of the caspase proteases in intracellular signaling pathways.
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PMID:Immune disorders caused by defects in the caspase cascade. 1290 72

Death ligands (such as Fas/CD95 ligand and TRAIL?Apo2L) and death receptors (such as Fas/CD95, TRAIL-R1?DR4, and TRAIL-R2/DR5) are involved in immune-mediated neutralization of activated or autoreactive lymphocytes, virus-infected cells, and tumor cells. Consequently, dysregulation of death receptor-dependent apoptotic signaling pathways has been implicated in the development of autoimmune diseases, immunodeficiency, and cancer. Moreover, the death ligand TRAIL has gained considerable interest as a potential anticancer agent, given its ability to induce apoptosis of tumor cells without affecting most types of untransformed cells. The FLICE-inhibitory protein (FLIP) potently blocks TRAIL-mediated cell death by interfering with caspase-8 activation. Pharmacologic down-regulation of FLIP might serve as a therapeutic means to sensitize tumor cells to apoptosis induction by TRAIL.
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PMID:FLIP protein and TRAIL-induced apoptosis. 1511 Jan 78

Although tightly regulated programmed cell death (apoptosis) possesses great importance for tissue homeostasis, several pathologic processes are associated with organ failure due to adversely activated cell apoptosis. Transient increase in apoptosis has been shown to cause organ damage during fulminant hepatitis B, autoimmune diseases, ischemia-reperfusion injury, sepsis, or allograft rejection. A defined and temporary inhibition of cell apoptosis may therefore be of high clinical relevance. Activation of death receptors results in caspase-8 recruitment to the death-inducing signaling complex, which initiates the apoptotic process through cleavage of caspase-8 and downstream substrates. This initial step may be inhibited by the caspase-8 inhibitor FLIP (FLICE inhibitory protein). To specifically inhibit the initiation of death receptor-mediated apoptosis we constructed a fusion protein containing FLIP fused N-terminally to the human immunodeficiency virus TAT domain. This TAT domain allows the fusion protein to cross the cell membrane and thus makes the FLIP domain able to interfere with the death-inducing signaling complex inside of the cell. We observed that incubation of lymphocytic Jurkat or BJAB cells with TAT-FLIPS proteins significantly inhibits Fas-induced activation of procaspase-8 and downstream caspases, preventing cells from undergoing apoptosis. Systemic application of TAT-FLIPS prolongs survival and reduces multi-organ failure due to Fas-receptor-mediated lethal apoptosis in mice. Therefore, application of cellular FLIPS in the form of a TAT fusion protein may open a promising, easily applicable new tool for providing protection against transient, pathologically increased apoptosis in various diseases.
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PMID:Transduction of the TAT-FLIP fusion protein results in transient resistance to Fas-induced apoptosis in vivo. 1530 99

In this study, we showed the existence of a positive correlation between the amount of human immunodeficiency virus-type 1 (HIV-1) RNA in HIV-1 seropositive subjects and the plasma levels of TRAIL. Since it has been previously demonstrated that HIV-1 Tat protein up-regulates the expression of TRAIL in monocytic cells whereas tat-expressing lymphoid cells are more resistant to TRAIL cytotoxicity, we next investigated the effect of Tat on the expression/activity of both apical caspase-8 and -10, which play a key role in mediating the initial phases of apoptosis by TRAIL, and c-FLIP. Jurkat lymphoblastoid human T cell lines stably transfected with a plasmid expressing wild-type (HIV-1) tat gene showed normal levels of caspase-8 but significantly decreased levels of caspase-10 at both mRNA and protein levels with respect to Jurkat transfected with the control plasmid or with a mutated (cys22) non-functional tat cDNA. A significant decrease of caspase-10 expression/activity was also observed in transient transfection experiments with plasmid carrying tat cDNA. Moreover, c-FLIP(L) and c-FLIP(S) isoforms were up-regulated in tat-expressing cells at both mRNA and protein level in comparison with control cells. Taken together, these results provide a molecular basis to explain the resistance of tat-expressing Jurkat cells to apoptosis induced by TRAIL and, possibly, to other death-inducing ligands.
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PMID:HIV-1 Tat protein concomitantly down-regulates apical caspase-10 and up-regulates c-FLIP in lymphoid T cells: a potential molecular mechanism to escape TRAIL cytotoxicity. 1557 81

Caspase-8, a proapoptotic protease, has an essential role in lymphocyte activation and protective immunity. We show that caspase-8 deficiency (CED) in humans and mice specifically abolishes activation of the transcription factor nuclear factor kappaB (NF-kappaB) after stimulation through antigen receptors, Fc receptors, or Toll-like receptor 4 in T, B, and natural killer cells. Caspase-8 also causes the alphabeta complex of the inhibitor of NF-kappaB kinase (IKK) to associate with the upstream Bcl10-MALT1 (mucosa-associated lymphatic tissue) adapter complex. Recruitment of the IKKalpha, beta complex, its activation, and the nuclear translocation of NF-kappaB require enzyme activity of full-length caspase-8. These findings thus explain the paradoxical association of defective apoptosis and combined immunodeficiency in human CED.
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PMID:Requirement for caspase-8 in NF-kappaB activation by antigen receptor. 1574 28

Caspase-8 is best known for its cell death function via death receptors. Recent evidence indicates that caspase-8 also has nonapoptotic functions. Caspase-8 deficiency is associated with pathologies that are unexpected for a proapoptotic molecule, such as abrogation of activation-induced lymphocyte proliferation, perturbed immune homeostasis, and immunodeficiency. In this study, we report the long-term physiological consequences of T cell-specific deletion of caspase-8 (tcasp8-/-). We show that tcasp8-/- mice develop an age-dependent lethal lymphoproliferative and lymphoinfiltrative immune disorder characterized by lymphoadenopathy, splenomegaly, and accumulation of T cell infiltrates in the lungs, liver, and kidneys. Peripheral casp8-/- T cells manifest activation marker up-regulation and are proliferating in the absence of any infection or stimulation. We also provide evidence suggesting that this immune disorder is different from the autoimmune lymphoproliferative syndrome. Interestingly, the condition described in tcasp8-/- mice manifests features consistent with the disorder described in humans with Caspase-8 deficiency. These findings suggest that tcasp8-/- mice may serve as an animal model to evaluate Caspase-8-deficient patient prognosis and therapy. Overall, our study uncovers novel in vivo functions for caspase-8 in immune regulation.
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PMID:Caspase-8 deficiency in T cells leads to a lethal lymphoinfiltrative immune disorder. 1615 84

We have previously shown that hepatocytes exposed to hepatitis C virus (HCV) and human immunodeficiency virus (HIV) envelope proteins undergo apoptosis. In this article, we further elucidate the signaling mechanisms that mediate this effect. We found that, in human hepatocellular carcinoma (HepG2) cells, HCV E2 protein and HIV glycoprotein (gp) 120 significantly up-regulated the Fas ligand (FasL) and enhanced the formation of the Fas death-inducing signaling complex downstream of Fas receptor activation. Moreover, after stimulation with HCV E2 and HIV gp120, enhanced expression of caspases 2 and 7 and increased caspase 3 activity were observed. In addition, we showed up-regulation of the proapoptotic molecule Bid and its association with caspase 8 after treatment with these envelope proteins. We also found that HCV E2 and HIV gp120 induced a partial translocation of Bid to the mitochondria, which resulted in the release of cytochrome C and the apoptosis-inducing factor. Thus, the results of this study suggest that FasL and Bid play an important role in HCV and HIV envelope protein-induced apoptosis.
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PMID:Molecular mechanism of hepatic injury in coinfection with hepatitis C virus and HIV. 1626 11

Vpr of human immunodeficiency virus type 1 causes cell cycle arrest at the G(2)/M phase and induces apoptosis after G(2)/M arrest in primate cells. We have reported previously that Vpr also induces apoptosis independently of G(2)/M arrest in human HeLa cells. By contrast, Vpr does not induce G(2)/M arrest in rodent cells, but it retards cell growth. To clarify the relationship between cell cycle arrest and apoptosis, we expressed Vpr endogenously in rodent cells and investigated cell cycle profiles and apoptosis. We show here that Vpr induces cell cycle arrest at the G(1) phase and apoptosis in rodent cells. Vpr increased the activity of caspase-3 and caspase-9, but not of caspase-8. Moreover, Vpr-induced apoptosis could be inhibited by inhibitors of caspase-3 and caspase-9, but not by inhibitor of caspase-8. We also showed that Vpr induces the release of cytochrome c from mitochondria into the cytosol and disrupts the mitochondrial transmembrane potential. Finally, we showed that apoptosis occurred in HeLa cells through an identical pathway. These results suggest that disruption of mitochondrial functions by Vpr induces apoptosis via cell cycle arrest at G(1), but that apoptosis is independent of G(2)/M arrest. Furthermore, it appears that Vpr acts species-specifically with respect to induction of cell cycle arrest but not of apoptosis.
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PMID:Human immunodeficiency virus type 1 Vpr induces cell cycle arrest at the G(1) phase and apoptosis via disruption of mitochondrial function in rodent cells. 1648 Sep 11

While Cryptosporidium parvum infection of the intestine has been reported in both immunocompetent and immunocompromised individuals, biliary infection is seen primarily in adult AIDS patients and is associated with development of AIDS cholangiopathy. However, the mechanisms of pathogen-induced AIDS cholangiopathy remain unclear. Since we previously demonstrated that the Fas/Fas ligand (FasL) system is involved in paracrine-mediated C. parvum cytopathicity in cholangiocytes, we also tested the potential synergistic effects of human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat)-mediated FasL regulation on C. parvum-induced apoptosis in cholangiocytes by semiquantitative reverse transcription-PCR, immunoblotting, immunofluorescence analysis, and immunogold electron microscopy. H69 cells do not express CXCR4 and CCR5, which are receptors required for direct HIV-1 viral infection. However, recombinant biologically active HIV-1-associated Tat protein increased FasL expression in the cytoplasm of cholangiocytes without a significant increase in apoptosis. We found that C. parvum-induced apoptosis was associated with translocation of intracellular FasL to the cell membrane surface and release of full-length FasL from infected H69 cells. Tat significantly (P < 0.05) increased C. parvum-induced apoptosis in bystander cells in a dose-dependent manner. Moreover, Tat enhanced both C. parvum-induced FasL membrane translocation and release of full-length FasL. In addition, the FasL neutralizing antibody NOK-1 and the caspase-8 inhibitor Z-IETD-fmk both blocked C. parvum-induced apoptosis in cholangiocytes. The data demonstrated that HIV-1 Tat enhances C. parvum-induced cholangiocyte apoptosis via a paracrine-mediated, FasL-dependent mechanism. Our results suggest that concurrent active HIV replication, with associated production of Tat protein, and C. parvum infection synergistically increase cholangiocyte apoptosis and thus jointly contribute to AIDS-related cholangiopathies.
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PMID:The human immunodeficiency virus type 1 tat protein enhances Cryptosporidium parvum-induced apoptosis in cholangiocytes via a Fas ligand-dependent mechanism. 1711 88

In addition to its pro-apoptotic function in the death receptor pathway, roles for caspase-8 in mediating T-cell proliferation, maintaining lymphocyte homeostasis, and suppressing immunodeficiency have become evident. Humans with a germline point mutation of CASPASE-8 have multiple defects in T cells, B cells, and NK cells, most notably attenuated activation and immunodeficiency. By generating mice with B-cell-specific inactivation of caspase-8 (bcasp8(-/-)), we show that caspase-8 is dispensable for B-cell development, but its loss in B cells results in attenuated antibody production upon in vivo viral infection. We also report an important role for caspase-8 in maintaining B-cell survival following stimulation of the Toll-like receptor (TLR)2, -3, and -4. In response to TLR4 stimulation, caspase-8 is recruited to a complex containing IKKalphabeta, and its loss resulted in delayed NFkappaB nuclear translocation and impaired NFkappaB transcriptional activity. Our study supports dual roles for caspase-8 in apoptotic and nonapoptotic functions and demonstrates its requirement for TLR signaling and in the regulation of NFkappaB function.
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PMID:Essential role for caspase-8 in Toll-like receptors and NFkappaB signaling. 1721 98


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