Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.22.61 (caspase-8)
 6,833 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The death effector domain (DED) is a protein/protein interaction domain only found in proteins that are involved in apoptosis signaling. DEDD is a novel apoptosis signaling molecule that carries an N-terminal DED with complete sequence identity between the murine, rat, bovine and human domains. We previously identified two nuclear localization signals (NLS) responsible for DEDDs nuclear localization when transiently expressed. Using a new anti-DEDD antibody that allows us to stain endogenous DEDD in immunofluorescence microscopy we now detect a significant amount of DEDD in nucleoli of all cells tested. When overexpressed, DEDD localizes to nucleoli-like structures, activates caspase-6 and specifically inhibits RNA polymerase I (Pol I) dependent transcription in vivo as shown by blockage of BrUTP incorporation. The DED in DEDD is sufficient for its DNA binding, caspase-6 activating and Pol I specific transcriptional repressor activity. We have identified a third NLS in DEDD and only mutation of all three NLS generated a protein, DEDD Delta NLS1-3, that mainly localized to the cytoplasm. This protein no longer induced apoptosis, indicating that in contrast to other DED proteins, such as FADD, caspase-8 or c-FLIP, DEDD induces apoptosis from within the nucleus. This effect is abolished when specific point mutations are made within the DED. The DED in DEDD therefore represents a novel domain that is structurally similar to other DEDs but functionally different from classical DEDs found in FADD or caspase-8.
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PMID:Nuclear localization of DEDD leads to caspase-6 activation through its death effector domain and inhibition of RNA polymerase I dependent transcription. 1175 64

Although chondrocyte apoptosis has been noted in arthritic joints, the mechanism is not clear. To investigate whether Fas-mediated apoptosis has a role in this process, the presence of Fas mRNA and expression of cell surface Fas protein in monolayer-cultured human articular chondrocytes was analyzed. Fas mRNA was found in all chondrocyte samples analyzed; moreover, the majority of cells in chondrocyte populations expressed cell-surface Fas (12-90%, average 49%). Nevertheless, treatment with an agonistic anti-Fas antibody did not induce significant apoptosis in these chondrocytes in vitro. However, it was also found that chondrocytes express Fas-associated death domain-like interleukin-1beta-converting enzyme-inhibitory protein (FLIP), a molecule which blocks Fas-mediated apoptosis. Correspondingly, activation of caspase-8 was minimal in these cultured chondrocytes. In conclusion, although human articular chondrocytes do express cell-surface Fas, this receptor did not fully mediate death-inducing signals in vitro. This resistance to Fas may be partly due to the constitutive expression of FLIP.
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PMID:Expression of Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP) in human articular chondrocytes: possible contribution to the resistance to Fas-mediated death of in vitro cultured human articular chondrocytes. 1176 24

To understand the function of the individual oncogenes of HPV16 in modulating the cellular response to apoptogenic signals, we used human keratinocytes immortalized with either E6, E7 or E6/E7 oncoproteins as model system. Applying CD95 antibodies or recombinant CD95 ligand, only the E7-immortalized cells underwent extensive apoptosis. In contrast, E6- and E6/E7-expressing keratinocytes were resistant. Dominance of E6 correlated with significant down-regulation of p53, c-Myc, p21 and Bcl-2. CD95 was found to be reduced in resistant HPV-positive cells, while there were no quantitative differences in expression levels of FADD, FLICE/caspase-8 or caspase-3. Notably, in contrast to primary human keratinocytes, all immortalized cells showed a general reduction of c-FLIP, an inhibitory protein which normally prevents unscheduled CD95-induced apoptosis. E6- and E6/E7-positive keratinocytes, however, can be sensitized to CD95 apoptosis by blocking proteasome-mediated proteolysis. CD95-resistant HPV-positive cells underwent apoptosis within 3-5 h upon co-incubation with MG132 and agonistic antibodies or CD95 ligand, which was preceded by a strong re-expression of p53 and c-Myc, but not of other half-life controlled proteins such as Bax or IkappaBalpha. Blockage of proteasomal activity alone did not result in apoptosis, although the same set of pro-apoptotic proteins was up-regulated. Performing similar experiments with cervical carcinoma cells expressing mutated p53 (C33a) or with p53-'null' lung carcinoma cells (H1299), no CD95 cell killing occurred even though c-Myc was strongly induced. These data indicate that the reduced bioavailability of p53 is a key-regulatory event in perturbation of CD95 signaling in HPV16 immortalized keratinocytes.
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PMID:Restoration of p53 expression sensitizes human papillomavirus type 16 immortalized human keratinocytes to CD95-mediated apoptosis. 1180 60

The caspase-8 inhibitor c-FLIP blocks death receptor-mediated cell death and plays an essential role in the regulation of lymphocyte homeostasis and the immune escape of tumors. The murine thymoma cell line EL-4 was resistant to Fas ligand (FasL)-induced apoptosis by constitutive expression of FLIP (L). Cycloheximide downregulated the expression of FLIP (L) and markedly sensitized EL-4 cells to FasL-induced apoptosis. In contrast, DNA-damaging agents sensitized EL-4 cells to FasL-induced cell death via an increase of cell-surface Fas without any influence on FLIP (L) expression. Enforced expression of transfected Fas rendered EL-4 cells highly susceptible to FasL-induced cell death. These findings demonstrate that susceptibility to FasL-induced cell death mainly depends on the expression level of c-FLIP versus cell-surface Fas.
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PMID:Expression level of c-FLIP versus Fas determines susceptibility to Fas ligand-induced cell death in murine thymoma EL-4 cells. 1182 81

Evasion of immune surveillance is a key step in malignant progression. Interactions between transformed hematopoietic cells and their environment may initiate events that confer resistance to apoptosis and facilitate immune evasion. In this report, we demonstrate that beta(1) integrin-mediated adhesion to fibronectin inhibits CD95-induced caspase-8 activation and apoptosis in hematologic tumor cell lines. This adhesion-dependent inhibition of CD95-mediated apoptosis correlated with enhanced c-Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein-long (c-FLIP(L)) cytosolic solubility compared with nonadhered cells. Cytosolic c-FLIP(L) protein preferentially associated with cytosolic Fas-associated death domain protein (FADD) and localized to the death-inducing signal complex after CD95 ligation in adherent cells. The incorporation of c-FLIP(L) in the death-inducing signal complex prevented procaspase-8 processing and activation of the effector phase of apoptosis. Adhesion to fibronectin increased c-FLIP(L) cytosolic solubility and availability for FADD binding by redistributing c-FLIP(L) from a preexisting membrane-associated fraction. Increased cytosolic availability of c-FLIP(L) for FADD binding was not related to increased levels of RNA or protein synthesis. These data show that adhesion of anchorage-independent cells to fibronectin provides a novel mechanism of resistance to CD95-mediated programmed cell death by regulating the cellular localization and availability of c-FLIP(L).
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PMID:Adhesion-mediated intracellular redistribution of c-Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein-long confers resistance to CD95-induced apoptosis in hematopoietic cancer cell lines. 1185 50

Two ovarian cancer cell lines named NOS4 and SKOV-3 have been shown to have different sensitivities to a cytotoxic anti-Fas antibody, CH-11. Although both cell lines express Fas molecules on the cell surfaces at the same intensities, apoptosis is induced by CH-11 in NOS4 cells but not in SKOV-3 cells. In this study, the different apoptosis-sensitivities of these cells were assessed. Both cell lines express almost the same levels of FADD, RIP, c-FLIP, FAP-1, Bax, Bcl-2 and Bcl-XL. Evidence of caspase-8, caspase-9 and caspase-3 activation and of cleavage of PARP and Bid was obtained in NOS4 cells but not in SKOV-3 cells. When triggered by FasL protein, DNA fragmentation and caspase-8 activation were observed in SKOV-3 cells, though they were not as clear as in NOS4 cells. All the anti-Fas antibody-mediated signals for apoptosis induction in NOS4 cells were completely blocked by a caspase-8-specific inhibitor, Z-IETD-FMK. These results indicate that the different sensitivities to the anti-Fas antibody are solely dependent on the activation of caspase-8, which could be influenced by yet unknown qualitative or quantitative abnormalities in molecules involved in DISC formation.
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PMID:Activation of caspase-8 is critical for sensitivity to cytotoxic anti-Fas antibody-induced apoptosis in human ovarian cancer cells. 1186 94

Death effector domain-containing proteins are involved in important cellular processes such as death-receptor induced apoptosis, NF-kappaB activation and ERK activation. Here we report the identification of a novel nuclear DED-containing protein, FLAME-3. FLAME-3 shares significant sequence (46.6% identical) and structural homology to another DED-containing protein, DEDD. FLAME-3 interacts with DEDD and c-FLIP (FLAME-1) but not with the other DED-containing proteins FADD, caspase-8 or caspase-10. FLAME-3 translocates to, and sequesters c-FLIP in the nucleus upon overexpression in human cell lines. Using the yeast two-hybrid system to identify DEDD-interacting proteins, the TFIIIC102 subunit of human transcription factor TFIIIC was identified as a DEDD- and FLAME-3-specific interacting protein. Co-expression of either DEDD or FLAME-3 with hTFIIIC102 in MCF-7 cells induces the translocation from the cytoplasm and sequestration of hTFIIIC102 in the nucleus, indicating that DEDD and FLAME-3 form strong heterocomplexes with hTFIIIC102 and might be important regulators of the activity of the hTFIIIC transcriptional complex. Consistent with this, overexpression of DEDD or FLAME-3 in 293 cells inhibited the expression of a luciferase-reporter gene under the control of the NF-kappaB promoter. Our data provide the first direct evidence for the involvement of DED-containing proteins in the regulation of components of the general transcription machinery in the nucleus.
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PMID:Death effector domain-containing proteins DEDD and FLAME-3 form nuclear complexes with the TFIIIC102 subunit of human transcription factor IIIC. 1196 97

Chemokine receptors are members of the G protein coupled receptor (GPCR) supergene family whose expression is highly restricted to hematopoietic cells. Although the primary role of chemokine and chemokine receptor interaction is believed to be regulation of chemotaxis of leukocytes, subsequent information clearly suggests that multiple immune regulatory functions are attributed to chemokine receptor signaling. We recently showed that activation of the CC chemokine 9 receptor (CCR9), a thymus-specific chemokine receptor, led to potent cFLIP(L)-independent resistance to cycloheximide-induced apoptosis and modest resistance to Fas-mediated apoptosis possibly via activation of multiple signaling components involving Akt and glycogen synthase kinase 3beta. The fact that these two apoptotic signals involve activation of similar arrays of death execution machinery such as caspase-8, caspase-9, or caspase-3, suggests that chemokine receptor signaling may provide a wide range of antiapoptotic activities to hematopoietic cells under certain biological conditions. GPCR is a large family of cell surface receptors, many of which are critically involved in hormonal and behavioral control. Recent observations also suggest that GPCR signaling plays a pivotal role in immune cell activation. Heterotrimeric G protein is an integral part of GPCR signaling. Thus, dissection of signaling components involved in the CCR9-mediated antiapoptosis could be a framework for cell survival mechanisms and may provide options for therapeutic interventions for neurdegenerative diseases or T cell malfunctioning.
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PMID:Role of the CC chemokine receptor 9/TECK interaction in apoptosis. 1199 71

Chronic lymphocytic leukemia (CLL) cells develop chemo-resistance over time. Most anticancer agents function through induction of apoptosis, and therefore resistance against these agents is likely to be caused by selection for CLL cells with defects in the particular apoptosis pathway that is triggered by these drugs. Anticancer agents that function through alternative apoptotic pathways might therefore be useful in treating chemo-resistant CLL. Triterpenoids represent a class of naturally occurring and synthetic compounds with demonstrated antitumor activity. We examined the effects of CDDO (triterpenoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid) on CLL B cells in vitro. CDDO induced apoptosis in a dose-dependent manner in all (n = 30) CLL samples tested, including previously untreated and chemo-resistant CLL specimens. CDDO induced rapid proteolytic processing of caspase-8, but not caspase-9, in CLL B cells, suggesting activation of a mitochondria-independent pathway. CDDO-induced apoptosis of CLL B cells was blocked by cytokine response modifier A (CrmA), a suppressor of caspase-8, but not by X-linked inhibitor of apoptosis protein-baculovirus IAP repeat-3 (XIAP-BIR3), a fragment of XIAP, which selectively inhibits caspase-9. Examination of CDDO effects on expression of several apoptosis-relevant genes demonstrated significant reductions in the levels of caspase-8 homolog Fas-ligand interleukin-1-converting enzyme (FLICE)-inhibitory protein (c-FLIP), an endogenous antagonist of caspase-8. However, reductions of FLIP achieved by FLIP antisense oligonucleotides were insufficient for triggering apoptosis, indicating that CDDO has other targets in CLL B cells besides FLIP. These data suggest that the synthetic triterpenoid CDDO should be further explored as a possible therapeutic agent for treatment of chemo-resistant CLL.
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PMID:The triterpenoid CDDO induces apoptosis in refractory CLL B cells. 1235 9

Primary B cells from B cell chronic lymphocytic leukaemia (B-CLL) were resistant to the novel selective cytotoxic agent, TNF-related apoptosis-inducing ligand (TRAIL). Low levels of the death-inducing TRAIL receptors, TRAIL-R1 and TRAIL-R2 but not the putative 'decoy' receptors, TRAIL-R3 and TRAIL-R4, were expressed on the surface of B-CLL cells. Resistance to TRAIL was upstream of caspase-8 activation, as little or no caspase-8 was processed in TRAIL-treated B-CLL cells. Low levels of a TRAIL death-inducing signalling complex (DISC) were formed in these cells, accompanied by the recruitment of endogenous FADD, caspase-8 and c-FLIP(L) but not c-FLIP(S). Both caspase-8 and c-FLIP(L) were cleaved to form two stable intermediates of approximately 43 kDa, which remained associated with the DISC. Caspase-8 was not further processed to its active heterotetramer. Thus the resistance of B-CLL cells to TRAIL may be due partly to low surface expression of the death receptors resulting in low levels of DISC formation and also to the high ratio of c-FLIP(L) to caspase-8 within the DISC, which would prevent further activation of caspase-8. Our results highlight the possibility of sensitising B-CLL cells to TRAIL by modulation of c-FLIP levels or by upregulation of surface expression of death receptors.
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PMID:Mechanisms of resistance to TRAIL-induced apoptosis in primary B cell chronic lymphocytic leukaemia. 1236 Apr 7


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