Inhibition of tyrosine phosphatases induces apoptosis independent from the CD95 system.
(49/2199)
The inhibition of protein tyrosine phosphatases by pervanadate, a potent activator of B- and T-cells through the induction of tyrosine phosphorylation and downstream signaling events in different activation cascades, efficiently induced apoptosis in lymphoid cell lines. Pervanadate-elicited apoptosis could be blocked by the tyrosine kinase inhibitor herbimycin A. This apoptotic process involved the activation of caspases 3, 8 and 9, the induction of mitochondrial permeability transition, the release of cytochrome C and the fragmentation of chromosomal DNA. T-cells lacking the CD95 receptor or caspase-8 and T-cells stably overexpressing a transdominant negative form of the adaptor protein FADD were still susceptible to pervanadate-induced apoptosis, excluding the involvement of the CD95 system or other FADD-dependent death receptors. The apoptotic program initiated by the inhibition of tyrosine phosphatases did not require the presence of the tyrosine kinase p56lck or phosphatase CD45, whereas Bcl-2 overexpression protected T-cells from pervanadate-induced cytochrome C release, caspase-8 cleavage and apoptosis. (+info)
Cleavage of the death domain kinase RIP by caspase-8 prompts TNF-induced apoptosis.
(50/2199)
Although the molecular mechanisms of TNF signaling have been largely elucidated, the principle that regulates the balance of life and death is still unknown. We report here that the death domain kinase RIP, a key component of the TNF signaling complex, was cleaved by Caspase-8 in TNF-induced apoptosis. The cleavage site was mapped to the aspartic acid at position 324 of RIP. We demonstrated that the cleavage of RIP resulted in the blockage of TNF-induced NF-kappaB activation. RIPc, one of the cleavage products, enhanced interaction between TRADD and FADD/MORT1 and increased cells' sensitivity to TNF. Most importantly, the Caspase-8 resistant RIP mutants protected cells against TNF-induced apopotosis. These results suggest that cleavage of RIP is an important process in TNF-induced apoptosis. Further more, RIP cleavage was also detected in other death receptor-mediated apoptosis. Therefore, our study provides a potential mechanism to convert cells from life to death in death receptor-mediated apoptosis. (+info)
Modulation of the NF-kappa B pathway by virally encoded death effector domains-containing proteins.
(51/2199)
Death Effector Domains (DEDs) have been known to mediate the recruitment of Caspase 8 and its homologs to the aggregated death-inducing signaling complex (DISC), consisting of the death domain (DD)-containing receptors and various signaling proteins. In addition, several viruses were recently shown to encode proteins with DEDs (also called FLICE inhibitory proteins or vFLIPs) which have the ability of blocking cell death induced by DD-containing receptors. We provide evidence that vFLIPs can also modulate the NF-kappaB pathway and physically interact with several signaling proteins, such as the TRAFs, RIP, NIK and the IKKs. Modulation of the NF-kappaB pathway may play a role in the natural history of infection by these viruses. (+info)
Selective up-regulation of phosphatidylinositol 3'-kinase activity in Th2 cells inhibits caspase-8 cleavage at the death-inducing complex: a mechanism for Th2 resistance from Fas-mediated apoptosis.
(52/2199)
In this study the mechanism of differential sensitivity of CD3-activated Th1- and Th2-type cells to Fas-mediated apoptosis was explored. We show that the Fas-associated death domain protein (FADD)/caspase-8 pathway is differentially regulated by CD3 activation in the two subsets. The apoptosis resistance of activated Th2-type cells is due to an incomplete processing of caspase-8 at the death-inducing signaling complex (DISC) whereas recruitment of caspase-8 to the DISC of Th1- and Th2-like cells is comparable. Activation of phosphatidylinositol 3'-kinase upon ligation of CD3 in Th2-type cells blocked caspase-8 cleavage to its active fragments at the DISC, thereby preventing induction of apoptosis. This study offers a new pathway for phosphatidylinositol 3'-kinase in mediating protection from Fas-induced apoptosis. (+info)
Caspase 8: igniting the death machine.
(53/2199)
Intense research into the signaling pathways of apoptosis has revealed a dominant role for proteases belonging to the caspase family, which in humans has 11 members at present. Two papers in the September issue of Structure with Folding & Design have for the first time revealed the structure of the key apoptotic initiator, caspase 8. (+info)
Expression of caspases 3, 6 and 8 is increased in parallel with apoptosis and histological aggressiveness of the breast lesion.
(54/2199)
The aim of this investigation was to study the expression of caspases 3, 6 and 8 and their association to apoptosis in preneoplastic and neoplastic lesions of the breast. The material consisted of nine benign breast epithelial hyperplasias, 15 atypical hyperplasias, 74 in situ and 82 invasive carcinomas. The extent of apoptosis was assessed by the TUNEL method and caspase 3, 6 and 8 expression by immunohistochemistry with specific antibodies. Increased caspase 3 immunopositivity, as compared to staining of normal breast ductal epithelium, was seen in 22% of benign epithelial hyperplasias, 25% of atypical hyperplasias, 58% of in situ carcinomas and 90% of invasive carcinomas. The corresponding percentages for caspase 6 and 8 were 11%, 25%, 60%, 87% and 22%, 57%, 84%, 83% respectively. In high-grade in situ lesions there were significantly more cases with strong caspase 3, 6 and 8 immunoreactivity than in low- and intermediate-grade lesions (P = 0.0045, P = 0.049 and P = 0.0001 respectively). In invasive carcinomas, however, no association between a high tumour grade and caspase 3, 6 or 8 expression was found (P = 0.27, P = 0.26 and P = 0.69 respectively). The mean apoptotic index was 0.14 +/- 0.14% in benign epithelial hyperplasias, 0.17 +/- 0.12% in atypical hyperplasias, 0.61 +/- 0.88% in in situ carcinomas and 0.94 +/- 1.21% in invasive carcinomas. In all cases strong caspase 3, 6 and 8 positivity was significantly associated with the extent of apoptosis (P < 0.001, P = 0.015 and P = 0.050 respectively). The results show that synthesis of caspases 3, 6 and 8 is up-regulated in neoplastic breast epithelial cells in parallel to the increase in the apoptotic index and progression of the breast lesions. (+info)
Conformational and molecular basis for induction of apoptosis by a p53 C-terminal peptide in human cancer cells.
(55/2199)
A p53-derived C-terminal peptide induced rapid apoptosis in breast cancer cell lines carrying endogenous p53 mutations or overexpressed wild-type (wt) p53 but was not toxic to nonmalignant human cell lines containing wt p53. Apoptosis occurred through a Fas/APO-1 signaling pathway involving increased extracellular levels of Fas/FasL in the absence of protein synthesis, as well as activation of a Fas/APO-1-specific protease, FLICE. The peptide activity was p53-dependent, and it had no effect in three tumor cell lines with null p53. Furthermore, the C-terminal peptide bound to p53 protein in cell extracts. Thus, p53-dependent, Fas/APO-1 mediated apoptosis can be induced in breast cancer cells with mutant p53 similar to the recently described Fas/APO-1 induced apoptosis by wt p53. However, mutant p53 without p53 peptide does not induce a Fas/APO-1 activation or apoptosis. Docking of the computed low energy conformations for the C-terminal peptide with those for a recently defined proline-rich regulatory region from the N-terminal domain of p53 suggests a unique low energy complex between the two peptide domains. The selective and rapid induction of apoptosis in cancer cells carrying p53 abnormalities may lead to a novel therapeutic modality. (+info)
Programmed cell death of embryonic motoneurons triggered through the Fas death receptor.
(56/2199)
About 50% of spinal motoneurons undergo programmed cell death (PCD) after target contact, but little is known about how this process is initiated. Embryonic motoneurons coexpress the death receptor Fas and its ligand FasL at the stage at which PCD is about to begin. In the absence of trophic factors, many motoneurons die in culture within 2 d. Most (75%) of these were saved by Fas-Fc receptor body, which blocks interactions between Fas and FasL, or by the caspase-8 inhibitor tetrapeptide IETD. Therefore, activation of Fas by endogenous FasL underlies cell death induced by trophic deprivation. In the presence of neurotrophic factors, exogenous Fas activators such as soluble FasL or anti-Fas antibodies triggered PCD of 40-50% of purified motoneurons over the following 3-5 d; this treatment led to activation of caspase-3, and was blocked by IETD. Sensitivity to Fas activation is regulated: motoneurons cultured for 3 d with neurotrophic factors became completely resistant. Levels of Fas expressed by motoneurons varied little, but FasL was upregulated in the absence of neurotrophic factors. Motoneurons resistant to Fas activation expressed high levels of FLICE-inhibitory protein (FLIP), an endogenous inhibitor of caspase-8 activation. Our results suggest that Fas can act as a driving force for motoneuron PCD, and raise the possibility that active triggering of PCD may contribute to motoneuron loss during normal development and/or in pathological situations. (+info)