A novel protein that interacts with the death domain of Fas/APO1 contains a sequence motif related to the death domain

Molecular cloning and characterisation of the rock bream, Oplegnathus fasciatus, Fas (CD95/APO-1), and its expression analysis in response to bacterial or viral infection

Fas belongs to the tumour necrosis factor (TNF) receptor superfamily and can transmit a death signal leading to apoptosis. In the present study, we isolated the full-length cDNA for rock bream (Oplegnathus fasciatus) Fas (RbFas). The full-length RbFas cDNA was 1770 bp long and contained an open reading frame of 957 bp that encoded 319 amino acid residues with a predicted molecular mass of 35.1 kDa. The 319 amino-acid predicted RbFas sequence is homologous to other Fas sequences, contains three cysteine-rich domains and a death domain (DD) and two potential N-glycosylation sites. Expression of RbFas mRNA was detected in nine different tissues from healthy rock bream and was the highest in red blood cells. In analyses of mitogen-stimulated RbFas expression in peripheral blood leucocytes, expression of RbFas mRNA was observed between 1 and 36 h after stimulation with LPS, and 1 and 3 h stimulation with poly I:C. In the case of bacterial injection, the RbFas transcript peaked 6 h after injection in both the kidney and the spleen. Otherwise, the RbFas transcript peaked after 1 h in spleen and 6 h in kidney following injection with RSIV.

Functional complementation between FADD and RIP1 in embryos and lymphocytes

FADD is a common adaptor shared by several death-receptors (DRs) for signaling apoptosis through recruitment and activation of caspase 81-3. DRs are essential for immune homeostasis, but dispensable during embryogenesis. Surprisingly, FADD^−/− mice die in utero4-5 and conditional deletion of FADD leads to impaired lymphocyte proliferation6-7. How FADD regulates embryogenesis and lymphocyte responses has been a long standing enigma. FADD could directly bind to RIP1, a serine/threonine kinase which mediates both necrosis and NF-κB activation. Here we show that FADD^−/− embryos contain elevated levels of RIP1 and exhibit massive necrosis. To investigate potential in vivo functional interaction between RIP1 and FADD, null alleles of RIP1 were crossed into FADD^−/− mice. Strikingly, RIP1 deficiency allowed normal embryogenesis of FADD^−/− mice. Conversely, the developmental defect of RIP1^−/− lymphocytes was partially corrected by FADD deletion. Furthermore, RIP1 deficiency fully restored normal proliferation in FADD^−/− T cells but not in FADD^−/− B cells. FADD^−/−RIP1^−/− double knockout (DKO) T cells are resistant to death induced by Fas or TNFα and display reduced NF-κB activity. Therefore, our data demonstrate an unexpected cell type-specific interplay between FADD and RIP1, which is critical for the regulation of apoptosis and necrosis during embryogenesis and lymphocyte function.

Expression of serine 194-phosphorylated Fas-associated death domain protein correlates with proliferation in B-cell non-Hodgkin lymphomas

Fas-associated death domain protein is a key component of the extrinsic apoptotic pathway. In addition, in animal models, Fas-associated death domain protein phosphorylation at serine 194 has been shown to affect cell proliferation, especially in T lymphocytes. The importance of Fas-associated death domain protein phosphorylation at serine 194 for the proliferation of B lymphocytes, however, is uncertain. Here we show in reactive lymph nodes that serine 194 phosphorylated Fas-associated death domain protein is expressed predominantly in the dark (proliferative) zone of germinal centers. In B-cell non-Hodgkin lymphoma cell lines, serine 194 phosphorylated Fas-associated death domain protein levels are substantially higher in highly proliferating cells and lower in serum-starved cells. We also used immunohistochemical analysis to assess Fas-associated death domain protein phosphorylation at serine 194 expression in 122 B-cell non-Hodgkin-type lymphomas. The mean percentage of serine 194 phosphorylated Fas-associated death domain protein positive tumor cells was 81% in Burkitt lymphoma, 41% in diffuse large B-cell lymphoma, 18% in follicular lymphoma, 18% in plasma cell myeloma, 12% in extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue, 11% in mantle cell lymphoma, and 2% in chronic lymphocytic leukemia/small lymphocytic lymphoma (P < .0001, Kruskal-Wallis test). Furthermore, in chronic lymphocytic leukemia/small lymphocytic lymphoma, serine 194 phosphorylated Fas-associated death domain protein was detected predominantly in proliferation centers. In the entire study group, the percentage of cells positive for serine 194 phosphorylated Fas-associated death domain protein correlated significantly with the proliferation index Ki-67 (Spearman R = 0.9, P < .0001). These data provide evidence that serine 194 phosphorylated Fas-associated death domain protein is involved in the proliferation of normal and neoplastic B cells and has features of a novel proliferation marker.

Defining the origins of the NOD-like receptor system at the base of animal evolution

Distinguishing self from nonself and the onset of defense effector mechanisms upon recognition of pathogens are essential for the survival of all life forms in the animal kingdom. The family of nucleotide -binding and oligomeriszation domain-like receptors (NLRs) was first identified in vertebrates and comprises a group of pivotal sensor protein of the innate immune system for microbial cell wall components or danger signals. Here, we provide first evidence that early diverging metazoans have large and complex NLR repertoires. The cnidarian NACHT/NB-ARC genes include novel combinations of domains, and the number of one specific type (NB-ARC and tetratricopeptide repeat containing) in Hydra is particularly large. We characterize the transcript structure and expression patterns of a selected HyNLR, HyNLR type 1 and describe putative interaction partners. In a heterologous expression system, we show induced proximity recruitment of an effector caspase (HyDD-Caspase) to the HyNLR type 1 protein upon oligomerization indicating a potential role of caspase activation downstream of NLR activation in Hydra. These results add substantially to our understanding of the ancestral innate immune repertoire as well as providing the first insights into putative cytoplasmic defense mechanisms at the base of animal evolution.

Neutrophils require SHP1 to regulate IL-1β production and prevent inflammatory skin disease

The regulation of neutrophil recruitment, activation, and disposal is pivotal for circumscribed inflammation. SHP1(Y208N/Y208N) mutant mice develop severe cutaneous inflammatory disease that is IL-1R dependent. Genetic reduction in neutrophil numbers and neutrophilic responses to infection is sufficient to prevent the spontaneous initiation of this disease. Neutrophils from SHP1(Y208N/Y208N) mice display increased pro-IL-1β production due to altered responses to MyD88-dependent and MyD88-independent signals. The IL-1R-dependent inflammatory disease in SHP1(Y208N/Y208N) mice develops independently of caspase 1 and proteinase 3 and neutrophil elastase. In response to Fas ligand, a caspase 1-independent inducer of IL-1β production, neutrophils from SHP1(Y208N/Y208N) mice produce elevated levels of IL-1β but display reduced caspase 3 and caspase 7 activation. In neutrophils deficient in SHP1, IL-1β induces high levels of pro-IL-1β suggesting the presence of a paracrine IL-1β loop. These data indicate that the neutrophil- and IL-1-dependent disease in SHP1(Y208N/Y208N) mice is a consequence of loss of negative regulation of TLR and IL-1R signaling.

FADD deficiency impairs early hematopoiesis in the bone marrow

Signal transduction mediated by Fas-associated death domain protein (FADD) represents a paradigm of coregulation of apoptosis and cellular proliferation. During apoptotic signaling induced by death receptors including Fas, FADD is required for the recruitment and activation of caspase 8. In addition, a death receptor-independent function of FADD is essential for embryogenesis. In previous studies, FADD deficiency in embryonic stem cells resulted in a complete lack of B cells and dramatically reduced T cell numbers, as shown by Rag1(-/-) blastocyst complementation assays. However, T-specific FADD-deficient mice contained normal numbers of thymocytes and slightly reduced peripheral T cell numbers, whereas B cell-specific deletion of FADD led to increased peripheral B cell numbers. It remains undetermined what impact an FADD deficiency has on hematopoietic stem cells and progenitors. The current study analyzed the effect of simultaneous deletion of FADD in multiple cell types, including bone marrow cells, by using the IFN-inducible Mx1-cre transgene. The resulting FADD mutant mice did not develop lymphoproliferation diseases, unlike Fas-deficient mice. Instead, a time-dependent depletion of peripheral FADD-deficient lymphocytes was observed. In the bone marrow, a lack of FADD led to a dramatic decrease in the hematopoietic stem cells and progenitor-enriched population. Furthermore, FADD-deficient bone marrow cells were defective in their ability to generate lymphoid, myeloid, and erythroid cells. Thus, the results revealed a temporal requirement for FADD. Although dispensable during lymphopoiesis post lineage commitment, FADD plays a critical role in early hematopoietic stages in the bone marrow.

Apigenin suppresses the growth of colorectal cancer xenografts via phosphorylation and up-regulated FADD expression

Apigenin is a flavonoid belonging to the flavone structural class. It has been implicated as a chemopreventive agent against prostate and breast cancers. However, to the best of our knowledge, no published data are available regarding apigenin in colorectal cancer (CRC). The effects and mechanisms of apigenin on CRC may vary significantly. This study aimed to analyze the effects of apigenin on the growth of CRC xenografts in nude mice derived from SW480, as well as to investigate the underlying mechanisms. Whole-body fluorescence imaging is an inexpensive optical system used to visualize gene expression in small mammals using reporter genes, such as eGFP as a reporter. In our study, the expression of eGFP may reflect the size of the tumor. A terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assay showed that apigenin promoted the apoptosis of CRC cells. Furthermore, the expression of five genes related to the proliferation and apoptosis of CRC, i.e., cyclin D1, BAG-1, Bcl-2, yrdC and Fas-associated protein with death domain (FADD), was detected by real-time quantitative RT-PCR. Among these genes, the up-regulated expression of FADD was noted in CRC xenograft tumors treated with apigenin. Immunohistochemistry and Western blotting confirmed the results at the protein level. Furthermore, Western blot analysis showed that apigenin induced the phosphorylation of FADD. Our findings suggest that apigenin enhances the expression of FADD and induces its phosphorylation, which may cause apoptosis of CRC cells and inhibition of tumor growth.

Oligodendrocyte-specific FADD deletion protects mice from autoimmune-mediated demyelination

Apoptosis of oligodendrocytes (ODCs), the myelin-producing glial cells in the CNS, plays a central role in demyelinating diseases such as multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. To investigate the mechanism behind ODC apoptosis in EAE, we made use of conditional knockout mice lacking the adaptor protein FADD specifically in ODCs (FADD(ODC-KO)). FADD mediates apoptosis by coupling death receptors with downstream caspase activation. In line with this, ODCs from FADD(ODC-KO) mice were completely resistant to death receptor-induced apoptosis in vitro. In the EAE model, FADD(ODC-KO) mice followed an ameliorated clinical disease course in comparison with control littermates. Lymphocyte and macrophage infiltration into the spinal cord parenchyma was significantly reduced, as was the extent of demyelination and proinflammatory gene expression. Collectively, our data show that FADD is critical for ODC apoptosis and the development of autoimmune demyelinating disease.

Programmed cell death of dendritic cells in immune regulation

Programmed cell death is essential for the maintenance of lymphocyte homeostasis and immune tolerance. Dendritic cells (DCs), the most efficient antigen-presenting cells, represent a small cell population in the immune system. However, DCs play major roles in the regulation of both innate and adaptive immune responses. Programmed cell death in DCs is essential for regulating DC homeostasis and consequently, the scope of immune responses. Interestingly, different DC subsets show varied turnover rates in vivo. The conventional DCs are relatively short-lived in most lymphoid organs, while plasmacytoid DCs are long-lived cells. Mitochondrion-dependent programmed cell death plays an important role in regulating spontaneous DC turnover. Antigen-specific T cells are also capable of killing DCs, thereby providing a mechanism for negative feedback regulation of immune responses. It has been shown that a surplus of DCs due to defects in programmed cell death leads to overactivation of lymphocytes and the onset of autoimmunity. Studying programmed cell death in DCs will shed light on the roles for DC turnover in the regulation of the duration and magnitude of immune responses in vivo and in the maintenance of immune tolerance.

The complex interplay between autophagy, apoptosis, and necrotic signals promotes T-cell homeostasis

Intense research efforts over the last two decades have focused on establishing the significance of apoptotic signaling in adaptive immunity. Without doubt, caspase-dependent apoptosis plays vital roles in many immune processes, including lymphocyte development, positive and negative selection, homeostasis, and self-tolerance. Cell biologists have developed new insights into cell death, establishing that other modes of cell death exist, such as programmed necrosis and type II/autophagic cell death. Additionally, immunologists have identified a number of immunological processes that are highly dependent upon cellular autophagy, including antigen presentation, lymphocyte development and function, pathogen recognition and destruction, and inflammatory regulation. In this review, we provide detailed mechanistic descriptions of cellular autophagy and programmed necrosis induced in response to death receptor ligation, including methods to identify them, and compare and contrast these processes with apoptosis. The crosstalk between these three processes is emphasized as newly formulated evidence suggests that this interplay is vital for efficient T-cell clonal expansion. This new evidence indicates that in addition to apoptosis, autophagy and programmed necrosis play significant roles in the termination of T-cell-dependent immune responses.

FasL and FADD delivery by a glioma-specific and cell cycle-dependent HSV-1 amplicon virus enhanced apoptosis in primary human brain tumors

BACKGROUND

Glioblastoma multiforme is the most malignant cancer of the brain and is notoriously difficult to treat due to the highly proliferative and infiltrative nature of the cells. Herein, we explored the combination treatment of pre-established human glioma xenograft using multiple therapeutic genes whereby the gene expression is regulated by both cell-type and cell cycle-dependent transcriptional regulatory mechanism conferred by recombinant HSV-1 amplicon vectors.

RESULTS

We demonstrated for the first time that Ki67-positive proliferating primary human glioma cells cultured from biopsy samples were effectively induced into cell death by the dual-specific function of the pG8-FasL amplicon vectors. These vectors were relatively stable and exhibited minimal cytotoxicity in vivo. Intracranial implantation of pre-transduced glioma cells resulted in better survival outcome when compared with viral vectors inoculated one week post-implantation of tumor cells, indicating that therapeutic efficacy is dependent on the viral spread and mode of viral vectors administration. We further showed that pG8-FasL amplicon vectors are functional in the presence of commonly used treatment regimens for human brain cancer. In fact, the combined therapies of pG8-FasL and pG8-FADD in the presence of temozolomide significantly improved the survival of mice bearing intracranial high-grade gliomas.

CONCLUSION

Taken together, our results showed that the glioma-specific and cell cycle-dependent HSV-1 amplicon vector is potentially useful as an adjuvant therapy to complement the current gene therapy strategy for gliomas.

Solution NMR investigation of the CD95/FADD homotypic death domain complex suggests lack of engagement of the CD95 C terminus

We have addressed complex formation between the death domain (DD) of the death receptor CD95 (Fas/APO-1) with the DD of immediate adaptor protein FADD using nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and size-exclusion chromatography with in-line light scattering. We find complexation to be independent of the C-terminal 12 residues of CD95 and insensitive to mutation of residues that engage in the high-order clustering of CD95-DD molecules in a recently reported crystal structure obtained at pH 4. Differential NMR linewidths indicate that the C-terminal region of the CD95 chains remains in a disordered state and (13)C-methyl TROSY data are consistent with a lack of high degree of symmetry for the complex. The overall molecular mass of the complex is inconsistent with that in the crystal structure, and the complex dissociates at pH 4. We discuss these findings using sequence analysis of CD95 orthologs and the effect of FADD mutations on the interaction with CD95.

A glycoprotein from Laminaria japonica induces apoptosis in HT-29 colon cancer cells

We isolated a novel glycoprotein from the brown alga Laminaria japonica that has antiproliferative effects on HT-29 colon cancer cells. We also identified the mechanism by which this glycoprotein, named LJGP, induces apoptosis. MTS assays showed that LJGP inhibited the proliferation of several cancer cell lines (AGS, HepG2, HT-29) in a dose-dependent manner. Especially in HT-29 cells, proliferation was significantly decreased. LJGP treatment on HT-29 displayed several apoptotic features, such as DNA fragmentation, sub-G1 arrest, caspase-3 activation, and PARP degradation. Consistent with sub-G1 arrest, LJGP decreased the expression of Cdk2, cyclin E, cyclin D1, PCNA, E2F-1, and phosphorylated pRb. Furthermore, the increase of p27 expression was observed. We also determined that LJGP-induced apoptosis leads to the formation of a death-induced signaling complex of Fas, FADD, and procaspase-8. LJGP induced the reduction of mitochondrial membrane potential with activation of the Bcl-2 family of proteins and caspase-9. These findings suggest that LJGP inhibits HT-29 cell proliferation by inducing apoptosis, which may be mediated via multiple pathways, including the Fas signaling pathway, the mitochondrial pathway, and cell cycle arrest. Therefore, LJGP can be a useful treatment option for colon cancer in humans.

Resistance of T-cell acute lymphoblastic leukemia to tumor necrosis factor--related apoptosis-inducing ligand-mediated apoptosis

OBJECTIVE

Cytotoxic ligands are involved in tumor immunity and graft-vs.-leukemia effect after allogeneic stem cell transplantation for leukemia. To clarify the susceptibility of T-cell acute lymphoblastic leukemia (T-ALL) to tumor immunity, sensitivity to recombinant human soluble Fas ligand (rhsFasL) and tumor necrosis factor-related apoptosis-inducing ligand (rhsTRAIL) was determined.

MATERIALS AND METHODS

Sensitivity to rhsFasL and rhsTRAIL and cell surface expression of their receptors were tested in T-ALL cell lines (n = 7) and patients' samples (n = 17) and compared with those in B-precursor ALL cell lines (n = 30). Expression of components of the death-inducing signaling complex and the TRAIL receptor genes (DR4/DR5), and the methylation status and promoter activity of the DR4/DR5 gene were tested in T-ALL cell lines.

RESULTS

T-ALL cell lines showed higher level of Fas expression and higher sensitivity to rhsFasL than did B-precursor ALL cell lines. Despite comparable expression of components of death-inducing signaling complex, cell lines and patients' samples of T-ALL showed TRAIL-resistance associated with low cell surface expression of DR4/DR5. Gene expression of DR4/DR5 in T-ALL cell lines was significantly lower than that in B-precursor ALL cell lines, and the methylation status of the gene promoter in T-ALL cell lines was associated with the gene expression level at least for DR4. The demethylating agent, 5-aza 2'deoxycytidine, upregulated the gene expression of DR4/DR5, but was insufficient for their surface expression due to low basal promoter activity.

CONCLUSIONS

In contrast to higher sensitivity to FasL, T-ALL showed resistance to TRAIL, which might be responsible for resistance to TRAIL-mediated cellular immunity.

P53 apoptosis mediator PERP: localization, function and caspase activation in uveal melanoma

p53 apoptosis effector related to PMP-22 (PERP) is a transcriptional target gene of p53 tumour suppressor that is specifically induced during apoptosis and not during cell cycle arrest. In primary uveal melanoma (UM), the most common intraocular malignancy in adults that has a reportedly unaffected signalling pathway upstream of and including p53, PERP expression is down-regulated in the metastatic monosomy 3-type tumours, compared with the less aggressive disomy 3-type tumours. Here, we demonstrate experimentally, by the use of full-length PERP-green fluorescent protein (GFP) fusions and real-time confocal microscopy, the intracellular targeting and plasma membrane localization of PERP in living UM cells and show that expression of PERP induces caspase-mediated apoptosis in UM cells. Induction of PERP expression in GFP-PERP-transfected UM cells leads to increased levels of cleaved caspase-8 forms, as well as to reduction of its full-length substrate Bid, but not to detectable processing of caspase-9. The levels of mature caspase-8, -9 and -3 proteins significantly correlate with PERP expression levels in primary UMs. Transcriptional profiling of PERP and caspase-8 in tumour specimens indicates that the positive association of PERP and caspase-8 proteins is a consequence of post-translational processing, most likely at the level of caspase-8 cleavage, and not of increased transcription of pro-caspase-8. We conclude that PERP expression leads to activation of an extrinsic receptor-mediated apoptotic pathway, with a possible subsequent engagement of the intrinsic apoptotic pathway. The findings underline the apoptotic pathway mediated by PERP as a critical mechanism employed by UM tumours to modulate susceptibility to apoptosis.

FADD: a regulator of life and death

FAS-associated protein with death domain (FADD) is the key adaptor protein transmitting apoptotic signals mediated by the main death receptors (DRs). Besides being an essential instrument in cell death, FADD is also implicated in proliferation, cell cycle progression, tumor development, inflammation, innate immunity, and autophagy. Recently, many of these new functions of FADD were shown to be independent of DRs. Moreover, FADD function is dictated by protein localization and phosphorylation state. Thus, FADD is a crucial and unique controller of many essential cellular processes. The full understanding of the networks dictating the ultimate function of FADD may provide a new paradigm for other multifaceted proteins.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Molecular modeling of BAD complex resided in a mitochondrion integrating glycolysis and apoptosis

BAD (Bcl-2 antagonist of cell death) and GK (glucokinase) reside in a mitochondrial complex together with PKA and PP1 catalytic units (PKAc and PP1c) and WAVE-1 that integrates glycolysis and apoptosis. Our research results reveal that BAD is phosphorylated and inactivated on Ser 75 in a BAD-Bcl-xL complex by PKA (targeted to mitochondria through association with WAVE1), resulting in the dissociation of BAD and its binding to GK. Moreover, GK can interact with PP1c and also distinguish WAVE1. On the other hand, BAD is dephosphorylated and activated on Ser75 by PP1c, leading to the separation of PKAc and its binding to the regulatory (R) subunit of PKA which by the dimerization domain of its R subunit connects with WAVE1 linked with GK of the complex. This may be the reason of the complex existing in liver mitochondria, regardless of phosphorylated and dephosphorylated BAD. Additionally, GK like PKA may also prevent Bcl-xL from rebinding to BAD by phosphorylating BAD at Ser 118. The BAD complex model reveals that BAD and GK play key roles because of BAD as a substrate for the PKA-PP1 pair and by BH3 domain directly interacting with GK. This is helpful for our development and research of the molecular mechanism of BAD integrating glycolysis and apoptosis.

Induction of apoptosis in hepatocellular carcinoma Smmc-7721 cells by vitamin K(2) is associated with p53 and independent of the intrinsic apoptotic pathway

Vitamin K(2) (VK(2)) can exert cell growth inhibitory effects in various human cancer cells. In this study, we investigated the cell growth inhibitory effects of VK(2) in hepatocellular carcinoma Smmc-7721 cells and the mechanisms involved. We found that VK(2)-inhibited cell proliferation in Smmc-7721 cells in a dose-dependent manner, and the IC50 of VK(2) in Smmc-7721 cells was 9.73 microM at 24 h. The data from flow cytometric analyses, DNA fragmentation assays, and caspase 3 activity assays revealed that apoptosis was the determining factor in VK(2) activity. Furthermore, a significant increase in p53 phosphorylation and protein level was exhibited in apoptotic cells treated with VK(2), although there were no changes in p53 mRNA expression. Bax expression was unaffected by VK(2) in Smmc-7721 cells. In addition, our study showed that caspase 3 was activated by caspase 8, not caspase 9, in Smmc-7721 cells treated with VK(2). In summary, these data suggested that VK(2) can inhibit the growth of Smmc-7721 cells by induction of apoptosis involving caspase 8 activation and p53. This apoptotic process was not mediated by the intrinsic apoptotic pathway.

Targeting MMP-9, uPAR, and cathepsin B inhibits invasion, migration and activates apoptosis in prostate cancer cells

Prostate cancer is one of the most commonly diagnosed cancers and the second leading cause of cancer deaths in Americans. The high mortality rate is mainly attributed to the invasiveness and metastasis of advanced prostate cancer. Targeting the molecules involved in metastasis could be an effective mode of treatment for prostate cancer. In this study, the therapeutic potential of siRNA-mediated targeting of matrix metalloproteinase-9 (MMP-9), urokinase plasminogen activator receptor (uPAR), and cathepsin B (CB) in prostate cancer was carried out using single and bi-cistronic siRNA-expressing constructs. Downregulation of MMP-9, uPAR, and CB inhibited matrigel invasion, in vitro angiogenesis and wound-healing migration ability of PC3 and DU145 prostate cancer cell lines. In addition, the siRNA treatments induced apoptosis in the tumor cells as determined by TUNEL and DNA laddering assays. An attempt to elucidate the apoptotic pathway showed the involvement of FAS-mediated activation of caspases-8 and -7. Further, mice with orthotopic prostate tumors treated with siRNA-expressing vectors showed significant inhibition in tumor growth and migration. In conclusion, we report that the siRNA-mediated knockdown of MMP-9, uPAR, and CB inhibits invasiveness and migration of prostate cancer cells and leads to apoptosis both in vitro and in vivo.

Death receptor 5-recruited raft components contributes to the sensitivity of Jurkat leukemia cell lines to TRAIL-induced cell death

In the present study we demonstrated Jurkat leukemia cell lines of TIB152 and TIB153 with different sensitivities to recombinant soluble TRAIL cytotoxicity. TRAIL receptor death receptor 5 (DR5) was constitutively localized in the rafts in both cell lines. FADD, caspase-8, and PI3K-p85 subunit were recruited into DR5 lipid rafts of TIB152 but not in TIB153 cells. The expression and enzyme activity of acid sphingomyelinase, which digests sphingomyeline to produce ceramide and plays an essential role in lipid raft assembling, were higher in the rafts of TIB152 than in TIB153. These data provide evidences that DR5-recruited raft components contribute to the different sensitivity of Jurkat leukemia cell lines to TRAIL-induced cell death and may throw some light on the development of better therapeutic strategies for the cancer cells resistant to TRAIL treatment.

Induction of apoptosis by immature plum in human hepatocellular carcinoma

In the present study, the effect of an extract of immature Prunus salicina Lindl. cv. Soldam fruit on the viability and induction of apoptosis in human hepatocellular carcinoma HepG2 cells was investigated. The results showed that in comparison with other cancer cells, the growth inhibition exerted by immature plum extracts was greatest in HepG2. Apoptosis in HepG2 cells mediated by immature plums was associated with "death receptor signaling." Immature plum extracts significantly increased the activation of caspase-8, -10, and -3 and expression of the caspase-3 target proteins alpha-fodrin (induces membrane blebbing and cell shrinkage), poly(ADP-ribose) polymerase (a nuclear enzyme that is involved in DNA repair following DNA nicks), and DNA fragmentation factor (induces apoptotic DNA fragmentation). The total yield of identified polyphenols in immature plum extract was 10 g/kg dry weight. The major components, (-)-epicatechin and (-)-gallocatechin gallate, were 34.7% and 28.6% of total polyphenols, respectively. (+)-Catechin, (-)-epicatechin gallate, and (-)-catechin gallate were also found. On the basis of these results, the immature plum (P. salicina Lindl. cv. Soldam) and its active compound, (-)-epicatechin, are expected to be a natural resource for developing novel therapeutic agents for cancer prevention and treatment.

Mind bomb 1 regulation of cFLIP interactions

Mind bomb 1 (Mib1) is a multidomain E3 ligase that directs ubiquitination of the Notch ligands Delta and Jagged to promote their endocytosis. Here we examine Notch-independent functions of Mib1 and find that its activities are linked to the initiation of the extrinsic cell death pathway. Expression of Mib1 induces a spontaneous, caspase-dependent cell death. Consistent with this, depletion of endogenous Mib1 decreases tumor-necrosis factor (TNF)-induced cell death. Mib1 was found to bind to cellular Fas-associated death domain (FADD)-like IL-1b converting enzyme (FLICE)-like inhibitory proteins (cFLIP-L and cFLIP-S), whereas only cFLIP-s can inhibit Mib1-induced cell death. The interaction between Mib1 and cFLIP decreases the association of caspase-8 with cFLIP, which activates caspase-8 and induces cell death. Collectively, these results suggest that in addition to a central role in Notch signaling, Mib1 has an important role in regulating the extrinsic cell death pathway.

Polypeptide fromChlamys farreriinhibits UVB-induced HaCaT cells apoptosis via inhibition CD95 pathway and reactive oxygen species

Polypeptide from Chlamys farreri (PCF) is a novel marine active product isolated from gonochoric Chinese scallop Chlamys farreri which has recently been found to be an effective antioxidant. In this study, we assessed the effect of PCF on UVB-induced intracellular signalling of apoptosis in HaCaT cells. Pre-treatment with PCF significantly inhibited UVB-induced apoptosis in HaCaT cells. PCF strongly reduced the intracellular reactive oxygen species (ROS) level followed by inhibiting the release of cytochrome c. The expression of CD95 and Fas-associating protein with death domain (FADD) was eliminated in a dose-dependent manner by PCF pre-treatment in UVB-irradiated HaCaT cells, followed by inhibition of cleavage of procaspase-8, whose activation induced cell apoptosis. Furthermore, pre-treatment with the ROS scavenger N-acetylcysteine (NAC) and the caspase-8 inhibitor z-IETD-fmk was found to effectively prevent UVB-induced apoptosis, suggesting that UVB-induced HaCaT cell apoptosis was partially due to generation of ROS and activation of the caspase-8 pathway. Consequently, the protective effect of PCF against UVB irradiation in HaCaT cells is exerted by suppression of generation of ROS followed by inhibition of cytochrome c release and inactivation of Fas-FADD-caspase-8 pathway, resulting in blockage of UVB-induced apoptosis.

Mammalian nitrilase 1 homologue Nit1 is a negative regulator in T cells

The mammalian Nit1 protein is homologous to plant and bacterial nitrilases. In flies and worms, Nit1 is fused to the 5' end of Fhit, suggesting that Nit1 may functionally interact with the Fhit pathway. Fhit has been shown to play a role of a tumor suppressor. Somatic loss of Fhit in human tissues is associated with a wide variety of cancers. Deletion of Fhit results in a predisposition to induced and spontaneous tumors in mice. It has been suggested that Nit1 collaborates with Fhit in tumor suppression. Similar to mice lacking Fhit, Nit1-deficient mice are more sensitive to carcinogen-induced tumors. It was previously shown that ectopic expression of Nit1 or Fhit led to caspase activation and apoptosis, and that both proteins may play a role in DNA damage-induced apoptosis. In this study, we analyzed the physiological function of Nit1 in T cells using Nit1-knockout mice. Nit1-deficient T cells can undergo apoptosis induced by DNA damage due to irradiation and chemical treatment. However, apoptosis induced by Fas or Ca(++) signals appeared to be compromised. Additionally, Nit1 deficiency resulted in T cell hyperproliferative responses induced by TCR stimulation. The expressions of T cell activation markers were elevated in Nit1(-/-) T cells. There was a spontaneous cell cycle entry and enhanced cell cycle progression in Nit1(-/-) T cells. These data indicate that Nit1 is a novel negative regulator in primary T cells.

The many roles of FAS receptor signaling in the immune system

FAS belongs to the subgroup of the tumor necrosis factor receptor (TNF-R) family that contains an intracellular "death domain" and triggers apoptosis. Its physiological ligand FASL is a member of the TNF cytokine family. Studies with mutant mice and cells from human patients have shown that FAS plays critical roles in the immune system, including the killing of pathogen-infected cells and the death of obsolete and potentially dangerous lymphocytes. Fas thereby functions as a guardian against autoimmunity and tumor development. FAS triggers apoptosis through FADD-mediated recruitment and activation of caspase-8. In certain cells such as hepatocytes, albeit not lymphocytes, FAS-induced apoptosis requires amplification through proteolytic activation of the proapoptotic BCL-2 family member BID. Curiously, several components of the FAS signaling machinery have been implicated in nonapoptotic processes, including cellular activation, differentiation, and proliferation. This review describes current understanding of Fas-induced apoptosis signaling and proposes experimental strategies for future advances.

The death domain of FADD is essential for embryogenesis, lymphocyte development, and proliferation

The Fas-associated death domain-containing protein (FADD) is an adaptor for relaying apoptotic signals initiated by death receptors such as Fas. Whereas a lack of death receptors has no effect on mouse development, FADD deficiency results in early embryonic lethality, indicating that FADD has additional functions independent of death receptors. We have previously shown that conditional deletion of FADD not only impairs apoptosis but also leads to defective lymphocyte proliferation. The non-apoptotic signaling mediated by FADD remains poorly understood. Earlier studies have suggested that FADD carboxyl terminal serine phosphorylation likely plays a role in FADD-mediated proliferation signaling in T cells. The FADD death domain is presumably only required for apoptotic signaling, as it interacts with death receptors which are dispensable during embryonic development and lymphocyte proliferation. To test this hypothesis, we have performed mutational analyses of the FADD death domain and identified a mutant, R117Q, which lacks binding to Fas and, thus, is incapable of apoptotic signaling in cell lines. Unexpectedly, this death domain point mutation disrupted mouse embryonic development as shown by in vivo functional reconstitution analyses. Interestingly, a second FADD death domain mutant, V121N, retained normal Fas binding and apoptotic signaling ability but also failed to support mouse development. Furthermore, lymphocyte proliferation responses were impaired by V121N. This reverse genetic study has revealed a previously unappreciated role of the FADD death domain, which likely functions as a molecular switch regulating two distinct signals leading to apoptosis and cell proliferation and is critical for embryogenesis, lymphocyte development, and proliferation.

A critical role for Fas/CD-95 dependent signaling pathways in the pathogenesis of hyperoxia-induced brain injury

OBJECTIVE

Prematurely born infants are at risk for development of neurocognitive impairment in later life. Oxygen treatment has been recently identified as a trigger of neuronal and oligodendrocyte apoptosis in the developing rodent brain. We investigated the role of the Fas death receptor pathway in oxygen-triggered developmental brain injury.

METHODS

Six-day-old Wistar rats were exposed to 80% oxygen for various periods (2, 6, 12, 24, 48, and 72 hours), and mice deficient in either Fas (B6.MRL-Tnfrsf6(lpr)) or Fas ligand (B6Smn.C3-Fasl(gld)) and control mice (C57BL/6J) were exposed to 80% oxygen for 24 hours. Polymerase chain reaction, Western blotting, and caspase activity assays of thalamus and cortex tissue were performed.

RESULTS

Fas and Fas ligand messenger RNA and protein were upregulated. Furthermore, hyperoxia resulted in induction of downstream signaling events of Fas, such as Fas-associated death domain (FADD), the long and short form of FADD-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP-L, FLIP-S), and cleavage of caspase-8 and caspase-3. Injection of a selective caspase-8 inhibitor (TRP801, 1mg/kg) at the beginning of hyperoxia blocked subsequent caspase-3 cleavage in this model. B6.MRL-Tnfrsf6(lpr) mice were protected against oxygen-mediated injury, confirming Fas involvement in hyperoxia-induced cell death. Mice deficient in Fas ligand did not differ from control animals in the amount of cell death.

INTERPRETATION

We conclude that neonatal hyperoxia triggers Fas receptor and its downstream signaling events in a Fas ligand-independent fashion. Lack of functional Fas receptors and selective pharmacological inhibition of caspase-8 prevents activation of caspase-3 and provides significant neuroprotection.

Apoptosis signaling pathways

Cell death is often an active and highly choreographed process of cell suicide known as apoptosis. The molecular signals governing this process have been the subject of intense research in recent years. During apoptosis a profusion of pathways either promote cellular survival or lead to certain death. These pathways engage in constant crosstalk with those that control cell proliferation and other activities, in order to maintain the delicate balance between cell births and deaths. This commentary unit discusses two major pathways, active (antigen-induced) and passive (lymphokine-withdrawal) apoptosis, and provides background for the following unit on flow cytometry of apoptosis.

Changes in FADD levels, distribution, and phosphorylation in TNFalpha-induced apoptosis in hepatocytes is caspase-3, caspase-8 and BID dependent

FADD/MORT1 (The adaptor protein of Fas Associate Death Domain/Mediator of Receptor Induced Toxicity) is essential for signal transduction of death receptor signaling. We have previously shown that FADD is significantly up-regulated in TNFalpha/ActD induced apoptosis. Over-expression of FADD also induces death of lung cancer cells and primary hepatocytes. We hypothesize that the increase in detectable FADD levels require the proximal steps in apoptotic signaling and speculated that FADD would be redistributed in cells destined to undergo apoptosis. We show that monomeric non-phosphorylated FADD is up-regulated in hepatocytes treated with TNFalpha/ActD and that it accumulates in the cytoplasm. Nuclear phosphorylated FADD decreases with TNFalpha/ActD treatment. Dimeric FADD in the cytoplasm remains constant with TNFalpha/ActD. The change in FADD levels and distribution was dependent on caspase-3, caspase-8 activity and the presence of BID. Thus, changes in FADD levels and distribution are downstream of caspase activation and mitochondria changes that are initiated by the formation of the DISC complex. Changes in FADD levels and distribution may represent a novel feed-forward mechanism to propagate apoptosis signaling in hepatocytes.

Tumor necrosis factor p55 and p75 receptors are involved in chemical-induced apoptosis of dentate granule neurons

Localized tumor necrosis factor-alpha (TNFalpha) elevation has diverse effects in brain injury often attributed to signaling via TNFp55 or TNFp75 receptors. Both dentate granule cells and CA pyramidal cells express TNF receptors (TNFR) at low levels in a punctate pattern. Using a model to induce selective death of dentate granule cells (trimethyltin; 2 mg/kg, i.p.), neuronal apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ end labeling, active caspase 3 (AC3)] was accompanied by amoeboid microglia and elevated TNFalpha mRNA levels. TNFp55R (55 kDa type-1 TNFR) and TNFp75R (75 kDa type-2 TNFR) immunoreactivity in AC3(+) neurons displayed a pattern suggestive of receptor internalization and a temporal sequence of expression of TNFp55R followed by TNFp75R associated with the progression of apoptosis. A distinct ramified microglia response occurred around CA1 neurons and healthy dentate neurons that displayed an increase in the normal punctate pattern of TNFRs. Neuronal damage was decreased with i.c.v. injection of TNFalpha antibody and in TNFp55R-/-p75R-/- mice that showed higher constitutive mRNA levels for interleukin (IL-1alpha), macrophage inflammatory protein 1-alpha (MIP-1alpha), TNFalpha, transforming growth factor beta1, Fas, and TNFRSF6-assoicated via death domain (FADD). TNFp75R-/- mice showed exacerbated injury and elevated mRNA levels for IL-1alpha, MIP-1alpha, and TNFalpha. In TNFp55R-/- mice, constitutive mRNA levels for TNFalpha, IL-6, caspase 8, FADD, and Fas-associated phosphatase were higher; IL-1alpha, MIP-1alpha, and transforming growth factor beta1 lower. The mice displayed exacerbated neuronal death, delayed microglia response, increased FADD and TNFp75R mRNA levels, and co-expression of TNFp75R in AC3(+) neurons. The data demonstrate TNFR-mediated apoptotic death of dentate granule neurons utilizing both TNFRs and suggest a TNFp75R-mediated apoptosis in the absence of normal TNFp55R activity.

Costunolide-induced apoptosis is caused by receptor-mediated pathway and inhibition of telomerase activity in NALM-6 cells

Costunolide, isolated from the stem bark of Magnolia sieboldii, is a sesquiterpene lactone that exhibits various biological and immunological actions. We investigated the induction mechanism of apoptosis by costunolide in a human B cell leukemia NALM-6 cell culture system. Costunolide (10 microM)-induced apoptosis time-dependently increased, estimated by nuclear damage observation and flow cytometric analysis. Costunolide did not change Fas-associated factor 1 (FAF1), but the phosphorylation of Fas-associated death domain (FADD) at serine 194 increased from early treatment. The activation of caspase-8 and -9 and degradation of poly-(ADP-ribose) polymerase (PARP) was time-dependently detected by incubation with costunolide. Pretreatment of cells with caspase-3, -8 and broad spectrum caspase inhibitors significantly blocked costunolide-induced apoptosis, but caspase-9 inhibitor failed to block apoptosis. Telomerase activity was significantly suppressed after treatment with costunolide, and human telomerase reverse transcriptase (hTERT), a critical determinant of the enzyme activity of telomerase, decreased the expression of both mRNA and protein levels by costunolide. Costunolide-induced repression of telomerase was prevented by pretreatment of cells with caspase-3, -8 and broad spectrum caspase inhibitors, but caspase-9 inhibitor was no effect. These data suggest that one of the costunolide-induced apoptotic mechanisms is that the receptor-mediated pathway precedes the mitochondria-dependent pathway, caused by the inhibition of telomerase activity via suppression of hTERT in NALM-6 cells.

Mechanism of nuclear factor of activated T-cells mediated FasL expression in corticosterone -treated mouse Leydig tumor cells

BACKGROUND

Fas and FasL is important mediators of apoptosis. We have previously reported that the stress levels of corticosterone (CORT, glucocorticoid in rat) increase expression of Fas/FasL and activate Fas/FasL signal pathway in rat Leydig cells, which consequently leads to apoptosis. Moreover, our another study showed that nuclear factor of activated T-cells (NFAT) may play a potential role in up-regulation of FasL during CORT-treated rat Leydig cell. It is not clear yet how NFAT is involved in CORT-induced up-regulation of FasL. The aim of the present study is to investigate the molecular mechanisms of NFAT-mediated FasL expression in CORT-treated Leydig cells.

RESULTS

Western blot analysis showed that NFAT2 expression is present in mouse Leydig tumor cell (mLTC-1). CORT-induced increase in FasL expression in mLTC-1 was ascertained by Western Blot analysis and CORT-induced increase in apoptotic frequency of mLTC-1 cells was detected by FACS with annexin-V labeling. Confocal imaging of NFAT2-GFP in mLTC-1 showed that high level of CORT stimulated NFAT translocation from the cytoplasm to the nucleus. RNA interference-mediated knockdown of NFAT2 significantly attenuated CORT-induced up-regulation of FasL expression in mLTC. These results corroborated our previous finding that NFAT2 is involved in CORT-induced FasL expression in rat Leydig cells and showed that mLTC-1 is a suitable model for investigating the mechanism of CORT-induced FasL expression. The analysis of reporter constructs revealed that the sequence between -201 and +71 of mouse FasL gene is essential for CORT-induced FasL expression. The mutation analysis demonstrated that CORT-induced FasL expression is mediated via an NFAT binding element located in the -201 to +71 region. Co-transfection studies with an NFAT2 expression vector and reporter construct containing -201 to +71 region of FasL gene showed that NFAT2 confer a strong inducible activity to the FasL promoter at its regulatory region. In addition, chromatin immunoprecipitation assay further confirmed the results of reporter gene studies by showing the specific binding of NFAT2 to the -201 to +71 region.

CONCLUSION

In the present study, we demonstrated that NFAT2 directly stimulates transcription of FasL in high level CORT-treated mLTC-1. In conclusion, the present study provides further evidence for our finding that CORT-induced FasL expression in Leydig cells is mediated by NFAT.

Superoxide-mediated proteasomal degradation of Bcl-2 determines cell susceptibility to Cr(VI)-induced apoptosis

Hexavalent chromium [Cr(VI)] compounds are redox cycling environmental carcinogens that induce apoptosis as the primary mode of cell death. Defects in apoptosis regulatory mechanisms contribute to carcinogenesis induced by Cr(VI). Activation of apoptosis signaling pathways is tightly linked with the generation of reactive oxygen species (ROS). Likewise, ROS have been implicated in the regulation of Cr(VI)-induced apoptosis and carcinogenicity; however, its role in Cr(VI)-induced apoptosis and the underlying mechanism are largely unknown. We report that ROS, specifically superoxide anion (.O(-)(2), mediates Cr(VI)-induced apoptosis of human lung epithelial H460 cells. H460 rho(0) cells that lack mitochondrial DNA demonstrated a significant decrease in ROS production and apoptotic response to Cr(VI), indicating the involvement of mitochondrial ROS in Cr(VI)-induced apoptosis. In agreement with this observation, we found that Cr(VI) induces apoptosis mainly through the mitochondrial death pathway via caspase-9 activation, which is negatively regulated by the antiapoptotic protein Bcl-2. Furthermore, .O(-)(2) induced apoptosis in response to Cr(VI) exposure by downregulating and degrading Bcl-2 protein through the ubiquitin-proteasomal pathway. This study reveals a novel mechanism linking .O(-)(2) with Bcl-2 stability and provides a new dimension to ROS-mediated Bcl-2 downregulation and apoptosis induction.

Antiangiogenic systemic gene therapy combined with doxorubicin administration induced caspase 8 and 9-mediated apoptosis in endothelial cells and an anti-metastasis effect

Ad-PPE-Fas-c is an adenovector that expresses Fas-c under the control of the modified pre-proendothelin-1 (PPE-1) promoter. Fas-c is a chimeric death receptor containing the extracellular portion of tumour necrosis factor 1 receptor (TNFR1) and the transmembrane and intracellular portion of Fas. We recently demonstrated that Ad-PPE-Fas-c induced Fas-receptor-mediated endothelial cell apoptosis. Previously, doxorubicin was shown to enhance Fas-receptor clustering and the induction of its cascade. Therefore, the goal of this work was to test whether doxorubicin augments the capacity of Ad-PPE-Fas-c to induce endothelial cell apoptosis and to elucidate whether either the death-receptor-mediated apoptotic cascade or the mitochondria-associated apoptotic cascade is involved in the combined treatment effect. We found that a combined treatment of Ad-PPE-Fas-c and doxorubicin synergistically induced a reduction in endothelial cell viability and apoptosis. z-IETD-FMK, a caspase-8 inhibitor, and z-LEHD-FMK, a caspase-9 inhibitor, significantly decreased apoptosis induced by the combined treatment. Systemically administered combined therapy significantly reduced the lung metastases burden (70%) in mice as compared to each treatment alone. Thus, a combined treatment of Ad-PPE-Fas-c gene therapy and chemotherapy may be effective in the treatment of metastatic diseases and both the Fas cascade and the mitochondria-associated cascade are essential for this effect.

Essential role of TNF receptor superfamily 25 (TNFRSF25) in the development of allergic lung inflammation

We identify the tumor necrosis factor receptor superfamily 25 (TNFRSF25)/TNFSF15 pair as critical trigger for allergic lung inflammation, which is a cardinal feature of asthma. TNFRSF25 (TNFR25) signals are required to exert T helper cell 2 (Th2) effector function in Th2-polarized CD4 cells and co-stimulate interleukin (IL)-13 production by glycosphingolipid-activated NKT cells. In vivo, antibody blockade of TNFSF15 (TL1A), which is the ligand for TNFR25, inhibits lung inflammation and production of Th2 cytokines such as IL-13, even when administered days after airway antigen exposure. Similarly, blockade of TNFR25 by a dominant-negative (DN) transgene, DN TNFR25, confers resistance to lung inflammation in mice. Allergic lung inflammation–resistant, NKT-deficient mice become susceptible upon adoptive transfer of wild-type NKT cells, but not after transfer of DN TNFR25 transgenic NKT cells. The TNFR25/TL1A pair appears to provide an early signal for Th2 cytokine production in the lung, and therefore may be a drug target in attempts to attenuate lung inflammation in asthmatics.

TRAIL-R deficiency in mice promotes susceptibility to chronic inflammation and tumorigenesis

Preclinical data support the potential of the death-signaling receptors for TRAIL as targets for cancer therapy. However, it is unclear whether these death-signaling receptors suppress the emergence and growth of malignant tumors in vivo. Herein we show that TNF-related apoptosis-inducing ligand receptor (TRAIL-R), the only proapoptotic death-signaling receptor for TRAIL in the mouse, suppresses inflammation and tumorigenesis. Loss of a single TRAIL-R allele on the lymphoma-prone Emu-myc genetic background significantly reduced median lymphoma-free survival. TRAIL-R-deficient lymphomas developed with equal frequency irrespective of mono- or biallelic loss of TRAIL-R, had increased metastatic potential, and showed apoptotic defects relative to WT littermates. In addition, TRAIL-R-/- mice showed decreased long-term survival following a sublethal dose of ionizing radiation. Histological evaluation of moribund irradiated TRAIL-R-/- animals showed hallmarks of bronchopneumonia as well as tumor formation with increased NF-kappaB p65 expression. TRAIL-R also suppressed diethylnitrosamine-induced (DEN-induced) hepatocarcinogenesis, as an increased number of large tumors with apoptotic defects developed in the livers of DEN-treated TRAIL-R-/- mice. Thus TRAIL-R may function as an inflammation and tumor suppressor in multiple tissues in vivo.

Yes and PI3K bind CD95 to signal invasion of glioblastoma

Invasion of surrounding brain tissue by isolated tumor cells represents one of the main obstacles to a curative therapy of glioblastoma multiforme. Here we unravel a mechanism regulating glioma infiltration. Tumor interaction with the surrounding brain tissue induces CD95 Ligand expression. Binding of CD95 Ligand to CD95 on glioblastoma cells recruits the Src family member Yes and the p85 subunit of phosphatidylinositol 3-kinase to CD95, which signal invasion via the glycogen synthase kinase 3-beta pathway and subsequent expression of matrix metalloproteinases. In a murine syngeneic model of intracranial GBM, neutralization of CD95 activity dramatically reduced the number of invading cells. Our results uncover CD95 as an activator of PI3K and, most importantly, as a crucial trigger of basal invasion of glioblastoma in vivo.

A Fas-associated death domain protein/caspase-8-signaling axis promotes S-phase entry and maintains S6 kinase activity in T cells responding to IL-2

Fas-associated death domain protein (FADD) constitutes an essential component of TNFR-induced apoptotic signaling. Paradoxically, FADD has also been shown to be crucial for lymphocyte development and activation. In this study, we report that FADD is necessary for long-term maintenance of S6 kinase (S6K) activity. S6 phosphorylation at serines 240 and 244 was only observed after long-term stimulation of wild-type cells, roughly corresponding to the time before S-phase entry, and was poorly induced in T cells expressing a dominantly interfering form of FADD (FADDdd), viral FLIP, or possessing a deficiency in caspase-8. Defects in S6K1 phosphorylation were also observed. However, defective S6K1 phosphorylation was not a consequence of a wholesale defect in mammalian target of rapamycin function, because 4E-BP1 phosphorylation following T cell activation was unaffected by FADDdd expression. Although cyclin D3 up-regulation and retinoblastoma hypophosphorylation occurred normally in FADDdd T cells, cyclin E expression and cyclin-dependent kinase 2 activation were markedly impaired in FADDdd T cells. These results demonstrate that a FADD/caspase-8-signaling axis promotes T cell cycle progression and sustained S6K activity.

The long form of Fas apoptotic inhibitory molecule is expressed specifically in neurons and protects them against death receptor-triggered apoptosis

Death receptors (DRs) and their ligands are expressed in developing nervous system. However, neurons are generally resistant to death induction through DRs and rather their activation promotes neuronal outgrowth and branching. These results suppose the existence of DRs antagonists expressed in the nervous system. Fas apoptosis inhibitory molecule (FAIM(S)) was first identified as a Fas antagonist in B-cells. Soon after, a longer alternative spliced isoform with unknown function was identified and named FAIM(L). FAIM(S) is widely expressed, including the nervous system, and we have shown previously that it promotes neuronal differentiation but it is not an anti-apoptotic molecule in this system. Here, we demonstrate that FAIM(L) is expressed specifically in neurons, and its expression is regulated during the development. Expression could be induced by NGF through the extracellular regulated kinase pathway in PC12 (pheochromocytoma cell line) cells. Contrary to FAIM(S), FAIM(L) does not increase the neurite outgrowth induced by neurotrophins and does not interfere with nuclear factor kappaB pathway activation as FAIM(S) does. Cells overexpressing FAIM(L) are resistant to apoptotic cell death induced by DRs such as Fas or tumor necrosis factor R1. Reduction of endogenous expression by small interfering RNA shows that endogenous FAIM(L) protects primary neurons from DR-induced cell death. The detailed analysis of this antagonism shows that FAIM(L) can bind to Fas receptor and prevent the activation of the initiator caspase-8 induced by Fas. In conclusion, our results indicate that FAIM(L) could be responsible for maintaining initiator caspases inactive after receptor engagement protecting neurons from the cytotoxic action of death ligands.

Adaptor FADD is recruited by RTN3/HAP in ER-bound signaling complexes

It has been well established that FADD plays a critical role in the membrane bound death-inducing signaling complexes. Herein, we report that endogenous FADD could interact with ectopic or endogenous RTN3/HAP. ER-bound RTN3 protein recruited endogenous FADD to the ER membrane and subsequently initiated caspase-8 cascade, including activation of caspase-8, processing of Bid and release of cytochrome c from mitochondria. Furthermore, we demonstrated that endogenous FADD was recruited by ER-bound endogenous RTN3 to the ER membrane under the tunicamycin stimulation. The dominant negative form of FADD containing DD could abolish these RTN3 generated events in the caspase-8 cascade. Moreover, we found that RTN3 induced caspase-9 processing was only partially resulted from caspase-8 activation (data unshown), indicating that multiple caspase cascades participated in the apoptosis from RTN3 over-expression. Furthermore, NogoB/ASY, a homologue of RTN3 and a potential RTN3 interacting protein, also associated with FADD and induced cytochrome c release in a FADD dependent manner.