Fas-associated Protein Research Articles

Surface contamination of dental implants assessed by gene expression analysis in a whole‐blood in vitro assay. A preliminary study

We aimed at evaluating pyrogen contamination of dental implants made of titanium and zirconia by using gene expression analysis in a whole-blood in vitro assay. Titanium and zirconia implants (five each) were incubated in human whole blood. Samples were assayed for gene expression levels of toll-like receptor 4 (TLR4), TLR9, interleukin (IL)-1β, nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-kB), tumour necrosis factor (TNF)-α, and Fas-associated protein with death domain (FADD) as indicators of surface contamination resulting in lipopolysaccharides (LPS)-stimulated TLR- or TNF-mediated immune responses. Gene expression was assayed using real-time quantitative polymerase chain reaction (RT-qPCR). Non-stimulated blood from the same donor served as a negative control, and blood stimulated with LPS served as a positive control. After dry-heat treatment with dry heat, all implants were re-analysed as described above. Both implant systems contained surface contaminants evoking a pro-inflammatory response similar to that induced by LPS. After dry-heat treatment, gene expression was significantly decreased to levels similar to those of negative control samples. The results demonstrated LPS-like surface-bound contaminants in both tested implant systems. Depyrogenation with dry heat seems to be an effective means of reducing such contamination in dental implants.

Regulation of Protein Kinase C Inactivation by Fas-associated Protein with Death Domain

Protein kinase C (PKC) plays important roles in diverse cellular processes. PKC has been implicated in regulating Fas-associated protein with death domain (FADD), an important adaptor protein involved in regulating death receptor-mediated apoptosis. FADD also plays an important role in non-apoptosis processes. The functional interaction of PKC and FADD in non-apoptotic processes has not been examined. In this study, we show that FADD is involved in maintaining the phosphorylation of the turn motif and hydrophobic motif in the activated conventional PKC (cPKC). A phosphoryl-mimicking mutation (S191D) in FADD (FADD-D) abolished the function of FADD in the facilitation of the turn motif and hydrophobic motif dephosphorylation of cPKC, suggesting that phosphorylation of Ser-191 negatively regulates FADD. We show that FADD interacts with PP2A, which is a major phosphatase involved in dephosphorylation of activated cPKC and FADD deficiency abolished PP2A mediated dephosphorylation of cPKC. We show that FADD deficiency leads to increased stability and activity of cPKC, which, in turn, promotes cytoskeleton reorganization, cell motility, and chemotaxis. Collectively, these results reveal a novel function of FADD in a non-apoptotic process by modulating cPKC dephosphorylation, stability, and signaling termination.

Interleukin-25 as a candidate gene in immunogene therapy of pancreatic cancer

Abstract Pancreatic cancer is an aggressive type of malignancy. Generally, its promotion and progression are due to the disturbance in some cellular and molecular mechanisms, particularly deregulation of programmed cell death or apoptosis. Certainly, loss of counterbalance between generation and cell death will lead to the tumoural mass development in various tissues, such as pancreas. From earlier decades, a variety of treatments as chemotherapy, radiation and surgery have been employed in order to pancreatic cancer remedial purposes, which are associated with infirm medical outcome. Therefore, with regard to the anti-cancerous and pro-apoptotic properties of the cytokine interleukin-25 (IL-25), the authors intend to anticipate a new therapeutic strategy. IL-25 – known as IL-17E – is one of the major factors responsible for death receptor-mediated pathway. Broadly, its receptor is located on multifarious cells such as pancreatic cancerous cells. We proposed to select four groups of C57BL/6 mice, for IL-25 gene inoculation, via mesenchymal stem cells as a vector, in order to increase exposure of cancerous cells to IL-25. IL-25 could activate apoptotic mediators including tumour necrosis factor receptor associated factor (TRAF6), Fas-Associated protein with Death Domain (FADD) and caspases consequently. Probably this method will be efficient in pancreatic malignancy treatment, via inducing apoptosis in pancreatic tumoural cells.

RNASET2 — An autoantigen in anaplastic large cell lymphoma identified by protein array analysis

Characterising tumour-associated antigens (TAAs) not only represents an important approach to the identification of new diagnostic/prognostic markers, but can also provide information on disease processes and additional potential therapeutic targets. Preliminary screening of a protein macroarray, containing more than 12,000 different proteins, with sera from anaplastic lymphoma kinase (ALK)-negative and ALK-positive anaplastic large cell lymphoma (ALCL) patients identified ribonuclease and tumour suppressor protein Ribonuclease T2 (RNASET2), phosphatase lipid phosphate phosphatase-related protein type 3 (LPPR3) and apoptotic adaptor molecule Fas-associating protein (FADD) as ALK-negative ALCL-associated TAAs. Further validation of these observations was confirmed using the ALCL sera in reverse ELISAs. The circulating anti-RNASET2 autoantibodies present in ALCL patients' sera also recognised eukaryotically expressed RNASET2 protein. RNASET2 expression was then investigated in normal tissues and in lymphomas to explore its clinical potential. RNASET2 protein and mRNA levels showed highest expression in the spleen, leucocytes and pancreas. RNASET2 protein expression was not restricted to ALK-negative ALCL (81%), being expressed in ALK-positive ALCL (65%) as well as in a number of other lymphomas. The immunological recognition of RNASET2, its expression in ALCL and other lymphomas together with its known tumourigenic properties suggest that further studies on this autoantigen are warranted.

Fas Ligand-Fas Signaling Participates in Light-Induced Apoptotic Death in Photoreceptor Cells

We investigated the function of Fas in photoreceptors. Postmortem human eyes and mouse-derived photoreceptor cells (661W) were examined for Fas expression by in situ hybridization and immunofluorescence. 661W cells were treated with FasL or Fas agonistic antibody, or exposed to light with/without pharmacological manipulation of Fas signaling, followed by apoptosis detection by TUNEL, immunofluorescence and fluorescence activated cell scanning (FACS). Fractionated cellular extracts were used to detect protein expression or protein phosphorylation after immunoprecipitation by Western blot. Fas was expressed in the photoreceptor layer of human retina. Fas and a cleaved form of FasL were found on the cell surface of 661W cells. Treatment with FasL or Fas agonistic antibody induced apoptosis in 661W cells. Blocking the activity of FasL or administration of caspase-8 inhibitor z-IETD inhibited light-induced apoptosis. However, it simultaneously caused induction of necroptosis, which could be blocked by the receptor-interacting protein 1 (RIP1) inhibitor, necrostatin-1. Light exposure in the presence of z-IETD caused hyper-phosphorylation of RIP1. Light exposure did not elevate the expression of Fas, FasL, or the Fas-associated death domain adaptor protein (FADD). Cells or conditioned medium after light exposure induced apoptosis in dark-adapted cells, which could be attenuated by blockade of Fas. Fas has a pro-apoptotic role in photoreceptors. Under light stress, soluble and membrane-bound FasL can bind to Fas, inducing apoptosis via a paracrine mechanism. Although blocking Fas signaling inhibits apoptosis, it does not improve the overall photoreceptor survival due to a compensatory activation of necroptosis. Hence, prevention of photoreceptor loss from retinal photo-oxidative stress should target Fas and RIP1.

Effects of PACAP on Intracellular Signaling Pathways in Human Retinal Pigment Epithelial Cells Exposed to Oxidative Stress

The integrity of retinal pigment epithelial cells is critical for photoreceptor survival and vision. Pituitary adenylate cyclase activating polypeptide (PACAP) exerts retinoprotective effects against several types of injuries in vivo, including optic nerve transection, retinal ischemia, excitotoxic injuries, UVA-induced lesion, and diabetic retinopathy. In a recent study, we have proven that PACAP is also protective in oxidative stress-induced injury in human pigment epithelial cells (ARPE-19 cells). The aim of the present study was to investigate the possible mechanisms of this protection. ARPE cells were exposed to a 24-h hydrogen peroxide treatment. Expressions of kinases and apoptotic markers were studied by complex array kits and Western blot. Oxidative stress induced the activation of several apoptotic markers, including Bad, Bax, HIF-1α, several heat shock proteins, TNF-related apoptosis-inducing ligand, and Fas-associated protein with death domain, while PACAP treatment decreased them. The changes in the expression of MAP kinases showed that PACAP activated the protective ERK1/2 and downstream CREB, and decreased the activation of the pro-apoptotic p38MAPK and c-Jun N-terminal kinase, an effect opposite to that observed with only oxidative stress. Furthermore, PACAP increased the activation of the protective Akt pathway. In addition, the effects of oxidative stress on several other signaling molecules were counteracted by PACAP treatment (Chk2, Yes, Lyn, paxillin, p53, PLC, STAT4, RSK). These play a role in cell death, cell cycle, inflammation, adhesion, differentiation and proliferation. In summary, PACAP, acting at several levels, influences the balance between pro- and anti-apoptotic factors in favor of anti-apoptosis, thereby providing protection in oxidative stress-induced injury of human retinal pigment epithelial cells.

Abstract 4965: Oncoprotein PMLRARα directly suppresses Fas-mediated apoptosis through forming an apoptotic inhibitory complex with c-FLIP in vivo

Abstract Objective: Many genotoxic therapies, including radiation, depend on intact Fas signaling to eradicate cancer cells. Defective Fas signaling is an important cause of cancer resistance to therapy. Restoring Fas apoptosis or sensitizing cancer cells to Fas-mediated apoptosis would improve the efficacy of many cancer therapies. To elucidate a role for specific regulators of Fas signaling in cancer cells, we sought to identify potential modulators of Fas expressed in cancers and target them to selectively sensitize cancer cells to Fas-mediated apoptosis as a component of chemotherapy. Methods: Liquid chromatography tandem mass spectrometry was used to identify Fas-associated proteins; co-immunoprecipitation and Western blot were used to detect interactions of PMLRARα, PML, c-FLIP and Fas, and to examine the components of death-inducing signaling complex (DISC) and caspase-8 cleavage. Deletional mutagenesis was used to map the interaction domains. PML shRNA lentivirus and As2O3 were used to knock down PML and PMLRARα. Flow cytometry analysis of propidium iodide- and Annexin-V-stained cells was used to detect apoptosis. Mice were transfected with PMLRARα, monitored for survival, and tissues were analyzed for apoptosis by staining for cleaved caspase-3 and TUNEL. Results: We identified promyelocytic leukemia protein (PML) as a Fas-interacting protein using mass spectrometry analysis. The function of PML is blocked by its dominant-negative form PMLRARα. We found PMLRARα interaction with Fas in acute promyelocytic leukemia (APL)-derived cells and APL primary cells, and PML-Fas complexes in normal tissues. Binding of PMLRARα to Fas was mapped to the B-box domain of PML moiety and death domain of Fas. PMLRARα blockage of Fas apoptosis was demonstrated in U937/PR9 cells, human APL cells and transgenic mouse APL cells, in which PMLRARα recruited c-FLIPL/S and excluded procaspase-8 from Fas death signaling complex. PMLRARα expression in mice protected the mice against a lethal dose of agonistic anti-Fas antibody (P<.001) and the protected tissues contained Fas-PMLRARα-cFLIP complexes. Livers from PMLRARα-transfected mice contained fewer cleaved caspase-3 positive/apoptotic cells when compared with control vector-transfected mice. Conclusions: PMLRARα binds to Fas and blocks Fas-mediated apoptosis in APL by forming an apoptotic inhibitory complex with c-FLIP. These data suggest that PMLRARα is a cancer specific Fas-binding inhibitor of Fas-mediated apoptosis and thus, can contribute to cancer development and resistance to therapy. The newly discovered PMLRARα-Fas and PML-Fas complexes can be sites for modulation of apoptosis. By neutralizing the effect of death receptor inhibitors, such as PMLRARα, we can improve responses to many chemotherapeutic treatments that depend on activation of death receptors for effective elimination of cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4965. doi:1538-7445.AM2012-4965

Cytotoxicity of dioscin in human gastric carcinoma cells through death receptor and mitochondrial pathways

In the present study, the antiproliferative effect of dioscin on human gastric carcinoma SGC-7901 cells was confirmed by 3-(4, 5-dimethylthiahiazo-zyl)-2, 5-dip-henytetrazolium bromide and flow cytometry assays. Through acridine orange-ethidium bromide double fluorescent staining, apoptotic morphology of the cells was observed. Radioimmunoassays showed that the tumor necrosis factor (TNF)-α concentration in cells treated with dioscin significantly increased compared with untreated cells. Several proteins and mRNA related to the mitochondrial and death receptor pathways were investigated. We found that the expression of Bid, bcl-2 and bcl-xl was markedly downregulated, and the expression of Bak and Bax was upregulated. In addition, cytochrome c was released from the mitochondria into the cytosol, which indicates activation of the mitrochondrial pathway by dioscin. Furthermore, upregulation of Fas, FasL (Fas ligand), TNF-α, TNF receptor-1, TNF receptor-associated factor 1 and Fas-associated protein with death domain demonstrated involvement of the death receptor pathway. Increased mRNA expression of p53 was also found in dioscin-treated SGC-7901 cells, and the activation of caspase-3 and -8 was also observed. Consequently, this study clarifies the mechanism underlying the anticancer effect of dioscin, and also indicates that dioscin may be a potential drug treatment for human gastric cancer.

Cyclin D1 and FADD as Biomarkers in Head and Neck Squamous Cell Carcinoma

Cyclin D1 and FADD (Fas-associated protein with death domain) regulate the cell cycle and apoptosis, respectively, and are located on chromosome 11q13, which is frequently amplified in head and neck squamous cell carcinoma (HNSCC). This study evaluates these proteins as predictors of clinical outcomes for HNSCC. Historical cohort study. Academic tertiary care center. Two hundred twenty-two patients with upper aerodigestive HNSCC. Patients with tumors that were strongly positive for cyclin D1 and FADD had reduced overall (OS; P = .003 and P < .001), disease-specific (DSS; P = .039 and P < .001), and disease-free (DFS; P = .026 and P < .001) survival, respectively. Together, the 2 markers effectively stratified OS (P < .001), DSS (P < .001), and DFS (P = .002). Strong FADD staining correlated with greater alcohol consumption and varied significantly with primary tumor site: 56% of hypopharynx tumors expressed high levels of FADD but only 7% of glottis tumors. Using Cox regression analysis, FADD and N stage were significant independent predictors of DSS and DFS, whereas cyclin D1, FADD, and N stage were independently significant for OS. Cyclin D1 and FADD may have utility as predictors of long-term outcomes for patients with HNSCC. Further study is needed to determine if these proteins predict response to different treatment approaches or assist in selecting patients for multimodality therapy.

Occludin is required for apoptosis when claudin–claudin interactions are disrupted

Disruption of tight junctions is often seen during pathogen infection, inflammation, and tumor progression. Mislocalization of the tight junction proteins occludin and claudin in mammary epithelial monolayers leads to apoptosis through the extrinsic pathway. To further investigate the mechanism of this response, a normal mammary epithelial cell line (EpH4) as well as primary mammary epithelial cells were treated with a claudin-disrupting mimic peptide, DFYNP (aspartic acid–phenylalanine–tyrosine–asparagine–proline). Using fluorescent indicators, we found that caspase-3 activation, resulting from treatment with DFYNP, was restricted to EpH4 and primary mammary epithelial cells with mislocalized claudin-4. Mislocalized claudin-4 and occludin were colocalized in non-junctional puncta, and both molecules were found in the death-inducing signaling complex (DISC) where they colocalized with Fas, fas-associated protein with death domain (FADD), active caspase-8 and caspase-3 at distinct apical domains. Importantly, caspase-3 activation was totally repressed in primary mammary epithelial cells from occludin null mice. Thus, the apoptotic response appears to be initiated by the movement of occludin to the DISC suggesting that this molecule has signaling properties that initiate cell death when its tight junction location is disrupted.

Ubiquitination and degradation of the FADD adaptor protein regulate death receptor-mediated apoptosis and necroptosis

Fas-associated protein with death domain (FADD) is a pivotal component of death receptor-mediated extrinsic apoptosis and necroptosis. Here we show that FADD is regulated by Makorin Ring Finger Protein 1 (MKRN1) E3 ligase-mediated ubiquitination and proteasomal degradation. MKRN1 knockdown results in FADD protein stabilization and formation of the rapid death-inducing signalling complex, which causes hypersensitivity to extrinsic apoptosis by facilitating caspase-8 and caspase-3 cleavage in response to death signals. We also show that MKRN1 and FADD are involved in the regulation of necrosome formation and necroptosis upon caspase inhibition. Downregulation of MKRN1 results in severe defects of tumour growth upon tumour necrosis factor-related apoptosis-inducing ligand treatment in a xenograft model using MDA-MB-231 breast cancer cells. Suppression of tumour growth by MKRN1 depletion is relieved by simultaneous FADD knockdown. Our data reveal a novel mechanism by which fas-associated protein with death domain is regulated via an ubiquitination-induced degradation pathway.

Optimization of FRET algorithms for sensitized-emission FRET detection

Sensitized-emission fluorescence resonance energy transfer (FRET) detection method based on three-channel fluorescence microscopy is widely used. Several FRET algorithms, such as NFRET, FRETN, FR, FRETR, and FC/Df, are developed recently to quantitatively gauge and compare FRET signals between different experimental groups. However, the algorithms are difficult to choose and interpret. In this letter, we optimize the suitable yellow fluorescent protein (YFP) to cyan fluorescent protein (CFP) concentration ratio range for the above FRET algorithms. We also test the effect of YFP-to-CFP concentration ratio on the calculated energy transfer efficiency E and use the optimized FRET algorithms in the analysis of fas-associated protein with death domain (FADD) self-association directly in living cells.

Common variation in genes related to immune response and risk of childhood leukemia

An abnormal immune response to common infection(s) may be a plausible etiological mechanism in childhood leukemia. We investigated whether 931 tagging single nucleotide polymorphisms (SNPs) selected in gene regions related to immune response are associated with childhood leukemia susceptibility in a hospital-based case-control study (63 cases and 148 controls) conducted among Korean children. The AT or TT genotype of rs7939734 in Fas-associated protein with death domain (FADD) was associated with increased risk of childhood leukemia compared with the AA genotype (odds ratio [OR] = 2.26, 95% confidence interval [95% CI] = 1.20-4.25, p(trend) = 0.0007, min p = 0.002, false discovery rate [FDR] p = 0.17). The CG or GG genotype of rs2301696 in TRPM5 was associated with decreased risk of childhood leukemia compared with the CC genotype (OR = 0.30, 95% CI = 0.14-0.63, p(trend) = 0.002, min p = 0.004, FDR p = 0.17). Our findings suggest that genetic polymorphisms in immune response genes might play a role in childhood leukemia development with limited biologic evidence.

Hsp27 silencing coordinately inhibits proliferation and promotes Fas-induced apoptosis by regulating the PEA-15 molecular switch

Heat shock protein 27 (Hsp27) is emerging as a promising therapeutic target for treatment of various cancers. Although the role of Hsp27 in protection from stress-induced intrinsic cell death has been relatively well studied, its role in Fas (death domain containing member of the tumor necrosis factor receptor superfamily)-induced apoptosis and cell proliferation remains underappreciated. Here, we show that Hsp27 silencing induces dual coordinated effects, resulting in inhibition of cell proliferation and sensitization of cells to Fas-induced apoptosis through regulation of PEA-15 (15-kDa phospho-enriched protein in astrocytes). We demonstrate that Hsp27 silencing suppresses proliferation by causing PEA-15 to bind and sequester extracellular signal-regulated kinase (ERK), resulting in reduced translocation of ERK to the nucleus. Concurrently, Hsp27 silencing promotes Fas-induced apoptosis by inducing PEA-15 to release Fas-associating protein with a novel death domain (FADD), thus allowing FADD to participate in death receptor signaling. Conversely, Hsp27 overexpression promotes cell proliferation and suppresses Fas-induced apoptosis. Furthermore, we show that Hsp27 regulation of PEA-15 activity occurs in an Akt-dependent manner. Significantly, Hsp27 silencing in a panel of phosphatase and tensin homolog on chromosome 10 (PTEN) wild-type or null cell lines, and in LNCaP cells that inducibly express PTEN, resulted in selective growth inhibition of PTEN-deficient cancer cells. These data identify a dual coordinated role of Hsp27 in cell proliferation and Fas-induced apoptosis via Akt and PEA-15, and indicate that improved clinical responses to Hsp27-targeted therapy may be achieved by stratifying patient populations based on tumor PTEN expression.

PML and PMLRARα Interact with Fas to Regulate Fas-Mediated Apoptosis In Vivo

Abstract 2451 Background:Altered Fas signaling leads to resistance to various anticancer therapies. The presence of at least low level expression of Fas is required for the transformed phenotype of many cells. In order for Fas to offer this complex regulation and to prevent inadvertent Fas activation, we propose that Fas signaling is subjected to tight regulation and this regulation could produce resistance to apoptosis of cancer cells. Methods:Cell lines NB4 (PMLRARα positive), HL60, U937/PR9 (PMLRARα expression driven by metalothionine promoter), or transfected HEK293 cells were collected and cell extracts were prepared for immunoprecipitation and Western blot analysis with the indicated antibodies. Cellular fractionation was performed using the nuclear/cytosol fractionation kit (BioVision, Mountain View, CA), according to the manufacturer’s instructions. We expressed PMLRARα in C57B6 female mice by transfection of PMLRARα plasmid or empty-vector plasmid (12 mice per group) by tail vein inoculation using a hydrodynamic transfection method. Twenty-four hours after transfection, mice were challenged intraperitoneally with 2 μg/g mouse weight of agonistic Fas antibody Jo2, and monitored for survival. Liver tissues were stained with TUNEL assay and antibodies targeting apoptosis proteins. Differences between two groups were assessed using the 2-tailed student’s t test and a P value < 0.05 was considered to be statistically significant. Results:In this study, we identified, by mass spectrometry analysis of Fas-associated proteins, the proapoptotic promyelocytic leukemia protein (PML) as a Fas-interacting protein. PML is a ubiquitously expressed tumor suppressor, which is downregulated or mutated in over 50% of all cancers. PML promotes apoptosis especially under conditions of cell stress. The function of PML is blocked by its dominant-negative form promyelocytic leukemia - retinoic acid receptor α (PMLRARα). Our focus on PMLRARα showed that it interacts with Fas in acute promyelocytic leukemia-derived cell lines and APL primary cells. Because PMLRARα is considered to be a nuclear transcription factor, we fractionated cell compartment proteins and identified PMLRAR α-Fas complexes present only in the cytoplasmic fraction. Binding of PML to Fas was mapped to the B-box domain of PML and death domain of Fas. PMLRARα blockage of apoptosis was shown in U937/PR9 and NB4 cells, in which PMLRARα recruited c-FLIPL/S and excluded procaspase 8 from the Fas death-inducing signaling complex. PMLRARα expression in mice protected the mice against a lethal dose of agonistic anti-Fas antibody (P<.001). The protected mice tissues contained Fas-PMLRARα-cFLIP complexes. Knockdown of PML in 293 cells compared to non-targeted knockdown control cells showed lower rates of CH-11-induced apoptosis, suggesting a facilitating role of PML in Fas mediated apoptosis. To examine the prevalence of PML-Fas complexes in non cancer tissues, we screened over 6 mouse tissues and all contained PML-Fas complexes. Conclusion:Together, PMLRARα binds to Fas and blocks Fas-mediated apoptosis in APL through the accumulation of c-FLIP- Fas complexes. Furthermore, the common expression of PML-Fas complexes suggests Fas signaling is routinely regulated in the cytoplasm by PML, but susceptible to the blocking effects of PMLRARα in cancer. Disclosures:Karp:Schering Merck: Research Funding.

TNF-induced necroptosis in L929 cells is tightly regulated by multiple TNFR1 complex I and II members

TNF receptor 1 signaling induces NF-κB activation and necroptosis in L929 cells. We previously reported that cellular inhibitor of apoptosis protein-mediated receptor-interacting protein 1 (RIP1) ubiquitination acts as a cytoprotective mechanism, whereas knockdown of cylindromatosis, a RIP1-deubiquitinating enzyme, protects against tumor necrosis factor (TNF)-induced necroptosis. We report here that RIP1 is a crucial mediator of canonical NF-κB activation in L929 cells, therefore questioning the relative cytoprotective contribution of RIP1 ubiquitination versus canonical NF-κB activation. We found that attenuated NF-κB activation has no impact on TNF-induced necroptosis. However, we identified A20 and linear ubiquitin chain assembly complex as negative regulators of necroptosis. Unexpectedly, and in contrast to RIP3, we also found that knockdown of RIP1 did not block TNF cytotoxicity. Cell death typing revealed that RIP1-depleted cells switch from necroptotic to apoptotic death, indicating that RIP1 can also suppress apoptosis in L929 cells. Inversely, we observed that Fas-associated protein via a death domain, cellular FLICE inhibitory protein and caspase-8, which are all involved in the initiation of apoptosis, counteract necroptosis induction. Finally, we also report RIP1-independent but RIP3-mediated necroptosis in the context of TNF signaling in particular conditions.

FADD cleavage by NK cell granzyme M enhances its self-association to facilitate procaspase-8 recruitment for auto-processing leading to caspase cascade

Granzyme M (GzmM), an orphan Gzm, is constitutively and abundantly expressed in innate effector natural killer cells. We previously demonstrated that GzmM induces caspase (casp)-dependent apoptosis and cytochrome c release from mitochondria. We also resolved the crystal structure for GzmM and generated its specific inhibitor. However, how GzmM causes casp activation has not been defined. Here we found that casp-8 is an initiator caspase in GzmM-induced casp cascade, which causes other casp activation and Bid cleavage. GzmM does not directly cleave procaspase-3 and Bid, whose processing is casp dependent. Casp-8 knockdown or deficient cells attenuate or abolish GzmM-induced proteolysis of procaspase-3 and Bid. Extrinsic death receptor pathway adaptor Fas-associated protein with death domain (FADD) contributes to GzmM-induced casp-8 activation. GzmM specifically cleaves FADD after Met 196 to generate truncated FADD (tFADD) that enhances its self-association for oligomerization. The oligomerized tFADD facilitates procaspase-8 recruitment to promote its auto-processing leading to casp activation cascade. FADD-deficient cells abrogate GzmM-induced activation of casp-8 and apoptosis as well as significantly inhibit lymphokine-activated killer cell-mediated cytotoxicity. FADD processing by GzmM can potentiate killing efficacy against tumor cells and intracellular pathogens.

Human cell-death-inducing DFF45-like effector C induces apoptosis via caspase-8

Human cell-death-inducing DNA-fragmentation-factor (DFF45)-like effector C (CIDEC) is a potent apoptotic inducer. Previous studies have indicated that the Fat-specific protein 27 (Fsp27), a mouse homolog of CIDEC, induces apoptosis via caspase-3, -7, and -9 and triggers the release of cytochrome c from mitochondria, which implies that the mitochondrial pathway is involved in Fsp27-induced apoptosis. In the current study, we found that CIDEC-induced apoptosis was mediated by caspase-8. The caspase inhibitor assay showed that CIDEC-induced apoptosis was dramatically reduced in the presence of the general caspase inhibitor, the caspase-3 inhibitor, and the caspase-8 inhibitor, whereas the caspase-9 inhibitor only weakly inhibited CIDEC-induced apoptosis. These results confirmed that the activation of caspase-3 and caspase-8 were involved in CIDEC-induced apoptosis. Moreover, in caspase-3- or caspase-8-deficient cells, CIDEC-induced apoptosis were dramatically decreased, which demonstrated that CIDEC-induced apoptosis might require the activation of caspase-3 and caspase-8. Because caspase-8 in general is a key effecter of death-receptor pathway and activated by Fas-Associated protein with Death Domain (FADD), we examined whether FADD was involved in CIDEC-induced apoptosis. Our results demonstrated that CIDEC-induced apoptosis was independent of FADD, suggesting that CIDEC-induced apoptosis might be in a death-receptor-independent, caspase-8-dependent manner. It was also found that the region of amino acid 168-200 in carboxyl domain of CIDEC was critical for its crucial pro-apoptotic function.

Loss of Caspase-8 Protects Mice Against Inflammation-Related Hepatocarcinogenesis but Induces Non-Apoptotic Liver Injury

Disruption of the nuclear factor-κB (NF-κB) essential modulator (NEMO) in hepatocytes of mice (NEMO(Δhepa) mice) results in spontaneous liver apoptosis and chronic liver disease involving inflammation, steatosis, fibrosis, and development of hepatocellular carcinoma. Activation of caspase-8 (Casp8) initiates death receptor-mediated apoptosis. We investigated the pathogenic role of this protease in NEMO(Δhepa) mice or after induction of acute liver injury. We created mice with conditional deletion of Casp8 in hepatocytes (Casp8(Δhepa)) and Casp8(Δhepa)NEMO(Δhepa) double knockout mice. Acute liver injury was induced by Fas-activating antibodies, lipopolysaccharides, or concanavalin A. Spontaneous hepatocarcinogenesis was monitored by magnetic resonance imaging. Hepatocyte-specific deletion of Casp8 protected mice from induction of apoptosis and liver injury by Fas or lipopolysaccharides but increased necrotic damage and reduced survival times of mice given concanavalin A. Casp8(Δhepa)NEMO(Δhepa) mice were protected against steatosis and hepatocarcinogenesis but had a separate, spontaneous phenotype that included massive liver necrosis, cholestasis, and biliary lesions. The common mechanism by which inactivation of Casp8 induces liver necrosis in both injury models involves the formation of protein complexes that included the adaptor protein Fas-associated protein with death domain and the kinases receptor-interacting protein (RIP) 1 and RIP3-these have been shown to be required for programmed necrosis. We demonstrated that hepatic RIP1 was proteolytically cleaved by Casp8, whereas Casp8 inhibition resulted in accumulation of RIP complexes and subsequent liver necrosis. Inhibition of Casp8 protects mice from hepatocarcinogenesis following chronic liver injury mediated by apoptosis of hepatocytes but can activate RIP-mediated necrosis in an inflammatory environment.

Interferon-γ Exacerbates Dry Eye–Induced Apoptosis in Conjunctiva through Dual Apoptotic Pathways

To investigate the role of interferon (IFN)-γ in dry eye-associated conjunctival apoptosis. Desiccating stress (DS) was created in C57BL/6 (B6) and C57BL/6 IFN-γ-knockout (B6γKO) mice. A separate group of mice of both strains also received subconjunctival injections of exogenous IFN-γ or vehicle control (BSA) at days 0, +2, and +4 after DS. Immunoreactivity to active (Ac)-caspase-3, -8, and -9 and terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) were evaluated in cryosections. Goblet cell apoptosis was assessed by MUC5AC and TUNEL double staining. Levels of caspase-3, -8, -9, Fas, and Fas-associated protein with Death Domain (FADD) mRNA in conjunctiva were measured by real-time PCR. The activity of caspase-3, -8, or -9 was measured using fluorometric assay. Increased Ac-caspase-3 and -8 and TUNEL immunoreactivity were noted in conjunctival epithelia in B6 mice compared with B6γKO mice after DS, and exogenous IFN-γ administration further increased these parameters. DS-induced conjunctival apoptosis was greatest in the goblet cell area and was accompanied by a decrease in MUC5AC expression in the B6 and B6-IFN-γ-injected groups compared with the B6γKO and B6-BSA-injected groups. B6γKO mice were resistant to DS-induced apoptosis; however, B6γKO receiving IFN-γ yielded results similar to those for B6 wild-type. Caspase-9 production and activity were not increased with DS in B6 or B6γKO mice; however, the administration of IFN-γ significantly increased caspase-9 production and activity in both strains compared with vehicle-injected mice. IFN-γ plays a pivotal role in exacerbating conjunctival apoptosis through dual apoptotic pathways with DS.