Non-apoptotic signaling pathways activated by soluble Fas ligand in serum-starved human fibroblasts. Mitogen-activated protein kinases and NF-kappaB-dependent gene expression

Effects of DNA Origami-Based Nanoagent Design on Apoptosis Induction in a Large 3D Cancer Spheroid Model

DNA origami offers highly accurate control over shape and addressability on the nanoscale. This precise control makes it highly valuable in various fields, particularly precision nanotherapeutics. For cancer treatment, the extrinsic activation of programmed cell death by Fas receptor (FasR)/CD95-based nanoagents is a promising, minimally invasive strategy. However, treating large, solid tumors poses challenges for the design of DNA origami-based therapeutics, including drug distribution and altered cellular behavior. Here, these challenges are addressed by establishing design principles for nanoagents and testing them in a 3D cancer spheroid model. First, the ability of DNA origami nanostructures are assessed to penetrate large cancer spheroids, finding that penetration is influenced by the DNA origami size rather than its structural flexibility. Second, the capability of FasL-DNA origami-based nanoagents are evaluated to induce apoptosis in cancer spheroids, representing a more biologically relevant environment, compared to 2D studies. It is found that apoptosis induction is primarily determined by the FasL attachment strategy rather than the underlying DNA origami structure. The most effective nanoagents constructed in this study halted spheroid growth and eradicated all cancer cells within the spheroids. This study offers important insights into critical design considerations for DNA-based therapeutics for complex cellular environments, advancing DNA origami nanotherapeutic development.

Trichinella spiralis excretory/secretory proteins mediated larval invasion via inducing gut epithelial apoptosis and barrier disruption

BACKGROUND

Intestinal larva invasion is a crucial step of Trichinella spiralis infection. Intestinal infective larvae (IIL) and their excretory/secretory proteins (ESP) interact with gut epithelium, which often results in gut epithelium barrier injuries. Previous studies showed when T. spiralis invaded intestinal epithelium cells, the IIL ESP disrupted the tight junctions (TJs) of Caco-2 monolayer, but the mechanism is not clear. The IIL ESP might cause gut epithelial apoptosis, weaken the gut barrier and aid the larval invasion. The aim of this study was to investigate whether T. spiralis IIL ESP participate in enterocyte apoptosis and disrupt gut epithelial barrier to promote the larval invasion.

METHODOLOGY/PRINCIPAL FINDINGS

Cell viability was assessed by CCK-8 assay and the results showed that 200 μg/ml of IIL ESP incubated with Caco-2 cells for 18 h inhibited the Caco-2 cell viability. The results of trans-epithelial electrical resistance (TEER) and FITC-dextran showed that IIL ESP decreased the TEER, increased FITC-dextran flux in Caco-2 monolayer. qPCR, Western blot and immunofluorescence test (IFT) showed that IIL ESP decreased the mRNA and protein expression of TJs (ZO-1, E-cad, Occludin and Claudin-1). The IIL ESP-induced Caco-2 cell apoptosis was observed by DAPI, Hoechst 33358, TUNEL and Annexin V/PI staining. Besides, flow cytometry revealed an increasing apoptosis rate in Caco-2 cells after the IIL ESP treatment. qPCR and Western blot analysis indicated that IIL ESP activated caspases (Caspase 3, Caspase 9 and Caspase 8), up-regulated the pro-apoptotic factors (Bax and Cytochrome c) and down-regulated the anti-apoptosis molecule Bcl-2. Interestingly, pretreatment of Caco-2 cells with apoptosis inhibitor Z-VAD-FMK abrogated and recovered the barrier function of Caco-2 monolayer destroyed by IIL ESP. Furthermore, the Z-VAD-FMK pretreatment also impeded the in vitro larva invasion of Caco-2 monolayer.

CONCLUSIONS

T. spiralis IIL ESP induced gut epithelial apoptosis, reduced the TJs expression, damaged gut epithelial integrity and barrier function, and promoted larval invasion. These findings provided a basis of further understanding the interaction mechanism between T. spiralis and host gut epithelium, and they were valuable to the development new prevention and therapeutic strategy of early T. spiralis infection.

Study of alloferon, a novel immunomodulatory antimicrobial peptide (AMP), and its analogues

Antimicrobial peptides (AMPs) are widely distributed throughout the biosphere and represent a class of conserved peptide molecules with intrinsic antimicrobial properties. Their broad-spectrum antimicrobial activity and low risk to induce resistance have led to increased interest in AMPs as potential alternatives to traditional antibiotics. Among the AMPs, alloferon has been addressed due to its immunomodulatory properties that augment both innate and adaptive immune responses against various pathogens. Alloferon and its analogues have demonstrated pharmaceutical potential through their ability to enhance Natural Killer (NK) cell cytotoxicity and stimulate interferon (IFN) synthesis in both mouse and human models. Additionally, they have shown promise in augmenting antiviral and antitumor activities in mice. In this article, we provide a comprehensive review of the biological effects of alloferon and its analogues, incorporating our own research findings as well. These insights may contribute to a deeper understanding of the therapeutic potential of these novel AMPs.

A novel Fas ligand plays an important role in cell apoptosis of Crassostrea hongkongensis: molecular cloning, expression profiles and functional identification of ChFasL

Background

Apoptosis regulates normal development, homeostasis, immune tolerance and response to environmental stress by eliminating unwanted or diseased cells, and plays a key role in non-specific immunity of invertebrates. The exogenous pathway mediated by death receptors and death ligands is a very important pathway for cell apoptosis. Death ligands are mainly members of the tumour necrosis factor (TNF) family, of which FasL is an important member. The deep involvement of FasL in vertebrates cell apoptosis and immunity has been reported many times, but there is limited research on the FasL gene in shellfish, and its functional importance in oyster cell apoptosis and immunity remains unclear.

Methods

The full length of ChFasL was identified and cloned based on the genome of Crassostrea hongkongensis. Quantitative PCR was used to detect the relative expression of ChFasL in different developmental stages and tissues, as well as the changes of relative expression in hemocytes after bacterial infection. The expression position of ChFasL in HEK293T cells was also located by subcellular localization, and the effect of increased recombinant protein content on the activity of reporter genes p53 and p21 was studied by dual-fluorescence reporter gene. Finally, the changes of apoptosis rate in hemocytes after ChFasL silencing was identified by RNA interference technology.

Results

We identified a novel FasL gene from C. hongkongensis and named it ChFasL. We found that ChFasL has potential N-linked glycosylation site, a transmembrane domain and a TNF region, which was a typical characteristics of TNF family. ChFasL was expressed in all developmental stages of larvae and in all tissues of oysters. After stimulation by V. alginolyticus or S. haemolyticus, its relative expression in hemocytes increased significantly, suggesting that ChFasL was deeply engaged in the immune response process of C. hongkongensis to external microbial stimulation. The results of subcellular localization showed that ChFasL was mainly distributed in the cytoplasm of HEK293T cells. With the overexpression of the recombinant protein pcDNA3 1- ChFasL, the activity of p53 and p21 significantly increased, showing a positive regulatory effect. Moreover, after dsRNA successfully reduced the relative expression of ChFasL, the apoptosis rate of hemocytes was significantly lower than that the dsGFP group.

Conclusion

These results comprehensively confirmed the important role of ChFasL in the apoptosis process of C. hongkongensis, which provided the basis and premise for the in-depth understanding of the immune function of apoptosis in molluscs, and also contributed to the research on the pathogenic death mechanism and disease resistance breeding of marine bivalves.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

Current Pharmacogenetic Perspective on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Adverse drug reactions are a public health issue that draws widespread attention, especially for Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) which have high mortality and lack of efficacious treatment. Though T-cell-mediated HLA-interacted immune response has been extensively studied, our understanding of the mechanism is far from satisfactory. This review summarizes infection (virus, bacterial, and mycoplasma infection), an environmental risk factor, as a trigger for SJS/TEN. The mutations or polymorphisms of drug metabolic enzymes, transporters, receptors, the immune system genes, and T-cell-mediated apoptosis signaling pathways that contribute to SJS/TEN are discussed and summarized. Epigenetics, metabolites, and mobilization of regulatory T cells and tolerogenic myeloid precursors are emerged directions to study SJS/TEN. Ex vivo lymphocyte transformation test has been exploited to aid in identifying the causative drugs. Critical questions on the pathogenesis of SJS/TEN underlying gene polymorphisms and T cell cytotoxicity remain: why some of the patients carrying the risky genes tolerate the drug and do not develop SJS/TEN? What makes the skin and mucous membrane so special to be targeted? Do they relate to skin/mucous expression of transporters? What is the common machinery underlying different HLA-B alleles associated with SJS/TEN and common metabolites?

Soluble FAS ligand is not required for pancreatic islet inflammation or beta-cell destruction in non-obese diabetic mice

CD8⁺ T cells play a central role in beta-cell destruction in type 1 diabetes. CD8⁺ T cells use two main effector pathways to kill target cells, perforin plus granzymes and FAS ligand (FASL). We and others have established that in non-obese diabetic (NOD) mice, perforin is the dominant effector molecule by which autoreactive CD8⁺ T cells kill beta cells. However, blocking FASL pharmacologically was shown to protect NOD mice from diabetes, indicating that FASL may have some role. FASL can engage with its receptor FAS on target cells either as membrane bound or soluble FASL. It has been shown that membrane-bound FASL is required to stimulate FAS-induced apoptosis in target cells, whereas excessive soluble FASL can induce NF-κB-dependent gene expression and inflammation. Because islet inflammation is a feature of autoimmune diabetes, we tested whether soluble FASL could be important in disease pathogenesis independent of its cell death function. We generated NOD mice deficient in soluble FASL, while maintaining expression of membrane-bound FASL due to a mutation in the FASL sequence required for cleavage by metalloproteinase. NOD mice lacking soluble FASL had normal numbers of lymphocytes in their spleen and thymus. Soluble FASL deficient NOD mice had similar islet inflammation as wild-type NOD mice and were not protected from diabetes. Our data indicate that soluble FASL is not required in development of autoimmune diabetes.

Non-apoptotic Fas (CD95) Signaling on T Cells Regulates the Resolution of Th2-Mediated Inflammation

Fas (CD95/APO-1) and its ligand (FasL/CD95L) promote the resolution of type 2 lung inflammation and eosinophilia. We previously found that Fas-deficiency on T cells, but not eosinophils, delayed resolution of inflammation. However, Fas can signal both cell death and have a positive signaling function that can actually activate cells. In this study, we investigated whether Fas-induced death or Fas-activated signaling pathways promote resolution of allergic lung inflammation. By increasing T cell survival through two Fas-independent pathways, using Bim-deficient T cells or Bcl-xL overexpressing T cells, no differences in resolution of Th2-mediated inflammation was observed. Furthermore, Th2 cells were inherently resistant to Fas-mediated apoptosis and preferentially signaled through non-apoptotic pathways following FasL treatment. Utilizing Fas-mutant mice deficient in apoptotic but sufficient for non-apoptotic Fas signaling pathways, we demonstrate that non-apoptotic Fas signaling in T cells drives resolution of Th2-mediated airway inflammation. Our findings reveal a previously unknown role for non-apoptotic Fas signaling on Th2 cells in the induction of resolution of type 2 inflammation.

Interleukin-15 Is Associated with Severity and Mortality in Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

Early diagnosis and prognosis monitoring for Stevens-Johnson syndrome/toxic epidermal necrolysis (TEN) still remain a challenge. This study aims to explore any cytokine/chemokine with prognostic potential in Stevens-Johnson syndrome/TEN. Through screening a panel of 28 serological factors, IL-6, IL-8, IL-15, tumor necrosis factor-α, and granulysin were upregulated in patients with Stevens-Johnson syndrome/TEN and selected for the further validation in total 155 patients with Stevens-Johnson syndrome/TEN, including 77 from Taiwan and 78 from the Registry of Severe Cutaneous Adverse Reactions. Among these factors evaluated, the levels of IL-15 (r = 0.401; P < 0.001) and granulysin (r = 0.223; P = 0.026) were significantly correlated with the disease severity in 112 samples after excluding patients with insufficient data to calculate the score of TEN. In addition, IL-15 was also associated with mortality (P = 0.002; odds ratio, 1.09; 95% confidence interval, 1.03-1.14; P = 0.001; adjusted odds ratio, 1.10; 95% confidence interval, 1.04-1.16). Consistent results were obtained after the exclusion of Taiwanese patients with sepsis to rule out possible confounders. Moreover, IL-15 was shown to enhance cytotoxicity of cultured natural killer cells and blister cells from patients with TEN. Our findings highlight a usefulness of IL-15 in prognosis monitoring and therapeutic intervention of this devastating condition.

γδ T Cells and dendritic cells in refractory Lyme arthritis

Lyme disease is a multisystem infection transmitted by tick vectors with an incidence of up to 300,000 individuals/yr in the United States. The primary treatments are oral or i.v. antibiotics. Despite treatment, some individuals do not recover and have prolonged symptoms affecting multiple organs, including the nervous system and connective tissues. Inflammatory arthritis is a common symptom associated with Lyme pathology. In the past decades, γδ T cells have emerged as candidates that contribute to the transition from innate to adaptive responses. These cells are also differentially regulated within the synovia of patients affected by RLA. Here, we review and discuss potential cellular mechanisms involving γδ T cells and DCs in RLA. TLR signaling and antigen processing and presentation will be the key concepts that we review in aid of understanding the impact of γδ T cells in RLA.

Targeting the Fas/FasL system in Rheumatoid Arthritis therapy: Promising or risky?

Rheumatoid Arthritis (RA) is a chronic inflammatory disease affecting synovial joints. Tumor necrosis factor (TNF) α is a key component of RA pathogenesis and blocking this cytokine is the most common strategy to treat the disease. Though TNFα blockers are very efficient, one third of the RA patients are unresponsive or present side effects. Therefore, the development of novel therapeutic approaches is required. RA pathogenesis is characterized by the hyperplasia of the synovium, closely associated to the pseudo-tumoral expansion of fibroblast-like synoviocytes (FLS), which invade and destroy the joint structure. Hence, depletion of RA FLS has been proposed as an alternative therapeutic strategy. The TNF family member Fas ligand (FasL) was reported to trigger apoptosis in FLS of arthritic joints by binding to its receptor Fas and therefore suggested as a promising candidate for targeting the hyperplastic synovial tissue. However, this cytokine is pleiotropic and recent data from the literature indicate that Fas activation might have a disease-promoting role in RA by promoting cell proliferation. Therefore, a FasL-based therapy for RA requires careful evaluation before being applied. In this review we aim to overview what is known about the apoptotic and non-apoptotic effects of Fas/FasL system and discuss its relevance in RA.

Loss of c-REL but not NF-κB2 prevents autoimmune disease driven by FasL mutation

FASL/FAS signaling imposes a critical barrier against autoimmune disease and lymphadenopathy. Mutant mice unable to produce membrane-bound FASL (FasL(Δm/Δm)), a prerequisite for FAS-induced apoptosis, develop lymphadenopathy and systemic autoimmune disease with immune complex-mediated glomerulonephritis. Prior to disease onset, FasL(Δm/Δm) mice contain abnormally high numbers of leukocytes displaying activated and elevated NF-κB-regulated cytokine levels, indicating that NF-κB-dependent inflammation may be a key pathological driver in this multifaceted autoimmune disease. We tested this hypothesis by genetically impairing canonical or non-canonical NF-κB signaling in FasL(Δm/Δm) mice by deleting the c-Rel or NF-κB2 genes, respectively. Although the loss of NF-κB2 reduced the levels of inflammatory cytokines and autoantibodies, the impact on animal survival was minor due to substantially accelerated and exacerbated lymphoproliferative disease. In contrast, a marked increase in lifespan resulting from the loss of c-REL coincided with a striking reduction in classical parameters of autoimmune pathology, including the levels of cytokines and antinuclear autoantibodies. Notably, the decrease in regulatory T-cell numbers associated with loss of c-REL did not exacerbate autoimmunity in FasL(Δm/Δm)c-rel(-/-) mice. These findings indicate that selective inhibition of c-REL may be an attractive strategy for the treatment of autoimmune pathologies driven by defects in FASL/FAS signaling that would be expected to circumvent many of the complications caused by pan-NF-κB inhibition.

Cytotoxic proteins and therapeutic targets in severe cutaneous adverse reactions

Severe cutaneous adverse reactions (SCARs), such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN), are rare but life-threatening conditions induced mainly by a variety of drugs. Until now, an effective treatment for SJS/TEN still remains unavailable. Current studies have suggested that the pathobiology of drug-mediated SJS and TEN involves major histocompatibility class (MHC) I-restricted activation of cytotoxic T lymphocytes (CTLs) response. This CTLs response requires several cytotoxic signals or mediators, including granulysin, perforin/granzyme B, and Fas/Fas ligand, to trigger extensive keratinocyte death. In this article, we will discuss the cytotoxic mechanisms of severe cutaneous adverse reactions and their potential applications on therapeutics for this disease.

Life in the Fas lane: differential outcomes of Fas signaling

Fas, also known as CD95 or APO-1, is a member of the tumor necrosis factor/nerve growth factor superfamily. Although best characterized in terms of its apoptotic function, recent studies have identified several other cellular responses emanating from Fas. These responses include migration, invasion, inflammation, and proliferation. In this review, we focus on the diverse cellular outcomes of Fas signaling and the molecular switches identified to date that regulate its pro- and anti-apoptotic functions. Such switches occur at different levels of signal transduction, ranging from the receptor through to cross-talk with other signaling pathways. Factors identified to date including other extracellular signals, proteins recruited to the death-inducing signaling complex, and the availability of different intracellular components of signal transduction pathways. The success of therapeutically targeting Fas will require a better understanding of these pathways, as well as the regulatory mechanisms that determine cellular outcome following receptor activation.

A characterization of four B16 murine melanoma cell sublines molecular fingerprint and proliferation behavior

Background

One of the most popular and versatile model of murine melanoma is by inoculating B16 cells in the syngeneic C57BL6J mouse strain. A characterization of different B16 modified cell sub-lines will be of real practical interest. For this aim, modern analytical tools like surface enhanced Raman spectroscopy/scattering (SERS) and MTT were employed to characterize both chemical composition and proliferation behavior of the selected cells.

Methods

High quality SERS signal was recorded from each of the four types of B16 cell sub-lines: B164A5, B16GMCSF, B16FLT3, B16F10, in order to observe the differences between a parent cell line (B164A5) and other derived B16 cell sub-lines. Cells were incubated with silver nanoparticles of 50–100 nm diameter and the nanoparticles uptake inside the cells cytoplasm was proved by transmission electron microscopy (TEM) investigations. In order to characterize proliferation, growth curves of the four B16 cell lines, using different cell numbers and FCS concentration were obtained employing the MTT proliferation assay. For correlations doubling time were calculated.

Results

SERS bands allowed the identification inside the cells of the main bio-molecular components such as: proteins, nucleic acids, and lipids. An "on and off" SERS effect was constantly present, which may be explained in terms of the employed laser power, as well as the possible different orientations of the adsorbed species in the cells in respect to the Ag nanoparticles. MTT results showed that among the four tested cell sub-lines B16 F10 is the most proliferative and B164A5 has the lower growth capacity. Regarding B16FLT3 cells and B16GMCSF cells, they present proliferation ability in between with slight slower potency for B16GMCSF cells.

Conclusion

Molecular fingerprint and proliferation behavior of four B16 melanoma cell sub-lines were elucidated by associating SERS investigations with MTT proliferation assay.

TNFα induces survival through the FLIP-L-dependent activation of the MAPK/ERK pathway

Activation of tumor necrosis factor receptor-1 can trigger survival or apoptosis pathways. In many cellular models, including the neuronal cell model PC12, it has been demonstrated that inhibition of protein synthesis is sufficient to render cells sensitive to apoptosis induced by TNFα. The survival effect is linked to the translocation of the transcription factor nuclear factor-kappa B (NF-κB) to the nucleus and activation of survival-related genes such as FLICE-like inhibitory protein long form (FLIP-L) or IAPs. Nonetheless, we previously reported an NF-κB-independent contribution of Bcl-xL to cell survival after TNFα treatment. Here, we demonstrate that NF-κB-induced increase in FLIP-L expression levels is essential for mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) activation. We demonstrate that FLIP-L behaves as a Raf-1 activator through both protein-protein interaction and Raf-1 kinase activation, without the requirement of the classical Ras activation. Importantly, prevention of FLIP-L increase by NF-κB inhibition or knockdown of endogenous FLIP-L blocks MAPK/ERK activation after TNFα treatment. From a functional point of view, we show that inhibition of the MAPK/ERK pathway and the NF-κB pathway are equally relevant to render PC12 cells sensitive to cell death induced by TNFα. Apoptosis induced by TNFα under these conditions is dependent on jun nuclear kinase1/2 JNK1/2-dependent Bim upregulation. Therefore, we report a previously undescribed and essential role for MAPK/ERK activation by FLIP-L in the decision between cell survival and apoptosis upon TNFα stimulation.

Involvement of soluble Fas Ligand in germ cell apoptosis in testis of rats undergoing autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a model of chronic inflammation and infertility useful for studying immune and germ cell (GC) interactions. EAO is characterized by severe damage of seminiferous tubules (STs) with GCs that undergo apoptosis and sloughing. Based on previous results showing that Fas-Fas Ligand (L) system is one of the main mediators of apoptosis in EAO, in the present work we studied the involvement of Fas and the soluble form of FasL (sFasL) in GC death induction. EAO was induced in rats by immunization with testis homogenate and adjuvants; control (C) rats were injected with adjuvants; a group of non-immunized normal (N) rats was also studied. Activation of Fas employing an anti-Fas antibody decreased viability (trypan blue exclusion test) and induced apoptosis (TUNEL) of GCs from STs of N and EAO rats, an effect more pronounced on GCs from EAO STs. By Western blot we detected an increase in sFasL content in the testicular fluid of rats with severe EAO compared to N and C rats. By intratesticular injection of FasL conjugated to Strep-Tag molecule (FasL-Strep, BioTAGnology) and its immunofluorescent localization, we demonstrated that sFasL is able to enter the adluminal compartment of the STs. Moreover, FasL-Strep induced GC apoptosis in testicular fragments of N rats. By flow cytometry, we detected an increase in the number of membrane FasL-expressing CD4+ and CD8+ T cells in testis during EAO development but no expression of FasL by macrophages. Our results demonstrate that sFasL is locally produced in the chronically inflamed testis and that this molecule is able to enter the adluminal compartment of STs and induce apoptosis of Fas-bearing GCs.

Caspase-8 activity has an essential role in CD95/Fas-mediated MAPK activation

Stimulation of CD95/Fas/APO-1 results in the induction of both apoptotic and non-apoptotic signaling pathways. The processes regulating these two opposing pathways have not been thoroughly elucidated to date. In this study, using quantitative immunoblots, imaging, and mathematical modeling, we addressed the dynamics of the DED proteins of the death-inducing signaling complex (DISC), procaspase-8, and cellular FLICE inhibitory proteins (c-FLIPs) to the onset of CD95-mediated ERK1/2 and p38 mitogen-activated protein kinase (MAPK) activation. We found that CD95 DISC-induced caspase-8 activity is important for the initiation of ERK1/2 and p38 MAPK activation. The long c-FLIP isoform, c-FLIP(L), and the short c-FLIP isoform, c-FLIP(R), inhibited MAPK induction by blocking caspase-8 processing at the DISC. Furthermore, we built a mathematical model describing CD95 DISC-mediated MAPK activation and apoptosis. The model quantitatively defined the dynamics of DED proteins, procaspase-8, and c-FLIP, which lead to caspase-8 activation and induction of apoptotic and non-apoptotic signaling pathways. In conclusion, the combination of biochemical analysis with mathematical modeling provides evidence for an important role of caspase-8 in CD95-mediated activation of MAPKs, while c-FLIP exerts a regulatory function in this process.

Hematopoietic Fas deficiency does not affect experimental atherosclerotic lesion formation despite inducing a proatherogenic state

The Fas death receptor (CD95) is expressed on macrophages, smooth muscle cells, and T cells within atherosclerotic lesions. Given the dual roles of Fas in both apoptotic and nonapoptotic signaling, the aim of the present study was to test the effect of hematopoietic Fas deficiency on experimental atherosclerosis in low-density lipoprotein receptor-null mice (Ldlr(-/-)). Bone marrow from Fas(-/-) mice was used to reconstitute irradiated Ldlr(-/-) mice as a model for atherosclerosis. After 16 weeks on an 0.5% cholesterol diet, no differences were noted in brachiocephalic artery lesion size, cellularity, or vessel wall apoptosis. However, Ldlr(-/-) mice reconstituted with Fas(-/-) hematopoietic cells had elevated hyperlipidemia [80% increase, relative to wild-type (WT) controls; P < 0.001] and showed marked elevation of plasma levels of CXCL1/KC, CCL2/MCP-1, IL-6, IL-10, IL-12 subunit p70, and soluble Fas ligand (P < 0.01), as well as systemic microvascular inflammation. It was not possible to assess later stages of atherosclerosis because of increased mortality in Fas(-/-) bone marrow recipients. Our data indicate that hematopoietic Fas deficiency does not affect early atherosclerotic lesion development in Ldlr(-/-) mice.

Fas ligation and tumor necrosis factor α activation of murine astrocytes promote heat shock factor-1 activation and heat shock protein expression leading to chemokine induction and cell survival

Death-inducing ligands tumor necrosis factor alpha (TNFα) and Fas ligand (FasL) do not kill cultured astrocytes; instead they induce a variety of chemokines including macrophage-inflammatory protein-1α/CC chemokine ligand 3 (CCL3), monocyte chemoattractant protein-1 (CC CCL-2), macrophage-inflammatory protein-2/CXC chemokine ligand 2 (CXCL2, a murine homologue of interleukin 8), and interferon-induced protein of 10 kDa (CXCL10). Induction is enhanced by protein synthesis inhibition suggesting the existence of endogenous inhibitors. ERK, NF-κB, heat shock factor-1 (HSF-1) and heat shock proteins were examined for their possible roles in signal transduction. Inhibition of ERK activation by PD98059 partially inhibited expression of all but FasL-induced CXCL10. Although inhibition of NF-κB DNA binding inhibited chemokine induction, PD98059 did not inhibit TNFα-induced NF-κB DNA binding suggesting that ERK serves an NF-κB-independent pathway. Heat shock itself induced astrocytic chemokine expression; both TNFα and FasL induced HSF-1 DNA binding and Hsp72 production; and Hsp72-induced chemokine expression. Inhibition of either HSF-1 binding with quercetin or heat shock protein synthesis with KNK437 compromised chemokine induction without compromising cell survival. These data suggest that the induction of heat shock proteins via HSF-1 contribute to the TNFα- and FasL-induced expression of chemokines in astrocytes.

Insights into sepsis therapeutic design based on the apoptotic death pathway

Sepsis remains the leading cause of death in critically ill patients. A major problem contributing to sepsis-related high mortality is the lack of effective medical treatment. Thus, the key goal in critical care medicine is to develop novel therapeutic strategies that will impact favorably on septic patient outcome. While it is generally accepted that sepsis is an inflammatory state resulting from the systemic response to infection, apoptosis is implicated to be an important mechanism of the death of lymphocytes, gastrointestinal and lung epithelial cells, and vascular endothelial cells associated with the development of multiple organ failure in sepsis. The pivotal role of cell apoptosis is now highlighted by multiple studies demonstrating that prevention of cell apoptosis can improve survival in clinically relevant animal models of sepsis. In this review article, we address the scientific rationale for remedying apoptotic cell death in sepsis and propose that therapeutic efforts aimed at blocking cell signaling pathways leading to apoptosis may represent an attractive target for sepsis therapy.

The adaptor protein TRIP6 antagonizes Fas-induced apoptosis but promotes its effect on cell migration

The Fas/CD95 receptor mediates apoptosis but is also capable of triggering nonapoptotic signals. However, the mechanisms that selectively regulate these opposing effects are not yet fully understood. Here we demonstrate that the activation of Fas or stimulation with lysophosphatidic acid (LPA) induces cytoskeletal reorganization, leading to the association of Fas with actin stress fibers and the adaptor protein TRIP6. TRIP6 binds to the cytoplasmic juxtamembrane domain of Fas and interferes with the recruitment of FADD to Fas. Furthermore, through physical interactions with NF-κB p65, TRIP6 regulates nuclear translocation and the activation of NF-κB upon Fas activation or LPA stimulation. As a result, TRIP6 antagonizes Fas-induced apoptosis and further enhances the antiapoptotic effect of LPA in cells that express high levels of TRIP6. On the other hand, TRIP6 promotes Fas-mediated cell migration in apoptosis-resistant glioma cells. This effect is regulated via the Src-dependent phosphorylation of TRIP6 at Tyr-55. As TRIP6 is overexpressed in glioblastomas, this may have a significant impact on enhanced NF-κB activity, resistance to apoptosis, and Fas-mediated cell invasion in glioblastomas.

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.

p65 Negatively regulates transcription of the cyclin E gene

NF-kappaB family members play a pivotal role in many cellular and organismal functions, including the cell cycle. As an activator of cyclin D1 and p21(Waf1) genes, NF-kappaB has been regarded as a critical modulator of cell cycle. To study the involvement of NF-kappaB in G(1)/S phase regulation, the levels of selected transcriptional regulators were monitored following overexpression of NF-kappaB or its physiological induction by tumor necrosis factor-alpha. Cyclin E gene was identified as a major transcriptional target of NF-kappaB. Recruitment of NF-kappaB to the cyclin E promoter was correlated with the transrepression of cyclin E gene. Ligation-mediated PCR and micrococcal nuclease-Southern assays suggested the nucleosomal nature of this region while chromatin immunoprecipitation analysis confirmed the exchange of cofactors following tumor necrosis factor-alpha treatment or release from serum starvation. There was a progressive reduction in cyclin E transcription along with the accumulation of catalytically inactive cyclin E-cdk2 complexes and arrest of cells in G(1)/S-phase. Thus, our study clearly establishes NF-kappaB as a negative regulator of cell cycle through transcriptional repression of cyclin E.

Prokaryotic expression, purification, and production of polyclonal antibody against novel human serum inhibited related protein I (SI1)

A novel serum inhibited related gene (SI1) has been cloned in our lab by using mRNA differential display analysis of U251 cells in the presence or absence of serum, the expression of SI1 was dramatically inhibited by the addition of serum to serum starved cells. Previous reports suggested the potential significance of SI1 in regulating the cell cycle. In this study, the plasmid construction, protein expression and purification, as well as the generation of anti-SI1 polyclonal antibody are described. A full-length cDNA of Si1 was inserted in a prokaryotic expression plasmid pET28-b(+) and efficiently expressed in E. coli Rosetta (DE3) strain after induction by isopropyl-b-D: -thiogalactoside. The expressed 6His-tagged SI1 fusion protein was purified by Ni(+) affinity column and then used to immunize Balb/C mice, and the anti-SI1 polyclonal antibody was purified by protein A column. To determine the sensitivity and specificity of the antibody against SI1, a cell lysate of pEGFP-N2-SI1 plasmid transiently transfected Hela cell was identified by anti-GFP monoclonal antibody and anti-SI1 polyclonal antibody. Both the GFP-SI1 fusion protein and endogenous SI1 protein in Hela cell can be recognized by the anti-SI1 polyclonal antibody. The anti-SI1 polyclonal antibody will provide a useful tool for further characterization of SI1.

Evodiamine-induced human melanoma A375-S2 cell death was mediated by PI3K/Akt/caspase and Fas-L/NF-kappaB signaling pathways and augmented by ubiquitin-proteasome inhibition

Evodiamine, a major alkaloidal component of Evodiae fructus exhibits anti-tumor activities. We have previously reported that evodiamine has a marked inhibitory effect on IL-1 sensitive human melanoma A375-S2 cells proliferation, and this action might be through inactivation of PI3K signaling. However, the detailed molecular mechanisms of evodiamine-induced cell death remains poorly understood. In present study, we further confirmed that Akt is the main effector molecule involved in this pathway. Evodiamine also led to IkappaBalpha phosphorylation and degradation that reflect translocation of NF-kappaB. Pretreatment of A375-S2 cells with ubiquitin-proteasome inhibitor MG132 was shown to aggregate the evodiamine caused cell death at 24h. In addition, MG132 reduced ERK phosphorylation, increased caspase-3 activation, Fas-L expression and Bcl-2 cleavage in evodiamine-treated A375-S2 cells. These results suggested the PI3K/Akt/caspase and Fas-L/NF-kappaB signaling pathways might account for the responses of A375-S2 cell death induced by evodiamine, and these signals could be augmented by ubiquitin-proteasome pathway.

Membrane-bound Fas ligand only is essential for Fas-induced apoptosis

Fas ligand (FasL), an apoptosis-inducing member of the TNF cytokine family and its receptor, Fas, are critical for shutdown of chronic immune responses1-3 and prevention of autoimmunity4,5. Accordingly, mutations in their genes cause severe lymphadenopathy and autoimmune disease in mice6,7 and humans8,9. FasL function is regulated by deposition in the plasma membrane and metalloprotease-mediated shedding10,11. We generated gene-targeted mice that selectively lack either secreted FasL (ΔsFasL) or membrane-bound FasL (ΔmFasL) to resolve which of these forms is required for cell killing and to explore their hypothetical non-apoptotic activities. Mice lacking sFasL (FasL^Δs/Δs) appeared normal and their T cells readily killed target cells, whereas T cells lacking mFasL (FasL^Δm/Δm) could not kill cells through Fas activation. FasL^Δm/Δm mice developed lymphadenopathy and hyper-gammaglobulinaemia, similar to FasL^gld/gld mice, which express a mutant form of FasL that cannot bind Fas, but surprisingly, (on a C57BL/6 background) FasL^Δm/Δm mice succumbed to SLE-like autoimmune kidney destruction and histiocytic sarcoma, diseases that occur only rarely and considerably later in FasL^gld/gld mice. These results demonstrate that mFasL is essential for cytotoxic activity and constitutes the guardian against lymphadenopathy, autoimmunity and cancer whereas excess sFasL appears to promote autoimmunity and tumorigenesis through non-apoptotic activities.

Marie R, Wang TC, Lyle S, Kurt-Jones E, Houghton J. Human and mouse colon cancer utilizes CD95 signaling for local growth and metastatic spread to liver

BACKGROUND & AIMS

Analysis of clinical colon cancer specimens show alterations in the CD95 (Fas Ag/Fas L) pathway as tumors progress from local to metastatic disease, suggesting that this pathway may play a role in invasive behavior of colon cancer. However, direct causality between these alterations and clinical disease progression has not been shown.

METHODS

Surgically resected metastatic colon cancer samples were evaluated for Fas Ag/L and apoptosis. Alterations in the Fas-signaling pathway found in human samples were recreated through a series of staged transfection experiments in the MC38 mouse colon cancer cell line and the effects on growth tested in vitro and in vivo.

RESULTS

Expression of FLICE-like inhibitory protein confers apoptosis resistance, increasing the incidence of primary tumors through a survival advantage by avoiding apoptosis and inducing Fas-mediated proliferation. Coexpression of Fas L enables colon cancer cells to metastasize to the liver from local tumors as well as from intravenous injection of cells. MC38-FasL/FLICE-like inhibitory protein colon cancer cells induce apoptosis in hepatocytes via activation of type II Fas Ag signaling, thus creating a niche conducive to tumor growth and fueling their own growth via Fas proliferative signaling.

CONCLUSIONS

Alterations in the Fas Ag pathway which inhibit apoptosis and increase Fas-mediated proliferation directly increase local colon cancer growth, and enhance metastasis to the liver. Delineating points in the pathway responsible for growth and metastasis will offer targets that may be exploited for therapy.

Immunomodulation of experimental pulmonary fibrosis by intravenous immunoglobulin (IVIG)

OBJECTIVES

To assess the immunomodulatory effect of intravenous immunoglobulin (IVIG) using an experimental model of bleomycin-induced pulmonary fibrosis.

METHODS

Pulmonary fibrosis was induced in C57BL/6 mice by direct intratracheal injection of bleomycin. Mice were treated with IVIG 1 week prior to (prevention protocol), or 10 days following bleomycin injection, when the disease was in progress. The controls used in the study included mice given phosphate buffered saline (PBS) and mice subjected to a commercial individual-IgG. Collagen-I deposits in the affected lungs were detected by Sirius red staining of paraffin embedded lung sections. The collagen-I content was measured by employing the hydroxyproline assay.

RESULTS

Prevention of bleomycin-induced pulmonary fibrosis by IVIG has been demonstrated by reduced expression of collagen-I protein in the affected lungs. The hydroxyproline levels in the lungs of the IVIG-treated mice were 214.33 +/- 13.56 microg/1 g tissue, compared to the higher levels in lungs of IgG treated mice (342.44 +/- 35.60 microg/1 g tissue) or untreated controls 328.00 +/- 45.55 microg/1 g tissue, (p < 0.0001). Effective treatment of bleomycin-induced pulmonary fibrosis by IVIG has been demonstrated by the reduced expression of collagen-I protein in the affected lungs, detected by sirius red histological staining. The hydroxyproline levels in the lungs of the IVIG-treated mice were 261.00 +/- 18.81 microg/1 g tissue, in comparison to the higher levels in the lungs of the IgG treated mice (342.43 +/- 32.89 microg/1 g tissue) and of untreated controls (344.33 +/- 49.85 microg/1 g tissue), (p < 0.001).

CONCLUSIONS

Based on these preliminary studies, we conclude that IVIG may have a beneficial effect in the down regulation of collagen-I levels in the lungs of mice with bleomycin-induced pulmonary fibrosis.

Fas signal promotes lung cancer growth by recruiting myeloid-derived suppressor cells via cancer cell-derived PGE2

Fas/FasL system has been extensively investigated with respect to its capacity to induce cellular apoptosis. However, accumulated evidences show that Fas signaling also exhibits nonapoptotic functions, such as induction of cell proliferation and differentiation. Lung cancer is one of cancer's refractory to the immunotherapy, however, the underlying mechanisms remain to be fully understood. In this study, we show that Fas overexpression does not affect in vitro growth of 3LL cells, but promotes lung cancer growth in vivo. However, such tumor-promoting effect is not observed in FasL-deficient (gld) mice, and also not observed in the immune competent mice once inoculation with domain-negative Fas-overexpressing 3LL cells, suggesting the critical role of Fas signal in the promotion of lung cancer growth in vivo. More accumulation of myeloid-derived suppressor cells (MDSC) and Foxp3(+) regulatory T cells is found in tumors formed by inoculation with Fas-overexpressing 3LL cells, but not domain-negative Fas-overexpressing 3LL cells. Accordingly, Fas-ligated 3LL lung cancer cells can chemoattract more MDSC but not regulatory T cells in vitro. Furthermore, Fas ligation induces 3LL lung cancer cells to produce proinflammatory factor PGE(2) by activating p38 pathway, and in turn, 3LL cells-derived PGE(2) contribute to the Fas ligation-induced MDSC chemoattraction. Furthermore, in vivo administration of cyclooxygenase-2 inhibitor can significantly reduce MDSC accumulation in the Fas-overexpressing tumor. Therefore, our results demonstrate that Fas signal can promote lung cancer growth by recruiting MDSC via cancer cell-derived PGE(2), thus providing new mechanistic explanation for the role of inflammation in cancer progression and immune escape.

A new function of the Fas-FasL pathway in macrophage activation

Upon infection with the protozoan parasite Leishmania major, susceptible BALB/c mice develop unhealing lesions associated with the maturation of CD4(+)Th2 cells secreting IL-4. In contrast, resistant C57BL/6 mice heal their lesions, because of expansion and secretion of IFN-gamma of CD4(+) Th1 cells. The Fas-FasL pathway, although not involved in Th cell differentiation, was reported to be necessary for complete resolution of lesions. We investigate here the role of IFN-gamma and IL-4 on Fas-FasL nonapoptotic signaling events leading to the modulation of macrophage activation. We show that addition of FasL and IFN-gamma to BMMø led to their increased activation, as reflected by enhanced secretion of TNF, IL-6, NO, and the induction of their microbicidal activity, resulting in the killing of intracellular L. major. In contrast, the presence of IL-4 decreased the synergy of IFN-gamma/FasL significantly on macrophage activation and the killing of intracellular L. major. These results show that FasL synergizes with IFN-gamma to activate macrophages and that the tight regulation by IFN-gamma and/or IL-4 of the nonapoptotic signaling events triggered by the Fas-FasL pathway affects significantly the activation of macrophages to a microbicidal state and may thus contribute to the pathogenesis of L. major infection.

Reactive oxygen species are involved in FasL-induced caspase-independent cell death and inflammatory responses

Fas-mediated caspase-dependent cell apoptosis has been well investigated. However, recent studies have shown that Fas can induce nonapoptotic caspase-independent cell death (CICD) when caspase activity is inhibited. Currently, the molecular mechanism of this alternative cell death mediated by Fas remains unclear. In this study, we investigated the signaling pathway of Fas-induced CICD in mouse embryonic fibroblasts (MEFs) whose caspase function was disrupted by the pan-caspase inhibitor Z-VAD-FMK and its coupling to inflammatory responses. Our results revealed that receptor-interacting protein 1 and tumor necrosis factor receptor-associated factor 2 play important roles in FasL-induced CICD. This death is associated with intracellular reactive oxygen species (ROS) production from mitochondria, as a ROS scavenger (BHA), antioxidants (trolox, NAC), and a mitochondrial respiratory chain uncoupler (rotenone) could prevent this event. Furthermore, delayed and sustained JNK activation, mitochondrial membrane potential breakdown, and loss of intracellular GSH were observed. In addition to CICD, FasL also induces cyclooxygenase-2 and MIP-2 gene upregulation, and both responses are attributed to ROS-dependent JNK activation. Taken together, these results demonstrate alternative signaling pathways of Fas upon caspase inhibition in MEFs that are unrelated to the classical apoptotic pathway, but steer cells toward necrosis and an inflammatory response through ROS production.

Silencing of fas-associated death domain protects mice from septic lung inflammation and apoptosis

RATIONALE

A better understanding of the molecular mechanisms involved in the pathogenesis of sepsis and its resultant organ failure and new therapeutic approaches and targets are urgently needed. Accumulating evidence suggests that apoptosis plays an important role in the pathophysiology of sepsis and that apoptosis may be detrimental in septic acute lung injury (ALI).

OBJECTIVES

We tested the hypothesis that systemic administration of small interfering RNA (siRNA) targeting Fas-associated death domain (FADD), which recruits procaspase-8 into the death-inducing signaling complex, may be protective in septic ALI and mortality.

METHODS

Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in BALB/c mice. In vivo delivery of siRNA was performed by using a transfection reagent at 10 hours after CLP. As a negative control, animals received nonsense (scrambled) siRNA.

MEASUREMENTS AND MAIN RESULTS

In CLP-induced septic mice, surface expression of death receptors was up-regulated, and FADD was highly expressed. DNA fragmentation ladder and transferase-mediated dUTP nick end labeling assays showed that treatment with FADD siRNA suppressed apoptosis induction in septic lungs. This siRNA treatment prevented the ALI development in CLP mice, as indicated by the findings that blood-gas derangements, histologic lung damage, and increased pulmonary inflammatory cells were greatly improved. Finally, FADD siRNA administration dramatically improved the survival of CLP mice.

CONCLUSIONS

These results indicate the pathophysiologic significance of the death receptor apoptotic pathway, including FADD, in septic ALI and the potential usefulness of FADD siRNA for gene therapy of the septic syndrome.

Impact of TNF-R1 and CD95 internalization on apoptotic and antiapoptotic signaling

Internalization of cell surface receptors has long been regarded as a pure means to terminate signaling via receptor degradation. A growing body of information points to the fact that many internalized receptors are still in their active state and that signaling continues along the endocytic pathway. Thus endocytosis orchestrates cell signaling by coupling and integrating different cascades on the surface of endocytic vesicles to control the quality, duration, intensity, and distribution of signaling events. The death receptors tumor necrosis factor-receptor 1 (TNF-R1) and CD95 (Fas, APO-1) are known not only to signal for cell death via apoptosis but are also capable of inducing antiapoptotic signals via transcription factor NF-kappaB induction or activation of the proliferative mitogen-activated protein kinase (MAPK)/ERK (extracellular signal-regulated kinase) protein kinase cascades, resulting in cell protection and tissue regeneration. A clue to the understanding of these contradictory biological phenomena may arise from recent findings which reveal a regulatory role of receptor internalization and intracellular receptor trafficking in selectively transmitting signals, which lead either to apoptosis or to the survival of the cell. In this chapter, we discuss the dichotomy of pro- and antiapoptotic signaling of the death receptors TNF-R1 and CD95. First, we will address the role of lipid rafts and post-translational modifications of death receptors in regulating the formation of receptor complexes. Then, we will discuss the role of internalization in determining the fate of the receptors and subsequently the specificity of signaling events. We propose that fusion of internalized TNF-receptosomes with trans-Golgi vesicles should be recognized as a novel mechanism to transduce death signals along the endocytic route. Finally, the lessons learnt from the strategy of adenovirus to escape apoptosis by targeting death receptor internalization demonstrate the biological significance of TNF receptor compartmentalization for immunosurveillance.

Regulation of TNFR1 and CD95 signalling by receptor compartmentalization

The death receptors tumour-necrosis factor receptor-1 (TNFR1) and CD95 (also known as FAS and APO-1) transduce signals that promote cell death by apoptosis. However, these receptors are also capable of inducing anti-apoptotic signals through the activation of the transcription factor nuclear factor-kappaB (NF-kappaB) or through activation of the proliferative mitogen-activated protein kinase (MAPK) cascade. Recent findings reveal a role for receptor internalization and endosomal trafficking in selectively transmitting the signals that lead either to apoptosis or to the survival of the cell.

microRNAs and death receptors

Death receptors induce apoptosis through either the Type I or II pathway. In Type I cells, the initiator caspase-8 directly activates effector caspases such as caspase-3, whereas in Type II cells, the death signal is amplified through mitochondria thereby activating effector caspases causing cell death. Recently, there have been advances in elucidating the early events in the CD95 signaling pathways and how post-translational modifications regulate CD95 signaling. This review will focus on recent insights into the mechanisms of the two different types of CD95 signaling pathways, and will introduce miRNAs as regulators of death receptor signaling.

A novel juxtamembrane domain in tumor necrosis factor receptor superfamily molecules activates Rac1 and controls neurite growth

Members of the tumor necrosis factor receptor (TNFR) superfamily control cell fate determination, including cell death and differentiation. Fas (CD95) is the prototypical "death receptor" of the TNFR superfamily and signals apoptosis through well established pathways. In the adult nervous system, Fas induces apoptosis in the context of neuropathology such as stroke or amyotrophic lateral sclerosis. However, during nervous system development, Fas promotes neurite growth and branching. The molecular mechanisms underlying Fas-induced process formation and branching have remained unknown to date. Here, we define the molecular pathway linking Fas to process growth and branching in cell lines and in developing neurons. We describe a new cytoplasmic membrane proximal domain (MPD) that is essential for Fas-induced process growth and that is conserved in members of the TNFR superfamily. We show that the Fas MPD recruits ezrin, a molecule that links transmembrane proteins to the cytoskeleton, and activates the small GTPase Rac1. Deletion of the MPD, but not the death domain, abolished Rac1 activation and process growth. Furthermore, an ezrin-derived inhibitory peptide prevented Fas-induced neurite growth in primary neurons. Our results define a new domain, topologically and functionally distinct from the death domain, which regulates neuritogenesis via recruitment of ezrin and activation of Rac1.

Fas Ag-FasL coupling leads to ERK1/2-mediated proliferation of gastric mucosal cells

When cells within the gastric mucosa progress from metaplasia to dysplasia to cancer, they acquire a Fas Ag apoptosis-resistant phenotype. It is unusual to completely abolish the pathway, suggesting other forms of Fas Ag signaling may be important or even necessary for gastric cancer to progress. Little is known about alternate signaling of the Fas Ag pathway in gastric mucosal cells. Using a cell culture model of rat gastric mucosal cells, we show that gastric mucosal cells utilize a type II signaling pathway for apoptosis. Under conditions of low receptor stimulation or under conditions where apoptosis is blocked downstream of the death-inducing signal complex, Fas Ag signaling proceeds toward proliferative signaling. Under conditions favoring proliferative signaling, cFLIP is recruited to the Fas-associated death domain-like interleukin-1beta-converting enzyme at the death-inducing signal complex and activates ERK1/2. ERK1/2 in turn activates NF-kappaB. ERK1/2 stimulates proliferation, whereas NF-kappaB activation results in upregulation of the antiapoptotic protein survivin, further promoting proliferation over apoptosis. These results suggest that factors that inhibit apoptosis confer a growth advantage to the cells beyond the survival advantage of avoiding apoptosis and in effect convert the Fas Ag signaling pathway from a tumor suppressor to a tumor promoter.

Soluble Fas ligand inhibits angiogenesis in rheumatoid arthritis

The characteristics of rheumatoid arthritis (RA) pathology include the infiltration of inflammatory leukocytes, the proliferation of synovial cells, and the presence of extensive angiogenesis, referred to as rheumatoid pannus. Fas ligand is critical to the homeostatic regulation of the immune response, but its role in the angiogenic process of RA remains to be defined. In this study, we investigated whether soluble Fas ligand (sFasL) induces synoviocyte apoptosis and regulates angiogenesis of endothelial cells in RA. The levels of sFasL were elevated in the synovial fluids of RA patients when compared to those of osteoarthritis (OA) patients, and they correlated inversely with vascular endothelial growth factor₁₆₅ (VEGF₁₆₅) concentrations. sFasL, ranging from 10 to 100 ng/ml, induced the apoptosis of RA fibroblast-like synoviocytes (FLS) in vitro, and thereby decreased VEGF₁₆₅ production. In addition, sFasL inhibited VEGF₁₆₅-induced migration and chemotaxis of endothelial cells to basal levels in a manner independent of the Fas-mediated cell death. sFasL dose-dependently suppressed the VEGF₁₆₅-stimulated increase in pAkt expression in endothelial cells, which might be associated with its anti-migratory effect on endothelial cells. Moreover, sFasL strongly inhibited neovascularization in the Matrigel plug in vivo. Our data suggest that sFasL shows anti-angiogenic activity within RA joints not only by inducing apoptosis of VEGF₁₆₅-producing cells but also by blocking VEGF₁₆₅-induced migration of endothelial cells, independent of Fas-mediated apoptosis.

Caspase-8- and JNK-dependent AP-1 activation is required for Fas ligand-induced IL-8 production

Despite a dogma that apoptosis does not induce inflammation, Fas ligand (FasL), a well-known death factor, possesses pro-inflammatory activity. For example, FasL induces nuclear factor kappaB (NF-kappaB) activity and interleukin 8 (IL-8) production by engagement of Fas in human cells. Here, we found that a dominant negative mutant of c-Jun, a component of the activator protein-1 (AP-1) transcription factor, inhibits FasL-induced AP-1 activity and IL-8 production in HEK293 cells. Selective inhibition of AP-1 did not affect NF-kappaB activation and vice versa, indicating that their activations were not sequential events. The FasL-induced AP-1 activation could be inhibited by deleting or introducing the lymphoproliferation (lpr)-type point mutation into the Fas death domain (DD), knocking down the Fas-associated DD protein (FADD), abrogating caspase-8 expression with small interfering RNAs, or using inhibitors for pan-caspase and caspase-8 but not caspase-1 or caspase-3. Furthermore, wildtype, but not a catalytically inactive mutant, of caspase-8 reconstituted the FasL-induced AP-1 activation in caspase-8-deficient cells. Fas ligand induced the phosphorylation of two of the three major mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) but not p38 MAPK. Unexpectedly, an inhibitor for JNK but not for MAPK/ERK kinase inhibited the FasL-induced AP-1 activation and IL-8 production. These results demonstrate that FasL-induced AP-1 activation is required for optimal IL-8 production, and this process is mediated by FADD, caspase-8, and JNK.

Fas ligand enhances hematopoietic cell engraftment through abrogation of alloimmune responses and nonimmunogenic interactions

Early after transplantation, donor lineage-negative bone marrow cells (lin(-) BMC) constitutively upregulated their expression of Fas ligand (FasL), suggesting an involvement of the Fas/FasL axis in engraftment. Following the observation of impaired engraftment in the presence of a dysfunctional Fas/FasL axis in FasL-defective (gld) donors or Fas-defective (lpr) recipients, we expressed a noncleavable FasL chimeric protein on the surface of donor lin(-) BMC. Despite a short life span of the protein in vivo, expression of FasL on the surface of all the donor lin(-) BMC improved the efficiency of engraftment twofold. The FasL-coated donor cells efficiently blunted the host alloimmune responses in primary recipients and retained their hematopoietic reconstituting potential in secondary transplants. Surprisingly, FasL protein improved the efficiency of engraftment in syngeneic transplants. The deficient engraftment in lpr recipients was not reversed in chimeric mice with Fas(-) stroma and Fas(+) BMC, demonstrating that the host marrow stroma was also a target of donor cell FasL. Hematopoietic stem and progenitor cells are insensitive to Fas-mediated apoptosis and thus can exploit the constitutive expression of FasL to exert potent veto activities in the early stages of engraftment. Manipulation of the donor cells using ectopic FasL protein accentuated the immunogenic and nonimmunogenic interactions between the donor cells and the host, alleviating the requirement for a megadose of transplanted cells to achieve a potent veto effect. Disclosure of potential conflicts of interest is found at the end of this article.

Autoreactive MZ and B-1 B-cell activation by Faslpr is coincident with an increased frequency of apoptotic lymphocytes and a defect in macrophage clearance

Murine autoreactive anti-Smith (Sm) B cells are negatively regulated by anergy and developmental arrest, but are also positively selected into the marginal zone (MZ) and B-1 B-cell populations. Despite positive selection, anti-Sm production occurs only in autoimmune-prone mice. To investigate autoreactive B-cell activation, an anti-Sm transgene was combined with the lpr mutation, a mutation of the proapoptotic gene Fas (Fas(lpr)), on both autoimmune (MRL) and nonautoimmune backgrounds. Fas(lpr) induces a progressive and autoantigen-specific loss of anti-Sm MZ and B-1 B cells in young adult Fas(lpr) and MRL/Fas(lpr) mice that does not require that Fas(lpr) be B-cell intrinsic. This loss is accompanied by a bypass of the early pre-plasma cell (PC) tolerance checkpoint. Although the MRL bkg does not lead to a progressive loss of anti-Sm MZ or B-1 B cells, it induces a robust bypass of the early pre-PC tolerance checkpoint. Fas(lpr) mice have a high frequency of apoptotic lymphocytes in secondary lymphoid tissues and a macrophage defect in apoptotic cell phagocytosis. Since Sm is exposed on the surface of apoptotic cells, we propose that anti-Sm MZ and B-1 B-cell activation is the result of a Fas(lpr)-induced defect in apoptotic cell clearance.

Fas signaling in thyroid carcinomas is diverted from apoptosis to proliferation

PURPOSE

The death receptor Fas is present in thyroid carcinomas, yet fails to trigger apoptosis. Interestingly, Fas has been reported to be actually overexpressed in papillary thyroid carcinomas, suggesting that it may confer a survival advantage.

EXPERIMENTAL DESIGN

We investigated the expression and activation status of Fas pathway mediators in thyroid carcinoma cell lines and tumor specimens.

RESULTS

All cell lines tested express Fas-associated death domain, procaspase-8, procaspase-9, and procaspase-3; resistance to Fas-mediated apoptosis could not be attributed to lack of any of these apoptosis mediators. Moreover, Fas death domain mutations were not found in our study. The proteasome inhibitors MG132 and PS-341 (bortezomib, Velcade), which lead to accumulation of the nuclear factor kappaB (NF-kappaB) inhibitor IkappaB, did not sensitize SW579 cells to Fas-mediated apoptosis, suggesting that resistance to Fas-mediated apoptosis is not due to proteasome or NF-kappaB activity. Cross-linking of Fas in vitro induced recruitment of Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitory protein (FLIP) instead of procaspase-8. Inhibition of FLIP expression with a FLIP antisense oligonucleotide resulted in significant sensitization to Fas-mediated apoptosis. Fas cross-linking promoted BrdUrd incorporation; activated the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase, NF-kappaB, and activator protein-1 pathways in thyroid carcinoma cells in vitro; and protected cells from tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. We also found that good prognosis papillary thyroid carcinoma specimens exhibited higher immunoreactivity for cleaved (activated) caspase-8 than poor prognosis tumors.

CONCLUSIONS

In thyroid carcinomas, the proteolytic cleavage and activation of caspase-8 depends on the balance between expression levels for procaspase-8 and FLIP and correlates with favorable clinical prognosis. Fas may actually stimulate proliferation and confer a survival advantage to thyroid cancer cells.