Fas (CD95, APO-1) antigen expression and function in murine liver endothelial cells: implications for the regulation of apoptosis in liver endothelial cells

HELLP Syndrome—Holistic Insight into Pathophysiology

HELLP syndrome, also known as the syndrome of hemolysis, elevated liver enzymes, and low platelets, represents a severe pregnancy complication typically associated with hypertension. It is associated with increased risks of adverse complications for both mother and fetus. HELLP occurs in 0.2–0.8% of pregnancies, and, in 70–80% of cases, it coexists with preeclampsia (PE). Both of these conditions show a familial tendency. A woman with a history of HELLP pregnancy is at high risk for developing this entity in subsequent pregnancies. We cannot nominate a single worldwide genetic cause for the increased risk of HELLP. Combinations of multiple gene variants, each with a moderate risk, with concurrent maternal and environmental factors are thought to be the etiological mechanisms. This review highlights the significant role of understanding the underlying pathophysiological mechanism of HELLP syndrome. A better knowledge of the disease’s course supports early detection, an accurate diagnosis, and proper management of this life-threatening condition.

Visual deterioration in patients with photoreceptor loss after retinal reattachment surgery

PURPOSE

Assess the relationship between photoreceptor degeneration and visual function after retinal reattachment surgery (RRS) in a prospective cohort.

METHODS

Patients with rhegmatogenous retinal detachment (RRD) were reviewed before and 6 months after vitreoretinal surgery. Optical coherence tomographical thickness of the outer nuclear layer (ONL), outer retinal segment (ORS), retinal pigmented epithelium to ellipsoid zone (RPE-EZ) and external limiting membrane to EZ (ELM-EZ) were recorded 6 months post-operatively. These were compared to best corrected visual acuity (BCVA) and retinal sensitivity (Humphrey visual field).

RESULTS

Thirteen macula-off and 8 macula-on RRD patients were included. The mean ONL thickness was higher after macula-on RRD compared to macula-off RRD (97.70 ± 3.62 μm vs. 73.10 ± 4.98 μm). In all RRD eyes, every 1 μm decrease in ONL thickness correlated with a 0.052 dB decrease and in retinal sensitivity and every 1 μm decrease in ORS thickness was associated with a 0.062 dB reduction in retinal sensitivity. ORS, ELM-EZ and RPE-EZ thickness did not correlate with BCVA post-RRS.

CONCLUSION

There was greater ONL and ORS thinning following macula-off compared to macula-on RRD. Correlations between ONL and ORS thinning with decreased retinal sensitivity may be explained by RRD-induced photoreceptor death.

New aspects of hepatic endothelial cells in physiology and nonalcoholic fatty liver disease

The liver is the central metabolic hub for carbohydrate, lipid, and protein metabolism. It is composed of four major types of cells, including hepatocytes, endothelial cells (ECs), Kupffer cells, and stellate cells. Hepatic ECs are highly heterogeneous in both mice and humans, representing the second largest population of cells in liver. The majority of them line hepatic sinusoids known as liver sinusoidal ECs (LSECs). The structure and biology of LSECs and their roles in physiology and liver disease were reviewed recently. Here, we do not give a comprehensive review of LSEC structure, function, or pathophysiology. Instead, we focus on the recent progress in LSEC research and other hepatic ECs in physiology and nonalcoholic fatty liver disease and other hepatic fibrosis-related conditions. We discuss several current areas of interest, including capillarization, scavenger function, autophagy, cellular senescence, paracrine effects, and mechanotransduction. In addition, we summarize the strengths and weaknesses of evidence for the potential role of endothelial-to-mesenchymal transition in liver fibrosis.

Inflammatory and Fibrogenic Factors in Proliferative Vitreoretinopathy Development

Purpose

Proliferative vitreoretinopathy (PVR) occurs in 5%-10% of rhegmatogenous retinal detachment cases and is the principle cause for failure of retinal reattachment surgery. Although there are a number of surgical adjunctive agents available for preventing the development of PVR, all have limited efficacy. Discovering predictive molecular biomarkers to determine the probability of PVR development after retinal reattachment surgery will allow better patient stratification for more targeted drug evaluations.

Methods

Narrative literature review.

Results

We provide a summary of the inflammatory and fibrogenic factors found in ocular fluid samples during the development of retinal detachment and PVR and discuss their possible use as molecular PVR predictive biomarkers.

Conclusions

Studies monitoring the levels of the above factors have found that few if any have predictive biomarker value, suggesting that widening the phenotype of potential factors and a combinatorial approach are required to determine predictive biomarkers for PVR.

Translational Relevance

The identification of relevant biomarkers relies on an understanding of disease signaling pathways derived from basic science research. We discuss the extent to which those molecules identified as biomarkers and predictors of PVR relate to disease pathogenesis and could function as useful disease predictors. (http://www.umin.ac.jp/ctr/ number, UMIN000005604).

Placenta derived factors involved in the pathogenesis of the liver in the syndrome of haemolysis, elevated liver enzymes and low platelets (HELLP): A review

AIM

With this review we try to unravel if placenta-derived factors are able to initiate liver sinusoidal endothelial cells (LSEC) decay in HELLP syndrome and eventually cause the development of sinusoidal obstruction syndrome (SOS).

BACKGROUND

Haemolysis, Elevated Liver enzymes and Low Platelets (HELLP) syndrome is a severe complication of pregnancy. It is characterized by elevated liver enzymes, low platelet count and haemolytic anaemia. The risk of developing HELLP syndrome within a pregnancy is 0.1-0.8%. The mortality rate among women with HELLP syndrome is 0-24% and the perinatal death goes up to 37%. The aetiology of HELLP syndrome is not fully understood but the pathogenesis of the liver pathology in the HELLP syndrome resembles that of a SOS with endothelial damage of the LSECs which ultimately leads to liver failure.

OBJECTIVES

We hypothesize that placenta derived factors cause LSEC damage and thereby liver dysfunction.

METHODS

We searched in the PubMed database for relevant articles about placenta derived factors involved in endothelial activation especially in the liver. We yielded eventually 55 relevant articles.

RESULTS

Based on this literature search we associate that in HELLP syndrome there is an increase of soluble fms-like tyrosine kinase (sFlt1), vascular endothelial growth factor (VEGFR), soluble endoglin (sEng), galectin-1 (Gal-1), endothelin-1 (ET-1), Angiopoietin 2 (Angs-2), Asymmetric dimethylarginine (ADMA), activin B, inhibin A, Fas ligand (FasL) and heat shock protein 70 (Hsp70).

CONCLUSION

We assume that these eleven increased placenta derived factors are responsible for LSEC damage which eventually leads to liver failure. This concept shows a possible design of the complicated pathophysiology in HELLP syndrome. However further research is required.

Dysregulation of the Fas/FasL system in an experimental animal model of HELLP syndrome

INTRODUCTION

Placental FasL is up-regulated in women with HELLP (hemolysis elevated liver enzyme and low platelet) syndrome and has been proposed to contribute to the liver damage seen in these patients.

OBJECTIVE

This study aimed to determine if an experimental rodent model of HELLP also had dysregulation of Fas/FasL compared to normal pregnant (NP) rats. We also set out to determine if blockade of the endothelin system regulated Fas/FasL expression in HELLP rats.

STUDY DESIGN

On gestational day (GD) 12, sEng (7ug/kg) and sFlt-1 (4.7ug/kg) infusion began via mini-osmotic pump into NP rats. On GD19 plasma and tissue were collected and FasL and Fas were measured via enzyme linked immunosorbent assay and gene expression via real-time PCR.

RESULTS

HELLP rats had significantly more circulating and placental FasL compared to NP rats, whereas hepatic FasL was decreased and placental Fas was increased compared to NP rats. Administration of an endothelin A receptor antagonist (ET_A) beginning on GD12 significantly decreased placental expression of Fas in HELLP rats. Liver mRNA transcript of Fas was significantly increased in HELLP rats compared to NP rats.

CONCLUSION

These data suggest that rats in this experimental model of HELLP syndrome have abnormal expression of the Fas/FasL system. Future studies will examine the sources of Fas/FasL dysregulation in this model and if blockade could reduce some of the inflammation and hypertension associated with HELLP syndrome.

Protecting liver sinusoidal endothelial cells suppresses apoptosis in acute liver damage

AIM

Apoptosis is associated with various types of hepatic disorders. We have developed a novel cell-transfer drug delivery system (DDS) using a multifunctional envelope-type nano device that targets liver sinusoidal endothelial cells (LSECs). The purpose of this study was to determine the efficacy of the novel DDS containing siRNA at suppressing apoptosis in LSECs.

METHODS

Bax siRNA was transfected into a sinusoidal endothelial cell line (M1) to suppress apoptosis induced by an anti-Fas antibody and staurosporine. C57BL/6J mice were divided into three groups: (i) a control group, only intravenous saline; (ii) a nonselective group, injections of siRNA sealed in the nonselective DDS; and (iii) an LSEC-transfer efficient group, injections of siRNA sealed in an LSEC-transfer efficient DDS. Hepatic cell apoptosis was induced by an anti-Fas antibody.

RESULTS

Bax siRNA had an anti-apoptotic effect on M1 cells. Serum alanine aminotransferase was reduced in the LSEC-transfer efficient group, as were cleaved caspase-3 and the number of terminal deoxynucleotidyl transferase dUTP nick end labeling positive hepatocytes. Silver impregnation staining indicated that the sinusoidal space was maintained in the LSEC-transfer efficient group but not in the other groups. Electron microscopy showed that the LSECs were slightly impaired, although the sinusoidal structure was maintained in the LSEC-transfer efficient group.

CONCLUSION

Hepatocyte apoptosis was reduced by the efficient suppression of LSEC apoptosis with a novel DDS. Protecting the sinusoidal structure by suppressing LSEC damage will be an effective treatment for acute liver failure.

Plasmodium-infected erythrocytes (pRBC) induce endothelial cell apoptosis via a heme-mediated signaling pathway

Heme is cytotoxic to the plasmodium parasite, which converts it to an insoluble crystalline form called hemozoin (malaria pigment) in erythrocytes during replication. The increased serum levels of free heme cause tissue damage, activation of microvascular endothelial and glial cells, focal inflammation, activation of apoptotic pathways, and neuronal tissue damage. Several hypotheses have been proposed to explain how these causative factors exacerbate fatal malaria. However, none of them fully explain the detailed mechanisms leading to the high morbidity and mortality associated with malaria. We have previously reported that heme-induced brain microvascular endothelial cell (HBVEC) apoptosis is a major contributor to severe malaria pathogenesis. Here, we hypothesized that heme (at clinically relevant levels) induces inflammation and apoptosis in HBVEC, a process that is mediated by independent proinflammatory and proapoptotic signaling pathways. In this study, we determined the key signaling molecules associated with heme-mediated apoptosis in HBVEC in vitro using RT2 profiler polymerase chain reaction array technology and confirmed results using immunostaining techniques. While several expressed genes in HBVEC were altered upon heme stimulation, we determined that the apoptotic effects of heme were mediated through p73 (tumor protein p73). The results provide an opportunity to target heme-mediated apoptosis therapeutically in malaria-infected individuals.

SPARC (secreted protein acidic and rich in cysteine) knockdown protects mice from acute liver injury by reducing vascular endothelial cell damage

Secreted protein, acidic and rich in cysteine (SPARC) is involved in many biological process including liver fibrogenesis, but its role in acute liver damage is unknown. To examine the role of SPARC in acute liver injury, we used SPARC knock-out (SPARC(-/-)) mice. Two models of acute liver damage were used: concanavalin A (Con A) and the agonistic anti-CD95 antibody Jo2. SPARC expression levels were analyzed in liver samples from patients with acute-on-chronic alcoholic hepatitis (AH). SPARC expression is increased on acute-on-chronic AH patients. Knockdown of SPARC decreased hepatic damage in the two models of liver injury. SPARC(-/-) mice showed a marked reduction in Con A-induced necroinflammation. Infiltration by CD4+ T cells, expression of tumor necrosis factor-α and interleukin-6 and apoptosis were attenuated in SPARC(-/-) mice. Sinusoidal endothelial cell monolayer was preserved and was less activated in Con A-treated SPARC(-/-) mice. SPARC knockdown reduced Con A-induced autophagy of cultured human microvascular endothelial cells (HMEC-1). Hepatic transcriptome analysis revealed several gene networks that may have a role in the attenuated liver damaged found in Con A-treated SPARC(-/-) mice. SPARC has a significant role in the development of Con A-induced severe liver injury. These results suggest that SPARC could represent a therapeutic target in acute liver injury.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Effect of tea polyphenol on oxidative injury in S180 cells induced hepatocarcinoma mice

The purpose of this study was to evaluate the antioxidant nature of tea polyphenol on S180 cells induced liver cancer in mice. In the present study, hepatocellular carcinoma was induced by tumor transplantation of liver in situ. The antitumor activity of tea polyphenol has been determined in vivo in hepatocellular carcinoma mice after treatment of drug (50, 100, 150 mg/kg body weight) by gavage for 20 days. Results showed that a significant increase in serum aspartate transaminase (AST), alkaline phosphatase (ALP), alanine aminotransfere (ALT), malondialdehyde (MDA) level, decrease in serum white blood cells (WBC), serum total protein (TP), albumin (ALB), A/G, tumor necrosis factor-α (TNF-α) and interferon-gamma (IFN-γ), liver reduced glutathione (GSH) levels were observed. In addition, the levels of enzymic and non-enzymic antioxidants were decreased when subjected to S180 cells induction. These altered enzyme levels were ameliorated significantly by administration of tea polyphenol at the concentration of 50, 100, 150 mg/kg body weight in drug-treated animals. These results indicate that the protective effect of tea polyphenol was associated with inhibition of MDA induced by S180 cells and to maintain the antioxidant enzyme levels.

CD95 death receptor and epidermal growth factor receptor (EGFR) in liver cell apoptosis and regeneration

Recent evidence suggests that signaling pathways towards cell proliferation and cell death are much more interconnected than previously thought. Whereas not only death receptors such as CD95 (Fas, APO-1) can couple to both, cell death and proliferation, also growth factor receptors such as the epidermal growth factor receptor (EGFR) are involved in these opposing kinds of cell fate. EGFR is briefly discussed as a growth factor receptor involved in liver cell proliferation during liver regeneration. Then the role of EGFR in activating CD95 death receptor in liver parenchymal cells (PC) and hepatic stellate cells (HSC), which represent a liver stem/progenitor cell compartment, is described summarizing different ways of CD95- and EGFR-dependent signaling in the liver. Here, depending on the hepatic cell type (PC vs. HSC) and the respective signaling context (sustained vs. transient JNK activation) CD95-/EGFR-mediated signaling ends up in either liver cell apoptosis or cell proliferation.

PMLRARα binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo

Defective Fas signaling leads to resistance to various anticancer therapies. Presence of potential inhibitors of Fas which could block Fas signaling can explain cancer cells resistance to apoptosis. 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 PML-retinoic acid receptor α (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-FLIP(L/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. Taken together, PMLRARα binds to Fas and blocks Fas-mediated apoptosis in APL by forming an apoptotic inhibitory complex with c-FLIP. The presence of PML-Fas complexes across different tissues implicates that PML functions in apoptosis regulation and tumor suppression are mediated by direct interaction with Fas.

Delayed-onset caspase-dependent massive hepatocyte apoptosis upon Fas activation in Bak/Bax-deficient mice

The proapoptotic Bcl-2 family proteins Bak and Bax serve as an essential gateway to the mitochondrial pathway of apoptosis. When activated by BH3-only proteins, Bak/Bax triggers mitochondrial outer membrane permeabilization leading to release of cytochrome c followed by activation of initiator and then effector caspases to dismantle the cells. Hepatocytes are generally considered to be type II cells because, upon Fas stimulation, they are reported to require the BH3-only protein Bid to undergo apoptosis. However, the significance of Bak and Bax in the liver is unclear. To address this issue, we generated hepatocyte-specific Bak/Bax double knockout mice and administered Jo2 agonistic anti-Fas antibody or recombinant Fas ligand to them. Fas-induced rapid fulminant hepatocyte apoptosis was partially ameliorated in Bak knockout mice but not in Bax knockout mice, and was completely abolished in double knockout mice 3 hours after Jo2 injection. Importantly, at 6 hours, double knockout mice displayed severe liver injury associated with repression of XIAP, activation of caspase-3/7 and oligonucleosomal DNA breaks in the liver, without evidence of mitochondrial disruption or cytochrome c-dependent caspase-9 activation. This liver injury was not ameliorated in a cyclophilin D knockout background nor by administration of necrostatin-1, but was completely inhibited by administration of a caspase inhibitor after Bid cleavage.

CONCLUSION

Whereas either Bak or Bax is critically required for rapid execution of Fas-mediated massive apoptosis in the liver, delayed onset of mitochondria-independent, caspase-dependent apoptosis develops even in the absence of both. The present study unveils an extrinsic pathway of apoptosis, like that in type I cells, which serves as a backup system even in type II cells.

Coenzyme Q10 counteracts testicular injury induced by sodium arsenite in rats

The protective effect of coenzyme Q10 against testicular toxicity induced by sodium arsenite (10mg/kg/day, orally for two consecutive days) was investigated in rats. Coenzyme Q10 treatment (10mg/kg/day, i.p.) was applied for five consecutive days, starting three days before arsenite administration. Coenzyme Q10 significantly increased serum testosterone level which was reduced by sodium arsenite. Coenzyme Q10 significantly suppressed lipid peroxidation, restored the depleted antioxidant defenses, and attenuated the increases of tumor necrosis factor-α and nitric oxide resulted from arsenic administration. Also, the elevation of arsenic ion, and the reductions of selenium and zinc ions in testicular tissue were mitigated by coenzyme Q10. Histopathological examination showed that testicular injury mediated by arsenic was ameliorated by coenzyme Q10 treatment. Immunohistochemical analysis revealed that coenzyme Q10 significantly decreased the arsenic-induced expression of inducible nitric oxide synthase, nuclear factor-κB, Fas ligand and caspase-3 in testicular tissue. It was concluded that coenzyme Q10 represents a potential therapeutic option to protect the testicular tissue from the detrimental effects of arsenic intoxication.

The role of Fas ligand protein in the oxidative stress induced by azoxymethane on crypt colon of rats

PURPOSE: To study the protein Fas ligand (FasL) on the expression of apoptosis, using a model of oxidative stress induced by azoxymethane (AOM), in the crypt of colon in rats. METHODS: Wistar rats (n=14) were assigned into two groups: control (n=7) and AOM (n=7). A single subcutaneous administration of AOM (5mg/kg) or saline solution was performed at the beginning of third week and after three hours samples of proximal colon were collected. The expression of FasL was quantified (Software ImageLab) in percentage of areas in the top, base and all crypt. Results were expressed as mean ± sd (Shapiro-Wilks test and t Student test) (p < 0.05). RESULTS: In the animals of CG there was no significant difference between the FasL expression of the top (10.75±3.33) and basal (11.14±3.53) colon crypt (p=0.34293740). In the animals of AOM there was no significant difference between the FasL expression of the top (8.86±4.19) and basal (8.99±4.08) colon crypt (p=0.78486003). In the animals of CG (10.95±3.43) and AOM (8.92±4.13) there was a significant difference of the FasL expression (p=0.026466821). A significantly decrease on the FasL expression was observed in the animals of CG (10.75±3.33) and AOM (8.86±4.19) in the top crypt (p=0.00003755*). A significant decrease was also observed in the animals of CG (11.14±3.53) and AOM (8.99±4.08) in the basal colon crypt (p=0.00000381**). CONCLUSION: Azoxymethane induce the oxidative stress and the significantly decrease of FasL expression, although there is no significant difference between basal and top of colon crypt linked to consumption-activation of Fas ligand.

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.

Reduced Liver Apoptosis After Venous Systemic Oxygen Persufflation in Non-Heart-Beating Donors

Graft injury caused by warm ischemia in livers from non-heart-beating donors (NHBDs) strongly affects posttransplantation outcome and is associated with liver apoptosis, which is mediated by death receptors, such as Fas, a surface receptor of the tumor necrosis factor (TNF)-alpha family. The aim of this study was to test the ability of venous systemic oxygen persufflation (VSOP) to reduce apoptotic changes and Fas activation in the liver after warm ischemic insult in vivo. Livers of male Wistar rats were harvested 30 min after cardiac arrest from non-heart-beating donors (NHBD) with (NHBD + O2) or without (NHBD) application of gaseous oxygen during the cold storage period via the suprahepatic caval vein. After 24 h of storage in University of Wisconsin solution at 4 degrees C, viability of the livers was assessed upon isolated reperfusion in vitro. Conventional signs of tissue damage like enzyme release and bile production showed a significantly elevated nonspecific cell injury in the NHBD group. TUNEL staining revealed increased DNA fragmentation of sinusoidal endothelial cells in the NHBD group and more apoptotic hepatocytes than in the control group. All these alterations could be almost abrogated by the use of VSOP in the NHBD + O2 group. The immunohistochemical staining of Fas antigen expression showed a significantly elevated Fas receptor expression in the NHBD and NHBD + O2 groups, in accord with an eightfold increase of Fas receptor mRNA detected by real-time reverse-transcription polymerase chain reaction (RT-PCR). These results demonstrate that the postischemic apoptotic rate of sinusoidal endothelial cells in NHBD livers can be reduced by the use of VSOP. A significant improvement in liver integrity and viability was obtained with this technique, without influencing the expression of Fas expression.

Plasminogen activator inhibitor-1 protects endothelial cells from FasL-mediated apoptosis

Plasminogen activator inhibitor-1 (PAI-1) paradoxically enhances tumor progression and angiogenesis; however, the mechanism supporting this role is not known. Here we provide evidence that PAI-1 is essential to protect endothelial cells (ECs) from FasL-mediated apoptosis. In the absence of host-derived PAI-1, human neuroblastoma cells implanted in PAI-1-deficient mice form smaller and poorly vascularized tumors containing an increased number of apoptotic ECs. We observed that knockdown of PAI-1 in ECs enhances cell-associated plasmin activity and increases spontaneous apoptosis in vitro. We further demonstrate that plasmin cleaves FasL at Arg144-Lys145, releasing a soluble proapoptotic FasL fragment from the surface of ECs. The data provide a mechanism explaining the proangiogenic activity of PAI-1.

Cellular and molecular mechanisms of liver injury

Derangements in apoptosis of liver cells are mechanistically important in the pathogenesis of end-stage liver disease. Vulnerable hepatocytes can undergo apoptosis via an extrinsic, death receptor-mediated pathway, or alternatively intracellular stress can activate the intrinsic pathway of apoptosis. Both pathways converge on mitochondria, and mitochondrial dysfunction is a prerequisite for hepatocyte apoptosis. Persistent apoptosis is a feature of chronic liver diseases, and massive apoptosis is a feature of acute liver diseases. Fibrogenesis is stimulated by ongoing hepatocyte apoptosis, eventually resulting in cirrhosis of the liver in chronic liver diseases. Endothelial cell apoptosis occurs in ischemia-reperfusion injury. Natural killer and natural killer T cells remove virus-infected hepatocytes by death receptor-mediated fibrosis. Lastly, activated stellate cell apoptosis leads to slowing and resolution of apoptosis. This review summarizes recent cellular and molecular advances in the understanding of the injury mechanisms leading to end-stage liver disease.

Maintenance of Bad phosphorylation prevents apoptosis of rat hepatic sinusoidal endothelial cells in vitro and in vivo

To elucidate the mechanism of apoptosis of liver sinusoidal endothelial cells (SECs), we examined the phosphorylation status of Bad and its upstream signaling molecules during apoptosis in culture and after ischemia-reperfusion injury. Rat SECs were isolated by the immunomagnetic method, and 2 days after culture, most SECs underwent apoptosis, which was associated with decreased tyrosine phosphorylation of cellular proteins. Addition of orthovanadate (OV), a protein tyrosine phosphatase inhibitor, sustained cellular protein phosphorylation and strongly inhibited apoptosis. Bad was dephosphorylated at Ser-112 and Ser-136 during apoptosis, but the phosphorylation status of Bad was maintained in the presence of OV. OV activated the Akt, extracellular signal-regulated protein kinase, and p38 mitogen-activated protein kinase pathways, which are involved in Bad phosphorylation. In the absence of OV, depletion of Bad by RNA interference conferred resistance to apoptosis. Hepatic injury after ischemia-reperfusion was alleviated by OV treatment, with significant inhibition of SEC apoptosis. SEC apoptosis in vivo was associated with dephosphorylation of Bad, Akt, and extracellular signal-regulated protein kinase, which was blocked by OV treatment. Our data suggest that maintenance of Bad phosphorylation is important in the prevention of SEC apoptosis and that the anti-apoptotic property of OV might have therapeutic utility.

Apoptosis and necrosis in the liver: a tale of two deaths?

Death of hepatocytes and other hepatic cell types is a characteristic feature of liver diseases as diverse as cholestasis, viral hepatitis, ischemia/reperfusion, liver preservation for transplantation and drug/toxicant-induced injury. Cell death typically follows one of two patterns: oncotic necrosis and apoptosis. Necrosis is typically the consequence of acute metabolic perturbation with ATP depletion as occurs in ischemia/reperfusion and acute drug-induced hepatotoxicity. Apoptosis, in contrast, represents the execution of an ATP-dependent death program often initiated by death ligand/death receptor interactions, such as Fas ligand with Fas, which leads to a caspase activation cascade. A common event leading to both apoptosis and necrosis is mitochondrial permeabilization and dysfunction, although the mechanistic basis of mitochondrial injury may vary in different settings. Prevention of these modes of cell death is an important target of therapy, but controversies still exist regarding which mode of cell death predominates in various forms of liver disease and injury. Resolution of these controversies may come with the recognition that apoptosis and necrosis frequently represent alternate outcomes of the same cellular pathways to cell death, especially for cell death mediated by mitochondrial permeabilization. An understanding of processes leading to liver cell death will be important for development of effective interventions to prevent hepatocellular death leading to liver failure and to promote cancer and stellate cell death in malignancy and fibrotic disease.

In vivo upregulation of CD95 and CD95L causes synergistic inhibition of angiogenesis by TSP1 peptide and metronomic doxorubicin treatment

Antiangiogenic thrombospondin-1 (TSP1) induces endothelial cell death via a CD95-mediated cascade. We used this signaling pathway, where CD95/Fas is a rate-limiting intermediate, as a target to optimize the efficacy of TSP1 active peptide, DI-TSP. Like TSP1, DI-TSP upregulated endothelial CD95L in vivo. To modulate CD95 levels, we chose chemotherapy agent doxorubicin (DXR). DXR caused sustained upregulation of CD95 in the activated endothelium at 1/100 of the maximal tolerated dose. DI-TSP and DXR synergistically induced endothelial apoptosis in vitro, and in vivo, in developing murine vessels. Fas decoy, TSP1 receptor antibody and Pifithrin, a p53 inhibitor, severely decreased apoptosis and restored angiogenesis by DXR-DI-TSP combination, evidencing critical roles of CD95 and TSP1. Combined therapy synergistically blocked neovascularization and progression of the bladder and prostate carcinoma. Such informed design of a complex antiangiogenic therapy based on the rate-limiting molecular targets is a novel concept, which may yield new approaches to cancer treatment.

A murine model of NKT cell-mediated liver injury induced by alpha-galactosylceramide/d-galactosamine

Natural killer-T (NKT) cells are rich in the liver. However, their involvement in liver injury is not fully understood. We developed here a new murine model of NKT-cell-activation-associated liver injury, and investigated a role of tumor necrosis factor alpha (TNF-alpha) and Fas in pathogenesis. We injected intraperitoneally alpha-galactosylceramide (alpha-GalCer), an NKT-cell stimulant, into D-galactosamine (GalN)-sensitized mice. Survival rate, pathological changes of the liver, and plasma concentrations of cytokines were studied. Alpha-GalCer/GalN administration gave a lethal effect within 7 h, making pathological changes such as massive parenchymal hemorrhage, hepatocyte apoptosis, sinusoidal endothelial cell injury, and close apposition of lymphocytes to apoptotic hepatocytes. Anti-NK1.1 mAb-pretreated mice and Valpha14NKT knock out (KO) mice did not develop liver injury. Tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) were elevated at 4 h in the plasma. These cytokines were produced by hepatic lymphocytes as demonstrated by in vitro stimulation with alpha-GalCer. The lethal effect was suppressed in TNF-alpha KO mice, TNF receptor-1 KO mice, and lpr/lpr (Fas deficient) mice, whereas it was not in IFN-gamma KO mice. These results indicate that the present liver injury is characterized by parenchymal hemorrhage and hepatocyte apoptosis, and mediated by TNF-alpha secretion and direct cytotoxicity of alpha-GalCer-activated NKT cells.

Serum levels of the apoptosis-associated molecules, tumor necrosis factor-alpha/tumor necrosis factor type-I receptor and Fas/FasL, in sepsis

STUDY OBJECTIVE

s: Numerous reports suggest that apoptosis may play an important role in the sepsis syndrome. The objective of the present study was to examine the levels of molecules associated with apoptosis belonging to the tumor necrosis factor (TNF)-alpha/TNF type-I receptor (TNFRI) and Fas ligand (FasL)/Fas receptor (Fas) pathways in patients with sepsis.

PATIENTS AND METHODS

Twenty-two patients with sepsis (14 patients with severe sepsis and 8 patients with sepsis), and 6 healthy volunteers were evaluated. Sequential analysis of the serum levels of TNF-alpha, TNFRI, FasL, and Fas were performed in these patients using enzyme-linked immunosorbent assays.

RESULTS

Detectable levels of TNF-alpha were found in only 8 of 14 patients with severe sepsis. Patients with severe sepsis and sepsis had similarly increased levels of FasL, compared with healthy individuals (p < 0.05). Higher levels of TNFRI and Fas were found in patients with severe sepsis than in patients with sepsis and healthy volunteers (p < 0.001 and p < 0.01, respectively). Fas levels were also higher in patients who died than in those who survived (p < 0.01). A direct relationship was found between serum levels of TNFRI and Fas, and multiorgan dysfunction (sequential organ failure assessment score) [p < 0.0001].

CONCLUSIONS

These results suggest that the TNF-alpha/TNFRI and FasL/Fas systems may be involved in the pathogenesis of sepsis. Serum levels of the death-receptors, TNFRI and Fas, could serve as potential markers of the severity of human sepsis.

Protein kinase B inhibits apoptosis induced by actinomycin D in ECV304 cells through phosphorylation of caspase 8

Actinomycin D (act-D) anchors itself into DNA-base pairs by intercalation and thereby inhibits mRNA synthesis. It has been well established that act-D elicits apoptosis in various cell types involving endothelial cells. However, the regulatory mechanisms of actinomycin D-induced apoptotic cell death still remain unclear. Here, we investigated apoptotic cell death and its underlying regulatory mechanisms elicited by actinomycin D in ECV304. Act-D induced typical apoptotic features including chromatin condensation and translocation of phosphatidylserine. Since the phosphoinositide 3-OH kinase (PI3K)/protein kinase B (PKB) signaling pathway has been shown to prevent apoptosis in various cell types, it was of interest to determine if this pathway could protect against apoptosis induced by act-D. Inhibition of PI3K/PKB significantly increased act-D-induced apoptosis. Moreover, act-D-induced cell death was physiologically linked to PKB-mediated cell survival through caspase-8. These results suggest that cross-talk between the PKB and caspase-8 pathways may regulate the balance between cell survival and cell death in ECV304.

Immuno-localization of Fas and FasL in rat hepatic endothelial cells: influence of different fixation protocols

Immunocytochemistry has been widely used to localize molecules involved in apoptosis. In this short report, we describe with the aid of confocal laser scanning microscopy the immunolocalization of Fas and FasL on liver sinusoidal endothelial cells, and show how the localization of these two molecules differ when the cells are fixed with different fixation protocols. Methanol fixation shows diffuse staining of Fas and FasL in the cytoplasm, as well as in the nucleus. In contrast, paraformaldehyde fixation reveals the presence of Fas and FasL polarized at one side of the cell and only in the cytoplasm. After fixation with a combination of paraformaldehyde and glutaraldehyde the polarization is still present although the fluorescence is concentrated and located as bright dots in the cytoplasm. In conclusion, paraformaldehyde preserves the (nuclear) membrane-associated structures better then methanol and results in a more accurate localization of Fas and FasL. Understanding the different outcome of these common used fixation protocols will assist investigators to select the most suitable method for visualizing membrane-bound Fas and FasL.

Fas induces apoptosis in human coronary artery endothelial cells in vitro

Background

Published work suggests that some types of endothelial cells undergo apoptosis in response to ligation of the receptor Fas (CD95, APO1) but other types are resistant. Because heterogeneity among endothelial cells from different tissues, has been demonstrated, the purpose of this study was to determine, if Fas ligation and/or activation by human Fas ligand induces apoptosis and caspase activities, in cultured human coronary artery endothelial cells, and the differences between TNF-a and FAS induced apoptosis in these cells.

Results

Cultured human coronary artery endothelial cells (HCAEC) were exposed to the monoclonal Fas-activating antibody CH-11, to purified recombinant human Fas ligand, to the Fas-neutralizing antibody ZB4, or to purified recombinant human TNF-α. Apoptosis was detected by assessment of chromatin condensation and nuclear fragmentation and by assay of the enzymatic activities of Caspase 1 and Caspase 3 with membrane-permeable substrates applied to intact cells. Fas protein was detected by immunoblotting of HCAEC lysates. Apoptosis was induced in HCAEC by purified Fas ligand or by the monoclonal activating antibody CH-11 at concentrations of 25 or 200 ng/ml, but not by nonspecific isotype-matched immunoglobulins. The apoptotic index elicited by either Fas activator was equal to that induced by TNF-a (3.0-3.6-fold versus control, p < 0.01). The Fas-neutralizing antibody ZB4 abrogated HCAEC apoptosis induced by CH-11, but had no inhibitory effect on apoptosis in response to TNF-a. Fas ligation significantly increased the activities of both Caspase 1 and Caspase 3 at 20 hours of stimulation (1.7- and 2.0-fold versus control, both p < 0.05); in contrast, purified TNF-a increased the activity of Caspase 3 but not Caspase 1 (2.1-fold, p < 0.05). Western blotting of HCAEC lysates with antibody CH-11 identified a single immunoreactive protein of 90 kDa.

Conclusions

Cultured human coronary artery endothelial cells express functional Fas capable of inducing apoptosis in response to either purified Fas ligand or receptor-activating monoclonal antibodies, at levels equal to those inducible by purified TNF-α. Immunologic studies and differential kinetics of caspase activation suggest that Fas and TNF-α induce apoptosis in HCAEC by signaling pathways that are distinct but equal in potency.

Fc gamma Rs modulate cytotoxicity of anti-Fas antibodies: implications for agonistic antibody-based therapeutics

Development of anti-Fas Abs to treat diseases with insufficient Fas-mediated apoptosis has been limited by concern about hepatotoxicity. We report here that hepatotoxicity elicited by anti-Fas Ab Jo2 is dependent on FcgammaRIIB. Thus, following Jo2 treatment, all FcgammaRIIB(-/-) mice survived while 80% of wild-type and all FcR-gamma(-/-) mice died from acute liver failure. Microscopic examination suggests that FcgammaRIIB deficiency protects the hepatic sinusoidal endothelium, a cell type that normally coexpresses Fas and FcgammaRIIB. In vitro studies showed that FcgammaRIIB, but not FcgammaRI and FcgammaRIII, on neighboring macrophages substantially enhanced Jo2 mediated apoptosis of Fas expressing target cells. However, FcgammaRI and FcgammaRIII appeared essential for apoptosis-inducing activity of a non-hepatotoxic anti-Fas mAb HFE7A. These findings imply that by interacting with the Fc region of agonistic Abs, FcgammaRs can modulate both the desired and undesired consequences of Ab-based therapy. Recognizing this fact should facilitate development of safer and more efficacious agonistic Abs.

Differential effect of IL-18 on endothelial cell apoptosis mediated by TNF-alpha and Fas (CD95)

Interleukin-18 (IL-18) is a newly identified cytokine with proinflammatory activity. Numerous studies have shown that proinflammatory cytokines may regulate endothelial cells (EC) apoptosis mediated by members of the tumor necrosis factor (TNF) family, such as TNF-alpha and Fas. In this study we hypothesized that IL-18 may regulate the susceptibility of liver endothelial cells (LEC) to apoptosis induced by TNF and Fas. IL-18 increased the susceptibility of LEC to undergo apoptosis mediated by TNF but not by Fas. Since TNF-induced apoptosis is mediated by the type I TNF receptor (TNFRI), we investigated up-regulation of this receptor in IL-18-treated LEC. IL-18 induced up-regulation of the TNFRI on the surface of LEC. Partial blocking of LEC apoptosis induced by IL-18 and TNF was observed when the cells were pretreated with the broad-spectrum inhibitor of caspases z-VAD-fmk, suggesting involvement of the caspase pathway in apoptosis induced by these cytokines in these cells. Our results show that IL-18 differentially regulates apoptosis mediated by the death-inducing factors, TNF and Fas. To our knowledge, this is the first report that IL-18 may regulate endothelial cell apoptosis mediated by TNF. These results may have clinical implications in those clinical hepatic conditions associated with high levels of IL-18 and TNF.

Suppression of Fas-FasL-induced endothelial cell apoptosis prevents diabetic blood-retinal barrier breakdown in a model of streptozotocin-induced diabetes

Diabetic macular edema, resulting from increased microvascular permeability, is the most prevalent cause of vision loss in diabetes. The mechanisms underlying this complication remain poorly understood. In the current study, diabetic vascular permeability (blood-retinal barrier breakdown) is demonstrated to result from a leukocyte-mediated Fas-FasL-dependent apoptosis of the retinal vasculature. Following the onset of streptozotocin-induced diabetes, FasL expression was increased in rat neutrophils (P<0.005) and was accompanied by a simultaneous increase in Fas expression in the retinal vasculature. Static adhesion assays demonstrated that neutrophils from diabetic, but not control, rats induced endothelial cell apoptosis in vitro (P<0.005). The latter was inhibited via an antibody-based FasL blockade (P<0.005). In vivo, the inhibition of FasL potently reduced retinal vascular endothelial cell injury, apoptosis, and blood-retinal barrier breakdown (P<0.0001) but did not diminish leukocyte adhesion to the diabetic retinal vasculature. Taken together, these data are the first to identify leukocyte-mediated Fas-FasL-dependent retinal endothelial cell apoptosis as a major cause of blood-retinal barrier breakdown in early diabetes. These data imply that the targeting of the Fas-FasL pathway may prove beneficial in the treatment of diabetic retinopathy.

Intercellular adhesion molecule-1 in the heart

Intercellular adhesion molecule-1 (ICAM-1) belongs to the superfamily of immunoglobulin-like adhesion molecules. Up-regulation of ICAM-1 occurs in many different pathophysiological processes. Also, cardiomyocytes can express ICAM-1-for example, in acute myocardial infarction. Moreover, inhibition of ICAM-1 expression in the heart dramatically reduces infarct size. Hence, inhibitors of ICAM-1 may provide a novel therapeutic option for acute myocardial infarction.

CD95 engagement induces disseminated endothelial cell apoptosis in vivo: immunopathologic implications

Fas (CD95) is a death receptor involved in apoptosis induction on engagement by Fas ligand (CD95L). Although CD95L-mediated apoptosis has been proposed as a pathogenic mechanism in a wide range of diseases, including graft-versus-host disease, systemic CD95 engagement in mice by agonistic CD95-specific antibodies or by soluble multimeric CD95L (smCD95L), though lethal, has been reported to cause apoptosis only in a limited range of cell types, that is, hepatocytes, hepatic sinusoidal endothelial cells, and lymphocytes. Another member of the tumor necrosis factor (TNF)/CD95L family, TNF-alpha, induces disseminated vascular endothelial cell apoptosis, which precedes apoptosis of other cell types and lethal multiorgan failure. Here we show that systemic CD95 engagement in vivo by agonistic CD95-specific antibody or smCD95L causes rapid, extensive, and disseminated endothelial cell apoptosis throughout the body, by a mechanism that does not depend on TNF-alpha. Disseminated endothelial cell apoptosis was also the first detectable lesion in a murine model of acute tissue damage induced by systemic transfer of allogeneic lymphocytes and did not occur when allogeneic lymphocytes were from CD95L-defective mice. Both vascular and additional tissue lesions induced by agonistic CD95-specific antibody, smCD95L, or allogeneic lymphocytes were prevented by treatment with an inhibitor of caspase-8, the upstream caspase coupled to CD95 death signaling. Vascular lesions are likely to play an important role in the pathogenesis of allogeneic immune responses and of other diseases involving circulating CD95L-expressing cells or smCD95L, and the prevention of CD95-mediated death signaling in endothelial cells may have therapeutic implications in these diseases.

Doxorubicin induces apoptosis and CD95 gene expression in human primary endothelial cells through a p53-dependent mechanism

Regulation of the homeostasis of vascular endothelium is critical for the processes of vascular remodeling and angiogenesis under physiological and pathological conditions. Here we show that doxorubicin (Dox), a drug used in antitumor therapy, triggered a marked accumulation of p53 and induced CD95 gene expression and apoptosis in proliferating human umbilical vein endothelial cells (HUVECs). Transfection and site-directed mutagenesis experiments using the CD95 promoter fused to an intronic enhancer indicated the requirement for a p53 site for Dox-induced promoter activation. Furthermore, the p53 inhibitor pifithrin-alpha (PFT-alpha) blocked both promoter inducibility and protein up-regulation of CD95 in response to Dox. Up-regulated CD95 in Dox-treated cells was functional in eliciting apoptosis upon incubation of the cells with an agonistic CD95 antibody. However, Dox-mediated apoptosis was independent of CD95/CD95L interaction. The analysis of apoptosis in the presence of PFT-alpha and benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone revealed that both p53 and caspase activation are required for Dox-mediated apoptosis of HUVECs. Finally, Dox triggered Bcl-2 down-regulation, cytochrome c release from mitochondria, and the activation of caspases 9 and 3, suggesting the involvement of a mitochondrially operated pathway of apoptosis. These results highlight the role of p53 in the response of primary endothelial cells to genotoxic drugs and may reveal a novel mechanism underlying the antitumoral properties of Dox, related to its ability to induce apoptosis in proliferating endothelial cells.

Fas (CD95)- and tumor necrosis factor-mediated apoptosis in liver endothelial cells: role of caspase-3 and the p38 MAPK

Recently, we showed that TNF enhances the susceptibility of endothelial cells from murine liver sinusoids (LEC) to Fas-mediated apoptosis, suggesting that signals transduced by Fas and TNF receptors may synergistically increase intracellular death signals in these cells. In this work we evaluated whether caspase-3 and p38 are involved in LEC apoptosis induced by Fas and TNF. Here we show that LEC treated with Fas agonist (Jo2 mAb at 0.1 microg/ml) and TNF had a greater caspase-3 activity (twofold increase) than cells treated with each factor alone. There was a strong correlation between caspase-3 activity and cell killing induced by Jo2/TNF, indicating that this caspase plays a critical role in this process. Likewise, there was a significant increase in caspase-8 activity in LEC treated with Jo2 and TNF, compared with untreated cells or cells treated with each factor alone. Apoptosis of LEC induced by Jo2/TNF was partially reversed by SB203580, a p38 inhibitor, suggesting that p38 is involved in apoptosis of these cells. To our knowledge, this is the first report that apoptosis induced by Fas/TNF in LEC is associated with coactivation of both caspase-3 and p38. Potentially, both caspase-3 and p38 may be of great importance in endothelial cell pathology as molecular targets for preventing vascular damage due to endothelial cell apoptosis.

Recombinant human Fas ligand induces alveolar epithelial cell apoptosis and lung injury in rabbits

This study investigated whether recombinant human soluble Fas ligand (rh-sFasL) induces apoptosis of primary type II pneumocytes in vitro and lung injury in vivo. Type II cells isolated from normal rabbit lung expressed Fas on their surface and became apoptotic after an 18-h incubation with rh-sFasL. Fas expression in normal rabbit lungs was localized by immunohistochemistry to alveolar and airway epithelia and alveolar macrophages. The administration of 10 microg of rh-sFasL into the right lungs of rabbits resulted 24 h later in both significantly more bronchoalveolar lavage fluid total protein and significantly more tissue changes compared with those in the left lungs, which received rh-sFasL plus Fas:Ig (a fusion protein that binds and blocks sFasL). Tissue changes included thickening of the alveolar walls, neutrophilic infiltrates, apoptotic (terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive) cells in the alveolar walls, and increased expression of interleukin-8 by alveolar macrophages (as determined by immunohistochemistry). We conclude that the alveolar epithelium of normal rabbits expresses Fas and that sFasL induces lung injury and inflammation in rabbits.

Reduced expression of flice-inhibitory protein (FLIP) and NFkappaB is associated with death receptor-induced cell death in human aortic endothelial cells (HAECs)

We investigated the effects of TNF receptor 1 (TNFR1) and 2 (TNFR2) modulation on the death of human aortic endothelial cells (HAECs) resistant to TNF-alpha-induced cell death. Alteration of the transcription of anti-apoptotic proteins, including inhibitor of apoptosis protein 1, 2 (cIAP1, 2), TNF receptor-associated factor 1 (TRAF1), nuclear factor kappa B1 protein (NFkappaB1), and FLICE-inhibitory protein (FLIP) was assessed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). TNF-alpha (200 ng/ml) or actinomycin D (ActD) (5 ng/ml) did not kill cells, while 5 ng/ml of TNF-alpha and 5 ng/ml of ActD increased expression of Fas (CD95) and FasL (CD95L), and 45% of cells died. TNFR2 blockade suppressed NFkappaB1 and FLIP expression and increased cell death. TNFR1 blockade enhanced FLIP expression and decreased cell death. Cells insensitive to TNF-alpha may respond to TNF-alpha through TNFR that induces transcription of NFkappaB1 and FLIP. Down-regulation of these proteins may facilitate death of cells insensitive to TNF-alpha-induced cell death.