Mice lacking TNFalpha receptors 1 and 2 are resistant to death and fulminant liver injury induced by agonistic anti-Fas antibody

MAP kinase ERK5 modulates cancer cell sensitivity to extrinsic apoptosis induced by death-receptor agonists

Death receptor ligand TRAIL is a promising cancer therapy due to its ability to selectively trigger extrinsic apoptosis in cancer cells. However, TRAIL-based therapies in humans have shown limitations, mainly due inherent or acquired resistance of tumor cells. To address this issue, current efforts are focussed on dissecting the intracellular signaling pathways involved in resistance to TRAIL, to identify strategies that sensitize cancer cells to TRAIL-induced cytotoxicity. In this work, we describe the oncogenic MEK5-ERK5 pathway as a critical regulator of cancer cell resistance to the apoptosis induced by death receptor ligands. Using 2D and 3D cell cultures and transcriptomic analyses, we show that ERK5 controls the proteostasis of TP53INP2, a protein necessary for full activation of caspase-8 in response to TNFα, FasL or TRAIL. Mechanistically, ERK5 phosphorylates and induces ubiquitylation and proteasomal degradation of TP53INP2, resulting in cancer cell resistance to TRAIL. Concordantly, ERK5 inhibition or genetic deletion, by stabilizing TP53INP2, sensitizes cancer cells to the apoptosis induced by recombinant TRAIL and TRAIL/FasL expressed by Natural Killer cells. The MEK5-ERK5 pathway regulates cancer cell proliferation and survival, and ERK5 inhibitors have shown anticancer activity in preclinical models of solid tumors. Using endometrial cancer patient-derived xenograft organoids, we propose ERK5 inhibition as an effective strategy to sensitize cancer cells to TRAIL-based therapies.

ADAM Metalloproteinase Domain 17 Regulates Cholestasis-Associated Liver Injury and Sickness Behavior Development in Mice

Disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) is a ubiquitously expressed membrane-bound enzyme that mediates shedding of a wide variety of important regulators in inflammation including cytokines and adhesion molecules. Hepatic expression of numerous cytokines and adhesion molecules are increased in cholestatic liver diseases including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), however, the pathophysiological role of ADAM17 in regulating these conditions remains unknown. Therefore, we evaluated the role of ADAM17 in a mouse model of cholestatic liver injury due to bile duct ligation (BDL). We found that BDL enhanced hepatic ADAM17 protein expression, paralleled by increased ADAM17 bioactivity. Moreover, inhibition of ADAM17 bioactivity with the specific inhibitor DPC 333 significantly improved both biochemical and histological evidence of liver damage in BDL mice. Patients with cholestatic liver disease commonly experience adverse behavioral symptoms, termed sickness behaviors. Similarly, BDL in mice induces reproducible sickness behavior development, driven by the upregulated expression of cytokines and adhesion molecules that are in turn regulated by ADAM17 activity. Indeed, inhibition of ADAM17 activity significantly ameliorated BDL-associated sickness behavior development. In translational studies, we evaluated changes in ADAM17 protein expression in liver biopsies obtained from patients with PBC and PSC, compared to normal control livers. PSC and PBC patients demonstrated increased hepatic ADAM17 expression in hepatocytes, cholangiocytes and in association with liver-infiltrating immune cells compared to normal controls. In summary, cholestatic liver injury in mice and humans is associated with increased hepatic ADAM17 expression. Furthermore, inhibition of ADAM17 activity improves both cholestatic liver injury and associated sickness behavior development, suggesting that ADAM17 inhibition may represent a novel therapeutic approach for treating patients with PBC/PSC.

Disruption of the FasL/Fas axis protects against inflammation-derived tumorigenesis in chronic liver disease

Fas Ligand (FasL) and Fas (APO-1/CD95) are members of the TNFR superfamily and may trigger apoptosis. Here, we aimed to elucidate the functional role of Fas signaling in an experimental model of chronic liver disease, the hepatocyte-specific NEMO knockout (NEMO^Δhepa) mice. We generated NEMO^Δhepa /Fas^lpr mice, while NEMO^Δhepa, NEMO^f/f as well as Fas^lpranimals were used as controls, and characterized their phenotype during liver disease progression. Liver damage was evaluated by serum transaminases, histological, immunofluorescence procedures, and biochemical and molecular biology techniques. Proteins were detected by western Blot, expression of mRNA by RT-PCR, and infiltration of inflammatory cells was determined by FACs analysis, respectively. Fas^lpr mutation in NEMO^Δhepa mice resulted in overall decreased liver injury, enhanced hepatocyte survival, and reduced proliferation at 8 weeks of age compared with NEMO^Δhepa mice. Moreover, NEMO^Δhepa/Fas^lpr animals elicited significantly decreased parameters of liver fibrosis, such as Collagen IA1, MMP2, and TIMP1, and reduced proinflammatory macrophages and cytokine expression. At 52 weeks of age, NEMO^Δhepa/Fas^lpr exhibited less malignant growth as evidenced by reduced HCC burden associated with a significantly decreased number of nodules and LW/BW ratio and decreased myeloid populations. Deletion of TNFR1 further reduced tumor load of 52-weeks-old NEMO^Δhepa/Fas^lpr mice. The functionality of FasL/Fas might affect inflammation-driven tumorigenesis in an experimental model of chronic liver disease. These results help to develop alternative therapeutic approaches and extend the limitations of tumor therapy against HCC.

TNFα sensitizes hepatocytes to FasL-induced apoptosis by NFκB-mediated Fas upregulation

Although it is well established that TNFα contributes to hepatitis, liver failure and associated hepatocarcinogenesis via the regulation of inflammation, its pro-apoptotic role in the liver has remained enigmatic. On its own, TNFα is unable to trigger apoptosis. However, when combined with the transcriptional inhibitor GaLN, it can cause hepatocyte apoptosis and liver failure in mice. Moreover, along with others, we have shown that TNFα is capable of sensitizing cells to FasL- or drug-induced cell death via c-Jun N-terminal kinase (JNK) activation and phosphorylation/activation of the BH3-only protein Bim. In this context, TNFα could exacerbate hepatocyte cell death during simultaneous inflammatory and T-cell-mediated immune responses in the liver. Here we show that TNFα sensitizes primary hepatocytes, established hepatocyte cell lines and mouse embryo fibroblasts to FasL-induced apoptosis by the transcriptional induction and higher surface expression of Fas via the NFκB pathway. Genetic deletion, diminished expression or dominant-negative inhibition of the NFκB subunit p65 resulted in lower Fas expression and inhibited TNFα-induced Fas upregulation and sensitization to FasL-induced cell death. By hydrodynamic injection of p65 shRNA into the tail vein of mice, we confirm that Fas upregulation by TNFα is also NFκB-mediated in the liver. In conclusion, TNFα sensitization of FasL-induced apoptosis in the liver proceeds via two parallel signaling pathways, activation of JNK and Bim phosphorylation and NFκB-mediated Fas upregulation.

α-1-antitrypsin inhibits acute liver failure in mice

Acute liver failure remains a critical clinical condition, with high mortality rates, and increased apoptosis of hepatocytes represents a key event in the cause of liver failure. Alpha-1-antitrypsin (AAT) is synthesized and secreted mainly by hepatocytes, and plasma purified AAT is used for augmentation therapy in patients with AAT deficiency. Because AAT therapy exerts antiinflammatory and immune modulatory activities in various experimental models, and it was recently suggested that AAT exerts antiapoptotic activities, we aimed to explore whether administration of AAT may represent a therapeutic strategy to treat acute liver failure in mice. Well-established preclinical models of acute liver failure such as the Jo2 FAS/CD95 activating model and models of acetaminophen and α-amanitin poisoning were used. Therapeutic effects of AAT were evaluated by monitoring animal survival, histopathological changes, measurement of caspase activity, and serum cytokine levels. Systemic treatment with AAT significantly decreased Jo2-induced liver cell apoptosis and prolonged survival of mice. Native and oxidized (lacking elastase inhibitory activity) forms of AAT were equally effective in preventing acute liver injury and showed direct inhibition of active caspase-3 and -8 in liver homogenates and in a cell-free system in vitro. Concomitantly, mice treated with AAT showed significantly lower serum levels of tumor necrosis factor alpha (TNF-α), which also paralleled the reduced activity of ADAM17 (TACE). Noticeably, the increased survival and a reduction of apoptotic hepatocytes were also observed in the α-amanitin and acetaminophen-induced liver injury mouse models.

CONCLUSION

Our data suggest that systemic administration of AAT can be a promising therapy to treat acute liver failure and clinical studies to explore this treatment in humans should be initiated.

Death receptors as targets in cancer

Anti-tumour therapies based on the use pro-apoptotic receptor agonists, including TNF-related apoptosis-inducing ligand (TRAIL) or monoclonal antibodies targeting TRAIL-R1 or TRAIL-R2, have been disappointing so far, despite clear evidence of clinical activity and lack of adverse events for the vast majority of these compounds, whether combined or not with conventional or targeted anti-cancer therapies. This brief review aims at discussing the possible reasons for the lack of apparent success of these therapeutic approaches and at providing hints in order to rationally design optimal protocols based on our current understanding of TRAIL signalling regulation or resistance for future clinical trials.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

JNK activation is required for TNFα-induced apoptosis in human hepatocarcinoma cells

BACKGROUND

A frequent distinctive feature of tumors, hepatocellular carcinomas included, is resistance to apoptosis induced by a variety of agents, among which the pleiotropic cytokine tumor necrosis factor-α (TNF). Compared to other cell types, hepatocytes and hepatoma-derived cell lines are poorly susceptible to TNF-induced apoptosis, which is largely ascribed to activation of the prosurvival transcription factor NF-κB and can be overcome by associating TNF to low doses of protein synthesis inhibitors or other drugs.

AIMS

This study analyses the molecular mechanisms by which TNF, in combination with cycloheximide (CHX), induces apoptosis in human hepatoma-derived Huh7 cells, focusing on the role played by JNK.

METHODS

Huh7 cell cultures were treated with TNF + CHX in the presence or in the absence of the pancaspase inhibitor zVADfmk or of the JNK inhibitor SP600125 as well as after suppression of JNK expression by RNAi. Apoptosis was assessed both by light microscopy and by flow cytometry, JNK and caspase activation by western blotting and/or enzymatic assay.

RESULTS

TNF + CHX-induced death of Huh7 cells involved JNK activation since it was partially prevented by suppressing JNK activity or expression. Moreover, apoptosis was significantly reduced also by zVADfmk, while SP600125 and zVADfmk combined totally abrogated cell death in an additive fashion.

CONCLUSIONS

These results demonstrate a causal role for JNK and caspases in TNF+CHX-induced apoptosis of Huh7 human hepatoma cells. Therefore, strategies aimed at enhancing both pathways should provide a profitable basis to overcome the resistance of hepatocarcinoma cells to TNF-dependent apoptosis.

A role for cGMP in inducible nitric-oxide synthase (iNOS)-induced tumor necrosis factor (TNF) α-converting enzyme (TACE/ADAM17) activation, translocation, and TNF receptor 1 (TNFR1) shedding in hepatocytes

We and others have previously shown that the inducible nitric-oxide synthase (iNOS) and nitric oxide (NO) are hepatoprotective in a number of circumstances, including endotoxemia. In vitro, hepatocytes are protected from tumor necrosis factor (TNF) α-induced apoptosis via cGMP-dependent and cGMP-independent mechanisms. We have shown that the cGMP-dependent protective mechanisms involve the inhibition of death-inducing signaling complex formation. We show here that LPS-induced iNOS expression leads to rapid TNF receptor shedding from the surface of hepatocytes via NO/cGMP/protein kinase G-dependent activation and surface translocation of TNFα-converting enzyme (TACE/ADAM17). The activation of TACE is associated with the up-regulation of iRhom2 as well as the interaction and phosphorylation of TACE and iRhom2, which are also NO/cGMP/protein kinase G-dependent. These findings suggest that one mechanism of iNOS/NO-mediated protection of hepatocytes involves the rapid shedding of TNF receptor 1 to limit TNFα signaling.

TRAIL signaling and synergy mechanisms used in TRAIL-based combination therapies

TRAIL and agonistic antibodies raised against TRAIL death receptors are highly promising new anticancer agents. In this brief review, we describe the recent advances in the molecular understanding of TRAIL signaling and the progress made in using TRAIL or agonistic antibodies clinically in mono- and combination therapies. Synergies have been reported in various scenarios of TRAIL-based multidrug treatments, and these can be used to potentiate the efficacy of therapies targeting TRAIL death receptors. We pay particular attention to structure the current knowledge on the diverse molecular mechanisms that are thought to give rise to these synergies and describe how different signaling features evoking synergies can be associated with distinct classes of drugs used in TRAIL-based combination treatments.

Tumor necrosis factor α sensitizes primary murine hepatocytes to Fas/CD95-induced apoptosis in a Bim- and Bid-dependent manner

Fas/CD95 is a critical mediator of cell death in many chronic and acute liver diseases and induces apoptosis in primary hepatocytes in vitro. In contrast, the proinflammatory cytokine tumor necrosis factor α (TNFα) fails to provoke cell death in isolated hepatocytes but has been implicated in hepatocyte apoptosis during liver diseases associated with chronic inflammation. Here we report that TNFα sensitizes primary murine hepatocytes cultured on collagen to Fas ligand (FasL)-induced apoptosis. This synergism is time-dependent and is specifically mediated by TNFα. Fas itself is essential for the sensitization, but neither Fas up-regulation nor endogenous FasL is responsible for this effect. Although FasL is shown to induce Bid-independent apoptosis in hepatocytes cultured on collagen, the sensitizing effect of TNFα is clearly dependent on Bid. Moreover, both c-Jun N-terminal kinase activation and Bim, another B cell lymphoma 2 homology domain 3 (BH3)-only protein, are crucial mediators of TNFα-induced apoptosis sensitization. Bim and Bid activate the mitochondrial amplification loop and induce cytochrome c release, a hallmark of type II apoptosis. The mechanism of TNFα-induced sensitization is supported by a mathematical model that correctly reproduces the biological findings. Finally, our results are physiologically relevant because TNFα also induces sensitivity to agonistic anti-Fas-induced liver damage.

CONCLUSION

Our data suggest that TNFα can cooperate with FasL to induce hepatocyte apoptosis by activating the BH3-only proteins Bim and Bid.

Anoikis mediators in oral squamous cell carcinoma

Anoikis - apoptotic cell death triggered by loss of extracellular matrix (ECM) contacts - is dysregulated in many chronic debilitating and fatal diseases. Mechanisms rendering tumor cells resistant to anoikis, although not completely understood, possess significant therapeutic promise. In death receptor-mediated anoikis mechanisms, focal adhesion kinase (FAK) and receptor-interacting protein (RIP) dissociate, leading to association of RIP with Fas, formation of the death-inducing signaling complex (DISC), activation of caspase-3, and propagation of anoikis. In contrast, anoikis resistance is accomplished through constitutive activation of survival pathways that include integrin-dependent activation of FAK and extracellular-signal-regulated kinase (ERK). In addition, FAK and RIP association confers anoikis resistance by inhibiting the association of RIP with Fas and formation of the death signaling complex, which allows cells to escape anoikis. Up-regulation of CD44 also contributes to survival signals and promotes anoikis resistance. This review will focus on the roles of death receptors, prosurvival pathways, and the molecular players involved in anoikis escalation and resistance in oral squamous cell carcinoma.

Construction of mTNFR1shRNA plasmid and its biological effects on MHV-3 induced fulminant hepatitis in BALB/cJ mice

Previous study on TNFR1-mediated hepatocyte apoptosis has been implicated in the development of fulminant viral hepatitis. To interfere with the potentially effective target, plasmid named p-mTNFR1shRNA complimentary to the sequence responsible for mTNFR1 was also constructed and further confirmed by sequence analysis. To investigate the effect of mTNFR1shRNA plasmid on mTNFR1 expression in vivo and the disease progress in MHV-3 induced fulminant hepatitis mice model. By hydrodynamic injection of mTNFR1shRNA plasmid, the survival rate of mice, hepatic pathological change were examined and compared between mice with/without mTNFR1shRNA plasmid intervention. The expression of mTNFR1 was detected by Real-time PCR, immunohistochemistry staining. The mTNFR1shRNA plasmid significantly reduced mTNFR1 expression in vivo, markedly ameliorates inflammatory infiltration, prolonged the survival time period and elevated the survival rate from 0 up to 13.3% in Balb/cJ mice with MHV-3 induced fulminant hepatitis. This study was designed to explore the opportunity of RNA interference technique in inhibiting TNFR1 expression, which has been reported to be involved in the development of a variety of diseases including fulminant viral hepatitis and severe chronic hepatitis B.

Genetic analysis of the role of tumor necrosis factor receptors in functional outcome after traumatic brain injury in mice

We previously reported that tumor necrosis factor-alpha (TNF-alpha) and Fas receptor induce acute cellular injury, tissue damage, and motor and cognitive deficits after controlled cortical impact (CCI) in mice (Bermpohl et al. 2007 ); however, the TNF receptors (TNFR) involved are unknown. Using a CCI model and novel mutant mice deficient in TNFR1/Fas, TNFR2/Fas, or TNFR1/TNFR2/Fas, we tested the hypothesis that the combination of TNFR2/Fas is protective, whereas TNFR1/Fas is detrimental after CCI. Uninjured knockout (KO) mice showed no differences in baseline physiological variables or motor or cognitive function. Following CCI, mice deficient in TNFR2/Fas had worse post-injury motor and Morris water maze (MWM) performance than wild-type (WT) mice (p < 0.05 group effect for wire grip score and MWM performance by repeated measures ANOVA). No differences in motor or cognitive outcome were observed in TNFR1/Fas KO, or in TNFR2 or TNFR1 single KO mice, versus WT mice. Additionally, no differences in propidium iodide (PI)-positive cells (at 6 h) or lesion size (at 14 days) were observed between WT and TNFR1/Fas or TNFR2/Fas KO mice. Somewhat surprisingly, mice deficient in TNFR1/TNFR2/Fas also had PI-positive cells, lesion size, and motor and MWM deficits similar to those of WT mice. These data suggest a protective role for TNFR2/Fas in the pathogenesis of TBI. Further studies are needed to determine whether direct or indirect effects of TNFR1 deletion in TNFR2/Fas KO mice mediate improved functional outcome in TNFR1/TNFR2/Fas KO mice after CCI.

Protective effects of HFE7A, mouse anti-human/mouse Fas monoclonal antibody against acute and lethal hepatic injury induced by Jo2

HFE7A is a mouse anti-human/mouse Fas monoclonal antibody which, protects mice from fulminant hepatitis induced by Jo2. Herein, we report on the mechanism of the protective effect of HFE7A against Jo2-induced acute and lethal hepatic injury. HFE7A reduced the serum aminotransferase level which was elevated after Jo2 injection. HFE7A also inhibited caspase activation and mitochondrial depolarization in hepatocytes derived from apoptosis induced by Jo2 injection. The protective effect of HFE7A against Jo2-induced apoptosis in mouse hepatocytes was reproducible in vitro. The cell death and caspase activation in isolated mouse hepatocytes were induced by incubating these cells with Jo2 in vitro, and HFE7A inhibited the cell death and caspase activation in mouse hepatocytes in a dose-dependent manner. The affinity of HFE7A to mouse Fas was lower than that of Jo2. The binding of Jo2 to neither recombinant mouse Fas nor mouse hepatocytes was inhibited by an excessive amount of HFE7A. Interestingly, HFE7A bound to hepatocytes isolated from Fas knockout mice. From these results, it is suggested that HFE7A may exert a protective effect against Jo2-induced hepatitis not by competitively inhibiting the binding of Jo2 to Fas on hepatocytes, and that a distinct molecule other than Fas may possibly be involved in the protective effect of HFE7A against Jo2-induced hepatic injury.

Compartmentalized expression of c-FLIP in lung tissues of patients with idiopathic pulmonary fibrosis

Increased apoptosis of alveolar epithelial cells and impaired apoptosis of myofibroblasts have been linked to the pathogenesis of idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP). Fas, a death receptor of the TNF-receptor superfamily, has been implicated in apoptosis of both cell types, though the mechanisms are poorly understood. The goals of this study were: (1) to examine the localization of Fas-associated death-domain-like IL-1beta-converting enzyme inhibitory protein (c-FLIP), an NF-kappaB-dependent regulator of Fas-signaling, in lung tissues from IPF/UIP patients and control subjects; and (2) to compare c-FLIP expression with epithelial cell and myofibroblast apoptosis, proliferation, and NF-kappaB activation. c-FLIP expression was restricted to airway epithelial cells in control lung tissues. In contrast, in patients with IPF/UIP, c-FLIP was also expressed by alveolar epithelial cells in areas of injury and fibrosis, but was absent from myofibroblasts in fibroblastic foci and from alveolar epithelial cells in uninvolved areas of lung tissue. Quantification of apoptosis and proliferation revealed an absence of apoptotic or proliferating cells in fibroblastic foci and low levels of apoptosis and proliferation by alveolar epithelial cells. Quantification of NF-kappaB expression and nuclear translocation revealed strong staining and translocation in alveolar epithelial cells and weak staining and minimal nuclear translocation in myofibroblasts. These findings suggest that: (1) c-FLIP expression is induced in the abnormal alveolar epithelium of patients with IPF/UIP, (2) the resistance of myofibroblasts to apoptosis in patients with IPF/UIP occurs independently of c-FLIP expression, and (3) increased NF-kappaB activation and c-FLIP expression by the alveolar epithelium may be linked.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

A cell-type-specific requirement for IFN regulatory factor 5 (IRF5) in Fas-induced apoptosis

Apoptosis is a highly regulated process of cell suicide that occurs during development, host defense, and pathophysiology. The transcription factor IFN regulatory factor 5 (IRF5), known to be involved in the activation of innate immune responses, recently has been shown to be critical for DNA damage-induced apoptosis and tumor suppression. Here, we report on a cell-type-specific role of IRF5 in promoting apoptosis upon signaling through the death receptor Fas (CD95/APO-1/TNFRSF6). In particular, we show that mice deficient in the Irf5 gene are resistant to hepatic apoptosis and lethality in response to the in vivo administration of a Fas-activating monoclonal antibody, and that IRF5 is involved in a stage of Fas signaling that precedes the activation of caspase 8 and c-Jun N-terminal kinase (JNK). In addition to hepatocytes, IRF5 is also required for apoptosis in dendritic cells activated by hypomethylated CpG but not in thymocytes and embryonic fibroblasts in vitro. Thus, these findings reveal a cell-type-specific function for IRF5 in the complex regulatory mechanism of death-receptor-induced apoptosis.

Evidence that genetic deletion of the TNF receptor p60 or p80 inhibits Fas mediated apoptosis in macrophages

Almost 19 members of the tumor necrosis factor (TNF) superfamily have been identified that interact with 29 different receptors. Whether these receptors communicate with each other is not understood. Recently, we have shown that receptor activator of NF-kappaB ligand signaling is modulated by genetic deletion of the TNF receptor. In the current report, we investigated the possibility of a cross-talk between Fas and TNF-alpha signaling pathway in macrophage cell lines derived from wild-type (WT) mice and from mice with genetic deletion of the type 1 TNF receptor (p60(-/-)), the type 2 TNF receptor (p80(-/-)), or both receptors (p60(-/-)p80(-/-)). We found that the macrophages expressing TNF receptors were highly sensitive to apoptosis induced by anti-Fas. The genetic deletion of TNF receptors, however, made the cells resistance to anti-Fas-induced apoptosis. Anti-Fas induced activation of caspase-3 and PARP cleavage in WT cells but not in TNF receptor-deleted cells. This difference was found to be independent of the expression of Fas, Fas-associated protein with death domain (FADD) or TNF receptor-associated death domain (TRADD). We found that anti-Fas induced recruitment of TNFR1 into Fas-complex. We also found that TRADD, which mediates TNF signaling, was constitutively bound to Fas receptor in TNF receptor-deleted cells but not in wild-type cells. Transient transfection of TNFR1 in TNFR1-deleted cells sensitized them to anti-Fas-induced apoptosis. Overall our results demonstrate that Fas signaling is modulated by the TNF receptors and thus provide the evidence of cross-talk between the receptors of two cytokines.

RNA interference-mediated simultaneous down-regulation of urokinase-type plasminogen activator receptor and cathepsin B induces caspase-8-mediated apoptosis in SNB19 human glioma cells

The invasive character of gliomas depends on proteolytic cleavage of the surrounding extracellular matrix. Cathepsin B and urokinase-type plasminogen activator receptor (uPAR) together are known to be overexpressed in gliomas and, as such, are attractive targets for gene therapy. In the present study, we used plasmid constructs to induce the RNA interference (RNAi)-mediated down-regulation of uPAR and cathepsin B in SNB19 human glioma cells. We observed that the simultaneous down-regulation of uPAR and cathepsin B induces the up-regulation of proapoptotic genes and initiates a collapse in mitochondrial Deltapsi. Cathepsin B and uPAR down-regulated cells showed increases in the expression of activated caspase-8 and DFF40/caspase-activated DNase. Nuclear translocation of AIF and Fas ligand translocation to the cell membrane were also observed. Ki67 and X-linked inhibitor of apoptosis protein levels decreased, thereby indicating apoptosis. These results suggest the involvement of uPAR-cathepsin B complex on the cell surface and its role in maintaining the viability of SNB19 glioma cells. In conclusion, RNAi-mediated down-regulation of uPAR and cathepsin B initiates a partial extrinsic apoptotic cascade accompanied by the nuclear translocation of AIF. Our study shows the potential of RNAi-mediated down-regulation of uPAR and cathepsin B in developing new therapeutics for gliomas.

Hepatitis B virus sensitizes hepatocytes to TRAIL-induced apoptosis through Bax

Hepatitis B virus (HBV) infection afflicts >300 million people worldwide and is a leading cause of hepatocyte death, cirrhosis, and hepatocellular carcinoma. While the morphological characteristics of dying hepatocytes are well documented, the molecular mechanisms leading to the death of hepatocytes during HBV infection are not well understood. TRAIL, the TNF-related apoptosis-inducing ligand, has recently been implicated in the death of hepatocytes under certain inflammatory but not normal conditions. To determine the potential roles of TRAIL in HBV-induced hepatitis, we examined the effects of HBV and its X protein (HBx) on TRAIL-induced hepatocyte apoptosis both in vivo and in vitro. We found that hepatitis and hepatic cell death in HBV transgenic mice were significantly inhibited by a soluble TRAIL receptor that blocks TRAIL function. We also found that HBV or HBx transfection of a hepatoma cell line significantly increased its sensitivity to TRAIL-induced apoptosis. The increase in TRAIL sensitivity were associated with a dramatic up-regulation of Bax protein expression. Knocking down Bax expression using Bax-specific small interference RNA blocked HBV-induced hepatitis and hepatocyte apoptosis. The degradation of caspases 3 and 9, but not that of Bid or caspase-8, was preferentially affected by Bax knockdown. These results establish that HBV sensitizes hepatocytes to TRAIL-induced apoptosis through Bax and that Bax-specific small interference RNA can be used to inhibit HBV-induced hepatic cell death.

Minimal hepatic toxicity of Onyx-015: spatial restriction of coxsackie-adenoviral receptor in normal liver

We administered an adenoviral vector, Onyx-015, into the hepatic artery of patients with metastatic colorectal cancer involving the liver. Thirty-five patients enrolled in this multi-institutional phase I/II trial received up to eight arterial infusions of up to 2 × 10¹² viral particles. Hepatic toxicity was the primary dose-limiting toxicity observed in preclinical models. However, nearly 200 infusions of this adenoviral vector were administered directly into the hepatic artery without significant toxicity. Therefore, we undertook this analysis to determine the impact of repeated adenoviral exposure on hepatic function. Seventeen patients were treated at our institution, providing a detailed data set on the changes in hepatic function following repeated exposure to adenovirus. No changes in hepatic function occurred with the first treatment of Onyx-015 among these patients. Transient increases in transaminase levels occurred in one patient starting with the second infusion and transient increases in bilirubin was observed in two patients starting with the fifth treatment. These changes occurred too early to be explained by viral-mediated lysis of hepatocytes. In addition, viremia was observed starting 3–5 days after the viral infusion in half of the patient, but was not associated with hepatic toxicity. To further understand the basis for the minimal hepatic toxicity of adenoviral vectors, we evaluated the replication of adenovirus in primary hepatocytes and tumor cells in culture and the expression of the coxsackie-adenoviral receptor (CAR) in normal liver and colon cancer metastatic to the liver. We found that adenovirus replicates poorly in primary hepatocytes but replicates efficiently in tumors including tumors derived from hepatocytes. In addition, we found that CAR is localized at junctions between hepatocytes and is inaccessible to hepatic blood flow. CAR is not expressed on tumor vasculature but is expressed on tumor cells. Spatial restriction of CAR to the intercellular space in normal liver and diminished replication of adenovirus in hepatocytes may explain the minimal toxicity observed following repeated hepatic artery infusions with Onyx-015.

Blockade of TRAIL pathway ameliorates HBV-induced hepatocyte apoptosis in an acute hepatitis model

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) may play important roles during hepatitis B virus (HBV) infection. In this study, we used a recombinant human soluble death receptor 5 (sDR5) to explore its effect in a mouse model of HBV-induced acute hepatitis. By measuring blood transaminase activity and hepatocyte apoptosis, we found that sDR5 could alleviate liver damage by blocking TRAIL-induced apoptosis of HBV-transfected hepatocytes. sDR5 injection at 16 mg/kg 24h before HBV transfection was the most effective. Additionally, we showed that sDR5 was equally effective in protecting liver injury as the Stronger Neo-Minophagen C (SNMC), a commonly used drug for patients with liver diseases. Thus, sDR5 represents a potential novel therapeutic drug for patients with fulminant hepatitis.

Altered retinal neovascularization in TNF receptor-deficient mice

PURPOSE

Tumor necrosis factor alpha (TNF-alpha) has been shown to play an integral role in inflammation, apoptosis, and angiogenesis. We induced retinopathy in tumor necrosis factor receptor-deficient mice (TNFR-) in order to examine the role TNF-alpha plays in the pathogenesis of retinopathy of prematurity.

METHODS

On postnatal day (P) 7, TNFR-knockout mice and their congenic controls, B6129JF1 (B6129) mice, were exposed to 75% oxygen for up to 5 days and then allowed to recover in room air. Retinopathy was qualitatively assessed by examining fluorescein (FITC) angiography. Furthermore, retinal vascular changes were quantified by immunolabeling retinal vessels in cross sections with an anti-type IV collagen antibody. Disease pathology was quantified by counting preretinal neovascular nuclei. TUNEL analysis was performed to determine if TNFR-mice exhibited a reduced number of apoptotic cells after oxygen-induced retinopathy.

RESULTS

FITC-perfused retinas qualitatively demonstrated similar degrees of vascular development and vaso-obliteration on P12 in the room air and hyperoxia-exposed TNFR- and B6129 mice. On P17, the hyperoxia-exposed TNFR- and B6129 mice qualitatively appeared to develop a similar degree of retinal neovascularization. However, FITC-perfused retinal flat mounts on P21 suggested that the hyperoxia-exposed TNFR-mice had a prolonged neovascular response compared to the hyperoxia-exposed B6129 mice. Type IV collagen staining revealed delayed development of the deep intraretinal vessels in the TNFR-room control mice and hyperoxia-exposed TNFR-mice, as compared with B6129 controls. On P17, the average number of preretinal nuclei was similar between the hyperoxia-exposed TNFR-mice and B6129 mice. However, on P21, the neovascularization in the B6129 mice had regressed (3.9 +/- 0.57, preretinal nuclei), whereas neovascularization in the TNFR-mice remained prominent (25.6 +/- 6.3, preretinal nuclei). On P21, the B6129 mice exhibited increased apoptosis in preretinal vascular tufts as compared with TNFR- mice.

CONCLUSIONS

TNFR- mice had both an altered development of the intraretinal vessels and altered angiogenic response after hyperoxia. Therefore, absence of the TNF-alpha pathway appears to disrupt the local microenvironment promoting angiogenesis in the deep retinal vascular network, as well as altering tuft regression by modifying endothelial cell apoptosis.

Protein-tyrosine Phosphatase 1B Deficiency Protects against Fas-induced Hepatic Failure

Genetic disruption of protein-tyrosine phosphatase 1B (PTP1B) in mice leads to increased insulin sensitivity and resistance to weight gain. Although PTP1B has been implicated as a regulator of multiple signals, its function in other physiological responses in vivo is poorly understood. Here we demonstrate that PTP1B-null mice are resistant to Fas-induced liver damage and lethality, as evident by reduced hepatic apoptosis in PTP1B-null versus wild type mice and reduced levels of circulating liver enzymes. Activation of pro-apoptotic caspases-8, -9, -3, and -6 was attenuated in livers from PTP1B-null mice following Fas receptor stimulation, although components of the death-inducing signaling complex were intact. Activation of anti-apoptotic regulators, such as the hepatocyte growth factor/Met receptor tyrosine kinase, as well as Raf, ERK1/2, FLIP(L), and the NF-kappaB pathway, was elevated in response to Fas activation in livers from PTP1B-null mice. Using PTP1B-deficient primary hepatocytes, we show that resistance to Fas-mediated apoptosis is cell autonomous and that signals involving the Met, ERK1/2, and NF-kappaB pathways are required for cytoprotection. This study identifies a previously unknown physiological role for PTP1B in Fas-mediated liver damage and points to PTP1B as a potential therapeutic target against hepatotoxic agents.

TNF-alpha sensitizes normal and fibrotic human lung fibroblasts to Fas-induced apoptosis

Pulmonary accumulation of fibroblasts and myofibroblasts in idiopathic pulmonary fibrosis/usual interstitial pneumonia (IFP/UIP) has been linked to (1) increased migration of a circulating pool of fibrocytes, (2) cell proliferation, and (3) resistance to apoptosis. The mechanism of physiologic apoptosis of lung fibroblasts is poorly understood. Using normal and fibrotic human lung fibroblasts and the human lung fibroblast cell line, MRC-5, we examined the regulation of Fas-induced apoptosis by the proinflammatory cytokines TNF-alpha and IFN-gamma. Herein, we show that the basal resistance of lung fibroblasts and myofibroblasts to Fas-induced apoptosis is overcome by sensitization with TNF-alpha. IFN-gamma did not sensitize cells to Fas-induced apoptosis, but exhibited synergistic activity with TNF-alpha. Sensitization by TNF-alpha was observed in MRC-5 cells and in fibroblasts and myofibroblasts from normal and fibrotic human lung, suggesting that this represents a conserved mechanism to engage Fas-induced apoptosis. The mechanism of sensitization was localized at the level of recruitment of the adapter protein, FADD, to the cytoplasmic domain of Fas. Collectively, these findings suggest that fibroblast apoptosis involves two steps, sensitization and induction, and that inadequate pulmonary inflammation in IPF/UIP may favor fibroblast accumulation by reducing sensitization to apoptosis.

The transfer of reductive energy and pace of proteome turnover: a theory of integrated catabolic control

Hundreds of cell proteins undergo reversible transitions among redox states. Coordinate control and common functions served by redox-modified proteins are unknown. The suspect "redox code" integrating metabolome, proteome, and genome remains undefined. Protein redox control involves coupling of the population redox partition to transfer of reductive energy from source to sink. Lessons in metabolic programs under redox coordination might be found in nutritional desperation where reductive transfer from fuel fails to feed pathways to protein reduction. Upon nutritional interruption, proteolysis initially increases. However, catabolism secondarily declines in later starvation so as to postpone loss of the minimal proteome under synthetic failure and delay death. Integrated proteome turnover is paced by reductive transfer coupled to redox states of proteins serving diverse functions. Some continuing proteolysis is redox-independent. Cathepsin B is a model, redox-responsive, catabolic machine among proteins involved in turnover. The CysHis pair is simultaneously a redox-responsive site, an inhibitory metal-binding site, and a peptidolytic reaction mechanism. Pro-region cleavage generates permissive reaction conditions, but not necessarily the maximal peptidolytic rate. Mature cathepsin B can be inactivated by partition into multiple oxidation states. Cathepsin B can be reductively activated by glutathione or disulfhydryl reductases, and redox-buffered by glutathione homodisulfide/glutathione. Topics in protease regulation include: (a) the rate of total cell transfer of nutrient reductive energy from NADPH source potential to reductive pathways, (b) the distribution of reductive energy routed through parallel interactive pathways to protease, (c) the rate of transfer from protease through pathways to oxygen (reactive oxygen species) acceptor at sink potential, and (d) the linkage of protease state partition to relative rates of reductions and oxidations. Cell iron, sulfur, and oxygen redox are inseparable. The interaction of the CysHis site with iron provides a sensor, integrator, and effector switch coupling cathepsin B to metal-sulfuroxygen redox. Artificial metal-redox-proton switching is a new concept in protein engineering; however, nature has already applied "nanotechnology" to protein redox control.

Hepatic mitochondrial glutathione: transport and role in disease and toxicity

Synthesized in the cytosol of cells, a fraction of cytosolic glutathione (GSH) is then transported into the mitochondrial matrix where it reaches a high concentration and plays a critical role in defending mitochondria against oxidants and electrophiles. Evidence mainly from kidney and liver mitochondria indicated that the dicarboxylate and the 2-oxoglutarate carriers contribute to the transport of GSH across the mitochondrial inner membrane. However, differential features between kidney and liver mitochondrial GSH (mGSH) transport seem to suggest the existence of additional carriers the identity of which remains to be established. One of the characteristic features of the hepatic mitochondrial transport of GSH is its regulation by membrane fluidity. Conditions leading to increased cholesterol deposition in the mitochondrial inner membrane such as in alcohol-induced liver injury decrease membrane fluidity and impair the mitochondrial transport of GSH. Depletion of mitochondrial GSH by alcohol is believed to contribute to the sensitization of the liver to alcohol-induced injury through tumor necrosis factor (TNF)-mediated hepatocellular death. Through control of mitochondrial electron transport chain-generated oxidants, mitochondrial GSH modulates cell death and hence its regulation may be a key target to influence disease progression and drug-induced cell death.

New pharmacokinetic and pharmacodynamic tools for interferon-alpha (IFN-alpha) treatment of human cancer

Interferon alpha (IFN-alpha) has been widely used in the treatment of human solid and haematologic malignancies. Although the antitumour activity of IFN-alpha is well recognised at present, no major advances have been achieved in the last few years. Recent findings have provided new information on the molecular mechanisms of the antitumour activity of the cytokine. In fact, IFN-alpha appears to block cell proliferation, at least in part, through the induction of apoptotic effects. This cytokine can also regulate the progression of tumour cells through the different phases of the cell cycle inducing an increase of the expression of the cyclin-dependent kinase inhibitors p21 and p27. However, it must be considered that IFN-alpha is a physiologic molecule with ubiquitously expressed receptors that is likely to activate survival mechanisms in the cell. We have recently identified an epidermal growth factor (EGF) Ras-dependent protective response to the apoptosis induced by IFN-alpha in epidermoid cancer cells. The identification of tissue- and/or tumour-specific survival pathways and their selective targeting might provide a new approach to improve the efficacy of IFN-alpha-based treatment of human cancer. Moreover, new pegylated species of IFN-alpha are now available with a more favourable pharmacokinetic profile. We will review these achievements, and we will specifically address the topic of IFN-alpha-based molecularly targeted combinatory antitumour approaches.

Activated natural killer T cells induce liver injury by Fas and tumor necrosis factor-alpha during alcohol consumption

BACKGROUND & AIMS

Chronic alcohol abuse induces liver injury and increases the severity of viral hepatitis, but the precise mechanisms responsible are not well understood. In particular, little is known about the role of natural killer T cells in alcohol-induced liver injury. Natural killer T cells are mediators of important regulator and effector functions making use of Fas and tumor necrosis factor (TNF)-alpha in apoptosis induction. This report analyzes the role of natural killer T cells, Fas, and TNF-alpha in a model of chronic alcohol consumption.

METHODS

Mice fed alcohol by intragastric tube were assayed for serum alanine aminotransferase values, liver histology, and liver mononuclear cells before and after activation of natural killer T cells by ligand alpha-galactosylceramide.

RESULTS

In alcohol-consuming animals, liver natural killer T cells increase, and further activation by alpha-galactosylceramide causes lethal liver injury. This is explained by alcohol-induced hepatocyte sensitization to cell-mediated lysis, which develops concomitant to increased cytolytic activity of natural killer T cells. Natural killer T cell-mediated apoptosis proceeds by the Fas pathway, and Fas is essential for alcohol-associated liver injury. TNF-alpha plays an additional role as a defect in TNF receptor-1 inhibits alcohol-associated liver injury. Alcohol-fed natural killer T cell-deficient Jalpha281(-/-) mice express a delay in alcohol-induced liver injury.

CONCLUSIONS

Alcohol consumption induces an increase of natural killer T cells in the liver and a high sensitivity of hepatocytes to cell-mediated lysis. Stimulation of natural killer T cells during alcohol consumption induces serious liver injury by a mechanism that involves concomitant signals by Fas and tumor necrosis factor receptor-1 on alcohol-stressed hepatocytes.