Interferon gamma (IFNgamma ) and tumor necrosis factor alpha synergism in ME-180 cervical cancer cell apoptosis and necrosis. IFNgamma inhibits cytoprotective NF-kappa B through STAT1/IRF-1 pathways

We investigated the molecular mechanism of the synergism between interferon gamma (IFNgamma) and tumor necrosis factor alpha (TNFalpha) documented in a variety of biological occasions such as tumor cell death and inflammatory responses. IFNgamma/TNFalpha synergistically induced apoptosis of ME-180 cervical cancer cells. IFNgamma induced STAT1 phosphorylation and interferon regulatory factor 1 (IRF-1) expression. Transfection of phosphorylation-defective STAT1 inhibited IFNgamma/TNFalpha-induced apoptosis, whereas IRF-1 transfection induced susceptibility to TNFalpha. Dominant-negative IkappaBalpha transfection sensitized ME-180 cells to TNFalpha. IFNgamma pretreatment attenuated TNFalpha- or p65-induced NF-kappaB reporter activity, whereas it did not inhibit p65 translocation or DNA binding of NF-kappaB. IRF-1 transfection alone inhibited TNFalpha-induced NF-kappaB activity, which was reversed by coactivator p300 overexpression. Caspases were activated by IFNgamma/TNFalpha combination; however, caspase inhibition did not abrogate IFNgamma/TNFalpha-induced cell death. Instead, caspase inhibitors directed IFNgamma/TNFalpha-treated ME-180 cells to undergo necrosis, as demonstrated by Hoechst 33258/propidium iodide staining and electron microscopy. Taken together, our results indicate that IFNgamma and TNFalpha synergistically act to destroy ME-180 tumor cells by either apoptosis or necrosis, depending on caspase activation, and STAT1/IRF-1 pathways initiated by IFNgamma play a critical role in IFNgamma/TNFalpha synergism by inhibiting cytoprotective NF-kappaB. IFNgamma/TNFalpha synergism appears to activate cell death machinery independently of caspase activation, and caspase activation seems to merely determine the mode of cell death.     

NF-kappaB activation represses tumor necrosis factor-alpha-induced autophagy

Activation of NF-kappaB and autophagy are two processes involved in the regulation of cell death, but the possible cross-talk between these two signaling pathways is largely unknown. Here, we show that NF-kappaB activation mediates repression of autophagy in tumor necrosis factor-alpha (TNFalpha)-treated Ewing sarcoma cells. This repression is associated with an NF-kappaB-dependent activation of the autophagy inhibitor mTOR. In contrast, in cells lacking NF-kappaB activation, TNFalpha treatment up-regulates the expression of the autophagy-promoting protein Beclin 1 and subsequently induces the accumulation of autophagic vacuoles. Both of these responses are dependent on reactive oxygen species (ROS) production and can be mimicked in NF-kappaB-competent cells by the addition of H2O2. Small interfering RNA-mediated knockdown of beclin 1 and atg7 expression, two autophagy-related genes, reduced TNFalpha- and reactive oxygen species-induced apoptosis in cells lacking NF-kappaB activation and in NF-kappaB-competent cells, respectively. These findings demonstrate that autophagy may amplify apoptosis when associated with a death signaling pathway. They are also evidence that inhibition of autophagy is a novel mechanism of the antiapoptotic function of NF-kappaB activation. We suggest that stimulation of autophagy may be a potential way bypassing the resistance of cancer cells to anti-cancer agents that activate NF-kappaB.     

Tumor necrosis factor alpha up-regulates non-lymphoid Fas-ligand following superantigen-induced peripheral lymphocyte activation

Members of the tumor necrosis factor (TNF) and TNF receptor families play important roles in inducing apoptosis and mediating the inflammatory response. Activated T lymphocytes can trigger the expression of Fas-ligand on non-lymphoid tissue, such as intestinal epithelial cells (IEC), and this, in turn, can induce apoptosis in the T cells. Here, we examine the role of TNFalpha in this feedback regulation. Injection of TNFalpha into mice caused a rapid up-regulation of Fas-ligand mRNA in IEC. TNFalpha-induced activation of the Fas-ligand promoter in IEC requires NF-kappaB as this was blocked by an I-kappaBalphaM super-repressor and by mutation of an NF-kappaB site in the Fas-ligand promoter. Activation of T cells by antigen induced Fas-ligand expression in IEC in vivo in wild type, but not in TNFalpha-/- or TNFR1-/- mice. These results define a novel pathway wherein TNFalpha, produced by activated T cells in the intestine, induce Fas-ligand expression in IEC. This is the first observation that one member of the TNF superfamily mediates the regulation of another family member and represents a potential feedback mechanism controlling lymphocyte infiltration and inflammation in the small intestine.     

Phosphatidylinositol 3-kinase gamma signaling through protein kinase Czeta induces NADPH oxidase-mediated oxidant generation and NF-kappaB activation in endothelial cells

We addressed the role of class 1B phosphatidylinositol 3-kinase (PI3K) isoform PI3Kgamma in mediating NADPH oxidase activation and reactive oxidant species (ROS) generation in endothelial cells (ECs) and of PI3Kgamma-mediated oxidant signaling in the mechanism of NF-kappaB activation and intercellular adhesion molecule (ICAM)-1 expression. We used lung microvascular ECs isolated from mice with targeted deletion of the p110gamma catalytic subunit of PI3Kgamma. Tumor necrosis factor (TNF) alpha challenge of wild type ECs caused p110gamma translocation to the plasma membrane and phosphatidylinositol 1,4,5-trisphosphate production coupled to ROS production; however, this response was blocked in p110gamma-/- ECs. ROS production was the result of TNFalpha activation of Ser phosphorylation of NADPH oxidase subunit p47(phox) and its translocation to EC membranes. NADPH oxidase activation failed to occur in p110gamma-/- ECs. Additionally, the TNFalpha-activated NF-kappaB binding to the ICAM-1 promoter, ICAM-1 protein expression, and PMN adhesion to ECs required functional PI3Kgamma. TNFalpha challenge of p110gamma-/- ECs failed to induce phosphorylation of PDK1 and activation of the atypical PKC isoform, PKCzeta. Thus, PI3Kgamma lies upstream of PKCzeta in the endothelium, and its activation is crucial in signaling NADPH oxidase-dependent oxidant production and subsequent NF-kappaB activation and ICAM-1 expression.     

IAP antagonists target cIAP1 to induce TNFalpha-dependent apoptosis

XIAP prevents apoptosis by binding to and inhibiting caspases, and this inhibition can be relieved by IAP antagonists, such as Smac/DIABLO. IAP antagonist compounds (IACs) have therefore been designed to inhibit XIAP to kill tumor cells. Because XIAP inhibits postmitochondrial caspases, caspase 8 inhibitors should not block killing by IACs. Instead, we show that apoptosis caused by an IAC is blocked by the caspase 8 inhibitor crmA and that IAP antagonists activate NF-kappaB signaling via inhibtion of cIAP1. In sensitive tumor lines, IAP antagonist induced NF-kappaB-stimulated production of TNFalpha that killed cells in an autocrine fashion. Inhibition of NF-kappaB reduced TNFalpha production, and blocking NF-kappaB activation or TNFalpha allowed tumor cells to survive IAC-induced apoptosis. Cells treated with an IAC, or those in which cIAP1 was deleted, became sensitive to apoptosis induced by exogenous TNFalpha, suggesting novel uses of these compounds in treating cancer.     

Effects of epidermal growth factor (EGF), transforming growth factor-alpha (TGFalpha), and 2,3,7,8-tetrachlorodibenzo-p-dioxin on fusion of embryonic palates in serum-free organ culture using wild-type, EGF knockout, and TGFalpha knockout mouse strains

BACKGROUND: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is teratogenic in mice, producing cleft palate (CP). TCDD exposure disrupts expression of epidermal growth factor (EGF) receptor, EGF, and transforming growth factor-alpha (TGFalpha) in the palate and affects proliferation and differentiation of medial epithelial cells. EGF knockout embryos are less susceptible to the induction of CP by TCDD. This study used palate organ culture to examine the hypothesis that EGF enables a response to TCDD. METHODS: The midfacial tissues from wild-type (WT), EGF knockout, C57BL/6J, and TGFalpha knockout embryos were placed in organ culture on gestational day (GD) 12. Palatal explants were cultured for 4 days in serum-free Bigger's (BGJ) medium with 0.1% dimethyl sulfoxide (DMSO) or 1 x 10(-8) M TCDD with or without 2 ng of EGF/ml, 1 or 2 ng of TGFalpha/ml. Effects on palatal fusion were evaluated on day 4 of culture. EGF levels in explants and medium were determined using Luminex technology. RESULTS: In serum-free, control medium, palates from all of the strains fused. EGF knockout palates cultured with TCDD (no EGF) fused, but those cultured with TCDD + 2 ng of EGF/ml failed to fuse (p < 0.05 vs. control or TCDD without EGF). TGFalpha knockout palates failed to fuse when cultured with TCDD + 2 ng of TGFalpha/ml. EGF levels increased in tissue and accumulated in the medium after 24 hr of culture. CONCLUSIONS: This study demonstrated that providing EGF to the palates of EGF knockout mice restored the response to TCDD. These studies support the hypothesis that the mechanism for induction of CP by TCDD is mediated via the EGFR pathway.     

Tumor necrosis factor and reactive oxygen species cooperative cytotoxicity is mediated via inhibition of NF-kappaB

BACKGROUND: Tumor necrosis factor alpha (TNFalpha) plays a key role in pathogenesis of brain injury. However, TNFalpha exhibits no cytotoxicity in primary cultures of brain cells. This discrepancy suggests that other pathogenic stimuli that exist in the setting of brain injury precipitate TNFalpha cytotoxicity. The hypothesis was tested that reactive oxygen species (ROS), that are released early after brain injury, act synergistically with TNFalpha in causing cell death. MATERIALS AND METHODS: Cultured human and rat brain capillary endothelial cells (RBEC), and cortical astrocytes were treated with TNFalpha alone or together with different doses of H2O2, and apoptotic cell death and DNA fragmentation were measured by means of 3'-OH-terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Hoechst fluorescence assay, respectively. The effect of H2O2 on TNFalpha-induced activation of nuclear factor kappa B (NF-kappaB) was measured by Western blots of cytoplasmic and nuclear extracts of RBEC using anti-inhibitor of NF-kappaB (IkappaB) and anti-p65 subunit of NF-kappaB antibodies. Nuclear translocation of NF-kappaB was investigated by immunofluorescent staining of RBEC with anti-p65 antibodies. RESULTS: TNFalpha alone had no cytotoxic effect in brain endothelial cells and astrocytes at concentrations up to 100 ng/ml. Co-treatment with 5-10 microM of H2O2 caused a two-fold increase in the number of apoptotic cells 24 hr later. Similar doses (1-3 microM) of H2O2 initiated early DNA fragmentation. H2O2 inhibited TNFalpha-induced accumulation of p65 in the nucleus, although it had no effect on degradation of the IkappaB in cytoplasm. Immunostaining confirmed that H2O2 inhibited p65 transport to the nucleus. CONCLUSIONS: Reactive oxygen species could act synergistically with TNFalpha in causing cytotoxicity via inhibition of a cytoprotective branch of TNFalpha signaling pathways, which starts with NF-kappaB activation.     

The mitochondrial permeability transition augments Fas-induced apoptosis in mouse hepatocytes

Tumor necrosis factor-alpha receptor 1 and Fas recruit overlapping signaling pathways. To clarify the differences between tumor necrosis factor alpha (TNFalpha) and Fas pathways in hepatocyte apoptosis, primary mouse hepatocytes were treated with TNFalpha or an agonist anti-Fas antibody after infection with an adenovirus expressing an IkappaB superrepressor (Ad5IkappaB). Treatment with TNFalpha induced apoptosis in Ad5IkappaB-infected mouse hepatocytes, as we previously reported for rat hepatocytes. Ad5IkappaB plus anti-Fas antibody or actinomycin D plus anti-Fas antibody rapidly induced apoptosis, whereas anti-Fas antibody alone produced little cytotoxicity. The proteasome inhibitor (MG-132) and a dominant-negative mutant of nuclear factor-kappaB-inducing kinase also promoted TNFalpha- and Fas-mediated apoptosis. Expression of either crmA or a dominant-negative mutant of the Fas-associated death domain protein prevented TNFalpha- and Fas-mediated apoptosis. In addition, the caspase inhibitors, DEVD-cho and IETD-fmk, inhibited TNFalpha- and Fas-mediated apoptosis. In Ad5IkappaB-infected hepatocytes, caspases-3 and -8 were activated within 2 h after treatment with anti-Fas antibody or within 6 h after TNFalpha treatment. Confocal microscopy demonstrated onset of the mitochondrial permeability transition (MPT) and mitochondrial depolarization by 2-3 h after anti-Fas antibody treatment and 8-10 h after TNFalpha treatment, followed by cytochrome c release. The combination of the MPT inhibitors, cyclosporin A, and trifluoperazine, protected Ad5IkappaB-infected hepatocytes from TNFalpha-mediated apoptosis. After anti-Fas antibody, cyclosporin A and trifluoperazine decreased cytochrome c release but did not prevent caspase-3 activation and cell-death. In conclusion, nuclear factor-kappaB activation protects mouse hepatocytes against both TNFalpha- and Fas-mediated apoptosis. TNFalpha and Fas recruit similar but nonidentical, pathways signaling apoptosis. The MPT is obligatory for TNFalpha-induced apoptosis. In Fas-mediated apoptosis, the MPT accelerates the apoptogenic events but is not obligatory for them.     

An antiapoptotic protein, c-FLIPL, directly binds to MKK7 and inhibits the JNK pathway

Inhibition of NF-kappaB activation increases susceptibility to tumor necrosis factor (TNF)alpha-induced cell death, concurrent with caspases and prolonged c-Jun N-terminal kinase (JNK) activation, and reactive oxygen species (ROS) accumulation. However, the detailed mechanisms are unclear. Here we show that cellular FLICE-inhibitory protein (c-FLIP) is rapidly lost in NF-kappaB activation-deficient, but not wild-type fibroblasts upon TNFalpha stimulation, indicating that NF-kappaB normally maintains the cellular levels of c-FLIP. The ectopic expression of the long form of c-FLIP (c-FLIPL) inhibits TNFalpha-induced prolonged JNK activation and ROS accumulation in NF-kappaB activation-deficient fibroblasts. Conversely, TNFalpha induces prolonged JNK activation and ROS accumulation in c-Flip-/- fibroblasts. Moreover, c-FLIPL directly interacts with a JNK activator, MAP kinase kinase (MKK)7, in a TNFalpha-dependent manner and inhibits the interactions of MKK7 with MAP/ERK kinase kinase 1, apoptosis-signal-regulating kinase 1, and TGFbeta-activated kinase 1. This stimuli-dependent interaction of c-FLIPL with MKK7 might selectively suppress the prolonged phase of JNK activation. Taken that ROS promote JNK activation and activation of the JNK pathway may promote ROS accumulation, c-FLIPL might block this positive feedback loop, thereby suppressing ROS accumulation.     

4-1BB promotes the survival of CD8+ T lymphocytes by increasing expression of Bcl-xL and Bfl-1

4-1BB, a T cell costimulatory receptor, prolongs CD8(+) T cell survival. In these studies, 4-1BB stimulation was shown to increase expression of the antiapoptotic genes bcl-x(L) and bfl-1 via 4-1BB-mediated NF-kappaB activation. This signaling pathway was specifically inhibited by PDTC and was different from the pathways that enhanced CD8(+) T cell proliferation. The results suggest a role for the antiapoptotic activities of Bcl-x(L) and Bfl-1 proteins in 4-1BB-mediated CD8(+) T cell survival in vivo.     

Inhibition of nuclear factor-kappaB attenuates artherosclerosis in apoE/LDLR - double knockout mice.

Nuclear factor - kappaB (NF-kappaB) is a good therapeutic target for cardiovascular disease and numerous efforts are being made to develop safe NF-kappaB inhibitors. Nowadays many authors address NF-kappaB as a major therapeutic target in atherosclerosis, especially for preventive measures, in the light of two main hypothesis of atherosclerosis: oxidation and inflammation. We hypothesized that ammonium pyrrolidinedithioocarbamate (PDTC) - a well-known inhibitor of NF-kappaB could inhibit the development of atherosclerosis in this experimental model. We used apoE/LDLR - DKO mouse model, which is considered as a one of the best models to study the anti-atherosclerotic effect of drugs. In this model PDTC inhibited atherogenesis, measured both by "en face" method (25,15+/-2,9% vs. 15,63+/-0,6%) and "cross-section" method (565867+/-39764 microm2 vs. 291695+/-30384 microm2). Moreover, PDTC did not change the profile of cholesterol and triglycerides in blood. To our knowledge, this is the first report that shows the effect of PDTC on atherogenesis in gene-targeted apoE/LDLR - double knockout mice.