NF-kappa B-dependent Fas ligand expression

Mesenchymal stromal cells for the treatment of ocular autoimmune diseases

Mesenchymal stromal cells, commonly referred to as MSCs, have emerged as a promising cell-based therapy for a range of autoimmune diseases thanks to several therapeutic advantages. Key among these are: 1) the ability to modulate innate and adaptive immune responses and to promote tissue regeneration, 2) the ease of their isolation from readily accessible tissues and expansion at scale in culture, 3) their low immunogenicity enabling use as an allogeneic "off-the-shelf" product, and 4) MSC therapy's safety and feasibility in humans, as demonstrated in more than one thousand clinical trials. Evidence from preclinical studies and early clinical trials indicate the therapeutic potential of MSCs and their derivatives for efficacy in ocular autoimmune diseases such as autoimmune uveoretinitis and Sjögren's syndrome-related dry eye disease. In this review, we provide an overview of the current understanding of the therapeutic mechanisms of MSCs, and summarize the results from preclinical and clinical studies that have used MSCs or their derivatives for the treatment of ocular autoimmune diseases. We also discuss the challenges to the successful clinical application of MSC therapy, and suggest strategies for overcoming them.

Interferon-Gamma and Fas Are Involved in Porphyromonas gingivalis-Induced Apoptosis of Human Extravillous Trophoblast-Derived HTR8/SVneo Cells via Extracellular Signal-Regulated Kinase 1/2 Pathway

BACKGROUND

A number of studies recently revealed a link between periodontal disease and preterm birth (PTB). PTB can be induced by dental infection with Porphyromonas gingivalis (Pg), a periodontopathic bacterium. This study aims to investigate responses of human extravillous trophoblast-derived HTR8/SVneo cells to Pg infection.

METHODS

Cell apoptosis, cell viability, protein expression, and cytokine production in HTR8 cells were measured via: 1) flow cytometry, 2) CCK-8 assay, 3) western blot, and 4) enzyme-linked immunosorbent assay methods, respectively.

RESULTS

Pg decreased cell viability and increased cell apoptosis, active caspase-3 and Fas expression, and interferon-gamma (IFN-γ) secretion in HTR8 cells. Extracellular signal-regulated kinase (ERK) 1/2 inhibitor U0126 and FasL neutralizing antibody NOK1 that blocks FasL/Fas interaction both significantly suppressed Pg-induced apoptosis. U0126 also inhibited IFN-γ secretion and Fas expression close to control levels. Moreover, treatment with recombinant IFN-γ also significantly decreased number of viable HTR8 cells and increased Fas expression, suggesting IFN-γ may play an important role in Pg-induced apoptosis of HTR8 cells, at least partially through regulation of Fas expression.

CONCLUSIONS

To the best of the authors' knowledge, this is the first study to demonstrate Pg induces IFN-γ secretion, Fas expression, and apoptosis in human extravillous trophoblast-derived HTR8/SVneo cells in an ERK1/2-dependent manner, and IFN-γ (explored by recombinant IFN-γ) and Fas are involved in Pg-induced apoptosis. The finding that Pg infection abnormally regulates inflammation and apoptosis of human trophoblasts may give new insights into the possible link of PTB with maternal periodontal disease and periodontal pathogens.

Mitoxantrone, More than Just Another Topoisomerase II Poison

Mitoxantrone is a synthetic anthracenedione originally developed to improve the therapeutic profile of the anthracyclines and is commonly applied in the treatment of breast and prostate cancers, lymphomas, and leukemias. A comprehensive overview of the drug's molecular, biochemical, and cellular pharmacology is presented here, beginning with the cardiotoxic nature of its predecessor doxorubicin and how these properties shaped the pharmacology of mitoxantrone itself. Although mitoxantrone is firmly established as a DNA topoisomerase II poison within mammalian cells, it is now clear that the drug interacts with a much broader range of biological macromolecules both covalently and noncovalently. Here, we consider each of these interactions in the context of their wider biological relevance to cancer therapy and highlight how they may be exploited to further enhance the therapeutic value of mitoxantrone. In doing so, it is now clear that mitoxantrone is more than just another topoisomerase II poison.

Oxysterol-binding protein-related protein 8 (ORP8) increases sensitivity of hepatocellular carcinoma cells to Fas-mediated apoptosis

Human hepatoma (HCC) has been reported to be strongly resistant to Fas-mediated apoptosis. However, the underlying mechanisms are poorly understood. In this study the function of oxysterol-binding protein-related protein 8 (ORP8) in human hepatoma cells apoptosis was assessed. We found that ORP8 is down-regulated, whereas miR-143, which controls ORP8 expression, is up-regulated in clinical HCC tissues as compared with liver tissue from healthy subjects. ORP8 overexpression triggered apoptosis in primary HCC cells and cell lines, which coincided with a relocation of cytoplasmic Fas to the cell plasma membrane and FasL up-regulation. Co-culture of HepG2 cells or primary HCC cells with Jurkat T-cells or T-cells, respectively, provided further evidence that ORP8 increases HCC cell sensitivity to Fas-mediated apoptosis. ORP8-induced Fas translocation is p53-dependent, and FasL was induced upon ORP8 overexpression via the endoplasmic reticulum stress response. Moreover, ORP8 overexpression and miR-143 inhibition markedly inhibited tumor growth in a HepG2 cell xenograft model. These results indicate that ORP8 induces HCC cell apoptosis through the Fas/FasL pathway. The role of ORP8 in Fas translocation to the plasma membrane and its down-regulation by miR-143 offer a putative mechanistic explanation for HCC resistance to apoptosis. ORP8 may be a potential target for HCC therapy.

Liguzinediol improved the heart function and inhibited myocardial cell apoptosis in rats with heart failure

AIM

Liguzinediol is a novel derivative of ligustrazine isolated from the traditional Chinese medicine Chuanxiong (Ligusticum wallichii Franch), and produces significant positive inotropic effect in isolated rat hearts. In this study we investigated the effects of liguzinediol on a rat model of heart failure.

METHODS

To induce heart failure, male SD rats were injected with doxorubicin (DOX, 2 mg/kg, ip) once a week for 4 weeks. Then the rats were administered with liguzinediol (5, 10, 20 mg·kg(-1)·d(-1), po) for 2 weeks. Hemodynamic examination was conducted to evaluate heart function. Myocardial cell apoptosis was examined morphologically. The expression of related genes and proteins were analyzed using immunohistochemical staining and Western blot assays, respectively.

RESULTS

Oral administration of liguzinediol dose-dependently improved the heart function in DOX-treated rats. Electron microscopy revealed that liguzinediol (10 mg·kg(-1)·d(-1)) markedly attenuated DOX-induced injury of cardiomyocytes, and decreased the number of apoptotic bodies in cardiomyocytes. Furthermore, liguzinediol significantly decreased Bax protein level, and increased Bcl-2 protein level in cardiomyocytes of DOX-treated rats, led to an increase in the ratio of Bcl-2/Bax. Moreover, liguzinediol significantly decreased the expression of both cleaved caspase-3 and NF-κB in cardiomyocytes of DOX-treated rats. Administration of digitalis (0.0225 mg·kg(-1)·d(-1)) also markedly improved the heart function and the morphology of cardiomyocytes in DOX-treated rats.

CONCLUSION

Liguzinediol improves the heart function and inhibits myocardial cell apoptosis in the rat model of heart failure, which is associated with regulating Bcl-2, Bax, caspase-3 and NF-κB expression.

Receptor interacting protein-2 plays a critical role in human lung epithelial cells survival in response to Fas-induced cell-death

Lung epithelial cell death is critical to the lung injury that occurs in the acute respiratory distress syndrome. It is known that FasL plays a prominent role in this lung cell death pathway and may work in part through activation of the receptor interacting protein-2 (RIP2). RIP2 is serine/threonine kinase with a C-terminal caspase activation and recruitment domain (CARD). This CARD contains a highly conserved, predicted tyrosine phosphorylation site. Thus, involvement of tyrosine phosphorylation in the CARD domain of RIP2 may play a critical role in Fas-mediated apoptosis in the human lung immune system. To test this hypothesis, human lung epithelial cells (BEAS-2B) were induced to undergo cell death in response to the Fas agonist antibody CH11 with and without manipulation of endogenous RIP2 concentrations. We show that CH11 increases lung epithelial cell death in a dose-dependent manner as determined by LDH release and nuclear condensation. Fas-induced LDH release was inhibited by RIP2 knock-down. Reduced levels of RIP2 in BEAS-2B cells after treatment with RIP2 siRNA were confirmed by immunoblot. Overexpression of RIP2 in BEAS-2B cells synergized with Fas ligand-induced LDH release in a dose-dependent manner. Finally, mutation of the tyrosine phosphorylation site in CARD of RIP2 protected BEAS-2B cells from Fas ligand induced cell death. Thus RIP2's CARD tyrosine phosphorylation may represent a new therapeutic target to promote the survival of human lung epithelial cells in disorders that lead to acute lung injury and ARDS.

PEG-liposomal oxaliplatin induces apoptosis in human colorectal cancer cells via Fas/FasL and caspase-8

Since cellular uptake of PEG [poly(ethylene glycol)]-liposomal L-OHP (oxaliplatin) induces bioactive changes in CRC (colorectal cancer), we have investigated its apoptotic effect and anticancer mechanism. Human CRC SW480 cells were treated with PEG-liposomal L-OHP and a caspase-8 inhibitor [Z-IETD-FMK (benzyloxycarbonyl-Ile-Glu-Thr-dl-Asp-fluoromethylketone)]. Apoptosis was measured by FCM (flow cytometry) and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) assay. Expression of Fas/FasL and cytochrome c was detected using FCM and an immunofluorescence assay. Expression of caspase-8, Bid, caspase-9, caspase-7 and activated caspase-3 (P17) was examined by Western blot analyses. The results indicated that PEG-liposomal L-OHP (28 μg/ml L-OHP) induced marked apoptosis in SW480 cells compared with 28 μg/ml free L-OHP. The expression levels of Fas, FasL, cytochrome c, caspase-9, caspase-7 and activated caspase-3 proteins were up-regulated, with a corresponding increase in apoptosis; however, expression of caspase-8 and Bid were down-regulated as apoptosis increased. When cells were treated with Z-IETD-FMK, apoptosis was inhibited, but there was little impact on the expression of Fas, FasL, cytochrome c, Bid, caspase-9, caspase-7 and activated caspase-3. These findings indicate that PEG-liposomal L-OHP enhances the anticancer potency of the chemotherapeutic agent; moreover, Fas/FasL and caspase-8 signalling pathways play a key role in mediating PEG-liposomal L-OHP-induced apoptosis.

Underlying mechanisms of cAMP- and glucocorticoid-mediated inhibition of FasL expression in activation-induced cell death

Glucocorticoids (GCs) and cAMP-dependent signaling pathways exert diverse and relevant immune regulatory functions, including a tight control of T cell death and homeostasis. Both of these signaling molecules inhibit TCR-induced cell death and FasL expression, but the underlying mechanisms are still poorly understood. Therefore, to address this question, we performed a comprehensive screening of signaling pathways downstream of the TCR, in order to define which of them are targets of cAMP- and GC-mediated inhibition. We found that cAMP inhibited NF-κB and ERK pathways through a PKA-dependent mechanism, while Dexamethasone blocked TCR-induced NF-κB signaling. Although GCs and cAMP inhibited the induction of endogenous FasL mRNA expression triggered by TCR activation, they potentiated TCR-mediated induction of FasL promoter activity in transient transfection assays. However, when the same FasL promoter was stably transfected, the facilitatory effect of GCs and cAMP became inhibitory, thus resembling the effects on endogenous FasL mRNA expression. Hence, the endogenous chromatinization status known to occur in integrated or genomic vs. episomic DNA might be critical for proper regulation of FasL expression by cAMP and GCs. Our results suggest that the chromatinization status of the FasL promoter may function as a molecular switch, controlling cAMP and GC responsiveness and explaining why these agents inhibit FasL expression in T cells but induce FasL in other cell types.

FasL expression in activated T lymphocytes involves HuR-mediated stabilization

A prolonged activation of the immune system is one of the main causes of hyperproliferation of lymphocytes leading to defects in immune tolerance and autoimmune diseases. Fas ligand (FasL), a member of the TNF superfamily, plays a crucial role in controlling this excessive lymphoproliferation by inducing apoptosis in T cells leading to their rapid elimination. Here, we establish that posttranscriptional regulation is part of the molecular mechanisms that modulate FasL expression, and we show that in activated T cells FasL mRNA is stable. Our sequence analysis indicates that the FasL 3'-untranslated region (UTR) contains two AU-rich elements (AREs) that are similar in sequence and structure to those present in the 3'-UTR of TNFα mRNA. Through these AREs, the FasL mRNA forms a complex with the RNA-binding protein HuR both in vitro and ex vivo. Knocking down HuR in HEK 293 cells prevented the phorbol 12-myristate 13-acetate-induced expression of a GFP reporter construct fused to the FasL 3'-UTR. Collectively, our data demonstrate that the posttranscriptional regulation of FasL mRNA by HuR represents a novel mechanism that could play a key role in the maintenance and proper functioning of the immune system.

NFkappaB: a promising target for natural products in cancer chemoprevention

The transcription factor nuclear factor kappa B (NFkappaB) is found in nearly all animal cell types. It is involved in cellular responses to stimuli such as stress, cytokines, free radicals, ultraviolet irradiation, oxidized LDL and microbial antigens, and has been shown to regulate the expression of a number of genes including bcl-2, bcl-xl, cIAP, suvivin, TRAF, COX-2, MMP-9, iNOS and cell cycle-regulatory components. Many carcinogens, inflammatory agents and tumor promoters have been shown to activate NFkappaB, and resulting tumors demonstrate misregulated NFkappaB. Incorrect regulation of NFkappaB has been linked to inflammatory and autoimmune diseases, septic shock, viral infection and improper immune development. Aberrant regulation of NFkappaB is involved in cancer development and progression as well as in drug resistance. Inhibitors of NFkappaB mediate effects potentially leading to antitumor responses or greater sensitivity to the action of antitumor agents. Tools have been developed for the rapid assessment of NFkappaB activity, so in concert with a better understanding of NFkappaB activation mechanisms, many agents capable of suppressing NFkappaB activation have been identified. The present article focuses on the functions of NFkappaB, its role in human cancer and the therapeutic potential and benefit of targeting NFkappaB by natural products in cancer chemoprevention.

No Life Without Death

Apoptosis-programed cell death-is the most common form of death in the body. Once apoptosis is induced, proper execution of the cell death program requires the coordinated activation and execution of multiple molecular processes. Here, we describe the pathways and the basic components of the death-inducing machinery. Since apoptosis is a key regulator of tissue homeostasis, an imbalance of apoptosis results in severe diseases like cancer, autoimmunity, and AIDS.

Is osteoarthritis an infection-associated disease and a target for chemotherapy?

The treatment of osteoarthritis (OA) continues to be a challenge, and current treatment modalities are disappointing. New approaches in therapy may be developed as a result of evidence of the involvement of inflammatory cytokines in the progression of OA. Cotrimoxazole (sulfamethoxazole/trimethoprim) was noted to have anti-inflammatory properties and has been used in the therapy of several autoimmune diseases. Analyzing our own and world experience, we propose that OA and degenerative joint and spine disease might be infection-associated diseases and a target for sulfamethoxazole/trimethoprim therapy.

Transcriptional regulation of FasL expression and participation of sTNF-alpha in response to sertoli cell injury

The Fas/FasL signaling pathway has previously been demonstrated to be critical for triggering germ cell apoptosis in response to mono-(2-ethylhexyl)phthalate (MEHP)-induced Sertoli cell injury. Although Sertoli cells ubiquitously express the FasL protein, MEHP-induced germ cell apoptosis appears to tightly correlate with increased levels of Sertoli cell FasL. Here we characterize the transcriptional regulation of the murine FasL gene in Sertoli cells after MEHP exposure. A serial deletion strategy for 1.5 kb of the 5'-upstream activating sequence of the FasL promoter was used to determine transcriptional activity in response to MEHP. Luciferase activity of the FasL promoter in the rat Sertoli cell line ASC-17D revealed that two regions, -500 to -324 and -1250 to -1000, were necessary to drive the inducible transcription of FasL. Sequence analysis of these two regions revealed two cis-regulatory elements, NF-kappaB and Sp-1. By site-directed mutagenesis, electrophoretic mobility shift and chromatin immunoprecipitation assays, it was confirmed that MEHP-induced FasL expression is enhanced through the transcriptional regulation of both NF-kappaB and Sp-1. Experiments performed both in vitro and in vivo revealed that MEHP exposure results in an increased production of sTNF-alpha and that sTNF-alpha-mediated NF-kappaB activation causes robust increases in FasL levels in both the ASC-17D Sertoli cell line and in primary rat Sertoli cell/germ cell co-cultures. In the seminiferous epithelium, Sertoli cells express TNFR1, whereas germ cells produce TNF-alpha. Therefore, sTNF-alpha released by germ cells after MEHP-induced Sertoli cell injury acts upon Sertoli cell TNFR1 and activates NF-kappaB and Sp-1 that consequently causes a robust induction of FasL expression. These novel findings point to a potential "feed-forward" signaling mechanism by which germ cells prompt Sertoli cells to trigger their apoptotic elimination.

Genomic cloning of feline Fas ligand gene and characterization of the transcription regulatory region

The feline Fas ligand gene was molecularly cloned from a feline genomic library and its genomic organization was determined. The feline Fas ligand gene contained four exons and spanned approximately 10 kb in the genome, and thus had the same structure as the human Fas ligand gene. The promoter region of the feline Fas ligand gene was further characterized by deletion mapping. The region between nucleotides -459 and -172 relative to the ATG codon was essential for the promoter activity when transfected into human and feline lymphoid cells. The characterization of the feline Fas ligand gene in the present study will be useful for further investigations of the regulatory mechanism of feline Fas ligand expression.

Porphyromonas gingivalis enhances FasL expression via up-regulation of NFkappaB-mediated gene transcription and induces apoptotic cell death in human gingival epithelial cells

The interaction between epithelial cells and micro-organisms is often a crucial initiating event in infectious diseases. Infection with Porphyromonas gingivalis, a Gram-negative anaerobe, is strongly associated with severe periodontal disease. This bacterium possesses an array of virulence factors, some of which can induce apoptosis. The tumour necrosis factor (TNF) receptor family is involved in the regulation of cellular homeostasis, cell surface molecules involved in phagocytosis, Fas ligand (L) expression and activation of the caspase cascade resulting in DNA fragmentation and cell blebbing. The current study examined the role of nuclear factor-kappaB (NFkappaB) in FasL-mediated apoptotic cell death in primary human gingival epithelial cells (HGEC) induced by heat-killed P. gingivalis, probably through TLR signalling pathways. A marked up-regulation of TLR2 and Fas-FasL was detected in HGEC stimulated with P. gingivalis. Activation of NFkappaB by P. gingivalis in HGEC was demonstrated by an NFkappaB promoter luciferase assay as well as by phosphorylation of p65 as detected by Western blotting. Activation of cleaved caspase-3 and caspase-8 resulted in apoptotic cell death of HGEC. The survival proteins c-IAP-1/c-IAP-2 were decreased in HGEC exposed to P. gingivalis. HGEC apoptosis induced by P. gingivalis was inhibited by an anti-human FasL monoclonal antibody. Blockade of NFkappaB by helenalin resulted in down-regulation of FasL whereas a caspase-8 inhibitor did not decrease FasL. Taken together, these studies show that P. gingivalis can induce epithelial cell apoptosis through Fas-FasL up-regulation and activation of caspase-3 and caspase-8.

Scopoletin induces apoptosis in human promyeloleukemic cells, accompanied by activations of nuclear factor κB and caspase-3

Scopoletin (6-methoxy-7-hydroxycoumarin) is a phenolic coumarin and a member of the phytoalexins. In this study we investigated whether scopoletin caused apoptosis in HL-60 promyelocytic cells and, if so, by what mechanisms. We found that scopoletin induced apoptosis as confirmed by a characteristic ladder pattern of discontinuous DNA fragments in a dose-dependent manner. The signal cascade activated by scopoletin included the heterodimeric redox-sensitive transcription factor NF-kappaB, which exhibited an upregulation of nuclear factor-kappa B (NF-kappaB) translocation to the nucleus by increase of IkappaBalpha degradation. In addition, scopoletin activated caspase-3 as was evidenced by both the proteolytic cleavage of the proenzyme and increased protease activity. Activation of caspase-3 resulted in the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP) to 85 kDa cleavage product in time-and dose-dependent fashions. Prior treatment of the cells with pyrrolidine dithiocarbamate, a potent inhibitor of NF-kappaB activation, or Ac-DEVD-CHO, a specific caspase-3 inhibitor, prevented scopoletin-induced caspase-3 activation, PARP cleavage, and finally DNA fragmentation. Taken together, these results suggest that scopoletin induces NF-kappaB activation, which, in turn, causes activation of caspase-3, degradation of PARP, and eventually leads to apoptotic cell death in HL-60 cells.

Impaired apoptosis and immune senescence - cause or effect?

Aged animals and humans exhibit a decreased T-cell activation response although they also exhibit increased susceptibility to responses to self-antigens and a loss of self-tolerance. The age-related alteration in T-cell reactivity, polyclonal expansion of T cells, and enhanced production of autoantibodies may reflect the numerous age-associated alterations in the T-cell arm of the immune system that have been revealed in numerous studies. These studies suggest that subpopulations of T cells are not deleted appropriately in older animals. They further suggest that an age-related impairment of Fas/Fas ligand (FasL)-mediated apoptosis - which plays a major role in activation-induced cell death (AICD) of T cells - may contribute to compromised regulation of the immune system. The likely mechanisms that may lead to impaired induction of FasL in AICD senescent T cells include an age-related shift from the apoptosis-sensitive T-helper 1 cell (Th1) response to the AICD-resistant Th2 response, aberrant T-cell receptor/CD3 downstream-signaling pathways, and altered CD28/B7-mediated T-cell costimulatory signals. Pathologically, accumulation of AICD-senescent T cells is associated with a defective cytotoxic T lymphocyte response and generation of autoreactive T cells. Based on the accumulating evidence, we propose that the emergence of the FasL(lo) AICD-senescent T cells is not only an effect of immune aging but also an important cause of T-cell proliferative senescence in both humans and mice.

HIV-1 Trans-Activator of Transcription Substitutes for Oxidative Signaling in Activation-Induced T Cell Death

Termination of an immune response requires elimination of activated T lymphocytes by activation-induced cell death (AICD). In AICD, CD95 (Apo-1/Fas) ligand (L) triggers apoptosis of CD95-positive activated T lymphocytes. In AIDS patients, AICD is strongly enhanced and accelerated. We and others have previously shown that HIV-1 trans-activator of transcription (HIV-1 Tat) sensitizes T cells toward CD95-mediated apoptosis and up-regulates CD95L expression by affecting the cellular redox balance. In this study, we show that it is hydrogen peroxide (H(2)O(2)) that functions as an essential second messenger in TCR signaling. The H(2)O(2) signal combined with simultaneous calcium (Ca(2+)) influx into the cytosol constitutes the minimal requirement for induction of CD95L expression. Either signal alone is insufficient. We further show that HIV-1 Tat interferes with TCR signaling and induces a H(2)O(2) signal. H(2)O(2) generated by HIV-1 Tat combines with CD4-dependent calcium influx and causes massive T cell apoptosis. Thus, our data provide an explanation for CD4(+) T lymphocyte depletion during progression of AIDS.

Taurine attenuates CD3/interleukin-2-induced T cell apoptosis in an in vitro model of activation-induced cell death (AICD)

Interleukin (IL)-2 immunotherapy is used for the treatment of metastatic melanoma and renal cell carcinoma and mediates its effects through the clonal expansion of lymphocytes. Although IL-2 remains the most effective form of therapy for these cancers, response rates are poor and dose escalation is hampered by side effects, which include vascular leak and lymphopenia. The mechanism underlying T cell loss is currently unidentified but could be the induction of activation-induced cell death (AICD) mediated by FasL. Our previous studies have shown that the amino acid taurine can attenuate apoptosis induced by a number of factors in different cell types. Here, we induced T cell AICD via CD3 and IL-2 stimulation and investigated the effect of taurine on lymphocyte apoptosis. Anti-CD3-activated Jurkat T cells treated with IL-2 significantly increased FasL expression, which was associated with increased apoptosis. Treatment with taurine prior to stimulation down-regulated FasL protein expression and partially inhibited apoptosis. Inhibition of FasL-signalling resulted in an identical reduction in apoptosis. As the kinetics of AICD are completely different in circulating T cells, we repeated these experiments in such cells to confirm our finding. Stimulation of CD4(+) circulating T cells induced apoptosis in sensitized, but not freshly isolated T cells, which was abrogated partially by taurine. In Jurkat cells it was determined that taurine-mediated down-regulation of FasL protein expression was associated with decreased FasL mRNA expression and reduced NFkappaB activation. These results reveal one possible mechanism underlying the lymphopenia observed with IL-2 immunotherapy, involving increased FasL expression leading to apoptosis. Taurine may be of use in reversing the lymphopenia associated with IL-2, thereby augmenting its immunotherapeutic potential.

The −844C/T polymorphism in the Fas ligand promoter associates with Taiwanese SLE

FasL expression is critical in T-cell activation-induced apoptosis, which is involved in lupus pathogenesis. This study identified two SNPs in the FasL promoter regions from -1145 to -45 by genomic DNA sequencing. The -844C/T polymorphism was previously described by its location in and affect on the CCAAT/enhancer-binding protein beta (C/EBPB beta)-binding site and the other (-1094A/C, a novel polymorphism) was located at the NF-kappaB transcription-binding site. FasL gene promoter polymorphisms were genotyped in 260 systemic lupus erythematosus (SLE) patients and 280 healthy controls using MassArray matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry. The distribution of FasL promoter -844C/C genotype, predominant in Taiwanese, was skewed in Taiwanese SLE patients (odds ratio: 1.53; P-value=0.014). FasL promoter -844C/T polymorphism genotype distributions of Taiwanese, African Americans, and Caucasians differed. Moreover, no particular clinical association of -844C/T and -1094A/C polymorphisms with SLE was found in patients in Taiwan. This study confirmed that -844C/C genotype is associated with lupus susceptibility. The -1094A/C polymorphism is not significantly associated with lupus disease susceptibility, albeit the role of NF-kappaB pathway in FasL promoter activation remains unclear. Fas/FasL pathway may contribute to SLE polygenic disease entity.

Characterization of molecular events in a series of bladder urothelial carcinoma cell lines with progressive resistance to arsenic trioxide

Our previous studies have shown that arsenic trioxide (As2O3), a novel anti-cancer agent, may be active against urothelial carcinomas. A series of bladder urothelial carcinoma cells with progressive As2O3 resistance were established and studied to reveal molecular events in relation to the mechanisms of resistance to As2O3. A sensitive parental line (NTUB1) and three As2O3-resistant sublines (NTUB1/As) were used with their IC50s being 0.9, 1.2, 2.5 and 4.9 microM, respectively. Cellular resistance to As2O3 was associated with a lowered proliferation profile (increased p53 and p21Waf1/Cip1 and decreased c-Myc levels) and a greater resistance to apoptosis (elevated Bcl-2 levels). Cells with a stronger resistance had higher expressions of superoxide dismutase (Cu/Zn) and hMSH2 (but not hMLH1). GSH contents were up-regulated in resistant cells in a dose-dependent manner. The DNA-binding activities of NF-kappaB and AP-1 were down-regulated in resistant cells in a dose-dependent manner. Profound molecular alterations occur during the acquisition of secondary As2O3 resistance. Our in vitro cellular model may help to reveal resistance mechanisms to As2O3 in bladder urothelial carcinoma cells.

T Cell Division and Death Are Segregated by Mutation of TCRβ Chain Constant Domains

We have studied the role of the T cell receptor (TCR) beta chain transmembrane and cytoplasmic domains (betaTM/Cyto) in T cell signaling. Upon antigen stimulation, T lymphocytes expressing a TCR with mutant and betaTM and Cyto domains accumulate in large numbers and are specifically defective in undergoing activation-induced cell death (AICD). The mutant TCR poorly recruits the protein adaptor Carma-1 and is subsequently impaired in activating NF-kappaB. This signaling defect leads to a reduced expression of Fas ligand (FasL) and to a reduction in AICD. These beta chain domains are involved in discriminating cell division and apoptosis.

NF-kappaB-dependent induction of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas/FasL is crucial for efficient influenza virus propagation

Activation of the transcription factor NF-kappaB is a hallmark of infections by viral pathogens including influenza viruses. Because gene expression of many proinflammatory and antiviral cytokines is controlled by this factor, the concept emerged that NF-kappaB and its upstream regulator IkappaB kinase are essential components of the innate antiviral immune response to infectious pathogens. In contrast to this common view we report here that NF-kappaB activity promotes efficient influenza virus production. On a molecular level this is due to NF-kappaB-dependent viral induction of the proapoptotic factors tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and FasL, which enhance virus propagation in an autocrine and paracrine fashion. Thus, NF-kappaB acts both proapoptotically and provirally in the context of an influenza virus infection.

Function and regulation of the CD95 (APO-1/Fas) ligand in the immune system

CD95/CD95L mediated apoptosis is an important mechanism of immune homeostasis. It is instrumental for termination of an immune response and mainly be involved in peripheral tolerance. Dysregulation of the CD95/CD95L system leads to severe diseases. In this review, we present a survey of the role of the CD95/CD95L system in the immune system and, particularly, focus on the signals and transcription factors (NF-AT, Egr, NF-kappaB, AP-1, c-Myc, Nur77, IRFs, SP-1, ALG-4, ROR(gamma)t, and CIITA) involved in CD95L expression. It should also be evident from this review that a profound insight into the molecular mechanisms of CD95L activation should allow to explore potential therapeutic means to treat CD95/CD95L-dependent diseases.

Cellular origin of ionizing radiation-induced NF-kappaB activation in vivo and role of NF-kappaB in ionizing radiation-induced lymphocyte apoptosis

PURPOSE

To investigate the cellular origin of ionizing radiation (IR)-induced NF-kappaB activation in vivo and the role of NF-kappaB in IR-induced lymphocyte apoptosis.

MATERIALS AND METHODS

NF-kappaB activities were analysed by gel shift/supershift assay in isolated murine T- and B-cells, macrophages (MPhi) and tissues from normal and T- and B-cell-deficient Rag1 mice with or without exposure to IR. IR-induced lymphocyte apoptosis was determined by analysis of 3,3'-dihexyloxacarbocyanine iodide (DiOC(6)) uptake, annexin-V staining and the sub-G0/1 population, or by TUNEL assay.

RESULTS

The results showed that IR activated NF-kappaB in lymphocytes, including both T- and B-cells, but failed to do so in MPhi. Furthermore, T- and B-cell-deficient Rag1 mice exposed to IR exhibited a significant reduction in NF-kappaB activation as compared with normal mice. Although NF-kappaB1 (p50) gene knockout or NF-kappaB decoy oligonucleotide treatment specifically inhibited IR-induced lymphocyte NF-kappaB activation, they had no significant effect on IR-induced lymphocyte apoptosis.

CONCLUSIONS

This finding suggests that lymphocytes are the main cellular origin of IR-induced NF-kappaB activation in vivo. However, NF-kappaB activation has no significant effect on IR-induced lymphocyte apoptosis.

Pathophysiological mechanisms in osteoarthritis lead to novel therapeutic strategies

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with aging. At the molecular level, OA is characterized by an imbalance between anabolic (i.e. extracellular matrix biosynthesis) and catabolic (i.e. extracellular matrix degradation) pathways in which articular cartilage is the principal site of tissue injury responses. The pathophysiology of OA also involves the synovium in that 'nonclassical' inflammatory synovial processes contribute to OA progression. Chondrocytes are critical to the OA process in that the progression of OA can be judged by the vitality of chondrocytes and their ability to resist apoptosis. Growth factors exemplified by insulin-like growth factor-1, its binding proteins and transforming growth factor-beta contribute to anabolic pathways including compensatory biosynthesis of extracellular matrix proteins. Catabolic pathways are altered by cytokine genes such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) which are upregulated in OA. In addition, IL-1 and TNF-alpha downregulate extracellular matrix protein biosynthesis while concomitantly upregulating matrix metalloproteinase (MMP) gene expression. When MMPs are activated, cartilage extracellular matrix degradation ensues apparently because levels of endogenous cartilage MMP inhibitors cannot regulate MMP activity. Therapeutic strategies designed to modulate the imbalance between anabolic and catabolic pathways in OA may include neutralizing cytokine activity or MMP gene expression or inhibiting signaling pathways which result in apoptosis dependent on mature caspase activity or mitogen-activated protein kinase (MAPK) activity. MAPK activity appears critical for regulating chondrocyte and synoviocyte apoptosis and MMP genes.

NF-kappaB-independent actions of sulfasalazine dissociate the CD95L- and Apo2L/TRAIL-dependent death signaling pathways in human malignant glioma cells

Death receptor-mediated apoptosis of human malignant glioma cells triggered by CD95 ligand (CD95L) or Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) share several features, including processing of multiple caspases and mitochondrial cytochrome c release. We here report that CD95L-induced cell death is inhibited by sulfasalazine (SS) in all of four human glioma cell lines, both in the absence and presence of cycloheximide (CHX). Coexposure to CD95L and SS prevents the CD95L-evoked processing of caspases 2, 3, 8 and 9, the release of cytochrome c from mitochondria, and the loss of BCL-x(L) protein. This places the protective effect of SS proximal to most known events triggered by the CD95-dependent signaling pathway in glioma cells. CD95L promotes the accumulation of nuclear factor kappa B (NF-kappaB) in the nucleus and induces the DNA-binding activity of NF-kappaB assessed by electrophoretic mobility shift assay. The total levels of p50, p65 and IkappaBalpha remain unchanged, but the levels of phosphorylated IkappaBalpha and of nuclear p65 increase, in response to CD95L. IkappaBalpha phosphorylation as well as nuclear NF-kappaB translocation and DNA binding are blocked by SS. However, unlike SS, dominant-negative IkappaBalpha (IkappaBdn) does not block apoptosis, suggesting that SS inhibits CD95L-mediated apoptosis in an NF-kappaB-independent manner. In contrast to CD95L, the cytotoxic effects of Apo2L/TRAIL are enhanced by SS, and SS facilitates Apo2L/TRAIL-evoked caspase processing, cytochrome c release, and nuclear translocation of p65. These effects of SS are nullified in the presence of CHX, suggesting that the effects of SS and CHX are redundant or that enhanced apoptosis mediated by SS requires protein synthesis. IkappaBdn fails to modulate Apo2L/TRAIL-induced apoptosis. Similar effects of SS on CD95L- and Apo2L/TRAIL-induced apoptosis are observed in MCF-7 breast and HCT116 colon carcinoma cells. Interestingly, HCT cells lacking p21 (80S14(p21-/-)) are only slightly protected by SS from CD95L-induced apoptosis, but sensitized to Apo2L/TRAIL-induced apoptosis, indicating a link between the actions of SS and p21. Thus, SS modulates the death cascades triggered by CD95L and Apo2L/TRAIL in opposite directions in an NF-kappaB-independent manner, and SS may be a promising agent for the augmentation of Apo2L/TRAIL-based cancer therapies.

Death receptors and melanoma resistance to apoptosis

Impaired ability to undergo programmed cell death in response to a wide range of external stimuli acquires melanomas a selective advantage for progression and metastasis as well as their notorious resistance to therapy. Better understanding of mechanisms that govern apoptosis has enabled identification of diverse routes by which melanomas manage to escape stimuli of apoptosis. Changes at genomic, transcriptional and post-translational levels of G-proteins and protein kinases (Ras, B-Raf) and their transcription factor effectors (c-Jun, ATF2, Stat3 and NF-kappaB) affects TNF, Fas and TRAIL receptors, which play important roles in acquiring melanoma's resistance to apoptosis. Here, we summarize our current understanding of changes that alters the regulation of death receptors during melanoma development.

Diminished NF-kappaB activation and PDGF-B expression in glomerular endothelial cells subjected to chronic shear stress

We tested the hypothesis that in endothelial cells, chronic arterial shear stress represses both the transactivator nuclear factor-kappaB (NF-kappaB) and subsequent platelet-derived growth factor (PDGF)-B gene transcription. Bovine aortic endothelial (BAE) and glomerular capillary endothelial (GEN) cells were subjected to chronic (9 days) arterial shear stress (10 dyne/cm(2)). Chronic shear stress reduced PDGF-B transcripts in BAE cells by 59 +/- 23% compared to controls, and by 70 +/- 14% in GEN cells. While PDGF-B mRNA levels were not significantly changed in BAE cells subjected to acute (4 h) shear stress, in GEN cells PDGF-B transcript abundance fell by 59 +/- 3%. PDGF-B mRNA stability was unchanged. We investigated the possibility that these effects were due to decreased nuclear NF-kappaB. NF-kappaB levels were much lower in nuclei of chronic shear stress-treated cells compared to controls. This represents classical inactivation of NF-kappaB since cytoplasmic NF-kappaB/I-kappaB (the inhibitory protein of NF-kappaB) levels were elevated in shear stress-treated cells. Further supporting NF-kappaB regulation of PDGF-B, activation of NF-kappaB by interleukin (IL)-1beta resulted in increased PDGF-B transcript levels. Treatment of cells with MG-132, an inhibitor of NF-kappaB activation, resulted in a dramatic decrease in basal PDGF-B transcript levels, and essentially abrogated the response to IL-1beta. Thus, repression of NF-kappaB activation in endothelial cells by shear stress decreases PDGF-B gene expression, while activators of NF-kappaB increase PDGF-B transcription.

Protection of islets by in situ peptide-mediated transduction of the Ikappa B kinase inhibitor Nemo-binding domain peptide

We have previously demonstrated that adenoviral gene transfer of the NF-kappaB inhibitor IkappaB to human islets results in protection from interleukin (IL)-1beta-mediated dysfunction and apoptosis. Here we report that human and mouse islets can be efficiently transduced by a cationic peptide transduction domain (PTD-5) without impairment of islet function. PTD mediated delivery of a peptide inhibitor of the IL-1beta-induced IkappaB kinase (IKK), derived from IKKbeta (NBD; Nemo-binding domain), and completely blocked the detrimental effects of IL-1beta on islet function and NF-kappaB activity, in a similar manner to Ad-IkappaB. We also demonstrate that mouse islets can be transduced in situ by infusion of the transduction peptide through the bile duct prior to isolation, resulting in 40% peptide transduction of the beta-cells. Delivery of the IKK inhibitor transduction fusion peptide (PTD-5-NBD) in situ to mouse islets resulted in improved islet function and viability after isolation. These results demonstrate the feasibility of using PTD-mediated delivery to transiently modify islets in situ to improve their viability and function during isolation, prior to transplantation.

Regulation of the immune system by NF-kappaB and IkappaB

NF-kappaB/Rel transcription factor family participates in diverse biological processes including embryo development, hematopoiesis, immune regulation, as well as neuronal functions. In this review, the NF-kappaB/Rel signal transduction pathways and their important roles in the regulation of immune system will be discussed. NF-kappaB/Rel members execute distinct functions in multiple immune cell types via the regulation of target genes essential for cell proliferation, survival, effector functions, cell trafficking and communication, as well as the formation of lymphoid architecture. Consequently, proper activation of NF-kappaB/Rel during immune responses to allergens, auto-antigens, allo-antigens, and pathogenic infection is crucial for the integrity of host innate and adaptive immunity.

Activation of nuclear factor-kappaB during doxorubicin-induced apoptosis in endothelial cells and myocytes is pro-apoptotic: the role of hydrogen peroxide

Doxorubicin (DOX) is a widely used anti-tumour drug. Cardiotoxicity is a major toxic side effect of DOX therapy. Although recent studies implicated an apoptotic pathway in DOX-induced cardiotoxicity, the mechanism of DOX-induced apoptosis remains unclear. In the present study, we investigated the role of reactive oxygen species and the nuclear transcription factor nuclear factor kappaB (NF-kappaB) during apoptosis induced by DOX in bovine aortic endothelial cells (BAECs) and adult rat cardiomyocytes. DOX-induced NF-kappaB activation is both dose- and time-dependent, as demonstrated using electrophoretic mobility-shift assay and luciferase and p65 (Rel A) nuclear-translocation assays. Addition of a cell-permeant iron metalloporphyrin significantly suppressed NF-kappaB activation and apoptosis induced by DOX. Overexpression of glutathione peroxidase, which detoxifies cellular H(2)O(2), significantly decreased DOX-induced NF-kappaB activation and apoptosis. Inhibition of DOX-induced NF-kappaB activation by a cell-permeant peptide SN50 that blocks translocation of the NF-kappaB complex into the nucleus greatly diminished DOX-induced apoptosis. Apoptosis was inhibited when IkappaB mutant vector, another NF-kappaB inhibitor, was added to DOX-treated BAECs. These results suggest that NF-kappaB activation in DOX-treated endothelial cells and myocytes is pro-apoptotic, in contrast with DOX-treated cancer cells, where NF-kappaB activation is anti-apoptotic. Removal of intracellular H(2)O(2) protects endothelial cells and myocytes from DOX-induced apoptosis, possibly by inhibiting NF-kappaB activation. These findings suggest a novel mechanism for enhancing the therapeutic efficacy of DOX.

Toll-like receptor 2 contributes to liver injury by Salmonella infection through Fas ligand expression on NKT cells in mice

BACKGROUND & AIMS

Toll-like receptors (TLRs) for bacterial constitutes are expressed not only by phagocytes but also by some subsets of T cells. We previously reported that natural killer T cells (NKT cells) play an important role in liver injury induced by Salmonella infection. In the present study, we investigated whether TLRs on NKT cells are involved in Salmonella-induced liver injury.

METHODS

Gene expression of TLR2 was examined in sorted natural killer, NKT, and T cells from livers of naive mice by the reverse-transcription polymerase chain reaction method. Serum alanine aminotransferase level and FasL expression on liver lymphocytes were examined in TLR2-deficient (TLR2(-/-)) and FasL-deficient gld/gld mice before and after intraperitoneal inoculation of Salmonella choleraesuis 31N-1 using an enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

TLR2 gene was abundantly expressed by NKT cells freshly isolated from naive mice. FasL expression on liver NKT cells increased in TLR2(+/-) mice but not in TLR2(-/-) mice after Salmonella infection. Serum alanine aminotransferase level was significantly lower in the TLR2(-/-) and gld/gld mice than in the control mice after infection.

CONCLUSIONS

TLR2 may contribute to liver injury induced by Salmonella infection via FasL induction on liver NKT cells.

Mechanism of rapid transcriptional induction of tumor necrosis factor alpha-responsive genes by NF-kappaB

NF-kappaB induces the expression of genes involved in immune response, apoptosis, inflammation, and the cell cycle. Certain NF-kappaB-responsive genes are activated rapidly after the cell is stimulated by cytokines and other extracellular signals. However, the mechanism by which these genes are activated is not entirely understood. Here we report that even though NF-kappaB interacts directly with TAF(II)s, induction of NF-kappaB by tumor necrosis factor alpha (TNF-alpha) does not enhance TFIID recruitment and preinitiation complex formation on some NF-kappaB-responsive promoters. These promoters are bound by the transcription apparatus prior to TNF-alpha stimulus. Using the immediate-early TNF-alpha-responsive gene A20 as a prototype promoter, we found that the constitutive association of the general transcription apparatus is mediated by Sp1 and that this is crucial for rapid transcriptional induction by NF-kappaB. In vitro transcription assays confirmed that NF-kappaB plays a postinitiation role since it enhances the transcription reinitiation rate whereas Sp1 is required for the initiation step. Thus, the consecutive effects of Sp1 and NF-kappaB on the transcription process underlie the mechanism of their synergy and allow rapid transcriptional induction in response to cytokines.

The biological role of the Fas/FasL system during tumor formation and progression

The cells of an organism are constantly exposed to conflicting environmental cues that signal cell survival or cell death. Survival signals are delivered by autocrine or paracrine factors that actively suppress a default death pathway. This default death pathway appears to be activated by dedicated death receptors such as Fas, the TRAIL-receptors and other tumor necrosis factor receptor superfamily proteins (TNFR SFPs). Our understanding of how these counteracting receptor systems are modulated during tumorigenesis is only moderate. Nevertheless, there is now broad evidence that susceptibility of tumor cells towards Fas-mediated apoptosis is largely reduced. In addition, tumor cells frequently exhibit de novo expression of Fas-ligand (FasL) which plays a significant role in local tissue destruction, metastatic spread and immune escape of the tumor cells. Restoring the apoptotic potential of cancer cells upon modulating the expression and activity of certain key components of the cell death machinery is an attractive and obvious therapeutic anti-cancer strategy.

H(2)O(2) induces upregulation of Fas and Fas ligand expression in NGF-differentiated PC12 cells: modulation by cAMP

Fas, (APO-1/CD95), a transmembrane glycoprotein belonging to the tumor necrosis (TNF) receptor superfamily, transduces apoptotic death upon crosslinking by its cognate ligand (FasL). As upregulation of Fas/FasL expression occurs in neuropathological conditions (e.g., stroke, central nervous system [CNS] trauma and seizures) associated with oxidative damage, we questioned whether reactive oxygen species (ROS) can directly affect Fas and FasL expression in neuronal cells. Utilizing rat PC12 cells neuronally differentiated with nerve growth factor (NGF), we observed that concentrations of H(2)O(2) inducing apoptotic cell death rapidly trigger the expression of Fas mRNA and protein as well as FasL mRNA. Although NGF-addition to naive PC12 downregulated constitutive Fas and FasL transcription, the H(2)O(2)-induced Fas and FasL mRNA upregulation invariably occurred either in the presence or in the absence of NGF. Similarly, phorbol 1,2-myristate 1, 3-acetate (PMA), a potent protein kinase C (PKC) activator, did not modify Fas and FasL mRNA upregulation subsequent to H(2)O(2) exposure. On the contrary, forskolin and dibutyryl cAMP, which elevate intracellular cAMP by independent mechanisms, both counteracted H(2)O(2)-induced Fas, but not FasL, mRNA upregulation and increased constitutive expression of FasL mRNA. Altogether, our data show that oxidative stress is a major stimulus in eliciting Fas and FasL expression in NGF-differentiated PC12 cells. Moreover, we describe here for the first time the existence of cAMP-dependent mechanism(s) modulating Fas and FasL expression.

Intracellular signal transduction of cells in response to carcinogenic metals

Epidemiological and animal studies suggest that several metals and metal-containing compounds are potent mutagens and carcinogens. These metals include chromium, arsenic, vanadium, nickel, and others. During the last two decades, chemical and cellular studies have contributed enormously to our understanding of the mechanisms of metal-induced pathophysiological processes. Although each of these metals is unique in its mechanism of action, some common signaling molecules, such as reactive oxygen species (ROS), may be shared by many of the carcinogenic metals. New techniques are now available to reveal the mechanisms of carcinogenesis in precise molecular terms. In this review, we focused our attentions on carcinogenic metal-induced signal transduction pathways leading to the activation of NF-kappaB, cell apoptosis and cell cycle progression, three crucial steps or events involved in the transformation and carcinogenesis. This review summarizes current knowledge and our recent studies concerning intracellular signal transduction pathways initiated by carcinogenic metals and the cross-talk that occurs among these pathways in cells in response to metals.

Increased circulating levels of soluble Fas ligand are correlated with disease activity in patients with fibrosing lung diseases

OBJECTIVE

The Fas-Fas ligand (FasL) pathway is one of the important apoptosis-signalling molecule systems. We previously determined that this pathway may be involved in the pathogenesis of fibrosing lung diseases. In the present study, we evaluated the clinical significance of the levels of soluble forms of Fas (sFas) and FasL (sFasL) in serum from patients with fibrosing lung diseases.

METHODOLOGY

We measured sFas, sFasL, KL-6 (a measure of alveolar type II cell damage), surfactant protein D (SP-D), and surfactant protein A (SP-A) levels in serum from 35 patients with idiopathic pulmonary fibrosis (IPF), 17 patients with interstitial pneumonia associated with collagen vascular diseases (CVD-IP), and 13 normal healthy controls using enzyme-linked immunosorbent assays (ELISA).

RESULTS

The serum levels of sFasL were significantly increased in patients with active IPF and CVD-IP, compared with those with inactive disease and controls. There was no significant difference in sFasL levels between patients with inactive disease and controls. Serum sFasL levels were significantly correlated with lactate dehydrogenase and KL-6 levels in IPF. The decrease in sFasL levels following corticosteroid therapy was not correlated with the clinical course of IPF. There was no significant difference in serum sFas levels between IPF or CVD-IP patients and controls.

CONCLUSIONS

Although further studies need to be performed on a large number of patients with histologically proven IPF or CVD-IP, it would seem that serum sFasL levels may reflect the activity of IPF and CVD-IP.

CRE-mediated transcriptional activation is involved in cAMP protection of T-cell receptor-induced apoptosis but not in cAMP potentiation of glucocorticoid-mediated programmed cell death

Apoptosis of thymic cells induced by glucocorticoids (GC) and T-cell receptor (TCR) engagement are mutually antagonistic. We demonstrate that cAMP enhances GC and antagonizes TCR (anti-CD3) apoptosis on the same cell (DO-11.10 and 2B4.11 T-cell hybridomas). We analyzed the activity of several transcription factors in this cAMP dual, stimulus-dependent, regulatory action. Anti-CD3 increases kB-activity which is inhibited by CPTcAMP or dexamethasone (DEX), supporting the proapoptotic role of NFkB on TCR-induced apoptosis. Anti-CD3 not only increases kB- but diminishes GC response element (GRE)-activity induced by DEX, suggesting that TCR-mediated blockade of GC-induced apoptosis involves not only the proposed antiapoptotic action of NF-kB on GC, but also the inhibition of GRE-regulated proapoptotic genes. To test the involvement of CRE-driven transcription in the cAMP dual apoptotic regulation, cells were transfected with a CRE decoy DNA oligomer. Blockade of CRE transactivation with decoy targeting of CRE completely blocked the protection of TCR-induced apoptosis by cAMP, while it did not modify the enhancement by cAMP on GC-induced apoptosis. We show that CRE-binding factors have a definite role in T-cell apoptosis: they are involved in cAMP protection of TCR- but not in cAMP potentiation of GC-induced apoptosis.

Sustained hyposmotic stress induces cell death: apoptosis by defeat

We describe sustained hyposmotic stress as a novel type of environmental condition enforcing apoptosis. In a dose- and time-dependent fashion, hyposmotic stress leads to a delayed type of apoptosis with considerable variations in constitutive sensitivity among different cell types. For example, after 48 h at 84 mosmol/l, the death rate ranged from 10.8 +/- 0.7% in AsPc1 human pancreatic carcinoma cells to 72.0 +/- 1.6% in HK-2 human kidney tubule cells. Caspase inhibitors rendered cells more resistant to hyposmolar stress; the caspase 3 inhibitor Ac-Asp-Glu-Val-aspartic acid aldehyde was the most efficient. After 24 h of stress, HT-29 colon carcinoma and HK-2 cells had increased their mitochondrial mass. This went along with an increase in mitochondrial membrane potential in HT-29 cells but with a decrease in HK-2 cells. Starting at 2 h of stress, we detected transient CD95L transcription followed by surface expression of CD95L in HT-29 but not in HK-2 cells. Inhibitory CD95L antibody partially inhibited specific death in HT-29 but not in HK-2 cells. Thus, as in other types of stress-induced apoptosis, the CD95/CD95L system is one of the different routes to suicide optionally used by hyposmotically stressed cells. Our findings may have clinical implications for the prevention and treatment of tissue damage caused by severe hyposmolar states.

Lung fibroblasts inhibit activation-induced death of T cells through PGE(2)-dependent mechanisms

Activation-induced cell death (AICD) is a regulatory mechanism eliminating excess activated T cells, mainly through a Fas/Fas ligand-dependent mechanism. The goal of this study was to determine whether mouse primary lung fibroblasts are capable of modulating AICD. Using T cell hybridoma DO11.10, we found that fibroblasts in coculture rescue T cells from AICD. Fibroblast-conditioned medium (FCM) also inhibited apoptosis of T cells activated with immobilized anti-CD3 antibody. The effects of lung fibroblasts are mediated, in part, by secreted prostaglandin E(2) (PGE(2)) because treatment of fibroblasts with indomethacin decreased antiapoptotic activity of FCM. Addition of exogenous PGE(2) to FCM from fibroblast cultures treated with indomethacin restored the inhibitory activity of FCM. Expression of Fas receptor and Fas ligand by anti-CD3-activated DO11.10 cells was not affected by PGE(2). However, the same concentrations of PGE(2) significantly downregulated activation of caspase-8 and caspase-3. These results demonstrate that lung fibroblasts inhibit the AICD of T cells by secreting PGE(2), which downregulates caspase activation and apoptosis.

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti-inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti-inflammatory and antiproliferative effects independent of cyclooxygenase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF-kappaB and AP-1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKbeta, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF-kappaB and AP-1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARgamma, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase-independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.

New insights into the role of nuclear factor-kappaB in cell growth regulation

The nuclear factor (NF)-kappaB family of eukaryotic transcription factors plays an important role in the regulation of immune response, embryo and cell lineage development, cell apoptosis, cell-cycle progression, inflammation, and oncogenesis. A wide range of stimuli, including cytokines, mitogens, environmental particles, toxic metals, and viral or bacterial products, activate NF-kappaB, mostly through IkappaB kinase (IKK)-dependent phosphorylation and subsequent degradation of its inhibitor, the IkappaB family of proteins. Activated NF-kappaB translocates into the nucleus where it modulates the expression of a variety of genes, including those encoding cytokines, growth factors, acute phase response proteins, cell adhesion molecules, other transcription factors, and several cell apoptosis regulators. During the past few years, tremendous progress has been achieved in our understanding on how intracellular signaling pathways are transmitted in either a linear or a network manner leading to the activation of NF-kappaB and subsequent cell growth control. However, a detailed molecular mechanism of NF-kappaB regulating cell growth has yet to be determined. Elucidation of the relationships between NF-kappaB activation and cell growth will be important in developing new strategies for the treatment of various human diseases, such as chronic autoimmune disorder and cancer.

Human Notch-1 inhibits NF-kappa B activity in the nucleus through a direct interaction involving a novel domain

Notch participates in diverse cell fate decisions throughout embryonic development and postnatal life. Members of the NF-kappaB/Rel family of transcription factors are involved in the regulation of a variety of genes important for immune function. The biological activity of the NF-kappaB transcription factors is controlled by IkappaB proteins. Our previous work demonstrated that an intracellular, constitutively active form of human Notch-1/translocation-associated Notch homologue-1 (Notch(IC)) functions as an IkappaB molecule with specificity for the NF-kappaB p50 subunit and physically interacts with NF-kappaB in T cells. In the current study, we investigated the roles of different domains of Notch(IC) in the regulation of NF-kappaB-directed gene expression and NF-kappaB DNA binding activity. We found that Notch(IC) localizes to the nucleus and that a region in the N-terminal portion of Notch(IC), not the six ankyrin repeats, is responsible for the inhibitory effects of Notch on NF-kappaB-directed gene expression and NF-kappaB DNA binding activity. The N-terminal portion of Notch(IC) inhibited p50 DNA binding and interacted specifically with p50 subunit, not p65 of NF-kappaB. The interaction between Notch and NF-kappaB indicates that in addition to its role in the development of the immune system, Notch-1 may also have critical functions in the immune response, inflammation, viral infection, and apoptosis through control of NF-kappaB-mediated gene expression.

c-Jun NH2-terminal kinase activation leads to a FADD-dependent but Fas ligand-independent cell death in Jurkat T cells

Persistent c-Jun NH2-terminal kinase (JNK) activation induces cell death. Different mechanisms are ascribed to JNK-induced cell death. Most of the JNK-apoptosis studies employ stress stimuli known to activate kinases other than JNK. Here we used overexpression of mitogen-activated protein kinase kinase 7 (MKK7) to activate selectively JNK in T lymphoma Jurkat cells. Similar to that reported previously, Fas ligand (FasL) expression was up-regulated by JNK activation. Dominant negative-FADD and caspase-8 inhibitor benzyloxycarbonyl-Ile-Glu-Thr-Asp effectively inhibited MKK7-induced cell death, supporting a major involvement of FADD cascade. However, MKK7-induced cell death was not prevented by antagonist antibody ZB4 and Fas-Fc, indicating that Fas-FasL interaction is minimally involved. Confocal microscopy revealed that persistent JNK activation led to clustering of Fas. Our results suggest that, in contrast to that reported previously, JNK alone-induced death in Jurkat cells is FADD-dependent but is not triggered by Fas-FasL interaction.

Differential regulation of the expression of CD95 ligand, receptor activator of nuclear factor-kappa B ligand (RANKL), TNF-related apoptosis-inducing ligand (TRAIL), and TNF-alpha during T cell activation

Members of TNF superfamily are characterized by their ability to inflict apoptosis upon binding to their cognate receptors in a homotrimeric manner. These proteins are expressed on different cell types under various conditions. However, the mechanisms governing the expression of these molecules remain elusive. We have found that the TCR signal can elicit the expression of receptor activator of NF-kappaB ligand (RANKL), TNF-alpha, CD95L, and TNF-related apoptosis inducing ligand (TRAIL) in T cell hybridoma A1.1 cells, thus allowing us to examine the expression pattern of these molecules under precisely the same conditions. We have previously reported that CD95L expression requires both protein kinase C (PKC) translocation and Ca2+ mobilization and is inhibited by cyclosporin A, and dexamethasone. We demonstrate now that activation-induced expression of RANKL is mediated by Ca2+ mobilization. PKC activation does not induce RANKL expression nor does it synergize with the Ca2+ signal. Activation-induced RANKL expression is blocked by cyclosporin A, but not by dexamethasone. The expression of TNF, in contrast, is mediated by PKC, but not by Ca2+. TNF-alpha expression is not inhibited by cyclosporin A, but is sensitive to dexamethasone. A1.1 cells constitutively express TRAIL at low levels. Stimulation with anti-CD3 leads to an initial reduction and subsequent increase in TRAIL expression. TRAIL induction is not inhibited by cyclosporin A, but highly sensitive to dexamethasone. Therefore, expression of the TNF superfamily genes is regulated by distinct signals. Detailed understanding of the regulatory mechanisms could provide crucial information concerning the role of these molecules in the modulation of the immune system.

Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit expression of Fas ligand in activated T lymphocytes by regulating c-Myc, NF-kappa B, NF-AT, and early growth factors 2/3

Activation-induced cell death in T cells, a major mechanism for limiting an ongoing immune response, is initiated by Ag reengagement and mediated through Fas/Fas ligand interactions. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP), two multifunctional neuropeptides, modulate innate and adaptive immunity. We reported previously that VIP/PACAP protect T cells from activation-induced cell death through down-regulation of Fas ligand (FasL). In this study, we investigate the molecular mechanisms involved in the protective effect of VIP and PACAP. VIP/PACAP reduce in a dose-dependent manner anti-CD3-induced apoptosis in 2B4.11 T cell hybridomas. The protective effect is mediated through the specific type 2 VIP receptor, and the cAMP/protein kinase A pathway. A functional study demonstrates that VIP/PACAP inhibit activation-induced FasL expression. VIP/PACAP inhibit the expression and/or DNA-binding activity of several transcriptional factors involved in FasL expression, i.e., c-myc, NF-kappaB, NF-ATp, and early growth factors (Egr) 2/3. The inhibition of NF-kappaB binding is due to the stabilization of I-kappaB (inhibitory protein that dissociates from NF-kappaB), through the inhibition of I-kappaB kinase alpha activity. Subsequently, p65 nuclear translocation is significantly reduced. The inhibition in NF-ATp binding results from a calcineurin-independent reduction in NF-ATp nuclear translocation. VIP/PACAP inhibit the expression of Egr2 and 3, but not of Egr1. The effects on the transcriptional factors are mediated through type 2 VIP receptor with cAMP as secondary messenger.

Protection of human islets from the effects of interleukin-1beta by adenoviral gene transfer of an Ikappa B repressor

Interleukin-1beta (IL-1beta) is a pro-inflammatory cytokine that inhibits beta cell function and promotes Fas-triggered apoptosis. IL-1beta is thought to act early in the initiation of the autoimmune destruction of pancreatic beta cells in type I diabetes. IL-1beta promotes beta cell impairment, in part, by activating NF-kappaB transcription factor-dependent signaling pathways. We have examined whether beta cells could be protected from the effects of IL-1beta by overexpressing an inhibitor of NF-kappaB activity, IkappaB, by adenoviral gene transfer to intact human islets in culture. Infection of islets with an adenoviral vector encoding a non-phosphorylatable, non-degradable variant of IkappaBalpha resulted in normal insulin responses to glucose in the presence of IL-1beta. Furthermore, nitric oxide production was prevented and, more importantly, Fas-triggered apoptosis was inhibited following IkappaBalpha gene transfer. These results suggest that blocking the NF-kappaB pathway might prevent cytokine-induced beta cell impairment as a means of facilitating islet transplantation.