Anti-Fas/APO-1 antibody-mediated apoptosis of cultured human glioma cells. Induction and modulation of sensitivity by cytokines

Dendritic Cells Are Resistant to Apoptosis Through the Fas (CD95/APO-1) Pathway

Immunoregulation of lymphocytes and macrophages in the peripheral immune system is achieved in part by activation-induced cell death. Members of the TNF receptor family including Fas (CD95) are involved in the regulation of activation-induced cell death. To determine whether activation-induced cell death plays a role in regulation of dendritic cells (DCs), we examined interactions between Ag-presenting murine DCs and Ag-specific Th1 CD4+ T cells. Whereas mature bone marrow- or spleen-derived DCs expressed high levels of Fas, these DCs were relatively insensitive to Fas-mediated killing by the agonist mAb, Jo-2, as well as authentic Fas ligand expressed on the CD4+ T cell line, A.E7. The insensitivity to Fas-mediated apoptosis was not affected by priming with IFN-γ and/or TNF-α or by blocking the DC survival signals TNF-related activation-induced cytokine and CD40L. However, apoptosis could be induced with C2-ceramide, suggesting that signals proximal to the generation of ceramide might mediate resistance to Fas. Analysis of protein expression of several anti-apoptotic mediators revealed that expression of the intracellular inhibitor of apoptosis Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein was significantly higher in Fas-resistant DCs than in Fas-sensitive macrophages, suggesting a possible role for Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein in DC resistance to Fas-mediated apoptosis. Our results demonstrate that murine DCs differ significantly from other APC populations in susceptibility to Fas-mediated apoptosis during cognate presentation of Ag. Because DCs are most notable for initiation of an immune response, resistance to apoptosis may contribute to this function.

Tumor necrosis factor-alpha and interferon-gamma induce expression of functional Fas ligand on HT29 and MCF7 adenocarcinoma cells

Tumor cells develop diverse mechanisms to escape from immune surveillance, including expression of Fas ligand (FasL), a 40-kDa type II transmembrane protein that mediates apoptosis by binding to its cognate receptor Fas (APO-1/CD95). Upon activation, T lymphocytes and natural killer (NK) cells express Fas and thus become sensitive to FasL-mediated apoptosis. Here we show that tumor necrosis factor-alpha (TNF-alpha) in addition to interferon-gamma (IFN-gamma) induces cell surface expression of functional FasL in human HT29 colon and MCF7 breast adenocarcinoma cells that constitutively lack cell surface expression of FasL. These cells, expressing FasL, are capable of inducing apoptosis in Fas-positive Jurkat T cells mediated by plasma membrane-bound FasL and soluble forms of FasL. By contrast, mutational deletion of Fas cell surface expression as well as inhibition of caspase family proteases involved in Fas signaling and monoclonal antibodies neutralizing FasL protect Jurkat T cells from apoptosis caused by the FasL-expressing HT29 or MCF7 cells. These results demonstrate that TNF-alpha and IFN-gamma induce expression of functional FasL in adenocarcinoma cells which thereby can kill T lymphocytes by the FasL/Fas pathway.

Multiple sclerosis and central nervous system demyelination

Multiple sclerosis (MS) is characterized by multifocal areas within the CNS of demyelination with relative but not absolute axonal sparing. Initial lesion development appears dependent on T cell infiltration into the CNS; however, lesion expansion may reflect tissue injury induced by additional effector mechanisms derived from cells of the immune system and endogenous CNS cells (glial cells). This relative susceptibility to injury in MS of myelin and its cell of origin, the oligodendrocyte (OL), could reflect either the properties of the effectors or the targets. Effector-determined susceptibility could relate to presence of OL/myelin-restricted T cells or antibody. OLs, at least in vitro, express MHC class I molecules and are susceptible to CD8(+)T cell-mediated cytotoxicity. OL/myelin-specific antibodies are identified in MS lesions and could induce injury via complement- or ADCC-dependent mechanisms. OLs are susceptible to injury-mediated by non-specific cell effectors including NK cells, NK-like T cells (CD56(+)), and gamma/delta T cells via perforin/granzyme-dependent mechanisms. In vitro studies of OL injury mediated via tumor necrosis factor (TNF) and CD95 indicate that differential glial cell susceptibility to injury can depend on cell surface receptor expression and intracellular signaling pathways that are activated. These target-determined susceptibility factors may be amenable to neuroprotective therapies.

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

The Fas (CD95, APO-1) receptor is a membrane-associated polypeptide that can mediate apoptosis in various cell types. Although Fas receptor is expressed in endothelial cells (EC), little is known about its function in these cells. The expression of Fas by liver endothelial cells (LEC) suggests that upon stimulation, apoptosis may occur in these cells. We show that Fas is highly and constitutively expressed in cloned murine liver endothelial cells (LEC-1). In contrast, FasL expression was not detected at the protein and mRNA level in these cells. Our results show that Fas ligation in LEC-1 induces apoptotic cell death, indicating that Fas receptor is functional in these cells. The doses of Fas agonist required to induce LEC-1 apoptosis were higher than those used previously in other cells, including hepatocytes, suggesting that LEC-1 are highly resistant to the Fas apoptotic pathway. TNF treatment of LEC-1 induced up-regulation of Fas receptor on these cells. In contrast, TNF did not induce the expression of FasL on LEC-1. An increased susceptibility to Fas-mediated apoptosis was observed in TNF-treated LEC-1. Enhanced susceptibility to Fas-mediated apoptosis was also observed in LEC-1 pretreated with actinomycin D, suggesting that transcription of message coding for protective proteins is necessary to protect these cells against Fas-mediated apoptosis. Up-regulation of VCAM-1 and ICAM-1 was observed in LEC-1 treated with a dose of Fas agonist that does not induce apoptosis. To our knowledge, this is the first report that Fas mediates apoptosis in LEC, suggesting that apoptosis of these cells may participate in the liver damage observed in animals after receiving anti-Fas mAb or soluble FasL. Our findings also suggest that the Fas/FasL system may transduce activating signals independently of cell death in LEC-1.

Dual mechanism of Fas-induced cell death in neuroglioma cells: a role for reactive oxygen species

ApoI/Fas belongs to the tumor necrosis factor receptor (TNFR) superfamily and mediates cell death in various cell types. A dual mode of Fas-triggered cell death has been reported depending on cell types used in the experiments. The present study was carried out to test the possible role of reactive oxygen species in this dual mechanism in neuroglioma cells. Anti-Fas antibody caused dose-dependent and time-dependent increase in cell death measured by lactate dehydrogenase (LDH) release in control neuroglioma cells and in cells that were transfected with catalase cDNA. However, cells transfected with copper/zinc superoxide dismutase (Cu/ZnSOD) cDNA showed marked attenuation of Fas-induced LDH release. Moreover, flow cytometry and confocal microscopy revealed that Fas-induced cell death in control cells occur mostly through an apoptotic process. This process was also completely abrogated in cells overexpressing catalase or copper/zinc superoxide dismutase (Cu/ZnSOD). Further experiments revealed that Fas-induced cell death was associated with increased formation of superoxide anions in control neuroglioma cells and in cells overexpressing catalase. These increases were significantly suppressed by Cu/ZnSOD overexpression. These data indicate that Fas-mediated cell death in neuroglioma cells occur, in part, through the production of reactive oxygen species (ROS). These observations also suggest that Fas-induced cell death in these cells occur through apoptosis and necrosis. Thus overexpression of Cu/ZnSOD caused the suppression of both types of Fas-induced cell death whereas catalase prevented apoptotic but not necrotic cell death. These observations are discussed in terms of their support for a role for both peroxides and superoxide radicals in Fas-induced cell death.

Death ligand/receptor-independent caspase activation mediates drug-induced cytotoxic cell death in human malignant glioma cells

Death ligand/receptor interactions and caspase activation mediate drug-induced apoptosis in certain cancer cells. The molecular mechanisms responsible for the chemoresistance of human malignant gliomas are largely unknown. Here, we report that malignant glioma cells co-express CD95 and CD95L without undergoing suicidal or fratricidal apoptosis. Glioma cells do not commit CD95/CD95L-dependent suicide or fratricide even when RNA and protein synthesis are inhibited. This is because ectopic expression of the viral caspase inhibitor, crm-A, or exposure to a neutralizing CD95L antibody, block apoptosis induced by exogenous CD95L but not cell death induced by cytotoxic concentrations of inhibitors of RNA and protein synthesis. Although some cytotoxic drugs enhance the expression of CD95 or CD95L, crm-A fails to block drug-induced cytotoxic and clonogenic cell death, suggesting that the drug-induced changes in CD95 and CD95L expression are epiphenomenal. There is also no difference in drug-induced apoptosis between crm-A-transfected and control cells as assessed by electron microscopy, in situ DNA end labeling and DNA fragmentation. Further, glioma cells selected for resistance to CD95L do not acquire cross-resistance to chemotherapy. However, the broad spectrum caspase inhibitor, ZVAD-fmk, inhibits drug-induced cytotoxic cell death, suggesting a role of crm-A-insensitive caspases in drug-induced apoptosis of glioma cells. Thus, drug resistance of malignant glioma cells may involve deficiencies in two interrelated pathways that mediate death in order tumor cell types: (i) death ligand/receptor signalling; and (ii) caspase activation.

Tumor necrosis factor-alpha and interleukin-1beta increase the Fas-mediated apoptosis of human osteoblasts

Our recent work demonstrated functional Fas expression on human osteoblasts, and the histologic examination of the periarticular osteoporosis region in patients with rheumatoid arthritis (RA) showed apoptosis in osteoblasts. High concentrations of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and IL-6--which are thought to increase bone resorption--have been determined in RA synovium. We investigated the effect of these cytokines on the Fas-mediated apoptosis of human osteoblasts. The human osteoblastic cell line MG63 and human primary osteoblast-like cells from bone biopsy specimens were used as human osteoblasts. Fas expression on these cells was examined by flow cytometry, and Fas-mediated apoptosis induced by anti-Fas immunoglobulin M (IgM) was determined by a chromium 51 release assay, the presence of cells with hypodiploid DNA, staining with Hoechst 33258 dye, and the detection of DNA fragmentation on agarose gel electrophoresis. The proliferation of osteoblasts was analyzed by a tritiated thymidine incorporation assay. Spontaneous apoptosis was not found on cultured osteoblasts. The apoptosis of human osteoblasts was not induced by TNF-alpha, IL-1beta, or IL-6 alone in the absence of anti-Fas IgM. In addition, proliferation of the cells was not affected by these cytokines. Fas was constitutively expressed on unstimulated osteoblasts, and treatment of these cells with IL-1beta or TNF-alpha significantly augmented Fas expression. Human osteoblasts were committed to apoptosis with anti-Fas IgM, and the treatment of both IL-1beta and TNF-alpha markedly increased Fas-mediated apoptosis. TNF-alpha augmented both Fas expression and Fas-mediated apoptosis more efficiently than did IL-1beta. In addition, an additive effect on both Fas expression and Fas-mediated apoptosis was demonstrated when TNF-alpha and IL-1beta were added to osteoblasts. IL-6 influenced neither Fas expression nor the Fas-mediated apoptosis of osteoblasts. Furthermore, no synergistic effect of IL-6 with IL-1beta or TNF-alpha was observed. IL-1beta, TNF-alpha, or IL-6 did not change Bcl-2 expression. Our results suggest that IL-1beta and TNF-alpha regulate osteoblast cell number by up-regulating the Fas-mediated apoptosis of osteoblasts, one of the putative mechanisms inducing periarticular osteoporosis in patients with RA.

Heterogenous susceptibility to CD95-induced apoptosis in melanoma cells correlates with bcl-2 and bcl-x expression and is sensitive to modulation by interferon-gamma

The expression and functionality of the Fas receptor (CD95/APO-1) play an important role for the maintenance of tissue homeostasis. Various types of tumor cells have been shown to escape immune recognition by constitutive resistance to CD95-mediated apoptosis. Furthermore, several apoptosis-related proteins have been reported to influence CD95 sensitivity. We tested an unselected panel of 11 melanoma cell lines for sensitivity to CD95 and the corresponding expression of CD95, CD95L, bcl-2, bcl-x, bcl-xS, bax and FLIP proteins. Despite detection of CD95 cell-surface expression in 9 out of the 11 cell lines tested, only 3 melanoma cell lines were sensitive to anti-CD95-MAb-induced cell death. Apoptosis-related proteins CD95L, bcl-2, bcl-x, bcl-xS and bax were found to be heterogenously expressed in different melanoma cell lines tested. The susceptibility of melanoma cells to anti-CD95-MAb-mediated apoptosis was associated with low protein expression of both bcl-2 and bcl-x. The level of CD95 cell-surface expression in melanoma cells was no indicator for CD95 sensitivity. Furthermore, FLIP protein was detectable in 7 out of the 11 cell lines, but showed no correlation to CD95 sensitivity. Certain cytokines have been described as modulating the susceptibility of tumor cells to CD95-induced cell death. Since IFN-alpha was proved to be clinically efficient in melanoma therapy, we tested whether interferons have the ability to induce sensitivity to CD95 in primarily resistant melanoma cell lines. Here we show that IFN-gamma, but not IFN-alpha, is able to increase the susceptibility of sensitive cell lines and to induce CD95 sensitivity in resistant melanoma cell lines, accompanied by up-regulation of the protein expression level of CD95 and/or bcl-xS.

Relationship between Fas-ligand expression on carcinoma cell and cytotoxic T-lymphocyte response in lymphoepithelioma-like cancer of the stomach

The Fas/Fas-ligand (Fas-L) system is involved in the induction of apoptosis and mediates T-cell cytotoxicity. We investigated the Fas/Fas-L system and cytotoxic T lymphocytes (CTLs) in 30 lymphoepithelioma-like cancer of the stomach (LECS) in order to understand the immune evasion of the tumor cells. Epstein-Barr virus (EBV) was detected in 15 cases in 30 LECSs. The expressions of Fas and Fas-L in tumor cells, and TIA-1, CD4, CD8 and CD56 in lymphocytes were examined by immunohistochemical staining. Apoptosis of tumor cells and lymphocytes was detected by the terminal deoxynucleotidyl-mediated dUTP-nick end labeling method (TUNEL). Expression of Fas and Fas-L was detected in tumor cells in 10 and 17 LECS, respectively. CTL consisted predominantly of CD8 (CD8(+) > CD4(+)), whereas natural killer (NK) cells were detected in 4 cases only. In Fas-L-positive tumors, the TIA-1-positive lymphocyte count was significantly lower (p < 0.05) and the number of apoptotic lymphocytes was significantly higher (p < 0.05) than in Fas-L-negative cases. The number of TIA-1-positive lymphocytes in EBV(+) cases was significantly higher than that in the EBV(-) tumors (p < 0.05). The number of apoptotic tumor cells in EBV(+) tumors was significantly lower than in EBV(-) cases (p < 0.01). Our results suggest that in LECS, tumor cells expressing Fas-L may evade the immune attack by killing lymphocytes through the Fas/Fas-L system. However, in EBV(+) LECS tumors, our results indicate that a high number of CTL is associated with a reduction in the number of apoptotic tumor cells. Our findings indicate that the Fas/Fas-L system plays a role in immune evasion of tumor cells in EBV(+) tumors. Int. J. Cancer (Pred. Oncol.) 84:339-343, 1999.

p27 modulates cell cycle progression and chemosensitivity in human malignant glioma

The cell cycle regulatory protein p27, an inhibitor of cyclin-dependent kinases (CDK), has been attributed a role in (i) prognosis in breast and colon cancer, (ii) induction of apoptosis in cancer cells, and (iii) resistance to cancer chemotherapy. Here we report that p27 is widely expressed in human malignant gliomas in vivo and in glioma cell lines in vitro. Serum deprivation or confluency promotes p27 protein accumulation in vitro. Neither baseline p27 levels nor p27 levels induced by confluency or serum deprivation correlate with p53 status or drug sensitivity of human glioma cell lines. Expression of antisense p27 mRNA increased the doubling times in T98G glioma cells, whereas sense p27 mRNA had no such effect. There was a density-dependent and drug-specific modulation of chemosensitivity by sense or antisense mRNA expression in T98G cells. Taken together, these data define a strong p27 response to altered growth conditions and suggest a role for p27 in modulating response to chemotherapy in human malignant glioma cells.

PTEN gene transfer in human malignant glioma: sensitization to irradiation and CD95L-induced apoptosis

The tumor suppressor gene PTEN (MMAC1, TEP1) encodes a dual-specificity phosphatase and is considered a progression-associated target of genetic alterations in human gliomas. Recently, it has been reported that the introduction of wild type PTEN into glioma cells containing endogenous mutant PTEN alleles (U87MG, LN-308), but not in those which retain wild-type PTEN (LN-18, LN-229), causes growth suppression and inhibits cellular migration, spreading and focal adhesion. Here, we show that PTEN gene transfer has no effect on the chemosensitivity of the four cell lines. Further, a correlational analysis of the endogenous PTEN status of 12 human glioma cell lines with their sensitivity to seven different cancer chemotherapy drugs reveals no link between PTEN and chemosensitivity. In contrast, ectopic expression of wild type PTEN, but not the PTEN(G129R) mutant, in PTEN-mutant gliomas markedly sensitizes these cells to irradiation and to CD95-ligand (CD95L)-induced apoptosis. PTEN-mediated facilitation of CD95L-induced apoptosis is associated with enhanced CD95L-evoked caspase 3 activity. Protein kinase B (PKB/Akt), previously shown to inhibit CD95L-induced apoptosis in nonglial COS7 cells, is inactivated by dephosphorylation. Interestingly, both PTEN-mutant U87MG and PTEN-wild-type LN-229 cells contain phosphorylated PKB constitutively. Wild-type PTEN gene transfer promotes dephosphorylation of PKB specifically in U87MG cells but not in LN-229 cells. Sensitization of U87MG cells to CD95L-apoptosis by wild-type PTEN is blocked by insulin-like growth factor-1 (IGF-1). The protection by IGF-1 is inhibited by the phosphoinositide 3-OH (PI 3) kinase inhibitor, wortmannin. Although PKB is a down-stream target of PI 3 kinase, the protection by IGF-1 was not associated with the reconstitution of PKB phosphorylation. Thus, PTEN may sensitize human malignant glioma cells to CD95L-induced apoptosis in a PI 3 kinase-dependent manner that may not require PKB phosphorylation.

Estrogen deficiency accelerates autoimmune exocrinopathy in murine Sjögren's syndrome through fas-mediated apoptosis

Estrogenic action has been suggested to be responsible for the strong female preponderance of autoimmune diseases, but the role of estrogens in the female has not been well characterized. We evaluated the effects of estrogen deficiency in a murine model for autoimmune exocrinopathy of Sjögren's syndrome (SS). Severe destructive autoimmune lesions developed in the salivary and lacrimal glands in estrogen-deficient mice, and these lesions were recovered by estrogen administration. We detected an intense estrogen receptor in splenic CD8(+) T cells compared with that in CD4(+) T cells, and concanavalin-A-stimulated blastogenesis of splenic CD8(+) T cells with estrogens was much higher than that of CD4(+) T cells. We found a significant increase in serum autoantibody production against the organ-specific autoantigen alpha-fodrin. Moreover, an increased proportion of TUNEL+ apoptotic epithelial duct cells was observed in estrogen-deficient mice. It was demonstrated that Fas-mediated apoptosis in cultured salivary gland cells was clearly inhibited by estrogens in vitro. These results indicate that dysfunction of regulatory T cells by estrogen deficiency may play a crucial role on acceleration of organ-specific autoimmune lesions, and estrogenic action further influences target epithelial cells through Fas-mediated apoptosis in a murine model for SS.

Treatment of experimental glioma by administration of adenoviral vectors expressing Fas ligand

Fas ligand (FasL) is a cytokine, produced by activated T cells and NK cells, that triggers apoptosis of Fas-positive target cells including human glioma cells. As shown here, in vitro infection of rat F98 and human LN18 glioma cell lines with recombinant adenovirus (rAd) expressing FasL cDNA under control of the cytomegalovirus promoter (rAd-CMV-FasL) induced striking cytotoxicity in Fas-positive glioma cell lines but not in the Fas-negative F98 glioma subline F98/ZH. The extent of FasL-mediated cytotoxic effects outranged the expectations based on expression of beta-galactosidase (beta-Gal) by F98 cells infected with a control virus expressing the lacZ gene (rAd-CMV-lacZ). The detection of FasL bioactivity in supernatants of infected cells provides evidence of a bystander mechanism involving the cytotoxic action of FasL on uninfected cells. In F98 tumor-bearing rats, infection with rAd-CMV-FasL increased the mean survival time by 50% compared with infection with rAd-CMV-lacZ or untreated controls. These data suggest that viral vector transduction of the FasL gene could be part of a successful glioma gene therapy.

Selective potentiation of drug cytotoxicity by NSAID in human glioma cells: the role of COX-1 and MRP

Here, we report that nonsteroidal anti-inflammatory drugs (NSAID) enhance the cytotoxic effects of doxorubicin and vincristine in T98G human malignant glioma cells. The cytotoxicity of BCNU, cisplatin, VM26, camptothecin, and cytarabine is unaffected by NSAID. No free radical formation is induced by doxorubicin or vincristine in the absence or presence of NSAID. Doxorubicin and vincristine cytotoxicity in the absence or presence of NSAID are unaffected by free radical scavengers. Functional inhibitors of phospholipase A2 (PLA2), such as dexamethasone and quinacrine, do not mimick the effects of NSAID. T98G cells, but not LN-18, LN-229, LN-308, or A172 glioma cells, express cyclooxygenase (COX-1) and NSAID do not modulate drug cytotoxicity in the other cell lines, except T98G. Thus, augmentation of doxorubicin and vincristine cytotoxicity by NSAID correlates with COX-1 expression. However, ectopic expression of COX-1 in LN-229 cells does not induce the phenotype of T98G cells, indicating that COX-1 inhibition does not mediate the effects of NSAID on drug cytotoxicity. In contrast, a multidrug resistance (MDR) phenotype due to expression of the multidrug resistance-associated protein (MRP) is most prominent in T98G cells and is amenable to modulation by indomethacin, suggesting that inhibition of MRP is at least in partly responsible for the potentiation of doxorubicin and vincristine cytotoxicity by NSAID.

Induction of Antitumor Immunity with Fas/APO-1 Ligand (CD95L)-Transfected Neuroblastoma Neuro-2a Cells

Fas/Apo-1 (CD95)-Fas ligand (FasL) system has been implicated in the suppression and stimulation of immune responses. We examined the induction of antitumor immunity with neuroblastoma Neuro-2a cells transfected with FasL cDNA (Neuro-2a+FasL). Neuro-2a+FasL cells expressed FasL on the cell surface and secreted soluble FasL. Histologic and flow cytometric analyses revealed that Neuro-2a+FasL cells caused neutrophils to infiltrate into the injected site, resulting in strong inflammation. Neutrophil infiltration was inhibited by treatment with anti-FasL mAb and did not occur in Fas-deficient lpr mice. Normal syngeneic mice rejected Neuro-2a+FasL cells after the inflammation and acquired tumor-specific protective immunity. CD8+ T cells were responsible for the antitumor immunity. Neuro-2a+FasL cells formed tumors after far longer latency compared with mock-transfected Neuro-2a+Neo cells in nude mice, and immune competent mice rejected Neuro-2a cells but not sarcoma S713a cells when they were injected with Neuro-2a+FasL cells in a mixture. These results suggest that neutrophils attracted through the Fas-FasL system may impair tumor cells by inflammation at the initial step, followed by development of CD8+ T cell-dependent tumor-specific antitumor immunity, leading to complete eradication of tumor cells. Importantly, the treatment with Neuro-2a+FasL cells exhibited therapeutic efficacy against growing tumors.

Studies of the mechanism of cytolysis by tumour-infiltrating lymphocytes

In order to determine the mechanism of tumour destruction by tumour-infiltrating lymphocytes (TIL), we examined the ability of both CD4+ and CD8+ effector TIL, and TIL clones, to manifest granzyme-mediated and Fas-mediated destruction of tumour targets. In many in vitro studies TIL have been shown to manifest anti-tumour reactivity, yet many tumours escape immunological destruction. To investigate the role of Fas expression and the concomitant sensitivity to the inducibility of apoptotic death, we derived TIL from four melanomas and one glioma. The glioma, and all but one of the melanomas, expressed Fas, but Fas-mediated apoptosis could only be detected if the targets were treated with cyclohexamide. The melanomas and the glioma all expressed detectable cytoplasmic Bcl-2 protein, known to exert anti-apoptotic activity. Lysis of tumours by CD8-enriched cultures and CD8+ clones was Ca2+-dependent and could not be modified by an anti-Fas MoAb. In CD4-enriched cultures or CD4+ clones with cytotoxic potential against tumour cells, cytotoxicity was also Ca2+-dependent. As Ca2+-dependent cytotoxicity is usually the result of secretion of perforin/granzyme-B, we investigated the presence of perforin in cytotoxic CD4+ clones and demonstrated the presence of granular deposits of this enzyme in some of the CD4+ clones. Although an anti-Fas MoAb did not block the lysis of melanoma targets by CD4+ clones, the examination of Fas-dependent targets demonstrated that these clones also had the potential to kill by the Fas/Fas ligand system. These data suggest that the predominant mechanism in tumour killing by TIL appears to be perforin-granzyme-dependent, and that the solid tumour cell lines we studied are less susceptible to Fas-mediated apoptosis. As non-apoptotic pathways may enhance tumour immunogenicity, exploitation of the perforin-granzyme-dependent cytotoxic T lymphocyte (CTL) pathways may be important for achieving successful anti-tumour responses.

Boswellic acids and malignant glioma: induction of apoptosis but no modulation of drug sensitivity

Steroids are essential for the control of oedema in human malignant glioma patients but may interfere with the efficacy of chemotherapy. Boswellic acids are phytotherapeutic anti-inflammatory agents that may be alternative drugs to corticosteroids in the treatment of cerebral oedema. Here, we report that boswellic acids are cytotoxic to malignant glioma cells at low micromolar concentrations. In-situ DNA end labelling and electron microscopy reveal that boswellic acids induce apoptosis. Boswellic acid-induced apoptosis requires protein, but not RNA synthesis, and is neither associated with free radical formation nor blocked by free radical scavengers. The levels of BAX and BCL-2 proteins remain unaltered during boswellic acid-induced apoptosis. p21 expression is induced by boswellic acids via a p53-independent pathway. Ectopic expression of wild-type p53 also induces p21, and facilitates boswellic acid-induced apoptosis. However, targeted disruption of the p21 genes in colon carcinoma cells enhances rather than decreases boswellic acid toxicity. Ectopic expression of neither BCL-2 nor the caspase inhibitor, CRM-A, is protective. In contrast to steroids, subtoxic concentrations of boswellic acids do not interfere with cancer drug toxicity of glioma cells in acute cytotoxicity or clonogenic cell death assays. Also, in contrast to steroids, boswellic acids synergize with the cytotoxic cytokine, CD95 ligand, in inducing glioma cell apoptosis. This effect is probably mediated by inhibition of RNA synthesis and is not associated with changes of CD95 expression at the cell surface. Further studies in laboratory animals and in human patients are required to determine whether boswellic acids may be a useful adjunct to the medical management of human malignant glioma.

Interferon-gamma rescues TNF-alpha-induced apoptosis mediated by up-regulation of TNFR2 on EoL-1 cells

Recent studies show that apoptosis is important for the resolution of chronic inflammation. Using a human myeloblastic leukemia cell line, EoL-1, we investigated the effect of interferon-gamma (IFN-gamma), which differentiates EoL-1 into monocyte/macrophage-like cells on Fas antigen (Fas)- and tumor necrosis factor-alpha (TNF alpha)-induced apoptosis. Both TNF and anti-Fas monoclonal antibody (CH-11) induced apoptosis of EoL-1 cells. Pretreatment with IFN-gamma for 72 hours enhanced the CH-11-induced apoptosis with up-regulation of Fas. However, the treatment markedly inhibited the TNF-induced apoptosis. In flow cytometric analysis, EoL-1 expressed two types of tumor necrosis factor receptors (TNFR1 and TNFR2), and the expression of TNFR2 but not of TNFR1 was up-regulated significantly after the IFN-gamma treatment. The TNF-induced apoptosis was mimicked by a TNFR1 stimulating antibody (htr-9), and was reversed by a TNFR1 blocking antibody (H398). Although the TNFR1-mediated cytotoxic signal was not affected by IFN-gamma pretreatment, blocking TNFR2 by a specific antagonistic antibody (utr-1) canceled the inhibitory effect of IFN-gamma. In conclusion, TNF-induced apoptosis was mediated preferentially by TNFR1, and the anti-apoptotic effect of IFN-gamma was result from up-regulated TNFR2 in EoL-1 cell line. This cell line is a useful model to provide new insights into crosstalk among Fas/FasL-, TNF-, and IFN-gamma-mediated signaling.

Fas Ligand and Fas Are Expressed Constitutively in Human Astrocytes and the Expression Increases with IL-1, IL-6, TNF-α, or IFN-γ

Fas ligand (FasL) and Fas are mediators of apoptosis, which are implicated in the peripheral deletion of autoimmune cells, activation-induced T cell death, and cytotoxicity mediated by CD8+ T cells. Fas is also believed to be involved in several central nervous system diseases, but until now, the effector cells expressing FasL in the brain have not been identified. We investigated the expression levels of Fas and FasL with the stimulation of cytokines and the possible effector cells targeting Fas-bearing cells. Our data demonstrated that: 1) FasL is expressed constitutively on astrocytes taken from a fetus or an adult and that its expression increases when these cells are treated with IL-1, IL-6, or TNF-α in which the pretreatment of IFN-γ triggers astrocytes to express more FasL; 2) astrocytes induce apoptosis in MOLT-4 cells through FasL; 3) Fas is also expressed constitutively and is up-regulated by IL-1, IL-6, or TNF-α in which the pretreatment of IFN-γ triggers astrocytes to express more Fas; 4) apoptosis occurs when fetal astrocytes are treated with agonistic anti-Fas IgM Ab after culture with IFN-γ and TNF-α; and 5) TNF-related apoptosis inducing ligand is up-regulated in fetal astrocytes with stimuli of IL-1 or TNF-α. These findings suggest a possible role of astrocytes in the induction of apoptosis in central nervous system diseases.

Pancreatic cancer cells can evade immune surveillance via nonfunctional Fas (APO-1/CD95) receptors and aberrant expression of functional Fas ligand

BACKGROUND

The Fas (APO-1/CD95) receptor/Fas ligand (FasR/FasL) system plays a key role in immune surveillance. We investigated the possibility of a tumor escape mechanism involving the FasR/FasL system in pancreatic cancer cells.

METHODS

Fourteen pancreatic cancer cell lines and 3 pancreatic cancer surgical specimens were studied for their expression of FasR and FasL by flow cytometry, immunoblotting, and immunohistochemistry, FasR function was tested with an anti-FasR antibody. FasL function was assessed by coculture assays using pancreatic cancer cells and FasR-sensitive Jurkat T-cells.

RESULTS

FasR was expressed in normal pancreas, in 14 of 14 pancreatic cancer cell lines, and in 3 of 3 surgical specimens. However, only 1 of 14 cancer cell lines expressed functional FasR when grown in monolayer, although 3 additional cell lines displayed functional FasR when cultured in suspension. Normal pancreas did not express FasL, whereas 14 of 14 cancer cell lines and 3 of 3 surgical specimens expressed FasL. FasL expressed by pancreatic cancer cells mediated killing of Jurkat T-cells in coculture assays (P < .005).

CONCLUSIONS

These data suggest that pancreatic cancer cells have 2 potential mechanisms of evading Fas-mediated immune surveillance. A nonfunctional FasR renders them resistant to Fas-mediated apoptosis. The aberrant expression of functional FasL allows them to "counterattack" activated Fas-sensitive T-cells. Alone or in unison, these tumor escape mechanisms may contribute to the malignant and often rapid course of pancreatic cancer disease.

Bisindolylmaleimide VIII facilitates Fas-mediated apoptosis and inhibits T cell-mediated autoimmune diseases

Fas-mediated apoptosis is essential for the elimination of cells, and impaired apoptosis can have severe detrimental consequences. Bisindolylmaleimide VIII potentiated Fas-mediated apoptosis in human astrocytoma 1321N1 cells and in Molt-4T cells, both of which were devoid of apoptosis induced by anti-Fas antibody in the absence of bisindolylmaleimide VIII, and in Jurkat and CEM-6 T cells, which showed slight and moderate apoptotic responses, respectively, to low levels of Fas stimulation. Potentiation of Fas-mediated apoptosis by bisindolylmaleimide VIII was selective for activated, rather than non-activated, T cells, and was Fas-dependent, as it was not observed in T cells from Fas-deficient lpr/lpr mice. Administration of bisindolylmaleimide VIII to rats during autoantigen stimulation prevented the development of symptoms of T cell-mediated autoimmune diseases in two models, the Lewis rat model of experimental allergic encephalitis and the Lewis adjuvant arthritis model. Thus, the use of agents such as bisindolylmaleimide VIII may be therapeutically useful for supporting more effective elimination of detrimental cells through enhancement of Fas-dependent apoptosis signaling.

Potentiation of Fas-mediated apoptosis of murine granulosa cells by interferon-gamma, tumor necrosis factor-alpha, and cycloheximide

The Fas antigen is a transmembrane receptor belonging to the tumor necrosis factor-alpha (TNF) receptor family that, when activated by Fas ligand or agonistic antibodies, induces death by apoptosis. Although the presence of Fas antigen in ovarian tissues has been demonstrated, little is known about whether Fas antigen is functional in the ovary. This report shows that murine granulosa cells are initially resistant to antibody-induced Fas-mediated apoptosis, but will undergo apoptosis when cotreated with TNF and interferon-gamma (IFN) or cycloheximide (CX). Granulosa cells were obtained from follicles of 23-day-old mice 2 days after injection of PMSG. Twenty-four hours after plating, cells were pretreated with either 0 or 200 U/ml IFN, which has been shown to induce Fas antigen expression and is required for Fas-mediated killing in many cell types. At 48 h, cells were treated with 2 microg/ml control IgG, 2 microg/ml anti-Fas antigen antibody (Fas mAb), 10 ng/ml TNF, or Fas mAb and TNF. Cytotoxicity (percent killing) relative to control IgG was determined at 72 h by counting granulosa cells after trypsinization. In the absence of IFN, no cytotoxicity was observed. In the presence of IFN, neither TNF or Fas mAb alone was cytotoxic, but the combination of Fas mAb and TNF resulted in 25% killing (P < 0.05). Fas antigen messenger RNA (mRNA) was detectable in cultures not treated with cytokines and was increased 5-fold by TNF, 2-fold by IFN, and 17-fold by the combination of IFN and TNF. To test whether the presence of a labile inhibitor(s) of Fas-mediated killing in granulosa cells is the cause of resistance to Fas mAb, the protein synthesis inhibitor CX was used. Experiments were performed as described above, except that cells were treated with 0.5 microg/ml CX in conjunction with other treatments at 48 h. Fas mAb treatment in the presence of CX induced 25% cell death without IFN pretreatment and 38% with IFN (P < 0.05). TNF treatment in the presence of CX had no effect alone, but potentiated the effects of Fas mAb, resulting in 56% killing in the absence of IFN and 86% killing in the presence of IFN (P < 0.05). Cells stained positively for DNA fragmentation and annexin V binding, features characteristic of apoptosis. Because initial experiments showed that treatment with TNF alone increased Fas mRNA levels, the effect of pretreating cells for 24 h with TNF before treatment with Fas mAb was tested. Pretreatment with TNF or IFN alone did not promote Fas mAb-mediated killing, but combined pretreatment with TNF and IFN resulted in 25% killing in response to Fas mAb. Treatment of cells with the combination of IFN and TNF induced a 19-fold increase in Fas antigen mRNA levels. Corresponding increases in Fas antigen protein expression on the surface of cells in response to cytokine treatments were detected by immunocytochemistry. Human TNF did not duplicate the effects of mouse TNF in inducing Fas antigen mRNA expression and Fas mAb-induced killing. As human TNF interacts exclusively with the type I, but not the type II, TNF receptor in the mouse, potentiating effects of mouse TNF on the Fas pathway are probably mediated via the type II TNF receptor. The effects of cytokine treatments on levels of mRNA for FAP-1, an inhibitor of Fas-mediated apoptosis, were determined. FAP-1 mRNA was detectable in untreated granulosa cells, and levels were not altered by treatment with TNF and/or IFN. In summary, the Fas-mediated pathway of apoptosis is functional in mouse granulosa cells that are stimulated with IFN and TNF. These cytokines may function at least partially by increasing Fas antigen expression. Granulosa cells appear to have inhibitors of the Fas antigen pathway, as treatment with CX potentiates Fas-mediated death. TNF promotes Fas-mediated killing in the presence and absence of CX. Therefore, TNF is not likely to act simply by increasing Fas antigen expression or decreasing protein inhibitors of the Fas pathway, because TNF remains effec

Transforming growth factor-beta inhibits apoptosis induced by beta-amyloid peptide fragment 25-35 in cultured neuronal cells

Previously, we demonstrated that transforming growth factor-beta (TGF-beta) pretreatment protects neuroblastoma cell lines, human hNT neurons, and primary rat embryo hippocampal neurons (REHIPs) from degeneration caused by incubation with beta-amyloid peptide (Abeta). Here we present evidence suggesting that TGF-beta interferes with an apoptotic pathway induced by Abeta. TGF-beta preteatment decreases the amount of DNA laddering seen following Abeta treatment in neuroblastoma cells, while in REHIPs, TGF-beta decreases the number of positive cells detected in situ by Klenow labelling following Abeta treatment. RT-PCR shows that in REHIPs, Abeta decreases mRNA expression of Bcl-2, as well as the ratio of Bcl-xL/Bcl-xS, with little effect on Bax expression. These changes are expected to promote apoptosis. When REHIPs are incubated with TGF-beta before addition of Abeta, the Bcl-xL/Bcl-xS ratio and Bcl-2 levels are increased compared to cells treated with Abeta alone. Again there is little effect on Bax expression. Western blotting and immunohistochemistry experiments also show that TGF-beta maintains increased levels of Bcl-2 and Bcl-xL protein in REHIPs even in the presence of Abeta. This pattern of gene expression should function to decrease apoptosis. Similarly, RT-PCR analysis of mRNA prepared from hNT cells shows that TGF-beta pretreatment before addition of Abeta maintains a higher level of Bcl-2 expression and an increased Bcl-xL/Bcl-xS ratio as compared to cells treated with Abeta alone. In neuronal cell types treated with Abeta, TGF-beta appears to regulate expression of genes in the Bcl-2 family to favor an anti-apoptotic pathway.

The topoisomerase I inhibitors, camptothecin and beta-lapachone, induce apoptosis of human retinal pigment epithelial cells

The aim of the study was to determine whether the topoisomerase I inhibitors, camptothecin and beta-lapachone, are suitable agents for the adjuvant pharmacotherapy of proliferative vitreoretinopathy (PVR). The effects of the drugs on cultured human retinal pigment epithelial (RPE) cells were examined using growth assays, cytotoxicity assays, single cell agarose gel electrophoresis, in situ DNA end labeling and immunoblot analysis for apoptosis-regulatory proteins. Both agents killed RPE cells in a concentration-and time-dependent manner. Cell death was apoptotic as assessed by single cell agarose gel electrophoresis and in situ DNA end labeling. Camptothecin, but not beta-lapachone, induced accumulation of p53 and the major growth arrest-associated p53 response protein, p21. Both drugs enhanced expression of the proapoptotic BAX protein. Camptothecin, but not beta-lapachone, synergistically enhanced RPE cell apoptosis induced by the cytotoxic cytokine, CD95 ligand (CD95L). This effect was linked to camptothecin-induced inhibition of RNA synthesis. Atypical topoisomerase I inhibitors may be promising agents for the adjuvant pharmacotherapy of PVR. Experimental studies to assess possible ocular toxicity upon local administration and to confirm its therapeutic efficacy in an animal model of PVR are required.

Costimulatory molecules and cytotoxic T cells in chronic hepatitis C: defence mechanisms devoted to host integrity or harmful events favouring liver injury progression? A review

The recruitment of antigen-specific lymphocytes at liver site represents a prominent feature in patients chronically infected with hepatitis C virus (HCV). However, despite the strong and multispecific response, chronic infection leads in a significant number of cases to the development of cirrhosis and hepatocellular carcinoma. The finding that the expression of CD80 structure positively correlates with disease histological worsening points out a role for the costimulatory pathway in the progression of liver cell injury. On the other hand, the demonstration of CD95 and CD95-ligand positive cells in the context of periportal areas, a pattern which is not strictly associated to HCV tissue distribution, indicates the occurrence of either virus-infected or innocent bystander hepatocyte killing. Nonetheless, the persistence of HCV, in spite of cytotoxic T lymphocyte (CTL) liver recruitment, suggests a possible in-situ imbalance of cytotoxic activities, above all referred to perforin-granzyme-dependent necrosis. Altogether, these findings outline that several factors might be involved in HCV-driven immunopathogenesis. Therefore, the fully clarification of these mechanisms may offer a suitable therapeutical approach for the improvement of clinical outcome in chronic hepatitis C.

Molecular Mechanisms of Immune-Mediated Lysis of Murine Renal Cancer: Differential Contributions of Perforin-Dependent Versus Fas-Mediated Pathways in Lysis by NK and T Cells

Mice bearing the experimental murine renal cancer Renca can be successfully treated with some forms of immunotherapy. In the present study, we have investigated the molecular pathways used by NK and T cells to lyse Renca cells. Renca cells normally express low levels of Fas that can be substantially enhanced by either IFN-γ or TNF-α, and the combination of IFN-γ + TNF-α synergistically enhances cell-surface Fas expression. In addition, cells pretreated with IFN-γ and TNF-α are sensitive to lysis mediated by Fas ligand (FasL)-expressing hybridomas (dllS), cross-linking of anti-Fas Abs or soluble Fas (FasL). Lysis via Fas occurs by apoptosis, since Renca shows all the typical characteristics of apoptosis. No changes in levels of bcl-2 were observed after cytokine treatments. We also examined cell-mediated cytotoxic effects using activated NK cells and T cells from gld FasL-deficient mice, and perforin-deficient mice, as well as wild-type C57BL/6 and BALB/c mice. Interestingly, the granule-mediated pathway predominated in killing of Renca by activated NK cells, while the Fas/FasL pathway contributed significantly to cell-mediated killing of Renca by activated T cells. These results suggest that killing of Renca tumor cells by immune effector cells can occur by both granule and Fas-mediated cytotoxicity. However, for the Fas-mediated pathway to function, cell surface levels of Fas need to be increased beyond a critical threshold level by proinflammatory cytokines such as IFN-γ and TNF-α.

Apoptosis by retrovirus- and adenovirus-mediated gene transfer of Fas ligand to glioma cells: implications for gene therapy

Astrocytic tumors frequently express Fas/APO-1 (Fas), in sharp contrast to surrounding normal brain cells, providing a potential window through which selective killing of tumor cells could be pursued. To assess this possibility, we transduced Fas into U251, a glioma cell line resistant to anti-Fas antibody-mediated apoptosis, and obtained transfectants with high levels of Fas expression. Anti-Fas antibody showed significantly enhanced cytotoxicity for the transfectants, suggesting that U251 cells maintained an intercellular cascade of Fas-mediated apoptosis. When U251 transfectants with high-level Fas expression were transduced with Fas ligand-encoding gene via retrovirus, they were unaffected by exposure to anti-Fas antibody or Fas ligand adenovirus (Adeno-FL). Thus, retroviral induction of Fas ligand into the glioma cells with high levels of Fas led to the selection of cells that were resistant to Fas-dependent apoptosis. These resistant U251 transfectants were susceptible to FADD adenovirus (Adeno-FADD)-induced apoptosis, indicating that a cascade of death signals was blocked at the steps between Fas ligand and FADD. As for adenoviral transduction of Fas ligand into gliomas, gliomas with a relatively high level of expression of Fas were remarkably sensitive to Adeno-FL-induced apoptosis. Besides, Adeno-FADD induced pronounced apoptosis in all glioma cells. Our data suggest the possibility of using adenovirus-mediated transduction of Fas ligand and FADD genes as a therapeutic approach to target gliomas.

CD95-mediated apoptosis: no variation in cellular sensitivity during cell cycle progression

Sensitivity of CD95-mediated apoptosis has been reported to vary during cell cycle progression (FEBS Lett. (1997) 412, 91-93). Here, we report that three human glioma cell lines with different p53 status (i) undergo growth arrest and synchronous cell cycle re-entry after prolonged serum deprivation, (ii) do not exhibit cell cycle-related changes in CD95 expression at the cell surface, and (iii) do not exhibit cell cycle-related changes in susceptibility to DC95 ligand-induced apoptosis. In contrast, cell cycle-specific activity was demonstrated for various cancer chemotherapy drugs. Further, CD95 expression and susceptibility to CD95 ligand-induced apoptosis does not vary during cell cycle progression of Jurkat T cells, HeLa cervical carcinoma and HepG2 hepatocellular carcinoma cells. These results do not support a role for the cell cycle phase as an important predictor of vulnerability to CD95-mediated apoptosis.

Chemosensitivity of human malignant glioma: modulation by p53 gene transfer

Loss of wild-type p53 activity is one of the most common molecular abnormalities in human cancers including malignant gliomas. The p53 status is also thought to modulate sensitivity to irradiation and chemotherapy. Here, we studied the effect of a p53 gene transfer on the chemosensitivity of three human glioma cell lines with different endogenous p53 status (LN-229, wild-type; LN-18, mutant; LN-308, deleted), using the murine temperature-sensitive p53 val135 mutant. Expression of mutant p53 enhanced proliferation of LN-308 cells but reduced proliferation in the other cell lines. Expression of wild-type p53 caused reversible growth arrest of all cell lines but failed to induce apoptosis. Growth arrest induced by wild-type p53 was associated with strong induction of p21 expression. Strong induction of BAX expression and loss of BCL-2 expression, which are associated with p53-dependent apoptosis rather than growth arrest, were not observed. Wild-type p53 failed to sensitize glioma cells to cytotoxic drugs including BCNU, cytarabine, doxorubicin, teniposide and vincristine. The combined effects of wild-type p53 gene transfer and drug treatment were less than additive rather than synergistic, suggesting that the intracellular cascades activated by p53 and chemotherapy are redundant. Unexpectedly, forced expression of mutant p53 modulated drug sensitivity in that it enhanced the toxicity of some drugs but attenuated the effects of others. These effects may represent a dominant negative effect of mutant p53 in LN-229 cells which have wild-type p53 activity but must be considered a gain of function-type effect in the other two cell lines which have no wild-type p53 activity. Importantly, no clear-cut pattern emerged among the three cell lines studied. We conclude that somatic gene therapy based on the reintroduction of p53 will limit the proliferation of human malignant glioma cells but is unlikely to induce clinically relevant sensitization to chemotherapy in these tumors.

FADD gene therapy for malignant gliomas in vitro and in vivo

Fas/APO-1 (CD95), a cell surface cytokine receptor, triggers apoptotic cell death by specific agonist antibody, suggesting that Fas/APO-1 may be a promising target for treatment of tumors. In this study, we show that treatment with anti-Fas antibody effectively induced apoptosis in malignant glioma cell lines with high expression of Fas/APO-1 (n = 3). Malignant glioma cells with low or undetectable expression of Fas/APO-1 (n = 6), however, were resistant to Fas/APO-1-dependent cytotoxicity. The purpose of this study, therefore, was to determine whether resistant tumors could be made susceptible to apoptosis. FADD/MORT1 constitutes a novel protein that associates specifically with the cytoplasmic death domain of Fas/APO-1 and induces apoptosis. We investigated whether overexpression of FADD would induce apoptosis in malignant glioma cells without activating Fas/APO-1. Results indicated that about 85% of malignant glioma cells, regardless of Fas/APO-1 expression levels, underwent apoptosis after transient transfection with FADD expression vector. To further improve gene transfer of FADD into malignant glioma cells, we constructed a retroviral vector containing the FADD gene. The retroviral transfer of FADD gene significantly enhanced the transduction efficiency and effectively inhibited both in vitro and in vivo survival of malignant glioma cells through induction of apoptosis. These findings suggest that the FADD gene is a novel and useful tool for the treatment of malignant gliomas.

Chemotherapy primes malignant glioma cells for CD95 ligand-induced apoptosis up-stream of caspase 3 activation

The cytotoxic cytokine, CD95 ligand, is an experimental anti-cancer agent. Here, we describe a novel pathway of drug-mediated augmentation of CD95 ligand-induced apoptosis. We report that prolonged pre-exposure of human malignant glioma cells to different cytotoxic agents, VM26, cytarabine and cisplatin, induces strong sensitization to CD95 ligand-induced apoptosis. CD95 gene transfer does not prevent sensitization, suggesting that sensitization is not mediated by drug-induced CD95 expression. Priming with cytotoxic drugs greatly increases CD95 ligand-induced caspase 3 activity, indicating that the cytotoxic drugs positively modulate the CD95-dependent signalling cascade up-stream of caspase 3 activation.

Ex vivo malignant glioma cells are sensitive to Fas (CD95/APO-1) ligand-mediated apoptosis

Fas (also known as CD95/APO-1) is a cell surface receptor and member of the tumor necrosis factor receptor superfamily which mediates apoptosis in sensitive cells upon oligomerization by specific antibodies or by its ligand (FasL). Recently, human glioma cell lines were found to be susceptible to Fas-mediated apoptosis triggered by alpha-Fas antibodies. However, whether the Fas system can also be targeted in ex vivo high grade gliomas is at present unknown. In the present investigation, alpha-Fas antibodies and FasL were tested in short-term monolayer cultures or in colony forming assays established from freshly resected tumors of patients with anaplastic astrocytomas (WHO grade III) and glioblastoma multiforme (WHO grade IV). Anti-Fas antibodies induced only moderate apoptosis in four of the 19 tested glioma cell cultures. This contrasts FasL which induced apoptosis in all of the 19 tumor cell cultures analyzed. Mean cytotoxicity of glioma cell cultures treated for 48 h with alpha-Fas antibodies or FasL was 9.6% and 44.3%, respectively. Irrespective of whether alpha-Fas antibodies or FasL were used, pretreatment with recombinant hu (rhu) IFN-gamma and rhuTNF-alpha for 48 h did not sensitize glioma cells to Fas-mediated cytotoxicity. The long-term effect by FasL on tumor colony formation was more striking. FasL treatment resulted in more than 90% inhibition of clonal tumor cell growth of all the eight high grade gliomas analyzed. These results suggest that Fas targeting by FasL but not by alpha-Fas antibodies may provide a promising approach for locoregional glioma treatment.

Interferon-alpha enhances CD95L-induced apoptosis of human malignant glioma cells

CD95 ligand (CD95L)-induced apoptosis is a novel immunotherapeutic approach to malignant glioma. Here, we report that interferon-alpha (IFN-alpha) sensitizes LN-229 and T98G human malignant glioma cells to CD95L-induced apoptosis. In contrast to the effects of IFN-gamma and TNF-alpha which sensitize glioma cells to CD95 antibody-induced apoptosis in part by enhancing CD95 expression, IFN-alpha has no effect on CD95 expression at the cell surface of LN-229 and T98G cells. To confirm that changes in CD95 expression are not required for the effects of IFN-alpha, we show that IFN-alpha enhances CD95L-induced apoptosis even in CD95-transfected LN-308 glioma cells. These LN-308 cells have little endogenous CD95 expression but express high levels of CD95 from a stably integrated CD95 expression plasmid. The sensitizing effects of IFN-alpha appear to be independent of cell cycle effects of IFN-alpha and are unaffected by ectopic expression of the bcl-2 proto-oncogene. IFN-alpha enhances CD95L-induced activation of caspase-3, a critical mediator of CD95L-induced cell death. IFN-alpha also increases the cytotoxic effects of BCNU, teniposide and cytarabine in both cell lines, and of vincristine in LN-229 cells. Doxorubicin and 5-fluorouracil toxicity are unaffected by IFN-alpha. IFN-alpha may be a useful adjunct to novel strategies of immunochemotherapy for malignant gliomas that target CD95-mediated apoptosis.

CD95 ligand-induced apoptosis of human medulloblastoma cells

CD95 ligand (CD95L) is a cytotoxic cytokine that induces apoptosis in susceptible target cells. Medulloblastoma is the most common non-glial intrinsic malignancy of the brain. In this study, we have studied CD95-mediated apoptosis of human medulloblastoma cell lines. We found that DAOY, MED-1 and D-283 cells are susceptible to CD95L-induced apoptosis when RNA and protein synthesis are inhibited. Preexposure of D-283, but not DAOY or MED-1 cells, to interferon-gamma or tumor necrosis factor-alpha enhances CD95 expression and primes these cells for CD95-mediated apoptosis. Inhibitors of interleukin 1-converting enzyme (ICE)-like protease (caspase) activity block CD95L-induced cytotoxicity, suggesting that caspases mediate the death signal induced by CD95L in human medulloblastoma cells. Interestingly, medulloblastoma cells belong to an increasing number of tumor cell types that coexpress CD95 and CD95L. We conclude that CD95 may be a promising target of immunochemotherapy for human medulloblastoma.

Increased Fas-mediated cytotoxicity of CD4-positive T cells in patients with human T-lymphotropic virus type I-associated myelopathy

Using a 51Cr release assay, we investigated Fas-mediated cytotoxicity of peripheral blood CD4+ T cells of patients with human T-lymphotropic virus type-I (HTLV-I)-associated myelopathy (HAM) against T98G, a glioblastoma cell line which expresses Fas. Cytotoxic activity of CD4+ T cells against T98G was significantly higher in HAM patients than in controls. Moreover, when CD4+ T cells of HAM patients were preincubated with a monoclonal antibody to human Fas ligand (FasL), cytotoxic activity against T98G was significantly suppressed. These results suggest that damage to nervous tissues by the Fas/FasL system is involved in the pathogenesis of HAM.

Serum CD95 of relapsing remitting multiple sclerosis patients protects from CD95-mediated apoptosis

Failure of CD95-mediated apoptosis as a potential negative regulatory mechanism of T cell expansion may be involved in T cell-mediated autoimmune diseases such as multiple sclerosis (MS). Recently, soluble CD95 has been shown to be elevated in MS patients with active disease. Here, we report that the sera of MS patients inhibit CD95 ligand-induced apoptosis of susceptible target cells in a concentration-dependent manner and dependent on the amount of serum CD95 levels. Thus, MS sera contain biologically active inhibitors of T cell apoptosis that may allow for prolonged abnormal immune responses.

Local production of TGF beta1 inhibits cerebral edema, enhances TNF-alpha induced apoptosis and improves survival in a murine glioma model

We have previously reported that local secretion of either TNF-alpha or TGF beta1 by intracerebral SMA-560 malignant glioma tumor cells can reduce or eliminate tumor growth in mice. However, the use of TNF-alpha, while improving the overall survival of tumor bearing animals, was associated with early toxic deaths due to cerebral edema. In the present study, we demonstrate that TNF-alpha induces apoptosis of the SMA 560 cell line, as does TGF beta1, and that these two cytokines act in an additive fashion to enhance apoptosis and thus, to inhibit SMA 560 cell growth in vitro. Next, we show that the production of TGF beta1 when added to TNF-alpha production by central nervous system tumors in vivo abrogates any early deaths seen due to TNF-alpha toxicity and leads to a larger percentage of animals surviving CNS tumor challenge. Finally, we demonstrate that the production of TGF beta1 by tumor cells is associated with the abolition of tumor-associated cerebral edema in both TNF-alpha and in non-TNF-alpha producing tumors. These results are important for the development of effective and less toxic therapies for brain tumors, as well as for examining the pathogenesis of tumor-related cerebral edema.

Apoptosis and thyroiditis

The origin of the various forms of autoimmune thyroiditis remains unclear. Most investigations into the pathogenesis of these disorders have focused on immune abnormalities that might lead to an autoimmune response. However, no unique immune response to thyroid autoantigens has been identified that either is limited to patients with thyroiditis or is absolutely correlated with clinical disease expression. CD8 T-cell-mediated cytotoxicity is thought to be a major cause of thyroid follicular cell damage in thyroiditis. This damage is produced in part through the induction of apoptosis in thyroid cells. Recent studies have demonstrated that programmed cell death is regulated in thyroid cells and that a major pathway for immune-mediated apoptosis, the Fas pathway, is blocked by labile inhibitors in a manner that could prevent cytotoxicity. This review also examines several other types of regulation of apoptotic pathways in thyrocytes. We hypothesize that the regulation of programmed cell death pathways in the thyroid may alter the expression of autoimmune thyroid diseases by modifying the susceptibility of thyroid cells to immune-mediated apoptosis.

Malignant glioma: should chemotherapy be overthrown by experimental treatments?

Despite more than two decades of clinical research with chemotherapy, the outcome of malignant gliomas remains poor. Recent years have seen major advances in elucidation of the biology of these tumors, which in turn have led to the current development of innovative therapeutic strategies. The question confronting us at the end of the 1990s is whether we should continue to use and investigate chemotherapy or whether the time has come for experimental treatments. As a contribution to this debate, we reviewed the abundant literature on chemotherapy of malignant glioma, paying special attention to methodological features. The new treatment approaches based on current knowledge about glioma biology are then briefly summarized. Assessment of more than 20 years of chemotherapy trials is discouraging despite a few areas of modest success. Only patients with specific histology (oligodendroglioma, anaplastic astrocytoma) and good prognostic factors (young age, good performance status) may benefit from chemotherapy, with a possible reversal of neurological dysfunction. However, the real impact on survival is small (anaplastic astrocytoma) or undefined (oligodendroglioma). Furthermore, it is unfortunately obvious that the outcome of glioblastoma patients is not significantly modified by chemotherapy. We believe the time has come to explore the potential of novel biological therapies in glioblastoma patients. This could also be proposed for anaplastic astrocytoma and oligodendroglioma patients after failure of chemotherapy.

New aspects of immunotherapy of leptomeningeal metastasis

Immunotherapeutic approaches to leptomeningeal metastasis (LM) include the intrathecal application of cytokines such as interleukin-2 (IL-2) and interferon-alpha (IFN-alpha), and lymphokine-activated killer cells (LAK cells). Results in a rodent model of leptomeningeal gliomatosis with intrathecal IL-2 application are discouraging, but some clinical improvement and clearance of neoplastic cells from CSF have been seen in patients with LM from melanoma treated with intrathecal IL-2 alone, and in patients with LM from primary brain tumors and squamous cell carcinoma of the tongue treated with intrathecal LAK cells and IL-2. The neurotoxicity of this therapy, mainly increased intracranial pressure, has been considerable but generally manageable. However, IFN-alpha caused severe neurotoxicity in form of an only partly reversible progressive vegetative state in the majority of patients. Considering the small number of patients treated with IL-2 and LAK cells, its value for the treatment of LM could only be stated by further investigation. In future, the application of recently discovered cytokines such as Fas-ligand, the continuous paracrine cytokine release by genetically modified cells, or vaccination strategies using genetically modified tumor cells might offer new immunotherapeutic approaches in LM.

Anticonvulsant drugs fail to modulate chemotherapy-induced cytotoxicity and growth inhibition of human malignant glioma cells

Adjuvant chemotherapy after cytoreductive surgery and irradiation plays an increasingly important role in the management of human malignant glioma. Here we have examined the effect of three anticonvulsants most commonly administered to glioma patients, carbamazepine, phenytoin and valproic acid, on the cytotoxic and antiproliferative actions in vitro of several cancer chemotherapy drugs currently evaluated for human gliomas. We find that none of the anticonvulsants reduces glioma cell viability or proliferation or modulates glioma cell clonogenicity at clinically relevant concentrations when administered alone. Therapeutic concentrations of either drug fail to alter the effect of cancer chemotherapy drugs in acute cytotoxicity assays or modified clonogenicity assays. A lack of interactions of anticonvulsants and cytotoxic drugs is also observed when the glioma cells are preexposed to the anticonvulsants for prolonged times, suggesting that chronic exposure to anticonvulsants in vivo may not change intrinsic glioma cell sensitivity to cancer chemotherapy. Thus, changes in hepatic enzyme activity or immunological parameters, but not modulation of intrinsic chemotherapeutic drug sensitivity, may influence the choice of an anticonvulsant for seizure control in glioma patients receiving adjuvant chemotherapy.

APO2 ligand: a novel lethal weapon against malignant glioma?

APO2L (TRAIL) is a novel CD95L (Fas/APO-1-L) homologous cytotoxic cytokine that interacts with various receptors which transmit (DR4, DR5) or inhibit (DcR1, DcR2) an apoptotic signal. Here, we report that human glioma cell lines preferentially express mRNAs for agonistic death receptors DR4 (8/12) and DR5 (11/12) rather than the death-inhibitory decoy receptors DcR1 (4/12) and DcR2 (2/12). Ten of 12 cell lines are susceptible to APO2L-induced apoptosis. The resistant cell lines, U138MG and U373MG, are cross-resistant to CD95L-induced apoptosis. Similar to CD95L-induced apoptosis, APO2L-induced apoptosis is inhibited by ectopic expression of the caspase inhibitor, crm-A, or of bcl-2, or by coexposure to the corticosteroid, dexamethasone, or the lipoxygenase inhibitor, nordihydroguaretic acid. There is no correlation between p53 genetic status of the cell lines and their susceptibility to APO2L-induced apoptosis, but the latter is moderately enhanced by ectopic expression of wild-type p53. APO2L targeting may be a promising approach for selectively targeting apoptosis to human malignant glioma cells.

Fas expression on human fetal astrocytes without susceptibility to fas-mediated cytotoxicity

Fas (APO-1/CD95) is a cell surface receptor, initially identified in lymphoid cells, but more recently detected in the central nervous system under pathologic conditions. Ligation of the fas receptor by fas ligand or by agonist antibodies induces apoptotic cell death in most fas-expressing cells. In the current study, using dissociated cultures of human fetal central nervous system-derived cells, we detected fas expression on astrocytes but not on neurons. Such expression differs from our previous results using cultures of human adult central nervous system-derived cells, which demonstrated fas expression on oligodendrocytes but not on astrocytes; the oligodendrocytes were susceptible to cell death via this pathway. Using multiple assays of cell death, including nuclear propidium iodide and TUNEL staining to detect nuclear-directed injury, cytofluorometric propidium iodide inclusion, and lactate dehydrogenase release to detect membrane-directed injury, we found that fas ligation, however, did not induce cell death in the cultured fetal astrocytes. Cytokines that augmented (gamma-interferon) or inhibited (interleukin-4) fetal astrocyte proliferation did not alter fas expression or resistance to fas ligation. Cells obtained immediately ex vivo from human fetal but not from adult central nervous system tissue expressed fas; such expression was restricted to astrocytes as assessed by dual-stain immunohistochemistry. The fetal central nervous system cells did not express fas ligand. Our findings indicate that fas expression on central nervous system cells may reflect their state of maturity; expression may not, however, always be coupled to susceptibility to cell death via this pathway.

CD95 ligand: lethal weapon against malignant glioma?

CD95 (Fas/APO-1) and its ligand (CD95L) belong to a growing cytokine and cytokine receptor family that includes nerve growth factor (NGF) and tumor necrosis factor (TNF) and their corresponding receptors. CD95 expression increases during malignant progression from low-grade to anaplastic astrocytoma and is most prominent in perinecrotic areas of glioblastoma. There is, however, no evidence that CD95 expression in malignant gliomas is triggered by hypoxia or ischemia. Agonistic antibodies to CD95, or the natural ligand, CD95L, induce apoptosis in human malignant glioma cells in vitro. Glioma cell sensitivity to CD95-mediated apoptosis is regulated by CD95 expression at the cell surface and by the levels of intracellular apoptosis-regulatory proteins, including bcl-2 family members. Several cytotoxic drugs synergize with CD95L to kill glioma cells. For as yet unknown reasons, glioma cells may co-express CD95 and CD95L in vitro without undergoing suicide or fratricide. Yet, they kill T cells via CD95/CD95L interactions and are sensitive to exogenously added CD95L. Since CD95L is expressed in gliomas in vivo, too, forced induction of CD95 expression might promote therapeutic apoptosis in these tumors. That glioma cells differ from nontransformed T cells in their sensitivity to CD95 antibodies or recombinant ligand, may allow the development of selective CD95 agonists with high antitumor activity that spare normal brain tissue. A family of death ligand/receptor pairs related to CD95L/CD95, including APO2L (TRAIL) and its multiple receptors is beginning to emerge. Although several issues regarding glioma cell sensitivity to CD95L/CD95-mediated apoptosis await elucidation, CD95 is a promising target for the treatment of malignant glioma.

Programmed cell death: the influence of CD40, CD95 (Fas or Apo-I) and their ligands

Programmed cell death (PCD) or apoptosis is a process whereby developmental or environmental stimuli activate a specific series of events that culminate in cell death. PCD is essential for normal development and abnormality in the process can lead to defects ranging from embryonic lethality and tissue-specific perturbation of postnatal development to a high susceptibility to malignancy. Therapeutics that modulate the regulation of PCD may provide a new opportunity for the treatment of the PCD related diseases and cancer. CD40 and CD95 (Fas/Apo-I) are transmembrane proteins of the nerve growth factor/tumour necrosis factor alpha receptor superfamily. The death signal of PCD occurs when the CD95 receptor on the cell surface binds to the CD95 ligand (CD95L) or to the anti-CD95 monoclonal antibody (mAb). In contrast, PCD could be inhibited by the survival signal mediated from the binding of the CD40 receptor to the CD40 ligand (CD40L) or to the anti-CD40 mAb. In this review, the interaction of CD40/CD40L and CD95/CD95L on PCD in normal and malignant cells is discussed.

Failure of TGF beta1 and IL-12 to regulate human FasL and mTNF alloreactive cytotoxic T-cell pathways

The effect of TGFbeta1 and IL-12 on calcium-independent cytotoxic pathways was investigated. We have previously demonstrated that the regulatory effect of TGFbeta1 and IL-12 on human alloreative CTL activity was associated with regulation of perforin and granzyme B gene expression. To determine the effect of both cytokines on the alternative cytotoxic pathway involving FasL and mTNF, we first investigated the expression of both molecules on human primary alloactivated T cells. Our results show that human allostimulated T lymphocytes express FasL. Cell lysis experiments demonstrate that the FasL cytotoxic pathway is involved in the killing of specific target cells mediated by human alloreactive CTL. In addition, allogeneic stimulation induced significant mTNF expression on both CD4+ and CD8+ responder T cells. Using TNF-sensitive target cells, we also demonstrate that the mTNF-mediated cytotoxic pathway is involved in the cytotoxic activity of human primary allostimulated T lymphocytes. Neither TGFbeta1 nor IL-12 had an effect on FasL or mTNF expression. Furthermore, addition of TGFbeta1 or IL-12 at the initiation of the MLR had no significant effect on Fas- and mTNF-mediated cytotoxicity. Taken together, our results provide a novel insight into the differences between regulation by cytokines of perforin-dependent and -independent cytotoxic mechanisms. Unlike their role in the perforin/granzyme B pathway, TGFbeta1 and IL-12 do not appear to mediate any regulatory effect on FasL and mTNF cytotoxic pathways used by human alloreactive primary CTL.

Lack of cell surface Fas/APO-1 expression in pulmonary adenocarcinomas

The Fas receptor and ligand initiate an apoptotic pathway. Alterations in this pathway within tumor cells can result in escape from apoptosis and immune surveillance. We evaluated Fas protein expression in 42 primary pulmonary adenocarcinomas, and Fas expression and function in the lung adenocarcinoma cell lines A549 and A427. Immunohistochemical analysis demonstrated Fas protein expression in 47.6% of the tumors; however, Fas-positive tumors demonstrated cytoplasmic staining without cell surface expression. Northern blot analysis indicated that levels of Fas mRNA were similar in Fas protein-positive tumors to levels in normal lung tissue, but were reduced in Fas protein-negative tumors. Soluble form Fas was not detected in the majority of these tumors either by RT-PCR or Western blot analysis. Cell surface Fas protein expression was minimal in A549 and A427 cell lines as determined by flow cytometry. Both cell lines demonstrated Fas mRNA expression by Northern blot analysis and abundant protein expression by Western blot analysis. Transfection of the Fas cDNA derived from A549 cells induced surface Fas protein in COS cells; however, stable transfection of a native Fas cDNA into A549 cells failed to induce surface Fas protein expression. Parental A549 cells and A549 cells transfected with a Fas expression vector were resistant to Fas-mediated apoptosis. Transgenic expression of a FLAG-tagged Fas cDNA in A549 cells, with visualization of the Fas-FLAG protein using confocal microscopy, demonstrated that the Fas-FLAG protein was retained within cytoplasmic portions of the cell and was not translocated to the cell surface. These findings suggest that the Fas protein is reduced or not present on the cell surface in the primary lung tumors and is sequestered within A549 tumorigenic lung cells, and these alterations directly affect the cells resistance to Fas-mediated apoptosis.

Humoral immune response to p53 in malignant glioma

p53 immunoreactivity and humoral immune response to p53 were examined in 14 patients with malignant glioma, including 4 patients with leptomeningeal glioma cell dissemination. Twelve patients expressed p53 protein within the tumour tissue. p53 antibodies were detected in the serum in 2 of 14 patients but never in the cerebrospinal fluid (CSF). Soluble p53 protein was detected neither in serum nor in CSF of the glioma patients. CSF levels of the immunosuppressive cytokine, transforming growth factor (TGF)-beta, were elevated in the glioma patients, including those with a humoral response to p53. These preliminary findings raise the possibility of systemic humoral immune responses to antigens, including mutant p53, expressed by glioma cells in the central nervous system.