Fas/APO-1 expression and function on malignant cells of hematologic and nonhematologic origin

Death Receptors and Their Ligands in Inflammatory Disease and Cancer

On binding to their cognate ligands, death receptors can initiate a cascade of events that can result in two distinct outcomes: gene expression and cell death. The study of three different death receptor-ligand systems, the tumor necrosis factor (TNF)-TNF receptor 1 (TNFR1), the CD95L-CD95, and the TNF-related apoptosis-inducing ligand (TRAIL)-TRAIL-R1/2 system, has drawn the attention of generations of scientists over the past 50 years. This scientific journey, as often happens in science, has been anything but a straight line to success and discoveries in this field were often made by serendipity, catching the scientists by surprise. However, as Louis Pasteur pointed out, luck prefers the prepared mind. It is therefore not surprising that the most impactful discovery of the field to date, the fact that TNF inhibition serves as an effective treatment for several inflammatory and autoimmune diseases, has been like this. Luckily, the scientists who made this discovery were prepared and, most importantly, determined to harness their discovery for therapeutic benefit. Today's research on these death receptor-ligand systems has led to the discovery of a causal link between cell death induced by a variety of these systems and inflammation. In this review, we explain why we predict that therapeutic exploitation of this discovery may profoundly impact the future treatment of inflammatory disease and cancer.

The TNF Family of Ligands and Receptors: Communication Modules in the Immune System and Beyond

The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies (TNFSF/TNFRSF) include 19 ligands and 29 receptors that play important roles in the modulation of cellular functions. The communication pathways mediated by TNFSF/TNFRSF are essential for numerous developmental, homeostatic, and stimulus-responsive processes in vivo. TNFSF/TNFRSF members regulate cellular differentiation, survival, and programmed death, but their most critical functions pertain to the immune system. Both innate and adaptive immune cells are controlled by TNFSF/TNFRSF members in a manner that is crucial for the coordination of various mechanisms driving either co-stimulation or co-inhibition of the immune response. Dysregulation of these same signaling pathways has been implicated in inflammatory and autoimmune diseases, highlighting the importance of their tight regulation. Investigation of the control of TNFSF/TNFRSF activities has led to the development of therapeutics with the potential to reduce chronic inflammation or promote anti-tumor immunity. The study of TNFSF/TNFRSF proteins has exploded over the last 30 yr, but there remains a need to better understand the fundamental mechanisms underlying the molecular pathways they mediate to design more effective anti-inflammatory and anti-cancer therapies.

Fas Signaling Promotes Gastric Cancer Metastasis through STAT3-Dependent Upregulation of Fascin

BACKGROUND

Fas signaling-activated signal transducers and activators of transcription 3 (STAT3) is required for Fascin upregulation. As an actin-bundling protein, Fascin can mediate gastric cancer (GC) cell migration.

METHODS

Gastric cancer AGS cells were treated with anti-Fas (5 μg/ml) for 2 h, in order to stimulate the activation of the Fas signaling. The in vitro migration of Fas signaling-activated AGS cells was assessed using Transwell chambers. The levels of Fascin and phosphorylated STAT3 were detected by Western blotting analyses. Nude mice were injected intravenously with AGS cells treated with anti-Fas or treated with STAT3 inhibitor without anti-Fas; tumor pulmonary metastases were measured. Fascin protein expression in tumor tissues was detected by immunohistochemistry. The Fas and Fascin mRNA levels in tumor tissues from patients with GC were measured by real-time PCR and their correlation was analyzed.

RESULTS

The activation of Fas signaling promoted cell migration and resulted in STAT3-dependent Fascin upregulation in AGS cells. STAT3 enhanced Fascin levels in vivo. Fascin was the mediator of Fas signaling-induced AGS cell migration in vitro and in vivo. Furthermore, there was a positive correlation between Fas and Fascin mRNA levels in tumor tissues from GC patients.

CONCLUSIONS

Fas signaling promotes GC metastasis through the STAT3/Fascin pathway, which may provide a new target for GC therapy.

Life in the Fas lane: differential outcomes of Fas signaling

Fas, also known as CD95 or APO-1, is a member of the tumor necrosis factor/nerve growth factor superfamily. Although best characterized in terms of its apoptotic function, recent studies have identified several other cellular responses emanating from Fas. These responses include migration, invasion, inflammation, and proliferation. In this review, we focus on the diverse cellular outcomes of Fas signaling and the molecular switches identified to date that regulate its pro- and anti-apoptotic functions. Such switches occur at different levels of signal transduction, ranging from the receptor through to cross-talk with other signaling pathways. Factors identified to date including other extracellular signals, proteins recruited to the death-inducing signaling complex, and the availability of different intracellular components of signal transduction pathways. The success of therapeutically targeting Fas will require a better understanding of these pathways, as well as the regulatory mechanisms that determine cellular outcome following receptor activation.

Death receptor-ligand systems in cancer, cell death, and inflammation

The discovery of tumor necrosis factor (TNF) marked the beginning of one of the most fascinating journeys in modern biomedical research. For the moment, this journey has culminated in the development of drugs that inhibit TNF. TNF blockers have revolutionized the treatment of many chronic inflammatory diseases. Yet, the journey seems far from over. TNF is the founding member of a family of cytokines with crucial functions in cell death, inflammation, and cancer. Some of these factors, most prominently TNF, CD95L, and TRAIL, can induce cell death. The receptors that mediate this signal are therefore referred to as death receptors, even though they also activate other signals. Here I will take you on a journey into the discovery and study of death receptor-ligand systems and how this inspired new concepts in cancer therapy and our current understanding of the interplay between cell death and inflammation.

The role of apoptosis-induced proliferation for regeneration and cancer

Genes dedicated to killing cells must have evolved because of their positive effects on organismal survival. Positive functions of apoptotic genes have been well established in a large number of biological contexts, including their role in eliminating damaged and potentially cancerous cells. More recently, evidence has suggested that proapoptotic proteins-mostly caspases-can induce proliferation of neighboring surviving cells to replace dying cells. This process, that we will refer to as "apoptosis-induced proliferation," may be critical for stem cell activity and tissue regeneration. Depending on the caspases involved, at least two distinct types of apoptosis-induced proliferation can be distinguished. One of these types have been studied using a model in which cells have initiated cell death, but are prevented from executing it because of effector caspase inhibition, thereby generating "undead" cells that emit persistent mitogen signaling and overgrowth. Such conditions are likely to contribute to certain forms of cancer. In this review, we summarize the current knowledge of apoptosis-induced proliferation and discuss its relevance for tissue regeneration and cancer.

Nonapoptotic functions of FADD-binding death receptors and their signaling molecules

Death receptors (DRs) are surface receptors that when triggered have the capacity to induce apoptosis in cells by forming the death-inducing signaling complex (DISC). The first protein recruited to form the DISC is the adaptor protein FADD/Mort1. Some members of the DR family, CD95 and the TRAIL receptors DR4 and DR5, directly bind FADD, whereas others, such as TNF receptor I and DR3, initially bind another adaptor protein, TRADD, which then recruits FADD. While all DRs can activate both apoptotic and non-apoptotic pathways, it has been widely assumed that the main physiological role of FADD-binding death receptors is to trigger apoptosis. However, recent work has ascribed multiple non-apoptotic activities to these receptors and/or the signaling components of the DISC.

A role for caspase-8 and c-FLIPL in proliferation and cell-cycle progression of primary hepatocytes

Growth factors are known to favor both proliferation and survival of hepatocytes. In the present study, we investigated if c-FLIP(L) (cellular FLICE-inhibitory protein, long isoform) could be involved in epidermal growth factor (EGF)-stimulated proliferation of rat hepatocytes since c-FLIP(L) regulates both cell proliferation and procaspase-8 maturation. Treatment with MEK inhibitors prevented induction of c-FLIP(L) by EGF along with total inhibition of DNA replication. However, EGF failed to inhibit processing of procaspase-8 in the presence of EGF suggesting that c-FLIP(L) does not play its canonical anti-apoptotic role in this model. Downregulation of c-FLIP expression using siRNA oligonucleotides strongly reduced DNA replication but did not result in enhanced apoptosis. Moreover, intermediate cleavage products of c-FLIP(L) and caspase-8 were found in EGF-treated hepatocytes in the absence of caspase-3 maturation and cell death. To determine whether the Fas/FADD/caspase-8/c-FLIP(L) complex was required for this activity, Fas, procaspase-8 and Fas-associated death domain protein (FADD) expression or function was inhibited using siRNA or constructs encoding dominant negative mutant proteins. Inhibition of any of these components of the Fas/FADD/caspase-8 pathway decreased DNA replication suggesting a function of these proteins in cell-cycle arrest. Similar results were obtained when the IETD-like caspase activity detectable in EGF-treated hepatocytes was inhibited by the pan-caspase inhibitor, z-ASP. Finally, we demonstrated co-immunoprecipitation between EGFR and Fas within 15 min following EGF stimulation. In conclusion, our results indicate that the Fas/FADD/c-FLIP(L)/caspase-8 pathway positively controls the G(1)/S transition in EGF-stimulated hepatocytes. Our data provide new insights into the mechanisms by which apoptotic proteins participate to mitogenic signals during the G(1) phase.

FADD adaptor in cancer

FADD (Fas Associated protein with Death Domain) is a key adaptor molecule transmitting the death signal mediated by death receptors. In addition, this multiple functional protein is implicated in survival/proliferation and cell cycle progression. FADD functions are regulated via cellular sublocalization, protein phosphorylation, and inhibitory molecules. In the present review, we focus on the role of the FADD adaptor in cancer. Increasing evidence shows that defects in FADD protein expression are associated with tumor progression both in mice and humans. Better knowledge of the mechanisms leading to regulation of FADD functions will improve understanding of tumor growth and the immune escape mechanisms, and could open a new field for therapeutic interventions.

Absence or Low Expression of Fas-Associated Protein with Death Domain in Acute Myeloid Leukemia Cells Predicts Resistance to Chemotherapy and Poor Outcome

In acute myeloid leukemia (AML), coexpression of death receptors and ligands of the tumor necrosis factor (TNF) receptor/TNF-alpha superfamily on leukemic cells after chemotherapy is not always accompanied by apoptosis, suggesting that the apoptotic death receptor signaling pathway is disrupted. Because Fas-associated protein with death domain (FADD) is the main adaptor for transmitting the Fas, TNF-related apoptosis-inducing ligand receptors, and TNF receptor 1 death signal, expression of FADD was analyzed by Western blot and immunocytochemistry in leukemic cells of 70 de novo AML patients treated with the European Organization of Research and Treatment of Cancer AML-10 randomized trial before initiation of induction chemotherapy. Thirty seven percent of patients (17 of 46) with FADD negative/low (FADD(-/low)) leukemic cells had a primary refractory disease compared with 12% of FADD(+) patients (3 of 24; P = 0.05). FADD(-/low) expression was significantly associated with a worse event-free survival [EFS (P = 0.04)] and overall survival (P = 0.04). In multivariate analysis, FADD(-/low) protein expression was independently associated with a poor EFS and overall survival (P = 0.002 and P = 0.026, respectively). Importantly, FADD(-/low) protein expression predicted poor EFS even in patients with standard- or good-risk AML (P = 0.009). Thus, we identified low or absent expression of the FADD protein in leukemic cells at diagnosis as a poor independent prognostic factor that can predict worse clinical outcome even for patients with standard- or good-risk AML.

The expression of PEA-15 (phosphoprotein enriched in astrocytes of 15 kDa) defines subpopulations of astrocytes and neurons throughout the adult mouse brain

Phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) is an abundant phosphoprotein in primary cultures of mouse brain astrocytes. Its capability to interact with members of the apoptotic and mitogen activated protein (MAP) kinase cascades endows PEA-15 with anti-apoptotic and anti-proliferative properties. We analyzed the in vivo cellular sources of PEA-15 in the normal adult mouse brain using a novel polyclonal antibody. Immunohistochemical assays revealed numerous PEA-15-immunoreactive cells throughout the brain of wild-type adult mice while no immunoreactive signal was observed in the brain of PEA-15 -/- mice. Cell morphology and double immunofluorescent staining showed that both astrocytes and neurons could be cellular sources of PEA-15. Closer examination revealed that in a given area only part of the astrocytes expressed the protein. The hippocampus was the most striking example of this heterogeneity, a spatial segregation restricting PEA-15 positive astrocytes to the CA1 and CA3 regions. A PEA-15 immunoreactive signal was also observed in a few cells within the subventricular zone and the rostral migratory stream. In vivo analysis of an eventual PEA-15 regulation in astrocytes was performed using a model of astrogliosis occurring along motor neurons degeneration, the transgenic mouse expressing the mutant G93A human superoxyde-dismutase-1, a model of amyotrophic lateral sclerosis. We observed a marked up-regulation of PEA-15 in reactive astrocytes that had developed throughout the ventral horn of the lumbar spinal cord of the transgenic mice. The heterogeneous cellular expression of the protein and its increased expression in pathological situations, combined with the known properties of PEA-15, suggest that PEA-15 expression is associated with a particular metabolic status of cells challenged with potentially apoptotic and/or proliferative signals.

Calmodulin binding to the Fas death domain. Regulation by Fas activation

Fas (APO-1/CD95) is a cell surface receptor that initiates apoptotic pathways, and its cytoplasmic domain interacts with various molecules suggesting that Fas signaling is complex and regulated by multiple proteins. Calmodulin (CaM) is an intracellular Ca(2+)-binding protein, and it mediates many of the effects of Ca2+. Here, we demonstrate that CaM binds to Fas directly and identify the CaM-binding site on the cytoplasmic death domain (DD) of Fas. Fas binds to CaM-Sepharose and is co-immunoprecipitated with CaM. Other death receptors, such as tumor necrosis factor receptor, DR4, and DR5 do not bind to CaM. The interaction between Fas and CaM is Ca(2+)-dependent. Deletion mapping analysis with various GST-fused Fas cytoplasmic domain fragments revealed that the fragment containing helices 1, 2, and 3 of the Fas DD has the CaM-binding ability. Sequence analysis of this fragment predicted a potential CaM-binding site in helix 2 and connected loops. A valine 254 to asparagine mutation in this region, which is analogous to the identified mutant allele of Fas in lpr mice that have a deficiency in Fas-mediated apoptosis, showed reduced CaM binding. Computer modeling of the interaction between CaM and helix 2 of the Fas DD predicted that amino acids, which are important for Fas-CaM binding, and point mutations of these amino acids caused reduced Fas-CaM binding. The interaction between Fas and CaM is increased approximately 2-fold early upon Fas activation (at 30 min) and is decreased to approximately 50% of control at 2 h. These findings suggest a novel function of CaM in Fas-mediated apoptosis.

Co-expression of Fas (APO-1, CD95)/Fas ligand by BeWo and NJG choriocarcinoma cell lines

OBJECTIVE

Fas (CD95) is a transmembrane protein of the tumor necrosis factor receptor superfamily that induces apoptosis in susceptible cells on crosslinking by its ligand (FasL). The Fas loss of function and concurrent expression of its ligand (FasL) have been associated with malignant phenotype. In this study, we sought to investigate the hitherto undescribed expression of Fas and FasL on the immortalized human choriocarcinoma cell lines BeWo and NJG.

METHODS

Receptor and ligand expression was demonstrated using specific antibodies and multiple techniques including immunocytochemistry, confocal immunofluorescence microscopy, flow cytometry, immunoblots, and reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Data from this study indicate that human choriocarcinoma cell subtypes co-express both Fas and FasL. A specific cytoplasmic and membranous pattern of immunoreactivity was noted that was further confirmed at mRNA transcripts by RT-PCR. In addition, we provide evidence using flow cytometry that the Fas receptors are downregulated. The mean fluorescence intensities for NJG and BeWo were 1.47 +/- 0.5 and 1.59 +/- 0.4, while that for Fas-positive Jurkat cells was 25.6 +/- 3.1.

CONCLUSIONS

To our knowledge, this is the first report on the identification and constitutive co-expression of Fas and FasL in BeWo and NJG choriocarcinoma cells. Choriocarcinoma cells evade immune attack by downregulating the Fas receptor and by killing lymphocytes through expression of FasL. Taken together, our investigations suggest that the Fas/FasL system may represent a mechanism by which malignant trophoblasts become resistant to apoptosis, escape immune surveillance, and metastasize.

Loss of FADD protein expression results in a biased Fas-signaling pathway and correlates with the development of tumoral status in thyroid follicular cells

Downregulation of proapoptotic molecules like Fas or caspase 8, or upregulation of antiapoptotic molecules like FLICE inhibitory protein has been suggested to be a regulatory mechanism set up by tumor cells to block the death signal received via death receptors. In an in-depth study of the Fas/FasL-signaling pathway in thyroid tumor development, we have demonstrated that tumor cells specifically downregulate the multideath receptor adapter Fas-associated death domain (FADD). The regulation of FADD expression occurred only at the protein level. Furthermore, in the absence of FADD, Fas-signaling resulted in accelerated growth of thyrocytes. Since thyrocytes also acquired FasL expression during tumor development, the absence of FADD protein could lead to greater resistance to numerous death receptor-mediated apoptosis, stimulation of their own proliferation through Fas/FasL interaction, and the capacity to counter-attack the infiltrating lymphocytes.

Fas engagement induces neurite growth through ERK activation and p35 upregulation

Fas (also known as CD95), a member of the tumour-necrosis receptor factor family of 'death receptors', can induce apoptosis or, conversely, can deliver growth stimulatory signals. Here we report that crosslinking Fas on primary sensory neurons induces neurite growth through sustained activation of the extracellular-signal regulated kinase (ERK) pathway and the consequent upregulation of p35, a mediator of neurite outgrowth. In addition, functional recovery after sciatic nerve injury is delayed in Fas-deficient lpr mice and accelerated by local administration of antibodies against Fas, which indicates that Fas engagement may contribute to nerve regeneration in vivo. Our findings define a role for Fas as an inducer of both neurite growth in vitro and accelerated recovery after nerve injury in vivo.

Fas-ligand--iron fist or Achilles' heel?

Experimental and physiological expression of the pro-apoptotic molecule Fas-ligand can induce inflammation under certain conditions. Discussed here are the experimental situations, possible mechanisms, and pathways that mediate this response.

Loss of Fas (CD95/APO-1) regulatory function is an important step in early MALT-type lymphoma development

Fas (CD95, APO-1) mutations were found in autoimmune diseases and some lymphomas, suggesting impairment of Fas-mediated cell death signaling that may cause tumor development. Because mucosa-associated lymphoid tissue (MALT)-type lymphoma B cells recognize autoantigens and proliferate in response to antigen and T cell-mediated signals, it is suggestive that autoreactive B cell lymphoma precursor cells may have escaped the Fas-mediated checkpoint that normally operates in healthy individuals. Using different biochemical, molecular, and functional approaches, we analyzed the Fas signaling in malignant B cells from seven MALT-type lymphomas that were additionally characterized for the t(11;18)(q21;q21) and four gastric diffuse large B cell lymphomas (DLBL). All DLBLs and three of seven MALT-type lymphomas were resistant to Fas-mediated apoptosis in vitro. Moreover, four of five MALT-type lymphomas analyzed and one of three DLBLs analyzed showed mutations in Fas mRNA transcripts but no loss of heterozygosity in the Fas promotor region. Alternative mechanisms of resistance to apoptosis, such as decreased expression of Fas or production of soluble Fas were not operative. Therefore, it is suggestive that a subgroup of MALT-type lymphoma B cells, irrespective of t(11;18)(q21;q21), escape the censoring Fas pathway by mutating and inactivating Fas. This identifies a key regulatory step in early MALT-type lymphomagenesis.

Transfection of caspase-3 in the caspase-3–deficient Hodgkin's disease cell line, KMH2, results in enhanced sensitivity to CD95-, TRAIL-, and ARA-C–induced apoptosis

BACKGROUND

CD95(Fas/apo-1) is a cell surface protein member of the tumor necrosis factor receptor family that serves an important role in the induction of apoptosis in several cell types. Although expression of CD95 has been detected on Hodgkin/Reed Sternberg (HRS) cells in situ, our understanding of the biological significance of this molecule in Hodgkin's disease (HD) is limited.

DESIGN

We analyzed both CD95-related apoptotic signaling and its effects on the expression of several factors involved in the regulation of apoptotic mechanisms including: caspase-3, caspase-8, bcl-2, bcl-x, and Bax in HD cell lines (L-428, L-540, HDLM-2, HS-445, and KM-H2).

RESULTS

HD cell lines showed similar expression levels of CD95 and all but KM-H2 demonstrated variable increases in apoptosis after CD95 stimulation by the agonistic monoclonal antibody, CH11. There was no significant correlation between CD95 sensitivity and constitutive expression levels of caspase-8, bcl-2, bcl-x, and Bax. Caspase-3 transcript was demonstrated by reverse transcriptase polymerase chain reaction (RT-PCR) in all cell lines but protein was at low to nearly undetectable levels in KM-H2 cells. Transfection of KM-H2 cells with pro-caspase-3 resulted in a markedly enhanced apoptotic response to CD95 stimulation that was blocked by pretreatment with the caspase-3 inhibitor, DEVD-FMK. In addition, pro-caspase-3-transfected KM-H2 cells showed significantly increased sensitivity to other caspase-3-dependent apoptotic stimuli, including the death-inducing ligand, TRAIL, and the chemotherapeutic agent, Ara-C.

CONCLUSION

These data demonstrate that caspase-3 expression plays an important role in CD95-mediated apoptosis in HD cell lines. Furthermore, lack of or decreased expression of caspase-3 in HD cells impairs their apoptotic response not only to CD95 but also to other caspase-3-dependent apoptotic stimuli.

Caspase 8 expression and signaling in Fas injury-resistant human fetal astrocytes

Fas (APO-1/CD95) is a cell surface receptor initially identified in lymphoid cells, but more recently detected in the central nervous system under pathological, usually inflammatory, conditions. In most Fas expressing cells, triggering of Fas by its ligand or by antagonistic antibodies leads to apoptosis. Human fetal astrocytes (HFA) constitutively express Fas yet are resistant to cell death following Fas ligation. In the current study, using dissociated cultures of human fetal central nervous system-derived cells, we attempted to identify a basis for HFA resistance to Fas-mediated injury. We compared the components of the Fas signaling pathway of HFA to those of two human cell lines susceptible to Fas-mediated injury, U251 glioma and Jurkat T-cells. We found that HFA did not express caspase 8 (FLICE), the caspase primarily activated on Fas signaling. Although we could induce caspase 8 in HFA with the inflammatory cytokines IFNgamma and TNFalpha, HFA remained resistant to Fas-mediated injury. Addition of inflammatory cytokines to the extracellular milieu also increased FLIP mRNA (FLICE inhibitory protein). Furthermore, upon triggering of cytokine-treated cells with FasL, we observed upregulation of the cleavage product of FLIP (p43-FLIP) previously shown to associate with the DISC and to block caspase 8 recruitment, thereby inhibiting Fas-mediated death. Our findings indicate that caspase 8 and its regulators play a central role in determining the response to Fas ligation of HFA and support a role for Fas signaling in the developing central nervous system other than related to cytotoxicity.

Resveratrol--from the bottle to the bedside?

Resveratrol, a naturally occurring plant antibiotic has been the focus of a number of studies investigating its biological attributes, which include anti-oxidant activity, anti-platelet aggregation effect, anti-atherogenic property, estrogen-like growth promoting effect, growth inhibiting activity, immunomodulation, and chemoprevention. More recently, since the first report on the apoptosis inducing activity of resveratrol in human cancer cells, the interest in this molecule as a potential chemotherapy agent has significantly intensified. Not only has its role as an anti-cancer agent been corroborated, but the precise mechanism(s) of the anti-cancer activity of resveratrol is/are being elucidated. Our group has been active in studying the cross talk between the caspase family of proteases and mitochondria, in drug-induced apoptosis. In this regard, we have shown that the cancer preventive activity of resveratrol could be attributed to its ability to trigger apoptosis in human leukemia and breast carcinoma cells. The cytotoxicity of resveratrol is restricted against these transformed cell types due to its ability to selectively upregulate CD95-CD95L interaction on the tumor cell surface, unlike normal peripheral blood cells. Despite the involvement of the CD95 signaling pathway, apoptosis induced by resveratrol is not accompanied by robust caspase 8 activation, but involves mitochondrial release of cytochrome C and downstream activation of caspases 9 and 3. We also extrapolate these in vitro findings in a murine model of carcinogensis, and demonstrate in vivo induction of apoptosis in mouse skin papillomas. These findings highlight the chemotherapeutic potential of this polyphenolic compound.

Circulating levels of TNF alpha and TNF receptor superfamily members in lymphoid neoplasia

We have correlated the serum levels of TNF alpha and soluble TNF receptor superfamily members with clinico-pathologic parameters in patients of Hodgkin's disease (HD, N = 26) and non-Hodgkin's lymphoma (NHLs, N = 35). HD patients had significantly higher levels of TNF alpha, sTNFRI, and sTNFRII in serum while NHL patients had significantly higher levels of sTNFRI, sTNFRII, sCD27, and sFas as compared to controls. In NHL patients the levels of sCD27 correlated directly and significantly with the high-stage disease, bone marrow involvement, lymph nodal presentation, and serum LDH levels. Similarly in NHL patients, levels of sFas also correlated directly and significantly with the presence of high stage disease. HD patients with B symptoms had significantly higher levels of sTNFRII.

Expression of Fas and Fas-ligand in primary cutaneous T-cell lymphoma (CTCL): association between lack of Fas expression and aggressive types of CTCL

BACKGROUND

Fas (CD95; APO-1) is a transmembrane protein that mediates apoptosis upon cross-linking with Fas-ligand (Fas-L). Interaction of Fas-L expressed by cytotoxic T cells with Fas-expressing tumour cells plays an important part in antitumour immune responses.

OBJECTIVES

We aimed to investigate Fas and Fas-L expression in frozen and paraffin-embedded material from a large group of patients with cutaneous T-cell lymphoma (CTCL).

METHODS

Immunostaining with monoclonal antibodies against Fas and Fas-L was performed in material from 23 patients with mycosis fungoides (MF), 10 with lymphomatoid papulosis (LyP), 10 with CD30-positive primary cutaneous large T-cell lymphoma (LTCL) and nine with CD30-negative LTCL. The results were correlated with the type and stage of CTCL and clinical features.

RESULTS

Expression of Fas by the large majority of the neoplastic T cells was observed in 15 of 15 cases of plaque-stage MF, 10 of 10 cases of LyP and 10 of 10 cases of CD30-positive LTCL, but only in four of 12 cases of tumour-stage MF and two of nine cases of CD30-negative LTCL. In three of four MF patients in whom both plaques and tumours could be studied, a significant decrease in Fas expression was observed with progression from plaque-stage to tumour-stage disease. Fas-L was expressed by > 50% of the neoplastic T cells in 46 of 56 biopsies, and no clear relationship with type of CTCL and clinical behaviour was observed.

CONCLUSIONS

This study demonstrates loss of Fas expression in aggressive types of CTCL, but not in indolent types of CTCL. These data suggest that loss of Fas receptor expression may be one of the mechanisms that allow tumour cells to escape an effective immune response, and may contribute to the unfavourable prognosis of some types of CTCL.

Fas engagement accelerates liver regeneration after partial hepatectomy

Fas (CD95) is a receptor involved in induction of apoptotic cell death of Fas-bearing cells, including hepatocytes and T cells. Injection of Fas-specific antibodies into mice leads to fulminant hepatic failure and death. Fas also transduces growth-promoting signals in proliferating T cells, fibroblasts and some tumor cells. Here we show that partial hepatectomy, which triggers the immediate onset of liver regeneration, protected mice against the lethal effects of Fas-specific antibodies and prevented hepatocyte apoptosis in response to Fas engagement in vivo. Furthermore, Fas engagement accelerated liver regeneration after partial hepatectomy. Liver regeneration kinetics were delayed in mutant mice with decreased cell surface Fas expression (lpr mice). In contrast, regeneration was not delayed in lpr-cg mutant mice, which have a Fas mutation that prevents Fas-induced death but not Fas-dependent proliferative stimulation. Our results indicate that Fas engagement on cells in regenerating or healing tissues may promote cell growth.

Morphological changes in the nucleus and actin cytoskeleton in the process of Fas-induced apoptosis in Jurkat T cells

To investigate the early event of apoptosis, we monitored the morphological changes in the early stage of Fas-induced apoptosis in the human T-cell lymphoma cell line Jurkat, using confocal microscopy. Morphological changes in the nuclei were observed from 30 min after stimulation, and preceded the changes in the cytoskeleton. This kind of change was enhanced in the presence of EGTA but decreased in the presence of dihydrocytochalasin B, without any changes in caspase-3 activation. During the changes in shape of the cells, the actin cytoskeleton collapsed and shrank in the center. Even though nuclei also changed their shapes in apoptotic cells, they were partially TUNEL-negative, suggesting that they were not yet damaged at the DNA level. Our results suggest that, in the process of apoptosis in Jurkat cells, cell nuclei and cytoskeleton are changed first, then membrane blebbing and caspase-3 activation occur, and fragmentation of chromosomal DNA is last.

Ionizing radiation alters Fas antigen ligand at the cell surface and on exfoliated plasma membrane-derived vesicles: implications for apoptosis and intercellular signaling

Resident proteins that reside on the plasma membrane are continually exfoliated from the cell surface. Exfoliation is a selective, energy-dependent process that mediates intercellular communication. Ionizing radiation modulates the expression of many plasma membrane-bound growth regulators, including the "death" ligand, TNFSF6 (formerly known as FasL, CD95L). Here we report that ionizing radiation induces dose-dependent up-regulation of TNFSF6 on plasma membranes purified from SW620 cells, a TNFSF6-expressing colon cancer cell line. Serum-free medium conditioned by exposed and control cells was collected and exfoliated vesicles were obtained by ultracentrifugation. Western blot analysis of vesicles from unexposed cells and from cells treated with 10 Gy showed increased amounts of TNFSF6 compared to that on vesicles from unexposed cells. Cells treated with 4 Gy released vesicles having a low level of TNFSF6 on their surface relative to that on vesicles exfoliated from unexposed cells. When assayed for bioactivity, vesicles from unexposed cells induced the greatest level of apoptosis in TNFRSF6 (formerly known as FAS) receptor-bearing Jurkat cells (cell surviving fraction of 43.7 +/- 6.1; P < 0.05), followed by vesicles collected from cells treated with 4 Gy (79.6 +/- 2.6%; P < 0.05). Despite having a high level of TNFSF6 by Western analysis, vesicles collected from cells exposed to 10 Gy display minimal biological activity (77.9 +/- 3.2%; P < 0.05), suggesting that modification of the vesicle-associated ligand has occurred. Our results indicate that ionizing radiation increases the level of TNFSF6 exfoliated on extracellular vesicles. The data may provide a mechanism for abscopal and bystander effects after irradiation.

Irradiation-induced up-regulation of Fas in esophageal squamous cell carcinoma is not accompanied by Fas ligand-mediated apoptosis

BACKGROUND AND OBJECTIVES

Fas (APO-1) induces apoptosis after binding Fas ligand (FasL). Evidence suggests that tumors may use this interaction to evade the host immune response. Fas/FasL expression has not been reported in esophageal cancer. We hypothesized that Fas expression would render esophageal cancer cells susceptible to Fas ligation and that irradiation of the cells would increase Fas expression.

METHODS

Two human esophageal squamous cell carcinoma lines, KYSE 150, which has a wild-type (wt) p53 gene, and 410 (mutated p53), were irradiated. Reverse-transcriptase polymerase chain reaction was used to detect Fas and FasL expression. Fas protein was quantitated by enzyme-linked immunosorbent assay and its presence further confirmed by Western analysis. FasL was detected by Western analysis. Cells were treated with Fas monoclonal antibody (maximum 0.05 microg/ml)+/-cycloheximide, and viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cells were also transduced with FasL cDNA and then quantified.

RESULTS

Both lines expressed Fas and FasL, but only the KYSE 150 cell line displayed an increase in Fas following irradiation. No alteration in cell growth was detected for Fas antibody- or FasL-transduced groups versus controls.

CONCLUSIONS

We have demonstrated Fas and FasL expression in esophageal tumor lines. We have also shown that Fas levels are significantly increased in response to irradiation in a wt p53 line. However, cells were resistant to treatment with Fas antibody or following transduction with FasL, suggesting that these tumor cells may use Fas/FasL expression to evade the host immune response.

Fas and Fas ligand interactions suppress melanoma lung metastasis

Apoptosis induced by Fas (CD95) ligation is frequently lost during tumor progression; however, there is no direct evidence to support an association of Fas loss-of-function with metastatic tumor behavior. To determine whether Fas loss-of-function is critical for acquisition of the metastatic phenotype, we have compared the ability of Fas-sensitive K1735 murine melanomas to form spontaneous lung metastases in wild-type and Fas ligand-deficient mice. Fas-sensitive melanoma clones are highly tumorigenic but rarely metastatic in wild-type syngeneic mice. However, in Fas ligand-deficient mice, both the incidence and number of metastases are increased. These findings provide the first evidence that Fas-Fas ligand interactions can suppress metastasis and that tumor Fas loss-of-function may be causally linked to metastatic progression.

Fas/APO-1 (CD95)–Mediated Apoptosis Is Activated by Interferon-γ and Interferon- in Interleukin-6 (IL-6)–Dependent and IL-6–Independent Multiple Myeloma Cell Lines

A poor response to Fas-induced apoptosis is evident in some multiple myeloma (MM) cell lines and primary cells. In this study, we have examined the possibility to increase the sensitivity to Fas-induced apoptosis by pretreatment of MM cells with interferon-γ (IFN-γ) or interferon- (IFN-). Both IFN-γ and IFN- markedly increased the Fas-induced apoptosis in all cell lines tested (U-266-1970, U-266-1984, and U-1958). In the U-266-1970 and U-1958 cell lines, pretreatment with either IFN-γ or IFN- also inhibited proliferation in a dose-dependent manner. In contrast, IFN-γ activation of the Fas death pathway in the U-266-1984 cells was not accompanied by growth inhibition. Incubation with the IFNs increased the Fas antigen expression in one of three cell lines but did not alter the expression of Bcl-2 or Bax. The IFNs are important regulators of growth and survival in MM cells. Our results suggest that activation of Fas-mediated apoptosis is a novel mechanism by which the IFNs exert inhibitory effects on MM cells.

© 1998 by The American Society of Hematology.

Fas/APO-1 (CD95)–Mediated Apoptosis Is Activated by Interferon-γ and Interferon- in Interleukin-6 (IL-6)–Dependent and IL-6–Independent Multiple Myeloma Cell Lines

A poor response to Fas-induced apoptosis is evident in some multiple myeloma (MM) cell lines and primary cells. In this study, we have examined the possibility to increase the sensitivity to Fas-induced apoptosis by pretreatment of MM cells with interferon-γ (IFN-γ) or interferon- (IFN-). Both IFN-γ and IFN- markedly increased the Fas-induced apoptosis in all cell lines tested (U-266-1970, U-266-1984, and U-1958). In the U-266-1970 and U-1958 cell lines, pretreatment with either IFN-γ or IFN- also inhibited proliferation in a dose-dependent manner. In contrast, IFN-γ activation of the Fas death pathway in the U-266-1984 cells was not accompanied by growth inhibition. Incubation with the IFNs increased the Fas antigen expression in one of three cell lines but did not alter the expression of Bcl-2 or Bax. The IFNs are important regulators of growth and survival in MM cells. Our results suggest that activation of Fas-mediated apoptosis is a novel mechanism by which the IFNs exert inhibitory effects on MM cells.

© 1998 by The American Society of Hematology.

Comparative analysis of histological and immunohistological features in mycosis fungoides and Sézary syndrome

Mycosis fungoides (MF) and Sézary syndrome (SS) are closely related cutaneous T-cell lymphomas, which differ in several clinical aspects. We compared histological and immunophenotypical features of these two entities, which could be implicated in the dermotropism and epidermotropism, characteristic for both of them. Thirteen biopsy specimens from patients with established plaque-stage MF and 13 from SS patients were examined retrospectively, and 21 histological criteria were assessed. Further, 9 cryosections from MF lesions and 9 from SS lesions were stained for LFA, ICAM1, CD40, CD40-ligand, CD28, CD80, CTLA-4, CD86, FAS, FAS-ligand, CLA and CD15s. The only histological criteria that showed persistent differences were acanthosis (in 12 of 13 SS and in 7 of 13 MF specimens) and Pautrier collections (detected in 6 SS and 11 MF biopsies). Patterns of staining with the antibodies mentioned above were found to be similar. Our results indicate that these interaction molecules seem to be involved in the pathogenesis of MF and SS, but their immunohistochemical distribution does not contribute to the differentiation between the two entities.

Fas-Mediated Modulation of Bcr/Abl in Chronic Myelogenous Leukemia Results in Differential Effects on Apoptosis

Fas-R is expressed constitutively in CD34+ cells of patients with chronic myelogenous leukemia (CML); Fas-R triggering results in decreased proliferation rate due to apoptosis of clonogenic cells. We have already shown that α-interferon (IFN-α) enhances Fas-R expression on CML progenitor cells, thus increasing their sensitivity to Fas-R agonists. Although it appears that IFN-α can prime CML cells for the effects of Fas, the response to IFN-α in vivo is not a constant feature in CML patients. We studied the mechanisms of Fas-mediated apoptosis in 11 patients suffering from CML in chronic phase and tried to see whether there was a correlation between in vitro inducibility of apoptosis in CD34+ CML cells after Fas-R triggering and the clinical response to IFN-α. After priming with IFN-α, Fas triggering resulted in in vitro suppression of hematopoietic cell growth in seven of eight patients who had optimal hematologic response to IFN-α; in the same conditions, no inhibitory response to Fas-R agonist was observed in cells from three of three patients who proved to be poor responders to IFN-α. In responders to IFN-α, Fas-R agonist induced dose-dependent apoptosis of CD34+ cells; this effect was associated with a decrease in the bcr/abl protein level. In cells derived from patients with a poor response to IFN-α, the rate of apoptosis in culture remained unchanged in the presence of Fas-R agonist and nobcr/abl downmodulation was observed. Finally, we measuredbcr/abl mRNA by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and found that decreased bcr/ablprotein after Fas triggering was not associated with decreased amounts of specific mRNA, a finding which is consistent with a posttranscriptional regulation of the bcr/abl protein expression. It appears that Fas-mediated downmodulation of p210bcr/abl restores susceptibility to apoptosis of CML cells; in addition, in vitro studies on CML cells may predict response to IFN-α treatment.

© 1998 by The American Society of Hematology.

Mutation analysis of CD95 (APO-1/Fas) in childhood B-lineage acute lymphoblastic leukaemia

The CD95 system plays an important role in lymphocyte homeostasis, has been implicated in the development of lymphoid malignancies, exerts a tumour suppressor function, and contributes to drug-induced cytotoxicity. We hypothesized that mutations of CD95 may occur in childhood B-lineage acute lymphoblastic leukaemia (ALL), a disease known for its constitutive resistance towards CD95-mediated apoptosis. We investigated 32 primary B-lineage ALL of childhood and five B-lineage ALL cell lines. All primary leukaemias expressed CD9 5 and bcl-2 to a variable degree. Most of the leukaemias were resistant towards CD95-mediated apoptosis. However, using SSCP analysis, no mutations in the coding and proximal promoter region could be detected. We conclude that the resistance towards CD95-mediated apoptosis observed in most de novo B-lineage ALL is not caused by mutations of the CD95 death receptor.

Fas-Mediated Modulation of Bcr/Abl in Chronic Myelogenous Leukemia Results in Differential Effects on Apoptosis

Fas-R is expressed constitutively in CD34+ cells of patients with chronic myelogenous leukemia (CML); Fas-R triggering results in decreased proliferation rate due to apoptosis of clonogenic cells. We have already shown that α-interferon (IFN-α) enhances Fas-R expression on CML progenitor cells, thus increasing their sensitivity to Fas-R agonists. Although it appears that IFN-α can prime CML cells for the effects of Fas, the response to IFN-α in vivo is not a constant feature in CML patients. We studied the mechanisms of Fas-mediated apoptosis in 11 patients suffering from CML in chronic phase and tried to see whether there was a correlation between in vitro inducibility of apoptosis in CD34+ CML cells after Fas-R triggering and the clinical response to IFN-α. After priming with IFN-α, Fas triggering resulted in in vitro suppression of hematopoietic cell growth in seven of eight patients who had optimal hematologic response to IFN-α; in the same conditions, no inhibitory response to Fas-R agonist was observed in cells from three of three patients who proved to be poor responders to IFN-α. In responders to IFN-α, Fas-R agonist induced dose-dependent apoptosis of CD34+ cells; this effect was associated with a decrease in the bcr/abl protein level. In cells derived from patients with a poor response to IFN-α, the rate of apoptosis in culture remained unchanged in the presence of Fas-R agonist and nobcr/abl downmodulation was observed. Finally, we measuredbcr/abl mRNA by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and found that decreased bcr/ablprotein after Fas triggering was not associated with decreased amounts of specific mRNA, a finding which is consistent with a posttranscriptional regulation of the bcr/abl protein expression. It appears that Fas-mediated downmodulation of p210bcr/abl restores susceptibility to apoptosis of CML cells; in addition, in vitro studies on CML cells may predict response to IFN-α treatment.

© 1998 by The American Society of Hematology.

Differential regulation of CD95 (Fas/APO-1) expression in human blood eosinophils

CD95 (Fas, APO-1) is a cell surface receptor expressed on many cells including eosinophils which mediates apoptosis when ligated by agonistic antibodies or its natural ligand FasL. Since inhibition of apoptosis may play an important role in controlling tissue eosinophilia, we investigated the expression of CD95 on purified peripheral blood eosinophils from normal donors. Freshly isolated eosinophils expressed CD95 on the cell surface as well as CD95-specific mRNA at low levels which did not change during 24-h culture. Incubation of eosinophils with IL-3, IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF) did not modulate the basal expression of CD95. IFN-gamma as well as TNF-alpha, however, induced a significant, dose- and time-dependent increase in CD95 mRNA and cell surface expression as measured by reverse transcription-PCR and flow cytometry. Co-stimulation with IFN-gamma and TNF-alpha had synergistic effects on the CD95 surface expression on eosinophils. Addition of IL-3, IL-5 or GM-CSF to IFN-gamma- and TNF-alpha-stimulated eosinophils caused in a reduction of CD95 expression. Functional activity for CD95 following incubation with IFN-gamma and TNF-alpha was demonstrated by increased apoptosis in response to cross-linking with FasL. From these data, we conclude that IFN-gamma and TNF-alpha can up-regulate cell surface expression of CD95 on eosinophils, which leads to an increased susceptibility of eosinophils to Fas-mediated apoptosis. Thus, our results suggest that receptors involved in eosinophil apoptosis can be regulated by antagonistic cytokines.

Biologically Active Fas Antigen and Its Cognate Ligand Are Expressed on Plasma Membrane-Derived Extracellular Vesicles

Exfoliation of plasma membrane components is a directed process that consumes energy and requires active cell metabolism. Proteins involved in regulating the survival and proliferation of eukaryotic cells are released on exfoliated vesicles. We examine here whether the Fas receptor and its cognate ligand (FasL) are present on vesicles shed from high metastatic potential CX-1 cells and low metastatic potential MIP-101 cells and from HuT 78 cells, respectively. Rates of exfoliation at 2 hours and cumulative levels of extracellular vesicles in serum-free medium conditioned by CX-1 cells are increased by 1.8-fold and 1.6-fold, respectively, relative to that in medium conditioned by MIP-101 cells. Although vesicles shed from both cancer cell lines contain Fas antigen, the amount of Fas per vesicle and the percentage of vesicles containing Fas are increased for vesicles isolated from MIP-101 cells, relative to those from CX-1 cells, as determined by immunogold particle labeling and electron microscopy and by immunofluorescence microscopy and flow cytometry. Results of metabolic labeling with 35S-methionine indicate that Fas biosynthesis is reduced by up to 3.3-fold for CX-1 cells, relative to that of MIP-101 cells, consistent with the finding of decreased Fas on vesicles shed from the plasma membrane of CX-1 cells. Although mRNA for soluble Fas receptor is detectable in both cell lines, depletion of shed vesicles from serum-free medium by ultracentrifugation removes all detectable biological activity. FasL is detected on vesicles exfoliated from HuT 78 cells by immunoelectron microscopy and Western blot analysis. FasL-bearing vesicles induce apoptosis of Fas-expressing cancer cells at the same level as observed by treatment with monoclonal anti-Fas antibody. Furthermore, Fas-bearing extracellular vesicles from MIP-101 but not from CX-1 cells protect the CX-1 cell line from FasL-induced and anti-Fas–mediated apoptosis, indicating that Fas present on shed vesicles is biologically active. We conclude that the Fas antigen and its cognate ligand are exfoliated from the cell surface in a bioactive configuration. Exfoliation may provide a mechanism for long-range signal-directed apoptosis while maintaining Fas/FasL on a membrane surface.

Biologically Active Fas Antigen and Its Cognate Ligand Are Expressed on Plasma Membrane-Derived Extracellular Vesicles

Exfoliation of plasma membrane components is a directed process that consumes energy and requires active cell metabolism. Proteins involved in regulating the survival and proliferation of eukaryotic cells are released on exfoliated vesicles. We examine here whether the Fas receptor and its cognate ligand (FasL) are present on vesicles shed from high metastatic potential CX-1 cells and low metastatic potential MIP-101 cells and from HuT 78 cells, respectively. Rates of exfoliation at 2 hours and cumulative levels of extracellular vesicles in serum-free medium conditioned by CX-1 cells are increased by 1.8-fold and 1.6-fold, respectively, relative to that in medium conditioned by MIP-101 cells. Although vesicles shed from both cancer cell lines contain Fas antigen, the amount of Fas per vesicle and the percentage of vesicles containing Fas are increased for vesicles isolated from MIP-101 cells, relative to those from CX-1 cells, as determined by immunogold particle labeling and electron microscopy and by immunofluorescence microscopy and flow cytometry. Results of metabolic labeling with 35S-methionine indicate that Fas biosynthesis is reduced by up to 3.3-fold for CX-1 cells, relative to that of MIP-101 cells, consistent with the finding of decreased Fas on vesicles shed from the plasma membrane of CX-1 cells. Although mRNA for soluble Fas receptor is detectable in both cell lines, depletion of shed vesicles from serum-free medium by ultracentrifugation removes all detectable biological activity. FasL is detected on vesicles exfoliated from HuT 78 cells by immunoelectron microscopy and Western blot analysis. FasL-bearing vesicles induce apoptosis of Fas-expressing cancer cells at the same level as observed by treatment with monoclonal anti-Fas antibody. Furthermore, Fas-bearing extracellular vesicles from MIP-101 but not from CX-1 cells protect the CX-1 cell line from FasL-induced and anti-Fas–mediated apoptosis, indicating that Fas present on shed vesicles is biologically active. We conclude that the Fas antigen and its cognate ligand are exfoliated from the cell surface in a bioactive configuration. Exfoliation may provide a mechanism for long-range signal-directed apoptosis while maintaining Fas/FasL on a membrane surface.

Down-regulation of Fas gene expression in colon cancer is not a result of allelic loss or gene rearrangement

Expression of Fas, an apoptosis-inducing receptor, in colonic epithelium is progressively reduced during malignant transformation. We have examined the human Fas gene for loss of heterozygosity (LOH) and gross rearrangements in colon tumours and matched normal mucosa. Polymerase chain reaction (PCR) primers were designed to span a DraI restriction fragment length polymorphic site in the gene. Heterozygosity was detected in normal DNA samples by PCR amplification of the polymorphic site and restriction enzyme digestion. Thirty-eight of 88 patients (43%) with colon carcinomas were informative for the assay, and LOH was detected in 6 of the 38 (16%) corresponding tumours. Tumours from three patients with LOH did not express detectable Fas mRNA, and Fas expression was reduced or absent in 7 of 11 tumours from informative patients without LOH. Southern blotting of tumour DNA samples was used to detect rearrangement of the Fas gene, but no altered hybridization patterns were observed in 64 tumours analysed. These findings indicate that disruption of the Fas gene is not primarily responsible for the loss of Fas protein expression reported in colon cancer. We have also shown that loss of Fas gene transcription is common in these tumours, which may be due to epigenetic gene silencing.

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.

Gene transfer of alpha interferon into hematopoietic stem cells

Gene transfer or gene therapy has advantages in the treatment of a variety of disorders due to its selective expression within specific mammalian cells. IFN-alpha has been used in the management of leukemia, and gene transfer of the IFN-alpha gene into hematopoietic progenitor cells may have great potential for the treatment of chronic myelogenous leukemia (CML). Therefore, we examined the ability of adenovirus (Ad)-IFN-alpha gene construct to transfect normal bone marrow hematopoietic CD34+ stem cells and the production of IFN-alpha protein by these cells. Ad-cytomegalovirus (CMV) promoter-driven IFN-alpha at multiple doses was assessed to transfect highly purified CD34+ cells in liquid culture. Optimal transduction of CD34+ cells with the AdCMV-IFN-alpha construct was achieved using 120 plaque forming units (pfu). Flow cytometric determinations revealed that there was no significant difference in CD34+ cell viability for the 8 or 12-h transfection periods. Immunoassay of IFN-alpha produced by CD34+ cells shows that IFN-alpha levels increased several fold in transfected cells and this was not seen in CD34+ cells transfected with the heme oxygenase gene (HO-1). These in vitro data suggest that adenovirus-mediated gene transfer of IFN-alpha into hematopoietic stem cells can be achieved and that the IFN-alpha protein is produced by viable CD34 progenitor cells.

Reed-Sternberg cells and the TNF family of receptors/ligands

Treatment of cancer with means other than chemo- and radiation therapy becomes more and more important. Through the better understanding of tumor biology approaches towards the cure of cancer interfering with the pathophysiological mechanisms of malignancy can be considered. Hodgkin's disease is a good example for the role of the immune system in cancer. The Reed-Sternberg (RS) cells, malignant cells of Hodgkin's disease (HD), are surrounded by tumor infiltrating lymphocytes (TILs) and still evade immunesurveillance. In this respect the importance of the superfamily of tumor necrosis factor (TNF) receptors and ligands is becoming more and more clear. Ligand-receptor interaction either leads to death or survival signals. Many of these receptors and ligands are expressed by the RS cells and the surrounding lymphocytes. Their expression and function in HD are discussed and future directions for possible therapeutical investigations are proposed.

Modulation of resistance to anti-APO-1-induced apoptosis in osteosarcoma cells by cytokines

The CD95/APO-1 Fas receptor/ligand system plays a crucial role in growth control by mediating apoptosis in lymphoid and non-lymphoid cells. To investigate the role of CD95-mediated apoptosis in osteosarcoma, we studied 3 human osteosarcoma cell lines (HOS/TE 85, MG 63 and Saos-2) and osteoblasts derived from bone biopsies. In contrast to osteoblast-like cells, all cell lines were resistant to anti-APO-1-induced apoptosis despite constitutive CD95 expression at intermediate levels. Blocking of macromolecular synthesis by cycloheximide or actinomycin D or modulation of CD95 expression by cytokines (TNF-alpha and/or gamma-interferon) restored sensitivity to anti-APO-1-induced cell death. PCR analysis of the CD95 transcripts revealed the production of a truncated splice variant that codes for a soluble form of the CD95 receptor. Synthesis and secretion of soluble CD95 protein into the culture supernatant was demonstrated by Western blot analysis. Treatment with sensitizing cytokines led to up-regulation of full-length CD95 transcripts and the encoded membrane-bound CD95 protein but not the truncated mRNA splice variant and the corresponding soluble receptor, as shown by PCR and Western blot analysis. The biological activity of soluble CD95 secreted by osteosarcoma cells was demonstrated by the ability of osteosarcoma supernatants to protect the sensitive T-cell line Jurkat from anti-APO-1-mediated apoptosis. Our results suggest that the production of soluble CD95 by osteosarcoma cell lines that may block physiological death signals and the production of membrane-bound CD95 are differently regulated by cytokines via modulation of RNA splicing.

Fas ligand is not only expressed in immune privileged human organs but is also coexpressed with Fas in various epithelial tissues

AIMS

To confirm the recent data obtained in mice, showing that the Fas ligand (FasL) is involved in the phenomenon of "immune privilege" (the apparent defect of the immune system in specific anatomical sites) and to extend this finding to humans.

METHODS

The expression of FasL was analysed in a panel of histologically normal human tissues by reverse transcriptase polymerase chain reaction and Western blotting. The tissues sampled were brain, breast, bone marrow, oesophagus, kidney, liver, lung, lymph node, ovary, pancreas, pituitary gland, prostate, spleen, stomach (antrum and fundus), striated muscle, testis, thyroid, and uterus. These were obtained from patients with various neoplastic and non-neoplastic disorders; placental tissue was obtained after normal obstetric delivery, and spontaneous or voluntary abortion.

RESULTS

Strong FasL expression was detected in testis and placenta. FasL expression was also detectable, although it was seen to a lesser extent, in oesophagus, prostate, lung, and uterus, which also coexpressed variable amounts of Fas mRNA or protein or both. The other organs tested for FasL expression were all negative.

CONCLUSIONS

FasL in humans is expressed predominantly in immune "sanctuaries" such as testis and placenta, suggesting that, similar to mice, this expression may contribute to the immune privileged status of these organs, by preventing dangerous inflammatory responses. The coexpression of FasL and Fas in particular epithelia suggests that the physiological cell turnover of some tissues may be regulated by the Fas-FasL apoptotic pathway.

Apoptosis induced in human colorectal carcinoma by anti-Fas antibody

BACKGROUND

Apoptosis or programmed cell death has been shown to play an important role in the progression from polyps to carcinomas. Fas/APO-1 is a cell surface protein that can induce apoptosis in a variety of cell types upon specific binding. In this study seven human colorectal carcinoma (HCRC) cell lines of varying differentiation were analyzed for cell surface Fas expression. Fas-mediated apoptosis, and correlation of apoptosis with bcl-2 expression.

METHODS AND RESULTS

Using flow cytometry, all seven lines expressed varying amounts of cell surface Fas antigen. Exposure to anti-Fas antibody induced cell death in all the cell lines, albeit to varying degrees. The rate of apoptosis was quantitated using flow cytometry with propidium iodide staining of nuclear DNA. The poorly differentiated cell lines had a significantly decreased (p < 0.05) anti-Fas sensitivity as compared with the well-differentiated lines. Measurement of bcl-2 expression by flow cytometry showed an inverse correlation with anti-Fas sensitivity.

CONCLUSIONS

This study confirms that HCRC cell lines express Fas antigen and, more importantly, provides the first evidence that exposure to anti-Fas antibody can induce apoptosis. Fas-mediated apoptosis in HCRC cell lines may be regulated by bcl-2 and may correlate with the degree of differentiation.

Involvement of Fas-Mediated Apoptosis in the Inhibitory Effects of Interferon-α in Chronic Myelogenous Leukemia

Interferon-α (IFN-α) is an established treatment for chronic myelogenous leukemia (CML) in chronic phase, but the mechanism of its antileukemic activity is not clear. One possible mechanism of action might include the induction of apoptosis, and especially Fas-mediated cell killing may play an important role in the elimination of malignant cells. We investigated Fas receptor (Fas-R) expression and the consequences of Fas-R triggering in CML patients. Using two-color flow cytometry, we found a significantly higher number of Fas-R–expressing CD34+ cells in the bone marrow (BM) of CML patients compared with normal subjects. We have previously shown that IFN-γ induces Fas-R expression on CD34+ cells; in this study, we investigated whether IFN-α induces Fas-R expression on CML progenitor cells. Dose-dependent induction of Fas-R expression was observed after IFN-α stimulation of CD34+ cells from CML BM. In methylcellulose culture, IFN-α alone at a therapeutic concentration showed only marginal antiproliferative effects on both normal and CML BM progenitors. In contrast, a Fas-R agonist, the anti-CD95 monoclonal antibody CH11, inhibited colony formation from normal progenitors, and the inhibition was even stronger on CML progenitors. When CML BM cells were cultured in the presence of IFN-α, Fas-R–mediated inhibition of colony growth was potentiated in a dose-dependent fashion, consistent with IFN-α induction of Fas-R expression. This functional effect did not require the presence of accessory cells, since similar results were obtained with purified CD34+ cells. In suspension cultures, we demonstrated that suppression of CML hematopoiesis by IFN-α and Fas-R agonist was exerted through Fas-R–mediated induction of apoptosis. Our findings suggest that the Fas-R/Fas-ligand system might be involved in the immunologic regulation of CML progenitor growth and that its effect can be amplified by IFN-α.

The renal cell carcinoma lysis by a specific cytotoxic T cell clone is independent of the Fas/Fas-L cytotoxic pathway

The expression of Fas antigen at the surface of renal cell carcinoma and the susceptibility to Fas-mediated lysis by a tumor specific CTL clone were investigated. Renal cell carcinoma cell lines expressed Fas antigen and were susceptible to apoptosis mediated by antibodies to Fas/APO1. Using RT-PCR, we further showed that these cell lines expressed mRNA for Fas deleted transmembrane region, corresponding to a soluble form of Fas/APO-1. To investigate the role of the Fas/FasL pathway in the cytotoxic response against RCC cells, we analyzed the induction of Fas-L on a tumor specific T cell clone (CTL8C2), previously generated against one RCC cell line. Fas-L expression on CTL8C2 was detected by RT-PCR after stimulation with autologous tumor cells. However, the cytotoxic activity of CTL8C2 was completely abolished when EGTA was added, suggesting that the cytolysis was mainly mediated by a Ca+2-dependent pathway, perforin/granzyme-based.

Molecular, structural, and biological characteristics of the tumor necrosis factor ligand superfamily

The tumor necrosis factor receptor superfamily at present consists of ten different transmembrane (type I) glycoproteins with characteristic limited sequence homology for the cysteine-rich repeats in the extracellular domain. In parallel the tumor necrosis factor ligand super-family has been recognized by discovery of ligands for all members of the receptor superfamily. These molecules are also transmembrane (type II) glycoproteins, with the exception of lymphotoxin-alpha which is the only entirely secreted protein of the tumor necrosis factor-like proteins. Several members of the ligand superfamily, including tumor necrosis factor and CD95L also exist in a biologically active soluble form. The tumor necrosis factor ligand superfamily contains at present ten different proteins. In addition, NGFR p75 binds to a second family of proteins (neurotrophins). These nerve growth factor-like dimeric soluble molecules are basic neurotrophic factors and the five members (NGF, BDNF, NT-3, NT-4, NT-5) are not related to the tumor necrosis factor superfamily ligands. The members of the tumor necrosis factor ligand superfamily (TNF, LT-alpha, LT-beta, CD27L, CD30L, CD40L, CD95L, 4-IBB, OX40L, TRAIL) share common biological activities, but some properties are shared by only some ligands, while others are unique. The diverse biological activities triggered through tumor necrosis factor receptors have been linked to the regulation of cellular activation, including immune responses and inflammatory reactions, but also with the pathology of a series of human diseases.

Genomic organization and chromosomal mapping of the bovine Fas/APO-1 gene

The cell-surface protein Fas (APO-1) is a member of the tumor necrosis factor receptor (TNFR) superfamily and transduces apoptosis following binding of Fas ligand or exposure to certain anti-Fas antibodies. We have isolated the bovine Fas (bFas) gene and determined its genomic organization and chromosomal location. Our data indicate that bFas is a single-copy gene that contains 9 exons and spans approximately 31.5 kb. The 5'-flanking region lacks conventional TATA and CCAAT elements, but contains several putative regulatory elements, including multiple copies of Sp1, AP-2, E-box, and N-box consensus sites. Linkage analysis of two (CA) dinucleotide repeat microsatellites within intron 1 and physical assignment by fluorescence in situ hybridization (FISH) placed the bFas gene on bovine chromosome 26. Collectively, these data provide a basis for understanding the regulatory mechanisms that control bFas gene expression.

Fas ligand in human serum

The Fas ligand (FasL), a member of the tumor necrosis factor family, induces apoptosis in Fas-bearing cells. The membrane-bound human FasL was found to be converted to a soluble form (sFasL) by the action of a matrix metalloproteinase-like enzyme. Two neutralizing monoclonal anti-human FasL antibodies were identified, and an enzyme-linked immunosorbent assay (ELISA) for sFasL in human sera was established. Sera from healthy persons did not contain a detectable level of sFasL, whereas those from patients with large granular lymphocytic (LGL) leukemia and natural killer (NK) cell lymphoma did. These malignant cells constitutively expressed FasL, whereas peripheral NK cells from healthy persons expressed FasL only on activation. These results suggested that the systemic tissue damage seen in most patients with LGL leukemia and NK-type lymphoma is due to sFasL produced by these malignant cells. Neutralizing anti-FasL antibodies or matrix metalloproteinase inhibitors may be of use in modulating such tissue damage.