The antiapoptotic protein BAG3 is expressed in thyroid carcinomas and modulates apoptosis mediated by tumor necrosis factor-related apoptosis-inducing ligand

CONTEXT: We previously showed that BAG3 protein, a member of the BAG (Bcl-2-associated athanogene) co-chaperone family, modulates apoptosis in human leukemias. The expression of BAG3 in other tumor types has not been extensively investigated so far. OBJECTIVE: The objective of this study was to analyze BAG3 expression in thyroid neoplastic cells and investigate its influence in cell apoptotic response to TNF-related apoptosis-inducing ligand (TRAIL). DESIGN, SETTING, AND PATIENTS: We investigated BAG3 expression in human thyroid carcinoma cell lines, including NPA, and the effect of BAG3-specific small interfering RNA on TRAIL-induced apoptosis in NPA cells. Subsequently, we analyzed BAG3 expression in 30 benign lesions and 56 carcinomas from patients of the Naples Tumor Institute Fondazione Senatore Pascale. MAIN OUTCOME MEASURES: The main outcome measures were: analysis of BAG3 protein in NPA cells by Western blot and immunocytochemistry; analysis of apoptosis in TRAIL-stimulated NPA cells by flow cytometry; and evaluation of BAG3 expression in specimens from thyroid lesions by immunohistochemistry. RESULTS: BAG3 was expressed in human thyroid carcinoma cell lines; small interfering RNA-mediated downmodulation of its levels significantly (P < 0.0195) enhanced NPA cell apoptotic response to TRAIL. The protein was not detectable in 19 of 20 specimens of normal thyroid or goiters, whereas 54 of 56 analyzed carcinomas (15 follicular, 28 papillary, and 13 anaplastic) were clearly positive for BAG3 expression. CONCLUSIONS: BAG3 downmodulates the apoptotic response to TRAIL in human neoplastic thyroid cells. The protein is specifically expressed in thyroid carcinomas and not in normal thyroid tissue or goiter.     

Modulation of tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by chemotherapy in thyroid cancer cell lines.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in many human cancer cells but not in normal cells. Thyroid cancer cells, however, appear to be relatively resistant to TRAIL-induced apoptosis. We therefore investigated the effect of chemotherapy on TRAIL-induced apoptosis in thyroid cancer cells. We used six thyroid cancer cell lines: TPC-1, FTC-133, FTC-236, FTC-238, XTC-1, and ARO82-1. We used flow cytometry to measure apoptosis, dimethyl-thiazol-diphenyltetrazolium bromide (MTT) assay to measure antiproliferation effects and Western blot to determine the expression of Bcl family proteins. Troglitazone, paclitaxel, geldanamycin, and cycloheximide were used for pretreatment. We used the Student's t test and analysis of variance (ANOVA) for statistical analysis. All thyroid cancer cell lines, except the TPC-1 cell line, were resistant to TRAIL, and growth inhibition was less than 20% at concentration of 800 ng/mL of TRAIL. In both TPC-1 (TRAIL-sensitive) and FTC-133 (TRAIL-resistant) thyroid cancer cell lines, pretreatment with troglitazone, cycloheximide, and paclitaxel enhanced TRAIL-induced cell death significantly but pretreatment with geldanamycin did not. There were no significant changes in Bcl-2, Bcl-xl, and Bax protein expression after troglitazone treatment. In conclusion, TRAIL in combination with troglitazone, paclitaxel, and cycloheximide induces apoptosis in thyroid cancer cells at suboptimal concentrations that cannot be achieved using TRAIL alone.     

Involvement of glyceraldehyde-3-phosphate dehydrogenase in tumor necrosis factor-related apoptosis-inducing ligand-mediated death of thyroid cancer cells

TNF-related apoptosis-inducing ligand (TRAIL) is cytotoxic to most thyroid cancer cell lines, including those originating from anaplastic carcinomas, implying TRAIL as a promising therapeutic agent against thyroid cancers. However, signal transduction in TRAIL-mediated apoptosis is not clearly understood. In addition to its well-known glycolytic functions, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein, including its surprising role as a mediator for cell death. In this study we explored the involvement of GAPDH in TRAIL-mediated thyroid cancer cell death. In follicular undifferentiated thyroid cells, S-nitrosylation and nuclear translocation of GAPDH appear to mediate TRAIL-induced cell death at least partially, as evidenced by pretreatment with N-nitro-L-arginine methyl ester, a competitive nitric oxide synthase inhibitor that partially but significantly attenuated TRAIL-induced apoptosis through the reduction of S-nitrosylation and nuclear translocation of GAPDH. In addition, GAPDH small interfering RNA partially prevented the apoptotic effect of TRAIL, although TRAIL-induced nitric oxide synthase stimulation and production of nitric oxide were not attenuated. Furthermore, nuclear localization of GAPDH was observed in another thyroid cancer cell line, KTC2, which is also sensitive to TRAIL, but not in those TRAIL insensitive cell lines: ARO, KTC1, and KTC3. These data indicate that nitric oxide-mediated S-nitrosylation of GAPDH and subsequent nuclear translocation of GAPDH might function as a mediator of TRAIL-induced cell death in thyroid cancer cells.     

Chemotherapeutic agents augment TRAIL-induced apoptosis in human hepatocellular carcinoma cell lines

TNF-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in various transformed cell lines but not in almost-normal tissues. It is regulated by 2 death receptors, TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2, and 2 decoy receptors, TRAIL-R3 and TRAIL-R4. We investigated the expression of TRAIL-R- and TRAIL-induced apoptosis in human hepatocellular carcinomas (HCCs). TRAIL-R1, -R2, and -R4 were expressed in 6 HCC cell lines examined, but TRAIL-R3 was expressed in only 2 of the 6 cell lines. In addition, immunohistochemical results revealed a high and prevalent expression of TRAIL-R1 and -R2 in human HCC tissues. Despite the expression of TRAIL-R1 and -R2, all 6 HCC cell lines showed resistance to TRAIL-induced apoptosis with no relation to nuclear factor kappa B (NF-kappaB) levels induced by TRAIL. TRAIL-induced death signal was inhibited with both decreased caspase-8 and caspase-3 activity. However, TRAIL induced significant apoptosis in the presence of a subtoxic level of actinomycin D, indicating that the TRAIL-induced apoptotic pathway is in place in these cell lines. In addition, we found that treatment with conventional chemotherapeutic agents, doxorubicin and camptothecin, dramatically augmented TRAIL-induced cytotoxicity in most of the HCC cell lines. Actinomycin D and camptothecin almost completely suppressed NF-kappaB induction by TRAIL, whereas doxorubicin had little effect. These results indicate that TRAIL, in combination with chemotherapeutic agents, may have therapeutic potential in the treatment of human HCC.     

Over-expressing CYLD augments antitumor activity of TRAIL by inhibiting the NF-κB survival signaling in lung cancer cells

The death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in tumor cells. But studies have demonstrated that many tumor cells were resistant to TRAIL-induced apoptosis. CYLD is recognized as a negative regulator of nuclear factor-kappa B(NF-κB) activity. To explore a correlation between CYLD expression and responsiveness to TRAIL in lung cancer cell lines, we established lung cancer cell lines that stably express CYLD. Our data provided the first evidence that increased expression of CYLD directly blocks TRAIL-induced NF-κB activation, and consequently increases TRAIL-induced apoptosis in lung cancer cells. CYLD may act as a therapeutic target of lung cancer. Targeting CYLD, in combination with TRAIL, may be a new strategy to treat lung cancer with high NF-κB activity.     

Regulation of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in Burkitt's lymphoma cell lines

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in sensitive cells and may be suitable for novel anti-cancer therapies aimed at inducing apoptosis via the activation of TRAIL receptors on malignant cells. Here we have characterized the TRAIL sensitivity of a panel of Burkitt's lymphoma (BL) cell lines. Overall, 5/12 BL cell lines and 1/2 lymphoblastoid cell lines were sensitive to TRAIL-induced apoptosis, although only one BL cell line approached the sensitivity of Jurkat cells, a widely used model for TRAIL-induced apoptosis. Whereas, 4/5 of the Epstein-Barr virus (EBV)-negative cell lines were TRAIL sensitive, only 1/7 EBV-positive BL cell lines were TRAIL sensitive. However, isogenic BL cell lines with different EBV status were not differently sensitive to TRAIL, indicating that EBV is not a major determinant of TRAIL sensitivity. All cell lines expressed the death receptor (DR)5 TRAIL receptor, whereas expression of DR4 was more variable. Differences in the expression of downstream signalling molecules [Fas-associated death domain protein (FADD), caspase 8] and inhibitors [decoy receptor 1 (DcR1), cellular FLICE-like inhibitory protein (c-FLIP)] did not correlate with TRAIL sensitivity. Therefore, a subset of BL cell lines are sensitive to TRAIL-induced apoptosis, however, the molecular mechanism that determines responsiveness remains to be identified.     

TRAIL/bortezomib cotreatment is potentially hepatotoxic but induces cancer-specific apoptosis within a therapeutic window

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) represents a novel promising anticancer biotherapeutic. However, TRAIL-resistant tumor cells require combinatorial regimens to sensitize tumor but not normal cells for TRAIL-induced apoptosis. Here, we investigated the mechanism of the synergistic antitumor effect of bortezomib in combination with TRAIL in hepatoma, colon, and pancreatic cancer cells in comparison to the toxicity in primary human hepatocytes (PHH). TRAIL cotreatment at high but clinically relevant concentrations of bortezomib caused toxicity in PHH which potentially limits the clinical applicability of bortezomib/TRAIL cotreatment. However, at low concentrations of bortezomib TRAIL-resistant hepatoma, colon and pancreatic cancer cell lines but not PHH were efficiently sensitized for TRAIL-induced apoptosis. RNA interference and TRAIL receptor blockage experiments revealed that in bortezomib-treated hepatoma cells TRAIL-R1/TRAIL-R2 up-regulation, enhanced TRAIL DISC formation and cFLIPL down-regulation in addition to accumulation of Bak cooperatively sensitized for TRAIL. Bim, although accumulated upon bortezomib treatment, did not play a causal role for TRAIL sensitization in Hep3b cells. Combined treatment with bortezomib and TRAIL massively reduced the clonogenic capacity of hepatoma cells in vitro. Surviving clones could be resensitized for repeated TRAIL treatment. CONCLUSION: Bortezomib/TRAIL cotreatment bears the risk of severe hepatotoxicity at high but clinically relevant concentrations of bortezomib. However, within a wide therapeutic window bortezomib sensitized different cancer cells but not PHH for TRAIL-induced apoptosis.     

5-FU增强TRAIL诱导的胃癌BGC823细胞凋亡的实验研究

目的 观察5-FU对TRAIL诱导的胃癌BGC823细胞凋亡的影响,明确死亡受体5(DR5)在5-FU和TRAIL诱导凋亡中的作用.方法 采用MTT法测定细胞活力、流式细胞仪检测细胞凋亡、免疫印迹检测蛋白表达.结果 TRAIL可导致BGC823细胞轻度的增殖抑制和少量的细胞凋亡.与单药TRAIL和5-FU相比,TRAIL联合5-FU对细胞的增殖抑制和诱导凋亡作用明显增强(P＜0.05).免疫印迹结果显示,TRAIL没有改变DR5的蛋白表达,而5-FU作用BGC823细胞48 h后,DR5蛋白表达上调(P＜0.05).TRAIL和5-FU联合作用后,DR5蛋白表达同样明显上调(P均＜0.05).结论 5-FU通过上调DR5蛋白表达提高了BGC823细胞对TRAIL的敏感性.     

XAF1增加TRAIL诱导的肝癌细胞凋亡的敏感性

背景:肿瘤坏死因子(TNF)相关凋亡诱导配体(TRAIL)可特异性诱导肿瘤细胞凋亡,但部分肿瘤细胞对TRAIL不敏感甚至耐药。目的:探讨X连锁凋亡抑制蛋白(XIAP)相关因子1(XAF1)是否可增加TRAIL诱导的肝癌细胞株凋亡的敏感性。方法:重组人TRAIL(rhTRAIL)因子分别加入3株肝癌细胞株SMMC7721、HepG2和Bel-7404中培养,联合或不联合相同感染复数(MOI)的重组腺病毒Ad5/F35-XAF1和对照空病毒Ad5/F35-Null。作用48h后,以MTT法检测细胞活力,以Annexin V-FITC/PI法检测细胞凋亡率。结果:随着TRAIL浓度的增加,3株肝癌细胞株的细胞活力均不同程度降低。TRAIL与Ad5/F35-XAF1联合作用后,其细胞活力显著低于单独TRAIL组,而Ad5/F35-Null组细胞活力与单独TRAIL组无明显差异。与空白对照组和Ad5/F35-Null组相比,TRAIL组和Ad5/F35-XAF1组3株肝癌细胞株的凋亡率均显著增加。TRAIL与Ad5/F35-XAF1联合作用后,细胞凋亡率显著高于Ad5/F35-XAF1组或TRAIL组。结论:XAF1可明显增加TRAIL诱导的肝癌细胞凋亡的敏感性,两者联合应用对诱导不同肝癌细胞凋亡具有协同作用。     

Proteasome inhibition sensitizes hepatocellular carcinoma cells, but not human hepatocytes, to TRAIL

TRAIL exhibits potent anti-tumor activity on systemic administration in mice. Because of its proven in vivo efficacy, TRAIL may serve as a novel anti-neoplastic drug. However, approximately half of the tumor cell lines tested so far are TRAIL resistant, and potential toxic side effects of certain recombinant forms of TRAIL on human hepatocytes have been described. Pretreatment with the proteasome inhibitor MG132 and PS-341 rendered TRAIL-resistant hepatocellular carcinoma (HCC) cell lines but not primary human hepatocytes sensitive for TRAIL-induced apoptosis. We investigated the different levels of possible MG132-induced interference with resistance to apoptotic signal transduction. Although proteasome inhibition efficiently suppressed nuclear factor-kappaB (NF-kappaB) activity, specific suppression of NF-kappaB by mutIkappaBalpha failed to sensitize TRAIL-resistant cell lines for TRAIL-induced apoptosis. In contrast to the previously reported mechanism of sensitization by 5-fluorouracil (5-FU), cellular FLICE-inhibitory protein (cFLIP)(L) and cFLIP(S) were markedly upregulated in the TRAIL death inducing signaling complex (DISC) by proteasome inhibitor pretreatment. Compared with 5-FU pretreatment, caspase-8 was more efficiently recruited to the DISC in MG132 pretreated cells despite the presence of fewer death receptors and more cFLIP in the DISC. But downregulation of cFLIP by short interference RNA (siRNA) further sensitized the HCC cell lines. In conclusion, these results show that otherwise chemotherapy-resistant tumor cells can be sensitized for TRAIL-induced apoptosis at the DISC level in the presence of high levels of cFLIP, which suggests the existence of an additional factor that modulates the interaction of FADD and the TRAIL death receptors. Of clinical relevance, proteasome inhibitors sensitize HCC cells but not primary human hepatocytes for TRAIL-induced apoptosis.     

Apoptosis induced by FasL and TRAIL/Apo2L in the pathogenesis of thyroid diseases.

FasL and TRAIL/Apo2L participate in cell-mediated cytotoxicity by inducing apoptosis in susceptible cells via respective cell surface receptors. Normal and neoplastic thyroid tissues are resistant to FasL-induced apoptosis but are sensitized by Th-1-type cytokines. In Hashimoto's thyroiditis, both FasL and its receptor, Fas, are strongly upregulated and their interaction leads to the suicidal/fratricidal death of thyrocytes. In Graves' disease, FasL expression in thyroid follicular cells is induced by thionamides and kills infiltrating lymphocytes. In this condition, Th-2-type cytokines upregulate the anti-apoptotic molecules FLIP and Bcl-x(L) and protect thyrocytes from apoptosis. FasL is expressed by neoplastic thyrocytes and induces apoptosis of infiltrating lymphocytes. TRAIL/Apo2L kills thyroid carcinoma cells but spares normal thyrocytes, thus providing a potential therapy for thyroid cancer.     

The role of apoptosis-inducing receptors of the tumor necrosis factor family in thyroid cancer

The tumor necrosis factor (TNF) family comprises several ligands, such as the prototype TNF-alpha, the Fas ligand (FasL) and TNF-related apoptosis-inducing ligand (TRAIL/Apo2L), which trigger apoptosis in susceptible cells by activating respective cell-surface receptors. The study of these cell death pathways has attracted significant attention in several fields, including that of thyroid cancer, because they participate in immune system function, as an arm of cell-mediated cytotoxicity, and because recombinant ligands are available for pharmacological use. TNF-alpha is a pluripotent cytokine that induces both pro-apoptotic and anti-apoptotic effects on thyroid carcinoma cells. FasL triggers apoptosis in other tumor types, but thyroid carcinoma cells are resistant to this effect. On the other hand, TRAIL potently and selectively kills thyroid carcinoma cells. Consequently, TRAIL is the only member of the family with significant anticancer activity and an acceptable toxicity profile to be used as a novel therapy for thyroid cancer. The caspase inhibitor FLIP plays a significant role in negatively regulating receptor-induced apoptosis. Thelper 1-type cytokines, such as interferon-gamma, TNF-alpha and interleukin-1beta increase the sensitivity of both normal and neoplastic thyrocytes to FasL and TRAIL. On the other hand, IGF-I and other growth/survival factors produced in the local tumor microenvironment activate the phosphatidylinositol 3-kinase/Akt kinase pathway and exert an anti-apoptotic effect by upregulating several apoptosis inhibitors, including FLIP. Pharmacological modulation of apoptosis induced by FasL and TRAIL/Apo2L holds promise of therapeutic applications in human malignancies.     

Expression of TNF-related apoptosis-inducing Ligand receptors and antitumor tumor effects of TNF-related apoptosis-inducing Ligand in human hepatocellular carcinoma

AIM: To investigate the expression of TNF-related apoptosis -inducing Ligand (TRAIL) receptors and antitumor effects of TRAIL in hepatocellular carcinoma (HCC). METHODS: Expression of TRAIL receptors was determined in 60 HCC tissues, 20 normal liver samples and two HCC cell lines (HepG2 and SMMC-7721). The effects of TRAIL on promoting apoptosis in HCC cell lines were analyzed after the cells were exposed to the recombinant TRAIL protein, as well as transfected with TRAIL-expression construct. In vivo effects of TRAIL on tumor growth were investigated by using nude mice HCC model of hepG2. RESULTS: Both death receptors were expressed in all HCC tissues and normal hepatic samples. In contrast, 54 HCC tissues did not express DcR1 and 25 did not express DcR2. But both DcR were detectable in all of the normal liver tissues. The expression patterns of DR and DcR in HCC samples (higher DR expression level and lower DcR expression level) were quite different from those in normal tissue. DR5, DR4, and DcR2 expressed in both cell lines, while no DcR1 expression was detected. Recombinant TRAIL alone was found to have a slight activity as it killed a maximum of 15 % of HCC cells within 24 h. Transfection of the TRAIL cDNA failed to induce extensive apoptosis in HCC lines. In vivo administration of TRAIL gene could not inhibit tumor growth in nude mice HCC model. However, chemotherapeutic agents or anticancer cytokines dramatically augmented TRAIL-induced apoptosis in HCC cell lines. CONCLUSION: Loss of DcR (especially DcR1) in HCC may contribute to antitumor effects of TRAIL to HCC.HCC is insensitive towards TRAIL-mediated apoptosis, suggesting that the presence of mediators can inhibit the TRAIL cell-death-inducing pathway in HCC. TRAIL and chemotherapeutic agents or anticancer cytokines combination may be a novel strategy for the treatment of HCC.     

Chemical sensitization and regulation of TRAIL-induced apoptosis in a panel of B-lymphocytic leukaemia cell lines

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) effectively kills tumour cells but not normal cells. We investigated TRAIL sensitivity and the TRAIL-induced apoptosis signalling pathway in a panel of B-lymphocytic leukaemia cell lines. Depending upon TRAIL sensitivity, leukaemia cells could be divided into three groups: highly sensitive, moderately sensitive and resistant. TRAIL receptor-2 (DR5) plays an important role in transducing apoptosis signals. DR5 was internalized into the cytoplasm where it recruited FAS-associated death domain protein (FADD) under TRAIL stimulation in both sensitive and resistant cells. However, the active form of caspase-8 was recruited to FADD and only sensitive cells showed increased caspase-8 activity upon TRAIL stimulation. The caspase-8 specific inhibitor, Z-IETD, impaired caspase-8 activation and completely abrogated TRAIL-induced apoptosis. These results suggest that TRAIL resistance in B-lymphocytic leukaemia cells is due to negative regulation at the level of caspase-8 activation and that caspase-8 activation is an indispensable process in TRAIL-induced apoptosis. However, FADD-like interleukin-1 beta-converting enzyme inhibitory protein (c-FLIPL) was similarly expressed and down-regulated after TRAIL stimulation in both sensitive and resistant cells. Interestingly, in some cell lines, TRAIL sensitivity and caspase-8 activity was enhanced or restored with the treatment of cycloheximide (CHX). In addition, X-linked inhibitor of apoptosis (XIAP) levels decreased significantly and rapidly following treatment with CHX. Down-regulation of XIAP may be responsible for enhancement or restoration of TRAIL sensitivity after CHX treatment in B-lymphocytic leukaemia cells.     

Proteasome inhibitors synergize with tumor necrosis factor-related apoptosis-induced ligand to induce anaplastic thyroid carcinoma cell death

CONTEXT: Anaplastic thyroid carcinoma (ATC) is one of the most aggressive types of cancer characterized by complete refractoriness to multimodal treatment approaches. Therapeutic strategies based on the simultaneous use of proteasome inhibitors and death receptor ligands have been shown to induce apoptosis in several tumor types but have not yet been explored in ATC. OBJECTIVE AND METHODS: The aim of this study was to investigate the ability of the proteasome inhibitor Bortezomib to induce apoptosis in ATC cell lines. Bortezomib was used as a single agent or in combination with TNF-related apoptosis-induced ligand (TRAIL), a member of the TNF family that selectively induces tumor cell apoptosis. The molecular effects of Bortezomib were investigated by analyzing the expression of key regulators of cell cycle and apoptosis and the activation of different apoptotic pathways. RESULTS: Bortezomib induced apoptosis in ATC cells at doses achieved in the clinical setting, differently from conventional chemotherapeutic agents. Simultaneous treatment with low doses of Bortezomib and TRAIL had a synergistic effect in inducing massive ATC cell apoptosis. Bortezomib increased the expression of cytotoxic TRAIL receptors, p21 (WAF/CIP1) and proapoptotic second mitochondria-derived activator of caspases/direct inhibitor of apoptosis binding protein with low pI, and reduced the expression of antiapoptotic mediators such as cellular Fas-associated death domain-like IL-1beta converting enzyme inhibitory protein, Bcl-2, Bcl-X(L), and inhibitor of apoptosis-1, thus resulting in cell death induction through the mitochondrial apoptotic pathway. CONCLUSIONS: The combination of proteasome inhibitors and TRAIL synergizes to induce the destruction of chemoresistant neoplastic thyrocytes and could represent a promising therapeutic strategy for the treatment of anaplastic thyroid carcinoma.     

Pancreatic adenocarcinoma cell lines show variable susceptibility to TRAIL-mediated cell death.

BACKGROUND AND AIMS: Programmed cell death via the Fas receptor/Fas Ligand and DR4, DR5/TRAIL plays a major role in tumor escape and elimination mechanisms. It also promises to be an effective therapy alternative for aggressive tumors, as has been recently shown for colon, breast, and lung cancer cells. We attempted to clarify the role of these molecules in aggressivity of pancreatic carcinomas and to identify possible pathways as targets for therapy. METHODS: Five pancreatic cell lines were investigated for the expression of FasL/Fas, DcR3, DR4, DR5/TRAIL, DcR1, DcR2, and other death pathways related molecules such as Bax, bcl-xL, bcl-2, FADD, and caspase-3 by flow cytometry, immunoblotting, and RT/PCR, both semiquantitative and real time (TaqMan). The susceptibility of these cell lines to apoptosis mediated by recombinant TRAIL was investigated. The effect of therapeutic agents (gemcitabine) on their susceptibility to TRAIL induced apoptosis was studied as well. RESULTS: Pancreatic adenocarcinomas expressed high levels of apoptosis-inducing receptors and ligands. They showed differential susceptibility to cell death induced by TRAIL, despite expressing intact receptors and signaling machineries. Treatment with commonly used therapeutic agents did not augment their susceptibility to apoptosis. This could be explained by the fact that they expressed differentially high levels of decoy receptors, as well as molecules known as inhibitors of apoptosis. CONCLUSIONS: The data suggest that pancreatic carcinoma cells have developed different mechanisms to evade the immune system. One is the expression of nonfunctional receptors, decoy receptors, and molecules that block cell death, such as bcl2 and bcl-xL. The second is the expression of apoptosis-inducing ligands, such as TRAIL, that could induce cell death of immune cells. The success in treating malignant tumors by recombinant TRAIL might apply to some but not all pancreatic tumors because of their differential resistance to TRAIL-induced cell death.