Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a variety of tumour cells through activation of TRAIL-R1 and TRAIL-R2 death signalling receptors. Here, we describe the characterisation and activity of HGS-ETR1, the first fully human, agonistic TRAIL-R1 mAb that is being developed as an antitumour therapeutic agent. HGS-ETR1 showed specific binding to TRAIL-R1 receptor. HGS-ETR1 reduced the viability of multiple types of tumour cells in vitro, and induced activation of caspase 8, Bid, caspase 9, caspase 3, and cleavage of PARP, indicating activation of TRAIL-R1 alone was sufficient to induce both extrinsic and intrinsic apoptotic pathways. Treatment of cell lines in vitro with HGS-ETR1 enhanced the cytotoxicity of chemotherapeutic agents (camptothecin, cisplatin, carboplatin, or 5-fluorouracil) even in tumour cell lines that were not sensitive to HGS-ETR1 alone. In vivo administration of HGS-ETR1 resulted in rapid tumour regression or repression of tumour growth in pre-established colon, non-small-cell lung, and renal tumours in xenograft models. Combination of HGS-ETR1 with chemotherapeutic agents (topotecan, 5-fluorouracil, and irinotecan) in three independent colon cancer xenograft models resulted in an enhanced antitumour efficacy compared to either agent alone. Pharmacokinetic studies in the mouse following intravenous injection showed that HGS-ETR1 serum concentrations were biphasic with a terminal half-life of 6.9–8.7 days and a steady-state volume of distribution of approximately 60 ml kg−1. Clearance was 3.6–5.7 ml−1 day−1 kg−1. These data suggest that HGS-ETR1 is a specific and potent antitumour agent with favourable pharmacokinetic characteristics and the potential to provide therapeutic benefit for a broad range of human malignancies.
TRAIL receptor 1; TRAIL; apoptosis; antibody; chemotherapeutic agents
TRAIL is considered as a promising anti-cancer agent, because of its ability to induce apoptosis in cancer but not in most normal cells. However, growing evidence exist that many cancer cells are resistant to its apoptotic effects. SCLC is a typical example of tumor entity where TRAIL monotherapy is not efficient.
We demonstrated that doxorubicin and etoposide markedly sensitized SCLC cells expressing caspase-8 to apoptotic effects of TRAIL. The drug-mediated sensitization of these cells was associated with increase of surface and total DR5 protein level, specific cleavage of cFLIPL, decrease of cFLIPS level, and a strong activation of caspase-8. The involvement of mitochondria-mediated pathway was demonstrated by enhanced Bid cleavage, Bax activation, and cytochrome c release. Activation of caspase-8 induced by combined treatment was shown to occur upstream of mitochondria and effector caspases.
Our results highlight significant applicability of doxorubicin and etoposide in sensitization of SCLC cells expressing caspase-8 to treatment with TRAIL.
Proteasome inhibitors can resensitize cells that are resistant to tumors necrosis factor-related apoptotic-inducing ligand (TRAIL)-mediated apoptosis. However, the underlying mechanisms of this effect are unclear. To characterize the mechanisms of interaction between proteasome inhibitors and TRAIL protein, we evaluated the effects of combined treatment with the proteasome inhibitors bortezomib and MG132 and TRAIL protein on two TRAIL-resistant human colon cancer cell lines, DLD1-TRAIL/R and LOVO-TRAIL/R. Both bortezomib and MG132 in combination with TRAIL enhanced apoptotosis induction in these cells, as evidenced by enhanced cleavage of caspases 8, 9, and 3, Bid, poly (ADP-ribose) polymerase and by the release of cytochrome C and Smac. Subsequent studies showed that combined treatment with bortezomib or MG132 resulted in an increase of death receptor (DR) 5 and Bik at protein levels but had no effects on protein levels of DR4, Bax, Bak, Bcl-2, Bcl-XL, or Flice-inhibitory protein (FLIP). Moreover, c-Jun N-terminal kinase (JNK) is activated by these proteasome inhibitors. Blocking JNK activation with the JNK inhibitor SP600125 attenuated DR5 increase, but enhancement of apoptosis induction and increase of Bik protein were not affected. However, bortezomib-mediated TRAIL sensitization was partially blocked by using siRNA to knockdown Bik. Thus, our data suggests that accumulation of Bik may be critical for proteasome inhibitor-mediated re-sensitization of TRAIL.
Proteasome inhibitor; bortezomib; PS-341; tumor necrosis factor-related apoptotic-inducing ligand (TRAIL); resistance; death receptor 5; Bik
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is currently being investigated as a therapeutic agent for a variety of malignancies, as it triggers apoptosis specifically in transformed cells. However, TRAIL use as a stand alone therapeutic is hampered by the fact that many primary tumor cells are resistant to TRAIL-mediated apoptosis. Here, we investigated the extent to which pretreatment of TRAIL-resistant primary B-cell chronic lymphocytic leukemia (B-CLL) cells with histone deacetylase inhibitors (HDACis) could render them susceptible to killing by TRAIL. We found that HDAC inhibition in B-CLL cells led to increased TRAIL receptor expression, increased caspase activation, decreased expression of antiapoptotic regulators such as Bcl-2, and ultimately, enhanced TRAIL-induced apoptosis. Importantly, untransformed peripheral blood mononuclear cells remained largely resistant to TRAIL, even in the presence of HDACis. These results suggest that combination therapies using HDAC inhibition and TRAIL could prove beneficial for the treatment of B-CLL.
Chemotherapeutic genotoxins induce apoptosis in epithelial-cell-derived cancer cells. The death receptor ligand TRAIL also induces apoptosis in epithelial-cell-derived cancer cells but generally fails to induce apoptosis in nontransformed cells. We show here that the treatment of four different epithelial cell lines with the topoisomerase II inhibitor etoposide in combination with TRAIL (tumor necrosis factor [TNF]-related apoptosis-inducing ligand) induces a synergistic apoptotic response. The mechanism of the synergistic effect results from the etoposide-mediated increase in the expression of the death receptors 4 (DR4) and 5 (DR5). Inhibition of NF-κB activation by expression of kinase-inactive MEK kinase 1(MEKK1) or dominant-negative IκB (ΔIκB) blocked the increase in DR4 and DR5 expression following etoposide treatment. Addition of a soluble decoy DR4 fusion protein (DR4:Fc) to cell cultures reduced the amount of etoposide-induced apoptosis in a dose-dependent manner. The addition of a soluble TNF decoy receptor (TNFR:Fc) was without effect, demonstrating the specificity of DR4 binding ligands in the etoposide-induced apoptosis response. Thus, genotoxin treatment in combination with TRAIL is an effective inducer of epithelial-cell-derived tumor cell apoptosis relative to either treatment alone.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent with cancer-selective apoptogenic activity. It evokes the canonical caspase-mediated cell death pathway through death-inducing signaling complex (DISC) formation. We identified that Peroxiredoxin 6 (Prx6) interacts with caspase-10 and caspase-8 via the death effector domain (DED). Prx6 suppresses TRAIL-mediated cell death in human cancer cells, but not that induced by intrinsic apoptosis inducers such as etoposide, staurosporine, or A23187. Among Prx1–6 members, only Prx6 binds to DED caspases and is most effective in suppressing TRAIL or DED caspase-induced cell death. The antiapoptotic activity of Prx6 against TRAIL is not likely associated with its peroxidase activity but is associated with its ability to bind to DED caspases. Increased expression of Prx6 enhances the binding of Prx6 to caspase-10 but reduces TRAIL-induced DISC formation and subsequently caspase activation. Interestingly, Prx6 is highly upregulated in metastatic gastric cancer cells, which are relatively resistant to TRAIL as compared with primary cancer cells. Downregulation of Prx6 sensitizes the metastatic cancer cells to TRAIL-induced cell death. Taken together, these results suggest that Prx6 modulates TRAIL signaling as a negative regulator of caspase-8 and caspase-10 in DISC formation of TRAIL-resistant metastatic cancer cells.
peroxiredoxin 6; caspase-10; caspase-8; TRAIL; DISC; metastasis suppressor
The cysteine protease caspase-8 is an essential executioner of the death receptor (DR) apoptotic pathway. The physiological function of its homologue caspase-10 remains poorly understood, and the ability of caspase-10 to substitute for caspase-8 in the DR apoptotic pathway is still controversial. Here, we analysed the particular contribution of caspase-10 isoforms to DR-mediated apoptosis in neuroblastoma (NB) cells characterised by their resistance to DR signalling. Silencing of caspase-8 in tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-sensitive NB cells resulted in complete resistance to TRAIL, which could be reverted by overexpression of caspase-10A or -10D. Overexpression experiments in various caspase-8-expressing tumour cells also demonstrated that caspase-10A and -10D isoforms strongly increased TRAIL and FasL sensitivity, whereas caspase-10B or -10G had no effect or were weakly anti-apoptotic. Further investigations revealed that the unique C-terminal end of caspase-10B was responsible for its degradation by the ubiquitin–proteasome pathway and for its lack of pro-apoptotic activity compared with caspase-10A and -10D. These data highlight in several tumour cell types, a differential pro- or anti-apoptotic role for the distinct caspase-10 isoforms in DR signalling, which may be relevant for fine tuning of apoptosis initiation.
caspase-10; caspase-8; apoptosis; TRAIL; neuroblastoma
Most neuroblastoma cell lines do not express apical caspases 8 and 10, which play a key role in mediating tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) cytotoxicity in a variety of malignant cell types. In this study, we demonstrated that TRAIL induced a moderate but significant increase of apoptosis in the caspase 8/10-deficient SK-N-SH neuroblastoma cell line, through activation of a novel caspase 9/7 pathway. Concomitant to the induction of apoptosis, TRAIL also promoted a significant increase of prostaglandin E2 (PGE2) release by SK-N-SH cells. Moreover, coadministration of TRAIL plus indomethacin, a pharmacological inhibitor of cyclooxygenase (COX), showed an additive effect on SK-N-SH cell death. In spite of the ability of TRAIL to promote the phosphorylation of both ERK1/2 and p38/MAPK, which have been involved in the control of COX expression/activity, neither PD98059 nor SB203580, pharmacological inhibitors of the ERK1/2 and p38/MAPK pathways, respectively, affected either PGE2 production or apoptosis induced by TRAIL. Finally, both induction of apoptosis and PGE2 release were completely abrogated by the broad caspase inhibitor z-VAD-fmk, suggesting that both biologic end points were regulated in SK-N-SH cells through a caspase 9/7-dependent pathway.
TRAIL; cell death; caspases; neuroblastoma; prostanoids
Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily of cytokines, is one of the most promising candidates for cancer therapeutics. However, many osteosarcomas are resistant to TRAIL. Bisphosphonates are very effective in the treatment of bone problems associated with malignancies; the antitumor effects are due to the inhibition of protein prenylation that is essential for cell function and survival. The purpose of this study was to determine the effects of bisphosphonates on TRAIL-resistant MG 63 human osteosarcoma cells. The cells showed no response to TRAIL alone; however, pre-treatment with bisphosphonates significantly increased TRAIL-mediated apoptosis and cellular activation of caspase-3. Bisphosphonates significantly induced mRNA and protein expression of the TRAIL receptor, DR5. Bisphosphonates induced protein unprenylation in MG 63 cells; in addition, co-treatment with TRAIL also significantly increased protein unprenylation. Blocking of protein unprenylation using geranylgeraniol attenuated the cellular responses, including cell apoptosis and protein unprenylation induced by bisphosphonates and TRAIL. This is the first study to demonstrate that bisphosphonates markedly enhanced TRAIL-induced apoptosis in human osteosarcoma cells. These findings suggest that bisphosphonates may be a new and effective anticancer treatment with TRAIL proteins for TRAIL-resistant cancer cells.
apoptosis; diphosphonates; protein prenylation; receptors, TNF-related apoptosis-inducing ligand; TNF-Related apoptosis-inducing ligand
Members of the tumor necrosis factor (TNF) receptor superfamily and their activating ligands transmit apoptotic signals in a variety of systems. We now show that the binding of TNF-related, apoptosis-inducing ligand (TRAIL) to its cellular receptors DR5 (TRAILR2) and DR4 (TRAILR1) mediates reovirus-induced apoptosis. Anti-TRAIL antibody and soluble TRAIL receptors block reovirus-induced apoptosis by preventing TRAIL-receptor binding. In addition, reovirus induces both TRAIL release and an increase in the expression of DR5 and DR4 in infected cells. Reovirus-induced apoptosis is also blocked following inhibition of the death receptor-associated, apoptosis-inducing molecules FADD (for FAS-associated death domain) and caspase 8. We propose that reovirus infection promotes apoptosis via the expression of DR5 and the release of TRAIL from infected cells. Virus-induced regulation of the TRAIL apoptotic pathway defines a novel mechanism for virus-induced apoptosis.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is regarded as a promising candidate for anticancer therapy due to its selective toxicity to cancer cells. Nevertheless, because of TRAIL resistance in some cancer cells, combined treatment with sensitizing agents is required to enhance the anticancer potential of TRAIL. In this study, we investigated the underlying mechanism of apigenin-induced sensitization of HepG2 cells to TRAIL-induced cell death. Synergistic induction of apoptosis by combination was confirmed by examining the typical morphology changes of apoptosis, PARP-cleavage, and activation of effector caspases. Z-VAD-fmk, a pan-caspase inhibitor, inhibited the enhanced cell death by combined treatment of apigenin and TRAIL, demonstrating that a caspase-dependent pathway is involved in apigenin/TRAIL-mediated apoptosis. In addition, we found that apigenin/TRAIL co-treatment up-regulates DR5 cell surface expression. The synergistic induction of cell death by the apigenin/TRAIL combination was significantly attenuated by DR5 blocking chimera antibody. Next, using pharmacological inhibitors, we found that ERK activation is involved in the induction of DR5 expression. Inhibition of ERK1/2 by U0126 significantly decreased the apigenin/TRAIL-induced DR5 expression and apoptosis. Taken together, our results indicate that apigenin can enhance the apoptotic effect of TRAIL via ERK-induced up-regulation of DR5.
apigenin; apoptosis; DR5; ERK; HepG2; TRAIL
TNF-related apoptosis-inducing ligand (TRAIL) is a potential anticancer agent due to its selectivity in killing transformed cells. However, TRAIL can also stimulate TRAIL-resistant cancer cells’ proliferation and metastasis. Thus, acquired TRAIL resistance during TRAIL therapy would shift the patient’s treatment from beneficial to detrimental. In this study we focused on the acquired TRAIL resistance mechanism and demonstrated that the elevated expression of the anti-apoptotic factor cellular FLICE-like inhibitory protein (c-FLIP) and the pro-survival Bcl-2 family member myeloid cell leukemia 1 (Mcl-1) underlie the main mechanism of this type of TRAIL resistance in lung cancer cells. Chronic exposure to TRAIL resulted in lung cancer cell resistance to TRAIL-induced cytotoxicity, and this resistance was associated with the increase in the cellular levels of c-FLIP L and Mcl-1L. Overexpresssion of c-FLIPL suppressed recruitment of caspase-8 to the death-inducing signaling complex (DISC) while increased Mcl-1L expression blunted the mitochondrial apoptosis pathway. The elevation of c-FLIP L and Mcl-1L expression was due to Akt-mediated stabilization of these proteins in TRAIL-resistant cells. Importantly, suppressing c-FLIPL and Mcl-1L expression by RNA interference collectively alleviated acquired TRAIL resistance. Taken together, these results identify c-FLIPL and Mcl-1L as the major determinants of acquired TRAIL resistance and could be molecular targets for improving TRAIL’s therapeutic value against lung cancer.
TRAIL; c-FLIP; Mcl-1; Akt; apoptosis; lung cancer
Lyssaviruses, which are members of the Rhabdoviridae family, induce apoptosis, which plays an important role in the neuropathogenesis of rabies. However, the mechanisms by which these viruses mediate neuronal apoptosis have not been elucidated. Here we demonstrate that the early induction of apoptosis in a model of lyssavirus-infected neuroblastoma cells involves a TRAIL-dependent pathway requiring the activation of caspase-8 but not of caspase-9 or caspase-10. The activation of caspase-8 results in the activation of caspase-3 and caspase-6, as shown by an increase in the cleavage of the specific caspase substrate in lyssavirus-infected cells. However, neither caspase-1 nor caspase-2 activity was detected during the early phase of infection. Lyssavirus-mediated cell death involves an interaction between TRAIL receptors and TRAIL, as demonstrated by experiments using neutralizing antibodies and soluble decoy TRAIL-R1/R2 receptors. We also demonstrated that the decapsidation and replication of lyssavirus are essential for inducing apoptosis, as supported by UV inactivation, cycloheximide treatment, and the use of bafilomycin A1 to inhibit endosomal acidification. Transfection of cells with the matrix protein induced apoptosis using pathways similar to those described in the context of viral infection. Furthermore, our data suggest that the matrix protein of lyssaviruses plays a major role in the early induction of TRAIL-mediated apoptosis by the release of a soluble, active form of TRAIL. In our model, Fas ligand (CD95L) appears to play a limited role in lyssavirus-mediated neuroblastoma cell death. Similarly, tumor necrosis factor alpha does not appear to play an important role.
TNF-related apoptosis-inducing ligand (TRAIL) is a promising cytokine for killing tumor cells. However, a number of studies have demonstrated that different cancer cells resist TRAIL treatment and, moreover, TRAIL can promote invasion and metastasis in resistant cells. Here we report that TRAIL rapidly activates caspase-8 in a panel of non-small-cell lung carcinomas (NSCLCs). Adenocarcinomas derived from the lung in addition to high caspase-8 expression are characterized by increased expression of DR4 compared with adjacent non-neoplastic tissues. Blocking DR4 or lowering caspase-8 expression significantly reduced apoptosis in NSCLC cell lines, indicating the importance of DR4 and signifying that higher levels of caspase-8 in lung adenocarcinomas make them more susceptible to TRAIL treatment. Despite rapid and robust initial responsiveness to TRAIL, surviving cells quickly acquired resistance to the additional TRAIL treatment. The expression of cellular-FLIP-short (c-FLIPS) was significantly increased in surviving cells. Such upregulation of c-FLIPS was rapidly reduced and TRAIL sensitivity was restored by treatment with cycloheximide. Silencing of c-FLIPS, but not c-FLIP-long (c-FLIPL), resulted in a remarkable increase in apoptosis and significant reduction of clonogenic survival. Furthermore, chelation of intracellular Ca2+ or inhibition of calmodulin caused a rapid proteasomal degradation of c-FLIPS, a significant increase of the two-step processing of procaspase-8, and reduced clonogenicity in response to TRAIL. Thus, our results revealed that the upregulation of DR4 and caspase-8 expression in NSCLC cells make them more susceptible to TRAIL. However, these cells could survive TRAIL treatment via upregulation of c-FLIPS, and it is suggested that blocking c-FLIPS expression by inhibition of Ca2+/calmodulin signaling significantly overcomes the acquired resistance of NSCLC cells to TRAIL.
TRAIL; DR4; c-FLIPS; calcium; calmodulin; lung adenocarcinoma
The majority of leukaemic cells are resistant to apoptosis induced by tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Here, we show that sublethal concentrations of arsenic trioxide (ATO) specifically enhanced TRAIL-induced apoptosis in leukaemic but not in other tumour cell lines. The combination of ATO and TRAIL synergistically enhanced cleavage of caspase-8, which was blocked by the caspase inhibitor IETD.fmk as well as in cells deficient for caspase-8, suggesting a requirement for the death-inducing signalling complex. Arsenic trioxide led to increased cell surface expression of DR5 (death receptor 5), inhibition of the serine/threonine kinase Akt and downregulation of the short isoform of FLIP (FLICE-inhibitory protein, FLIPS). Inhibition of the phosphatidylinositol 3 kinase (PI3K) was equally efficient in sensitising leukaemic cells to TRAIL with similar effects on DR5 and FLIPS expression, suggesting that ATO may in part act through inhibition of the PI3K/Akt signalling pathway. These results indicate that the enhancement in TRAIL-mediated apoptosis induced by ATO is due to alteration in the levels of multiple components and regulators of the death receptor-mediated pathway. These findings offer a promising and novel strategy involving a combination of TRAIL and ATO, or more specific Akt inhibitors in the treatment of various haematopoietic malignancies.
arsenic trioxide; TRAIL; Akt; leukaemia; DR5; FLIP
Mesenchymal stem cells (MSC) are emerging as novel cell-based delivery agents; however, a thorough investigation addressing their therapeutic potential in medulloblastomas (MB) has not been explored to date. In this study, we engineered human MSC to express a potent and secretable variant of a tumor specific agent, tumor necrosis factor-apoptosis-inducing ligand (S-TRAIL) and assessed the ability of MSC-S-TRAIL mediated MB killing alone or in combination with a small molecule inhibitor of histone-deacetylase, MS-275, in TRAIL-sensitive and -resistant MB in vitro and in vivo. We show that TRAIL sensitivity/resistance correlates with the expression of its cognate death receptor (DR)5 and MSC-S-TRAIL induces caspase-3 mediated apoptosis in TRAIL-sensitive MB lines. In TRAIL-resistant MB, we show upregulation of DR4/5 levels when pre-treated with MS-275 and a subsequent sensitization to MSC-S-TRAIL mediated apoptosis. Using intracranially implanted MB and MSC lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that MSC-S-TRAIL has significant anti-tumor effects in mice bearing TRAIL-sensitive and MS-275 pre-treated TRAIL-resistant MBs. To our knowledge, this is the first study that explores the use of human MSC as MB-targeting therapeutic-vehicles in vivo in TRAIL-sensitive and resistant tumors, and has implications for developing effective therapies for patients with medulloblastomas.
Although signaling by death receptors involves the recruitment of common components into their death-inducing signaling complexes (DISCs), apoptosis susceptibility of various tumor cells to each individual receptor differs quite dramatically. Recently it was shown that, besides caspase-8, caspase-10 is also recruited to the DISCs, but its function in death receptor signaling remains unknown. Here we show that expression of caspase-10 sensitizes MCF-7 breast carcinoma cells to TRAIL- but not tumor necrosis factor (TNF)-induced apoptosis. This sensitization is most obvious at low TRAIL concentrations or when apoptosis is assessed at early time points. Caspase-10-mediated sensitization for TRAIL-induced apoptosis appears to be dependent on caspase-3, as expression of caspase-10 in MCF-7/casp-3 cells but not in caspase-3-deficient MCF-7 cells overcomes TRAIL resistance. Interestingly, neutralization of TRAIL receptor 2 (TRAIL-R2), but not TRAIL-R1, impaired apoptosis in a caspase-10-dependent manner, indicating that caspase-10 enhances TRAIL-R2-induced cell death. Furthermore, whereas processing of caspase-10 was delayed in TNF-treated cells, TRAIL triggered a very rapid activation of caspase-10 and -3. Therefore, we propose a model in which caspase-10 is a crucial component during TRAIL-mediated apoptosis that in addition actively requires caspase-3. This might be especially important in systems where only low TRAIL concentrations are supplied that are not sufficient for the fast recruitment of caspase-8 to the DISC.
Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumour necrosis factor cytokine family that induces apoptosis upon binding to its death domain containing receptors, TRAIL receptor 1 (DR4) and TRAIL receptor 2 (DR5). Expression of TRAIL receptors is higher in colorectal carcinoma (CRC) as compared to normal colorectal mucosa and targeted therapy with TRAIL leads to preferential killing of tumor cells sparing normal cells.
We investigated the expression of TRAIL and its receptors in a tissue microarray cohort of 448 Middle Eastern CRC. We also studied the correlation between TRAIL receptors and various clinico-pathological features including key molecular alterations and overall survival.
CRC subset with TRAIL-R1 expression was associated with a less aggressive phenotype characterized by early stage (p = 0.0251) and a histology subtype of adenocarcinomas (p = 0.0355). Similarly CRC subset with TRAIL-R2 expression was associated with a well-differentiated tumors (p < 0.0001), histology subtype of adenocarcinomas (p = 0.0010) and tumors in left colon (p = 0.0009). Over expression of pro apoptotic markers: p27KIP1 and KRAS4A isoforms was significantly higher in CRC subset with TRAIL-R1 and TRAIL-R2 expression; TRAIL-R1 expression was also associated with cleaved caspase-3(p = 0.0011). Interestingly, TRAIL-R2 expression was associated with a microsatellite stable (MS--S/L) phenotype (p = 0.0003) and with absence of KRAS mutations (p = 0.0481).
TRAIL-R1 expression was an independent prognostic marker for better survival in all CRC samples and even in the CRC group that received adjuvant therapy. The biological effects of TRAIL in CRC models, its enhancement of chemosensitivity towards standard chemotherapeutic agents and the effect of endogenous TRAIL receptor levels on survival make TRAIL an extremely attractive therapeutic target.
Epithelial ovarian cancer (EOC) cells often show increased activity of the PI3K/Akt pathway. In addition, we have previously shown that EOC ascites induce Akt activation in the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-sensitive EOC cell line, CaOV3, leading to TRAIL-mediated apoptosis inhibition. In this study, we investigated the role of Akt in intrinsic resistance to TRAIL, which is common in EOC cells. We report that Akt activation reduces the sensitivity of EOC cells to TRAIL. TRAIL-resistant SKOV3ip1 and COV2 cells were sensitized to TRAIL-induced apoptosis by PI3K or Akt inhibitors although inhibition of PI3K/Akt signaling pathway did not interfere with the recruitment and processing of caspase-8 to the death-inducing signaling complex. Conversely, overexpression of Akt1 in TRAIL-sensitive cells promoted resistance to TRAIL. Although the fact that TRAIL-induced caspase-8 activation was observed in both sensitive and resistant cell lines, Bid cleavage occurred only in sensitive cells or in SKOV3ip1 cells treated with LY294002. Bid expression was low in resistant cells and Akt activation downregulated its expression. Depletion of Bid by siRNA in OVCAR3 cells was associated with a decrease in TRAIL-mediated apoptosis. Overexpression of Bid only in SKOV3ip1 cells enhanced TRAIL-induced apoptosis. Simultaneous blockade of Akt pathway further increased TRAIL-induced apoptosis. Thus, Akt acts upstream of mitochondria and inhibits TRAIL-induced apoptosis by decreasing Bid protein levels and possibly inhibiting its cleavage.
death receptors; ovarian carcinoma; resistance; PI3K/Akt pathway; TRAIL; Bid
An imbalance between proliferation and apoptosis is one of the main features of carcinogenesis. TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis upon binding to the TRAIL death receptors, TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2, whereas binding to TRAIL-R3 and TRAIL-R4 might promote cell survival and proliferation. The anti-tumor activity of TRAIL-R1 and TRAIL-R2 agonists is currently investigated in clinical trials. To gain further insight into the regulation of apoptosis in hepatocellular carcinoma (HCC), we investigated the TRAIL pathway and the regulators of apoptosis caspase-8, Bcl-xL and Mcl-1 in patients with HCC regarding patient survival.
We analyzed 157 hepatocellular carcinoma patients who underwent partial liver resection or orthotopic liver transplantation and healthy control liver tissue using immunohistochemistry on tissue microarrays for the expression of TRAIL-R1 to TRAIL-R4, caspase-8, Bcl-xL and Mcl-1. Immunohistochemical data were evaluated for potential associations with clinico-pathological parameters and survival.
Whereas TRAIL-R1 was downregulated in HCC in comparison to normal liver tissue, TRAIL-R2 and –R4 were upregulated in HCC, especially in G2 and G3 tumors. TRAIL-R1 downregulation and upregulation of TRAIL-R2 and TRAIL-R4 correlated with tumor dedifferentiation (G2/G3). TRAIL-R3, Bcl-xL and Mcl-1 showed no differential expression in tumor tissue compared to normal tissue. The expression levels of TRAIL receptors did not correlate with patient survival after partial hepatectomy. Interestingly, in tumor tissue, but not in normal hepatocytes, caspase-8 showed a strong nuclear staining. Low cytosolic and high nuclear staining intensity of caspase-8 significantly correlated with impaired survival after partial hepatectomy, which, for cytosolic caspase-8, was independent from tumor grade.
Assessment of TRAIL-receptor expression patterns may have therapeutic implications for the use of TRAIL receptor agonists in HCC therapy. Tumor-specific nuclear localisation of caspase-8 in HCC suggests an apoptosis-independent function of caspase-8 and correlates with patient survival.
HCC; Apoptosis; TRAIL receptors; Nuclear caspase-8
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively kill tumor cells and, in combination with other agents, could enhance tumor therapy. We explored the combined therapeutic effects of a secretable form of (S) TRAIL-induced apoptosis and the downregulation of Bcl-2 in human gliomas. We constructed a lentiviral delivery system: 1) for the expression of short hairpin (sh) RNA to downregulate Bcl-2 and for the expression of S-TRAIL to induce apoptosis in glioma cells; and 2) to follow delivery in vitro and the fate of tumors in real time in vivo. We demonstrate that lentiviral-mediated simultaneous downregulation of Bcl-2 and S-TRAIL-induced apoptosis leads to an increased expression of activated caspase-3 and caspase-7, thus resulting in accelerated S-TRAIL-mediated apoptosis in glioma cells in vitro. Using a highly malignant human glioma model expressing EGFRvIII and firefly luciferase, we show that the combined effect of Bcl-2 downregulation and S-TRAIL-induced apoptosis results in complete eradication of gliomas compared to S-TRAIL monotherapy. These results show that simultaneous triggering of TRAIL-mediated death receptor pathway and downregulation of Bcl-2 by shRNA leads to enhanced eradication of gliomas and serves as a template in developing and monitoring combination therapies for the treatment of drug-resistant cancers.
Apoptosis; S-TRAIL; Bcl-2; gliomas; imaging
Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive human cancers, and novel treatment modalities are required. We investigated the therapeutic potential of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) in combination with the proteasome inhibitor bortezomib (Velcade) on human ESCC cell lines. Bortezomib enhanced the susceptibility to TRAIL in 12 of the 15 ESCC cell lines tested, even though most showed low sensitivity to TRAIL as a single agent. The enhancement of TRAIL-induced apoptosis by bortezomib was caspase-dependent. Increased processing of caspase-8 often accompanied enhancement of TRAIL-induced apoptosis by bortezomib. However, the increased cell surface expression of death receptors observed upon bortezomib treatment did not seem to be crucial for this effect. For some ESCC, bortezomib treatment resulted in a more efficient recruitment of caspase-8 and the Fas-associated death domain (FADD) to the death-inducing signaling complex (DISC). Additional downregulation of the cellular FLICE-inhibitory protein long isoform (c-FLIP(L)) could cooperate in the activation of the extrinsic pathway in some cases. For other ESCC, the crucial effect of bortezomib treatment appeared to be increased signaling via the intrinsic apoptotic pathway on subsequent exposure to TRAIL. Thus bortezomib could sensitize ESCC to TRAIL apoptosis by multiple molecular mechanisms of action. Therefore the combination of bortezomib and TRAIL might be a novel therapeutic strategy for ESCC patients who fail to respond to standard chemoradiotherapy that predominantly targets the mitochondrial apoptotic pathway.
apoptosis; esophageal cancer; proteasome inhibitor; TRAIL/Apo2L
Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that induces cancer cell death by apoptosis with some selectivity. TRAIL-induced apoptosis is mediated by the transmembrane receptors death receptor 4 (DR4) (also known as TRAIL-R1) and DR5 (TRAIL-R2). TRAIL can also bind decoy receptor 1 (DcR1) (TRAIL-R3) and DcR2 (TRAIL-R4) that fail to induce apoptosis since they lack and have a truncated cytoplasmic death domain, respectively. In addition, DcR1 and DcR2 inhibit DR4- and DR5-mediated, TRAIL-induced apoptosis and we demonstrate here that this occurs through distinct mechanisms. While DcR1 prevents the assembly of the death-inducing signaling complex (DISC) by titrating TRAIL within lipid rafts, DcR2 is corecruited with DR5 within the DISC, where it inhibits initiator caspase activation. In addition, DcR2 prevents DR4 recruitment within the DR5 DISC. The specificity of DcR1- and DcR2-mediated TRAIL inhibition reveals an additional level of complexity for the regulation of TRAIL signaling.
Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells while sparing normal cells. However, many cancer cells are resistant to TRAIL-induced cell death. Here, we report that paxilline, an indole alkaloid from Penicillium paxilli, can sensitize various glioma cells to TRAIL-mediated apoptosis. While treatment with TRAIL alone caused partial processing of caspase-3 to its p20 intermediate in TRAIL-resistant glioma cell lines, co-treatment with TRAIL and subtoxic doses of paxilline caused complete processing of caspase-3 into its active subunits. Paxilline treatment markedly upregulated DR5, a receptor of TRAIL, through a CHOP/GADD153-mediated process. In addition, paxilline treatment markedly downregulated the protein levels of the short form of the cellular FLICE-inhibitory protein (c-FLIPS) and the caspase inhibitor, survivin, through proteasome-mediated degradation. Taken together, these results show that paxilline effectively sensitizes glioma cells to TRAIL-mediated apoptosis by modulating multiple components of the death receptor-mediated apoptotic pathway. Interestingly, paxilline/TRAIL co-treatment did not induce apoptosis in normal astrocytes, nor did it affect the protein levels of CHOP, DR5 or survivin in these cells. Thus, combined treatment regimens involving paxilline and TRAIL may offer an attractive strategy for safely treating resistant gliomas.
apoptosis; astrocytes; glioma; paxilline; TNF-related apoptosis-inducing ligand
In this study, we examined the role of protein kinase C (PKC)-ɛ in the apoptosis and survival of glioma cells using tumor necrosis factor–related apoptosis inducing ligand (TRAIL)- stimulated cells and silencing of PKCɛ expression. Treatment of glioma cells with TRAIL induced activation, caspase-dependent cleavage, and down-regulation of PKCɛ within 3 to 5 hours of treatment. Overexpression of PKCɛ inhibited the apoptosis induced by TRAIL, acting downstream of caspase 8 and upstream of Bid cleavage and cytochrome c release from the mitochondria. A caspase-resistant PKCɛ mutant (D383A) was more protective than PKCɛ, suggesting that both the cleavage of PKCɛ and its down-regulation contributed to the apoptotic effect of TRAIL. To further study the role of PKCɛ in glioma cell apoptosis, we employed short interfering RNAs directed against the mRNA of PKCɛ and found that silencing of PKCɛ expression induced apoptosis of various glioma cell lines and primary glioma cultures. To delineate the molecular mechanisms involved in the apoptosis induced by silencing of PKCɛ, we examined the expression and phosphorylation of various apoptosis-related proteins. We found that knockdown of PKCɛ did not affect the expression of Bcl2 and Bax or the phosphorylation and expression of Erk1/2, c-Jun-NH2-kinase, p38, or STAT, whereas it selectively reduced the expression of AKT. Similarly, TRAIL reduced the expression of AKT in glioma cells and this decrease was abolished in cells overexpressing PKCɛ. Our results suggest that the cleavage of PKCɛ and its down-regulation play important roles in the apoptotic effect of TRAIL. Moreover, PKCɛ regulates AKT expression and is essential for the survival of glioma cells.