Transformation by oncogenic RAS sensitizes human colon cells to TRAIL-induced apoptosis by up-regulating death receptor 4 and death receptor 5 through a MEK-dependent pathway

RAS oncogenes play a major role in cancer development by activating an array of signaling pathways, most notably mitogen-activated protein kinases, resulting in aberrant proliferation and inhibition of apoptotic signaling cascades, rendering transformed cells resistant to extrinsic death stimuli. However, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is able to kill specific tumor cells through the engagement of its receptors, death receptor 4 (DR4) and death receptor 5 (DR5), and the activation of apoptotic pathways, providing promising targets for anticancer therapies. In this study, we show that TRAIL induces cell death in human colon adenocarcinoma cells in a MEK-dependent manner. We also report a prolonged MEK-dependent activation of ERK1/2 and increased c-FOS expression induced by TRAIL in this system. Our study reveals that transformation of the colon cell line Caco-2 by Ki- and mainly by Ha-ras oncogenes sensitizes these cells to TRAIL-induced apoptosis by causing specific MEK-dependent up-regulation of DR4 and DR5. These observations taken together reveal that RAS-MEK-ERK1/2 signaling pathway can sensitize cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 and overall imply that TRAIL-based therapeutic strategies using TRAIL agonists could be used in cases of human colon cancers bearing RAS mutations.     

Rapid and efficient cancer cell killing mediated by high-affinity death receptor homotrimerizing TRAIL variants

The tumour necrosis factor family member TNF-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in a variety of cancer cells through the activation of death receptors 4 (DR4) and 5 (DR5) and is considered a promising anticancer therapeutic agent. As apoptosis seems to occur primarily via only one of the two death receptors in many cancer cells, the introduction of DR selectivity is thought to create more potent TRAIL agonists with superior therapeutic properties. By use of a computer-aided structure-based design followed by rational combination of mutations, we obtained variants that signal exclusively via DR4. Besides an enhanced selectivity, these TRAIL-DR4 agonists show superior affinity to DR4, and a high apoptosis-inducing activity against several TRAIL-sensitive and -resistant cancer cell lines in vitro. Intriguingly, combined treatment of the DR4-selective variant and a DR5-selective TRAIL variant in cancer cell lines signalling by both death receptors leads to a significant increase in activity when compared with wild-type rhTRAIL or each single rhTRAIL variant. Our results suggest that TRAIL induced apoptosis via high-affinity and rapid-selective homotrimerization of each DR represent an important step towards an efficient cancer treatment.     

Sub-toxic dose of apigenin sensitizes HepG2 cells to TRAIL through ERK-dependent up-regulation of TRAIL receptor DR5

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.     

TRAIL apoptosis is enhanced by quercetin through Akt dephosphorylation

TNF-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapy that preferentially induces apoptosis in cancer cells. However, many neoplasms are resistant to TRAIL by mechanisms that are poorly understood. Here we demonstrated that human prostate cancer cells, but not normal prostate cells, are dramatically sensitized to TRAIL-induced apoptosis and caspase activation by quercetin. Quercetin, a ubiquitous bioactive plant flavonoid, has been shown to inhibit the proliferation of cancer cells. We have shown that quercetin can potentiate TRAIL-induced apoptotic death. Human prostate adenocarcinoma DU-145 and LNCaP cells were treated with various concentrations of TRAIL (10-200 ng/ml) and/or quercetin (10-200 microM) for 4 h. Quercetin, which caused no cytotoxicity by itself, promoted TRAIL-induced apoptosis. The TRAIL-mediated activation of caspase, and PARP (poly(ADP-ribose) polymerase) cleavage were both enhanced by quercetin. Western blot analysis showed that combined treatment with TRAIL and quercetin did not change the levels of TRAIL receptors (death receptors DR4 and DR5, and DcR2 (decoy receptor 2)) or anti-apoptotic proteins (FLICE-inhibitory protein (FLIP), inhibitor of apoptosis (IAP), and Bcl-2). However, quercetin promoted the dephosphorylation of Akt. Quercetin-induced potent inhibition of Akt phosphorylation. Taken together, the present studies suggest that quercetin enhances TRAIL-induced cytotoxicity by activating caspases and inhibiting phosphorylation of Akt.     

Myc Tagging along the TRAIL to Death Receptor 5

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL; also known as Apo2L) is an apoptotic cytokine that is being developed as a novel anticancer agent. TRAIL mediates its effect via death receptors 4 (DR4) and DR5 and appears to selectively induce apoptosis in cancer cells. The molecular basis of why normal cells seem to better tolerate this novel cytokine remains unknown. Recently, it has been reported that Myc oncoprotein by upregulating DR5 appears to augment cellular susceptibility to TRAIL and to DR5 agonistic antibodies. Several previous studies have already established that various clinically relevant agents by upregulating DR5 sensitize cells to TRAIL. However, the finding that DR5 is upregulated by an oncoprotein that is overexpressed in several tumor types is noteworthy and may spark future investigations aiming to explore the Myc and DR5 expression status of primary tumors and their ultimate vulnerability to DR5-targeted therapeutics.     

Phenethyl isothiocyanate sensitizes glioma cells to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is a promising antitumor therapy. However, many cancer cells, including malignant glioma cells, tend to be resistant to TRAIL, highlighting the need for strategies to overcome TRAIL resistance. Here we show that in combination with phenethyl isothiocyanate (PEITC), exposure to TRAIL induced apoptosis in TRAIL-resistant glioma cells. Subtoxic concentrations of PEITC significantly potentiated TRAIL-induced cytotoxicity and apoptosis in glioma cells. PEITC dramatically upregulated DR5 receptor expression but had no effects on DR4 receptor. PEITC enhances TRAIL-induced apoptosis through the downregulation of cell survival proteins and the upregulation of DR5 receptors through actions on the ROS-induced-p53.     

MiRNA regulation of TRAIL expression exerts selective cytotoxicity to prostate carcinoma cells

Prostate carcinoma is the most common cancer for men and among the leading cancer-related causes. Many evidences have shown that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) potently induces apoptosis in cancer cells, and thus, is a promising biologic agent for prostate carcinoma therapy. However, TRAIL expression mediated by the current vectors lacks tumor specificity, thereby exerting cytotoxicity to normal cells. To solve this problem, we inserted miRNA response elements (MREs), miR-143 and miR-145, expression levels of which were reduced in prostate carcinoma, as well as that of miR-122, which is specifically expressed in hepatic cells, into adenoviral vectors to control TRAIL expression (Ad-TRAIL-M3). qPCR data confirmed that miR-143, miR-145, and miR-122 levels were all decreased in prostate carcinoma cell lines and prostate cancer samples from patients. Luciferase assays showed that MREs-regulated luciferase expression was potently suppressed in normal cells, but not in prostate cancer cells. Ad-TRAIL-M3, which expresses TRAIL in a MREs-regulated manner, produced high level of TRAIL and suppressed the survival of prostate cancer cells by inducing apoptosis, while Ad-TRAIL-M3 had no TRAIL expression in normal cells and thus exerted no cytotoxicity to them. The studies on PC-3 tumor xenograft in mice further confirmed that Ad-TRAIL-M3 was able to inhibit the growth of tumors and possessed high biosafety. In conclusion, we successfully generated an adenoviral vector that expresses TRAIL in miRNA-regulated mechanism. This miRNA-based gene therapy may be promising for prostate carcinoma treatment.     

Curcumin enhances TRAIL-induced apoptosis of breast cancer cells by regulating apoptosis-related proteins

The TNF-related apoptosis inducing ligand (TRAIL) has promising anti-cancer therapeutic activity, although significant percentage of primary tumors resistant to TRAIL-induced apoptosis remains an obstacle to the extensive use of TRAIL-based mono-therapies. Natural compound curcumin could potentially sensitize resistant cancer cells to TRAIL. We found that the combination of TRAIL with curcumin can synergistically induces apoptosis in three TRAIL-resistant breast cancer cell lines. The mechanism behind this synergistic cell death was investigated by examining an effect of curcumin on the expression and activation of TRAIL-associated cell death proteins. Immunoblotting, RNA interference, and use of chemical inhibitors of TRAIL-activate signaling revealed differential effects of curcumin on the expression of Mcl-1 and activities of ERK and Akt. Curcumin-induced production of reactive oxygen species did not affect total expression of DR5 but it enhanced mobilization of DR5 to the plasma membrane. In these breast cancer cells curcumin also induced downregulation of IAP proteins. Taken together, our data suggest that a combination of TRAIL and curcumin is a potentially promising treatment for breast cancer, although the specific mechanisms involved in this sensitization could differ even among breast cancer cells of different origins.     

Metformin Causes G1-Phase Arrest via Down-Regulation of MiR-221 and Enhances TRAIL Sensitivity through DR5 Up-Regulation in Pancreatic Cancer Cells

Although many chemotherapeutic strategies against cancer have been developed, pancreatic cancer is one of the most aggressive and intractable types of malignancies. Therefore, new strategies and anti-cancer agents are necessary to treat this disease. Metformin is a widely used drug for type-2 diabetes, and is also known as a promising candidate anti-cancer agent from recent studies in vitro and in vivo. However, the mechanisms of metformin’s anti-cancer effects have not been elucidated. We demonstrated that metformin suppressed the expression of miR-221, one of the most well-known oncogenic microRNAs, in human pancreatic cancer PANC-1 cells. Moreover, we showed that the down-regulation of miR-221 by metformin caused G1-phase arrest via the up-regulation of p27, one of the direct targets of miR-221. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is also a promising agent for cancer treatment. While recent studies showed that treatment with only TRAIL was not effective against pancreatic cancer cells, the present data showed that metformin sensitized p53-mutated pancreatic cancer cells to TRAIL. Metformin induced the expressions of death receptor 5 (DR5), a receptor for TRAIL, and Bim with a pro-apoptotic function in the downstream of TRAIL-DR5 pathway. We suggest that the up-regulation of these proteins may contribute to sensitization of TRAIL-induced apoptosis. The combination therapy of metformin and TRAIL could therefore be effective in the treatment of pancreatic cancer.     

The combination of TRAIL and luteolin enhances apoptosis in human cervical cancer HeLa cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for cancer therapeutics. However, some tumor cells are resistant to TRAIL-induced apoptosis. Our previous studies have shown that luteolin, a naturally occurring flavonoid, induces the up-regulation of death receptor 5 (DR5), which is a receptor for TRAIL. Here, we show for the first time that luteolin synergistically acts with exogenous soluble recombinant human TRAIL to induce apoptosis in HeLa cells, but not in normal human peripheral blood mononuclear cells. The combined use of luteolin and TRAIL induced Bid cleavage and the activation of caspase-8. Also, human recombinant DR5/Fc chimera protein, caspase inhibitors, and DR5 siRNA efficiently reduced apoptosis induced by co-treatment with luteolin and TRAIL. These results raise the possibility that this combined treatment with luteolin and TRAIL might be promising as a new therapy against cancer.     

DR4-selective tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) variants obtained by structure-based design

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potential anticancer agent that selectively induces apoptosis in a variety of cancer cells by interacting with death receptors DR4 and DR5. TRAIL can also bind to decoy receptors (DcR1, DcR2, and osteoprotegerin receptor) that cannot induce apoptosis. Different tumor types respond either to DR4 or to DR5 activation, and chemotherapeutic drugs can increase the expression of DR4 or DR5 in cancer cells. Thus, DR4 or DR5 receptor-specific TRAIL variants would permit new and tumor-selective therapies. Previous success in generating a DR5-selective TRAIL mutant using computer-assisted protein design prompted us to make a DR4-selective TRAIL variant. Technically, the design of DR4 receptor-selective TRAIL variants is considerably more challenging compared with DR5 receptor-selective variants, because of the lack of a crystal structure of the TRAIL-DR4 complex. A single amino acid substitution of Asp at residue position 218 of TRAIL to His or Tyr was predicted to have a favorable effect on DR4 binding specificity. Surface plasmon resonance-based receptor binding tests showed a lowered DR5 affinity in concert with increased DR4 specificity for the designed variants, D218H and D218Y. Binding to DcR1, DcR2, and osteoprotegerin was also decreased. Cell line assays confirmed that the variants could not induce apoptosis in DR5-responsive Jurkat and A2780 cells but were able to induce apoptosis in DR4-responsive EM-2 and ML-1 cells.     

Halocynthiaxanthin and peridinin sensitize colon cancer cell lines to tumor necrosis factor-related apoptosis-inducing ligand

Carotenoids are compounds contained in foods and possess anticarcinogenic activity. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising candidate for cancer therapeutics due to its ability to induce apoptosis selectively in cancer cells. However, some tumors remain tolerant to TRAIL-induced apoptosis. Therefore, it is important to develop agents that overcome this resistance. We show, for the first time, that certain carotenoids sensitize cancer cells to TRAIL-induced apoptosis. Combined treatment with halocynthiaxanthin, a dietary carotenoid contained in oysters and sea squirts, and TRAIL drastically induced apoptosis in colon cancer DLD-1 cells, whereas each agent alone only slightly induced apoptosis. The combination induced nuclear condensation and poly(ADP-ribose) polymerase cleavage, which are major features of apoptosis. Various caspase inhibitors could attenuate the apoptosis induced by this combination. Furthermore, the dominant-negative form of a TRAIL receptor could block the apoptosis, suggesting that halocynthiaxanthin specifically facilitated the TRAIL signaling pathway. To examine the molecular mechanism of the synergistic effect of the combined treatment, we did an RNase protection assay. Halocynthiaxanthin markedly up-regulated a TRAIL receptor, death receptor 5 (DR5), among the death receptor-related genes, suggesting a possible mechanism for the combined effects. Moreover, we examined whether other carotenoids also possess the same effects. Peridinin, but not alloxanthin, diadinochrome, and pyrrhoxanthin, induced DR5 expression and sensitized DLD-1 cells to TRAIL-induced apoptosis. These results indicate that the combination of certain carotenoids and TRAIL is a new strategy to overcome TRAIL resistance in cancer cells.     

Resveratrol enhances antitumor activity of TRAIL in prostate cancer xenografts through activation of FOXO transcription factor

Background

Resveratrol (3, 4′, 5 tri-hydroxystilbene), a naturally occurring polyphenol, exhibits anti-inflammatory, antioxidant, cardioprotective and antitumor activities. We have recently shown that resveratrol can enhance the apoptosis-inducing potential of TRAIL in prostate cancer cells through multiple mechanisms in vitro. Therefore, the present study was designed to validate whether resveratrol can enhance the apoptosis-inducing potential of TRAIL in a xenograft model of prostate cancer.

Methodology/Principal Findings

Resveratrol and TRAIL alone inhibited growth of PC-3 xenografts in nude mice by inhibiting tumor cell proliferation (PCNA and Ki67 staining) and inducing apoptosis (TUNEL staining). The combination of resveratrol and TRAIL was more effective in inhibiting tumor growth than single agent alone. In xenografted tumors, resveratrol upregulated the expressions of TRAIL-R1/DR4, TRAIL-R2/DR5, Bax and p27^{/K IP1}, and inhibited the expression of Bcl-2 and cyclin D1. Treatment of mice with resveratrol and TRAIL alone inhibited angiogenesis (as demonstrated by reduced number of blood vessels, and VEGF and VEGFR2 positive cells) and markers of metastasis (MMP-2 and MMP-9). The combination of resveratrol with TRAIL further inhibited number of blood vessels in tumors, and circulating endothelial growth factor receptor 2-positive endothelial cells than single agent alone. Furthermore, resveratrol inhibited the cytoplasmic phosphorylation of FKHRL1 resulting in its enhanced activation as demonstrated by increased DNA binding activity.

Conclusions/Significance

These data suggest that resveratrol can enhance the apoptosis-inducing potential of TRAIL by activating FKHRL1 and its target genes. The ability of resveratrol to inhibit tumor growth, metastasis and angiogenesis, and enhance the therapeutic potential of TRAIL suggests that resveratrol alone or in combination with TRAIL can be used for the management of prostate cancer.     

The Herbal Compound Cryptotanshinone Restores Sensitivity in Cancer Cells That Are Resistant to the Tumor Necrosis Factor-related Apoptosis-inducing Ligand

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis and kills cancer cells but not normal cells. However, TRAIL resistance due to low level of TRAIL receptor expression is widely found in cancer cells and hampers its development for cancer treatment. Thus, the agents that can sensitize the tumor cells to TRAIL-mediated apoptosis are urgently needed. We investigated whether tanshinones, the major bioactive compounds of Salvia miltiorrhiza (danshen), can up-regulate TRAIL receptor expression. Among the major tanshinones being tested, cryptotanshinone (CT) showed the best ability to induce TRAIL receptor 2 (DR5) expression. We further showed that CT was capable of promoting TRAIL-induced cell death and apoptosis in A375 melanoma cells. CT-induced DR5 induction was not cell type-specific, as DR5 induction was observed in other cancer cell types. DR5 knockdown abolished the enhancing effect of CT on TRAIL responses. Mechanistically, induction of the DR5 by CT was found to be p53-independent but dependent on the induction of CCAAT/enhancer-binding protein-homologous protein (CHOP). Knockdown of CHOP abolished CT-induced DR5 expression and the associated potentiation of TRAIL-mediated cell death. In addition, CT-induced ROS production preceded up-regulation of CHOP and DR5 and consequent sensitization of cells to TRAIL. Interestingly, CT also converted TRAIL-resistant lung A549 cancer cells into TRAIL-sensitive cells. Taken together, our results indicate that CT can potentiate TRAIL-induced apoptosis through up-regulation of DR5.     

The effect of cisplatin on cytotoxicity of anticancer cytokine TRAIL and its receptor-selective mutant variant DR5-B<Superscript>1</Superscript>

Cytokine TRAIL selectively induces apoptosis in vitro and in vivo in tumor cells without affecting normal cells, but its therapeutic application is limited, since many primary tumors are insensitive to TRAIL. To improve the efficiency of TRAIL, we have previously developed TRAIL mutant variant DR5-B, which binds the apoptosis-inducing death receptor DR5 as efficiently as wild type TRAIL, but shows almost no affinity to other receptors. In this study, we investigated the effect of the chemotherapeutic agent cisplatin on the cytotoxicity of TRAIL variants in 12 tumor cell lines of various origin. Cisplatin effectively enhances the cytotoxic activity of TRAIL preparations. The synergistic effect is most pronounced in the prostate cancer cell lines, where the combined effect exceeds the sum of the separate effects by more than 2 times. The cytotoxicity of DR5-B variant is significantly higher compared to wild-type TRAIL in combination with cisplatin in 9 of 12 tumor cell lines.     

Celastrol, a Triterpene, Enhances TRAIL-induced Apoptosis through the Down-regulation of Cell Survival Proteins and Up-regulation of Death Receptors

Whether celastrol, a triterpene from traditional Chinese medicine, can modulate the anticancer effects of TRAIL, the cytokine that is currently in clinical trial, was investigated. As indicated by assays that measure plasma membrane integrity, phosphatidylserine exposure, mitochondrial activity, and activation of caspase-8, caspase-9, and caspase-3, celastrol potentiated the TRAIL-induced apoptosis in human breast cancer cells, and converted TRAIL-resistant cells to TRAIL-sensitive cells. When examined for its mechanism, we found that the triterpene down-regulated the expression of cell survival proteins including cFLIP, IAP-1, Bcl-2, Bcl-xL, survivin, and XIAP and up-regulated Bax expression. In addition, we found that celastrol induced the cell surface expression of both the TRAIL receptors DR4 and DR5. This increase in receptors was noted in a wide variety of cancer cells including breast, lung, colorectal, prostate, esophageal, and pancreatic cancer cells, and myeloid and leukemia cells. Gene silencing of the death receptor abolished the effect of celastrol on TRAIL-induced apoptosis. Induction of the death receptor by the triterpenoid was found to be p53-independent but required the induction of CAAT/enhancer-binding protein homologous protein (CHOP), inasmuch as gene silencing of CHOP abolished the induction of DR5 expression by celastrol and associated enhancement of TRAIL-induced apoptosis. We found that celastrol also induced reactive oxygen species (ROS) generation, and ROS sequestration inhibited celastrol-induced expression of CHOP and DR5, and consequent sensitization to TRAIL. Overall, our results demonstrate that celastrol can potentiate the apoptotic effects of TRAIL through down-regulation of cell survival proteins and up-regulation of death receptors via the ROS-mediated up-regulation of CHOP pathway.