TRAIL-mediated apoptosis requires NF-kappaB inhibition and the mitochondrial permeability transition in human hepatoma cells

Kaempferol sensitizes tumor necrosis factor-related apoptosis-inducing ligand-resistance chronic myelogenous leukemia cells to apoptosis

BACKGROUND

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand, TRAIL, an apoptosis-inducing cytokine, has attracted much attention in the treatment of cancer for its selective toxicity to malignant rather than normal cells. However, the apoptosis-inducing ability of TRAIL is weaker than expected primarily due to cancer cell resistance. As one of the dietary flavonoids, kaempferol, has been shown to be antiproliferative and might have a protective effect against TRAIL resistance, particularly for hematologic malignancies.

METHODS AND RESULTS

Here, we studied the potential of kaempferol to enhance the TRAIL-induced cytotoxicity and apoptosis in human chronic myelogenous leukemia (CML) cell line K-562, as well as the expression of specific genes with impact on TRAIL signal regulation. Analysis of flowcytometry data showed that treatment with kaempferol did enhance sensitivity of CML cells to pro-apoptotic effects of anti-TRAIL antibody. Although the gene expression levels were heterogeneous, cFLIP, cIAP1 and cIAP2 expression were generally downregulated where co-treatment of kaempferol and TRAIL was employed and these effects appeared to be dose-dependent. We further demonstrated that the expression of death receptors 4 and 5 tended to increase subsequent to the combination treatment.

CONCLUSIONS

Consequently, it is reasonable to conclude that sensitization of chronic leukemia cells to TRAIL by kaempferol in vitro should be considered as a way of focusing clinical attention on leukemia therapy.

OSMI-1 Enhances TRAIL-Induced Apoptosis through ER Stress and NF-κB Signaling in Colon Cancer Cells

Levels of O-GlcNAc transferase (OGT) and hyper-O-GlcNAcylation expression levels are associated with cancer pathogenesis. This study aimed to find conditions that maximize the therapeutic effect of cancer and minimize tissue damage by combining an OGT inhibitor (OSMI-1) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We found that OSMI-1 treatment in HCT116 human colon cancer cells has a potent synergistic effect on TRAIL-induced apoptosis signaling. Interestingly, OSMI-1 significantly increased TRAIL-mediated apoptosis by increasing the expression of the cell surface receptor DR5. ROS-induced endoplasmic reticulum (ER) stress by OSMI-1 not only upregulated CHOP-DR5 signaling but also activated Jun-N-terminal kinase (JNK), resulting in a decrease in Bcl2 and the release of cytochrome c from mitochondria. TRAIL induced the activation of NF-κB and played a role in resistance as an antiapoptotic factor. During this process, O-GlcNAcylation of IκB kinase (IKK) and IκBα degradation occurred, followed by translocation of p65 into the nucleus. However, combination treatment with OSMI-1 counteracted the effect of TRAIL-mediated NF-κB signaling, resulting in a more synergistic effect on apoptosis. Therefore, the combined treatment of OSMI-1 and TRAIL synergistically increased TRAIL-induced apoptosis through caspase-8 activation. Conclusively, OSMI-1 potentially sensitizes TRAIL-induced cell death in HCT116 cells through the blockade of NF-κB signaling and activation of apoptosis through ER stress response.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

BRD4 inhibition promotes TRAIL-induced apoptosis by suppressing the transcriptional activity of NF-κB in NSCLC

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and agonistic antibodies against TRAIL death receptors (DR) can induce apoptosis preferentially in tumor cells while causing virtually no damage to normal cells. However, their therapeutic potential is limited by occurring resistance in tumor cells, including non-small cell lung cancer (NSCLC). Thus, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. In the present study, we demonstrated that inhibition of Bromodomain-containing protein 4 (BRD4) or genetic knock-down of BRD4, an epigenetic reader and master transcription coactivator, can sensitize lung cancer cells to TRAIL. This sensitization is in a caspase-dependent manner. Inhibition of BRD4 by small molecule inhibitor (+)-JQ-1 and genetic knock-down of BRD4 can both recruit the FADD and activate caspases. The sensitization did not regulate the death receptors DR4 and DR5. Moreover, BRD4 inhibition can block TRAIL-induced IKK activation by suppressing the transcriptional activity of NF-κB. These findings indicate that targeting combination therapy with TRAIL and BRD4 inhibitors can be a promising strategy to overcome TRAIL resistance in NSCLC.

Anti‑inflammatory compounds moracin O and P from Morus alba Linn. (Sohakuhi) target the NF‑κB pathway

Accumulating evidence suggests that inflammation is linked to multiple pathological processes and induces cellular and molecular damage through the activation of inflammatory signaling pathways, including the NF-κB pathway. The aim of the present study was to identify natural anti-inflammatory products that can target NF-κB activity, in order to establish a novel therapeutic approach for inflammatory diseases. Using a 4T1 breast cancer cell line that expresses the firefly luciferase gene under the control of an NF-κB response element, 112 natural products were tested for their anti-inflammatory properties. Sohakuhi (Morus alba Linn. bark) extract was observed to strongly suppress NF-κB activity without affecting cell viability. To further examine the anti-inflammatory effect of Sohakuhi, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cellular damage of human HaCaT keratinocytes was evaluated. While TRAIL triggered the phosphorylation of the p65 subunit of NF-κB, leading to cellular damage in HaCaT cells, treatment with Sohakuhi extract protected HaCaT cells against TRAIL-induced cellular damage. Moreover, Sohakuhi treatment also upregulated the anti-apoptotic proteins Bcl-xL and Bcl-2. Importantly, through chemical fractionation of Sohakuhi extract, moracin O and P were confirmed to mediate its anti-inflammatory effects. Collectively, the present results indicated that Sohakuhi and moracin may represent potential candidates for the development of novel anti-inflammatory drugs.

Romo1 Inhibition Induces TRAIL-Mediated Apoptosis in Colorectal Cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to behave as an attractive anti-cancer agent in various cancers. Despite its promise TRAIL has limitations such as short half-life and rapid development of resistance. In this regard, approaches to sensitizers of TRAIL that can overcome the limitations of TRAIL are necessary. However, the molecular targets and mechanisms underlying sensitization to TRAIL-induced apoptosis are not fully understood. Here, we propose that reactive oxygen species modulator-1 (Romo1) as an attractive sensitizer of TRAIL. Romo1 is a mitochondrial inner membrane channel protein that controls reactive oxygen species (ROS) production, and its expression is highly upregulated in various cancers, including colorectal cancer. In the present study, we demonstrated that Romo1 inhibition significantly increased TRAIL-induced apoptosis of colorectal cancer cells, but not of normal colon cells. The combined effect of TRAIL and Romo1 inhibition was correlated with the activation of mitochondrial apoptosis pathways. Romo1 silencing elevated the protein levels of BCL-2-associated X protein (Bax) by downregulating the ubiquitin proteasome system (UPS). Romo1 inhibition downregulated the interaction between Bax and Parkin. Furthermore, Romo1 knockdown triggered the mitochondrial dysfunction and ROS generation. We validated the effect of combination in tumor xenograft model in vivo. In conclusion, our study demonstrates that Romo1 inhibition induces TRAIL-mediated apoptosis by identifying the novel mechanism associated with the Bax/Parkin interaction. We suggest that targeting of Romo1 is essential for the treatment of colorectal cancer and may be a new therapeutic approach in the future and contribute to the drug discovery.

Eukaryotic initiation factor 5B (eIF5B) provides a critical cell survival switch to glioblastoma cells via regulation of apoptosis

Physiological stress conditions attenuate global mRNA translation via modifications of key eukaryotic initiation factors. However, non-canonical translation initiation mechanisms allow cap-independent translation of certain mRNAs. We have previously demonstrated that eIF5B promotes cap-independent translation of the mRNA encoding the antiapoptotic factor, XIAP, during cellular stress. Here, we show that depletion of eIF5B sensitizes glioblastoma multiforme cells to TRAIL-induced apoptosis by a pathway involving caspases-8, −9, and −7, with no significant effect on cell cycle progression. eIF5B promotes evasion of apoptosis by promoting the translation of several IRES-containing mRNAs, encoding the antiapoptotic proteins XIAP, Bcl-xL, cIAP1, and c-FLIP_S. We also show that eIF5B promotes translation of nuclear factor erythroid 2-related factor 2 and suggest that reactive oxygen species contribute to increased apoptosis under conditions of eIF5B depletion. Finally, eIF5B depletion leads to decreased activation of the canonical NF-κB pathway. Taken together, our data suggest that eIF5B represents a regulatory node, allowing cancer cells to evade apoptosis by promoting the translation of pro-survival proteins from IRES-containing mRNAs.

MSC-Delivered Soluble TRAIL and Paclitaxel as Novel Combinatory Treatment for Pancreatic Adenocarcinoma

Pancreatic cancer is the fourth leading cause of cancer death in western countries with more than 100,000 new cases per year in Europe and a mortality rate higher than 90%. In this scenario, advanced therapies based on gene therapies are emerging, thanks to a better understanding of tumour architecture and cancer cell alterations. We have demonstrated the efficacy of an innovative approach for pancreatic cancer based on mesenchymal stromal cells (MSC) genetically engineered to produce TNF-related Apoptosis Inducing Ligand (TRAIL). Here we investigated the combination of this MSC-based approach with the administration of a paclitaxel (PTX)-based chemotherapy to improve the potential of the treatment, also accounting for a possible resistance onset.

Methods: Starting from the BXPC3 cell line, we generated and profiled a TRAIL-resistant model of pancreatic cancer, testing the impact of the combined treatment in vitro with specific cytotoxicity and metabolic assays. We then challenged the rationale in a subcutaneous mouse model of pancreatic cancer, assessing its effect on tumour size accounting stromal and parenchymal organization.

Results: PTX was able to restore pancreatic cancer sensitivity to MSC-delivered TRAIL by reverting its pro-survival gene expression profile. The two compounds cooperate both in vitro and in vivo and the combined treatment resulted in an improved cytotoxicity on tumour cells.

Conclusion: In summary, this study uncovers the potential of a combinatory approach between MSC-delivered TRAIL and PTX, supporting the combination of cell-based products and conventional chemotherapeutics as a tool to improve the efficacy of the treatments, also addressing possible mechanisms of resistance.

N-glycosylation of mouse TRAIL-R restrains TRAIL-induced apoptosis

The sensitivity of cells to death receptor-induced apoptosis is commonly controlled by multiple checkpoints in order to limit induction of excessive or unnecessary death. Although cytotoxic in various cancer cells, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) does not trigger apoptosis in most non-transformed cells. The molecular nature of the checkpoints that normally protect the cells from TRAIL-induced death are not fully understood. Endoplasmic reticulum (ER) stress has been reported to switch the sensitivity of human cells to the cytotoxic effect of TRAIL, suggesting that this cellular state perturbs some of these protective mechanisms. We found that tunicamycin (TU), but no other ER stress inducers, sensitized mouse fibroblasts and hippocampal neuronal cells to TRAIL-induced apoptosis. Importantly, the sensitization was specific to TRAIL and not caused by differences in ER stress induction. Instead, it relied on the inhibition of N-glycosylation of the mouse TRAIL receptor (mTRAIL-R). Inhibition of N-glycosylation did not alter cell surface expression of mTRAIL-R but enhanced its ability to bind TRAIL, and facilitated mTRAIL-R oligomerization, which resulted in enhanced death-inducing signaling complex (DISC) formation and caspase-8 activation. Remarkably, reconstitution of mTRAIL-R-deficient cells with a version of mTRAIL-R mutated for the three N-glycosylation sites identified in its ectodomain confirmed higher sensitivity to TRAIL-induced apoptosis. Together, our results demonstrate that inhibition of N-glycosylation of mTRAIL-R, and not ER stress induction, sensitizes mouse cells to TRAIL-induced apoptosis. We therefore reveal a new mechanism restraining TRAIL cytotoxicity in mouse cells.

Hopea odorata extract inhibits hepatocellular carcinoma via induction of caspase-dependent apoptosis

Introduction

Cancer is a disease with a global burden and is a major and increasing threat to public health. The demand for new modalities to treat and prevent cancer is high. Given the toxic side effects of standard treatments, such as chemotherapy, there is greater research interest in naturally derived compounds due to their selective toxicity to cancer cells. This study aimed to test the anticancer activity of a crude extract of Hopea odorata on hepatocellular carcinoma (HCC) HepG2 cell line.

Methods

Methanol extracts of H. odorata were prepared from the bark of H. odorata plants (H. odorata extract). The in vitro cytotoxicity of H. odorata extracts on human HCC cell line HepG2 compared to normal human fibroblasts (HFs) was assessed by Alamar Blue assay. Caspase-3/7 was detected using a reagent that consists of DEVD peptide conjugated to a nucleic acid-binding dye. Apoptosis induction by the H. odorata plant extract on HepG2 was evaluated by Annexin V/7-AAD using flow cytometry. Disintegrated nuclei of plant-treated cells were observed under a fluorescent microscope using Hoechst and propidium iodide (PI) staining. In addition, using the Hoechst/PI staining technique, the ratio of dead to total cells was determined by distinguishing Hoechst and PI fluorescent signals.

Results

We found that the IC₅₀ value of H. odorata extract on HepG2 was 12.67±5 µg/mL and on HF was 44±3 µg/mL. The IC₅₀ value of doxorubicin on HepG2 was 153.3±15 ng/mL and on HF was 6.3±0.6 ng/mL. The selectivity index (SI) of H. odorata extract for HepG2 cells was ~3.48, while the SI of doxorubicin for HepG2 cells was ~0.04. The ratio of dead to total cells increased in a dose-dependent manner for HepG2 cells when observed under a fluorescent microscope, while the ratio of dead to total cells barely changed for HF cells. The H. odorata extract inhibited HepG2 cells via the activation of caspase-3/7. At 250 µg/mL concentration of the H. odorata extract, 35% of HepG2 cells were induced into apoptosis, and the cells exhibited disintegrated nuclei under a fluorescent microscope.

Conclusion

These findings demonstrate that the methanolic bark extracts of H. odorata plant induce apoptosis and selective cytotoxicity toward HepG2 but not HF. Therefore, purification of compounds from H. odorata bark extracts may be useful as anticancer agents, and thus, more studies are warranted to investigate the anticancer properties of H. odorata.

Reversal of the Apoptotic Resistance of Non-Small-Cell Lung Carcinoma towards TRAIL by Natural Product Toosendanin

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively triggers cancer cell death via its association with death receptors on the cell membrane, but exerts negligible side effects on normal cells. However, some non-small-cell lung carcinoma (NSCLC) patients exhibited resistance to TRAIL treatment in clinical trials, and the mechanism varies. In this study, we described for the first time that toosendanin (TSN), a triterpenoid derivative used in Chinese medicine for pain management, could significantly sensitize human primary NSCLC cells or NSCLC cell lines to TRAIL-mediated apoptosis both in vitro and in vivo, while showing low toxicity against human primary cells or tissues. The underlying apoptotic mechanisms involved upregulation of death receptor 5 (DR5) and CCAAT/enhancer binding protein homologous protein, which is related to the endoplasmic reticulum stress response, and is further associated with reactive oxygen species generation and Ca²⁺ accumulation. Surprisingly, TSN also induced autophagy in NSCLC cells, which recruited membrane DR5, and subsequently antagonized the apoptosis-sensitizing effect of TSN. Taken together, TSN can be used to sensitize tumors and the combination of TRAIL and TSN may represent a useful strategy for NSCLC therapy; moreover, autophagy serves as an important drug resistance mechanism for TSN.

Inhibition of NF-κB Pathway and Modulation of MAPK Signaling Pathways in Glioblastoma and Implications for Lovastatin and Tumor Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL) Combination Therapy

Glioblastoma is a common malignant brain tumor and it is refractory to therapy because it usually contains a mixture of cell types. The tumor necrosis factor-related apoptosis inducing ligand (TRAIL) has been shown to induce apoptosis in a range of tumor cell types. Previously, we found that two human glioblastoma cell lines are resistant to TRAIL, while lovastatin sensitizes these glioblastoma cells to TRAIL-induced cell death. In this study, we investigated the mechanisms underlying the TRAIL-induced apoptosis in human glioblastoma cell lines by lovastatin. Furthermore, we have confirmed the anti-tumor effect of combination therapy with lovastatin and TRAIL in the subcutaneous brain tumor model. We showed that lovastatin significantly up-regulated the expression of death receptor 5 (DR5) in glioblastoma cell lines as well as in tumor-bearing mice with peri-tumoral administration of lovastatin. Further study in glioblastoma cell lines suggested that lovastatin treatment could inhibit NF-κB and Erk/MAPK pathways but activates JNK pathway. These results suggest that lovastatin sensitizes TRAIL-induced apoptosis by up-regulation of DR5 level via NF-κB inactivation, but also directly induces apoptosis by dysregulation of MAPK pathway. Our in vivo study showed that local peri-tumoral co-injection of lovastatin and TRAIL substantially reduced tumor growth compared with single injection of lovastatin or TRAIL in subcutaneous nude mice model. This study suggests that combined treatment of lovastatin and TRAIL is a promising therapeutic strategy to TRAIL-resistant glioblastoma.

ABC294640, a sphingosine kinase 2 inhibitor, enhances the antitumor effects of TRAIL in non-small cell lung cancer

Evidences suggest that tumor microenvironment may play an important role in cancer drug resistance. Sphingosine kinase 2 (SphK2) is proposed to be the key regulator of sphingolipid signaling. This study is aimed to investigate whether the combination of molecular targeting therapy using a specific inhibitor of SphK2 (ABC294640), with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can enhance the apoptosis of non-small cell lung cancer (NSCLC) cells. Our results revealed that NSCLC cells' sensitivity to TRAIL is correlated with the level of SphK2. Compared with TRAIL alone, the combination therapy enhanced the apoptosis induced by TRAIL, and knockdown of SphK2 by siRNA presented a similar effect. Combination therapy with ABC294640 increased the activity of caspase-3/8 and up-regulated the expression of death receptors (DR). Additional investigations revealed that translocation of DR4/5 to the cell membrane surface was promoted by adding ABC294640. However, expression of anti-apoptosis proteins such as Bcl(-)2 and IAPs was not significantly modified by this SphK2 inhibitor. Overall, this work demonstrates that SphK2 may contribute to the apoptosis resistance in NSCLC, thus indicating a new therapeutic target for resistant NSCLC cells.

The Deubiquitinase Inhibitor PR-619 Sensitizes Normal Human Fibroblasts to Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL)-mediated Cell Death

TNF-related apoptosis-inducing ligand (TRAIL) is a potential cancer therapy that selectively targets cancer cell death while non-malignant cells remain viable. Using a panel of normal human fibroblasts, we characterized molecular differences in human foreskin fibroblasts and WI-38 TRAIL-resistant cells and marginally sensitive MRC-5 cells compared with TRAIL-sensitive human lung and colon cancer cells. We identified decreased caspase-8 protein expression and protein stability in normal fibroblasts compared with cancer cells. Additionally, normal fibroblasts had incomplete TRAIL-induced caspase-8 activation compared with cancer cells. We found that normal fibroblasts lack the ubiquitin modification of caspase-8 required for complete caspase-8 activation. Treatment with the deubiquitinase inhibitor PR-619 increased caspase-8 ubiquitination and caspase-8 enzymatic activity and sensitized normal fibroblasts to TRAIL-mediated apoptosis. Therefore, posttranslational regulation of caspase-8 confers resistance to TRAIL-induced cell death in normal cells through blockade of initiation of the extrinsic cell death pathway.

Pattern Recognition Receptors in Cancer Progression and Metastasis

The innate immune system is an integral component of the inflammatory response to pathophysiological stimuli. Toll-like receptors (TLRs) and inflammasomes are the major sensors and pattern recognition receptors (PRRs) of the innate immune system that activate stimulus (signal)-specific pro-inflammatory responses. Chronic activation of PRRs has been found to be associated with the aggressiveness of various cancers and poor prognosis. Involvement of PRRs was earlier considered to be limited to infection- and injury-driven carcinogenesis, where they are activated by pathogenic ligands. With the recognition of damage-associated molecular patterns (DAMPs) as ligands of PRRs, the role of PRRs in carcinogenesis has also been implicated in other non-pathogen-driven neoplasms. Dying (apoptotic or necrotic) cells shed a plethora of DAMPs causing persistent activation of PRRs, leading to chronic inflammation and carcinogenesis. Such chronic activation of TLRs promotes tumor cell proliferation and enhances tumor cell invasion and metastasis by regulating pro-inflammatory cytokines, metalloproteinases, and integrins. Due to the decisive role of PRRs in carcinogenesis, targeting PRRs appears to be an effective cancer-preventive strategy. This review provides a brief account on the association of PRRs with various cancers and their role in carcinogenesis.

Toll-Like Receptors and Cancer: MYD88 Mutation and Inflammation

Pattern recognition receptors (PRRs) expressed on immune cells are crucial for the early detection of invading pathogens, in initiating early innate immune response and in orchestrating the adaptive immune response. PRRs are activated by specific pathogen-associated molecular patterns that are present in pathogenic microbes or nucleic acids of viruses or bacteria. However, inappropriate activation of these PRRs, such as the Toll-like receptors (TLRs), due to genetic lesions or chronic inflammation has been demonstrated to be a major cause of many hematological malignancies. Gain-of-function mutations in the TLR adaptor protein MYD88 found in 39% of the activated B cell type of diffuse large B cell lymphomas and almost 100% of Waldenström’s macroglobulinemia further highlight the involvement of TLRs in these malignancies. MYD88 mutations result in the chronic activation of TLR signaling pathways, thus the constitutive activation of the transcription factor NFκB to promote cell survival and proliferation. These recent insights into TLR pathway driven malignancies warrant the need for a better understanding of TLRs in cancers and the development of novel anti-cancer therapies targeting TLRs. This review focuses on TLR function and signaling in normal or inflammatory conditions, and how mutations can hijack the TLR signaling pathways to give rise to cancer. Finally, we discuss how potential therapeutic agents could be used to restore normal responses to TLRs and have long lasting anti-tumor effects.

The Anticancer Properties and Apoptosis-inducing Mechanisms of Cinnamaldehyde and the Herbal Prescription Huang-Lian-Jie-Du-Tang ( Huáng Lián Jiě Dú Tang) in Human Hepatoma Cells

Hepatocellular carcinoma (HCC) has long been one of the most important causes of cancer mortality in the world. Many natural products and traditional herbal medicines have been used to treat HCC in Asian countries such as Japan, Korea, Taiwan, and China. The present review aims to describe the anticancer properties and apoptotic mechanisms of cinnamaldehyde, the bioactive ingredient isolated from cinnamon trees, and the herbal prescription Huang-Lian-Jie-Du-Tang (黃連解毒湯 Huáng Lián Jiě Dú Tang; HLJDT) against human hepatoma cells in vitro and in vivo. Implication of their treatment for the development of targeted therapy against HCC is discussed.

Identification of novel molecular regulators of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in breast cancer cells by RNAi screening

INTRODUCTION

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) binds to its receptors, TRAIL-receptor 1 (TRAIL-R1) and TRAIL-receptor 2 (TRAIL-R2), leading to apoptosis by activation of caspase-8 and the downstream executioner caspases, caspase-3 and caspase-7 (caspase-3/7). Triple-negative breast cancer (TNBC) cell lines with a mesenchymal phenotype are sensitive to TRAIL, whereas other breast cancer cell lines are resistant. The underlying mechanisms that control TRAIL sensitivity in breast cancer cells are not well understood. Here, we performed small interfering RNA (siRNA) screens to identify molecular regulators of the TRAIL pathway in breast cancer cells.

METHODS

We conducted siRNA screens of the human kinome (691 genes), phosphatome (320 genes), and about 300 additional genes in the mesenchymal TNBC cell line MB231. Forty-eight hours after transfection of siRNA, parallel screens measuring caspase-8 activity, caspase-3/7 activity, or cell viability were conducted in the absence or presence of TRAIL for each siRNA, relative to a negative control siRNA (siNeg). A subset of genes was screened in cell lines representing epithelial TNBC (MB468), HER2-amplified breast cancer (SKBR3), and estrogen receptor-positive breast cancer (T47D). Selected putative negative regulators of the TRAIL pathway were studied by using small-molecule inhibitors.

RESULTS

The primary screens in MB231 identified 150 genes, including 83 kinases, 4 phosphatases, and 63 nonkinases, as potential negative regulators of TRAIL. The identified genes are involved in many critical cell processes, including apoptosis, growth factor-receptor signaling, cell-cycle regulation, transcriptional regulation, and DNA repair. Gene-network analysis identified four genes (PDPK1, IKBKB, SRC, and BCL2L1) that formed key nodes within the interaction network of negative regulators. A secondary screen of a subset of the genes identified in additional cell lines representing different breast cancer subtypes and sensitivities to TRAIL validated and extended these findings. Further, we confirmed that small-molecule inhibition of SRC or BCL2L1, in combination with TRAIL, sensitizes breast cancer cells to TRAIL-induced apoptosis, including cell lines resistant to TRAIL-induced cytotoxicity.

CONCLUSIONS

These data identify novel molecular regulators of TRAIL-induced apoptosis in breast cancer cells and suggest strategies for the enhanced application of TRAIL as a therapy for breast cancer.

Hypoxia-inducible factors have distinct and stage-specific roles during reprogramming of human cells to pluripotency

Pluripotent stem cells have distinct metabolic requirements, and reprogramming cells to pluripotency requires a shift from oxidative to glycolytic metabolism. Here, we show that this shift occurs early during reprogramming of human cells and requires hypoxia-inducible factors (HIFs) in a stage-specific manner. HIF1α and HIF2α are both necessary to initiate this metabolic switch and for the acquisition of pluripotency, and the stabilization of either protein during early phases of reprogramming is sufficient to induce the switch to glycolytic metabolism. In contrast, stabilization of HIF2α during later stages represses reprogramming, partly because of the upregulation of TNF-related apoptosis-inducing ligand (TRAIL). TRAIL inhibits induced pluripotent stem cell (iPSC) generation by repressing apoptotic caspase 3 activity specifically in cells undergoing reprogramming but not human embryonic stem cells (hESCs), and inhibiting TRAIL activity enhances human iPSC generation. These results shed light on the mechanisms underlying the metabolic shifts associated with the acquisition of a pluripotent identity during reprogramming.

Thymoquinone suppression of the human hepatocellular carcinoma cell growth involves inhibition of IL-8 expression, elevated levels of TRAIL receptors, oxidative stress and apoptosis

Hepatocellular carcinoma (HCC) is the fourth most common solid tumor worldwide. The chemokine interleukin-8 (IL-8) is overexpressed in HCC and is a potential target for therapy. Although the transcription factor NF-κB regulates IL-8 expression, and while thymoquinone (TQ; the most bioactive constituent of black seed oil) inhibits NF-κB activity, the precise mechanisms by which TQ regulates IL-8 and cancer cell growth remain to be clarified. Here, we report that TQ inhibited growth of HCC cells in a dose- and time-dependent manner, caused G2M cell cycle arrest, and stimulated apoptosis. Apoptosis was substantiated by activation of caspase-3 and -9, as well as cleavage of poly(ADP-ribose)polymerase. TQ treatments inhibited expression of NF-κB and suppressed IL-8 and its receptors. TQ treatments caused increased levels of reactive oxygen species (ROS) and mRNAs of oxidative stress-related genes, NQO1 and HO-1. Pretreatment of HepG2 cells with N-acetylcysteine, a scavenger of ROS, prevented TQ-induced cell death. TQ treatment stimulated mRNA expression of pro-apoptotic Bcl-xS and TRAIL death receptors, and inhibited expression of the anti-apoptotic gene Bcl-2. TQ enhanced TRAIL-induced death of HepG2 cells, in part by up-regulating TRAIL death receptors, inhibiting NF-κB and IL-8 and stimulating apoptosis. Altogether, these findings provide insights into the pleiotropic molecular mechanisms of TQ-dependent suppression of HCC cell growth and underscore potential of this compound as anti-HCC drug.

Membrane trafficking of death receptors: implications on signalling

Death receptors were initially recognised as potent inducers of apoptotic cell death and soon ambitious attempts were made to exploit selective ignition of controlled cellular suicide as therapeutic strategy in malignant diseases. However, the complexity of death receptor signalling has increased substantially during recent years. Beyond activation of the apoptotic cascade, involvement in a variety of cellular processes including inflammation, proliferation and immune response was recognised. Mechanistically, these findings raised the question how multipurpose receptors can ensure selective activation of a particular pathway. A growing body of evidence points to an elegant spatiotemporal regulation of composition and assembly of the receptor-associated signalling complex. Upon ligand binding, receptor recruitment in specialized membrane compartments, formation of receptor-ligand clusters and internalisation processes constitute key regulatory elements. In this review, we will summarise the current concepts of death receptor trafficking and its implications on receptor-associated signalling events.

The role of TRAIL in mediating autophagy in myositis skeletal muscle: a potential nonimmune mechanism of muscle damage

OBJECTIVE

Multinucleated cells are relatively resistant to classic apoptosis, and the factors initiating cell death and damage in myositis are not well defined. We hypothesized that nonimmune autophagic cell death may play a role in muscle fiber damage. Recent reports indicate that TRAIL may induce both NF-κB activation and autophagic cell death in other systems. We undertook this study to investigate the role of TRAIL in cell death and pathogenesis in vitro and in vivo, using myositis muscle tissues from humans and mice.

METHODS

Gene expression profiling was performed in myositis patient and control muscle specimens. Immunohistochemistry analysis was performed to confirm the gene array findings. We also analyzed TRAIL-induced cell death (apoptosis and autophagy) and NF-κB activation in vitro in cultured cells.

RESULTS

TRAIL was expressed predominantly in myositis muscle fibers, but not in biopsy specimens from normal or other dystrophic-diseased muscle. Autophagy markers were up-regulated in humans with myositis and in mouse models of myositis. TRAIL expression was restricted to regenerating/atrophic areas of muscle fascicles, blood vessels, and infiltrating lymphocytes. TRAIL induced NF-κB activation and IκB degradation in cultured cells that are resistant to TRAIL-induced apoptosis but that undergo autophagic cell death.

CONCLUSION

Our data demonstrate that TRAIL is expressed in myositis muscle and may mediate both activation of NF-κB and autophagic cell death in myositis. Thus, this nonimmune pathway may be an attractive target for therapeutic intervention in myositis.

Smad7 protein induces interferon regulatory factor 1-dependent transcriptional activation of caspase 8 to restore tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis

Smad7 has been known as a negative regulator for the transforming growth factor-β (TGF-β) signaling pathway through feedback regulation. However, Smad7 has been suspected to have other biological roles through the regulation of gene transcription. By screening differentially regulated genes, we found that the caspase 8 gene was highly up-regulated in Smad7-expressing cells. Smad7 was able to activate the caspase 8 promoter through recruitment of the interferon regulatory factor 1 (IRF1) transcription factor to the interferon-stimulated response element (ISRE) site. Interaction of Smad7 on the caspase 8 promoter was confirmed with electrophoretic mobility shift assay and chromatin immunoprecipitation experiment. Interestingly, Smad7 did not directly interact with the ISRE site, but it increased the binding activity of IRF1 with ISRE. These results support that Smad7 recruits IRF1 protein on the caspase 8 promoter and functions as a transcriptional coactivator. To confirm the biological significance of caspase 8 up-regulation, we tested tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated cell death assay in breast cancer cells. Smad7 in apoptosis-resistant MCF7 cells markedly sensitized the cells to TRAIL-induced cell death by restoring the caspase cascade. Furthermore, restoration of caspase 8-mediated apoptosis pathway repressed the tumor growth in the xenograft model. In conclusion, we suggest a novel role for Smad7 as a transcriptional coactivator for caspase 8 through the interaction with IRF1 in regulation of the cell death pathway.

Endoplasmic reticulum stress in skeletal muscle homeostasis and disease

Our appreciation of the role of endoplasmic reticulum (ER) stress pathways in both skeletal muscle homeostasis and the progression of muscle diseases is gaining momentum. This review provides insight into ER stress mechanisms during physiologic and pathological disturbances in skeletal muscle. The role of ER stress in the response to dietary alterations and acute stressors, including its role in autoimmune and genetic muscle disorders, has been described. Recent studies identifying ER stress markers in diseased skeletal muscle are noted. The emerging evidence for ER-mitochondrial interplay in skeletal muscle and its importance during chronic ER stress in activation of both inflammatory and cell death pathways (autophagy, necrosis, and apoptosis) have been discussed. Thus, understanding the ER stress-related molecular pathways underlying physiologic and pathological phenotypes in healthy and diseased skeletal muscle should lead to novel therapeutic targets for muscle disease.

A New Player in the Development of TRAIL Based Therapies for Hepatocarcinoma Treatment: ATM Kinase

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. HCCs are genetically and phenotypically heterogeneous tumors characterized by very poor prognosis, mainly due to the lack, at present, of effective therapeutic options, as these tumors are rarely suitable for radiotherapy and often resistant to chemotherapy protocols. In the last years, agonists targeting the Tumor Necrosis Factor Related Apoptosis Inducing Ligand (TRAIL) death receptor, has been investigated as a valuable promise for cancer therapy, based on their selectivity for malignant cells and low toxicity for healthy cells. However, many cancer models display resistance to death receptor induced apoptosis, pointing to the requirement for the development of combined therapeutic approaches aimed to selectively sensitize cancer cells to TRAIL. Recently, we identified ATM kinase as a novel modulator of the ability of chemotherapeutic agents to enhance TRAIL sensitivity. Here, we review the biological determinants of HCC responsiveness to TRAIL and provide an exhaustive and updated analysis of the molecular mechanisms exploited for combined therapy in this context. The role of ATM kinase as potential novel predictive biomarker for combined therapeutic approaches based on TRAIL and chemotherapeutic drugs will be closely discussed.

Apoptosis induced by mammalian reovirus is beta interferon (IFN) independent and enhanced by IFN regulatory factor 3- and NF-κB-dependent expression of Noxa

A variety of signal transduction pathways are activated in response to viral infection, which dampen viral replication and transmission. These mechanisms involve both the induction of type I interferons (IFNs), which evoke an antiviral state, and the triggering of apoptosis. Mammalian orthoreoviruses are double-stranded RNA viruses that elicit apoptosis in vitro and in vivo. The transcription factors interferon regulatory factor 3 (IRF-3) and nuclear factor kappa light-chain enhancer of activated B cells (NF-κB) are required for the expression of IFN-β and the efficient induction of apoptosis in reovirus-infected cells. However, it is not known whether IFN-β induction is required for apoptosis, nor have the genes induced by IRF-3 and NF-κB that are responsible for apoptosis been identified. To determine whether IFN-β is required for reovirus-induced apoptosis, we used type I IFN receptor-deficient cells, IFN-specific antibodies, and recombinant IFN-β. We found that IFN synthesis and signaling are dispensable for the apoptosis of reovirus-infected cells. These results indicate that the apoptotic response following reovirus infection is mediated directly by genes responsive to IRF-3 and NF-κB. Noxa is a proapoptotic BH3-domain-only protein of the Bcl-2 family that requires IRF-3 and NF-κB for efficient expression. We found that Noxa is strongly induced at late times (36 to 48 h) following reovirus infection in a manner dependent on IRF-3 and NF-κB. The level of apoptosis induced by reovirus is significantly diminished in cells lacking Noxa, indicating a key prodeath function for this molecule during reovirus infection. These results suggest that prolonged innate immune response signaling induces apoptosis by eliciting Noxa expression in reovirus-infected cells.

Bortezomib sensitizes malignant human glioma cells to TRAIL, mediated by inhibition of the NF-{kappa}B signaling pathway

Previous studies have shown that the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has significant apoptosis-inducing activity in some glioma cell lines, although many lines are either moderately or completely resistant, which has limited the therapeutic applicability of this agent. Because our recent studies showed that inhibition of proteasomal function may be independently active as an apoptosis-inducing stimulus in these tumors, we investigated the sensitivity of a panel of glioma cell lines (U87, T98G, U373, A172, LN18, LN229, LNZ308, and LNZ428) to TRAIL alone and in combination with the proteasome inhibitor bortezomib. Analysis of these cell lines revealed marked differences in their sensitivity to these treatments, with two (LNZ308 and U373) of the eight cell lines revealing no significant induction of cell death in response to TRAIL alone. No correlation was found between sensitivity of cells to TRAIL and expression of TRAIL receptors DR4, DR5, and decoy receptor DcR1, caspase 8, apoptosis inhibitory proteins XIAP, survivin, Mcl-1, Bcl-2, Bcl-Xl, and cFLIP. However, TRAIL-resistant cell lines exhibited a high level of basal NF-κB activity. Bortezomib was capable of potentiating TRAIL-induced apoptosis in TRAIL-resistant cells in a caspase-dependent fashion. Bortezomib abolished p65/NF-κB DNA-binding activity, supporting the hypothesis that inhibition of the NF-κB pathway is critical for the enhancement of TRAIL sensitization in glioma cells. Moreover, knockdown of p65/NF-κB by shRNA also enhanced TRAIL-induced apoptosis, indicating that p65/NF-κB may be important in mediating TRAIL sensitivity and the effect of bortezomib in promoting TRAIL sensitization and apoptosis induction.

Combined modality therapy with TRAIL or agonistic death receptor antibodies

Molecularly targeted therapies, such as antibodies and small molecule inhibitors have emerged as an important breakthrough in the treatment of many human cancers. One targeted therapy under development is tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) due to its ability to induce apoptosis in a variety of human cancer cell lines and xenografts, while lacking toxicity in most normal cells. TRAIL and apoptosis-inducing agonistic antibodies to the TRAIL death receptors have been the subject of many preclinical and clinical studies in the past decade. However, the sensitivity of individual cancer cell lines of a particular tumor type to these agents varies from highly sensitive to resistant. Various chemotherapy agents have been shown to enhance the apoptosis-inducing capacity of TRAIL receptor-targeted therapies and induce sensitization of TRAIL-resistant cells. This review provides an overview of the mechanisms associated with chemotherapy enhancement of TRAIL receptor-targeted therapies including modulation of the apoptotic (death receptor expression, FLIP, and Bcl-2 or inhibitors of apoptosis (IAP) families) as well as cell signaling (NFκB, Akt, p53) pathways. These mechanisms will be important in establishing effective combinations to pursue clinically and in determining relevant targets for future cancer therapies.

Inhibition of NF-kappaB signaling by quinacrine is cytotoxic to human colon carcinoma cell lines and is synergistic in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or oxaliplatin

Colorectal cancer is the third most common malignancy in the United States. Modest advances with therapeutic approaches that include oxaliplatin (L-OHP) have brought the median survival rate to 22 months, with drug resistance remaining a significant barrier. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is undergoing clinical evaluation. Although human colon carcinomas express TRAIL receptors, they can also demonstrate TRAIL resistance. Constitutive NF-kappaB activation has been implicated in resistance to TRAIL and to cytotoxic agents. We have demonstrated constitutive NF-kappaB activation in five of six human colon carcinoma cell lines; this activation is inhibited by quinacrine. Quinacrine induced apoptosis in colon carcinomas and potentiated the cytotoxic activity of TRAIL in RKO and HT29 cells and that of L-OHP in HT29 cells. Similarly, overexpression of IkappaBalpha mutant (IkappaBalphaM) or treatment with the IKK inhibitor, BMS-345541, also sensitized these cells to TRAIL and L-OHP. Importantly, 2 h of quinacrine pretreatment resulted in decreased expression of c-FLIP and Mcl-1, which were determined to be transcriptional targets of NF-kappaB. Extended exposure for 24 h to quinacrine did not further sensitize these cells to TRAIL- or L-OHP-induced cell death; however, exposure caused the down-regulation of additional NF-kappaB-dependent survival factors. Short hairpin RNA-mediated knockdown of c-FLIP or Mcl-1 significantly sensitized these cells to TRAIL and L-OHP. Taken together, data demonstrate that NF-kappaB is constitutively active in colon cancer cell lines and NF-kappaB, and its downstream targets may constitute an important target for the development of therapeutic approaches against this disease.

Repression of NF-kappaB and activation of AP-1 enhance apoptosis in prostate cancer cells

TNFalpha and TRAIL, 2 members of the tumor necrosis factor family, share many common signaling pathways to induce apoptosis. Although many cancer cells are sensitive to these proapoptotic agents, some develop resistance. Recently, we have demonstrated that upregulation of c-Fos/AP-1 is necessary, but insufficient for cancer cells to undergo TRAIL-induced apoptosis. Here we present a prostate cancer model with differential sensitivity to TNFalpha and TRAIL. We show that inhibition of NF-kappaB or activation of AP-1 can only partially sensitize resistant prostate cancer cells to proapoptotic effects of TNFalpha or TRAIL. Inhibition of NF-kappaB by silencing TRAF2, by silencing RIP or by ectopic expression of IkappaB partially sensitized resistant prostate cancer. Similarly, activation of c-Fos/AP-1 only partially sensitized resistant cancer cells to proapoptotic effects of TNFalpha or TRAIL. However, concomitant repression of NF-kappaB and activation of c-Fos/AP-1 significantly enhanced the proapoptotic effects of TNFalpha and TRAIL in resistant prostate cancer cells. Therefore, multiple molecular pathways may need to be modified, to overcome cancers that are resistant to proapoptotic therapies.

HCV induces oxidative and ER stress, and sensitizes infected cells to apoptosis in SCID/Alb-uPA mice

Hepatitis C virus (HCV) is a blood-borne pathogen and a major cause of liver disease worldwide. Gene expression profiling was used to characterize the transcriptional response to HCV H77c infection. Evidence is presented for activation of innate antiviral signaling pathways as well as induction of lipid metabolism genes, which may contribute to oxidative stress. We also found that infection of chimeric SCID/Alb-uPA mice by HCV led to signs of hepatocyte damage and apoptosis, which in patients plays a role in activation of stellate cells, recruitment of macrophages, and the subsequent development of fibrosis. Infection of chimeric mice with HCV H77c also led an inflammatory response characterized by infiltration of monocytes and macrophages. There was increased apoptosis in HCV-infected human hepatocytes in H77c-infected mice but not in mice inoculated with a replication incompetent H77c mutant. Moreover, TUNEL reactivity was restricted to HCV-infected hepatocytes, but an increase in FAS expression was not. To gain insight into the factors contributing specific apoptosis of HCV infected cells, immunohistological and confocal microscopy using antibodies for key apoptotic mediators was done. We found that the ER chaperone BiP/GRP78 was increased in HCV-infected cells as was activated BAX, but the activator of ER stress-mediated apoptosis CHOP was not. We found that overall levels of NF-kappaB and BCL-xL were increased by infection; however, within an infected liver, comparison of infected cells to uninfected cells indicated both NF-kappaB and BCL-xL were decreased in HCV-infected cells. We conclude that HCV contributes to hepatocyte damage and apoptosis by inducing stress and pro-apoptotic BAX while preventing the induction of anti-apoptotic NF-kappaB and BCL-xL, thus sensitizing hepatocytes to apoptosis.

Life and death by death receptors

Death receptors are members of the tumor necrosis factor receptor superfamily characterized by a cytoplasmic region known as the "death domain" that enables the receptors to initiate cytotoxic signals when engaged by cognate ligands. Binding to the ligand results in receptor aggregation and recruitment of adaptor proteins, which, in turn, initiates a proteolytic cascade by recruiting and activating initiator caspases 8 and 10. Death receptors were once thought to primarily induce cytotoxic signaling cascades. However, recent data indicate that they initiate multiple signaling pathways, unveiling a number of nonapoptosis-related functions, including regulation of cell proliferation and differentiation, chemokine production, inflammatory responses, and tumor-promoting activities. These noncytotoxic cascades are not simply a manifestation of inhibiting proapoptotic pathways but are intrinsically regulated by adaptor protein and receptor internalization processes. Insights into these various death receptor signaling pathways provide new therapeutic strategies targeting these receptors in pathophysiological processes.

A cell-based high-throughput screen to identify synergistic TRAIL sensitizers

We have developed a high-throughput screen (HTS) to search for novel molecules that can synergize with TRAIL, thus promoting apoptosis of ACHN renal tumor cells in a combinatorial fashion. The HTS detects synthetic compounds and pure natural products that can pre-sensitize the cancer cells to TRAIL-mediated apoptosis, yet have limited toxicity on their own. We have taken into account the individual effects of the single agents, versus the combination, and have identified hits that are synergistic, synergistic-toxic, or additive when combined with TRAIL in promoting tumor cell death. Preliminary mechanistic studies indicate that a subset of the synergistic TRAIL sensitizers act very rapidly to promote cleavage and activation of caspase-8 following TRAIL binding. Caspase-8 is an apical enzyme that initiates programmed cell death via the extrinsic apoptotic pathway. Thus, these TRAIL sensitizers may potentially reduce resistance of tumor cells to TRAIL-mediated apoptosis. Two representative sensitizers were found to increase levels of p53 but did not inhibit the proteasome, suggesting that early DNA damage-sensing pathways may be involved in their mechanisms of action.

BH3-only protein mimetic obatoclax sensitizes cholangiocarcinoma cells to Apo2L/TRAIL-induced apoptosis

Human cholangiocarcinomas evade apoptosis by overexpression of Mcl-1. The drug obatoclax (GX15-070) inhibits antiapoptotic members of the Bcl-2 family including Mcl-1. The purpose of this study is to determine if obatoclax sensitizes human cholangiocarcinoma cells to apoptosis. The human cholangiocarcinoma cell lines, KMCH, KMBC, and TFK, were employed for these studies. Protein expression was assessed by immunoblot and protein-protein interactions detected by coprecipitation of the polypeptide of interest with S-tagged Mcl-1. Activation of Bak and Bax was observed by immunocytochemistry with conformation-specific antisera. Obatoclax induced minimal apoptosis alone; however, it increased apoptosis 3- to 13-fold in all three cancer cell lines when combined with Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Obatoclax did not alter cellular expression of Bid, Bim, Puma, Noxa, Bak, Bax, Mcl-1, or cFLIP. Mcl-1 binding to Bak was readily identified in untreated cells, and this association was disrupted by treating the cells with obatoclax. Additionally, Bim binding to Mcl-1 was markedly decreased by obatoclax treatment. We also identified alterations in Bak and Bax conformation following treatment with obatoclax plus Apo2L/TRAIL but not with either Apo2L/TRAIL or obatoclax alone. In conclusion, obatoclax releases Bak and Bim from Mcl-1 and sensitizes human cholangiocarcinoma cells to Apo2L/TRAIL-induced apoptosis. Obatoclax is a potentially promising adjunctive agent for the treatment of this cancer.

Mitochondrial permeability transition in liver ischemia and reperfusion: role of c-Jun N-terminal kinase 2

The mitochondrial permeability transition (MPT) mediates hepatic necrosis after ischemia and reperfusion (I/R). Here, we studied the role of c-Jun N-terminal kinase 2 (JNK2) in MPT-induced liver injury. Wildtype (WT) and JNK2 knockout (KO) mice underwent 70% liver ischemia for 1 hr followed by reperfusion for 8 hr, after which hepatocyte injury and animal survival was assessed. Compared with WT, JNK2 KO mice had 38% less alanine transaminase release and 39% less necrosis by histology. Survival out to 14 days was also greater in JNK2 KO mice (57% vs. 11%), and overall Kaplan-Meier survival was improved. No difference in apoptosis was observed. Intravital multiphoton microscopy of potential-indicating rhodamine 123 after reperfusion revealed depolarized mitochondria in 82% of WT hepatocytes, which decreased to 43% in JNK2 KO hepatocytes. In conclusion, JNK2 contributes to hepatocellular injury and death after I/R in association with increased mitochondrial dysfunction via the MPT.

Inhibition of casein kinase 2 enhances the death ligand- and natural kiler cell-induced hepatocellular carcinoma cell death

Recent studies have shown that the inhibition of casein kinase 2 (CK2) sensitizes many cancer cells to Fas ligand- and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. However, it has not been demonstrated directly whether CK2 inhibition can also enhance the cytotoxicity of natural killer (NK) cells, which actually use the death ligands to kill cancer cells in vivo. To address whether NK cell-mediated cancer cell death is affected by the inhibition of CK2, we first checked whether the death ligand-induced apoptosis of hepatocellular carcinoma cells (HCCs) and HeLa were affected by CK2 inhibition. We then investigated the effect of CK2 inhibition on NK cytotoxicity against HCCs and HeLa cells and its mechanistic features. Inhibition of CK2 by emodin increased the apoptotic cell death of HepG2, Hep3B and HeLa when the cancer cell lines were treated with a soluble form of recombinant TRAIL or an agonistic antibody of Fas. This phenomenon appeared to be correlated with the expression level of death receptors on the cancer cell surface. More interestingly, the inhibition of CK2 also greatly increased the NK cell-mediated cancer cell killing. The NK cytotoxicity against the cancer cells increased about twofold when the target cells were pretreated with a specific CK2 inhibitor, emodin or 4,5,6,7-tetrabromobenzotriazole. Furthermore, the increase of the NK cytotoxicity against cancer cells by CK2 inhibition was granule-independent and mediated possibly by the death ligands on the NK cell surface. This suggests that CK2 inhibitors could be used to enhance the cytotoxicity of NK cells and consequently increase host tumour immunity.

TRAIL in cancer therapy: present and future challenges

Since its identification in 1995, TNF-related apoptosis-inducing ligand (TRAIL) has sparked growing interest in oncology due to its reported ability to selectively trigger cancer cell death. In contrast to other members of the TNF superfamily, TRAIL administration in vivo is safe. The relative absence of toxic side effects of this naturally occurring cytokine, in addition to its antitumoural properties, has led to its preclinical evaluation. However, despite intensive investigations, little is known in regards to the mechanisms underlying TRAIL selectivity or efficiency. An appropriate understanding of its physiological relevance, and of the mechanisms controlling cancer cells escape from TRAIL-induced cell death, will be required to optimally use the cytokine in clinics. The present review focuses on recent advances in the understanding of TRAIL signal transduction and discusses the existing and future challenges of TRAIL-based cancer therapy development.

Synergistic induction of tumor cell death by combining cisplatin with an oncolytic adenovirus carrying TRAIL

Chemoresistance and side effects are considered as the major obstacles in cisplatin-based chemotherapy of various human malignant tumors. Conjugation with cancer-specific apoptotic stimuli TRAIL or typical viro-agent ONYX-015 has been extensively investigated to enhance the antitumor activity of cisplatin. In this study, we presented a novel chemo-gene-virotherapeutic strategy to further improve the toxic effects in cancer cells and reduce the damage in normal cells. Here, an oncolytic adenoviral vector (ZD55), with a deletion of E1B 55-kDa gene, was employed to express the therapeutic TRAIL gene by constructing a recombinant virus ZD55-TRAIL. Exogenous gene delivery efficacy was determined by both in vitro and in vivo experiments and enhanced cytotoxicity of combined treatment of ZD55-TRAIL with cisplatin was evaluated in several cancer cell lines. Moreover, negative effects on normal cells have been tested in both L-02 and MRC-5 cell lines by MTT assay and apoptotic cell staining. According to our observation, combination of ZD55-TRAIL with cisplatin exhibited an apparent synergistic cytotoxicity in cancer cells, yet significantly abolished the negative toxicity in normal cells by reducing the dosage. Thus, a novel chemo-gene-virotherapeutic strategy for cancer therapy was proposed.

Trail induces cell migration and invasion in apoptosis-resistant cholangiocarcinoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for cancer therapy; however, many cholangiocarcinoma cells are resistant to TRAIL-mediated apoptosis. Resistance to apoptosis may unmask TRAIL signaling cascades favoring tumor biology. Thus our aim was to examine whether TRAIL is expressed by human cholangiocarcinomas, and if so, to determine whether it promotes a malignant phenotype. To address this objective, TRAIL expression in human liver specimens was evaluated by immunohistochemistry. The effect of TRAIL on tumor cell migration, invasion, and proliferation was examined in three human cholangiocarcinoma cell lines. TRAIL expression was upregulated by cholangiocytes in preneoplastic disease, primary sclerosing cholangitis, and human cholangiocarcinoma specimens. TRAIL promoted tumor cell migration and invasion but did not induce cell proliferation. TRAIL-mediated cell migration and invasion was NF-kappaB dependent. These data demonstrate that TRAIL promotes cell migration and invasion via a NF-kappaB-dependent pathway in human cholangiocarcinoma cell lines, an observation that has a potential negative implication for TRAIL in cancer therapy.