Bile acids up-regulate death receptor 5/TRAIL-receptor 2 expression via a c-Jun N-terminal kinase-dependent pathway involving Sp1

Mechanism of Bile Acid-Induced Programmed Cell Death and Drug Discovery against Cancer: A Review

Bile acids are major signaling molecules that play a significant role as emulsifiers in the digestion and absorption of dietary lipids. Bile acids are amphiphilic molecules produced by the reaction of enzymes with cholesterol as a substrate, and they are the primary metabolites of cholesterol in the body. Bile acids were initially considered as tumor promoters, but many studies have deemed them to be tumor suppressors. The tumor-suppressive effect of bile acids is associated with programmed cell death. Moreover, based on this fact, several synthetic bile acid derivatives have also been used to induce programmed cell death in several types of human cancers. This review comprehensively summarizes the literature related to bile acid-induced programmed cell death, such as apoptosis, autophagy, and necroptosis, and the status of drug development using synthetic bile acid derivatives against human cancers. We hope that this review will provide a reference for the future research and development of drugs against cancer.

Inflammatory-Dependent Bidirectional Effect of Bile Acids on NLRP3 Inflammasome and Its Role in Ameliorating CPT-11-Induced Colitis

Irinotecan (CPT-11) in combination with 5-fluorouracil and leucovorin is a first-line chemotherapy regimen for the treatment of colorectal cancer; however, its clinical application is limited by the dose-limiting gastrointestinal toxicity of colitis. In our previous studies, several bile acids (BAs) were found significantly elevated in the colon of the CPT-11-induced rat colitis model. On the other hand, NLRP3 inflammasome has been reported to play important roles in mediating colitis. Interestingly, BA was stated to activate the NLRP3 inflammasome in some studies, while in some other reports, it showed an inhibitory effect. We assumed that the inflammatory status in different circumstances might have contributed to the controversial findings. In this study, we first discovered, under non-inflammatory conditions, that supplementing BA could activate the NLRP3 inflammasome in THP-1-differentiated macrophages and promote inflammation. In lipopolysaccharide (LPS)-induced inflammatory macrophages, however, BA inhibited the NLRP3 inflammasome and reduced inflammation. Further experiments demonstrated that Takeda G protein-coupled receptor 5 (TGR5) is essential in mediating the inhibitory effect of BA, while phospho-SP1 (p-SP1) is key to the activation. Furthermore, we applied the above findings to ameliorate CPT-11-caused colitis in rats by inhibiting SP1 with mithramycin A (MitA) or activating TGR5 using oleanolic acid (OA). Our findings may shed light on the discovery of effective interventions for reducing dose-limiting chemotherapy-induced colitis.

Gut microbiota and related metabolites in the pathogenesis of nonalcoholic steatohepatitis and its resolution after bariatric surgery

Nonalcoholic fatty liver disease (NAFLD) is increasing in parallel with the rising prevalence of obesity, leading to major health and socioeconomic consequences. To date, the most effective therapeutic approach for NAFLD is weight loss. Accordingly, bariatric surgery (BS), which produces marked reductions in body weight, is associated with significant histopathological improvements in advanced stages of NAFLD, such as nonalcoholic steatohepatitis (NASH) and liver fibrosis. BS is also associated with substantial taxonomical and functional alterations in gut microbiota, which are believed to play a significant role in metabolic improvement after BS. Interestingly, gut microbiota and related metabolites may be implicated in the pathogenesis of NAFLD through diverse mechanisms, including specific microbiome signatures, short chain fatty acid production or the modulation of one-carbon metabolism. Moreover, emerging evidence highlights the potential association between gut microbiota changes after BS and NASH resolution. In this review, we summarize the current knowledge on the relationship between NAFLD severity and gut microbiota, as well as the role of the gut microbiome and related metabolites in NAFLD improvement after BS.

FXR activation prevents liver injury induced by Tripterygium wilfordii preparations

Tripterygium glycosides tablets (TGT) and Tripterygium wilfordii tablets (TWT) are the preparations of Tripterygium wilfordii used to treat rheumatoid arthritis (RA) in the clinic, but the hepatotoxicity was reported frequently. This study aimed to determine the potential toxicity mechanism of liver injury induced by the preparations of Tripterygium wilfordii in mice.Here, we performed metabolomic analysis, pathological analysis and biochemical analysis of samples from mice with liver injury induced by TGT and TWT, which revealed that liver injury was associated with bile acid metabolism disorder. Quantitative real-time PCR (QPCR) and western blot indicated that the above changes were accompanied by inhibition of farnesoid X receptor (FXR) signalling.Liver injury from TWT could be alleviated by treatment of the FXR agonist obeticholic acid (OCA) via activation of the FXR to inhibit the c-Jun N-terminal kinase (JNK) pathway and improve bile acid metabolism disorder by activating bile salt export pump (BSEP) and organic solute-transporter-β (OSTB). The data demonstrate that FXR signalling pathway plays a key role in T. wilfordii-induced liver injury, which could be alleviated by activated FXR.These results indicate that FXR activation by OCA may offer a promising therapeutic opportunity against hepatotoxicity from the preparations of T. wilfordii.

Gut microbiota and their metabolites in the progression of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent liver disorder worldwide. It comprises a spectrum of conditions that range from steatosis to non-alcoholic steatohepatitis, with progression to cirrhosis and hepatocellular carcinoma. Currently, there is no FDA-approved pharmacological treatment for NAFLD. The pathogenesis of NAFLD involves genetic and environmental/host factors, including those that cause changes in intestinal microbiota and their metabolites. In this review, we discuss recent findings on the relationship(s) of microbiota signature with severity of NAFLD and the role(s) microbial metabolites in NAFLD progression. We discuss how metabolites may affect NAFLD progression and their potential to serve as biomarkers for NAFLD diagnosis or therapeutic targets for disease management.

Tankyrase Inhibitors Target Colorectal Cancer Stem Cells via AXIN-Dependent Downregulation of c-KIT Tyrosine Kinase

Cancer stem cells (CSC) constitute heterogeneous cell subpopulations of a tumor. Although targeting CSCs is important for cancer eradication, no clinically approved drugs that target CSCs have been established. Tankyrase poly(ADP-ribosyl)ates and destabilizes AXIN, a negative regulator of β-catenin, and promotes β-catenin signaling. Here, we report that tankyrase inhibitors downregulate c-KIT tyrosine kinase and inhibit the growth of CD44-positive colorectal CSCs. c-KIT expression in CD44-positive subpopulations of colorectal cancer COLO-320DM cells is associated with their tumor-initiating potential in vivo Tankyrase inhibitors downregulate c-KIT expression in established cell lines, such as COLO-320DM and DLD-1, and colorectal cancer patient-derived cells. These effects of tankyrase inhibitors are caused by reducing the recruitment of SP1 transcription factor to the c-KIT gene promoter and depend on AXIN2 stabilization but not β-catenin downregulation. Whereas c-KIT knockdown inhibits the growth of CD44-positive COLO-320DM cells, c-KIT overexpression in DLD-1 cells confers resistance to tankyrase inhibitors. Combination of a low-dose tankyrase inhibitor and irinotecan significantly inhibited the growth of COLO-320DM tumors in a mouse xenograft model. These observations suggest that tankyrase inhibitors target c-KIT-positive colorectal CSCs and provide a novel therapeutic strategy for cancer.

Salvianolic acid B protects against ANIT-induced cholestatic liver injury through regulating bile acid transporters and enzymes, and NF-κB/IκB and MAPK pathways

The purpose of this study was to investigate the pharmacological effects of salvianolic acid B (SA-B) on α-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury with the focus on bile acid homeostasis and anti-inflammatory pathways. Rats were randomly assigned into four groups. The control group was given normal saline (i.p.) for 7 consecutive days and on the 5th day was given the vehicle (i.g.). Model group was treated with normal saline (i.p.) for 7 days and administrated with ANIT (75 mg/kg, i.g.) on the 5th day. The SA-B groups were treated with SA-B (15 mg/kg and 30 mg/kg, i.p.) for 7 consecutive days as well as ANIT (75 mg/kg, i.g.) on the 5th day. We found that the serum levels of ALT, γ-GT, TBA, and other liver function indexes were found to be lower in the SA-B treatment groups than in the model group. SA-B also upregulated the transporters and enzymes involved in bile acid homeostasis such as Bsep, Oatp2, and Cyp3a2 in rats and BSEP, CYP3A4, and OATP2 in human cell lines. Moreover, SA-B suppressed NF-κB translocation into the nucleus, inhibited phosphorylation of p38 and JNK, and inhibited inflammation markers including IL-1β, IL-6, TGF-β, TNF-α, and COX-2 to extenuate cholestatic liver injury both in vivo and vitro. Taken together, our findings suggest that anti-cholestatic effects of SA-B may be associated with its ability to regulate NF-κB/IκB and MAPK inflammatory signaling pathways to inhibit inflammation and regulate transporters and enzymes to maintain bile acid homeostasis.

Chrysanthemulide A induces apoptosis through DR5 upregulation via JNK-mediated autophagosome accumulation in human osteosarcoma cells

Osteosarcoma is the most frequent malignant primary bone tumor, and it generally develops a multidrug resistance. Chrysanthemulide A (CA) is a sesquiterpenoid from the herb Chrysanthemum indicum that has demonstrated a great anti-osteosarcoma potential. In this study, CA-induced apoptotic cell death resulted in the activation of the caspase-8-mediated caspase cascade, as evidenced by the cleavage of the substrate protein Bid and the caspase-8 inhibitor Z-VAD-FMK. The CA treatment upregulated the expression of death receptor 5 (DR5) in both whole cells and the cell membrane. Blocking DR5 expression by the small interfering RNA (siRNA) treatment decreased the caspase-8-mediated caspase cascade and efficiently attenuated CA-induced apoptosis, suggesting the critical role of DR5 in CA-induced apoptotic cell death. CA-induced upregulation of the DR5 protein was accompanied by the accumulation of LC3B-II, indicating the formation of autophagosomes. Importantly, DR5 upregulation was mediated by transcriptionally controlled autophagosome accumulation, as blockade of autophagosomes by LC3B or ATG-5 siRNA substantially decreased DR5 upregulation. Furthermore, CA activated the c-Jun N-terminal kinase (JNK) signaling pathway, and treatment with JNK siRNAs or inhibitor SP600125 significantly attenuated CA-mediated autophagosome accumulation and DR5-mediated cell apoptosis. Finally, CA sensitized the osteosarcoma cells to the DR5 ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptotic cell death. Above all, these results suggest that CA induces apoptosis through upregulating DR5 via JNK-mediated autophagosome accumulation and that combined treatment with CA and TRAIL might be a promising therapy for osteosarcoma.

Vemurafenib Limits Influenza A Virus Propagation by Targeting Multiple Signaling Pathways

Influenza A viruses (IAV) can cause severe global pandemic outbreaks. The currently licensed antiviral drugs are not very effective and prone to viral resistance. Thus, novel effective and broadly active drugs are urgently needed. We have identified the cellular Raf/MEK/ERK signaling cascade as crucial for IAV replication and suitable target for an antiviral intervention. Since this signaling cascade is aberrantly activated in many human cancers, several clinically approved inhibitors of Raf and MEK are now available. Here we explored the anti-IAV action of the licensed B-RafV600E inhibitor Vemurafenib. Treatment of B-RafWT cells with Vemurafenib induced a hyperactivation of the Raf/MEK/ERK cascade rather than inhibiting its activation upon IAV infection. Despite this hyperactivation, which has also been confirmed by others, Vemurafenib still strongly limited IAV-induced activation of other signaling cascades especially of p38 and JNK mitogen-activated protein kinase (MAPK) pathways. Most interestingly, Vemurafenib inhibited virus-induced apoptosis via impaired expression of apoptosis-inducing cytokines and led to hampered viral protein expression most likely due to the decreased activation of p38 and JNK MAPK. These multiple actions resulted in a profound and broadly active inhibition of viral replication, up to a titer reduction of three orders of a magnitude. Thus, while Vemurafenib did not act similar to MEK inhibitors, it displays strong antiviral properties via a distinct and multi-target mode of action.

JNK-signaling: A multiplexing hub in programmed cell death

Jun N-terminal kinases or JNKs have been shown to be involved in a wide array of signaling events underlying tumorigenesis and tumor progression. Through its interaction with a diverse set of signaling proteins and adaptors, JNKs regulate cell proliferation, invasive migration, therapy resistance, and programmed cell death. JNKs have been shown to play a role in apoptotic as well as non-apoptotic programmed cell death mechanisms including those of necroptosis, ferroptosis, pyroptosis, and autophagy. Most of the tumorigenic regulatory functions of JNKs can be related to their ability to module cell death via these programmed cell death mechanisms. JNKs stimulate or inhibit cell death in a context-dependent manner by stimulating the expression of specific genes as well as by modulating the activities of pro- and anti-apoptotic proteins through distinct phosphorylation events. This review summarizes our current understanding of the role of JNK in programmed cell death and its impact on cancer growth, progression, and therapy.

Inhibition of JNK signalling mediates PPARα-dependent protection against intrahepatic cholestasis by fenofibrate

BACKGROUND AND PURPOSE

Fenofibrate, a PPARα agonist, is the most widely prescribed drug for treating hyperlipidaemia. Although fibrate drugs are reported to be beneficial for cholestasis, their underlying mechanism has not been determined.

EXPERIMENTAL APPROACH

Wild-type mice and Pparα-null mice were pretreated orally with fenofibrate for 3 days, following which α-naphthylisothiocyanate (ANIT) was administered to induce cholestasis. The PPARα agonist WY14643 and JNK inhibitor SP600125 were used to determine the role of PPARα and the JNK pathway, respectively, in cholestatic liver injury. The same fenofibrate regimen was applied to investigate its beneficial effects on sclerosing cholangitis in a DDC-induced cholestatic model.

KEY RESULTS

Fenofibrate, 25 mg·kg^-1 twice a day, totally attenuated ANIT-induced cholestasis and liver injury as indicated by biochemical and histological analyses. This protection occurred in wild-type, but not in Pparα-null, mice. Alterations in bile acid synthesis and transport were found to be an adaptive response rather than a direct effect of fenofibrate. WY14643 attenuated ANIT-induced cholestasis and liver injury coincident with inhibition of JNK signalling. Although SP600125 did not affect cholestasis, it inhibited liver injury in the ANIT model when the dose of fenofibrate used was ineffective. Fenofibrate was also revealed to have a beneficial effect in the sclerosing cholangitis model.

CONCLUSIONS AND IMPLICATIONS

These data suggest that the protective effects of fenofibrate against cholestasis-induced hepatic injury are dependent on PPARα and fenofibrate dose, and are mediated through inhibition of JNK signalling. This mechanism of fenofibrate protection against intrahepatic cholestasis may offer additional therapeutic opportunities for cholestatic liver diseases.

Intracellular localization of DR5 and related regulatory pathways as a mechanism of resistance to TRAIL in cancer

TNF-related apoptosis-inducing ligand (TRAIL) is a prominent cytokine capable of inducing apoptosis. It can bind to five different cognate receptors, through which diverse intracellular pathways can be activated. TRAIL's ability to preferentially kill transformed cells makes it a promising potential weapon for targeted tumor therapy. However, recognition of several resistance mechanisms to TRAIL-induced apoptosis has indicated that a thorough understanding of the details of TRAIL biology is still essential before this weapon can be confidently unleashed. Critical to this aim is revealing the functions and regulation mechanisms of TRAIL's potent death receptor DR5. Although expression and signaling mechanisms of DR5 have been extensively studied, other aspects, such as its subcellular localization, non-signaling functions, and regulation of its membrane transport, have only recently attracted attention. Here, we discuss different aspects of TRAIL/DR5 biology, with a particular emphasis on the factors that seem to influence the cell surface expression pattern of DR5, along with factors that lead to its nuclear localization. Disturbance of this balance apparently affects the sensitivity of cancer cells to TRAIL-mediated apoptosis, thus constituting an eligible target for potential new therapeutic agents.

Hepatic 3D spheroid models for the detection and study of compounds with cholestatic liability

Drug-induced cholestasis (DIC) is poorly understood and its preclinical prediction is mainly limited to assessing the compound's potential to inhibit the bile salt export pump (BSEP). Here, we evaluated two 3D spheroid models, one from primary human hepatocytes (PHH) and one from HepaRG cells, for the detection of compounds with cholestatic liability. By repeatedly co-exposing both models to a set of compounds with different mechanisms of hepatotoxicity and a non-toxic concentrated bile acid (BA) mixture for 8 days we observed a selective synergistic toxicity of compounds known to cause cholestatic or mixed cholestatic/hepatocellular toxicity and the BA mixture compared to exposure to the compounds alone, a phenomenon that was more pronounced after extending the exposure time to 14 days. In contrast, no such synergism was observed after both 8 and 14 days of exposure to the BA mixture for compounds that cause non-cholestatic hepatotoxicity. Mechanisms behind the toxicity of the cholestatic compound chlorpromazine were accurately detected in both spheroid models, including intracellular BA accumulation, inhibition of ABCB11 expression and disruption of the F-actin cytoskeleton. Furthermore, the observed synergistic toxicity of chlorpromazine and BA was associated with increased oxidative stress and modulation of death receptor signalling. Combined, our results demonstrate that the hepatic spheroid models presented here can be used to detect and study compounds with cholestatic liability.

Hydrophobic bile acids suppress expression of AE2 in biliary epithelial cells and induce bile duct inflammation in primary biliary cholangitis

Understanding the mechanisms of chronic inflammation in primary biliary cholangitis (PBC) is essential for successful treatment. Earlier work has demonstrated that patients with PBC have reduced expression of the anion exchanger 2 (AE2) on biliary epithelial cells (BEC) and deletion of AE2 gene has led to a PBC-like disorder in mice. To directly address the role of AE2 in preventing PBC pathogenesis, we took advantage of our ability to isolate human BEC and autologous splenic mononuclear cells (SMC). We studied the influence of hydrophobic bile acids, in particular, glycochenodeoxycholic acid (GCDC), on AE2 expression in BEC and the subsequent impact on the phenotypes of BEC and local inflammatory responses. We demonstrate herein that GCDC reduces AE2 expression in BEC through induction of reactive oxygen species (ROS), which enhances senescence of BEC. In addition, a reduction of AE2 levels by either GCDC or another AE2 inhibitor upregulates expression of CD40 and HLA-DR as well as production of IL-6, IL-8 and CXCL10 from BEC in response to toll like receptor ligands, an effect suppressed by inhibition of ROS. Importantly, reduced AE2 expression enhances the migration of autologous splenic mononuclear cells (SMC) towards BEC. In conclusion, our data highlight a key functional role of AE2 in the maintenance of the normal physiology of BEC and the pathogenic consequences of reduced AE2 expression, including abnormal intrinsic characteristics of BEC and their production of signal molecules that lead to the chronic inflammatory responses in small bile ducts.

PP2A inhibitors arrest G2/M transition through JNK/Sp1- dependent down-regulation of CDK1 and autophagy-dependent up-regulation of p21

Protein phosphatase 2A (PP2A) plays an important role in the control of the cell cycle. We previously reported that the PP2A inhibitors, cantharidin and okadaic acid (OA), efficiently repressed the growth of cancer cells. In the present study, we found that PP2A inhibitors arrested the cell cycle at the G2 phase through a mechanism that was dependent on the JNK pathway. Microarrays further showed that PP2A inhibitors induced expression changes in multiple genes that participate in cell cycle transition. To verify whether these expression changes were executed in a PP2A-dependent manner, we targeted the PP2A catalytic subunit (PP2Ac) using siRNA and evaluated gene expression with a microarray. After the cross comparison of these microarray data, we identified that CDK1 was potentially the same target when treated with either PP2A inhibitors or PP2Ac siRNA. In addition, we found that the down-regulation of CDK1 occurred in a JNK-dependent manner. Luciferase reporter gene assays demonstrated that repression of the transcription of CDK1 was executed through the JNK-dependent activation of the Sp1 transcription factor. By constructing deletion mutants of the CDK1 promoter and by using ChIP assays, we identified an element in the CDK1 promoter that responded to the JNK/Sp1 pathway after stimulation with PP2A inhibitors. Cantharidin and OA also up-regulated the expression of p21, an inhibitor of CDK1, via autophagy rather than PP2A/JNK pathway. Thus, this present study found that the PP2A/JNK/Sp1/CDK1 pathway and the autophagy/p21 pathway participated in G2/M cell cycle arrest triggered by PP2A inhibitors.

Inhibition of NF-κB by deoxycholic acid induces miR-21/PDCD4-dependent hepatocellular apoptosis

MicroRNAs (miRNAs/miRs) are key regulators of liver metabolism, while toxic bile acids participate in the development of several liver diseases. We previously demonstrated that deoxycholic acid (DCA), a cytotoxic bile acid implicated in the pathogenesis of non-alcoholic fatty liver disease, inhibits miR-21 expression in hepatocytes. Here, we investigated the mechanisms by which DCA modulates miR-21 and whether miR-21 contributes for DCA-induced cytotoxicity. DCA inhibited miR-21 expression in primary rat hepatocytes in a dose-dependent manner, and increased miR-21 pro-apoptotic target programmed cell death 4 (PDCD4) and apoptosis. Both miR-21 overexpression and PDCD4 silencing hampered DCA-induced cell death. Further, DCA decreased NF-κB activity, shown to represent an upstream mechanism leading to modulation of the miR-21/PDCD4 pathway. In fact, NF-κB overexpression or constitutive activation halted miR-21-dependent apoptosis by DCA while opposite results were observed upon NF-κB inhibition. In turn, DCA-induced oxidative stress resulted in caspase-2 activation and NF-κB/miR-21 inhibition, in a PIDD-dependent manner. Finally, modulation of the NF-κB/miR-21/PDCD4 pro-apoptotic pathway by DCA was also shown to occur in the rat liver in vivo. These signalling circuits may constitute appealing targets for bile acid-associated liver pathologies.

Inhibition of Notch1 signaling overcomes resistance to the death ligand Trail by specificity protein 1-dependent upregulation of death receptor 5

The Notch1 signaling pathway contributes to tumorigenesis by influencing differentiation, proliferation and apoptosis. Here, we demonstrate that inhibition of the Notch1 signaling pathway sensitizes glioblastoma cell lines and glioblastoma initiating cells to apoptosis induced by the death ligand TRAIL. This sensitization occurs through transcriptional upregulation of the death receptor 5 (DR5, TRAIL-R2). The increase in DR5 expression is abrogated by concomitant repression of the transcription factor Sp1, which directly binds to the DR5 promoter in the absence of Notch1 as revealed by chromatin immunoprecipitation. Consistent with these findings, Notch1 inhibition resulted in increased DR5 promoter activity, which was impaired by mutation of one out of two Sp1-binding sites within the proximal DR5 promoter. Moreover, we demonstrate that JNK signaling contributes to the regulation of DR5 expression by Notch1. Taken together, our results identify Notch1 as key driver for TRAIL resistance and suggest Notch1 as a promising target for anti-glioblastoma therapy.

Infliximab as a treatment option for patients with rheumatoid arthritis and primary biliary cirrhosis

Rheumatoid arthritis (RA) is a chronic inflammatory systemic disease which commonly requires treatment with biologic agents targeting various inflammatory pathways. Tumor necrosis factor alpha is a proinflammatory cytokine which plays a pivotal role not only in the pathogenesis of RA but also in other autoimmune diseases such as primary biliary cirrhosis. The co-existence of more than one autoimmune disorder in the same individual is very challenging in the daily practice as therapy strategies applicable to one disease setting may cause clinical and/or biochemical relapse of the other clinical entity. As a result, treatment options able to control different diseases are highly desirable among rheumatologists and other specialties. In that respect, we present a case of a 61-year-old female patient with RA and concomitant primary biliary cirrhosis with poor clinical response to conventional disease-modifying drugs for RA. The introduction of tumor necrosis factor alpha antagonist infliximab led to significant clinical improvement of RA and to stabilization of liver function. In this case review study, we discuss aspects of pathophysiology of primary biliary cirrhosis associated with tumor necrosis alpha and we review the available data of similar published cases.

Activation of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor gene expression following DNA demethylation in placental choriocarcinoma and transformed cell lines

We characterised DNA methylation and gene expression of four tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR4, DR5, DcR1 and DcR2 in three choriocarcinoma (JAR, JEG-3, BeWo) and two transformed (HTR-8/SVneo and HPT-8) cell lines. DR4 mRNA was detected in JAR, JEG-3, BeWo and HTR-8/SVneo cells, whereas DR5 was present in all detected cells. DcR1 transcripts were expressed only in JAR, JEG-3 and BeWo cells, whereas DcR2 transcripts were detected only in HTR-8/SVneo and HPT-8 cells. Hypermethylated DR4 promoter was observed in JAR, JEG-3, BeWo and HTR-8/SVneo cells, hypermethylated DcR1 promoter in HTR-8/SVneo and HPT-8 cells and hypermethylated DcR2 promoter in JAR, JEG-3 and BeWo cells. Restoration of DR4, DcR1 and DcR2 expression with decreased DNA methylation of these genes was induced by the DNA demethylation agent 5-aza-2'-deoxycytidine (5-aza-CdR) in trophoblast cells, whereas DR5 expression did not exhibit any change. Significant negative correlation between the expression and DNA methylation of these genes was also observed. In all tested cell lines, only HPT-8 demonstrated sensitivity to TRAIL-induced apoptosis. Combined treatment with 5-aza-CdR and TRAIL resulted in apoptosis in JAR, JEG-3, BeWo and HTR-8/SVneo cells but not in HPT-8 cells. The results indicate that DNA methylation is associated with TRAIL receptor expression and might be involved in trophoblast apoptosis.

Camptothecin sensitizes human hepatoma Hep3B cells to TRAIL-mediated apoptosis via ROS-dependent death receptor 5 upregulation with the involvement of MAPKs

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various types of malignant cancer cells, but several cancers have acquired potent resistance to TRAIL-induced cell death by unknown mechanisms. Camptothecin (CPT) is a quinolone alkaloid that induces cytotoxicity in a variety of cancer cell lines. However, it is not known whether CPT triggers TRAIL-induced cell death. In this study, we found that combined treatment with subtoxic doses of CPT and TRAIL (CPT-TRAIL) potentially enhanced apoptosis in a caspase-dependent manner. CPT-TRAIL effectively induced the expression of death receptor (DR) 5, which is a specific receptor of TRAIL, and treatment with a chimeric blocking antibody for DR5 reduced CPT-TRAIL-induced cell death, indicating that CPT functionally triggers DR5-mediated cell death in response to TRAIL. CPT-induced generation of reactive oxygen species (ROS) also preceded the upregulation of DR5 in response to TRAIL. The involvement of ROS in DR5 upregulation confirmed that pretreatment with antioxidants, including N-acetyl-L-cysteine and glutathione, significantly inhibits CPT-TRAIL-induced cell death by suppressing DR5 expression. The specific inhibitors of ERK and p38 also decreased CPT-TRAIL-induced cell death by blocking DR5 expression. In conclusion, our results suggest that CPT sensitizes cancer cells to TRAIL-mediated apoptosis via ROS and ERK/p38-dependent DR5 upregulation.

Two death-inducing human TRAIL receptors to target in cancer: similar or distinct regulation and function?

The emergence during evolution of two tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors, receptor-1/DR4 and -2/DR5, able to induce apoptosis has raised the question whether they differ in function and regulation, which is of key importance for selecting either DR4 or DR5 selective pro-apoptotic agents for cancer treatment. In this review we found practically no information regarding possible differences in DR4 and DR5 function based on structural differences. On the other hand, a panel of different DR4 or DR5 selective pro-apoptotic agonists have been developed that were explored for efficacy in different tumour types in a large number of studies. Leukemic cells appear mainly sensitive for DR4-induced apoptosis, contrasting the situation in other tumour types that show heterogeneity in receptor preference and, in some cases, a slight overall preference for DR5. Both receptors were found to mediate intracellular stress-induced apoptosis, although this is most frequently reported for DR5. Interestingly, DR5 was also found to transmit non-apoptotic signalling in resistant tumour cells and recently nuclear localization and a role in microRNA maturation has been described. DR4 expression is most heavily regulated by promoter methylation, intracellular trafficking and post-translational modifications. DR5 expression is predominantly regulated at the transcriptional level, which may reflect its ability to respond to cellular stressors. It will be important to further increase our understanding of the mechanisms determining TRAIL receptor preference in order to select the appropriate TRAIL receptor selective agonists for therapy, and to develop novel strategies to enhance apoptosis activation in tumours.

Regulation of the extrinsic apoptotic pathway by microRNA-21 in alcoholic liver injury

IL-6/Stat3 is associated with the regulation of transcription of key cellular regulatory genes (microRNAs) during different types of liver injury. This study evaluated the role of IL-6/Stat3 in regulating miRNA and miR-21 in alcoholic liver disease. By microarray, we identified that ethanol feeding significantly up-regulated 0.8% of known microRNAs in mouse liver compared with controls, including miR-21. Similarly, the treatment of normal human hepatocytes (N-Heps) and hepatic stellate cells (HSCs) with ethanol and IL-6 significantly increased miR-21 expression. Overexpression of miR-21 decreased ethanol-induced apoptosis in both N-Heps and HSCs. The expression level of miR-21 was significantly increased after Stat3 activation in N-Heps and HSCs, in support of the concept that the 5'-promoter region of miR-21 is regulated by Stat3. Using real time PCR, we confirmed that miR-21 activation is associated with ethanol-linked Stat3 binding of the miR-21 promoter. A combination of bioinformatics, PCR array, dual-luciferase reporter assay, and Western blot analysis revealed that Fas ligand (TNF superfamily, member 6) (FASLG) and death receptor 5 (DR5) are the direct targets of miR-21. Furthermore, inhibition of miR-21 by specific Vivo-Morpholino and knock-out of IL-6 in ethanol-treated mice also increased the expression of DR5 and FASLG in vivo during alcoholic liver injury. The identification of miR-21 as an important regulator of hepatic cell survival, transformation, and remodeling in vitro, as well as its upstream modulators and downstream targets, will provide insight into the involvement of altered miRNA expression in contributing to alcoholic liver disease progression and testing novel therapeutic approaches for human alcoholic liver diseases.

Poly(ADP-ribose) polymerase inhibitors sensitize cancer cells to death receptor-mediated apoptosis by enhancing death receptor expression

Recombinant human tumor necrosis factor-α-related apoptosis inducing ligand (TRAIL), agonistic monoclonal antibodies to TRAIL receptors, and small molecule TRAIL receptor agonists are in various stages of preclinical and early phase clinical testing as potential anticancer drugs. Accordingly, there is substantial interest in understanding factors that affect sensitivity to these agents. In the present study we observed that the poly(ADP-ribose) polymerase (PARP) inhibitors olaparib and veliparib sensitize the myeloid leukemia cell lines ML-1 and K562, the ovarian cancer line PEO1, non-small cell lung cancer line A549, and a majority of clinical AML isolates, but not normal marrow, to TRAIL. Further analysis demonstrated that PARP inhibitor treatment results in activation of the FAS and TNFRSF10B (death receptor 5 (DR5)) promoters, increased Fas and DR5 mRNA, and elevated cell surface expression of these receptors in sensitized cells. Chromatin immunoprecipitation demonstrated enhanced binding of the transcription factor Sp1 to the TNFRSF10B promoter in the presence of PARP inhibitor. Knockdown of PARP1 or PARP2 (but not PARP3 and PARP4) not only increased expression of Fas and DR5 at the mRNA and protein level, but also recapitulated the sensitizing effects of the PARP inhibition. Conversely, Sp1 knockdown diminished the PARP inhibitor effects. In view of the fact that TRAIL is part of the armamentarium of natural killer cells, these observations identify a new facet of PARP inhibitor action while simultaneously providing the mechanistic underpinnings of a novel therapeutic combination that warrants further investigation.

Impaired bile acid handling and aggravated liver injury in mice expressing a hepatocyte-specific RXRα variant lacking the DNA-binding domain

BACKGROUND & AIMS

Retinoid X Receptor α (RXRα) is the principal heterodimerization partner of class II Nuclear Receptors (NRs), and a major regulator of gene expression of numerous hepatic processes, including bile acid (BA) homeostasis through multiple partners. Specific contributions of hepatic RXRα domains in heterodimer function in response to either BA load or ductular cholestasis are not fully characterized.

METHODS

Wild-type (WT) mice and mice expressing a hepatocyte-specific RXRα lacking the DNA-Binding-Domain (hs-RxrαΔex4(-/-)), which retains partial ability to heterodimerize with its partners, were fed a 1% cholic acid (CA) diet for 5 days, a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet for 3 weeks, or control diet.

RESULTS

Serum ALT (6.5-fold; p<0.05), AST (9.3-fold; p=0.06) and BA (2.8-fold; p<0.05) were increased in CA-fed hs-RxαΔex4(-/-) mice compared to CA-fed WT mice, but were equally induced between genotypes by DDC-feeding. CA-feeding elevated total (4.4-fold; p=0.06) and unconjugated (2.2-fold; p<0.02) bilirubin levels in hs-RxrαΔex4(-/-) mice compared to WT mice, but not in DDC-fed hs-RxrαΔex4(-/-) mice. Increased necrosis and inflammation was observed in CA-fed, but not in DDC-fed hs-RxrαΔex4(-/-) mice. Apoptotic markers DR5, CK8, CK18 RNA were increased in CA- and DDC-fed hs-RxrαΔex4(-/-) mice. Cleaved caspase 3, CK18 and p-JNK protein were elevated in CA-fed but not in DDC-fed hs-RxrαΔex4(-/-) mice. Induction of Ostβ and Cyp2b10 RNA was impaired in CA-fed and DDC-fed hs-RxrαΔex4(-/-) mice. Surprisingly, DDC-fed hs-RxrαΔex4(-/-) mice showed attenuated fibrosis compared to DDC-fed WT mice.

CONCLUSIONS

These two models of cholestasis identify common and injury-specific roles for RXRα heterodimers and the functional relevance of an intact RXRα-DBD in the hepatocytic adaptive cholestatic response.

Genome sequence of Anopheles sinensis provides insight into genetics basis of mosquito competence for malaria parasites

BACKGROUND

Anopheles sinensis is an important mosquito vector of Plasmodium vivax, which is the most frequent and widely distributed cause of recurring malaria throughout Asia, and particularly in China, Korea, and Japan.

RESULTS

We performed 454 next-generation sequencing and obtained a draft sequence of A. sinensis assembled into scaffolds spanning 220.8 million base pairs. Analysis of this genome sequence, we observed expansion and contraction of several immune-related gene families in anopheline relative to culicine mosquito species. These differences suggest that species-specific immune responses to Plasmodium invasion underpin the biological differences in susceptibility to Plasmodium infection that characterize these two mosquito subfamilies.

CONCLUSIONS

The A. sinensis genome produced in this study, provides an important resource for analyzing the genetic basis of susceptibility and resistance of mosquitoes to Plasmodium parasites research which will ultimately facilitate the design of urgently needed interventions against this debilitating mosquito-borne disease.

c-Jun N-terminal kinase 1/c-Jun activation of the p53/microRNA 34a/sirtuin 1 pathway contributes to apoptosis induced by deoxycholic acid in rat liver

MicroRNAs (miRs) are increasingly associated with metabolic liver diseases. We have shown that ursodeoxycholic acid, a hydrophilic bile acid, counteracts the miR-34a/sirtuin 1 (SIRT1)/p53 pathway, activated in the liver of nonalcoholic steatohepatitis (NASH) patients. In contrast, hydrophobic bile acids, particularly deoxycholic acid (DCA), activate apoptosis and are increased in NASH. We evaluated whether DCA-induced apoptosis of rat hepatocytes occurs via miR-34a-dependent pathways and whether they connect with c-Jun N-terminal kinase (JNK) induction. DCA enhanced miR-34a/SIRT1/p53 proapoptotic signaling in a dose- and time-dependent manner. In turn, miR-34a inhibition and SIRT1 overexpression significantly rescued targeting of the miR-34a pathway and apoptosis by DCA. In addition, p53 overexpression activated the miR-34a/SIRT1/p53 pathway, further induced by DCA. DCA increased p53 expression as well as p53 transcriptional activation of PUMA and miR-34a itself, providing a functional mechanism for miR-34a activation. JNK1 and c-Jun were shown to be major targets of DCA, upstream of p53, in engaging the miR-34a pathway and apoptosis. Finally, activation of this JNK1/miR-34a proapoptotic circuit was also shown to occur in vivo in the rat liver. These results suggest that the JNK1/p53/miR-34a/SIRT1 pathway may represent an attractive pharmacological target for the development of new drugs to arrest metabolism- and apoptosis-related liver pathologies.

Bile acid receptors as targets for drug development

The intracellular nuclear receptor farnesoid X receptor and the transmembrane G protein-coupled receptor TGR5 respond to bile acids by activating transcriptional networks and/or signalling cascades. These cascades affect the expression of a great number of target genes relevant for bile acid, cholesterol, lipid and carbohydrate metabolism, as well as genes involved in inflammation, fibrosis and carcinogenesis. Pregnane X receptor, vitamin D receptor and constitutive androstane receptor are additional nuclear receptors that respond to bile acids, albeit to a more restricted set of species of bile acids. Recognition of dedicated bile acid receptors prompted the development of semi-synthetic bile acid analogues and nonsteroidal compounds that target these receptors. These agents hold promise to become a new class of drugs for the treatment of chronic liver disease, hepatocellular cancer and extrahepatic inflammatory and metabolic diseases. This Review discusses the relevant bile acid receptors, the new drugs that target bile acid signalling and their possible applications.

Apoptosis and necrosis in the liver

Because of its unique function and anatomical location, the liver is exposed to a multitude of toxins and xenobiotics, including medications and alcohol, as well as to infection by hepatotropic viruses, and therefore, is highly susceptible to tissue injury. Cell death in the liver occurs mainly by apoptosis or necrosis, with apoptosis also being the physiologic route to eliminate damaged or infected cells and to maintain tissue homeostasis. Liver cells, especially hepatocytes and cholangiocytes, are particularly susceptible to death receptor-mediated apoptosis, given the ubiquitous expression of the death receptors in the organ. In a quite unique way, death receptor-induced apoptosis in these cells is mediated by both mitochondrial and lysosomal permeabilization. Signaling between the endoplasmic reticulum and the mitochondria promotes hepatocyte apoptosis in response to excessive free fatty acid generation during the metabolic syndrome. These cell death pathways are partially regulated by microRNAs. Necrosis in the liver is generally associated with acute injury (i.e., ischemia/reperfusion injury) and has been long considered an unregulated process. Recently, a new form of "programmed" necrosis (named necroptosis) has been described: the role of necroptosis in the liver has yet to be explored. However, the minimal expression of a key player in this process in the liver suggests this form of cell death may be uncommon in liver diseases. Because apoptosis is a key feature of so many diseases of the liver, therapeutic modulation of liver cell death holds promise. An updated overview of these concepts is given in this article.

Pro-apoptotic role of the MEK/ERK pathway in ursodeoxycholic acid-induced apoptosis in SNU601 gastric cancer cells

Ursodeoxycholic acid (UDCA) has been regarded as a suppressor of gastrointestinal cancer, but the mechanisms underlying its antitumor effects are not fully understood. Previously, we reported the antitumor effect of UDCA by demonstrating that UDCA induces apoptosis of gastric cancer cells. Bile acids are known to activate the ERK pathway and ERK is a representative oncogenic kinase in cancer cells. Here, we investigated the role of ERK in UDCA-induced gastric cancer cell apoptosis. We found that UDCA enhanced the phosphorylation of ERK1/2 and MEK1/2. The prevention of MEK by the pharmacologic inhibitors PD98059 and U0126, resulted in decreased UDCA-induced apoptosis as shown by the reduction of apoptotic body formation, caspase-8 activity, and caspase-3, -6 and PARP cleavage, indicating that ERK exerts pro-apoptotic activity upon exposure to UDCA. In addition, U0126 reduced UDCA-triggered TNF-related apoptosis-inducing ligand receptor 2 (TRAIL-R2/DR5) expression. In gene silencing studies, we observed that RNA interference of ERK2 decreased apoptosis and reduced DR5 overexpression. Lipid raft disrupting agent, methyl-β-cyclodextrin, blunted the phosphorylation of ERK1/2, indicating that ERK activation is regulated in a lipid raft-dependent manner. On the other hand, tumor-promoting bile acid, deoxycholic acid (DCA), also phosphorylated ERK in SNU601 cells. However, the DCA-triggered ERK pathway exerted anti-apoptotic function in the cells. Suppression of the ERK pathway enhanced DCA-induced apoptosis, and ERK activation was observed to be lipid raft-independently controlled. These results indicated that UDCA and DCA may cause differential responses in gastric cancer cells through the ERK signaling molecule. Thus, ERK activation may be a possible mechanism by which UDCA and DCA represent differential activities in gastrointestinal cancer.

Molecular mechanisms of ursodeoxycholic acid toxicity & side effects: ursodeoxycholic acid freezes regeneration & induces hibernation mode

Ursodeoxycholic acid (UDCA) is a steroid bile acid approved for primary biliary cirrhosis (PBC). UDCA is reported to have “hepato-protective properties”. Yet, UDCA has “unanticipated” toxicity, pronounced by more than double number of deaths, and eligibility for liver transplantation compared to the control group in 28 mg/kg/day in primary sclerosing cholangitis, necessitating trial halt in North America. UDCA is associated with increase in hepatocellular carcinoma in PBC especially when it fails to achieve biochemical response (10 and 15 years incidence of 9% and 20% respectively). “Unanticipated” UDCA toxicity includes hepatitis, pruritus, cholangitis, ascites, vanishing bile duct syndrome, liver cell failure, death, severe watery diarrhea, pneumonia, dysuria, immune-suppression, mutagenic effects and withdrawal syndrome upon sudden halt. UDCA inhibits DNA repair, co-enzyme A, cyclic AMP, p53, phagocytosis, and inhibits induction of nitric oxide synthatase. It is genotoxic, exerts aneugenic activity, and arrests apoptosis even after cellular phosphatidylserine externalization. UDCA toxicity is related to its interference with drug detoxification, being hydrophilic and anti-apoptotic, has a long half-life, has transcriptional mutational abilities, down-regulates cellular functions, has a very narrow difference between the recommended (13 mg/kg/day) and toxic dose (28 mg/kg/day), and it typically transforms into lithocholic acid that induces DNA strand breakage, it is uniquely co-mutagenic, and promotes cell transformation. UDCA beyond PBC is unjustified.

Ursodeoxycholic acid protects colon cancer HCT116 cells from deoxycholic acid-induced apoptosis by inhibiting apoptosome formation

We previously demonstrated that ursodeoxycholic acid (UDC) requires prolonged (≥5 h) preincubation to exhibit effective protection of colon cancer HCT116 cells from deoxycholic acid (DC)-induced apoptosis. Although UDC diminished DC-mediated caspase-9 activation, cytochrome c release from the mitochondria was not inhibited, indicating that UDC acts on the steps of caspase-9 activation. In the present study, therefore, we investigated the effects of UDC on the factors involved in caspase-9 activation. We found that UDC had no significant effect on the expression of antiapoptotic XIAP. Furthermore, UDC did not affect the expression or release of proapoptotic Smac/DIABLO, or the association of XIAP and Smac/DIABLO. In contrast, association of Apaf-1 and caspase-9 stimulated by 500 μM DC was inhibited by UDC pretreatment. Although UDC caused remarkable activation of Akt/PKB, phosphatidylinositol-3-kinase (PI3K) inhibitor did not significantly reduce UDC-mediated cytoprotection. Furthermore, phosphorylation of threonine residues on caspase-9 after UDC pretreatment could not be detected. UDC-mediated cytoprotection was independent of the MAPK pathway, and cyclic AMP (cAMP) analogue did not inhibit DC-induced apoptosis. Our results indicate that UDC protects colon cancer cells from apoptosis induced by hydrophobic bile acids, by inhibiting apoptosome formation independently of the survival signals mediated by the PI3K, MAPK, or cAMP pathways.

Ameliorated ConA-induced hepatitis in the absence of PKC-theta

Severe liver injury that occurs when immune cells mistakenly attack an individual's own liver cells leads to autoimmune hepatitis. In mice, acute hepatitis can be induced by concanavalin A (ConA) treatment, which causes rapid activation of CD1d-positive natural killer (NK) T cells. These activated NKT cells produce large amounts of cytokines, which induce strong inflammation that damages liver tissues. Here we show that PKC-θ^−/− mice were resistant to ConA-induced hepatitis due to essential function of PKC-θ in NKT cell development and activation. A dosage of ConA (25 mg/kg) that was lethal to wild-type (WT) mice failed to induce death resulting from liver injury in PKC-θ^−/− mice. Correspondingly, ConA-induced production of cytokines such as IFNγ, IL-6, and TNFα, which mediate the inflammation responsible for liver injury, were significantly lower in PKC-θ^−/− mice. Peripheral NKT cells had developmental defects at early stages in the thymus in PKC-θ^−/− mice, and as a result their frequency and number were greatly reduced. Furthermore, PKC-θ^−/− bone marrow adoptively transferred to WT mice displayed similar defects in NKT cell development, suggesting an intrinsic requirement for PKC-θ in NKT cell development. In addition, upon stimulation with NKT cell-specific lipid ligand, peripheral PKC-θ^−/− NKT cells produced lower levels of inflammatory cytokines than that of WT NKT cells, suggesting that activation of NKT cells also requires PKC-θ. Our results suggest PKC-θ is an essential molecule required for activation of NKT cell to induce hepatitis, and thus, is a potential drug target for prevention of autoimmune hepatitis.

TRAIL dependent fratricidal killing of gp120 primed hepatocytes by HCV core expressing hepatocytes

The mechanism by which HIV and HCV cooperatively accelerate hepatocyte damage is not clearly understood; however, each virus affects the TRAIL: TRAIL-receptor system. We, therefore, questioned whether the independent effects of HCV and HIV combine to synergistically result in TRAIL dependent hepatocyte killing. We describe that Huh7 hepatocytes treated with HIV gp120 results in both increase TRAIL-R2 expression and an acquired sensitivity to TRAIL mediated killing. Moreover HCV infection and HCV core expression alone in Huh7 cells upregulates TRAIL. Co-incubation of HIV gp120 primed hepatocytes with HCV core expressing hepatocytes results in the selective death of the HIV gp120 primed hepatocytes that is selectively blocked by TRAIL-R2-Fc fusion protein. Liver biopsies from HIV mono-infected patients have increased TRAIL-R2; biopsies from HCV infected patients have increased TRAIL, while co-infected liver biopsies have increased PARP cleavage within hepatocytes indicating enhanced apoptosis. These findings suggest a pathogenic model to understand why HIV/HCV co-infection accelerates liver injury.

Guggulsterone sensitizes hepatoma cells to TRAIL-induced apoptosis through the induction of CHOP-dependent DR5: involvement of ROS-dependent ER-stress

Guggulsterone (GGS) has anti-tumor and anti-angiogenesis potential by suppressing nuclear factor-κB and STAT3 activity. Although GGS has been suggested as a potential therapeutic agent for treating various cancers, the underlying molecular mechanisms are unknown. Therefore, we investigated whether GGS sensitizes hepatocellular carcinoma cells (HCC) to apoptosis mediated by tumor necrosis factor-related apoptosis inducing ligand (TRAIL). The apoptotic mechanism induced by treatment with a GGS/TRAIL combination involved the loss of mitochondrial transmembrane potential and consequent activation of caspases. GGS also induced upregulation of the death receptor DR5 for TRAIL. The effects seemed to be associated with eIF2α and CHOP activation, which are related to the endoplasmic reticulum (ER) stress response and apoptosis. This relationship was suggested by the observation that CHOP downregulation by specific siRNA attenuated both GGS-mediated DR5 upregulation and the cytotoxicity induced by GGS/TRAIL co-treatment. Moreover, salubrinal, a specific eIF-2α phosphorylation-inducing agent, enhanced the expression of CHOP and DR5 induced by GGS and sensitized cells to GGS/TRAIL-induced apoptosis. Thus, GGS-induced eIF2α phosphorylation seems to be important for CHOP and DR5 upregulation. Furthermore, these events were accompanied by an increase in the generation of reactive oxygen species. Pretreatment with N-acetyl-L-cysteine and glutathione inhibited GGS-induced ER-stress, and CHOP and DR5 upregulation and almost completely blocked GGS/TRAIL-induced apoptosis. These results collectively indicate that DR5 induction via eIF-2α and CHOP is crucial for the marked synergistic effects induced by TRAIL and GGS. Taken together, these results indicate that a GGS/TRAIL combination could represent a novel important tool for cancer therapy.

Death receptor 5 and cellular FLICE-inhibitory protein regulate pemetrexed-induced apoptosis in human lung cancer cells

Pemetrexed is a clinically available anti-folate therapeutic agent used in combination with cisplatin for the management of patients with malignant pleural mesothelioma and advanced non-small cell lung cancer. Pemetrexed inhibits three enzymes in purine and pyrimidine synthesis necessary for precursor DNA nucleotides which in turn disrupts growth and survival of normal and cancer cells. The mechanism by which pemetrexed induces apoptosis remains largely uncharacterised. In the current study, we examined the downstream effect of pemetrexed in inducing apoptosis in lung cancer cells. We showed that pemetrexed induced apoptosis via up-regulation of Death Receptor 5 (DR5), an important death receptor for tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL). In addition, we discovered a synergistic effect of combination pemetrexed and recombinant TRAIL in inducing apoptosis. Modulating DR5 induction by small interfering RNA abrogated the ability of pemetrexed to induce apoptosis. In addition, silencing of C/EBP homologous protein (CHOP) expression reduced DR5 expression, demonstrating that the transcriptional factor CHOP has a pivotal role on DR5 up-regulation following pemetrexed treatment. In addition, enforced expression of cellular FLICE-inhibitory protein (c-FLIP), a known inhibitor of caspase 8, protected neoplastic cells from apoptosis despite pemetrexed and/or TRAIL therapy. Thus, our findings demonstrate the efficacy and mechanistic underpinnings of pemetrexed-induced apoptosis, and they suggest pemetrexed may have clinical utility when used in combination with TRAIL for the management of patients with lung cancer.

Transcriptional regulation of bone morphogenetic protein 4 by tumor necrosis factor and its relationship with age-related macular degeneration

Bone morphogenetic protein-4 (BMP4) may be involved in the molecular switch that determines which late form of age-related macular degeneration (AMD) an individual develops. BMP4 expression is high in retinal pigment epithelium (RPE) cells in late, dry AMD patients, while BMP4 expression is low in the wet form of the disease, characterized by choroidal neovascularization (CNV). Here, we sought to determine the mechanism by which BMP4 is down-regulated in CNV. BMP4 expression was decreased within laser-induced CNV lesions in mice at a time when tumor necrosis factor (TNF) expression was high (7 d postlaser) and was reexpressed in RPE when TNF levels declined (14 d postlaser). We found that TNF, an important angiogenic stimulus, significantly down-regulates BMP4 expression in cultured human fetal RPE cells, ARPE-19 cells, and RPE cells in murine posterior eye cup explants. We identified two specificity protein 1 (Sp1) binding sites in the BMP4 promoter that are required for basal expression of BMP4 and its down-regulation by TNF. Through c-Jun NH(2)-terminal kinase (JNK) activation, TNF modulates Sp1 phosphorylation, thus decreasing its affinity to the BMP4 promoter. The down-regulation of BMP4 expression by TNF in CNV and mechanisms established might be useful for defining novel targets for AMD therapy.

Piceatannol enhances TRAIL-induced apoptosis in human leukemia THP-1 cells through Sp1- and ERK-dependent DR5 up-regulation

Although piceatannol (PIC) is known to mediate anti-cancer, anti-inflammatory, and anti-oxidant activities, little is known about the mechanism of PIC in terms of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. In this study, we examined whether combined treatment with PIC and TRAIL synergistically induces apoptosis in THP-1 leukemia cells. Results indicate that PIC substantially enhances TRAIL-induced cell death including DNA fragmentation and poly(ADP-ribose) polymerase cleavage. Consistent with TRAIL-induced apoptosis, PIC significantly increased the mRNA and protein expression levels of DR5, a death receptor of TRAIL. Further, PIC enhanced DR5 promoter activity via Sp1 activation. Interestingly, the DR5 chimera antibodies significantly suppressed PIC and TRAIL-mediated apoptosis. The inhibitor of ERK also decreased PIC and TRAIL-induced apoptosis by blocking DR5 expression. In conclusion, our results suggest that PIC sensitizes TRAIL-induced-apoptosis via Sp1- and ERK-dependent DR5 up-regulation.

2-Tellurium-bridged β-cyclodextrin, a thioredoxin reductase inhibitor, sensitizes human breast cancer cells to TRAIL-induced apoptosis through DR5 induction and NF-κB suppression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity via membrane receptors on cancer cells without deleterious side effects for normal tissue. Unfortunately, breast cancer cells, as many other cancer types, develop resistance to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. 2-Tellurium-bridged β-cyclodextrin (2-TeCD) is a synthetic organotellurium compound, with both glutathione peroxidase-like catalytic ability and thioredoxin reductase inhibitor activity. In the present study, we reported that 2-TeCD sensitized TRAIL-resistant human breast cancer cells and xenograft tumors to undergo apoptosis. In vitro, 2-TeCD efficiently sensitized MDA-MB-468 and T47D cells, but not untransformed human mammary epithelial cells, to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly (adenosine diphosphate-ribose) polymerase cleavage. From a mechanistic standpoint, we showed that 2-TeCD treatment of breast cancer cells significantly upregulated the messenger RNA and protein levels of TRAIL receptor, death receptor (DR) 5, in a transcription factor Sp1-dependent manner. 2-TeCD treatment also suppressed TRAIL-induced nuclear factor-κB (NF-κB) prosurvival pathways by preventing cytosolic IκBα degradation, as well as p65 nuclear translocation. Consequently, the combined administration suppressed anti-apoptotic molecules that are transcriptionally regulated by NF-κB. In vivo, 2-TeCD and TRAIL were well tolerated in mice and their combination significantly inhibited growth of MDA-MB-468 xenografts and promoted apoptosis. Upregulation of DR5 and downregulation of NF-κB by the dual treatment were also observed in tumor tissues. Overall, 2-TeCD sensitizes resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.

Biliary apotopes and anti-mitochondrial antibodies activate innate immune responses in primary biliary cirrhosis

Our understanding of primary biliary cirrhosis (PBC) has been significantly enhanced by the rigorous dissection of the multilineage T and B cell response against the immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2). PDC-E2 is a ubiquitous protein present in mitochondria of nucleated cells. However, the damage of PBC is confined to small biliary epithelial cells (BECs). We have previously demonstrated that BECs translocate immunologically intact PDC-E2 to apoptotic bodies and create an apotope. To define the significance of this observation, we have studied the ability of biliary or control epithelial apotopes to induce cytokine secretion from mature monocyte-derived macrophages (MDMphis) from either patients with PBC or controls in the presence or absence of anti-mitochondrial antibodies (AMAs). We demonstrate that there is intense inflammatory cytokine production in the presence of the unique triad of BEC apotopes, macrophages from patients with PBC, and AMAs. The cytokine secretion is inhibited by anti-CD16 and is not due to differences in apotope uptake. Moreover, MDMphis from PBC patients cultured with BEC apoptotic bodies in the presence of AMAs markedly increase tumor necrosis factor-related apoptosis-inducing ligand expression.

CONCLUSION

These results provide a mechanism for the biliary specificity of PBC, the recurrence of disease after liver transplantation, and the success of ursodiol in treatment. They further emphasize the critical role of the innate immune system in the perpetuation of this autoimmune disease.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

Butein sensitizes human hepatoma cells to TRAIL-induced apoptosis via extracellular signal-regulated kinase/Sp1-dependent DR5 upregulation and NF-kappaB inactivation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cell death in various types of cancer cells but has little or no effect on normal cells. Human hepatoma cells are resistant to TRAIL-induced apoptosis. Although butein is known to mediate anticancer, anti-inflammatory, and antioxidant activities, little is known about the mechanism of butein in terms of TRAIL-induced apoptosis of human hepatoma cells. In this study, we determined that butein enhances TRAIL-induced apoptosis in hepatoma cells through upregulation of DR5. Luciferase analysis showed that a 5'-flanking region containing four Sp1-binding sites within the DR5 promoter was enhanced by butein (-305/-300). Electrophoretic mobility shift assays and chromatin immunoprecipitation studies were used to analyze the elevation of Sp1 binding to DR5 promoter sites by butein. Point mutations of the Sp1-binding site also attenuated promoter activity. Furthermore, pretreatment of the blocking chimeric antibody and small interfering RNA for DR5 significantly suppressed TRAIL-mediated apoptosis by butein in Hep3B cells. Butein also stimulated extracellular signal-regulated kinase (ERK) activation, and the ERK inhibitor PD98059 blocked butein-induced DR5 expression and suppressed binding of Sp1 to the DR5 promoter. Additionally, generation of reactive oxygen species had no effect on cell viability, although pretreatment with N-acetyl-l-cysteine or glutathione inhibited combined treatment-induced reactive oxygen species. Indeed, butein repressed the TRAIL-mediated activation of NF-kappaB and decreased its transcriptional activity. Our results suggest that butein could sensitize certain human hepatoma cells to TRAIL-induced apoptosis through stimulating its death signaling and by repressing the survival function in these cells.