Fas ligand-induced apoptosis is regulated by nitric oxide through the inhibition of fas receptor clustering and the nitrosylation of protein kinase Cε

Extracellular Vesicles Inhibit the Response of Pancreatic Ductal Adenocarcinoma Cells to Gemcitabine and TRAIL Treatment

Pancreatic ductal adenocarcinoma remains an aggressive cancer with a low 5-year survival rate. Although gemcitabine has been a standard treatment for advanced pancreatic cancer, patients often develop resistance to this therapeutic. We have previously shown that treating pancreatic cancer cells in vitro with a combination of gemcitabine and the cytokine TRAIL significantly reduced both cell viability and survival. The data presented here demonstrate that this response to treatment is inhibited when cells are incubated with a conditioned medium derived from untreated cells. We show that this inhibition is specifically mediated by extracellular vesicles present in the conditioned medium, as seen by a significant decrease in apoptosis. Additionally, we further demonstrate that this effect can be reversed in the presence of GW4869, an inhibitor of exosome biogenesis and release. These results show that pancreatic cancer cell-derived extracellular vesicles can confer resistance to treatment with gemcitabine and TRAIL. The implications of these findings suggest that removal of EVs during treatment can improve the response of cells to gemcitabine and TRAIL treatment in vitro.

Modulation of CD95-mediated signaling by post-translational modifications: towards understanding CD95 signaling networks

CD95 is a member of the death receptor family and is well-known to promote apoptosis. However, accumulating evidence indicates that in some context CD95 has not only the potential to induce apoptosis but also can trigger non-apoptotic signal leading to cell survival, proliferation, cancer growth and metastasis. Despite extensive investigations focused on alterations in the expression level of CD95 and associated signal molecules, very few studies, however, have investigated the effects of post-translational modifications such as glycosylation, phosphorylation, palmitoylation, nitrosylation and glutathionylation on CD95 function. Post-translational modifications of CD95 in mammalian systems are likely to play a more prominent role than anticipated in CD95 induced cell death. In this review we will focus on the alterations in CD95-mediated signaling caused by post-translational modifications of CD95.

An insight into the role of the death receptor CD95 throughout pregnancy: Guardian, facilitator, or foe

The prototype death receptor CD95 (Fas) and its ligand, CD95L (FasL), have been thoroughly studied due to their role in immune homeostasis and elimination of infected and transformed cells. The fact that CD95 is present in female reproductive cells and modulated during embryogenesis and pregnancy has raised interest in its role in immune tolerance to the fetoplacental unit. CD95 has been shown to be critical for proper embryonic formation and survival. Moreover, altered expression of CD95 or its ligand causes autoimmunity and has also been directly involved in recurrent pregnancy losses and pregnancy disorders. The objective of this review is to summarize studies that evaluate the mechanisms involved in the activation of CD95 to provide an updated global view of its effect on the regulation of the maternal immune system. Modulation of the CD95 system components may be the immune basis of several common pregnancy disorders.

First trimester placental endothelial cells from pregnancies with abnormal uterine artery Doppler are more sensitive to apoptotic stimuli

Failure of the placental capillary network to develop normally is associated with early onset fetal growth restriction (FGR) and pre-eclampsia (PE). Although the symptoms are observed at term, the problem begins in the first trimester. However, investigations at this clinically relevant time are hindered by difficulties in identifying earlystage pregnancies that are at risk of developing FGR/PE. Using uterine artery Doppler ultrasound in the first trimester as a proxy measure of poor placentation, we have identified pregnancies at increased risk of developing early onset FGR/PE. Placental endothelial cells (PEC) isolated from pregnancies at increased risk of developing FGR/PE grew more slowly and their basal rate of apoptosis was significantly higher than that seen in the normal group. The pro-apoptotic stimulus, TNFα, induced apoptosis in cells from both groups but this was significantly greater in the high risk group. TNF receptor expression was unaffected. Inhibition of nitric oxide (NO) production significantly increased the sensitivity of cells from the normal pregnancies to TNFα but not in the high risk group establishing a functional role for NO in this system. In conclusion, first trimester PEC from pregnancies at increased risk of developing early onset FGR/PE were inherently more sensitive to apoptotic stimuli and this was functionally linked to the synthesis of NO. This may contribute to the poor placental vascular development seen in on going pregnancies.

Implication of 4E-BP1 protein dephosphorylation and accumulation in pancreatic cancer cell death induced by combined gemcitabine and TRAIL

Pancreatic cancer cells show varying sensitivity to the anticancer effects of gemcitabine. However, as a chemotherapeutic agent, gemcitabine can cause intolerably high levels of toxicity and patients often develop resistance to the beneficial effects of this drug. Combination studies show that use of gemcitabine with the pro-apoptotic cytokine TRAIL can enhance the inhibition of survival and induction of apoptosis of pancreatic cancer cells. Additionally, following combination treatment there is a dramatic increase in the level of the hypophosphorylated form of the tumour suppressor protein 4E-BP1. This is associated with inhibition of mTOR activity, resulting from caspase-mediated cleavage of the Raptor and Rictor components of mTOR. Use of the pan-caspase inhibitor Z-VAD-FMK indicates that the increase in level of 4E-BP1 is also caspase-mediated. ShRNA-silencing of 4E-BP1 expression renders cells more resistant to cell death induced by the combination treatment. Since the levels of 4E-BP1 are relatively low in untreated pancreatic cancer cells these results suggest that combined therapy with gemcitabine and TRAIL could improve the responsiveness of tumours to treatment by elevating the expression of 4E-BP1.

Regulation of cell death receptor S-nitrosylation and apoptotic signaling by Sorafenib in hepatoblastoma cells

Nitric oxide (NO) plays a relevant role during cell death regulation in tumor cells. The overexpression of nitric oxide synthase type III (NOS-3) induces oxidative and nitrosative stress, p53 and cell death receptor expression and apoptosis in hepatoblastoma cells. S-nitrosylation of cell death receptor modulates apoptosis. Sorafenib is the unique recommended molecular-targeted drug for the treatment of patients with advanced hepatocellular carcinoma. The present study was addressed to elucidate the potential role of NO during Sorafenib-induced cell death in HepG2 cells. We determined the intra- and extracellular NO concentration, cell death receptor expression and their S-nitrosylation modifications, and apoptotic signaling in Sorafenib-treated HepG2 cells. The effect of NO donors on above parameters has also been determined. Sorafenib induced apoptosis in HepG2 cells. However, low concentration of the drug (10nM) increased cell death receptor expression, as well as caspase-8 and -9 activation, but without activation of downstream apoptotic markers. In contrast, Sorafenib (10 µM) reduced upstream apoptotic parameters but increased caspase-3 activation and DNA fragmentation in HepG2 cells. The shift of cell death signaling pathway was associated with a reduction of S-nitrosylation of cell death receptors in Sorafenib-treated cells. The administration of NO donors increased S-nitrosylation of cell death receptors and overall induction of cell death markers in control and Sorafenib-treated cells. In conclusion, Sorafenib induced alteration of cell death receptor S-nitrosylation status which may have a relevant repercussion on cell death signaling in hepatoblastoma cells.

Inhibition of DDAH1, but not DDAH2, results in apoptosis of a human trophoblast cell line in response to TRAIL

STUDY QUESTION

Does inhibition of dimethylarginine dimethylaminohydrolase (DDAH) increase the sensitivity of trophoblasts to TRAIL-induced apoptosis?

SUMMARY ANSWER

Inhibition of DDAH1, but not DDAH2, increases the sensitivity of trophoblasts to TRAIL-induced apoptosis.

WHAT IS KNOWN ALREADY

Successful human pregnancy is dependent on adequate trophoblast invasion and remodelling of the maternal spiral arteries. Increased trophoblast apoptosis is seen in pregnancies complicated by pre-eclampsia. The mechanism underlying this increase is unknown. We have previously shown that nitric oxide (NO) is involved in regulating trophoblast motility and invasion, and have also demonstrated an important role for NO in regulating trophoblast sensitivity to apoptotic stimuli. DDAH is an enzyme that metabolizes asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthesis, previously shown to be elevated in the plasma of pre-eclamptic mothers.

STUDY DESIGN, SIZE, DURATION

This study used the human extravillous trophoblast-derived cell line SGHPL-4 cells. All experiments were performed at least three times.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The effect of DDAH on trophoblast apoptosis was examined using siRNA and time-lapse microscopy. Changes in the expression of DDAH were followed by PCR and western blot analysis. Receptor expression was followed by flow cytometry.

MAIN RESULTS AND THE ROLE OF CHANCE

Inhibiting the expression of DDAH1, but not DDAH2, resulted in a significant increase in the sensitivity of the EVT cell line SGHPL-4 to tumour necrosis factor related apoptosis inducing ligand (TRAIL) induced apoptosis (P < 0.01). This response could be mimicked by the addition of Asymmetric Dimethylarginine (ADMA), an endogenous inhibitor of NO synthesis and the substrate for both isoforms of DDAH. We further showed that this increased sensitivity to apoptosis is accompanied by a significant increase in the expression of TRAIL receptor 2 (TR2; P < 0.05) but not TRAIL receptor 1 (TR1).

LIMITATIONS, REASONS FOR CAUTION

This study was performed only in vitro using a well characterized trophoblast cell line, SGHPL-4, derived from first trimester extravillous trophoblasts.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides new insight into the role of the DDAH/ADMA pathway in the regulation of trophoblast function. Both dysregulation of DDAH and the accumulation of ADMA have been associated with the development of pre-eclampsia. This is the first study to implicate the DDAH/ADMA pathway as a mechanism that might underlie the poor trophoblast invasion seen in this common pregnancy disorder.

STUDY FUNDING/COMPETING INTEREST(S)

B.A.L. was supported by a grant from Action Medical Research UK (SP4577). A.E.W. was supported by a grant from the Wellcome Trust (091550). There are no competing interests and the authors have no conflict interest to declare.

Role of the eIF4E binding protein 4E-BP1 in regulation of the sensitivity of human pancreatic cancer cells to TRAIL and celastrol-induced apoptosis

BACKGROUND INFORMATION

Tumour cells can be induced to undergo apoptosis after treatment with the tumour necrosis factor α-related death-inducing ligand (TRAIL). Although human pancreatic cancer cells show varying degrees of response they can be sensitised to the pro-apoptotic effects of TRAIL in the presence of celastrol, a natural compound extracted from the plant Tripterygium wilfordii Hook F. One important aspect of the cellular response to TRAIL is the control of protein synthesis, a key regulator of which is the eukaryotic initiation factor 4E-binding protein, 4E-BP1.

RESULTS

We examined the effects of celastrol and TRAIL in several pancreatic cancer cell lines. In cells that are normally resistant to TRAIL, synergistic effects of TRAIL plus celastrol on commitment to apoptosis and inhibition of protein synthesis were observed. These were associated with a strong up-regulation and dephosphorylation of 4E-BP1. The enhancement of 4E-BP1 expression, which correlated with a threefold increase in the level of the 4E-BP1 transcript, was blocked by inhibitors of reactive oxygen species and the JNK protein kinase. When the expression of 4E-BP1 was reduced by an inducible micro-RNA, TRAIL-mediated apoptosis was inhibited.

CONCLUSION

These results suggest that 4E-BP1 plays a critical role in the mechanism by which TRAIL and celastrol together cause apoptotic cell death in human pancreatic tumour cells.

Monocarboxylate transporter 8 modulates the viability and invasive capacity of human placental cells and fetoplacental growth in mice

Monocarboxylate transporter 8 (MCT8) is a well-established thyroid hormone (TH) transporter. In humans, MCT8 mutations result in changes in circulating TH concentrations and X-linked severe global neurodevelopmental delay. MCT8 is expressed in the human placenta throughout gestation, with increased expression in trophoblast cells from growth-restricted pregnancies. We postulate that MCT8 plays an important role in placental development and transplacental TH transport. We investigated the effect of altering MCT8 expression in human trophoblast in vitro and in a Mct8 knockout mouse model. Silencing of endogenous MCT8 reduced T3 uptake into human extravillous trophoblast-like cells (SGHPL-4; 40%, P<0.05) and primary cytotrophoblast (15%, P<0.05). MCT8 over-expression transiently increased T3 uptake (SGHPL-4∶30%, P<0.05; cytotrophoblast: 15%, P<0.05). Silencing MCT8 did not significantly affect SGHPL-4 invasion, but with MCT8 over-expression T3 treatment promoted invasion compared with no T3 (3.3-fold; P<0.05). Furthermore, MCT8 silencing increased cytotrophoblast viability (∼20%, P<0.05) and MCT8 over-expression reduced cytotrophoblast viability independently of T3 (∼20%, P<0.05). In vivo, Mct8 knockout reduced fetal:placental weight ratios compared with wild-type controls at gestational day 18 (25%, P<0.05) but absolute fetal and placental weights were not significantly different. The volume fraction of the labyrinthine zone of the placenta, which facilitates maternal-fetal exchange, was reduced in Mct8 knockout placentae (10%, P<0.05). However, there was no effect on mouse placental cell proliferation in vivo. We conclude that MCT8 makes a significant contribution to T3 uptake into human trophoblast cells and has a role in modulating human trophoblast cell invasion and viability. In mice, Mct8 knockout has subtle effects upon fetoplacental growth and does not significantly affect placental cell viability probably due to compensatory mechanisms in vivo.

Targeting hepatoma using nitric oxide donor strategies

AIMS

The study evaluated the role of increased intracellular nitric oxide (NO) concentration using NO donors or stably NO synthase-3 (NOS-3) overexpression during CD95-dependent cell death in hepatoma cells. The expression of cell death receptors and caspase activation, RhoA kinase activity, NOS-3 expression/activity, oxidative/nitrosative stress, and p53 expression were analyzed. The antitumoral activity of NO was also evaluated in the subcutaneous implantation of NOS-3-overexpressing hepatoma cells, as well NO donor injection into wild-type hepatoma-derived tumors implanted in xenograft mouse models.

RESULTS

NO donor increased CD95 expression and activation of caspase-8 and 3 in HepG2, Huh7, and Hep3B cells. NOS-3 overexpression increased oxidative/nitrosative stress, p53 and CD95 expression, cellular Fas-associated death domain (FADD)-like IL-1beta converting enzyme (FLICE) inhibitory protein long (cFLIP(L)) and its short isoform (cFLIP(S)) shift, and cell death in HepG2 (4TO-NOS) cells. The inhibition of RhoA kinase and p53 knockdown using RNA interference reduced cell death in 4TO-NOS cells. The supplementation with hydrogen peroxide (H(2)O(2)) increased NOS-3 activity and cell death in 4TO-NOS cells. NOS-3 overexpression or NO donor injection into hepatoma-derived tumors reduced the size and increased p53 and cell death receptor expression in nude mice.

INNOVATION AND CONCLUSIONS

The increase of intracellular NO concentration promoted oxidative and nitrosative stress, Rho kinase activity, p53 and CD95 expression, and cell death in cultured hepatoma cells. NOS-3-overexpressed HepG2 cells or intratumoral NO donor administration reduced tumor cell growth and increased the expression of p53 and cell death receptors in tumors developed in a xenograft mouse model.

Nitric oxide modulates metalloproteinase-2, collagen deposition and adhesion rate after polypropylene mesh implantation in the intra-abdominal wall

Prosthetic meshes are commonly used to correct abdominal wall defects. However, the inflammatory reaction induced by these devices in the peritoneum is not completely understood. We hypothesized that nitric oxide (NO), produced by nitric oxide synthase 2 (NOS2) may modulate the response induced by mesh implants in the abdominal wall and, consequently, affect the outcome of the surgical procedure. Polypropylene meshes were implanted in the peritoneal side of the abdominal wall in wild-type and NOS2-deficient (NOS2(-/-)) mice. After 15 days tissues around the mesh implant were collected, and inflammatory markers (the cytokine interleukin 1β (IL-1β) and NO) and tissue remodeling (collagen and metalloproteinases (MMP) 2 and 9) were analyzed. The lack of NOS2-derived NO induced a higher incidence of visceral adhesions at the mesh implantation site compared with wild-type mice that underwent the same procedure (P<0.05). Additionally, higher levels of IL-1β were present in the mesh-implanted NOS2(-/-) animals compared with control and wild-type mice. Mesh implantation induced collagen I and III deposition, but in smaller amounts in NOS2(-/-) mice. MMP-9 activity after the surgical procedure was similarly increased in both groups. Conversely, MMP-2 activity was unchanged in mesh-implanted wild-type mice, but was significantly increased in NOS2(-/-) mice (P<0.01), due to decreased S-nitrosylation of the enzyme in these animals. We conclude that NOS2-derived NO is crucial for an adequate response to and integration of polypropylene mesh implants in the peritoneum. NO deficiency results in a prolonged inflammatory reaction to the mesh implant, and reduced collagen deposition may contribute to an increased incidence of visceral adhesions.

Trophoblast fusion

The villous trophoblast of the human placenta is the epithelial cover of the fetal chorionic villi floating in maternal blood. This epithelial cover is organized in two distinct layers, the multinucleated syncytiotrophoblast directly facing maternal blood and a second layer of mononucleated cytotrophoblasts. During pregnancy single cytotrophoblasts continuously fuse with the overlying syncytiotrophoblast to preserve this end-differentiated layer until delivery. Syncytial fusion continuously supplies the syncytiotrophoblast with compounds of fusing cytotrophoblasts such as proteins, nucleic acids and lipids as well as organelles. At the same time the input of cytotrophoblastic components is counterbalanced by a continuous release of apoptotic material from the syncytiotrophoblast into maternal blood. Fusion is an essential step in maintaining the syncytiotrophoblast. Trophoblast fusion was shown to be dependant on and regulated by multiple factors such as fusion proteins, proteases and cytoskeletal proteins as well as cytokines, hormones and transcription factors. In this chapter we focus on factors that may be involved in the fusion process of trophoblast directly or that may prepare the cytotrophoblast to fuse.

Pre-eclampsia: fitting together the placental, immune and cardiovascular pieces

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early- and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.

The induction of reactive oxygen species and loss of mitochondrial Omi/HtrA2 is associated with S-nitrosoglutathione-induced apoptosis in human endothelial cells

The pathophysiological relevance of S-nitrosoglutathione (GSNO)-induced endothelial cell injury remains unclear. The main objective of this study was to elucidate the molecular mechanisms of GSNO-induced oxidative stress in endothelial cells. Morphological evaluation through DAPI staining and propidium iodide (PI) flow cytometry was used to detect apoptosis. In cultured EA.hy926 endothelial cells, exposure to GSNO led to a time- and dose-dependent apoptotic cascade. When intracellular reactive oxygen species (ROS) production was measured in GSNO-treated cells with the fluorescent probes 5-(and-6)-carboxy-2',7'-dichlorofluorescein diacetate, we observed elevated ROS levels and a concomitant loss in mitochondrial membrane potential, indicating that GSNO-induced death signaling is mediated through a ROS-mitochondrial pathway. Importantly, we found that peroxynitrite formation and Omi/HtrA2 release from mitochondria were involved in this phenomenon, whereas changes of death-receptor dependent signaling were not detected in the same context. The inhibition of NADPH oxidase activation and Omi/HtrA2 by a pharmacological approach provided significant protection against caspase-3 activation and GSNO-induced cell death, confirming that GSNO triggers the death cascade in endothelial cells in a mitochondria-dependent manner. Taken together, our results indicate that ROS overproduction and loss of mitochondrial Omi/HtrA2 play a pivotal role in reactive nitrogen species-induced cell death, and the modulation of these pathways can be of significant therapeutic benefit.

The paradox of caspase 8 in human villous trophoblast fusion

Differentiation and subsequent fusion of villous cytotrophoblasts with the overlying syncytiotrophoblast is an essential process for growth and maintenance of the villous trophoblast layer in the human placenta. The understanding of intrinsic mechanisms behind this process is in its infancy, while the list of suggested factors, involved in intercellular fusion of trophoblasts, rapidly increased in the recent past and promises progress on this issue. The early stages of the apoptosis cascade, in particular caspase 8, was suggested to trigger differentiation of cytotrophoblasts, priming them for upcoming fusion. This may sound paradoxical, especially for those who still associate caspase activity with apoptosis only. Here, we summarize data on caspase 8 in the villous trophoblast layer, with a specific focus on localization of pro- and active forms, the sites of its activation and deactivation, and its role and regulation during fusion. Moreover, we revisit the knowledge on fusogens in the villous trophoblast, compare in vitro models for trophoblast fusion and discuss methods to quantify fusion.

Lupeol: connotations for chemoprevention

The perception of chemoprevention lies still in its infancy. Intervention, to slow down, arrest or reverse the process of carcinogenesis, by the use of either natural or synthetic substances individually or in combination therapy has emerged as a promising and pragmatic medical approach to reduce cancer risk. Pentacyclic lupane-type triterpenes exemplified by lupeol [lup-20(29)-en-3b-ol], are principally found in common fruit plants such as olive, mango, fig, etc. Although, lupeol exhibits an array of biological activities like anti-inflammatory, anti-arthritic, anti-mutagenic and anti-malarial activity both in in vitro and in vivo systems yet, extensive exploration in regard to establish its role as chemopreventive compound is warranted. Interest in developing lupeol based potent anti-neoplastic agents, has led to the discovery of a host of highly active derivatives exhibiting greater potencies and better therapeutic indices. This review asserts on the chemopreventive prospects of lupeol and reveals potential chemoprevention drug targets, central to which are the cell cycle regulatory pathway genes and tries to explain the mechanism operating behind its action.