Structural determinants of DISC function: new insights into death receptor-mediated apoptosis signalling

Ethanolic extract of Thevetia peruviana flowers enhances TNF-α and TRAIL-induced apoptosis of human cervical cancer cells via intrinsic and extrinsic pathways

Tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) are promising candidates for cancer treatment due to their ability to induce apoptosis through death receptor stimulation. However, their usage may be limited due to the resistance of cancer cells to TNF-α- and TRAIL-induced apoptosis. Currently, there is interest in screening for natural products that can sensitize cancer cells to TNF-α- and TRAIL-induced apoptosis for their use in combination with TNF-α or TRAIL. It was previously reported that the bark extract of Thevetia peruviana showed a reversal effect on TRAIL-resistance in human gastric adenocarcinoma cell lines. In the present study, the effects of the ethanolic extract of T. peruviana flowers on TNF-α- and TRAIL-induced apoptosis of human cervical cancer HeLa cells were investigated in vitro by determining cell viability and apoptosis using a WST-1 cell proliferation assay and immunoblot analysis, respectively. The ethanolic extract of T. peruviana flowers promoted TNF-α and TRAIL-mediated cell death through the activation of the caspase cascade, poly(ADP-ribose) polymerase and BH3-interacting domain death agonist cleavage. Combined treatment using the extract plus TNF-α resulted in downregulation of anti-apoptotic protein, including myeloid cell leukemia sequence-1, B-cell lymphoma-extra large (Bcl-XL), X-linked inhibitor of apoptosis protein and survivin, while the combined treatment with TRAIL downregulated Bcl-XL. Thus, the ethanolic extract of T. peruviana flowers has potential in sensitizing the TNF-α- and TRAIL-induced apoptosis of HeLa cells via the intrinsic and extrinsic pathways.

Inducing death in tumor cells: roles of the inhibitor of apoptosis proteins

The heterogeneous group of diseases collectively termed cancer results not just from aberrant cellular proliferation but also from a lack of accompanying homeostatic cell death. Indeed, cancer cells regularly acquire resistance to programmed cell death, or apoptosis, which not only supports cancer progression but also leads to resistance to therapeutic agents. Thus, various approaches have been undertaken in order to induce apoptosis in tumor cells for therapeutic purposes. Here, we will focus our discussion on agents that directly affect the apoptotic machinery itself rather than on drugs that induce apoptosis in tumor cells indirectly, such as by DNA damage or kinase dependency inhibition. As the roles of the Bcl-2 family have been extensively studied and reviewed recently, we will focus in this review specifically on the inhibitor of apoptosis protein (IAP) family. IAPs are a disparate group of proteins that all contain a baculovirus IAP repeat domain, which is important for the inhibition of apoptosis in some, but not all, family members. We describe each of the family members with respect to their structural and functional similarities and differences and their respective roles in cancer. Finally, we also review the current state of IAPs as targets for anti-cancer therapeutics and discuss the current clinical state of IAP antagonists.

The cationic small molecule GW4869 is cytotoxic to high phosphatidylserine-expressing myeloma cells

We have discovered that a small cationic molecule, GW4869, is cytotoxic to a subset of myeloma cell lines and primary myeloma plasma cells. Biochemical analysis revealed that GW4869 binds to anionic phospholipids such as phosphatidylserine - a lipid normally confined to the intracellular side of the cell membrane. However, interestingly, phosphatidylserine was expressed on the surface of all myeloma cell lines tested (n = 12) and 9/15 primary myeloma samples. Notably, the level of phosphatidylserine expression correlated well with sensitivity to GW4869. Inhibition of cell surface phosphatidylserine exposure with brefeldin A resulted in resistance to GW4869. Finally, GW4869 was shown to delay the growth of phosphatidylserine-high myeloma cells in vivo. To the best of our knowledge, this is the first example of using a small molecule to target phosphatidylserine on malignant cells. This study may provide the rationale for the development of phosphatidylserine-targeting small molecules for the treatment of surface phosphatidylserine-expressing cancers.

The Janus Face of Death Receptor Signaling during Tumor Immunoediting

Cancer immune surveillance is essential for the inhibition of carcinogenesis. Malignantly transformed cells can be recognized by both the innate and adaptive immune systems through different mechanisms. Immune effector cells induce extrinsic cell death in the identified tumor cells by expressing death ligand cytokines of the tumor necrosis factor ligand family. However, some tumor cells can escape immune elimination and progress. Acquisition of resistance to the death ligand-induced apoptotic pathway can be obtained through cleavage of effector cell expressed death ligands into a poorly active form, mutations or silencing of the death receptors, or overexpression of decoy receptors and pro-survival proteins. Although the immune system is highly effective in the elimination of malignantly transformed cells, abnormal/dysfunctional death ligand signaling curbs its cytotoxicity. Moreover, DRs can also transmit pro-survival and pro-migratory signals. Consequently, dysfunctional death receptor-mediated apoptosis/necroptosis signaling does not only give a passive resistance against cell death but actively drives tumor cell motility, invasion, and contributes to consequent metastasis. This dual contribution of the death receptor signaling in both the early, elimination phase, and then in the late, escape phase of the tumor immunoediting process is discussed in this review. Death receptor agonists still hold potential for cancer therapy since they can execute the tumor-eliminating immune effector function even in the absence of activation of the immune system against the tumor. The opportunities and challenges of developing death receptor agonists into effective cancer therapeutics are also discussed.

Redox signaling and oxidative stress: Cross talk with TNF-related apoptosis inducing ligand activity

Redox regulation plays a key role in several physiopathological contexts and free radicals, from nitric oxide and superoxide anion up to other forms of reactive oxygen species (ROS), have been demonstrated to be involved in different biological and regulatory processes. The data reported in the current literature describe a link between ROS, inflammation and programmed cell death that is attracting interest as new pathways to be explored and targeted for therapeutic purposes. In this light, there is also growing attention to the involvement of this link in the activity of the TNF-related apoptosis inducing ligand (TRAIL). TRAIL is a member of the TNF ligands super family able to mediate multiple intracellular signals, with the potential to lead to a range of biological effects in different cell types. In particular, the hallmark of TRAIL is the ability to induce selective apoptosis in transformed cells leaving normal cells almost unaffected and this feature has already opened the door to several clinical studies for cancer treatment. Moreover, TRAIL plays a role in several physiological and pathological processes of both innate and adaptive immune systems and of the cardiovascular context, with a strong clinical potential. Nonetheless, several issues still need to be clarified about the signaling mediated by TRAIL to gain deeper insight into its therapeutic potential. In this light, the aim of this review is to summarize the main preclinical evidences about the interplay between TRAIL and redox signaling, with particular emphasis to the implications in vascular physiopathology and cancer.

Targeting Inhibitor of Apoptosis Proteins Protects from Bleomycin-Induced Lung Fibrosis

Accumulation of apoptosis-resistant fibroblasts is a hallmark of pulmonary fibrosis. We hypothesized that disruption of inhibitor of apoptosis protein (IAP) family proteins would limit lung fibrosis. We first show that transforming growth factor-β1 and bleomycin increase X-linked IAP (XIAP) and cellular IAP (cIAP)-1 and -2 in murine lungs and mesenchymal cells. Functional blockade of XIAP and the cIAPs with AT-406, an orally bioavailable second mitochondria-derived activator of caspases (Smac) mimetic, abrogated bleomycin-induced lung fibrosis when given both prophylactically and therapeutically. To determine whether the reduction in fibrosis was predominantly due to AT-406-mediated inhibition of XIAP, we compared the fibrotic response of XIAP-deficient mice (XIAP(-/y)) with littermate controls and found no difference. We found no alterations in total inflammatory cells of either wild-type mice treated with AT-406 or XIAP(-/y) mice. AT-406 treatment limited CCL12 and IFN-γ production, whereas XIAP(-/y) mice exhibited increased IL-1β expression. Surprisingly, XIAP(-/y) mesenchymal cells had increased resistance to Fas-mediated apoptosis. Functional blockade of cIAPs with AT-406 restored sensitivity to Fas-mediated apoptosis in XIAP(-/y) mesenchymal cells in vitro and increased apoptosis of mesenchymal cells in vivo, indicating that the increased apoptosis resistance in XIAP(-/y) mesenchymal cells was the result of increased cIAP expression. Collectively, these results indicate that: (1) IAPs have a role in the pathogenesis of lung fibrosis; (2) a congenital deficiency of XIAP may be overcome by compensatory mechanisms of other IAPs; and (3) broad functional inhibition of IAPs may be an effective strategy for the treatment of lung fibrosis by promoting mesenchymal cell apoptosis.

Sestrin2 facilitates death receptor-induced apoptosis in lung adenocarcinoma cells through regulation of XIAP degradation

Apoptosis plays a critical physiological role in controlling cell number and eliminating damaged, non-functional and transformed cells. Cancerous cells as well as some types of normal cells are often resistant to cell death induced by pro-inflammatory cytokines through death receptors. This potentially allows cancer cells to evade the control from the immune system and to proceed toward a more malignant stage, although the mechanisms of this evasion are not well established. We have recently identified the stress-responsive Sestrin2 protein as a critical regulator of cell viability under stress conditions. Sestrin2 is a member of a small family of antioxidant proteins and inhibitors of mechanistic Target of Rapamycin Complex 1 (mTORC1) kinase. Down-regulation of Sestrin1/2 leads to genetic instability and accelerates the growth of lung adenocarcinoma xenografts. Here we addressed the potential role of Sestrin2 in regulation of cell death induced by TNFR1 and related Fas and TRAIL receptors in lung adenocarcinoma cells. We found that Sestrin2 silencing strongly inhibits cytokine-induced cell death through a mechanism independent of ROS and mTORC1 regulation. We determined that the X-linked inhibitor of apoptosis protein (XIAP) plays a critical role in the control of cytokine-induced cell death by Sestrin2. Thus our study defines a new, previously unrecognized role of Sestrin2 in the regulation of apoptosis.

Gan-Lu-Siao-Du-yin, a prescription of traditional Chinese medicine, inhibited enterovirus 71 replication, translation, and virus-induced cell apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Gan-Lu-Siao-Du-yin (GLSDY) is a prescription of traditional Chinese medicine. GLSDY contains 11 ingredients and is commonly used for endemic diseases. Enterovirus 71 (EV71) is an endemic disease that can cause meningoencephalitis with mortality and neurologic sequelae without any effective management. It is unknown whether GLSDY is effective against EV71 infection.

AIM OF THE STUDY

To test the hypothesis that GLSDY can protect cell from EV71-induced injury.

MATERIALS AND METHODS

Effects of a hot water extract of GLSDY on EV71 were tested in human foreskin fibroblast cells (CCFS-1/KMC) and human rhabdomyosarcoma cells (RD cells) by plaque reduction assay and flow cytometry respectively. Inhibition of viral replication was further examined by reverse quantitative RT-PCR (qRT-PCR). Its effect on viral protein translation and virus-induced apoptosis were examined by western blot.

RESULTS

GLSDY was dose-dependently effective against EV71 infection (p<0.0001) in both CCFS-1/KMC cells and RD cells. GLSDY was highly effective when supplemented after viral inoculation (P<0.0001) with an IC50 of 8.7μg/mL. GLSDY inhibited viral RNA replication (P<0.0001), formation of viral structural proteins (VP0, VP1, VP2 and VP3) and non-structural proteins (protease 2B and 3AB). Furthermore, 300μg/mL GLSDY is effective to inhibit virus-induced apoptosis possibly through direct inhibition of caspase-8 and indirectly by inhibition of Bax.

CONCLUSIONS

GLSDY is cheap and readily available to manage EV71 infection by inhibiting viral replication, viral protein formations, and EV71-induced apoptosis.

Clinical perspectives of TRAIL: insights into central nervous system disorders

The TNF-related apoptosis inducing ligand TRAIL is a member of the TNF superfamily that has been firstly studied and evaluated for its anti-cancer activity, and the insights into its biology have already led to the identification of several TRAIL-based anticancer strategies with strong clinical therapeutic potentials. Nonetheless, the TRAIL system is far more complex and it can lead to a wider range of biological effects other than the ability of inducing apoptosis in cancer cells. By virtue of the different receptors and the different signalling pathways involved, TRAIL plays indeed a role in the regulation of different processes of the innate and adaptive immune system and this feature makes it an intriguing molecule under consideration in the development/progression/treatment of several immunological disorders. In this context, central nervous system represents a peculiar anatomic site where, despite its "status" of immune-privileged site, both innate and adaptive inflammatory responses occur and are involved in several pathological conditions. A number of studies have evaluated the role of TRAIL and of TRAIL-related pathways as pro-inflammatory or protective stimuli, depending on the specific pathological condition, confirming a twofold nature of this molecule. In this light, the aim of this review is to summarize the main preclinical evidences of the potential/involvement of TRAIL molecule and TRAIL pathways for the treatment of central nervous system disorders and the key suggestions coming from their assessment in preclinical models as proof of concept for future clinical studies.

T-cell development of resistance to apoptosis is driven by a metabolic shift in carbon source and altered activation of death pathways

We developed a model system to investigate apoptotic resistance in T cells using osmotic stress (OS) to drive selection of death-resistant cells. Exposure of S49 (Neo) T cells to multiple rounds of OS followed by recovery of surviving cells resulted in the selection of a population of T cells (S49 (OS 4-25)) that failed to die in response to a variety of intrinsic apoptotic stimuli including acute OS, but remained sensitive to extrinsic apoptotic initiators. Genome-wide microarray analysis comparing the S49 (OS 4-25) with the parent S49 (Neo) cells revealed over 8500 differentially regulated genes, with almost 90% of those identified being repressed. Surprisingly, our data revealed that apoptotic resistance is not associated with expected changes in pro- or antiapoptotic Bcl-2 family member genes. Rather, these cells lack several characteristics associated with the initial signaling or activation of the intrinsic apoptosis pathway, including failure to increase mitochondrial-derived reactive oxygen species, failure to increase intracellular calcium, failure to deplete glutathione, failure to release cytochrome c from the mitochondria, along with a lack of induced caspase activity. The S49 (OS 4-25) cells exhibit metabolic characteristics indicative of the Warburg effect, and, despite numerous changes in mitochondria gene expression, the mitochondria have a normal metabolic capacity. Interestingly, the S49 (OS 4-25) cells have developed a complete dependence on glucose for survival, and glucose withdrawal results in cell death with many of the essential characteristics of apoptosis. Furthermore, we show that other dietary sugars such as galactose support the viability of the S49 (OS 4-25) cells in the absence of glucose; however, this carbon source sensitizes these cells to die. Our findings suggest that carbon substrate reprogramming for energy production in the S49 (OS 4-25) cells results in stimulus-specific recognition defects in the activation of intrinsic apoptotic pathways.

Tumor Necrosis Factor-like Cytokine TL1A and Its Receptors DR3 and DcR3: Important New Factors in Mucosal Homeostasis and Inflammation

Tumor necrosis factor (TNF)-like cytokine 1A (TL1A) is a member of the TNF superfamily of proteins (TNFSF15), which signals through association with death domain receptor 3 (DR3). Decoy receptor 3 (DcR3) competes with DR3 for TL1A binding and inhibits functional signaling. These proteins are significantly upregulated in inflamed intestinal tissues, and their pathogenetic importance for inflammatory bowel disease (IBD) is suggested by accumulating evidence. TL1A/DR3 induce costimulatory signals to activated lymphocytes, including the gut-specific populations of CD4+CD161+ and CD4+CCR9+ cells, affecting all major effector pathways and inducing the mucosal upregulation of Th1, Th2, and Th17 factors. They may also participate in mucosal homeostasis and defense against pathogens through their effects on the development and function of the recently described innate lymphoid cells. T-regulatory lymphocytes highly express DR3, and they respond to TL1A stimulation also. Mechanistic studies by transgenic expression of TL1A, deletion of TL1A or DR3, and therapeutic blockade by anti-TL1A antibodies all support the critical involvement of the corresponding pathways in the pathogenesis of chronic mucosal inflammation. Wide genome association studies have identified IBD-specific polymorphisms in TNFSF15 gene, which have functional implications and serve as poor prognostic factors. Recently, TL1A blockade in mice was presented as a unique pharmacological treatment for the reversal of established intestinal fibrosis. Finally, TL1A/DR3 signaling seems to critically participate in extraintestinal inflammatory conditions that are frequently associated with IBD as part of the gut-joint-skin-eye axis. These converging lines of evidence make TL1A/DR3 a suitable model for personalized approaches to IBD therapy.

Deficiency in the mitochondrial apoptotic pathway reveals the toxic potential of autophagy under ER stress conditions

Endoplasmic reticulum (ER) stress-induced cell death is normally associated with activation of the mitochondrial apoptotic pathway, which is characterized by CYCS (cytochrome c, somatic) release, apoptosome formation, and caspase activation, resulting in cell death. In this study, we demonstrate that under conditions of ER stress cells devoid of CASP9/caspase-9 or BAX and BAK1, and therefore defective in the mitochondrial apoptotic pathway, still undergo a delayed form of cell death associated with the activation of caspases, therefore revealing the existence of an alternative stress-induced caspase activation pathway. We identified CASP8/caspase-8 as the apical protease in this caspase cascade, and found that knockdown of either of the key autophagic genes, ATG5 or ATG7, impacted on CASP8 activation and cell death induction, highlighting the crucial role of autophagy in the activation of this novel ER stress-induced death pathway. In line with this, we identified a protein complex composed of ATG5, FADD, and pro-CASP8 whose assembly coincides with caspase activation and cell death induction. Together, our results reveal the toxic potential of autophagy in cells undergoing ER stress that are defective in the mitochondrial apoptotic pathway, and suggest a model in which the autophagosome functions as a platform facilitating pro-CASP8 activation. Chemoresistance, a common problem in the treatment of cancer, is frequently caused by the downregulation of key mitochondrial death effector proteins. Alternate stress-induced apoptotic pathways, such as the one described here, may become of particular relevance for tackling the problem of chemoresistance in cancer cells.

The versatile roles of CARDs in regulating apoptosis, inflammation, and NF-κB signaling

CARD subfamily is the second largest subfamily in the DD superfamily that plays important roles in regulating various signaling pathways, including but not limited to NF-kB activation signaling, apoptosis signaling and inflammatory signaling. The CARD subfamily contains 33 human CARD-containing proteins, regulating the assembly of many signaling complexes, including apoptosome, inflammsome, nodosome, the CBM complex, PIDDosome, the TRAF2 complex, and the MAVS signalosome, by homotypic CARD-CARD interactions. The mechanism of how CARDs find the right binding partner to form a specific complex remains unclear. This review uses different classification schemes to update the classification of CARD-containing proteins. Combining the classification based on domain structures, functions, associated signaling complexes, and roles would help better understand the structural and function diversity of CARD-containing proteins. This review also summarizes recent structural studies on CARDs. Especially, the CARD-containing complexes can be divided into the homodimeric, heterodimeric, oligomeric, filamentous CARD complexes and the CARD-ubiquitin complex. This review will give an overview of the versatile roles of CARDs in regulating signaling transduction, as well as the therapeutic drugs targeting CARD-containing proteins.

Curcumin inhibits apoptosis and brain edema induced by hypoxia-hypercapnia brain damage in rat models

Curcumin, extracted from South Asian spice turmeric, has been determined to have the promising ability in antioxidation and anti-inflammation. However, the effect of curcumin on treating brain damage has been not reported. In this article, the aim was to evaluate the effect of curcumin on cell apoptosis in rats exposed to hypoxia-hypercapnia and explore the therapeutic potential of curcumin in hypoxia-hypercapnia brain damage (HHBD). Sprague Dawley rats were randomly assigned into 3 groups: control group, hypoxia-hypercapnia group and curcumin group. The Fas/FasL expressions in HHBD rats treated by curcumin were measured by immunohistochemical staining and western blotting. The pathological changes of brain cells were observed by transmission electron microscope. Rats with HHBD showed significant increase of Fas/FasL expression and ultrastructural changes in brain tissue cells. Curcumin intervention effectively reversed the Fas/FasL-mediated apoptosis and HHBD-induced brain edema. Curcumin may be a potential therapeutic alternative for HHBD.

Tanshinone IIA Facilitates TRAIL Sensitization by Up-regulating DR5 through the ROS-JNK-CHOP Signaling Axis in Human Ovarian Carcinoma Cell Lines

Tanshinone IIA (TIIA) extracted from Salvia miltiorrhiza has been shown to possess antitumor and TRAIL-sensitizing activity. The involvement of DR5 in the mechanism whereby TIIA exerts its effects is unknown. This study aimed to explore the mechanism underlying TIIA augmentation of TRAIL-induced cell death in ovarian carcinoma cells. Cell viability was determined by MTS assay. Real-time RT-PCR and Western blotting were used to assess the mRNA and protein expression of relating signaling proteins. Transcriptional activation was explored by a dual-luciferase reporter assay. We found that TIIA sensitized human ovarian carcinoma cells to TRAIL-induced extrinsic apoptosis. Combined treatment with subtoxic concentrations of TIIA and TRAIL was more effective than single treatments with respect to cytotoxicity, clonogenic inhibition, and the induction of caspase-8 and PARP activity in ovarian carcinoma cell lines TOV-21G and SKOV3. TIIA induced DR5 protein and mRNA expression in a concentration-dependent manner. DR5/Fc treatment markedly suppressed the TRAIL cytotoxicity enhanced by TIIA. These results indicate that DR5 plays an essential role in TIIA-induced TRAIL sensitization and that induction of DR5 by TIIA is mediated through the up-regulation of CCAAT/enhancer-binding protein homologous protein (CHOP). Knockdown of CHOP gene expression by shRNA attenuated DR5 up-regulation and rescued cell viability under the treatment of TIIA-TRAIL combination. TIIA promoted JNK-mediated signaling to up-regulated CHOP and thereby inducing DR5 expression as shown by the ability of a JNK inhibitor to potently suppress the TIIA-mediated activation of CHOP and DR5. In addition, the quenching of ROS using NAC prevented the induction of JNK phosphorylation and CHOP induction. Furthermore, inhibition of ROS by NAC significantly attenuated TRAIL sensitization by TIIA. Taken together, these data suggest that TIIA enhances TRAIL-induced apoptosis by upregulating DR5 receptors through the ROS-JNK-CHOP signaling axis in human ovarian carcinoma cells.

Effect of nuclear factor-κB and angiotensin II receptor type 1 on the pathogenesis of rat non-alcoholic fatty liver disease

AIM: To investigate the roles of nuclear factor (NF)-κB and angiotensin II receptor type 1 (AT1R) in the pathogenesis of non-alcoholic fatty liver disease (NAFLD).

METHODS: Forty-two healthy adult male Sprague-Dawley rats were randomly divided into three groups: the control group (normal diet), the model group, and the intervention group (10 wk of a high-fat diet feeding, followed by an intraperitoneal injection of PDTC); 6 rats in each group were sacrificed at 6, 10, and 14 wk. After sacrifice, liver tissue was taken, paraffin sections of liver tissue specimens were prepared, hematoxylin and eosin (HE) staining was performed, and pathological changes in liver tissue (i.e., liver fibrosis) were observed by light microscopy. NF-κB expression in liver tissue was detected by immunohistochemistry, and the expression of AT1R in the liver tissue was detected by reverse transcription-polymerase chain reaction (RT-PCR). The data are expressed as mean ± SD. A two-sample t test was used to compare the control group and the model group at different time points, paired t tests were used to compare the differences between the intervention group and the model group, and analysis of variance was used to compare the model group with the control group. Homogeneity of variance was analyzed with single factor analysis of variance. H variance analysis was used to compare the variance. P < 0.05 was considered statistically significant.

RESULTS: The NAFLD model was successful after 6 wk and 10 wk. Liver fibrosis was found in four rats in the model group, but in only one rat in the intervention group at 14 wk. Liver steatosis, inflammation, and fibrosis were gradually increased throughout the model. In the intervention group, the body mass, rat liver index, serum lipid, and transaminase levels were not increased compared to the model group. In the model group, the degree of liver steatosis was increased at 6, 10, and 14 wk, and was significantly higher than in the control group (P < 0.01). In the model group, different degrees of liver cell necrosis were visible and small leaves, punctated inflammation, focal necrosis, and obvious ballooning degeneration were observed. Partial necrosis and confluent necrosis were observed. In the model group, liver inflammatory activity scores at 6, 10, and 14 wk were higher than in the control group (P < 0.01). Active inflammation in liver tissue in the intervention group was lower than in the model group (P < 0.05). HE staining showed liver fibrosis only at 14 wk in 4/6 rats in the model group and in 1/6 rats in the intervention group. NF-κB positive cells were stained yellow or ensemble yellow, and NF-κB was localized in the cytoplasm and/or nucleus. The model group showed NF-κB activation at 6, 10, and 14 wk in liver cells; at the same time points, there were statistically significant differences in the control group (P < 0.01). Over time, NF-κB expression increased; this was statistically lower (P < 0.05) at 14 weeks in the intervention group compared to the model group, but significantly increased (P < 0.05) compared with the control group; RT-PCR showed that AT1R mRNA expression increased gradually in the model group; at 14 wk, the expression was significantly different compared with expression at 10 weeks as well as at 6 weeks (P < 0.05). In the model group, AT1R mRNA expression was significantly higher than at the same time point in the control group (P < 0.01).

CONCLUSION: With increasing severity of NAFLD, NF-κB activity is enhanced, and the inhibition of NF-κB activity may reduce AT1R mRNA expression in NAFLD.

Molecular crosstalk between apoptosis, necroptosis, and survival signaling

Our current knowledge of the molecular mechanisms regulating the signaling pathways leading to cell survival, cell death, and inflammation has shed light on the tight mutual interplays between these processes. Moreover, the fact that both apoptosis and necrosis can be molecularly controlled has greatly increased our interest in the roles that these types of cell death play in the control of general processes such as development, homeostasis, and inflammation. In this review, we provide a brief update on the different cell death modalities and describe in more detail the intracellular crosstalk between survival, apoptotic, necroptotic, and inflammatory pathways that are activated downstream of death receptors. An important concept is that the different cell death processes modulate each other by mutual inhibitory mechanisms, serve as alternative back-up death routes in the case of a defect in the first-line cell death response, and are controlled by multiple feedback loops. We conclude by discussing future perspectives and challenges in the field of cell death and inflammation research.

Cell death controlling complexes and their potential therapeutic role

Programmed cell death plays a central role in the regulation of homeostasis and development of multicellular organisms. Deregulation of programmed cell death is connected to a number of disorders, including cancer and autoimmune diseases. Initiation of cell death occurs in the multiprotein complexes or high molecular weight platforms. Composition, structure, and molecular interactions within these platforms influence the cellular decision toward life or death and, therefore, define the induction of a particular cell death program. Here, we discuss in detail the key cell-death complexes-including DISC, complex II, and TNFRI complex I/II, and the necrosome, RIPoptosome, apoptosome, and PIDDosome-that control apoptosis or necroptosis pathways as well as their regulation. The possibility of their pharmacological targeting leading to the development of new strategies of interference with cell death programs via control of the high molecular weight platforms will be discussed.

Anti-tumor activities of lipids and lipid analogues and their development as potential anticancer drugs

Lipids have the potential for development as anticancer agents. Endogenous membrane lipids, such as ceramides and certain saturated fatty acids, have been found to modulate the viability of tumor cells. In addition, many tumors over-express cyclooxygenase, lipoxygenase or cytochrome P450 enzymes that mediate the biotransformation of ω-6 polyunsaturated fatty acids (PUFAs) to potent eicosanoid regulators of tumor cell proliferation and cell death. In contrast, several analogous products from the biotransformation of ω-3 PUFAs impair particular tumorigenic pathways. For example, the ω-3 17,18-epoxide of eicosapentaenoic acid activates anti-proliferative and proapoptotic signaling cascades in tumor cells and the lipoxygenase-derived resolvins are effective inhibitors of inflammatory pathways that may drive tumor expansion. However, the development of potential anti-cancer drugs based on these molecules is complex, with in vivo stability a major issue. Nevertheless, recent successes with the antitumor alkyl phospholipids, which are synthetic analogues of naturally-occurring membrane phospholipid esters, have provided the impetus for development of further molecules. The alkyl phospholipids have been tested against a range of cancers and show considerable activity against skin cancers and certain leukemias. Very recently, it has been shown that combination strategies, in which alkyl phospholipids are used in conjunction with established anticancer agents, are promising new therapeutic approaches. In future, the evaluation of new lipid-based molecules in single-agent and combination treatments may also be assessed. This could provide a range of important treatment options in the management of advanced and metastatic cancer.

Regulation of apoptosis by heat shock proteins

Thermotolerance, the acquired resistance of cells to stress, is a well-established phenomenon. Studies of the key mediators of this response, the heat shock proteins (HSPs), have led to the discovery of the important roles played by these proteins in the regulation of apoptotic cell death. Apoptosis is critical for normal tissue homeostasis and is involved in diverse processes including development and immune clearance. Apoptosis is tightly regulated by both proapoptotic and antiapoptotic factors, and dysregulation of apoptosis plays a significant role in the pathophysiology of many diseases. In the recent years, HSPs have been identified as key determinants of cell survival, which can modulate apoptosis by directly interacting with components of the apoptotic machinery. Therefore, manipulation of the HSPs could represent a viable strategy for the treatment of diseases. Here, we review the current knowledge with regard to the mechanisms of HSP-mediated regulation of apoptosis.

Arrestins in apoptosis

Programmed cell death (apoptosis) is a coordinated set of events eventually leading to the massive activation of specialized proteases (caspases) that cleave numerous substrates, orchestrating fairly uniform biochemical changes than culminate in cellular suicide. Apoptosis can be triggered by a variety of stimuli, from external signals or growth factor withdrawal to intracellular conditions, such as DNA damage or ER stress. Arrestins regulate many signaling cascades involved in life-or-death decisions in the cell, so it is hardly surprising that numerous reports document the effects of ubiquitous nonvisual arrestins on apoptosis under various conditions. Although these findings hardly constitute a coherent picture, with the same arrestin subtypes, sometimes via the same signaling pathways, reported to promote or inhibit cell death, this might reflect real differences in pro- and antiapoptotic signaling in different cells under a variety of conditions. Recent finding suggests that one of the nonvisual subtypes, arrestin-2, is specifically cleaved by caspases. Generated fragment actively participates in the core mechanism of apoptosis: it assists another product of caspase activity, tBID, in releasing cytochrome C from mitochondria. This is the point of no return in committing vertebrate cells to death, and the aspartate where caspases cleave arrestin-2 is evolutionary conserved in vertebrate, but not in invertebrate arrestins. In contrast to wild-type arrestin-2, its caspase-resistant mutant does not facilitate cell death.