Apoptosis induction by caspase-8 is amplified through the mitochondrial release of cytochrome c

Caspase-mediated pathways in retinal ganglion cell injury: a novel therapeutic target for glaucoma

Glaucoma is a complex disease of the optic nerve leading to vision loss and blindness, with high worldwide incidence and disproportionate prevalence in older populations. Primary open-angle glaucoma, caused by a reduction in outflow of aqueous humor through the trabecular meshwork, is the most common subset of the disease, though its underlying molecular mechanisms are not well understood. While increased intraocular pressure is the most common risk factor in glaucoma progression, the disease is ultimately characterized by the loss of retinal ganglion cells (RGCs) and destruction of the optic nerve. Given the irreversibility of RGC death, neuroprotection of RGCs is a promising avenue of glaucoma prevention and treatment. The caspase family of proteins are integral members of the apoptotic death cascade. They have been shown to play a significant role in RGC death in numerous models of retinal injury. Direct inhibition of several caspase family members, through targeted siRNAs and peptidomimetics, demonstrate promising capacity to reduce caspase expression and preserve RGCs following intraocular pressure increase or optic injury. A wide variety of alternative therapeutics targeted for RGC survival, including neurotrophins, immunomodulators, cytoprotectants, and endogenous hormones, also display indirect caspase-inhibiting capabilities. Following intraocular pressure increase or external retinal injury, both direct and indirect caspase inhibitors elicit higher RGC counts, increased RGC layer thickness, and attenuation of RGC damage, clearly demonstrating the neuroprotective abilities of caspase inhibitors. Caspase inhibition, particularly by direct approaches of siRNA or peptidomimetic-based therapeutics, has the potential to achieve substantial neuroprotection in the glaucomatous eye.

Response characteristic and potential molecular mechanism of tail resorption in Bufo gargarizans after exposure to lead and copper, alone or combined

Tail resorption during amphibian metamorphosis is one of the most dramatic processes that is obligatorily dependent on thyroid hormone (TH). Heavy metals could result in thyroid gland damages and disturb TH homeostasis. Lead (Pb) and copper (Cu) often co-exist in natural aquatic ecosystems. However, there is still little information on how tail resorption responds to alone or combined exposure to Pb and Cu. Our study investigated the effects of Pb and Cu alone or combined exposure on the morphological parameters of the tail, histological changes of thyroid gland and tail, and gene expression programs involved in cell death of the tail in Bufo gargarizans tadpoles at the climax of metamorphosis. Results demonstrated that Pb, Cu and Pb-Cu mixture exposure resulted in a significantly longer tail compared with control. Damages to notochord, muscle, skin and spinal cord of the tail were found in Pb and Cu exposure groups. The colloid area, the height of follicular cells and number of phagocytic vesicles of thyroid gland in Pb-Cu mixture exposure groups were significantly reduced. In addition, the expression levels of TH, apoptosis, autophagy, degradation of cellular components and oxidative stress-related genes in the tail were significantly altered following Pb and Cu exposure. The present work revealed the relationship between environmental pollutants and tail resorption, providing scientific basis for amphibian protection.

Singlet Oxygen, Photodynamic Therapy, and Mechanisms of Cancer Cell Death

Photodynamic therapy (PDT) can be developed into an important arsenal against cancer; it is a minimally invasive therapy, which is used in the treatment or/and palliation of a variety of cancers and benign diseases. The removal of cancerous tissue is achieved with the use of photosensitizer and a light source, which excites the photosensitizer. This excitation causes the photosensitizer to generate singlet oxygen and other reactive oxygen species. PDT has been used in several types of cancers including nonmelanoma skin cancer, bladder cancer, esophageal cancer, head and neck cancer, and non-small cell lung cancer (NSCLC). Although it is routinely used in nonmelanoma skin cancer, it has not been widely adopted in other solid cancers due to a lack of clinical data showing the superiority of PDT over other forms of treatment. Singlet oxygen used in PDT can alter the activity of the catalase, which induces immunomodulation through HOCl signaling. The singlet oxygen can induce apoptosis through both the extrinsic and intrinsic pathways. The extrinsic pathway of apoptosis starts with the activation of the Fas receptor by singlet oxygen that leads to activation of the caspase-7 and caspase-3. In the case of the intrinsic pathway, disruption caused by singlet oxygen in the mitochondria membrane leads to the release of cytochrome c, which binds with APAF-1 and procaspase-9, forming a complex, which activates caspase-3. Mechanisms of PDT action can vary according to organelles affected. In the plasma membrane, membrane disruption is caused by the oxidative stress leading to the intake of calcium ions, which causes swelling and rupture of cells due to excess intake of water, whereas disruption of lysosome causes the release of the cathepsins B and D, which cleave Bid into tBid, which changes the mitochondrial outer membrane permeability (MOMP). Oxidative stress causes misfolding of protein in the endoplasmic reticulum. When misfolding exceeds the threshold, it triggers unfolding protein response (UPR), which leads to activation of caspase-9 and caspase-3. Finally, the activation of p38 MAPK works as an alternative pathway for the induction of MOMP.

Genomic signatures of artificial selection in the Pacific oyster, Crassostrea gigas

The Pacific oyster, Crassostrea gigas, is an important aquaculture shellfish around the world with great economic and ecological value. Selective breeding programs have been carried out globally to improve production and performance traits, while genomic signatures of artificial selection remain largely unexplored. In China, we performed selective breeding of C. gigas for over a decade, leading to production of several fast‐growing strains. In the present study, we conducted whole‐genome resequencing of 20 oysters from two fast‐growing strains that have been successively selected for 10 generations, and 20 oysters from the two corresponding wild populations. Sequencing depth of >10× was achieved for each sample, leading to identification of over 12.20 million SNPs. The population structures investigated with three independent methods (principal component analysis, phylogenetic tree, and structure) suggested distinct patterns among selected and wild oyster populations. Assessment of the linkage disequilibrium (LD) decay clearly indicated the changes in genetic diversity during selection. Fixation index (F_st) combined with cross‐population composite likelihood ratio (XP‐CLR) allowed for identification of 768 and 664 selective sweeps (encompassing 1042 and 872 genes) tightly linked to selection in the two fast‐growing strains. KEGG enrichment and functional analyses revealed that 33 genes are important for growth regulation, which act as key components of various signaling pathways with close connection and further take part in regulating the process of cell cycle. This work provides valuable information for the understanding of genomic signatures for long‐term selective breeding and will also be important for growth study and genome‐assisted breeding of the Pacific oyster in the future.

Albumin protects the liver from tumor necrosis factor α-induced immunopathology

Besides its oncotic power, albumin exerts pleiotropic actions, including binding, transport, and detoxification of endogenous and exogenous molecules, antioxidant activity, and modulation of immune and inflammatory responses. In particular, recent studies have demonstrated that albumin reduces leukocyte cytokine production. Here, we investigated whether albumin also has the ability to protect tissues from the damaging actions of these inflammatory mediators. We circumscribed our investigation to tumor necrosis factor (TNF) α, which exemplifies the connection between immunity and tissue injury. In vivo experiments in analbuminemic mice showed that these mice exhibit a more pronounced response to a model of TNFα-mediated liver injury induced by the administration of lipopolysaccharide (LPS) and D-galactosamine (D-gal). A tissue protective action against LPS/D-gal liver injury was also observed during the administration of human albumin to humanized mice expressing the human genes for albumin and neonatal Fc receptor (hAlb^+/+ /hFcRn^+/+ ) with preestablished carbon tetrachloride (CCl₄ )-induced early cirrhosis. The cytoprotective actions of albumin against TNFα-induced injury were confirmed ex vivo, in precision-cut liver slices, and in vitro, in primary hepatocytes in culture. Albumin protective actions were independent of its scavenging properties and were reproduced by recombinant human albumin expressed in Oryza sativa. Albumin cytoprotection against TNFα injury was related to inhibition of lysosomal cathepsin B leakage accompanied by reductions in mitochondrial cytochrome c release and caspase-3 activity. These data provide evidence that in addition to reducing cytokines, the albumin molecule also has the ability to protect tissues against inflammatory injury.

Mitochondrial Fission Protein 1: Emerging Roles in Organellar Form and Function in Health and Disease

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1's role in both endocrine and neurological disorders.

The Effects of Lactobacillus plantarum-12 Crude Exopolysaccharides on the Cell Proliferation and Apoptosis of Human Colon Cancer (HT-29) Cells

The exopolysaccharide (EPS) of some Lactobacillus strains has been reported to exert anti-cancer activities. In this study, the effects of crude EPSs produced by four Lactobacillus plantarum strains (Lactobacillus plantarum-12, L. plantarum-14, L. plantarum-32, and L. plantarum-37) on HT-29 cell proliferation and apoptosis were studied. The results showed that the inhibition rate of the crude EPS produced by L. plantarum-12 on HT-29 cell proliferation was significantly higher than that of the EPS produced by the other three strains. L. plantarum-12 crude EPS (50, 100, 250, 500 μg/ml) exerted inhibitory effects on the expression of proliferating cell nuclear antigen (PCNA) in HT-29 cells in a positive dose-dependent manner. The reactive oxygen species (ROS) level and apoptosis rate were also increased in HT-29 cells treated with different concentrations of L. plantarum-12 crude EPS compared with control cells. Further studies found that the expression of the pro-apoptotic proteins Bax, Cyt C, caspase-3, caspase-8 and caspase-9 was upregulated and that the expression of the anti-apoptosis protein Bcl-2 was decreased in HT-29 cells treated with L. plantarum-12 crude EPS compared with control cells. The results suggested that the EPS produced by L. plantarum-12 could inhibit the proliferation of the human colon cancer cell line HT-29 through the mitochondrial pathway.

Association of Caspase-8 Genotypes With Oral Cancer Risk in Taiwan

BACKGROUND/AIM

Recently, mounting evidence has shown that caspase-8 (CASP8) rs3834129 (-652, 6N insertion/deletion) polymorphism may serve as a genetic biomarker for personal risk of various cancer types. The contribution of CASP8 rs3834129 polymorphism has been investigated in several oral cancer populations, but not in Taiwan. This study investigated the role of CASP8 rs3834129 polymorphism on oral risk in Taiwan.

MATERIALS AND METHODS

CASP8 rs3834129 polymorphic genotypes were determined and their associations with oral cancer risk were investigated among 788 patients with oral cancer and 956 age- and gender-matched healthy controls via polymerase chain reaction-restrictive fragment length polymorphism (PCR-RFLP) methodology. In addition, the interaction of CASP8 rs3834129 genotype with personal behavior and clinicopathological features were also examined.

RESULTS

The frequencies of II, ID and DD genotypes for CASP8 rs3834129 were 57.5, 36.5 and 6.0% in the patient group and 54.0, 39.0 and 7.0% in the healthy control group, respectively (p for trend=0.3052), genotypes were not significantly differentially distributed between the two groups. The comparisons in allelic frequency distribution also supported the findings that the D variant allele may not serve as a determinant of risk for oral cancer. There was no interaction of CASP8 rs3834129 genotype with age, gender, smoking, alcohol or betel quid consumption in regard to oral cancer risk.

CONCLUSION

Our results indicate that the caspase-8 genotype does not appear to play a direct role in personal susceptibility to oral cancer in Taiwan.

Fenbendazole induces apoptosis of porcine uterine luminal epithelial and trophoblast cells during early pregnancy

Fenbendazole, is an effective benzimidazole anthelmintic that prevents parasite infection in both human and veterinary health care. Although the well-known and effect of benzimidazole was recently shown to have a broad spectrum of biological abilities, such as anticancer and anti-inflammation activities, the mechanism of benzimidazole's antiproliferative effect via cell signaling pathways and its role in preimplantation has not been studied. Therefore, the purpose of this study was to determine the effects of fenbendazole on porcine trophectoderm and luminal epithelial cells. First, we investigated cell viability in response to a low dose of fenbendazole, which highly inhibited cell proliferation. In addition, we investigated apoptotic molecules in the mitochondria, imbalanced intracellular calcium homeostasis, and the expression of some genes involved in apoptosis to explain the decrease in proliferation. Finally, we examined the intracellular mechanisms of fenbendazole by measuring the extracellular signal-regulated kinase, PI3K/AKT, and c-Jun N-terminal kinase signaling proteins by western blot analysis. Our findings suggest that fenbendazole functions as an effective anti-proliferative molecule that induces critical apoptosis in the porcine trophectoderm and uterine luminal epithelial cells by disrupting the mitochondria membrane potential during early pregnancy.

Sensitization and synergistic anti-cancer effects of Furanodiene identified in zebrafish models

Furanodiene is a natural terpenoid isolated from Rhizoma Curcumae, a well-known Chinese medicinal herb that presents anticancer effects in various types of cancer cell lines. In this study, we have successfully established zebrafish xenografts with 5 various human cancer cell lines; and validated these models with anti-cancer drugs used clinically for treating human cancer patients. We found that Furanodiene was therapeutically effective for human JF 305 pancreatic cancer cells and MCF-7 breast cancer cells xenotranplanted into zebrafish. Furanodiene showed a markedly synergistic anti-cancer effect when used in combination with 5-FU (5-Fluorouracil) for both human breast cancer MDA-MB-231 cells and human liver cancer BEL-7402 cells xenotransplanted into zebrafish. Unexpectedly, Furanodiene reversed multiple drug resistance in the zebrafish xenotransplanted with cis-Platinum-resistant human non-small cell lung cancer cells and Adriamycin-resistant human breast cancer cells. Furanodiene played its anti-cancer effects through anti-angiogenesis and inducing ROS production, DNA strand breaks and apoptosis. Furanodiene suppresseed efflux transporter Pgp (P-glycoprotein) function and reduced Pgp protein level, but no effect on Pgp related gene (MDR1) expression. These results suggest sensitizition and synergistic anti-cancer effects of Furanodiene that is worthy of a further investigation.

SOX2 participates in spermatogenesis of Zhikong scallop Chlamys farreri

As an important transcription factor, SOX2 involves in embryogenesis, maintenance of stem cells and proliferation of primordial germ cell (PGC). However, little was known about its function in mature gonads. Herein, we investigated the SOX2 gene profiles in testis of scallop, Chlamys farreri. The level of C. farreri SOX2 (Cf-SOX2) mRNA increased gradually along with gonadal development and reached the peak at mature stage, and was located in all germ cells, including spermatogonia, spermatocytes, spermatids and spermatozoa. Knockdown of Cf-SOX2 using RNAi leaded to a mass of germ cells lost, and only a few spermatogonia retained in the nearly empty testicular acini after 21 days. TUNEL assay showed that apoptosis occurred in spermatocytes. Furthermore, transcriptome profiles of the testes were compared between Cf-SOX2 knockdown and normal scallops, 131,340 unigenes were obtained and 2,067 differential expression genes (DEGs) were identified. GO and KEGG analysis showed that most DEGs were related to cell apoptosis (casp2, casp3, casp8), cell proliferation (samd9, crebzf, iqsec1) and spermatogenesis (htt, tusc3, zmynd10, nipbl, mfge8), and enriched in p53, TNF and apoptosis pathways. Our study revealed Cf-SOX2 is essential in spermatogenesis and testis development of C. farreri and provided important clues for better understanding of SOX2 regulatory mechanisms in bivalve testis.

CASP8 rs3834129 (-652 6N insertion/deletion) Polymorphism and Colorectal Cancer Susceptibility: An Updated Meta-Analysis

CASP8 rs3834129 polymorphism (-652 6N insertion/deletion) is a genetic alteration which might affect the apoptosis pathway caspase enzyme. The impaired caspase enzyme would lead to the change of cancer risk. By now, the role of CASP8 rs3834129 polymorphism has been widely investigated. However, the relationship of this genetic variant on colorectal cancer (CRC) susceptibility still remains inconsistent. Therefore, we further investigated the role of rs3834129 polymorphism on CRC risk. Eligible published studies were retrieved from EMBASE, PubMed, CNKI and WANFANG database updates to March 2018. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the relationship strengths. In general, we successfully retrieved 13 studies (8 publications) involving 13058 cases and 14418 controls. The meta-analysis results demonstrated that rs3834129 polymorphism was associated with a decreased CRC risk in heterozygous model (ID vs. II: OR = 0.94, 95% CI = 0.88-0.99), but not the homozygous and allele models. Furthermore, significantly decreased risk was also found among Asian (ID vs. II: OR = 0.86, 95% CI = 0.76-0.98), and high quality score group (ID vs. II: OR = 0.90, 95% CI = 0.81-1.00) in the stratified analyses. Taken together, we showed that CASP8 rs3834129 polymorphism influences CRC susceptibility in a weak impact manner. More case-control studies are warranted to validate such relationship.

Alterations in the nucleocytoplasmic transport in apoptosis: Caspases lead the way

Apoptosis is a mode of regulated cell death that is indispensable for the morphogenesis, development and homeostasis of multicellular organisms. Caspases are cysteine-dependent aspartate-specific proteases, which function as initiators and executors of apoptosis. Caspases are cytosolic proteins that can cleave substrates located in different intracellular compartments during apoptosis. Many years ago, the involvement of caspases in the regulation of nuclear changes, a hallmark of apoptosis, was documented. Accumulated data suggest that apoptosis-associated alterations in nucleocytoplasmic transport are also linked to caspase activity. Here, we aim to discuss the current state of knowledge regarding this process. Particular attention will be focused on caspase nuclear entry and their functions in the demolition of the nucleus upon apoptotic stimuli.

Caspase-8 function, and phosphorylation, in cell migration

Caspase-8 is involved in a number of cellular functions, with the most well established being the control of cell death. Yet caspase-8 is unique among the caspases in that it acts as an environmental sensor, transducing a range of signals to cells, modulating responses that extend far beyond simple survival. Ranging from the control of apoptosis and necroptosis and gene regulation to cell adhesion and migration, caspase-8 uses proteolytic and non-proteolytic functions to alter cell behavior. Novel interacting partners provide mechanisms for caspase-8 to position itself at signaling nodes that affect a variety of signaling pathways. Here, we examine the catalytic and noncatalytic modes of action by which caspase-8 influences cell adhesion and migration. The mechanisms vary from post-cleavage remodeling of the cytoskeleton to signaling elements that control focal adhesion turnover. This is facilitated by caspase-8 interaction with a host of cell proteins ranging from the proteases caspase-3 and calpain-2 to adaptor proteins such as p85 and Crk, to the Src family of tyrosine kinases.

Trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine induces lipid peroxidation-associated apoptosis via the intrinsic and extrinsic apoptosis pathways in a first-trimester placental cell line

Trichloroethylene (TCE), a prevalent environmental contaminant, is a potent renal and hepatic toxicant through metabolites such as S-(1, 2-dichlorovinyl)-l-cysteine (DCVC). However, effects of TCE on other target organs such as the placenta have been minimally explored. Because elevated apoptosis and lipid peroxidation in placenta have been observed in pregnancy morbidities involving poor placentation, we evaluated the effects of DCVC exposure on apoptosis and lipid peroxidation in a human extravillous trophoblast cell line, HTR-8/SVneo. We exposed the cells in vitro to 10-100μM DCVC for various time points up to 24h. Following exposure, we measured apoptosis using flow cytometry, caspase activity using luminescence assays, gene expression using qRT-PCR, and lipid peroxidation using a malondialdehyde quantification assay. DCVC significantly increased apoptosis in time- and concentration-dependent manners (p<0.05). DCVC also significantly stimulated caspase 3, 7, 8 and 9 activities after 12h (p<0.05), suggesting that DCVC stimulates the activation of both the intrinsic and extrinsic apoptotic signaling pathways simultaneously. Pre-treatment with the tBID inhibitor Bl-6C9 partially reduced DCVC-stimulated caspase 3 and 7 activity, signifying crosstalk between the two pathways. Additionally, DCVC treatment increased lipid peroxidation in a concentration-dependent manner. Co-treatment with the antioxidant peroxyl radical scavenger (±)-α-tocopherol attenuated caspase 3 and 7 activity, suggesting that lipid peroxidation mediates DCVC-induced apoptosis in extravillous trophoblasts. Our findings suggest that DCVC-induced apoptosis and lipid peroxidation in extravillous trophoblasts could contribute to poor placentation if similar effects occur in vivo in response to TCE exposure, indicating that further studies into this mechanism are warranted.

Cell death and restoration of TRAIL-sensitivity by ciglitazone in resistant cervical cancer cells

Known activators of the Peroxisome Proliferator-Activated Receptor γ (PPARγ), thiazolidinediones (TZD) induce apoptosis in a variety of cancer cells through dependent and/or independent mechanisms of the receptor. We tested a panel of TZD (Rosiglitazone, Pioglitazone, Ciglitazone) to shed light on their potential therapeutic effects on three cervical cancer cell lines (HeLa, Ca Ski, C-33 A). In these cells, only ciglitazone triggered apoptosis through PPARγ-independent mechanisms and in particular via both extrinsic and intrinsic pathways in Ca Ski cells containing Human PapillomaVirus (HPV) type 16. It also inhibits cervical cancer xenograft development in nude mice. Ciglitazone kills cervical cancer cells by activating death receptor signalling pathway, caspase cascade and BH3 interacting-domain death agonist (Bid) cleavage through the up-regulation of Death Receptor 4 (DR4)/DR5 and soluble and membrane-bound TNF related apoptosis inducing ligand (TRAIL). Importantly, the drug let TRAIL-resistant Ca Ski cells to respond to TRAIL through the downregulation of cellular FLICE-Like Inhibitory Protein (c-FLIP) level. For the first time, we revealed that ciglitazone is able to decrease E6 viral oncoprotein expression known to block TRAIL pathway and this was associated with cell death. Our results highlight the capacity of ciglitazone to restore TRAIL sensitivity and to prevent E6 blocking action to induce apoptosis in cervical cancer cells.

Caspases in retinal ganglion cell death and axon regeneration

Retinal ganglion cells (RGC) are terminally differentiated CNS neurons that possess limited endogenous regenerative capacity after injury and thus RGC death causes permanent visual loss. RGC die by caspase-dependent mechanisms, including apoptosis, during development, after ocular injury and in progressive degenerative diseases of the eye and optic nerve, such as glaucoma, anterior ischemic optic neuropathy, diabetic retinopathy and multiple sclerosis. Inhibition of caspases through genetic or pharmacological approaches can arrest the apoptotic cascade and protect a proportion of RGC. Novel findings have also highlighted a pyroptotic role of inflammatory caspases in RGC death. In this review, we discuss the molecular signalling mechanisms of apoptotic and inflammatory caspase responses in RGC specifically, their involvement in RGC degeneration and explore their potential as therapeutic targets.

iTRAQ-based quantitative proteomics analysis of molecular mechanisms associated with Bombyx mori (Lepidoptera) larval midgut response to BmNPV in susceptible and near-isogenic strains

Bombyx mori nucleopolyhedrovirus (BmNPV) has been identified as a major pathogen responsible for severe economic loss. Most silkworm strains are susceptible to BmNPV, with only a few highly resistant strains thus far identified. Here we investigated the molecular basis of silkworm resistance to BmNPV using susceptible (the recurrent parent P50) and resistant (near-isogenic line BC9) strains and a combination of iTRAQ-based quantitative proteomics, reverse-transcription quantitative PCR and Western blotting. By comparing the proteomes of infected and non-infected P50 and BC9 silkworms, we identified 793 differentially expressed proteins (DEPs). By gene ontology and KEGG enrichment analyses, we found that these DEPs are preferentially involved in metabolism, catalytic activity, amino sugar and nucleotide sugar metabolism and carbon metabolism. 114 (14.38%) DEPs were associated with the cytoskeleton, immune response, apoptosis, ubiquitination, translation, ion transport, endocytosis and endopeptidase activity. After removing the genetic background and individual immune stress response proteins, we identified 84 DEPs were found that are potentially involved in resistance to BmNPV. Further studies showed that a serine protease was down-regulated in P50 and up-regulated in BC9 after BmNPV infection. Taken together, these results provide insights into the molecular mechanism of silkworm response to BmNPV.

BIOLOGICAL SIGNIFICANCE

Bombyx mori nucleopolyhedrovirus (BmNPV) is highly pathogenic, causing serious losses in sericulture every year. However, the molecular mechanisms of BmNPV infection and host defence remain unclear. Here we combined quantitative proteomic, bioinformatics, RT-qPCR and Western blotting analyses and found that BmNPV invasion causes complex protein alterations in the larval midgut, and that these changes are related to cytoskeleton, immune response, apoptosis, ubiquitination, translation, ion transport, endocytosis and endopeptidase activity. Five important differentially expression proteins were validation by independent approaches. These finding will help address the molecular mechanisms of silkworm resistance to BmNPV and provide a molecular target for resisting BmNPV.

Mitochondrial permeability transition pore: a promising target for the treatment of Parkinson's disease

Among the neurodegenerative diseases (ND), Parkinson's disease affects 6.3 million people worldwide characterized by the progressive loss of dopaminergic neurons in substantia nigra. The mitochondrial permeability transition pore (mtPTP) is a non-selective voltage-dependent mitochondrial channel whose opening modifies the permeability properties of the mitochondrial inner membrane. It is recognized as a potent pharmacological target for diseases associated with mitochondrial dysfunction and excessive cell death including ND such as Parkinson's disease (PD). Imbalance in Ca²⁺ concentration, change in mitochondrial membrane potential, overproduction of reactive oxygen species (ROS), or mutation in mitochondrial genome has been implicated in the pathophysiology of the opening of the mtPTP. Different proteins are released by permeability transition including cytochrome c which is responsible for apoptosis. This review aims to discuss the importance of PTP in the pathophysiology of PD and puts together different positive as well as negative aspects of drugs such as pramipexole, ropinirole, minocyclin, rasagilin, and safinamide which act as a blocker or modifier for mtPTP. Some of them may be detrimental in their neuroprotective nature.

Ischemic optic neuropathy as a model of neurodegenerative disorder: A review of pathogenic mechanism of axonal degeneration and the role of neuroprotection

Optic neuropathy is a neurodegenerative disease which involves optic nerve injury. It is caused by acute or intermittent insults leading to visual dysfunction. There are number of factors, responsible for optic neuropathy, and the optic nerve axon is affected in all type which causes the loss of retinal ganglion cells. In this review we will highlight various mechanisms involved in the cell loss cascades during axonal degeneration as well as ischemic optic neuropathy. These mechanisms include oxidative stress, excitotoxicity, angiogenesis, neuroinflammation and apoptosis following retinal ischemia. We will also discuss the effect of neuroprotective agents in attenuation of the negative effect of factors involve in the disease occurrence and progression.

Transcriptomic differences in intra-abdominal adipose tissue in extremely obese adolescents with different stages of NAFLD

Mechanisms responsible for progression of nonalcoholic fatty liver disease (NAFLD) to steatohepatitis (NASH) remain poorly defined. To examine the potential contribution of adipose tissue to NAFLD progression, we performed a complete transcriptomic analysis using RNA sequencing (RNA-Seq) on intra-abdominal adipose tissue (IAT) from severely obese adolescents [M_age 16.9 ± 0.4 yr, body mass index (BMI) z-score 2.7 ± 0.1] undergoing bariatric surgery and liver biopsy categorized into three groups: no steatosis (normal, n = 8), steatosis only (n = 13), or NASH (n = 10) by liver histology. Age, body weight, and BMI did not differ among groups, but subjects with NASH were more insulin resistant (increased homeostatic model assessment/insulin resistance, P < 0.05 vs. other groups). RNA-Seq revealed 175 up- and 492 downregulated mRNA transcripts (≥±1.5-fold, false discovery rate <0.10) in IAT between NASH vs. Normal, with "mitochondrial dysfunction, P = 4.19E-7" being the top regulated canonical pathway identified by Ingenuity Pathway Analysis; only 19 mRNA transcripts were up- and 148 downregulated when comparing Steatosis vs. Normal, with suppression of "EIF2 signaling, P = 1.79E-27" being the top regulated pathway indicating increased cellular stress. A comparison of IAT between NASH vs. Steatosis found 515 up- and 175 downregulated genes, with "antigen presentation, P = 6.03E-18" being the top regulated canonical pathway and "inflammatory response" the top diseases and disorders function. Unique transcriptomic differences exist in IAT from severely obese adolescents with distinct stages of NAFLD, providing an important resource for identifying potential novel therapeutic targets for childhood NASH.

Dysregulation of a potassium channel, THIK-1, targeted by caspase-8 accelerates cell shrinkage

Activation of caspases is crucial for the execution of apoptosis. Although the caspase cascade associated with activation of the initiator caspase-8 (CASP8) has been investigated in molecular and biochemical detail, the physiological role of CASP8 is not fully understood. Here, we identified a two-pore domain potassium channel, tandem-pore domain halothane-inhibited K⁺ channel 1 (THIK-1), as a novel CASP8 substrate. The intracellular region of THIK-1 was cleaved by CASP8 in apoptotic cells. Overexpression of THIK-1, but not its mutant lacking the CASP8-target sequence in the intracellular portion, accelerated cell shrinkage in response to apoptotic stimuli. In contrast, knockdown of endogenous THIK-1 by RNA interference resulted in delayed shrinkage and potassium efflux. Furthermore, a truncated THIK-1 mutant lacking the intracellular region, which mimics the form cleaved by CASP8, led to a decrease of cell volume of cultured cells without apoptotic stimulation and excessively promoted irregular development of Xenopus embryos. Taken together, these results indicate that THIK-1 is involved in the acceleration of cell shrinkage. Thus, we have demonstrated a novel physiological role of CASP8: creating a cascade that advances the cell to the next stage in the apoptotic process.

Docetaxel induces Bcl-2- and pro-apoptotic caspase-independent death of human prostate cancer DU145 cells

Docetaxel is a useful chemotherapeutic agent for the first-line treatment of hormone-refractory prostate cancer. Abnormal expression of Bcl-2 is commonly found in cancer cells, which increases their anti-apoptotic potency and chemo-resistance. We investigated the effects of Bcl-2 expression status on the susceptibility of DU145 cells, an androgen-independent human prostate cancer cell line, to docetaxel and other anticancer agents. A panel of Bcl-2-expressing DU145 cell lines was established. Bcl-2 expression levels were unrelated to the susceptibility of DU145 cells to docetaxel. The sensitivity of DU145 cells to cisplatin fluctuated, and the sensitivity to tumor necrosis factor (TNF)-α was decreased by Bcl-2 overexpression. In a xenograft mouse model, overexpression of Bcl-2 drastically decreased the sensitivity of DU145 cells to cisplatin and TNF-α; however, there was no change in the response to docetaxel. Fluorescent microscopy revealed that Bcl-2-overexpression had no effect on the docetaxel-induced death of DU145 cells, but significantly decreased DU145 cell death induced by cisplatin or TNF-α. Interestingly, docetaxel hardly induced caspase-3/7 activation in control or Bcl-2-overexpressing DU145 cells, but did at a low level in LNCaP cells, another prostate cancer cell line. Moreover, in contrast to LNCaP cells, the reduced viabilities of docetaxel-treated control and Bcl-2-overexpressing DU145 cells were not restored by the addition of either a Bid inhibitor or a panel of pro-apoptotic caspase inhibitors. These findings indicate that the antitumor effects of docetaxel on DU145 cells are independent of both Bcl-2 and pro-apoptotic caspases.

Giant seaperch iridovirus (GSIV) induces mitochondria-mediated cell death that is suppressed by bongkrekic acid and cycloheximide in a fish cell line

Giant seaperch iridovirus (GSIV) induces cell death by an unknown mechanism. We postulated that this mechanism involves mitochondria-mediated cell death. Cell viability assays revealed a steady increase in dead grouper fin cells (GF-1) after GSIV infection, from 11% at 2 days post-infection (dpi) to 67% at 5 dpi. Annexin V/PI staining revealed GSIV infection induced apoptosis in a steadily increasing fraction of cells, from 4% at 1 dpi to 29% at 5 dpi. Furthermore, post-apoptotic necrosis was apparent at 4 and 5 dpi in the late replication stage. In the early replication stage, JC-1 dye revealed mitochondrial membrane potential (ΔΨm) loss in 42% of infected cells at 1 dpi, increasing to 98% at 3 dpi. Phosphatidylserine (PS) exposure and loss of ΔΨm from apoptosis/necrosis was attenuated by treatment with the adenine nucleotide translocase inhibitor bongkrekic acid (BKA) and the protein synthesis inhibitor cyclohexamide (CHX). These data suggest GSIV induces GF-1 apoptotic/necrotic cell death through pathways that require newly synthesized protein and involve the mitochondrial function.

Dual biological functions of the apoptotic activity and anti-inflammatory effect by alcyonolide congeners from the Okinawan soft coral, Cespitularia sp

In our current study, alcyonolide and its congeners isolated from the Okinawan soft coral, Cespitularia sp., have shown an antitumor activity in HCT116 colon cancer cells. This study investigated the biological activities of these compounds (1-12) for the apoptotic activity in the HCT116 cells and the anti-inflammatory effect in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. As a result, the apoptotic cells with a nuclear condensation were detected by treatment with these compounds. The apoptotic cells dependent on the caspase 3/7 activation was also induced in the low concentration range of 2.5-10 μM. While a similar concentration of the compounds inhibited the NO production in the LPS-stimulated inflammatory RAW264.7 cells, the pro-inflammatory gene expressions of the iNOS and COX-2 mRNA were also suppressed. The structurally unique alcyonolides (5, 12) having the dual biological activity of apoptotic activity and anti-inflammatory effect could be a potential development as pharmaceutical agents.

New Insights into the Role of Ubiquitin Networks in the Regulation of Antiapoptosis Pathways

Ubiquitin is a small modifier protein that conjugates on lysine (Lys) residues of substrates, and it can be targeted by another ubiquitin molecule to form chains through conjugation on the intrinsic Lys residues and methionine (Met) 1 residue. Ubiquitination of substrates by such chains determines the fate of substrates, thereby influencing various biological processes. In this chapter, we focus on apoptosis with an emphasis on the regulation by ubiquitination. The signal transduction of apoptosis is governed not only by the classical function of ubiquitin, which is proteasome-dependent degradation of substrates, but also by the apoptosis signaling complex formation guided by different types of ubiquitin chains. Ubiquitinations of pro- and antiapoptotic proteins are tightly regulated by particular sets of enzymes, such as ubiquitin E3 ligases and deubiquitinases (DUBs). We further discuss ubiquitination in the tumor necrosis factor (TNF) signaling pathway as an example for the ubiquitin-dependent regulation of apoptosis and cell survival.

Trop2 gene: a novel target for cervical cancer treatment

OBJECT

Trop2 plays an important role in proliferation and invasion of tumors. Extensive research has shown that the expression level of Trop2 is closely related to the progress of cervical diseases. This study was to explore the effects of Trop2 on cell proliferation and apoptosis in cervical cancer.

METHODS

Trop2 was knocked down by shRNA in CaSki cells. The expression level of mRNA and protein was detected by real-time PCR and western blot, respectively. Cell proliferation was determined by CCK-8 and clone formation assay; apoptosis was measured by flow cytometry; cell cycle and apoptosis-related proteins cyclinD1, P53, bcl-2, bax, caspase 3, 8 and 9 were analyzed as well to investigate possible mechanism.

RESULTS

Trop2 expression was effectively repressed in CaSki cells by Trop2 shRNA, which resulted in inhibition of proliferation and colony formation, whereas apoptosis rate was significantly increased. Furthermore, in Trop2 knockdown CaSki cells, the expression of cyclinD1 and bcl-2 was significantly down-regulated, while that of P53 and bax was up-regulated accompanied by increased activities of caspase 9 and 3 but not caspase 8.

CONCLUSIONS

Trop2 is important in proliferation and apoptosis regulation in CaSki cells, which may become a novel target for cervical cancer treatment.

Transcriptome analysis gene expression in the liver of Coilia nasus during the stress response

Background

The estuarine tapertail anchovy (Coilia nasus) is widely distributed in the Yangtze River, the coastal waters of China, Korea, and the Ariake Sound of Japan. It is a commercially important species owing to its nutritional value and delicate flavor. However, Coilia nasus is strongly responsive to stress, this often results in death, which causes huge losses. In this study, we used next-generation sequencing technologies to study changes in gene expression in response to loading stress and the mechanism of death caused by loading stress in Coilia nasus.

Results

Using next-generation RNA-seq technologies on an Illumina HiSeq 2000 platform, we assembled a de novo transcriptome and tested for differential expression in response to stress. A total of 65,129 unigenes were generated, the mean unigene size and N50 were 607 bp and 813 bp, respectively. Of the assembled unigenes, we identified 2,990 genes that were significantly up-regulated, while 3,416 genes were significantly down-regulated in response to loading stress. Pathway enrichment analysis based on loading stress-responsive unigenes identified significantly stress related pathways. “Metabolism” and “immunity” were the two most frequently represented categories. In the “metabolism” category, “glucose metabolism” and “lipid metabolism” were major subclasses. The transcriptional expression of rate-limiting enzymes in “glucose metabolism” and “lipid metabolism” was detected by RT-qPCR, all were significantly increased after stress. Apoptosis associated proteins tumor necrosis factor alpha (TNF-α), caspase 9, cytochrome c and caspase 3 in the stress group were significantly elevated, moreover, liver injury indicators (Alanine aminotransferase, ALT, and aspartate transaminase, AST) were also significantly elevated, which indicates that loading stress induced liver injury.

Conclusion

This study provided abundant unigenes that could contribute greatly to the discovery of novel genes in fish. The alterations in predicted gene expression patterns reflected possible responses to stress. Loading stress may induce liver injury through the mitochondrial apoptosis pathway, which was activated by TNF-α. Taken together, our data not only provide information that will aid the identification of novel genes from fish, but also shed new light on the understanding of mechanisms by which physical stressors cause death in fish.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-558) contains supplementary material, which is available to authorized users.

Methods for the study of caspase activation in the Xenopus laevis oocyte and egg extract

The study of apoptosis and caspases has advanced greatly over recent decades. Studies conducted in the Xenopus laevis egg extract and oocyte model system have significantly contributed to these advances. Twenty years ago, Newmeyer and colleagues first showed that the X. laevis egg extract, when incubated at room temperature, reconstituted the key molecular events of cellular apoptosis including cytochrome c release, nuclear condensation, internucleosomal fragmentation, and caspase activation. The biochemical tractability of the egg extract system allows for robust study of apoptotic events and caspase activation. Its nature as a cell-free extract system allows substrates to be very simply added by pipette, and their effects on apoptosis and caspase activation and their placement in the apoptotic signaling pathway (e.g., pre- or post-mitochondrial) are subsequently very simply studied using the techniques described in this chapter. Also described in this chapter are assays that allow the study of caspase activation in intact oocytes, another valuable tool available when using the X. laevis model organism. Overall, the X. laevis egg extract/oocyte model is a robust, efficient, and biochemically tractable system that is ideal for the study of apoptosis and caspase activation.

Molecular mechanisms of anticancer action and cell selectivity of short α-helical peptides

Development of functional biomaterials and drugs with good biocompatibility towards host cells but with high potency against cancer cells is a challenging endeavor. By drawing upon the advantageous features of natural antimicrobial peptides and α-helical proteins, we have designed a new class of short α-helical peptides G(IIKK)(n)I-NH2 (n = 1-4) with different potency and high selectivity against cancer cells. We show that the peptides with n = 3 and 4 kill cancer cells effectively whilst remaining benign to the host cells at their working concentrations, through mechanistic processes similar to their bactericidal effects. The high cell selectivity could stem from their preferential binding to the outer cell membranes containing negative charges and high fluidity. In addition to rapid membrane-permeabilizing capacities, the peptides can also induce the programmed cell death of cancer cells via both mitochondrial pathway and death receptor pathway, without inducing non-specific immunogenic responses. Importantly, these peptides can also inhibit tumor growth in a mouse xenograft model without eliciting side effects. Whilst this study reveals the clinical potential of these peptides as potent drugs and for other medical and healthcare applications, it also points to the significance of fundamental material research in the future development of highly selective peptide functional materials.

Sialic acid-binding lectin (leczyme) induces caspase-dependent apoptosis-mediated mitochondrial perturbation in Jurkat cells

Sialic acid binding lectin (SBL) isolated from Rana catesbeiana oocytes is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity. However, the mechanism of antitumor effects of SBL is unclear to date and the validity for human leukemia cells has not been fully studied. We report here that SBL shows cytotoxicity for some human leukemia cell lines including multidrug-resistant (MDR) cells. The precise mechanisms of SBL-induced apoptotic signals were analyzed by combinational usage of specific caspase inhibitors and the mitochondrial membrane depolarization detector JC-1. It was demonstrated that SBL causes mitochondrial perturbation and the apoptotic signal is amplified by caspases and cell death is executed in a caspase-dependent manner. The efficacy of this combinational usage was shown for the first time, to distinguish the apoptotic pathway in detail. SBL selectively kills tumor cells, is able to exhibit cytotoxicity regardless of P-glycoprotein expression and has potential as an alternative to conventional DNA-damaging anticancer drugs.

Increased neuronal survival in the brainstem during liver injury: role of γ-aminobutyric acid and serotonin chitosan nanoparticles

γ-Aminobutyric acid (GABA)- and serotonin (5-HT)-mediated cell signaling, neuronal survival enhancement, and reduced neuronal death in brainstem during liver injury followed by active liver regeneration have a critical role in maintaining routine bodily functions. In the present study, GABAB and 5-HT2A receptor functional regulation, interrelated actions of neuronal survival factors, and expression of apoptotic factors in the brainstem during GABA and 5-HT chitosan nanoparticles-induced active liver regeneration in partially hepatectomized rats were evaluated. Partially hepatectomized rats were treated with the nanoparticles, and receptor assays and confocal microscopic studies of GABAB and 5-HT2A receptors, gene expression studies of GABAB and 5-HT2A receptors, nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), Akt-1, phospholipase C, Bax, and caspase-8 were performed with the brainstems of experimental animals. A significant decrease in GABAB and 5-HT2A receptor numbers and gene expressions denoted a homeostatic adjustment by the brain to trigger the sympathetic innervations during elevated DNA synthesis in the liver. The neuronal apoptosis resulting from the loss of liver function after partial hepatectomy was minimized by nanoparticle treatment in rats compared with rats with no treatment during regeneration. This was confirmed from the gene expression patterns of NF-κB, TNF-α, Akt-1, phospholipase C, Bax, and caspase-8. The present study revealed the potential of GABA and 5-HT chitosan nanoparticles for increasing neuronal survival in the brainstem during liver injury following regeneration, which avoids many neuropsychiatric problems.

γ-tocotrienol enhances the chemosensitivity of human oral cancer cells to docetaxel through the downregulation of the expression of NF-κB-regulated anti-apoptotic gene products

Taxanes, including docetaxel, are widely used for the treatment of squamous cell carcinoma of the head and neck. However, the gastrointestinal toxicity of docetaxel has limited its high-dose clinical use. In this study, we examined the synergistic anticancer effects of combined low-dose docetaxel and γ-tocotrienol treatment on human oral cancer (B88) cells. We treated B88 cells with docetaxel and γ-tocotrienol at concentrations of 0.5 nM and 50 μM, respectively. When cells were treated with either agent alone at a low dose, no significant cytotoxic effect was observed. However, the simultaneous treatment of cells with both agents almost completely suppressed cell growth. Whereas docetaxel stimulated the expression of nuclear factor-κB (NF-κB) p65 protein in B88 cells, γ-tocotrienol slightly inhibited the expression of constitutive nuclear p65 protein. Of note, the combined treatment with both agents inhibited docetaxel-induced nuclear p65 protein expression. Electrophoretic mobility shift assay (EMSA) revealed that the simultaneous treatment with these agents suppressed the NF-κB DNA binding activity in B88 cells. In addition, γ-tocotrienol downregulated the docetaxel-induced expression of NF-κB-regulated gene products associated with the inhibition of apoptosis. Furthermore, the activation of initiator caspases, caspases-8 and -9, and the effector caspase, caspase-3, was detected following treatment with both agents. Finally, apoptosis was also clearly observed as demonstrated by the cleavage of poly(ADP-ribose) polymerase (PARP) and nuclear fragmentation through the activation of caspase-3 by combined treatment with docetaxel and γ-tocotrienol. These findings suggest that the combination treatment with these agents may provide enhanced therapeutic response in oral cancer patients, while avoiding the toxicity associated with high-dose β-tubulin stabilization monotherapy.

Perinuclear localization of the HIV-1 regulatory protein Vpr is important for induction of G2-arrest

The HIV-1 accessory protein Vpr induces G2 cell cycle arrest and apoptosis. Previous studies indicate that the induction of G2-arrest requires the localization of Vpr to the nuclear envelope. Here we show that treatment of Vpr-expressing HeLa cells with the caspase 3 inhibitor Z-DEVD-fmk induced accumulation of Vpr at the nuclear lamina, while other proteins or structures of the nuclear envelope were not influenced. Furthermore, Z-DEVD-fmk enhances the Vpr-mediated G2-arrest that even occurred in HIV-1(NL4-3)-infected T-cells. Mutation of Pro-35, which is important for the integrity of helix-α1 in Vpr, completely abrogated the Z-DEVD-fmk-mediated accumulation of Vpr at the nuclear lamina and the enhancement of G2-arrest. As expected, inhibition of caspase 3 reduced the induction of apoptosis by Vpr. Taken together, we could show that besides its role in Vpr-mediated apoptosis induction caspase 3 influences the localization of Vpr at the nuclear envelope and thereby augments the Vpr-induced G2-arrest.

The molecular mechanism of apoptosis upon caspase-8 activation: quantitative experimental validation of a mathematical model

Caspase-8 (CASP8) is a cysteine protease that plays a pivotal role in the extrinsic apoptotic signaling pathway via death receptors. The kinetics, dynamics, and selectivity with which the pathway transmits apoptotic signals to downstream molecules upon CASP8 activation are not fully understood. We have developed a system for using high-sensitivity FRET-based biosensors to monitor the protease activity of CASP8 and its downstream effector, caspase-3, in living single cells. Using this system, we systematically investigated the caspase cascade by regulating the magnitude of extrinsic signals received by the cell. Furthermore, we determined the molar concentration of five caspases and Bid required for hierarchical transmission of apoptotic signals in a HeLa cell. Based on these quantitative experimental data, we validated a mathematical model suitable for estimation of the kinetics and dynamics of caspases, which predicts the minimal concentration of CASP8 required to act as an initiator. Consequently, we found that less than 1% of the total CASP8 proteins are sufficient to set the apoptotic program in motion if activated. Taken together, our findings demonstrate the precise cascade of CASP8-mediated apoptotic signals through the extrinsic pathway.

Suppressive effect of recombinant human thioredoxin on ultraviolet light-induced inflammation and apoptosis in murine skin

Thioredoxin (TRX) is a small ubiquitous protein, which regulates cellular redox status and scavenges reactive oxygen species. The present study was conducted to investigate the effect of TRX on ultraviolet (UV)-B-mediated inflammatory and apoptotic responses. Ear swelling after UV-B irradiation was significantly reduced in TRX-transgenic mice compared to wild-type mice. Administration i.p. of recombinant human TRX also reduced acute skin inflammatory reaction, such as skin erythema and swelling. Histologically, numbers of inflammatory cells including neutrophils and lymphocytes were significantly reduced and the average size of the caliber of blood vessels were also reduced in recombinant human TRX-injected mice. The number of apoptotic keratinocytes, in terms of sunburn cells, activated-caspase-3-positive cells and terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells were all significantly reduced in recombinant human TRX-injected mice. Immunohistochemical intensity of 8-hydroxy-2'-deoxyguanosine was strikingly reduced in recombinant human TRX-injected mouse. Western blotting showed that administration of recombinant human TRX attenuated duration of phosphorylation of p38 mitogen-activated protein kinases and intensity of phosphorylation of c-Jun N-terminal kinase in the early phase, which play important roles in inflammatory and apoptotic signaling. Collectively, these findings indicated that recombinant human TRX attenuated inflammatory and apoptotic responses caused by UV-B. Possible mechanisms for this might be via redox regulation of stress signaling and reduction of reactive oxygen species.

FLASH knockdown sensitizes cells to Fas-mediated apoptosis via down-regulation of the anti-apoptotic proteins, MCL-1 and Cflip short

FLASH (FLICE-associated huge protein or CASP8AP2) is a large multifunctional protein that is involved in many cellular processes associated with cell death and survival. It has been reported to promote apoptosis, but we show here that depletion of FLASH in HT1080 cells by siRNA interference can also accelerate the process. As shown previously, depletion of FLASH halts growth by down-regulating histone biosynthesis and arrests the cell cycle in S-phase. FLASH knockdown followed by stimulating the cells with Fas ligand or anti-Fas antibodies was found to be associated with a more rapid cleavage of PARP, accelerated activation of caspase-8 and the executioner caspase-3 and rapid progression to cellular disintegration. As is the case for most anti-apoptotic proteins, FLASH was degraded soon after the onset of apoptosis. Depletion of FLASH also resulted in the reduced intracellular levels of the anti-apoptotic proteins, MCL-1 and the short isoform of cFLIP. FLASH knockdown in HT1080 mutant cells defective in p53 did not significantly accelerate Fas mediated apoptosis indicating that the effect was dependent on functional p53. Collectively, these results suggest that under some circumstances, FLASH suppresses apoptosis.

GRIM-19-mediated translocation of STAT3 to mitochondria is necessary for TNF-induced necroptosis

Tumor necrosis factor (TNF) can induce necroptosis, wherein inhibition of caspase activity prevents apoptosis but initiates an alternative programmed necrosis. The activity of receptor-interacting serine/threonine-protein kinase 1 (RIPK-1) is required for necroptosis to proceed, with suppression of RIPK-1 expression or inhibition of RIPK-1 activity with necrostatin-1 preventing TNF-induced necroptosis. Downstream from the TNF receptor, the generation of reactive oxygen species at the mitochondria has been identified as necessary for the execution of necroptosis; with antioxidants and inhibitors of mitochondrial complex I preventing TNF-induced cytotoxicity. However, components of the signaling pathway that lie between activated RIPK-1 and the mitochondria are unknown. In the study reported here we demonstrate that during TNF-induced necroptosis, STAT3 is phosphorylated on serine 727, which is dependent on RIPK-1 expression or activity. The phosphorylation of STAT3 induces interaction with GRIM-19, a subunit of mitochondrial complex I, with a resultant translocation of STAT3 to the mitochondria, where it induces an increase in reactive oxygen species production and cell death.

Sequential caspase-2 and caspase-8 activation is essential for saikosaponin a-induced apoptosis of human colon carcinoma cell lines

In this study, we investigated the signaling pathways implicated in SSa-induced apoptosis of human colon carcinoma (HCC) cell lines. SSa-induced apoptosis of HCC cells was associated with proteolytic activation of caspase-9, caspase-3, and PARP cleavages and decreased levels of IAP family members, such as XIAP and c-IAP-2, but not of survivin. The fluorescence intensity of DiOC6 was significantly reduced after SSa treatment. CsA significantly inhibited SSa-induced loss of mitochondrial transmembrane potential and moderately inhibited SSa-induced cell death. SSa treatment also enhanced the activities of caspase-2 and caspase-8, Bid cleavage, and the conformational activation of Bax. Additionally, SSa-induced apoptosis was inhibited by both the selective caspase-2 inhibitor z-VDVAD-fmk and the selective caspase-8 inhibitor z-IETD-fmk and also by si-RNAs against caspase-2 and caspase-8. The selective caspase-9 inhibitor, z-LEHD-fmk, also inhibited SSa-induced apoptosis, albeit to a lesser extent compared to z-VDVAD-fmk and z-IETD-fmk, indicating that both mitochondria-dependent and mitochondria-independent pathways are associated with SSa-induced apoptosis. Both z-VDVAD-fmk and z-IETD-fmk significantly attenuated the colony-inhibiting effect of SSa. Moreover, inhibition of caspase-2 activation by the pharmacological inhibitor z-VDVAD-fmk, or by knockdown of protein levels using a si-RNA, suppressed SSa-induced caspase-8 activation, Bid cleavage, and the conformational activation of Bax. Although caspase-8 is an initiator caspase like caspase-2, the inhibition of caspase-8 activation by knockdown using a si-RNA did not suppress SSa-induced caspase-2 activation. Altogether, our results suggest that sequential activation of caspase-2 and caspase-8 is a critical step in SSa-induced apoptosis.

Essential role of caspase-8 in p53/p73-dependent apoptosis induced by etoposide in head and neck carcinoma cells

Background

Caspase-8 is a key upstream mediator in death receptor-mediated apoptosis and also participates in mitochondria-mediated apoptosis via cleavage of proapoptotic Bid. However, the role of caspase-8 in p53- and p73-dependent apoptosis induced by genotoxic drugs remains unclear. We recently reported that the reconstitution of procaspase-8 is sufficient for sensitizing cisplatin- but not etoposide-induced apoptosis, in chemoresistant and caspase-8 deficient HOC313 head and neck squamous cell carcinoma (HNSCC) cells.

Results

We show that p53/p73-dependent caspase-8 activation is required for sensitizing etoposide-induced apoptosis by utilizing HOC313 cells carrying a temperature-sensitive p53G285K mutant. Restoration of wild-type p53 function under the permissive conditions, together with etoposide treatment, led to substantial transcriptional activation of proapoptotic Noxa and PUMA, but failed to induce apoptosis. In addition to p53 restoration, caspase-8 reconstitution was needed for sensitization to etoposide-induced apoptosis, mitochondria depolarization, and cleavage of the procaspases-3, and -9. In etoposide-sensitive Ca9-22 cells carrying a temperature-insensitive mutant p53, siRNA-based p73 knockdown blocked etoposide-induced apoptosis and procaspase-8 cleavage. However, induction of p73 protein and up-regulation of Noxa and PUMA, although observed in Ca9-22 cells, were hardly detected in etoposide-treated HOC313 cells under non-permissive conditions, suggesting a contribution of p73 reduction to etoposide resistance in HOC313 cells. Finally, the caspase-9 inhibitor Ac-LEHD-CHO or caspase-9 siRNA blocked etoposide-induced caspase-8 activation, Bid cleavage, and apoptosis in both cell lines, indicating that p53/p73-dependent caspase-8 activation lies downstream of mitochondria.

Conclusions

we conclude that p53 and p73 can act as upstream regulators of caspase-8, and that caspase-8 is an essential mediator of the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells. Our data suggest the importance of caspase-8-mediated positive feedback amplification in the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells.

Mathematical modeling and sensitivity analysis of the integrated TNFα-mediated apoptotic pathway for identifying key regulators

TNFα-mediated apoptosis is one of the complex and tightly regulated cellular processes as it involves the activation of both pro- and anti-apoptotic signaling pathways. Thus, it is important to elucidate the molecular players of this process and their dynamics in order to gain an in-depth understanding of the mechanisms underlying apoptosis. To this end, we proposed an integrated model of TNFα-mediated apoptosis pathway in Type I cells, formulated based on the principles of mass action kinetics. The model includes major apoptotic modules-the extrinsic and intrinsic pathways, the NFκB survival signaling and various regulatory mechanisms. We performed simulations and sensitivity analyses to study the role of NFκB pathway in regulating apoptosis, and identified IAP as one of the more potent regulators of apoptosis.

S6 kinase 2 promotes breast cancer cell survival via Akt

The 40S ribosomal protein S6 kinase (S6K) acts downstream of mTOR, which plays important roles in cell proliferation, protein translation, and cell survival and is a target for cancer therapy. mTOR inhibitors are, however, of limited success. Although Akt is believed to act upstream of mTOR, persistent inhibition of p70 S6 kinase or S6K1 can activate Akt via a negative feedback loop. S6K exists as two homologues, S6K1 and S6K2, but little is known about the function of S6K2. In the present study, we have examined the effects of S6K2 on Akt activation and cell survival. Silencing of S6K1 caused a modest decrease, whereas knockdown of S6K2 caused a substantial increase in TNF-α and TRAIL (TNF-related apoptosis-inducing ligand)-mediated apoptosis. In contrast to S6K1, depletion of S6K2 by siRNA decreased basal and TNF-induced Akt phosphorylation. Ectopic expression of constitutively active Akt in MCF-7 cells restored cell survival in S6K2-depleted cells. We have previously shown that activation of Akt induces downregulation of Bid via p53. Knockdown of S6K2 caused an increase in p53, and downregulation of p53 by siRNA decreased Bid level. Silencing of Bid blunted the ability of S6K2 deficiency to enhance TNF-induced apoptosis. Taken together, our study shows that the two homologues of S6K have distinct effects on Akt activation and cell survival. Thus, targeting S6K2 may be an effective therapeutic strategy to treat cancers.

Interaction between the mouse homologue of CD99 and its ligand PILR as a mechanism of T cell receptor-independent thymocyte apoptosis

Here, we show that the interaction between two membrane proteins, the mouse homologue of CD99 (designated D4) and its ligand, paired immunoglobulin-like type 2 receptor (PILR), is one of the major mechanisms of thymocyte apoptosis. Using the polymeric fusion protein of PILR and IgG1 (PILR-Ig), we demonstrated that D4 ligation in the absence of T cell receptor (TCR) engagement leads to the induction of apoptosis, mainly at the double-positive stage of thymocytes. This was further confirmed by a blocking study in which blocking the interaction between D4 and PILR by soluble D4 protein led to reduced apoptosis in the fetal thymic organ culture with wild type and TCRalpha(-/-) mice. Furthermore, the dissection of intracellular signaling pathway demonstrated that D4 cross-linking led to caspase activation without any change in mitochondrial membrane potential. Based on these data, we propose a mechanism for thymocyte depletion in which the interaction between D4 and PILR delivers an active signal.

Reactive oxygen species and p38 mitogen-activated protein kinase induce apoptotic death of U937 cells in response to Naja nigricollis toxin-gamma

The aim of the present study is to elucidate the signalling components related to Naja nigricollis toxin--induced apoptosis in human leukaemia U937 cells. It was found that toxin--induced apoptotic cell death was attributed mainly to activation of p38 mitogen-activated protein kinase (MAPK), reactive oxygen species (ROS) generation and loss of mitochondrial membrane potential (deltapsim). Subsequent modulation of Bcl-2 family member and cytochrome c release accompanied with activation of caspase-9 and -3 were involved in the death of U937 cells. SB202190 (p38 MAPK inhibitor) and N-acetylcysteine (antioxidant) significantly attenuated toxin--induced cell death and loss of deltapsim, and completely abolished the production of ROS. In contrast to N-acetylcysteine, degradation of Bcl-2/Bcl-XL and mitochondrial localization of Bax were notably decreased by SB202190. Inhibitors of electron transport (rotenone and antimycin A) or inhibitor of mitochondrial permeability transition pore (cyclosporine A) reduced the effect of toxin- on ROS generation, loss of deltapsim and cytochrome c release. Noticeably, pre-treatment with N-acetylcysteine or rotenone eliminated markedly ROS accompanied with reduction in p38 MAPK activation. Taken together, these results suggest that the cytotoxicity of toxin- is initiated by p38-MAPK-mediated mitochondrial dysfunction followed by ROS production and activation of caspases, and that ROS further augments p38 MAPK activation and mitochondrial alteration.