Clinical, biochemical, and genetic spectrum of MADD in a South African cohort: an ICGNMD study

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder resulting from pathogenic variants in three distinct genes, with most of the variants occurring in the electron transfer flavoprotein-ubiquinone oxidoreductase gene (ETFDH). Recent evidence of potential founder variants for MADD in the South African (SA) population, initiated this extensive investigation. As part of the International Centre for Genomic Medicine in Neuromuscular Diseases study, we recruited a cohort of patients diagnosed with MADD from academic medical centres across SA over a three-year period. The aim was to extensively profile the clinical, biochemical, and genomic characteristics of MADD in this understudied population.

METHODS

Clinical evaluations and whole exome sequencing were conducted on each patient. Metabolic profiling was performed before and after treatment, where possible. The recessive inheritance and phase of the variants were established via segregation analyses using Sanger sequencing. Lastly, the haplotype and allele frequencies were determined for the two main variants in the four largest SA populations.

RESULTS

Twelve unrelated families (ten of White SA and two of mixed ethnicity) with clinically heterogeneous presentations in 14 affected individuals were observed, and five pathogenic ETFDH variants were identified. Based on disease severity and treatment response, three distinct groups emerged. The most severe and fatal presentations were associated with the homozygous c.[1067G > A];c.[1067G > A] and compound heterozygous c.[976G > C];c.[1067G > A] genotypes, causing MADD types I and I/II, respectively. These, along with three less severe compound heterozygous genotypes (c.[1067G > A];c.[1448C > T], c.[740G > T];c.[1448C > T], and c.[287dupA*];c.[1448C > T]), resulting in MADD types II/III, presented before the age of five years, depending on the time and maintenance of intervention. By contrast, the homozygous c.[1448C > T];c.[1448C > T] genotype, which causes MADD type III, presented later in life. Except for the type I, I/II and II cases, urinary metabolic markers for MADD improved/normalised following treatment with riboflavin and L-carnitine. Furthermore, genetic analyses of the most frequent variants (c.[1067G > A] and c.[1448C > T]) revealed a shared haplotype in the region of ETFDH, with SA population-specific allele frequencies of < 0.00067-0.00084%.

CONCLUSIONS

This study reveals the first extensive genotype-phenotype profile of a MADD patient cohort from the diverse and understudied SA population. The pathogenic variants and associated variable phenotypes were characterised, which will enable early screening, genetic counselling, and patient-specific treatment of MADD in this population.

Total recall: the role of PIDDosome components in neurodegeneration

The PIDDosome is a multiprotein complex that includes p53-induced protein with a death domain 1 (PIDD1), receptor-interacting protein-associated ICH-1/CED-3 homologous protein with a death domain (RAIDD), and caspase-2, the activation of which is driven by PIDDosome assembly. In addition to the key role of the PIDDosome in the regulation of cell differentiation, tissue homeostasis, and organogenesis and regeneration, caspase-2, RAIDD and PIDD1 engagement in neuronal development was shown. Here, we focus on the involvement of PIDDosome components in neurodegenerative disorders, including retinal neuropathies, different types of brain damage, and Alzheimer's disease (AD), Huntington's disease (HD), and Lewy body disease. We also discuss pathogenic variants of PIDD1, RAIDD, and caspase-2 that are associated with intellectual, behavioral, and psychological abnormalities, together with prospective PIDDosome inhibition strategies and their potential clinical application.

Generation of a human induced pluripotent stem cell line (LZUSHi002-A) from a MADD patient with ETFDH mutation

Multiple acyl-coenzyme A dehydrogenase deficiency (MADD) is an inborn metabolic disorder that affects fatty acid oxidation and the catabolism of branched-chain amino acids, vitamins B and energy metabolism. In this study, the induced pluripotent stem cell (iPSC) line LZUSHi002-A from PBMCs of a 10-year-old male patient with ETFDH mutations using the episomal plasmids was established, which is an ideal in vitro model to understand the exact pathogenesis of MADD.

FANCI functions as a repair/apoptosis switch in response to DNA crosslinks

Cells counter DNA damage through repair or apoptosis, yet a direct mechanism for this choice has remained elusive. When facing interstrand crosslinks (ICLs), the ICL-repair protein FANCI heterodimerizes with FANCD2 to initiate ICL excision. We found that FANCI alternatively interacts with a pro-apoptotic factor, PIDD1, to enable PIDDosome (PIDD1-RAIDD-caspase-2) formation and apoptotic death. FANCI switches from FANCD2/repair to PIDD1/apoptosis signaling in the event of ICL-repair failure. Specifically, removing key endonucleases downstream of FANCI/FANCD2, increasing ICL levels, or allowing damaged cells into mitosis (when repair is suppressed) all suffice for switching. Reciprocally, apoptosis-committed FANCI reverts from PIDD1 to FANCD2 after a failed attempt to assemble the PIDDosome. Monoubiquitination and deubiquitination at FANCI K523 impact interactor selection. These data unveil a repair-or-apoptosis switch in eukaryotes. Beyond ensuring the removal of unrepaired genomes, the switch's bidirectionality reveals that damaged cells can offset apoptotic defects via de novo attempts at lesion repair.

Centriolar distal appendages activate the centrosome-PIDDosome-p53 signalling axis via ANKRD26

Centrosome amplification results into genetic instability and predisposes cells to neoplastic transformation. Supernumerary centrosomes trigger p53 stabilization dependent on the PIDDosome (a multiprotein complex composed by PIDD1, RAIDD and Caspase-2), whose activation results in cleavage of p53's key inhibitor, MDM2. Here, we demonstrate that PIDD1 is recruited to mature centrosomes by the centriolar distal appendage protein ANKRD26. PIDDosome-dependent Caspase-2 activation requires not only PIDD1 centrosomal localization, but also its autoproteolysis. Following cytokinesis failure, supernumerary centrosomes form clusters, which appear to be necessary for PIDDosome activation. In addition, in the context of DNA damage, activation of the complex results from a p53-dependent elevation of PIDD1 levels independently of centrosome amplification. We propose that PIDDosome activation can in both cases be promoted by an ANKRD26-dependent local increase in PIDD1 concentration close to the centrosome. Collectively, these findings provide a paradigm for how centrosomes can contribute to cell fate determination by igniting a signalling cascade.

Mechanism of filament formation in UPA-promoted CARD8 and NLRP1 inflammasomes

NLRP1 and CARD8 are related cytosolic sensors that upon activation form supramolecular signalling complexes known as canonical inflammasomes, resulting in caspase-1 activation, cytokine maturation and/or pyroptotic cell death. NLRP1 and CARD8 use their C-terminal (CT) fragments containing a caspase recruitment domain (CARD) and the UPA (conserved in UNC5, PIDD, and ankyrins) subdomain for self-oligomerization, which in turn form the platform to recruit the inflammasome adaptor ASC (apoptosis-associated speck-like protein containing a CARD) or caspase-1, respectively. Here, we report cryo-EM structures of NLRP1-CT and CARD8-CT assemblies, in which the respective CARDs form central helical filaments that are promoted by oligomerized, but flexibly linked, UPAs surrounding the filaments. Through biochemical and cellular approaches, we demonstrate that the UPA itself reduces the threshold needed for NLRP1-CT and CARD8-CT filament formation and signalling. Structural analyses provide insights on the mode of ASC recruitment by NLRP1-CT and the contrasting direct recruitment of caspase-1 by CARD8-CT. We also discover that subunits in the central NLRP1CARD filament dimerize with additional exterior CARDs, which roughly doubles its thickness and is unique among all known CARD filaments. Finally, we engineer and determine the structure of an ASCCARD-caspase-1CARD octamer, which suggests that ASC uses opposing surfaces for NLRP1, versus caspase-1, recruitment. Together these structures capture the architecture and specificity of the active NLRP1 and CARD8 inflammasomes in addition to key heteromeric CARD-CARD interactions governing inflammasome signalling.

A role for alternative splicing in circadian control of exocytosis and glucose homeostasis

The circadian clock is encoded by a negative transcriptional feedback loop that coordinates physiology and behavior through molecular programs that remain incompletely understood. Here, we reveal rhythmic genome-wide alternative splicing (AS) of pre-mRNAs encoding regulators of peptidergic secretion within pancreatic β cells that are perturbed in Clock-/- and Bmal1-/- β-cell lines. We show that the RNA-binding protein THRAP3 (thyroid hormone receptor-associated protein 3) regulates circadian clock-dependent AS by binding to exons at coding sequences flanking exons that are more frequently skipped in clock mutant β cells, including transcripts encoding Cask (calcium/calmodulin-dependent serine protein kinase) and Madd (MAP kinase-activating death domain). Depletion of THRAP3 restores expression of the long isoforms of Cask and Madd, and mimicking exon skipping in these transcripts through antisense oligonucleotide delivery in wild-type islets reduces glucose-stimulated insulin secretion. Finally, we identify shared networks of alternatively spliced exocytic genes from islets of rodent models of diet-induced obesity that significantly overlap with clock mutants. Our results establish a role for pre-mRNA alternative splicing in β-cell function across the sleep/wake cycle.

Human DENND1A.V2 Drives Cyp17a1 Expression and Androgen Production in Mouse Ovaries and Adrenals

The DENND1A locus is associated with polycystic ovary syndrome (PCOS), a disorder characterized by androgen excess. Theca cells from ovaries of PCOS women have elevated levels of a DENND1A splice variant (DENND1A.V2). Forced expression of this variant in normal theca cells increases androgen biosynthesis and CYP17A1 expression, whereas knockdown of the transcript in PCOS theca cells reduced androgen production and CYP17A1 mRNA. We attempted to create a murine model of PCOS by expressing hDENND1A.V2 using standard transgenic approaches. There is no DENND1A.V2 protein equivalent in mice, and the murine Dennd1a gene is essential for viability since Dennd1a knockout mice are embryonically lethal, suggesting that Dennd1a is developmentally critical. Three different hDENND1A.V2 transgenic mice lines were created using CMV, Lhcgr, and TetOn promoters. The hDENND1A.V2 mice expressed hDENND1A.V2 transcripts. While hDENND1A.V2 protein was not detectable by Western blot analyses, appropriate hDENND1A.V2 immunohistochemical staining was observed. Corresponding Cyp17a1 mRNA levels were elevated in ovaries and adrenals of CMV transgenic mice, as were plasma steroid production by theca interstitial cells isolated from transgenic ovaries. Even though the impact of robust hDENND1A.V2 expression could not be characterized, our findings are consistent with the notion that elevated hDENND1A.V2 has a role in the hyperandrogenemia of PCOS.

Reversal of CYLD phosphorylation as a novel therapeutic approach for adult T-cell leukemia/lymphoma (ATLL)

Adult T-cell leukemia/lymphoma (ATLL) is a malignancy of mature T cells associated with chronic infection by human T-cell lymphotropic virus type-1 (HTLV-1). ATLL patients with aggressive subtypes have dismal outcomes. We demonstrate that ATLL cells co-opt an early checkpoint within the tumor necrosis factor receptor 1 (TNFR1) pathway, resulting in survival advantage. This early checkpoint revolves around an interaction between the deubiquitinase CYLD and its target RIPK1. The status of RIPK1 K63-ubiquitination determines cell fate by creating either a prosurvival signal (ubiquitinated RIPK1) or a death signal (deubiquitinated RIPK1). In primary ATLL samples and in cell line models, an increased baseline level of CYLD phosphorylation was observed. We therefore tested the hypothesis that this modification of CYLD, which has been reported to inhibit its deubiquitinating function, leads to increased RIPK1 ubiquitination and thus provides a prosurvival signal to ATLL cells. CYLD phosphorylation can be pharmacologically reversed by IKK inhibitors, specifically by TBK1/IKKε and IKKβ inhibitors (MRT67307 and TPCA). Both of the IKK sub-families can phosphorylate CYLD, and the combination of MRT67307 and TPCA have a marked effect in reducing CYLD phosphorylation and triggering cell death. ATLL cells overexpressing a kinase-inactive TBK1 (TBK1-K38A) demonstrate lower CYLD phosphorylation and subsequently reduced proliferation. IKK blockade reactivates CYLD, as evidenced by the reduction in RIPK1 ubiquitination, which leads to the association of RIPK1 with the death-inducing signaling complex (DISC) to trigger cell death. In the absence of CYLD, RIPK1 ubiquitination remains elevated following IKK blockade and it does not associate with the DISC. SMAC mimetics can similarly disrupt CYLD phosphorylation and lead to ATLL cell death through reduction of RIPK1 ubiquitination, which is CYLD dependent. These results identify CYLD as a crucial regulator of ATLL survival and point to its role as a potential novel target for pharmacologic modification in this disease.

Apoptotic effects of rhein through the mitochondrial pathways, two death receptor pathways, and reducing autophagy in human liver L02 cells

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) is a major component of many medicinal herbs such as Rheum palmatum L. and Polygonum multiflorum. Despite being widely used, intoxication cases associated with rhein-containing herbs are often reported. Currently, there are no available reports addressing the effects of rhein on apoptosis in human liver L02 cells. Thus, the aim of this study is to determine the cytotoxic effects and the underlying mechanism of rhein on human normal liver L02 cells. In the present study, the methyl thiazolyl tetrazolium assay demonstrated that rhein decreased the viability of L02 cells in dose-dependent and time-dependent ways. Rhein was found to trigger apoptosis in L02 cells as shown by Annexin V-fluoresceine isothiocyanate (FITC) apoptosis detection kit and cell mitochondrial membrane potential (MMP) assay, with nuclear morphological changes demonstrated by Hoechst 33258 staining. Detection of intracellular superoxide dismutase activity, lipid oxidation (malondialdehyde) content, and reactive oxygen species (ROS) levels showed that apoptosis was associated with oxidative stress. Moreover, it was observed that the mechanism implicated in rhein-induced apoptosis was presumably via the death receptor pathway and the mitochondrial pathway, as illustrated by upregulation of TNF-α, TNFR1, TRADD, and cleaved caspase-3, and downregulation of procaspase-8, and it is suggested that rhein may increase hepatocyte apoptosis by activating the increase of TNF-α level. Meanwhile, rhein upregulates the expression of Bax and downregulates the expression of procaspase-9 and -3, and it is suggested that the mitochondrial pathway is activated and rhein-induced apoptosis may be involved. In addition, we also want to explore whether rhein-induced apoptosis is related to the autophagic changes induced by rhein. The results showed that rhein treatment increased P62 and decreased LC3-II and beclin-1, which means that autophagy was weakened. The results of our studies indicated that rhein induced caspase-dependent apoptosis via both the Fas death pathway and the mitochondrial pathway by generating ROS, and meanwhile the autophagy tended to weaken.

A tandem death effector domain-containing protein inhibits the IMD signaling pathway via forming amyloid-like aggregates with the caspase-8 homolog DREDD

Negative regulation of the immune signaling pathway involves diverse negative regulators that target different signaling molecules. One of the signaling molecules, DREDD, which activates the NF-κB transcription factor Relish in the IMD pathway, is a homolog of mammalian caspase-8. Some structural related proteins have been identified to regulate the activity of caspase-8 in signaling complex assembly. However, it is unknown in insects whether the IMD pathway undergoes such a down-regulation. In this study, we explored the regulatory role of a newly identified protein BmCaspase-8 like (BmCasp8L) in silkworm, which displays high sequence similarity with the N-terminus of BmDREDD to the IMD pathway, and investigated its mechanism. Domain prediction, phylogenic analysis and gene architecture suggests BmCasp8L acts as a potential inhibitor to BmDREDD. We then found it is highly expressed in the fat body and hemocytes, and suppresses the cleavage of BmRelish and BmIMD mediated by BmDREDD upon PGN stimulation, resulting in deficiency in antimicrobial peptides production. Besides the inhibitory role in the IMD pathway, it also suppresses the BmDREDD-induced apoptosis. By investigating the amyloidal activity of BmCasp8L and its interaction with BmDREDD and BmFADD, we demonstrated that BmCasp8L forms amyloid-like aggregates in vitro as well as in vivo, and it inactivates BmDREDD by blending into the amyloidal speck-like structure formed by BmDREDD and BmFADD that is required for BmDREDD activity. Taken together, our results demonstrate BmCasp8L inhibits the IMD signaling pathway via forming amyloidal aggregates with BmDREDD, suggesting an evolutionarily conserved regulatory mechanism of innate immune signaling pathway.

MADD silencing enhances anti-tumor activity of TRAIL in anaplastic thyroid cancer

ATC is an aggressive disease with limited therapeutic options due to drug resistance. TRAIL is an attractive anti-cancer therapy that can trigger apoptosis in a cancer cell-selective manner. However, TRAIL resistance is a major clinical obstacle for its use as a therapeutic drug. Previously, we demonstrated that MADD is a cancer cell pro-survival factor that can modulate TRAIL resistance. However, its role, if any, in overcoming TRAIL resistance in ATC is unknown. First, we characterized ATC cell lines as either TRAIL resistant, TRAIL sensitive or moderately TRAIL sensitive and evaluated MADD expression/cellular localization. We determined the effect of MADD siRNA on cellular growth and investigated its effect on TRAIL treatment. We assessed the effect of combination treatment (MADD siRNA and TRAIL) on mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) levels. The effect of combination treatment on tumor growth was assessed in vivo. We found increased levels of MADD in ATC cells relative to Nthy-ori 3-1. MADD protein localizes in the cytosol (endoplasmic reticulum and Golgi body) and membrane. MADD knockdown resulted in spontaneous cell death that was synergistically enhanced when combined with TRAIL treatment in otherwise resistant ATC cells. Combination treatment resulted in a significant reduction in MMP and enhanced generation of ROS indicating the putative mechanism of action. In an orthotopic mouse model of TRAIL-resistant ATC, treatment with MADD siRNA alone reduced tumor growth that, when combined with TRAIL, resulted in significant tumor regressions. We demonstrated the potential clinical utility of MADD knockdown in sensitizing cells to TRAIL-induced apoptosis in ATC.

MADD Expression in Lung Adenocarcinoma and its Impact on Proliferation and Apoptosis of Lung Adenocarcinoma Cells

OBJECTIVE

This study investigated the expression of MAPK-activating death domaincontaining protein (MADD) in lung adenocarcinoma and its impact on lung adenocarcinoma SPCA- 1 cell proliferation and apoptosis.

METHODS

Clinicopathological lung specimens were collected. MADD expression levels in normal human lung and human lung adenocarcinoma tissues were detected by immunohistochemistry. Lung adenocarcinoma SPC-A-1 cells were cultured, and IG20 gene expression in the SPC-A-1 cells was detected using reverse-transcription PCR. SPC-A-1 cells were transfected with a plasmid carrying the MADD gene and a lentiviral vector capable of silencing MADD expression. CCK-8 assay, western blot and flow cytometry were performed to detect MADD expression, proliferation and apoptosis in the SPC-A-1 cells.

RESULTS

MADD expression levels in the lung adenocarcinoma tissue were significantly higher than those in the normal lung tissue and lung squamous carcinoma cells. MADD can be expressed in lung adenocarcinoma SPC-A-1 cells. High MADD expression can inhibit SPC-A-1 cell apoptosis and enhance SPC-A-1 cell proliferative activity, while silencing MADD expression can promote apoptosis and reduce SPC-A-1 cell proliferation.

CONCLUSION

MADD expression is significantly upregulated in lung adenocarcinoma tissue. MADD can promote lung adenocarcinoma cell growth by inhibiting apoptosis. This study may improve lung adenocarcinoma levels in patients and, thus, is worthy of clinical promotion.

Melittin Induced G1 Cell Cycle Arrest and Apoptosis in Chago-K1 Human Bronchogenic Carcinoma Cells and Inhibited the Differentiation of THP-1 Cells into Tumour- Associated Macrophages

Background: Bronchogenic carcinoma (lung cancer) is one of the leading causes of death. Although many compounds isolated from natural products have been used to treat it, drug resistance is a serious problem, and alternative anti-cancer drugs are required. Here, melittin from Apis mellifera venom was used, and its effects on bronchogenic carcinoma cell proliferation and tumour-associated macrophage differentiation were evaluated. Methods: The half maximal inhibitory concentration (IC50) of melittin was measured by MTT. Cell death was observed by annexin V and propidium iodide (PI) co-staining followed by flow cytometry. Cell cycle arrest was revealed by PI staining and flow cytometry. To investigate the tumour microenvironment, differentiation of circulating monocytes (THP-1) into tumour-associated macrophages (TAMs) was assayed by sandwich-ELISA and interleukin (IL)-10 levels were determined. Cell proliferation and migration was observed by flat plate colony formation. Secretion of vascular endothelial growth factor (VEGF) was detected by ELISA. The change in expression levels of CatS, Bcl-2, and MADD was measured by quantitative RT-PCR. Results: Melittin was significantly more cytotoxic (p < 0.01) to human bronchogenic carcinoma cells (ChaGo-K1) than to the control human lung fibroblasts (Wi-38) cells. At 2.5 μM, melittin caused ChaGo-K1 cells to undergo apoptosis and cell cycle arrest at the G1 phase. The IL-10 levels showed that melittin significantly inhibited the differentiation of THP-1 cells into TAMs (p < 0.05) and reduced the number of colonies formed in the treated ChaGo-K1 cells compared to the untreated cells. However, melittin did not affect angiogenesis in ChaGo-K1 cells. Unlike MADD, Bcl-2 was up-regulated significantly (p < 0.05) in melittin-treated ChaGo-K1 cells. Conclusion: Melittin can be used as an alternative agent for lung cancer treatment because of its cytotoxicity against ChaGo-K1 cells and the inhibition of differentiation of THP-1 cells into TAMs.

RAIDD mutations underlie the pathogenesis of thin lissencephaly (TLIS)

Abnormal regulation of caspase-2-mediated neuronal cell death causes neurodegenerative diseases and defective brain development. PIDDosome is caspase-2 activating complex composed of PIDD, RAIDD, and caspase-2. Recent whole-exome sequencing study showed that the RAIDD mutations in the death domain (DD), including G128R, F164C, R170C, and R170H mutations, cause thin lissencephaly (TLIS) by reducing caspase-2-mediated neuronal apoptosis. Given that the molecular structure of the RAIDD DD:PIDD DD complex is available, in this study, we analyzed the molecular mechanisms underlying TLIS caused by the RAIDD TLIS variants by performing mutagenesis and biochemical assays.

Detection of RIPK1 in the FADD-Containing Death Inducing Signaling Complex (DISC) During Necroptosis

FAS-associated protein with death domain (FADD) is a signaling molecule required by members of the TNF receptor superfamily (TNFRSF) such as FAS and TNFR1 to induce apoptosis. FADD is a small adapter molecule that functions as a scaffold to recruit procaspase-8 and other regulators. The FADD-containing signaling complex that initiates the apoptotic cascade has been termed the death inducing signaling complex (DISC). In the absence of FADD, death receptors cannot induce apoptosis and in appropriate cell types, these death receptors then induce necroptosis. Necroptosis can also be induced by death receptors in FADD-sufficient cells when caspase-8 is inhibited, usually accomplished by the addition of caspase inhibitors. Under such necroptotic conditions, the immunoprecipitation of FADD to isolate the DISC can be utilized to examine components of this complex. Here, we describe the immunoprecipitation of FADD and subsequent western-blotting to identify RIPK1 in this complex during necroptosis.

miR-181 interacts with signaling adaptor molecule DENN/MADD and enhances TNF-induced cell death

MicroRNAs are small noncoding RNAs, which regulate the expression of protein coding transcripts through mRNA degradation or translational inhibition. Numerous reports have highlighted the role of miRNAs in regulating cell death pathways including the expression of genes involved in the induction of apoptosis. Tumor necrosis factor alpha (TNF-α) is a proinflammatory cytokine which can send pro-death signals through its receptor TNFR1. Diverse adaptor molecules including DENN/MADD adaptor protein have been shown to modulate TNF-α pro-death signaling via recruitment of MAP kinases to TNFR1 and activation of pro-survival NFκB signaling. Herein, we investigated the role of microRNA-181 (miR-181) in regulating DENN/MADD expression levels and its subsequent effects on TNF-α-induced cell death. Using bioinformatics analyses followed by luciferase reporter assays we showed that miR-181 interacts with the 3’ UTR of DENN/MADD transcripts. miR-181 overexpression also led to decreased endogenous DENN/MADD mRNA levels in L929 murine fibroblasts. Flow cytometric analysis of miR-181 transfected cells showed this miRNA accentuates mitochondrial membrane potential loss caused by TNF-α. These findings were associated with enhanced apoptosis of L929 cells following TNF-α treatment. Overall, these data point to the potential role of miR-181 in regulating TNF-α pro-death signaling, which could be of importance from pathogenesis and therapeutic perspectives in inflammatory disorders associated with tissue degeneration and cell death.

CD95 Stimulation with CD95L and DISC Analysis

CD95 and its ligand CD95L play a major role in immune surveillance and homeostasis. CD95L is expressed by activated T lymphocytes and NK cells to induce apoptosis in cancer and virus-infected cells. The goal of this chapter is to describe a method used to immunoprecipitate CD95 and analyze its associated protein complex in cells stimulated with a cytotoxic CD95L (i.e., Ig-CD95L).

Cryo-EM Structure of Caspase-8 Tandem DED Filament Reveals Assembly and Regulation Mechanisms of the Death-Inducing Signaling Complex

Caspase-8 activation can be triggered by death receptor-mediated formation of the death-inducing signaling complex (DISC) and by the inflammasome adaptor ASC. Caspase-8 assembles with FADD at the DISC and with ASC at the inflammasome through its tandem death effector domain (tDED), which is regulated by the tDED-containing cellular inhibitor cFLIP and the viral inhibitor MC159. Here we present the caspase-8 tDED filament structure determined by cryoelectron microscopy. Extensive assembly interfaces not predicted by the previously proposed linear DED chain model were uncovered, and were further confirmed by structure-based mutagenesis in filament formation in vitro and Fas-induced apoptosis and ASC-mediated caspase-8 recruitment in cells. Structurally, the two DEDs in caspase-8 use quasi-equivalent contacts to enable assembly. Using the tDED filament structure as a template, structural analyses reveal the interaction surfaces between FADD and caspase-8 and the distinct mechanisms of regulation by cFLIP and MC159 through comingling and capping, respectively.

Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer

Pancreatic cancer is highly malignant with limited therapy and a poor prognosis. TRAIL-activating therapy has been promising, however, clinical trials have shown resistance and limited responses of pancreatic cancers. We investigated the effects of calmodulin(CaM) antagonists, trifluoperazine(TFP) and tamoxifen(TMX), on TRA-8-induced apoptosis and tumorigenesis of TRA-8-resistant pancreatic cancer cells, and underlying mechanisms. TFP or TMX alone did not induce apoptosis of resistant PANC-1 cells, while they dose-dependently enhanced TRA-8-induced apoptosis. TMX treatment enhanced efficacy of TRA-8 therapy on tumorigenesis in vivo. Analysis of TRA-8-induced death-inducing-signaling-complex (DISC) identified recruitment of survival signals, CaM/Src, into DR5-associated DISC, which was inhibited by TMX/TFP. In contrast, TMX/TFP increased TRA-8-induced DISC recruitment/activation of caspase-8. Consistently, caspase-8 inhibition blocked the effects of TFP/TMX on TRA-8-induced apoptosis. Moreover, TFP/TMX induced DR5 expression. With a series of deletion/point mutants, we identified CaM antagonist-responsive region in the putative Sp1-binding domain between -295 to -300 base pairs of DR5 gene. Altogether, we have demonstrated that CaM antagonists enhance TRA-8-induced apoptosis of TRA-8-resistant pancreatic cancer cells by increasing DR5 expression and enhancing recruitment of apoptotic signal while decreasing survival signals in DR5-associated DISC. Our studies support the use of these readily available CaM antagonists combined with TRAIL-activating agents for pancreatic cancer therapy.

TNFα sensitizes neuroblastoma cells to FasL-, cisplatin- and etoposide-induced cell death by NF-κB-mediated expression of Fas

BACKGROUND

Patients with high-risk neuroblastoma (NBL) tumors have a high mortality rate. Consequently, there is an urgent need for the development of new treatments for this condition. Targeting death receptor signaling has been proposed as an alternative to standard chemo- and radio-therapies in various tumors. In NBL, this therapeutic strategy has been largely disregarded, possibly because ~50-70% of all human NBLs are characterized by caspase-8 silencing. However, the expression of caspase-8 is detected in a significant group of NBL patients, and they could therefore benefit from treatments that induce cell death through death receptor activation. Given that cytokines, such as TNFα, are able to upregulate Fas expression, we sought to address the therapeutic relevance of co-treatment with TNFα and FasL in NBL.

METHODS

For the purpose of the study we used a set of eight NBL cell lines. Here we explore the cell death induced by TNFα, FasL, cisplatin, and etoposide, or a combination thereof by Hoechst staining and calcein viability assay. Further assessment of the signaling pathways involved was performed by caspase activity assays and Western blot experiments. Characterization of Fas expression levels was achieved by qRT-PCR, cell surface biotinylation assays, and cytometry.

RESULTS

We have found that TNFα is able to increase FasL-induced cell death by a mechanism that involves the NF-κB-mediated induction of the Fas receptor. Moreover, TNFα sensitized NBL cells to DNA-damaging agents (i.e. cisplatin and etoposide) that induce the expression of FasL. Priming to FasL-, cisplatin-, and etoposide-induced cell death could only be achieved in NBLs that display TNFα-induced upregulation of Fas. Further analysis denotes that the high degree of heterogeneity between NBLs is also manifested in Fas expression and modulation thereof by TNFα.

CONCLUSIONS

In summary, our findings reveal that TNFα sensitizes NBL cells to FasL-induced cell death by NF-κB-mediated upregulation of Fas and unveil a new mechanism through which TNFα enhances the efficacy of currently used NBL treatments, cisplatin and etoposide.

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.

Silencer of death domains controls cell death through tumour necrosis factor-receptor 1 and caspase-10 in acute lymphoblastic leukemia

Resistance to apoptosis remains a significant problem in drug resistance and treatment failure in malignant disease. NO-aspirin is a novel drug that has efficacy against a number of solid tumours, and can inhibit Wnt signaling, and although we have shown Wnt signaling to be important for acute lymphoblastic leukemia (ALL) cell proliferation and survival inhibition of Wnt signaling does not appear to be involved in the induction of ALL cell death. Treatment of B lineage ALL cell lines and patient ALL cells with NO-aspirin induced rapid apoptotic cell death mediated via the extrinsic death pathway. Apoptosis was dependent on caspase-10 in association with the formation of the death-inducing signaling complex (DISC) incorporating pro-caspase-10 and tumor necrosis factor receptor 1 (TNF-R1). There was no measurable increase in TNF-R1 or TNF-α in response to NO-aspirin, suggesting that the process was ligand-independent. Consistent with this, expression of silencer of death domain (SODD) was reduced following NO-aspirin exposure and lentiviral mediated shRNA knockdown of SODD suppressed expansion of transduced cells confirming the importance of SODD for ALL cell survival. Considering that SODD and caspase-10 are frequently over-expressed in ALL, interfering with these proteins may provide a new strategy for the treatment of this and potentially other cancers.

Systems biology of death receptor networks: live and let die

The extrinsic apoptotic pathway is initiated by death receptor activation. Death receptor activation leads to the formation of death receptor signaling platforms, resulting in the demolition of the cell. Despite the fact that death receptor-mediated apoptosis has been studied to a high level of detail, its quantitative regulation until recently has been poorly understood. This situation has dramatically changed in the last years. Creation of mathematical models of death receptor signaling led to an enormous progress in the quantitative understanding of the network regulation and provided fascinating insights into the mechanisms of apoptosis control. In the following sections, the models of the death receptor signaling and their biological implications will be addressed. Central attention will be given to the models of CD95/Fas/APO-1, an exemplified member of the death receptor signaling pathways. The CD95 death-inducing signaling complex (DISC) and regulation of CD95 DISC activity by its key inhibitor c-FLIP, have been vigorously investigated by modeling approaches, and therefore will be the major topic here. Furthermore, the non-linear dynamics of the DISC, positive feedback loops and bistability as well as stoichiometric switches in extrinsic apoptosis will be discussed. Collectively, this review gives a comprehensive view how the mathematical modeling supported by quantitative experimental approaches has provided a new understanding of the death receptor signaling network.

IG20/MADD plays a critical role in glucose-induced insulin secretion

Pancreatic β-cell dysfunction is a common feature of type 2 diabetes. Earlier, we had cloned IG20 cDNA from a human insulinoma and had shown that IG20/MADD can encode six different splice isoforms that are differentially expressed and have unique functions, but its role in β-cell function was unexplored. To investigate the role of IG20/MADD in β-cell function, we generated conditional knockout (KMA1ko) mice. Deletion of IG20/MADD in β-cells resulted in hyperglycemia and glucose intolerance associated with reduced and delayed glucose-induced insulin production. KMA1ko β-cells were able to process insulin normally but had increased insulin accumulation and showed a severe defect in glucose-induced insulin release. These findings indicated that IG20/MADD plays a critical role in glucose-induced insulin release from β-cells and that its functional disruption can cause type 2 diabetes. The clinical relevance of these findings is highlighted by recent reports of very strong association of the rs7944584 single nucleotide polymorphism (SNP) of IG20/MADD with fasting hyperglycemia/diabetes. Thus, IG20/MADD could be a therapeutic target for type 2 diabetes, particularly in those with the rs7944584 SNP.

Targeting c-Met receptor overcomes TRAIL-resistance in brain tumors

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) induced apoptosis specifically in tumor cells. However, with approximately half of all known tumor lines being resistant to TRAIL, the identification of TRAIL sensitizers and their mechanism of action become critical to broadly use TRAIL as a therapeutic agent. In this study, we explored whether c-Met protein contributes to TRAIL sensitivity. We found a direct correlation between the c-Met expression level and TRAIL resistance. We show that the knock down c-Met protein, but not inhibition, sensitized brain tumor cells to TRAIL-mediated apoptosis by interrupting the interaction between c-Met and TRAIL cognate death receptor (DR) 5. This interruption greatly induces the formation of death-inducing signaling complex (DISC) and subsequent downstream apoptosis signaling. Using intracranially implanted brain tumor cells and stem cell (SC) lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that SC expressing a potent and secretable TRAIL (S-TRAIL) have a significant anti-tumor effect in mice bearing c-Met knock down of TRAIL-resistant brain tumors. To our best knowledge, this is the first study that demonstrates c-Met contributes to TRAIL sensitivity of brain tumor cells and has implications for developing effective therapies for brain tumor patients.

Use of the tumor repressor DEDD as a prognostic marker of cancer metastasis

DEDD, a member of a family of death effector domain-containing proteins, plays crucial roles in mediating apoptosis, regulating cell cycle, and inhibiting cell mitosis. Our recent work demonstrates that DEDD is a novel tumor repressor, which impedes metastasis by reversing the epithelial-mesenchymal transition (EMT) process in breast and colon cancers. DEDD expression therefore may represent a prognostic marker and potential therapeutic target for the prevention and treatment of cancer metastasis. To reveal the anti-metastatic roles of DEDD in these cancer cells, a number of experiments, including immunohistochemistry, the establishment of stably overexpressing or silencing cancer cells, chemoinvasion assay, soft agar assay, protein degradation, and protein-protein interaction were used in our in vitro and in vivo studies. This chapter focuses on the details of these experiments to provide references for the researchers to investigate the function of a gene in the regulation of tumor metastasis.

Substantial conformational change mediated by charge-triad residues of the death effector domain in protein-protein interactions

Protein conformational changes are commonly associated with the formation of protein complexes. The non-catalytic death effector domains (DEDs) mediate protein-protein interactions in a variety of cellular processes, including apoptosis, proliferation and migration, and glucose metabolism. Here, using NMR residual dipolar coupling (RDC) data, we report a conformational change in the DED of the phosphoprotein enriched in astrocytes, 15 kDa (PEA-15) protein in the complex with a mitogen-activated protein (MAP) kinase, extracellular regulated kinase 2 (ERK2), which is essential in regulating ERK2 cellular distribution and function in cell proliferation and migration. The most significant conformational change in PEA-15 happens at helices α2, α3, and α4, which also possess the highest flexibility among the six-helix bundle of the DED. This crucial conformational change is modulated by the D/E-RxDL charge-triad motif, one of the prominent structural features of DEDs, together with a number of other electrostatic and hydrogen bonding interactions on the protein surface. Charge-triad motif promotes the optimal orientation of key residues and expands the binding interface to accommodate protein-protein interactions. However, the charge-triad residues are not directly involved in the binding interface between PEA-15 and ERK2.

Cetuximab enhances TRAIL-induced gastric cancer cell apoptosis by promoting DISC formation in lipid rafts

TRAIL is a member of the tumor necrosis factor family that selectively induces cancer cell apoptosis. However, gastric cancer cells are insensitive to TRAIL. Our and others studies showed that the inhibition of EGFR pathway activation could increase the sensitivity of TRAIL in cancer cells. But the detailed mechanism is not fully understood. In the present study, compared with TRAIL or cetuximab (an anti-EGFR monoclonal antibody) alone, treatment with the TRAIL/cetuximab combination significantly promoted death receptor 4 (DR4) clustering as well as the translocation of both DR4 and Fas-associated death domain-containing protein (FADD) into lipid rafts. This in turn resulted in caspase-8 cleavage and the formation of the death-inducing signaling complex (DISC) in these lipid rafts. Cholesterol-depletion with methyl-β-cyclodextrin partially prevented DR4 clustering and DISC formation, and thus partially reversed apoptosis induced by the TRAIL/cetuximab dual treatment. These results indicate that cetuximab increases TRAIL-induced gastric cancer cell apoptosis at least partially through the promotion of DISC formation in lipid rafts.

Death receptors as targets in cancer

Anti-tumour therapies based on the use pro-apoptotic receptor agonists, including TNF-related apoptosis-inducing ligand (TRAIL) or monoclonal antibodies targeting TRAIL-R1 or TRAIL-R2, have been disappointing so far, despite clear evidence of clinical activity and lack of adverse events for the vast majority of these compounds, whether combined or not with conventional or targeted anti-cancer therapies. This brief review aims at discussing the possible reasons for the lack of apparent success of these therapeutic approaches and at providing hints in order to rationally design optimal protocols based on our current understanding of TRAIL signalling regulation or resistance for future clinical trials.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Down-modulation of expression, or dephosphorylation, of IG20/MADD in tumor necrosis factor-related apoptosis-inducing ligand-resistant thyroid cancer cells makes them susceptible to treatment with this ligand

BACKGROUND

The IG20/MADD gene is overexpressed in thyroid cancer tissues and cell lines, and can contribute to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance. The ability of the MADD protein to resist TRAIL-induced apoptosis is dependent upon its phosphorylation by Akt. Interestingly, while TRAIL induces a significant reduction in the levels of phospho-Akt (pAkt) and phospho-MADD (pMADD) in TRAIL-sensitive cells, it fails to do so in TRAIL-resistant cells. In this study, we investigated if MADD phosphorylation by Akt was contributing to TRAIL resistance in thyroid cancer cells.

METHODS

We determined the susceptibility of different thyroid cancer cell lines to TRAIL-induced apoptosis by fluorescence-activated cell sorting (FACS) analysis. We tested for various TRAIL resistance factors by FACS analyses or for IG20/MADD expression by quantitative reverse transcription-polymerase chain reaction. We determined the levels of pAkt and pMADD upon TRAIL treatment in thyroid cancer cells by Western blotting. We tested if down-modulation of IG20/MADD gene expression using shRNA or phosphorylation using a dominant negative Akt (DN-Akt) or pretreatment with LY294002, a PI3 kinase inhibitor, could help overcome TRAIL resistance.

RESULT

BCPAP and TPC1 cells were susceptible, while KTC1 and FTC133 cells were resistant, to TRAIL-induced apoptosis. The differential susceptibility to TRAIL was not related to the levels of expression of death receptors, decoy receptors, or TRAIL. KTC1 and FTC133 cells showed higher levels of IG20/MADD expression relative to BCPAP and TPC1, and were rendered susceptible to TRAIL treatment upon IG20/MADD knockdown. Interestingly, upon TRAIL treatment, the pAkt and pMADD levels were reduced in TRAIL-sensitive BCPAP and TPC1 cells, while they remained unchanged in the resistant KTC1 and FTC133 cells. While expression of a constitutively active Akt in BCPAP and TPC1 cells rendered them resistant to TRAIL, pretreating KTC1 and FTC133 cells with LY294002 rendered them TRAIL-sensitive. Moreover, expression of a DN-Akt in KTC1 and FTC133 cells reduced the levels of pAkt and pMADD and sensitized them to TRAIL-induced apoptosis.

CONCLUSION

Our results show that pMADD is an important TRAIL resistance factor in certain thyroid cancer cells and suggest that down-modulation of either IG20/MADD expression or phosphorylation can render TRAIL-resistant thyroid cancer cells sensitive to TRAIL.

Identification of 5-hydroxy-3,6,7,8,3´,4´-hexamethoxyflavone from Hizikia fusiforme involved in the induction of the apoptosis mediators in human AGS carcinoma cells

An 80% ethanol extract of Hizikia fusiforme was obtained and followed by successive fractionation using the organic solvents n-hexane, ethyl acetate, and n-butanol to identify the antioxidative substance. The aqueous part of the nbutanol fractionation step, showing high antioxidative activity, was subjected to reverse-phase liquid chromatography. As a result, a substance purified from a BB-2 fraction showed high antioxidative activity. The m/z 419 [M+H] molecular ion peak in the fraction was observed by the analysis of the ESI-LC/MS spectrum. By the analysis of 1H NMR (500 MHz, DMSO-d6) and 13C NMR (125 MHz, DMSO-d6) spectra, a unique compound of the fraction was biochemically identified as a 5-hydroxy-3,6,7,8,3´,4´- hexamethoxyflavone (5HHMF). We also investigated the effect of 5HHMF on human gastric AGS carcinoma cells. Western blot analysis suggested that the flavone substantially increased the levels of the death receptor-associated apoptosis mediators Fas, Fas L, FADD, TRADD, and DR4 in a concentration-dependent manner. The levels of Fas, Fas L, TRADD, and DR4 in the cells treated with 5HHMF (5 microgram/ml) were approximately 26.4-, 12.8-, 6.7-, and 9.8- times higher than those of non-treated cells, respectively. Of note, the level of FADD protein in the cells exposed to 5HHMF (1 microgram/ml) increased approximately 9.6-times. In addition, the cleavage of caspase-3, -8, and -9 in cultured AGS cells treated with 5HHMF was significantly confirmed. Therefore, our results suggest that 5HHMF from H. fusiforme is involved in the induction of death receptor-associated apoptosis mediators in human gastric AGS carcinoma cells.

TRAF2 Sets a threshold for extrinsic apoptosis by tagging caspase-8 with a ubiquitin shutoff timer

Apoptotic caspase activation mechanisms are well defined, yet inactivation modes remain unclear. The death receptors (DRs), DR4, DR5, and Fas, transduce cell-extrinsic apoptotic signals by recruiting caspase-8 into a death-inducing signaling complex (DISC). At the DISC, Cullin3-dependent polyubiquitination on the small catalytic subunit of caspase-8 augments stimulation. Here we report that tumor necrosis factor receptor-associated factor 2 (TRAF2) interacts with caspase-8 at the DISC, downstream of Cullin3. TRAF2 directly mediates RING-dependent, K48-linked polyubiquitination on the large catalytic domain of caspase-8. This modification destines activated caspase-8 molecules to rapid proteasomal degradation upon autoprocessing and cytoplasmic translocation. TRAF2 depletion lowers the signal threshold for DR-mediated apoptosis, altering cell life versus death decisions in vitro and in vivo. Thus, TRAF2 sets a critical barrier for cell-extrinsic apoptosis commitment by tagging activated caspase-8 with a K48-ubiquitin shutoff timer. These results may have important implications for caspase regulation mechanisms.

Splice variants in apoptotic pathway

Elimination of superfluous or mutated somatic cells is provided by various mechanisms including apoptosis, and deregulation of apoptotic signaling pathways contributes to oncogenesis. 40 years have passed since the term "apoptosis" was introduced by Kerr et al. in 1972; among the programmed cell death, a variety of therapeutic strategies especially targeting apoptotic pathways have been investigated. Alternative precursor messenger RNA splicing, by which the process the exons of pre-mRNA are spliced in different arrangements to produce structurally and functionally distinct mRNA and proteins, is another field in progress, and it has been recognized as one of the most important mechanisms that maintains genomic and functional diversity. A variety of apoptotic genes are regulated through alternative pre-mRNA splicing as well, some of which have important functions as pro-apoptotic and anti-apoptotic factors. In this article we summarized splice variants of some of the apoptotic genes including BCL2L1, BIRC5, CFLAR, and MADD, as well as the regulatory mechanisms of alternative splicing of these genes. If the information of the apoptosis and aberrant splicing in each of malignancies is integrated, it will become possible to target proper variants for apoptosis, and the trans-elements themselves can become specific targets of cancer therapy as well. This article is part of a Special Issue entitled "Apoptosis: Four Decades Later".

The role of death effector domain-containing proteins in acute oxidative cell injury in hepatocytes

Apoptosis is a mechanism that regulates hepatic tissue homeostasis and contributes to both acute and chronic injury in liver disease. The apoptotic signaling cascade involves activation of the death-inducing signaling complex (DISC) and subsequent recruitment of proteins containing death effector domains (DED), which regulate downstream effector molecules. Prominent among these are the Fas-associated death domain (FADD) and the cellular caspase 8-like inhibitory protein (cFLIP), and alterations in these proteins can lead to severe disruption of physiological processes, including acute liver failure or hepatocellular carcinoma. Their role in cell signaling events independent of the DISC remains undetermined. Oxidative stress can cause cell injury from direct effects on molecules or by activating intracellular signaling pathways including the mitogen-activated protein kinases (MAPKs). In this context, prolonged activation of the cJun N-terminal kinase (JNK)/AP-1/cJun signaling pathway promotes hepatocellular apoptosis, whereas activation of the extracellular signal-regulated kinase (Erk) exerts protection. We investigated the roles of FADD and cFLIP in acute oxidant stress induced by the superoxide generator menadione in hepatocytes. Menadione resulted in dose-dependent predominantly necrotic cell death. Hepatocytes expressing a truncated, dominant-negative FADD protein were partially protected, whereas cFLIP-deficient hepatocytes displayed increased cell death from menadione. In parallel, Erk phosphorylation was enhanced in hepatocytes expressing dnFADD and decreased in cFLIP-deficient hepatocytes. Hepatocyte injury was accompanied by increased release of proapoptotic factors and increased JNK/cJun activation. Thus, FADD and cFLIP contribute to the regulation of cell death from acute oxidant stress in hepatocytes involving MAPK signaling. This implies that DED-containing proteins are involved in the regulation of cellular survival beyond their role in cell death receptor-ligand-mediated apoptosis.

[Expression of MADD in lung adenocarcinoma tissues and its effects on proliferation and apoptosis of lung adenocarcinoma A549 cells]

AIM

To investigate the expression of MAPK-activating death domain protein (MADD) in lung adenocarcinoma tissues and its effects on proliferation and apoptosis of lung adenocarcinoma A549 cells.

METHODS

Immunohistochemistry was used to detect the expression of MADD in lung normal and tumor tissues. The expression of IG20 gene in A549 cells was measured by reverse transcription polymerase chain reaction. A549 cells were transfected with pEYFP-MADD plasmids carrying MADD gene or pNL-SIN-GFP-MID lentiviral vectors used for RNA interference. MADD expression and cell proliferation and apoptosis were determined by Western blot, MTT assay, and flow cytometry.

RESULTS

The expression levels of MADD were higher in lung adenocarcinoma and squamous cell carcinoma tissues than that in lung normal tissues, and lung adenocarcinoma tissues expressed more MADD than lung squamous cell carcinoma tissues. The transcript encoding MADD was expressed in A549 cells. The transfection of pEYFP-MADD plasmids could increase MADD expression and cell proliferation of A549 cells, while the A549 cells transfected with pNL-SIN-GFP-MID lentiviral vectors showed significantly decreases in the MADD level and proliferation. It is shown that MADD overexpression could inhibit A549 cell apoptosis, and knock down of MADD could promote apoptosis of them.

CONCLUSION

The expression of MADD increases obviously in lung adenocarcinoma, and MADD can promote survival of lung adenocarcinoma cells by inhibiting apoptosis.

Cellular and molecular mechanisms of apoptosis in age-related muscle atrophy

Age-related muscle atrophy is due to loss of muscle fibers as well as atrophy of the remaining fibers. Evidence shows that loss of myofibers may be, in part, due to apoptosis. Two major apoptotic pathways have been extensively studied which are the mitochondrion-mediated and receptor-mediated pathways. However, other pathways exist, such as the p53 pathway. To date, it is not completely clear what pathways are responsible for loss of fibers in age-related muscle atrophy. Evidence suggests that multiple pathways may play a role. In this review article the effects of aging on the mitochondrion-, receptor-, and p53-mediated apoptotic pathways in skeletal muscle are discussed.

Inhibition of IGF-1R-dependent PI3K activation sensitizes colon cancer cells specifically to DR5-mediated apoptosis but not to rhTRAIL

BACKGROUND

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) initiates apoptosis in tumor cells upon binding to its cognate agonistic receptors, death receptors 4 and 5 (DR4 and DR5). The activity of the insulin-like growth factor 1 (IGF-1) survival pathway is often increased in cancer, influencing both cell proliferation and apoptosis. We hypothesized that inhibiting the IGF-1 receptor (IGF-1R) using NVP-AEW541, a small molecular weight tyrosine kinase inhibitor of the IGF-1R, could increase death receptor (DR)-mediated apoptosis in colon cancer cells.

METHODS

The analyses were performed by caspase assay, flow cytometry, Western blotting, immunoprecipitation and fluorescent microscopy.

RESULTS

Preincubation with NVP-AEW541 surprisingly decreased apoptosis induced by recombinant human TRAIL (rhTRAIL) or an agonistic DR4 antibody while sensitivity to an agonistic DR5 antibody was increased. NVP-AEW541 could inhibit IGF-1-induced activation of the phosphatidylinositol 3-kinase (PI3K) pathway. The effects of the PI3K inhibitor LY294002 on TRAIL-induced apoptosis were similar to those of NVP-AEW541, further supporting a role for IGF-1R-mediated activation of PI3K. We show that PI3K inhibition enhances DR5-mediated caspase 8 processing but also lowers DR4 membrane expression and DR4-mediated caspase 8 processing. Inhibition of PI3K reduced rhTRAIL sensitivity independently of the cell line preference for either DR4- or DR5-mediated apoptosis signaling.

CONCLUSIONS

Our study indicates that individual effects on DR4 and DR5 apoptosis signaling should be taken into consideration when combining DR-ligands with PI3K inhibition.

SHIP-1 inhibits CD95/APO-1/Fas-induced apoptosis in primary T lymphocytes and T leukemic cells by promoting CD95 glycosylation independently of its phosphatase activity

SHIP-1 (SH2 (Src homology 2)-containing inositol 5'-phosphatase-1) functions as a negative regulator of immune responses by hydrolyzing phosphatidylinositol-3,4,5-triphosphate generated by phosphoinositide-3 (PI 3)-kinase activity. As a result, SHIP-1 deficiency in mice results in myeloproliferation and B-cell lymphoma. On the other hand, SHIP-1-deficient mice have a reduced T-cell population, but the underlying mechanisms are unknown. In this work, we hypothesized that SHIP-1 plays anti-apoptotic functions in T cells upon stimulation of the death receptor CD95/APO-1/Fas. Using primary T cells from SHIP-1(-/-) mice and T leukemic cell lines, we report that SHIP-1 is a potent inhibitor of CD95-induced death. We observed that a small fraction of the SHIP-1 pool is localized to the endoplasmic reticulum (ER), in which it promotes CD95 glycosylation. This post-translational modification requires an intact SH2 domain of SHIP-1, but is independent of its phosphatase activity. The glycosylated CD95 fails to oligomerize upon stimulation, resulting in impaired death-inducing signaling complex (DISC) formation and downstream apoptotic cascade. These results uncover an unanticipated inhibitory function for SHIP-1 and emphasize the role of glycosylation in the regulation of CD95 signaling in T cells. This work may also provide a new basis for therapeutic strategies using compounds inducing apoptosis through the CD95 pathway on SHIP-1-negative leukemic T cells.

Extracellular signal-regulated kinase (ERK) inhibition attenuates cigarette smoke extract (CSE) induced-death inducing signaling complex (DISC) formation in human lung fibroblasts (MRC-5) cells

Cigarette smoke (CS), a major risk factor in emphysema, causes cell death by incompletely understood mechanisms. Death-inducing signaling complex (DISC) formation is an initial event in Fas-mediated apoptosis. We demonstrated cigarette smoke extract (CSE) induced DISC formation in human lung fibroblasts (MRC-5). The aim of this study was to investigate the involvement of extracellular signal-regulated kinase (ERK) MAPK activation in CSE induced DISC formation. Immunoprecipitation (IP) for Fas and Western Immunoblot (IB) analysis for caspase 8 were then performed to show DISC. Lactate dehydrogenase (LDH) release was measured using a cytotoxicity detection kit. MTT assay was used as a measure of cell viability. We demonstrated that CSE induces DISC formation in MRC-5 using IP for Fas and IB for caspase 8. ERK was expressed in MRC-5 exposed to CSE. MEK-1 inhibitor (PD98059) decreased DISC formation in MRC-5 exposed to 20% CSE at 1 hr, and cell viability, as assessed by colorimetric MTT assay, was increased in MEK-1 inhibitor treated MRC-5 cells after 24 hr CSE exposure compared to the control. Inhibiting ERK significantly decreased the caspase-3,-8 activity in MEK-1 inhibitor treated MRC-5 cells compared to the control.The DISC formation, initial event of extrinsic apoptotic pathway, is a primary component of CSE- induced death in MRC-5, and ERK activation plays an active role in the DISC formation and downstream pathway. These results suggest that modulation of ERK may have therapeutic potential in the prevention of smoke-related lung injury.

Dynamics within the CD95 death-inducing signaling complex decide life and death of cells

This study explores the dilemma in cellular signaling that triggering of CD95 (Fas/APO-1) in some situations results in cell death and in others leads to the activation of NF-kappaB. We established an integrated kinetic mathematical model for CD95-mediated apoptotic and NF-kappaB signaling. Systematic model reduction resulted in a surprisingly simple model well approximating experimentally observed dynamics. The model postulates a new link between c-FLIP(L) cleavage in the death-inducing signaling complex (DISC) and the NF-kappaB pathway. We validated experimentally that CD95 stimulation resulted in an interaction of p43-FLIP with the IKK complex followed by its activation. Furthermore, we showed that the apoptotic and NF-kappaB pathways diverge already at the DISC. Model and experimental analysis of DISC formation showed that a subtle balance of c-FLIP(L) and procaspase-8 determines life/death decisions in a nonlinear manner. We present an integrated model describing the complex dynamics of CD95-mediated apoptosis and NF-kappaB signaling.

The death effector domain-containing DEDD forms a complex with Akt and Hsp90, and supports their stability

Insulin secretion and glucose transport are the major mechanisms to balance glucose homeostasis. Recently, we found that the death effector domain-containing DEDD inhibits cyclin-dependent kinase-1 (Cdk1) function, thereby preventing Cdk1-dependent inhibitory phosphorylation of S6 kinase-1 (S6K1), downstream of phosphatidylinositol 3-kinase (PI3K), which overall results in maintenance of S6K1 activity. Here we newly show that DEDD forms a complex with Akt and heat-shock protein 90 (Hsp90), and supports the stability of both proteins. Hence, in DEDD(-/-) mice, Akt protein levels are diminished in skeletal muscles and adipose tissues, which interferes with the translocation of glucose-transporter 4 (GLUT4) upon insulin stimulation, leading to inefficient incorporation of glucose in these organs. Interestingly, as for the activation of S6K1, suppression of Cdk1 is involved in the stabilization of Akt protein by DEDD, since diminishment of Cdk1 in DEDD(-/-) cells via siRNA expression or treatment with a Cdk1-inhibitor, increases both Akt and Hsp90 protein levels. Such multifaceted involvement of DEDD in glucose homeostasis by supporting both insulin secretion (via maintenance of S6K1 activity) and glucose uptake (via stabilizing Akt protein), may suggest an association of DEDD-deficiency with the pathogenesis of type 2 diabetes mellitus.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid sensitises human hepatocellular carcinoma cells to TRAIL-induced apoptosis by TRAIL-DISC activation

This paper shows that the histone deacetylase inhibitor SAHA sensitised at sub-toxic doses human hepatocellular carcinoma cells (HepG2, Hep3B and SK-Hep1) to TRAIL-induced apoptosis, while it was ineffective in primary human hepatocytes (PHHs). In particular in HCC cells SAHA increased the expression of death receptor 5 (DR5) and caused a decrement of c-Flip. These two modifications provoked in the presence of TRAIL the rapid production of TRAIL-DISC and the activation of caspase-8. Consequently SAHA/TRAIL combination induced many apoptotic events, such as a cleavage of Bid into tBid, dissipation of mitochondrial membrane potential, activation of caspase-3 with the consequent cleavage of both NF-kB and Akt. The decrease in NF-kB level seemed to be responsible for the reduction in the content of IAP family antiapoptotic proteins while the decrease in Akt level caused a reduction in phospho-Bad. These events led to the activation of caspase-9, which contributed to the strong apoptotic activity of TRAIL. Sensitisation of human hepatocellular carcinoma cells to TRAIL-induced apoptosis by SAHA may suggest new strategies for the treatment of liver tumours.

MADD, a splice variant of IG20, is indispensable for MAPK activation and protection against apoptosis upon tumor necrosis factor-alpha treatment

We investigated the physiological role of endogenous MAPK-activating death domain-containing protein (MADD), a splice variant of the IG20 gene, that can interact with TNFR1 in tumor necrosis factor-alpha (TNFalpha)-induced activation of NF-kappaB, MAPK, ERK1/2, JNK, and p38. Using exon-specific short hairpin RNAs expressing lentiviruses, we knocked down the expression of all IG20 splice variants or MADD, which is overexpressed in cancer cells. Abrogation of MADD expression rendered cells highly susceptible to TNFalpha-induced apoptosis in the absence of cycloheximide. It also resulted in a dramatic loss in TNFalpha-induced activation of MAPK without any apparent effect on NF-kappaB activation. This observation was substantiated by an accompanying loss in the activation of p90RSK, a key downstream target of MAPK, whereas the NF-kappaB-regulated interleukin 6 levels remained unaffected. Endogenous MADD knockdown, however, did not affect epidermal growth factor-induced MAPK activation thereby demonstrating the specific requirement of MADD for TNF receptor-mediated MAPK activation. Re-expression of short hairpin RNA-resistant MADD in the absence of endogenous IG20 expression rescued the cells from TNFalpha-induced apoptosis. The requirement for MADD was highly specific for TNFalpha-induced activation of MAPK but not the related JNK and p38 kinases. Loss of MADD expression resulted in reduced Grb2 and Sos1/2 recruitment to the TNFR1 complex and decreased Ras and MEKK1/2 activation. These results demonstrate the essential role of MADD in protecting cancer cells from TNFalpha-induced apoptosis by specifically activating MAPKs through Grb2 and Sos1/2 recruitment, and its potential as a novel cancer therapeutic target.

Calmodulin binding to the Fas-mediated death-inducing signaling complex in cholangiocarcinoma cells

We have previously demonstrated that the antagonists of calmodulin (CaM) induce apoptosis of cholangiocarcinoma cells partially through Fas-mediated apoptosis pathways. Recently, CaM has been shown to bind to Fas, which is regulated during Fas or CaM antagonist-mediated apoptosis in Jurkat cells and osteoclasts. Accordingly, the present studies were designed to determine whether Fas interacts with CaM in cholangiocarcinoma cells and to elucidate its role in regulating Fas-mediated apoptosis. CaM bound to Fas in cholangiocarcinoma cells. CaM was identified in the Fas-mediated death inducing signaling complex (DISC). The amount of CaM recruited into the DISC was increased after Fas-stimulation, a finding confirmed by immunofluorescent analysis that demonstrated increased membrane co-localization of CaM and Fas upon Fas-stimulation. Consistently, increased Fas microaggregates in response to Fas-stimulation were found to bind to CaM. Fas-induced recruitment of CaM into the DISC was inhibited by the Ca(2+) chelator, EGTA, and the CaM antagonist, trifluoperazine (TFP). TFP decreased DISC-induced cleavage of caspase-8. Further, inhibition of actin polymerization, which has been demonstrated to abolish DISC formation, inhibited the recruitment of CaM into the DISC. These results suggest an important role of CaM in mediating DISC formation, thus regulating Fas-mediated apoptosis in cholangiocarcinoma cells. Characterization of the role of CaM in Fas-mediated DISC formation and apoptosis signaling may provide important insights in the development of novel therapeutic targets for cholangiocarcinoma.

A protective role for the human SMG-1 kinase against tumor necrosis factor-alpha-induced apoptosis

The human suppressor of morphogenesis in genitalia-1 (hSMG-1) protein kinase plays dual roles in mRNA surveillance and genotoxic stress response pathways in human cells. Here, we report that small interfering RNA-mediated depletion of hSMG-1, but not ATM, ATR, hUpf1, or hUpf2, in human U2OS osteosarcoma cells markedly increases the magnitude and accelerates the rate of apoptosis induced by tumor necrosis factor-alpha (TNFalpha) stimulation. The increase in TNFalpha-mediated cell killing observed in hSMG-1-depleted cells is not related to the suppression of nonsense-mediated mRNA decay or to the inhibition of TNFalpha-induced NF-kappaB activation. Rather, we observed that loss of hSMG-1 accelerates the degradation of the long form of the FLICE-inhibitory protein (FLIP(L)), an inhibitor of death-inducing signaling complex-mediated caspase-8 activation, in TNFalpha-treated cells. These results suggest that hSMG-1 plays an important role in cell survival during TNFalpha-induced stress.

Protein kinase C alpha and zeta differentially regulate death-inducing signaling complex formation in cigarette smoke extract-induced apoptosis

Cigarette smoke, a major risk factor in emphysema, causes cell death by incompletely understood mechanisms. Death-inducing signaling complex (DISC) formation is an initial event in Fas-mediated apoptosis. We demonstrate that cigarette smoke extract (CSE) induces DISC formation in human lung fibroblasts (MRC-5) and promotes DISC trafficking from the Golgi complex to membrane lipid rafts. We demonstrate a novel role of protein kinase C (PKC) in the regulation of DISC formation and trafficking. The PKC isoforms, PKCalpha, zeta, epsilon, and eta, were activated by CSE exposure. Overexpression of wild-type PKCalpha inhibited, while PKCzeta promoted, CSE-induced cell death. Dominant-negative (dn)PKCzeta protected against CSE-induced cell death by suppressing DISC formation and caspase-3 activation, while dnPKCalpha enhanced cell death by promoting these events. DISC formation was augmented by wortmannin, an inhibitor of PI3K. CSE-induced Akt phosphorylation was reduced by dnPKCalpha, but it was increased by dnPKCzeta. Expression of PKCalpha in vivo inhibited DISC formation, caspase-3/8 activation, lung injury, and cell death after prolonged cigarette smoke exposure, whereas expression of PKCzeta promoted caspase-3 activation. In conclusion, CSE-induced DISC formation is differentially regulated by PKCalpha and PKCzeta via the PI3K/Akt pathway. These results suggest that modulation of PKC may have therapeutic potential in the prevention of smoke-related lung injury.