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Current Opinion in Structural Biology Dec 2014Members of the NOD-like receptor (NLR) family mediate the innate immune response to a wide range of pathogens, tissue damage and other cellular stresses. They achieve... (Review)
Review
Members of the NOD-like receptor (NLR) family mediate the innate immune response to a wide range of pathogens, tissue damage and other cellular stresses. They achieve modulation of these signals by forming oligomeric signaling platforms, which in analogy to the apoptosome are predicted to adopt a defined oligomeric architecture and will here be referred to as NLR oligomers. Once formed, oligomers of the NLR proteins NLRP3 or NLRC4 'recruit' the adaptor protein ASC and the effector caspase-1, whereby NLRC4 can also directly interact with caspase-1. This results in large multi-protein assemblies, termed inflammasomes. Ultimately, the formation of these inflammasomes leads to the activation of caspase-1, which then processes the cytokines IL-1β and IL-18 triggering the immune response. Here we review new insights into NLR structure and implications on NLR oligomer formation as well as the nature of multi-protein inflammasomes. Of note, so dubbed 'canonical inflammasomes' can also be triggered by the NLR NLRP1b and the non-NLR protein AIM2, however the most detailed mechanistic information at hand pertains to NLRC4 while NLRP3 represents the quintessential inflammasome trigger. Thus these two NLRs are mainly used as examples in this article.
Topics: Apoptosomes; Apoptotic Protease-Activating Factor 1; CARD Signaling Adaptor Proteins; Calcium-Binding Proteins; Carrier Proteins; Caspase 10; Cytoskeletal Proteins; DNA-Binding Proteins; Gene Expression Regulation; Humans; Immunity, Innate; Inflammasomes; Interleukin-18; Interleukin-1beta; NLR Family, Pyrin Domain-Containing 3 Protein; Protein Conformation; Pyrin; Signal Transduction
PubMed: 25201319
DOI: 10.1016/j.sbi.2014.08.011 -
Medicinal Research Reviews Jul 2011Programmed cell death, apoptosis, is a highly regulated cellular pathway, responsible for the elimination of cells in the organism that are no longer needed or... (Review)
Review
Programmed cell death, apoptosis, is a highly regulated cellular pathway, responsible for the elimination of cells in the organism that are no longer needed or extensively damaged. Defects in the regulation of apoptosis could be at the molecular basis of different diseases, either when it is insufficient or excessive. The formation of the macromolecular complex, apoptosome, is a key event in this pathway, which has also been defined as the intrinsic apoptosis pathway. The apoptosome is a holoenzyme multiprotein complex formed by cytochrome c-activated apoptotic protease-activating factor (Apaf-1), dATP, and procaspase-9. Recent studies have produced a wealth of information about the regulation and functions of Apaf-1, but additional studies aimed at elucidating its role as a signaling device at the crosstalk between different signaling pathways are needed to take advantage for the development of modulators of apoptosis pathways and possible therapeutic applications.
Topics: Apoptosomes; Apoptotic Protease-Activating Factor 1; Humans; Models, Biological
PubMed: 20099266
DOI: 10.1002/med.20198 -
Journal of Molecular Endocrinology Aug 2016Enhanced inflammation and reduced apoptosis sustain the growth of endometriotic lesions. Alterations in the expression of estrogen receptor-alpha (ERα) and estrogen... (Review)
Review
Enhanced inflammation and reduced apoptosis sustain the growth of endometriotic lesions. Alterations in the expression of estrogen receptor-alpha (ERα) and estrogen receptor-beta (ERβ) accompany the conversion of resident endometrial cells within the normal uterine environment to ectopic lesions located in extrauterine sites. Recent studies highlighted in this focused review linked ERβ to dysregulation of apoptotic and inflammatory networks involving novel interacting partners in endometriosis. The elucidation of these nongenomic actions of ERβ using human cells and mouse models is an important step in understanding key regulatory pathways that are disrupted leading to disease establishment and progression.
Topics: Animals; Apoptosis; Endometriosis; Endometrium; Estrogen Receptor alpha; Estrogen Receptor beta; Female; Gene Expression Regulation; Humans; Inflammasomes; Inflammation; Models, Biological; Protein Binding; Signal Transduction
PubMed: 27272520
DOI: 10.1530/JME-16-0080 -
Immunity Feb 2016Some forms of regulated cell death, such as apoptosis, are precipitated by the activation of cysteine proteases of the caspase family, including caspase 8, 9, and 3.... (Review)
Review
Some forms of regulated cell death, such as apoptosis, are precipitated by the activation of cysteine proteases of the caspase family, including caspase 8, 9, and 3. Other caspases, such as caspase 1 and 4, are well known for their pro-inflammatory functions but regulate cell death in a limited number of pathophysiological settings. Accumulating evidence suggests that the most conserved function of mammalian caspases is not to control cell death sensu stricto, but to regulate inflammatory and immune reactions to dying cells and infectious challenges. Here, we review the molecular and cellular mechanisms though which mammalian caspases connect cell-death signaling to the maintenance of organismal homeostasis.
Topics: Animals; Caspases; Cell Death; Homeostasis; Humans; Signal Transduction
PubMed: 26885855
DOI: 10.1016/j.immuni.2016.01.020 -
The Journal of Biological Chemistry Sep 2014The protease caspase-9 is activated on the apoptosome, a multiprotein signal transduction platform that assembles in response to mitochondria-dependent apoptosis...
The protease caspase-9 is activated on the apoptosome, a multiprotein signal transduction platform that assembles in response to mitochondria-dependent apoptosis initiation. Despite extensive molecular research, the assembly of the holo-apoptosome and the process of caspase-9 activation remain incompletely understood. Here, we therefore integrated quantitative data on the molecular interactions and proteolytic processes during apoptosome formation and apoptosis execution and conducted mathematical simulations to investigate the resulting biochemical signaling, quantitatively and kinetically. Interestingly, when implementing the homodimerization of procaspase-9 as a prerequisite for activation, the calculated kinetics of apoptosis execution and the efficacy of caspase-3 activation failed to replicate experimental data. In contrast, assuming a scenario in which procaspase-9 is activated allosterically upon binding to the apoptosome backbone, the mathematical simulations quantitatively and kinetically reproduced all experimental data. These data included a XIAP threshold concentration at which apoptosis execution is suppressed in HeLa cervical cancer cells, half-times of procaspase-9 processing, as well as the molecular timer function of the apoptosome. Our study therefore provides novel mechanistic insight into apoptosome-dependent apoptosis execution and suggests that caspase-9 is activated allosterically by binding to the apoptosome backbone. Our findings challenge the currently prevailing dogma that all initiator procaspases require homodimerization for activation.
Topics: Allosteric Regulation; Apoptosis; Apoptosomes; Apoptotic Protease-Activating Factor 1; Caspase 9; Catalytic Domain; Computer Simulation; Enzyme Activation; HeLa Cells; Humans; Kinetics; Models, Molecular; Protein Binding; Protein Multimerization; Protein Precursors; Systems Biology
PubMed: 25107908
DOI: 10.1074/jbc.M114.590034 -
International Journal of Oncology May 2014The intrinsic apoptosis pathway represents an important mechanism of stress-induced death of cancer cells. To gain insight into the functional status of the apoptosome...
The intrinsic apoptosis pathway represents an important mechanism of stress-induced death of cancer cells. To gain insight into the functional status of the apoptosome apparatus in non-small cell lung carcinoma (NSCLC), we studied its sensitivity to activation, the assembly of apoptosome complexes and stability of their precursors, and the importance of X-linked inhibitor of apoptosis (XIAP) in the regulation of apoptosome activity, using cell-free cytosols from NSCLC cell lines and NSCLC tumours and lungs from 62 surgically treated patients. Treatment of cytosol samples with cytochrome c (cyt-c) and dATP induced proteolytic processing of procaspase-9 to caspase-9, which was followed by procaspase-3 processing to caspase-3, and by generation of caspase-3-like activity in 5 of 7 studied NSCLC cell lines. Further analysis demonstrated formation of high-Mr Apaf-1 complexes associated with cleaved caspase-9 in the (cyt-c + dATP)-responsive COLO-699 and CALU-1 cells. By contrast, in A549 cells, Apaf-1 and procaspase-9 co-eluted in the high-Mr fractions, indicating formation of an apoptosome complex unable of procaspase-9 processing. Thermal pre-treatment of cell-free cytosols in the absence of exogenous cyt-c and dATP lead to formation of Apaf-1 aggregates, unable to recruit and activate procaspase-9 in the presence of cyt-c and dATP, and to generate caspase‑3‑like activity. Further studies showed that the treatment with cyt-c and dATP induced a substantially higher increase of caspase-3-like activity in cytosol samples from NSCLC tumours compared to matched lungs. Tumour histology, grade and stage had no significant impact on the endogenous and the (cyt-c + dATP)-induced caspase-3-like activity. Upon addition into the cytosol, the XIAP-neutralizing peptides AVPIAQK and ATPFQEG only moderately heightened the (cyt-c + dATP)-induced caspase‑3‑like activity in some NSCLC tumours. Taken together, the present study provides evidence that the apoptosome apparatus is functional in the majority of NSCLCs and that its sensitivity to the (cyt-c + dATP)-mediated activation is often enhanced in NSCLCs compared to lungs. They also indicate that XIAP does not frequently and effectively suppress the activity of apoptosome apparatus in NSCLCs.
Topics: Aged; Apoptosis; Apoptotic Protease-Activating Factor 1; Carcinoma, Non-Small-Cell Lung; Caspase 3; Caspase 9; Caspase Inhibitors; Cell Line, Tumor; Cytochromes c; Cytosol; Deoxyadenine Nucleotides; Female; Gene Expression Regulation, Neoplastic; Humans; Lung; Lung Neoplasms; Male; Middle Aged; X-Linked Inhibitor of Apoptosis Protein
PubMed: 24626292
DOI: 10.3892/ijo.2014.2333 -
Protein & Cell Sep 2010Apoptotic regulation is critical to organismal homeostasis and protection against many human disease processes such as cancer. Significant research efforts over the past... (Review)
Review
Apoptotic regulation is critical to organismal homeostasis and protection against many human disease processes such as cancer. Significant research efforts over the past several decades have illuminated many signaling molecules and effecter proteins responsible for this form of programmed cell death. Recent evidence suggests that transfer RNA (tRNA) regulates apoptotic sensitivity at the level of cytochrome c-mediated apoptosome formation. This finding unexpectedly places tRNA at the nexus of cellular biosynthesis and survival. Here we review the current understanding of both the apoptotic machinery and tRNA biology. We describe the evidence linking tRNA and cytochrome c in depth, and speculate on the implications of this link in cell biology.
Topics: Animals; Apoptosis; Caspase 9; Cytochromes c; Humans; Models, Biological; Nucleic Acid Conformation; RNA, Transfer
PubMed: 21113408
DOI: 10.1007/s13238-010-0107-x -
Annals of the New York Academy of... Jul 2010Mitochondrial bioenergetic function is a key to cell life and death. Cells need energy not only to support their vital functions but also to die gracefully. Execution of... (Review)
Review
Mitochondrial bioenergetic function is a key to cell life and death. Cells need energy not only to support their vital functions but also to die gracefully. Execution of an apoptotic program includes energy-dependent steps, including kinase signaling, formation of the apoptosome, and effector caspase activation. Under conditions of bioenergetic collapse, cells are diverted toward necrotic demise. Mitochondrial outer membrane permeabilization (MOMP) is a decisive event in the execution of apoptosis. It is also causally linked to a decline in bioenergetic function via different mechanisms, not merely due to cytochrome c dispersion. MOMP-induced bioenergetic deficiency is usually irreversible and commits cells to die, even when caspases are inactive. Here, we discuss the mechanisms by which MOMP impacts bioenergetics in different cell death paradigms.
Topics: Apoptosis; Caspases; Cell Death; Cell Survival; Cytochromes c; Energy Metabolism; Enzyme Activation; HeLa Cells; Humans; Mitochondria; Mitochondrial Membranes; NAD; Necrosis; Oxygen; bcl-2-Associated X Protein
PubMed: 20649539
DOI: 10.1111/j.1749-6632.2010.05633.x -
Nature Cell Biology Dec 2008Apoptosis is induced by caspases, which are members of the cysteine protease family. Caspases are synthesized as inactive zymogens and initiator caspases first gain...
Apoptosis is induced by caspases, which are members of the cysteine protease family. Caspases are synthesized as inactive zymogens and initiator caspases first gain activity by associating with an oligomeric complex of their adaptor proteins, such as the apoptosome. Activated initiator caspases subsequently cleave and activate effector caspases. Although such a proteolytic cascade would predict that a small number of active caspases could irreversibly amplify caspase activity and trigger apoptosis, many cells can maintain moderate levels of caspase activity to perform non-apoptotic roles in cellular differentiation, shape change and migration. Here we show that the Drosophila melanogaster apoptosome engages in a feedback inhibitory loop, which moderates its activation level in vivo. Specifically, the adaptor protein Apaf-1 lowers the level of its associated initiator caspase Dronc, without triggering apoptosis. Conversely, Dronc lowers Apaf-1 protein levels. This mutual suppression depends on the catalytic site of Dronc and a caspase cleavage site within Apaf-1. Moreover, the Drosophila inhibitor of apoptosis protein 1 (Diap1) is required for this process. We speculate that this feedback inhibition allows cells to regulate the degree of caspase activation for apoptotic and non-apoptotic purposes.
Topics: Animals; Apoptosomes; Apoptotic Protease-Activating Factor 1; Caspases; Drosophila Proteins; Drosophila melanogaster; Eye; Feedback, Physiological; Inhibitor of Apoptosis Proteins
PubMed: 19011620
DOI: 10.1038/ncb1803 -
Genes & Development Nov 2015The apoptotic protease-activating factor 1 (Apaf-1) controls the onset of many known forms of intrinsic apoptosis in mammals. Apaf-1 exists in normal cells as an...
The apoptotic protease-activating factor 1 (Apaf-1) controls the onset of many known forms of intrinsic apoptosis in mammals. Apaf-1 exists in normal cells as an autoinhibited monomer. Upon binding to cytochrome c and dATP, Apaf-1 oligomerizes into a heptameric complex known as the apoptosome, which recruits and activates cell-killing caspases. Here we present an atomic structure of an intact mammalian apoptosome at 3.8 Å resolution, determined by single-particle, cryo-electron microscopy (cryo-EM). Structural analysis, together with structure-guided biochemical characterization, uncovered how cytochrome c releases the autoinhibition of Apaf-1 through specific interactions with the WD40 repeats. Structural comparison with autoinhibited Apaf-1 revealed how dATP binding triggers a set of conformational changes that results in the formation of the apoptosome. Together, these results constitute the molecular mechanism of cytochrome c- and dATP-mediated activation of Apaf-1.
Topics: Adenosine Triphosphate; Animals; Apoptosomes; Apoptotic Protease-Activating Factor 1; Caspase 9; Cell Line; Cryoelectron Microscopy; Cytochromes c; Enzyme Activation; Humans; Models, Molecular; Mutation; Protein Binding; Protein Structure, Tertiary
PubMed: 26543158
DOI: 10.1101/gad.272278.115