Abstract
Apoptosis in response to TRAIL or TNF requires the activation of initiator caspases, which then activate the effector caspases that dismantle cells and cause death. However, little is known about the dynamics and regulatory logic linking initiators and effectors. Using a combination of live-cell reporters, flow cytometry, and immunoblotting, we find that initiator caspases are active during the long and variable delay that precedes mitochondrial outer membrane permeabilization (MOMP) and effector caspase activation. When combined with a mathematical model of core apoptosis pathways, experimental perturbation of regulatory links between initiator and effector caspases reveals that XIAP and proteasome-dependent degradation of effector caspases are important in restraining activity during the pre-MOMP delay. We identify conditions in which restraint is impaired, creating a physiologically indeterminate state of partial cell death with the potential to generate genomic instability. Together, these findings provide a quantitative picture of caspase regulatory networks and their failure modes.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Apoptosis / physiology*
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Apoptosis Regulatory Proteins
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Caspases / metabolism*
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Enzyme Activation*
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HeLa Cells
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Humans
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / metabolism
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Luminescent Proteins / genetics
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Luminescent Proteins / metabolism
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Mathematics
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Membrane Potentials / physiology
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Mitochondria / metabolism
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Mitochondrial Proteins / genetics
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Mitochondrial Proteins / metabolism
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Models, Theoretical
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Poly(ADP-ribose) Polymerases / genetics
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Poly(ADP-ribose) Polymerases / metabolism
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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RNA Interference
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Signal Transduction / physiology*
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TNF-Related Apoptosis-Inducing Ligand / genetics
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TNF-Related Apoptosis-Inducing Ligand / metabolism
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X-Linked Inhibitor of Apoptosis Protein / genetics
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X-Linked Inhibitor of Apoptosis Protein / metabolism
Substances
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Apoptosis Regulatory Proteins
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DIABLO protein, human
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Intracellular Signaling Peptides and Proteins
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Luminescent Proteins
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Mitochondrial Proteins
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Proto-Oncogene Proteins c-bcl-2
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Recombinant Fusion Proteins
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TNF-Related Apoptosis-Inducing Ligand
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X-Linked Inhibitor of Apoptosis Protein
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Poly(ADP-ribose) Polymerases
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Caspases