Abstract
Caspase-8 is a key effector of death-receptor-triggered apoptosis. In a previous study, we demonstrated, however, that caspase-8 can also be activated in a death receptor-independent manner via the mitochondrial apoptosis pathway, downstream of caspase-3. Here, we show that caspases-3 and -8 mediate a mitochondrial amplification loop that is required for the optimal release of cytochrome c, mitochondrial permeability shift transition, and cell death during apoptosis induced by treatment with the microtubule-damaging agent paclitaxel (Taxol). In contrast, Smac release from mitochondria followed a different pattern, and therefore seems to be regulated independently from cytochrome c release. Taxol-induced cell death was inhibited by the use of synthetic, cell-permeable caspase-3- (zDEVD-fmk) or caspase-8-specific (zIETD-fmk) inhibitors. Apoptosis signaling was not affected by a dominant-negative FADD mutant (FADD-DN), thereby excluding a role of death receptor signaling in the amplification loop and drug-induced apoptosis. The inhibitor experiments were corroborated by the use of BJAB cells overexpressing the natural serpin protease inhibitor, cytokine response modifier A. These data demonstrate that the complete activation of mitochondria, release of cytochrome c, and execution of drug-induced apoptosis require a mitochondrial amplification loop that depends on caspases-3 and -8 activation. In addition, this is the first report to demonstrate death receptor-independent caspase-8 autoprocessing in vivo.
Publication types
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Antineoplastic Agents, Phytogenic / pharmacology*
-
Apoptosis / drug effects*
-
Apoptosis / physiology
-
Apoptosis Regulatory Proteins
-
Arabidopsis Proteins*
-
B-Lymphocytes / drug effects*
-
B-Lymphocytes / enzymology
-
B-Lymphocytes / pathology
-
Burkitt Lymphoma / enzymology
-
Burkitt Lymphoma / pathology*
-
Carrier Proteins / metabolism
-
Caspase 3
-
Caspase 8
-
Caspase 9
-
Caspase Inhibitors
-
Caspases / physiology*
-
Cysteine Proteinase Inhibitors / pharmacology
-
Cytochrome c Group / analysis
-
Enzyme Activation / drug effects
-
Fatty Acid Desaturases / chemistry
-
Fatty Acid Desaturases / genetics
-
Fatty Acid Desaturases / physiology
-
Humans
-
Intracellular Membranes / drug effects
-
Intracellular Membranes / metabolism
-
Intracellular Signaling Peptides and Proteins
-
Microtubules / drug effects
-
Mitochondria / drug effects
-
Mitochondria / metabolism*
-
Mitochondrial Proteins / metabolism
-
Models, Biological
-
Neoplasm Proteins / antagonists & inhibitors
-
Neoplasm Proteins / physiology*
-
Oligopeptides / pharmacology
-
Paclitaxel / pharmacology*
-
Permeability / drug effects
-
Protein Structure, Tertiary
-
Receptors, Tumor Necrosis Factor / physiology*
-
Recombinant Fusion Proteins / physiology
-
Serpins / genetics
-
Serpins / physiology
-
Signal Transduction
-
Tumor Cells, Cultured / drug effects
-
Tumor Cells, Cultured / enzymology
-
Viral Proteins*
Substances
-
Antineoplastic Agents, Phytogenic
-
Apoptosis Regulatory Proteins
-
Arabidopsis Proteins
-
Carrier Proteins
-
Caspase Inhibitors
-
Cysteine Proteinase Inhibitors
-
Cytochrome c Group
-
DIABLO protein, human
-
Intracellular Signaling Peptides and Proteins
-
Mitochondrial Proteins
-
Neoplasm Proteins
-
Oligopeptides
-
Receptors, Tumor Necrosis Factor
-
Recombinant Fusion Proteins
-
Serpins
-
Viral Proteins
-
benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone
-
benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone
-
interleukin-1beta-converting enzyme inhibitor
-
Fatty Acid Desaturases
-
Fad7 protein, Arabidopsis
-
CASP3 protein, human
-
CASP8 protein, human
-
CASP9 protein, human
-
Caspase 3
-
Caspase 8
-
Caspase 9
-
Caspases
-
Paclitaxel