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Updated: Jul 17, 2026
Lighting Up the Pathways to Caspase Activation Using Bimolecular Fluorescence Complementation
Published on: March 5, 2018
Caspase-8 can be activated by interchain proteolysis without receptor-triggered dimerization during drug-induced
Dennis Sohn1, Klaus Schulze-Osthoff, Reiner U Jänicke
1Institute of Molecular Medicine, Heinrich-Heine-University, D-40225 Düsseldorf, Germany.
Abstract:
Proteases of the caspase family are thought to be activated by proteolytic processing of their inactive zymogens. However, although proteolytic cleavage is sufficient for executioner caspases, a different mechanism has been recently proposed for initiator caspases, such as caspase-8, which are believed to be activated by proximity-induced dimerization. According to this model, dimerization rather than proteolytic processing is considered as the critical event for caspase-8 activation. Such a mechanism would suggest that in the absence of a dimerization platform such as the death-inducing signaling complex, caspase-8 proteolytic cleavage would result in an inactive enzyme. As several studies have described caspase-8 cleavage during mitochondrial apoptosis, we now investigated whether caspase-8 becomes indeed catalytically active in this pathway. Using an in vivo affinity labeling approach, we demonstrate that caspase-8 is activated in etoposide-treated cells in vivo in the absence of the receptor-induced death-inducing signaling complex formation. Furthermore, we show that both caspase-3 and -6 are required for the efficient activation of caspase-8. Our data therefore indicate that interchain cleavage of caspase-8 in the mitochondrial pathway is sufficient to produce an active enzyme even in the absence of receptor-driven procaspase-8 dimerization.
Insights
Caspase-8 activation in mitochondrial apoptosis is sufficient via cleavage, independent of death-inducing signaling complex dimerization. Caspase-3 and -6 are crucial for this process, challenging prior models of initiator caspase activation.
Area of Science:
- Cellular biology
- Molecular mechanisms of apoptosis
- Enzyme activation pathways
Background:
- Caspase proteases are key regulators of apoptosis.
- Initiator caspases, like caspase-8, were thought to require dimerization for activation.
- The role of proteolytic processing versus dimerization in caspase-8 activation remained unclear, especially in mitochondrial apoptosis.
Purpose of the Study:
- To investigate whether caspase-8 becomes catalytically active during mitochondrial apoptosis.
- To determine if caspase-8 activation occurs independently of the death-inducing signaling complex (DISC).
- To elucidate the role of other caspases in caspase-8 activation within the mitochondrial pathway.
Main Methods:
- In vivo affinity labeling to detect active caspase-8.
- Induction of apoptosis using etoposide.
- Assessment of caspase-3 and caspase-6 involvement in caspase-8 activation.
Main Results:
- Caspase-8 was found to be activated in etoposide-treated cells, independent of DISC formation.
- Proteolytic cleavage of caspase-8 in the mitochondrial pathway was sufficient for catalytic activity.
- Caspase-3 and caspase-6 were identified as necessary for efficient caspase-8 activation.
Conclusions:
- Interchain cleavage of caspase-8 during mitochondrial apoptosis generates an active enzyme.
- Receptor-driven procaspase-8 dimerization is not essential for caspase-8 activation in this context.
- This finding refines the understanding of initiator caspase activation mechanisms in apoptosis.
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