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BID-dependent and BID-independent pathways for BAX insertion into mitochondria
S C Ruffolo1, D G Breckenridge, M Nguyen
1Department of Biochemistry, McIntyre Medical Sciences Building, McGill University, Montreal, Quebec, Canada H3G 1Y6.
Cell Death and Differentiation
|January 4, 2001
Summary
Caspases, like caspase-8, can trigger BAX protein insertion into mitochondria. A parallel pathway also allows BAX insertion independent of Bid, uncoupling it from cytochrome c release.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- BAX protein normally remains inactive, preventing mitochondrial membrane integration without apoptotic signals.
- Caspase activation is a key event in apoptosis, leading to cellular dismantling.
Purpose of the Study:
- To investigate the role of caspases and their products in initiating BAX insertion into mitochondria.
- To explore the existence and mechanism of Bid-independent pathways for BAX mitochondrial translocation.
Main Methods:
- In vivo and in vitro experiments using cell cultures and purified proteins.
- Utilizing Bid-null mouse embryo fibroblasts to study Bid-independent signaling.
- Assessing BAX insertion and cytochrome c release in response to death signals like TNF-alpha and E1A.
Main Results:
- Caspase-8 and its cleavage product, tBID, were shown to initiate BAX insertion into mitochondrial membranes.
- tBID was found to relieve inhibition of BAX transmembrane anchoring by its NH2-terminal domain.
- Bid-null cells demonstrated a Bid-independent pathway for BAX mitochondrial insertion upon TNF-alpha or E1A stimulation.
- In the absence of Bid, cytochrome c release was uncoupled from BAX membrane insertion.
Conclusions:
- Caspases, particularly through tBID, can actively initiate BAX mitochondrial translocation.
- A distinct Bid-independent pathway facilitates BAX insertion into mitochondria.
- Cytochrome c release can be dissociated from BAX membrane insertion in specific cellular contexts, particularly when Bid is absent.
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