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Bcl-XL cooperatively associates with the Bap31 complex in the endoplasmic reticulum, dependent on procaspase-8 and
Abstract:
Bap31 is a polytopic integral membrane protein of the endoplasmic reticulum and forms a complex with Bcl-2/Bcl-XL and procaspase-8 (Ng, F. W. H., Nguyen, M., Kwan, T., Branton, P. E., Nicholson, W. D., Cromlish, J. A., and Shore, G. C. (1997) J. Cell Biol. 139, 327-338). In co-transfected human cells, procaspase-8 is capable of interacting with Ced-4, an important adaptor molecule in Caenorhabditis elegans that binds to and activates the C. elegans procaspase, proCed-3. Here, we show that the predicted death effector homology domain within the cytosolic region of Bap31 interacts with Ced-4 and contributes to recruitment of procaspase-8. Bcl-XL, which binds directly but weakly to the polytopic transmembrane region of Bap31, indirectly and cooperatively associates with the Bap31 cytosolic domain, dependent on the presence of procaspase-8 and Ced-4. Ced-4Deltac does not interact with Bcl-XL but rather displaces it from Bap31, suggesting that an endogenous Ced-4-like adaptor is a normal constituent of the Bap31 complex and is required for stable association of Bcl-XL with Bap31 in vivo. These findings indicate that Bap31 is capable of recruiting essential components of a core death regulatory machinery.
Insights
Bap31 protein recruits procaspase-8 and Ced-4, key components of cell death regulation. This interaction is crucial for Bcl-XL binding to Bap31, suggesting Bap31
Area of Science:
- Cell Biology
- Molecular Biology
- Apoptosis Research
Background:
- Bap31 is an endoplasmic reticulum membrane protein.
- Bap31 forms complexes with Bcl-2/Bcl-XL and procaspase-8.
- Ced-4 is an adaptor molecule in Caenorhabditis elegans that activates procaspase.
Purpose of the Study:
- To investigate the interaction between Bap31, Ced-4, and procaspase-8.
- To elucidate the role of Bap31 in recruiting components of the cell death machinery.
- To understand the mechanism of Bcl-XL association with Bap31.
Main Methods:
- Co-transfection of human cells.
- Analysis of protein-protein interactions using Bap31 and its mutants.
- Investigating the role of the death effector homology domain of Bap31.
Main Results:
- The death effector homology domain of Bap31 interacts with Ced-4, aiding procaspase-8 recruitment.
- Bcl-XL binds weakly to Bap31's transmembrane region and cooperatively to the cytosolic domain.
- Procaspase-8 and Ced-4 are necessary for stable Bcl-XL association with Bap31.
- A modified Ced-4 (Ced-4Deltac) displaces Bcl-XL from Bap31.
Conclusions:
- Bap31 acts as a scaffold to recruit essential components of the cell death regulatory machinery.
- An endogenous Ced-4-like adaptor is likely part of the Bap31 complex.
- The interaction network involving Bap31, Ced-4, procaspase-8, and Bcl-XL is critical for apoptosis regulation.