Uncleaved BAP31 in association with A4 protein at the endoplasmic reticulum is an inhibitor of Fas-initiated release of cytochrome c from mitochondria.
BAP31 is a polytopic integral protein of the endoplasmic reticulum membrane and, like BID, is a preferred substrate of caspase-8. Upon Fas/CD95 stimulation, BAP31 is cleaved within its cytosolic domain, generating proapoptotic p20 BAP31. In human KB epithelial cells expressing the caspase-resistant mutant crBAP31, Fas stimulation resulted in cleavage of ... BID and insertion of BAX into mitochondrial membrane, but subsequent oligomerization of BAX and BAK, egress of cytochrome c to the cytosol, and apoptosis were impaired. Bap31-null mouse cells expressing crBAP31 cannot generate the endogenous p20 BAP31 cleavage product, yet crBAP31 conferred resistance to cellular condensation and cytochrome c release in response to activation of ectopic FKBPcasp8 by FK1012z. Full-length BAP31, therefore, is a direct inhibitor of these caspase-8-initiated events, acting independently of its ability to sequester p20, with which it interacts. Employing a novel split ubiquitin yeast two-hybrid screen for BAP31-interacting membrane proteins, the putative ion channel protein of the endoplasmic reticulum, A4, was detected and identified as a constitutive binding partner of BAP31 in human cells. Ectopic A4 that was introduced into A4-deficient cells cooperated with crBAP31 to resist Fas-induced egress of cytochrome c from mitochondria and cytoplasmic apoptosis.
Mesh Terms:
Adenosine Triphosphatases, Antigens, CD95, Apoptosis, Caspase 8, Caspase 9, Caspases, Cycloheximide, Cytochrome c Group, Cytoplasm, Dimerization, Dose-Response Relationship, Drug, Endoplasmic Reticulum, Enzyme Activation, Epithelial Cells, Humans, Membrane Proteins, Microscopy, Fluorescence, Mitochondria, Models, Biological, Precipitin Tests, Protein Binding, Time Factors, Transfection, Two-Hybrid System Techniques, Ubiquitin
Adenosine Triphosphatases, Antigens, CD95, Apoptosis, Caspase 8, Caspase 9, Caspases, Cycloheximide, Cytochrome c Group, Cytoplasm, Dimerization, Dose-Response Relationship, Drug, Endoplasmic Reticulum, Enzyme Activation, Epithelial Cells, Humans, Membrane Proteins, Microscopy, Fluorescence, Mitochondria, Models, Biological, Precipitin Tests, Protein Binding, Time Factors, Transfection, Two-Hybrid System Techniques, Ubiquitin
J. Biol. Chem.
Date: Apr. 18, 2003
PubMed ID: 12529377
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