title: A novel Apaf-1-independent putative caspase-2 activation complex.
abstract: Caspase activation is a key event in apoptosis execution. In stress-induced apoptosis, the mitochondrial pathway of caspase activation is believed to be of central importance. In this pathway, cytochrome c released from mitochondria facilitates the formation of an Apaf-1 apoptosome that recruits and activates caspase-9. Recent data indicate that in some cells caspase-9 may not be the initiator caspase in stress-mediated apoptosis because caspase-2 is required upstream of mitochondria for the release of cytochrome c and other apoptogenic factors. To determine how caspase-2 is activated, we have studied the formation of a complex that mediates caspase-2 activation. Using gel filtration analysis of cell lysates, we show that caspase-2 is spontaneously recruited to a large protein complex independent of cytochrome c and Apaf-1 and that recruitment of caspase-2 to this complex is sufficient to mediate its activation. Using substrate-binding assays, we also provide the first evidence that caspase-2 activation may occur without processing of the precursor molecule. Our data are consistent with a model where caspase-2 activation occurs by oligomerization, independent of the Apaf-1 apoptosome.
authors.affiliation: Hanson Institute, Adelaide, Australia 5000.
authors.forename: Stuart H
authors.initials: SH
authors.lastname: Read
authors.forename: Belinda C
authors.initials: BC
authors.lastname: Baliga
authors.forename: Paul G
authors.initials: PG
authors.lastname: Ekert
authors.forename: David L
authors.initials: DL
authors.lastname: Vaux
authors.forename: Sharad
authors.initials: S
authors.lastname: Kumar
mesh_terms: D000818:Animals; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D053143:Caspase 2; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002457:Cell Extracts / Q000032:analysis; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D046911:Macromolecular Substances; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D008970:Molecular Weight; D022423:Myeloid Cells / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D011506:Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: C506592:APAF1 protein, human; C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; D002457:Cell Extracts; D003574:Cytochrome c Group; D008164:Luminescent Proteins; D046911:Macromolecular Substances; D011506:Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D012965:Sodium Chloride; D011189:Potassium Chloride; D053143:Caspase 2; D020169:Caspases