title: Bcl-XL interacts with Apaf-1 and inhibits Apaf-1-dependent caspase-9 activation.
abstract: Recent studies indicate that Caenorhabditis elegans CED-4 interacts with and promotes the activation of the death protease CED-3, and that this activation is inhibited by CED-9. Here we show that a mammalian homolog of CED-4, Apaf-1, can associate with several death proteases, including caspase-4, caspase-8, caspase-9, and nematode CED-3 in mammalian cells. The interaction with caspase-9 was mediated by the N-terminal CED-4-like domain of Apaf-1. Expression of Apaf-1 enhanced the killing activity of caspase-9 that required the CED-4-like domain of Apaf-1. Furthermore, Apaf-1 promoted the processing and activation of caspase-9 in vivo. Bcl-XL, an antiapoptotic member of the Bcl-2 family, was shown to physically interact with Apaf-1 and caspase-9 in mammalian cells. The association of Apaf-1 with Bcl-XL was mediated through both its CED-4-like domain and the C-terminal domain containing WD-40 repeats. Expression of Bcl-XL inhibited the association of Apaf-1 with caspase-9 in mammalian cells. Significantly, recombinant Bcl-XL purified from Escherichia coli or insect cells inhibited Apaf-1-dependent processing of caspase-9. Furthermore, Bcl-XL failed to inhibit caspase-9 processing mediated by a constitutively active Apaf-1 mutant, suggesting that Bcl-XL regulates caspase-9 through Apaf-1. These experiments demonstrate that Bcl-XL associates with caspase-9 and Apaf-1, and show that Bcl-XL inhibits the maturation of caspase-9 mediated by Apaf-1, a process that is evolutionarily conserved from nematodes to humans.
authors.affiliation: Departments of Pathology and Comprehensive Cancer Center, 1500 East Medical Center Drive, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Hu
authors.forename: M A
authors.initials: MA
authors.lastname: Benedict
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: N
authors.initials: N
authors.lastname: Inohara
authors.forename: G
authors.initials: G
authors.lastname: Núñez
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1; D017173:Caenorhabditis elegans / Q000502:physiology; D053453:Caspase 9; D020169:Caspases; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007668:Kidney; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014162:Transfection; D051020:bcl-X Protein
chemical_list: C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; C494811:BCL2L1 protein, human; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D003546:Cysteine Endopeptidases