title: The Birc6 (Bruce) gene regulates p53 and the mitochondrial pathway of apoptosis and is essential for mouse embryonic development.
abstract: Baculoviral inhibitor of apoptosis repeat-containing (Birc)6 gene/BIRC6 (Bruce/APOLLON) encodes an inhibitor of apoptosis and a chimeric E2/E3 ubiquitin ligase in mammals. The physiological role of Bruce in antiapoptosis is unknown. Here, we show that deletion of the C-terminal half of Bruce, including the UBC domain, causes activation of caspases and apoptosis in the placenta and yolk sac, leading to embryonic lethality. This apoptosis is associated with up-regulation and nuclear localization of the tumor suppressor p53 and activation of mitochondrial apoptosis, which includes up-regulation of Bax, Bak, and Pidd, translocation of Bax and caspase-2 onto mitochondria, release of cytochrome c and apoptosis-inducing factor, and activation of caspase-9 and caspase-3. Mutant mouse embryonic fibroblasts are sensitive to multiple mitochondrial death stimuli but resistant to TNF. In addition, eliminating p53 by RNA interference rescues cell viability induced by Bruce ablation in human cell line H460. This viability preservation results from reduced expression of proapoptotic factors Bax, Bak, and Pidd and from prevention of activation of caspase-2, -9, and -3. The amount of second mitochondrial-derived activator of caspase and Omi does not change. We conclude that p53 is a downstream effector of Bruce, and, in response to loss of Bruce function, p53 activates Pidd/caspase-2 and Bax/Bak, leading to mitochondrial apoptosis.
authors.affiliation: Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
authors.forename: Jinyu
authors.initials: J
authors.lastname: Ren
authors.forename: Mingan
authors.initials: M
authors.lastname: Shi
authors.forename: Renshui
authors.initials: R
authors.lastname: Liu
authors.forename: Qi-Heng
authors.initials: QH
authors.lastname: Yang
authors.forename: Teri
authors.initials: T
authors.lastname: Johnson
authors.forename: William C
authors.initials: WC
authors.lastname: Skarnes
authors.forename: Chunying
authors.initials: C
authors.lastname: Du
mesh_terms: D000818:Animals; D017209:Apoptosis; D053143:Caspase 2; D020169:Caspases / Q000378:metabolism; D020964:Embryo Loss; D047108:Embryonic Development / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D006720:Homozygote; D051034:Inhibitor of Apoptosis Proteins; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics* / Q000502:physiology; D010920:Placenta / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism; D015017:Yolk Sac / Q000473:pathology; D050998:bcl-2 Homologous Antagonist-Killer Protein
chemical_list: C490597:BIRC6 protein, mouse; C494773:Bak1 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D050998:bcl-2 Homologous Antagonist-Killer Protein; D053143:Caspase 2; D020169:Caspases