title: Export of mitochondrial AIF in response to proapoptotic stimuli depends on processing at the intermembrane space.
abstract: Apoptosis-inducing factor (AIF) is a mitochondrial intermembrane flavoprotein that is translocated to the nucleus in response to proapoptotic stimuli, where it induces nuclear apoptosis. Here we show that AIF is synthesized as an approximately 67-kDa preprotein with an N-terminal extension and imported into mitochondria, where it is processed to the approximately 62-kDa mature form. Topology analysis revealed that mature AIF is a type-I inner membrane protein with the N-terminus exposed to the matrix and the C-terminal portion to the intermembrane space. Upon induction of apoptosis, processing of mature AIF to an approximately 57-kDa form occurred caspase-independently in the intermembrane space, releasing the processed form into the cytoplasm. Bcl-2 or Bcl-XL inhibited both these events. These findings indicate that AIF release from mitochondria occurs by a two-step process: detachment from the inner membrane by apoptosis-induced processing in the intermembrane space and translocation into the cytoplasm. The results also suggest the presence of a unique protease that is regulated by proapoptotic stimuli in caspase-independent cell death.
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otera
authors.forename: Shigenori
authors.initials: S
authors.lastname: Ohsakaya
authors.forename: Zen-Ichiro
authors.initials: Z
authors.lastname: Nagaura
authors.forename: Naotada
authors.initials: N
authors.lastname: Ishihara
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Mihara
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D051033:Apoptosis Inducing Factor; D002458:Cell Fractionation; D018076:DNA, Complementary / Q000235:genetics; D005420:Flavoproteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000502:physiology*; D008954:Models, Biological; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014162:Transfection; D051020:bcl-X Protein
chemical_list: C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; C494811:BCL2L1 protein, human; D018076:DNA, Complementary; D005420:Flavoproteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D049452:Green Fluorescent Proteins