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Title: Export of mitochondrial AIF in response to proapoptotic stimuli depends on processing at the intermembrane space. Author: Otera H, Ohsakaya S, Nagaura Z, Ishihara N, Mihara K. Journal: EMBO J; 2005 Apr 06; 24(7):1375-86. PubMed ID: 15775970. 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.[Abstract] [Full Text] [Related] [New Search]