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Molecular characterization of mitochondrial apoptosis-inducing factor


Mitochondria play a key part in the regulation of apoptosis (cell death)1,2. Their intermembrane space contains several proteins that are liberated through the outer membrane in order to participate in the degradation phase of apoptosis3,4,5,6,7,8,9. Here we report the identification and cloning of an apoptosis-inducing factor, AIF5, which is sufficient to induce apoptosis of isolated nuclei. AIF is a flavoprotein of relative molecular mass 57,000 which shares homology with the bacterial oxidoreductases; it is normally confined to mitochondria but translocates to the nucleus when apoptosis is induced. Recombinant AIF causes chromatin condensation in isolated nuclei and large-scale fragmentation of DNA. It induces purified mitochondria to release the apoptogenic proteins cytochrome c and caspase-9. Microinjection of AIF into the cytoplasm of intact cells induces condensation of chromatin, dissipation of the mitochondrial transmembrane potential, and exposure of phosphatidylserine in the plasma membrane. None of these effects is prevented by the wide-ranging caspase inhibitor known as Z-VAD.fmk. Overexpression of Bcl-2, which controls the opening of mitochondrial permeability transition pores, prevents the release of AIF from the mitochondrion but does not affect its apoptogenic activity. These results indicate that AIF is a mitochondrial effector of apoptotic cell death.

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Figure 1: Alignment of mouse and human AIF amino-acid sequences withbenzene 1,2-dioxygenase system ferredoxin NADH reductase from Pseudomonas putida (BDSF; 30% amino-acid identity with mouse AIF).
Figure 2: Subcellular and submitochondrial distribution of AIF.
Figure 3: Effects of AIF on isolated nuclei and mitochondria.
Figure 4: Effects of AIF on intact cells.


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We thank P. M. Alzari for suggestions, M. Geuskens for electron microscopy, G.Salvesen for caspase-8, D. Andrews for Rat-1 cells, and S. Arya and S. Chung for expression constructs. This work was supported by grants from ANRS, ARC, CNRS, FF, FRM, INSERM, LNC, and PRFMMIP (to G.K.), the NIH, the NSF Science and Technology Center for Molecular Biotechnology (to R.A.), and Amgen (to D.P.S. and J.M.P.). S.A.S. and I.M. hold postdoctoral fellowships from the European Commission and from the Spanish Ministry of Science, respectively.

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Correspondence to Guido Kroemer.

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Susin, S., Lorenzo, H., Zamzami, N. et al. Molecular characterization of mitochondrial apoptosis-inducing factor. Nature 397, 441–446 (1999).

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