Mitochondrio-nuclear translocation of AIF in apoptosis and necrosis

Apoptosis inducing factor (AIF) is a novel apoptotic effector protein that induces chromatin condensation and large-scale (similar to 50 kbp) DNA frag mentation when added to purified nuclei in vitro. Confocal and electron mic roscopy reveal that, in normal cells, ATF is strictly confined to mitochond ria and thus colocalizes with heat shock protein 60 (hsp60). On induction o f apoptosis by staurosporin, c-Myc, etoposide, or ceramide, AIF (but not hs p60) translocates to the nucleus. This suggests that only the outer mitocho ndrial membrane (which retains AIF in the intermembrane space) but not the inner membrane (which retains hsp60 in the matrix) becomes protein permeabl e. The mitochondrio-nuclear redistribution of AIF is prevented by a Bcl-2 p rotein specifically targeted to mitochondrial membranes. The pan-caspase in hibitor Z-VAD.fmk does not prevent the staurosporin-induced translocation o f ATF, although it does inhibit oligonucleosomal DNA fragmentation and arre sts chromatin condensation at an early stage. ATP depletion is sufficient t o cause AIF translocation to the nucleus, and this phenomenon is accelerate d by the apoptosis inducer staurosporin. However, in conditions in which bo th glycolytic and respiratory ATP generation is inhibited, cells fail to ma nifest any sign of chromatin condensation and advanced DNA fragmentation, t hus manifesting a 'necrotic' phenotype. Both in the presence of Z-VAD.fmk a nd in conditions of ATP depletion, AIF translocation correlates with the ap pearance of large-scale DNA fragmentation. Altogether, these data are compa tible with the hypothesis that AIF is a caspase-independent mitochondrial d eath effector responsible for partial chromatinolysis.-Daugas, E., Susin, S . A., Zamzami, N., Ferri, K., Irinopoulou, T., Larochette, N., Prevost, RI. -C., Leber, B., Andrews, D., Penninger, J., Kroemer, G. Mitochondria nuclea r translocation of AIF in apoptosis and necrosis.