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Mitochondrio-nuclear translocation of AIF in apoptosis and necrosis
Abstract:
Apoptosis inducing factor (AIF) is a novel apoptotic effector protein that induces chromatin condensation and large-scale ( approximately 50 kbp) DNA fragmentation when added to purified nuclei in vitro. Confocal and electron microscopy reveal that, in normal cells, AIF is strictly confined to mitochondria and thus colocalizes with heat shock protein 60 (hsp60). On induction of apoptosis by staurosporin, c-Myc, etoposide, or ceramide, AIF (but not hsp60) translocates to the nucleus. This suggests that only the outer mitochondrial membrane (which retains AIF in the intermembrane space) but not the inner membrane (which retains hsp60 in the matrix) becomes protein permeable. The mitochondrio-nuclear redistribution of AIF is prevented by a Bcl-2 protein specifically targeted to mitochondrial membranes. The pan-caspase inhibitor Z-VAD. fmk does not prevent the staurosporin-induced translocation of AIF, although it does inhibit oligonucleosomal DNA fragmentation and arrests chromatin condensation at an early stage. ATP depletion is sufficient to cause AIF translocation to the nucleus, and this phenomenon is accelerated by the apoptosis inducer staurosporin. However, in conditions in which both glycolytic and respiratory ATP generation is inhibited, cells fail to manifest any sign of chromatin condensation and advanced DNA fragmentation, thus manifesting a 'necrotic' phenotype. Both in the presence of Z-VAD. fmk and in conditions of ATP depletion, AIF translocation correlates with the appearance of large-scale DNA fragmentation. Altogether, these data are compatible with the hypothesis that AIF is a caspase-independent mitochondrial death effector responsible for partial chromatinolysis.
Insights
Apoptosis inducing factor (AIF) is a mitochondrial protein that moves to the nucleus during apoptosis, causing DNA fragmentation independently of caspases. This suggests AIF is a key effector in programmed cell death.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Apoptosis inducing factor (AIF) is a novel protein implicated in programmed cell death.
- In healthy cells, AIF is localized within mitochondria, colocalizing with heat shock protein 60 (hsp60).
Purpose of the Study:
- To investigate the role and mechanism of AIF translocation during apoptosis.
- To determine if AIF-mediated cell death is dependent on caspases.
Main Methods:
- Confocal and electron microscopy to track AIF localization.
- Induction of apoptosis using various agents (staurosporin, c-Myc, etoposide, ceramide).
- Inhibition of caspases and ATP depletion to assess their impact on AIF translocation and DNA fragmentation.
Main Results:
- AIF translocates from mitochondria to the nucleus upon apoptotic stimuli, while hsp60 remains in mitochondria.
- Bcl-2 protein targeted to mitochondria prevents AIF redistribution.
- AIF translocation occurs independently of caspases and is linked to large-scale DNA fragmentation, even under ATP depletion.
- ATP depletion alone can induce AIF translocation, but complete ATP depletion prevents DNA fragmentation, leading to necrosis.
Conclusions:
- AIF is a caspase-independent mitochondrial effector protein.
- AIF translocation to the nucleus is a critical event in inducing large-scale DNA fragmentation during apoptosis.
- AIF is responsible for partial chromatinolysis, a key feature of programmed cell death.