Apoptosis-inducing factor (AIF): key to the conserved caspase-independent pathways of cell death?

Numerous pro-apoptotic signal transducing molecules act on mitochondria and provoke the permeabilization of the outer mitochondrial membrane, thereby triggering the release of potentially toxic mitochondrial proteins. One of these proteins, apoptosis-inducing factor (AIF), is a phylogenetically old flavoprotein which, in healthy cells, is confined to the mitochondrial intermembrane space. Upon lethal signaling, AIF translocates, via the cytosol,to the nucleus where it binds to DNA and provokes caspase-independent chromatin condensation. The crystal structures of both human and mouse AIF have been determined, and the fine mechanisms accounting for its oxidoreductase activity and its electrostatic interaction with double-stranded DNA have been elucidated. Importantly, the apoptogenic and oxidoreductase functions of AIF can be dissociated. Thus, mutations that abolish the AIF-DNA interaction suppress AIF-induced chromatin condensation, yet have no effect on the NADH oxidase activity. Recent studies suggest AIF to be a major factor determining caspase-independent neuronal death, emphasizing the central role of mitochondria in the control of physiological and pathological cell demise

An AIF orthologue regulates apoptosis in yeast

Apoptosis-inducing factor (AIF), a key regulator of cell death, is essential for normal mammalian development and participates in pathological apoptosis. The proapoptotic nature of AIF and its mode of action are controversial. Here, we show that the yeast AIF homologue Ynr074cp controls yeast apoptosis. Similar to mammalian AIF, Ynr074cp is located in mitochondria and translocates to the nucleus of yeast cells in response to apoptotic stimuli. Purified Ynr074cp degrades yeast nuclei and plasmid DNA. YNR074C disruption rescues yeast cells from oxygen stress and delays age-induced apoptosis. Conversely, overexpression of Ynr074cp strongly stimulates apoptotic cell death induced by hydrogen peroxide and this effect is attenuated by disruption of cyclophilin A or the yeast caspase YCA1. We conclude that Ynr074cp is a cell death effector in yeast and rename it AIF-1 (Aif1p, gene AIF1)

AIF deficiency compromises oxidative phosphorylation

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein that, after apoptosis induction, translocates to the nucleus where it participates in apoptotic chromatinolysis. Here, we show that human or mouse cells lacking AIF as a result of homologous recombination or small interfering RNA exhibit high lactate production and enhanced dependency on glycolytic ATP generation, due to severe reduction of respiratory chain complex I activity. Although AIF itself is not a part of complex I, AIF-deficient cells exhibit a reduced content of complex I and of its components, pointing to a role of AIF in the biogenesis and/or maintenance of this polyprotein complex. Harlequin mice with reduced AIF expression due to a retroviral insertion into the AIF gene also manifest a reduced oxidative phosphorylation (OXPHOS) in the retina and in the brain, correlating with reduced expression of complex I subunits, retinal degeneration, and neuronal defects. Altogether, these data point to a role of AIF in OXPHOS and emphasize the dual role of AIF in life and death