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Programmed necrosis induced by DNA alkylating agents, such as MNNG, is a caspase-independent mode of cell death mediated by apoptosis-inducing factor (AIF). After poly(ADP-ribose) polymerase 1, calpain, and Bax activation, AIF moves from the mitochondria to the nucleus where it induces chromatinolysis and cell death. The mechanisms underlying the nuclear action of AIF are, however, largely unknown. We show here that, through its C-terminal proline-rich binding domain (PBD, residues 543–559), AIF associates in the nucleus with histone H2AX. This interaction regulates chromatinolysis and programmed necrosis by generating an active DNA-degrading complex with cyclophilin A (CypA). Deletion or directed mutagenesis in the AIF C-terminal PBD abolishes AIF/H2AX interaction and AIF-mediated chromatinolysis. H2AX genetic ablation or CypA downregulation confers resistance to programmed necrosis. AIF fails to induce chromatinolysis in H2AX or CypA-deficient nuclei. We also establish that H2AX is phosphorylated at Ser139 after MNNG treatment and that this phosphorylation is critical for caspase-independent programmed necrosis. Overall, our data shed new light in the mechanisms regulating programmed necrosis, elucidate a key nuclear partner of AIF, and uncover an AIF apoptogenic motif. [ABSTRACT FROM AUTHOR]

Caspase-independent programmed necrosis is a highly regulated cellular demise that displays morphological and biochemical necrotic hallmarks, such as an earlier permeability of the plasma membrane and lactate dehydrogenase (LDH) leakiness. This form of programmed cell death (PCD) is regulated by AIF, a FAD-dependent oxidoreductase, which is released from the mitochondria to the nucleus where it induces chromatin tcondensation and DNA fragmentation. Some years ago, it was established that the sequential activation of poly(ADP-ribose) polymerase- 1 (PARP-1), calpains and Bax regulates the mitochondrial AIF release associated to programmed necrosis. But, what happens when AIF is in the nucleus? How does this protein induce chromatinolysis and programmed necrosis? Recently, we have unraveled some of the mechanisms underlying the nuclear action of AIF in this type of caspase-independent cell death. Indeed, AIF plays a key role in programmed necrosis by its ability to organize a DNA-degrading complex with H2AX and Cyclophiline A (CypA). The AIF/H2AX link is indeed a critical event and explains the nuclear AIF apoptogenic action. In the present article, we outline the current knowledge on cell death by programmed necrosis and discuss the relevance of the AIF/H2AX/CypA DNA-degrading complex in the regulation of this original form of cell death.