title: Calpain I induces cleavage and release of apoptosis-inducing factor from isolated mitochondria.
abstract: The translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus has been implicated in the mechanism of glutamate excitotoxicity in cortical neurons and has been observed in vivo following acute rodent brain injuries. However, the mechanism and time course of AIF redistribution to the nucleus is highly controversial. Because elevated intracellular calcium is one of the most ubiquitous features of neuronal cell death, this study tested the hypothesis that cleavage of AIF by the calcium-activated protease calpain mediates its release from mitochondria. Both precursor and mature forms of recombinant AIF were cleaved near the amino terminus by calpain I in vitro. Mitochondrial outer membrane permeabilization by truncated Bid induced cytochrome c release from isolated liver or brain mitochondria but only induced AIF release in the presence of active calpain. Enzymatic inhibition of calpain by calpeptin precluded AIF release, demonstrating that proteolytic activity was required for release. Calpeptin and the mitochondrial permeability transition pore antagonist cyclosporin A also inhibited calcium-induced AIF release from mouse liver mitochondria, implicating the involvement of an endogenous mitochondrial calpain in release of AIF during permeability transition. Cleavage of AIF directly decreased its association with pure lipid vesicles of mitochondrial inner membrane composition. Taken together, these results define a novel mechanism of AIF release involving calpain processing and identify a potential molecular checkpoint for cytoprotective interventions.
authors.affiliation: The Buck Institute for Age Research, Novato, California 94945, USA. bpolster@buckinstitute.org
authors.forename: Brian M
authors.initials: BM
authors.lastname: Polster
authors.forename: Gorka
authors.initials: G
authors.lastname: Basañez
authors.forename: Aitor
authors.initials: A
authors.lastname: Etxebarria
authors.forename: J Marie
authors.initials: JM
authors.lastname: Hardwick
authors.forename: David G
authors.initials: DG
authors.lastname: Nicholls
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D051033:Apoptosis Inducing Factor; D051023:BH3 Interacting Domain Death Agonist Protein; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D002154:Calpain / Q000378:metabolism* / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology; D005420:Flavoproteins / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism*; D008930:Mitochondria, Liver; D024101:Mitochondrial Proteins / Q000378:metabolism*; D010539:Permeability; D051381:Rats; D017208:Rats, Wistar
chemical_list: C494829:AIFM1 protein, human; C494831:Aifm1 protein, rat; D051033:Apoptosis Inducing Factor; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; C494816:Bid protein, rat; D002352:Carrier Proteins; D005420:Flavoproteins; D008081:Liposomes; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C494830:AIFM1 protein, mouse; D002154:Calpain