title: Nuclear translocation of X-linked inhibitor of apoptosis (XIAP) determines cell fate after hypoxia ischemia in neonatal brain.
abstract: The inhibitors of apoptosis (IAPs) are emerging as key proteins in the control of cell death. In this study, we evaluated the expression and subcellular distribution of the antiapoptotic protein X-linked IAP (XIAP), and its interactions with the XIAP-associated factor 1 (XAF1) in neonatal rat brain following hypoxia-ischemia (HI). HI triggered the mitochondrial release of cytochrome c, Smac/DIABLO, and caspase 3 activation. Confocal microscopy detected XIAP-specific immunofluorescence in the cytoplasm under normal condition, which exhibited a diffuse distribution at 6 h post-HI and by 12 h the majority of XIAP was redistributed into the nucleus. XIAP nuclear translocation was confirmed by subcellular fractionations and by expressing FLAG-tagged XIAP in primary cortical neurons. Over-expression of XIAP significantly reduced, whereas XIAP gene silencing further enhanced cell death, demonstrating a specific requirement of cytoplasmic XIAP for cell survival. An elevated level of cytosolic XIAP was also evident under the conditions of neuroprotection by fibroblast growth factor-1. XAF1 expression was increased temporally and there was increased nuclear co-localization with XIAP in hypoxic-ischemic cells. XIAP co-immunoprecipitated > 9-fold XAF1 protein concurrent with decreased association with caspases 9 and 3. This is evidenced by the enhanced caspase 3 activity and neuronal death. Our findings implicate XIAP nuclear translocation in neuronal death and point to a novel mechanism in the regulation of hypoxic-ischemic brain injury.
authors.affiliation: The Hugo W. Moser Research Institute at Kennedy Krieger, Baltimore, Maryland, USA.
authors.forename: Juliet C
authors.initials: JC
authors.lastname: Russell
authors.forename: Heather
authors.initials: H
authors.lastname: Whiting
authors.forename: Nicholas
authors.initials: N
authors.lastname: Szuflita
authors.forename: Mir Ahamed
authors.initials: MA
authors.lastname: Hossain
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000502:physiology; D016923:Cell Death / Q000502:physiology; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism / Q000502:physiology; D006801:Humans; D020925:Hypoxia-Ischemia, Brain / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology
chemical_list: D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human