title: Nondegradative ubiquitination of apoptosis inducing factor (AIF) by X-linked inhibitor of apoptosis at a residue critical for AIF-mediated chromatin degradation.
abstract: Apoptosis inducing factor (AIF) is a mediator of caspase-independent cell death that is also necessary for mitochondrial energy production. How these seemingly opposite cellular functions of AIF are controlled is poorly understood. X-linked inhibitor of apoptosis (XIAP) is an endogenous inhibitor of caspases that also regulates several caspase-independent signaling pathways. The RING domain of XIAP possesses E3 ubiquitin ligase activity, though the importance of this function to signal regulation remains incompletely defined. XIAP binds and ubiquitinates AIF, and in this study, we determined the functional consequences of XIAP-mediated AIF ubiquitination. Unlike canonical ubiquitination, XIAP-dependent AIF ubiquitination did not lead to proteasomal degradation of AIF. Experiments using ubiquitin mutants demonstrated that the XIAP-dependent ubiquitin linkage was not formed through the commonly used lysine 48, suggesting a noncanonical ubiquitin linkage is employed. Further studies demonstrated that only lysine 255 of AIF was a target of XIAP-dependent ubiquitination. Using recombinant AIF, we determined that mutating lysine 255 of AIF interferes with the ability of AIF not only to bind DNA but also to degrade chromatin in vitro. These data indicate that XIAP regulates the death-inducing activity of AIF through nondegradative ubiquitination, further defining the role of XIAP in controlling AIF and caspase-independent cell death pathways.
authors: Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, United States.
authors: Eric M
authors: EM
authors: Lewis
authors: Amanda S
authors: AS
authors: Wilkinson
authors: Nicole Y
authors: NY
authors: Davis
authors: David A
authors: DA
authors: Horita
authors: John C
authors: JC
authors: Wilkinson
mesh_terms: D019943:Amino Acid Substitution; D051033:Apoptosis Inducing Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D002470:Cell Survival; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054829:RING Finger Domains; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism; D054875:Ubiquitination; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000737:chemistry / Q000378:metabolism*
chemical_list: C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; D002843:Chromatin; D004268:DNA-Binding Proteins; D050505:Mutant Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D009243:NAD; D044767:Ubiquitin-Protein Ligases; D008239:Lysine