title: A1 functions at the mitochondria to delay endothelial apoptosis in response to tumor necrosis factor.
abstract: Tumor necrosis factor (TNF) does not cause endothelial apoptosis unless the expression of cytoprotective genes is blocked. We have previously demonstrated that one of the TNF-inducible cytoprotective genes is the Bcl-2 family member, A1. A1 is induced by the action of the transcription factor, NFkappaB, in response to inflammatory mediators. In this report we demonstrate that, as with other cell types, inhibition of NFkappaB initiates microvascular endothelial apoptosis in response to TNF. A1 is able to inhibit this apoptosis over 24 h. We demonstrate that A1 is localized to and functions at the mitochondria. Whereas A1 is able to inhibit mitochondrial depolarization, loss of cytochrome c, cleavage of caspase 9, BID, and poly(ADP-ribose) polymerase, it does not block caspase 8 or caspase 3 cleavage. In contrast, A1 is not able to prevent endothelial apoptosis by TNF over 72 h, when NFkappaB signaling is blocked. On the other hand, the caspase inhibitor, benzyloxycarbonyl-VAD-formylmethyl ketone, completely blocks TNF-induced endothelial apoptosis over 72 h. Our findings indicate that A1 is able to maintain temporary survival of endothelial cells in response to TNF by maintaining mitochondrial viability and function. However, a mitochondria-independent caspase pathway eventually results in endothelial death despite mitochondrial protection by A1.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver General Hospital, and St. Paul's Hospital, Vancouver, British Columbia V6Z 1Y6, Canada.
authors.forename: P J
authors.initials: PJ
authors.lastname: Duriez
authors.forename: F
authors.initials: F
authors.lastname: Wong
authors.forename: K
authors.initials: K
authors.lastname: Dorovini-Zis
authors.forename: R
authors.initials: R
authors.lastname: Shahidi
authors.forename: A
authors.initials: A
authors.lastname: Karsan
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000502:physiology*; D003609:Dactinomycin / Q000494:pharmacology; D004727:Endothelium / Q000166:cytology; D018398:Homeodomain Proteins; D006801:Humans; D008833:Microcirculation; D016253:Microscopy, Immunoelectron; D015778:Minor Histocompatibility Antigens; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*; D051818:Replication Protein C; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: C096816:BCL2-related protein A1; D003574:Cytochrome c Group; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C096063:MATA1 protein, S cerevisiae; D015778:Minor Histocompatibility Antigens; D016328:NF-kappa B; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; D003513:Cycloheximide; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D051818:Replication Protein C