title: Coupling endoplasmic reticulum stress to the cell death program. An Apaf-1-independent intrinsic pathway.
abstract: Accumulation of misfolded proteins and alterations in Ca2+ homeostasis in the endoplasmic reticulum (ER) causes ER stress and leads to cell death. However, the signal-transducing events that connect ER stress to cell death pathways are incompletely understood. To discern the pathway by which ER stress-induced cell death proceeds, we performed studies on Apaf-1(-/-) (null) fibroblasts that are known to be relatively resistant to apoptotic insults that induce the intrinsic apoptotic pathway. While these cells were resistant to cell death initiated by proapoptotic stimuli such as tamoxifen, they were susceptible to apoptosis induced by thapsigargin and brefeldin-A, both of which induce ER stress. This pathway was inhibited by catalytic mutants of caspase-12 and caspase-9 and by a peptide inhibitor of caspase-9 but not by caspase-8 inhibitors. Cleavage of caspases and poly(ADP-ribose) polymerase was observed in cell-free extracts lacking cytochrome c that were isolated from thapsigargin or brefeldin-treated cells. To define the molecular requirements for this Apaf-1 and cytochrome c-independent apoptosis pathway further, we developed a cell-free system of ER stress-induced apoptosis; the addition of microsomes prepared from ER stress-induced cells to a normal cell extract lacking mitochondria or cytochrome c resulted in processing of caspases. Immunodepletion experiments suggested that caspase-12 was one of the microsomal components required to activate downstream caspases. Thus, ER stress-induced programmed cell death defines a novel, mitochondrial and Apaf-1-independent, intrinsic apoptotic pathway.
authors.affiliation: Buck Institute for Age Research, Novato, California 94945 and the Department of Medicine III, Johannes Gutenberg University, Mainz D-55101, Germany.
authors.forename: Rammohan V
authors.initials: RV
authors.lastname: Rao
authors.forename: Susana
authors.initials: S
authors.lastname: Castro-Obregon
authors.forename: Harald
authors.initials: H
authors.lastname: Frankowski
authors.forename: Martin
authors.initials: M
authors.lastname: Schuler
authors.forename: Veronica
authors.initials: V
authors.lastname: Stoka
authors.forename: Gabriel
authors.initials: G
authors.lastname: del Rio
authors.forename: Dale E
authors.initials: DE
authors.lastname: Bredesen
authors.forename: H Michael
authors.initials: HM
authors.lastname: Ellerby
mesh_terms: D016475:3T3 Cells; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis; D053454:Caspase 12; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death; D002474:Cell-Free System; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000473:pathology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006360:Heat-Shock Proteins; D051379:Mice; D018832:Molecular Chaperones / Q000096:biosynthesis; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D013347:Subcellular Fractions; D013629:Tamoxifen / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D016588:Anticarcinogenic Agents; C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011500:Protein Synthesis Inhibitors; D011506:Proteins; D013629:Tamoxifen; D020126:Brefeldin A; D011064:Poly Adenosine Diphosphate Ribose; D019284:Thapsigargin; C506440:Casp12 protein, mouse; C506434:Casp9 protein, mouse; D053454:Caspase 12; D053453:Caspase 9; D020169:Caspases; D002118:Calcium