title: Critical role of endogenous Akt/IAPs and MEK1/ERK pathways in counteracting endoplasmic reticulum stress-induced cell death.
abstract: Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of many diseases and in cancer therapy. Although the unfolded protein response is known to alleviate ER stress by reducing the accumulation of misfolded proteins, the exact survival elements and their downstream signaling pathways that directly counteract ER stress-stimulated apoptotic signaling remain elusive. Here, we have shown that endogenous Akt and ERK are rapidly activated and act as downstream effectors of phosphatidylinositol 3-kinase in thapsigargin- or tunicamycin-induced ER stress. Introduction of either dominant-negative Akt or MEK1 or the inhibitors LY294002 and U0126 sensitized cells to ER stress-induced cell death in different cell types. Reverse transcription-PCR analysis of gene expression during ER stress revealed that cIAP-2 and XIAP, members of the IAP family of potent caspase suppressors, were strongly induced. Transcription of cIAP-2 and XIAP was up-regulated by the phosphatidylinositol 3-kinase/Akt pathway as shown by its reversal by dominant-negative Akt or LY294002. Ablation of these IAPs by RNA interference sensitized cells to ER stress-induced death, which was reversed by the caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone. The protective role of IAPs in ER stress coincided with Smac release from mitochondria to the cytosol. Furthermore, it was shown that mTOR was not required for Akt-mediated survival. These results represent the first demonstration that activation of endogenous Akt/IAPs and MEK/ERK plays a critical role in controlling cell survival by resisting ER stress-induced cell death signaling.
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular Physiology and Biophysics.
authors.forename: Ping
authors.initials: P
authors.lastname: Hu
authors.forename: Zhang
authors.initials: Z
authors.lastname: Han
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Couvillon
authors.forename: John H
authors.initials: JH
authors.lastname: Exton
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002470:Cell Survival; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D005799:Genes, Dominant; D006801:Humans; D020287:In Situ Nick-End Labeling; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011489:Protein Denaturation; D017510:Protein Folding; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013347:Subcellular Fractions; D058570:TOR Serine-Threonine Kinases; D013778:Tetrazolium Salts / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D004791:Enzyme Inhibitors; D048369:MAP Kinase Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D013778:Tetrazolium Salts; D019284:Thapsigargin; D013844:Thiazoles; D014415:Tunicamycin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C546842:MTOR protein, human; C494918:AKT1 protein, human; C022616:thiazolyl blue