title: Discordance of UPR signaling by ATF6 and Ire1p-XBP1 with levels of target transcripts.
abstract: Accumulation of misfolded proteins within the lumen of the mammalian endoplasmic reticulum (ER) activates the unfolded protein response (UPR). ATF6 and Ire1p are ER-associated proteins that control UPR-specific transcription systems in mammals; UPR signaling involves cleavage of ATF6 and splicing of XBP1 mRNA initiated by Ire1p. We tested the hypothesis that activation of ATF6 and/or Ire1p determines the levels of mRNAs derived from target genes encoding GRP78/BiP and EDEM. By subjecting dermal fibroblasts to multiple stresses, strong correlations were found between ATF6 activation and XBP1 splicing, and between GRP78/BiP mRNA and EDEM mRNA accumulation. Surprisingly, there was no reasonable correlation between activation of either signal transducer with accumulation of either target transcript. Thus, ATF6 and Ire1p signaling do not define the magnitude of UPR-dependent mRNA increases, even though they may be necessary for gene activation, suggesting the existence of additional stress-sensitive factors acting as "coincidence detectors" for transcript accumulation.
authors.affiliation: Department of Pharmacology, University of Texas, Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9041, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Shang
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lehrman
mesh_terms: D051702:Activating Transcription Factor 6; D001383:Azetidinecarboxylic Acid / Q000494:pharmacology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007212:Indolizines / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D000071701:Regulatory Factor X Transcription Factors; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D012867:Skin / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*; D000071717:X-Box Binding Protein 1; D054836:Indolizidines
chemical_list: D051702:Activating Transcription Factor 6; D001383:Azetidinecarboxylic Acid; D004268:DNA-Binding Proteins; D004229:Dithiothreitol; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases; D007212:Indolizines; D008565:Membrane Proteins; D017346:Protein Serine-Threonine Kinases; D000071701:Regulatory Factor X Transcription Factors; D019284:Thapsigargin; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C497111:ATF6 protein, human; C000717247:HSPA5 protein, human; C000605543:XBP1 protein, human; C403982:ERN2 protein, human; C037806:castanospermine; D054836:Indolizidines