title: Selective, potent blockade of the IRE1 and ATF6 pathways by 4-phenylbutyric acid analogues.
abstract: OBJECTIVE
  4-Phenylbutyric acid (4-PBA) is a chemical chaperone that eliminates the accumulation of unfolded proteins in the endoplasmic reticulum (ER). However, its chaperoning ability is often weak and unable to attenuate the unfolded protein response (UPR) in vitro or in vivo. To develop more potent chemical chaperones, we synthesized six analogues of 4-PBA and evaluated their pharmacological actions on the UPR.
  
  
  METHODS
  NRK-52E cells were treated with ER stress inducers (tunicamycin or thapsigargin) in the presence of each of the 4-PBA analogues; the suppressive effects of these analogues on the UPR were assessed using selective indicators for individual UPR pathways.
  
  
  RESULTS
  2-POAA-OMe, 2-POAA-NO2 and 2-NOAA, but not others, suppressed the induction of ER stress markers GRP78 and CHOP. This suppressive effect was more potent than that of 4-PBA. Of the three major UPR branches, the IRE1 and ATF6 pathways were markedly blocked by these compounds, as indicated by suppression of XBP1 splicing, inhibition of UPRE and ERSE activation, and inhibition of JNK phosphorylation. Unexpectedly, however, these agents did not inhibit phosphorylation of PERK and eIF2α triggered by ER stress. These compounds dose-dependently inhibited the early activation of NF-κB in ER stress-exposed cells. 2-POAA-OMe and 2-POAA-NO2 also inhibited ER stress-induced phosphorylation of Akt.
  
  
  CONCLUSIONS
  The 4-PBA analogues 2-POAA-OMe, 2-POAA-NO2 and 2-NOAA strongly inhibited activation of the IRE1 and ATF6 pathways and downstream pathogenic targets, including NF-κB and Akt, in ER stress-exposed cells. These compounds may be useful for therapeutic intervention in ER stress-related pathological conditions.
authors.affiliation: Department of Molecular Signaling, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Shotaro
authors.initials: S
authors.lastname: Nakajima
authors.forename: Hironori
authors.initials: H
authors.lastname: Kato
authors.forename: Liubao
authors.initials: L
authors.lastname: Gu
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yoshitomi
authors.forename: Kaoru
authors.initials: K
authors.lastname: Nagai
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Shinmori
authors.forename: Susumu
authors.initials: S
authors.lastname: Kokubo
authors.forename: Masanori
authors.initials: M
authors.lastname: Kitamura
mesh_terms: D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D060588:LIM Domain Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008840:Microfilament Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010654:Phenylbutyrates / Q000494:pharmacology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D000071701:Regulatory Factor X Transcription Factors; D015398:Signal Transduction / Q000187:drug effects*; D051742:Transcription Factor CHOP / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D056811:Unfolded Protein Response / Q000187:drug effects*; D000071717:X-Box Binding Protein 1; D019892:eIF-2 Kinase / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP
chemical_list: D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; D006360:Heat-Shock Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D060588:LIM Domain Proteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D016328:NF-kappa B; D010654:Phenylbutyrates; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000071701:Regulatory Factor X Transcription Factors; D051742:Transcription Factor CHOP; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; D019892:eIF-2 Kinase; C507006:Afdn protein, rat; C497251:Ddit3 protein, rat; C051684:GRP78 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP; C000605545:Xbp1 protein, rat; C075773:4-phenylbutyric acid; C486557:Ern2 protein, rat
keywords: 4-phenylbutyric acid; ATF6; IRE1; PERK-eIF2α; chemical chaperone; endoplasmic reticulum (ER) stress; unfolded protein response (UPR)