title: ATF4 and the integrated stress response are induced by ethanol and cytochrome P450 2E1 in human hepatocytes.
abstract: OBJECTIVE
  Molecular mechanisms underlying alcoholic liver disease (ALD) are still not fully understood. Activating transcription factor-4 (ATF4) is the master coordinator of the integrated stress response (ISR), an adaptive pathway triggered by multiple stressors. which can promote cell death and induce metabolic dysregulation if the stress is intense or prolonged. The aim of this study was to assess the effect of alcohol on the ISR signaling pathway in human liver cells and to define the role of cytochrome P450 2E1 (CYP2E1) in this response.
  
  
  METHODS
  Primary cultured human hepatocytes and human HepG2 cells over-expressing CYP2E1 by adenoviral infection were exposed to ethanol (25-100mM) for 8-48h.
  
  
  RESULTS
  Ethanol treatment of both liver cells up-regulated ATF4 as well as the pro-survival and the pro-apoptotic transcriptional program of the ISR. Indeed, in CYP2E1-expressing HepG2 cells exposed to ethanol, the expression of ISR target genes (HMOX-1, GCLC, AsnS, IGFBP-1, GADD34,CHOP, ATF3, CHAC1) was induced. Up-regulation of ATF4 and the ISR transcriptional program was decreased by addition of the anti-oxidant glutathione. Several mechanisms mediated ATF4 protein induction, including, at early times, the phosphorylation of eIF2α which controls ATF4 translation, and, at later times, increased mRNA level and increased stability of the protein. A decrease in cell survival was also observed.
  
  
  CONCLUSIONS
  This study demonstrates that both CYP2E1 and ethanol induce ATF4 and the integrated stress response, a pathway which coordinates signals from multiple stresses, as well as established risk factors for ALD, and can display detrimental cellular effects upon prolonged activation.
authors.affiliation: INSERM UMR-S 747, Paris, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Magne
authors.forename: Etienne
authors.initials: E
authors.lastname: Blanc
authors.forename: Beatrice
authors.initials: B
authors.lastname: Legrand
authors.forename: Danièle
authors.initials: D
authors.lastname: Lucas
authors.forename: Robert
authors.initials: R
authors.lastname: Barouki
authors.forename: Hélène
authors.initials: H
authors.lastname: Rouach
authors.forename: Michèle
authors.initials: M
authors.lastname: Garlatti
mesh_terms: D051701:Activating Transcription Factor 4 / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism*; D000431:Ethanol / Q000633:toxicity*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D008108:Liver Diseases, Alcoholic / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012307:Risk Factors; D015398:Signal Transduction / Q000187:drug effects; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics / Q000502:physiology
chemical_list: C497109:ATF4 protein, human; D015852:Eukaryotic Initiation Factor-2; D012333:RNA, Messenger; D051701:Activating Transcription Factor 4; D000431:Ethanol; D019392:Cytochrome P-450 CYP2E1