title: Endoplasmic reticulum stress in HepG2 cells inhibits apolipoprotein A-I secretion.
abstract: OBJECTIVE
  Endoplasmic reticulum (ER) stress modulates gene expression and has been implicated in causing dyslipidemias. To determine if ER stress may contribute to hypoalphalipoproteinemia through suppression of apo A-I gene expression, human hepatoma cell line Hep G2 was treated with ER stress inducers and the changes in apo A-I gene expression were compared to albumin gene expression.
  
  
  METHODS
  HepG2 cells were treated with tunicamycin (TM) and thapsigargin (TG), two potent inducers of ER stress, and apo A-I and albumin protein levels, mRNA levels, and promoter activity were measured. ER stress was measured using the ER stress-responsive alkaline phosphatase assay and by Western blot quantitation of ER stress markers such as glucose-regulated protein-78 (GRP-78), phosphorylated Jun N-terminal kinase (phospho-JNK), total JNK, phosphorylated eukaryotic initiation factor 2 alpha (phospho eIF2α), and total eIF2α.
  
  
  RESULTS
  TM and TG induced ER stress in HepG2 cells and reduced apo A-I and albumin secretion in a dose-dependent manner. Intracellular albumin levels increased in cells treated with TM and TG while intracellular apo A-I levels decreased. Albumin mRNA and albumin gene promoter activity were reduced in proportion to the decrease in albumin secreted while changes in the apo A-I mRNA levels and promoter activity were modest and did not account for the reduction in apo A-I secretion.
  
  
  CONCLUSIONS
  These results indicate that apo A-I secretion is inhibited by ER stress possibly by affecting cellular degradation pathways. However, ER stress does not affect apo A-I secretion by regulating gene expression.
authors.affiliation: The Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Florida, Jacksonville College of Medicine, Jacksonville, FL 32209, USA.
authors.forename: Emad
authors.initials: E
authors.lastname: Naem
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Haas
authors.forename: Norman C W
authors.initials: NC
authors.lastname: Wong
authors.forename: Arshag D
authors.initials: AD
authors.lastname: Mooradian
mesh_terms: D000418:Albumins / Q000235:genetics / Q000378:metabolism; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects*; D056945:Hep G2 Cells; D006801:Humans; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D019284:Thapsigargin / Q000008:administration & dosage / Q000494:pharmacology*; D014415:Tunicamycin / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000418:Albumins; D016632:Apolipoprotein A-I; D015415:Biomarkers; D012333:RNA, Messenger; D014415:Tunicamycin; D019284:Thapsigargin