title: Elongation Factor 1A-1 Is a Mediator of Hepatocyte Lipotoxicity Partly through Its Canonical Function in Protein Synthesis.
abstract: Elongation factor 1A-1 (eEF1A-1) has non-canonical functions in regulation of the actin cytoskeleton and apoptosis. It was previously identified through a promoter-trap screen as a mediator of fatty acid-induced cell death (lipotoxicity), and was found to participate in this process downstream of ER stress. Since ER stress is implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD), we investigated the mechanism of action of eEF1A-1 in hepatocyte lipotoxicity. HepG2 cells were exposed to excess fatty acids, followed by assessments of ER stress, subcellular localization of eEF1A-1, and cell death. A specific inhibitor of eEF1A-1 elongation activity, didemnin B, was used to determine whether its function in protein synthesis is involved in lipotoxicity. Within 6 h, eEF1A-1 protein was modestly induced by high palmitate, and partially re-localized from its predominant location at the ER to polymerized actin at the cell periphery. This early induction and subcellular redistribution of eEF1A-1 coincided with the onset of ER stress, and was later followed by cell death. Didemnin B did not prevent the initiation of ER stress by high palmitate, as indicated by eIF2α phosphorylation. However, consistent with sustained inhibition of eEF1A-1-dependent elongation activity, didemnin B prevented the recovery of protein synthesis and increase in GRP78 protein that are normally associated with later phases of the response to ongoing ER stress. This resulted in decreased palmitate-induced cell death. Our data implicate eEF1A-1, and its function in protein synthesis, in hepatocyte lipotoxicity.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1.
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Stoianov
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1.
authors.forename: Debra L
authors.initials: DL
authors.lastname: Robson
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1.
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Hetherington
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1; Department of Medicine, Western University, London, ON, Canada, N6A 5C1; Robarts Research Institute, Western University, London, ON, Canada, N6A 5C1.
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Sawyez
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1.
authors.forename: Nica M
authors.initials: NM
authors.lastname: Borradaile
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D047630:Depsipeptides / Q000494:pharmacology; D004041:Dietary Fats / Q000633:toxicity; D019422:Dietary Sucrose / Q000633:toxicity; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D020738:Leptin / Q000172:deficiency; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D023421:Models, Animal; D065626:Non-alcoholic Fatty Liver Disease / Q000139:chemically induced / Q000378:metabolism; D010168:Palmitates / Q000633:toxicity*; D010441:Peptide Chain Elongation, Translational; D020648:Peptide Elongation Factor 1 / Q000502:physiology*; D021381:Protein Transport
chemical_list: D047630:Depsipeptides; D004041:Dietary Fats; D019422:Dietary Sucrose; C094814:EEF1A1 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D020738:Leptin; D010168:Palmitates; D020648:Peptide Elongation Factor 1; C000606749:eEF1A-1 protein, mouse; C030051:didemnins