title: Downregulation of the small GTPase SAR1A: a key event underlying alcohol-induced Golgi fragmentation in hepatocytes.
abstract: The hepatic asialoglycoprotein receptor (ASGP-R) is posttranslationally modified in the Golgi en route to the plasma membrane, where it mediates clearance of desialylated serum glycoproteins. It is known that content of plasma membrane-associated ASGP-R is decreased after ethanol exposure, although the mechanisms remain elusive. Previously, we found that formation of compact Golgi requires dimerization of the largest Golgi matrix protein giantin. We hypothesize that ethanol-impaired giantin function may be related to altered trafficking of ASGP-R. Here we report that in HepG2 cells expressing alcohol dehydrogenase and hepatocytes of ethanol-fed rats, ethanol metabolism results in Golgi disorganization. This process is initiated by dysfunction of SAR1A GTPase followed by altered COPII vesicle formation and impaired Golgi delivery of the protein disulfide isomerase A3 (PDIA3), an enzyme that catalyzes giantin dimerization. Additionally, we show that SAR1A gene silencing in hepatocytes mimics the effect of ethanol: dedimerization of giantin, arresting PDIA3 in the endoplasmic reticulum (ER) and large-scale alterations in Golgi architecture. Ethanol-induced Golgi fission has no effect on ER-to-Golgi transportation of ASGP-R, however, it results in its deposition in cis-medial-, but not trans-Golgi. Thus, alcohol-induced deficiency in COPII vesicle formation predetermines Golgi fragmentation which, in turn, compromises the Golgi-to-plasma membrane transportation of ASGP-R.
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, Omaha, NE, USA.
authors.forename: Armen
authors.initials: A
authors.lastname: Petrosyan
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, Omaha, NE, USA.|Nebraska Western Iowa Health Care System, VA Service, Department of Research Service, Omaha, NE, USA.
authors.forename: Pi-Wan
authors.initials: PW
authors.lastname: Cheng
authors.affiliation: Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, USA.|Nebraska Western Iowa Health Care System, VA Service, Department of Research Service, Omaha, NE, USA.
authors.forename: Dahn L
authors.initials: DL
authors.lastname: Clemens
authors.affiliation: Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, USA.|Nebraska Western Iowa Health Care System, VA Service, Department of Research Service, Omaha, NE, USA.
authors.forename: Carol A
authors.initials: CA
authors.lastname: Casey
mesh_terms: D000426:Alcohol Dehydrogenase / Q000378:metabolism; D000818:Animals; D037263:Asialoglycoprotein Receptor / Q000378:metabolism; D022181:COP-Coated Vesicles / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D000431:Ethanol / Q000494:pharmacology*; D020868:Gene Silencing / Q000187:drug effects; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000077614:Golgi Matrix Proteins; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008565:Membrane Proteins / Q000378:metabolism; D055442:Metabolome / Q000187:drug effects; D051379:Mice; D008954:Models, Biological; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D010641:Phenotype; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D055503:Protein Multimerization / Q000187:drug effects; D051381:Rats
chemical_list: D037263:Asialoglycoprotein Receptor; D000077614:Golgi Matrix Proteins; D008565:Membrane Proteins; C087574:macrogolgin; D000431:Ethanol; D000426:Alcohol Dehydrogenase; C493083:SAR1A protein, human; D020559:Monomeric GTP-Binding Proteins; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human