title: Vitamin K epoxide reductase contributes to protein disulfide formation and redox homeostasis within the endoplasmic reticulum.
abstract: The transfer of oxidizing equivalents from the endoplasmic reticulum (ER) oxidoreductin (Ero1) oxidase to protein disulfide isomerase is an important pathway leading to disulfide formation in nascent proteins within the ER. However, Ero1-deficient mouse cells still support oxidative protein folding, which led to the discovery that peroxiredoxin IV (PRDX4) catalyzes a parallel oxidation pathway. To identify additional pathways, we used RNA interference in human hepatoma cells and evaluated the relative contributions to oxidative protein folding and ER redox homeostasis of Ero1, PRDX4, and the candidate oxidants quiescin-sulfhydryl oxidase 1 (QSOX1) and vitamin K epoxide reductase (VKOR). We show that Ero1 is primarily responsible for maintaining cell growth, protein secretion, and recovery from a reductive challenge. We further show by combined depletion with Ero1 that PRDX4 and, for the first time, VKOR contribute to ER oxidation and that depletion of all three activities results in cell death. Of importance, Ero1, PRDX4, or VKOR was individually capable of supporting cell viability, secretion, and recovery after reductive challenge in the near absence of the other two activities. In contrast, no involvement of QSOX1 in ER oxidative processes could be detected. These findings establish VKOR as a significant contributor to disulfide bond formation within the ER.
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, ON, Canada.
authors.forename: Lori A
authors.initials: LA
authors.lastname: Rutkevich
authors.forename: David B
authors.initials: DB
authors.lastname: Williams
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004220:Disulfides / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D055785:Gene Knockdown Techniques; D056945:Hep G2 Cells; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction / Q000187:drug effects; D010088:Oxidoreductases / Q000378:metabolism; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000378:metabolism; D054464:Peroxiredoxins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D064417:Vitamin K Epoxide Reductases
chemical_list: D004220:Disulfides; D008562:Membrane Glycoproteins; C405327:ERO1A protein, human; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C515980:PRDX4 protein, human; D054464:Peroxiredoxins; D064417:Vitamin K Epoxide Reductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; C117183:QSOX1 protein, human; D004229:Dithiothreitol