title: Identification of protein disulfide isomerase 1 as a key isomerase for disulfide bond formation in apolipoprotein B100.
abstract: Apolipoprotein (apo) B is an obligatory component of very low density lipoprotein (VLDL), and its cotranslational and posttranslational modifications are important in VLDL synthesis, secretion, and hepatic lipid homeostasis. ApoB100 contains 25 cysteine residues and eight disulfide bonds. Although these disulfide bonds were suggested to be important in maintaining apoB100 function, neither the specific oxidoreductase involved nor the direct role of these disulfide bonds in apoB100-lipidation is known. Here we used RNA knockdown to evaluate both MTP-dependent and -independent roles of PDI1 in apoB100 synthesis and lipidation in McA-RH7777 cells. Pdi1 knockdown did not elicit any discernible detrimental effect under normal, unstressed conditions. However, it decreased apoB100 synthesis with attenuated MTP activity, delayed apoB100 oxidative folding, and reduced apoB100 lipidation, leading to defective VLDL secretion. The oxidative folding-impaired apoB100 was secreted mainly associated with LDL instead of VLDL particles from PDI1-deficient cells, a phenotype that was fully rescued by overexpression of wild-type but not a catalytically inactive PDI1 that fully restored MTP activity. Further, we demonstrate that PDI1 directly interacts with apoB100 via its redox-active CXXC motifs and assists in the oxidative folding of apoB100. Taken together, these findings reveal an unsuspected, yet key role for PDI1 in oxidative folding of apoB100 and VLDL assembly.
authors.affiliation: Degenerative Diseases Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037.
authors.forename: Shiyu
authors.initials: S
authors.lastname: Wang
authors.affiliation: Degenerative Diseases Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037.
authors.forename: Shuin
authors.initials: S
authors.lastname: Park
authors.affiliation: Degenerative Diseases Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037.
authors.forename: Vamsi K
authors.initials: VK
authors.lastname: Kodali
authors.affiliation: Soonchunhyang Institute of Med-Bio Science, Soonchunhayng University, Cheonan-si, Choongchengnam-do 330-930, Republic of Korea.
authors.forename: Jaeseok
authors.initials: J
authors.lastname: Han
authors.affiliation: Degenerative Diseases Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037.
authors.forename: Theresa
authors.initials: T
authors.lastname: Yip
authors.affiliation: Division of Geriatrics and Nutrition Sciences, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: Zhouji
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Division of Gastroenterology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: Nicholas O
authors.initials: NO
authors.lastname: Davidson
authors.affiliation: Degenerative Diseases Research Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037 rkaufman@sanfordburnham.org.
authors.forename: Randal J
authors.initials: RJ
authors.lastname: Kaufman
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100 / Q000096:biosynthesis / Q000737:chemistry*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006706:Homeostasis; D050356:Lipid Metabolism; D051379:Mice; D018384:Oxidative Stress; D019704:Protein Disulfide-Isomerases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051381:Rats
chemical_list: D053299:Apolipoprotein B-100; D019704:Protein Disulfide-Isomerases