title: Action of protein disulfide isomerase on proinsulin exit from endoplasmic reticulum of pancreatic β-cells.
abstract: For insulin synthesis, the proinsulin precursor is translated at the endoplasmic reticulum (ER), folds to include its three native disulfide bonds, and is exported to secretory granules for processing and secretion. Protein disulfide isomerase (PDI) has long been assumed to assist proinsulin in this process. Herein we have examined the effect of PDI knockdown (PDI-KD) in β-cells. The data establish that upon PDI-KD, oxidation of proinsulin to form native disulfide bonds is unimpaired and in fact enhanced. This is accompanied by improved proinsulin exit from the ER and increased total insulin secretion, with no evidence of ER stress. We provide evidence for direct physical interaction between PDI and proinsulin in the ER of pancreatic β-cells, in a manner requiring the catalytic activity of PDI. In β-cells after PDI-KD, enhanced export is selective for proinsulin over other secretory proteins, but the same effect is observed for recombinant proinsulin trafficking upon PDI-KD in heterologous cells. We hypothesize that PDI exhibits unfoldase activity for proinsulin, increasing retention of proinsulin within the ER of pancreatic β-cells.
authors: Division of Metabolism, Endocrinology and Diabetes and the Cellular and Molecular Biology Program, University of Michigan Medical Center, Ann Arbor, Michigan 48105-51714.
authors: Gautam
authors: G
authors: Rajpal
authors: Division of Cellular and Molecular Biology, Toronto General Research Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada.
authors: Irmgard
authors: I
authors: Schuiki
authors: Division of Metabolism, Endocrinology and Diabetes and the Cellular and Molecular Biology Program, University of Michigan Medical Center, Ann Arbor, Michigan 48105-51714.
authors: Ming
authors: M
authors: Liu
authors: Division of Cellular and Molecular Biology, Toronto General Research Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada.
authors: Allen
authors: A
authors: Volchuk
authors: Division of Metabolism, Endocrinology and Diabetes and the Cellular and Molecular Biology Program, University of Michigan Medical Center, Ann Arbor, Michigan 48105-51714. Electronic address: parvan@umich.edu.
authors: Peter
authors: P
authors: Arvan
mesh_terms: D001483:Base Sequence; D004220:Disulfides / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology*; D011384:Proinsulin / Q000737:chemistry / Q000378:metabolism*; D019704:Protein Disulfide-Isomerases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport
chemical_list: D004220:Disulfides; D011384:Proinsulin; D019704:Protein Disulfide-Isomerases