PDI reductase acts on Akita mutant proinsulin to initiate retrotranslocation along the Hrd1/Sel1L-p97 axis.
In mutant INS gene-induced diabetes of youth (MIDY), characterized by insulin deficiency, MIDY proinsulin mutants misfold and fail to exit the endoplasmic reticulum (ER). Moreover, these mutants bind and block ER exit of wild-type (WT) proinsulin, inhibiting insulin production. The ultimate fate of ER-entrapped MIDY mutants is unclear, but previous studies implicated ER-associated degradation (ERAD), a pathway that retrotranslocates misfolded ER proteins to the cytosol for proteasomal degradation. Here we establish key ERAD machinery components used to triage the Akita proinsulin mutant, including the Hrd1-Sel1L membrane complex, which conducts Akita proinsulin from the ER lumen to the cytosol, and the p97 ATPase, which couples the cytosolic arrival of proinsulin with its proteasomal degradation. Surprisingly, we find that protein disulfide isomerase (PDI), the major protein oxidase of the ER lumen, engages Akita proinsulin in a novel way, reducing proinsulin disulfide bonds and priming the Akita protein for ERAD. Efficient PDI engagement of Akita proinsulin appears linked to the availability of Hrd1, suggesting that retrotranslocation is coordinated on the lumenal side of the ER membrane. We believe that, in principle, this form of diabetes could be alleviated by enhancing the targeting of MIDY mutants for ERAD to restore WT insulin production.
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109.
Kaiyu
K
He
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109 Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI 48109.
Corey Nathaniel
CN
Cunningham
Division of Metabolism Endocrinology and Diabetes, Comprehensive Diabetes Center, University of Michigan Medical School, Ann Arbor, MI 48109.
Nandini
N
Manickam
Division of Metabolism Endocrinology and Diabetes, Comprehensive Diabetes Center, University of Michigan Medical School, Ann Arbor, MI 48109.
Ming
M
Liu
Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI 48109 Division of Metabolism Endocrinology and Diabetes, Comprehensive Diabetes Center, University of Michigan Medical School, Ann Arbor, MI 48109 btsai@umich.edu) parvan@med.umich.edu).
Peter
P
Arvan
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109 Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI 48109 btsai@umich.edu) parvan@med.umich.edu).
Billy
B
Tsai
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1; D004721:Endoplasmic Reticulum / Q000378:metabolism; D060746:Endoplasmic Reticulum-Associated Degradation; D006801:Humans; D007328:Insulin / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D011384:Proinsulin / Q000235:genetics / Q000378:metabolism*; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D017510:Protein Folding; D000069284:Protein Translocation Systems; D011506:Proteins / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D000069284:Protein Translocation Systems; D011506:Proteins; C492169:Sel1h protein, mouse; D011384:Proinsulin; D010088:Oxidoreductases; C498235:Syvn1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D000251:Adenosine Triphosphatases; C404942:p97 ATPase; D019704:Protein Disulfide-Isomerases