Endoplasmic Reticulum Chaperone Glucose-Regulated Protein 94 Is Essential for Proinsulin Handling

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Seyed Mojtaba Ghiasi, Tina Dahlby, Caroline Hede Andersen, Leena Haataja, Sólrun Petersen, Muhmmad Omar-Hmeadi, Mingyu Yang, Celina Pihl, Sophie Emilie Bresson, Muhammad Saad Khilji, Kristian Klindt, Oana Cheta, Marcelo J Perone, Björn Tyrberg, Clara Prats, Sebastian Barg, Anders Tengholm, Peter Arvan, Thomas Mandrup-Poulsen, Michal Tomasz Marzec

Although endoplasmic reticulum (ER) chaperone binding to mutant proinsulin has been reported, the role of protein chaperones in the handling of wild-type proinsulin is underinvestigated. Here, we have explored the importance of glucose-regulated protein 94 (GRP94), a prominent ER chaperone known to fold insulin-like growth factors, in proinsulin handling within β-cells. We found that GRP94 coimmunoprecipitated with proinsulin and that inhibition of GRP94 function and/or expression reduced glucose-dependent insulin secretion, shortened proinsulin half-life, and lowered intracellular proinsulin and insulin levels. This phenotype was accompanied by post-ER proinsulin misprocessing and higher numbers of enlarged insulin granules that contained amorphic material with reduced immunogold staining for mature insulin. Insulin granule exocytosis was accelerated twofold, but the secreted insulin had diminished bioactivity. Moreover, GRP94 knockdown or knockout in β-cells selectively activated protein kinase R-like endoplasmic reticulum kinase (PERK), without increasing apoptosis levels. Finally, GRP94 mRNA was overexpressed in islets from patients with type 2 diabetes. We conclude that GRP94 is a chaperone crucial for proinsulin handling and insulin secretion.

OriginalsprogEngelsk
TidsskriftDiabetes
Vol/bind68
Udgave nummer4
Sider (fra-til)747-760
Antal sider14
ISSN0012-1797
DOI
StatusUdgivet - apr. 2019

ID: 215325271