Midori Ikezaki, Shiho Minakata, Kazuchika Nishitsuji, Shotaro Tabata, In-Sook Lee Matsui, Maki Takatani, Jiro Usukura, Yukishige Ito, Yoshito Ihara
Biochimie 2020 Apr - MayOxidative folding of proinsulin in the endoplasmic reticulum (ER) is critical for the proper sorting and secretion of insulin from pancreatic β-cells. Here, by using non-cell-based insulin aggregation assays and mouse insulinoma-derived MIN6 cells, we searched for a candidate molecular chaperone for (pro)insulin when its oxidative folding is compromised. We found that interaction between insulin and calreticulin (CRT), a lectin that acts as an ER-resident chaperone, was enhanced by reductive stress in MIN6 cells. Co-incubation of insulin with recombinant CRT prevented reductant-induced aggregation of insulin. Furthermore, lysosomal degradation of proinsulin, which was facilitated by dithiothreitol-induced reductive stress, depended on CRT in MIN6 cells. Together, our results suggest that CRT may be a protective molecule against (pro)insulin aggregation when oxidative folding is defective, e.g. under reductive stress conditions, in vitro and in cultured cells. Because CRT acts as a molecular chaperone for not only glycosylated proteins but also non-glycosylated polypeptides, we also propose that (pro)insulin is a novel candidate client of the chaperone function of CRT. Copyright © 2020 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.
Midori Ikezaki, Shiho Minakata, Kazuchika Nishitsuji, Shotaro Tabata, In-Sook Lee Matsui, Maki Takatani, Jiro Usukura, Yukishige Ito, Yoshito Ihara. Calreticulin protects insulin against reductive stress in vitro and in MIN6 cells. Biochimie. 2020 Apr - May;171-172:1-11
PMID: 32004653
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