Leucine-973 is a crucial residue differentiating insulin and IGF-1 receptor signaling
Hirofumi Nagao, … , Matthias Mann, C. Ronald Kahn
Hirofumi Nagao, … , Matthias Mann, C. Ronald Kahn
Published December 22, 2022
Citation Information: J Clin Invest. 2023;133(4):e161472. https://doi.org/10.1172/JCI161472.
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Research Article Endocrinology Metabolism

Leucine-973 is a crucial residue differentiating insulin and IGF-1 receptor signaling

Abstract

Insulin and IGF-1 receptors (IR and IGF1R) are highly homologous and share similar signaling systems, but each has a unique physiological role, with IR primarily regulating metabolic homeostasis and IGF1R regulating mitogenic control and growth. Here, we show that replacement of a single amino acid at position 973, just distal to the NPEY motif in the intracellular juxtamembrane region, from leucine, which is highly conserved in IRs, to phenylalanine, the highly conserved homologous residue in IGF1Rs, resulted in decreased IRS-1/PI3K/Akt/mTORC1 signaling and increased Shc/Gab1/MAPK cell cycle signaling. As a result, cells expressing L973F-IR exhibited decreased insulin-induced glucose uptake, increased cell growth, and impaired receptor internalization. Mice with knockin of the L973F-IR showed similar alterations in signaling in vivo, and this led to decreased insulin sensitivity, a modest increase in growth, and decreased weight gain when mice were challenged with a high-fat diet. Thus, leucine-973 in the juxtamembrane region of the IR acts as a crucial residue differentiating IR signaling from IGF1R signaling.

Authors

Hirofumi Nagao, Weikang Cai, Bruna B. Brandão, Nicolai J. Wewer Albrechtsen, Martin Steger, Arijeet K. Gattu, Hui Pan, Jonathan M. Dreyfuss, F. Thomas Wunderlich, Matthias Mann, C. Ronald Kahn

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Figure 7

Effects of L973F substitution on IR signaling in fasting/refed mice and primary cells.

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Effects of L973F substitution on IR signaling in fasting/refed mice and ...
(A) Immunoblot analysis of insulin signaling in gastrocnemius muscle of WT and L973F-IR mice (6-month-old males) starved overnight (15 hours) and then refed for 2 hours, followed by sacrifice and tissue harvest. (B) Quantification of p-IRS1Y608, p-AktS473, p-Foxo1T24, p-PRAS40T246, and p-ShcY239/240. The level of each phosphorylated protein in WT fasting mice was set at 1. Data are represented as mean ± SEM. *P < 0.05; ***P < 0.001, fasting, not refed (F) versus refed (RF). ##P < 0.01; ###P < 0.001, WT versus L973F-IR mice, 2-way ANOVA. (C) Immunoblot analysis of insulin signaling in primary hepatocytes from WT and L973F-IR mice stimulated with 0, 1, 10, or 100 nM insulin for 15 minutes. (D) Densitometric analysis of phosphorylated proteins following insulin stimulation. The level of each phosphorylated protein in cells from WT mice stimulated with 100 nM insulin was set at 1. Data are represented as mean ± SEM (n = 3). *P < 0.05; **P < 0.01; ***P < 0.001, WT-IR versus L973F-IR, 2-way ANOVA.