Insulin/IGF-1 and TNF-α stimulate phosphorylation of IRS-1 at inhibitory Ser307 via distinct pathways
Liangyou Rui, … , Andrea Dunaif, Morris F. White
Liangyou Rui, … , Andrea Dunaif, Morris F. White
Published January 15, 2001
Citation Information: J Clin Invest. 2001;107(2):181-189. https://doi.org/10.1172/JCI10934.
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Article

Insulin/IGF-1 and TNF-α stimulate phosphorylation of IRS-1 at inhibitory Ser307 via distinct pathways

Abstract

Serine/threonine phosphorylation of IRS-1 might inhibit insulin signaling, but the relevant phosphorylation sites are difficult to identify in cultured cells and to validate in isolated tissues. Recently, we discovered that recombinant NH2-terminal Jun kinase phosphorylates IRS-1 at Ser307, which inhibits insulin-stimulated tyrosine phosphorylation of IRS-1. To monitor phosphorylation of Ser307 in various cell and tissue backgrounds, we prepared a phosphospecific polyclonal antibody designated αpSer307. This antibody revealed that TNF-α, IGF-1, or insulin stimulated phosphorylation of IRS-1 at Ser307 in 3T3-L1 preadipocytes and adipocytes. Insulin injected into mice or rats also stimulated phosphorylation of Ser307 on IRS-1 immunoprecipitated from muscle; moreover, Ser307 was phosphorylated in human muscle during the hyperinsulinemic euglycemic clamp. Experiments in 3T3-L1 preadipocytes and adipocytes revealed that insulin-stimulated phosphorylation of Ser307 was inhibited by LY294002 or wortmannin, whereas TNF-α–stimulated phosphorylation was inhibited by PD98059. Thus, distinct kinase pathways might converge at Ser307 to mediate feedback or heterologous inhibition of IRS-1 signaling to counterregulate the insulin response.

Authors

Liangyou Rui, Vincent Aguirre, Jason K. Kim, Gerald I. Shulman, Anna Lee, Anne Corbould, Andrea Dunaif, Morris F. White

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Figure 9

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Models for the function of Ser307 phosphorylation. Upon insulin stimulat...
Models for the function of Ser307 phosphorylation. Upon insulin stimulation, IRS-1 is tyrosyl-phosphorylated by the IR, resulting in the activation of PI 3-kinase that mediates Ser307 phosphorylation. Ser307 phosphorylation subsequently inhibits the ability of IRS-1 to be further tyrosyl phosphorylated by the IR and to propagate insulin signaling. An increase in Ser307 phosphorylation, such as that possibly trigged by TNF-α in chronic obesity, also induces insulin resistance. As β cells compensate for insulin insensitivity with compensatory hyperinsulinemia, chronic insulin stimulation induces more Ser307 phosphorylation through the PI 3-kinase pathway, thus further increasing the pool of inactive, Ser307 phosphorylated IRS-1. This vicious cycle might continue until hyperinsulinemia fails to compensate for insulin resistance.