O-Linked N-Acetylglucosamine Modification of Insulin Receptor Substrate-1 Occurs in Close Proximity to Multiple SH2 Domain Binding Motifs

Abstract

Insulin receptor substrate-1 (IRS-1)1 is a highly phosphorylated adaptor protein critical to insulin and IGF-1 receptor signaling. Many of the metabolic and mitogenic effects elicited by insulin and IGF-1 are mediated and modulated by posttranslational modifications of IRS-1, and tight regulation at the posttranslational level is crucial for maintaining insulin sensitivity and controlling growth factor-induced proliferation. Following hormonal stimulation, IRS-1 is phosphorylated by the receptor tyrosine kinases creating SH2 domain docking sites for downstream binding partners including the p85 regulatory subunits of phosphatidylinositol 3-kinase, Grb2, and the tyrosine phosphatase SHP2 (PTPN11) (1). Binding of p85 phosphatidylinositol 3-kinase and Grb2 activate the PI3K/Akt and Ras-MAPK pathways, respectively, whereas binding of SHP2 results in tyrosine dephosphorylation and signal attenuation (2). Positive and negative feedback regulation by Ser/ Thr kinases, such as Akt (3), c-Jun N-terminal kinase (JNK) (4), S6K (5), and ERK (6), impact the interactions of IRS-1 with SH2 domain proteins and the receptor thereby affecting the duration and outcome of the signal. IRS-1 has been described as a central node for the integration of information regarding the nutrient and stress status of the cell (7). This information is encoded by site-specific phosphorylation by a number of kinases that regulate the specificity of effects that are elicited following receptor stimulation. Many sites of Ser/Thr phosphorylation have been identified on IRS-1, and cross-talk among Tyr and Ser/Thr phosphorylations at specific residues is evidence of dynamic and complex posttranslational regulation (8, 9). Inappropriate phosphorylation of IRS-1 resulting in the disruption of interactions of IRS-1 with binding partners From the

Changes in glucose tolerance and leptin responsiveness of rats offered a choice of lard, sucrose, and chow

“…Normally only ϳ3% of glucose enters the hexosamine biosynthetic pathway (HBP), but this can increase when glucose load increases. Increased activity of the HBP in transgenic mice (14) or aging rats (17) results in insulin resistance because multiple insulin signaling proteins are subject to O-linked glycosylation (6,32,33). Leptin and insulin have some signaling proteins in common (43,66), and it is possible that consumption of sucrose solution leads to O-linked glycosylation of proteins and transcription factors that are critical for effective leptin signaling.…”

Regulation of Insulin Receptor Substrate 1 (IRS-1)/AKT Kinase-mediated Insulin Signaling by O-Linked β-N-Acetylglucosamine in 3T3-L1 Adipocytes

“…A growing number of publications are beginning to elucidate the role that O-GlcNAc plays in the cellular function of Type II diabetes (13,22,24,(53)(54)(55)(56)(57)(58) …”

The intersections betweenO-GlcNAcylation and phosphorylation: implications for multiple signaling pathways

“…The interaction between OGT and PtdIns(3,4,5)P 3 does not increase the basal activity of OGT (Yang et al, 2008); however, upon translocation to the plasma membrane, OGT associates with the insulin receptor (IR) and becomes tyrosine phosphorylated, which in turn increases OGT activity (Whelan et al, 2008). This redistribution and activation of OGT allows for the dynamic modification by O-GlcNAcylation of downstream targets in the pathway, including IR-b, insulin receptor substrate 1 (IRS-1) (Ball et al, 2006;Klein et al, 2009), Akt and OGT itself (Vosseller et al, 2002;Whelan et al, 2008;Yang et al, 2008). The sites of OGT modification in the rat IRS-1 protein are serine 914, serine 1009, serine 1036 and serine 1041, whereas human IRS-1 is modified at serine 984/985, serine 1011 and within residues 1025-1045.…”

“…The sites of OGT modification in the rat IRS-1 protein are serine 914, serine 1009, serine 1036 and serine 1041, whereas human IRS-1 is modified at serine 984/985, serine 1011 and within residues 1025-1045. In both species, these residues are all located in the C-terminus, which is rich in docking sites for Src-homology 2 (SH2)-domain-containing proteins (Ball et al, 2006;Klein et al, 2009). In livers of mice that are overexpressing OGT, the addition of O-GlcNAc to IRS-1 directly correlates with an increase in IRS-1 phosphorylation at serine 307 and serines 632/635, which are sites known to attenuate the insulin signaling cascade (Yang et al, 2008).…”