Pleiotropic insulin signals are engaged by multisite phosphorylation of IRS-1.

Abstract

IRS-1 (insulin receptor substrate 1) is a principal insulin receptor substrate that undergoes tyrosine phosphorylation during insulin stimulation. It contains over 20 potential tyrosine phosphorylation sites, and we suspect that multiple insulin signals are enabled when the activated insulin receptor kinase phosphorylates several of them. Tyrosine-phosphorylated IRS-1 binds specifically to various cellular proteins containing Src homology 2 (SH2) domains (SH2 proteins). We identified some of the tyrosine residues of IRS-1 that undergo insulin-stimulated phosphorylation by the purified insulin receptor and in intact cells during insulin stimulation. Automated sequencing and manual radiosequencing revealed the phosphorylation of tyrosine residues 460, 608, 628, 895, 939, 987, 1172, and 1222; additional sites remain to be identified. Immobilized SH2 domains from the 85-kDa regulatory subunit (p85c) of the phosphatidylinositol 3'-kinase bind preferentially to tryptic phosphopeptides containing Tyr(P)-608 and Tyr(P)-939. By contrast, the SH2 domain in GRB2 and the amino-terminal SH2 domain in SHPTP2 (Syp) specifically bind to Tyr(P)-895 and Tyr(P)-1172, respectively.These results confirm that p85a recognizes YMXM motifs and suggest that GRB2 prefers a phosphorylated YVNI motif, whereas SHPTP2 (Syp) binds to a phosphorylated YIDL motif. These results extend the notion that IRS-1 is a multisite docking protein that engages various downstream regulatory elements during insulin signal transmission.IRS-1 (insulin receptor substrate 1) is a principal insulin receptor substrate that undergoes tyrosine phosphorylation during insulin stimulation. It was originally identified as a 185-kDa phosphoprotein in antiphosphotyrosine antibody (aPY) immunoprecipitates from insulin-stimulated Fao hepatoma cells (42). IRS-1 was subsequently purified and cloned from rat liver and found to be expressed in most cells and tissues (2, 28, 37). Several observations suggest that IRS-1 plays a central role in signal transduction by the insulin receptor. During differentiation of 3T3-L1 fibroblasts into insulin-sensitive adipocytes, IRS-1 expression increases coordinately with that of the insulin receptor and . Overexpression of IRS-1 in Chinese hamster ovary (CHO) cells increases insulin-stimulated mitogenesis (36), and microinjection of recombinant IRS-1 into Xenopus oocytes significantly increases their sensitivity to insulin and IGF-1 (8). Moreover, a myeloid progenitor cell (32D) which contains few insulin receptors and no detectable IRS-1 is completely insensitive to insulin even after expression of the insulin receptor; however, expression of IRS-1 together with the insulin receptor restores a normal insulin mitogenic response (41). Thus, IRS-1 may be an essential element for certain insulin responses.During ligand binding, insulin and other growth factor receptors undergo autophosphorylation on specific tyrosine residues (16). Most evidence suggests that the tyrosine kinase is essential for biological activity. In the case of the epide...

Insulin activates Stat3 independently of p21ras-ERK and PI-3K signal transduction

“…This observation suggests that for receptors with intrinsic tyrosine kinase activity, autophosphorylated tyrosine residues may provide docking-sites that bring STATs to the membrane where they can then be phosphorylated by the receptor kinase itself. The insulin receptor however, is somewhat di erent from the EGFR, as its major substrate IRS-1 tends to provide the phosphotyrosine residues necessary for docking of SH2-containing proteins rather than the autophosphorylated receptor itself (Sun et al, 1991(Sun et al, , 1993Skolnik et al, 1993). The phosphorylation of IRS-1 upon tyrosine residues results in interactions .…”

Signal transduction cascades and hepatitis B and C related hepatocellular carcinoma

“…11,12 Insulin receptor substrate-1 is a Ϸ185 kDa docking protein that transmits growth factorstimulated mitogenic and metabolic signals by interacting with downstream src-homology 2 domain (SH2)-containing molecules through specific tyrosyl phosphorylated motifs located within the C-terminus. 13,14 For example, the 897 YVNI motif of IRS-1 binds to the growth factor receptor-bound protein 2 (Grb2) adapter molecule, the 1180 YIDL motif binds to Syp protein tyrosine phosphatase, and 613 YMPM and 942 YMKM motifs bind to the p85 subunit of phosphatidylinositol-3 kinase (PI3K). 13,[15][16][17][18][19] The Grb2 binds to PY-IRS-1 19,20 leading to sequential activation of p21 ras , mitogen-activated protein kinase kinase (MAPKK), and MAP kinase (MAPK) [20][21][22][23] (see Fig.…”

The Tek/Tie2 receptor signals through a novel Dok-related docking protein, Dok-R

“…For instance, when the insulin receptor is stimulated by insulin, it speci®cally recruits the docking molecule IRS-1 through its PTB domain and subsequently phosphorylates IRS-1 on tyrosine residues (Sun et al, 1993). In addition, the epidermal growth factor (EGF) receptor can use the adapter molecules Shc and Gab1 as substrates when stimulated (Pelicci et al, 1992;Holgado-Madruga et al, 1996).…”