Phosphatidylinositol 3'-kinase associates with an insulin receptor substrate-1 serine kinase distinct from its intrinsic serine kinase.
Serine phosphorylation of insulin receptor substrate-1 (IRS-1) has been proposed as a counter-regulatory mechanism in insulin and cytokine signalling. Here we report that IRS-1 is phosphorylated by a wortmannin insensitive phosphatidylinositol 3'-kinase (PI 3-kinase)-associated serine kinase (PAS kinase) distinct from PI 3-kinase serine kinase. We found that PI 3-kinase immune ... complexes contain 5-fold more wortmannin-insensitive serine kinase activity than SH2-containing protein tyrosine phosphatase-2 (SHP2) and IRS-1 immune complexes. Affinity chromatography of cell lysates with a glutathione S-transferase fusion protein for the p85 subunit of PI 3-kinase showed that PAS kinase associated with the p85 subunit of PI 3-kinase. This interaction required unoccupied SH2 domain(s) but did not require the PI 3-kinase p110 subunit binding domain. In terms of function, PAS kinase phosphorylated IRS-1 and, after insulin stimulation, PAS kinase phosphorylated IRS-1 in PI 3-kinase-IRS-1 complexes. Phosphopeptide mapping showed that insulin-dependent in vivo sites of IRS-1 serine phosphorylation were comparable to those of PAS kinase phosphorylated IRS-1. More importantly, PAS kinase-dependent phosphorylation of IRS-1 reduced by 4-fold the ability of IRS-1 to act as an insulin receptor substrate. Taken together, these findings indicate that: (a) PAS kinase is distinct from the intrinsic serine kinase activity of PI 3-kinase, (b) PAS kinase associates with the p85 subunit of PI 3-kinase through SH2 domain interactions, and (c) PAS kinase is an IRS-1 serine kinase that can reduce the ability of IRS-1 to serve as an insulin receptor substrate.
Mesh Terms:
Androstadienes, Humans, Insulin, Insulin Receptor Substrate Proteins, Intracellular Signaling Peptides and Proteins, Phosphatidylinositol 3-Kinases, Phosphoproteins, Phosphorylation, Protein Phosphatase 2, Protein Tyrosine Phosphatase, Non-Receptor Type 11, Protein Tyrosine Phosphatase, Non-Receptor Type 6, Protein Tyrosine Phosphatases, Protein-Serine-Threonine Kinases, Receptor, Insulin, Recombinant Fusion Proteins, SH2 Domain-Containing Protein Tyrosine Phosphatases, Tyrosine, Wortmannin, src Homology Domains
Androstadienes, Humans, Insulin, Insulin Receptor Substrate Proteins, Intracellular Signaling Peptides and Proteins, Phosphatidylinositol 3-Kinases, Phosphoproteins, Phosphorylation, Protein Phosphatase 2, Protein Tyrosine Phosphatase, Non-Receptor Type 11, Protein Tyrosine Phosphatase, Non-Receptor Type 6, Protein Tyrosine Phosphatases, Protein-Serine-Threonine Kinases, Receptor, Insulin, Recombinant Fusion Proteins, SH2 Domain-Containing Protein Tyrosine Phosphatases, Tyrosine, Wortmannin, src Homology Domains
Biochem. J.
Date: Oct. 15, 1998
PubMed ID: 9761740
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