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  • Title: The PI3-kinase serine kinase phosphorylates its p85 subunit and IRS-1 in PI3-kinase/IRS-1 complexes.
    Author: Freund GG, Wittig JG, Mooney RA.
    Journal: Biochem Biophys Res Commun; 1995 Jan 05; 206(1):272-8. PubMed ID: 7818531.
    Abstract:
    Insulin receptor tyrosine kinase activity accounts for tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), but the serine kinase(s) responsible for serine phosphorylation of IRS-1 is(are) unknown. In vitro kinase assays performed on PI3-kinase and IRS-1 immunoprecipitates demonstrated insulin-dependent serine phosphorylation of IRS-1. IRS-1 was associated with both insulin-dependent and independent serine kinases. Only the insulin-dependent serine kinase preferred Mn2+ over Mg2+ and was recovered from cell lysates containing dithiothreitol. In complexes of tyrosine phosphorylated recombinant IRS-1 and PI3-kinase, phosphorylation of IRS-1 was associated with decreased phosphorylation of the p85 subunit of PI3-kinase. These results are consistent with PI3-kinase being responsible for insulin-dependent serine phosphorylation of IRS-1 and suggest that this phosphorylation reaction may affect functions of both IRS-1 and the PI3-kinase.
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