Insulin stimulation of phosphatidylinositol 3-kinase activity and association with insulin receptor substrate 1 in liver and muscle of the intact rat

F. Folli, M. J.A. Saad, J. M. Backer, C. R. Kahn

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215 Scopus citations


Growth factors stimulate the enzyme phosphatidylinositol (PI) 3-kinase in cells in culture. Insulin rapidly stimulates tyrosine phosphorylation of its endogenous substrate, insulin receptor substrate 1 (IRS-1), and in vitro IRS- 1 associates with PI 3-kinase, thus activating the enzyme. We have examined whether insulin is capable of stimulating the PI 3-kinase pathway in two physiological target tissues for the actions of insulin in vivo, liver and skeletal muscle. After intraportal injection of insulin into anesthetized rats, there was a 2-fold stimulation of total hepatic PI 3-kinase activity in liver and muscle extracts and a 10- to 20-fold increase in PI 3-kinase activity immunoprecipitated with anti-IRS-1 antibodies. Stimulation of PI 3- kinase was accompanied by an association between this enzyme and IRS-1 as detected by immunoprecipitation of liver and muscle extracts with anti-IRS-1 antibodies and Western blotting with antibodies to the 85-kDa subunit of PI 3-kinase. Immunoprecipitation with anti-p85 antibodies and phosphotyrosine immunoblotting revealed no tyrosine phosphorylation of PI 3-kinase, but demonstrated co-precipitation of tyrosine-phosphorylated IRS-1, as well as another phosphotyrosine protein of ~135-140 kDa. Thus, IRS-1 phosphorylation plays a significant role in the activation of PI 3-kinase in vivo by insulin.

Original languageEnglish (US)
Pages (from-to)22171-22177
Number of pages7
JournalJournal of Biological Chemistry
Issue number31
Publication statusPublished - Jan 1 1992
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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