Insulin stimulation of phosphatidylinositol 3-kinase activity and association with insulin receptor substrate 1 in liver and muscle of the intact rat.
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 approximately 135-140 kDa. Thus, IRS-1 phosphorylation plays a significant role in the activation of PI 3-kinase in vivo by insulin.
Folli
F
F
Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Boston, MA.
Saad
M J
MJ
Backer
J M
JM
Kahn
C R
CR
D000818:Animals; D015153:Blotting, Western; D004789:Enzyme Activation; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D019869:Phosphatidylinositol 3-Kinases; D010770:Phosphotransferases / Q000378:metabolism*; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D007328:Insulin; D019000:Phosphotyrosine; D014443:Tyrosine; D010770:Phosphotransferases; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin