In vivo phosphorylation of insulin receptor substrate 1 at serine 789 by a novel serine kinase in insulin-resistant rodents

J Biol Chem. 2002 Jul 19;277(29):26530-9. doi: 10.1074/jbc.M201494200. Epub 2002 May 2.


Insulin resistance is a key pathophysiologic feature of obesity and type 2 diabetes and is associated with other human diseases, including atherosclerosis, hypertension, hyperlipidemia, and polycystic ovarian disease. Yet, the specific cellular defects that cause insulin resistance are not precisely known. Insulin receptor substrate (IRS) proteins are important signaling molecules that mediate insulin action in insulin-sensitive cells. Recently, serine phosphorylation of IRS proteins has been implicated in attenuating insulin signaling and is thought to be a potential mechanism for insulin resistance. However, in vivo increased serine phosphorylation of IRS proteins in insulin-resistant animal models has not been reported before. In the present study, we have confirmed previous findings in both JCR:LA-cp and Zucker fatty rats, two genetically unrelated insulin-resistant rodent models, that an enhanced serine kinase activity in liver is associated with insulin resistance. The enhanced serine kinase specifically phosphorylates the conserved Ser(789) residue in IRS-1, which is in a sequence motif separate from the ones for MAPK, c-Jun N-terminal kinase, glycogen-synthase kinase 3 (GSK-3), Akt, phosphatidylinositol 3'-kinase, or casein kinase. It is similar to the phosphorylation motif for AMP-activated protein kinase, but the serine kinase in the insulin-resistant animals was shown not to be an AMP-activated protein kinase, suggesting a potential novel serine kinase. Using a specific antibody against Ser(P)(789) peptide of IRS-1, we then demonstrated for the first time a striking increase of Ser(789)-phosphorylated IRS-1 in livers of insulin-resistant rodent models, indicating enhanced serine kinase activity in vivo. Taken together, these data strongly suggest that unknown serine kinase activity and Ser(789) phosphorylation of IRS-1 may play an important role in attenuating insulin signaling in insulin-resistant animal models.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Casein Kinases
  • Glycogen Synthase Kinase 3
  • Glycogen Synthase Kinases
  • Humans
  • Insulin Receptor Substrate Proteins
  • Insulin Resistance*
  • JNK Mitogen-Activated Protein Kinases
  • Liver / enzymology
  • Male
  • Mice
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinases / metabolism
  • Molecular Sequence Data
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Protein Kinases / metabolism
  • Protein-Serine-Threonine Kinases / metabolism*
  • Rats
  • Rats, Zucker
  • Sequence Alignment
  • Serine / metabolism*


  • IRS1 protein, human
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, mouse
  • Irs1 protein, rat
  • Phosphoproteins
  • Serine
  • Protein Kinases
  • Phosphatidylinositol 3-Kinases
  • Glycogen Synthase Kinases
  • Casein Kinases
  • Protein-Serine-Threonine Kinases
  • Calcium-Calmodulin-Dependent Protein Kinases
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinases
  • Glycogen Synthase Kinase 3