Action of insulin receptor substrate-3 (IRS-3) and IRS-4 to stimulate translocation of GLUT4 in rat adipose cells

Mol Endocrinol. 1999 Mar;13(3):505-14. doi: 10.1210/mend.13.3.0242.

Abstract

The insulin receptor initiates insulin action by phosphorylating multiple intracellular substrates. Previously, we have demonstrated that insulin receptor substrates (IRS)-1 and -2 can mediate insulin's action to promote translocation of GLUT4 glucose transporters to the cell surface in rat adipose cells. Although IRS-1, -2, and -4 are similar in overall structure, IRS-3 is approximately 50% shorter and differs with respect to sites of tyrosine phosphorylation. Nevertheless, as demonstrated in this study, both IRS-3 and IRS-4 can also stimulate translocation of GLUT4. Rat adipose cells were cotransfected with expression vectors for hemagglutinin (HA) epitope-tagged GLUT4 (GLUT4-HA) and human IRS-1, murine IRS-3, or human IRS-4. Overexpression of IRS-1 led to a 2-fold increase in cell surface GLUT4-HA in cells incubated in the absence of insulin; overexpression of either IRS-3 or IRS-4 elicited a larger increase in cell surface GLUT4-HA. Indeed, the effect of IRS-3 in the absence of insulin was approximately 40% greater than the effect of a maximally stimulating concentration of insulin in cells not overexpressing IRS proteins. Because phosphatidylinositol (PI) 3-kinase is essential for insulin-stimulated translocation of GLUT4, we also studied a mutant IRS-3 molecule (IRS-3-F4) in which Phe was substituted for Tyr in all four YXXM motifs (the phosphorylation sites predicted to bind to and activate PI 3-kinase). Interestingly, overexpression of IRS-3-F4 did not promote translocation of GLUT4-HA, but actually inhibited the ability of insulin to stimulate translocation of GLUT4-HA to the cell surface. Our data suggest that IRS-3 and IRS-4 are capable of mediating PI 3-kinase-dependent metabolic actions of insulin in adipose cells, and that IRS proteins play a physiological role in mediating translocation of GLUT4.

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Adipocytes / metabolism*
  • Animals
  • Biological Transport
  • Glucose Transporter Type 4
  • Humans
  • Insulin / metabolism
  • Insulin / pharmacology
  • Insulin Receptor Substrate Proteins
  • Male
  • Monosaccharide Transport Proteins / metabolism*
  • Muscle Proteins*
  • Mutation
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoproteins / drug effects
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Phosphotyrosine / metabolism
  • Rats
  • Receptor, Insulin / drug effects
  • Receptor, Insulin / genetics
  • Receptor, Insulin / metabolism
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Repetitive Sequences, Amino Acid
  • Transfection

Substances

  • Adaptor Proteins, Signal Transducing
  • Glucose Transporter Type 4
  • IRS3P protein, human
  • IRS4 protein, human
  • IRS4 protein, rat
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Irs3 protein, rat
  • Irs4 protein, mouse
  • Monosaccharide Transport Proteins
  • Muscle Proteins
  • Phosphoproteins
  • Recombinant Proteins
  • SLC2A4 protein, human
  • Slc2a4 protein, rat
  • Phosphotyrosine
  • Phosphatidylinositol 3-Kinases
  • Receptor, Insulin