Insulin receptor substrate-4 signaling in quiescent rat hepatocytes and in regenerating rat liver

Hepatology. 2003 Jun;37(6):1461-9. doi: 10.1053/jhep.2003.50245.

Abstract

This study was designed to characterize insulin receptor substrate-4 (IRS-4) in isolated rat hepatocytes and to examine its role in liver regeneration. Subcellular fractionation revealed that 85% of IRS-4 is located at isolated hepatocyte plasma membranes. The distribution of IRS-4 among intracellular compartments remained unchanged in insulin-stimulated cells. Two bands corresponding to 145 and 138 kd were observed in immunoblotting experiments. Immunoprecipitation of hepatocyte lysates with a highly specific antibody against IRS-4 led to an insulin and insulin-like growth factor 1 (IGF-1)-dependent increase in phosphotyrosine residues of the 145-kd band. IRS-4 was found to be associated with Src homology 2 (SH2) domain-containing proteins (phosphatidylinositol 3-kinase [PI 3-kinase] and Src homology phosphatase [SHP-2]) and with protein kinase C zeta (PKC zeta). Insulin and IGF-1 elicited a rapid and dose-dependent binding of these 3 proteins to IRS-4. These data suggest that IRS-4 is insulin-/IGF-1-activated by phosphorylation and not by translocation, inducing the recruitment of SH2 domain-containing proteins and PKC zeta to the membrane. To evaluate the possible role of IRS-4 in liver regeneration, we also examined this system after partial hepatectomy (PH). One day after PH, IRS-1 expression increased, consistent with a stimulatory role in the regenerative process, whereas it decreased 7 days after liver resection. This drastic IRS-1 depletion occurred at the expense of increased IRS-2 and IRS-4 expression 7 days after PH. In addition, at this period of time after surgery, the in vivo insulin stimulation of remnant rat livers showed an increase in IRS-4/PI 3-kinase association. Given that 1 and 7 days after PH isolated hepatocytes responded similarly to insulin in terms of induced cell proliferation, a compensatory role is proposed for IRS-2/4 induction. In conclusion, IRS-4 is activated by insulin and IGF-1-like IRS-1 in rat hepatocytes, and the induced expression of IRS-4 is a compensatory mechanism that plays a role in conditions of liver regeneration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Division / drug effects
  • Hepatocytes / cytology
  • Hepatocytes / metabolism*
  • Insulin / pharmacology
  • Insulin Receptor Substrate Proteins
  • Insulin-Like Growth Factor I / pharmacology
  • Intracellular Signaling Peptides and Proteins
  • Liver Regeneration / physiology*
  • Male
  • Phosphoproteins / metabolism*
  • Phosphorylation / drug effects
  • Precipitin Tests
  • Rats
  • Rats, Wistar
  • Receptor, Insulin / metabolism
  • Signal Transduction*
  • Subcellular Fractions / metabolism
  • Tissue Distribution

Substances

  • IRS4 protein, rat
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Intracellular Signaling Peptides and Proteins
  • Irs1 protein, rat
  • Irs2 protein, rat
  • Phosphoproteins
  • Insulin-Like Growth Factor I
  • Receptor, Insulin