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IRS-2 mediates the antiapoptotic effect of insulin in neonatal hepatocytes

Angela M Valverde1, Isabel Fabregat, Deborah J Burks

  • 1Instituto de Bioquímica/Departamento de Bioquímica y Biología Molecular II, Centro Mixto CSIC/UCM, Facultad de Farmacia, Universidad Complutense, Madrid, Spain. valverde@farm.ucm.es

Hepatology (Baltimore, Md.)
|November 27, 2004
PubMed

Insights

Insulin receptor substrate-2 (IRS-2) is crucial for insulin's liver cell survival signals. Its absence triggers apoptosis, which insulin cannot prevent, highlighting IRS-2's essential role in insulin's protective effects.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Endocrinology

Background:

  • Insulin resistance is linked to impaired insulin signaling in hepatocytes.
  • Insulin receptor substrate-2 (IRS-2) plays a key role in insulin signal transduction.
  • The role of IRS-2 in hepatocyte survival signaling requires further elucidation.

Purpose of the Study:

  • To investigate the role of IRS-2 in mediating insulin's anti-apoptotic effects in hepatocytes.
  • To determine the downstream signaling pathways involved in IRS-2-dependent hepatocyte survival.

Main Methods:

  • Generated immortalized hepatocyte cell lines from IRS-2(-/-) and wild-type mice.
  • Induced apoptosis via serum withdrawal and assessed caspase activation and DNA fragmentation.
  • Utilized adenoviral vectors to express constitutively active or dominant-negative Foxo1, and to reintroduce IRS-2.
  • Measured protein phosphorylation (e.g., Bad), protein localization (e.g., Foxo1), and gene expression (e.g., Bcl-xL, Bim).

Main Results:

  • Hepatocytes lacking IRS-2 exhibited accelerated apoptosis upon serum withdrawal, characterized by earlier caspase-3 activation and DNA laddering.
  • Insulin protected wild-type hepatocytes from apoptosis but failed to rescue IRS-2(-/-) hepatocytes.
  • In IRS-2(-/-) cells, insulin did not phosphorylate Bad or promote Foxo1 nuclear export.
  • Reconstitution of IRS-2 in IRS-2(-/-) hepatocytes restored insulin's ability to promote survival signaling and inhibit apoptosis.
  • Epidermal growth factor (EGF) could rescue IRS-2(-/-) hepatocytes, indicating a parallel survival pathway.

Conclusions:

  • IRS-2 signaling is essential for mediating insulin's survival effects in hepatocytes, specifically through phosphatidylinositol 3-kinase (PI 3-kinase)/Akt/Foxo1 pathway activation.
  • The absence of IRS-2 renders hepatocytes susceptible to apoptosis, a process insulin cannot counteract.
  • IRS-2 is critical for regulating the expression of pro- and anti-apoptotic genes, thereby controlling cell fate.

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