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Insulin stimulates phosphorylation of the forkhead transcription factor FKHR on serine 253 through a

J Nakae1, B C Park, D Accili

  • 1Developmental Endocrinology Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.

The Journal of Biological Chemistry
|May 29, 1999
PubMed

Insights

Mutations in the Daf-2 gene cause developmental arrest in C. elegans, but Daf-16 gene mutations counteract this effect. FKHR phosphorylation by insulin suggests it is a key player in insulin signaling pathways.

Area of Science:

  • Molecular Biology
  • Genetics
  • Cell Signaling

Background:

  • Mutations in the insulin/insulin-like growth factor-1 receptor homologue Daf-2 gene in C. elegans lead to developmental arrest.
  • The Daf-16 gene, encoding a forkhead transcription factor, counteracts Daf-2 mutations, indicating its role in Daf-2 signaling.
  • FKHR genes are mammalian homologues of Daf-16, and FKHR proteins have potential phosphorylation sites for Akt kinase.

Purpose of the Study:

  • To investigate whether insulin affects the phosphorylation of FKHR.
  • To determine if PI 3-kinase activity and specific Akt phosphorylation sites are involved in insulin-mediated FKHR phosphorylation.

Main Methods:

  • Studied endogenous FKHR and recombinant c-Myc/FKHR fusion protein phosphorylation in murine hepatocytes.
  • Utilized wortmannin treatment to assess the role of PI 3-kinase.
  • Mutated specific Akt phosphorylation sites (Serine 253, Threonine 24, Serine 316) on FKHR to evaluate their impact on insulin-induced phosphorylation.

Main Results:

  • Insulin stimulated the phosphorylation of both endogenous and recombinant FKHR.
  • Insulin-induced FKHR phosphorylation was inhibited by wortmannin, indicating PI 3-kinase dependence.
  • Mutation of Serine 253 abolished insulin-induced FKHR phosphorylation, while mutations at Threonine 24 and Serine 316 did not.

Conclusions:

  • FKHR phosphorylation is regulated by insulin in a PI 3-kinase-dependent manner.
  • Serine 253 is a critical site for insulin-induced FKHR phosphorylation.
  • FKHR may function as a downstream effector in insulin signaling pathways.

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