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Foxo1 mediates insulin-like growth factor 1 (IGF1)/insulin regulation of osteocalcin expression by antagonizing Runx2

Shengyong Yang1, Haiyan Xu, Shibing Yu

  • 1Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15240, USA.

The Journal of Biological Chemistry
|April 8, 2011
PubMed

Insights

Forkhead transcription factor Foxo1 negatively regulates osteocalcin gene expression by inhibiting Runx2 activity in osteoblasts. Insulin-like growth factor 1 (IGF1) and insulin signaling counteract this inhibition, promoting osteoblast function.

Area of Science:

  • Molecular biology
  • Cell biology
  • Endocrinology

Background:

  • Osteocalcin is a key protein in bone metabolism.
  • Insulin-like growth factor 1 (IGF1) and insulin signaling pathways are crucial for osteoblast function.
  • Forkhead transcription factor Foxo1 is a downstream mediator of IGF1/insulin signaling.

Purpose of the Study:

  • To elucidate the molecular mechanisms by which Foxo1 regulates Runx2 activity and osteocalcin gene expression in osteoblasts.
  • To investigate the role of IGF1/insulin signaling in modulating Foxo1's regulation of osteocalcin.

Main Methods:

  • Co-immunoprecipitation assays to assess protein-protein interactions.
  • Electrophoretic mobility shift assays (EMSA) to evaluate DNA-binding activity.
  • Chromatin immunoprecipitation (ChIP) assays to determine in vivo promoter interactions.
  • Gene expression analysis of osteocalcin (Bglap2) mRNA levels.

Main Results:

  • Foxo1 directly interacts with Runx2 and inhibits Runx2-dependent osteocalcin gene transcription and promoter activity.
  • IGF1 and insulin promote Foxo1 phosphorylation and nuclear exclusion, thereby relieving its inhibitory effect on Runx2.
  • IGF1 enhances Runx2 binding to the osteocalcin promoter via PI3K/AKT signaling, while Foxo1 knockdown increases this interaction.

Conclusions:

  • Foxo1 acts as a novel negative regulator of the osteoblast transcription factor Runx2.
  • Foxo1 mediates the inhibitory effects of IGF1/insulin signaling on osteocalcin expression in osteoblasts.

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