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A GSK3beta phosphorylation site in axin modulates interaction with beta-catenin and Tcf-mediated gene expression

E h Jho1, S Lomvardas, F Costantini

  • 1Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, 701 West 168th Street, New York, New York, 10032, USA.

Biochemical and Biophysical Research Communications
|December 3, 1999
PubMed

Insights

Wnt signaling regulates beta-catenin stability by inhibiting GSK3beta. This study identifies specific Axin phosphorylation sites targeted by GSK3beta, revealing how Axin releases beta-catenin to activate gene expression.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • Wnt signaling controls gene expression via beta-catenin stabilization.
  • Axin acts as a scaffold protein promoting beta-catenin phosphorylation by GSK3beta.
  • The precise mechanism of GSK3beta inhibition by Dishevelled remains unclear.

Purpose of the Study:

  • To investigate the phosphorylation of Axin by GSK3beta.
  • To identify specific GSK3beta phosphorylation sites on Axin.
  • To elucidate the role of Axin phosphorylation in Wnt signaling.

Main Methods:

  • In vitro and in vivo phosphorylation assays.
  • Site-directed mutagenesis of Axin.
  • Lef/Tcf reporter assays to measure Wnt signaling activity.
  • Analysis of Axin-beta-catenin binding.

Main Results:

  • Axin is phosphorylated by GSK3beta at specific Ser/Thr residues (T609, S614) in vitro and in vivo.
  • Mutations at these sites reduce Axin's ability to modulate Wnt signaling.
  • Mutations disrupt the binding between Axin and beta-catenin.
  • These findings suggest Axin phosphorylation by GSK3beta is crucial for beta-catenin regulation.

Conclusions:

  • GSK3beta directly phosphorylates Axin at T609 and S614.
  • This phosphorylation event is critical for Axin's role in the beta-catenin destruction complex.
  • Inhibition of GSK3beta during Wnt signaling likely leads to Axin dephosphorylation and beta-catenin release, promoting target gene expression.

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