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APC is essential for targeting phosphorylated beta-catenin to the SCFbeta-TrCP ubiquitin ligase

YunYun Su1, Chunjiang Fu, Shinji Ishikawa

  • 1Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15213, USA.

Molecular Cell
|December 9, 2008
PubMed

Insights

Adenomatous polyposis coli (APC) protein protects phosphorylated beta-catenin from dephosphorylation by protein phosphatase 2A (PP2A). This protection is crucial for ubiquitin-dependent degradation of beta-catenin, a key transcription factor.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Ubiquitin-dependent proteolysis regulates beta-catenin levels, a transcription factor suppressed in the absence of Wnt signaling.
  • Formation of an SCF(beta-TrCP) E3 ubiquitin ligase binding site on beta-catenin is critical for its degradation.

Purpose of the Study:

  • To investigate the role of adenomatous polyposis coli (APC) in protecting the SCF(beta-TrCP) binding site on beta-catenin.
  • To elucidate the mechanism by which APC influences beta-catenin ubiquitination and degradation.

Main Methods:

  • Investigated the interaction between phosphorylated beta-catenin, APC, protein phosphatase 2A (PP2A), and the SCF(beta-TrCP) complex.
  • Utilized mutational analysis of APC to assess its effect on beta-catenin phosphorylation and ubiquitination.

Main Results:

  • Wild-type APC protects the phosphorylated beta-catenin SCF(beta-TrCP) binding site from PP2A-mediated dephosphorylation.
  • Mutant APC lacking protective function allows PP2A to dephosphorylate beta-catenin, blocking ubiquitination and degradation.
  • APC ensures beta-catenin ubiquitination by safeguarding its N-terminal phosphorylated residues from dephosphorylation.

Conclusions:

  • APC acts as a crucial protector of the beta-catenin E3 ligase binding site, ensuring its recognition and subsequent degradation.
  • This APC-mediated protection mechanism is vital for maintaining cellular beta-catenin homeostasis and preventing uncontrolled Wnt signaling.

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