APC-mediated downregulation of beta-catenin activity involves nuclear sequestration and nuclear export

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Published on: June 17, 2014

K L Neufeld1, F Zhang, B R Cullen

  • 1Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City 84112, USA. kristi.neufeld@genetics.utah.edu

EMBO Reports
|March 27, 2001
PubMed

Insights

Nuclear adenomatous polyposis coli (APC) protein controls colon cancer by regulating beta-catenin. Nuclear APC binds beta-catenin, promoting its export and reducing cancer-promoting activity.

Area of Science:

  • Molecular biology
  • Cell biology
  • Cancer research

Background:

  • Adenomatous polyposis coli (APC) mutations initiate most colon carcinomas.
  • APC regulates cytoplasmic beta-catenin, a key Wnt pathway mediator, targeting it for degradation.
  • The function of nuclear APC, especially concerning nuclear beta-catenin, is not fully understood.

Purpose of the Study:

  • To investigate the role of nuclear APC in regulating nuclear beta-catenin levels and activity.
  • To determine how nuclear localization signals (NLSs) and nuclear export signals (NESs) of APC affect beta-catenin.
  • To elucidate the mechanism by which nuclear APC influences beta-catenin-mediated transcription.

Main Methods:

  • Utilizing APC mutants lacking functional NLSs or NESs.
  • Assessing the impact of blocked nuclear export on wild-type APC function.
  • Measuring beta-catenin levels and transcriptional activity.
  • Investigating the interaction between endogenous APC and beta-catenin in the nucleus.

Main Results:

  • APC mutants lacking NLSs or NESs failed to downregulate nuclear beta-catenin.
  • Wild-type APC could not reduce nuclear beta-catenin when its nuclear export was inhibited.
  • APC mutants lacking NLSs could not inhibit beta-catenin transcriptional activation.
  • APC lacking NESs retained the ability to inhibit beta-catenin activity, suggesting nuclear sequestration.

Conclusions:

  • Nuclear APC binding to beta-catenin is crucial for controlling nuclear beta-catenin levels.
  • The nuclear export of beta-catenin, facilitated by APC, is a critical regulatory step.
  • Nuclear APC plays a significant role in suppressing colon carcinogenesis by modulating the Wnt pathway.

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