Nucleo-cytoplasmic distribution of beta-catenin is regulated by retention

J Cell Sci. 2006 Apr 1;119(Pt 7):1453-63. doi: 10.1242/jcs.02864.

Abstract

beta-catenin is the central signalling molecule of the canonical Wnt pathway, where it activates target genes in a complex with LEF/TCF transcription factors in the nucleus. The regulation of beta-catenin activity is thought to occur mainly on the level of protein degradation, but it has been suggested that beta-catenin nuclear localization and hence its transcriptional activity may additionally be regulated via nuclear import by TCF4 and BCL9 and via nuclear export by APC and axin. Using live-cell microscopy and fluorescence recovery after photobleaching (FRAP), we have directly analysed the impact of these factors on the subcellular localization of beta-catenin, its nucleo-cytoplasmic shuttling and its mobility within the nucleus and the cytoplasm. We show that TCF4 and BCL9/Pygopus recruit beta-catenin to the nucleus, and APC, axin and axin2 enrich beta-catenin in the cytoplasm. Importantly, however, none of these factors accelerates the nucleo-cytoplasmic shuttling of beta-catenin, i.e. increases the rate of beta-catenin nuclear import or export. Moreover, the cytoplasmic enrichment of beta-catenin by APC and axin is not abolished by inhibition of CRM-1-dependent nuclear export. TCF4, APC, axin and axin2 move more slowly than beta-catenin in their respective compartment, and concomitantly decrease beta-catenin mobility. Together, these data indicate that beta-catenin interaction partners mainly regulate beta-catenin subcellular localization by retaining it in the compartment in which they are localized, rather than by active transport into or out of the nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenomatous Polyposis Coli Protein / metabolism
  • Axin Protein
  • Blotting, Western
  • Cell Line
  • Cell Nucleus / metabolism*
  • Cytoplasm / metabolism*
  • Cytoskeletal Proteins / metabolism
  • Fluorescence Recovery After Photobleaching
  • Fluorescent Antibody Technique
  • Genes, Reporter
  • Humans
  • Luciferases / metabolism
  • Microscopy, Video
  • Neoplasm Proteins / metabolism
  • Repressor Proteins / metabolism
  • TCF Transcription Factors / metabolism
  • Transcription Factor 7-Like 2 Protein
  • Transcription Factors
  • Two-Hybrid System Techniques
  • beta Catenin / metabolism*

Substances

  • AXIN2 protein, human
  • Adenomatous Polyposis Coli Protein
  • Axin Protein
  • BCL9 protein, human
  • Cytoskeletal Proteins
  • Neoplasm Proteins
  • Repressor Proteins
  • TCF Transcription Factors
  • TCF7L2 protein, human
  • Transcription Factor 7-Like 2 Protein
  • Transcription Factors
  • beta Catenin
  • Luciferases