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

E Krieghoff, J Behrens, B Mayr - Journal of cell science, 2006 - journals.biologists.com
E Krieghoff, J Behrens, B Mayr
Journal of cell science, 2006journals.biologists.com
β-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 β-catenin activity is thought to occur mainly on the level of protein degradation, but it has
been suggested that β-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 …
β-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 β-catenin activity is thought to occur mainly on the level of protein degradation, but it has been suggested that β-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 β-catenin, its nucleo-cytoplasmic shuttling and its mobility within the nucleus and the cytoplasm. We show that TCF4 and BCL9/Pygopus recruit β-catenin to the nucleus, and APC, axin and axin2 enrich β-catenin in the cytoplasm. Importantly, however, none of these factors accelerates the nucleo-cytoplasmic shuttling of β-catenin, i.e. increases the rate of β-catenin nuclear import or export. Moreover, the cytoplasmic enrichment of β-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 β-catenin in their respective compartment, and concomitantly decrease β-catenin mobility. Together, these data indicate that β-catenin interaction partners mainly regulate β-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.
journals.biologists.com