A highly active subset of β-catenin is specifically expelled from the nucleus by RanBP3, according to Hendriksen et al. on page 785. This active pool is just a tiny fraction of total β-catenin, but should be the focus of future studies on Wnt signaling.
Wnt signals are converted into changes in gene expression by β-catenin, which turns on the TCF/Lef transcription factors. In a search for nuclear β-catenin–interacting proteins, the authors picked up RanBP3 in a pull-down assay. As RanBP3 is a cofactor for CRM1-mediated nuclear export, the logical next step was to look at β-catenin export.
Nuclear levels of total β-catenin were not affected by RanBP3, but the authors found a more specific target. A very small, almost invisible, fraction of β-catenin—the active dephosporylated form—relocated from the nucleus to the cytoplasm upon RanBP3 overexpression. Only by using tumor cell lines with unusually high...
