Distinct hydrophobic "patches" in the N- and C-tails of beta-catenin contribute to nuclear transport.

ß-catenin is a key mediator of Wnt signaling and its deregulated nuclear accumulation can drive cancer progression. While the central armadillo (Arm) repeats of ß-catenin stimulate nuclear entry, the N- and C-terminal "tail" sequences are thought to regulate turnover and transactivation. We show here that the N- and C-tails are also potent transport sequences. The unstructured tails of ß-catenin, when individually fused to a GFP-reporter, could enter and exit the nucleus rapidly in live cells. Proximity ligation assays and pull-down assays identified a weak interaction between the tail sequences and the FG-repeats of nucleoporins, consistent with a possible direct translocation of ß-catenin through the nuclear pore complex. Extensive alanine mutagenesis of the tail sequences revealed that nuclear translocation of ß-catenin was dependent on specific uniformly distributed patches of hydrophobic residues, whereas the mutagenesis of acidic amino acids had no effect. Moreover, the mutation of hydrophobic patches within the N-tail and C-tail of full length ß-catenin reduced nuclear transport rate and diminished its ability to activate transcription. We propose that the tail sequences can contribute to ß-catenin transport and suggest a possible similar role for hydrophobic unstructured regions in other proteins.