WITHDRAWN: The hydrophobic rich N- and C-terminal tails of beta-catenin facilitate nuclear import of beta-catenin.

Abstract beta-catenin is a key mediator of Wnt signaling and when deregulated, its nuclear accumulation can cause cancer. While the armadillo repeats in the centre of beta-catenin stimulate nuclear entry, the N- and C-terminal "tail" sequences are currently thought to regulate turnover and transactivation. We show here that the beta-catenin N- and C-tails are also potent nuclear transport sequences. The unstructured tails of beta-catenin, when individually fused to a GFP-reporter, were found to enter and exit the nucleus rapidly in live cells. Biochemical assays with purified components demonstrate a direct interaction between each of the tail sequences with the FG-repeats of nucleoporins Nup-62, 98, 153 and 358. Consistent with direct translocation through the nuclear pore complex, overexpression of the N-tail sequence competed with importin-beta translocation suggesting a shared transport route. Extensive alanine mutagenesis of the tail sequences revealed that nuclear translocation of beta-catenin was dependent on specific hydrophobic residues, whereas mutation of acidic amino acids had no effect. Moreover, the mutation of hydrophobic sequences within the N-tail and C-tail of full length beta-catenin significantly reduced nuclear transport rate and diminished its ability to activate transcription. The importance of beta-catenin-Nup interactions was further validated by disrupting such complexes through overexpression of Nup FG-repeat peptides in SW480 colon cancer cells, leading to reduced nuclear import and increased cytoplasmic turnover of beta-catenin. We now propose that the tail and armadillo sequences each contribute to beta-catenin transport, and our findings have broad implications for how hydrophobic unstructured regions can facilitate nuclear transport of proteins.