Fine-tuning of nuclear-catenin by Chibby and 14-3-3.

Chibby (Cby) is an evolutionarily conserved antagonist of beta-catenin, a central player of the canonical Wnt signaling pathway, which acts as a transcriptional coactivator. Cby physically interacts with the C-terminal activation domain of beta-catenin and blocks its transcriptional activation potential through competition with DNA-binding Tcf/Lef transcription factors. Our recent study revealed a second mechanism for Cby-mediated beta-catenin inhibition in which Cby cooperates with 14-3-3 adaptor proteins to facilitate nuclear export of beta-catenin, following phosphorylation of Cby by Akt kinase. Therefore, our findings unravel a novel molecular mechanism regulating the dynamic nucleo-cytoplasmic trafficking of beta-catenin and provide new insights into the cross-talk between the Wnt and Akt signaling pathways. Here, we review recent literature concerning Cby function and discuss our current understanding of the relationship between Wnt and Akt signaling.