Chibby cooperates with 14-3-3 to regulate beta-catenin subcellular distribution and signaling activity

beta-Catenin functions in both cell-cell adhesion and as a transcriptional coactivator in the canonical Wnt pathway. Nuclear accumulation of beta-catenin is the hallmark of active Wnt signaling and is frequently observed in human cancers. Although beta-catenin shuttles in and out of the nucleus, the molecular mechanisms underlying its translocation remain poorly understood. Chibby (Cby) is an evolutionarily conserved molecule that inhibits beta-catenin-mediated transcriptional activation. Here, we identified 14-3-3epsilon and 14-3-3zeta as Cby-binding partners using affinity purification/mass spectrometry. 14-3-3 proteins specifically recognize serine 20 within the 14-3-3-binding motif of Cby when phosphorylated by Akt kinase. Notably, 14-3-3 binding results in sequestration of Cby into the cytoplasm. Moreover, Cby and 14-3-3 form a stable tripartite complex with beta-catenin, causing beta-catenin to partition into the cytoplasm. Our results therefore suggest a novel paradigm through which Cby acts in concert with 14-3-3 proteins to facilitate nuclear export of beta-catenin, thereby antagonizing beta-catenin signaling.