Axil, a member of the Axin family, interacts with both glycogen synthase kinase 3β and β-catenin and inhibits axis formation of Xenopus embryos

Using a past two-hybrid method, we identified a novel protein which interacts with glycogen synthase kinase 3 beta (GSK-3 beta). This protein had 44% amino acid identity with Axin, a negative regulator of the Wnt signaling pathway. We designated this protein Axil for Axin like. Like Axin, Axil ventralized Xenopus embryos and inhibited Xwnt8-induced Xenopus axis duplication. Axil was phosphorylated by GSK-3 beta. Axil bound not only to GSK-3 beta but also to beta-catenin, and the GSK-3 beta-binding site of Axil was distinct from the beta-catenin-binding site. Furthermore, Axil enhanced GSK-3 beta-dependent phosphorylation of beta-catenin. These results indicate that Axil negatively regulates the Wnt signaling pathway by mediating GSK-3 beta-dependent phosphorylation of beta-catenin, thereby inhibiting axis formation.