Axil, a Member of the Axin Family, Interacts with Both Glycogen Synthase Kinase 3β and β-Catenin and Inhibits Axis Formation ofXenopus Embryos

ABSTRACT

Using a yeast two-hybrid method, we identified a novel protein which interacts with glycogen synthase kinase 3β (GSK-3β). 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-3β. Axil bound not only to GSK-3β but also to β-catenin, and the GSK-3β-binding site of Axil was distinct from the β-catenin-binding site. Furthermore, Axil enhanced GSK-3β-dependent phosphorylation of β-catenin. These results indicate that Axil negatively regulates the Wnt signaling pathway by mediating GSK-3β-dependent phosphorylation of β-catenin, thereby inhibiting axis formation.

ACKNOWLEDGMENTS

We are grateful to Y. Takai, K. Tanaka, A. Nagafuchi, S. Tsukita, S. Nagata, J. R. Woodgett, Y. Hata, F. Tamanoi, C. W. Turck, Q. Hu, and M. Nakata for donating plasmids, cDNA libraries, GSK peptide 1, and antibodies. We thank the Research Center for Molecular Medicine, Hiroshima University School of Medicine, for the use of their facilities.

This work was supported by a grant-in-aid for scientific research (B) from the Ministry of Education, Science, and Culture, Japan (1996, 1997), and by grants from the Yamanouchi Foundation for Research on Metabolic Disorders (1996, 1997), the Fukuyama Transporting Shibuya Longevity and Health Foundation (1996), the Tsuchiya Foundation (1996), and the Kato Memorial Bioscience Foundation (1997).