The First Armadillo Repeat Is Involved in the Recognition and Regulation of β-Catenin Phosphorylation by Protein Kinase CK1

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 103; no. 52; pp. 19725 - 19730
• Main Authors: Bustos, Victor H., Ferrarese, Anna, Venerando, Andrea, Marin, Oriano, Allende, Jorge E., Pinna, Lorenzo A.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 26-12-2006; National Acad Sciences
• Subjects: Amino Acid Motifs; Amino acids; Animals; Antibodies; Armadillos; beta Catenin - genetics; beta Catenin - metabolism; Biological Sciences; Casein Kinase I - genetics; Casein Kinase I - metabolism; Circular Dichroism; Gene Deletion; Genetic mutation; Glycogen; Kinetics; Mutation - genetics; Phosphorylation; Phosphoserine - metabolism; Physiological regulation; Protein Binding; Protein isoforms; Proteins; Surface Plasmon Resonance; Zebrafish
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0609424104

Multiple phosphorylation of β-catenin by glycogen synthase kinase 3 (GSK3) in the Wnt pathway is primed by CK1 through phosphorylation of Ser-45, which lacks a typical CK1 canonical sequence. Synthetic peptides encompassing amino acids 38-64 of β-catenin are phosphorylated by CK1 on Ser-45 with low affinity ($K_{m} \approx1 mM$), whereas intact β-catenin is phosphorylated at Ser-45 with very high affinity ($K_{m} \approx200 nM$). Peptides extended to include a putative CK1 docking motif (FXXXF) at 70-74 positions or a F74AA mutation in full-length β-catenin had no significant effect on CK1 phosphorylation efficiency. β-Catenin C-terminal deletion mutants up to residue 181 maintained their high affinity, whereas removal of the 131-181 fragment, corresponding to the first armadillo repeat, was deleterious, resulting in a 50-fold increase in$K_{m}$value. Implication of the first armadillo repeat in β-catenin targeting by CK1 is supported in that the Y142E mutation, which mimics phosphorylation of Tyr-142 by tyrosine kinases and promotes dissociation of β-catenin from a-catenin, further improves CK1 phosphorylation efficiency, lowering the$K_{m}$value to < 50 nM, approximating the physiological concentration of β-catenin. In contrast, α-catenin, which interacts with the N-terminal region of β-catenin, prevents Ser-45 phosphorylation of CK1 in a dosedependent manner. Our data show that the integrity of the N-terminal region and the first armadillo repeat are necessary and sufficient for high-affinity phosphorylation by CK1 of Ser-45. They also suggest that β-catenin association with α-catenin and β-catenin phosphorylation by CK1 at Ser-45 are mutually exclusive.