The first armadillo repeat is involved in the recognition and regulation of beta-catenin phosphorylation by protein kinase CK1.
Multiple phosphorylation of beta-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 beta-catenin are phosphorylated by CK1 on Ser-45 with low affinity (K(m) approximately 1 mM), whereas intact beta-catenin is phosphorylated at Ser-45 with very high affinity (K(m) approximately 200 nM). Peptides extended to include a putative CK1 docking motif (FXXXF) at 70-74 positions or a F74AA mutation in full-length beta-catenin had no significant effect on CK1 phosphorylation efficiency. beta-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 beta-catenin targeting by CK1 is supported in that the Y142E mutation, which mimics phosphorylation of Tyr-142 by tyrosine kinases and promotes dissociation of beta-catenin from alpha-catenin, further improves CK1 phosphorylation efficiency, lowering the K(m) value to <50 nM, approximating the physiological concentration of beta-catenin. In contrast, alpha-catenin, which interacts with the N-terminal region of beta-catenin, prevents Ser-45 phosphorylation of CK1 in a dose-dependent 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 beta-catenin association with alpha-catenin and beta-catenin phosphorylation by CK1 at Ser-45 are mutually exclusive.
Bustos
Victor H
VH
Venetian Institute for Molecular Medicine, 35129 Padova, Italy.
Ferrarese
Anna
A
Venerando
Andrea
A
Marin
Oriano
O
Allende
Jorge E
JE
Pinna
Lorenzo A
LA
D020816:Amino Acid Motifs; D000818:Animals; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D017353:Gene Deletion; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D020349:Surface Plasmon Resonance; D015027:Zebrafish; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D051176:beta Catenin; D010768:Phosphoserine; D047389:Casein Kinase I