Threonine 393 of beta-catenin regulates interaction with Axin.
CK2 is a regulatory kinase implicated in embryonic development and in cancer. Among the CK2 substrates is beta-catenin, a protein with dual function in Wnt signaling and cell adhesion. Previously, we reported that CK2 activity is required for beta-catenin stability and we identified threonine (T) 393 as a major CK2 phosphorylation site in beta-catenin. However, it is not known whether phosphorylation at T393 increases beta-catenin stability and if so, what is the mechanism. In this study we investigate the molecular mechanism of beta-catenin stabilization through phosphorylation at T393. We found that pseudophosphorylation of beta-catenin at T393 resulted in a stable activated form of beta-catenin with decreased affinity for Axin in vitro. This phosphomimetic mutant also displayed decreased regulation by Axin in vivo in a bioassay in Xenopus laevis embryos. In contrast, the binding of T393 pseudophosphorylated beta-catenin to E-cadherin was unaffected. Further analysis showed that pseudophosphorylation at T393 did not prevent beta-catenin phosphorylation by GSK3beta. Interestingly, we found that in the presence of pseudophophorylated beta-catenin and another activated form of beta-catenin, the recruitment of GSK3beta to Axin is enhanced. These findings indicate that phosphorylation of T393 by CK2 may affect the stability of beta-catenin through decreased binding to Axin. In addition, the increased recruitment of GSK3beta to the destruction complex in the presence of activated beta-catenin mutants could be a feedback mechanism to suppress overactive Wnt signaling.
Wu
Hao
H
Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Symes
Karen
K
Seldin
David C
DC
Dominguez
Isabel
I
D000818:Animals; D060466:Axin Protein; D001665:Binding Sites; D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004625:Embryo, Nonmammalian / Q000378:metabolism; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction; D013912:Threonine / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D014981:Xenopus / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics* / Q000378:metabolism*
D060466:Axin Protein; D015820:Cadherins; D012097:Repressor Proteins; D029867:Xenopus Proteins; C555454:axin1 protein, Xenopus; D051176:beta Catenin; D013912:Threonine