Focus of Research:
Co-Authors Hao Wu, Karen Symes, David C. Seldin, and Isabel Dominguez
CK2 is a regulatory kinase implicated in embryonic development and in cancer. Among the CK2 substrates is live-catenin, a protein with dual function in Wnt signaling and cell adhesion. Previously, we reported that CK2 activity is required for live-catenin stability and we identified threonine (T) 393 as a major CK2 phosphorylation site in live-catenin. However, it is not known whether phosphorylation at T393 increases live-catenin stability and if so, what is the mechanism. In this study we investigate the molecular mechanism of live-catenin stabilization through phosphorylation at T393. We found that pseudophosphorylation of live-catenin at T393 resulted in a stable activated form of live-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 live-catenin to E-cadherin was unaffected. Further analysis showed that pseudophosphorylation at T393 did not prevent live-catenin phosphorylation by GSK3live. Interestingly, we found that in the presence of pseudophophorylated live-catenin and another activated form of live-catenin, the recruitment of GSK3live to Axin is enhanced. These findings indicate that phosphorylation of T393 by CK2 may affect the stability of live-catenin through decreased binding to Axin. In addition, the increased recruitment of GSK3live to the destruction complex in the presence of activated live-catenin mutants could be a feedback mechanism to suppress overactive Wnt signaling.
J. Cell. Biochem. 2009; Sep 1;108(1):52-63