Current Site Of Practice: Boston University School of Medicine
Focus of Research:
Fellowship Year: 2007 – 2008
Attended: Boston University
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
Co-Authors I. Dominguez, G. E. Sonenshein, and D. C. Seldin
CK2 is a highly conserved tetrameric serine/ threonine kinase present in all eukaryotic organisms. It is constitutively active, and appears to be regulated by level of expression and activity, and subcellular localization. In turn, it has been postulated to control the function of many proteins through changes in phosphorylation that affect protein stability, protein-protein interactions, and subcellular localization. Through these mechanisms, CK2 regulates many fundamental cellular properties. An enzyme that carries out such a master regulatory function is likely to be important in organismic development and in cancer. We have shown that overexpression of CK2 catalytic subunits is capable of promoting tumorigenesis, and that loss of CK2 catalytic subunits in development can be lethal. Through studies in cells, mice, and frogs, we and others have identified the Wnt and NF-kB pathways as two key signal transduction pathways that are regulated by CK2 activity, in embryonic development and in cancer. These results suggest that inhibiting CK2 could be useful in treating cancer, but dangerous to developing organisms.
Cell. Mol. Life Sci. 2009; Jun;66(11-12):1850-7
Co-Authors Vipul C. Chitalia, Rebecca L. Foy, Markus M. Bachschmid, Liling Zeng, Maria V. Panchenko, Mina I. Zhou, Ajit Bharti, David C. Seldin, Stewart H. Lecker, Isabel Dominguez and Herbert T. Cohen
The von Hippel–Lindau protein pVHL suppresses renal tumorigenesis in part by promoting the degradation of hypoxia-inducible HIF-α transcription factors; additional mechanisms have been proposed. pVHL also stabilizes the plant homeodomain protein Jade-1, which is a candidate renal tumour suppressor that may correlate with renal cancer risk. Here we show that Jade-1 binds the oncoprotein &live;-catenin in Wnt-responsive fashion. Moreover, Jade-1 destabilizes wild- type &live;-catenin but not a cancer-causing form of &live;-catenin. Whereas the well-established &live;-catenin E3 ubiquitin ligase component &live;-TrCP ubiquitylates only phosphorylated &live;-catenin, Jade-1 ubiquitylates both phosphorylated and non-phosphorylated &live;-catenin and therefore regulates canonical Wnt signalling in both Wnt-off and Wnt-on phases. Thus, the different characteristics of &live;-TrCP and Jade-1 may ensure optimal Wnt pathway regulation. Furthermore, pVHL downregulates &live;-catenin in a Jade-1-dependent manner and inhibits Wnt signalling, supporting a role for Jade-1 and Wnt signalling in renal tumorigenesis. The pVHL tumour suppressor and the Wnt tumorigenesis pathway are therefore directly linked through Jade-1.
Nat Cell Biol. 2008; 10(10):1208-16