beta-catenin mediates Wnt signaling by acting as the essential co-activator for TCF transcription factors. Wnt signaling increases the half-life and therefore the absolute level of beta-catenin in responding cells. The current model states that these changes in beta-catenin stability set the threshold for Wnt signaling. However, we find that pharmacological inhibition of proteasome activity by ALLN leads to accumulation of cytosolic beta-catenin but not to increased TCF-mediated transcription. In addition, in temperature-sensitive ubiquitylation mutant CHO cells inhibition of ubiquitylation increases beta-catenin levels, but does not induce transcriptional activation of TCF reporter genes. Using an antibody specific for beta-catenin dephosphorylated at residues Ser37 and Thr41, we show that Wnt signals specifically increase the levels of dephosphorylated beta-catenin, whereas ALLN does not. We conclude that changes in the phosphorylation status of the N-terminus of beta-catenin that occur upon Wnt signaling independently affect the signaling properties and half-life of beta-catenin. Hence, Wnt signals are transduced via N-terminally dephosphorylated beta-catenin.

*Signal Transduction, *Zebrafish Proteins, Animals, CHO Cells, Calpain/antagonists & inhibitors, Cricetinae, Cytoskeletal Proteins/*physiology, DNA-Binding Proteins/physiology, Leupeptins/pharmacology, Lymphoid Enhancer-Binding Factor 1, Phosphorylation, Proto-Oncogene Proteins/*physiology, Research Support, Non-U.S. Gov't, Trans-Activators/*physiology, Transcription Factors/physiology, Transcription, Genetic/physiology, Wnt Proteins, beta Catenin,
E M B O Reports
Epub 2001 Dec 19
Erasmus MC: University Medical Center Rotterdam

Staal, F.J.T, van Noort, M, Strous, G.J.A.M, & Clevers, H.C. (2002). Wnt signals are transmitted through N-terminally dephosphorylated beta-catenin. E M B O Reports, 3(1), 63–68. doi:10.1093/embo-reports/kvf002