Intracellular Signals Activated by Canonical Wnt Ligands Independent of GSK3 Inhibition and ß-Catenin Stabilization.

ABSTRACT

In contrast to non-canonical ligands, canonical Wnts promote the stabilization of ß-catenin, which is a prerequisite for formation of the TCF4/ß-catenin transcriptional complex and activation of its target genes. This pathway is initiated by binding of Wnt ligands to the Frizzled/LRP5/6 receptor complex, and it increases the half-life of ß-catenin by precluding the phosphorylation of ß-catenin by GSK3 and its binding to the ßTrCP1 ubiquitin ligase. Other intercellular signals are also activated by Wnt ligands that do not inhibit GSK3 and increase ß-catenin protein but that either facilitate ß-catenin transcriptional activity or stimulate other transcriptional factors that cooperate with it. In this review, we describe the layers of complexity of these signals and discuss their crosstalk with ß-catenin in activation of transcriptional targets.