Figure 1
The Wnt signaling pathway. Wnt ligands bind to the frizzled receptor (Fzd) and activate the cytoplasmic protein dishevelled
(Dvl) to inhibit the activity of glycogen synthase kinase-3β (GSK3β) or GSK3B. Gsk3β phosphorylates cytoplasmic β-catenin, targeting it for degradation at the proteosome. Inhibition of GSK3β activity therefore
stabilizes the cytoplasmic pool of β-catenin, some of which then translocates to the nucleus to interact with members of the
T-cell factor (TCF) family of transcription factors, leading to changes in the transcription of Wnt target genes. A variety
of growth factors (GF), such as insulin, insulin-like growth factor 1, and epidermal growth factor, bind to specific receptors
(GFR) and activate phosphatidylinositol 3-kinases (PI3K), which can interact with the Wnt signaling pathway at the level of
GSK3β. However, it is unclear whether the same subcellular pool of GSK3β can be targetted by both PI3K and Wnt. The schematic
also shows pharmacological agents that influence developmental processes through actions at specific stages of the Wnt signaling
pathway (see main text for details).