Fig. 6
From: Complex and pleiotropic signaling pathways regulated by the secreted protein augurin
Augurin is an inhibitor of the canonical Wnt/ β-catenin signaling pathway. In the absence of WNT ligand, β-catenin is retained in a complex with axin, APC, CK1α and GSK-3β (destruction complex). Phosphorylation by CK1α and GSK-3β prepares β-catenin to undergo proteasomal degradation (left panel). Upon Wnt binding to Frizzled (Fzd) and LRP5/6, the destruction complex function is disrupted. The suppression of GSK-3β activity leads to β-catenin accumulation into the cytoplasm and translocation to the nucleus, where it interacts with the TCF/LEF transcription factors to activate the transcription of their target genes (right panel). Augurin specifically represses the canonical Wnt/β-catenin signaling pathway, however through which receptor it exerts its action and the precise mechanisms of Wnt signaling repression remain to be unveiled [37]