Wnt / β-Catenin Signaling Pathway
Pathway Description:The conserved Wnt/β-Catenin pathway regulates stem cell pluripotency and cell fate decisions during development. This developmental cascade integrates signals from other pathways, including retinoic acid, FGF, TGF-β, and BMP, within different cell types and tissues. The Wnt ligand is a secreted glycoprotein that binds to Frizzled receptors, which triggers displacement of the multifunctional kinase GSK-3β from a regulatory APC/ Axin/GSK-3β-complex. In the absence of Wnt-signal (Off-state), β-catenin, an integral E-cadherin cell-cell adhesion adaptor protein and transcriptional co-regulator, is targeted by coordinated phosphorylation by CK1 and the APC/Axin/GSK-3β-complex leading to its ubiquitination and proteasomal degradation through the β-TrCP/SKP pathway. In the presence of Wnt ligand (On-state), the co-receptor LRP5/6 is brought in complex with Wnt-bound Frizzled. This leads to activation of Dishevelled (Dvl) by sequential phosphorylation, poly-ubiquitination, and polymerization, which displaces GSK-3β from APC/Axin through an unclear mechanism that may involve substrate trapping and/ or endosome sequestration. The transcriptional effects of Wnt ligand is mediated via Rac1-dependent nuclear translocation of β-catenin and the subsequent recruitment of LEF/ TCF DNA-binding factors as co-activators for transcription, acting partly by displacing Groucho-HDAC co-repressors. Additionally, β-catenin has also been shown to cooperate with the homeodomain factor Prop1 in context-dependent activation as well as repression complexes. Importantly, researchers have found β-catenin point mutations in human tumors that prevent GSK-3β phosphorylation and thus lead to its aberrant accumulation. E-cadherin, APC, and Axin mutations have also been documented in tumor samples, underscoring the deregulation of this pathway in cancer. Furthermore, GSK-3β is involved in glycogen metabolism and other signaling pathways, which has made its inhibition relevant to diabetes and neurodegenerative disorders.
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We would like to thank Dr. Hans Widlund, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, for contributing to this diagram.
created January 2003
revised December 2012