title: Nuclear GSK-3beta inhibits the canonical Wnt signalling pathway in a beta-catenin phosphorylation-independent manner.
abstract: Beta-catenin is the central signalling molecule of the canonical Wnt pathway, where it activates target genes in a complex with lymphoid enhancer factor/T-cell factor transcription factors in the nucleus. The regulation of beta-catenin activity is thought to occur via a cytoplasmatic multiprotein complex that includes the serine/threonine kinase glycogen synthase kinase-3beta (GSK-3beta) that phosphorylates beta-catenin, marking it for degradation by the proteasome. Here, we provide evidence showing that GSK-3beta has a nuclear function in downregulating the activity of beta-catenin. Using colorectal cell lines that express a mutant form of beta-catenin, which cannot be phosphorylated by GSK-3beta and ectopically expressed mutant beta-catenin protein, we show that nuclear GSK-3beta functions in a mechanism that does not involve beta-catenin phosphorylation to reduce the levels of Wnt signalling. We show that GSK-3beta enters the nucleus, forms a complex with beta-catenin and lowers the levels of beta-catenin/TCF-dependent transcription in a mechanism that involves GSK-3beta-Axin binding.
authors.affiliation: Department of Anatomy and Anthropology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: M
authors.initials: M
authors.lastname: Caspi
authors.forename: A
authors.initials: A
authors.lastname: Zilberberg
authors.forename: H
authors.initials: H
authors.lastname: Eldar-Finkelman
authors.forename: R
authors.initials: R
authors.lastname: Rosin-Arbesfeld
mesh_terms: D015820:Cadherins / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D015179:Colorectal Neoplasms / Q000473:pathology*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction; D014158:Transcription, Genetic; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D015820:Cadherins; D051153:Wnt Proteins; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D046988:Proteasome Endopeptidase Complex