title: Regulation of β-catenin nuclear dynamics by GSK-3β involves a LEF-1 positive feedback loop.
abstract: Nuclear localization of β-catenin is integral to its role in Wnt signaling and cancer. Cellular stimulation by Wnt or lithium chloride (LiCl) inactivates glycogen synthase kinase-3β (GSK-3β), causing nuclear accumulation of β-catenin and transactivation of genes that transform cells. β-catenin is a shuttling protein; however, the mechanism by which GSK-3β regulates β-catenin nuclear dynamics is poorly understood. Here, fluorescence recovery after photobleaching assays were used to measure the β-catenin-green fluorescent protein dynamics in NIH 3T3 cells before and after GSK-3β inhibition. We show for the first time that LiCl and Wnt3a cause a specific increase in β-catenin nuclear retention in live cells and in fixed cells after detergent extraction. Moreover, LiCl reduced the rate of nuclear export but did not affect import, hence biasing β-catenin transport toward the nucleus. Interestingly, the S45A mutation, which blocks β-catenin phosphorylation by GSK-3β, did not alter nuclear retention or transport, implying that GSK-3β acts through an independent regulator. We compared five nuclear binding partners and identified LEF-1 as the key mediator of Wnt3a and LiCl-induced nuclear retention of β-catenin. Thus, Wnt stimulation triggered a LEF-1 positive feedback loop to enhance the nuclear chromatin-retained pool of β-catenin by 100-300%. These findings shed new light on regulation of β-catenin nuclear dynamics.
authors.affiliation: Westmead Institute for Cancer Research, The University of Sydney, Westmead Millennium Institute at Westmead Hospital, Westmead, New South Wales 2145, Australia.
authors.forename: Cara
authors.initials: C
authors.lastname: Jamieson
authors.forename: Manisha
authors.initials: M
authors.lastname: Sharma
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D051821:Lymphoid Enhancer-Binding Factor 1; D051153:Wnt Proteins; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride