title: Regulation of beta-catenin trafficking to the membrane in living cells.
abstract: Beta-catenin is a key mediator of the Wnt signaling process and accumulates in the nucleus and at the membrane in response to Wnt-mediated inhibition of GSK-3beta. In this study we used live cell photobleaching experiments to determine the dynamics and rate of recruitment of beta-catenin at membrane adherens junctions (cell adhesion) and membrane ruffles (cell migration). First, we confirmed the nuclear-cytoplasmic shuttling of GFP-tagged beta-catenin, and found that a small mobile pool of beta-catenin can move from the nucleus to membrane ruffles in NIH 3T3 fibroblasts with a t(0.5) of approximately 30 s. Thus, beta-catenin can shuttle between the nucleus and plasma membrane. The localized recruitment of beta-catenin-GFP to membrane ruffles was more rapid, and the strong recovery observed after bleaching (mobile fraction 53%, t(0.5) approximately 5 s) is indicative of high turnover and transient association. In contrast, beta-catenin-GFP displayed poor recovery at adherens junctions in MDCK epithelial cells (mobile fraction 10%, t(0.5) approximately 8 s), indicating stable retention at these membrane structures. We previously identified IQGAP1 as an upstream regulator of beta-catenin at the membrane, and this is supported by photobleaching assays which now reveal IQGAP1 to be more stably anchored at membrane ruffles than beta-catenin. Further analysis showed that LiCl-mediated inactivation of the kinase GSK-3beta increased beta-catenin membrane ruffle staining; this correlated with a faster rate of recruitment and not increased membrane retention of beta-catenin. In summary, beta-catenin displays a high turnover rate at membrane ruffles consistent with its dynamic internalization and recycling at these sites by macropinocytosis.
authors.affiliation: Westmead Institute for Cancer Research, The University of Sydney, Westmead Millennium Institute at Westmead Hospital, Westmead, NSW 2145, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Johnson
authors.forename: Manisha
authors.initials: M
authors.lastname: Sharma
authors.forename: Cara
authors.initials: C
authors.lastname: Jamieson
authors.forename: Jasmine M
authors.initials: JM
authors.lastname: Henderson
authors.forename: Myth T S
authors.initials: MT
authors.lastname: Mok
authors.forename: Linda
authors.initials: L
authors.lastname: Bendall
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002465:Cell Movement; D036681:Fluorescence Recovery After Photobleaching; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D018021:Lithium Chloride / Q000494:pharmacology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D021381:Protein Transport; D013997:Time Factors; D051176:beta Catenin / Q000378:metabolism*; D020703:ras GTPase-Activating Proteins / Q000378:metabolism
chemical_list: C101203:IQ motif containing GTPase activating protein 1; D051176:beta Catenin; D020703:ras GTPase-Activating Proteins; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride