title: Glycogen synthase kinase-3 and Axin function in a beta-catenin-independent pathway that regulates neurite outgrowth in neuroblastoma cells.
abstract: We have sought to determine the roles of beta-catenin and the Wnt signaling pathway in neurite outgrowth using a model cell system, the Neuro-2a neuroblastoma cell line. Activation of the Wnt signaling pathway disrupts a multiprotein complex that includes beta-catenin, Axin, and glycogen synthase kinase-3 (GSK-3), which would otherwise promote the phosphorylation and degradation of beta-catenin. Stabilized beta-catenin accumulates in the cytosol and in the nucleus; in the nucleus it binds to TCF family transcription factors, forming a bipartite transcriptional activator of Wnt target genes. These events can be mimicked by lithium (Li(+)), which inhibits GSK-3 activity. Both Li(+) and the GSK-3 inhibitor SB415286 induced neurite outgrowth of Neuro-2a cells. Li(+)-induced neurite outgrowth did not require beta-catenin-/TCF-dependent transcription, and increasing levels of beta-catenin either by transfection or using Wnt-3A was not sufficient to induce neurite outgrowth. Interestingly, Axin, which is also a substrate for GSK-3, was destabilized by Li(+) and ectopic expression of Axin inhibited Li(+)-induced neurite outgrowth. Deletion analysis of Axin indicated that this inhibition required the GSK-3 binding site, but not the beta-catenin binding site. Our results suggest that a signaling pathway involving Axin and GSK-3, but not beta-catenin, regulates Li(+)-induced neurite outgrowth in Neuro-2a cells.
authors.affiliation: MRC Laboratory for Molecular Cell Biology, University College London, London, UK.
authors.forename: M H
authors.initials: MH
authors.lastname: Orme
authors.forename: A L
authors.initials: AL
authors.lastname: Giannini
authors.forename: M D
authors.initials: MD
authors.lastname: Vivanco
authors.forename: R M
authors.initials: RM
authors.lastname: Kypta
mesh_terms: D000818:Animals; D060466:Axin Protein; D001665:Binding Sites / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017353:Gene Deletion; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D046911:Macromolecular Substances; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes; D016501:Neurites / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009447:Neuroblastoma / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000187:drug effects / Q000502:physiology; D015533:Transcriptional Activation / Q000502:physiology; D014407:Tumor Cells, Cultured; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: D060466:Axin Protein; C495267:CTNNB1 protein, mouse; D017077:Culture Media, Conditioned; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D046912:Multiprotein Complexes; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D008094:Lithium; D038362:Glycogen Synthase Kinase 3