title: Ectopic γ-catenin expression partially mimics the effects of stabilized β-catenin on embryonic stem cell differentiation.
abstract: β-catenin, an adherens junction component and key Wnt pathway effector, regulates numerous developmental processes and supports embryonic stem cell (ESC) pluripotency in specific contexts. The β-catenin homologue γ-catenin (also known as Plakoglobin) is a constituent of desmosomes and adherens junctions and may participate in Wnt signaling in certain situations. Here, we use β-catenin((+/+)) and β-catenin((-/-)) mouse embryonic stem cells (mESCs) to investigate the role of γ-catenin in Wnt signaling and mESC differentiation. Although γ-catenin protein is markedly stabilized upon inhibition or ablation of GSK-3 in wild-type (WT) mESCs, efficient silencing of its expression in these cells does not affect β-catenin/TCF target gene activation after Wnt pathway stimulation. Nonetheless, knocking down γ-catenin expression in WT mESCs appears to promote their exit from pluripotency in short-term differentiation assays. In β-catenin((-/-)) mESCs, GSK-3 inhibition does not detectably alter cytosolic γ-catenin levels and does not activate TCF target genes. Intriguingly, β-catenin/TCF target genes are induced in β-catenin((-/-)) mESCs overexpressing stabilized γ-catenin and the ability of these genes to be activated upon GSK-3 inhibition is partially restored when wild-type γ-catenin is overexpressed in these cells. This suggests that a critical threshold level of total catenin expression must be attained before there is sufficient signaling-competent γ-catenin available to respond to GSK-3 inhibition and to regulate target genes as a consequence. WT mESCs stably overexpressing γ-catenin exhibit robust Wnt pathway activation and display a block in tri-lineage differentiation that largely mimics that observed upon overexpression of β-catenin. However, β-catenin overexpression appears to be more effective than γ-catenin overexpression in sustaining the retention of markers of naïve pluripotency in cells that have been subjected to differentiation-inducing conditions. Collectively, our study reveals a function for γ-catenin in the regulation of mESC differentiation and has implications for human cancers in which γ-catenin is mutated and/or aberrantly expressed.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Sujeivan
authors.initials: S
authors.lastname: Mahendram
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Kelly
authors.forename: Sabrina
authors.initials: S
authors.lastname: Paez-Parent
authors.forename: Sharmeen
authors.initials: S
authors.lastname: Mahmood
authors.forename: Enio
authors.initials: E
authors.lastname: Polena
authors.forename: Austin J
authors.initials: AJ
authors.lastname: Cooney
authors.forename: Bradley W
authors.initials: BW
authors.lastname: Doble
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D002460:Cell Line; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D015870:Gene Expression; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D055550:Protein Stability; D021381:Protein Transport; D051820:TCF Transcription Factors / Q000235:genetics; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000235:genetics* / Q000378:metabolism; D051185:gamma Catenin / Q000235:genetics* / Q000378:metabolism
chemical_list: D051820:TCF Transcription Factors; D051176:beta Catenin; D051185:gamma Catenin; D038362:Glycogen Synthase Kinase 3