title: Regulation of the follistatin gene by RSPO-LGR4 signaling via activation of the WNT/β-catenin pathway in skeletal myogenesis.
abstract: WNT signaling plays multiple roles in skeletal myogenesis during gestation and postnatal stages. The R-spondin (RSPO) family of secreted proteins and their cognate receptors, members of leucine-rich repeat-containing G protein-coupled receptor (LGR) family, have emerged as new regulatory components of the WNT signaling pathway. We previously showed that RSPO2 promoted myogenic differentiation via activation of WNT/β-catenin signaling in mouse myoblast C2C12 cells in vitro. However, the molecular mechanism by which RSPO2 regulates myogenic differentiation is unknown. Herein, we show that depletion of the LGR4 receptor severely disrupts myogenic differentiation and significantly diminishes the response to RSPO2 in C2C12 cells, showing a requirement of LGR4 in RSPO signaling during myogenic differentiation. We identify the transforming growth factor β (TGF-β) antagonist follistatin (Fst) as a key mediator of RSPO-LGR4 signaling in myogenic differentiation. We further demonstrate that Fst is a direct target of the WNT/β-catenin pathway. Activation and inactivation of β-catenin induced and inhibited Fst expression, respectively, in both C2C12 cells and mouse embryos. Specific TCF/LEF1 binding sites within the promoter and intron 1 region of the Fst gene were required for RSPO2 and WNT/β-catenin-induced Fst expression. This study uncovers a molecular cross talk between WNT/β-catenin and TGF-β signaling pivotal in myogenic differentiation.
authors.affiliation: Program in Stem Cell Biology and Regenerative Medicine, Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine, USA.
authors.forename: Xiang Hua
authors.initials: XH
authors.lastname: Han
authors.forename: Yong-Ri
authors.initials: YR
authors.lastname: Jin
authors.forename: Leonard
authors.initials: L
authors.lastname: Tan
authors.forename: Tatiana
authors.initials: T
authors.lastname: Kosciuk
authors.forename: Jin-Seon
authors.initials: JS
authors.lastname: Lee
authors.forename: Jeong Kyo
authors.initials: JK
authors.lastname: Yoon
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D038681:Follistatin / Q000378:metabolism*; D051379:Mice; D024510:Muscle Development / Q000235:genetics*; D032446:Myoblasts / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D019699:Thrombospondins / Q000235:genetics* / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics* / Q000378:metabolism; D000098907:R-Spondins
chemical_list: D038681:Follistatin; D043562:Receptors, G-Protein-Coupled; D019699:Thrombospondins; D051153:Wnt Proteins; D051176:beta Catenin; C495267:CTNNB1 protein, mouse; C496200:LGR4 protein, mouse; C518904:RSPO2 protein, mouse; D000098907:R-Spondins