title: R-Spondin potentiates Wnt/β-catenin signaling through orphan receptors LGR4 and LGR5.
abstract: The Wnt/β-catenin signaling pathbway controls many important biological processes. R-Spondin (RSPO) proteins are a family of secreted molecules that strongly potentiate Wnt/β-catenin signaling, however, the molecular mechanism of RSPO action is not yet fully understood. We performed an unbiased siRNA screen to identify molecules specifically required for RSPO, but not Wnt, induced β-catenin signaling. From this screen, we identified LGR4, then an orphan G protein-coupled receptor (GPCR), as the cognate receptor of RSPO. Depletion of LGR4 completely abolished RSPO-induced β-catenin signaling. The loss of LGR4 could be compensated by overexpression of LGR5, suggesting that LGR4 and LGR5 are functional homologs. We further demonstrated that RSPO binds to the extracellular domain of LGR4 and LGR5, and that overexpression of LGR4 strongly sensitizes cells to RSPO-activated β-catenin signaling. Supporting the physiological significance of RSPO-LGR4 interaction, Lgr4-/- crypt cultures failed to grow in RSPO-containing intestinal crypt culture medium. No coupling between LGR4 and heterotrimeric G proteins could be detected in RSPO-treated cells, suggesting that LGR4 mediates RSPO signaling through a novel mechanism. Identification of LGR4 and its relative LGR5, an adult stem cell marker, as the receptors of RSPO will facilitate the further characterization of these receptor/ligand pairs in regenerative medicine applications.
authors: Developmental and Molecular Pathways, Novartis Institutes for Biomedical Research, Novartis Pharma AG, Postfach, Basel, Switzerland. heinz.ruffner@novartis.com
authors: Heinz
authors: H
authors: Ruffner
authors: Joëlle
authors: J
authors: Sprunger
authors: Olga
authors: O
authors: Charlat
authors: Juliet
authors: J
authors: Leighton-Davies
authors: Bianka
authors: B
authors: Grosshans
authors: Adrian
authors: A
authors: Salathe
authors: Svenja
authors: S
authors: Zietzling
authors: Valérie
authors: V
authors: Beck
authors: Maxime
authors: M
authors: Therier
authors: Andrea
authors: A
authors: Isken
authors: Yang
authors: Y
authors: Xie
authors: Yue
authors: Y
authors: Zhang
authors: Huaixiang
authors: H
authors: Hao
authors: Xiaoying
authors: X
authors: Shi
authors: Dong
authors: D
authors: Liu
authors: Qinhui
authors: Q
authors: Song
authors: Ieuan
authors: I
authors: Clay
authors: Gabriele
authors: G
authors: Hintzen
authors: Jan
authors: J
authors: Tchorz
authors: Laure C
authors: LC
authors: Bouchez
authors: Gregory
authors: G
authors: Michaud
authors: Peter
authors: P
authors: Finan
authors: Vic E
authors: VE
authors: Myer
authors: Tewis
authors: T
authors: Bouwmeester
authors: Jeff
authors: J
authors: Porter
authors: Marc
authors: M
authors: Hild
authors: Fred
authors: F
authors: Bassilana
authors: Christian N
authors: CN
authors: Parker
authors: Feng
authors: F
authors: Cong
mesh_terms: D018076:DNA, Complementary / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008024:Ligands; D008954:Models, Biological; D016366:Open Reading Frames; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology; D019699:Thrombospondins / Q000502:physiology*; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*; D000098907:R-Spondins
chemical_list: D018076:DNA, Complementary; D019204:GTP-Binding Proteins; D008024:Ligands; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; D019699:Thrombospondins; D051153:Wnt Proteins; D051176:beta Catenin; C411562:LGR4 protein, human; C116884:LGR5 protein, human; C503243:RSPO1 protein, human; D000098907:R-Spondins