title: LGR5 interacts and cointernalizes with Wnt receptors to modulate Wnt/β-catenin signaling.
abstract: LGR5, a seven-transmembrane domain receptor of the rhodopsin family, is a Wnt target gene and a bona fide marker of adult stem cells in the gastrointestinal tract and hair follicle bulge. Recently, we and others demonstrated that LGR5 and its homologues function as receptors of the R-spondin family of stem cell factors to potentiate Wnt/β-catenin signaling. However, the mechanism of how LGR5 enhances the signaling output remains unclear. Here we report that following costimulation with the ligands R-spondin1 and Wnt3a, LGR5 interacts and forms a supercomplex with the Wnt coreceptors LRP6 and Fzd5 which is rapidly internalized and then degraded. Internalization of LGR5 is mediated through a dynamin- and clathrin-dependent pathway. Inhibition of this endocytic process has no effect on LGR5 signaling. Deletion of the C-terminal tail of LGR5 maintains its ability to interact with LRP6, yet this LGR5 mutant exhibits increased signaling activity and a decreased rate of endocytosis in response to R-spondin1 compared to the wild-type receptor. This study provides direct evidence that LGR5 becomes part of the Wnt signaling complex at the membrane level to enhance Wnt/β-catenin signaling. However, internalization of LGR5 does not appear to be essential for potentiating the canonical Wnt signaling pathway.
authors.affiliation: Brown Foundation Institute of Molecular Medicine, Texas Therapeutics Institute, University of Texas Health Science Center at Houston, Houston, Texas, USA. Kendra.S.Carmon@uth.tmc.edu
authors.forename: Kendra S
authors.initials: KS
authors.lastname: Carmon
authors.forename: Qiushi
authors.initials: Q
authors.lastname: Lin
authors.forename: Xing
authors.initials: X
authors.lastname: Gong
authors.forename: Anthony
authors.initials: A
authors.lastname: Thomas
authors.forename: Qingyun
authors.initials: Q
authors.lastname: Liu
mesh_terms: D004705:Endocytosis; D051157:Frizzled Receptors / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D009154:Mutation; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D060490:Receptors, Wnt / Q000378:metabolism*; D019699:Thrombospondins / Q000378:metabolism; D060449:Wnt Signaling Pathway; D060509:Wnt3A Protein / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism; D000098907:R-Spondins
chemical_list: D051157:Frizzled Receptors; D043562:Receptors, G-Protein-Coupled; D060490:Receptors, Wnt; D019699:Thrombospondins; D060509:Wnt3A Protein; D051176:beta Catenin; C498589:FZD5 protein, human; C116884:LGR5 protein, human; C503243:RSPO1 protein, human; D000098907:R-Spondins; C555510:WNT3A protein, human