title: The R-spondin protein family.
abstract: The four vertebrate R-spondin proteins are secreted agonists of the canonical Wnt/β-catenin signaling pathway. These proteins are approximately 35 kDa, and are characterized by two amino-terminal furin-like repeats, which are necessary and sufficient for Wnt signal potentiation, and a thrombospondin domain situated more towards the carboxyl terminus that can bind matrix glycosaminoglycans and/or proteoglycans. Although R-spondins are unable to initiate Wnt signaling, they can potently enhance responses to low-dose Wnt proteins. In humans, rare disruptions of the gene encoding R-spondin1 cause a syndrome of XX sex reversal (phenotypic male), palmoplantar keratosis (a thickening of the palms and soles caused by excess keratin formation) and predisposition to squamous cell carcinoma of the skin. Mutations in the gene encoding R-spondin4 cause anonychia (absence or hypoplasia of nails on fingers and toes). Recently, leucine-rich repeat-containing G-protein-coupled receptor (Lgr)4, Lgr5 and Lgr6, three closely related orphans of the leucine-rich repeat family of G-protein-coupled receptors, have been identified as receptors for R-spondins. Lgr5 and Lgr6 are markers for adult stem cells. Because R-spondins are potent stimulators of adult stem cell proliferation in vivo and in vitro, these findings might guide the therapeutic use of R-spondins in regenerative medicine.
authors.affiliation: Hubrecht Institute, Developmental Biology and Stem Cell Research, Royal Netherlands Academy of Arts and Sciences, University Medical Center Utrecht, The Netherlands.
authors.forename: Wim B M
authors.initials: WB
authors.lastname: de Lau
authors.forename: Berend
authors.initials: B
authors.lastname: Snel
authors.forename: Hans C
authors.initials: HC
authors.lastname: Clevers
mesh_terms: D058531:46, XX Testicular Disorders of Sex Development / Q000235:genetics; D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000235:genetics; D006801:Humans; D005810:Multigene Family; D009154:Mutation; D009264:Nails, Malformed / Q000151:congenital / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000235:genetics; D012878:Skin Neoplasms / Q000235:genetics; D019699:Thrombospondins / Q000235:genetics*; D051153:Wnt Proteins / Q000235:genetics; D060449:Wnt Signaling Pathway / Q000235:genetics; D051176:beta Catenin / Q000235:genetics; D000098907:R-Spondins
chemical_list: D043562:Receptors, G-Protein-Coupled; D019699:Thrombospondins; D051153:Wnt Proteins; D051176:beta Catenin; C503243:RSPO1 protein, human; D000098907:R-Spondins; C516169:RSPO4 protein, human