RSPO1 is a secreted protein that belongs to the R-spondin (RSPO) family. It regulates Wnt signalling by inhibiting internalization of LRP6 []. It also regulates the canonical Wnt/beta-catenin-dependent pathway and non-canonical Wnt signalling by acting as an inhibitor of ZNRF3, an important regulator of the Wnt signalling pathway []. The R-spondin (RSPO) family is a small group of four secreted proteins (RSPO1-RSPO4) that have pleiotropic functions in development and stem cell growth by strongly enhancing Wnt pathway activation. They contain an N-terminal secretory signal peptide sequence, two tandem furin-like cysteine-rich (Fu-CRD) domains, a thrombospondin type I repeat (TSP) domain, and a C-terminal basic amino acid-rich (BR) domain. Leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4), LGR5, and LGR6 have been identified as receptors for RSPOs [].
