Figure 9

SFRP mode of action may rely on multiple interactions with Wnt ligands and/or Frizzled receptors. Schematic representation of possible mechanisms by which SFRPs could modulate Wnt/Frizzled signalling. (a) SFRPs can antagonize Wnt activity by directly binding to the ligand through its Netrin-related domain. (b) SFRPs could interact directly with Frizzled receptors through their corresponding CRD motifs and prevent signal transduction. (c) Frizzled, Wnt and SFRP molecules could form heterotrimeric complexes, where SFRP could present the Wnt ligand to the Frizzled receptor thanks to the differential interactions of the CRD and NTR domains. (d) In the absence of Wnt ligands, SFRPs can directly bind a Frizzled receptor and transduce a signal. See the text for further details.