Fig. 5. SFRP interactions with molecules unrelated to Wnt signalling. (A) SFRP2 binds to the fibronectin (FN)–integrin-
5β1 complex, promoting cell adhesion and inhibiting apoptosis. (B) Sizzled binds to and inhibits the activity of BMP1/Tolloid metalloproteinases that cleave chordin, a BMP signalling antagonist. Thus, Sizzled favours chordin stabilisation, which in turn inactivates BMP signalling. (C) SFRP1 interacts with RANKL, preventing it from binding to RANK, and thus inhibits osteoclast formation.