Insulin-like growth factor-binding protein 7 is a soluble cell adhesion molecule.

Abstract

Insulin-like growth factor-binding protein 7 (IGFBP7) is a secreted protein with diverse roles in angiogenesis, cell differentiation, tissue remodeling, and regulating cell signaling and is linked to numerous human diseases. The molecular basis of the multifunctionality of IGFBP7 remains unclear. Using cryo-electron microscopy, we show that IGFBP7 assembles into a barrel-shaped dodecamer in the presence of heparin. The carboxyl-terminal IgC2 domain forms the central core of the barrel, which is capped by the amino-terminal heparin-binding IB domain at both ends. This homo-oligomer can simultaneously engage heparan sulfate proteoglycans on adjacent cells, functioning as a soluble "cell glue" to drive cell-cell adhesion. Furthermore, IGFBP7 enhances and prolongs signaling of receptor tyrosine kinases, including insulin receptor and c-MET, through its adhesion activity. These findings reveal a structural mechanism for IGFBP7's pleiotropy and establish it as a universal adhesion factor.