The transforming growth factor-β-inducibie matrix protein βig-h3 interacts with fibronectin

Proper growth and development require the orderly synthesis and deposition of individual components of the extracellular matrix (ECM) into well ordered networks. Once formed, the ECM maintains tissue structure and houses resident cells. One ECM component, betaig-h3, is a highly conserved transforming growth factor-beta-inducible protein that has been hypothesized to function as a bifunctional linker between individual matrix components and resident cells. To gain insights into its physiological function, full-length betaig-h3 protein was produced using a baculovirus expression system and purified under native conditions. Human fibroblasts attached and spread on betaig-h3-coated plates and developed actin stress fibers. Purified betaig-h3 binds fibronectin (FN) and type I collagen (Col I) but does not bind gelatin. Using defined fragments of FN, we localized the betaig-h3 recognition region to the gelatin/collagen binding domain present in the N-terminal region of the FN molecule. Our results identify FN and Col I as two ligands of betaig-h3 in the ECM.