Prodomains of Transforming Growth Factor β (TGFβ) Superfamily Members Specify Different Functions EXTRACELLULAR MATRIX INTERACTIONS AND GROWTH FACTOR BIOAVAILABILITY

The specific functions of the prodomains of TGF beta superfamily members are largely unknown. Interactions are known between prodomains of TGF beta-1-3 and latent TGF beta-binding proteins and between prodomains of BMP-2, -4, -7, and -10 and GDF-5 and fibrillins, raising the possibility that latent TGF beta-binding proteins and fibrillins may mediate interactions with all other prodomains of this superfamily. This possibility is tested in this study. Results show that the prodomain of BMP-5 interacts with the N-terminal regions of fibrillin-1 and -2 in a site similar to the binding sites for other bone morphogenetic proteins. However, in contrast, the prodomain of GDF-8 (myostatin) interacts with the glycosaminoglycan side chains of perlecan. The binding site for the GDF-8 prodomain is likely the heparan sulfate chain present on perlecan domain V. These results support and extend the emerging concept that TGF beta superfamily prodomains target their growth factor dimers to extracellular matrix macromolecules. In addition, biochemical studies of prodomain.growth factor complexes were performed to identify inactive complexes. For some members of the superfamily, the prodomain is noncovalently associated with its growth factor dimer in an inactive complex; for others, the prodomain.growth factor complex is active, even though the prodomain is noncovalently associated with its growth factor dimer. Results show that the BMP-10 prodomain, in contrast to BMP-4, -5, and -7 prodomains, can inhibit the bioactivity of the BMP-10 growth factor and suggest that the BMP-10 complex is like TGF beta and GDF-8 complexes, which can be activated by cleavage of the associated prodomain.