BETAGLYCAN PRESENTS LIGAND TO THE TGF-BETA SIGNALING RECEPTOR

Transforming growth factor beta (TGFbeta) signals through a heteromeric protein kinase receptor that has a limited ability to bind ligand. This limitation is overcome by the action of betaglycan (TGFbeta type III receptor), a separate TGFbeta-binding membrane protein of previously unknown function. Betaglycan presents TGFbeta directly to the kinase subunit of the signaling receptor, forming a high affinity ternary complex. Membrane betaglycan increases TGFbeta binding to the signaling receptor, enhances cell responsiveness to TGFbeta, and eliminates marked biological differences between TGFbeta isoforms. Thus, betaglycan is a direct regulator of TGFbeta access to the signaling receptors.