Transforming growth factor-beta (TGF-beta) is a multi-functional peptide that regulates growth and differentiation of a wide variety of cell types. The purpose of this project is to determine the role that the endogenously-produced TGF-beta may play in the control of growth of normal and transformed cells, and to study the regulation of TGF-beta action in this context. To this end, polyclonal antisera have been raised against TGF-beta and synthetic peptides corresponding to regions of the putative precursor, and these are being used as tools in the immunochemical characterization of the latent forms of TGF-beta. Extensive analysis of the distribution and modulation of the cellular receptor for TGF-beta has shown that binding of TGF-beta to its receptor is not a major control point in TGF-beta action. However, normal and transformed cells have been shown to secrete TGF-beta in biologically inactive form that is unable to bind to the receptor, and it is anticipated that activation of this latent form will be a critical regulatory step in TGF-beta action. Using immunochemical techniques, the latent form of TGF-beta secreted by human platelets has been shown to be a high molecular weight complex in which mature TGF-beta is noncovalently associated with precursor sequences and a further unidentified component; this probably represents a delivery complex. A second latent form of TGF-beta, found in serum, has been identified as TGF-beta bound to alpha-2macroglobulin; this probably represents a clearance complex. In collaboration with Genentech, Inc., the latent form of TGF-beta made by recombinant constructs has been purified to homogeneity and this material will be used to study the biological activities of latent TGF-beta, the in vivo activation mechanism and the in vivo pharmacokinetics of the latent form. It is anticipated that this will be the clinically useful form of the molecule.
