TGF-beta: from latent to active

The transforming growth factor-betas (TGF-beta s) are synthesized as precur sor proteins that are modified intracellularly prior to secretion. One of c he most relevant intracellular modifications is the cleavage of the C-termi nal pro-region from the N-terminal portion of the protein. The C-terminal p ro-region is referred to as the latency-associated peptide (LAP) while the N-terminal region is called the mature TGF-beta or active TGF-beta. However , with some exceptions the LAP noncovalently associates with the mature TGF -beta prior to secretion. When the mature TGF-beta is associated with the L AP it is called L-TGF-beta and cannot interact with its receptor and has no biological effect. The TGF-beta s and their receptors are very ubiquitousl y expressed, suggesting that the regulation of TGF-beta activity is likely to be complex and multifactorial. However, one of che most important means of controlling the biological effects of TGF-beta 3 is the regulation of co nverting L-TGF-beta to active TGF-beta. The current literature supports two major mechanisms of activation of L-TGF-beta and suggests that the mechani sm of activation of L-TGF-beta may be varied and context-dependent. For TGF -beta to become biologically active the LAP has to be either released from its associations with L-TGF-beta or undergo conformational change such that the LAP is not released from the L-TGF-beta complex but exposes the TGF-be ta receptor binding site. Since TGF-beta has been associated with the patho genesis of numerous diseases, the various mechanisms of activation of L-TGF -beta in context offer the possibility of controlling TGF-beta activity loc alized to the organ of involvement and to a more specific disease process. (C) 1999 Editions scientifiques et medicales Elsevier.