THE PRO DOMAIN OF PRE-PRO-TRANSFORMING GROWTH FACTOR-BETA-1 WHEN INDEPENDENTLY EXPRESSED IS A FUNCTIONAL BINDING-PROTEIN FOR THE MATURE GROWTH-FACTOR

Transforming growth factor β1 (TGF-β1) is proteolytically derived from the carboxyl terminus of a 390 amino acid precursor molecule termed pre-pro-TGF-β1. Prevous studies have suggested that the pro piece of pre-pro-TGF-β1 may play an important role in the formation of an inactive, latent complex. These latent forms are thought to be important in the regulation of TGF-β1 activity. To understand this latent complex in more detail, we have expressed the pro domain of pre-pro-TGF-β1 in tissue culture cells independent of the mature growth factor. A stop codon was genetically engineered into the cDNA of pre-pro-TGF-β1 by changing the Arg-278 codon from CGA to the STOP codon TGA. The resulting protein is truncated just prior to the amino-terminal Ala residue of the mature growth factor. Transient expression studies and immunoblotting indicate that this pro piece is readily made and secreted by the COS-1 cells; the major form of the expressed pro piece, when analyzed by SDS-polyacrylamide gel electrophoresis, behaves as a disulfide-linked dimer (Mr 80000). Bioassays, using mink lung indicator cells, reveal that the pro domain forms an inactive complex with exogenously added mature TGF-β1. Treatment of this complex with heat or acid results in the release of active TGF-β1, indicating an in vitro structure similar to natural, latent TGF-β1 complexes. The pro piece from TGF-β1 was also found to form latent structures with two closely related family members, TGF-β1.2 and TGF-β2. Cross-linking studies using radioiodinated TGF-β1 suggest a one to one association between the dimer of the pro domain and mature TGF-β1. © 1990, American Chemical Society. All rights reserved.