Purification and Initial Characterization of a Type β Transforming Growth Factor from Human Placenta

A polypeptide transforming growth factor (TGF) that induces anchorage-dependent rat kidney fibroblasts to grow in soft agar has been isolated from human placenta and purified to homogeneity. This polypeptide is classified as a type β TGF because it does not compete with epidermal growth factor (EGF) for membrane receptor sites but does require EGF for induction of anchorage-independent growth of indicator cells. Purification of this peptide was achieved by acid/ethanol extraction of the placenta, followed by gel filtration, cation exchange, and HPLC of the acid-soluble proteins. Homogeneity of the TGF-β from the final column was shown by its constant specific activity and amino acid composition across the peak of soft agar colony-forming activity and by its migration as a single band at Mr23,000-25,000 on NaDodSO4/polyacrylamide gel electrophoresis. Under reducing conditions, the protein migrated on a gel as a single band at Mr13,000. The purified placental TGF-β caused half-maximal growth stimulation of indicator cells in soft agar at 64-72 pg/ml (3 pM) in the presence of EGF at 2 ng/ml (0.34 nM).