Purification and characterization of transforming growth factor-beta 2.3 and -beta 1.2 heterodimers from bovine bone

A unique form of transforming growth factor-beta (TGF-beta), TGF-beta 2.3 heterodimer, has been purified from bovine bone extract. TGF-beta 2.3 migrated as a single 25-kDa band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas under reducing conditions it migrated as a 12.5 kDa band. The TGF-beta 2.3 reacted positively with anti-TGF-beta 2 and anti-TGF-beta 3 antibodies on immunoblots. Equal levels of TGF-beta 2 and TGF-beta 3 sequences were detected by N-terminal sequencing. TGF-beta 2.3 eluted as a single sharp peak by reverse-phase high performance liquid chromatography. However, prior reduction of the protein with dithiothreitol resulted in the protein eluting in two peaks, one containing predominantly TGF-beta 3 and the other containing predominantly TGF-beta 2. TGF-beta 2.3 inhibited proliferation of mink lung epithelial cells and promoted the formation of colonies of normal rat kidney fibroblasts in culture with specific biological activity similar to those of TGF-beta 1 and TGF-beta 2. These results demonstrate that the protein is TGF-beta 2.3 heterodimer, consisting of one polypeptide chain each of TGF-beta 2 and TGF-beta 3 linked by one or more disulfide bonds. In addition, TGF-beta 1.2 heterodimer, previously found only in porcine platelets, has also been purified from bovine bone extract.