Recombinant transforming growth factor type beta 3: biological activities and receptor-binding properties in isolated bone cells.

We have recently cloned the cDNA for transforming growth factor type beta 3 (TGF-beta 3), a new member of the TGF-beta gene family. We examined the biological effects of recombinant TGF-beta 3 protein in osteoblast-enriched bone cell cultures. In this report we demonstrate that TGF-beta 3 is a potent regulator of functions associated with bone formation, i.e., mitogenesis, collagen synthesis, and alkaline phosphatase activity. In a direct comparison between TGF-beta 3 and TGF-beta 1, TGF-beta 3 appeared to be three- to fivefold more potent than TGF-beta 1. Our cross-linking experiments with iodinated TGF-beta showed that in osteoblast-enriched bone cell cultures, both TGF-beta 3 and TGF-beta 1 associated with the same three cell surface binding sites. Scatchard analysis of receptor competition studies indicated the presence of high-affinity binding sites for TGF-beta 3 in the picomolar range. TGF-beta 3 showed an approximately fourfold-higher apparent affinity than TGF-beta 1 in overall binding.