Human Transforming Growth Factor- β3: Recombinant Expression, Purification, and Biological Activities in Comparison with Transforming Growth Factors-β 1 and -β2

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Abstract
Recent cDNA characterization has predicted the existence of a new member of the transforming growth factor family, transforming growth factor-β3 (TGFβ3). However, nothing is known about the biological activities of the TGFβ3 protein, since it has not been purified from any natural sources. We report here the recombinant expression in mammalian cells and the purification to apparent homogeneity of human TGFβ3. The TGFβ3 was evaluated in comparison with purified TGFβ1 and TGFβ2 in several assays for its effects on stimulation or inhibition of proliferation of mammalian cells. These analyses revealed that TGFβ3 exerts activities similar to the two other TGFβ species, but that there are distinct differences in potencies between the different TGFβ forms depending on the cell type and assay used. INTRODUCTION Transforming growth factor-β (TGFβ) was first identified as a factor that could stimulate some rodent fibroblast cell lines to grow in soft agar (1, 2). Subsequently, it became clear that TGFβ has a variety of biological activities in many distinct cell systems. While it can induce the proliferation of fibroblasts in monolayer, it is also a potent inhibitor of cell growth for many cell types, a modulator of differentiation, and a stimulator of extracellular matrix production and deposition (3–5). A vast majority of the biological and structural characterization studies have been performed using TGFβ purified from human platelets (6, 7).