CHARACTERIZATION OF TRANSFORMING GROWTH-FACTOR-BETA GROWTH-REGULATORYEFFECTS AND RECEPTORS ON BOVINE MAMMARY CELLS

Transforming growth factor-beta (TGF-beta) has been shown to inhibit m ammary morphogenesis, growth, and differentiation in murine studies. W e have characterized TGF-beta receptors and their autoregulation, and the growth response to TGF-beta 1 and TGF-beta 2 in cultured bovine ma mmary epithelium (MAC-T) and fibroblasts. Affinity labelling studies r evealed that fibroblast and epithelial cells contained type I, II, and III (betaglycan) receptors, with the type III receptor being the pred ominant binding component. On both fibroblasts and epithelial cells, T GF-beta 1 and TGF-beta 2 had equal binding affinities for the type I a nd II receptors, but TGF-beta 2 had a higher affinity for the type III receptor. Also, preincubation of MACT cells with 50 pM TGF-beta 1 or TGF-beta 2 markedly downregulated TGF-beta receptors. Proliferative re sponse was measured using both total DNA and H-3-thymidine incorporati on. Both TGF-beta isoforms were effective in inhibiting proliferation of MAC-T cells and fibroblasts. Inhibition of proliferation was not al tered following immortalization of fibroblasts with SV-40 Large-T-anti gen (LT), even when the cells acquired a transformed phenotype. Inhibi tion of proliferation was not a result of cytotoxicity, as TGF-beta at concentrations 1,000-fold higher than ED(50) levels did not increase cell death. Moreover, the inhibition was reversible as shown by return of cellular proliferation to control levels following TGF-beta remova l. Although growth inhibition was not transient as culture of MAC-T ce lls in TGF-beta resulted in sustained inhibition of proliferation for at least 144 h. (C) 1995 Wiley-Liss, Inc.