The multifunctional role of transforming growth factor (TGF)-ßs on mammary epithelial cell biology

The transforming growth factor-βs are potent growth inhibitors of normal and transformed breast epithelial cells in culture. In vivo, these peptides modulate the development of the mouse mammary gland. Tissue-specific overexpression of mature TGF-β1 in transgenic mice results in mammary gland atrophy and prevention of carcinogen-induced breast tumorigenesis. However, the inhibitory effect of endogenous or exogenous TGF-βs on established tumor cells is less clear. Several published circumstantial and more direct data argue that, in some cases, the tumor cell TGF-βs may contribute to the maintenance and/or progression of tumor cells in an intact host by modulating their interaction with host factors. This differential role of the TGF-βs on mammary cells as determined by their normal or transformed phenotype as well as the biological and clinical implications of these data are discussed.