Transforming growth factor beta (TGF beta) is now known to have a number of effects other than inducing phenotypic transformation of fibroblastic cells: TGF beta controls proliferation, differentiation, and other functions in many cell types. In this paper we have analyzed the action of TGF beta 1 on a system of differentiated epithelial rat thyroid cells in culture (FRTL5), which depend on the addition of thyrotropin for their growth. TGF beta 1 is able to inhibit the growth of thyroid cells

more »

... reducing cell response to thyrotropin. Moreover, in analogy to the effect produced upon other differentiated cells in culture, such as myoblasts and adipocytes, TGF beta 1 modulates the expression of FRTL5-specific thyroid markers, reducing thyroglobulin biosynthesis and the ability to concentrate the iodide.