Thyroid growth factors and oncogenes

Actions of epidermal growth factor and its receptor in the thyroid

Since its discovery by Stanley Cohen (1962), epidermal growth factor (EGF) has been found to influence the growth and function of most mammalian cells. EGF is secreted, after cleavage of a large precursor molecule, as a 53-amino acid polypeptide that exerts its effects through the epidermal growth factor receptor (EGF-R), a single 170-kD transmembrane molecule exhibiting intrinsic tyrosine kinase activity of crucial importance to signal transduction (Hsuan et al 1989). Although generally mitogenic, EGF has a wide range of other effects, which vary considerably among organs, cell types, and species. [For a comprehensive update, see the review by Fisher and Lakshmanan (1990).] This article summarizes the present knowledge of EGF actions on thyroid follicular cells (thyrocytes), discusses the possible role of EGF in physiological and pathological conditions of the thyroid gland, and points out some issues that warrant further studies.