EGF and TGF- 1 Effects on Thyroid Function

Normal epithelial thyroid cells in culture are inhibited by TGF-1. Instead, transformed thyroid cell lines are frequently resistant to its growth inhibitory effect. Loss of TGF- responsiveness could be due to a reduced expression of TGF- receptors, as shown in transformed rat thyroid cell lines and in human thyroid tumors, or to alterations of other genes controlling TGF- signal transduction pathway. However, in thyroid neoplasia, a complex pattern of alterations occurring during transformation and progression has been identified. Functionally, TGF-1 acts as a tumor suppressor in the early stage of transformation or as a tumor promoter in advanced cancer. This peculiar pleiotropic behaviour of TGF- may result from cross-talk with signalling pathways mediated by other growth factors, among which EGF-like ligands play an important role. This paper reports evidences on TGF-1 and EGF systems in thyroid tumors and on the cross-talk between these growth factors in thyroid cancer.