RESUMO
Smad proteins are the key effectors of the transforming growth factor ß (TGFß) signaling pathway in mammalian cells. Smad4 plays an important role in human physiology, and its mutations were found with high frequency in wide range of human cancer. In this study, we have functionally characterized Smad4 C324Y mutation, isolated from a nodal metastasis of papillary thyroid carcinoma. We demonstrated that the stable expression of Smad4 C324Y in FRTL-5 cells caused a significant activation of TGFß signaling, responsible for the acquisition of transformed phenotype and invasive behavior. The coexpression of Smad4 C324Y with Smad4 wild-type determined an increase of homo-oligomerization of Smad4 with receptor-regulated Smads and a lengthening of nuclear localization. FRTL-5 clones overexpressing Smad4 C324Y showed a strong reduction of response to antiproliferative action of TGFß1, acquired the ability to grow in anchorage-independent conditions, showed a fibroblast-like appearance and a strong reduction of the level of E-cadherin, one crucial event of the epithelial-mesenchymal transition process. The acquisition of a mesenchymal phenotype gave the characteristics of increased cellular motility and a significant reduction in adhesion to substrates such as fibronectin and laminin. Overall, our results demonstrate that the Smad4 C324Y mutation plays an important role in thyroid carcinogenesis and can be considered as a new prognostic and therapeutic target for thyroid cancer.
Assuntos
Carcinoma/genética , Proteína Smad4/genética , Neoplasias da Glândula Tireoide/genética , Fator de Crescimento Transformador beta1/metabolismo , Carcinoma/metabolismo , Carcinoma/patologia , Carcinoma Papilar , Adesão Celular , Linhagem Celular Tumoral , Movimento Celular , Proliferação de Células , Progressão da Doença , Humanos , Mutação , Invasividade Neoplásica , Proteína Smad4/metabolismo , Câncer Papilífero da Tireoide , Neoplasias da Glândula Tireoide/metabolismo , Neoplasias da Glândula Tireoide/patologiaRESUMO
Normal epithelial thyroid cells in culture are inhibited by TGF-ß1. Instead, transformed thyroid cell lines are frequently resistant to its growth inhibitory effect. Loss of TGF-ß responsiveness could be due to a reduced expression of TGF-ß receptors, as shown in transformed rat thyroid cell lines and in human thyroid tumors, or to alterations of other genes controlling TGF-ß signal transduction pathway. However, in thyroid neoplasia, a complex pattern of alterations occurring during transformation and progression has been identified. Functionally, TGF-ß1 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-ß 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-ß1 and EGF systems in thyroid tumors and on the cross-talk between these growth factors in thyroid cancer.