Lack of responsiveness to TGF-β1 in a thyroid carcinoma cell line with functional type I and type II TGF-β receptors and Smad proteins, suggests a novel mechanism for TGF-β insensitivity in carcinoma cells

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine. In the present study we have investigated the expression of TGF-beta receptors (T beta R's) and SMAD proteins in non-neoplastic and neoplastic thyroid follicle cells. We found expression of all T beta R's (type I, II and III) and SMAD proteins analysed (Smad2, Smad3, Smad4, Smad6 and Smad7). Five out of six human anaplastic thyroid carcinoma cell lines were growth inhibited by addition of TGF-beta 1, and therefore considered to be TGF-responsive. One cell line however, HTh 7, did not respond to TGF-beta 1 with growth inhibition, induction of the extracellular matrix protein fibronectin or immediate early genes junB, Smad6 and Smad7 mRNA. Analysis of the TGF-beta intracellular signalling pathway in HTh 7 cells showed that receptors were capable of signalling, e.g. Smad2 phosphorylation and SMAD nuclear translocation. In summary, our data shows abundant expression of TGF-beta signalling components in thyroid follicle cells, and the escape from TGF-beta sensitivity in one anaplastic thyroid carcinoma despite an apparently functional TGF-beta/SMAD-signalling pathway, indicating a novel mechanism for TGF-beta insensitivity. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.