Transforming Growth Factor-β1 Induces a Mesenchyme-Like Cell Shape without Epithelial Polarization in Thyrocytes and Inhibits Thyroid Folliculogenesis in Collagen Gel Culture

Transforming growth factor-β1 (TGFβ1) induces a mesenchyme-like cell shape in some epithelial cell types. To clarify the role of TGFβ1 in the morphological regulation of thyrocytes, we performed collagen gel culture of porcine thyrocytes with serum-free medium. TGFβ1-nontreated cells organized follicles. In contrast, the cells treated with 10 ng/ml TGFβ1 became spindle shaped, i.e. they resembled mesenchymal fibroblasts, and did not form follicles. To characterize the spindle-shaped cells, we examined the fine structures and expression of thyroglobulin (Tg) and cytoskeletal proteins using electron microscopy, immunohistochemistry, and immunoblotting. TGFβ1-nontreated cells had microvilli at the apical side facing follicle lumen and had basal lamina at the basal side in contact with collagen gel. TGFβ1-treated cells showed both microvilli and basal lamina at the basal side. TGFβ1-nontreated cells expressed Tg, whereas TGFβ1-treated cells showed no expression. TGFβ1-nontreated cells barely expressed vimenti...