| dc.description.abstract | The thyroid gland is mainly composed of epithelial cells (thyrocytes) organized as follicles. The cells are connected by junction complexes that link them together into a cohesive simple epithelium. The junctions are also important for the establishment of a semipermeable barrier that restricts the paracellular flow of ions and other solutes. In the first part of this thesis, the effects of thyroid stimulating hormone (TSH) and pro-inflammatory cytokines on the epithelial barrier of primary cultured human thyrocytes were investigated. Thyroid follicle segments were prepared from surgically excised paradenomatous tissue and from resected glands with Graves´ disease. The cells formed tight, but low resistant monolayers on permeable filters in bicameral chambers. Addition of TSH further increased the transepithelial resistance to approximately 1000 * x cm2 after 3-5 days. TSH also induced an ordered organization of the tight junction protein ZO-1, promoted a polarized (apical-basolateral) ultrastructure and stimulated the secretion of thyroglobulin (Tg), preferentially in the apical direction. Treatment with IL-1a for 1-2 days induced a decreased transepithelial resistance and an increased paracellular leakage of both small ([3H]inulin) and large (125I-Tg) radiotracers irrespective of TSH and without signs of cytotoxicity. Electron microscopy showed that the main target of IL-1a action was the adherens junction where large amounts of stress fibers were formed. In contrast, other pro-inflammatory cytokines, i.e. IL-6, TNF-a, IFN-g and TGF-b, had no effect on the thyroid epithelial barrier.Changes in cell-cell adhesion have previously been correlated with tumor cell invasion and metastasis. In the second part of the thesis, cadherin-mediated adhesion and morphology in thyroid carcinoma cell lines and in cultured non-neoplastic pig and human thyrocytes were examined. E-cadherin negative cell lines established from anaplastic thyroid carcinomas (ATC) showed a variable down-regulation of catenins, known to anchor cadherins to the cytoskeleton. The reduced expression was most notable for g-catenin and p120ctn. Furthermore, the electrophoretic mobility of p120ctn was altered. A demethylating agent, 5-aza-2´-deoxycytidine, increased protein expression of E-cadherin and g-catenin although some cell lines were unresponsive. N-cadherin was detected in E-cadherin negative ATC cell lines but not in freshly isolated and primary cultured human and pig follicle segments. However, N-cadherin expression was also induced by 1-2 subcultivations of non-neoplastic thyrocytes. In this process, the upregulation of N-cadherin was paralleled by downregulation of E-cadherin and morphological alterations such as multilayering and loss of barrier function. Unexpectedly, one ATC cell line, KAT-4, expressed normal levels of E-cadherin and catenins and had a maintained epithelial morphology despite loss of barrier function and lack of contact-inhibited growth. KAT-4 cells also had a unique aberration of E-cadherin.In conclusion, human thyrocytes form a highly differentiated epithelium when grown on filter in the presence of TSH. The epithelial barrier is abrogated by IL-1a. Cultured anaplastic thyroid carcioma cells display N-cadherin-mediated adhesion and reduced catenin expression. A switch from E- to N-cadherin occurs in subcultured non-neoplastic thyrocytes. The results may have importance for the understanding of thyroid autoimmunity and tumor progression | en |
