The genetic events involved in thyroid carcinogenesis are still incompletely understood. Several rearrangements and mutations of oncogenes have been implicated in the development of thyroid papillary carcinomas, follicular adenomas and carcinomas. However, none of these molecular alterations is suitable either as a general marker for the diagnosis of thyroid carcinomas or to differentiate between thyroid follicular adenomas and carcinomas. In order to identify new genes with altered expression which could serve as such markers, we analyzed RNA from thyroid tumor and normal tissue using a novel technique called restriction-mediated differential display. Several differentially expressed genes were identified, including the gene for IgG Fc binding protein (Fc BP). Differential expression of Fc BP was confirmed by quantitative realtime RT-PCR. Our experiments showed that IgG Fc binding protein (Fc BP) is differentially expressed in normal thyroid tissue, thyroid adenomas and thyroid carcinomas. While the Fc BP gene is constitutively expressed in normal thyroid tissue, its expression is significantly increased in follicular thyroid adenomas and significantly decreased in papillary and follicular thyroid carcinomas. Thus, measurement of the expression levels of Fc BP in thyroid biopsies might help to make the otherwise difficult distinction between a thyroid follicular adenoma and a follicular carcinoma.

The extracellular matrix (ECM) and basement membranes (BM, a specialized form of ECM) greatly influence proliferation, differentiation, and function of cells and the structure of tissues. While a considerable amount of information is available on thyroid cellular proliferation, differentiation and function, much less is known about thyroid ECM and BM. In this study the presence of the ECM/BM components fibronectin, collagen IV, alpha1, beta1, gamma1 laminin, several laminin variants, osteonectin, and perlecan was demonstrated in cryosections of nonadenomatous and toxic adenoma human thyroid tissue. Also, positive immunohistochemical staining for collagen IV, laminin, perlecan, and fibronectin was obtained in sections of human thyroid tissue cultured in a three-dimensional (alginate) culture system. The present study provides methods and data that will facilitate the investigation of the interaction between cells and ECM in thyroid tissue.

Interactions between follicular epithelial cells and extracellular matrix (ECM) are supposed to play an important role in the development and maintenance of thyroid tissue architecture. In the present study we have therefore investigated the synthesis of ECM components by a feline thyroid cell line which is able to form follicle-like structures in vitro, and also in v-ras-transfected and controltransfected sublines. Transfections were performed by lipofection with pZSR (viral Harvey ras gene; neo) and pSV2-neo (control, neo only) plasmids. We have adapted a semisolid culture system composed exclusively of polymerized alginate and therefore devoid of ECM components. Feline cells embedded in alginate gels as single cells and cultured for up to 90 days formed cell clusters within 10 days. Follicle-like structures were formed in the original cell lines and also in the v-ras-and controltransfected cells. Differences in proliferation rates were observed, the v-ras-transfected cells growing up to two to three times faster than the non-transfected cells. Immunostaining was done using rabbit first antibodies directed against mouse collagen IV, human fibronectin, laminin (tumor Engelbreth-Holm-Swarm laminin), perlecan and other ECM components. For comparison, immunostaining was also performed on cryosections of nodular goiters of six hyperthyroid cats. The cell lines and their transfected clones stained strongly positive for collagen IV and fibronectin, and positively but less strongly for laminin and perlecan. The cat goiter tissue stained positively for collagen IV, laminin, perlecan, and fibronectin, and positive staining for S-laminin (containing the 2-chain) was seen in blood vessel walls in this tissue.In conclusion, cat cell lines grow three-dimensionally in alginate beads over several weeks, they form follicle-like structures and express the same ECM components as the native cat goiter tissue. Transfection with v-ras does increase proliferation rate, but does not fundamentally alter formation of follicle-like structures and ECM expression. Alginate gel culture is a promising new tool for the study of follicular morphogenesis, polarity, the expression pattern of ECM components and of the interaction between thyrocytes and ECM. It avoids interference caused by gels composed of ECM components.

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