Kerstin Westermark

Thyrotropin modulates EGF receptor function in porcine thyroid follicle cells

Porcine thyroid follicle cells in monolayer cultures were shown to contain one single class of high-affinity EGF receptors with Kd = 4.5 X 10(-10) M and approximately 20 000-25 000 receptors per cell. Suspension cultures of aggregated follicle cells, exposed to TSH for 3 days, showed a 3-fold increase in [125I]EGF binding. Scatchard analysis demonstrated that this was due to an increase in receptor number. Other cAMP-elevating agents (cholera toxin, dibutyryl cAMP, forskolin) induced a similar effect. In suspension cultures, preincubation with TSH or cholera toxin for 2 days reduced the subsequent [3H]thymidine incorporation. This inhibition was overcome by a low concentration of EGF (0.1 ng/ml). At higher concentrations of EGF (1-10 ng/ml) the incorporation of [3H]thymidine was potentiated 2-3-fold in cultures preexposed to TSH or cholera toxin. The results demonstrate the presence of a high-affinity EGF receptor in porcine thyroid follicle cells. Receptor expression, as well as responsiveness to the mitogenic action of EGF, is modulated in vitro by TSH, through a cAMP-dependent process.

Functional properties of porcine-thyroid follicles in suspension

Porcine thyroid follicle cells were isolated (about 10(7) cells per gram of tissue) and cultured in small aggregates in agarose-coated culture dishes. The aggregates became arranged into follicle-like structures capable of iodide uptake and organification. In the presence of TSH (0.2 mU/ml), the aggregation of follicles was enhanced, and iodide uptake as well as TSH-stimulated organification of iodide was increased compared with that in the control. In culture, the active iodide metabolism was gradually lost over a 7-day period. This was not due to a disappearance of the TSH-adenylate cyclase system, since cAMP production was retained and stimulated by TSH (half-maximal effect at about 1 mU/ml). Acutely TSH stimulated iodide efflux and iodide organification (half-maximal effect at about 20 microU/ml). The stimulatory effect on organification was transient: within an hour further organification proceeded as in the absence of hormone. The effects on efflux and organification were already maximal at low TSH concentrations, whereas cAMP production was stimulated with up to 50-fold higher TSH levels, i.e. the findings were typical of spare receptors. In the continued presence of epidermal growth factor, a potent mitogen for thyroid cells, the follicles increased in size and contained one single large lumen. Their capability to take up and organify iodide was reduced.

Fibrosis in undifferentiated (anaplastic) thyroid carcinomas : evidence for a dual action of tumour cells in collagen type I synthesis

The mechanisms involved in stromal reactions and fibrosis in solid malignant tumours are incompletely understood. In the present study, collagen type I production was investigated in tissues and cell lines derived from human undifferentiated (anaplastic) thyroid carcinomas, a highly aggressive, often fibrotic malignancy with mesenchymal phenotype. In situ hybridization showed the expression of pro‐α1(I) collagen mRNA throughout the stromal part of the tumours. However, immunofluorescence staining using an anti‐pro‐collagen type I antibody revealed the synthesis of pro‐collagen type I protein mainly in stromal cells juxtaposed to nests of tumour cells. In one out of five tissue samples from human undifferentiated thyroid carcinomas, pro‐α1(I) collagen mRNA expression was also found in a small number of tumour cells. Several well‐characterized cell lines established from undifferentiated thyroid carcinomas, two from tumours included in the present study, expressed both pro‐α1(I) collagen and prolyl 4‐hydroxylase mRNA, and three of these cell lines also synthesized native triple‐helical collagen type I. Taken together, these data suggest that stromal fibroblasts are the main producers of collagen type I in anaplastic thyroid tumours. The carcinoma cells seem to play a regulatory role, stimulating the synthesis of collagen type I protein in the surrounding stroma by increasing pro‐α1(I) collagen mRNA translation. However, collagen type I production by the carcinoma cells might also contribute to the marked desmoplasia commonly seen in these tumours. Copyright

Collagen type I expression in experimental anaplastic thyroid carcinoma: Regulation and relevance for tumorigenicity

Fibrosis in solid malignancies plays a significant role in tumor pathophysiology. Potential mechanisms for collagen type I deposition in anaplastic thyroid carcinoma (ATC) were investigated using 6 characterized ATC cell lines. Three of these cell lines, which produced collagen type I, had, as a group, a poor tumorigenicity when inoculated in athymic mice. This group of cells generated tumors in 4 of 24 injected animals (17%). Pro‐α1(I) collagen mRNA‐expressing carcinoma and stromal cells were interdispersed in the tumors generated by these ATC cells. By contrast, the 3 noncollagen‐producing ATC cell lines were all tumorigenic with a tumor take of 60% in the whole group. In the latter tumors, pro‐α1(I) collagen mRNA‐expressing cells were confined to the stromal compartment, well delineated from carcinoma cell islets. To study the influence of ATC cells on collagen type I synthesis by fibroblasts, we used AG 1518 diploid human fibroblasts cultured on poly‐(2‐hydroxyethyl methacrylate) (poly[HEMA])‐coated plates. This culture condition allows the study of the effect of collagen mRNA translation in the regulation of collagen type I synthesis. Conditioned media from the 6 ATC cell lines did not influence collagen synthesis. The ATC cell line KAT‐4 stimulated fibroblast synthesis of collagen type I when the two cell types were cocultured on poly[HEMA]‐coated substrates. Specific inhibitors of PDGF and TGF‐β reduced the KAT 4 carcinoma cell‐induced stimulation of collagen type I synthesis. Our data suggest that collagen type I production by carcinoma cells correlates negatively with tumorigenicity and that the formation of a well‐defined stroma is of importance for tumor growth. Furthermore, our data suggest that tumor cells are able to stimulate collagen mRNA translation in stromal fibroblasts in direct cell‐cell contact by, at least in part, transferring PDGF or TGF‐β.

Expression of c-Myc, TGF-α and EGF-Receptor in Sporadic Medullary Thyroid Carcinoma

In 20 patients with sporadic medullary thyroid carcinoma (MTC), immuno-histochemistry was used to localize the expression of the c-Myc oncoprotein, transforming growth factor alpha (TGF-α) and epidermal growth factor receptor (EGFR) and these three markers were analysed regarding their relation to histopathological and histochemical variables of the tumours. The detection rates of c-Myc. TGF-α and EGFR were 90%, 90% and 95% respectively. Concomitant demonstration of the markers was reflected in significant associations (correlation factor between TGF-α and EGFR was 0.93, p < 0.001). The markers were almost invariably located within the cytoplasm, which might suggest their crucial role in growth regulation and cell differentiation; this seems especially true of TGF-α and EGFR. The different markers showed no relation to either histopathological or histochemical variables (tumour behaviour, tumour size, tumour cell type). The prominent co-expression of c-Myc, TGF-α and EGFR proteins indicates that in MTC th...