Growth Factor Control of Rat Thyroid Follicular Cell Proliferation

Abstract

We have investigated the proliferative responses of rat thyroid follicular cells in serum-free culture to a range of growth factors including TSH, epidermal growth factor, and insulin, added singly or in combination. Follicles released from normal thyroids by collagenase/dispase digestion were cultured in suspension in agarose-coated microtiter plates to prevent monolayer formation. Growth responses were measured by [3H] thymidine incorporation and by autoradiography over successive 24- or 36-h periods. Insulin, even in the absence of other growth factors, stimulated [3H]thymidine incorporation in a concentration-dependent manner, rising from basal levels of 486 +/- (SE) 18 cpm to 4222 +/- 367 cpm/5 X 10(4) cells at 8 micrograms/ml. In contrast, TSH alone had no effect. In the presence of threshold levels (0.08 micrograms/ml) of insulin, however, there was a highly significant (P less than 0.001) response to TSH, [3H]thymidine incorporation rising from 1089 +/- 163 cpm in the absence of TSH to a maximum of 7548 +/- 585 with 1 mU/ml TSH. There was a synergistic interaction between insulin and TSH over the concentrations tested. Epidermal growth factor either alone or in combination with insulin failed to produce a significant response. Parallel autoradiographic studies were concordant with the [3H]thymidine incorporation data. We conclude that whereas in the absence of other growth factors TSH is unable to stimulate DNA synthesis in isolated rat thyroid follicles, the inclusion of just a single growth factor, insulin, permits a marked response. These observations emphasize the need for inclusion of appropriate permissive growth factor(s) when assessing the in vitro effect of a suspected tissue-specific mitogen.

Loss of dependence on IGF-1 for proliferation of human thyroid adenoma cells

“…Such bell-shaped responses are a welldocumented feature of in vitro studies of cell proliferation (Bodger et al, 1979;Yen & Lewin, 1981) and have been previously reported in human thyroid follicular epithelium derived from normal glands, Graves' disease and multinodular goitre (Ollis et al, 1986) although, interestingly, not in cultures of follicular epithelium derived from other mammalian species (Roger et al, 1982;Valente et al, 1983;Smith et al, 1986).…”

“…Since our previous work has always shown a close correlation between peaks of 3H-TdR incorporation, as measured by scintillation counting, and increases in the autoradiographic nuclear labelling index (Williams et al, 1987;Smith et al, 1986), the analysis of suspension cultures in this study was performed by 3H-TdR scintillation counting alone. However, all critical comparisons of growth responses were confirmed by use of autoradiographic nuclear labelling index in the monolayer cultures.…”

Phagocytosis of Fluorescent Beads by Rat Thyroid Follicular Cells (FRTL-5): Comparison with Iodide Trapping as an Index of Functional Activity of Thyrocytes In Vitro

“…Although numerous in vitro thyroid follicular cell culture systems have been described (1,12,25,35,36,39), secretion of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) is seldom measured in vitro due to the reduced ability of follicular cells growing in monolayer culture (i.e., lacking follicular organization) to concentrate and efficiently iodinate thyroglobulin. Thyroid function in vitro is often assessed by evaluating specific phases of hormone synthesis including iodide trapping (41 ); thyroglobulin expression (5, 11, 21, 24, 27, 3$), secretion (16,18), and iodination (28,33); thyroid peroxidase synthesis ( 17,44) and activity (20); and thyroid-stimulating hormone (TSH) receptor expression.…”

Effect of Monensin on DNA Synthesis in Cultured Human Thyroid Cells.

“…However, the growth promoting effect of TSAb or TGI remains controversial [6][7][8][9][10]. EGF or other factors such as insulin, IGF-1, or interleukin-1 also stimulate the growth of thyroid follicular cells [11][12][13][14][15][16][17][18][19][20]. Several investigators claimed that TGI was actually a contamination of EGF [8,9].…”

“…Several investigators claimed that TGI was actually a contamination of EGF [8,9]. Moreover, the signal transduction pathway of these growth factors remains unclear [3][4][5][11][12][13][14][15][16][17][18][19][20].…”