Related Experiment Videos
Mitogenic effects of thyrotropin and adenosine 3',5'-monophosphate in differentiated normal human thyroid cells in
P Roger1, M Taton, J Van Sande
1Institute of Interdisciplinary Research, School of Medicine, Free University of Brussels, Campus Erasme, Belgium.
Abstract:
Previous studies of human thyroid cells in culture (mostly from pathological tissues) failed to demonstrate a mitogenic effect of TSH, leading to the proposal that the growth effect of TSH in vivo might be indirect. To reexamine the influence of TSH on DNA synthesis and cell proliferation, we established primary cultures of normal thyroid tissue from nine subjects. When seeded in a 1% serum-supplemented medium, thyroid follicles released by collagenase/dispase digestion developed as a cell monolayer that responded to TSH by rounding up and by cytoplasmic retraction. When seeded in serum-free medium, the cells remained associated in dense aggregates surrounded by few slowly spreading cells. In the latter condition, the cells responded to TSH and other stimulators of cAMP production, such as cholera toxin and forskolin, by displaying very high iodide-trapping levels. Exposure to serum irreversibly abolished this differentiated function. TSH stimulated the proliferation (as shown by DNA content per culture dish) of 1% serum cultured cells (doubling times were reduced from 106 to 76 h) and increased by 100% the [3H]thymidine labeling indices. In serum-free cultured cells (dense aggregates or cell monolayers after initial seeding with serum), control levels of DNA synthesis were lower, and up to 8-fold stimulation of DNA synthesis occurred in response to 100 mU/L TSH (stimulation was consistently detected with 20 mU/L), based on measurements of [3H]thymidine incorporation into acid-precipitable material and counts of labeled nuclei on autoradiographs (up to 40% labeled nuclei within 24 h). The mitogenic effect of TSH required a high insulin concentration (8.3 X 10(-7) mol/L) or a low insulin-like growth factor I concentration. The mitogenic effects of TSH were mimicked in part by cholera toxin, forskolin, and dibutyryl cAMP. Epidermal growth factor and phorbol myristate ester also stimulated thyroid cell proliferation and DNA synthesis, but they potently inhibited TSH-stimulated iodide transport. We conclude that TSH, acting at least in part through cAMP, is a potent growth factor for human thyroid cells and thus provide an experimental basis in vitro for the well established in vivo goitrogenic action of TSH.
Insights
Thyroid-stimulating hormone (TSH) is a potent growth factor for human thyroid cells, stimulating DNA synthesis and proliferation in vitro. This finding supports TSH's known goitrogenic action in vivo.
Area of Science:
- Endocrinology
- Cell Biology
Background:
- Previous studies using pathological thyroid tissues failed to show TSH's mitogenic effect in vitro.
- This led to speculation that TSH's in vivo growth effect might be indirect.
Purpose of the Study:
- To re-evaluate the influence of TSH on human thyroid cell DNA synthesis and proliferation.
- To establish primary cultures of normal human thyroid cells for experimental investigation.
Main Methods:
- Primary cultures of normal human thyroid cells were established.
- Cells were cultured in serum-supplemented and serum-free media.
- TSH's effect on DNA synthesis, cell proliferation, and iodide trapping was measured.
- Effects of other signaling molecules (cholera toxin, forskolin, IGF-I, EGF) were assessed.
Main Results:
- TSH significantly stimulated DNA synthesis and proliferation in thyroid cells cultured with 1% serum.
- In serum-free conditions, TSH markedly increased DNA synthesis (up to 8-fold) and iodide trapping.
- Mitogenic effects of TSH were dependent on insulin or IGF-I and partially mimicked by cAMP analogs.
- EGF and phorbol myristate ester also stimulated proliferation but inhibited TSH-induced iodide transport.
Conclusions:
- TSH acts as a potent growth factor for human thyroid cells, at least partly via cAMP signaling.
- These in vitro findings provide experimental support for TSH's established in vivo goitrogenic effects.