The G2M arrest caused by iodide is unrelated to the effects of iodide at adenylate cyclase

Effect of iodine on early stage thyroid autonomy

Thyroid autonomy is a frequent cause of thyrotoxicosis in regions with iodine deficiency. Epidemiological data suggest that iodide may influence the course of pre-existing thyroid autonomy. Making use of FRTL-5 cells stably expressing a constitutively activating TSH receptor mutation as an in vitro model of thyroid autonomy, we investigated the impact of iodide on proliferation, function and changes in global gene expression. We demonstrate that iodine inhibits growth in TSHR WT and L629F mutant FRTL-5 cells and downregulates e.g. protocadherin cluster (Pcdha1-13) and thyroid responsive element (Thrsp). In addition functional genes e.g. iodotyrosine deiodinase (iyd) and oncogen junB are upregulated, while sodium-iodide-symporter (Nis) and thyroid peroxidase (Tpo) are downregulated by iodide. Iodide tunes down the biological activity of autonomous thyrocytes and may thus be of therapeutic benefit not only to prevent the occurrence of somatic TSHR mutations, causing thyroid autonomy, but also to slow down the development of clinically relevant disease.

Moderate doses of iodide in vivo inhibit cell proliferation and the expression of thyroperoxidase and Na+/I- symporter mRNAs in dog thyroid

The function and the growth of adult thyroid gland is controlled by the opposite actions of thyrotropin (TSH) and iodide, the main substrate of the gland. Iodide deprivation leads to stimulation of the thyroid, improving the efficiency of iodide transport for hormone biosynthesis. We have investigated cell proliferation and thyroid specific gene expression 24 and 48 h after administering KI to dogs previously treated with goitrogens and perchlorate. In the hypothyroid dogs T3 and T4 serum levels decreased from 53 +/- 4 to < 30 ng/dl and from 1.6 +/- 0.6 to < 1 microg/dl respectively; TSH concentration increased from 0.16 +/- 0.02 to 2.7 +/- 0.4 ng/ml. After a 24 h moderate KI treatment (300 microg KI/dog of +/- 10 kg) serum T3 concentrations rose higher than the initial normal values, while T4 concentrations increased to reach values equivalent to the normal level. The high TSH concentration did not change significantly. The hyperplasia of the chronically stimulated thyroid resulting from goitrogens/NaClO4 treatment was not modified by this short term treatment with KI. In contrast, KI decreased the weight of the total gland and the level of cell proliferation, as determined by the fraction of cells incorporating BrdU. The effect of acute administration of KI on the expression of four major thyroid genes, the TSH receptor (TSHr), thyroglobulin (Tg), thyroperoxidase (TPO), and Na+/I- symporter (NIS) was analyzed by Northern blot. Tg, TPO and NIS mRNA expressions were up-regulated by chronic stimulation. The expression of the mRNAs of TSHr and Tg did not significantly differ between hyperstimulated and KI-treated dogs while TPO and NIS mRNA expression decreased after a 48 h KI treatment. TPO and NIS are therefore the only of these four genes whose expression is acutely modulated by iodide in vivo. Under TSH stimulation low doses of iodide resulted in: (1) decreased cell proliferation, (2) reestablished synthesis and secretion of thyroid hormones, (3) diminished TPO and NIS mRNA expression. Notably low doses of iodide under the same conditions had no effect on Tg and TSHr mRNA expression.