Regulation by Thyroid-Stimulating Hormone of Sodium/Iodide Symporter Gene Expression and Protein Levels in FRTL-5 Cells

Abstract

To investigate the mechanism of I- transport stimulation by TSH, we studied the effects of TSH on Na+/I- symporter (NIS) messenger RNA (mRNA) and protein levels in FRTL-5 cells and correlated these with I- transport activity. When 1 mU/ml TSH was added to quiescent FRTL-5 cells, a 12-h latency was observed before the onset of increased I- transport activity, which reached a maximum [approximately 27 times basal (5H medium) levels] at 72 h. In contrast, Northern blot analysis, using rat NIS complementary DNA as a probe, revealed that addition of TSH to these cells significantly increased NIS mRNA at 3-6 h, reaching a maximum after 24 h (approximately 5.9 times basal levels). Forskolin and (Bu)2cAMP mimicked this stimulatory effect on both the I- transport activity and mRNA levels. D-ribofranosylbenzimidazole, a transcription inhibitor, almost completely blocked TSH-induced stimulation of I- transport and NIS mRNA levels. Western blot analysis demonstrated that TSH increased NIS protein levels at 36 h, reaching a maximum at 72 h, in parallel with the kinetics of TSH-induced I- transport activity. However, it also showed that the amount of NIS protein already present in FRTL-5 cell membranes before the addition of TSH was about one third of the maximum level induced by TSH. These results indicate that stimulation of I- transport activity by TSH in thyrocytes is partly due to a rapid increase in NIS gene expression, followed by a relatively slow NIS protein synthesis. However, the existence of an abundant amount of protein in quiescent FRTL-5 cells with very low I- transport activity also suggests that this activity is controlled by another TSH-regulated factor(s).

Retinoic acid induces sodium/iodide symporter gene expression and radioiodide uptake in the MCF-7 breast cancer cell line

“…It has been reported that the iodide uptake in thyroid cells is stimulated by TSH via the cAMP͞adenylate cyclase pathway (4,7,8,37). Treatment of MCF-7 cells with 0.1-100 M forskolin, an agonist of adenylate cyclase, however, did not increase the iodide uptake (data not shown).…”

“…The up-regulation of NIS by TSH in thyroid cells has been well characterized (4,7,37) and contrasts with tRA stimulation in MCF-7 cells. NIS mRNA levels are rapidly increased in TSH-stimulated FRTL-5 rat thyroid cells; however, there is a 12-h latency before the onset of increased iodide uptake and maximum uptake is observed at 72 h (7,37). In contrast, in MCF-7 cells, tRA increased NIS mRNA, NIS protein, and iodide uptake levels by 6 h, reaching a maximum at 12, 24, and 48 h, respectively, and no latency period of iodide uptake was observed.…”

“…Iodide trapped in thyroid follicular cells is organified as thyroglobulin by the action of thyroperoxidase and used to synthesize thyroid hormone. NIS gene expression in thyroid cells is regulated by thyrotropin (TSH) via the cAMPdependent pathway (4,7,8). Thyroid cancer requires high levels of TSH to induce or to maximally stimulate 131 I uptake (1).…”

Evidence for Transcriptional and Posttranscriptional Alterations of the Sodium/Iodide Symporter Expression in Hypofunctioning Benign and Malignant Thyroid Tumors

“…Thus, the impairment of hNIS gene expression occurring in hypofunctioning thyroid tumors could simply result from a switching off of the pathway controlling the expression of hNIS gene. In vitro studies on thyroid cell models and in vivo studies in rodents indicate that the main regulator of NIS gene expression is TSH and that the hormone primarily acts at the level of transcription, [23][24][25][26][27] but also exerts posttranscriptional regulatory actions. 21 Because patients with a cold nodule, be it an adenoma or a carcinoma, are generally euthyroid with a plasma TSH concentration within the normal range, and as TSH receptor expression is maintained in these tumors, 28 it is reasonable to think that the impairment of hNIS expression occurring in hypofunctioning thyroid tumors could result from alterations of regulatory elements along the TSH-activated pathway.…”

Inhibitory Effect of Thyrotropic Hormone on Apoptosis Induced by Actinomycin D in a Functioning Rat Thyroid Cell Line.

“…Cells and culture conditions FRTL-5 cells were cultured in Coon's modified Ham's F12 medium with 5% calf serum and a six-hormone mixture (6H) composed of insulin (10 ag/ml), cortisone (10 nM), human transferrin (5 ig/ml), glycyl-L-histidyl-L-lysine (10 ng/ml), somatostatin (10 ng/ml ) and TSH (1 mU/ml), as described previously [9,10]. Cells were maintained at 37°C in an atmosphere saturated with water and containing 95% air-5% C02.…”