INCREASED EXPRESSION OF THE NA+ I- SYMPORTER IN CULTURED HUMAN THYROID-CELLS EXPOSED TO THYROTROPIN AND IN GRAVES THYROID-TISSUE/

The Na+/I- symporter (NIS) is important in hormone synthesis in the th yroid gland. NIS activity, as reflected by I- uptake, was increased by TSH (1 mU/mL) or forskolin (10 mu mol/L) in primary cultured human th yroid cells. Northern blot analysis revealed that incubation of these cells with TSH or forskolin for 24 h increased the abundance of NIS me ssenger ribonucleic acid (mRNA) 2.3- and 2.5-fold, respectively. Immun oblot analysis revealed 2.7- and 2.4-fold increases, respectively, in the amount of NIS protein after 48 h, suggesting that elevated levels of intracellular cAMP induced the expression of NIS in human thyrocyte s. We then studied the levels of NIS mRNA and protein in Graves' thyro id tissue and found that the amount of NIS mRNA in thyroid tissue from individuals with Graves' disease (n = 5) was 3.8 times that in normal thyroid tissue (n = 5). The abundance of NIS mRNA was significantly c orrelated with that of thyroid peroxidase or thyroglobulin mRNAs, but not with that of TSH receptor mRNA, in the Graves' and normal thyroid tissue specimens. The amount of NIS protein was also increased 3.1-fol d in Graves' thyroid tissue compared with that in normal thyroid tissu e. The increased expression of NIS may thus contribute to the developm ent of Graves' disease.