Thyroid hormone receptors and type I iodothyronine 5'-deiodinase activity of human thyroid toxic adenomas and benign cold nodules.

The majority of thyroid adenomas are of clonal origin. In a subset of toxic adenomas (TAs) and cold nodules (CNs) activating mutations in the thyrotropin (TSH) receptor or G s -alpha gene may explain the altered functions in these benign tumours. The present study was undertaken to investigate the status of functional thyroid hormone receptors, major thyroid hormone signal mediators, in both the human TAs and CNs in comparison with a normal thyroid tissue from the same patient. Electrophoretic mobility shift assays using a DR4 ("direct repeats" 4), a thyroid hormone responsive element (TRE) of human type I iodothyronine 5'-deiodinase demonstrated the DNA-binding of thyroid hormone receptors (TRs) in thyroid tissue nuclear extracts. A significant increase (p < 0.05) in the functional binding properties of TRs to the DR4 thyroid hormone responsive element was found in TAs when compared to normal thyroid tissue. Contrary, a marked diminution in the TR-TRE complex formation was found in CNs in comparison with normal thyroid tissue. In addition, functional activity of the iodothyronine 5'-deiodinase (5'DI) was analyzed in benign tumours, thyroid TAs and CNs in comparison with that of normal thyroid tissue. A significantly increased (p < 0.01) activity of 5'DI was demonstrated in TAs, and in contrast, decreased values of the enzyme activity were found in CNs when compared to a normal tissue. From the data it is suggested that both the status of TR-TRE complex formation and the activity of the 5'DI may be altered in benign tumours of human thyroid gland.