[Thyroglobulin gene expression in cultured thyroid cells: regulation by thyrotropin].

The influence of thyrotropin (TSH) on thyroglobulin (Tgb) biosynthesis has been studied porcine thyroid cells maintained in primo culture. After 4 days of culture and 1-hr labelling with 35S Met, Tgb specific radioactivity was 10 times higher in TSH-treated cells than in control cells. The levels at which TSH action occurred have been described. i) In TSH cell extracts, 70 p. 100 of the Tgb mRNA sequences, quantified by hybridization to a specific 3H cDNA probe, were located in highly polymeric polysomes, while 70 p. 100 of the Tgb mRNA in the control extracts were in light polysomes. This suggests that TSH specifically or non-specifically stimulates the initiation of translation on Tgb mRNA. ii) The relative amount of Tgb mRNA in the cytoplasm of TSH-treated cells was 3 times higher than in the control cells. This correlates with the fact that Tgb biosynthesis relative to total protein synthesis increased similarly, indicating that TSH controls relative Tgb biosynthesis by specifically regulating cytoplasmic Tgb mRNA content. iii) The nuclear RNA of TSH-treated cells contained 2.2 times more Tgb mRNA sequences than the nuclear RNA of control cells, showing that TSH specifically regulates Tgb gene expression at the nuclear level (transcription or stabilization).