The tissue-specific expression of the thyroglobulin gene requires interaction between thyroid-specific and ubiquitous factors.
Thyroid-specific expression of the rat thyroglobulin gene is mediated by transcriptional control. Sufficient DNA sequence information to confer thyroid-specific expression to a heterologous gene is contained between positions -168 and +39. DNA-binding studies have demonstrated that this region interacts with two thyroid-specific factors (TTF-1 and TTF-2), and a ubiquitous factor (UFA). Here we have characterized three elements within the promoter, A, K, and C, which are important for promoter activity in thyroid cells. We have shown by mutational analysis that the interaction of TTF-1 with the A and C regions. UFA with the A region, and TTF-2 with the K region are required for full promoter activity. The complex interactions in the A region can be replaced by the substitution of the UFA/TTF-1-binding site with a high-affinity TTF-1 binding site. There is a correlation between the presence of TTF-1 and TTF-2 DNA-binding activities and the expression of thyroglobulin, which implies that the mechanism restricting thyroglobulin expression to thyroid cells is mediated through the control of the expression, or the activity, of TTF-1 and TTF-2.