Induction of nuclear protein factors specific for hormone-responsive region during activation of thyroglobulin gene by thyrotropin in rat thyroid FRTL-5 cells.

We have investigated the mechanism of stimulation of thyroglobulin gene expression by thyrotropin (TSH) and cAMP in rat thyroid FRTL-5 cells. In contrast to the c-fos gene, induction of the thyroglobulin gene by TSH or cAMP is slow (10 h) and sensitive to cycloheximide treatment. We have identified a TSH and cAMP-responsive region of thyroglobulin gene between - 171 and - 140 base pairs from the transcription initiation site. The hormone-responsive region contains DNA sequence elements similar to the consensus cAMP-responsive element as well as the transcription factor AP-1-binding site but with opposite sequence polarity. Three DNA-protein complexes are formed when the hormone-responsive region is incubated with nuclear extracts of FRTL-5 cells. Formation of these complexes is dependent on TSH or cAMP stimulation, thus suggesting that the factors involved in binding to the hormone-responsive region may be induced by TSH. Although the identity of these factors is not yet known, they do not appear to be related to either cAMP-responsive element-binding protein or AP-1. These results suggest that thyroglobulin gene expression in FRTL-5 cells may be mediated by nuclear factors that are induced by cAMP in contrast to other genes (e.g. c-fos) whose activation involves post-translational modification of the pre-existing proteins specific for cAMP-responsive element.