TTF-2 does not appear to be a key mediator of the effect of cyclic AMP on thyroglobulin gene transcription in primary cultured dog thyrocytes.

TTF-2 is a thyroid-specific winged-helix transcription factor which has been proposed to play a key role in the hormonal control of thyroglobulin and thyroperoxidase genes transcription in FRTL-5 cells. We have analyzed TTF-2 DNA-binding activity in primary cultures of dog thyrocytes maintained in control condition or in the presence of the cAMP agonist forskolin. Binding of 35S-labelled nuclear proteins to the TTF-2 recognition sequence identified the presence of two molecular species of 41.5 and 42.5 kDa. TTF-2 DNA-binding activity was clearly detectable in nuclear extracts from unstimulated cells and appeared increased in forskolin-treated cells. Thus, the presence of TTF-2 DNA-binding activity does not correlate with the cAMP-dependent activity of thyroglobulin and thyroperoxidase genes in this cell system. In addition, the mutation of the TTF-2 binding site in the thyroglobulin promoter resulted in a very reduced but still clearly cAMP-dependent promoter activity when assayed by transient expression in the same cells. These results do not support a dominant role for TTF-2 in the cAMP-dependent control of thyroglobulin gene transcription in primary cultured thyrocytes.