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 ha s been proposed to play a key role in the hormonal control of thyroglo bulin and thyroperoxidase genes transcription in FRTL-5 cells. We have analyzed TTF-2 DNA-binding activity in primary cultures of dog thyroc ytes maintained in control condition or in the presence of the cAMP ag onist forskolin. Binding of S-35-labelled nuclear proteins to the TTF- 2 recognition sequence identified the presence of two molecular specie s of 41.5 and 42.5 kDa. TTF-2 DNA-binding activity was clearly detecta ble in nuclear extracts from unstimulated cells and appeared increased in forskolin-treated cells. Thus, the presence of TTF-2 DNA-binding a ctivity does not correlate with the cAMP-dependent activity of thyrogl obulin and thyroperoxidase genes in this cell system. In addition, the mutation of the TTF-2 binding site in the thyroglobulin promoter resu lted in a very reduced but still clearly cAMP-dependent promoter activ ity when assayed by transient expression in the same cells. These resu lts do not support a dominant role for TTF-2 in the cAMP-dependent con trol of thyroglobulin gene transcription in primary cultured thyrocyte s. (C) 1998 Academic Press.