In contrast to the glucocorticoid receptor, the thyroid hormone receptor is translated in the DNA binding state and is not associated with hsp90

In vitro transcription and translation of the human 1,25-dihydroxyvitamin D3 receptor cDNA

A fragment of the complementary deoxyribonucleic acid to the human 1,25-dihydroxyvitamin D3 receptor protein containing essentially the entire open reading frame was transcribed and translated in vitro. The resulting protein was then demonstrated to exhibit the physical and functional features, i.e. molecular weight, immunoreactivity, 1,25-dihydroxyvitamin D3 binding, and DNA-cellulose binding, of the native human receptor from the T47D cell line. This validates the authenticity of the cDNA in a cell free system and provides a biochemical means of generating this rare and labile macromolecule to use in heretofore difficult structure/function studies.

The viral erbA oncogene protein, a constitutive repressor in animal cells, is a hormone-regulated activator in yeast

The v-erbA oncogene is a retrovirus-transduced and altered copy of a cellular gene for a thyroid hormone receptor. In animal cells, the v-erbA protein fails to respond to hormone and acts as a dominant negative allele, inhibiting gene activation normally conferred by the wild-type thyroid hormone receptor. We report here that, unexpectedly, the v-erbA protein acts as a hormone-regulated transcriptional activator in S. cerevisiae. We suggest that the ability of v-erbA protein to function as a transcriptional repressor or an activator is determined by interaction with, or modification by, other cellular factors, and that this phenomenon may be relevant to understanding ligand regulation of the normal thyroid and steroid hormone receptors.

Ligand-activated thyroid hormone and retinoic acid receptors inhibit growth factor receptor promoter expression

Thyroid hormone (T3) and retinoic acid (RA) receptors mediate ligand-dependent inhibition of epidermal growth factor (EGF) receptor and c-erbB2/neu promoter activities. Ligand-activated T3 and RA receptors act via a 36 bp 5' fragment of the EGF receptor gene in vivo and, in the presence of nuclear extract, bind with high affinity to this region in vitro. Both ligand binding and DNA binding domains of T3 and RA receptors are required for promoter inhibition. When both receptors are expressed in the presence of a single ligand, inhibition is reversed, indicating that the hormone-activated receptor is competed by the unliganded receptor. These results suggest that ligand regulates transcriptional inhibitory functions of the T3 and RA receptors and describe novel regulation of growth factor receptor gene expression.