Alpha and beta thyroid hormone receptors bind immediately adjacent to the rat growth hormone gene TATA box in a negatively hormone-responsive promoter region

We report that alpha and beta type rat thyroid hormone receptors bind specifically and with high affinity to the 10-base pair sequence immediately 3' of the rat growth hormone TATA box (positions -25 to -16) in a region of the rat growth hormone promoter which can be negatively hormone responsive (nTRE). The receptors have approximately 7-fold lower affinity in vitro for the nTRE than for the thyroid hormone-responsive enhancer of the rat growth hormone gene (TRE). Proteins extracted with high salt concentration from rat pituitary cell nuclei enhance binding of the receptors to both the TRE and nTRE. A modification of the avidin-biotin complex DNA binding assay which enhances the sensitivity of the assay approximately 100-fold was used in these studies. The immediate proximity of a receptor binding site to the rat growth hormone TATA box suggests that direct interaction between receptor and TFIID (the TATA binding protein) mediates nTRE activity.     

Transcriptional regulation of the Xenopus laevis Stromelysin-3 gene by thyroid hormone is mediated by a DNA element in the first intron

The matrix metalloproteinase (MMP) stromelysin-3 (ST3) (MMP11) was first isolated as a breast cancer-associated gene and is expressed in diverse human carcinomas and various developmental processes involving apoptosis. The Xenopus laevis ST3 is highly up-regulated by thyroid hormone (T3) during amphibian metamorphosis, and its expression is spatially and temporally correlated with apoptosis in different tissues. Furthermore, it has been shown in vivo and in organ cultures to play a critical role in regulating T3-induced epithelial cell death during intestinal metamorphosis. Earlier studies suggest that ST3 is a direct T3 response gene, although a thyroid hormone response element (TRE) was not found in the initial analysis of the ST3 promoter. Here, we have identified a strong TRE consisting of two nearly perfect direct repeats of the consensus nuclear hormone receptor binding element AGGTCA separated by 4 bp in the first intron of the Xenopus ST3 gene. We show that the heterodimers of T3 receptor (TR) and 9-cis-retinoic acid receptor bind to the TRE both in vitro and in vivo in the context of chromatin. Furthermore, T3 induces strong activation of the promoter through the intronic TRE. Interestingly, although the unliganded TR/9-cis-retinoic acid receptor was able to recruit corepressors to the promoter, it had little repressive effect on the promoter in vivo. These results suggest that the intronic TRE mediates the inductive effect of T3 and that promoter context plays an important role in gene repression by unliganded TR.     

Direct repeats as selective response elements for the thyroid hormone, retinoic acid, and vitamin D3 receptors.

We report here the identification of thyroid hormone response elements (TREs) that consist of a direct repeat, not a palindrome, of the half-sites. Unlike palindromic TREs, direct repeat TREs do not confer a retinoic acid response. The tandem TRE can be converted into a retinoic acid response element by increasing the spacing between the half-sites by 1 nucleotide, and the resulting retinoic acid response element is no longer a TRE. Decreasing the half-site spacing by 1 nucleotide converts the TRE to a vitamin D3 response element, while eliminating response to T3. These results correlate well with DNA-binding affinities of the thyroid hormone, retinoic acid, and vitamin D3 receptors. This study points to the general importance of tandem repeat hormone response elements and suggests a simple physiologic code exists in which half-site spacing plays a critical role in achieving selective hormonal response.     

Multihormonal regulation of the human, rat, and bovine growth hormone promoters: differential effects of 3',5'-cyclic adenosine monophosphate, thyroid hormone, and glucocorticoids

We have analyzed the effects of a variety of hormones on activity of the rat GH (rGH), human GH, (hGH), and bovine GH (bGH) promoters. After transient transfection of rat pituitary tumor cells, all three promoters are induced by addition of 8-bromo-cAMP. Sequences required for the cAMP responsiveness of the hGH and rGH promoter lie within 183 base pairs of the mRNA start site. Although the rGH promoter is thyroid hormone (T3) responsive in this system, a construct containing 2.7 kilobases of the hGH promoter 5'-flanking sequences is not. Since we also found that the bGH promoter is T3 responsive in these cells, the hGH results are not likely to be due to a species specific factor required for induction in rat pituitary cells. The hGH promoter is weakly induced by dexamethasone whereas the rGH promoter does not respond to glucocorticoids. The hGH and rGH promoters are not responsive to TRH. These results illustrate the potential heterogeneity in hormonal responses of the same gene in different species.