Role of GHF-1 in the Regulation of the Rat Growth Hormone Gene Promoter by Thyroid Hormone and Retinoic Acid Receptors

Teresa Palomino,Domingo Barettino,Ana Aranda

doi:10.1074/jbc.273.42.27541

Teresa Palomino, Domingo Barettino + Show 1 more

Open Access

https://doi.org/10.1074/jbc.273.42.27541

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Abstract

In non-pituitary HeLa cells the unliganded thyroid hormone or retinoic acid receptors cause a strong activation of the rat growth hormone promoter that is repressed by their ligands. In contrast, after expression of the pituitary-specific transcription factor GHF-1, thyroid hormone and retinoic acid produce a stimulation similar to that found in pituitary cells. Therefore, GHF-1 changes a ligand-dependent inhibition into a ligand-dependent activation. The essential role of GHF-1 on the rat growth hormone promoter was also demonstrated with AF-2-defective T3 receptor mutants that show a normal activation of this promoter in the presence of GHF-1. Furthermore, a truncated T3 receptor, which lacks the N-terminus and the DNA binding domain, was able to stimulate this promoter in the presence of GHF-1 and exogenous RXR receptors, suggesting the importance of protein to protein interactions in this regulation. This study shows that the final transcriptional effect depends not only on the type of regulatory promoter response elements but also on the presence of other transcriptional activators, in the case of the growth hormone promoter, the tissue-specific transcription factor GHF-1, which plays a coactivator-like role in this promoter.

Highlights

Expression of the rGH1 gene has been analyzed to understand cell type-specific transcriptional control as well as regulation by nuclear receptors [1]
Stimulation of the rGH Promoter by TR in HeLa Cells; T3independent and T3-dependent Components of Synergistic Interactions between GHF-1 and TR— expression of the GH gene is restricted to pituitary cells, a measure of promoter activity was routinely obtained in non-pituitary HeLa cells
GHF-1 Is Able to Confer Ligand-independent and Ligand-dependent Activity to a Mutant TR Lacking the A/B Region and the DNA Binding Domain—A deletion mutant of TR, TR-(120 – 408), which lacks the first 120 amino acids and cannot bind to DNA, was expressed alone or with RXR to test its ability to Regulation of rat GH Promoter Activity by Unliganded T3 and retinoic acid (RA) Receptors in Non-pituitary Cells—A hormone-independent activation of the rat GH promoter by TR and RAR in HeLa cells, which was reversed after ligand addition has been observed

Summary

Introduction

Expression of the rGH1 gene has been analyzed to understand cell type-specific transcriptional control as well as regulation by nuclear receptors [1]. A constitutive activation by unliganded TR, which was reversed by T3, was displayed by the Ϫ145GH-CAT construct (Fig. 1B, left panel), which lacks the TRE, indicating that this element is not involved in T3-independent transactivation and that the putative binding site mediating this effect is located within the first 145 bp of the promoter.

Results

Conclusion