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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
 
 

Vitamin D interferes with transactivation of the growth hormone gene by thyroid hormone and retinoic acid.

The thyroid hormone, retinoic acid (RA), and vitamin D regulate gene expression by binding to similar receptors which act as ligand-inducible transcription factors. Incubation of pituitary GH4C1 cells with nanomolar concentrations of vitamin D markedly reduces the response of the rat growth hormone mRNA to thyroid hormone triiodothyronine (T3) and RA. The stimulation of growth hormone gene expression by both ligands is mediated by a common hormone response element (TREGH) present in the 5'-flanking region of the gene, and the inhibition caused by vitamin D is due to transcriptional interference of the vitamin D receptor on this DNA element. No inhibition of the basal promoter activity by the vitamin was observed. The response to T3 and RA of a heterologous promoter containing this element, the palindromic T3- and RA-responsive sequence TREPAL, or a direct repeat of the same motif is also inhibited by vitamin D. In contrast, vitamin D strongly induces the activity of constructs containing a vitamin D response element, and neither T3 nor RA reduces vitamin D-mediated transactivation. Transfection with an expression vector for the retinoid X receptor alpha (RXR alpha) increases transactivation by T3 and RA but does not abolish the inhibition caused by the vitamin. Gel retardation experiments show that the vitamin D receptor ( VDR) as a heterodimer with RXR weakly binds to the T3- and RA-responsive elements. Additionally, VDR displaces binding of T3 and RA receptors in a dose-dependent manner. Our data suggest the formation of TR- VDR and RAR- VDR heterodimers with RXR. The fact that the same response element mediates opposite effects of at least four different nuclear receptors provides a greater complexity and flexibility of the transcriptional responses to their ligands.[1]

References

  1. Vitamin D interferes with transactivation of the growth hormone gene by thyroid hormone and retinoic acid. Garcia-Villalba, P., Jimenez-Lara, A.M., Aranda, A. Mol. Cell. Biol. (1996) [Pubmed]
 
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