Ligand-induced recruitment of a histone deacetylase in the negative-feedback regulation of the thyrotropin β gene

We have investigated ligand-dependent negative regulation of the thyroid-stimulating hormone beta (TSH beta) gene. Thyroid hormone (T3) markedly repressed activity of the TSH beta promoter that had been stably integrated into GH(3) pituitary cells, through the conserved negative regulatory element (NRE) in the promoter. By DNA affinity binding assay, we show that the NRE constitutively binds to the histone deacetylase 1 (HDAC1) present in GH3 cells. Significantly, upon addition of T3, the NRE further recruited the thyroid hormone receptor (TR beta) and another deacetylase, HDAC2, This recruitment coincided with an alteration of in vivo chromatin structure, as revealed by changes in restriction site accessibility. Supporting the direct interaction between TR and HDAC, in vitro assays showed that TR, through its DNA binding domain, strongly bound to HDAC2, Consistent with the role for HDACs in negative regulation, an inhibitor of the enzymes, trichostatin A, attenuated T3-dependent promoter repression. We suggest that ligand-dependent histone deacetylase recruitment is a mechanism of the negative-feedback regulation, a critical function of the pituitary-thyroid axis.