In vivo interaction of steroid receptor coactivator (SRC)-1 and the activation function-2 domain of the thyroid hormone receptor (TR) beta in TRbeta E457A knock-in and SRC-1 knockout mice

• Published in: Endocrinology (Philadelphia) 2009-08, Vol.150 (8), p.3927
• Main Authors: Alonso, Manuela, Goodwin, Charles, Liao, Xiaohui, Ortiga-Carvalho, Tania, Machado, Danielle S, Wondisford, Fredric E, Refetoff, Samuel, Weiss, Roy E
• Format: Article
• Language: English
• Subjects: Animals; Histone Acetyltransferases - genetics; Histone Acetyltransferases - metabolism; Mice; Mice, Knockout; Mice, Transgenic; Nuclear Receptor Coactivator 1; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Protein Structure, Tertiary; Reverse Transcriptase Polymerase Chain Reaction; Thyroid Function Tests; Thyroid Hormone Receptors alpha - genetics; Thyroid Hormone Receptors alpha - metabolism; Thyroid Hormone Receptors beta - genetics; Thyroid Hormone Receptors beta - metabolism; Thyroid Hormones - blood; Thyroid Hormones - deficiency; Thyroid Hormones - pharmacology; Thyrotropin - blood; Thyrotropin - genetics; Thyroxine - blood; Transcription Factors - genetics; Transcription Factors - metabolism; Triiodothyronine - pharmacology
• ISSN: 1945-7170
• DOI: 10.1210/en.2009-0093

The activation function-2 (AF-2) domain of the thyroid hormone (TH) receptor (TR)-beta is a TH-dependent binding site for nuclear coactivators (NCoA), which modulate TH-dependent gene transcription. In contrast, the putative AF-1 domain is a TH-independent region interacting with NCoA. We determined the specificity of the AF-2 domain and NCoA interaction by evaluating thyroid function in mice with combined disruption of the AF-2 domain in TRbeta, due to a point mutation (E457A), and deletion of one of the NCoAs, steroid receptor coactivator (SRC)-1. The E457A mutation was chosen because it abolishes NCoA recruitment in vitro while preserving normal TH binding and corepressor interactions resulting in resistance to TH. At baseline, disruption of SRC-1 in the homozygous knock-in (TRbeta(E457A/E457A)) mice worsened the degree of resistance to TH, resulting in increased serum T(4) and TSH. During TH deprivation, disruption of AF-2 and SRC-1 resulted in a TSH rise 50% of what was seen when AF-2 alone was removed, suggesting that SRC-1 was interacting outside of the AF-2 domain. Therefore, 1) during TH deprivation, SRC-1 is necessary for activating the hypothalamic-pituitary-thyroid axis; 2) ligand-dependent repression of TSH requires an intact AF-2; and 3) SRC-1 may interact with the another region of the TRbeta or the TRalpha to regulate TH action in the pituitary. This report demonstrates the dual interaction of NCoA in vivo: the TH-independent up-regulation possibly through another domain and TH-dependent down-regulation through the AF-2 domain.