Negative regulation by thyroid hormone receptor requires an intact coactivator-binding surface.
Thyroid hormone (TH) action is mediated by TH receptors (TRs), which are members of the nuclear hormone receptor superfamily. In vitro studies have demonstrated that TR activity is regulated by interactions with corepressor and coactivator proteins (CoRs and CoAs, respectively). TH stimulation is thought to involve dissociation of CoRs and recruitment of CoAs to the liganded TR. In contrast, negative regulation by TH is thought to occur via recruitment of CoRs to the liganded TR. The physiological role of CoAs bound to TRs, however, has yet to be defined. In this study, we used gene-targeting techniques to mutate the TR-beta locus within its activation function-2 (AF-2) domain (E457A). This mutation was chosen because it completely abolished CoA recruitment in vitro, while preserving normal triiodothyronine (T3) binding and CoR interactions. As expected, TH-stimulated gene expression was reduced in homozygous E457A mice. However, these animals also displayed abnormal regulation of the hypothalamic-pituitary-thyroid axis. Serum thyroxine, T3, and thyroid-stimulating hormone (TSH) levels and pituitary Tshb mRNA levels were inappropriately elevated compared with those of WT animals, and L-T3 treatment failed to suppress serum TSH and pituitary Tshb mRNA levels. Therefore, the AF-2 domain of TR-beta is required for positive and, paradoxically, for negative regulation by TH in vivo.
Ortiga-Carvalho
Tania M
TM
Department of Medicine and Committee on Molecular Metabolism and Nutrition, Pritzker School of Medicine, The University of Chicago, Chicago, Illinois, USA.
Shibusawa
Nobuyuki
N
Nikrodhanond
Amisra
A
Oliveira
Karen J
KJ
Machado
Danielle S
DS
Liao
Xiao-Hui
XH
Cohen
Ronald N
RN
Refetoff
Samuel
S
Wondisford
Fredric E
FE
D000818:Animals; D002460:Cell Line; D005260:Female; D005786:Gene Expression Regulation; D018390:Gene Targeting; D005982:Glutathione Transferase / Q000378:metabolism; D051548:Histone Acetyltransferases; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D007453:Iodide Peroxidase / Q000378:metabolism; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056971:Nuclear Receptor Co-Repressor 1; D056920:Nuclear Receptor Coactivator 1; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism; D037042:Thyroid Hormone Receptors beta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
C539127:NCOR1 protein, human; C539128:Ncor1 protein, mouse; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D020033:Protein Isoforms; D012097:Repressor Proteins; D037042:Thyroid Hormone Receptors beta; D013963:Thyroid Hormones; D014157:Transcription Factors; D007453:Iodide Peroxidase; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; C538861:Ncoa1 protein, mouse; D056920:Nuclear Receptor Coactivator 1; D005982:Glutathione Transferase