Thyroid hormone response elements differentially modulate the interactions of thyroid hormone receptors with two receptor binding domains in the steroid receptor coactivator-1.
Ligand-dependent transcriptional activation by nuclear receptors is mediated by interactions with coactivators. Recently, a consensus interaction motif (LXXLL) has been identified in a number of coactivators such as steroid receptor coactivator-1 (SRC-1). SRC-1 contains three such motifs in the central (nuclear receptor binding domain-1, NBD-1) and a single one in the C-terminal (NBD-2) regions. To define the nature and role of the two NBDs in SRC-1, interaction studies between the two NBDs and thyroid hormone receptor (TR) were performed. Although NBD-1 and NBD-2 showed similar ligand- and AF-2-dependent interactions with TR in solution, these two NBDs possessed distinct interaction properties with TR when TR is bound to a thyroid hormone-response element (TRE). Both in vitro and in vivo interaction studies demonstrate that NBD-1, but not NBD-2, exhibits ligand-dependent interaction with TR in the presence of TREs. In addition, a natural isoform of SRC-1, SRC-1E, which lacks NBD-2, preserved TR as well as progesterone receptor-mediated coactivator function on reporter gene expression. Finally, we found that NBD-1 failed to interact with a TR and retinoid X receptor heterodimer complex on a transcriptionally inactive direct repeat +4 TRE in electrophoretic mobility shift assays. These observations indicate that DNA-induced, as well as ligand-induced, conformational change(s) of TR may influence the nature of its binding to SRC-1, and that the two NBDs of SRC-1 may play different roles to regulate ligand-dependent transactivation of TRs.
Takeshita
A
A
Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. takeshita@rascal.med.harvard.edu
Yen
P M
PM
Ikeda
M
M
Cardona
G R
GR
Liu
Y
Y
Koibuchi
N
N
Norwitz
E R
ER
Chin
W W
WW
D000818:Animals; D001665:Binding Sites; D004247:DNA / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D051548:Histone Acetyltransferases; D056920:Nuclear Receptor Coactivator 1; D011487:Protein Conformation; D051381:Rats; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D047488:Retinoid X Receptors; D013963:Thyroid Hormones / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D047488:Retinoid X Receptors; D013963:Thyroid Hormones; D014157:Transcription Factors; D004247:DNA; D051548:Histone Acetyltransferases; D056920:Nuclear Receptor Coactivator 1