Role of the conserved C-terminal region of thyroid hormone receptor-alpha in ligand-dependent transcriptional activation.
The ligand binding domain (LBD) of thyroid hormone (T3) receptors contains subdomains that participate in transcriptional activation, hormone-relieved repression and dimerization. A sequence conserved within the nuclear receptor superfamily is found at positions 397-405 of the 408-amino acid chicken T3 receptor-alpha (cTR alpha) and is deleted in the related avian v-erbA. Since v-erbA exhibits compromised ligand binding and transcriptional activation, this conserved region may play a role in ligand-dependent transcriptional activation. Transfections reveal that cTR alpha(1-392) and site-directed mutants cTR alpha(L398R) and cTR alpha(F399E) are inactive, while cTR alpha(1-403) displays reduced ligand-dependent transcriptional activity. The loss of transcriptional activity in cTR alpha(1-392) is not caused by impaired DNA binding or receptor dimer formation. Proteolytic protection assays reveal that both transcriptionally active and inactive cTR alpha derivatives undergo T3-mediated conformational changes. Gal4 chimeras containing the final 16, 35 or 44 amino acids of cTR alpha indicate that the conserved C-terminal region does not function as an independent transactivation domain. Our results are consistent with a model in which ligand plays a structural role to position the conserved C-terminal regions of cTR alpha and related receptors in a transcriptionally active conformation.
Selmi-Ruby
S
S
Division of Molecular Endocrinology, Department of Medicine, New York University Medical Center, NY 10016, USA.
Casanova
J
J
Malhotra
S
S
Roussett
B
B
Raaka
B M
BM
Samuels
H H
HH
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D014176:Protein Biosynthesis; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation; D014162:Transfection; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D014284:Triiodothyronine; D015500:Chloramphenicol O-Acetyltransferase