Titration by estrogen receptor activation function-2 of targets that are downstream from coactivators.
Cross-interference (squelching) among nuclear receptors has been proposed to reflect the titration of coactivators that bind the receptors in a hormone-dependent manner. We have tested whether the coactivators are the only target titrated during squelching of one receptor by another, or whether proteins needed for coactivator function are titrated as well. That the coactivators are indeed one target of squelching is apparent. The isolated ligand-binding domain of the estrogen receptor (ER-LBD) squelches transcriptional activation by the thyroid hormone receptor (TR) only when the LBD is bound to ligands that promote coactivator interactions and only when regions of the LBD that promote coactivator interactions are undisturbed. Furthermore, the ER-LBD and the TR compete in vitro for the related p160 coactivators, SRC1a and GRIP1 (glucocorticoid receptor interacting protein 1), or the putative corepressor, RIP140. Finally TR action becomes more potent when coactivator levels are raised. Nonetheless, supplying excess SRC1a or GRIP1 does not abolish squelching by the ER. In fact, squelching becomes even more severe when coactivators are abundant. Supplying combinations of coactivators from the p160 class and the CREB-binding protein (CBP)/p300 class makes squelching most severe. Elevated RIP140 inhibits TR action, but also protects the residual TR action from squelching by the ER-LBD. We conclude that ER-LBD squelches TR both by titrating p160-CBP coactivators and additionally by cooperating with the coactivators to titrate a second factor. The second factor would be needed by the TR for coactivator-mediated transcriptional stimulation.
Lopez
G N
GN
Metabolic Research Unit, University of California, San Francisco 94143, USA.
Webb
P
P
Shinsako
J H
JH
Baxter
J D
JD
Greene
G L
GL
Kushner
P J
PJ
D048868:Adaptor Proteins, Signal Transducing; D001667:Binding, Competitive; D050882:CREB-Binding Protein; D002352:Carrier Proteins / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D051548:Histone Acetyltransferases; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056920:Nuclear Receptor Coactivator 1; D051958:Nuclear Receptor Coactivator 2; D000078723:Nuclear Receptor Interacting Protein 1; D029543:Nucleocytoplasmic Transport Proteins; D016601:RNA-Binding Proteins; D011960:Receptors, Estrogen / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013629:Tamoxifen / Q000378:metabolism / Q000494:pharmacology; D017186:Titrimetry; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C491719:MYBBP1A protein, human; C498001:NCOA2 protein, human; C000627127:NRIP1 protein, human; D009687:Nuclear Proteins; D051958:Nuclear Receptor Coactivator 2; D000078723:Nuclear Receptor Interacting Protein 1; D029543:Nucleocytoplasmic Transport Proteins; D016601:RNA-Binding Proteins; D011960:Receptors, Estrogen; D011965:Receptors, Glucocorticoid; D011980:Receptors, Progesterone; D011988:Receptors, Thyroid Hormone; D011994:Recombinant Proteins; D015534:Trans-Activators; D035581:Transcription Factor TFIIB; D014157:Transcription Factors; D014284:Triiodothyronine; D013629:Tamoxifen; D004958:Estradiol; D015500:Chloramphenicol O-Acetyltransferase; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; D056920:Nuclear Receptor Coactivator 1