Modulation of Coactivator Recruitment by Cooperative Ligand Binding to Human Estrogen Receptor .ALPHA. and .BETA.

Abstract

Estrogen receptor (ER) is a member of the nuclear receptor superfamily, and functions as a ligand-dependent transcription factor with roles in cell growth and differentiation. In addition to endogenous estrogen, 17b bestradiol (E 2 ) and artificial antagonists, many suspected environmental estrogenic chemicals are reported to bind to ER, with various affinities and transcriptional responses. ER is also an allosteric protein and shows a positive cooperative interaction with E 2 . Cooperativity affects inter-subunit interaction, and while ligand-bound ER interacts with coactivators, antagonist-bound ER does not. We therefore hypothesized that ligand-binding characteristics influence coactivator recruitment to the ER dimer, and thereby affect transcriptional activity. We investigated the interaction between ER and human Steroid Receptor Coactivator-1 (SRC-1), in the presence of compounds exhibiting various Hill coefficients. In the case of both ER subtypes (ERa a and ERb b), the Hill coefficients of the compounds tested correlated with the affinity of the ER-ligand complex to SRC-1, with the exception of ERb b-4-n-nonylphenol and ER-antagonist complexes. This is the first report to investigate the relationship between Hill coefficients of ligand binding and coactivator interaction with the ER-ligand complex. We also examined the proteolytic digestion of ER using trypsin, in the presence and absence of compounds with various Hill coefficients, to investigate ligand-dependent conformational changes in ER. We used not only agonists and antagonists but also compounds of weak biological activity (partial agonists). Our results shed light on the subtle modulation of transcriptional activation by chemical agents.

Differential recruitment of co-regulatory proteins to the human estrogen receptor 1 in response to xenoestrogens

“…Conversely, GEN weakly induced SRC-1(4) interaction with the ER, but this relation was not induced by E2. These results are not in complete agreement with a previous report where the complete RID of SRC-1 was recruited to ESR1 by GEN and BPA with K d values of 21 nM and 104 nM, respectively (Suzuki et al, 2007). Perhaps differential sensitivity between the assays may account for this discrepancy.…”

“…A number of studies have addressed the potential role of differential recruitment of co-regulatory proteins to explain ligand and cell type-specific effects of E2 by focusing on the p160 family of coactivators, specifically SRCs (SRC-1,-2,-3) (Chang et al, 1999a; Mc Ilroy et al, 2006; Suzuki et al, 2007). Fewer studies have focused on the role of these coactivators in ligand-specific transcriptional activation by ESR1, particularly with respect to differential cellular responses to xenoestrogens.…”

Engineering Bacterial Transcription Regulation To Create a Synthetic in Vitro Two-Hybrid System for Protein Interaction Assays

“…The data are consistent with the activities of these compounds as the only known antagonists of the ERα/NCOA1 interaction in the 67-compound library. , Since the hybrid fusion proteins were synthesized during the IVT2H assay, the concentrations of ERα LBD and NCOA1 RID started at zero and increased to an estimated micromolar range at the end of the IVT2H reactions (Figure S5, Supporting Information). This could explain that higher IC 50 values were obtained in the IVT2H assays than those of biochemical inhibition assays in which the protein concentrations are often fixed at a low nanomolar range . Nevertheless, the rank order of inhibition observed in the IVT2H assay for these compounds seemed to be consistent with other assays (Figure B). , …”

Ligand-Induced Allosteric Effects Governing SR Signaling

“…However, these combined differences introduce distinct shapes and properties into the ligand binding pocket, causing the same ligand to drive differential biological outcomes based on the receptor subtypes. For example, (R,R)-5,11-cis-diethyl-5,6,11,12tetrahydrochrysene-2,8-diol (THC) is a partial agonist for ER but antagonist for ER [92,93].…”