Single-Chain Estrogen Receptors (ERs) Reveal that the ER / Heterodimer Emulates Functions of the ER Dimer in Genomic Estrogen Signaling Pathways

Department of Biochemistry and Biophysics , University of Rochester, Rochester, New York, United States
Molecular and Cellular Biology (Impact Factor: 4.78). 10/2004; 24(17):7681-94. DOI: 10.1128/MCB.24.17.7681-7694.2004
Source: PubMed


The effects of estrogens, particularly 17beta-estradiol (E2), are mediated by estrogen receptor alpha (ERalpha) and ERbeta. Upon binding to E2, ERs homo- and heterodimerize when coexpressed. The ER dimer then regulates the transcription of target genes through estrogen responsive element (ERE)-dependent and -independent pathways that constitute genomic estrogen signaling. Although ERalpha and ERbeta have similar ERE and E2 binding properties, they display different transregulatory capacities in both ERE-dependent and -independent signaling pathways. It is therefore likely that the heterodimerization provides novel functions to ERs by combining distinct properties of the contributing partners. The elucidation of the role of the ER heterodimer is critical for the understanding of physiology and pathophysiology of E2 signaling. However, differentially determining target gene responses during cosynthesis of ER subtypes is difficult, since dimers formed are a heterogeneous population of homo- and heterodimers. To circumvent the pivotal dimerization step in ER action and hence produce a homogeneous ER heterodimer population, we utilized a genetic fusion strategy. We joined the cDNAs of ERalpha and/or ERbeta to produce single-chain ERs to simulate the ER homo- and heterodimers. The fusion ERs interacted with ERE and E2 in a manner similar to that observed with the ER dimers. The homofusion receptors mimicked the functions of the parent ER dimers in the ERE-dependent and -independent pathways in transfected mammalian cells, whereas heterofusion receptors emulated the transregulatory properties of the ERalpha dimer. These results suggest that ERalpha is the functionally dominant partner in the ERalpha/beta heterodimer.

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Available from: Jing Huang
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    • "Transient transfections for simulated ERE-dependent and ERE-independent pathways were accomplished as described previously (Yi et al. 2002a, Huang et al. 2004, Li et al. 2004). Transfected cells were treated without or with 10 K9 M E 2 in the absence or presence of 10 K7 M 4HT and/or 10 K7 M ICI for 24 h to examine the effects of ligands on ER-mediated transcriptional responses from the ERE-dependent and EREindependent signaling pathways. "
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    ABSTRACT: 17β-estradiol (E2) plays important roles in functions of many tissues. E2 effects are mediated by estrogen receptor (ER) α and β. ERs regulate transcriptions through estrogen responsive element (ERE)-dependent and ERE-independent modes of action. ER binding to ERE constitutes the basis of the ERE-dependent pathway. Direct/indirect ER interactions with transcription complexes define the ERE-independent signaling. ERs share functional features. Ligand-bound ERs nevertheless induce distinct transcription profiles. Live cell imaging indicates a dynamic nature of gene expressions by highly mobile ERs. However, the relative contribution of ER mobility at the ERE-independent pathway to the overall kinetics of ER mobility remains undefined. We used fluorescent recovery after photo-bleaching (FRAP) approach to assess the ligand-mediated mobilities ERE binding-defective ERs, EREBD. The decrease in ERα mobility with E2 or the selective ER modulator 4-hydroxyl-tamoxifen (4HT) was largely due to the interaction of the receptor with ERE. Thus, ERα bound to E2 or 4HT mediates transcriptions from the ERE-independent pathway with remarkably fast kinetics that contributes fractionally to the overall motility of the receptor. The antagonist ICI 182,780 immobilized ERαs. The mobilities of ERβ and ERβEBD in the presence of ligands were indistinguishable kinetically. Thus, ERβ mobility is independent of the nature of ligands and the mode of interaction with target sites. Chimeric ERs indicated that the carboxyl-termini are critical regions for the subtype-specific mobility. Therefore, while ERs are highly mobile molecules interacting with target sites with fast kinetics, an indication of the hit-and-run model of transcription, they differ mechanistically to modulate transcriptions.
    Full-text · Article · Sep 2012 · Journal of Molecular Endocrinology
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    • "Each of these forms is encoded by a separate gene (ESR1 and ESR2, respectively). Hormone-activated estrogen receptors form dimers and since the two forms are coexpressed in many cell types, the receptors may form ERα (αα) or ERβ (ββ) homodimers or ERαβ (αβ) heterodimers (Li X et al. 2004) [1] Estrogen receptor alpha and beta show significant overall sequence homology and both are composed of five domains. "

    Full-text · Article · Apr 2012
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    • "The ERE-tk81-luc, constructed by inserting the fragment of the herpes simplex thymidine kinase promoter and two copies of the vitellogenin estrogen response element (ERE) into pA3luc was a gift from Dr. Larry Jameson [22], expression vetors for ERα was received from Dr. Pierre Chambon [23]. The hERβ expression vector was kindly provided by Dr. Mesut Muyan [24]. "
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    ABSTRACT: Ginseng has been used as a traditional medicine for treatment of many diseases and for general health maintenance in people of all ages. Ginseng is also used to ameliorate menopausal systems. We investigated the estrogenic activity of Korean red ginseng (KRG) in a transient transfection system, using estrogen receptor (ER) and estrogen-responsive luciferase plasmids in MCF-7 cells. The extract activated both ERα and ERβ. KRG modulated the mRNA levels of estrogen-responsive genes such as pS2 and ESR1 and decreased the protein level of ERα. In order to examine in vivo estrogenic activity of KRG, sixteen female Sprague-Dawley rats separated into four groups were studied for nine weeks: non-ovariectomized (OVX) rats treated with olive oil, OVX rats treated with olive oil, OVX rats treated with 17-β-estradiol (E2) in olive oil, and OVX rats treated with KRG extract in olive oil. The experiments were repeated for three times and the data of twelve rats were combined. Body weight of OVX rats was greater than that of sham-operated control rats and was decreased by E2 treatment. Uterine weight increased after E2 treatment compared to OVX rats. However, no difference in body or uterine weight was observed with KRG intake. KRG induced reductions in total cholesterol, low density lipoprotein cholesterol/total cholesterol, high density lipoprotein cholesterol/total cholesterol, and low density lipoprotein cholesterol/high density lipoprotein cholesterol, but not to the same degree as did E2 intake. These results show that KRG does contain estrogenic activity as manifested by in vitro study but the activity is not strong enough to elicit physiological responses.
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