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Ishii H, Hattori Y, Ozawa H. Estrogen Receptor α Isoforms Generated by Alternative Use of Cryptic Exons. J NIPPON MED SCH 2023; 90:364-371. [PMID: 37558429 DOI: 10.1272/jnms.jnms.2023_90-507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/11/2023]
Abstract
Estrogen receptor α (ERα) regulates several physiological functions. In pathophysiological conditions, ERα is involved in the development and progression of estrogen-sensitive tumors. The ERα gene contains multiple 5'-untranslated exons and eight conventional coding exons and presents multiple isoforms generated by alternative promoter usage and alternative splicing. This gene also possesses non-conventional exons in the 3'- and intronic regions, and alternative use of cryptic exons contributes to further diversity of ERα mRNAs and proteins. Recently, the genomic organization of ERα genes and the splicing profiles of their transcripts were comparatively analyzed in humans, mice, and rats, and multiple ERα isoforms with distinct structures and functions were identified. These transcripts contain cryptic sequences that encode insertion-containing or truncated ERα proteins. In particular, alternative cryptic exons with in-frame stop codons yield transcripts encoding C-terminally-truncated ERα proteins. The C-terminally-truncated ERα isoforms lack part or all of the ligand-binding domain but possess an isoform-specific sequence. Some of these isoforms exhibit constitutive transactivation and resistance to estrogen receptor antagonists. Although numerous studies have reported conflicting results regarding their functions, the critical determinant for their gain-of-function has been identified structurally. Here we review recent progress in ERα variant research concerning the genomic organization of ERα genes, splicing profiles of ERα transcripts, and transactivation properties of ERα isoforms.
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Affiliation(s)
- Hirotaka Ishii
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
| | - Yujiro Hattori
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
| | - Hitoshi Ozawa
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
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Saito K, Dickey JE, Rodeghiero SR, Toth BA, Kelly MJ, Deng Y, Singh U, Deng G, Jiang J, Cui H. Hypomorphism of a Novel Long ERα Isoform Causes Severe Reproductive Dysfunctions in Female Mice. Endocrinology 2022; 163:6742225. [PMID: 36181426 DOI: 10.1210/endocr/bqac160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Indexed: 11/19/2022]
Abstract
Estrogen receptor alpha (ERα)-mediated estrogen signaling plays a pivotal role in both reproductive and nonreproductive functions. Transcriptional regulation of the ERα gene is highly complex, with multiple transcript variants being differentially produced across the tissues. However, tissue-specific variation and physiological specificity of the ERα variants are not yet fully understood. In an attempt to generate a Cre-dependently restorable ERα-null mouse for functional genetic studies, we unexpectedly produced ERα hypomorphic mice with biased downregulation of a previously unappreciated long ERα isoform that is enriched in the female reproductive organs (uterus and ovaries) and the pituitary but minimally expressed in the brain. Female homozygous mutant mice were capable of pregnancy but displayed irregular estrus cycle and rarely kept newborn pups alive. No significant morphological and pathological changes in reproductive system or disruption of body weight homeostasis were seen in female homozygous mutant mice. Collectively, our results define a tissue-specific enriched long ERα isoform and its preferential role in female reproductive function rather than body weight homeostasis.
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Affiliation(s)
- Kenji Saito
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Jacob E Dickey
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Samuel R Rodeghiero
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Brandon A Toth
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Matthew J Kelly
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Yue Deng
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Uday Singh
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Guorui Deng
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Jingwei Jiang
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
| | - Huxing Cui
- Department of Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
- Iowa Neuroscience Institute, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
- F.O.E. Diabetes Research Center, University of Iowa Carver College of Medicine, Iowa City, IA 52241, USA
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Ishii H, Hattori Y, Ozawa H. Identification of Novel C-Terminally Truncated Estrogen Receptor β Variant Transcripts and Their Distribution in Humans. J NIPPON MED SCH 2021; 88:54-62. [DOI: 10.1272/jnms.jnms.2021_88-105] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Hirotaka Ishii
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
| | - Yujiro Hattori
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
| | - Hitoshi Ozawa
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School
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Ishii H, Hattori Y, Ozawa H. Identification of a novel C-terminally truncated estrogen receptor α variant (ERαi34) with constitutive transactivation and estrogen receptor antagonist resistance. Mol Cell Endocrinol 2020; 503:110693. [PMID: 31881246 DOI: 10.1016/j.mce.2019.110693] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Revised: 12/07/2019] [Accepted: 12/23/2019] [Indexed: 11/20/2022]
Abstract
Constitutively active estrogen receptor α (ERα) variants with C-terminal truncation are candidate molecules for gain of both endocrine- and chemotherapy-resistance in estrogen-sensitive tumors. Our previous reports using artificially truncated ERα constructs demonstrated that ERα variants encoded in 1-2-3-cryptic exon- and 1-2-3-4-cryptic exon-types of transcripts have potentials to display constitutive transactivation of an estrogen response element reporter. However, naturally occurring 1-2-3-cryptic exon-type ERα variants have not been cloned yet. Therefore, the present study was designed to identify naturally occurring ERα variants encoded in 1-2-3-cryptic exon-type ERα transcripts. We cloned a novel C-terminally truncated ERα variant (ERαi34) encoded in a 1-2-3-i34 transcript from MCF-7 cells and characterized its constitutive and ER antagonist-resistant transactivation in transfected cells. Stable transfection of the variant into MCF-7 cells augmented basal cell proliferation insensitive to fulvestrant. Collectively, we validated the structure-based mechanisms underlying constitutive and ER antagonist-resistant transactivation by C-terminally truncated ERα variants.
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Affiliation(s)
- Hirotaka Ishii
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan.
| | - Yujiro Hattori
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan.
| | - Hitoshi Ozawa
- Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan.
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Applicability of Anti-Human Estrogen Receptor β Antibody PPZ0506 for the Immunodetection of Rodent Estrogen Receptor β Proteins. Int J Mol Sci 2019; 20:ijms20246312. [PMID: 31847265 PMCID: PMC6941125 DOI: 10.3390/ijms20246312] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/06/2019] [Accepted: 12/11/2019] [Indexed: 12/12/2022] Open
Abstract
Several lines of controversial evidence concerning estrogen receptor β (ERβ) remain to be solved because of the unavailability of specific antibodies against ERβ. The recent validation analysis identified a monoclonal antibody (PPZ0506) with sufficient specificity against human ERβ. However, the specificity and cross-reactivity of PPZ0506 antibody against ERβ proteins from laboratory animals have not been confirmed. In the present study, we aimed to validate the applicability of PPZ0506 to rodent studies. The antibody exhibited specific cross-reactivity against mouse and rat ERβ proteins in immunoblot and immunocytochemical experiments using transfected cells. In immunohistochemistry for rat tissue sections, PPZ0506 showed immunoreactive signals in the ovary, prostate, and brain. These immunohistochemical profiles of rat ERβ proteins in rat tissues accord well with its mRNA expression patterns. Although the antibody was reported to show the moderate signals in human testis, no immunoreactive signals were observed in rat testis. Subsequent RT-PCR analysis revealed that this species difference in ERβ expression resulted from different expression profiles related to the alternative promoter usage between humans and rats. In conclusion, we confirmed applicability of PPZ0506 for rodent ERβ studies, and our results provide a fundamental basis for further examination of ERβ functions.
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Meitzen J, Britson KA, Tuomela K, Mermelstein PG. The expression of select genes necessary for membrane-associated estrogen receptor signaling differ by sex in adult rat hippocampus. Steroids 2019; 142:21-27. [PMID: 28962849 PMCID: PMC5874170 DOI: 10.1016/j.steroids.2017.09.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 09/14/2017] [Accepted: 09/22/2017] [Indexed: 12/21/2022]
Abstract
17β-estradiol can rapidly modulate neuron function via membrane estrogen receptors (ERs) in a sex-specific manner. For example, female rat hippocampal neurons express palmitoylated versions of ERα and ERβ that associate with the plasma membrane. These membrane-associated ERs are organized by caveolin proteins into functional signaling microdomains with metabotropic glutamate receptors (mGluRs). ER/mGluR signaling mediates several sex-specific estradiol actions on hippocampal neuron function. An important unanswered question regards the mechanism by which sex-specific membrane-associated ER signaling is generated, especially since it has been previously demonstrated that mGluR action is not sex-specific. One possibility is that the genes necessary for the ER membrane complex are differentially expressed between males and females, including genes that encode ERα and β, caveolin 1 and 3, and/or the palmitoylacyltransferases DHHC-7 and -21. Thus we used qPCR to test the hypothesis that these genes show sex differences in expression in neonatal and adult rat hippocampus. As an additional control we tested the expression of the 20 other DHHC palmitoylacyltransferases with no known connections to ER. In neonatal hippocampus, no sex differences were detected in gene expression. In adult hippocampus, the genes that encode caveolin 1 and DHHC-7 showed decreased expression in females compared to males. Thus, select genes differ by sex at specific developmental stages, arguing for a more nuanced model than simple widespread perinatal emergence of sex differences in all genes enabling sex-specific estradiol action. These findings enable the generation of new hypotheses regarding the mechanisms by which sex differences in membrane-associated ER signaling are programmed.
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Affiliation(s)
- John Meitzen
- Dept. of Biological Sciences, North Carolina State University, Raleigh, NC, United States; W.M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, United States; Center for Human Health and the Environment, North Carolina State University, Raleigh, NC, United States; Comparative Medicine Institute, North Carolina State University, Raleigh, NC, United States.
| | - Kyla A Britson
- Cellular and Molecular Medicine Graduate Program, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Krista Tuomela
- Medical College of Wisconsin, Milwaukee, WI, United States
| | - Paul G Mermelstein
- Dept. of Neuroscience, University of Minnesota, Minneapolis, MN, United States
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Frankl-Vilches C, Gahr M. Androgen and estrogen sensitivity of bird song: a comparative view on gene regulatory levels. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2018; 204:113-126. [PMID: 29209770 PMCID: PMC5790841 DOI: 10.1007/s00359-017-1236-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 11/02/2017] [Accepted: 11/09/2017] [Indexed: 12/16/2022]
Abstract
Singing of songbirds is sensitive to testosterone and its androgenic and estrogenic metabolites in a species-specific way. The hormonal effects on song pattern are likely mediated by androgen receptors (AR) and estrogen receptor alpha (ERα), ligand activated transcription factors that are expressed in neurons of various areas of the songbirds' vocal control circuit. The distribution of AR in this circuit is rather similar between species while that of ERα is species variant and concerns a key vocal control area, the HVC (proper name). We discuss the regulation of the expression of the cognate AR and ERα and putative splice variants. In particular, we suggest that transcription factor binding sites in the promoter of these receptors differ between bird species. Further, we suggest that AR- and ERα-dependent gene regulation in vocal areas differs between species due to species-specific DNA binding sites of putative target genes that are required for the transcriptional activity of the receptors. We suggest that species differences in the distribution of AR and ERα in vocal areas and in the genomic sensitivity to these receptors contribute to species-specific hormonal regulation of the song.
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Affiliation(s)
- Carolina Frankl-Vilches
- Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, 82319, Seewiesen, Germany
| | - Manfred Gahr
- Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, 82319, Seewiesen, Germany.
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