title: The AF-1-deficient estrogen receptor ERα46 isoform is frequently expressed in human breast tumors.
abstract: To date, all studies conducted on breast cancer diagnosis have focused on the expression of the full-length 66-kDa estrogen receptor alpha (ERα66). However, much less attention has been paid to a shorter 46-kDa isoform (ERα46), devoid of the N-terminal region containing the transactivation function AF-1. Here, we investigated the expression levels of ERα46 in breast tumors in relation to tumor grade and size, and examined the mechanism of its generation and its specificities of coregulatory binding and its functional activities.
  
  
  
  Using approaches combining immunohistochemistry, Western blotting, and proteomics, antibodies allowing ERα46 detection were identified and the expression levels of ERα46 were quantified in 116 ERα-positive human breast tumors. ERα46 expression upon cellular stress was studied, and coregulator bindings, transcriptional, and proliferative response were determined to both ERα isoforms.
  
  
  
  ERα46 was expressed in over 70% of breast tumors at variable levels which sometimes were more abundant than ERα66, especially in differentiated, lower-grade, and smaller-sized tumors. We also found that ERα46 can be generated via internal ribosome entry site-mediated translation in the context of endoplasmic reticulum stress. The binding affinities of both unliganded and fully-activated receptors towards co-regulator peptides revealed that the respective potencies of ERα46 and ERα66 differ significantly, contributing to the differential transcriptional activity of target genes to 17β estradiol (E2). Finally, increasing amounts of ERα46 decrease the proliferation rate of MCF7 tumor cells in response to E2.
  
  
  
  We found that, besides the full-length ERα66, the overlooked ERα46 isoform is also expressed in a majority of breast tumors. This finding highlights the importance of the choice of antibodies used for the diagnosis of breast cancer, which are able or not to detect the ERα46 isoform. In addition, since the function of both ERα isoforms differs, this work underlines the need to develop new technologies in order to discriminate ERα66 and ERα46 expression in breast cancer diagnosis which could have potential clinical relevance.
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France.|Pôle IUC Oncopole CHU, Institut Universitaire du Cancer de Toulouse - Oncopole, 1 avenue Irène Joliot-Curie, 31059, Toulouse cedex 9, France.
authors.forename: Elodie
authors.initials: E
authors.lastname: Chantalat
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Boudou
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France.
authors.forename: Henrik
authors.initials: H
authors.lastname: Laurell
authors.affiliation: UMR CNRS 6290, Institut de Genétique et Développement de Rennes, Equipe SP@RTE, Rennes, 35042 Cedex, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Palierne
authors.affiliation: PamGene International B.V, P.O. Box 1345, 5200, BJ, 's-Hertogenbosch, The Netherlands.
authors.forename: René
authors.initials: R
authors.lastname: Houtman
authors.affiliation: PamGene International B.V, P.O. Box 1345, 5200, BJ, 's-Hertogenbosch, The Netherlands.
authors.forename: Diana
authors.initials: D
authors.lastname: Melchers
authors.affiliation: Pôle IUC Oncopole CHU, Institut Universitaire du Cancer de Toulouse - Oncopole, 1 avenue Irène Joliot-Curie, 31059, Toulouse cedex 9, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Rochaix
authors.affiliation: Pôle IUC Oncopole CHU, Institut Universitaire du Cancer de Toulouse - Oncopole, 1 avenue Irène Joliot-Curie, 31059, Toulouse cedex 9, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Filleron
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Stella
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France.
authors.forename: Odile
authors.initials: O
authors.lastname: Burlet-Schiltz
authors.affiliation: Pôle IUC Oncopole CHU, Institut Universitaire du Cancer de Toulouse - Oncopole, 1 avenue Irène Joliot-Curie, 31059, Toulouse cedex 9, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Brouchet
authors.affiliation: INSERM U1085, IRSET (Institut de Recherche en Santé, Environnement et Travail), Université de Rennes 1, 35000, Rennes, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Flouriot
authors.affiliation: UMR CNRS 6290, Institut de Genétique et Développement de Rennes, Equipe SP@RTE, Rennes, 35042 Cedex, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Métivier
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Arnal
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France.
authors.forename: Coralie
authors.initials: C
authors.lastname: Fontaine
authors.affiliation: INSERM U1048, Institut des Maladies Métaboliques et Cardiovasculaires, Université de Toulouse, BP 84225, 31 432, Toulouse cedex 04, France. francoise.lenfant@inserm.fr.
authors.forename: Françoise
authors.identifier: 0000-0003-0024-7241
authors.initials: F
authors.lastname: Lenfant
mesh_terms: D017398:Alternative Splicing; D001943:Breast Neoplasms / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D016000:Cluster Analysis; D059865:Endoplasmic Reticulum Stress; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000235:genetics* / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D011485:Protein Binding; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D020543:Proteome; D040901:Proteomics / Q000379:methods; D012189:Retrospective Studies
chemical_list: C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D020033:Protein Isoforms; D020543:Proteome; D004958:Estradiol
keywords: Activation function; Breast cancer; Diagnosis; Estrogen receptor ERα; Internal ribosomal entry site; Isoforms