Oestrogen Receptor α AF-1 and AF-2 Domains Have Cell
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ARTICLE DOI: 10.1038/s41467-018-07175-0 OPEN Oestrogen receptor α AF-1 and AF-2 domains have cell population-specific functions in the mammary epithelium Stéphanie Cagnet1, Dalya Ataca 1, George Sflomos1, Patrick Aouad1, Sonia Schuepbach-Mallepell2, Henry Hugues3, Andrée Krust4, Ayyakkannu Ayyanan1, Valentina Scabia1 & Cathrin Brisken 1 α α 1234567890():,; Oestrogen receptor (ER ) is a transcription factor with ligand-independent and ligand- dependent activation functions (AF)-1 and -2. Oestrogens control postnatal mammary gland development acting on a subset of mammary epithelial cells (MECs), termed sensor cells, which are ERα-positive by immunohistochemistry (IHC) and secrete paracrine factors, which stimulate ERα-negative responder cells. Here we show that deletion of AF-1 or AF-2 blocks pubertal ductal growth and subsequent development because both are required for expres- sion of essential paracrine mediators. Thirty percent of the luminal cells are ERα-negative by IHC but express Esr1 transcripts. This low level ERα expression through AF-2 is essential for cell expansion during puberty and growth-inhibitory during pregnancy. Cell-intrinsic ERα is not required for cell proliferation nor for secretory differentiation but controls transcript levels of cell motility and cell adhesion genes and a stem cell and epithelial mesenchymal transition (EMT) signature identifying ERα as a key regulator of mammary epithelial cell plasticity. 1 Swiss Institute for Experimental Cancer Research, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. 2 Department of Biochemistry, University of Lausanne, CH-1066 Epalinges, Switzerland. 3 Centre Hospitalier Universitaire Vaudois, Department of Laboratory Medecine, University Hospital of Lausanne, CH-1011 Lausanne, Switzerland. 4 Institut de Génétique et de Biologie Moléculaire et Cellulaire (CNRS UMR7104; INSERM U596; ULP, Collège de France) and Institut Clinique de la Souris, Illkirch, Strasbourg, France. These authors contributed equally: Stéphanie Cagnet, Dalya Ataca, George Sflomos. Correspondence and requests for materials should be addressed to C.B. (email: cathrin.brisken@epfl.ch) NATURE COMMUNICATIONS | (2018) 9:4723 | DOI: 10.1038/s41467-018-07175-0 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-07175-0 estrogens, 17β-estradiol (E2) and its metabolites, are extended beyond the sub-iliac lymph node to fill 61% of the fat Opivotal for the development and the physiology of the pad (Fig. 1b, c). In AF-10 and AF-20 littermates, no TEBs were breast and impinge on breast carcinogenesis. The oes- found and fat pad filling remained <3% (Fig. 1b, c). In adult, 8- to trogen receptor α (ERα) is expressed in 40% of the luminal cells 12-week-old WT females, fat pads were filled up to 80%, in their that make up the inner layer of the mammary epithelium sur- AF-10 and AF-20 littermates to 5.1% and 3% only, respectively rounded by basal/myoepithelial cells1. Oestrogens drive pubertal (Fig. 1c, Supplementary Figure 1b). In older WT females, which development in the mouse mammary gland and induce expres- have been exposed to repeated oestrous cycle related peaks of E2 sion of the progesterone receptor (PgR), activation of which and progesterone, side branching occurred (Supplementary Fig- drives cell proliferation during subsequent oestrous cycling and ure 1c, d; Fig. 1c) whereas the block of ductal growth persisted in pregnancy. Both hormones rely on paracrine factors to activate AF-20 females (Supplementary Figure 1b, c) as observed in stem cells and induce proliferation of other mammary epithelial ERα−/− females16. In older AF-10 females, few ducts occasionally cells (MECs)2. extended beyond the lymph node (Supplementary Figure 1c, d, The ERα belongs to the nuclear receptor family and is com- Fig. 1c). Mutant ducts were atrophic with decreased ductal dia- posed of six modular domains, namely, A to F3. Ligand- meters (Supplementary Figure 1c, d) but structurally intact with independent and ligand-dependent activation functions, AF-1 luminal and basal cell layers as revealed by histological analysis and AF-2 map to the A/B and E domains, respectively4,5. Ligand- (Supplementary Figure 1e). Immunohistochemistry (IHC) independent signalling results from phosphorylation of different revealed expression of ERα protein in AF-10 and AF-20 mammary serine residues in AF-1 by for instance MAPK6, GSK-37 or epithelia at levels comparable to WT controls (Fig. 1d), as cyclinA/cdk28. Upon activation, the receptor dimerises and reported for their uteri13,14. This excluded the possibility that the translocates to the nucleus where it interacts either directly with mutant ERα proteins were unstable and their expression in MECs the DNA via specific DNA sequences known as the oestrogen was reduced or lost. Thus, the phenotypes reflect the specific response elements, or indirectly via DNA-binding proteins like deletions of AF-1 or AF-2 domain and show that both are AP-19. Full ligand-dependent transcriptional activity relies on required for ERα function during ductal elongation. synergistic activities of AF-1 and AF-25. A small fraction of the ERα is found at the plasma membrane; it elicits rapid, non- Endocrine disturbances in AF-10 and AF-20 mice.AdultAF-10, genomic responses, which modulate multiple signalling pathways − − AF-20 and ERα / female mice were reported to have increased and create cross-talk between membrane and nuclear ERα10. serum levels of E2, luteinizing hormone and testosterone as mea- More than 70% of all breast cancers express the ERα and this is sured by radioimmunoassay17.Ourfinding that mammary gland exploited therapeutically. The most widely used agent, tamoxifen, development was already affected before puberty begged the ques- antagonises AF-211 and agonises AF-112, and is used in primary tion whether endocrine disturbances may occur earlier. As plasma and secondary breast cancer prevention. Most insights into the steroid hormone levels are very low prior to puberty, we used liquid molecular mechanisms underlying ERα signalling stem from chromatography tandem–mass spectrometry (LC–MS). We con- in vitro studies with ERα-positive (ERα+) breast cancer cell lines, firmed that both E2 and testosterone levels increased significantly in in particular MCF-7 cells which express very high levels of the all three mutants in adulthood. E2 was detected at levels of 12 pg/ml receptor and are exquisitely sensitive to E2. How ER signalling in plasma of WT females and increased almost 2-fold in AF-10 and occurs in vivo in normal and cancerous tissue is poorly under- − − threefold in AF-20 and ERα / females. Testosterone levels raised stood. To dissect the different aspects of ERα signalling in vivo, from on average 0.1 ng/ml in plasma of WT females to 0.7 ng/ml mice lacking specifically the AF-1 domain (AF-10)13 or the AF-2 − − plasma levels in AF-10, 1.5 ng/ml in AF-20 and 1.4 ng/ml in ERα / domain (ERαAF-20)14 were generated and compared to mice − − females (Fig. 2a). Plasma progesterone levels varied in WT females lacking the entire ERα (ERα / ); all three strains are viable but due to oestrous cycling not observed in the mutants in which have impaired reproductive functions, and distinct organ – ovarian cycles are not established. All three mutants had decreased defects13 15. The role of the AF-1 and the AF-2 domains in the − − 11-deoxycorticosterone levels while 17-OH-progesterone levels mammary epithelium was not analysed. Using ERα / mice, we − − were increased in ERα / females (Fig. 2a). have previously shown that ERα is required for ductal elongation Progesterone levels increased specifically in peripubertal AF-20 in the mammary epithelium16. females whereas androstenedione levels increased in peripubertal Here, we explore the role of AF-1 and AF-2 vs. intact ERα − − ERα / and pubertal AF-20 females (Fig. 2a). Testosterone was signalling in mammary gland development; we demonstrate dif- significantly increased in peripubertal AF-10 females. Hence, ferential roles that are dependent on cell type and/or ERα protein complex alterations of the endocrine milieu occurred already levels and uncover important functions of the ERα in apparently before and during puberty. ERα-luminal responder cells. An overall analysis of the average fold-changes in steroid levels in ERα mutants compared to WT and heterozygous littermates in Results relation to their biosynthetic pathways revealed comparable decrease of plasma levels of the progesterone derivatives, 11- Mammary gland development in ERαAF-10 and ERαAF-20 deoxycorticosterone and corticosterone, in all mutants in mice. To assess the impact of germ-line deletion of ERα ligand- adulthood (Fig. 2b). The levels of E2 and its precursors 17OH- dependent, AF-2, vs. ligand-independent, AF-1, genomic actions progesterone, androstenedione, and testosterone, were close to on mammary gland development, we analysed mammary glands − − WT levels in AF-10 mice but deviated similarly in ERα / and of AF-10 and AF-20 females and their respective WT littermates AF-20 females are in line with negative feedback loops of the E2 (Fig. 1a) at critical developmental stages using whole-mount biosynthetic pathway being regulated by ligand-dependent ER stereomicroscopy (Fig. 1b, Supplementary Figure 1a–d). Before activity. the onset of ovarian function, on postnatal day 21, all females had rudimentary ductal systems (Supplementary Figure 1a) with on average 4.7% fat pad filling in WT and <3% fat pad filling in