Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Exacerbation of SLE by activation of estrogen receptor||MolecularInitiatingEvent|
|Homo sapiens||Homo sapiens||High||NCBI|
|Mus musculus||Mus musculus||High||NCBI|
|All life stages||High|
Key Event Description
Estrogen receptor alpha (ERα) was discovered in the late 1960s and was cloned and characterized in 1985 (Melissa C. 2011). ERα and ERβ show a high degree of similarity when compared at the amino acid level (Dahlman-Wright K. 2006). 17β-estradiol (E2) activates ERα and ERβ with the same affinity although they share only 56% similarity in their ligand binding domains (Monroe DG. 2005, Papoutsi Z. 2009). The hormone binding domain of the estrogen receptor is required not only for binding estradiol but also to form stable homodimers of the protein and mediate transcriptional activation by the receptor. A direct genomic interaction occurs between the estrogen receptor (ER) ligand complex and specific sequences of DNA known as estrogen response elements (ERE). (Parker MG. 1993, Goldstein RA. 1993, Sasson S. 1991, Brandt ME. 1997). Transcriptional activation by ERα is mediated by two distinct activation functions: the constitutively active AF-1 domain, located in the N-terminal domain of the receptor protein, and the ligand-dependent AF-2 domain, located in the C-terminal domain of the receptor protein (Delaunay F. 2000). In addition to above classical mechanism, ERα is also able to play roles both in ER binding and transcriptional activation; phosphorylation of ER and other proteins involved in transcriptional activation with cellular amounts of coactivators and adaptor proteins (Carolyn MK. 2001).
ERs are expressed in a variety of immunocompetent cells, including CD4+ (Th1, Th2, Th17, and Tregs) and CD8+ cells and macrophages (Salem ML. 2004, Robinson DP. 2014). One recent study examined ERα expression in resting and activated PBMC subsets and found that ERα was expressed at higher levels in CD4+ T cells than B cells (Melissa C. 2011).
How It Is Measured or Detected
Recombinant human estrogen receptor hormone-binding domain (HBD) fragment is isolated from Escherichia coli. Purified HBD peptide is assayed for their ability to bind estradiol, [3H] estradiol binding using low concentrations (0.15 nM), by Radioreceptor Assay. Moreover HBD dimer dissociation is measured using size exclusion chromatography (Brandt ME. 1997).
On the other hand, a conditionally active form of STAT (the signal transducers and activator of transcription) 6 by fusing the HBD of a modified form of the mouse estrogen receptor (ER) gene is prepared as STAT6-ER fusion protein (STAT6:ER). 4-Hydroxytamoxifen (4-HT), estrogen analogue, (Research Biochemicals Institute, Natick, MA) was used to activate STAT6 fusion protein. M12.4.1 cells, transfected with the luciferase reporter gene by inserting three copies of human STAT6 binding site oligonucleotide, are used nuclear extracts and electrophoretic mobility shift assay (EMSA) with 1 μM 4HT. STAT6:ER DNA-binding activity is strongly and rapidly (within 1 hr) induced after addition of 4HT to these cells. BA/F3 cells prepared as the same manner are stimulated with 1 μM 4HT for 24 h at 37°C. The cells were harvested and assayed for luciferase activities using a Luciferase Assay Kit (Promega, Madison, WI). (Kamogawa et al. 1998).
Domain of Applicability
ERα is mainly expressed in uterus, prostate (stroma), ovary (theca cells), testes (Leydig cells), epididymis, bone, breast, various regions of the brain, liver, and white adipose tissue (Dahlman-Wright K. 2006). ERs is widely expressed in most tissue types including most immune cells (Couse JF. 1997). ERα and ERβ show a high degree of similarity when compered at the amino acid level (Dahlman-Wright K. 2006). Interspecies sequence identities for the entire ERα receptor are 88.5% (human-mouse), 87.5% (human-rat), and 97.5% (mouse-rat). For the ligand binding domain (ERα-LBD) alone, the interspecies sequence identities are 95.5% (human-mouse), 95.1% (human-rat), and 99.2% (mouse-rat) (White R. 1987). ERα is found in female reproductive organs, yet is robustly expressed in kidney, liver, heart, and lungs in males and females, as well as on most immune cells (Chelsea C. 2017).
Evidence for Perturbation by Stressor
Overview for Molecular Initiating Event
- Melissa, C. and Gary, G (2011). Estrogen Receptors in Immunity and Autoimmunity. Clinical Reviews in Allergy & Immunology 40:66-73.
- Dahlman-Wright, K., Cavailles, V., Fuqua, S. A., Jordan, V. C., Katzenellenbogen, J. A., Korach, K. S., Maggi, A., Muramatsu, M., Parker M. G. and Jan-Åke, G. (2006). International Union of Pharmacology. LXIV. Estrogen Receptors. Pharmacological Review 58: 773-781.
- Monroe DG, Secreto FJ, Subramaniam M, Getz BJ, Khosla S, Spelsberg TC. Estrogen receptor alpha and beta heterodimers exert unique effects on estrogen- and tamoxifen-dependent gene expression in human U2OS osteosarcoma cells. Molecular endocrinology (Baltimore, Md). 2005; 19:1555–1568.
- Papoutsi Z, Zhao C, Putnik M, Gustafsson JA, Dahlman-Wright K. Binding of estrogen receptor alpha/beta heterodimers to chromatin in MCF-7 cells. J Mol Endocrinol. 2009; 43:65–72.
- Parker MG, Arbuckle N, Dauvois S, Danielian P, White R. Structure and function of the estrogen receptor. Ann N Y Acad Sci. 1993. 684:119-26.
- Goldstein RA, Katzenellenbogen JA, Wolynes PG, et al. Three-dimensional model for the hormone binding domains of steroid receptors. Proc Natl Acad Sci. 1993;90(21):9949-53.
- Sasson S. Equilibrium binding analysis of estrogen agonists and antagonists: relation to the activation of the estrogen receptor. Pathol Biol (Paris). 1991;39(1):59-69.
- Brandt ME, Vickery LE. Cooperativity and dimerization of recombinant human estrogen receptor hormone-binding domain. J Biol Chem. 1997;272(8):4843-9.
- Delaunay, F., Pettersson, K., Tujague, M., and Gustafsson, J. A. (2000). Functional Differences between the Amino-Terminal Domains of Estrogen Receptors α and β. Molecular Pharmacology 58: 584-590.
- Carolyn MK. Estrogen receptor interaction with estrogen response elements. Nucleic Acids Res. 2001 Jul 15; 29(14): 2905–2919.
- Salem M. L. (2004). Estrogen, a double-edged sword: modulation of TH1- and TH2-mediated inflammations by differential regulation of TH1/TH2 cytokine production. Current Drug Targets - Inflammation & Allergy 3(1): 97-104.
- Robinson, D. P., Hall, O. J., Nilles, T. L., Bream, J.H. and Klein, S.L. (2014). 17β-estradiol protects females against influenza by recruiting neutrophils and increasing virus-specific CD8 T cell responses in the lungs. Journal of Virology 88 (9): 4711-4720.
- Kamogawa, Y., Lee, H.J., Johnston, J.A., McMahon, M., O’Garra, A., and Arai, N. (1998). Cutting Edge: A conditionally active form of STAT6 can mimic certain effects of IL-4. J. Immunol. 161, 1074–1077.
- Couse JF, Lindzey J, Grandien K, Gustafsson JA, Korach KS. (1997) Tissue distribution and quantitative analysis of estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta) messenger ribonucleic acid in the wild-type and ERalphaknockout mouse. Endocrinology 138(11):4613–4621.
- White, R., Lees, JA., Needham, M., Ham, J. and Parker, M. (1987). Structural Organization and Expression of the Mouse Estrogen Receptor. Molecular Endocrinology 1 (10): 735–744.
- Chelsea, C., Neelakshi, R., J., Matteo C., Michael, M., x. and Roberto C. (2017). Estrogen Receptor a Signaling Exacerbates Immune-Mediated Nephropathies through Alteration of Metabolic Activity. The Journal of Immunology 200:512-522