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Relationship: 2020


The title of the KER should clearly define the two KEs being considered and the sequential relationship between them (i.e., which is upstream and which is downstream). Consequently all KER titles take the form “upstream KE leads to downstream KE”.  More help

Binding to estrogen receptor (ER)-α leads to Induction of GATA3 expression

Upstream event
Upstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help
Downstream event
Downstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes. Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

This table is automatically generated upon addition of a KER to an AOP. All of the AOPs that are linked to this KER will automatically be listed in this subsection. Clicking on the name of the AOP in the table will bring you to the individual page for that AOP. More help
AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Binding to estrogen receptor (ER)-α in immune cells leading to exacerbation of systemic lupus erythematosus (SLE) adjacent Moderate Moderate Cataia Ives (send email) Under development: Not open for comment. Do not cite Under Development

Taxonomic Applicability

Select one or more structured terms that help to define the biological applicability domain of the KER. In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. Authors can indicate the relevant taxa for this KER in this subsection. The process is similar to what is described for KEs (see pages 30-31 and 37-38 of User Handbook) More help

Sex Applicability

Authors can indicate the relevant sex for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of the User Handbook). More help

Life Stage Applicability

Authors can indicate the relevant life stage for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of User Handbook). More help

Key Event Relationship Description

Provide a brief, descriptive summation of the KER. While the title itself is fairly descriptive, this section can provide details that aren’t inherent in the description of the KEs themselves (see page 39 of the User Handbook). This description section can be viewed as providing the increased specificity in the nature of upstream perturbation (KEupstream) that leads to a particular downstream perturbation (KEdownstream), while allowing the KE descriptions to remain generalised so they can be linked to different AOPs. The description is also intended to provide a concise overview for readers who may want a brief summation, without needing to read through the detailed support for the relationship (covered below). Careful attention should be taken to avoid reference to other KEs that are not part of this KER, other KERs or other AOPs. This will ensure that the KER is modular and can be used by other AOPs. More help

The hormone binding domain (HBD) of the ERα is required not only for binding ligand but also to form stable homodimers of the protein and mediate transcriptional activation by the receptor.  There are two ligand-dependent signaling pathway.  One is “classical” and the other is “tethered” pathway.  A direct genomic interaction occurs between the 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).  This is called “classical” signaling pathway.  In addition to above classical mechanism, ligand-activated ERα interact with other transcription factor complexes and bind to non-EREs by attaching to other transcription factors and not with ERE directly. (Carolyn MK. 2001).  This is also called “tethered” signaling pathway.  The transcription factors GATA3 and STAT6 are essential for the establishment and/or maintenance of these interactions (Spilianakis and Flavell, 2004).  In the tethered pathway, STAT6-ER fusion protein induce GATA-3 mRNA expression.  Furthermore, in mammary gland but not in immune cells, GATA3 and ERα regulate each other and, along with FOXA1, can nucleate a remodeling complex at heterochromatic enhancer regions of ERα target genes, leading to the opening and epigenetic marking of sites for active transcription (Eeckhoute J. 2007, Kong SL. 2011).  Alone, FOXA1 or ERα are not sufficient to fully open the chromatin, supporting a bona fide pioneer activity for GATA3 (Eeckhoute J. 2007, Kong SL. 2011).

Evidence Supporting this KER

Assembly and description of the scientific evidence supporting KERs in an AOP is an important step in the AOP development process that sets the stage for overall assessment of the AOP (see pages 49-56 of the User Handbook). To do this, biological plausibility, empirical support, and the current quantitative understanding of the KER are evaluated with regard to the predictive relationships/associations between defined pairs of KEs as a basis for considering WoE (page 55 of User Handbook). In addition, uncertainties and inconsistencies are considered. More help
Biological Plausibility
Define, in free text, the biological rationale for a connection between KEupstream and KEdownstream. What are the structural or functional relationships between the KEs? For example, there is a functional relationship between an enzyme’s activity and the product of a reaction it catalyses. Supporting references should be included. However, it is recognised that there may be cases where the biological relationship between two KEs is very well established, to the extent that it is widely accepted and consistently supported by so much literature that it is unnecessary and impractical to cite the relevant primary literature. Citation of review articles or other secondary sources, like text books, may be reasonable in such cases. The primary intent is to provide scientifically credible support for the structural and/or functional relationship between the pair of KEs if one is known. The description of biological plausibility can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured (see page 40 of the User Handbook for further information).   More help

STAT6-ER fusion protein (STAT6:ER) induce expression of GATA-3 mRNAs in presence of 4-Hydroxytamoxifen (4-HT), estrogen analogue (Kurata H. 1999, Zhu J. 2001).  Furthermore, A constitutively active form of Stat6 (STAT6VT) introduced GATA3 expression and resulted in both Th2 differentiation and enhanced cell expansion without IL-4 (Zhu J. 2001, Horiuchi S. 2011).  CD4 T cells from Stat6-knockout mice are not able to drive Th2 differentiation and cell expansion under ThN conditions with added IL-4 (Zhu J. 2001).  Therefore, it is considered that activated STAT6 after ligand-biniding to ERα induce GATA3 expression in immune cells.

Uncertainties and Inconsistencies
In addition to outlining the evidence supporting a particular linkage, it is also important to identify inconsistencies or uncertainties in the relationship. Additionally, while there are expected patterns of concordance that support a causal linkage between the KEs in the pair, it is also helpful to identify experimental details that may explain apparent deviations from the expected patterns of concordance. Identification of uncertainties and inconsistencies contribute to evaluation of the overall WoE supporting the AOPs that contain a given KER and to the identification of research gaps that warrant investigation (seep pages 41-42 of the User Handbook).Given that AOPs are intended to support regulatory applications, AOP developers should focus on those inconsistencies or gaps that would have a direct bearing or impact on the confidence in the KER and its use as a basis for inference or extrapolation in a regulatory setting. Uncertainties that may be of academic interest but would have little impact on regulatory application don’t need to be described. In general, this section details evidence that may raise questions regarding the overall validity and predictive utility of the KER (including consideration of both biological plausibility and empirical support). It also contributes along with several other elements to the overall evaluation of the WoE for the KER (see Section 4 of the User Handbook).  More help

The “tethered” pathway is confirmed indirectly using artificial STAT6-ER fusion protein but not endogenous STAT6.  It remains unknown whether the “classical” pathway is utilized after binding to ERα in immune cells.

Response-response Relationship
This subsection should be used to define sources of data that define the response-response relationships between the KEs. In particular, information regarding the general form of the relationship (e.g., linear, exponential, sigmoidal, threshold, etc.) should be captured if possible. If there are specific mathematical functions or computational models relevant to the KER in question that have been defined, those should also be cited and/or described where possible, along with information concerning the approximate range of certainty with which the state of the KEdownstream can be predicted based on the measured state of the KEupstream (i.e., can it be predicted within a factor of two, or within three orders of magnitude?). For example, a regression equation may reasonably describe the response-response relationship between the two KERs, but that relationship may have only been validated/tested in a single species under steady state exposure conditions. Those types of details would be useful to capture.  More help





This sub-section should be used to provide information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). This can be useful information both in terms of modelling the KER, as well as for analyzing the critical or dominant paths through an AOP network (e.g., identification of an AO that could kill an organism in a matter of hours will generally be of higher priority than other potential AOs that take weeks or months to develop). Identification of time-scale can also aid the assessment of temporal concordance. For example, for a KER that operates on a time-scale of days, measurement of both KEs after just hours of exposure in a short-term experiment could lead to incorrect conclusions regarding dose-response or temporal concordance if the time-scale of the upstream to downstream transition was not considered. More help


Known modulating factors
This sub-section presents information regarding modulating factors/variables known to alter the shape of the response-response function that describes the quantitative relationship between the two KEs (for example, an iodine deficient diet causes a significant increase in the slope of the relationship; a particular genotype doubles the sensitivity of KEdownstream to changes in KEupstream). Information on these known modulating factors should be listed in this subsection, along with relevant information regarding the manner in which the modulating factor can be expected to alter the relationship (if known). Note, this section should focus on those modulating factors for which solid evidence supported by relevant data and literature is available. It should NOT list all possible/plausible modulating factors. In this regard, it is useful to bear in mind that many risk assessments conducted through conventional apical guideline testing-based approaches generally consider few if any modulating factors. More help

The Th1/Th2 shift is one of the most important immunologic changes during the menstrual cycle and gestation.  Immune activity shifts across the menstrual cycle, with higher follicular-phase Th1 cell activity and higher luteal-phase Th2 cell activity (Tierney KL. 2015).  This is due to the progressive increase of estrogens, which reach peak level in the third trimester of pregnancy. At these high levels, estrogens suppress the Th1-mediated responses and stimulate Th2-mediated immunologic responses (Doria A. 2006).  The effects of ERα signaling on T cells appear to be estrogen-dose dependent, i.e., low doses of estrogen stimulate a Th1 response, but higher doses promote a Th2 response (Priyanka HP. 2013).

Known Feedforward/Feedback loops influencing this KER
This subsection should define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits? In some cases where feedback processes are measurable and causally linked to the outcome, they should be represented as KEs. However, in most cases these features are expected to predominantly influence the shape of the response-response, time-course, behaviours between selected KEs. For example, if a feedback loop acts as compensatory mechanism that aims to restore homeostasis following initial perturbation of a KE, the feedback loop will directly shape the response-response relationship between the KERs. Given interest in formally identifying these positive or negative feedback, it is recommended that a graphical annotation (page 44) indicating a positive or negative feedback loop is involved in a particular upstream to downstream KE transition (KER) be added to the graphical representation, and that details be provided in this subsection of the KER description (see pages 44-45 of the User Handbook).  More help


Domain of Applicability

As for the KEs, there is also a free-text section of the KER description that the developer can use to explain his/her rationale for the structured terms selected with regard to taxonomic, life stage, or sex applicability, or provide a more generalizable or nuanced description of the applicability domain than may be feasible using standardized terms. More help



List of the literature that was cited for this KER description using the appropriate format. Ideally, the list of references should conform, to the extent possible, with the OECD Style Guide (OECD, 2015). More help
  1. 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.
  2. 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.
  3. 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.
  4. Brandt ME, Vickery LE. Cooperativity and dimerization of recombinant human estrogen receptor hormone-binding domain. J Biol Chem. 1997;272(8):4843-9.
  5. 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.
  6. Carolyn MK. Estrogen receptor interaction with estrogen response elements. Nucleic Acids Res. 2001 Jul 15; 29(14): 2905-2919.
  7. Spilianakis CG & Flavell RA, Long-range intrachromosomal interactions in the T helper type 2 cytokine locus. Nature Immunology. 2004; 5: 1017-1027.
  8. Eeckhoute J, Positive Cross-Regulatory Loop Ties GATA-3 to Estrogen Receptor α Expression in Breast Cancer. Cancer Res. 2007; 67(13):6477-83.
  9. Kong SL, Cellular reprogramming by the conjoint action of ERα, FOXA1, and GATA3 to a ligand‐inducible growth state. Mol Syst Biol (2011)7:526
  10. Kurata, H., Lee, H. J., O’Garra, A. and Arai, N. (1999). Ectopic expression of activated STAT6 induces the expression of Th2-specific cytokines and transcription factors in developing Th1 cells. Immunity 11: 677-688.
  11. Zhu, J., Guo, L., Watson, C. J., Hu-Li, J. and Paul, W. E. (2001). STAT6 is necessary and sufficient for IL-4's role in Th2 differentiation and cell expansion. The Journal of Immunology 166(12): 7276-7281.
  12. Horiuchi S, Genome-wide analysis reveals unique regulation of transcription of Th2-specific genes by GATA3. (2011) J Immunol. 1;186(11):6378-89.
  13. Lambert KC, Curran EM, et al. Estrogen receptor alpha (ERalpha) deficiency in macrophages results in increased stimulation of CD4+ T cells while 17beta-estradiol acts through ERalpha to increase IL-4 and GATA-3 expression in CD4+ T cells independent of antigen presentation. J Immunol. 2005; 175(9): 5716-23.
  14. 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.
  15. Tierney, K. L., Julia, R. H. and Gregory, E. D. (2015). Sexual activity modulates shifts in Th1/Th2 cytokine profile across the menstrual cycle: An observational study. Fertility and Sterility 104 (6): 1513-1521.
  16. Doria, A., Iaccarino, L., Sarzi-Puttini, P., Ghirardello, A., Zampieri, S., Arienti, S., Cutolo, M. and Todesco, S. (2006). Estrogens in pregnancy and systemic lupus erythematosus. Annals of the New York Academy of Sciences 1069: 247-256.
  17. Priyanka HP, Krishnan HC, Singh RV, Hima L, Thyagarajan S. Estrogen modulates in vitro T cell responses in a concentration- and receptor-dependent manner: effects on intracellular molecular targets and antioxidant enzymes. Mol Immunol. 2013;56(4):328-39.