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Relationship: 3561

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Agonism, Estrogen receptor leads to SIX1 gene expression, increased

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Agonism, Estrogen receptor
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help
SIX1 gene expression, increased

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

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Early-life estrogen receptor agonism leading to endometrial adenosquamous carcinoma via promotion of sine oculis homeobox 1 progenitor cells adjacent High Not Specified Travis Karschnik (send email) Under Development: Contributions and Comments Welcome

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) 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.  More help
Term Scientific Term Evidence Link
Homo sapiens Homo sapiens NCBI
mouse Mus musculus High NCBI
Vertebrates Vertebrates NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Female High
Male

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help
Term Evidence
Perinatal High
Birth to < 1 month High
3 to < 6 months High
6 to < 12 months High
1 to < 2 years High
Adult High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Genistein (GEN) and diethylstilbestrol (DES), known estrogen receptor agonists, induce Sine oculis homeobox 1 (SIX1) gene expression in neonatal exposures, in the female murine model.  There is evidence that this occurs through epigenetic modification during developmental exposures.  This epigenetic modification appears necessary for adults to continue overexpression of SIX1 in response to estrogen receptor agonism.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2024) employed by the Endocrine Disruptor Screening Program (EDSP).  A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies.  Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated.  The present effort focused primarily on empirical studies with laboratory rodents and other mammals.

Suen et al., 2016 was used as an originating publication followed by further investigation of the bibliography and google scholar to retrieve full articles.  Searches were also conducted using key terms "ER agonism", "SIX1 expression" and various animal and laboratory animal models.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help
Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field 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.   More help

Jefferson et al., 2013 presented data suggesting in vivo developmental exposure to estrogenic endocrine-disrupting chemicals can modify the epigenetic landscape of the SIX1 locus via a consolidation of associated histone (H3K27me3, HK3K4me3, H4K5ac, and H3K9ac) modifications over time.  And, that these activating histone marks could explain the increased Six1 expression in adult uteri after DES treatment.

Jefferson et al., 2011 showed, in control mice, SIX1 is expressed in the cervix and vagina but not in the uterus.  This suggests developmental influence by regulators of anterior-posterior patterning like Hoxa genes.  Jefferson et al., 2013 couldn’t identify a consensus estrogen response element (ERE) upstream from the Six1 transcription start site; however, the increased expression of this gene in response to DES suggests either that there is a regulatory ERE located elsewhere or that a non–ERE-mediated tethering mechanism of transcriptional activation occurs (Heldring et al., 2007 and Jakacka et al., 2002).

Suen et al., 2019 proposed a model for the role of SIX1 in epigentic modification during developmental exposures to ER agonsists.  “During normal uterine development, a population of poorly differentiated CK14+/18+ epithelial cells arise in the endometrial glands. Under normal conditions (no DES exposure) transient SIX1 expression mediates differentiation of these cells into mature luminal CK14-/18+ cells in the presence of endogenous estrogen. Neonatal exposure to DES results in epigenetic alterations that lead to initiation and promotion of the CK14+/18+ population either directly (e.g. via ER activation) or indirectly (e.g. via increased response to endogenous estrogen levels after puberty) (Newbold et al., 1990; Ostrander et al., 1985). The initiated CK14+/18+ cells that may ultimately become transformed serve as a pool of cancer cells-of-origin (Visvader 2011, Rycaj and Tang 2015). Persistent upregulation of SIX1 enables many of the CK14+/18+ cells to differentiate into mature CK14+/18-/SIX1+ basal cells or CK14-/18+/SIX1+ luminal cells. These basal cells surround luminal cells and may in some cases progress to squamous metaplasia (Suen et al., 2018). SIX1+ cell types that exhibit more mature basal (CK14+/18-) or luminal (CK14-/18+) differentiation patterns may be inherently less susceptible to transformation because of their more advanced differentiation state (Schwitalla et al., 2013, White and Lowry 2015). In our model, the absence of SIX1 results in a differentiation blockade of CK14+/18+ epithelial cells, leading to dysplastic endometrial glands and a larger pool of progenitor cells that may be later promoted to neoplasia following DES exposure.”

SIX1 has demonstrated autoregulatory expression via SIX homeoprotein binding sites during sensory organ development (Sato et al., 2012 and Grifone et al., 2005).  DES-mediated initiation of inappropriate Six1 expression during neonatal treatment could cause a persistent positive feedback loop in the absence of appropriate inhibitory mechanisms and thereby result in continued Six1 expression (Jefferson et al., 2013).

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help
Time-scale
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?). More help

Suen et al., 2016 performed SIX1 immunohistochemistry on uteri collected on the final day of treatment (PND5) with GEN (50 mg/kg/day) or DES (1mg/kg/day) and at 6 months of age, when endometrial carcinoma was first observed.  They found SIX1 was not present at either PND5 or in the vast majority of mice at 6 months of age in controls.  In contrast, in both neonatally GEN and DES exposed groups, nuclear SIX1 was present on PND5 and continue to be present at 6 months of age.

Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Taxonomic Applicability

The evidence presented here is focused on human and mouse models.  However, estrogen receptor and subsequent six1 expression could plausibly occur across a variety of vertebrates consider the conservation of both estrogen receptors and the six1 gene.

Lifestage Applicability

Estrogen agonism and its affect on SIX1 expression have been measured during embyogenesis and, when re-activated, in adults under certain conditions.  

Sex Applicability

The evidence presented here is related to the effects of estrogen agonism on six1 expression in females.  However, estrogen receptor agonism and downstream effects on six1 could happen in males as well.

References

List of the literature that was cited for this KER description. More help

Grifone, R., Demignon, J., Houbron, C., Souil, E., Niro, C., Seller, M. J., ... & Maire, P. (2005). Six1 and Six4 homeoproteins are required for Pax3 and Mrf expression during myogenesis in the mouse embryo.

Heldring, N., Isaacs, G. D., Diehl, A. G., Sun, M., Cheung, E., Ranish, J. A., & Kraus, W. L. (2011). Multiple sequence-specific DNA-binding proteins mediate estrogen receptor signaling through a tethering pathway. Molecular endocrinology, 25(4), 564-574.

Jakacka, M., Ito, M., Martinson, F., Ishikawa, T., Lee, E. J., & Jameson, J. L. (2002). An estrogen receptor (ER) α deoxyribonucleic acid-binding domain knock-in mutation provides evidence for nonclassical ER pathway signaling in vivo. Molecular Endocrinology, 16(10), 2188-2201.

Jefferson, W. N., Chevalier, D. M., Phelps, J. Y., Cantor, A. M., Padilla-Banks, E., Newbold, R. R., ... & Williams, C. J. (2013). Persistently altered epigenetic marks in the mouse uterus after neonatal estrogen exposure. Molecular endocrinology, 27(10), 1666-1677.

Jefferson, W. N., Padilla-Banks, E., Phelps, J. Y., Gerrish, K. E., & Williams, C. J. (2011). Permanent oviduct posteriorization after neonatal exposure to the phytoestrogen genistein. Environmental health perspectives, 119(11), 1575–1582.

Newbold, R. R., Bullock, B. C., & McLachlan, J. A. (1990). Uterine adenocarcinoma in mice following developmental treatment with estrogens: a model for hormonal carcinogenesis. Cancer research, 50(23), 7677-7681.

Ostrander, P. L., Mills, K. T., & Bern, H. A. (1985). Long-term responses of the mouse uterus to neonatal diethylstilbestrol treatment and to later sex hormone exposure. Journal of the National Cancer Institute, 74(1), 121-135.

Reichenberger, K. J., Coletta, R. D., Schulte, A. P., Varella-Garcia, M., & Ford, H. L. (2005). Gene amplification is a mechanism of Six1 overexpression in breast cancer. Cancer research, 65(7), 2668-2675.
 

Rycaj, K., & Tang, D. G. (2015). Cell-of-origin of cancer versus cancer stem cells: assays and interpretations. Cancer research, 75(19), 4003-4011.

Sato, S., Ikeda, K., Shioi, G., Nakao, K., Yajima, H., & Kawakami, K. (2012). Regulation of Six1 expression by evolutionarily conserved enhancers in tetrapods. Developmental biology, 368(1), 95-108.

Schwitalla, S., Fingerle, A. A., Cammareri, P., Nebelsiek, T., Göktuna, S. I., Ziegler, P. K., ... & Greten, F. R. (2013). Intestinal tumorigenesis initiated by dedifferentiation and acquisition of stem-cell-like properties. Cell, 152(1), 25-38.

Suen, A. A., Jefferson, W. N., Wood, C. E., Padilla-Banks, E., Bae-Jump, V. L., & Williams, C. J. (2016). SIX1 oncoprotein as a biomarker in a model of hormonal carcinogenesis and in human endometrial cancer. Molecular Cancer Research, 14(9), 849-858.

Suen, A. A., Jefferson, W. N., Williams, C. J., & Wood, C. E. (2018). Differentiation patterns of uterine carcinomas and precursor lesions induced by neonatal estrogen exposure in mice. Toxicologic pathology, 46(5), 574-596.

Suen, A. A., Jefferson, W. N., Wood, C. E., & Williams, C. J. (2019). SIX1 regulates aberrant endometrial epithelial cell differentiation and cancer latency following developmental estrogenic chemical exposure. Molecular Cancer Research, 17(12), 2369-2382.

Visvader, J. E. (2011). Cells of origin in cancer. Nature, 469(7330), 314-322.

White, A. C., & Lowry, W. E. (2015). Refining the role for adult stem cells as cancer cells of origin. Trends in cell biology, 25(1), 11-20.