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Relationship: 3626

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

Promotion, SIX1 positive progenitor cells in endometrium leads to Endometrial squamous metaplasia, Increase

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Promotion, SIX1 positive progenitor cells in endometrium

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Endometrial squamous metaplasia, Increase

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	Moderate	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
Mus musculus	Mus musculus	High	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Female	High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Embryo	High
Adult	High
Birth to < 1 month	High
1 to < 3 months	High
6 to < 12 months	High
1 to < 2 years	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

Due to the pressure applied by six1 expression on cell proliferation and progenitor population expansion, the early developmental establishment of six1+ progenitor cells in the endometrium allows for subseqent altered differentiation, including squamous metaplasia.

Suen et al., 2016 and Jefferson et al., 2011 both observed distinct cell-type specific six1 transcript expression differences. “In the vaginal and cervical epithelium, SIX1 localized to the stratified squamous epithelium, with highest expression in the basal and suprabasal layers. In the endocervix, nuclear SIX1 immunolabeling was observed in simple columnar glandular epithelial cells only when there was a layer of progenitor-like basal cells directly subjacent to the luminal cells. SIX1 expression was not observed in endometrial luminal epithelium or morphologically normal glands. SIX1 was present in the uteri of a few control mice but was limited to small focal areas of squamous metaplasia in the uterine body.” (Suen et al., 2016). In contrast, SIX1 was present in the uterus in low numbers after just 5 days of GEN or DES treatment. At 6 months of age, SIX1 localized to basal cell and squamous metaplasia in nonneoplastic endometrial glands of most mice neonatally exposed to GEN or DES.

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.

A set of related publications, Suen et al., 2016, 2018, and 2019 were used as originating publications followed by further investigation of the bibliography and google scholar to retrieve full articles.

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

Dysregulated six1 expression promotes progenitor expansion and plasticity. Importantly, six1 expression is not normally seen in the endometrial epithelium. However, under the influence of neonatal estrogen treatments, established six1+ progenitor cells do occur. Subsequent expansion of undifferentiated or poorly committed cells can predispose to aberrant differentiations pathways, including metaplastic changes.

Similarly, six1 has been shown to regulate epithelial cell fate, including promoting to a basal/squamous phenotype in other tissues (e.g., breast, reproductive tract) (McCoy et al., 2009 and Terakawa et al., 2020).

The endometrium itself is a hormone/inflammatory responsive environment in which cues may push progenitors toward a squamous fate as a protective differentiation pathway.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

The following studies measure concurrent squamous metaplasia and six1+ immunolabeling as well as establish differences between six1+ and six1 deleted mice in terms of metaplastic change in a specific uterine tissus (uterine horn).

Suen et al., 2016 and 2018 measured six1 localized to basal and squamous metaplasia in nonneoplastic endometrial glands of most mice neonatally exposed to GEN or DES.

Suen et al., 2019 further investigated the role of developmental DES treatment in six1+ and six1 deleted mice and found region specific (uterine horns) incidence of metaplastic change in the six1+ group, relative to the six1 deleted group, at 6 and 12 months. They concluded that these data indicate DES-induced six1 acts as a differentiation factor leading to basal cell and squamous metaplasia in the region.

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

Suen et al., 2019 also found a higher incidence of endometrial carcinoma in DES Six1 deleted compared to DES Six1+ mice at 6 months. By 12 months, both genotypes had a similarly high incidence and distribution of neoplastic lesions. This seems to demonstrate that SIX1 expression isn’t required for DES-induced carcinogenesis in the uterus and instead suggests that it may provide some degree of protection (as seen at the 6 month timestep) by promoting metaplastic change. They go on to note that neoplastic cells within DES-exposed Six1 deleted mice were not confined to a the uterine horn or uterine body. This finding indicates that conditional Six1 deletion does not shift the location of carcinoma development in a way that is similar to the shift in the appearance of basal cell metaplasia

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

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. 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 measured uteri from GEN and DES exposed mice at 5 days, and 6, 12, and 18 months after treatment. They found no evidence of basal cell, squamous metaplasia, or other proliferative lesions until the observations at 6 months, which continued prominently at 12 and 18 months as well. Notably, both basal cell and squamous metaplasia were prominent features of atypical hyperplasias and carcinomas in GEN or DES exposed mice.

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 derive from mouse tissues. The taxonomic applicability could plausibly be extended to other mammals expressing the six1 protein and having a uterus.measured.

Lifestage Applicability

The evidence pres eneted here were made during postnatal day 1 through 18 months. The lifestage applicability is relevent to the early developmental stages, where estrogenic influences come into play, and subsequent development to adulthood where the effects are measured.

Sex Applicability

The sex applicability is limited to females as a consequence of the measurement occuring on endometrial tissue.

References

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

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.

McCoy, E. L., Iwanaga, R., Jedlicka, P., Abbey, N. S., Chodosh, L. A., Heichman, K. A., ... & Ford, H. L. (2009). Six1 expands the mouse mammary epithelial stem/progenitor cell pool and induces mammary tumors that undergo epithelial-mesenchymal transition. The Journal of clinical investigation, 119(9), 2663-2677.

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.

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., 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.

Terakawa, J., Serna, V. A., Nair, D. M., Sato, S., Kawakami, K., Radovick, S., ... & Kurita, T. (2020). SIX1 cooperates with RUNX1 and SMAD4 in cell fate commitment of Müllerian duct epithelium. Cell Death & Differentiation, 27(12), 3307-3320.