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Relationship: 2612


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

Increased activation, Nuclear factor kappa B (NF-kB) leads to Antagonism, Estrogen receptor

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). 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

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
DNA damage and mutations leading to Metastatic Breast Cancer adjacent Moderate Moderate Agnes Aggy (send email) Under development: Not open for comment. Do not cite Under Development

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
human Homo sapiens High NCBI
mice Mus sp. 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
Not Otherwise Specified Moderate

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

Upstream event: Increased, NF kB activity

Downstream event: Estrogen receptor, Reduced

The described Key Event Relationship (KER) outlines a sequence of events involving the activation of the nuclear factor kappa B (NF-κB) pathway and its impact on the estrogen receptor. The upstream event is marked by "Increased NF-κB activity," signifying an elevation in the activation of the NF-κB signaling pathway. NF-κB is a transcription factor that plays a crucial role in various cellular processes, including inflammation, immune response, and cell survival.

The downstream event in this KER is "Reduced Estrogen receptor," indicating a decrease in the levels or activity of the estrogen receptor. The NF-κB pathway has been linked to the modulation of estrogen receptor function. Increased NF-κB activity can lead to the downregulation or interference of estrogen receptor signaling, which can affect cellular responses to estrogen and its related pathways.

This KER emphasizes the intricate cross-talk between signaling pathways and transcriptional regulation within cells. The heightened NF-κB activity can exert downstream effects on the estrogen receptor, potentially impacting hormone-related processes and cellular functions. Understanding these interactions contributes to a broader comprehension of how cellular pathways influence each other and how changes in one pathway can lead to consequences in another.

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

With meticulous adherence to OECD guidelines, a rigorous evidence collection approach was undertaken to validate the Key Event Relationship (KER) "Increased activation of Nuclear factor kappa B (NF-kB) leads to Antagonism of the Estrogen receptor." Commencing with heightened NF-kB activation, a range of cellular assays was employed to confirm NF-kB's increased translocation, DNA binding, and transcriptional activity. This direct evidence substantiated the initial event, reinforcing the mechanistic understanding of NF-kB's activation.

Mechanistic insights were further gleaned through experimental studies that elucidated the interaction between NF-kB and the Estrogen receptor. Co-immunoprecipitation assays and molecular binding studies confirmed the direct antagonistic effect of NF-kB on the Estrogen receptor's function. Functional assays assessed changes in estrogen-responsive gene expression upon NF-kB activation, providing empirical support for the KER.

Parallel investigations involving pharmacological NF-kB activation and genetic manipulation bolstered the relationship's mechanistic plausibility. Cross-validation across cell types, experimental conditions, and species further enhanced the reliability and generalizability of the relationship.

Real-world relevance was established by observing the implications of NF-kB activation in scenarios involving endocrine disruption, inflammation, and hormone-related diseases. Integrating diverse experimental findings, mechanistic insights, and relevant contextual studies in accordance with OECD principles, a substantiated and robust evidence base for the KER "Increased activation of Nuclear factor kappa B (NF-kB) leads to Antagonism of the Estrogen receptor" was effectively constructed.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Activation NF-κB in breast cancer leads to loss of Estrogen Receptor (ER) expression and Human Epidermal Growth Fac- tor Receptor 2 (HER-2) overexpressed via epidermal growth factor receptor (EGFR) and Mitogen Activated Protein Kinase (MAPK) pathway (Laere et al.,2007). Indeed, the binding of epidermal growth factor (EGF) to its receptor (EGFR) activates NF-B, which most likely contributes to this transcription factor's increased activity in ER negative breast cancer cells (Shostak et al.,2011). Because of constitutive production of cytokines and growth factors, loss of ER function has been linked to constitutive NF-kB activity and hyperactive MAPK, resulting in aggressive, metastatic, hormone-resistant malignancies (Ali et al., 2002). Activation of the progesterone receptor can reduce DNA binding and transcriptional activity by inhibiting NF-B-driven gene expression (Kalkhoven et al., 1996). HER-2 stimulates NF-B via the conventional route, which includes IKK (Merkhofer et al., 2010).

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

-NF-kB activation in breast cancer has been extensively documented in oestrogen receptor negative (ER) breast tumours and ER breast cancer cell lines, implying a significant inhibitory interaction between both signalling pathways (Biswas et al, 2000, 2001, 2004; Zhou et al, 2005). A rise in both NF-kB DNA-binding activity (Nakshatri et al, 1997) and expression of NF-kB target genes such IL8 coincides with a transition from oestrogen dependence to oestrogen independence in breast cancer, indicating inhibitory cross-talk. The fact that some breast tumours that are resistant to the tumoricidal action of anti-estrogens become sensitised to apoptosis and show a drop in NF-kB activity after treatment with oestrogen supports the inverse relationship between ER and NF-kB activity.

-This shows that oestrogen's proapoptotic actions in these tumours are mediated via NF-kB suppression.

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

No specific uncertainties and inconsistencies reported to the best of our knowledge.

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

Estradiol has been shown to decrease transcriptional activity and expression of NF-kB in a variety of experimental models (Biswas et al., 2005;Lobanova et al.,2007). Estrogen treatment of MCF-7 or MCF-7/H cells resulted in a significant suppression of NF-kB activity in both cell lines, according to research. The antiestrogen tamoxifen boosted NF-kB activity in the cells, indicating that ER plays a key role in NF-kB down-regulation in both parent and hypoxia-tolerant cells.

-MCF-7/T2H cells were discovered to have a partial tolerance to acute cobalt chloride-induced hypoxia while maintaining their estrogen-independent phenotype. In contrast to the MCF-7/H subline, MCF-7/T2H cells had a non-affected baseline NF-kB level, indicating that estrogens are responsible for NF-kB downregulation (Scherbakov et al., 2009).

Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help

Differential Sensitivity of ER α and ERβ Cells to the NF-kB Inhibitor Go6976. A differential sensitivity to Go6976 by ER α and ERβ breast cancer cells was observed (Holloway et al.,2004). The ER α cells were more sensitive and less viable after treatment with this NF-kB inhibitor. The IC50 (50% killing) by Go6976 was 1 mM for Era of MDA-MB435 and MDA-MB231 breast cancer cells, whereas it was greater than 10 mM for ERa of MCF-7 and T47D or the normal mammary epithelial H16N  cells . At 10 mM Go6976, about 80% of the ERa cells were killed, whereas only 15–30% of ERa and normal H16N cells were sensitive to this compound. The relative resistance of the H16N normal human mammary cells indicates a possible high therapeutic index of Go6976 against ERa cancer cells.

This observation is consistent with the previously observed role of NF-kB as an antiapoptotic agent. FACS analysis demonstrated accumulation of sub-G1 population (67%) in Go6976- treated (48 h at 1 mM) ERa vs. only 10–15% in ERa cells, indicating enhanced apoptotic cell death preferentially of ERa cells caused by this low molecular weight compound.

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

Key events connected by this KER occur within hours of exposure.

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

- Multiple pathways are implicated in the crosstalk between NF-KB and ER. Through many mechanisms, including collaboration with FOXA1 to strengthen latent ER-binding sites and trigger translation of their synergistic genes, NF-KB directly interacts with the DNA-binding activity of ER (Franco et al. 2015). Furthermore, NF-KB affects ER via interacting with its ER co-activator or co-repressor, which changes ER transcriptional activity (Park et al. 2005). Similar to ER, NF-KB has been reported to have a role as a downstream effector for the growth factor pathway, which is recognized to be involved in both ligand-dependent and non-ligand-dependent ER activation, leading to resistance to a wide range of anti- oestrogen drugs (Zhou et al. 2005a, Sas et al. 2012, Frasor et al. 2015).

-NF-KB is also involved in the anti-apoptotic pathway and immune surveillance systems, both of which have been linked to endocrine resistance (Hu et al. 2015; Lim et al. 2016). Furthermore, NF-KB inhibition of ER activity has been observed. The zinc finger repressor B-lymphocyte-induced maturation protein (BLIMP1), which can bind to the ER promoter area and restrict ER transcription, is triggered by the NFB subunit RelB. (Wang et al. 2009). Increasing data suggests that NF-KB plays an important role in the complexities of the endocrine resistance environment in breast cancer.

-NF-KB and ERS1 mutations in breast cancer patients who are resistant to endocrine therapy

TNF needs NF-KB and FOXA1 to change the breast cancer cell transcriptome by modulating latent ER-binding sites.

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

KER has been observed in humans and animals irrespective of the gender and life stage.


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

Ali, S., & Coombes, R. C. (2002). Endocrine-responsive breast cancer and strategies for combating resistance. Nature Reviews Cancer2(2), 101-112.

Kalkhoven, E., Wissink, S., van der Saag, P. T., & van der Burg, B. (1996). Negative Interaction between the RelA (p65) Subunit of NF-κB and the Progesterone Receptor (). Journal of Biological Chemistry271(11), 6217-6224.

Allred, D. C., & Mohsin, S. K. (2000). Biological features of premalignant disease in the human breast. Journal of mammary gland biology and neoplasia5(4), 351-364.

Biswas, D. K., Shi, Q., Baily, S., Strickland, I., Ghosh, S., Pardee, A. B., & Iglehart, J. D. (2004). NF-κB activation in human breast cancer specimens and its role in cell proliferation and apoptosis. Proceedings of the National Academy of Sciences101(27), 10137-10142.

 Biswas, D. K., Martin, K. J., McAlister, C., Cruz, A. P., Graner, E., Dai, S. C., & Pardee, A. B. (2003). Apoptosis caused by chemotherapeutic inhibition of nuclear factor-κB activation. Cancer research63(2), 290-295.


Biswas, D. K., Cruz, A. P., Gansberger, E., & Pardee, A. B. (2000). Epidermal growth factor-induced nuclear factor κB activation: a major pathway of cell-cycle progression in estrogen-receptor negative breast cancer cells. Proceedings of the National Academy of Sciences97(15), 8542-8547.

Biswas, D. K., Dai, S. C., Cruz, A., Weiser, B., Graner, E., & Pardee, A. B. (2001). The nuclear factor kappa B (NF-κB): a potential therapeutic target for estrogen receptor negative breast cancers. Proceedings of the National Academy of Sciences98(18), 10386-10391.

 Biswas, D. K., Singh, S., Shi, Q., Pardee, A. B., & Iglehart, J. D. (2005). Crossroads of estrogen receptor and NF-κB signaling. Science's STKE2005(288), pe27-pe27. 

Franco, H. L., Nagari, A., & Kraus, W. L. (2015). TNFα signaling exposes latent estrogen receptor binding sites to alter the breast cancer cell transcriptome. Molecular cell58(1), 21-34.

Frasor, J., El-Shennawy, L., Stender, J. D., & Kastrati, I. (2015). NFκB affects estrogen receptor expression and activity in breast cancer through multiple mechanisms. Molecular and cellular endocrinology418, 235-239..

Holloway, J. N., Murthy, S., & El-Ashry, D. (2004). A cytoplasmic substrate of mitogen-activated protein kinase is responsible for estrogen receptor-α down-regulation in breast cancer cells: the role of nuclear factor-κB. Molecular Endocrinology18(6), 1396-1410.

Hu, R., Warri, A., Jin, L., Zwart, A., Riggins, R. B., Fang, H. B., & Clarke, R. (2015). NF-κB signaling is required for XBP1 (unspliced and spliced)-mediated effects on antiestrogen responsiveness and cell fate decisions in breast cancer. Molecular and cellular biology35(2), 379-390.

Manginstar, C., Islam, A. A., Sampepajung, D., Hamdani, W., Bukhari, A., Syamsu, S. A., ... & Faruk, M. (2021). The relationship between NFKB, HER2, ER expression and anthracycline-based neoadjuvan chemotherapy response in local advanced stadium breast cancer: A cohort study in Eastern Indonesia. Annals of Medicine and Surgery63, 102164.

Lim, S. O., Li, C. W., Xia, W., Cha, J. H., Chan, L. C., Wu, Y., ... & Hung, M. C. (2016). Deubiquitination and stabilization of PD-L1 by CSN5. Cancer cell30(6), 925-939.

Lobanova, Y. S., Scherbakov, A. M., Shatskaya, V. A., & Krasil’nikov, M. A. (2007). Mechanism of estrogen-induced apoptosis in breast cancer cells: role of the NF-κB signaling pathway. Biochemistry (moscow)72(3), 320-327.

McCarthy, S. A., Samuels, M. L., Pritchard, C. A., Abraham, J. A., & McMahon, M. (1995). Rapid induction of heparin-binding epidermal growth factor/diphtheria toxin receptor expression by Raf and Ras oncogenes. Genes & development9(16), 1953-1964.

Merkhofer, E. C., Cogswell, P., & Baldwin, A. S. (2010). Her2 activates NF-κB and induces invasion through the canonical pathway involving IKKα. Oncogene29(8), 1238-1248.

Nakshatri, H., Bhat-Nakshatri, P., Martin, D. A., Goulet Jr, R. J., & Sledge Jr, G. W. (1997). Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth. Molecular and cellular biology17(7), 3629-3639.

Norris, J. L., & Baldwin, A. S. (1999). Oncogenic Ras enhances NF-κB transcriptional activity through Raf-dependent and Raf-independent mitogen-activated protein kinase signaling pathways. Journal of Biological Chemistry274(20), 13841-13846.

Osako, T., Nishimura, R., Okumura, Y., Toyozumi, Y., & Arima, N. (2012). Predictive significance of the proportion of ER-positive or PgR-positive tumor cells in response to neoadjuvant chemotherapy for operable HER2-negative breast cancer. Experimental and therapeutic medicine3(1), 66-71.

Park, K. J., Krishnan, V., O’Malley, B. W., Yamamoto, Y., & Gaynor, R. B. (2005). Formation of an IKKα-dependent transcription complex is required for estrogen receptor-mediated gene activation. Molecular cell18(1), 71-82.

Pearson, G., English, J. M., White, M. A., & Cobb, M. H. (2001). ERK5 and ERK2 cooperate to regulate NF-κB and cell transformation. Journal of Biological Chemistry276(11), 7927-7931.

Sampepajung, E., Hamdani, W., Sampepajung, D., & Prihantono, P. (2021). Overexpression of NF-kB as a predictor of neoadjuvant chemotherapy response in breast cancer. Breast Disease, (Preprint), 1-9.

Sarkar, D. K., Jana, D., Patil, P. S., Chaudhari, K. S., Chattopadhyay, B. K., Chikkala, B. R., ... & Chowdhary, P. (2013). Role of NF-κB as a prognostic marker in breast cancer: a pilot study in Indian patients. Indian journal of surgical oncology4(3), 242-247.

Sas, L., Lardon, F., Vermeulen, P. B., Hauspy, J., Van Dam, P., Pauwels, P., ... & Van Laere, S. J. (2012). The interaction between ER and NFκB in resistance to endocrine therapy. Breast Cancer Research14(4), 1-14.

Scherbakov, A. M., Lobanova, Y. S., Shatskaya, V. A., & Krasil’nikov, M. A. (2009). The breast cancer cells response to chronic hypoxia involves the opposite regulation of NF-kB and estrogen receptor signaling. Steroids74(6), 535-542.

Shostak, K., & Chariot, A. (2011). NF-κB, stem cells and breast cancer: the links get stronger. Breast Cancer Research13(4), 1-7.

Singh, S., Shi, Q., Bailey, S. T., Palczewski, M. J., Pardee, A. B., Iglehart, J. D., & Biswas, D. K. (2007). Nuclear factor-κB activation: a molecular therapeutic target for estrogen receptor–negative and epidermal growth factor receptor family receptor–positive human breast cancer. Molecular cancer therapeutics6(7), 1973-1982.

Song, R. D., Zhang, Z., Mor, G., & Santen, R. J. (2005). Down-regulation of Bcl-2 enhances estrogen apoptotic action in long-term estradiol-depleted ER+ breast cancer cells. Apoptosis10(3), 667-678.

Troppmair, J., Hartkamp, J., & Rapp, U. R. (1998). Activation of NF-κB by oncogenic Raf in HEK 293 cells occurs through autocrine recruitment of the stress kinase cascade. Oncogene17(6), 685-690.

Van Laere, S. J., Van der Auwera, I., Van den Eynden, G. G., Van Dam, P., Van Marck, E. A., Vermeulen, P. B., & Dirix, L. Y. (2007). NF-κB activation in inflammatory breast cancer is associated with oestrogen receptor downregulation, secondary to EGFR and/or ErbB2 overexpression and MAPK hyperactivation. British journal of cancer97(5), 659-669.

Wang, X., & Belguise, K. (2009). O’ Neill, CF, Sanchez-Morgan, N. Romagnoli, M., Eddy, SF, Mineva, ND, Yu, Z., Min, C., Trinkaus-Randall, V. et al, 3832-3844.

Zhou, Y., Eppenberger-Castori, S., Eppenberger, U., & Benz, C. C. (2005). The NFkB pathway and endocrine-resistant breast cancer. Endocrine Related Cancer12(1), S37.