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Event: 26
Key Event Title
Antagonism, Androgen receptor
Short name
Biological Context
Level of Biological Organization |
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Molecular |
Cell term
Cell term |
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eukaryotic cell |
Organ term
Key Event Components
Key Event Overview
AOPs Including This Key Event
AOP Name | Role of event in AOP | Point of Contact | Author Status | OECD Status |
---|---|---|---|---|
AR antagonism leading to short AGD | MolecularInitiatingEvent | Evgeniia Kazymova (send email) | Under development: Not open for comment. Do not cite | Under Development |
AR antagonism leading to NR | MolecularInitiatingEvent | Evgeniia Kazymova (send email) | Under development: Not open for comment. Do not cite | Under Development |
AR antagonism leading to decreased fertility | MolecularInitiatingEvent | Cataia Ives (send email) | Under development: Not open for comment. Do not cite | Under Development |
Androgen receptor antagonism and testicular cancer | MolecularInitiatingEvent | Brendan Ferreri-Hanberry (send email) | Under development: Not open for comment. Do not cite | |
AR antagonism leading to hypospadias | MolecularInitiatingEvent | Brendan Ferreri-Hanberry (send email) | Under development: Not open for comment. Do not cite | |
Adverse Outcome Pathways diagram related to PBDEs associated male reproductive toxicity | MolecularInitiatingEvent | Cataia Ives (send email) | Under development: Not open for comment. Do not cite |
Taxonomic Applicability
Term | Scientific Term | Evidence | Link |
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mammals | mammals | High | NCBI |
Life Stages
Life stage | Evidence |
---|---|
During development and at adulthood | High |
Sex Applicability
Term | Evidence |
---|---|
Mixed | High |
Key Event Description
The androgen receptor (AR) and its function
The AR is a ligand-activated transcription factor belonging to the steroid hormone nuclear receptor family (Davey & Grossmann, 2016). The AR has three domains: the N-terminal domain, the DNA-binding domain and the ligand-binding domain, with the latter being most evolutionary conserved. Testosterone (T) and the more biologically active dihydrotestosterone (DHT) are endogenous ligands for the AR (MacLean et al, 1993; MacLeod et al, 2010; Schwartz et al, 2019). In teleost fishes, 11-ketotestosterone is the second main ligand (Schuppe et al, 2020). Human AR mutations and mouse knock-out models have established a pivotal role for the AR in masculinization and spermatogenesis (Walters et al, 2010). Apart from the essential role for AR in male reproductive development and function (Walters et al, 2010), the AR is also expressed in many other tissues and organs such as bone, muscles, ovaries, and the immune system (Rana et al, 2014).
AR antagonism as Key Event
The main function of the AR is to activate gene transcription in cells. Canonical signaling occurs by ligands (androgens) binding to AR in the cytoplasm which results in translocation to the cell nucleus, receptor dimerization and binding to specific regulatory DNA sequences (Heemers & Tindall, 2007). The gene targets regulated by AR activation depends on cell/tissue type and what stage of development activation occur, and is, for instance, dependent on available co-factors. Apart from the canonical signaling pathway, AR can also initiate cytoplasmic signaling pathways with other functions than the nuclear pathway, for instance rapid change in cell function by ion transport changes (Heinlein & Chang, 2002) and association with Src kinase to activate MAPK/ERK signaling and activation of the PI3K/Akt pathway (Leung & Sadar, 2017).
How It Is Measured or Detected
AR antagonism can be measured in vitro by transient or stable transactivation assays to evaluate nuclear receptor activation. There is already a validated test guideline for AR (ant)agonism adopted by the OECD, Test No. 458: Stably Transfected Human Androgen Receptor Transcriptional Activation Assay for Detection of Androgenic Agonist and Antagonist Activity of Chemicals (OECD, 2016). This test guideline contains three different methods. More information on limitations, advantages, protocols, and availability and description of cells are given in the test guideline.
Besides these validated methods, other transiently or stably transfected reporter cell lines are available as well as yeast based systems (Campana et al, 2015; Körner et al, 2004). AR nuclear translocation can be monitored by various assays (Campana et al 2015), for example by monitoring fluorescent rat AR movement in living cells (Tyagi et al 2020), with several human AR translocation assays being commercially available; e.g. Fluorescent AR Nuclear Translocation Assay (tGFP-hAR/HEK293) or Human Androgen NHR Cell Based Antagonist Translocation LeadHunter Assay.
Additional information on AR interaction can be obtained employing competitive AR binding assays (Freyberger et al 2010, Shaw et al 2018), which can also inform on relative potency of the compounds, though not on downstream effect of the AR binding.
The recently developed AR dimerization assay provides an assay with an improved ability to measure potential stressor-mediated disruption of dimerization/activation (Lee et al, 2021).
Domain of Applicability
Both the DNA-binding and ligand-binding domains of the AR are highly evolutionary conserved, whereas the transactivation domain show more divergence which may affect AR-mediated gene regulation across species (Davey & Grossmann, 2016). Despite certain inter-species differences, AR function mediated through gene expression is highly conserved, with mutations studies from both humans and rodents showing strong correlation for AR-dependent development and function (Walters et al, 2010).
This KE is applicable for both sexes, across developmental stages into adulthood, in numerous cells and tissues and across mammalian taxa. It is, however, acknowledged that this KE most likely has a much broader domain of applicability extending to non-mammalian vertebrates. AOP developers are encouraged to add additional relevant knowledge to expand on the applicability to also include other vertebrates.
References
Campana C, Pezzi V, Rainey WE (2015) Cell based assays for screening androgen receptor ligands. Semin Reprod Med 33: 225-234.
Freyberger A, Weimer M, Tran HS, Ahr HJ. Assessment of a recombinant androgen receptor binding assay: initial steps towards validation. Reprod Toxicol. 2010 Aug;30(1):2-8. doi: 10.1016/j.reprotox.2009.10.001. Epub 2009 Oct 13. PMID: 19833195.
OECD (2022). Test No. 251: Rapid Androgen Disruption Activity Reporter (RADAR) assay. Paris: OECD Publishing doi:10.1787/da264d82-en.
Shaw J, Leveridge M, Norling C, Karén J, Molina DM, O'Neill D, Dowling JE, Davey P, Cowan S, Dabrowski M, Main M, Gianni D. Determining direct binders of the Androgen Receptor using a high-throughput Cellular Thermal Shift Assay. Sci Rep. 2018 Jan 9;8(1):163. doi: 10.1038/s41598-017-18650-x. PMID: 29317749; PMCID: PMC5760633.
Tyagi RK, Lavrovsky Y, Ahn SC, Song CS, Chatterjee B, Roy AK (2000) Dynamics of intracellular movement and nucleocytoplasmic recycling of the ligand-activated androgen receptor in living cells. Mol Endocrinol 14: 1162-1174