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Key Event Title
Altered, Transcription of genes by AR
|Level of Biological Organization|
Key Event Components
|regulation of gene expression||androgen receptor||decreased|
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 foetal feminisation||KeyEvent||Agnes Aggy (send email)||Open for adoption|
|Decreased testosterone synthesis leading to short AGD||KeyEvent||Cataia Ives (send email)||Under development: Not open for comment. Do not cite||Under Development|
|AR antagonism leading to NR||KeyEvent||Evgeniia Kazymova (send email)||Under development: Not open for comment. Do not cite||Under Development|
|AR antagonism leading to decreased fertility||KeyEvent||Cataia Ives (send email)||Under development: Not open for comment. Do not cite||Under Development|
|5α-reductase inhibition leading to short AGD||KeyEvent||Allie Always (send email)||Under development: Not open for comment. Do not cite||Under Development|
|Adult, reproductively mature||High|
Key Event Description
The Androgen Receptor and its function
Androgens act by binding to the Androgen receptor (AR) in androgen-responsive tissues (Davey and Grossmann 2016). Human AR mutations and mouse knockout models have established the fundamental role of AR in masculinization and spermatogenesis (Maclean et al.; Walters et al. 2010; Rana et al. 2014). The AR is also expressed in many other tissues such as bone, muscles, ovaries and within the immune system (Rana et al. 2014).
Altered transcription of genes by the AR as a Key Event
The AR belongs to the steroid hormone nuclear receptor family. It is a ligand-activated transcription factor with three domains; the N-terminal domain, the DNA-binding domain, and the ligand-binding domain with the latter being the most evolutionary conserved (Davey and Grossmann 2016). Upon activation by ligand-binding, the AR translocate from the cytoplasm to the cell nucleus, dimerizes, binds to androgen response elements in the DNA to modulate gene transcription (Davey and Grossmann 2016). The transcriptional targets varies between different cells and tissues, as well as with developmental stages and is, for instance, dependent on available co-regulators (Bevan and Parker 1999; Heemers and Tindall 2007).
Several known and proposed target genes of AR canonical signaling have been identified by analysis of gene expression following treatments with AR agonists (Bolton et al. 2007; Ngan et al. 2009) and can for instance be found in the Androgen-Responsive Gene Database (Jiang et al. 2009).
How It Is Measured or Detected
Decreased transcription of genes by the AR can be measured by measuring the transcription level of known downstream target genes by RT-qPCR or other transcription analyses approaches, eg transcriptomics.
Indirect approaches include the use of transient or stable transactivation assays including the validated OECD test guideline assay, Test No. 458: Stably Transfected Human Androgen Receptor Transcriptional Activation Assay for Detection of Androgenic Agonist and Antagonist Activity of Chemicals (OECD 2016). The stably transfected AR-EcoScreenTM cell line is freely available for the Japanese Collection of Research Bioresources (JCRB) Cell Bank under reference number JCRB1328. These cell-based transcriptional activation assays are typically used to detect AR agonists and antagonists. However, these types of assays are well suited to measure this KE as what they measure is exactly AR transcriptional activity. Other assays along this line include the AR-CALUX reporter gene assay that is derived from human U2-OS cells stably transfected with the human AR and an AR responsive reporter gene (van der Burg et al. 2010).
Known downstream target gene transcription level can be measured in tissues by RT-qPCR or other gene expression analyses approaches.
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 and Grossmann 2016). Despite certain inter-species differences, AR function mediated through gene expression is highly conserved, with mutation 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 taxa.
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Bolton EC, So AY, Chaivorapol C, et al (2007) Cell- and gene-specific regulation of primary target genes by the androgen receptor. Genes Dev 21:2005–2017. doi: 10.1101/gad.1564207
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