Key Event Title
|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|
|AR antagonism leading to foetal feminisation||KeyEvent|
|Decreased testosterone synthesis leading to short AGD||KeyEvent|
|AR antagonism leading to NR||KeyEvent|
|AR antagonism leading to decreased fertility||KeyEvent|
|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).
Decreased 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.
Evidence for Perturbation by Stressor
Using analysis of androgen-regulated gene expression in the LNCaP prostate cancer cell line (Ngan et al. 2009).
Using analysis of androgen-regulated gene expression in the LNCaP prostate cancer cell line (Ngan et al. 2009) and using the AR-CALUX reporter assay in antagonism mode, cyproterone acetate showed an IC50 of 7.1 nM (Sonneveld et al. 2005).
Using transiently AR-transfected CHO cells, epoxiconazole showed a LOEC of 1.6 mM and an IC50 of 10 mM (Kjærstad et al. 2010).
Analysis of androgen-regulated gene expression in the LNCaP prostate cancer cell line (Ngan et al. 2009) and using the AR-CALUX reporter assay in antagonism mode, flutamide showed an IC50 of 1.3 uM (Sonneveld et al. 2005).
Using hAR-EcoScreen Assay, triticonazole showed a LOEC for antagonisms of 0.8 mM and an IC50 of 2.8 (±0.1) mM (Draskau et al. 2019)
Using gene expression analysis of the androgen-regulated genes ornithine decarboxylase, prostatic binding protein C3 as well as insulin-like growth factor I. Gene expression levels were reduced in ventral prostates of male Wistar pups at postnatal day 16 following in utero and lactational exposure from maternal perinatal dosing with prochloraz (50 and 150 mg/kg/day) from gestational day 7 to postnatal day 16 (Laier et al. 2006). Also, using transiently AR-transfected CHO cells, prochloraz showed a LOEC of 6.3 mM and an IC50 of 13 mM (Kjærstad et al. 2010).
Using transiently AR-transfected CHO cells, propiconazole showed a LOEC of 12.5 mM and an IC50 of 18 mM (Kjærstad et al. 2010).
Using transiently AR-transfected CHO cells, tebuconazole showed a LOEC of 3.1 mM and an IC50 of 8.1 mM (Kjærstad et al. 2010).
Using hAR-EcoScreen Assay, triticonazole showed a LOEC for antagonisms of 0.2 mM and an IC50 of 0.3 (±0.01) mM (Draskau et al. 2019).
Using the AR-CALUX reporter assay in antagonism mode, vinclozolin showed an IC50of 1.0 uM (Sonneveld et al. 2005).
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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
Davey RA, Grossmann M (2016) Androgen Receptor Structure, Function and Biology: From Bench to Bedside. Clin Biochem Rev 37:3–15
Draskau MK, Boberg J, Taxvig C, et al (2019) In vitro and in vivo endocrine disrupting effects of the azole fungicides triticonazole and flusilazole. Environ Pollut 255:113309. doi: 10.1016/j.envpol.2019.113309
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Heemers H V., Tindall DJ (2007) Androgen receptor (AR) coregulators: A diversity of functions converging on and regulating the AR transcriptional complex. Endocr. Rev. 28:778–808
Jiang M, Ma Y, Chen C, et al (2009) Androgen-Responsive Gene Database: Integrated Knowledge on Androgen-Responsive Genes. Mol Endocrinol 23:1927–1933. doi: 10.1210/me.2009-0103
Kjærstad MB, Taxvig C, Nellemann C, et al (2010) Endocrine disrupting effects in vitro of conazole antifungals used as pesticides and pharmaceuticals. Reprod Toxicol 30:573–582. doi: 10.1016/J.REPROTOX.2010.07.009
Laier P, Metzdorff SB, Borch J, et al (2006) Mechanisms of action underlying the antiandrogenic effects of the fungicide prochloraz. Toxicol Appl Pharmacol 213:160–71. doi: 10.1016/j.taap.2005.10.013
Maclean HE, Chu S, Warne GL, Zajact JD Related Individuals with Different Androgen Receptor Gene Deletions
MacLeod DJ, Sharpe RM, Welsh M, et al (2010) Androgen action in the masculinization programming window and development of male reproductive organs. In: International Journal of Andrology. Blackwell Publishing Ltd, pp 279–287
Ngan S, Stronach EA, Photiou A, et al (2009) Microarray coupled to quantitative RT–PCR analysis of androgen-regulated genes in human LNCaP prostate cancer cells. Oncogene 28:2051–2063. doi: 10.1038/onc.2009.68
OECD (2016) Test No. 458: Stably Transfected Human Androgen Receptor Transcriptional Activation Assay for Detection of Androgenic Agonist and Antagonist Activity of Chemicals, OECD Guide. OECD Publishing
Rana K, Davey RA, Zajac JD (2014) Human androgen deficiency: Insights gained from androgen receptor knockout mouse models. Asian J. Androl. 16:169–177
Sonneveld E, Jansen HJ, Riteco JAC, et al (2005) Development of Androgen-and Estrogen-Responsive Bioassays, Members of a Panel of Human Cell Line-Based Highly Selective Steroid-Responsive Bioassays. Toxicol Sci 83:136–148. doi: 10.1093/toxsci/kfi005
van der Burg B, Winter R, Man H yen, et al (2010) Optimization and prevalidation of the in vitro AR CALUX method to test androgenic and antiandrogenic activity of compounds. Reprod Toxicol 30:18–24. doi: 10.1016/j.reprotox.2010.04.012
Walters KA, Simanainen U, Handelsman DJ (2010) Molecular insights into androgen actions in male and female reproductive function from androgen receptor knockout models. Hum Reprod Update 16:543–558. doi: 10.1093/humupd/dmq003