Detection of oestrogenic chemicals by assaying the expression level of oestrogen regulated genes.
The oestrogen receptor belongs to the superfamily of nuclear receptors. Classically, nuclear receptors are thought to reside either in the nucleus or in the cytoplasm where they interact with their ligand which induces a conformational change that exposes the DNA binding domain. This is followed by dimerisation and binding of their corresponding response elements. By interacting with the transcriptional apparatus they then either activate or repress the transcription of target genes. However, this is a highly simplified view, since the activated oestrogen receptor interacts with other signal transduction pathways and its intrinsic transcriptional activity is highly influenced by phosphorylation and by its interaction with other proteins. This is clearly observed when the oestrogenicity of antioestrogens is tested since some compounds activate the receptor in yeast, but not in mammalian cells. However, when specific kinases are activated antioestrogens can also function as oestrogens in mammalian cells. Moreover, components of the MAP kinase and perhaps the cAMP and other pathways are activated before the receptor even enters the nucleus. Thus, when analysing the effects of oestrogenic compounds, it is important to assay both their potency as activators of transcription as the effects caused by interactions with other signal transduction pathways. This may be possible by combining assay methods, such as direct in vitro measurement of interaction between a potential oestrogenic chemical and the receptor or the yeast E-screen, with methods that are based on mammalian cells or whole animals. An alternative is to assay gene expression directly by methods such as differential display, where the expression of both genes known to be regulated directly by the receptor and genes regulated by other pathways can be monitored. Thereby it may be possible to assign different responses to the activation of distinct pathways.
Jørgensen
M
M
Department of Growth and Reproduction, Rigshospitalet, Copenhagen, Denmark.
Hummel
R
R
Bévort
M
M
Andersson
A M
AM
Skakkebaek
N E
NE
Leffers
H
H
D000818:Animals; D004967:Estrogens / Q000032:analysis / Q000235:genetics* / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D011960:Receptors, Estrogen / Q000819:agonists* / Q000032:analysis / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects
D004967:Estrogens; D011960:Receptors, Estrogen