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One-way inhibiting cross-talk between arylhydrocarbon receptor (AhR) and estrogen receptor (ER) signaling in primary cultures of rainbow trout hepatocytes

Artikel i vetenskaplig tidskrift
Författare Johanna Gräns
Britt Wassmur
Malin C. Celander
Publicerad i Aquatic Toxicology
Volym 100
Nummer/häfte 3
Sidor 263-270
ISSN 0166-445X
Publiceringsår 2010
Publicerad vid Zoologiska institutionen
Sidor 263-270
Språk en
Länkar dx.doi.org/10.1016/j.aquatox.2010.0...
Ämnesord AhR, ER, fish, hepatocytes, aromatic hydrocarbons, estrogens
Ämneskategorier Biologiska vetenskaper, Biofarmaci, Toxikologi, Cell- och molekylärbiologi, Fysiologi

Sammanfattning

The aryl hydrocarbon receptor (AhR) and the estrogen receptor (ER) are ligand activated transcription factors, both of which can be activated by environmental pollutants. The AhR regulates cytochrome P450 1A (CYP1A) expression and can be induced by aromatic hydrocarbons. The ER regulates vitellogenin (VTG) expression and can be induced by estrogenic substances. Both responses are established biomarkers used to assess pollutants in the aquatic environment, but can be affected in situations of mixed exposure. Crosstalk between these receptor pathways have been suggested, although there are conflicting data in the literature. We investigated crosstalk between ER-VTG and AhR-CYP1A signaling pathways in primary cultures of rainbow trout hepatocytes, using quantitative PCR (qPCR) for mRNA analyses and studies of CYP1A catalytic function and protein expression. The model agonists -naphthoflavone (BNF) and 17-ethinylestradiol (EE2) were used for AhR and ER activation, respectively. Combined exposure to BNF and EE2 reduced the EE2-mediated induction of VTG mRNA expression with 40 %, but had no effect on the BNF-mediated CYP1A mRNA expression, indicative of a one-way inhibiting AhR-ER crosstalk. However, basal expression of CYP1A mRNA was reduced 40 % upon exposure to EE2 alone, implying different crosstalk mechanism between basal and induced CYP1A gene expression. The mammalian ER antagonist fulvestrant (ICI) is commonly described as an absolute ER antagonist. Although, ICI failed to reverse the ER activation caused by EE2 in the present study. The CYP1A mediated EROD activity was reduced by 80 % in cells co-treated with BNF and EE2, compared to cells exposed to BNF alone. In vitro inhibiting studies suggests that this reduction was a result of inhibition of the CYP1A catalyst by EE2 as EE2 acted as a potent inhibitor (IC50: 4,6 µM) of the EROD activity. In addition, ICI also acted as a potent inhibitor of the EROD enzyme (IC50: 0,6 µM). Taken together, our data supports a one-way inhibiting AhR-ER cross-talk in rainbow trout hepatocytes exposed to a mixture of BNF and EE2. Furthermore, this study demonstrates the importance of addressing the impact of mixed exposure on established biomarker responses, i.e. induction of EROD activity and VTG synthesis. Hence, the observed “cocktail-effect” as a result of inhibiting AhR-ER cross-talk can result in decreased VTG induction and consequently underestimation of levels of estrogenic contaminants. Likewise, inhibition of the EROD activity by e.g. estrogens and anti-estrogens can lead to underestimation of levels of aromatic hydrocarbons in biomonitoring studies in the aquatic environment.

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