Abstract
The toxicity by 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is thought to be caused by activation of the aryl hydrocarbon receptor (AHR). However, our understanding of how AHR activation by TCDD leads to toxic effects is poor. Ideally we would like to manipulate AHR activity in specific tissues and at specific times. One route to this is expressing dominant negative AHRs (dnAHRs). This work describes the construction and characterization of dominant negative forms of the zebrafish Ahr2 in which the C-terminal transactivation domain was either removed, or replaced with the inhibitory domain from the Drosophila engrailed repressor protein. One of these dnAhr2s was selected for expression from the ubiquitously active e2fα promoter in transgenic zebrafish. We found that these transgenic zebrafish expressing dnAhr2 had reduced TCDD induction of the Ahr2 target gene cyp1a, as measured by 7-ethoxyresorufin-O-deethylase activity. Furthermore, the cardiotoxicity produced by TCDD, pericardial edema, heart malformation, and reduced blood flow, were all mitigated in the zebrafish expressing the dnAhr2. These results provide in vivo proof-of-principle results demonstrating the effectiveness of dnAHRs in manipulating AHR activity in vivo, and demonstrating that this approach can be a means for blocking TCDD toxicity.
Highlights
The aryl hydrocarbon receptor (AHR) is the ligand-activated subunit of a heterodimeric transcription factor found in numerous vertebrate cell types [1]
Agonist binding at the AHR PAS B domain triggers a conformational change that moves the normally cytosolic receptor into the nucleus where it dimerizes with its partner, the AHR nuclear translocator (ARNT)
We find that transgenic expression of a dnAhr2 produces highly significant, albeit incomplete, protection from several end points of TCDD toxicity
Summary
The aryl hydrocarbon receptor (AHR) is the ligand-activated subunit of a heterodimeric transcription factor found in numerous vertebrate cell types [1]. The activated heterodimer binds to canonical DNA sequences known as AHR Enhancers (AHREs) to drive transcription of target genes [2]. Activation of the AHR induces transcription of a core set of genes involved in xenobiotic metabolism. These include genes encoding cytochrome P450 1A (CYP1A), and UDP-glucuronosyltransferase (UDPGT) involved in biotransformation. Because these enzymes degrade the ligands that activate AHR, the system acts as an environmental sensor that facilitates the detoxification of xenobiotics [3]. TCDD is noteworthy in being poorly degraded by the enzymes induced by AHR, and because it is lipophilic, this stable AHR agonist has a long half-life in biological systems
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
