Combination effects of AHR agonists and Wnt/β-catenin modulators in zebrafish embryos: Implications for physiological and toxicological AHR functions

Wnt/beta-catenin signaling regulates essential biological functions and acts in developmental toxicity of some chemicals. The aryl hydrocarbon receptor (AHR) is well-known to mediate developmental toxicity of persistent dioxin-like compounds (DLCs). Recent studies indicate a crosstalk between beta-catenin and the AHR in some tissues. However the nature of this crosstalk in embryos is poorly known. We observed that zebrafish embryos exposed to the beta-catenin inhibitor XAV939 display effects phenocopying those of the dioxin-like 3,3',4,4',5-pentachlorobiphenyl (PCB126). This led us to investigate the AHR interaction with beta-catenin during development and ask whether developmental toxicity of DLCs involves antagonism of p-catenin signaling. We examined phenotypes and transcriptional responses in zebrafish embryos exposed to XAV939 or to a beta-catenin activator, 1-azakenpaullone, alone or with AHR agonists, either PCB126 or 6-formylindolo[3,2-b]carbazole (FICZ). Alone 1-azakenpaullone and XAV939 both were embryo-toxic, and we found that in the presence of FICZ, the toxicity of 1-azakenpaullone decreased while the toxicity of XAV939 increased. This rescue of 1-azakenpaullone effects occurred in the time window of Ahr2-mediated toxicity and was reversed by morpholino-oligonudeotide knockdown of Ahr2. Regarding PCB126, addition of either 1-azakenpaullone or XAV939 led to lower mortality than with PCB126 alone but surviving embryos showed severe edemas. 1-Azakenpaullone induced transcription of beta-catenin-associated genes, while PCB126 and FICZ blocked this induction. The data indicate a stage-dependent antagonism of p-catenin by Ahr2 in zebrafish embryos. We propose that the AHR has a physiological role in regulating beta-catenin during development, and that this is one point of intersection linking toxicological and physiological AHR-governed processes. (C) 2015 Elsevier Inc. All rights reserved.