Significance of AHR nuclear translocation sequence in 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cPLA 2 α activation and hydronephrosis.

The aryl hydrocarbon receptor (AHR) plays a major role in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced toxicity phenotypes. TCDD bound to AHR elicits both genomic action in which target genes are transcriptionally upregulated and nongenomic action in which cytosolic phospholipase A2 α (cPLA2 α) is rapidly activated. However, how either of these actions, separately or in combination, induces toxicity phenotypes is largely unknown. In this study, we used AHRnls/nls mice as a model in which AHR was mutated to lack nuclear translocation sequence (NLS), and AHRd/- mice as the corresponding control. Using this model, we studied TCDD-induced alterations in cPLA2 α activation and related factors because of the pivotal roles of cPLA2 α both in AHR's nongenomic action and in regulation of causative genes of TCDD-induced hydronephrosis. Dams were orally administered TCDD at a dose of 300 µg/kg body weight on postnatal day 1, and pups subsequently exposed to TCDD via milk were examined for gene expression on PND 7 and for histological changes on PND 14. The activation of the AHR genomic action and hydronephrosis onset were observed in the control group but not in the AHRnls/nls group. An ex vivo experiment using peritoneal macrophages exposed to 100 nM TCDD resulted in rapid activation of cPLA2 α, an indicator of the nongenomic action, only in the control group but not in the AHRnls/nls group. These results indicated that an NLS is required for the AHR's genomic and nongenomic actions.