P24: Inhibition of 3-methylcholanthrene (3MC)-induced Cyp1a1 Expression by Hypoxic Agent in Zebrafish Embryos

Abstract

Cyp1A1 transcription is induced by polycyclic aromatic hydrocarbons (PAHs), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (3MC), through the AHR pathway. Ligand-activated aryl hydrocarbon receptor (AHR) interacts with aryl hydrocarbon receptor nuclear translocator (ARNT), and this heterodimeric complex binds to aryl hydrocarbon response elements (AHRE) in the regulatory region of the Cyp1A1 gene, thereby inducing Cyp1A1 transcription. In hypoxic conditions, accumulated hypoxia-induced factor-1α (HIF-1α) interacts with ARNT, and this dimer binds to the regulatory region of these target genes and activates their expression. Because ARNT plays a critical role in both the AHR- and HIF-1α-mediated pathways, activation of HIF-1α may sequester ARNT, thus inhibiting the AHR-mediated pathway. To determine whether the 3MC-induced AHR pathway can be inhibited by the hypoxia-inducing agent, cobalt chloride, fertilized zebrafish embryos, and embryos (F 4 ) of stable transgenic zebrafish containing the EGFP reporter gene driven by AHRE were treated with vehicle (0.1% DMSO) or 3MC (60 μM). Immediately, 3 MC-treated embryos were transferred to media in either normoxic or hypoxic conditions induced by cobalt chloride. 3MC-induced Cyp1A1 mRNA expression was significantly inhibited by cobalt chloride treatment. 3MC-induced EGFP expression in the liver and head area of stable transgenic zebrafish embryos was reduced by cobalt chloride treatment. In this study, we have shown that the hypoxic condition induced by cobalt chloride inhibited 3MC-induced Cyp1A1 transcription in zebrafish embryos. This might be due to the sequestering of ARNT by HIF-1α or another mechanism.