Induction of two forms of eel cytochrome P450 1A genes by 3-methylcholanthrene

In eel (Anguilla japonica), exposure to polyaromatic hydrocarbons such as 3 -methylcholanthrene leads to induction of two CYP1A enzymes, CYP1A1 and CYP 1A6. We studied the time course and tissue specificity of induction of mess enger RNAs for CYP1A1 and CYP1A6 in eel by administering 3-methylcholanthre ne intraperitoneally. In both cases, the drug induced a rapid increase of m RNAs and biphasic expression. In the liver, mRNA levels of CYP1A1 and CYP1A 6 increased 22-fold at 3 hours and 27-fold at 6 hours after the administrat ion, respectively, showing initial peaks in the induction. After the initia l inductions, mRNA levels decreased unexpectedly. Following these temporary decreases, the mRNA levels again increased and reached levels that were 35 and 41 times the basal levels at 24 hours after administration, respective ly. CYP1A1 and CYP1A6 resembled each other also in the tissue specificity o f gene expression; the expression levels were liver > gill > intestine > ki dney. The rapid induction, the biphasic expression, and the tissue-specific expression were common features of gene expression in CYP1A1 and CYP1A6 an d may come from common structures of the regulatory regions of the two gene s.