Induction of drug metabolizing enzymes in human liver cell line Hep G2

Human cytochrome P-450, UDP-glucuronosyltransferase and sulphotransferase activities have been measured in the cell line Hep G2 following treatment of cells with 3-methylcholanthrene or phenobarbital. 3-Methylcholanthrene treatment caused a 20–30-fold increase in the O-deethylation of 7-ethoxycoumarin. The glucuronidation and sulphation of the product 7-hydroxycoumarin were increased 36 and 7 fold, respectively. In comparison, phenobarbital treatment did not increase these activities significantly. However, phenobarbital-inducible proteins were identified on ‘Western blots’ using antibodies to a rat liver phenobarbital inducible P-450 form. The molecular masses of the proteins did not coincide with those expected for cytochromes P-450. However, characteristic of P-450 forms, the synthesis of these proteins was suppressed by 3-methylcholanthrene treatment. The Hep G2 cell line represents a potentially useful model for studying the regulation of human P-450 genes.