Expression and induction of a large set of drug-metabolizing enzymes by the highly differentiated human hepatoma cell line BC2

The BC2 cell line derived from the human hepatocarcinoma, HGB, undergoes a spontaneous sharp differentiation process in culture as it becomes confluen t, remains stably differentiated for several weeks, and may return to proli feration thereafter under appropriate density conditions. The relevance of the line as an hepatic model has been evaluated. Cells synthesize a large n umber of plasma proteins, and rates of glycogen and urea synthesis increase with time of confluency and become sensitive to insulin, reflecting the pr ocess of differentiation. Differentiated BC2 cells express the most relevan t cytochrome P-450 (CYP) isozyme activities (CYP1A1/2, 2A6, 2B6, 2C9, 2E1, and 3A4) and conjugating enzymes (glutathione S-transferase and UDP-glucuro nyltransferase) and also respond to model inducers. Methylcholanthrene indu ced an increase in CYP1A1/2 enzyme activity (eightfold), phenobarbital indu ced CYP2B6 activity (1.7-fold), and dexamethasone induced CYP3A4 activity ( fivefold). In parallel, expression of the most relevant liver-enriched tran scription factors, HNF-4, HNF-1, C/EBP-alpha and C/EBP-beta mRNAs, was sign ificantly increased in differentiated cultures. This increase was largest i n HNF-1 and HNF-4, which supports the idea that a redifferentiation process towards the hepatic phenotype takes place. BC2 is an hepatic cell line tha t is able to express most hepatic functions, especially the drug-biotransfo rmation function, far more efficiently than any previously described human hepatoma cell line.