Ethanol increases content and activity of human cytochrome P4502E1 in a transduced HepG2 cell line

Using recombinant retroviral expression, a HepG2 cell line which stably and constitutively expresses the coding sequences of the human cytochrome P4502E1 was previously established. Addition of ethanol (2 to 100 mM) to the culture medium of this cell line for two days resulted in an increase in the content of P4502E1 as determined by immunoblotting and an increase in HepG2 microsomal oxidation of p-nitrophenol, aniline, and N,N-dimethylnitrosamine. The ethanol-induced increase in microsomal oxidation of these substrates was prevented by ligands and inhibitors of P4502E1 as well as anti-human P4502E1 IgG and corresponded to the increase in P4502E1 content. Several other agents including pyrazole, 4-methylpyrazole, isoniazid, pyridine, and DMSO also increased the content of P4502E1 in this cell line but not oxidation of substrates, presumably a reflection of remaining tightly bound to the active site of P4502E1. Slot blot analysis indicated that ethanol addition did not increase P4502E1 mRNA levels. These results indicate that ethanol can increase the content of P4502E1 as well as catalytic oxidation of substrates dependent on P4502E1 in this experimental model, perhaps by stabilization of the protein against degradation.