INTERFERON-GAMMA DOWN-REGULATES CYTOCHROME-P450 3A GENES IN PRIMARY CULTURES OF WELL-DIFFERENTIATED RAT HEPATOCYTES

Administration of interferons of both the gamma and alfa/beta classes down-regulates hepatic cytochrome P450 (CYP) genes when administered t o humans or rats, In male rats, interferons decrease expression of CYP 3A2 at a pretranslational level, but because interferons also release other cytokines in vivo it is unclear whether this is a direct effect on hepatocytes. We therefore examined the effects of rat recombinant i nterferon gamma (IFN-gamma) on CYP3A2, other 3A genes, and 2C11 in sta ble primary cultures of male rat hepatocytes. Hepatocytes were culture d on matrigel in Williams' E, and messenger RN-As (mRNAs) for 3A2, 3A1 -like CYPs, and 2C11 mRNA were determined by RNase protection assays. CYP3A and 2C11 proteins were immunoquantified, and their catalytic act ivities were estimated by testosterone hydroxylation pathways. In cont rol cells, 3A2 mRNA decreased initially but then recovered, and stable levels (15% of freshly isolated cells) were attained between days 3 a nd 7. Phenobarbital increased 3A2 mRNA to 60-120% values of freshly is olated cells, and mRNA for 3A1-like CYPs were increased 20-fold. In bo th control and phenobarbital-treated hepatocytes, rat recombinant IFN- gamma (33 U/mL) reduced mRNA for 3A2 and 3A1-like CYPs, as well as 3A protein and testosterone 6 beta-hydroxylase activity. Interferon had n o effect on CYP2C11 at mRNA or protein levels in untreated cells, alth ough a reduction in 2C11 protein was evident in phenobarbital-treated cultures. It is concluded that interferon directly alters expression o f constitutive and inducible CYP3A genes in well-differentiated male r at hepatocytes in culture, but has no effect on constitutive expressio n of CYP2C11.