Cytochrome P4501A1 and cytochrome P4501A2 are downregulated at both transcriptional and post-transcriptional levels by conditions resulting in interferon-alpha/beta induction.

The interferon mediated downregulation of constitutive and inducible cytochrome P450 enzymes occurs through a pretranslational mechanism which depresses the mRNA encoding cytochrome P450s. We measured the transcription rates of CYP1A genes and the turnover of CYP1A mRNA in rats treated with the interferon-alpha/beta inducer polyinosinic acid-polycytidylic acid. The rate of transcription of CYP1A1 and CYP1A2 genes was significantly decreased in hepatic nuclei isolated from male rats treated with polyinosinic acid-polycytidylic acid (10 mg/kg). In addition the rate of degradation of hepatic CYP1A1 and CYP1A2 mRNA was examined following the inhibition of de novo transcription by actinomycin D (1 mg/kg). Messenger RNA levels were analysed by Northern and slot blotting with a 1.2 kb murine CYP1A1 cDNA probe. Interferon significantly augmented the rate of loss of CYP1A1 and CYP1A2 mRNAs suggesting that post-transcriptional degradation of mRNA contributes to the pre-translational events that cause cytochrome P450 downregulation. These results support the involvement of both transcriptional and post-transcriptional mechanisms in the loss of cytochrome P450s mediated by interferon inducers.