Down-regulation of P4501A1 and P4501A2 mRNA expression in isolated hepatocytes by oxidative stress.

We have previously shown that the inflammatory mediator interleukin-1 suppressed transcription of CYP1A1 and CYP1A2 mRNAs (Barker, C.W., Fagan, J.B., and Pasco, D.S. (1992) J. Biol. Chem. 267, 8050-8055). Since many of the actions of inflammatory mediators are mimicked by oxidative stress, we treated isolated hepatocytes with 0.25-1.0 mM H2O2 to determine whether expression of these genes is also modulated by oxidative stress. Inducer-dependent accumulation of CYP1A1 and CYP1A2 mRNAs were maximally reduced approximately 50 and 70%, respectively, by 1.0 mM H2O2. Run-on transcription analysis suggested that the effect of H2O2 was mediated transcriptionally. The reduction in CYP1A mRNA levels was not due to a reduction in the levels of all mRNAs due to some general toxic effect since H2O2 did not reduce glyceraldehyde-3-phosphate dehydrogenase, alpha-tubulin, beta-fibrinogen, or albumin mRNA levels, and did not increase lactate dehydrogenase released into the medium. Insulin-mimicked H2O2 action, reducing the expression of both mRNAs, and N-acetylcysteine, which increases intracellular glutathione levels, completely reversed the insulin effect on both mRNAs and the H2O2 effect on CYP1A1 mRNA, but only partially reversed the H2O2 effect on CYP1A2 mRNA. This study indicates that the CYP1A1 and CYP1A2 genes are responsive to oxidative stress and that the majority of this responsiveness can be modified by cellular redox potential.