Mechanism of the synergistic induction of CYP2H by isopentanol plus ethanol: Comparison to glutethimide and relation to induction of 5-aminolevulinate synthase

We had previously found that combined treatment with isopentanol and ethano l synergistically induced CYP2H protein and activity in cultured chick nepa toytes, Here we investigated the mechanism of induction of CYP2H by the alc ohols and whether they caused a coordinate induction of 5-aminolevulinate s ynthase (ALAS) mRNA. Treatment with isopentanol alone or in combination wit h ethanol resulted in coordinate increases in CYP2H1 and ALAS mRNAs, With i sopentanol alone, the amounts of CYP2H1 and ALAS mRNAs at 4 to 6 h were sim ilar to those observed after treatment with the alcohol combination, but de clined by 11 h. Readdition of isopentanol at 11 h again increased the expre ssion of both mRNAs, indicating that the decreases at 11 h were due to limi ting amounts of inducer. Similar results were observed in cells exposed to low concentrations of glutethimide. In the combined alcohol treatment, incr eases in CYP2H1 and ALAS mRNAs were sustained from 4 h to 11 h after additi on of the alcohols, but decreased to control levels by 24 h. Using pulse la beling to measure de novo synthesis of CYP2H1/2 protein, we found that the increases in CYP2H1/2 protein reflected the increases in CYP2H1 mRNA. The h alf-life of CYP2H1/2 protein, measured from pulse-chase experiments, was ap proximately twofold greater than the half-life of CYP2H1 mRNA. Our results indicate that the alcohols and glutethimide coordinately increase ALAS and CYP2H1 mRNA, and that increases in CYP2H1/2 protein arise from increases in its mRNA. (C) 1998 Academic Press.