Induction of cytochrome P-450 1A2 by oxidized tryptophan in Hepa lclc7 cells

Recent studies from this laboratory have demonstrated that L-tryptophan, af ter oxidation either by UV-irradiation or ozone, induces aryl hydrocarbon r eceptor (AhR) activation and binding of the liganded AhR complex to its spe cific DNA recognition site, thereby initiating transcription of the cytochr ome P-450 1a1 (Cyp1a1) gene with concomitant increase of CYP1A1 protein and 7-ethoxyresorufinO-deethylase activity in wild-type mouse hepatoma cells, Hepa lclc7 (Hepa-1), in culture. Temporary inhibition of protein synthesis by cycloheximide resulted in superinduction of oxidized tryptophan-inducibl e CYP1A1 mRNA, protein, and 7-ethoxyresorufin O-deethylase activity in Hepa -1 cells. In the present communication, the results obtained by immunoblot analyses with monoclonal CYP1A1/1A2 antibody (NIH 1-7-1) demonstrate that b oth UV- or ozone-oxidized tryptophan also induce CYP1A2 protein in Hepa-1 c ells. CYP1A2 mRNA, detected by reverse transcription-polymerase chain react ion, was markedly induced in the UV- or ozone-oxidized tryptophan-treated c ells. Temporary inhibition of protein synthesis by cycloheximide further in duced oxidized tryptophan-inducible CYP1A2 mRNA as well as the protein in H epa-1 cells. This is the first report demonstrating the induction of CYP1A2 mRNA and protein in Hepa-1 cells.