INDUCTION OF CYTOCHROME P4501A1 BY PHOTOOXIDIZED TRYPTOPHAN IN HEPA LCLC7 CELLS

Mouse hepatoma Hepa-1c1c7 (Hepa-1) cells were cultivated in the presen ce of UV-irradiated amino acids. The results demonstrated that all of the amino acids tested, UV-oxidized tryptophan caused the highest indu ction of 7-ethoxyresorufin O-deethylase (EROD) activity compared with the controls (P < 0.01). The induction of EROD activity by oxidized tr yptophan was dose dependent, and maximal induction was obtained at 12 hr after administration. Studies with various Hepa-1 mutants, which ar e defective in either the aryl hydrocarbon (Ah) receptor or Ah recepto r nuclear translocator protein, indicated that the induction of EROD a ctivity by oxidized tryptophan occurs through the Ah receptor. Gel mob ility shift assays using nuclear extracts of Hepa-1 cells revealed tha t oxidized products of tryptophan can induce both Ah receptor transfor mation and binding of the liganded Ah receptor complex to its specific DNA recognition site. CYP1A1 mRNA, quantified by reverse transcriptio n-polymerase chain reaction, and CYP1A1 protein were induced markedly in the oxidized tryptophan group compared with the controls. Injection of isolated oxidized tryptophan products into adult male rats caused significant induction of EROD activity in the pulmonary and hepatic mi crosomes compared with the controls (P < 0.01). These results demonstr ated that oxidized tryptophan induces Ah receptor activation and bindi ng of the liganded Ah receptor complex to its specific DNA recognition site, thereby initiating transcription and translation of the CYP1A1 gene with concomitant increase of EROD activity in Hepa-1 cells. Induc tion of EROD activity in the liver and lungs after injection of isolat ed oxidized tryptophan products into rats suggests that a similar mech anism may be operative in vivo. Copyright (C) 1996 Elsevier Science In c.