Rk. Sindhu et al., INDUCTION OF CYTOCHROME P4501A1 BY PHOTOOXIDIZED TRYPTOPHAN IN HEPA LCLC7 CELLS, Biochemical pharmacology, 52(12), 1996, pp. 1883-1893
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.