TY - JOUR
T1 - The mechanism of action of α-naphthoflavone as an inhibitor of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced CYP1A1 gene expression
AU - Merchant, M.
AU - Arellano, L.
AU - Safe, S.
N1 - Funding Information:
i This work was supported by the Texas Agricultural Station and the National Institutes of Health (ES03843); Burroughs Welcome Toxicology Scholar. x To whom correspondence should be addressed.
PY - 1990/8/15
Y1 - 1990/8/15
N2 - Treatment of rat hepatoma H-4-II E cells with α-naphthoflavone (αNF) (10-8, 10-7, 10-6 m) resulted in only minimum induction of ethoxyresorufin O-deethylase (EROD) activity and cytochrome P4501A1 mRNA levels only at 10-6 m. In contrast, 2,3,7,8-tetrachlorodi-benzo-p-dioxin (TCDD) caused maximum or near maximum induction responses at 10-8 and 10-9 m. In a timecourse study with TCDD (10-9 m), and TCDD plus αNF (cotreated), αNF significantly inhibited the induction of EROD activity and cytochrome P4501A1 mRNA levels by TCDD for 6-24 h after initial exposure of the cells to the chemicals. In addition, treatment of the cells with 10-9 m TCDD in the presence or absence of 10-8, 10-7, and 10-9 m αNF showed that the latter compound inhibited the induction effects by TCDD in a concentration-dependent manner and these inhibitory effects could be overcome, in part, by a higher concentration of TCDD (10-8 m). Treatment of the rat hepatoma H-4-II E cells with [3H]TCDD showed that within 60 min, there was an initial rapid increase in nuclear [3H]TCDD receptor complex levels (38 fmol/mg protein) which decreased to less than 10 fmol/mg protein within 4 h and remained relatively constant for up to 24 h. However, in cells treated with [3H]TCDD (10-9m) plus αNF (10-6 m) the levels of the nuclear [3H]TCDD receptor complex were <5 fmol/mg protein throughout the 24-h time course. These data, coupled with the results which indicate that the αNF competitively inhibits the binding of [3H]-TCDD to the cytosolic aryl hydrocarbon (Ah) receptor, suggest that αNF inhibits the TCDD-mediated induction of CYP1A1 gene transcription and translation by direct competition for cytosolic Ah receptor binding sites.
AB - Treatment of rat hepatoma H-4-II E cells with α-naphthoflavone (αNF) (10-8, 10-7, 10-6 m) resulted in only minimum induction of ethoxyresorufin O-deethylase (EROD) activity and cytochrome P4501A1 mRNA levels only at 10-6 m. In contrast, 2,3,7,8-tetrachlorodi-benzo-p-dioxin (TCDD) caused maximum or near maximum induction responses at 10-8 and 10-9 m. In a timecourse study with TCDD (10-9 m), and TCDD plus αNF (cotreated), αNF significantly inhibited the induction of EROD activity and cytochrome P4501A1 mRNA levels by TCDD for 6-24 h after initial exposure of the cells to the chemicals. In addition, treatment of the cells with 10-9 m TCDD in the presence or absence of 10-8, 10-7, and 10-9 m αNF showed that the latter compound inhibited the induction effects by TCDD in a concentration-dependent manner and these inhibitory effects could be overcome, in part, by a higher concentration of TCDD (10-8 m). Treatment of the rat hepatoma H-4-II E cells with [3H]TCDD showed that within 60 min, there was an initial rapid increase in nuclear [3H]TCDD receptor complex levels (38 fmol/mg protein) which decreased to less than 10 fmol/mg protein within 4 h and remained relatively constant for up to 24 h. However, in cells treated with [3H]TCDD (10-9m) plus αNF (10-6 m) the levels of the nuclear [3H]TCDD receptor complex were <5 fmol/mg protein throughout the 24-h time course. These data, coupled with the results which indicate that the αNF competitively inhibits the binding of [3H]-TCDD to the cytosolic aryl hydrocarbon (Ah) receptor, suggest that αNF inhibits the TCDD-mediated induction of CYP1A1 gene transcription and translation by direct competition for cytosolic Ah receptor binding sites.
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U2 - 10.1016/0003-9861(90)90416-V
DO - 10.1016/0003-9861(90)90416-V
M3 - Article
C2 - 2166479
AN - SCOPUS:0025294713
SN - 0003-9861
VL - 281
SP - 84
EP - 89
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 1
ER -