Mechanism of benzo[a]pyrene-induced Cyp1a-1 gene expression in mouse Hepa 1c1c7 cells: role of the nuclear 6 s and 4 s proteins

Arch Biochem Biophys. 1992 Jan;292(1):250-7. doi: 10.1016/0003-9861(92)90076-9.


Treatment of wild-type (wt) aryl hydrocarbon (Ah)-responsive mouse Hepa 1c1c7 cells with benzo[a]pyrene (B[a]P) caused a concentration-dependent induction of ethoxyresorufin O-deethylase (EROD) activity. In contrast, B[a]P was inactive as an inducer in Ah nonresponsive class 1 and class 2 mutant cell lines. In parallel experiments, the nuclear fractions from wt cells treated with 10(-7) M [3H]B[a]P contained both the 4 s carcinogen binding protein and the 6 s (Ah receptor) complexes, whereas only the 4 s complex was present in the nuclear fraction of the class 2 mutant cells. The results obtained from cotreatment of wt Hepa 1c1c7 cells with 10(-6) or 10(-7) M B[a]P and 5 x 10(-7) or 10(-7) M 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) showed that MCDF inhibited the induction of EROD activity and Cyp1a-1 mRNA levels by B[a]P. Moreover, using 10(-7) M [3H]B[a]P and unlabeled MCDF, it was shown that MCDF not only inhibited the induction response but also caused a concentration-dependent decrease in levels of the nuclear 6 s complex but not the 4 s complex. In contrast, in situ competition studies with unlabeled 10(-6) M benzo[ghi]-perylene (B[ghi]P) resulted in the elimination of the nuclear [3H]B[a]P 4 s complex (but not the 6 s complex); however, the EROD activity and Cyp1a-1 mRNA levels in cells treated with 10(-7) M B[a]P in the presence or absence of 10(-6) M B[ghi]P were not significantly different. These results indicate that the 4 s binding protein is not required for the induction of Cyp1a-1 gene expression in Hepa 1c1c7 cells and suggest that B[a]P and 2,3,7,8-tetrachlorodibenzo-p-dioxin induce Cyp1a-1 gene expression via a common mechanism which involves binding to the Ah receptor.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Benzo(a)pyrene / pharmacology*
  • Binding, Competitive
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Cell Line
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 Enzyme System / biosynthesis
  • Cytochrome P-450 Enzyme System / genetics*
  • Enzyme Induction
  • Gene Expression Regulation, Neoplastic / drug effects
  • Glycine N-Methyltransferase
  • Liver Neoplasms, Experimental / enzymology
  • Liver Neoplasms, Experimental / genetics*
  • Methyltransferases*
  • Mice
  • Molecular Sequence Data
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Nuclear Proteins / physiology*
  • Oxidoreductases / biosynthesis
  • Oxidoreductases / genetics*
  • Receptors, Aryl Hydrocarbon
  • Receptors, Drug / drug effects


  • Carrier Proteins
  • Nuclear Proteins
  • Receptors, Aryl Hydrocarbon
  • Receptors, Drug
  • Benzo(a)pyrene
  • Cytochrome P-450 Enzyme System
  • Oxidoreductases
  • Cytochrome P-450 CYP1A1
  • Methyltransferases
  • Glycine N-Methyltransferase