Preferential inducibility of CYP1A1 and CYP1A2 by TCDD: differential regulation in primary human hepatocytes versus transformed human cells

Biochem Biophys Res Commun. 2006 Mar 10;341(2):399-407. doi: 10.1016/j.bbrc.2005.12.203. Epub 2006 Jan 11.


Cytochrome P4501A1 (CYP1A1) induction, a marker of aryl hydrocarbon (Ah) receptor activation, has been associated with carcinogenicity of the environmental agent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Consistently, we show that TCDD treatment led to induction of CYP1A1 in responsive human cancer cell lines including HepG2, LS174T, and MCF-7, as determined by Western blotting and CYP1A form-selective R-warfarin 6- and 8-hydroxylation. TCDD, however, preferably induced CYP1A2, not CYP1A1, in primary human hepatocytes. Such CYP1A form-preferred induction at the protein level was apparently uncorrelated with non-preferred mRNA induction in any cells studied. Moreover, while both genes were up-regulated by TCDD in primary hepatocytes and HepG2 cells, the induction of CYP1A1 and CYP1A2 at the mRNA level was distinguishable, indicated by the marked differences in activation kinetics and the response to the protein synthesis inhibitors, anisomycin and cycloheximide. Furthermore, formation of total benzo(a)pyrene (BaP)-DNA adducts was not altered following BaP exposure in TCDD-treated primary hepatocytes, whereas significantly elevated, in a CYP1A1-dependent manner, in the treated HepG2 cells. Taken together, our findings, demonstrating the complexities of TCDD-associated human Ah receptor function and differential regulations of CYP 1A enzymes, suggest clearly the need for caution when extrapolating data obtained in cell-based models.

MeSH terms

  • Anisomycin / pharmacology
  • Aryl Hydrocarbon Receptor Nuclear Translocator / chemistry
  • Benzo(a)pyrene / chemistry
  • Blotting, Western
  • Cell Line
  • Cell Line, Transformed
  • Cell Line, Tumor
  • Cycloheximide / pharmacology
  • Cytochrome P-450 CYP1A1 / genetics*
  • Cytochrome P-450 CYP1A2 / genetics*
  • DNA Adducts
  • Dioxins / chemistry
  • Environmental Pollutants / toxicity*
  • Gene Expression Regulation, Neoplastic* / drug effects
  • Hepatocytes / metabolism*
  • Humans
  • Kinetics
  • Polychlorinated Dibenzodioxins / toxicity*
  • Protein Synthesis Inhibitors / pharmacology
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Time Factors
  • Up-Regulation
  • Warfarin / pharmacology


  • DNA Adducts
  • Dioxins
  • Environmental Pollutants
  • Polychlorinated Dibenzodioxins
  • Protein Synthesis Inhibitors
  • RNA, Messenger
  • Aryl Hydrocarbon Receptor Nuclear Translocator
  • Benzo(a)pyrene
  • Warfarin
  • Anisomycin
  • Cycloheximide
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP1A2