Lack of CYP1A1 expression is involved in unresponsiveness of the human hepatoma cell line SK-HEP-1 to dioxin

Toxicol Lett. 2005 Dec 30;160(1):22-33. doi: 10.1016/j.toxlet.2005.06.003. Epub 2005 Jul 28.

Abstract

The aryl hydrocarbon receptor (AhR) mediates a wide variety of toxic effects due to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The human hepatoma cell line SK-HEP-1 expresses AhR and ARNT. However, TCDD failed to induce CYP1A1 and XRE-dependent reporter genes in these cells. Although CYP1A1 was not induced by TCDD exposure, both CYP1B1 and AhR repressor (AhRR) were constitutively expressed. The AhR antagonist alpha-naphthoflavone altered the basal level of XRE-dependent reporter gene expression dose-dependently. As our results suggested the activation of AhR signals by putative endogenous ligands, we established SK-HEP-1-derived cell lines that stably expressed CYP1A1. The inducibility of XRE-dependent reporter genes and CYP1B1 by TCDD was restored in these cells. Our findings demonstrated the presence of endogenous ligands in SK-HEP-1 cells due to the absence of the metabolizing enzyme CYP1A1, but not CYP1B1, which allowed the constitutive expression of AhR target genes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors
  • Aryl Hydrocarbon Hydroxylases / biosynthesis
  • Aryl Hydrocarbon Hydroxylases / genetics
  • Aryl Hydrocarbon Hydroxylases / metabolism
  • Aryl Hydrocarbon Receptor Nuclear Translocator / metabolism
  • Benzoflavones / pharmacology
  • Carcinoma, Hepatocellular
  • Cell Line, Tumor
  • Cytochrome P-450 CYP1A1 / antagonists & inhibitors
  • Cytochrome P-450 CYP1A1 / biosynthesis
  • Cytochrome P-450 CYP1A1 / deficiency*
  • Cytochrome P-450 CYP1A1 / genetics
  • Cytochrome P-450 CYP1B1
  • Dioxins / metabolism
  • Dioxins / toxicity*
  • Ellipticines / pharmacology
  • Enzyme Inhibitors / pharmacology
  • Gene Expression / drug effects
  • Humans
  • Liver / drug effects*
  • Liver / enzymology*
  • Liver / metabolism
  • Plasmids
  • RNA, Messenger / biosynthesis
  • RNA, Messenger / genetics
  • Receptors, Aryl Hydrocarbon / agonists
  • Receptors, Aryl Hydrocarbon / antagonists & inhibitors
  • Receptors, Aryl Hydrocarbon / genetics
  • Receptors, Aryl Hydrocarbon / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transfection

Substances

  • Benzoflavones
  • Dioxins
  • Ellipticines
  • Enzyme Inhibitors
  • RNA, Messenger
  • Receptors, Aryl Hydrocarbon
  • ellipticine
  • Aryl Hydrocarbon Receptor Nuclear Translocator
  • alpha-naphthoflavone
  • Aryl Hydrocarbon Hydroxylases
  • CYP1B1 protein, human
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP1B1