Activation of nuclear receptor CAR by an environmental pollutant perfluorooctanoic acid

Arch Toxicol. 2017 Jun;91(6):2365-2374. doi: 10.1007/s00204-016-1888-3. Epub 2016 Nov 10.

Abstract

Perfluorocarboxylic acids (PFCAs) including perfluorooctanoic acid (PFOA) are environmental pollutants showing high accumulation, thermochemical stability and hepatocarcinogenicity. Peroxisome proliferator-activated receptor α is suggested to mediate their toxicities, but the precise mechanism remains unclear. Previous reports also imply a possible role of constitutive androstane receptor (CAR), a key transcription factor for the xenobiotic-induced expression of various genes involved in drug metabolism and disposition as well as hepatocarcinogenesis. Therefore, we have investigated whether PFCAs activate CAR. In wild-type but not Car-null mice, mRNA levels of Cyp2b10, a CAR target gene, were increased by PFOA treatment. PFCA treatment induced the nuclear translocation of CAR in mouse livers. Since CAR activators are divided into two types, ligand-type activators and phenobarbital-like indirect activators, we investigated whether PFCAs are CAR ligands or not using the cell-based reporter gene assay that can detect CAR ligands but not indirect activators. As results, neither PFCAs nor phenobarbital increased reporter activities. Interestingly, in mouse hepatocytes, pretreatment with the protein phosphatase inhibitor okadaic acid prevented an increase in Cyp2b10 mRNA levels induced by phenobarbital as reported, but not that by PFOA. Finally, in human hepatocyte-like HepaRG cells, PFOA treatment increased mRNA levels of CYP2B6, a CAR target gene, as did phenobarbital. Taken together, our present results suggest that PFCAs including PFOA are indirect activators of mouse and human CAR and that the mechanism might be different from that for phenobarbital. The results imply a role of CAR in the hepatotoxicity of PFCAs.

Keywords: Cytochrome P450; Environmental pollutant; Hepatocarcinogenesis; Liver hypertrophy; Nuclear receptor.

MeSH terms

  • Animals
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Caprylates / toxicity*
  • Cell Line
  • Cell Nucleus / metabolism
  • Cytochrome P450 Family 2 / metabolism*
  • Cytoplasm / metabolism
  • Environmental Pollutants / toxicity*
  • Fluorocarbons / toxicity*
  • Gene Expression Regulation / drug effects
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism
  • Humans
  • Liver / drug effects
  • Liver / metabolism
  • Mice, Inbred C57BL
  • Mice, Knockout
  • PPAR alpha / genetics
  • PPAR alpha / metabolism
  • Primary Cell Culture
  • Protein Transport
  • RNA, Messenger / metabolism
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Steroid Hydroxylases / metabolism*

Substances

  • Caprylates
  • Environmental Pollutants
  • Fluorocarbons
  • PPAR alpha
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • constitutive androstane receptor
  • perfluorooctanoic acid
  • Steroid Hydroxylases
  • Aryl Hydrocarbon Hydroxylases
  • Cyp2b10 protein, mouse
  • Cytochrome P450 Family 2