Nrf2/ARE pathway activation, HO-1 and NQO1 induction by polychlorinated biphenyl quinone is associated with reactive oxygen species and PI3K/AKT signaling

Chem Biol Interact. 2014 Feb 25;209:56-67. doi: 10.1016/j.cbi.2013.12.005. Epub 2013 Dec 17.


Nrf2/ARE pathway plays an important role in adapt to oxidative stress caused by pro-oxidants and electrophiles through up-regulating phase II detoxifying enzymes. Our previous study has demonstrated that PCB quinone exposure causes severe cellular oxidative stress (Toxicology In Vitro 26 (2012) 841-848). There are no reports describing the ability of PCB quinone on Nrf2/ARE activation. In the present study, we found that exposure to PCB29-pQ resulted in a significant increase in Nrf2 and Keap1 expression in total protein, as well as the Nrf2 targeting genes, including NQO1 and HO-1. Next, immunocytochemistry analysis identified the accumulation of Nrf2 in nucleus subsequent to PCB29-pQ treatment. The increased Nrf2 and constant Keap1 expression in nucleus suggested the dissociation of Nrf2/Keap1 complex. Similarly, mRNA level of Nrf2 was elevated significantly with PCB29-pQ treatment, but not Keap1. Additionally, PCB29-pQ treatment led to significant up-regulation of the mRNA level of antioxidant enzymes, NQO1 and HO-1, in a concentration-dependent manner. Electrophoretic mobility shift assay and luciferase reporter assay further confirmed the formation of Nrf2-ARE complex. PCB29-pQ treatment has no effect on mitogen-activated protein kinase signaling, however, phospho-AKT was up-regulated and GSK-3β was down-regulated. Pretreatment with LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), suppressed the phosphorylation of AKT and inhibited PCB29-pQ induced Nrf2/HO-1 activation, meanwhile, GSK-3β expression was increased accordingly. At last, reactive oxygen species (ROS) scavengers inhibited PCB29-pQ induced Nrf2 activation partly. These results suggested that Nrf2 activation by PCB29-pQ in HepG2 cells is associated with ROS and AKT pathway but not MAPK signaling, the activation of Nrf2/ARE may be an adaptive response to oxidative stress.

Keywords: HO-1; Keap1; MAPK; NQO1; PCB; ROS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzoquinones / chemistry
  • Benzoquinones / toxicity
  • Blotting, Western
  • Elafin / metabolism
  • Environmental Pollutants / toxicity
  • Enzymes / metabolism
  • Gene Expression Regulation / drug effects*
  • Heme Oxygenase-1 / metabolism
  • Hep G2 Cells
  • Humans
  • Immunohistochemistry
  • Molecular Structure
  • NAD(P)H Dehydrogenase (Quinone) / metabolism
  • NF-E2-Related Factor 2 / metabolism*
  • Oncogene Protein v-akt / metabolism*
  • Polychlorinated Biphenyls / chemistry
  • Polychlorinated Biphenyls / toxicity
  • Reactive Oxygen Species / metabolism*
  • Signal Transduction / drug effects*
  • Vesicular Transport Proteins / metabolism*


  • 2,3,5-trichloro-6-phenyl-(1,4)benzoquinone
  • Benzoquinones
  • Elafin
  • Environmental Pollutants
  • Enzymes
  • NF-E2-Related Factor 2
  • NFE2L2 protein, human
  • PI3 protein, human
  • Reactive Oxygen Species
  • VPS52 protein, human
  • Vesicular Transport Proteins
  • Polychlorinated Biphenyls
  • Heme Oxygenase-1
  • NAD(P)H Dehydrogenase (Quinone)
  • NQO1 protein, human
  • Oncogene Protein v-akt