Nrf2/ARE pathway activation, HO-1 and NQ01 induction by polychlorinated biphenyl quinone is associated with reactive oxygen. species and PI3K/AKT signaling

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 Keapl 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 Keapl expression in nucleus suggested the dissociation of Nrf2/Keap1 complex. Similarly, mRNA level of Nrf2 was elevated significantly with PCB29-pQ treatment, but not Keapl. 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-3p was down-regulated. Pretreatment with LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), suppressed the phosphorylation of ART and inhibited PCB29-pQ induced Nrf2/HO-1 activation, meanwhile, GSK-30 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 ART pathway but not MAPK signaling, the activation of NI-f2/ARE may be an adaptive response to oxidative stress. (c) 2013 Elsevier Ireland Ltd. All rights reserved.