PI3K/Akt Pathway Mediates Nrf2/ARE Activation in Human L02 Hepatocytes Exposed to Low-Concentration HBCDs

Abstract

We investigated the effects of hexabromocyclododecanes (HBCDs) at environmentally relevant concentrations on human L02 hepatocytes and explored possible underlying molecular mechanism(s), focusing on functional interactions between the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) and nuclear factor-erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) pathways. The results showed that low concentrations of HBCDs could stimulate cell proliferation in a "DNA-dependent protein kinase catalytic subunit" (DNA-PKcs)-dependent manner, increase protein levels and nuclear translocation of transcription factor Nrf2, and upregulate expression of its target gene heme oxygenase-1 (HO-1). Electrophoretic mobility-shift assays (EMSAs) showed that ARE was a prominent element for HO-1 induction after low-concentration HBCDs exposure. The relationship between PI3K/Akt pathway and Nrf2/HO-1 axis was demonstrated by the finding that pretreatment with PI3K inhibitors (wortmannin, LY294002) attenuated the upregulation of Nrf2 expression induced by HBCDs exposure. Furthermore, knock-down of DNA-PKcs through small interfering RNA blocked Nrf2/HO-1 axis activation in L02 cells exposed to low-concentration HBCDs. Moreover, DNA-PKcs and phosphorylated Akt at Ser(473) proved to be crucial in regulating the Nrf2-ARE pathway. Thus, the PI3K/Akt pathway is essential in regulating Nrf2-ARE pathway activation in L02 cells induced by low-concentration HBCDs.