Activation of Phosphatidylinositol 3-Kinase and Akt bytert-Butylhydroquinone Is Responsible for Antioxidant Response Element-Mediated rGSTA2 Induction in H4IIE Cells

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Abstract
The protective adaptive response to electrophiles and reactive oxygen species is mediated by enhanced expression of phase II detoxifying genes, including glutathione S-transferases, through activation of antioxidant response element (ARE). The current study was designed to investigate the role of phosphatidylinositol 3-kinase (PI3-kinase)-Akt and mitogen-activated protein (MAP) kinase signaling pathways in the induction of rGSTA2 bytert-butylhydroquinone (t-BHQ). Nuclear ARE complex was activated 1 to 6 h after treatment of H4IIE cells with t-BHQ. The rGSTA2 mRNA level was elevated 6 to 24 h after t-BHQ treatment, which led to the enzyme induction. Activities of PI3-kinase and Akt were increased 10 min through 6 h after t-BHQ treatment, whereas wortmannin or LY294002, PI3-kinase inhibitors, completely abolished ARE binding activity and increases in rGSTA2 mRNA and protein. Extracellular signal-regulated kinase (ERK), p38 MAP kinase, and c-Jun N-terminal kinase (JNK) were all activated by t-BHQ. Treatment with PD98059, an ERK inhibitor, however, increased rGSTA2 mRNA and further enhanced t-BHQ-induced expression of rGSTA2. Neither SB203580 nor overexpression of JNK1 dominant negative mutant altered t-BHQ–inducible rGSTA2 expression. These results demonstrated that t-BHQ activated PI3-kinase and Akt, which was responsible for ARE-mediated rGSTA2 induction, and that ERK might negatively regulate rGSTA2 expression, whereas activation of p38 MAP kinase or of JNK by t-BHQ was not associated with the enzyme induction.