Hydrogen peroxide mediates arsenite activation of p70(s6k) and extracellular signal-regulated kinase

Abstract

To define the mechanism of arsenite-induced tumor promotion, we examined the role of reactive oxygen species (ROS) in the signaling pathways of cells exposed to arsenite. Arsenite treatment resulted in the persistent activation of p70(s6k) and extracellular signal-regulated kinase 1/2 (ERK1/2) which was accompanied by an increase in intracellular ROS production. The predominant produced appeared to be H2O2, because the arsenite-induced increase in dichlorofluorescein (DCF) fluorescence was completely abolished by pretreatment with catalase but not with heat-inactivated catalase. Elimination of H2O2 by catalase or N-acetyl-(L)-Cysteine inhibited the arsenite-induced activation of p70(s6k) and ERK1/2, indicating the possible role of H2O2 in the arsenite activation of the p70(s6k) and the ERK1/2 signaling pathways. A specific inhibitor of p70(s6k), rapamycin, and calcium chelators significantly blocked the activation of p70(s6k) induced by arsenite. While the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002 completely abrogated arsenite activation of p70(s6k), ERK1/2 activation by arsenite was not affected by these inhibitors, indicating that H2O2 might act as an upstream molecule of PI3K as well as ERK1/2. Consistent with these results, none of the inhibitors impaired H2O2 production by arse