A study to decipher the mechanism involved in the oxidation of the phosphatase PTEN by reactive oxygen species and its relevance to the activation of the survival kinase AKT by growth factors.

Abstract

Constitutive activation of the PI3K/Akt survival pathway and increase in intracellular reactive oxygen species such as superoxide and hydrogen peroxide are two characteristics associated with tumor cells survival and proliferation. However, the mechanism by which ROS inhibit apoptosis or induce cell growth is not clearly understood. Using diethyldithiocarbamate, an inhibitor of Cu/ZnSOD, silencing of the Cu/ZnSOD gene with specific small interference RNA to increase intracellular level of supweroxide and exposure of mouse embryonic fibroblasts to physiologically relevant concentration of hydrogen peroxide, I demonstrate that both ROS are able to induce the activation of the survival kinase Akt in the absence of growth factors in the culture medium. Using alkylation of cysteine residues by N-ethylmaleimide and differential reduction of oxidized protein by DTT and ascorbate, I demonstrate that activation of Akt by either ROS was due to an oxidative modification of the tumor suppressor PTEN that was identified as S-nitrosylation rather than a disulfide bond modification of the protein as previously reported.