Inhibition of hypoxia/reoxygenation-induced oxidative stress in HGF-stimulated antiapoptotic signaling: role of PI3-K and Akt kinase upon rac1

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Abstract
Rac1-regulated reactive oxygen species (ROS) production has been implicated in apoptosis. In contrast, pleiotropic protein kinase Akt protects against apoptosis. However, the pro- and antiapoptotic mechanisms of rac1 and Akt, respectively, and the intersection between these mechanisms are incompletely understood. In a model of oxidative stress and apoptosis induced by hypoxia/reoxygenation (H/R) in primary hepatocytes, activation of the PI3–K Akt axis by the prosurvival hepatocyte growth factor (HGF) inhibited H/R-stimulated rac1 activation and intracellular ROS production, and suppressed apoptosis. Suppression of PI3-K or Akt activity abrogated the inhibitory effect of HGF on rac1 activity and rac1-regulated oxidative stress. Furthermore, constitutive activation of Akt or PI3-K in the absence of HGF was sufficient to phosphorylate rac1, inhibit rac1 activation, and suppress rac1-regulated ROS production. These findings demonstrate that growth factor-stimulated activation of PI3-K–Akt is necessary and sufficient to suppress intracellular oxidative stress and apoptosis by inhibiting activation of pro-apoptotic, prooxidative rac1 GTPase.