Hypoxic condition interferes with phosphorylation of Akt at Thr(308) in cultured rat pheochromocytoma-12 cells.

Phosphorylation of Akt induced under hypoxic or ischemic conditions has been reported only for residue Ser(473). We examined whether Akt can be phosphorylated at Thr(308), another phosphorylation site on Akt, and can exhibit neuroprotective effects under conditions of hypoxia/reoxygenation, comparing pheochromocytoma-12 (PC12) cells transfected with constitutively active Akt (Myr-pCMV cells) and those transfected with pCMV vector only (pCMV cells). Expression levels of Akt phosphorylated at Ser(473) were 2.1-fold higher in Myr-pCMV cells compared with pCMV cells, before the onset of hypoxia, which were increased transiently during hypoxia, and then decreased gradually during reoxygenation. In contrast, Akt phosphorylated at Thr(308) was not detected in pCMV cells under any conditions but was expressed in Myr-pCMV cells prior to hypoxia, followed by an immediate decrease during hypoxia and a further decline during reoxygenation. However, G1-arrest of the cell cycle observed at 12 h after hypoxia in pCMV cells was prevented in Myr-pCMV cells. These findings suggest that hypoxia activates Akt by phosphorylation at Ser(473) only, which is sufficient to elicit a neuroprotective function against hypoxic neuronal damage.