Hypoxia activates Akt and induces phosphorylation of GSK-3 in PC12 cells

Akt is a serine/threonine kinase that has been shown to play a central role in promoting cell survival and opposing apoptosis. We evaluated the effect of hypoxia on Akt in rat pheochromocytoma (PC12) cells. PC12 cells were ex posed to varying levels of hypoxia, including 21%, 15%, 10%, 5%, and 1% O-2 . Hypoxia dramatically Increased phosphorylation of Akt (Ser(473)). This ef fect peaked after 6 h exposure to hypoxia, but persisted strongly for up to 24 h. Phosphorylation of Akt was paralleled with a progressive increase in phosphorylation of glycogen synthase kinase-3 (GSK-3), one of its downstre am substrates. The effect of hypoxia on phosphorylation of Akt was complete ly blocked by pretreatment of the cells with wortmannin (100 nM), indicatin g that this effect is mediated by phosphatidylinositol 3-kinase (P13K). In contrast, whereas hypoxia also strongly induced phosphorylation of the tran scription factors CREB and EPAS1, these effects persisted in the presence o f wortmannin. Thus, hypoxia regulates both P13K-dependent and P13K-independ ent signaling pathways. Furthermore, activation of the P13K and Akt signali ng pathways may be one mechanism by which cells adapt and survive under con ditions of hypoxia. (C) 2001 Elsevier Science Inc. All rights reserved.