Regulation of Cu/Zn-Superoxide Dismutase Expression via the Phosphatidylinositol 3 Kinase/Akt Pathway and Nuclear Factor-κB

Abstract

Aerobic cells adjust the expression of antioxidant enzymes to maintain reactive oxygen species within tolerable levels. In addition, phosphatidylinositol 3 kinase (PI3K) and its downstream protein kinase effector Akt adapt cells to survive in the presence of oxidative stress. Here we provide evidence for an association between these two defense systems via transcriptional regulation of Cu/Zn-superoxide dismutase (Cu/Zn-SOD). PC12 pheochromocytoma cells expressing active Akt1 exhibit lower ROS levels in response to hydrogen peroxide, as determined with the superoxide-sensitive probe hydroethidine. Transfection of constitutive or 4-hydroxytamoxifen-inducible versions of Akt1 results in higher messenger RNA and protein levels of Cu/Zn-SOD. Luciferase reporter constructs, carrying different length fragments of the human sod1 gene promoter, have identified a region between -552 and -355 that is targeted by PI3K and Akt and that contains a putative site of regulation by nuclear factor-κB (NF-κB). Nerve growth factor (NGF) and Akt augment the transactivating activity and produce higher nuclear levels of p65-NF-κB. Electrophoretic mobility shift assays indicate that the putative NF-κB regulatory sequence binds p65-NF-κB more efficiently in nuclear extracts from these cells. A dominant-negative mutant of IκBα further demonstrates that the PI3K/Akt axis targets the sod1 promoter at the level of the newly characterized NF-κB site. These results illustrate a new mechanism by which the PI3K/Akt pathway protects cells against oxidative stress, involving the upregulation of Cu/Zn-SOD gene expression, and the results identify NF-κB as a key mediator in the regulation of this gene.