Article ID Journal Published Year Pages File Type
1911515 Free Radical Biology and Medicine 2006 15 Pages PDF
Abstract

The molecular mechanisms involved in modulation of the antioxidant cell defence by survival signals remain largely unexplored. Here, we report a mechanistic connection between the survival signal elicited by nerve growth factor (NGF) and the antioxidant cell defence represented by heme oxygenase-1 (HO-1) at the level of a newly identified Sp1 site in the human ho1 proximal promoter. By using luciferase reporter constructs we identified a PI3K-responsive region containing a GC-box that resembled the response element for Sp1. Indeed, transfection of Sp1-deficient SL2 cells, electrophoretic mobility shift assays, the use of the GC-box binding drug mithramycin, and mutation of the GC-box provided evidence for a Sp1-like site in the PI3K-sensitive region. Then, we observed with the use of a Sp1–Gal4 chimera that PI3K regulates the transactivating capacity of Sp1. Cotransfection of active PI3K and PKC-ζ expression vectors resulted in substantial increase of Sp1 phosphorylation and in synergistic activation of both Sp1-Gal4 and endogenous Sp1. Moreover, these effects were mimicked by cotransfection of active MEK and ERK expression vectors and were blocked by the MEK inhibitor PD98059. Inhibition of HO-1 with Sn protoporphyrin IX and blockage of Sp-1-mediatied upregulation of HO-1 with mithramycin attenuated antioxidant and cytoprotective functions of NGF against hydrogen peroxide. This study elucidates how NGF contributes to protection of target cells against oxidative stress.

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