Manganese superoxide dismutase modulates hypoxia-inducible factor-1A induction via superoxide

Abstract

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that plays an important role in O2 homeostasis. Numerous observations suggest that changes in reactive oxygen species affect HIF-1α stabilization and HIF-1α transcriptional activation in many cell types. The antioxidant enzyme manganese superoxide dismutase (MnSOD) modulates the cellular redox environment by converting superoxide (O2•-) to hydrogen peroxide and dioxygen. Previous results from our group have shown that overexpression of MnSOD in MCF-7 cells alters stabilization of HIF-1α under hypoxic conditions; however, the underlying mechanism(s) is not known. Here, we tested the hypothesis that MnSOD regulates the expression of HIF-1α by modulating the steady-state level of O2•-. We found that decreasing MnSOD with small interfering RNA in MCF-7 cells resulted in (a) an associated increase in the hypoxic accumulation of HIF-1α immunoreactive protein, (b) a significant increase in the levels of O2•- (P < 0.01), but (c) no significant change in the steady-state level of H2O2. Removal of O 2•- using spin traps (α-4-pyridyl-1-oxide-N- tert-butylnitrone and 5,5-dimethyl-1-pyrroline N-oxide) or the O 2•- scavenger Tempol or an SOD mimic (AEOL10113) resulted in a decrease in HIF-1A protein, consistent with the hypothesis that O2•- is an important molecular effector responsible for hypoxic stabilization of HIF-1α. The evidence from both genetic and pharmaceutical manipulation is consistent with our hypothesis that O 2•- can contribute to the stabilization of HIF-1α. ©2008 American Association for Cancer Research.