Dual role of mitochondrial reactive oxygen species in hypoxia signaling:: Activation of nuclear factor-κB via c-SRC- and oxidant-dependent cell death

Hypoxia is a prominent feature of solid tumor development and is known to stimulate mitochondrial ROS (mROS), which, in turn, can activate hypoxia-inducible transcription factorto- and nuclear factor-kappa B (NF-kappa B). Because NF-kappa B plays a central role in carcinogenesis, we examined the mechanism of mROS-mediated NF-kappa B activation and the fate of cancer cells during hypoxia after mitochondrial reduced glutathione (mGSH) depletion. Hypoxia generated mROS in hepatoma (HepG2, H35), neuroblastoma (SH-SY5Y), and colon carcinoma (DLD-1) cells, leading to hypoxia-inducible transcription factor-1 alpha-dependent gene expression and c-Src activation that was prevented in cells expressing a redox-insensitive c-Src mutant (C487A). c-Src stimulation activated NF-kappa B without I kappa B-alpha degradation due to I kappa B-alpha tyrosine phosphorylation that was inhibited by rotenone/TTFA or c-Src antagonism. The c-Src-NF-kappa B signaling contributed to the survival of cells during hypoxia as c-Src inhibition or p65 down-regulation by small interfering RNA-sensitized HepG2 cells to hypoxia-induced cell death. Moreover, selective mGSH depletion resulted in an accelerated and enhanced mROS generation by hypoxia that killed SH-SY5Y and DLD-1 cells without disabling the c-Src-NF-kappa B pathway. Thus, although mROS promote cell survival by NF-kappa B activation via c-Src, mROS overgeneration may be exploited to sensitize cancer cells to hypoxia.