Supplementary Figure 6 from Dual Role of Mitochondrial Reactive Oxygen Species in Hypoxia Signaling: Activation of Nuclear Factor-κB via c-SRC– and Oxidant-Dependent Cell Death
ARTICLE ABSTRACT
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 factor-1α and nuclear factor-κB (NF-κB). Because NF-κB plays a central role in carcinogenesis, we examined the mechanism of mROS-mediated NF-κB 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-1α–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-κB without IκB-α degradation due to IκB-α tyrosine phosphorylation that was inhibited by rotenone/TTFA or c-Src antagonism. The c-Src–NF-κB 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-κB pathway. Thus, although mROS promote cell survival by NF-κB activation via c-Src, mROS overgeneration may be exploited to sensitize cancer cells to hypoxia. [Cancer Res 2007;67(15):7368–77]
