H2O2 transit through the mitochondrial intermembrane space promotes tumor cell growth in vitro and in vivo

Cancer cells experience increased levels of oxidant stress as a consequence of oncogene activation, nucleotide biosynthesis, and growth factor receptor signaling. Mitochondria contribute to this redox stress by generating reactive oxygen species (ROS) along the electron transport chain, which are released to the matrix and the intermembrane space (IMS). Assessing the contribution of mitochondrial ROS in cancer cells is techni-cally difficult, as electron transport chain inhibitors can in-crease or decrease ROS generation, while they also block oxidative phosphorylation and ATP synthesis. Mitochondria-targeted antioxidant compounds can scavenge ROS in the matrix compartment but do not act on ROS released to the IMS. We assessed the importance of mitochondrial ROS for tumor cell proliferation, survival, and for tumor xenograft growth by stably expressing a hydrogen peroxide (H2O2) scavenger, peroxiredoxin-5, in the mitochondrial IMS (IMS-Prdx5) in 143B osteosarcoma and HCT116 colorectal cancer cell lines. IMS-Prdx5 attenuates hypoxia-induced ROS signaling as assessed independently in cytosol and IMS, HIF-1 alpha stabilization and activity, and cellular proliferation under normoxic and hypoxic culture conditions. It also suppressed tumor growth in vivo. Stable expression of nondegradable HIF-1 alpha only partially rescued proliferation in IMS-Prdx5-expressing cells, indicating that mitochondrial H2O2 signaling contributes to tumor cell proliferation and survival through HIF-dependent and HIF-independent mechanisms.

Automated summary

Cancer cells experience increased levels of oxidant stress due to oncogene activation, nucleotide biosynthesis, and growth factor receptor signaling. Mitochondrial ROS contribute to this stress. Assessing the importance of mitochondrial ROS in cancer cells is difficult due to the effects of electron transport chain inhibitors. This study showed that mitochondrial H2O2 signaling contributes to tumor cell proliferation and survival through HIF-dependent and HIF-independent mechanisms.