Median overall survival is very low in patients with glioblastoma (GBM), largely because these tumors become resistant to therapy. Recently, we found that a decrease in the cytosolic labile iron pool underlies the acquisition of radioresistance. Both cytosolic and mitochondrial iron are important for regulating ROS production, which largely facilitates tumor progression and response to therapy. Here, we investigated the role of the mitochondrial iron transporters mitoferrin-1 (MFRN1) and mitoferrin-2 (MFRN2) in GBM progression. Analysis of The Cancer Genome Atlas database revealed upregulation of MFRN1 mRNA and downregulation of MFRN2 mRNA in GBM tumor tissue compared with non-GBM tissue, yet only the tumor expression level of MFRN1 mRNA negatively correlated with overall survival in patients. Overexpression of MFRN1 in glioma cells significantly increased the level of mitochondrial iron, enhanced the proliferation rate and anchorage-independent growth of these cells, and significantly decreased mouse survival in an orthotopic model of glioma. Finally, MFRN1 overexpression stimulated the upregulation of glutathione, which protected glioma cells from 4-hydroxynonenal-induced protein damage. Overall, these results demonstrate a mechanistic link between MFRN1-mediated mitochondrial iron metabolism and GBM progression. Manipulation of MFRN1 may provide a new therapeutic strategy for improving clinical outcomes in patients with GBM.

Copper is an essential trace element, yet chronic copper exposure can lead to toxicity in humans, and high levels of copper have been found in the blood or tumors of patients with various forms of cancer and may affect cancer severity and response to treatment. Copper is required for the activation of cytochrome c oxidase (CcO), the mitochondrial complex that facilitates oxidative phosphorylation (OXPHOS)-mediated ATP production. We recently reported that the increased activation of CcO underlies the acquisition of treatment resistance in glioblastoma (GBM) cells. However, the potential role of copper in GBM progression or treatment resistance has not been investigated. Here, we present evidence that exposure to 20 µM copper, the maximum allowable limit for public water supplies set by the U.S. Environmental Protection Agency, promotes GBM tumor growth and reduces overall survival in vivo and increases GBM cell resistance to radiation and chemotherapy in vitro. In vitro exposure to 20 µM copper substantially increased the activity of CcO, elevated the rate and level of ATP production, and triggered a metabolic shift to an OXPHOS phenotype in GBM cells. Furthermore, copper exposure led to a substantial increase in the accumulation of glutathione and glutathione precursors in these cells. These findings establish copper as a tumor promoter in GBM and suggest that copper mediates these effects through the upregulation of CcO activity, which enhances OXPHOS metabolism and glutathione production.