The Nuclear-Encoded Cytochrome c Oxidase Subunit COX4-1 Enhances Hypoxia Tolerance in Glioblastoma Cells

Glioblastoma (GBM) is the most common and aggressive primary brain cancer in adults. While chemo- and radiotherapy are often effective in treating newly diagnosed GBM, increasing evidence suggests that treatment-induced metabolic alterations promote tumor recurrence and further resistance. In addition, GBM tumors are typically hypoxic, which further contributes to treatment resistance. Recent studies have shown that changes in glioma cell metabolism driven by a shift in the isoform expression of mitochondrial cytochrome c oxidase (CcO) subunit 4 (COX4), a key regulatory subunit of mammalian CcO, may underlie the treatment-induced metabolic alterations in GBM cells. However, the impact of hypoxia on GBM energetics is not fully understood. Using isogenic GBM cell lines expressing either COX4-1 or the alternative COX4 isoform, COX4-2, we found that COX4-1 expressing cells maintained a more oxidative metabolism under hypoxia, characterized by increased CcO activity and ATP production, enhanced assembly of CcO-containing mitochondrial supercomplexes, and reduced superoxide production. Furthermore, COX4-1 expression was sufficient to increase radioresistance under hypoxic conditions. Untargeted metabolomic analysis revealed that the most significantly upregulated pathways in COX4-1-expressing cells under hypoxia were purine and methionine metabolism. In contrast, COX4-2-expressing cells showed increased activation of glycolysis and the Warburg effect. Our study provides new insights into how CcO regulatory subunits influence cellular metabolic networks and radioresistance in GBM under hypoxia, identifying potential therapeutic targets for improved treatment strategies.