P 247 - Free radical production and detoxification in complex IV deficient cancer cells

Abstract

Mitochondrial membrane potential (DYm) is one of the key drivers of free radical production. Changes in DYm strongly affect free radical turnover in both mitochondria and cytosol. We found that in cytochrome c oxidase deficient HCT116 cells F1Fo ATP synthase (mATPase) is reversed in order to maintain DYm polarisation. For small energy costs, mATPase enables mitochondrial protein import, Ca2+ turnover and Krebs cycle activity. Although glycolysis is the main source of ATP in COX-deficient cells, the DYm does not decrease upon inhibition of the adenine nucleotide translocators, suggesting their redundant role. The ATP-Mg/Pi carriers and substrate level phosphorylation can continuously support the mATPase activity and hence DYm polarisation. Intriguingly, in COX-deficient cells complex III contributes to DYm maintenance, redox state, and free radical (H2O2) production. An enlarged mitochondrial free radical detoxification machinery (e.g. elevated SOD2) protects the cells from oxidative damage. Although cytosol is known as the main area of free radical synthesis in COX-deficient HCT116 cells, and NAD(P)H levels are increased, the expression of genes involved in glutathione-dependent reactions does not change, suggesting an involvement of alternative mechanisms of free radical quenching. An observed large increase in fatty acid deposition is likely to contribute to cell protection.