Role of UCP2 in the energy metabolism of the cancer cell line A549

The uncoupling protein UCP2 is a mitochondrial carrier whose transport activity remains controversial. The physiological contexts in which UCP2 is expressed have led to the assumption that, like UCP1, it uncouples oxidative phosphorylation and as a result it lowers the generation of reactive oxygen species. Other reports have involved UCP2 in the Warburg effect and results showing that UCP2 catalyzes the export of matrix C4 metabolites to facilitate glutamine utilization, suggests that the carrier could be involved in the metabolic adaptations required for cell proliferation. We have examined the role of UCP2 in the energy metabolism of the lung adenocarcinoma cell line A549 and show that UCP2 silencing decreased the basal rate of respiration although this inhibition was not compensated by an increase in glycolysis. Silencing did not lead to changes in proton leakage, as determined from the rate of respiration in the absence of ATP synthesis, or changes in the rate of formation of reactive oxygen species. The decrease in energy metabolism did not alter the cellular energy charge. The decreased cell proliferation observed in UCP2-silenced cells would explain the decreased cellular ATP demand. We conclude that UCP2 does not operate as an uncoupling protein while our results are consistent with its activity as a C4-metabolite carrier involved in the metabolic adaptations of proliferating cells. Highlights UCP2 silencing decreases respiration without a compensatory increase in aerobic glycolysis ATP levels remain unchanged despite the reduction in energy metabolism UCP2 silencing decreases cell proliferation that could explain the decrease in energy demand UCP2 silencing does not change the proton leakage rate Data support the proposed involvement of UCP2 in the Warburg effect