Bioenergetics of cancer cells: insights into the Warburg effect and regulation of ATP synthase

The study reported here offers new insights into the metabolic changes associated with the Warburg effect (i.e. aerobic glycolysis) in cancer cells and into the possible role of IF1, the endogenous inhibitor of ATP synthase that preserves cellular energy when it works in reverse, hydrolyzing ATP. We investigated biochemical and main bioenergetic parameters in cell lines derived from three human tumors: osteosarcoma (143B), colon carcinoma (HCT116), and cervix carcinoma (HeLa). The combination analysis of cellular glucose consumption, lactate production, ATP-linked respiration rate, ATP level, cell culture medium acidification rate, and ROS level demonstrates that aerobic glycolysis is differently expressed by the three different types of tumor cells, although all cell types exhibited a Warburg phenotype. The superoxide anion level was found to be lower in HCT116 cells, which showed the highest ratio between oxidative phosphorylation and glycolysis rates, while ROS level was similar in all cells examined, suggesting that mitochondria in HCT116 are very efficient in both energy production and limiting their oxidative stress. Additionally, IF1 KD cells of all kinds of tumor showed higher level of ROS compared to their related IF1-expressing cells. Most of the results reported here clearly demonstrate that aerobic glycolysis is completely independent on both the level of IF1 and the IF1/ATP synthase ratio, excluding the contribution of an IF1-dependent mechanism in the metabolic shift of cancer cells towards glycolysis. Indeed, the study provides a detailed analysis of the bioenergetics of tumor cells exhibiting very different IF1/ATP synthase ratios and shows that IF1 KD cells of all tumor types had a higher level of ROS than their related IF1-expressing cells. Overall, the comprehensive picture of tumor cell bioenergetics would facilitate the identification of appropriate drugs for targeted tumor treatments, such as ATP synthase-IF1 immunotherapy that would strongly limit cellular resistance to severe hypoxia or anoxia, where IF1 plays an effective critical role.