Abstract
The H(+)-ATP synthase is a reversible engine of mitochondria that synthesizes or hydrolyzes ATP upon changes in cell physiology. ATP synthase dysfunction is involved in the onset and progression of diverse human pathologies. During ischemia, the ATP hydrolytic activity of the enzyme is inhibited by the ATPase inhibitory factor 1 (IF1). The expression of IF1 in human tissues and its participation in the development of human pathology are unknown. Here, we have developed monoclonal antibodies against human IF1 and determined its expression in paired normal and tumor biopsies of human carcinomas. We show that the relative mitochondrial content of IF1 increases significantly in carcinomas, suggesting the participation of IF1 in oncogenesis. The expression of IF1 varies significantly in cancer cell lines. To investigate the functional activity of IF1 in cancer, we have manipulated its cellular content. Overexpression of IF1 or of its pH-insensitive H49K mutant in cells that express low levels of IF1 triggers the up-regulation of aerobic glycolysis and the inhibition of oxidative phosphorylation with concurrent mitochondrial hyperpolarization. Treatment of the cells with the H(+)-ATP synthase inhibitor oligomycin mimicked the effects of IF1 overexpression. Conversely, small interfering RNA-mediated silencing of IF1 in cells that express high levels of IF1 promotes the down-regulation of aerobic glycolysis and the increase in oxidative phosphorylation. Overall, these findings support that the mitochondrial content of IF1 controls the activity of oxidative phosphorylation mediating the shift of cancer cells to an enhanced aerobic glycolysis, thus supporting an oncogenic role for the de-regulated expression of IF1 in cancer.
Highlights
In oxidative phosphorylation, ATP is synthesized by the mitochondrial ATP synthase, a Hϩ-driven rotatory engine of the inner membrane that utilizes as driving force for ATP synthesis the Hϩ electrochemical gradient generated by the respiratory chain [1,2,3,4]
We document that IF1 plays a regulatory role in controlling cellular energetic metabolism, strongly supporting its participation as an additional molecular switch used by cancer cells to trigger the induction of aerobic glycolysis, i.e. their Warburg phenotype
Determination of oligomycinsensitive respiration in normal rat kidney (NRK) cells transfected with IF1 showed that the oxygen consumption rates were significantly diminished when compared with controls (Fig. 3A), indicating that IF1 is interfering with the activity of the Hϩ-ATP synthase
Summary
ATP is synthesized by the mitochondrial ATP synthase, a Hϩ-driven rotatory engine of the inner membrane that utilizes as driving force for ATP synthesis the Hϩ electrochemical gradient generated by the respiratory chain [1,2,3,4]. The relative expression of IF1 in cell lines indicated a very large variability in the mitochondrial content of the ATPase inhibitor (Fig. 1C). We analyzed the relative expression of IF1 (IF1/-F1-ATPase ratio) in paired normal and tumor biopsies derived from breast, colon, and lung cancer patients (Fig. 1, E–H).
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