The role of the ATPase inhibitor factor 1 (IF) in cancer cells adaptation to hypoxia and anoxia.

The physiological role of the mitochondrial ATP synthase complex is to generate ATP through oxidative phosphorylation. Indeed, the enzyme can reverse its activity and hydrolyze ATP under ischemic conditions, as shown in isolated mitochondria and in mammalian heart and liver. However, what occurs when cancer cells experience hypoxia or anoxia has not been well explored. In the present study, we investigated the bioenergetics of cancer cells under hypoxic/anoxic conditions with particular emphasis on ATP synthase, and the conditions driving it to work in reverse. In this context, we further examined the role exerted by its endogenous inhibitor factor, IF, that it is overexpressed in cancer cells. Metabolic and bioenergetic analysis of cancer cells exposed to severe hypoxia (down to 0.1% O) unexpectedly showed that Δψ is preserved independently of the presence of IF and that ATP synthase still phosphorylates ADP though at a much lower rate than in normoxia. However, when we induced an anoxia-mimicking condition by collapsing Δμ with the FCCP uncoupler, the IF-silenced clones only reversed the ATP synthase activity hydrolyzing ATP in order to reconstitute the electrochemical proton gradient. Notably, in cancer cells IF overexpression fully prevents ATP synthase hydrolytic activity activation under uncoupling conditions. Therefore, our results suggest that IF overexpression promotes cancer cells survival under temporary anoxic conditions by preserving cellular ATP despite mitochondria dysfunction.