ATP5IF1 and cancer: The IF1 protein is differentially expressed in highly proliferative cancer and non-cancer cells [3,23,30], its phosphorylation state and activity as an inhibitor of ATP synthase depends on the cell cycle phase [27], it is re-expressed when differentiated cells are reprogrammed into iPSC [34], it has a very short half-life [23] when compared to other subunits of the enzyme [35], and it is tissue- and species-specifically expressed in differentiated cells of mammalian tissues [28], emphasizing the complexity of its regulation and activities.