Bafilomycin A1 activates HIF-dependent signalling in human colon cancer cells via mitochondrial uncoupling

Synopsis Mitochondrial uncoupling is implicated in many patho(physiological) states. Using confocal live cell imaging and an optical O-2 sensing technique, we show that moderate uncoupling of the mitochondria with plecomacrolide Baf (bafilomycin A1) causes partial depolarization of the mitochondria and deep sustained deoxygenation of human colon cancer HCT116 cells subjected to 6% atmospheric O-2. A decrease in iO(2) (intracellular 02) to 0-10 mu M, induced by Baf, is sufficient for stabilization of HIFs (hypoxia inducible factors) HIF-1 alpha and HIF-2 alpha, coupled with an increased expression of target genes including GLUT1 (glucose transporter 1), HIF PHD2 (prolyl hydroxylase domain 2) and CAIX (carbonic anhydrase IX). Under the same hypoxic conditions, treatment with Baf causes neither decrease in iO(2) nor HIF-alpha stabilization in the low-respiring HCT116 cells deficient in COX (cytochrome c-oxidase). Both cell types display equal capacities for HIF-alpha stabilization by hypoxia mimetics DMOG (dimethyloxalylglycine) and CoCl2, thus suggesting that the effect of Baf under hypoxia is driven mainly by mitochondrial respiration. Altogether, by activating HIF signalling under moderate hypoxia, mitochondrial uncoupling can play an important regulatory role in colon cancer metabolism and modulate adaptation of cancer cells to natural hypoxic environments.