SPATIAL AND METABOLIC REQUIREMENTS OF MITOCHONDRIA DURING MDA-MB-231 CELL MIGRATION IN VITRO
The highly metastatic breast cancer cell line, MDA-MB-231, exhibits an altered glycolytic process known as the Warburg effect. The Warburg effect is characterized by increased cellular influx of glucose, use of glycolytic intermediates for anabolic reactions, and preferential conversion of pyruvate into lactate despite presence of oxygen. This suggests that mitochondria have a lessened metabolic role during times of cell growth; however, it is unclear if the Warburg effect is employed during cellular migration as the need for ATP increases for actin filament elongation at a cell’s leading edge. Mitochondria have been shown to accumulate in anterior regions of migrating MDA-MB-231 cells aiding in velocity, persistence of migration. Furthermore, MDA-MB-231 cells displaying mitochondria of a fissioned phenotype have increased migration and invasion capabilities. It may be mitochondria are trafficked to anterior regions for supplying ATP via electron transport chain (ETC) for cellular migration. Location and morphology of mitochondria during MDA-MB-231 cell migration via scratch wound assays were compared between non-migratory (NMIG) and migratory cells (MIG), as well as between migratory cells treated with increasing concentrations of epidermal growth factor (EGF; 0 ng/ml, 10 ng/ml, 100 ng/ml). Mitochondrial location was quantified by measuring fluorescence intensity in z stacks of cell images labeled with MitoTracker ® Green- FM. To determine if ETC is necessary for cellular migration, migration rates were measured in cells treated with increasing concentrations of sodium azide (NaN3), a known inhibitor of Complex IV of ETC. Our data showed no redistribution of mitochondria between NMIG cells and MIG cells. In cells treated with EGF there was significant decrease in posterior localization, yet no overall redistribution of mitochondria to a specific location. Furthermore, fissioned mitochondria were the dominant phenotype displayed within all migratory MDA-MB-231 cells and were primarily found in anterior cell regions. The process of migration, yet not EGF treatment, showed an effect upon mitochondrial phenotype. Migration rates were significantly slowed through inhibition of ETC with 100 mM NaN3. Although migration does not cause an overall redistribution of mitochondria to anterior regions, the increased presence of fissioned mitochondria in lamellipodia of migratory cells suggests that mitochondria may promote migration by increasing the local supply of ATP through oxidative phosphorylation.