Alteration of the F1Fo ATP Synthase Causes Metabolic Remodeling in Breast Cancer Cells

Objectives The F1Fo ATP synthase is a multienzyme complex that produces mitochondrial ATP. Aberrant expression or assembly of F1Fo ATP synthase subunits leads to alterations in energy metabolism. We recently found that breast cancer cells exposed to fluid shear stress (FSS) have significantly enhanced metastatic behavior including chemoresistance and cell proliferation. Chemoresistance depends upon active transport systems, and cell division and growth require ATP. Therefore, we hypothesized that circulating breast cancer cells undergo altered energy metabolism via FSS-induced changes in F1Fo ATP synthase subunits and subsequent mitochondrial remodeling. Methods Non-metastatic MCF7 and metastatic MDA-MB-231 human breast cancer cells were treated with or without FSS and cultured. Cellular proliferation was assayed by measuring cell number and gap distance. Metabolic profile including intracellular ATP and oxygen consumption rate were analyzed. We also quantified abundance of F1Fo ATP synthase subunits using immunoblotting. Results Treatment with FSS significantly increased proliferation of both MCF7 and MDA-MB-231 human breast cancer cells. FSS significantly increased intracellular ATP in MDA-MB-231 breast cancer cells while ATP levels in MCF7 were not significantly changed. MDA-MB-231 cells retained increased ATP after treatment with the uncoupler FCCP, indicating remodeling and decreased reliance on mitochondrial energy metabolism. Interestingly, oxygen consumption rate was significantly increased in both MCF7 and MDA-MB-231 by FSS. We further quantified the abundance of F1Fo ATP synthase subunits in both cell lines. The β- and c-subunits of the F1Fo ATP synthase were significantly depleted in both lines of FSS-treated breast cancer cells. Conclusions Our data show that FSS alters abundance of the F1Fo ATP synthase subunits leading to metabolic remodeling. We suggest that FSS may influence non-metastatic (MCF7) and metastatic cancer cells (MDA-MB-231) differently. Underlying changes in mitochondrial and cytoplasmic ATP production in these cells is still under investigation. However, it is possible that reactive oxygen species generated during FSS may signal a switch to cytoplasmic intracellular energy metabolism. Funding Sources Alabama Life Research Institute Pilot Project (University of Alabama)