Vacuolar ATPase driven potassium transport in highly metastatic breast cancer cells

• Ouabain at high doses is not selective towards promoting cell death in cancer cells.
• MDA-MB453 cells lack Na–K ATPase expression but have higher potassium flux.
• Potassium uptake in MDA-MB453 cells is dependent upon vacuolar H+-ATPase activity.
• We identified KCNQ2 as a novel K+ channel highly expressed in MDA-MB453.
• KCNQ2 may be partially responsible for increased K+ flux in MDA-MB453 cells.

Breast cancer is the second leading cause of death in women and thus has received a great deal of attention by researchers. Recent studies suggested decreased occurrence of cancer in patients treated with cardiac glycosides (CGs) for heart conditions. Because CGs induce their cellular effects via the Na+, K+ ATPase (Na–K), we treated four breast cancer cell lines (MCF-7, T47D, MDA-MB453, and MDA-MB231) and a non-cancerous breast ductal epithelial cell line (MCF-10A) with ouabain, a well-characterized CG, and measured cell proliferation by measuring bromodeoxyuridine incorporation. Ouabain (1 μM) decreased cell proliferation in all cell lines studied except MDA-MB453 cells. Western blot of Na–K α and β subunits showed α1, α3, and β1 expression in all cell lines except MDA-MB453 cells where Na–K protein and mRNA were absent. Potassium uptake, measured as rubidium (86Rb) flux, and intracellular potassium were both significantly higher in MDA-MB453 cells compared to MCF-10A cells. RT-qPCR suggested a 7 fold increase in voltage-gated potassium channel (KCNQ2) expression in MDA-MB453 cells compared to MCF-10A cells. Inhibition of KCNQ2 prevented cell growth and 86Rb uptake in MDA-MB453 cells but not in MCF-10A cells. All cancer cells had significantly higher vacuolar H-ATPase (V-ATPase) activity than MCF-10A cells. Inhibition of V-ATPase decreased 86Rb uptake and intracellular potassium in MDA-MB453 cells but not in MCF-10A cells. The findings point to the absence of Na–K, high hERG and KCNQ2 expression, elevated V-ATPase activity and sensitivity to V-ATPase inhibitors in MDA-MB453. We conclude that cancer cells exhibit fundamentally different metabolic pathways for maintenance of intracellular ion homeostasis.