Proton pumps, angiogenesis, and metastatic breast cancer

We have previously shown the relationship between metastatic potential and plasmalemmal V-H⁺-ATPase (pm V-ATPase) expression in tumor cells. This led us to hypothesize that pm V-ATPase activity is involved in invasion. Angiogenesis involves invasion of adjacent tissues by microvascular endothelial cells, thus we hypothesized that pm V-ATPases contribute to pHⁱⁿ regulation and invasion in microvascular endothelial cells. Immunocytochemical experiments revealed pm V-ATPases at the leading edge of cancer and microvascular endothelial cells. We monitored pHⁱⁿ from leading- to lagging-edge at the single cell level using confocal/spectral imaging microscopy. Our data indicate that the pHⁱⁿ is more alkaline at the leading than at the lagging edge, in both these cell types, suggesting the presence of pHⁱⁿ gradients. Line scanning confocal microscopy demonstrated pHⁱⁿ oscillations whose magnitude were larger in the lagging than the leading edge. Exposure of the cell's leading edge to bafilomycin A_1, a V-H⁺-ATPase inhibitor, decreased the migratory capabilities of the cells. Inhibitors for P- and F-type ATPases had no effect on these phenomena. Altogether, these data indicate that pm V-ATPases play a role in pHⁱⁿ regulation and invasion in tumor and microvascular endothelial cells. This could offer a potential target to modulate angiogenesis and metastasis.