Vacuolar-type H(+)-ATPases are functionally expressed in plasma membranes of human tumor cells

Abstract

Mammalian cells generally regulate their intracellular pH (pHi) via collaboration between Na(+)-H+ exchanger and HCO3- transport. In addition, a number of normal mammalian cells have been identified that express H(+)-adenosinetriphosphatases (ATPases) in their plasma membranes. Because tumor cells often maintain a high pHi, we hypothesized that they might functionally express H(+)-ATPases in their plasma membranes. In the first phase of the present study, we screened 19 normal and tumorigenic human cell lines for the presence of plasmalemmal H(+)-ATPase activity using bafilomycin A1 to inhibit V-type H(+)-ATPase and Sch-28080 to inhibit P-type H(+)-K(+)-ATPase. Bafilomycin A1 decreased pHi in the six tumor cell lines with the highest resting pHi in the absence of HCO3-. Sch-28080 did not affect pHi in any of the human cells. Simultaneous measurement of pH in the cytoplasm and in the endosomes/lysosomes localized the activity of bafilomycin to the plasma membrane in three cell lines. In the second phase of this study, these three cell lines were shown to recover from NH4(+)-induced acid loads in the absence of Na+. This recovery was inhibited by N-ethylmaleimide, bafilomycin A1, and ATP depletion and was not significantly affected by vanadate, Sch-28080, or hexamethyl amiloride. These results indicate that a vacuolar type H(+)-ATPase is expressed in the plasma membrane of some tumor cells.

Modulation of potassium channel function confers a hyperproliferative invasive phenotype on embryonic stem cells

“…Significant correlations have been found between neoplastic potential and bioelectrical properties of cells (45)(46)(47)(48)(49). These biophysical properties are not simply markers but are functional signals; misexpression of an ion transporter induces tumorigenicity in fibroblasts (50), and inhibition of EAG channel function suppresses neoplasm in an animal model in vivo (51).…”

The Amino-terminal Domain of the Vacuolar Proton-translocating ATPase a Subunit Controls Targeting and in Vivo Dissociation, and the Carboxyl-terminal Domain Affects Coupling of Proton Transport and ATP Hydrolysis

“…Acidification of these compartments is crucial for such processes as receptor-mediated endocytosis, intracellular trafficking, the processing and degradation of macromolecules, and the coupled transport of small molecules. In addition, V-ATPases in the plasma membrane of specialized cells function in such processes as pH homeostasis (9), bone resorption (10), renal acidification (11), potassium transport (12), and tumor metastasis (13). In yeast, the VATPase functions to create the driving force for uptake of small molecules and ions into the vacuole (14) and is important for post-Golgi protein trafficking (15)(16)(17).…”

Subunit Interactions in the Clathrin-coated Vesicle Vacuolar (H+)-ATPase Complex

“…Acidification of intracellular compartments is important for such processes as protein degradation, intracellular protein targeting, and receptor-mediated endocytosis (1-6), while V-ATPases in the plasma membrane function in renal acidification, bone resorption, and tumor metastasis (7)(8)(9).…”