V-ATPase is a candidate therapeutic target for Ewing sarcoma

Abstract

Suppression of oxidative phosphorylation combined with enhanced aerobic glycolysis and the resulting increased generation of protons are common features of several types of cancer. An efficient mechanism to escape cell death resulting from intracellular acidification is proton pump activation. In Ewing sarcoma (ES), although the tumor-associated chimeric gene EWS-FLI1 is known to induce the accumulation of hypoxia-induced transcription factor HIF-1α, derangements in metabolic pathways have been neglected so far as candidate pathogenetic mechanisms. In this paper, we observed that ES cells simultaneously activate mitochondrial respiration and high levels of glycolysis. Moreover, although the most effective detoxification mechanism of proton intracellular storage is lysosomal compartmentalization, ES cells show a poorly represented lysosomal compartment, but a high sensitivity to the anti-lysosomal agent bafilomycin A1, targeting the V-ATPase proton pump. We therefore investigated the role of V-ATPase in the acidification activity of ES cells. ES cells with the highest GAPDH and V-ATPase expression also showed the highest acidification rate. Moreover, the localization of V-ATPase was both on the vacuolar and the plasma membrane of all ES cell lines. The acidic extracellular pH that we reproduced in vitro promoted high invasion ability and clonogenic efficiency. Finally, targeting V-ATPase with siRNA and omeprazole treatments, we obtained a significant selective reduction of tumor cell number. In summary, glycolytic activity and activation of V-ATPase are crucial mechanisms of survival of ES cells and can be considered as promising selective targets for the treatment of this tumor.

The effect of extracellular acidosis on the behaviour of mesenchymal stem cells in vitro

“…In BM-MSC, we did not find any significant difference in the expression of senescence related genes, while the expression of genes related to stress response was significantly increased, confirming our previous results (Avnet et al, 2017). Moreover, as we have already demonstrated in cancer cells of mesenchymal origin (Avnet et al, 2013;, acidic pHe did not increase cell apoptosis in normal cells of the same origin: short-term exposure to acidic pHe induced the expression of anti-apoptotic genes and the expression of pro-apoptotic genes was not affected. In addition, the number of apoptotic cells with pyknotic nuclei in DPSC and BM-MSC cultures was significantly reduced at pH 6.5 vs. pH 7.4.…”

The acidic microenvironment as a possible niche of dormant tumor cells

“…In this context, acidic tumor microenvironment promotes in tumor cells a low-proliferating phenotype, which does not revert even in the presence of a high level of growth factors [23]. It has also been shown by several reports that extracellular acidosis increases the percentage of cells in G0 phase [24]. Indeed, exposure to acidosis alters growth factor signaling and reduces serum ability to stimulate Raf/ERK/mTORC1 kinase pathway [25].…”

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

“…Increased cancer cell invasive activity is frequently associated with aberrant V‐ATPase plasma membrane localization suggesting that increased acidification of the extracellular space plays an important role 29, 33, 34, 37, 47, 48, 49, 50, 51, 52…”