Inhibitors of vacuolar ATPase proton pumps inhibit human prostate cancer cell invasion and prostate-specific antigen expression and secretion

Abstract

Vacuolar ATPases (V-ATPases) comprise specialized and ubiquitously distributed pumps that acidify intracellular compartments and energize membranes. To gain new insights into the roles of V-ATPases in prostate cancer (PCa), we studied the effects of inhibiting V-ATPase pumps in androgen-dependent (LNCaP) and androgen-independent (C4-2B) cells of a human PCa progression model. Treatment with nanomolar concentrations of the V-ATPase inhibitors bafilomycin A or concanamycin A reduced the in vitro invasion in both cell types by 80%, regardless that V-ATPase was prominent at the plasma membrane of C4-2B cells and only traces were detected in the low-metastatic LNCaP parental cells. In both cell types, intracellular V-ATPase was excessive and co-localized with prostate-specific antigen (PSA) in the Golgi compartment. V-ATPase inhibitors reversibly excluded PSA from the Golgi and led to the accumulation of largely dispersed PSA-loaded vesicles of lysosomal composition. Inhibition of acridine orange staining and transferrin receptor recycling suggested defective endosomal and lysosomal acidification. The inhibitors, additionally, interfered with the AR-PSA axis under conditions that reduced invasion. Bafilomycin A significantly reduced steady-state and R1881-induced PSA mRNA expression and secretion in the LNCaP cells which are androgen-dependent, but not in the C4-2B cells which are androgen ablation-resistant. In the C4-2B cells, an increased susceptibility to V-ATPase inhibitors was detected after longer treatments, as proliferation was reduced and reversibility of bafilomycin-induced responses impaired. These findings make V-ATPases attractive targets against early and advanced PCa tumors. What's new? Vacuolar adenosine triphosphatases (V-ATPases) pump protons across cell membranes. Within the cell, this increases the acidity of cellular compartments and affects protein processing. When V-ATPases acidify the extracellular space, they can increase tumor-cell motility, proliferation, multi-drug resistance, and metastasis. In this study, the authors investigated the effects of V-ATPase inhibitors on the invasiveness of prostate-cancer cells and on mRNA levels of prostate-specific antigen (PSA). They found that the cancer cells became less invasive, and expression of PSA mRNA was down-regulated. This indicates that V-ATPases could provide a valuable new therapeutic target. Copyright © 2012 UICC.