F-actin reorganization by V-ATPase inhibition in prostate cancer

Abstract

The vacuolar ATPase (V-ATPase) proton pump sustains cellular pH homeostasis, and its inhibition triggers numerous stress responses. However, the cellular mechanisms involved remain largely elusive in cancer cells. We studied V-ATPase in the prostate cancer (PCa) cell line PC-3, which has characteristics of highly metastatic PCa. V-ATPase inhibitors impaired endo-lysosomal pH, vesicle trafficking, migration, and invasion. V-ATPase accrual in the Golgi and recycling endosomes suggests that traffic of internalized membrane vesicles back to the plasma membrane was particularly impaired. Directed movement provoked co-localization of V-ATPase containing vesicles with F-actin near the leading edge of migrating cells. V-ATPase inhibition prompted prominent F-actin cytoskeleton reorganization. Filopodial projections were reduced, which related to reduced migration velocity. F-actin formed novel cytoplasmic rings. F-actin rings increased with extended exposure to sublethal concentrations of V-ATPase inhibitors, from 24 to 48 h, as the amount of alkalinized endo-lysosomal vesicles increased. Studies with chloroquine indicated that F-actin rings formation was pH-dependent. We hypothesize that these novel F-actin rings assemble to overcome widespread traffic defects caused by V-ATPase inhibition, similar to F-actin rings on the surface of exocytic organelles.

V-ATPase-dependent repression of androgen receptor in prostate cancer cells

“…Under normoxic conditions, HIF-1α is rapidly turned over by a process that involves hydroxylation by prolyl hydroxylase, which targets HIF-1α for degradation by the proteasome [ 32 , 34 ]. Prolyl hydroxylases require iron as a co-factor [ 32 , 34 ], and notably, V-ATPase inhibition decreases endocytosis of the transferrin receptor (TfR) [ 11 ], thus lowering intracellular iron concentrations [ 52 , 53 ].…”

“…To summarize, loss of V-ATPase activity causes alkalinization of endo-lysosomal compartments (Figure 2 ). This disrupted pH homeostasis negatively affects TfR endocytic trafficking (Figure 5 ) [ 2 , 11 ], leading to reduced iron uptake [ 56 ]. Under low intracellular iron concentrations, HIF-1α hydroxylation is blocked (Figure 5 ), thus increasing its stability and function.…”

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

“…In breast cancer 4T1 cells, following lentiviral depletion of V 1 C1 subunit expression, the actin cytoskeletons lost their regular orientation resulting in decreased migratory and invasive activity, suggesting that V 1 C1 is able to regulate actin cytoskeleton rearrangements 62. Moreover, V‐ATPase inhibition is associated with F‐actin reorganization in PC‐3 prostate cancer cells 63. In addition, inhibition of V‐ATPase using archazolid A or V o c subunit siRNA in SKBR3 breast cancer cells altered the distribution and localization of EGFR and Rac‐1, which are associated with cellular migration 64…”

Proton pump inhibitor use and risk of breast cancer, prostate cancer, and malignant melanoma: An Icelandic population‐based case‐control study

“…Among these, membrane‐bound proteins are the vacuolar type H + ATPases (V‐ATPases), which are complex multisubunit proteins that can be found in a variety of cellular membranes where they facilitate the transport of protons and regulate intracellular and extracellular pH . Plasmalemmal expression of V‐ATPases has been associated with increased cancer cell survival, enhanced metastatic potential and the development of multidrug resistance through the acidification of the tumor microenvironment . Furthermore, inhibition of V‐ATPase function, via either V‐ATPase specific inhibitors or proton pump inhibitors (PPIs), has been shown to have anticarcinogenic effects in a variety of cell‐based and animal‐based models, including breast cancer, prostate cancer, and melanoma …”

“…[4][5][6] Plasmalemmal expression of V-ATPases has been associated with increased cancer cell survival, enhanced metastatic potential and the development of multidrug resistance through the acidification of the tumor microenvironment. [7][8][9][10][11][12][13] Furthermore, inhibition of V-ATPase function, via either V-ATPase specific inhibitors or proton pump inhibitors (PPIs), has been shown to have anticarcinogenic effects in a variety of cell-based and animal-based models, including breast cancer, 14,15 prostate cancer, 16 and melanoma. 17,18 PPIs are commonly used drugs that are generally well tolerated and routinely prescribed for acid-related disorders of the gastrointestinal tract.…”