Vacuolar H+ ATPase expression and activity is required for Rab27B-dependent invasive growth and metastasis of breast cancer

ASPSCR1::TFE3 orchestrates the angiogenic program of alveolar soft part sarcoma

Alveolar soft part sarcoma (ASPS) is a soft part malignancy affecting adolescents and young adults. ASPS is characterized by a highly integrated vascular network, and its high metastatic potential indicates the importance of ASPS's prominent angiogenic activity. Here, we find that the expression of ASPSCR1::TFE3, the fusion transcription factor causatively associated with ASPS, is dispensable for in vitro tumor maintenance; however, it is required for in vivo tumor development via angiogenesis. ASPSCR1::TFE3 is frequently associated with super-enhancers (SEs) upon its DNA binding, and the loss of its expression induces SE-distribution dynamic modification related to genes belonging to the angiogenesis pathway. Using epigenomic CRISPR/dCas9 screening, we identify Pdgfb, Rab27a, Sytl2, and Vwf as critical targets associated with reduced enhancer activities due to the ASPSCR1::TFE3 loss. Upregulation of Rab27a and Sytl2 promotes angiogenic factor-trafficking to facilitate ASPS vascular network construction. ASPSCR1::TFE3 thus orchestrates higher ordered angiogenesis via modulating the SE activity.

The 3D in vivo chorioallantoic membrane model and its role in breast cancer research

PURPOSE

We aimed to evaluate the role of the chorioallantoic membrane model (CAM) in breast cancer research.

METHODS

The following is an overview of the use of the CAM in the field of breast cancer research based on a PubMed literature query.

RESULTS

The CAM is a 3D in vivo model that can be used for the analysis of tumor growth, biology and angiogenesis of primary tumor tissue or tumor cell lines. The CAM model has been used in breast cancer research for drug testing, migration assays and the evaluation of vascularization, amongst others. The CAM model is a valuable method that offers a better imitation of the physiological phenomena compared to 2D or 3D in vitro models.

CONCLUSION

The CAM model has primarily and successfully been utilized for the assessment of the tumor biology of established breast cancer cell lines. Further, the CAM model is a promising method to analyze patient derived primary tumor material and could be used as a "patient-specific 3D-tumor-therapy-model" for the cost-efficient evaluation of anti-cancer drugs to find the optimal treatment for breast cancer patients.

Ameliorating cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90 with omeprazole

BACKGROUND

Cancer cachexia, characterized by muscle and fat tissue wasting, is a major determinant of cancer-related mortality without established treatment. Recent animal data revealed that cancer cells induce muscle wasting by releasing Hsp70 and Hsp90 as surface proteins on extracellular vesicles (EVs). Here, we test a therapeutic strategy for ameliorating cancer cachexia by inhibiting the release of Hsp70 and Hsp90 using proton pump inhibitor omeprazole.

METHODS

Omeprazole effect on Hsp70/90 release through EVs by Lewis lung carcinoma (LLC) cells in vitro, serum levels of Hsp70/90 and Hsp70/90-carrying EVs in LLC tumour-bearing mice, and LLC-induced muscle protein degradation pathways in C2C12 myotubes and mice were determined. Omeprazole effect on endolysosomal pH and Rab27b expression in LLC cells were analysed.

RESULTS

Omeprazole treatment of LLC cells inhibited Hsp70/90 and Hsp70/90-carrying EV release in a dose-dependent manner (1 to 10 μM) and attenuated the catabolic activity of LLC cell-conditioned medium on C2C12 myotubes. Systemic omeprazole administration to LLC tumour-bearing mice (5 mg/kg/day subcutaneously) for 2 weeks blocked elevation of serum Hsp70, Hsp90, and Hsp70/90-carrying EVs, abrogated skeletal muscle catabolism, and prevented loss of muscle function as well as muscle and epididymal fat mass without altering tumour growth. Consequently, median survival increased by 23.3%. Mechanistically, omeprazole increased cancer cell endolysosomal pH level dose-dependently (0.1 to 1 μM) by inhibiting vacuolar H⁺ -ATPase. Further, omeprazole suppressed the highly elevated expression of Rab27b, a key regulator of EV release, in LLC cells.

CONCLUSIONS

Omeprazole ameliorates cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90.

The V-ATPases in cancer and cell death

Transmembrane ATPases are membrane-bound enzyme complexes and ion transporters that can be divided into F-, V-, and A-ATPases according to their structure. The V-ATPases, also known as H⁺-ATPases, are large multi-subunit protein complexes composed of a peripheral domain (V1) responsible for the hydrolysis of ATP and a membrane-integrated domain (V0) that transports protons across plasma membrane or organelle membrane. V-ATPases play a fundamental role in maintaining pH homeostasis through lysosomal acidification and are involved in modulating various physiological and pathological processes, such as macropinocytosis, autophagy, cell invasion, and cell death (e.g., apoptosis, anoikis, alkaliptosis, ferroptosis, and lysosome-dependent cell death). In addition to participating in embryonic development, V-ATPase pathways, when dysfunctional, are implicated in human diseases, such as neurodegenerative diseases, osteopetrosis, distal renal tubular acidosis, and cancer. In this review, we summarize the structure and regulation of isoforms of V-ATPase subunits and discuss their context-dependent roles in cancer biology and cell death. Updated knowledge about V-ATPases may enable us to design new anticancer drugs or strategies.

The Autophagy-Inducing Mechanisms of Vitexin, Cinobufacini, and Physalis alkekengi Hydroalcoholic Extract against Breast Cancer in vitro and in vivo

OBJECTIVES

Owing to inefficiency of chemotherapy towards cancer treatment, formulation and application of herbal drug compounds will open new avenues with this regard. In this study, the anticancer effects of itexin, cinobufacini, and Physalis alkekengi (P. alkekengi) were assessed.

METHODS

Herein, synergistic effects of vitexin, cinobufacini, and P. alkekengi hydroalcoholic extract were assessed against estrogen-receptor (EGFR2)-positive breast cancer mouse model. Sixty ER + breast cancer BALB/c mice (six groups each including ten members) were included. The anticancer effects of P. alkekengi hydroalcoholic extract, vitexin, and cinobufacini were administered against EGFR2 cancerous cells for 14 days. The tumor size, cytotoxic effects, and expression of Beclin-1, LC3-II, and ATG5 autophagy-related genes were investigated using RT-qPCR technique. The data was analyzed using chi-square, ANOVA, and multinomial logistic regression tests.

KEY FINDINGS

The 50% lethal dose (LD50) of P. alkekengi and vitexin against the breast cancer cells included 12 mg/kg, respectively, while cinobufacini LD50 was 24 mg/kg but had no toxicity against CRL7242 breast normal cells. Furthermore, 24 mg/kg of the P. alkekengi, vitexin, and cinobufacini significantly increased the ATG5, Beclin-1, and LC3-II gene expression.

CONCLUSION

Considering anticancer effects of P. alkekengi, vitexin, and cinobufacini against breast cancer through induction of the autophagy pathway, the compound formulations can be applied as anticancer therapies.

Rab27B enhances drug resistance in hepatocellular carcinoma by promoting exosome-mediated drug efflux

Liver cancer is a major threat to human life and health, and chemotherapy has been the standard non-surgical treatment for liver cancer. However, the emergence of drug resistance of liver cancer cells has hindered the therapeutic effect of chemical drugs. The discovery of exosomes has provided new insights into the mechanisms underlying tumour cell resistance. In this study, we aimed to determine the proteins associated with drug resistance in tumour cells and to elucidate the underlying mechanisms. We found that Rab27B expression in drug (5-fluorouracil, 5Fu)-resistant Bel7402 (Bel/5Fu) cells increased significantly compared with that in drug-sensitive Bel7402 cells. In addition, Bel/5Fu cells secreted more exosomes under 5Fu stimulation. The number of exosomes secreted by Bel/5Fu cells significantly reduced after knocking down Rab27B, and the cellular concentration of 5Fu increased, enhancing its therapeutic effect. We also found that the administration of classical drug efflux pump (P-glycoprotein, P-gp) inhibitors together with knockdown of Rab27B further improved the therapeutic effects of chemotherapy drugs. In conclusion, our findings suggest that Rab27B could be a new therapeutic target in liver cancer.

Interplay Between V-ATPase G1 and Small EV-miRNAs Modulates ERK1/2 Activation in GBM Stem Cells and Nonneoplastic Milieu

The ATP6V1G1 subunit (V1G1) of the vacuolar proton ATPase (V-ATPase) pump is crucial for glioma stem cells (GSC) maintenance and in vivo tumorigenicity. Moreover, V-ATPase reprograms the tumor microenvironment through acidification and release of extracellular vesicles (EV). Therefore, we investigated the role of V1G1 in GSC small EVs and their effects on primary brain cultures. To this end, small EVs were isolated from patients-derived GSCs grown as neurospheres (NS) with high (V1G1^HIGH-NS) or low (V1G1^LOW-NS) V1G1 expression and analyzed for V-ATPase subunits presence, miRNA contents, and cellular responses in recipient cultures. Our results show that NS-derived small EVs stimulate proliferation and motility of recipient cells, with small EV derived from V1G1^HIGH-NS showing the most pronounced activity. This involved activation of ERK1/2 signaling, in a response reversed by V-ATPase inhibition in NS-producing small EV. The miRNA profile of V1G1^HIGH-NS-derived small EVs differed significantly from that of V1G1^LOW-NS, which included miRNAs predicted to target MAPK/ERK signaling. Mechanistically, forced expression of a MAPK-targeting pool of miRNAs in recipient cells suppressed MAPK/ERK pathway activation and blunted the prooncogenic effects of V1G1^HIGH small EV. These findings propose that the GSC influences the brain milieu through a V1G1-coordinated EVs release of MAPK/ERK-targeting miRNAs. Interfering with V-ATPase activity could prevent ERK-dependent oncogenic reprogramming of the microenvironment, potentially hampering local GBM infiltration. IMPLICATIONS: Our data identify a novel molecular mechanism of gliomagenesis specific of the GBM stem cell niche, which coordinates a V-ATPase-dependent reprogramming of the brain microenvironment through the release of specialized EVs.

Drug Sequestration in Lysosomes as One of the Mechanisms of Chemoresistance of Cancer Cells and the Possibilities of Its Inhibition

Resistance to chemotherapeutics and targeted drugs is one of the main problems in successful cancer therapy. Various mechanisms have been identified to contribute to drug resistance. One of those mechanisms is lysosome-mediated drug resistance. Lysosomes have been shown to trap certain hydrophobic weak base chemotherapeutics, as well as some tyrosine kinase inhibitors, thereby being sequestered away from their intracellular target site. Lysosomal sequestration is in most cases followed by the release of their content from the cell by exocytosis. Lysosomal accumulation of anticancer drugs is caused mainly by ion-trapping, but active transport of certain drugs into lysosomes was also described. Lysosomal low pH, which is necessary for ion-trapping is achieved by the activity of the V-ATPase. This sequestration can be successfully inhibited by lysosomotropic agents and V-ATPase inhibitors in experimental conditions. Clinical trials have been performed only with lysosomotropic drug chloroquine and their results were less successful. The aim of this review is to give an overview of lysosomal sequestration and expression of acidifying enzymes as yet not well known mechanism of cancer cell chemoresistance and about possibilities how to overcome this form of resistance.

Exploring the Therapeutic Potential of Membrane Transport Proteins: Focus on Cancer and Chemoresistance

Improving the therapeutic efficacy of conventional anticancer drugs represents the best hope for cancer treatment. However, the shortage of druggable targets and the increasing development of anticancer drug resistance remain significant problems. Recently, membrane transport proteins have emerged as novel therapeutic targets for cancer treatment. These proteins are essential for a plethora of cell functions ranging from cell homeostasis to clinical drug toxicity. Furthermore, their association with carcinogenesis and chemoresistance has opened new vistas for pharmacology-based cancer research. This review provides a comprehensive update of our current knowledge on the functional expression profile of membrane transport proteins in cancer and chemoresistant tumours that may form the basis for new cancer treatment strategies.

Metabolic Plasticity of Melanoma Cells and Their Crosstalk With Tumor Microenvironment

Cutaneous melanoma (CM) is a highly aggressive and drug resistant solid tumor, showing an impressive metabolic plasticity modulated by oncogenic activation. In particular, melanoma cells can generate adenosine triphosphate (ATP) during cancer progression by both cytosolic and mitochondrial compartments, although CM energetic request mostly relies on glycolysis. The upregulation of glycolysis is associated with constitutive activation of BRAF/MAPK signaling sustained by BRAF^V600E kinase mutant. In this scenario, the growth and progression of CM are strongly affected by melanoma metabolic changes and interplay with tumor microenvironment (TME) that sustain tumor development and immune escape. Furthermore, CM metabolic plasticity can induce a metabolic adaptive response to BRAF/MEK inhibitors (BRAFi/MEKi), associated with the shift from glycolysis toward oxidative phosphorylation (OXPHOS). Therefore, in this review article we survey the metabolic alterations and plasticity of CM, its crosstalk with TME that regulates melanoma progression, drug resistance and immunosurveillance. Finally, we describe hallmarks of melanoma therapeutic strategies targeting the shift from glycolysis toward OXPHOS.

The impact of tumour pH on cancer progression: strategies for clinical intervention

Dysregulation of cellular pH is frequent in solid tumours and provides potential opportunities for therapeutic intervention. The acidic microenvironment within a tumour can promote migration, invasion and metastasis of cancer cells through a variety of mechanisms. Pathways associated with the control of intracellular pH that are under consideration for intervention include carbonic anhydrase IX, the monocarboxylate transporters (MCT, MCT1 and MCT4), the vacuolar-type H⁺-ATPase proton pump, and the sodium-hydrogen exchanger 1. This review will describe progress in the development of inhibitors to these targets.

ATP6L promotes metastasis of colorectal cancer by inducing epithelial-mesenchymal transition

ATP6L, the C subunit of the V-ATPase V0 domain, is involved in regulating the acidic tumor micro-environment and may promote tumor progression. However, the expression and functional role of ATP6L in tumors have not yet been well explored. In this study, we found that ATP6L protein overexpression was related to colorectal cancer histological differentiation (P < 0.001), presence of metastasis (P < 0.001) and recurrence (P = 0.02). ATP6L expression in the liver metastatic foci was higher than in the primary foci (P = 0.04). ATP6L expression was notably concomitant with epithelial-mesenchymal transition (EMT) immunohistochemical features, such as reduced expression of the epithelial marker E-cadherin (P = 0.021) and increased expression of the mesenchymal marker vimentin (P = 0.004). Results of in vitro and in vivo experiments showed that ATP6L expression could alter cell morphology, regulate EMT-associated protein expression, and enhance migration and invasion. The effect of ATP6L on metastasis was further demonstrated in a tail vein injection mice model. In addition, the mouse xenograft model showed that ATP6L-overexpressing HCT116 cells grew into larger tumor masses, showed less necrosis and formed more micro-vessels than the control cells. Taken together, our results suggest that ATP6L promotes metastasis of colorectal cancer by inducing EMT and angiogenesis, and is a potential target for tumor therapy.

A cell-based assay for CD63-containing extracellular vesicles

Extracellular vesicles (EVs) are thought to be important in cell-cell communication and have elicited extraordinary interest as potential biomarkers of disease. However, quantitative methods to enable elucidation of mechanisms underlying release are few. Here, we describe a cell-based assay for monitoring EV release using the EV-enriched tetraspanin CD63 fused to the small, ATP-independent reporter enzyme, Nanoluciferase. Release of CD63-containing EVs from stably expressing cell lines was monitored by comparing luciferase activity in culture media to that remaining in cells. HEK293, U2OS, U87 and SKMel28 cells released 0.3%-0.6% of total cellular CD63 in the form of EVs over 5 hrs, varying by cell line. To identify cellular machinery important for secretion of CD63-containing EVs, we performed a screen of biologically active chemicals in HEK293 cells. While a majority of compounds did not significantly affect EV release, treating cells with the plecomacrolides bafilomycin or concanamycin, known to inhibit the V-ATPase, dramatically increased EV release. Interestingly, alkalization of the endosomal lumen using weak bases had no effect, suggesting a pH-independent enhancement of EV release by V-ATPase inhibitors. The ability to quantify EVs in small samples will enable future detailed studies of release kinetics as well as further chemical and genetic screening to define pathways involved in EV secretion.

Isoform-specific gene disruptions reveal a role for the V-ATPase subunit a4 isoform in the invasiveness of 4T1-12B breast cancer cells

The vacuolar H+-ATPase (V-ATPase) is an ATP-driven proton pump present in various intracellular membranes and at the plasma membrane of specialized cell types. Previous work has reported that plasma membrane V-ATPases are key players in breast cancer cell invasiveness. The two subunit a-isoforms known to target the V-ATPase to the plasma membrane are a3 and a4, and expression of a3 has been shown to correlate with plasma membrane localization of the V-ATPase in various invasive human breast cancer cell lines. Here we analyzed the role of subunit a-isoforms in the invasive mouse breast cancer cell line, 4T1-12B. Quantitation of mRNA levels for each isoform by quantitative RT-PCR revealed that a4 is the dominant isoform expressed in these cells. Using a CRISPR/Cas9-based approach to disrupt the genes encoding each of the four V-ATPase subunit a-isoforms, we found that ablation of only the a4-encoding gene significantly inhibits invasion and migration of 4T1-12B cells. Additionally, cells with disrupted a4 exhibited reduced V-ATPase expression at the leading edge, suggesting that the a4 isoform is primarily responsible for targeting the V-ATPase to the plasma membrane in 4T1-12B cells. These findings suggest that different subunit a-isoforms may direct V-ATPases to the plasma membrane of different invasive breast cancer cell lines. They further suggest that expression of V-ATPases at the cell surface is the primary factor that promotes an invasive cancer cell phenotype.

ZIP4 Promotes Muscle Wasting and Cachexia in Mice With Orthotopic Pancreatic Tumors by Stimulating RAB27B-Regulated Release of Extracellular Vesicles From Cancer Cells

BACKGROUND & AIMS

Cachexia, which includes muscle wasting, is a frequent complication of pancreatic cancer. There are no therapies that reduce cachexia and increase patient survival, so it is important to learn more about its mechanisms. The zinc transporter ZIP4 promotes growth and metastasis of pancreatic tumors. We investigated its effects on muscle catabolism via extracellular vesicle (EV)-mediated stimulation of mitogen-activated protein kinase 14 (p38 MAPK).

METHODS

We studied nude mice with orthotopic tumors grown from human pancreatic cancer cell lines (AsPC-1 and BxPC-3); tumors were removed 8 days after cell injection and analyzed by histology. Mouse survival was analyzed by Kaplan-Meier curves. ZIP4 was knocked down in AsPC-1 and BxPC-3 cells with small hairpin RNAs; cells with empty vectors were used as controls. Muscle tissues were collected from mice and analyzed by histology and immunohistochemistry. Conditioned media from cell lines and 3-dimensional spheroid/organoid cultures of cancer cells were applied to C2C12 myotubes. The myotubes and the media were analyzed by immunoblots, enzyme-linked immunosorbent assays, and immunofluorescence microscopy. EVs were isolated from conditioned media and analyzed by immunoblots.

RESULTS

Mice with orthotopic tumors grown from pancreatic cancer cells with knockdown of ZIP4 survived longer and lost less body weight and muscle mass than mice with control tumors. Conditioned media from cancer cells activated p38 MAPK, induced expression of F-box protein 32 and UBR2 in C2C12 myotubes, and also led to loss of myofibrillar protein myosin heavy chain and myotube thinning. Knockdown of ZIP4 in cancer cells reduced these effects. ZIP4 knockdown also reduced pancreatic cancer cell release of heat shock protein (HSP) 70 and HSP90, which are associated with EVs, by decreasing CREB-regulated expression of RAB27B.

CONCLUSIONS

ZIP4 promotes growth of orthotopic pancreatic tumors in mice and loss of muscle mass by activating CREB-regulated expression of RAB27B, required for release of EVs from pancreatic cancer cells. These EVs activate p38 MAPK and induce expression of F-box protein 32 and UBR2 in myotubes, leading to loss of myofibrillar myosin heavy chain and myotube thinning. Strategies to disrupt these pathways might be developed to reduce pancreatic cancer progression and accompanying cachexia.

Functional implications of Rab27 GTPases in Cancer

Background

The Rab27 family of small GTPases promotes the progression of breast cancer, melanoma, and other human cancers. In this review, we discuss the role of Rab27 GTPases in cancer progression and the potential applications of these targets in cancer treatment.

Main body

Elevated expression of Rab27 GTPases is associated with poor prognosis and cancer metastasis. Moreover, these GTPases govern a variety of oncogenic functions, including cell proliferation, cell motility, and chemosensitivity. In addition, small GTPases promote tumor growth and metastasis by enhancing exosome secretion, which alters intracellular microRNA levels, signaling molecule expression, and the tumor microenvironment.

Conclusion

Rab27 GTPases may have applications as prognostic markers and therapeutic targets in cancer treatment.

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

Vacuolar ATPase (V-ATPase) is an ATP-dependent H+ -transporter that pumps protons across intracellular and plasma membranes. It consists of a large multi-subunit protein complex and influences a wide range of cellular processes. This review focuses on emerging evidence for the roles for V-ATPase in cancer. This includes how V-ATPase dysregulation contributes to cancer growth, metastasis, invasion and proliferation, and the potential link between V-ATPase and the development of drug resistance.

Prognostic significance and function of the vacuolar H+-ATPase subunit V1E1 in esophageal squamous cell carcinoma

Vacuolar H⁺-ATPase (V-ATPase), a hetero-multimeric ATP-driven proton pump has recently emerged as a critical regulator of mTOR-induced amino acid sensing for cell growth. Although dysregulated activity of cell growth regulators is often associated with cancer, the prognostic significance and metabolic roles of V-ATPase in esophageal cancer progression remain unclear. Here, we show that high levels of V-ATPase subunit V1E1 (V-ATPase V1E1) were significantly associated with shortened disease-free survival in patients with esophageal squamous cell carcinoma (ESCC). Multivariate analysis identified the V-ATPase V1E1 as an independent adverse prognostic factor (hazard ratio;1.748, P = 0.018). In addition, depletion of V-ATPase V1E1 resulted in reduced cell motility, decreased glucose uptake, diminished levels of lactate, and decreased ATP production, as well as inhibition of glycolytic enzyme expression in TE8 esophageal cancer cells. Consistent with these results, the Cancer Genome Atlas (TCGA) data and Gene Set Enrichment Analysis (GSEA) showed a high frequency of copy number alterations of the V-ATPase V1E1 gene, and identified a correlation between levels of V-ATPase V1E1 mRNA and Pyruvate Kinase M2 (PKM2) in ESCC. High expression levels of both V-ATPase V1E1 and phosphorylated PKM2 (p-PKM2), a key player in cancer metabolism, were associated with poorer prognosis in ESCC. Collectively, our findings suggest that expression of the V-ATPase V1E1 has prognostic significance in ESCC, and is closely linked to migration, invasion, and aerobic glycolysis in esophageal cancer cells.

The a3 isoform of subunit a of the vacuolar ATPase localizes to the plasma membrane of invasive breast tumor cells and is overexpressed in human breast cancer

The vacuolar (H+)-ATPases (V-ATPases) are a family of ATP-driven proton pumps that acidify intracellular compartments and transport protons across the plasma membrane. Previous work has demonstrated that plasma membrane V-ATPases are important for breast cancer invasion in vitro and that the V-ATPase subunit a isoform a3 is upregulated in and critical for MDA-MB231 and MCF10CA1a breast cancer cell invasion. It has been proposed that subunit a3 is present on the plasma membrane of invasive breast cancer cells and is overexpressed in human breast cancer. To test this, we used an a3-specific antibody to assess localization in breast cancer cells. Subunit a3 localizes to the leading edge of migrating breast cancer cells, but not the plasma membrane of normal breast epithelial cells. Furthermore, invasive breast cancer cells express a3 throughout all intracellular compartments tested, including endosomes, the Golgi, and lysosomes. Moreover, subunit a3 knockdown in MB231 breast cancer cells reduces in vitro migration. This reduction is not enhanced upon addition of a V-ATPase inhibitor, suggesting that a3-containing V-ATPases are critical for breast cancer migration. Finally, we have tested a3 expression in human breast cancer tissue and mRNA prepared from normal and cancerous breast tissue. a3 mRNA was upregulated 2.5-47 fold in all breast tumor cDNA samples tested relative to normal tissue, with expression generally correlated to cancer stage. Furthermore, a3 protein expression was increased in invasive breast cancer tissue relative to noninvasive cancer and normal breast tissue. These studies suggest that subunit a3 plays an important role in invasive human breast cancer.

Tumor cell cholesterol depletion and V-ATPase inhibition as an inhibitory mechanism to prevent cell migration and invasiveness in melanoma

BACKGROUND

V-ATPase interactions with cholesterol enriched membrane microdomains have been related to metastasis in a variety of cancers, but the underlying mechanism remains at its beginnings. It has recently been reported that the inhibition of this H⁺ pump affects cholesterol mobilization to the plasma membrane.

METHODS

Inhibition of melanoma cell migration and invasiveness was assessed by wound healing and Transwell assays in murine cell lines (B16F10 and Melan-A). V-ATPase activity was measured in vitro by ATP hydrolysis and H⁺ transport in membrane vesicles, and intact cell H⁺ fluxes were measured by using a non-invasive Scanning Ion-selective Electrode Technique (SIET).

RESULTS

Cholesterol depletion by 5mM MβCD was found to be inhibitory to the hydrolytic and H⁺ pumping activities of the V-ATPase of melanoma cell lines, as well as to the migration and invasiveness capacities of these cells. Nearly the same effects were obtained using concanamycin A, a specific inhibitor of V-ATPase, which also promoted a decrease of the H⁺ efflux in live cells at the same extent of MβCD.

CONCLUSIONS

We found that cholesterol depletion significantly affects the V-ATPase activity and the initial metastatic processes following a profile similar to those observed in the presence of the V-ATPase specific inhibitor, concanamycin.

GENERAL SIGNIFICANCE

The results shed new light on the functional role of the interactions between V-ATPases and cholesterol-enriched microdomains of cell membranes that contribute with malignant phenotypes in melanoma.

Vacuolar ATPase as a possible therapeutic target in human acute myeloid leukemia

INTRODUCTION

V-ATPase is a proton pump expressed both in the membrane of intracellular organelles (e.g. endosomes, lysosomes, Golgi structures) and the plasma membrane. It is an important regulator of organellar functions, intracellular molecular trafficking, intercellular communication and intracellular signaling. It is therefore considered as a possible therapeutic target in the treatment of human malignancies. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for original articles and reviews describing the possible importance of V-ATPase for leukemogenesis and chemosensitivity in human myeloid cells, especially acute myeloid leukemia (AML) cells. Expert commentary: The expression of V-ATPase in the primary human AML cells varies between patients, and high levels are associated with high constitutive release of a wide range of soluble mediators. Several of the molecules included in the V-ATPase interactome may also be important in leukemogenesis and/or development of chemoresistance in human AML. Therapeutic targeting of V-ATPase should therefore be regarded as a possible therapeutic strategy in human AML, but the efficiency of such targeting will probably differ between patients. The possibility of toxicity, especially hematological toxicity and immunosuppression, also has to be clarified.

Cancer-derived extracellular vesicles: the 'soil conditioner' in breast cancer metastasis?

It has been recognized that cancer-associated mortality is more often a result of the disrupted physiological functions in multiple organs following metastatic dissemination of cancer cells, rather than the presence and growth of the primary tumor. Despite advances in our understanding of the events leading to cancer initiation, growth, and acquisition of invasive properties, we are still unable to effectively treat metastatic disease. It is now being accepted that the secretion of extracellular vesicles, such as exosomes from cancer cells, has a profound impact on the initiation and propagation of metastatic breast cancer. These cancer-secreted vesicles differ from other means of cellular communication due to their capability of bulk delivery and organotropism. Here, we provide an overview of the role of extracellular vesicles in breast cancer metastasis and discuss key areas that may facilitate our understanding of metastatic breast cancer to guide our efforts towards providing better therapies.

Molecular machineries of pH dysregulation in tumor microenvironment: potential targets for cancer therapy

Introduction: Cancer is an intricate disorder/dysfunction of cells that can be defined as a genetic heterogeneity in human disease. Therefore, it is characterized by several adaptive complex hallmarks. Among them, the pH dysregulation appears as a symbol of aberrant functions within the tumor microenvironment (TME). In comparison with normal tissues, in the solid tumors, we face with an irregular acidification and alkalinization of the extracellular and intracellular fluids. Methods: In this study, we comprehensively discussed the most recent reports on the hallmarks of solid tumors to provide deep insights upon the molecular machineries involved in the pH dysregulation of solid tumors and their impacts on the initiation and progression of cancer. Results: The dysregulation of pH in solid tumors is fundamentally related to the Warburg effect and hypoxia, leading to expression of a number of molecular machineries, including: NHE1, H+ pump V-ATPase, CA-9, CA-12, MCT-1, GLUT-1. Activation of proton exchangers and transporters (PETs) gives rise to formation of TME. This condition favors the cancer cells to evade from the anoikis and apoptosis, granting them aggressive and metastasis phenotype, as well as resistance to chemotherapy and radiation therapy. This review aimed to discuss the key molecular changes of tumor cells in terms of bio-energetics and cancer metabolism in relation with pH dysregulation. During this phenomenon, the intra- and extracellular metabolites are altered and/or disrupted. Such molecular alterations provide molecular hallmarks for direct targeting of the PETs by potent relevant inhibitors in combination with conventional cancer therapies as ultimate therapy against solid tumors. Conclusion: Taken all, along with other treatment strategies, targeting the key molecular machineries related to intra- and extracellular metabolisms within the TME is proposed as a novel strategy to inhibit or block PETs that are involved in the pH dysregulation of solid tumors.

The Function of V-ATPases in Cancer

The vacuolar ATPases (V-ATPases) are a family of proton pumps that couple ATP hydrolysis to proton transport into intracellular compartments and across the plasma membrane. They function in a wide array of normal cellular processes, including membrane traffic, protein processing and degradation, and the coupled transport of small molecules, as well as such physiological processes as urinary acidification and bone resorption. The V-ATPases have also been implicated in a number of disease processes, including viral infection, renal disease, and bone resorption defects. This review is focused on the growing evidence for the important role of V-ATPases in cancer. This includes functions in cellular signaling (particularly Wnt, Notch, and mTOR signaling), cancer cell survival in the highly acidic environment of tumors, aiding the development of drug resistance, as well as crucial roles in tumor cell invasion, migration, and metastasis. Of greatest excitement is evidence that at least some tumors express isoforms of V-ATPase subunits whose disruption is not lethal, leading to the possibility of developing anti-cancer therapeutics that selectively target V-ATPases that function in cancer cells.

MiR-20a-5p promotes radio-resistance by targeting Rab27B in nasopharyngeal cancer cells

BACKGROUND

MicroRNAs (miRNAs) was reported to be involved in cancer radio-resistance, which remains a major obstacle for effective cancer therapy.

METHODS

The differently expressed miRNAs were detected by RNA-seq experiment in nasopharyngeal cancer (NPC) cells. MiR-20a-5p was selected as our target, which was subject to finding its target gene Rab27B via bioinformatics analysis. The qRT-PCR, western blot and the luciferase reporter assays were performed to confirm Rab27B as the target of miR-20a-5p. In addition, the roles of miR-20a-5p in NPC radio-resistance were detected by transfection of either miR-20a-5p-mimic or miR-20a-5p-antagomiR. The involvement of Rab27B with NPC radio-resistance was also detected by the experiments with siRNA-mediated repression of Rab27B or over-expression of GFP-Rab27B. Wound healing and invasion assays were performed to detect the roles of both miR-20a-5p and Rab27B.

RESULTS

MiR-20a-5p promotes NPC radio-resistance. We identified that its target gene Rab27B negatively correlates with miR-20a-5p-mediated NPC radio-resistance by systematic studies of a radio-sensitive (CNE-2) and resistant (CNE-1) NPC cell lines. Repression of Rab27B by siRNA suppresses cell apoptosis and passivates CNE-2 cells, whereas over-expression of Rab27B triggered cell apoptosis and sensitizes CNE-1 cells.

CONCLUSIONS

MiR-20a-5p and its target gene Rab27B might be involved in the NPC radio-resistance. Thus the key players and regulators involved in this pathway might be the potential targets for developing effective therapeutic strategies against NPC.

The asialoglycoprotein receptor suppresses the metastasis of hepatocellular carcinoma via LASS2-mediated inhibition of V-ATPase activity

The asialoglycoprotein receptor (ASGR), which is expressed mainly in hepatocytes, is downregulated in poorly differentiated hepatocellular carcinoma (HCC). Here we investigated the role of ASGR1 in HCC metastasis as well as the possible underlying molecular mechanisms. We found that ASGR1 was downregulated in HCC tissue compared with adjacent non-tumorous liver tissue and that lower ASGR1 expression was associated with higher TNM stage and poorer prognosis in HCC patients. ASGR1 overexpression inhibited hepatoma cell migration and invasion in vitro and in vivo, while ASGR1 knockdown had the opposite effects. Furthermore, ASGR1 interacted directly with human longevity assurance homolog 2 of yeast LAG1 (LASS2). Knockdown of LASS2 attenuated the inhibitory effects of ASGR1 on hepatoma cell migration and invasion in vitro. ASGR1 decreased V-ATPase activity in hepatoma cells, and this was reversed by LASS2 knockdown. Finally, HCC patients with low LASS2 levels had poor prognosis, while those with high ASGR1 and LASS2 levels had better prognosis. Thus, ASGR1 may act as a potential metastasis suppressor in HCC, and the combination of ASGR1 and LASS2 may help predict the prognosis of HCC patients.

The vacuolar H+ ATPase is a novel therapeutic target for glioblastoma

The vacuolar H⁺ ATPase (V-ATPase) is a proton pump responsible for acidification of cellular microenvironments, an activity exploited by tumors to survive, proliferate and resist to therapy. Despite few observations, the role of V-ATPase in human tumorigenesis remains unclear.

We investigated the expression of ATP6V0C, ATP6V0A2, encoding two subunits belonging to the V-ATPase V0 sector and ATP6V1C, ATP6V1G1, ATPT6V1G2, ATP6V1G3, which are part of the V1 sector, in series of adult gliomas and in cancer stem cell-enriched neurospheres isolated from glioblastoma (GBM) patients. ATP6V1G1 expression resulted significantly upregulated in tissues of patients with GBM and correlated with shorter patients' overall survival independent of clinical variables.

ATP6V1G1 knockdown in GBM neurospheres hampered sphere-forming ability, induced cell death, and decreased matrix invasion, a phenotype not observed in GBM monolayer cultures. Treating GBM organotypic cultures or neurospheres with the selective V-ATPase inhibitor bafilomycin A1 reproduced the effects of ATP6V1G1 siRNA and strongly suppressed expression of the stem cell markers Nestin, CD133 and transcription factors SALL2 and POU3F2 in neurospheres.

These data point to ATP6V1G1 as a novel marker of poor prognosis in GBM patients and identify V-ATPase inhibition as an innovative therapeutic strategy for GBM.

Recent Insights into the Structure, Regulation, and Function of the V-ATPases

The vacuolar (H(+))-ATPases (V-ATPases) are ATP-dependent proton pumps that acidify intracellular compartments and are also present at the plasma membrane. They function in such processes as membrane traffic, protein degradation, virus and toxin entry, bone resorption, pH homeostasis, and tumor cell invasion. V-ATPases are large multisubunit complexes, composed of an ATP-hydrolytic domain (V1) and a proton translocation domain (V0), and operate by a rotary mechanism. This review focuses on recent insights into their structure and mechanism, the mechanisms that regulate V-ATPase activity (particularly regulated assembly and trafficking), and the role of V-ATPases in processes such as cell signaling and cancer. These developments have highlighted the potential of V-ATPases as a therapeutic target in a variety of human diseases.

CERS2 suppresses tumor cell invasion and is associated with decreased V-ATPase and MMP-2/MMP-9 activities in breast cancer

Ceramide synthase 2 (CERS2) is the gene identified from a human liver cDNA library in 2001. Our previous studies have shown higher expression of CERS2 in the breast cancer patients was associated with fewer lymph node metastases. However, the molecular mechanism of CERS2 involved is unknown. Here, we found CERS2 was heterogeneously expressed in various breast cancer cells. The mRNA and protein expression levels of CERS2 in MCF7 cells, which are poorly invasive breast cancer cells, were obviously higher than that in the highly invasive cells MDA-MB-231. Results showed overexpression of CERS2 in MDA-MB-231 cells could significantly inhibit the migration and invasion ability, whereas CERS2 knockdown in MCF7 cells could significantly increase the migration and invasion ability. Overexpression of CERS2 in MDA-MB-231 cells significantly reduced the V-ATPase activity, increased the extracellular pH and decreased the pH-dependent activity of MMP-2 and MMP-9 matrix metalloproteinases (MMPs). CERS2 knockdown in MCF7 cells significantly increased the V-ATPase activity, decreased the extracellular pH and increased the activity of MMP-2 and MMP-9. Taken together, CERS2 can significantly inhibit breast cancer cell invasion and is associated with the decrease of the V-ATPase activity and extracellular hydrogen ion concentration, and in turn the activation of secreted MMP-2/MMP-9 and degradation of extracellular matrix (ECM), which ultimately suppressed tumor's invasion. Thus, CERS2 may represent a novel target for selectively disrupting V-ATPase activity and the invasive potential of cancer cells.

MiR-193a-3p and miR-193a-5p suppress the metastasis of human osteosarcoma cells by down-regulating Rab27B and SRR, respectively

MicroRNAs have been identified as key players in the development and progression of osteosarcoma, which is the most common primary malignancy of bone. Sequencing-based miR-omic and quantitative real-time PCR analyses suggested that the expression of miR-193a-3p and miR-193a-5p was decreased by DNA methylation at their promoter region in a highly metastatic osteosarcoma cell line (MG63.2) relative to their expression in the less metastatic MG63 cell line. Further wound-healing and invasion assays demonstrated that both miR-193a-3p and miR-193a-5p suppressed osteosarcoma cell migration and invasion. Moreover, introducing miR-193a-3p and miR-193a-5p mimics into MG63.2 cells or antagomiRs into MG63 cells confirmed their critical roles in osteosarcoma metastasis. Additionally, bioinformatics prediction along with biochemical assay results clearly suggested that the secretory small GTPase Rab27B and serine racemase (SRR) were direct targets of miR-193a-3p and miR-193a-5p, respectively. These two targets are indeed involved in the miR-193a-3p- and miR-193a-5p-induced suppression of osteosarcoma cell migration and invasion. MiR-193a-3p and miR-193a-5p play important roles in osteosarcoma metastasis through down-regulation of the Rab27B and SRR genes and therefore may serve as useful biomarkers for the diagnosis of osteosarcoma and as potential candidates for the treatment of metastatic osteosarcoma.

Correlation Between RAB27B and p53 Expression and Overall Survival in Pancreatic Cancer

OBJECTIVES

RAB27B is a member of the Rab family GTPases involved in vesicle trafficking, and p53 has recently been implicated in regulating the exosome secretion pathway. Because exosome secretion plays an important role in modulating tumor microenvironment and invasive growth, we hypothesized that RAB27B and p53 expression might be associated with the aggressive behavior in pancreatic ductal adenocarcinoma, one of the most deadly human malignancies.

METHODS

We determined protein expression of RAB27B and p53 in 260 pancreatic tissues (186 malignant and 74 normal or benign) by immunohistochemistry analysis on tissue microarray and their correlation with patients' clinical parameters and overall survival.

RESULTS

We found that a high RAB27B protein expression (RAB27B) was significantly associated with perineural and vascular invasion, as well as distant metastasis. Patients with a high RAB27B expression had significantly poorer overall survival in both univariate and multivariate analyses. A significant correlation between RAB27B and p53 expression was observed.

CONCLUSIONS

Our data indicate that RAB27B expression is an independent prognostic marker for pancreatic ductal adenocarcinoma and suggest that RAB27B-regulated exosome secretion pathway represents a novel therapeutic target in pancreatic cancer.

Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells

Development of resistance to platinum compounds significantly hinders successful ovarian cancer (OVCA) treatment. In tumor cells, dysregulated pH gradient across cell membranes is a key physiological mechanism of metastasis/chemo-resistance. These pH alterations are mediated by aberrant activation of key multi-subunit proton pumps, Vacuolar-ATPases (V-ATPases). In tumor cells, its 'a2' isoform (V-ATPase-V0a2) is a component of functional plasma-membrane complex and promotes tumor invasion through tumor-acidification and immuno-modulation. Its involvement in chemo-resistance has not been studied. Here, we show that V-ATPase-V0a2 is over-expressed in acquired-cisplatin resistant OVCA cells (cis-A2780/cis-TOV112D). Of all the 'a' subunit isoforms, V-ATPase-V0a2 exhibited an elevated expression on plasma membrane of cisplatin-resistant cells compared to sensitive counterparts. Immuno-histochemistry revealed V-ATPase-V0a2 expression in both low grade (highly drug-resistant) and high grade (highly recurrent) human OVCA tissues indicating its role in a centralized mechanism of tumor resistance. In cisplatin resistant cells, shRNA mediated inhibition of V-ATPase-V0a2 enhanced sensitivity towards both cisplatin and carboplatin. This improved cytotoxicity was mediated by enhanced cisplatin-DNA-adduct formation and suppressed DNA-repair pathway, leading to enhanced apoptosis. Suppression of V0a2 activity strongly reduced cytosolic pH in resistant tumor cells, which is known to enhance platinum-associated DNA-damage. As an indicator of reduced metastasis and chemo-resistance, in contrast to plasma membrane localization, a diffused cytoplasmic localization of acidic vacuoles was observed in V0a2-knockdown resistant cells. Interestingly, pre-treatment with monoclonal V0a2-inhibitory antibody enhanced cisplatin cytotoxicity in resistant cells. Taken together, our findings suggest that the isoform specific inhibition of V-ATPase-V0a2 could serve as a therapeutic strategy for chemo-resistant ovarian carcinoma and improve efficacy of platinum drugs.

Vacuolar ATPase 'a2' isoform exhibits distinct cell surface accumulation and modulates matrix metalloproteinase activity in ovarian cancer

Tumor associated vacuolar H+-ATPases (V-ATPases) are multi-subunit proton pumps that acidify tumor microenvironment, thereby promoting tumor invasion. Subunit ‘a’ of its V0 domain is the major pH sensing unit that additionally controls sub-cellular targeting of V-ATPase and exists in four different isoforms. Our study reports an elevated expression of the V-ATPase-V0a2 isoform in ovarian cancer(OVCA) tissues and cell lines(A2780, SKOV-3 and TOV-112D). Among all V0’a’ isoforms, V0a2 exhibited abundant expression on OVCA cell surface while normal ovarian epithelia did not. Sub-cellular distribution of V-ATPase-V0a2 confirmed its localization on plasma-membrane, where it was also co-associated with cortactin, an F-actin stabilizing protein at leading edges of cancer cells. Additionally, V0a2 was also localized in early and late endosomal compartments that are sites for modulations of several signaling pathways in cancer. Targeted inhibition of V-ATPase-V0a2 suppressed matrix metalloproteinase activity(MMP-9 & MMP-2) in OVCA cells. In conclusion, V-ATPase-V0a2 isoform is abundantly expressed on ovarian tumor cell surface in association with invasion assembly related proteins and plays critical role in tumor invasion by modulating the activity of matrix-degrading proteases. This study highlights for the first time, the importance of V-ATPase-V0a2 isoform as a distinct biomarker and possible therapeutic target for treatment of ovarian carcinoma.

Technical innovation in adjuvant radiotherapy: Evolution and evaluation of new treatments for today and tomorrow

Recent innovations in breast cancer radiotherapy include intensity modulated radiotherapy, brachytherapy and intraoperative radiotherapy and current trials are seeking to evaluate their value in optimizing local control while maintaining cosmetic effects. Future clinical dividends in local control and survival may come from the identification of molecular signatures of breast cancer radiosensitivity, the development of predictive signatures and identification of immunohistochemical markers of risk of local recurrence. The importance of tumour heterogeneity is being increasingly recognized as an important factor in determining radiotherapy response and an improved understanding of the biology of the tumour microenvironment may identify targets that allow enhanced radiosensitisation or reversal of radioresistance when inhibited. This review describes recent developments in these areas.

Bafilomycin A1 inhibits the growth and metastatic potential of the BEL-7402 liver cancer and HO-8910 ovarian cancer cell lines and induces alterations in their microRNA expression

The vacuolar H⁺-ATPase (V-ATPase) is commonly highly activated in cancer cells and is a potential target of anti-cancer therapy. Bafilomycin A1 is a specific inhibitor of the c subunit of V-ATPase. In the present study, the effects of bafilomycin A1 on the BEL-7402 hepatocellular carcinoma and HO-8910 ovarian cancer cell lines were respectively studied. In addition, the bafilomycin A1-induced alterations in the mRNAs and microRNAs (miRNAs) in the cells were detected using microarray methods. The results demonstrated that the growth of the two cell lines was retarded and the metastatic potential was inhibited by bafilomycin A1. Transmission electron microscopy and assays of capsase-3 and -9 suggested that bafilomycin A1 induced apoptosis. Gene Ontology analysis of the microarrays of mRNA-miRNA integrity showed altered pathways following bafilomycin A1 treatment, including pathways regulating glucose or lipid metabolism, DNA repair or duplication and lysosomes. Quantitative polymerase chain reaction analysis confirmed that miR-923, miR-1246, miR-149*, miR-638 and miR-210 were upregulated and miR-99a, miR-181a-2* and miR-339-5p were downregulated following bafilomycin A1 treatment. The overlapped altered miRs may be effective targets for the two types of solid tumor, and may have potential for application to the treatment of other types of solid tumor.

Inhibition of the vacuolar ATPase induces Bnip3-dependent death of cancer cells and a reduction in tumor burden and metastasis

The pro-apoptotic protein Bnip3 is induced by hypoxia and is present in the core regions of most solid tumors. Bnip3 induces programmed necrosis by an intrinsic caspase independent mitochondrial pathway. Many tumor cells have evolved pathways to evade Bnip3-mediated death attesting to the physiological relevance of the survival threat imposed by Bnip3. We have reported that acidosis can trigger the Bnip3 death pathway in hypoxic cells therefore we hypothesized that manipulation of intracellular pH by pharmacological inhibition of the vacuolar (v)ATPase proton pump, a significant pH control pathway, may activate Bnip3 and promote death of hypoxic cells within the tumor. Here we confirm that bafilomycin A1 (BafA1), a selective vATPase inhibitor, significantly increased death of breast cancer cells in a hypoxia and Bnip3-dependent manner and significantly reduced tumor growth in MCF7 and MDA-MB-231 mouse xenografts. Combined treatment of cells with BafA1 and the ERK1/2 inhibitor U0126 further augmented cell death. Combined treatment of mice containing MDA-MB-231 xenografts with BafA1 and the ERK1/2 inhibitor sorafenib was superior to either treatment alone and supported tumor regression. BafA1 and sorafenib treatments alone reduced MDA-MB-231 cell metastasis and again the combination was significantly more effective than either treatment alone and was without apparent side effects. These results present a novel mechanism to destroy hypoxic tumor cells that may help reverse the resistance of hypoxic tumors to radiation and chemotherapy and perhaps target tumor stem cells.

Activity of plasma membrane V-ATPases is critical for the invasion of MDA-MB231 breast cancer cells

The vacuolar (H(+))-ATPases (V-ATPases) are a family of ATP-driven proton pumps that couple ATP hydrolysis with translocation of protons across membranes. Previous studies have implicated V-ATPases in cancer cell invasion. It has been proposed that V-ATPases participate in invasion by localizing to the plasma membrane and causing acidification of the extracellular space. To test this hypothesis, we utilized two separate approaches to specifically inhibit plasma membrane V-ATPases. First, we stably transfected highly invasive MDA-MB231 cells with a V5-tagged construct of the membrane-embedded c subunit of the V-ATPase, allowing for extracellular expression of the V5 epitope. We evaluated the effect of addition of a monoclonal antibody directed against the V5 epitope on both V-ATPase-mediated proton translocation across the plasma membrane and invasion using an in vitro Matrigel assay. The addition of anti-V5 antibody resulted in acidification of the cytosol and a decrease in V-ATPase-dependent proton flux across the plasma membrane in transfected but not control (untransfected) cells. These results demonstrate that the anti-V5 antibody inhibits activity of plasma membrane V-ATPases in transfected cells. Addition of the anti-V5 antibody also inhibited in vitro invasion of transfected (but not untransfected) cells. Second, we utilized a biotin-conjugated form of the specific V-ATPase inhibitor bafilomycin. When bound to streptavidin, this compound cannot cross the plasma membrane. Addition of this compound to MDA-MB231 cells also inhibited in vitro invasion. These studies suggest that plasma membrane V-ATPases play an important role in invasion of breast cancer cells.

Tumor metastasis suppressor gene-1 and tumors

Tumor metastasis suppressor gene-1 (TMSG-1) is a newly discovered tumor metastasis suppressor gene that plays important roles in promoting apoptosis and inhibiting invasion and metastasis of tumor cells. The inhibitory function of TMSG-1 in tumor cells may be related to vacuolar H⁺-ATPase and ceramide, but the underlying mechanism remains unknown. This review discusses the discovery of TMSG-1, the structure of TMSG-1 protein, as well as its possible mechanisms of action, expression in tumors and applications.

Prognostic value of Rab27B nuclear expression in gastrointestinal stromal tumors

Rab proteins of the endocytosis and exocytosis pathways both play critical roles in cancer progression, and Rab27B has a significant relationship with several types of human cancer. However, the association between Rab27B expression and clinical features to determine its clinicopathological significance in gastrointestinal tumor (GIST) has not been investigated. To examine the expression of Rab27B in GIST and investigate the association between its expression and patient prognosis, immunohistochemistry analysis with tissue microarray was used to evaluate expression of Rab27B in 162 patients with GIST. The relationship between Rab27B expression and patient prognosis was analyzed. High nuclear staining of Rab27B was detected in 88 of 162 (54.32%) GIST tissues. Positive staining of Rab27B was significantly associated with tumor size (P = 0.006), mitotic index (P = 0.013), Armed Forces Institute of Pathology Miettinen risk classification (P = 0.002), and tumor grade (P = 0.021). Kaplan-Meier survival curves showed that GIST patients with low Rab27B nuclear expression (P = 0.038) and mitotic index <5 per 50 high-power fields (P = 0.029) had a more favorable prognosis. These findings indicate that Rab27B nuclear expression is correlated with several clinicopathological features of GIST patients, and it may serve as an unfavorable prognostic marker.

V-ATPase inhibition regulates anoikis resistance and metastasis of cancer cells

Fighting metastasis is a major challenge in cancer therapy and novel therapeutic targets and drugs are highly appreciated. Resistance of invasive cells to anoikis, a particular type of apoptosis induced by loss of cell-matrix contact, is a major prerequisite for their metastatic spread. Inducing anoikis in metastatic cancer cells is therefore a promising therapeutic approach. The vacuolar-ATPase (V-ATPase), a proton pump located at the membrane of acidic organelles, has recently come to focus as an antimetastatic cancer target. As V-ATPase inhibitors have shown to prevent invasion of tumor cells and are able to induce apoptosis, we proposed that V-ATPase inhibition induces anoikis-related pathways in invasive cancer cells. We used the V-ATPase inhibitor archazolid to investigate the mechanism of anoikis induction in various metastatic cancer cells (T24, MDA-MB-231, 4T1, 5637) in vitro. Anoikis induction by archazolid was characterized by decreased c-FLIP expression and caspase-8 activation as well as reduction of active integrin-β1 and an early increase of the proapoptotic protein BIM. However, we observed that archazolid also induces mechanisms opposing anoikis such as degradation of BIM mediated by extracellular signal-regulated kinase (ERK), Akt and Src kinases at later time points and induction of reactive oxygen species. Still, intravenous injection of archazolid-treated 4T1-Luc2 mouse breast cancer cells resulted in reduced metastasis in mouse lungs. Thus, V-ATPase inhibition is not only an interesting option to reduce cancer metastasis, but also to better understand anoikis resistance and to find choices to fight against it.

Regulation of endothelial signaling and migration by v-ATPase

The vacuolar ATPase (v-ATPase) is a proton pump, able to acidify intracellular compartments and the pericellular space. v-ATPase has extensively been studied in various functional contexts, e.g., migration of tumor cells, and inhibition of v-ATPase has been proven as intriguing novel therapeutic concept. Since the role of v-ATPase in endothelial cell migration and angiogenesis has scarcely been investigated, we examined the consequences of pharmacological inhibition of v-ATPase (by concanamycin) on proliferation, migration, VEGF-receptor 2 (VEGFR2) trafficking and signaling, as well as Notch-mediated transcription in endothelial cells [human microvascular endothelial cells (HMEC-1) and human umbilical vein endothelial cells (HUVEC)] Treatment of the cells with 3 or 10 nM of the v-ATPase inhibitor concanamycin for 48 h or longer inhibited proliferation and arrested cell cycle in the G2/M phase in HMEC-1, while a G1 phase arrest occurred in HUVEC. Already after 24 h these concentrations reduced migration (scratch assay, chemotactic gradient). Activation of the small GTPase Rac1 in freshly adherent cells was reduced by concanamycin. Downstream signaling of the VEGFR2 (phosphorylation of ERK1/2 and AKT), as well as autophosphorylation of VEGFR2 were inhibited. VEGFR2 on the cell surface was reduced, and sequestered in a lysosomal compartment. In addition, concanamycin blocked transcription of the Notch target genes Hey1 and Hey2 after stimulation with DLL4. Since the impaired signaling pathways (Rac-1, VEGFR2, Notch) all depend on vesicular recycling circuits, we conclude that the disturbance of these is the main mode of action of v-ATPase inhibition in endothelial cells, offering an attractive multi-factorial anti-angiogenic approach.

The function of vacuolar ATPase (V-ATPase) a subunit isoforms in invasiveness of MCF10a and MCF10CA1a human breast cancer cells

The vacuolar H(+) ATPases (V-ATPases) are ATP-driven proton pumps that transport protons across both intracellular and plasma membranes. Previous studies have implicated V-ATPases in the invasiveness of various cancer cell lines. In this study, we evaluated the role of V-ATPases in the invasiveness of two closely matched human breast cancer lines. MCF10a cells are a non-invasive, immortalized breast epithelial cell line, and MCF10CA1a cells are a highly invasive, H-Ras-transformed derivative of MCF10a cells selected for their metastatic potential. Using an in vitro Matrigel assay, MCF10CA1a cells showed a much higher invasion than the parental MCF10a cells. Moreover, this increased invasion was completely sensitive to the specific V-ATPase inhibitor concanamycin. MCF10CA1a cells expressed much higher levels of both a1 and a3 subunit isoforms relative to the parental line. Isoforms of subunit a are responsible for subcellular localization of V-ATPases, with a3 and a4 targeting V-ATPases to the plasma membrane of specialized cells. Knockdown of either a3 alone or a3 and a4 together using isoform-specific siRNAs inhibited invasion by MCF10CA1a cells. Importantly, overexpression of a3 but not the other a subunit isoforms greatly increased the invasiveness of the parental MCF10a cells. Similarly, overexpression of a3 significantly increased expression of V-ATPases at the plasma membrane. These studies suggest that breast tumor cells employ particular a subunit isoforms to target V-ATPases to the plasma membrane, where they function in tumor cell invasion.

The expression of V-ATPase is associated with drug resistance and pathology of non-small-cell lung cancer

Objective

This article aims to investigate the expression of vacuolar-H + −ATPase (V-ATPase) in non-small cell lung cancer (NSCLC) and its variations with pathological type and grade. Furthermore, to evaluate the chemotherapy drug sensitivity of different cancer tissues as well as its correlation with V-ATPase expression in NSCLC.

Methods

V-ATPase expression was examined in 92 NSCLC tissue samples using the immunohistochemical Envision method and immunofluorescence assay. The location of V-ATPase expression was observed by confocal laser scanning microscopy and the difference of its expression rate was evaluated. The sensitivity of cancer tissues to chemotherapy drug was examined using MTT assay and its correlation with the V-ATPase expression was tested in NSCLC by Spearman rank correlation analysis.

Results

V-ATPase expression was mainly localized in the cell membrane and cytoplasm. The expression rate of V-ATPase was 71.43% in squamous cell lung cancer, significantly lower than that of the lung adenocarcinoma (83.72%, P = 0.000). In different pathological grades of squamous cell lung cancer, the expression rate of V-ATPase was 58.33% in grade II, significantly lower than that of the grade III (84.00%, P = 0.014). The expression rate of V-ATPase in grade II lung adenocarcinoma was 76.67%, significantly lower than that of the grade ΙΙΙ adenocarcinoma (100.0%, P = 0.012). Correlation analysis showed that the sensitivity of NSCLC tissues to cyclophosphamide, gemcitabine, doxorubicin, paclitaxel and cisplatin was significantly correlated with the V-ATPase expression rate (P < 0.05).

Conclusions

V-ATPase was overexpressed in NSCLC. The expression of V-ATPase was related to the pathological type and grade of cancer and was likely associated with chemotherapy drug resistance in NSCLC.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/7515811511020000

Rab27 GTPases distribute extracellular nanomaps for invasive growth and metastasis: implications for prognosis and treatment

The Rab27 family of small GTPases regulates exocytosis of distinct vesicle types including multivesicular endosomes, which results in the release of exosomes. Exosomes are nanometer-sized membrane vesicles that enclose soluble factors such as proteins and nucleic acids within a lipid bilayer and can travel toward distant tissues to influence multiple aspects of cell behavior. In our view that tumors are endocrine organs producing exosomes, Rab27 GTPases and their effector proteins are critical determinants for invasive growth and metastasis. Rab27 proteins and their effectors may serve as prognostic biomarkers or as targets for patient-tailored therapy.