NHE1 mediates MDA-MB-231 cells invasion through the regulation of MT1-MMP

Parabens promotes invasive properties of multiple human cells: A potential cancer-associated adverse outcome pathway

Parabens are esters of p-hydroxybenzoic acid, which have been used as preservatives and considered safe for nearly a century, until the last two decades when concerns began to be raised about their association with cancers. Knowledge of the mode of action of parabens on the metastatic properties of different cancer cells is still very limited. In the present study, we investigated the effects of methylparaben (MP) and propylparaben (PP) on cell invasion and/or migration in multiple human cancerous and noncancerous cells, including hepatocellular carcinoma cells (HepG2), cervical carcinoma cells (HeLa), breast carcinoma cells (MCF-7), and human placental trophoblasts (HTR-8/SVneo). MP and PP at concentrations in a range of 5-500 μg/L significantly promoted the invasion of four cell lines, with a minimum effective concentration of 5 μg/L. MP and PP up-regulated the expression levels and enzymatic activities of matrix metalloproteinase 2 and 9 (MMP2 and MMP9), as well as altered the expression of the tissue inhibitors of metalloproteinase 1 and 2 (TIMP1 and TIMP2) in four cell lines, suggesting MMPs/TIMPs as potential key events (KEs) for paraben-induced cell invasion. Activation of the p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal protein kinases 1/2 (JNK1/2) signaling pathways was required for MP- and PP-promoted invasion of four cell lines, suggesting MAPK signaling pathways as candidates for KEs in cancer or noncancerous cells response to paraben exposure. This study showed for the first time that the two widely used parabens, MP and PP, promoted invasive capacity of multiple human cells through a common mode of action. This study provides evidence for the establishment of a potential cancer-associated AOP for parabens based on pathway-specific mechanism(s), which contributes towards assessing the health risks of these environmental chemicals.

Voltage-gated sodium channels: from roles and mechanisms in the metastatic cell behavior to clinical potential as therapeutic targets

During the second half of the last century, the prevalent knowledge recognized the voltage-gated sodium channels (VGSCs) as the proteins responsible for the generation and propagation of action potentials in excitable cells. However, over the last 25 years, new non-canonical roles of VGSCs in cancer hallmarks have been uncovered. Their dysregulated expression and activity have been associated with aggressive features and cancer progression towards metastatic stages, suggesting the potential use of VGSCs as cancer markers and prognostic factors. Recent work has elicited essential information about the signalling pathways modulated by these channels: coupling membrane activity to transcriptional regulation pathways, intracellular and extracellular pH regulation, invadopodia maturation, and proteolytic activity. In a promising scenario, the inhibition of VGSCs with FDA-approved drugs as well as with new synthetic compounds, reduces cancer cell invasion in vitro and cancer progression in vivo. The purpose of this review is to present an update regarding recent advances and ongoing efforts to have a better understanding of molecular and cellular mechanisms on the involvement of both pore-forming α and auxiliary β subunits of VGSCs in the metastatic processes, with the aim at proposing VGSCs as new oncological markers and targets for anticancer treatments.

The Physiological Function and Potential Role of the Ubiquitous Na+/H+ Exchanger Isoform 8 (NHE8): An Overview Data

The Na⁺/H⁺ exchanger transporters (NHE) play an important role in various biologic processes including Na⁺ absorption, intracellular pH homeostasis, cell volume regulation, proliferation, and apoptosis. The wide expression pattern and cellular localization of NHEs make these proteins pivotal players in virtually all human tissues and organs. In addition, recent studies suggest that NHEs may be one of the primeval transport protein forms in the history of life. Among the different isoforms, the most well-characterized NHEs are the Na⁺/H⁺ exchanger isoform 1 (NHE1) and Na⁺/H⁺ exchanger isoform 3 (NHE3). However, Na⁺/H⁺ exchanger isoform 8 (NHE8) has been receiving attention based on its recent discoveries in the gastrointestinal tract. In this review, we will discuss what is known about the physiological function and potential role of NHE8 in the main organ systems, including useful overviews that could inspire new studies on this multifaceted protein.

Inhibition of c-MYC-miRNA 19 Pathway Sensitized CML K562 Cells to Etoposide via NHE1 Upregulation

As a previously discovered target of DNA damage, Na⁺/H⁺ exchanger 1 (NHE1) plays a role in regulation of intracellular pH (pH_i) through the extrusion of intracellular proton (H⁺) in exchange for extracellular sodium (Na⁺). Its abnormal expression and dysfunction have been reported in solid tumor and hematopoietic malignancies. Here, we reported that suppression of NHE1 in BCR-ABL⁺ hematopoietic malignancies' K562 cells treated with Etoposide was manipulated by miR-19 and c-MYC. Inhibition of miR-19 or c-MYC enhanced the expression of NHE1 and sensitized K562 cells to Etoposide in vitro. The in vivo nude mouse transplantation model was also performed to confirm the enhanced sensitivity of K562 cells to Etoposide by inhibiting the miR-19 or c-MYC pathway. TCGA analysis conferred a negative correlation between miR-19 level and leukemia patients' survival. Thus, our results provided a potential management by which the c-MYC-miRNA 19 pathway might have a crucial impact on sensitizing K562 cells to Etoposide in the therapeutic approaches.

The positive feedback loop of NHE1-ERK phosphorylation mediated by BRAFV600E mutation contributes to tumorigenesis and development of glioblastoma

The v-raf murine sarcoma viral oncogene homolog B1 (BRAF) activating mutation V600E (BRAFV600E) is involved in glioblastoma multiforme (GBM). Na/H exchanger 1 (NHE1), a main pH regulator affecting cell microenvironment, is hyper-expressed in GBM. However, the relationship between BRAFV600E signal pathway and NHE1 in GMB cells remains unclear. This study found that NHE1 was a downstream target of BRAFV600E and an upstream factor of extracellular signal-regulated kinase (ERK). In addition, there was a positive feedback loop between NHE1-ERK phosphorylation under regulation of BRAFV600E mutation contributing to the proliferation and invasion of GBM cells. Moreover, the proliferation and invasion abilities of BRAFV600E-mutant and BRAF wild type GBM cells were all suppressed by the NHE1 inhibitor, BRAFV600E inhibitor and combination of them. The inhibitory effect of combination of the two inhibitors was better than each single drug both in vitro and in vivo. Combination of BRAFV600E and NHE1 inhibitors could be considered as a new therapeutic regimen for GBM, especially for GBM with BRAFV600E.

Matrix Metalloproteinases Shape the Tumor Microenvironment in Cancer Progression

Cancer progression with uncontrolled tumor growth, local invasion, and metastasis depends largely on the proteolytic activity of numerous matrix metalloproteinases (MMPs), which affect tissue integrity, immune cell recruitment, and tissue turnover by degrading extracellular matrix (ECM) components and by releasing matrikines, cell surface-bound cytokines, growth factors, or their receptors. Among the MMPs, MMP-14 is the driving force behind extracellular matrix and tissue destruction during cancer invasion and metastasis. MMP-14 also influences both intercellular as well as cell-matrix communication by regulating the activity of many plasma membrane-anchored and extracellular proteins. Cancer cells and other cells of the tumor stroma, embedded in a common extracellular matrix, interact with their matrix by means of various adhesive structures, of which particularly invadopodia are capable to remodel the matrix through spatially and temporally finely tuned proteolysis. As a deeper understanding of the underlying functional mechanisms is beneficial for the development of new prognostic and predictive markers and for targeted therapies, this review examined the current knowledge of the interplay of the various MMPs in the cancer context on the protein, subcellular, and cellular level with a focus on MMP14.

Advances in research on the regulatory mechanism of NHE1 in tumors

Tumors pose a major threat to human health and present with difficulties that modern medicine has yet to overcome. It has been demonstrated that the acid-base balance of the tumor microenvironment is closely associated with the dynamic balance in the human body and that it regulates several processes, such as cell proliferation and differentiation, intracellular enzyme activity, and cytoskeletal assembly and depolymerization. It has been well established that the regulation of intra- and extracellular pH depends on a series of functional ion transporters and hydrogen ion channels, such as the Na⁺/H⁺ exchanger (NHE) protein and thee Cl/HCO₃- exchange protein, among which the NHE1 member of the NHE family has been attracting increasing attention in recent years, particularly in studies on the correlation between pH regulation and tumors. NHE1 is a housekeeping gene encoding a protein that is widely expressed on the surface of all plasma membranes. Due to its functional domain, which determines the pHi at its N-terminus and C-terminus, NHE1 is involved in the regulation of the cellular pH microenvironment. It has been reported in the literature that NHE1 can regulate cell volume, participate in the transmembrane transport of intracellular and extracellular ions, affect cell proliferation and apoptosis, and regulate cell behavior and cell cycle progression; however, research on the role of NHE1 in tumorigenesis and tumor development in various systems is at its early stages. The aim of the present study was to review the current research on the correlation between the NHE family proteins and various systemic tumors, in order to indicate a new direction for antitumor drug development with the pH microenvironment as the target.

Targeting the pH Paradigm at the Bedside: A Practical Approach

The inversion of the pH gradient in malignant tumors, known as the pH paradigm, is increasingly becoming accepted by the scientific community as a hallmark of cancer. Accumulated evidence shows that this is not simply a metabolic consequence of a dysregulated behavior, but rather an essential process in the physiopathology of accelerated proliferation and invasion. From the over-simplification of increased lactate production as the cause of the paradigm, as initially proposed, basic science researchers have arrived at highly complex and far-reaching knowledge, that substantially modified that initial belief. These new developments show that the paradigm entails a different regulation of membrane transporters, electrolyte exchangers, cellular and membrane enzymes, water trafficking, specialized membrane structures, transcription factors, and metabolic changes that go far beyond fermentative glycolysis. This complex world of dysregulations is still shuttered behind the walls of experimental laboratories and has not yet reached bedside medicine. However, there are many known pharmaceuticals and nutraceuticals that are capable of targeting the pH paradigm. Most of these products are well known, have low toxicity, and are also inexpensive. They need to be repurposed, and this would entail shorter clinical studies and enormous cost savings if we compare them with the time and expense required for the development of a new molecule. Will targeting the pH paradigm solve the "cancer problem"? Absolutely not. However, reversing the pH inversion would strongly enhance standard treatments, rendering them more efficient, and in some cases permitting lower doses of toxic drugs. This article's goal is to describe how to reverse the pH gradient inversion with existing drugs and nutraceuticals that can easily be used in bedside medicine, without adding toxicity to established treatments. It also aims at increasing awareness among practicing physicians that targeting the pH paradigm would be able to improve the results of standard therapies. Some clinical cases will be presented as well, showing how the pH gradient inversion can be treated at the bedside in a simple manner with repurposed drugs.

Cancer and pH Dynamics: Transcriptional Regulation, Proteostasis, and the Need for New Molecular Tools

An emerging hallmark of cancer cells is dysregulated pH dynamics. Recent work has suggested that dysregulated intracellular pH (pHi) dynamics enable diverse cancer cellular behaviors at the population level, including cell proliferation, cell migration and metastasis, evasion of apoptosis, and metabolic adaptation. However, the molecular mechanisms driving pH-dependent cancer-associated cell behaviors are largely unknown. In this review article, we explore recent literature suggesting pHi dynamics may play a causative role in regulating or reinforcing tumorigenic transcriptional and proteostatic changes at the molecular level, and discuss outcomes on tumorigenesis and tumor heterogeneity. Most of the data we discuss are population-level analyses; lack of single-cell data is driven by a lack of tools to experimentally change pHi with spatiotemporal control. Data is also sparse on how pHi dynamics play out in complex in vivo microenvironments. To address this need, at the end of this review, we cover recent advances for live-cell pHi measurement at single-cell resolution. We also discuss the essential role for tool development in revealing mechanisms by which pHi dynamics drive tumor initiation, progression, and metastasis.

Pathological role of ion channels and transporters in the development and progression of triple-negative breast cancer

Breast cancer is a common malignancy in women. Among breast cancer types, triple-negative breast cancer (TNBC) tends to affect younger women, is prone to axillary lymph node, lung, and bone metastases; and has a high recurrence rate. Due to a lack of classic biomarkers, the currently available treatments are surgery and chemotherapy; no targeted standard treatment options are available. Therefore, it is urgent to find a novel and effective therapeutic target. As alteration of ion channels and transporters in normal mammary cells may affect cell growth, resulting in the development and progression of TNBC, ion channels and transporters may be promising new therapeutic targets for TNBC. This review summarizes ion channels and transporters related to TNBC and may provide new tumor biomarkers and help in the development of novel targeted therapies.

Physiological and pathophysiological role of ion channels and transporters in the colorectum and colorectal cancer

The incidence of colorectal cancer has increased annually, and the pathogenesis of this disease requires further investigation. In normal colorectal tissues, ion channels and transporters maintain the water‐electrolyte balance and acid/base homeostasis. However, dysfunction of these ion channels and transporters leads to the development and progression of colorectal cancer. Therefore, this review focuses on the progress in understanding the roles of ion channels and transporters in the colorectum and in colorectal cancer, including aquaporins (AQPs), Cl⁻ channels, Cl⁻/HCO3‐ exchangers, Na⁺/HCO3‐ transporters and Na⁺/H⁺ exchangers. The goal of this review is to promote the identification of new targets for the treatment and prognosis of colorectal cancer.

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.

MMP3 activity rather than cortical stiffness determines NHE1-dependent invasiveness of melanoma cells

Background

Both cell adhesion and matrix metalloproteinase (MMP) activity depend on pH at the cell surface. By regulating extracellular juxtamembrane pH, the Na⁺/H⁺ exchanger NHE1 plays a significant part in human melanoma (MV3) cell migration and invasion. Because NHE1, besides its pH-regulatory transport function, also serves as a structural element tying the cortical actin cytoskeleton to the plasma membrane, we investigated whether NHE1 affects cortical stiffness of MV3 cells, and how this makes an impact on their invasiveness.

Methods

NHE1 overexpressing MV3 cells were compared to the corresponding mock-transfected control cells. NHE1 expression was verified by Western blotting, cariporide (HOE642) was used to inhibit NHE1 activity, cell stiffness was determined by atomic force microscopy, and F-actin was visualized by phalloidin-staining. Migration on, and invasion of, native and glutaraldehyde-fixed collagen I substrates were analyzed using time-lapse video microscopy and Boyden-chamber assays, respectively. MMP secretion and activity were detected by Western blot and zymography, respectively. MMP activity was inhibited with NNGH.

Results

The cortical, but not the bulk stiffness, was significantly higher in NHE1 overexpressing cells. This increase in cortical stiffness was accompanied by a reorganization of the cortical cytoskeleton, i.e. a condensation of F-actin underneath and along the plasma membrane. However, it was not affected by NHE1 inhibition. Nevertheless, actin dynamics is required for cell invasion as demonstrated with the application of cytochalasin D. NHE1 overexpression was associated with an elevated MMP3 secretion and an increase in the invasion of a native matrix. This increase in invasiveness could be antagonized by the MMP inhibitor NNGH. Transmigration through a glutaraldehyde-fixed, indigestible substrate was not affected by NHE1 overexpression.

Conclusion

NHE1, as a structural element and independently of its transport activity, contributes to the organization of the cortical F-actin meshwork and thus impacts cortical stiffness. Since NHE1 overexpression stimulates MMP3 secretion but does not change transmigration through a fixed substrate, MV3 cell invasion of a native substrate depends on MMP activity rather than on a modifiable cortical stiffness.

Function of ion transporters in maintaining acid-base homeostasis of the mammary gland and the pathophysiological role in breast cancer

The incidence of breast cancer is increasing year by year, and the pathogenesis is still unclear. Studies have shown that the high metabolism of solid tumors leads to an increase in hypoxia, glycolysis, production of lactic acid and carbonic acid, and extracellular acidification; a harsh microenvironment; and ultimately to tumor cell death. Approximately 50% of locally advanced breast cancers exhibit hypoxia and/or local hypoxia, and acid-base regulatory proteins play an important role in regulating milk secretion and maintaining mammary gland physiological function. Therefore, ion transporters have gradually become a hot topic in mammary gland and breast cancer research. This review focuses on the research progress of ion transporters in mammary glands and breast cancer. We hope to provide new targets for the treatment and prognosis of breast cancer.

DCLK1 Plays a Metastatic-Promoting Role in Human Breast Cancer Cells

Background

Doublecortin-like kinase 1 (DCLK1) has been universally identified as a cancer stem cell (CSC) marker and is found to be overexpressed in many types of cancers including breast cancer. However, there is little data regarding the functional role of DCLK1 in breast cancer metastasis. In the present study, we sought to investigate whether and how DCLK1 plays a metastatic-promoting role in human breast cancer cells.

Methods

We used Crispr/Cas9 technology to knock out DCLK1 in breast cancer cell line BT474, which basically possesses DCLK1 at a higher level, and stably overexpressed DCLK1 in another breast cancer cell line, T47D, that basically expresses DCLK1 at a lower level. We further analyzed the alterations of metastatic characteristics and the underlying mechanisms in these cells.

Results

It was shown that, compared with the corresponding control cells, DCLK1 overexpression led to an increase in metastatic behaviors including enhanced migration and invasion of T47D cells. By contrast, forced depletion of DCLK1 drastically inhibited these metastatic characteristics in BT474 cells. Mechanistically, the epithelial-mesenchymal transition (EMT) program, which is critical for cancer metastasis, was prominently activated in DCLK1-overexpressing cancer cells, evidenced by a decrease in an epithelial marker ZO-1 and an enhancement in several mesenchymal markers including ZEB1 and Vimentin. In addition, DCLK1 overexpression induced the ERK MAPK pathway, which resultantly enhanced the expression of MT1-MMP that is also involved in cancer metastasis. Knockout of DCLK1 could reverse these events, further supporting a metastatic-promoting role for DCLK1.

Conclusions

Collectively, our data suggested that DCLK1 overexpression may be responsible for the increased metastatic features in breast cancer cells. Targeting DCLK1 may become a therapeutic option for breast cancer metastasis.

Structural and Functional Changes in the Na+/H+ Exchanger Isoform 1, Induced by Erk1/2 Phosphorylation

The human Na⁺/H⁺ exchanger isoform 1 (NHE1) is a plasma membrane transport protein that plays an important role in pH regulation in mammalian cells. Because of the generation of protons by intermediary metabolism as well as the negative membrane potential, protons accumulate within the cytosol. Extracellular signal-regulated kinase (ERK)-mediated regulation of NHE1 is important in several human pathologies including in the myocardium in heart disease, as well as in breast cancer as a trigger for growth and metastasis. NHE1 has a N-terminal, a 500 amino acid membrane domain, and a C-terminal 315 amino acid cytosolic domain. The C-terminal domain regulates the membrane domain and its effects on transport are modified by protein binding and phosphorylation. Here, we discuss the physiological regulation of NHE1 by ERK, with an emphasis on the critical effects on structure and function. ERK binds directly to the cytosolic domain at specific binding domains. ERK also phosphorylates NHE1 directly at multiple sites, which enhance NHE1 activity with subsequent downstream physiological effects. The NHE1 cytosolic regulatory tail possesses both ordered and disordered regions, and the disordered regions are stabilized by ERK-mediated phosphorylation at a phosphorylation motif. Overall, ERK pathway mediated phosphorylation modulates the NHE1 tail, and affects the activity, structure, and function of this membrane protein.

Acidification of Tumor at Stromal Boundaries Drives Transcriptome Alterations Associated with Aggressive Phenotypes

Acidosis is a fundamental feature of the tumor microenvironment, which directly regulates tumor cell invasion by affecting immune cell function, clonal cell evolution, and drug resistance. Despite the important association of tumor microenvironment acidosis with tumor cell invasion, relatively little is known regarding which areas within a tumor are acidic and how acidosis influences gene expression to promote invasion. Here, we injected a labeled pH-responsive peptide to mark acidic regions within tumors. Surprisingly, acidic regions were not restricted to hypoxic areas and overlapped with highly proliferative, invasive regions at the tumor-stroma interface, which were marked by increased expression of matrix metalloproteinases and degradation of the basement membrane. RNA-seq analysis of cells exposed to low pH conditions revealed a general rewiring of the transcriptome that involved RNA splicing and enriched for targets of RNA binding proteins with specificity for AU-rich motifs. Alternative splicing of Mena and CD44, which play important isoform-specific roles in metastasis and drug resistance, respectively, was sensitive to histone acetylation status. Strikingly, this program of alternative splicing was reversed in vitro and in vivo through neutralization experiments that mitigated acidic conditions. These findings highlight a previously underappreciated role for localized acidification of tumor microenvironment in the expression of an alternative splicing-dependent tumor invasion program. SIGNIFICANCE: This study expands our understanding of acidosis within the tumor microenvironment and indicates that acidosis induces potentially therapeutically actionable changes to alternative splicing.

CIAPIN1 Targeted NHE1 and ERK1/2 to Suppress NSCLC Cells' Metastasis and Predicted Good Prognosis in NSCLC Patients Receiving Pulmonectomy

Objective

Cytokine-induced apoptosis inhibitor 1 (CIAPIN1) acts as a downstream effector of the receptor tyrosine kinase-Ras signaling pathway and has been reported as a candidate tumor suppressor gene in various cancers. Our current study was aimed at investigating the prognostic impact of CIAPIN1 on Non-Small-Cell Lung Carcinoma (NSCLC) patients and the effect of CIAPIN1 on NSCLC A549 cells' metastasis.

Methods

Western blot analysis was applied to detect CIAPIN1 expression; Kaplan-Meier survival analysis was used to evaluate the effect of CIAPIN1 on NSCLC patients' prognosis. Wound healing assay, Transwell chamber invasion analysis, and tumorigenicity assay in BALB/c nude mice were used to measure the metastasis potential of A549 cells.

Results

We found that CIAPIN1 overexpression indicated good survival duration during the follow-up period. CIAPIN1 overexpression inhibited the migration, invasion, MMPs, and EMT-associated markers in A549 cells. Further, NHE1 (Na+/H+ exchanger 1) expression and ERK1/2 phosphorylation decreased along with CIAPIN1 upregulation. Importantly, treating A549 cells with CIAPIN1 overexpression with the NHE1-specific inhibitor, Cariporide, further inhibited the metastatic capacity, MMP expression, EMT-associated markers, and phosphorylated ERK1/2. Treatment with the MEK1-specific inhibitor, PD98059, induced nearly the same suppression of CIAPIN1 overexpression-dependent metastatic capacity, MMP expression, and EMT-associated markers as was observed with Cariporide. Further, Cariporide and PD98059 exert synergistical suppression of A549 cells' metastatic capacity.

Conclusion

Thus, the current results implied a potential management by which CIAPIN1 upregulation may have a crucial effect on the suppression of NSCLC, indicating that overexpression of CIAPIN1 might serve as a combination with chemotherapeutical agents in NSCLC therapy.

Cutaneous pH landscape as a facilitator of melanoma initiation and progression

Melanoma incidence is on the rise and currently causes the majority of skin cancer-related deaths. Yet, therapies for metastatic melanoma are still insufficient so that new concepts are essential. Malignant transformation of melanocytes and melanoma progression are intimately linked to the cutaneous pH landscape and its dysregulation in tumour lesions. The pH landscape of normal skin is characterized by a large pH gradient of up to 3 pH units between surface and dermis. The Na⁺ /H⁺ exchanger NHE1 is one of the major contributors of acidity in superficial skin layers. It is also activated by the most frequent mutation in melanoma, BRAF^{V 600E} , thereby causing pH dysregulation during melanoma initiation. Melanoma progression is supported by an extracellular acidification and/or NHE1 activity which promote the escape of single melanoma cells from the primary tumour, migration and metastatic spreading. We propose that viewing melanoma against the background of the acid-base physiology of the skin provides a better understanding of the pathophysiology of this disease and allows the development of novel therapeutic concepts.

Increased expression of Na+/H+ exchanger isoform 1 predicts tumor aggressiveness and unfavorable prognosis in epithelial ovarian cancer

Na⁺/H⁺ exchanger isoform 1 (NHE1), which is a regulator of intracellular and extracellular pH via ion exchange, has been demonstrated to serve an important role in cell differentiation, migration and invasion in solid tumors and hematological malignancies. However, the potential role of NHE1 in epithelial ovarian cancer (EOC) remains unclear. In the present study, the expression pattern and the prognostic value of NHE1 were investigated in EOC. EOC tissues, non-cancerous tumors and normal ovarian tissues were collected, and the expression levels of NHE1 were determined using the reverse transcription-quantitative polymerase chain reaction, western blotting and immunohistochemistry. The expression pattern of NHE1 was also evaluated in ovarian cancer cell lines using western blotting and immunofluorescence. In addition, the association between the NHE1 expression pattern and the clinicopathological features and the clinical prognosis of patients with EOC was also analyzed. The expression levels of NHE1 were identified to be significantly increased in EOC tissues compared with non-cancerous tumors and normal ovarian tissues (P<0.05). Furthermore, the increased expression of NHE1 was associated with an advanced International Federation of Gynecology and Obstetrics stage (FIGO III–IV; P<0.001) and the presence of high-grade carcinoma (grades 2–3, P<0.001). Overexpressed NHE1 was identified as a risk factor of shorter PFS (P<0.001) and OS (P<0.001). A multivariate Cox's regression analysis revealed that NHE1 was an independent prognostic factor for the prediction of the outcome of patients with EOC. NHE1 may, therefore, serve as a potential therapeutic target to inhibit tumor aggressiveness.

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.

mDia1 regulates breast cancer invasion by controlling membrane type 1-matrix metalloproteinase localization

Mammalian diaphanous-related formin 1 (mDia1) expression has been linked with progression of malignant cancers in various tissues. However, the precise molecular mechanism underlying mDia1-mediated invasion in cancer cells has not been fully elucidated. In this study, we found that mDia1 is upregulated in invasive breast cancer cells. Knockdown of mDia1 in invasive breast cancer profoundly reduced invasive activity by controlling cellular localization of membrane type 1-matrix metalloproteinase (MT1-MMP) through interaction with microtubule tracks. Gene silencing and ectopic expression of the active form of mDia1 showed that mDia1 plays a key role in the intracellular trafficking of MT1-MMP to the plasma membrane through microtubules. We also demonstrated that highly invasive breast cancer cells possessed invasive activity in a 3D culture system, which was significantly reduced upon silencing mDia1 or MT1-MMP. Furthermore, mDia1-deficient cells cultured in 3D matrix showed impaired expression of the cancer stem cell marker genes, CD44 and CD133. Collectively, our findings suggest that regulation of cellular trafficking and microtubule-mediated localization of MT1-MMP by mDia1 is likely important in breast cancer invasion through the expression of cancer stem cell genes.

Environmental carcinogenesis and pH homeostasis: Not only a matter of dysregulated metabolism

According to the World Health Organization, around 20% of all cancers would be due to environmental factors. Among these factors, several chemicals are indeed well recognized carcinogens. The widespread contaminant benzo[a]pyrene (B[a]P), an often used model carcinogen of the polycyclic aromatic hydrocarbons' family, has been suggested to target most, if not all, cancer hallmarks described by Hanahan and Weinberg. It is classified as a group I carcinogen by the International Agency for Research on Cancer; however, the precise intracellular mechanisms underlying its carcinogenic properties remain yet to be thoroughly defined. Recently, the pH homeostasis, a well known regulator of carcinogenic processes, was suggested to be a key actor in both cell death and Warburg-like metabolic reprogramming induced upon B[a]P exposure. The present review will highlight those data with the aim of favoring research on the role of H⁺ dynamics in environmental carcinogenesis.

Roles of pH and the Na+/H+ exchanger NHE1 in cancer: From cell biology and animal models to an emerging translational perspective?

Acidosis is characteristic of the solid tumor microenvironment. Tumor cells, because they are highly proliferative and anabolic, have greatly elevated metabolic acid production. To sustain a normal cytosolic pH homeostasis they therefore need to either extrude excess protons or to neutralize them by importing HCO₃^-, in both cases causing extracellular acidification in the poorly perfused tissue microenvironment. The Na⁺/H⁺ exchanger isoform 1 (NHE1) is a ubiquitously expressed acid-extruding membrane transport protein, and upregulation of its expression and/or activity is commonly correlated with tumor malignancy. The present review discusses current evidence on how altered pH homeostasis, and in particular NHE1, contributes to tumor cell motility, invasion, proliferation, and growth and facilitates evasion of chemotherapeutic cell death. We summarize data from in vitro studies, 2D-, 3D- and organotypic cell culture, animal models and human tissue, which collectively point to pH-regulation in general, and NHE1 in particular, as potential targets in combination chemotherapy. Finally, we discuss the possible pitfalls, side effects and cellular escape mechanisms that need to be considered in the process of translating the plethora of basic research data into a clinical setting.

Glioma-mediated microglial activation promotes glioma proliferation and migration: roles of Na+/H+ exchanger isoform 1

Microglia play important roles in extracellular matrix remodeling, tumor invasion, angiogenesis, and suppression of adaptive immunity in glioma. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates microglial activation and migration. However, little is known about the roles of NHE1 in intratumoral microglial activation and microglia-glioma interactions. Our study revealed up-regulation of NHE1 protein expression in both glioma cells and tumor-associated Iba1(+) microglia in glioma xenografts and glioblastoma multiforme microarrays. Moreover, we observed positive correlation of NHE1 expression with Iba1 intensity in microglia/macrophages. Glioma cells, via conditioned medium or non-contact glioma-microglia co-cultures, concurrently upregulated microglial expression of NHE1 protein and other microglial activation markers (iNOS, arginase-1, TGF-β, IL-6, IL-10 and the matrix metalloproteinases MT1-MMP and MMP9). Interestingly, glioma-stimulated microglia reciprocally enhanced glioma proliferation and migration. Most importantly, inhibition of microglial NHE1 activity via small interfering RNA (siRNA) knockdown or the potent NHE1-specific inhibitor HOE642 significantly attenuated microglial activation and abolished microglia-stimulated glioma migration and proliferation. Taken together, our findings provide the first evidence that NHE1 function plays an important role in glioma-microglia interactions, enhancing glioma proliferation and invasion by stimulating microglial release of soluble factors. NHE1 upregulation is a novel marker of the glioma-associated microglial activation phenotype. Inhibition of NHE1 represents a novel glioma therapeutic strategy by targeting tumor-induced microglial activation.

Ion transporters in brain tumors

Ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions. They have recently emerged as important players in cancer progression. In this review, we discussed two important ion transporter proteins, sodium-potassium-chloride cotransporter isoform 1 (NKCC-1) and sodium-hydrogen exchanger isoform 1 (NHE-1) in Glioblastoma multiforme (GBM) and other malignant tumors. NKCC-1 is a Na(+)- dependent Cl(-) transporter that mediates the movement of Na(+), K(+), and Cl(-) ions across the plasma membrane and maintains cell volume and intracellular K(+) and Cl(-) homeostasis. NHE-1 is a ubiquitously expressed cell membrane protein which regulates intracellular pH (pH(i)) and extracellular pH (pH(e)) homeostasis and cell volume. Here, we summarized recent pre-clinical experimental studies on NKCC-1 and NHE-1 in GBM and other malignant tumors, such as breast cancer, hepatocellular carcinoma, and lung cancer cells. These studies illustrated that pharmacological inhibition or down-regulation of these ion transporter proteins reduces proliferation, increases apoptosis, and suppresses migration and invasion of cancer cells. These new findings reveal the potentials of these ion transporters as new targets for cancer diagnosis and/or treatment.

Metabolic changes associated with tumor metastasis, part 1: tumor pH, glycolysis and the pentose phosphate pathway

Metabolic adaptations are intimately associated with changes in cell behavior. Cancers are characterized by a high metabolic plasticity resulting from mutations and the selection of metabolic phenotypes conferring growth and invasive advantages. While metabolic plasticity allows cancer cells to cope with various microenvironmental situations that can be encountered in a primary tumor, there is increasing evidence that metabolism is also a major driver of cancer metastasis. Rather than a general switch promoting metastasis as a whole, a succession of metabolic adaptations is more likely needed to promote different steps of the metastatic process. This review addresses the contribution of pH, glycolysis and the pentose phosphate pathway, and a companion paper summarizes current knowledge regarding the contribution of mitochondria, lipids and amino acid metabolism. Extracellular acidification, intracellular alkalinization, the glycolytic enzyme phosphoglucose isomerase acting as an autocrine cytokine, lactate and the pentose phosphate pathway are emerging as important factors controlling cancer metastasis.

Polysaccharides from Korean Citrus hallabong peels inhibit angiogenesis and breast cancer cell migration

Although the peel of the hallabong (Citrus sphaerocarpa) fruit is rich in polysaccharides, which are valuable dietary ingredients for human health, it is normally wasted. The present study aimed to utilize the peel waste and identify properties it may have against breast cancer metastasis. Hallabong peel extract containing crude polysaccharides was fractionated by gel permeation chromatography to produce four different polysaccharide fractions (HBE-I, -II, -III, and -IV). The HBE polysaccharides significantly blocked tube formation of human umbilical vein vascular endothelial cells (HUVECs), at a concentration of 12.5 or 25 μg/mL. Tube formation appeared to be more sensitive to HBE-II than to other HBE polysaccharides. HBE-II also inhibited breast cancer cell migration, through downregulation of matrix metalloproteinase-9 (MMP-9) in MDA-MB-231 triple-negative breast cancer cells. Therefore, inhibition of tube formation and MMP-9-mediated migration observed in HUVEC and MDA-MB-231 cells, respectively, are likely to be important therapeutic targets in triple-negative breast cancer metastasis.

Protective effect of simvastatin on impaired intestine tight junction protein ZO-1 in a mouse model of Parkinson's disease

Recently, several studies showed that gastrointestinal tract may be associated with pathophysiology of Parkinson's disease (PD). Intestine tight junction protein zonula occluden-1 (ZO-1) is an important component of intestinal barrier which can be degraded by matrix metallopeptidase 9 (MMP-9). In our previous study, a significant decline in ZO-1 was observed along with enhanced MMP-9 activity in the duodenum and distal colon of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In this study, the protective effect of simvastatin on ZO-1 was investigated using an MPTP mouse model of PD. Seven days after the end of MPTP application, the expression level of ZO-1 was evaluated by immunohistochemistry. The protein expression levels of ZO-1 and MMP9 were detected by Western blotting. Meanwhile, MMP-9 activity was analyzed by gelatin zymography. MPTP treatment led to a decrease in the expression of ZO-1, which was accompanied by elevated MMP-9 activity. Treatment with simvastatin could partly reverse the MPTP-induced changes in ZO-1 expression and reduce MMP-9 protein and activity. Taken together, these findings suggest that simvastatin administration may partially reverse the impairment of ZO-1 induced by MPTP via inhibiting the activity of MMP9, fortify the impaired intestinal barrier and limit gut-derived toxins that pass across the intestinal barrier.

Knock-down of CIAPIN1 sensitizes K562 chronic myeloid leukemia cells to Imatinib by regulation of cell cycle and apoptosis-associated members via NF-κB and ERK5 signaling pathway

CIAPIN1 (cytokine-induced apoptosis inhibitor 1) was recently identified as an essential downstream effector of the Ras signaling pathway. However, its potential role in regulating myeloid leukemia cells sensitivity to Imatinib remains unclear. In this study, we found depletion of CIAPIN1 inhibited proliferation and triggered more apoptosis of K562CML (chronic myeloid leukemia) cells with or without Imatinib treatment. Meanwhile, CIAPIN1 depletion decreased ERK5 phosphorylation and NF-κB activity. Importantly, treating CIAPIN1-depleted K562 cells with ERK5 signaling pathway specific inhibitor, XMD8-92, further inhibited proliferation and promoted apoptosis with or without Imatinib treatment. Treatment with the NF-κB specific inhibitor, Bay 11-7082, induced nearly the same inhibition of proliferation and promotion of apoptosis conferred by CIAPIN1 depletion as was observed with XMD8-92 treatment. Further, XMD8-92 and Bay 11-7082 synergistically inhibited proliferation and promoted apoptosis of CIAPIN1-depleted K562 cells with or without Imatinib treatment. The nude mice transplantation model was also performed to confirm the enhanced sensitivity of CIAPIN1-depleted K562 cells to Imatinib. Thus, our results provided a potential management by which CIAPIN1 knock-down might have a crucial impact on enhancing sensitivity of K562 cells to Imatinib in the therapeutic approaches, indicating that CIAPIN1 knock-down might serve as a combination with chemotherapeutical agents in leukemia diseases therapy.

Regulation of invadopodia by the tumor microenvironment

The tumor microenvironment consists of stromal cells, extracellular matrix (ECM), and signaling molecules that communicate with cancer cells. As tumors grow and develop, the tumor microenvironment changes. In addition, the tumor microenvironment is not only influenced by signals from tumor cells, but also stromal components contribute to tumor progression and metastasis by affecting cancer cell function. One of the mechanisms that cancer cells use to invade and metastasize is mediated by actin-rich, proteolytic structures called invadopodia. Here, we discuss how signals from the tumor environment, including growth factors, hypoxia, pH, metabolism, and stromal cell interactions, affect the formation and function of invadopodia to regulate cancer cell invasion and metastasis. Understanding how the tumor microenvironment affects invadopodia biology could aid in the development of effective therapeutics to target cancer cell invasion and metastasis.

CIAPIN1 targets Na⁺/H⁺ exchanger 1 to mediate MDA-MB-231 cells' metastasis through regulation of MMPs via ERK1/2 signaling pathway

Cytokine-induced antiapoptotic inhibitor 1 (CIAPIN1) was recently identified as an essential downstream effector of the Ras signaling pathway and has been confirmed to be closely associated with various malignant tumors. However, its potential role in regulating breast cancer metastasis remains unclear. Matrix metalloproteinases (MMPs) are a broad family of zinc-biding endopeptidases that participate in the extracellular matrix (ECM) degradation that accompanies cancer cell invasion, metastasis and angiogenesis. In this study, we found up-regulation of CIAPIN1 by lentiviral expression vector inhibited the migration, invasion and MMPs expression of MDA-MB-231 cells. Further, CIAPIN1 over-expression decreased NHE1 (Na(+)/H(+) exchanger 1) expression and ERK1/2 phosphorylation. Importantly, treating CIAPIN1 over-expressed MDA-MB-231 cells with the NHE1 specific inhibitor, Cariporide, further inhibited the metastatic capacity, MMPs expression and phosphorylated ERK1/2. Treatment with the MEK1 specific inhibitor, PD98059, induced nearly the same suppression of CIAPIN1 over-expression-dependent migration, invasion and MMPs expression as was observed with Cariporide. Further, Cariporide and PD98059 synergistically suppressed migration, invasion and MMPs expression of CIAPIN1 over-expressed MDA-MB-231 cells. Thus, our results revealed the mechanism by which CIAPIN1 targeted NHE1 to mediate migration and invasion of MDA-MB-231 cells through regulation of MMPs via ERK1/2 signaling pathway.

Upregulation of NHE1 protein expression enables glioblastoma cells to escape TMZ-mediated toxicity via increased H⁺ extrusion, cell migration and survival

Sodium-hydrogen exchanger isoform 1 (NHE1) plays a role in survival and migration/invasion of several cancers and is an emerging new therapeutic target. However, the role of NHE1 in glioblastoma and the interaction of NHE1 expression and function in glioblastoma cells with cytotoxic temozolomide (TMZ) therapy remain unknown. In this study, we detected high levels of NHE1 protein only in primary human glioma cells (GC), glioma xenografts and glioblastoma, but not in human neural stem cells or astrocytes. GC exhibited an alkaline resting pHi (7.46±0.04) maintained by robust NHE1-mediated H(+) extrusion. GC treatment with TMZ for 2-24h triggered a transient decrease in pHi, which recovered by 48h and correlated with concurrent upregulation of NHE1 protein expression. NHE1 protein was colocalized with ezrin at lamellipodia and probably involved in GC migration. The TMZ-treated GC exhibited increased migration and invasion, which was attenuated by addition of NHE1 inhibitor HOE-642. Most importantly, NHE1 inhibition prevented prosurvival extracellular signal-regulated kinase activation and accelerated TMZ-induced apoptosis. Taken together, our study provides the first evidence that GC upregulate NHE1 protein to maintain alkaline pHi. Combining TMZ therapy with NHE1 inhibition suppresses GC migration and invasion, and also augments TMZ-induced apoptosis. These findings strongly suggest that NHE1 is an important cytoprotective mechanism in GC and presents a new therapeutic strategy of combining NHE1 inhibition and TMZ chemotherapy.

CD44 targets Na(+)/H(+) exchanger 1 to mediate MDA-MB-231 cells' metastasis via the regulation of ERK1/2

Background:

CD44, a transmembrane glycoprotein expressed in a variety of cells and tissues, has been implicated in tumour metastasis. But the molecular mechanisms of CD44-mediated tumour cell metastasis remain to be elucidated.

Methods:

The downregulation of CD44 was determined by immunofluorescence. Moreover, the motility of breast cancer cells was detected by wound-healing and transwell experiments. Then the spontaneous metastasis of CD44-silenced MDA-MB-231 cells was tested by histology with BALB/c nude mice.

Results:

A positive correlation between CD44 and Na⁺/H⁺ exchanger isoform 1 (NHE1) was found in two breast cancer cells. CD44 downregulation could inhibit the metastasis of MDA-MB-231 cells and the expressions of Na⁺/H⁺ exchanger 1. Moreover, CD44 overexpression upregulated the metastasis of MCF-7 cells, but the elevated metastatic ability was then inhibited by Cariporide. Interestingly, during these processes only the p-ERK1/2 was suppressed by CD44 downregulation and the expression of matrix metalloproteinases and metastatic capacity of MDA-MB-231 cells were greatly inhibited by the MEK1 inhibitor PD98059, which even had a synergistic effect with Cariporide. Furthermore, CD44 downregulation inhibits breast tumour outgrowth and spontaneous lung metastasis.

Conclusions:

Taken together, this work indicates that CD44 regulates the metastasis of breast cancer cells through regulating NHE1 expression, which could be used as a novel strategy for breast cancer therapy.

pH sensing and regulation in cancer

Cells maintain intracellular pH (pH_i) within a narrow range (7.1–7.2) by controlling membrane proton pumps and transporters whose activity is set by intra-cytoplasmic pH sensors. These sensors have the ability to recognize and induce cellular responses to maintain the pH_i, often at the expense of acidifying the extracellular pH. In turn, extracellular acidification impacts cells via specific acid-sensing ion channels (ASICs) and proton-sensing G-protein coupled receptors (GPCRs). In this review, we will discuss some of the major players in proton sensing at the plasma membrane and their downstream consequences in cancer cells and how these pH-mediated changes affect processes such as migration and metastasis. The complex mechanisms by which they transduce acid pH signals to the cytoplasm and nucleus are not well understood. However, there is evidence that expression of proton-sensing GPCRs such as GPR4, TDAG8, and OGR1 can regulate aspects of tumorigenesis and invasion, including cofilin and talin regulated actin (de-)polymerization. Major mechanisms for maintenance of pH_i homeostasis include monocarboxylate, bicarbonate, and proton transporters. Notably, there is little evidence suggesting a link between their activities and those of the extracellular H⁺-sensors, suggesting a mechanistic disconnect between intra- and extracellular pH. Understanding the mechanisms of pH sensing and regulation may lead to novel and informed therapeutic strategies that can target acidosis, a common physical hallmark of solid tumors.

Protease activity at invadopodial focal digestive areas is dependent on NHE1-driven acidic pHe

Degradation of the extracellular matrix (ECM) is a critical step of tumor cell invasion and requires protease-dependent proteolysis focalized at the invadopodia where the proteolysis of the ECM occurs. Most of the extracellular proteases belong to serine- or metallo-proteases and the invadopodia is where protease activity is regulated. While recent data looking at global protease activity in the growth medium reported that their activity and role in invasion is dependent on Na+/H+ exchanger 1 (NHE1)-driven extracellular acidification, there is no data on this aspect at the invadopodia, and an open question remains whether this acid extracellular pH (pHe) activation of proteases in tumor cells occurs preferentially at invadopodia. We previously reported that the NHE1 is expressed in breast cancer invadopodia and that the NHE1‑dependent acidification of the peri-invadopodial space is critical for ECM proteolysis. In the present study, using, for the first time, in situ zymography analysis, we demonstrated a concordance between NHE1 activity, extracellular acidification and protease activity at invadopodia to finely regulate ECM digestion. We demonstrated that: (i) ECM proteolysis taking place at invadopodia is driven by acidification of the peri-invadopodia microenvironment; (ii) that the proteases have a functional pHe optimum that is acidic; (iii) more than one protease is functioning to digest the ECM at these invadopodial sites of ECM proteolysis; and (iv) lowering pHe or inhibiting the NHE1 increases protease secretion while blocking protease activity changes NHE1 expression at the invadopodia.

Solute carriers (SLCs) in cancer

During tumor progression cells acquire an altered metabolism, either as a cause or as a consequence of an increased need of energy and nutrients. All four major classes of macromolecules are affected: carbohydrates, proteins, lipids and nucleic acids. As a result of the changed needs, solute carriers (SLCs) which are the major transporters of these molecules are differently expressed. This renders them important targets in the treatment of cancer. Blocking or activating SLCs is one possible therapeutic strategy. For example, some SLCs are upregulated in tumor cells due to the increased demand for energy and nutritional needs. Thus, blocking them and turning off the delivery of fuel or nutrients could be one way to interfere with tumor progression. Specific drug delivery to cancer cells via transporters is another approach. Some SLCs are also interesting as chemosensitizing targets because blocking or activating them may result in an altered response to chemotherapy. In this review we summarize the roles of SLCs in cancer therapy and specifically their potential as direct or indirect targets, as drug carriers or as chemosensitizing targets.

CUEDC2 sensitizes chronic myeloid leukemic cells to imatinib treatment

CUEDC2, a newly reported protein, has been found to be ubiquitously expressed in human tissues and repress NF-κB activity. To study the role of CUEDC2 in chronic myeloid leukemia (CML), we explored the function of CUEDC2 in CML cells through using the CML cell line K562 and its imatinib resistant cells K562/G01. K562 cells expressed a relatively higher level of CUEDC2 compared to K562/G01 cells. Knockdown of CUEDC2 in K562 cells resulted in decreased cell apoptosis after imatinib treatment; when CUEDC2 was overexpressed in K562/G01 cells, imatinib induced more cell apoptosis. By analyzing the activity of NF-κB, the results indicated a negative association between the expression of CUEDC2 and NF-κB signaling pathway in these CML cells. Our data suggested that the expression level of CUEDC2 has an inverse correlation with imatinib resistance and activity of NF-κB signaling pathway in CML cells, CUEDC2 could regulate imatinib sensitivity in CML cells at least partially through NF-κB signaling pathway.

Acidic extracellular microenvironment and cancer

Acidic extracellular pH is a major feature of tumor tissue, extracellular acidification being primarily considered to be due to lactate secretion from anaerobic glycolysis. Clinicopathological evidence shows that transporters and pumps contribute to H⁺ secretion, such as the Na⁺/H⁺ exchanger, the H⁺-lactate co-transporter, monocarboxylate transporters, and the proton pump (H⁺-ATPase); these may also be associated with tumor metastasis. An acidic extracellular pH not only activates secreted lysosomal enzymes that have an optimal pH in the acidic range, but induces the expression of certain genes of pro-metastatic factors through an intracellular signaling cascade that is different from hypoxia. In addition to lactate, CO₂ from the pentose phosphate pathway is an alternative source of acidity, showing that hypoxia and extracellular acidity are, while being independent from each other, deeply associated with the cellular microenvironment. In this article, the importance of an acidic extracellular pH as a microenvironmental factor participating in tumor progression is reviewed.

Inside out: targeting NHE1 as an intracellular and extracellular regulator of cancer progression

The sodium hydrogen exchanger isoform one is a critical regulator of intracellular pH, serves as an anchor for the formation of cytoplasmic signaling complexes, and modulates cytoskeletal organization. There is a growing interest in the potential for sodium hydrogen exchanger isoform one as a therapeutic target against cancer. Sodium hydrogen exchanger isoform one transport drives formation of membrane protrusions essential for cell migration and contributes to the establishment of a tumor microenvironment that leads to the rearrangement of the extracellular matrix further supporting tumor progression. Here, we focus on the potential impact that an inexpensive, $100 genome would have in identifying prospective therapeutic targets to treat tumors based upon changes in gene expression and variation of sodium hydrogen exchanger isoform one regulators. In particular, we will focus on the ezrin, radixin, moesin family proteins, calcineurin B homologous proteins, Ras/Raf/MEK/ERK signaling, and phosphoinositide signaling as they relate to the regulation of sodium hydrogen exchanger isoform one in cancer progression.

Inhibitory effects of dried longan (Euphoria longana Lam.) seed extract on invasion and matrix metalloproteinases of colon cancer cells

The critical step in colorectal cancer progression and associated mortality is cancer invasion, which depends on two key gelatinase enzymes, matrix metalloproteinases-2 and -9. Dried longan ( Euphoria longana Lam.) seed is a rich natural source of antioxidant polyphenols.This study evaluated the effect of dried longan seeds on colon cancer cell invasion via gelatinase function and expression. Three dried longan seed fractions were collected by Sephadex LH-20 column chromatography. They showed a potent inhibitor on colorectal cancer cell invasion and gelatinase activity. The antigelatinase activities of fractions 1 and 2 were a direct effect via Zn²⁺ chelation, whereas fraction 3 modulated indirectly through suppression of zymogen activators. Among the fractions, only fraction 3 reduced the gelatinase expression, which was correlated with the levels of tissue inhibitor of metalloproteinase-1 and may as well involve the p38 mitogen-activated protein kinases and the c-Jun N-terminal kinase signaling pathways. This primary research has manifested and encouraged the anticancer properties of dried longan seed extracts with potential inhibitory effects on cancer cell invasion as well as antigelatinase activity and expression in colon cancer cells.

Regulation of the Na+/H+ Exchanger (NHE1) in Breast Cancer Metastasis

The pH gradient in normal cells is tightly controlled by the activity of various pH-regulatory membrane proteins including the isoform protein of the Na(+)/H(+) exchanger (NHE1). NHE1 is constitutively active in a neoplastic microenvironment, dysregulating pH homeostasis and altering the survival, differentiation, and proliferation of cancer cells, thereby causing them to become tumorigenic. Cytoplasmic alkalinization in breast cancer cells occurs as a result of increased NHE1 activity and, while much is known about the pathophysiologic role of NHE1 in tumor progression with regard to ion flux, the regulation of its activity on a molecular level is only recently becoming evident. The membrane domain of NHE1 is sufficient for ion exchange. However, its activity is regulated through the phosphorylation of key amino acids in the cytosolic domain as well as by its interaction with other intracellular proteins and lipids. Here, we review the importance of these regulatory sites and what role they may play in the disrupted functionality of NHE1 in breast cancer metastasis.

pH regulators in invadosomal functioning: proton delivery for matrix tasting

Invadosomes are actin-rich finger-like cellular structures sensing and interacting with the surrounding extracellular matrix (ECM) and involved in its proteolytic remodeling. Invadosomes are structures distinct from other adhesion complexes, and have been identified in normal cells that have to cross tissue barriers to fulfill their function such as leukocytes, osteoclasts and endothelial cells. They also represent features of highly aggressive cancer cells, allowing them to escape from the primary tumor, to invade surrounding tissues and to reach systemic circulation. They are localized to the ventral membrane of cells grown under 2-dimensional conditions and are supposed to be present all around cells grown in 3-dimensional matrices. Indeed invadosomes are key structures in physiological processes such as inflammation and the immune response, bone remodeling, tissue repair, but also in pathological conditions such as osteopetrosis and the development of metastases. Invadosomes are subdivided into podosomes, found in normal cells, and into invadopodia specific for cancer cells. While these two structures exhibit differences in organization, size, number and half-life, they share similarities in molecular composition, participation in cell-matrix adhesion and promoting matrix degradation. A key determinant in invadosomal function is the recruitment and release of proteases, such as matrix metalloproteinases (MMPs), serine proteases and cysteine cathepsins, together with their activation in a tightly controlled and highly acidic microenvironment. Therefore numerous pH regulators such as V-ATPases and Na(+)/H(+) exchangers, are found in invadosomes and are directly involved in their constitution as well as their functioning. This review focuses on the participation of pH regulators in invadosome function in physiological and pathological conditions, with a particular emphasis on ECM remodeling by osteoclasts during bone resorption and by cancer cells.

Urokinase plasminogen activator receptor induced non-small cell lung cancer invasion and metastasis requires NHE1 transporter expression and transport activity

BACKGROUND: Non-small cell lung cancers (NSLC) are aggressive cancers that are insensitive to chemotherapies and accounts for nearly 33% of all cancer deaths in the United States. Two hallmarks of cancer that allow cells to invade and metastasize are sustained proliferation and enhanced motility. In this study we investigate the relationship between urokinase plasminogen activator (uPA)/uPA receptor (uPAR) signaling and Na(+)/H(+) exchanger isoform 1 (NHE1) expression and activity. METHODS AND RESULTS: The addition of 10nM uPA increased the carcinogenic potential of three NSCLC cell lines, NCI-H358, NCI-H460, and NCI-H1299. This included an increase in the rate of cell proliferation 1.6 to 1.9 fold; an increase in the percentage of cells displaying stress fibers 3.05 to 3.17 fold; and an increase in anchorage-independent growth from 1.64 to 2.0 fold. In each of these cases the increase was blocked when the experiments were performed with NHE1 inhibited by 10 μM EIPA (ethylisopropyl amiloride). To further evaluate the role of uPA/uPAR and NHE1 in tumor progression we assessed signaling events using full-length uPA compared to the uPA amino terminal fragment (ATF). Comparing uPA and ATF signaling in H460 cells, we found that both uPA and ATF increased stress fiber formation approximately 2 fold, while uPA increased matrix metalloproteinase 9 (MMP9) activity 5.44 fold compared to 2.81 fold for ATF. To expand this signaling study, two new cell lines were generated, one with reduced NHE1 expression (H460 NHE1 K/D) and one with reduced uPAR expression (H460 uPAR K/D). Using the K/D cell lines we found that neither uPA nor ATF could stimulate stress fiber formation or MMP9 activity in cells with dramatically decreased NHE1 or uPAR expression. Finally, using in vivo tumor formation studies in athymic mice we found that when mice were injected with H460 cells 80% of mice formed tumors with an average volume of 390 mm(3). This was compared to 20% of H460 uPAR K/D injected mice forming tumors with an average volume of 15 mm(3) and 10% of H460 NHE1 K/D injected mice forming tumors with an average volume of 5 mm(3). CONCLUSION: Taken together, these data demonstrate that uPA/uPAR-mediated tumor progression and metastasis requires NHE1 in NSCLC cells and suggests a potential therapeutic approach to blocking cancer progression.