Sodium/proton exchanger isoform 1 regulates intracellular pH and cell proliferation in human ovarian cancer

Role of solute carrier transporters in ovarian cancer (Review)

Solute carrier (SLC) transporters are involved in various biological processes associated with metabolic reprogramming and cancer, supporting the increased requirement of nutrients and energy. Over the past decade, there have been significant advancements in understanding the expression and function of SLCs in ovarian cancer (OC). This gynecological condition has a high mortality rate and limited treatment options; thus, early diagnosis remains a target clinically. OC exhibits complexity and heterogeneity, resulting in different clinical characteristics, resistance to chemotherapy drugs and poor prognosis. Additionally, SLCs have a different expression pattern between healthy and tumor tissue, and consequently, their inhibition or activation could modify signaling pathways involved in the tumor growth process, such as cell proliferation, apoptosis and drug accumulation. The present review aims to consolidate current data to provide a comprehensive understanding of the potential importance of SLCs in OC. Additionally, it seeks to offer guidance for further research on utilizing SLCs as prognostic biomarkers and therapeutic targets.

Development of UTX-143, a selective sodium-hydrogen exchange subtype 5 inhibitor, using amiloride as a lead compound

NHE5, an isoform of the Na+/H+ exchanger (NHE) protein, is an ion-transporting membrane protein that regulates intracellular pH and is highly expressed in colorectal adenocarcinoma. Therefore, we hypothesized that NHE5 inhibitors can be used as anticancer drugs. However, because NHE1 is ubiquitously expressed in all cells, it is extremely important to demonstrate its selective inhibitory activity against NHE5. We used amiloride, an NHE non-selective inhibitor, as a lead compound and created UTX-143, which has NHE5-selective inhibitory activity, using a structure-activity relationship approach. UTX-143 showed selective cytotoxic effects on cancer cells and reduced the migratory and invasive abilities of cancer cells. These results suggest a new concept wherein drugs exhibit cancer-specific cytotoxic effects through selective inhibition of NHE5 and the possibility of UTX-143 as a lead NHE5-selective inhibitor.

Ion Transport and Inhibitor Binding by Human NHE1: Insights from Molecular Dynamics Simulations and Free Energy Calculations

The human Na+/H+ exchanger (NHE1) plays a crucial role in maintaining intracellular pH by regulating the electroneutral exchange of a single intracellular H+ for one extracellular Na+ across the plasma membrane. Understanding the molecular mechanisms governing ion transport and the binding of inhibitors is of importance in the development of anticancer therapeutics targeting NHE1. In this context, we performed molecular dynamics (MD) simulations based on the recent cryo-electron microscopy (cryo-EM) structures of outward- and inward-facing conformations of NHE1. These simulations allowed us to explore the dynamics of the protein, examine the ion-translocation pore, and confirm that Asp267 is the ion-binding residue. Our free energy calculations did not show a significant difference between Na+ and K+ binding at the ion-binding site. Consequently, Na+ over K+ selectivity cannot be solely explained by differences in ion binding. Our MD simulations involving NHE1 inhibitors (cariporide and amiloride analogues) maintained stable interactions with Asp267 and Glu346. Our study highlights the importance of the salt bridge between the positively charged acylguanidine moiety and Asp267, which appears to play a role in the competitive inhibitory mechanism for this class of inhibitors. Our computational study provides a detailed mechanistic interpretation of experimental data and serves the basis of future structure-based inhibitor design.

Slc9a1 plays a vital role in chitosan oligosaccharide transport across the intestinal mucosa of mice

The mechanism underlying the intestinal transport of COS is not well understood. Here, transcriptome and proteome analyses were performed to identify potential critical molecules involved in COS transport. Enrichment analyses revealed that the differentially expressed genes in the duodenum of the COS-treated mice were mainly enriched in transmembrane and immune function. In particular, B2 m, Itgb2, and Slc9a1 were upregulated. The Slc9a1 inhibitor decreased the transport efficiency of COS both in MODE-K cells (in vitro) and in mice (in vivo). The transport of FITC-COS in Slc9a1-overexpressing MODE-K cells was significantly higher than that in empty vector-transfected cells (P < 0.01). Molecular docking analysis revealed the possibility of stable binding between COS and Slc9a1 through hydrogen bonding. This finding indicates that Slc9a1 plays a crucial role in COS transport in mice. This provides valuable insights for improving the absorption efficiency of COS as a drug adjuvant.

A methylation-driven genes prognostic signature and the immune microenvironment in epithelial ovarian cancer

Aberrant gene methylation has been implicated in the development and progression of tumors. In this study, we aimed to identity methylation driven genes involved in epithelial ovarian cancer (EOC) to establish a prognostic signature for patients with EOC. We identified and verified 6 MDGs that are closely related to the prognosis of ovarian cancer. A prognostic risk score model and nomogram for predicting the prognosis of ovarian cancer were constructed based on the six MDGs. It can also effectively reflect the immune environment and immunotherapy response of ovarian cancer. These MDGs have great significance to the implementation of individualized treatment and disease monitoring of ovarian cancer patients.

Intracellular pH affects mitochondrial homeostasis in cultured human corneal endothelial cells prepared for cell injection therapy

This study aimed to uncover the mechanism responsible for the clinical efficacy of cell injection therapy with fully differentiated cultured cells. Analysis of polarized expression of ion transporters on cultured human corneal endothelial cells (CECs) subpopulations (SPs) was performed. The intracellular pH (pHi) between two CEC SPs, distinct in the proportion of differentiated cells, was measured, and the association with mitochondrial respiration homeostasis was investigated. The effects of the ion transporter inhibition by their selective inhibitors or siRNA transfection were also explored. Na⁺/K⁺-ATPase, Aquaporin 1, SLC4A11, NBCe1, NHE1 as transporters, and ZO-1, were all selectively expressed in differentiated SPs, but were almost null in the cell-state-transitioned SPs. We also confirmed that the pHi of CEC SPs affected their mitochondrial respiration by modulating the expression of these ion transporters via inhibitors or siRNA transfection. Ion and water transporters might participate in the maintenance of pHi and mitochondria homeostasis in differentiated SPs, which may contribute, combined with integral barrier functions, to efficient water efflux. The differences in intracellular pH between the two SPs is attributed to variations in the expression profile of specific ion transporters and mitochondrial functions, which may associate with the efficacy of the SPs in cell injection therapy.

Repressed miR-34a Expression Dictates the Cell Fate to Corneal Endothelium Failure

Purpose

To reveal the mechanism triggering the functional disparity between degenerated and non-degenerated corneal endothelium cells in the water efflux from corneal stroma to the anterior chamber.

Methods

The varied levels of the microRNA (miR)-34, miR-378, and miR-146 family in human corneal endothelium and cultured cells thereof were investigated using 3D-Gene Human miRNA Oligo Chips. Concomitantly, CD44, p53, c-Myc, matrix metalloprotease (MMP)-2 expression, and Ras homolog gene family member A (Rho A) activity was correlated to the expression intensities of these microRNAs, partly complemented with their altered expression levels with the transfection of the corresponding mimics and inhibitors. The levels of miRs were further associated with intracellular pH (pHi) and mitochondrial energy homeostasis.

Results

P53-inducible miR-34a/b repressed CD44 expression, and CD44 was repressed with the elevated c-Myc. The repressed miR-34a activated the CD44 downstream factors Rho A and MMP-2. MiR-34a mimics downregulated pHi, inducing the skewing of mitochondrial respiration to oxidative phosphorylation. The oxidative stress (H₂O₂) induced on human corneal endothelial cells, which repressed miR-34a/b expression, may account for the impaired signaling cascade to mitochondrial metabolic homeostasis necessary for an efficient water efflux from the corneal stroma.

Conclusions

The upregulated expression of CD44, through repressed miR-34a/b by reactive oxygen species and elevated c-Myc by oxidative stress, may impair mitochondrial metabolic homeostasis, leading to human corneal endothelial failure.

Dihydroartemisinin prompts amplification of photodynamic therapy-induced reactive oxygen species to exhaust Na/H exchanger 1-mediated glioma cells invasion and migration

Photodynamic therapy (PDT) is a promising glioma therapy; however, its efficacy is compromised due to the PDT-induced reactive oxygen species (ROS) production being limited by the local hypoxic tumor microenvironment. Furthermore, Hypoxia activates sodium/hydrogen exchanger 1 (NHE1), an essential component for tumor progression and metastasis, enables glioma cells (GC) to escape PDT-mediated phototoxicity via increased H⁺ extrusion. However, interactions between NHE1 expression with ROS level involving response of GC remain unclear. Dihydroartemisinin (DHA), a ROS generator, has extensive anti-tumor effects. This study aimed to explore whether PDT along with DHA could amplify the total ROS levels and diminish GC invasion and migration by inhibiting NHE1 expression. Proliferation and invasion of U251 and LN229 cells were evaluated under different treatments using cell counting Kit-8 (CCK-8), transwell, and wound healing assays. ROS levels were measured using fluorescence probes and flow cytometry. NHE1 levels were detected by immunofluorescence and western blotting. Co-treatment effects and molecular events were further confirmed in a bilateral tumor-bearing nude mouse model. PDT with synergistic DHA significantly increased the total abundance of ROS to further suppress the invasion and migration of GC by reducing NHE1 levels in vitro. Using a bilateral glioma xenograft mouse model with primary and recurrent gliomas, we found that PDT markedly suppressed primary tumor growth, while PDT in synergy with DHA also suppressed recurrent tumors, and improved overall survival by regulating the ROS-NHE1 axis. No evident side effects were observed. Our results suggest that PDT with DHA can amplify the total ROS levels to weaken GC invasion and migration by suppressing NHE1 expression in vitro and in vivo, thus abolishing the resistance of GC to PDT. The synergistic therapy of PDT and DHA therefore represents a more efficient and safe strategy for comprehensive glioma treatment.

Emerging Roles for Ion Channels in Ovarian Cancer: Pathomechanisms and Pharmacological Treatment

Ovarian cancer (OC) is the deadliest gynecologic cancer, due to late diagnosis, development of platinum resistance, and inadequate alternative therapy. It has been demonstrated that membrane ion channels play important roles in cancer processes, including cell proliferation, apoptosis, motility, and invasion. Here, we review the contribution of ion channels in the development and progression of OC, evaluating their potential in clinical management. Increased expression of voltage-gated and epithelial sodium channels has been detected in OC cells and tissues and shown to be involved in cancer proliferation and invasion. Potassium and calcium channels have been found to play a critical role in the control of cell cycle and in the resistance to apoptosis, promoting tumor growth and recurrence. Overexpression of chloride and transient receptor potential channels was found both in vitro and in vivo, supporting their contribution to OC. Furthermore, ion channels have been shown to influence the sensitivity of OC cells to neoplastic drugs, suggesting a critical role in chemotherapy resistance. The study of ion channels expression and function in OC can improve our understanding of pathophysiology and pave the way for identifying ion channels as potential targets for tumor diagnosis and treatment.

Arsenic trioxide-increased MDCK cells proliferation requires activator protein 1-mediated increase of the sodium/proton exchanger 1 activity

The release of protons (H⁺) occurs via the Na⁺/H⁺ exchanger isoform 1 (NHE1) leading to a stable intracellular pH (pHi) in MDCK cells. Chronic intake of arsenic trioxide (ATO), in the drinking water, associated with higher morbidity and mortality in neoplastic tissues. ATO increased NHE1 expression and activity, resulting in intracellular alkalization and higher MDCK cells proliferation. Since the pro-proliferative transcription factor activator protein 1 (AP-1) gets activated by al alkaline intracellular pH, a phenomenon paralleled by higher NHEs activity, we asked whether ATO-increased MDCK cells proliferation involves AP-1-dependent NHE1 activation. Cells were exposed (48 h) to ATO (0.05 μmol/L), SR11302 (1 μmol/L, AP-1 inhibitor), HOE-694 (100 nmol/L, NHE1 inhibitor) and EIPA (50 μmol/L, NHE1/NHE3 inhibitor) in the presence of S3226 (10 μmol/L, NHE3 inhibitor), concanamycin A (0.1 μmol/L, V-ATPases inhibitor), and Schering (10 μmol/L, H⁺/K⁺-ATPase inhibitor). [³H]Thymidine incorporation, cell counting, wound healing assay, and AP-1 activity were determined. The pHi was measured in cells pre-loaded (10 min) with 2,7-bicarboxyethyl-5,6-carboxyfluorescein acetoxymethyl ester (12 mmol/L) and exposed to NH₄Cl (20 mmol/L). Basal pHi and recovery rate (dpHi/dt), intracellular buffer capacity (βi) and H⁺ flux (J_H⁺) were determined. NHE1 protein abundance was measured by Western blotting and immunofluorescence. ATO increased the cell growth (1.5 fold), basal pHi (0.4 pHi units), dpHi/dt (1.8 fold), J_H⁺ (1.4 fold), AP-1 activity and NHE1 protein abundance (1.3 fold). ATO also increased (1.5 fold) the nuclear/perinuclear NHE1 immunosignal. SR11302 and HOE-694 blocked ATO effects. Thus, ATO-increased proliferation resulted from AP-1-dependent NHE1 activation in MDCK cells.

Na+/H+ exchanger isoform 1 activity in AQP2-expressing cells can be either proliferative or anti-proliferative depending on extracellular pH

We have previously shown in renal cells that expression of the water channel Aquaporin-2 increases cell proliferation by a regulatory volume mechanism involving Na⁺/H⁺ exchanger isoform 2. Here, we investigated if Aquaporin-2 (AQP2) also modulates Na⁺/H⁺ exchanger isoform 1-dependent cell proliferation. We use two AQP2-expressing cortical collecting duct models: one constitutive (WT or AQP2-transfected RCCD₁ cell line) and one inducible (control or vasopressin-induced mpkCCD_c14 cell line). We found that Aquaporin-2 modifies Na⁺/H⁺ exchanger isoform 1 (NHE1) contribution to cell proliferation. In Aquaporin-2-expressing cells, Na⁺/H⁺ exchanger isoform 1 is anti-proliferative at physiological pH. In acid media, Na⁺/H⁺ exchanger isoform 1 contribution turned from anti-proliferative to proliferative only in AQP2-expressing cells. We also found that, in AQP2-expressing cells, NHE1-dependent proliferation changes parallel changes in stress fiber levels: at pH 7.4, Na⁺/H⁺ exchanger isoform 1 would favor stress fiber disassembly and, under acidosis, NHE1 would favor stress fiber assembly. Moreover, we found that Na⁺/H⁺ exchanger-dependent effects on proliferation linked to Aquaporin-2 relied on Transient Receptor Potential Subfamily V calcium channel activity. In conclusion, our data show that, in collecting duct cells, the water channel Aquaporin-2 modulates NHE1-dependent cell proliferation. In AQP2-expressing cells, at physiological pH, the Na⁺/H⁺ exchanger isoform 1 function is anti-proliferative and, at acidic pH, Na⁺/H⁺ exchanger isoform 1 function is proliferative. We propose that Na⁺/H⁺ exchanger isoform 1 modulates proliferation through an interplay with stress fiber formation.

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.

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.

Novel long-wavelength emissive lysosome-targeting ratiometric fluorescent probes for imaging in live cells

Lysosomes are acidic organelles containing many hydrolytic enzymes responsible for degrading macromolecules.

Ginsenoside Rg3 Decreases NHE1 Expression via Inhibiting EGF-EGFR-ERK1/2-HIF-1 α Pathway in Hepatocellular Carcinoma: A Novel Antitumor Mechanism

Na + /H + exchanger 1 (NHE1) plays a vital role in the oncogenesis and development of hepatocellular carcinoma (HCC) and has been regarded as a promising target for the treatment of HCC. Ginsenoside Rg3 (Rg3), a bioactive ginseng compound, is suggested to possess pleiotropic antitumor effects on HCC. However, the underlying mechanisms of Rg3 suppressing HCC remain unclear. In the present study, we uncovered a novel antitumor mechanism of Rg3 on HCC by decreasing NHE1 expression through in vivo and in vitro studies. Mechanistically, we demonstrated that epidermal growth factor (EGF) could dramatically upregulate NHE1 expression, while increasing the phosphorylated extracellular signal-regulated protein kinase (ERK1/2) level and hypoxia-inducible factor 1 alpha (HIF-1 α) expression. In the presence of ERK1/2-specific inhibitor PD98059, EGF stimulated HIF-1 α and NHE1 expression was obviously blocked in addition, the presence of HIF-1 α -specific inhibitor 2-methoxyestradiol (2-MeOE2) blocked EGF stimulated NHE1 expression. Moreover, results from in vivo and in vitro studies indicate that Rg3 treatment markedly decreased the expression of EGF, EGF receptor (EGFR), phosphorylated ERK1/2 and HIF-1 α . Conclusively, these findings suggested that NHE1 was stimulated by EGF, and Rg3 could decrease NHE1 expression by integrally inhibiting EGF-EGFR-ERK1/2-HIF- α signal axis in HCC. Together, our evidence indicated that Rg3 was an effective multi-targets antitumor agent for the treatment of HCC.

High SLC4A11 expression is an independent predictor for poor overall survival in grade 3/4 serous ovarian cancer

In this study, we aimed to examine the expression of SLC4A11 in ovarian cancer and in normal ovarian tissues, its prognostic value and the possible mechanism of its dysregulation. Bioinformatic analysis was performed by using data from the GEO datasets, the Cancer Genome Atlas-Ovarian Cancer (TCGA-OV) and the Human Protein Atlas (HPA). Results showed that SLC4A11 was upregulated in ovarian cancer compared with normal ovarian epithelial tissues. In patients with primary serous ovarian cancer in TCGA-OV, the cases with lymphatic invasion (N = 133) had significantly higher SLC4A11 expression than those without lymphatic invasion (N = 77) (p = 0.0069). High SLC4A11 expression was consistently associated with worse overall survival (OS). Univariate and multivariate analysis confirmed that high SLC4A11 expression was an independent prognostic factor for poor OS in grade 3/4 (G3/G4) tumors (HR = 1.416, 95%CI: 1.098–1.824, p = 0.007). 320 out of 578 (55.4%) ovarian cancer cases had SLC4A11 amplification. High methylation group had a significantly lower level of SLC4A11 expression. Based on these findings, we infer that high SLC4A11 expression is an independent predictor for poor OS in grade 3/4 serous ovarian cancer. Both DNA amplification and hypomethylation contribute to its upregulation in ovarian cancer.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Targeting pH regulating proteins for cancer therapy-Progress and limitations

Tumour acidity induced by metabolic alterations and incomplete vascularisation sets cancer cells apart from normal cellular physiology. This distinguishing tumour characteristic has been an area of intense study, as cellular pH (pH_i) disturbances disrupt protein function and therefore multiple cellular processes. Tumour cells effectively utilise pH_i regulating machinery present in normal cells with enhancements provided by additional oncogenic or hypoxia induced protein modifications. This overall improvement of pH regulation enables maintenance of an alkaline pH_i in the continued presence of external acidification (pH_e). Considerable experimentation has revealed targets that successfully disrupt tumour pH_i regulation in efforts to develop novel means to weaken or kill tumour cells. However, redundancy in these pH-regulating proteins, which include Na⁺/H⁺ exchangers (NHEs), carbonic anhydrases (CAs), Na⁺/HCO₃^- co-transporters (NBCs) and monocarboxylate transporters (MCTs) has prevented effective disruption of tumour pH_i when individual protein targeting is performed. Here we synthesise recent advances in understanding both normoxic and hypoxic pH regulating mechanisms in tumour cells with an ultimate focus on the disruption of tumour growth, survival and metastasis. Interactions between tumour acidity and other cell types are also proving to be important in understanding therapeutic applications such as immune therapy. Promising therapeutic developments regarding pH manipulation along with current limitations are highlighted to provide a framework for future research directives.