Effect of NHE1 antisense gene transfection on the biological behavior of SGC-7901 human gastric carcinoma cells

Evaluation of the effect of nitrate and chloride on Cd(II)-induced cell oxidative stress by scanning electrochemical microscopy

Cadmium (Cd) is one of the most prevalent toxic metal pollutants, which is widely distributed in various environmental media and organisms. Literature studies have documented that Cd could stimulate cellular oxidative stress, and the increased intracellular reactive oxygen species (ROS) might destroy certain proteins and DNA and subsequently lead to cell apoptosis. Although several studies have studied the co-exposure between cadmium and other metals, information on the potential effects of Cd and its counterions is still lacking. In the present study, we explored the effects of nitrate and chloride on oxidative stress induced by Cd(II) at environmental exposure levels in human breast cancer cells (MCF-7) using scanning electrochemical microscopy (SECM). After incubation in CdCl₂ or Cd(NO₃)₂, ROS production is concentration-dependent and time-dependent, and the variation trend is consistent. When MCF-7 cells were incubated at a constant Cd²⁺ concentration, it was found that the higher the concentration ratio of Cd(NO₃)₂/CdCl₂, the less ROS was generated. Combined with cell-viability, intracellular acidification as well as antioxidants system tests, we observed that nitrate could be reduced to nitrite and then inhibit Cd-induced oxidative stress. Benefitting from real-time in situ imaging of cells by SECM, H₂O₂ was detected and quantified in a noninvasive way, and the effect of Cd at environmental exposure levels on cellular oxidative stress was explored deeper and more comprehensively. Prospectively, cytotoxicological methods based on the SECM technique would be established to explore toxic pollutant co-exposure issues at environmental exposure levels.

The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity

The five plasma membrane Na⁺/H⁺ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pH_i regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na⁺ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na⁺/H⁺ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.

Pathophysiological role of ion channels and transporters in gastrointestinal mucosal diseases

The incidence of gastrointestinal (GI) mucosal diseases, including various types of gastritis, ulcers, inflammatory bowel disease and GI cancer, is increasing. Therefore, it is necessary to identify new therapeutic targets. Ion channels/transporters are located on cell membranes, and tight junctions (TJs) affect acid-base balance, the mucus layer, permeability, the microbiota and mucosal blood flow, which are essential for maintaining GI mucosal integrity. As ion channel/transporter dysfunction results in various GI mucosal diseases, this review focuses on understanding the contribution of ion channels/transporters to protecting the GI mucosal barrier and the relationship between GI mucosal disease and ion channels/transporters, including Cl-/HCO3- exchangers, Cl- channels, aquaporins, Na+/H+ exchangers, and K+ channels. Here, we provide novel prospects for the treatment of GI mucosal diseases.

Alteration and dysfunction of ion channels/transporters in a hypoxic microenvironment results in the development and progression of gastric cancer

BACKGROUND

Gastric cancer (GC) is one of the most common malignant cancers in the world and has only few treatment options and, concomitantly, a poor prognosis. It is generally accepted now that the tumor microenvironment, particularly that under hypoxia, plays an important role in cancer development. Hypoxia can regulate the energy metabolism and malignancy of tumor cells by inducing or altering various important factors, such as oxidative stress, reactive oxygen species (ROS), hypoxia-inducible factors (HIFs), autophagy and acidosis. In addition, altered expression and/or dysfunction of ion channels/transporters (ICTs) have been encountered in a variety of human tumors, including GC, and to play an important role in the processes of tumor cell proliferation, migration, invasion and apoptosis. Increasing evidence indicates that ICTs are at least partly involved in interactions between cancer cells and their hypoxic microenvironment. Here, we provide an overview of the different ICTs that regulate or are regulated by hypoxia in GC.

CONCLUSIONS AND PERSPECTIVES

Hypoxia is one of the major obstacles to cancer therapy. Regulating cellular responses and factors under hypoxia can inhibit GC. Similarly, altering the expression or activity of ICTs, such as the application of ion channel inhibitors, can slow down the growth and/or migration of GC cells. Since targeting the hypoxic microenvironment and/or ICTs may be a promising strategy for the treatment of GC, more attention should be paid to the interplay between ICTs and the development and progression of GC in such a microenvironment.

Roles of Ion and Water Channels in the Cell Death and Survival of Upper Gastrointestinal Tract Cancers

Ion and water channels were recently shown to be involved in cancer cell functions, and various transporter types have been detected in upper gastrointestinal tract (UGI) cancers. Current information on the expression and roles of these channels and transporters in the death and survival of UGI cancer cells was reviewed herein, and the potential of their regulation for cancer management was investigated. Esophageal cancer (EC) and gastric cancer (GC) cells and tissues express many different types of ion channels, including voltage-gated K⁺, Cl^-, and Ca²⁺, and transient receptor potential (TRP) channels, which regulate the progression of cancer. Aquaporin (AQP) 1, 3, and 5 are water channels that contribute to the progression of esophageal squamous cell carcinoma (ESCC) and GC. Intracellular pH regulators, including the anion exchanger (AE), sodium hydrogen exchanger (NHE), and vacuolar H⁺-ATPases (V-ATPase), also play roles in the functions of UGI cancer cells. We have previously conducted gene expression profiling and revealed that the regulatory mechanisms underlying apoptosis in ESCC cells involved various types of Cl^- channels, Ca²⁺ channels, water channels, and pH regulators (Shimizu et al., 2014; Ariyoshi et al., 2017; Shiozaki et al., 2017, 2018a; Kobayashi et al., 2018; Yamazato et al., 2018; Konishi et al., 2019; Kudou et al., 2019; Katsurahara et al., 2020, 2021; Matsumoto et al., 2021; Mitsuda et al., 2021). We have also previously demonstrated the clinicopathological and prognostic significance of their expression in ESCC patients, and shown that their pharmacological blockage and gene silencing had an impact on carcinogenesis, indicating their potential as targets for the treatment of UGI cancers. A more detailed understanding of the molecular regulatory mechanisms underlying cell death and survival of UGI cancers may result in the application of cellular physiological methods as novel therapeutic approaches.

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.

(Patho-)Physiology of Na+/H+ Exchangers (NHEs) in the Digestive System

Na⁺/H⁺ exchangers (NHEs) are expressed in virtually all human tissues and organs. Two major tasks of those NHE isoforms that are located in plasma membranes are cell volume control by Na⁺-uptake and cellular pH regulation by H⁺-extrusion. Several NHEs, particularly NHE 1–4 and 8, are involved in the pathogenesis of diseases of the digestive system such as inflammatory bowel disease (ulcerative colitis, Crohn’s disease) and gastric and colorectal tumorigenesis. In the present review, we describe the physiological purposes, possible malfunctions and pathophysiological effects of the different NHE isoforms along the alimentary canal from esophagus to colon, including pancreas, liver and gallbladder. Particular attention is paid to the functions of NHEs in injury repair and to the role of NHE1 in Barrett’s esophagus. The impact of NHEs on gut microbiota and intestinal mucosal integrity is also dealt with. As the hitherto existing findings are not always consistent, sometimes even controversial, they are compared and critically discussed.

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.

Rho-associated coiled-coil kinase (ROCK) signaling and disease

The small Rho GTPase family of proteins, encompassing the three major G-protein classes Rho, Rac and cell division control protein 42, are key mitogenic signaling molecules that regulate multiple cancer-associated cellular phenotypes including cell proliferation and motility. These proteins are known for their role in the regulation of actin cytoskeletal dynamics, which is achieved through modulating the activity of their downstream effector molecules. The Rho-associated coiled-coil kinase 1 and 2 (ROCK1 and ROCK2) proteins were the first discovered Rho effectors that were primarily established as players in RhoA-mediated stress fiber formation and focal adhesion assembly. It has since been discovered that the ROCK kinases actively phosphorylate a large cohort of actin-binding proteins and intermediate filament proteins to modulate their functions. It is well established that global cellular morphology, as modulated by the three cytoskeletal networks: actin filaments, intermediate filaments and microtubules, is regulated by a variety of accessory proteins whose activities are dependent on their phosphorylation by the Rho-kinases. As a consequence, they regulate many key cellular functions associated with malignancy, including cell proliferation, motility and viability. In this current review, we focus on the role of the ROCK-signaling pathways in disease including cancer.

The bradykinin B(2) receptor induces multiple cellular responses leading to the proliferation of human renal carcinoma cell lines

Background

The vasoactive peptide bradykinin (BK) acts as a potent growth factor for normal kidney cells, but there have been few studies on the role of BK in renal cell carcinomas.

Purpose

In this study, we tested the hypothesis that BK also acts as a mitogen in kidney carcinomas, and explored the effects of BK in human renal carcinoma A498 cells.

Methods

The presence of mRNAs for BK B₁ and BK B₂ receptors in A498 cells was demonstrated by reverse transcription–polymerase chain reaction. To study BK signaling pathways, we employed fluorescent measurements of intracellular Ca²⁺, measured changes in extracellular pH as a reflection of Na⁺/H⁺ exchange (NHE) with a Cytosensor microphysiometer, and assessed extracellular signal-regulated kinase (ERK) activation by Western blotting.

Results

Exposure to 100 nM of BK resulted in the rapid elevation of intracellular Ca²⁺, caused a ≥30% increase in NHE activity, and a ≥300% increase in ERK phosphorylation. All BK signals were blocked by HOE140, a BK B₂ receptor antagonist, but not by a B₁ receptor antagonist. Inhibitor studies suggest that BK-induced ERK activation requires phospholipase C and protein kinase C activities, and is Ca²⁺/calmodulin-dependent. The amiloride analog 5-(N-methyl-N-isobutyl)-amiloride (MIA) blocked short-term NHE activation and inhibited ERK phosphorylation, suggesting that NHE is critical for ERK activation by BK. BK induced an approximately 40% increase in the proliferation of A498 cells as assessed by bromodeoxyuridine uptake. This effect was blocked by the ERK inhibitor PD98059, and was dependent on NHE activity.

Conclusion

We conclude that BK exerts mitogenic effects in A498 cells via the BK B₂ receptor activation of growth-associated NHE and ERK.

Na+/H+ exchanger 1 gene expression in tissues of yellow chicken

The Na(+)/H(+) exchanger 1 (NHE1) transmembrane protein regulates intracellular pH, cell survival, cell growth, cell differentiation and plays a critical role in the progression of some diseases, including the pathogenesis of J avian leukosis. The chicken is an ideal model to study the function of NHE1 because it has developed highly efficient Na(+)-absorptive mechanisms in its small and large intestines. To date, there has been no detailed expression analysis to determine NHE1 expression in various tissues of the chicken. We determined the mRNA and protein expression levels of avian NHE1 by real-time quantitative PCR and immunohistochemical analysis. NHE1 mRNA was detected in all chicken tissues examined. Protein expression levels varied widely among tissues and did not always correlate with mRNA expression. Determining the mRNA and protein of NHE1 expression patterns in chicken should help to delineate the NHE1 role in different tissues and its contribution to physiological and pathological processes. These data provide the basis for examining the distinct function of chicken NHE1 compared with its mammalian counterpart.

Expression and modulation of Na(+) /H(+) exchanger 1 gene in hepatocellular carcinoma: A potential therapeutic target

BACKGROUND AND AIM

Na(+) /H(+) exchanger 1 (NHE1), a regulator of intracellular pH (pHi), plays a significant role in regulating tumor cell growth and apoptosis. In the present study, we determined its role in hepatocellular carcinoma (HCC).

METHODS

Immunohistochemistry was carried out to detect NHE1 expression in HCC tissue for the correlation of NHE1 with clinicopathological data from patients. NHE1-siRNA and 5- (N-ethyl-N-isopropyl) amiloride (EIPA, highly specific inhibitor of NHE1) were used to assess the function of NHE1 in HCC cells by using gene transfection, methyl thiazolyl tetrazolium (MTT), flow cytometry, and nude mouse xenograft assays as well as fluorescence spectroscopy.

RESULTS

We found that NHE1 expression was increased in HCC tissues and cells in which its expression was associated with the increased tumor size, venous invasion and advanced tumor stages. However, suppression of NHE1 expression by using NHE1-siRNA and EIPA reduced growth, but induced apoptosis of HCC cells. EIPA also inhibited tumor growth in nude mouse xenografts of HCC cells.

CONCLUSIONS

The data from our current study demonstrates that NHE1 was overexpressed in HCC and that inhibition of NHE1 could be a potential therapeutic target for HCC.

Role of Na+/H+ exchanger 1 in tumor invasion and metastasis

Mammalian Na⁺/H⁺ exchanger 1 (NHE1) is a membrane protein that regulates intracellular pH homeostasis by extruding one intracellular proton in exchange for one extracellular sodium. It has been demonstrated that NHE1 expression and activity are increased in tumor cells and contribute to the acidification of extracellular microenvironment. NHE1 and extracellular microenvironment play an important role in tumor invasion. In addition, NHE1 activation is involved in the formation of pseudopodia and invadopodia in tumor cells and therefore increases tumor invasion. Therefore, NHE1 may be a potential target for tumor therapy.

Activation of Na+/H+ exchanger 1 by neurotensin signaling in pancreatic cancer cell lines

Acidosis commonly observed in solid tumors like pancreatic cancer promotes genetic instability and selection of a more malignant phenotype of cancer cells. Overexpression or activation of integral membrane proteins mediating H+ efflux may contribute to extracellular acidification. Neurotensin (NT) induces intracellular alkalinization and stimulates interleukin-8 production in pancreatic cancer cells and, as demonstrated here, the stable NT analog Lys(8)-psi-Lys(9)NT(8-13) enhances the amiloride-sensitive, Na+-dependent transmembrane H+ flux by a factor of 2.05+/-0.28 and 2.69+/-0.07 in BxPC-3 and PANC-1 pancreatic cancer cells, respectively, by phosphorylation of the Na+/H+ exchanger 1 (NHE1). Human genome-wide gene expression analysis was performed to detect effects of Lys(8)-psi-Lys(9)NT(8-13) on BxPC-3 cells. Results indicated upregulation of genes involved in regulation of NHE1, hypoxic response and glycolysis in response to Lys(8)-psi-Lys(9)NT(8-13) even under normoxic conditions. Therefore, our findings suggest that growth factors like NT may be implicated in the early progression of pancreatic cancer by localized acidification and induction of an aerobic glycolytic phenotype with higher metastatic potential in small cell aggregates.

Repression of NHE1 expression by PPARgamma activation is a potential new approach for specific inhibition of the growth of tumor cells in vitro and in vivo

Ligand-induced activation of peroxisome proliferator-activated receptor gamma (PPARgamma) inhibits proliferation in cancer cells in vitro and in vivo; however, the downstream targets remain undefined. We report the identification of a peroxisome proliferator response element in the promoter region of the Na(+)/H(+) transporter gene NHE1, the overexpression of which has been associated with carcinogenesis. Exposure of breast cancer cells expressing high levels of PPARgamma to its natural and synthetic agonists resulted in downregulation of NHE1 transcription as well as protein expression. Furthermore, the inhibitory effect of activated PPARgamma on tumor colony-forming ability was abrogated on overexpression of NHE1, whereas small interfering RNA-mediated gene silencing of NHE1 significantly increased the sensitivity of cancer cells to growth-inhibitory stimuli. Finally, histopathologic analysis of breast cancer biopsies obtained from patients with type II diabetes treated with the synthetic agonist rosiglitazone showed significant repression of NHE1 in the tumor tissue. These data provide evidence for tumor-selective downregulation of NHE1 by activated PPARgamma in vitro and in pathologic specimens from breast cancer patients and could have potential implications for the judicious use of low doses of PPARgamma ligands in combination chemotherapy regimens for an effective therapeutic response.

Neurotensin signaling induces intracellular alkalinization and interleukin-8 expression in human pancreatic cancer cells

Pancreatic adenocarcinomas express neurotensin receptors in up to 90% of cases, however, their role in tumor biology and as a drug target is not clear. In the present study, a stable neurotensin (NT) analog induced intracellular calcium release and intracellular alkalinization in BxPC-3 and PANC-1 pancreatic cancer cells that was abolished by inhibitors of NT receptor (NTR) and sodium-proton exchanger 1 (NHE1), amiloride and SR 142948, respectively. Activation of NHE1 involved increased phosphorylation of dimethylfumarate-sensitive mitogen- and stress-activated kinase 1/2 (MSK1/2). NTR signaling appears to promote a metastatic phenotype in pancreatic cancer cells by induction of localized extracellular acidification in normoxic cells, preceeding acidosis induced by hypoxia and switch to glycolysis in addition to increased expression of interleukin-8 (IL-8).