Intracellular chloride regulates the G1/S cell cycle progression in gastric cancer cells

Chloride ions in health and disease

Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in differential regulation of cellular functions such as transcription and translation, post-translation modifications, cell cycle and proliferation, cell volume, and pH levels. In intracellular compartments, Cl- modulates the function of lysosomes, mitochondria, endosomes, phagosomes, the nucleus, and the endoplasmic reticulum. In extracellular fluid (ECF), Cl- is present in blood/plasma and interstitial fluid compartments. A reduction in Cl- levels in ECF can result in cell volume contraction. Cl- is the key physiological anion and is a principal compensatory ion for the movement of the major cations such as Na+, K+, and Ca2+. Over the past 25 years, we have increased our understanding of cellular signaling mediated by Cl-, which has helped in understanding the molecular and metabolic changes observed in pathologies with altered Cl- levels. Here, we review the concentration of Cl- in various organs and cellular compartments, ion channels responsible for its transportation, and recent information on its physiological roles.

Role of β3 subunit of the GABA type A receptor in triple negative breast cancer proliferation, migration, and cell cycle progression

Triple negative breast cancer (TNBC) is known for its heterogeneous nature and aggressive onset. The unresponsiveness to hormone therapies and immunotherapy and the toxicity of chemotherapeutics account for the limited treatment options for TNBC. Ion channels have emerged as possible therapeutic candidates for cancer therapy, but little is known about how ligand gated ion channels, specifically, GABA type A ligand-gated ion channel receptors (GABAAR), affect cancer pathogenesis. Our results show that the GABAA β3 subunit is expressed at higher levels in TNBC cell lines than non-tumorigenic cells, therefore contributing to the idea that limiting the GABAAR via knockdown of the GABAA β3 subunit is a potential strategy for decreasing the proliferation and migration of TNBC cells. We employed pharmacological and genetic approaches to investigate the role of the GABAA β3 subunit in TNBC proliferation, migration, and cell cycle progression. The results suggest that pharmacological antagonism or genetic knockdown of GABAA β3 subunit decreases TNBC proliferation and migration. In addition, GABAA β3 subunit knockdown causes cell cycle arrest in TNBC cell lines via decreased cyclin D1 and increased p21 expression. Our findings suggest that membrane bound GABAA receptors containing the β3 subunit can be further developed as a potential novel target for the treatment of TNBC.

Cancer Stem Cells of Esophageal Adenocarcinoma are Suppressed by Inhibitors of TRPV2 and SLC12A2

BACKGROUND

The potential of membrane transporters activated in cancer stem cells (CSCs) as new therapeutic targets for cancer is attracting increasing interest. Therefore, the present study examined the expression profiles of ion transport-related molecules in the CSCs of esophageal adenocarcinoma (EAC).

METHODS

Cells that highly expressed aldehyde dehydrogenase 1 family member A1 (ALDH1A1) were separated from OE33 cells, a human Barrett's EAC cell line, by fluorescence-activated cell sorting. CSCs were identified based on the formation of tumorspheres. Gene expression profiles in CSCs were examined by a microarray analysis.

RESULTS

Among OE33 cells, ALDH1A1 messenger RNA levels were higher in CSCs than in non-CSCs. Furthermore, CSCs exhibited resistance to cisplatin and had the capacity to redifferentiate. The results of the microarray analysis of CSCs showed the up-regulated expression of several genes related to ion channels/transporters, such as transient receptor potential vanilloid 2 (TRPV2) and solute carrier family 12 member 2 (SLC12A2). The cytotoxicities of the TRPV2 inhibitor tranilast and the SLC12A2 inhibitor furosemide were higher at lower concentrations in CSCs than in non-CSCs, and both markedly reduced the number of tumorspheres. The cell population among OE33 cells that highly expressed ALDH1A1 also was significantly decreased by these inhibitors.

CONCLUSIONS

Based on the present results, TRPV2 and SLC12A2 are involved in the maintenance of CSCs, and their specific inhibitors, tranilast and furosemide, respectively, have potential as targeted therapeutic agents for EAC.

Effects of TRPV2 on the Expression of PD-L1 and Its Binding Ability to PD-1 in Gastric Cancer

BACKGROUND

Transient receptor potential vanilloid 2 (TRPV2) is a member of the TRP superfamily of non-specific cation channels with functionally diverse roles. We herein investigated the effects of TRPV2 on the expression of programmed cell death-ligand 1 (PD-L1) and its binding ability to programmed cell death-1 (PD-1) in gastric cancer (GC).

METHODS

Knockdown (KD) experiments were performed on human GC cell lines using TRPV2 small-interfering RNA. The surface expression of PD-L1 and its binding ability to PD-1 were analyzed by flow cytometry. Eighty primary tissue samples were assessed by immunohistochemistry (IHC), and the relationships between IHC results, clinicopathological factors, and patient prognosis were analyzed. The molecular mechanisms underlying the effects of TRPV2 on the intracellular ion environment were also investigated.

RESULTS

TRPV2-KD decreased the expression level of PD-L1 in NUGC4 and MKN7 cells, thereby inhibiting its binding to PD-1. A survival analysis revealed that 5-year overall survival rates were significantly lower in the TRPV2 high expression and PD-L1-positive groups. In IHC multivariate analysis of GC patients, high TRPV2 expression was identified as an independent prognostic factor. Furthermore, a positive correlation was observed between the expression of TRPV2 and PD-L1. An immunofluorescence analysis showed that TRPV2-KD decreased the intracellular concentration of calcium ([Ca2+]i). Treatment with ionomycin/PMA (phorbol 12-myristate 13-acetate), which increased [Ca2+]i, upregulated the protein expression of PD-L1 and promoted its binding to PD-1.

CONCLUSIONS

The surface expression of PD-L1 and its binding ability to PD-1 in GC were regulated by TRPV2 through [Ca2+]i, indicating the potential of TRPV2 as a biomarker and target of immune checkpoint blockage for GC.

Physiological roles of chloride ions in bodily and cellular functions

Physiological roles of Cl-, a major anion in the body, are not well known compared with those of cations. This review article introduces: (1) roles of Cl- in bodily and cellular functions; (2) the range of cytosolic Cl- concentration ([Cl-]c); (3) whether [Cl-]c could change with cell volume change under an isosmotic condition; (4) whether [Cl-]c could change under conditions where multiple Cl- transporters and channels contribute to Cl- influx and efflux in an isosmotic state; (5) whether the change in [Cl-]c could be large enough to act as signals; (6) effects of Cl- on cytoskeletal tubulin polymerization through inhibition of GTPase activity and tubulin polymerization-dependent biological activity; (7) roles of cytosolic Cl- in cell proliferation; (8) Cl--regulatory mechanisms of ciliary motility; (9) roles of Cl- in sweet/umami taste receptors; (10) Cl--regulatory mechanisms of with-no-lysine kinase (WNK); (11) roles of Cl- in regulation of epithelial Na+ transport; (12) relationship between roles of Cl- and H+ in body functions.

Diclazuril-induced expression of CDK-related kinase 2 in the second-generation merozoites of Eimeria tenella

Diclazuril is a classic anticoccidial drug. The key molecules of diclazuril in anticoccidial action allows target screening for the development of anticoccidial drugs. Cyclin-dependent kinases (CDK) are prominent target proteins in apicomplexan parasites. In this study, a diclazuril anticoccidiosis animal model was established, and the transcription and translation levels of the CDK-related kinase 2 of Eimeria tenella (EtCRK2) were detected. mRNA and protein expression levels of EtCRK2 decreased in the infected/diclazuril group compared with those in the infected/control group. In addition, immunofluorescence analysis showed that EtCRK2 was localised in the cytoplasm of the merozoites. The fluorescence intensity of EtCRK2 in the infected/diclazuril group was significantly weaker than that in the infected/control group. The anticoccidial drug diclazuril against E.tenella affects the expression pattern of EtCRK2 molecule, and EtCRK2 is a potential target for new drug development.

TRPV3-ANO1 interaction positively regulates wound healing in keratinocytes

Transient receptor potential vanilloid 3 (TRPV3) belongs to the TRP ion channel super family and functions as a nonselective cation channel that is highly permeable to calcium. This channel is strongly expressed in skin keratinocytes and is involved in warmth sensation, itch, wound healing and secretion of several cytokines. Previous studies showed that anoctamin1 (ANO1), a calcium-activated chloride channel, was activated by calcium influx through TRPV1, TRPV4 or TRPA1 and that these channel interactions were important for TRP channel-mediated physiological functions. We found that ANO1 was expressed by normal human epidermal keratinocytes (NHEKs). We observed that ANO1 mediated currents upon TRPV3 activation of NHEKs and mouse skin keratinocytes. Using an in vitro wound-healing assay, we observed that either a TRPV3 blocker, an ANO1 blocker or low chloride medium inhibited cell migration and proliferation through p38 phosphorylation, leading to cell cycle arrest. These results indicated that chloride influx through ANO1 activity enhanced wound healing by keratinocytes.

Anoctamin 5 regulates the cell cycle and affects prognosis in gastric cancer

BACKGROUND

Anoctamin 5 (ANO5)/transmembrane protein 16E belongs to the ANO/ transmembrane protein 16 anion channel family. ANOs comprise a family of plasma membrane proteins that mediate ion transport and phospholipid scrambling and regulate other membrane proteins in numerous cell types. Previous studies have elucidated the roles and mechanisms of ANO5 activation in various cancer types. However, it remains unclear whether ANO5 acts as a plasma membrane chloride channel, and its expression and functions in gastric cancer (GC) have not been investigated.

AIM

To examine the role of ANO5 in the regulation of tumor progression and clinicopathological significance of its expression in GC.

METHODS

Knockdown experiments using ANO5 small interfering RNA were conducted in human GC cell lines, and changes in cell proliferation, cell cycle progression, apoptosis, and cellular movement were assessed. The gene expression profiles of GC cells were investigated following ANO5 silencing by microarray analysis. Immunohistochemical staining of ANO5 was performed on 195 primary tumor samples obtained from patients with GC who underwent curative gastrectomy between 2011 and 2013 at our department.

RESULTS

Reverse transcription-quantitative polymerase chain reaction (PCR) and western blotting demonstrated high ANO5 mRNA and protein expression, respectively, in NUGC4 and MKN45 cells. In these cells, ANO5 silencing inhibited cell proliferation and induced apoptosis. In addition, the knockdown of ANO5 inhibited G₁-S phase progression, invasion, and migration. The results of the microarray analysis revealed changes in the expression levels of several cyclin-associated genes, such as CDKN1A, CDK2/4/6, CCNE2, and E2F1, in ANO5-depleted NUGC4 cells. The expression of these genes was verified using reverse transcription-quantitative PCR. Immunohistochemical staining revealed that high ANO5 expression levels were associated with a poor prognosis. Multivariate analysis identified high ANO5 expression as an independent prognostic factor for 5-year survival in patients with GC (P = 0.0457).

CONCLUSION

ANO5 regulates the cell cycle progression by regulating the expression of cyclin-associated genes and affects the prognosis of patients with GC. These results may provide insights into the role of ANO5 as a key mediator in tumor progression and/or promising prognostic biomarker for GC.

Mechanisms Underlying Influence of Bioelectricity in Development

To execute the intricate process of development, cells coordinate across tissues and organs to determine where each cell divides and differentiates. This coordination requires complex communication between cells. Growing evidence suggests that bioelectrical signals controlled via ion channels contribute to cell communication during development. Ion channels collectively regulate the transmembrane potential of cells, and their function plays a conserved role in the development of organisms from flies to humans. Spontaneous calcium oscillations can be found in nearly every cell type and tissue, and disruption of these oscillations leads to defects in development. However, the mechanism by which bioelectricity regulates development is still unclear. Ion channels play essential roles in the processes of cell death, proliferation, migration, and in each of the major canonical developmental signaling pathways. Previous reviews focus on evidence for one potential mechanism by which bioelectricity affects morphogenesis, but there is evidence that supports multiple different mechanisms which are not mutually exclusive. Evidence supports bioelectricity contributing to development through multiple different mechanisms. Here, we review evidence for the importance of bioelectricity in morphogenesis and provide a comprehensive review of the evidence for several potential mechanisms by which ion channels may act in developmental processes.

LRRC8A influences the growth of gastric cancer cells via the p53 signaling pathway

BACKGROUND

Leucin-rich repeat containing protein A (LRRC8A), a component of the volume-regulated anion channel (VRAC), is activated by cell swelling and mediates regulatory volume decrease. We previously reported the expression of and important roles for several ion transporters in various gastrointestinal cancers, which have potential as novel targets for cancer treatment; however, the significance of LRRC8A in gastric cancer (GC) remains unclear.

MATERIALS AND METHODS

Knockdown experiments were performed by transfecting human GC cell lines with LRRC8A siRNA. Gene expression was then assessed using microarray analysis. Samples from 132 patients with GC were subjected to immunohistochemistry (IHC) for LRRC8A, and its relationships with clinicopathological factors and prognosis were examined.

RESULTS

The knockdown of LRRC8A suppressed the proliferation and movement of cells and enhanced apoptosis. The results of the microarray analysis showed the up- or down-regulated expression of genes related to the p53 signaling pathway (JNK, p53, p21, Bcl-2, and FAS) in LRRC8A-knockdown cells. IHC revealed a correlation between the expression of LRRC8A and the pT status (p = 0.015), and multivariate analysis identified the strong expression of LRRC8A as an independent prognostic factor for 5-year survival in GC patients (p = 0.0231).

CONCLUSIONS

The present results indicate that LRRC8A functions as a mediator of and/or biomarker for GC.

Roles of voltage‑gated potassium channels in the maintenance of pancreatic cancer stem cells

The targeting of membrane proteins that are activated in cancer stem cells (CSCs) represents one of the key recent strategies in cancer therapy. The present study analyzed ion channel expression profiles and functions in pancreatic CSCs (PCSCs). Cells strongly expressing aldehyde dehydrogenase 1 family member A1 (ALDH1A1) were isolated from the human pancreatic PK59 cell line using fluorescence-activated cell sorting, and PCSCs were identified based on tumorsphere formation. Microarray analysis was performed to investigate the gene expression profiles in PCSCs. ALDH1A1 messenger RNA levels were higher in PCSCs compared with non-PCSCs. PCSCs were resistant to 5-fluorouracil and capable of redifferentiation. The results of the microarray analysis revealed that gene expression related to ion channels, including voltage-gated potassium channels (Kv), was upregulated in PCSCs compared with non-PCSCs. 4-Aminopyridine (4-AP), a potent Kv inhibitor, exhibited greater cytotoxicity in PCSCs compared with non-PCSCs. In a xenograft model in nude mice, tumor volumes were significantly lower in mice inoculated with PK59 cells pre-treated with 4-AP compared with those in mice injected with non-treated cells. The present results identified a role of Kv in the persistence of PCSCs and suggested that the Kv inhibitor 4-AP may have potential as a therapeutic agent for pancreatic carcinoma.

The Role and Clinical Implications of the Retinoblastoma (RB)-E2F Pathway in Gastric Cancer

Gastric cancer is the most common malignant tumor in the digestive tract, with very high morbidity and mortality in developing countries. The pathogenesis of gastric cancer is a complex biological process mediated by abnormal regulation of proto-oncogenes and tumor suppressor genes. Although there have been some in-depth studies on gastric cancer at the molecular level, the specific mechanism has not been fully elucidated. RB family proteins (including RB, p130, and p107) are involved in cell cycle regulation, a process that largely depends on members of the E2F gene family that encode transcriptional activators and repressors. In gastric cancer, inactivation of the RB-E2F pathway serves as a core transcriptional mechanism that drives cell cycle progression, and is regulated by cyclins, cyclin-dependent kinases, cyclin-dependent kinase inhibitors, p53, Helicobacter pylori and some other upstream molecules. The E2F proteins are encoded by eight genes (i.e. E2F1 to E2F8), each of which may play a specific role in gastric cancer. Interestingly, a single E2F such as E2F1 can activate or repress transcription, and enhance or inhibit cell proliferation, depending on the cell environment. Thus, the function of the E2F transcription factor family is very complex and needs further exploration. Importantly, the presence of H. pylori in stomach mucosa may affect the RB and p53 tumor suppressor systems, thereby promoting the occurrence of gastric cancer. This review aims to summarize recent research progress on important roles of the complex RB-E2F signaling network in the development and effective treatment of gastric cancer.

Expression and Role of CFTR in Human Esophageal Squamous Cell Carcinoma

BACKGROUND

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-dependent chloride (Cl^-) anion conducting channel, and its role in esophageal squamous cell carcinoma (ESCC) was examined in the present study.

METHODS

Overexpression experiments were conducted on human ESCC cell lines following the transfection of a CFTR plasmid, and changes in cell proliferation, the cell cycle, apoptosis, migration, and invasion were assessed. A microarray analysis was performed to examine gene expression profiles. Fifty-three primary tumor samples collected from ESCC patients during esophagectomy were subjected to an immunohistochemical analysis.

RESULTS

Transfection of the CFTR plasmid into the ESCC KYSE 170 and KYSE 70 cell lines suppressed cell proliferation, migration, and invasion and induced apoptosis. The microarray analysis showed the up-regulated expression of genes involved in the p38 signaling pathway in CFTR plasmid-transfected KYSE 170 cells. Immunohistochemical staining revealed a relationship between the CFTR expression pattern at the invasive front and the pN category. A relationship was also observed between the weak expression of CFTR at the invasive front and a shorter postoperative survival in a prognostic analysis.

CONCLUSIONS

The overexpression of CFTR in ESCC activated the p38 signaling pathway and was associated with a good patient prognosis. These results indicate the potential of CFTR as a mediator of and/or a biomarker for ESCC.

Functional Analysis and Clinical Significance of Chloride Channel 2 Expression in Esophageal Squamous Cell Carcinoma

BACKGROUND

Chloride channel 2 (CLCN2) was recently shown to affect tumor behavior. The present study examined the functions of CLCN2 in the regulation of genes that play a role in tumor progression, as well as its clinicopathological significance in esophageal squamous cell carcinoma (ESCC).

METHODS

Knockdown experiments were conducted using CLCN2-small-interfering RNA, and changes in proliferation, survival, and cellular movement in human ESCC cell lines were investigated. A microarray analysis of gene expression profiles in CLCN2-depleted ESCC cells was conducted. Fifty-four primary ESCC samples were examined by immunohistochemistry (IHC).

RESULTS

The strong expression of CLCN2 was detected in TE5 and KYSE70 cells. Downregulated expression of CLCN2 enhanced proliferation and decreased apoptosis, whereas its upregulation inhibited proliferation and increased apoptosis. The effects of lubiprostone, a CLCN2 activator, were also investigated. In lubiprostone-treated cells, proliferation was inhibited and apoptosis was increased. The microarray analysis demonstrated that interferon (IFN) signaling-related genes were downregulated in CLCN2-depleted cells. IHC showed the presence of CLCN2 in the cytoplasm and cell membranes of ESCC cells. The prognostic analysis revealed a relationship between weak CLCN2 expression and shorter overall survival.

CONCLUSIONS

The present results indicate that tumor progression is regulated by CLCN2 through its effects on IFN signaling. Furthermore, weak CLCN2 expression was associated with poorer outcomes in ESCC patients. The present study will contribute to a clearer understanding of the role of CLCN2 as a mediator of ESCC, as well as its use as a biomarker for this cancer.

ANO9 regulates PD-L2 expression and binding ability to PD-1 in gastric cancer

The function of ANO9 in gastrointestinal cancer remains unclear. We investigated the biological behaviors and clinical prognostic values of ANO9 in gastric cancer (GC). Knockdown experiments were performed on human GC cell lines using ANO9 siRNA. Eighty‐four primary tissue samples from patients with advanced GC were examined immunohistochemically (IHC). Knockdown of ANO9 reduced the progression of cancer cells in MKN7 and MKN74 cells. A microarray analysis revealed that ANO9 regulated PD‐L2 via interferon (IFN)‐related genes. We confirmed using flow cytometry that the depletion of ANO9 reduced the binding ability to PD‐1 by downregulating the expression of PD‐L2 in MKN7 and MKN74 cells. IHC revealed a correlation between the expression of ANO9 and PD‐L2 and also that the strong expression of ANO9 was an independent poor prognostic factor in patients with advanced GC. The present results indicate that ANO9 regulates PD‐L2 and binding ability to PD‐1 via IFN‐related genes in GC. Therefore, ANO9 has potential as a biomarker and target of immune checkpoint blockage (ICB) for GC.

Role of ion channels during cell division

Ion channels are transmembrane proteins whose canonical function is the transport of ions across the plasma membrane to regulate cell membrane potential and play an essential role in neural communication, nerve conduction, and muscle contraction. However, over the last few years, non-canonical functions have been identified for many channels, having active roles in phagocytosis, invasiveness, proliferation, among others. The participation of some channels in cell proliferation has raised the question of whether they may play an active role in mitosis. There are several reports showing the participation of channels during interphase, however, the direct participation of ion channels in mitosis has received less attention. In this article, we summarize the current evidence on the participation of ion channels in mitosis. We also summarize some tools that would allow the study of ion channels and cell cycle regulatory molecules in individual cells during mitosis.

Increased intracellular Cl- concentration improves airway epithelial migration by activating the RhoA/ROCK Pathway

In the airway, Cl- is the most abundant anion and is critically involved in transepithelial transport. The correlation of the abnormal expression and activation of chloride channels (CLCs), such as cystic fibrosis transmembrane conductance regulators (CFTRs), anoctamin-1, and CLC-2, with cell migration capability suggests a relationship between defective Cl- transport and epithelial wound repair. However, whether a correlation exists between intracellular Cl- and airway wound repair capability has not been explored thus far, and the underlying mechanisms involved in this relationship are not fully defined. Methods: In this work, the alteration of intracellular chloride concentration ([Cl-]i) was measured by using a chloride-sensitive fluorescent probe (N-[ethoxycarbonylmethyl]-6-methoxyquinolium bromide). Results: We found that clamping with high [Cl-]i and 1 h of treatment with the CLC inhibitor CFTR blocker CFTRinh-172 and chloride intracellular channel inhibitor IAA94 increased intracellular Cl- concentration ([Cl-]i) in airway epithelial cells. This effect improved epithelial cell migration. In addition, increased [Cl-]i in cells promoted F-actin reorganization, decreased cell stiffness, and improved RhoA activation and LIMK1/2 phosphorylation. Treatment with the ROCK inhibitor of Y-27632 and ROCK1 siRNA significantly attenuated the effects of increased [Cl-]i on LIMK1/2 activation and cell migration. In addition, intracellular Ca2+ concentration was unaffected by [Cl-]i clamping buffers and CFTRinh-172 and IAA94. Conclusion: Taken together, these results suggested that Cl- accumulation in airway epithelial cells could activate the RhoA/ROCK/LIMK cascade to induce F-actin reorganization, down-regulate cell stiffness, and improve epithelial migration.

Effect of low temperature on the regulation of cell volume after hypotonic shock in gastric cancer cells

Although peritoneal lavage with distilled water performed after surgery prevents peritoneal seeding, cancer cells may avoid rupture under mild hypotonicity through regulatory volume decrease (RVD), which is the homeostatic regulation of ion and water transport. The aim of the present study was to investigate the effect of low temperature on cell volume and cell death under hypoosmolal conditions and determine the underlying molecular mechanisms in gastric cancer (GC). Three human GC cell lines (NUGC4, KATO‑III and MKN45) were exposed to hypotonic solutions, and the effects of low temperature on cell volume and viability were examined. Low temperature‑induced changes in membrane transporters were evaluated, and knockdown and overexpression experiments were conducted to determine their effects on cell volume during hypotonic stimulation. Low temperature (24˚C) during hypotonic stimulation inhibited RVD and enhanced the cytocidal effects on GC cells. The expression of leucine‑rich repeat containing protein A (LRRC8A), a component of a Cl‑ channel, was decreased, and aquaporin 5 (AQP5) expression was increased at low temperatures. LRRC8A knockdown markedly slowed the decrease in cell volume following cell swelling by hypotonic shock. AQP5 overexpression enhanced initial cell swelling after hypotonic shock and increased the final cell volume. These results suggest that a hypotonic solution at low temperature increased initial water influx via activation of AQP5 and decreased Cl‑ efflux via inhibition of LRRC8A. Therefore, low temperature enhanced the hypotonicity‑induced cytocidal effects on GC cells, and these results may contribute to the development of a novel lavage method effective in reducing peritoneal recurrence in GC.

Repurposed Biguanide Drugs in Glioblastoma Exert Antiproliferative Effects via the Inhibition of Intracellular Chloride Channel 1 Activity

The lack of in-depth knowledge about the molecular determinants of glioblastoma (GBM) occurrence and progression, combined with few effective and BBB crossing-targeted compounds represents a major challenge for the discovery of novel and efficacious drugs for GBM. Among relevant molecular factors controlling the aggressive behavior of GBM, chloride intracellular channel 1 (CLIC1) represents an emerging prognostic and predictive biomarker, as well as a promising therapeutic target. CLIC1 is a metamorphic protein, co-existing as both soluble cytoplasmic and membrane-associated conformers, with the latter acting as chloride selective ion channel. CLIC1 is involved in several physiological cell functions and its abnormal expression triggers tumor development, favoring tumor cell proliferation, invasion, and metastasis. CLIC1 overexpression is associated with aggressive features of various human solid tumors, including GBM, in which its expression level is correlated with poor prognosis. Moreover, increasing evidence shows that modification of microglia ion channel activity, and CLIC1 in particular, contributes to the development of different neuropathological states and brain tumors. Intriguingly, CLIC1 is constitutively active within cancer stem cells (CSCs), while it seems less relevant for the survival of non-CSC GBM subpopulations and for normal cells. CSCs represent GBM development and progression driving force, being endowed with stem cell-like properties (self-renewal and differentiation), ability to survive therapies, to expand and differentiate, causing tumor recurrence. Downregulation of CLIC1 results in drastic inhibition of GBM CSC proliferation in vitro and in vivo, making the control of the activity this of channel a possible innovative pharmacological target. Recently, drugs belonging to the biguanide class (including metformin) were reported to selectively inhibit CLIC1 activity in CSCs, impairing their viability and invasiveness, but sparing normal stem cells, thus representing potential novel antitumor drugs with a safe toxicological profile. On these premises, we review the most recent insights into the biological role of CLIC1 as a potential selective pharmacological target in GBM. Moreover, we examine old and new drugs able to functionally target CLIC1 activity, discussing the challenges and potential development of CLIC1-targeted therapies.

The Mechanistic Role of the Calcium-Activated Chloride Channel ANO1 in Tumor Growth and Signaling

Multiple studies have described the high expression and amplification of Anoctamin 1 (ANO1) in various cancers, including, but not limited to breast cancer, head and neck cancer, gastrointestinal stromal tumors and glioblastoma. ANO1 has been demonstrated to be critical for tumor growth in breast and head and neck cancers through its regulation of EGFR signaling and pathway modulators like MAPK and protein kinase B. However, the discovery of ANO1 as a calcium activated chloride channel came as a surprise to the field and has given rise to many questions. How does a chloride channel promote oncogenesis? Is the chloride channel function of ANO1 important for its role in cancer? Does ANO1 exhibits chloride-independent functions in cancer cells? This review summarizes the current understanding of ANO1's function in cancer, provides a synopsis of the findings addressing the open questions in the field and gives an outlook on the promising future of ANO1 as a potential therapeutic target for the treatment of various cancers.

WNK1 is required for proliferation induced by hypotonic challenge in rat vascular smooth muscle cells

Hypotonic challenge evoked vascular cell proliferation through activation of volume-regulated Cl^- channel (VRCC), leading to a decrease in the intracellular Cl^- concentration ([Cl^-]_i). We hypothesize that the decrease in [Cl^-]_i may activate one or several Cl^--sensitive kinases, resulting in a subsequent signaling cascade. In this study we demonstrated that WNK1, a Cl^--sensitive kinase, was involved in VRCC-induced proliferative signaling pathway in A10 vascular smooth muscle cells in vitro. A10 cells were exposed to a hypotonic challenge (225 mosmol·kg^-1·H₂0), which caused significantly increase in WNK1 phosphorylation without altering WNK1 protein expression. WNK1 overexpression significantly increased hypotonic-induced A10 cell proliferation, whereas silencing of WNK1 caused an opposite action. WNK1 mutation did not affect hypotonic-induced WNK1 phosphorylation and cell proliferation. Silencing of WNK1 caused cell cycle arrest at G₀/G₁ phase and prevented transition from G₁ to S phase, whereas the WNK1 overexpression accelerated cell cycle transition from G₁ to S phase. Silencing of WNK1 significantly inhibited cyclin D1/cyclin E1 expression and increased p27kip/p21cip expression. WNK1 overexpression significantly increased cyclin D1/cyclin E1 expression and reduced p27^KIP/p21^CIP expression. In addition, WNK1 knockdown or overexpression significantly attenuated or increased the hypotonic-induced phosphorylation of Akt and PI3K respectively.In conclusion, the reduction in [Cl^-]_i caused by hypotonic challenge-induced VRCC opening evokes WNK1 phosphorylation in A10 VSMCs, which mediates cell cycle transition from G₀/G₁ to S phase and proliferation through the PI3K-Akt signaling pathway.

Expression and role of anion exchanger 1 in esophageal squamous cell carcinoma

Recent studies have described important roles for the anion exchanger (AE) in epithelial carcinogenesis and tumor behavior. The objectives of the present study were to investigate the role of AE1 in the regulation of genes involved in tumor progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC). An immunohistochemical analysis was performed on 61 primary tumor samples obtained from ESCC patients who underwent esophagectomy. AE1 was primarily located in the cell membranes or cytoplasm of carcinoma cells, and its distribution pattern was related to the histological degree of the differentiation of SCC or the pT category. Among patients with pT2-3 ESCC, the 5-year survival rate of patients with diffuse AE1 expression (40.2%) was significantly lower than that of patients with focal expression (74.0%). AE1 was strongly expressed in KYSE150 and TE8 human ESCC cells. The depletion of AE1 using siRNA inhibited cell proliferation, migration, and invasion and induced apoptosis. The results of the microarray analysis revealed that MAPK and Hedgehog signaling pathway-related genes, such as DHH, and GLI1, were down-regulated in AE1-depleted KYSE150 cells. In conclusions, the results of the present study suggest that the diffuse expression of AE1 is related to a worse prognosis in patients with advanced ESCC, and that it regulates tumor progression by affecting MAPK and Hedgehog signaling pathways. These results provide an insight into the role of AE1 as a mediator of and/or a biomarker for ESCC.

Therapeutic applications of dichloroacetate and the role of glutathione transferase zeta-1

Dichloroacetate (DCA) has several therapeutic applications based on its pharmacological property of inhibiting pyruvate dehydrogenase kinase. DCA has been used to treat inherited mitochondrial disorders that result in lactic acidosis, as well as pulmonary hypertension and several different solid tumors, the latter through its ability to reverse the Warburg effect in cancer cells and restore aerobic glycolysis. The main clinically limiting toxicity is reversible peripheral neuropathy. Although administration of high doses to rodents can result in liver cancer, there is no evidence that DCA is a human carcinogen. In all studied species, including humans, DCA has the interesting property of inhibiting its own metabolism upon repeat dosing, resulting in alteration of its pharmacokinetics. The first step in DCA metabolism is conversion to glyoxylate catalyzed by glutathione transferase zeta 1 (GSTZ1), for which DCA is a mechanism-based inactivator. The rate of GSTZ1 inactivation by DCA is influenced by age, GSTZ1 haplotype and cellular concentrations of chloride. The effect of DCA on its own metabolism complicates the selection of an effective dose with minimal side effects.

GSTZ1 expression and chloride concentrations modulate sensitivity of cancer cells to dichloroacetate

Dichloroacetate (DCA), commonly used to treat metabolic disorders, is under investigation as an anti-cancer therapy due to its ability to reverse the Warburg effect and induce apoptosis in tumor cells. While DCA's mechanism of action is well-studied, other factors that influence its potential as a cancer treatment have not been thoroughly investigated. Here we show that expression of glutathione transferase zeta 1 (GSTZ1), the enzyme responsible for conversion of DCA to its inactive metabolite, glyoxylate, is downregulated in liver cancer and upregulated in some breast cancers, leading to abnormal expression of the protein. The cellular concentration of chloride, an ion that influences the stability of GSTZ1 in the presence of DCA, was also found to be abnormal in tumors, with consistently higher concentrations in hepatocellular carcinoma than in surrounding non-tumor tissue. Finally, results from experiments employing two- and three-dimensional cultures of HepG2 cells, parental and transduced to express GSTZ1, demonstrate that high levels of GSTZ1 expression confers resistance to the effect of high concentrations of DCA on cell viability. These results may have important clinical implications in determining intratumoral metabolism of DCA and, consequently, appropriate oral dosing.

Chloride intracellular channel 1 regulates migration and invasion in gastric cancer by triggering the ROS-mediated p38 MAPK signaling pathway

Chloride intracellular channel 1 (CLIC1) has been demonstrated to be overexpressed in gastric cancer, and elevated CLIC1 expression levels are markedly associated with the processes of tumor cell migration and invasion. However, the regulatory mechanism and signaling pathway underlying these processes have remained to be elucidated. The present study examined the impact of N-acetyl cysteine (NAC), indanyloxyacetic acid (IAA)-94 and SB203580, inhibitors of reactive oxygen species (ROS), as well as CLIC1 and p38 mitogen-activated protein kinase (MAPK) on the migration and invasion of SGC-7901 gastric cancer cells in a hypoxia-reoxygenation (H-R) microenvironment. The results demonstrated that intracellular ROS and CLIC1 levels were increased under H-R conditions, and that functional inhibition of CLIC1 significantly decreased the H-R-elevated ROS generation and p-p38 MAPK levels in SGC-7901 cells, as well as inhibited the migration and invasion of SGC-7901 cells. In addition, the expression levels of MMP-2 and MMP-9 were inhibited by NAC, IAA-94 and SB203580. These results indicated that CLIC1 regulates gastric cancer-cell migration and invasion via the ROS-mediated p38 MAPK signaling pathway.

Carbonic Anhydrase XII as an Independent Prognostic Factor in Advanced Esophageal Squamous Cell Carcinoma

BACKGROUND

Although recent studies described important roles for carbonic anhydrase (CA) XII in epithelial carcinogenesis and tumor behavior, a consensus has not yet been reached regarding its clinicopathological significance in esophageal squamous cell carcinoma (ESCC). In the present study, we investigated its prognostic significance in ESCC.

MATERIALS AND METHODS

An immunohistochemical analysis was performed on 70 primary tumor samples obtained from ESCC patients who underwent esophagectomy, and the relationships between the expression of CA XII and various clinicopathological features or prognosis were analyzed.

RESULTS

Immunohistochemical staining showed that CA XII was primarily found in the cell membranes of carcinoma cells. Although the expression of CA XII was related to the pT category, it had no prognostic impact. We then examined the expression of CA XII according to the pT category. In pT2-3 ESCC, the 3-year survival rate of patients with the high grade expression of CA XII (29.1 %) was significantly lower than that of patients with the low grade expression of CA XII (70.3 %). Furthermore, a multivariate analysis demonstrated that the expression of CA XII was one of the most important independent prognostic factors following radical esophagectomy in pT2-3 ESCC.

CONCLUSION

These results suggest that the expression of CA XII may be a valuable prognostic factor for patients with advanced ESCC. The results of the present study provide an insight into the role of CA XII as a biomarker in ESCC.

Bioelectrical regulation of cell cycle and the planarian model system

Cell cycle regulation through the manipulation of endogenous membrane potentials offers tremendous opportunities to control cellular processes during tissue repair and cancer formation. However, the molecular mechanisms by which biophysical signals modulate the cell cycle remain underappreciated and poorly understood. Cells in complex organisms generate and maintain a constant voltage gradient across the plasma membrane known as the transmembrane potential. This potential, generated through the combined efforts of various ion transporters, pumps and channels, is known to drive a wide range of cellular processes such as cellular proliferation, migration and tissue regeneration while its deregulation can lead to tumorigenesis. These cellular regulatory events, coordinated by ionic flow, correspond to a new and exciting field termed molecular bioelectricity. We aim to present a brief discussion on the biophysical machinery involving membrane potential and the mechanisms mediating cell cycle progression and cancer transformation. Furthermore, we present the planarian Schmidtea mediterranea as a tractable model system for understanding principles behind molecular bioelectricity at both the cellular and organismal level. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Cellular physiological approach for treatment of gastric cancer

Recent studies show that ion channels/transporters play important roles in fundamental cellular functions that would be involved in the cancer process. We review the evidence for their expression and functioning in human gastric cancer (GC), and evaluate the potential of cellular physiological approach in clinical management. Various types of ion channels, such as voltage-gated K⁺ channels, intracellular Cl^- channels and transient receptor potential channels have been found to express in GC cells and tissues, and to control cell cycles. With regard to water channels, aquaporin 3 and 5 play an important role in the progression of GC. Regulators of intracellular pH, such as anion exchanger, sodium-hydrogen exchanger, vacuolar H⁺-ATPases and carbonic anhydrases are also involved in tumorigenesis of GC. Their pharmacological manipulation and gene silencing affect cellular behaviours, suggesting their potential as therapeutic targets for GC. Our studies indicate the intracellular Cl^- concentration could act as a mediator of cellular signaling and control cell cycle progression in GC cells. Further, we demonstrate the cytocidal effects of hypotonic shock on GC cells, and indicate that the blockade of Cl^- channels/transporters enhances these effects by inhibiting regulatory volume decrease. A deeper understanding of molecular mechanisms may lead to the discovery of these cellular physiological approaches as a novel therapeutic strategy for GC.

The K-Cl cotransporter KCC3 as an independent prognostic factor in human esophageal squamous cell carcinoma

The objectives of the present study were to investigate the role of K–Cl cotransporter 3 (KCC3) in the regulation of cellular invasion and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC). Immunohistochemical analysis performed on 70 primary tumor samples obtained from ESCC patients showed that KCC3 was primarily found in the cytoplasm of carcinoma cells. Although the expression of KCC3 in the main tumor (MT) was related to several clinicopathological features, such as the pT and pN categories, it had no prognostic impact. KCC3 expression scores were compared between the MT and cancer nest (CN), and the survival rate of patients with a CN > MT score was lower than that of patients with a CN ≤ MT score. In addition, the survival rate of patients in whom KCC3 was expressed in the invasive front of tumor was lower than that of the patients without it. Furthermore, multivariate analysis demonstrated that the expression of KCC3 in the invasive front was one of the most important independent prognostic factors. The depletion of KCC3 using siRNAs inhibited cell migration and invasion in human ESCC cell lines. These results suggest that the expression of KCC3 in ESCC may affect cellular invasion and be related to a worse prognosis in patients with ESCC.

Efficacy of a hypotonic treatment for peritoneal dissemination from gastric cancer cells: an in vivo evaluation

The aim of the present study was to determine the efficacy of a hypotonic treatment for peritoneal dissemination from gastric cancer cells using an in vivo model. We firstly evaluated the toxicity of a peritoneal injection of distilled water (DW) (2 mL for 3 days) in mice. Macroscopic and microscopic examinations revealed that the peritoneal injection of DW did not severely damage the abdominal organs of these mice. MKN45 gastric cancer cells preincubated with NaCl buffer or DW for 20 minutes in vitro were then intraperitoneally injected into nude mice, and the development of dissemination nodules was analyzed. The total number, weight, and volume of the dissemination nodules were significantly decreased by the DW preincubation. We then determined whether the peritoneal injection of DW inhibited the establishment of peritoneal dissemination. After a peritoneal injection of MKN45 cells into nude mice, NaCl buffer or DW was injected into the abdominal cavity for 3 days. The total volume of dissemination nodules was significantly lower in DW-injected mice than in NaCl-injected mice. In conclusion, we demonstrated the safeness of a peritoneal injection of DW. Furthermore, the development of dissemination nodules from gastric cancer cells was prevented by a preincubation with or peritoneal injection of DW.

Role of the Na+/K+/2Cl- cotransporter NKCC1 in cell cycle progression in human esophageal squamous cell carcinoma

AIM: To investigate the role of Na⁺/K⁺/2Cl^- cotransporter 1 (NKCC1) in the regulation of genes involved in cell cycle progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC).

METHODS: An immunohistochemical analysis was performed on 68 primary tumor samples obtained from ESCC patients that underwent esophagectomy. NKCC1 expression in human ESCC cell lines was analyzed by Western blotting. Knockdown experiments were conducted using NKCC1 small interfering RNA, and the effects on cell cycle progression were analyzed. The gene expression profiles of cells were analyzed by microarray analysis.

RESULTS: Immunohistochemical staining showed that NKCC1 was primarily found in the cytoplasm of carcinoma cells and that its expression was related to the histological degree of differentiation of SCC. NKCC1 was highly expressed in KYSE170 cells. Depletion of NKCC1 in these cells inhibited cell proliferation via G₂/M phase arrest. Microarray analysis identified 2527 genes with altered expression levels in NKCC1depleted KYSE170. Pathway analysis showed that the top-ranked canonical pathway was the G₂/M DNA damage checkpoint regulation pathway, which involves MAD2L1, DTL, BLM, CDC20, BRCA1, and E2F5.

CONCLUSION: These results suggest that the expression of NKCC1 in ESCC may affect the G₂/M checkpoint and may be related to the degree of histological differentiation of SCCs. We have provided a deeper understanding of the role of NKCC1 as a mediator and/or a biomarker in ESCC.

The Ca(2+) -activated Cl(-) channel, ANO1 (TMEM16A), is a double-edged sword in cell proliferation and tumorigenesis

Since anoctamin 1 ANO1 (TMEM16A) was found to be a molecular component of Ca²⁺-activated Cl⁻ channels, its role in tumorigenesis has gained attention at a fast pace. ANO1 overexpression frequently occurs in the cancer tissues along with 11q13 chromosome amplification. Poor prognosis of many types of cancers has been closely correlated with ANO1 gene amplification and protein overexpression. ANO1 is now considered an excellent biomarker for certain cancers. Recent research suggests that it is the channel function of ANO1 that is involved in the tumorigenesis. However, how the overexpression of the functional ANO1 causes malignant transformation of tissues via signaling pathways, for example, MAPK remains to be investigated. Clarification of the reasons in future will avail to make ANO1 as a target for cancer treatment.

Elevated toll-like receptor 3 inhibits pancreatic β-cell proliferation through G1 phase cell cycle arrest

Activation of the innate and acquired immune systems plays an important role in chronic inflammatory diseases and conditions such as obesity, insulin resistance, type 2 diabetes mellitus and atherosclerosis, with additional roles in regulation of cell proliferation and survival. Here, we provide evidence that TLR3 can respond to nutrient signals and induce loss of β-cell mass through induction of G1 cycle arrest. Activation of TLR3 by polyinosinic-polycytidylic acid [poly (I:C)] was shown to trigger the decline of cyclin D1/2 protein levels in pancreatic β-cell lines, which could be reversed by the proteasome inhibitor MG132. P38 was also found to interfere with this degradation which may be associated with G1 cycle arrest. Moreover, inhibitory effects of TLR3 on β-cell growth were supported by gene silencing of TRIF, which could inhibit p38 activity in response to poly (I:C) stimuli. These results support a role for TLR3 in β-cell mass loss in metabolic surplus and raise the possibility that TRIF/p38 signaling may be involved in G1 phase cycle arrest through ubiquitin/proteasome-dependent degradation of cyclin D.

Enhancement of tubulin polymerization by Cl(-)-induced blockade of intrinsic GTPase

In growing neurite of neuronal cells, it is suggested that α/β-tubulin heterodimers assemble to form microtubule, and assembly of microtubule promotes neurite elongation. On the other hand, recent studies reveal importance of intracellular Cl(-) in regulation of various cellular functions such as cell cycle progression, differentiation, cell migration, and elongation of neurite in neuronal cells. In this study, we investigated effects of Cl(-) on in vitro tubulin polymerization. We found that efficiency of in vitro tubulin polymerization (the number of microtubule) was higher (3 to 5-fold) in Cl(-)-containing solutions than that in Cl(-)-free solutions containing Br(-) or NO(3)(-). On the other hand, GTPase activity of tubulin was lower (2/3-fold) in Cl(-)-containing solutions than that in Cl(-)-free solutions containing Br(-) or NO(3)(-). Efficiency of in vitro tubulin polymerization in solutions containing a non-hydrolyzable analogue of GTP (GpCpp) instead of GTP was much higher than that in the presence of GTP. Effects of replacement of GTP with GpCpp on in vitro tubulin polymerization was weaker in Cl(-) solutions (10-fold increases) than that in Br(-) or NO(3)(-) solutions (20-fold increases), although the efficiency of in vitro tubulin polymerization in Cl(-) solutions containing GpCpp was still higher than that in Br(-) or NO(3)(-) solutions containing GpCpp. Our results suggest that a part of stimulatory effects of Cl(-) on in vitro tubulin polymerization is mediated via an inhibitory effect on GTPase activity of tubulin, although Cl(-) would also regulate in vitro tubulin polymerization by factors other than an inhibitory effect on GTPase activity.