The inhibition of KCa3.1 channels activity reduces cell motility in glioblastoma derived cancer stem cells

Expression of KCNN4 in adult-type diffuse gliomas and its correlations with clinicopathological features and patient prognosis

BACKGROUND

The KCa3.1 channel (KCNN4) is extensively investigated as an oncogene in human cancers. The current study aimed to explore the clinicopathological significance of KCNN4 expression in patients with primary adult-type diffuse gliomas.

METHODS

Demographic, RNA-seq, and follow-up data of 477 patients were retrospectively reviewed. Patients were divided into the experimental and validation groups (278 and 199). KCNN4-related genes were determined by Pearson correlation analysis, and enrichment analyses and tumor-infiltrating immune cell assessments were applied to explore the potential mechanisms of KCNN4 involving glioma progression. The Kaplan-Meier method and the Cox regression analysis were used to evaluate the prognostic value of KCNN4 expression.

RESULTS

KCNN4 showed significantly higher expression level in glioblastoma, IDH-wildtype, followed by astrocytoma, IDH-mutant and oligodendroglioma, IDH-mutant and 1p/19q-codeleted (p < 0.001). Enrichment analyses and tumor-infiltrating immune cell assessments suggested that KCNN4 could involve glioma progression through extracellular regulation, affecting immune response, and modulating subcellular trafficking. At last, the Kaplan-Meier analysis showed that high KCNN4 expression was significantly correlated with poor progression-free and overall survival (p < 0.001 for both). While multivariate Cox regression analysis obtained an insignificant result.

CONCLUSIONS

KCNN4 was identified to be overexpressed in glioma cells and its expression level is positively related to tumor malignancy. It potentially participates in glioma biology by affecting extracellular regulation, subcellular trafficking, and immune escape. Additionally, high KCNN4 expression was correlated with poor survival outcomes of patients. The results can shed new light on the mechanisms of glioma progression, and provide a potential therapeutic target for treating gliomas.

Piezo1, the new actor in cell volume regulation

All animal cells control their volume through a complex set of mechanisms, both to counteract osmotic perturbations of the environment and to enable numerous vital biological processes, such as proliferation, apoptosis, and migration. The ability of cells to adjust their volume depends on the activity of ion channels and transporters which, by moving K+, Na+, and Cl- ions across the plasma membrane, generate the osmotic gradient that drives water in and out of the cell. In 2010, Patapoutian's group identified a small family of evolutionarily conserved, Ca2+-permeable mechanosensitive channels, Piezo1 and Piezo2, as essential components of the mechanically activated current that mediates mechanotransduction in vertebrates. Piezo1 is expressed in several tissues and its opening is promoted by a wide range of mechanical stimuli, including membrane stretch/deformation and osmotic stress. Piezo1-mediated Ca2+ influx is used by the cell to convert mechanical forces into cytosolic Ca2+ signals that control diverse cellular functions such as migration and cell death, both dependent on changes in cell volume and shape. The crucial role of Piezo1 in the regulation of cell volume was first demonstrated in erythrocytes, which need to reduce their volume to pass through narrow capillaries. In HEK293 cells, increased expression of Piezo1 was found to enhance the regulatory volume decrease (RVD), the process whereby the cell re-establishes its original volume after osmotic shock-induced swelling, and it does so through Ca2+-dependent modulation of the volume-regulated anion channels. More recently we reported that Piezo1 controls the RVD in glioblastoma cells via the modulation of Ca2+-activated K+ channels. To date, however, the mechanisms through which this mechanosensitive channel controls cell volume and maintains its homeostasis have been poorly investigated and are still far from being understood. The present review aims to provide a broad overview of the literature discussing the recent advances on this topic.

Challenges in the Therapeutic Targeting of KCa Channels: From Basic Physiology to Clinical Applications

Calcium-activated potassium (KCa) channels are ubiquitously expressed throughout the body and are able to regulate membrane potential and intracellular calcium concentrations, thereby playing key roles in cellular physiology and signal transmission. Consequently, it is unsurprising that KCa channels have been implicated in various diseases, making them potential targets for pharmaceutical interventions. Over the past two decades, numerous studies have been conducted to develop KCa channel-targeting drugs, including those for disorders of the central and peripheral nervous, cardiovascular, and urinary systems and for cancer. In this review, we synthesize recent findings regarding the structure and activating mechanisms of KCa channels. We also discuss the role of KCa channel modulators in therapeutic medicine. Finally, we identify the major reasons behind the delay in bringing these modulators to the pharmaceutical market and propose new strategies to promote their application.

M2 muscarinic receptors negatively modulate cell migration in human glioblastoma cells

Glioblastoma (GB) is a very aggressive human brain tumor. The high growth potential and invasiveness make this tumor surgically and pharmacologically untreatable. Our previous work demonstrated that the activation of the M2 muscarinic acetylcholine receptors (M2 mAChRs) inhibited cell proliferation and survival in GB cell lines and in the cancer stem cells derived from human biopsies. The aim of the present study was to investigate the ability of M2 mAChR to modulate cell migration in two different GB cell lines: U87 and U251. By wound healing assay and single cell migration analysis performed by time-lapse microscopy, we demonstrated the ability of M2 mAChRs to negatively modulate cell migration in U251 but not in the U87 cell line. In order to explain the different effects observed in the two cell lines we have evaluated the possible involvement of the intermediate conductance calcium-activated potassium (IKCa) channel. IKCa channel is present in the GB cells, and it has been demonstrated to modulate cell migration. Using the perforated patch-clamp technique we have found that selective activation of M2 mAChR significantly reduced functional density of the IKCa current in U251 but not in U87 cells. To understand whether the M2 mAChR mediated reduction of ion channel density in the U251 cell line was relevant for the cell migration impairment, we tested the effects of TRAM-34, a selective inhibitor of the IKCa channel, in wound healing assay. We found that it was able to markedly reduce U251 cell migration and significantly decrease the number of invadopodia-like structure formations. These results suggest that only in U251 cells the reduced cell migration M2 mAChR-mediated might involve, at least in part, the IKCa channel.

Efficacy of combined tumor irradiation and KCa3.1-targeting with TRAM-34 in a syngeneic glioma mouse model

The intermediate-conductance calcium-activated potassium channel KCa3.1 has been proposed to be a new potential target for glioblastoma treatment. This study analyzed the effect of combined irradiation and KCa3.1-targeting with TRAM-34 in the syngeneic, immune-competent orthotopic SMA-560/VM/Dk glioma mouse model. Whereas neither irradiation nor TRAM-34 treatment alone meaningfully prolonged the survival of the animals, the combination significantly prolonged the survival of the mice. We found an irradiation-induced hyperinvasion of glioma cells into the brain, which was inhibited by concomitant TRAM-34 treatment. Interestingly, TRAM-34 did neither radiosensitize nor impair SMA-560's intrinsic migratory capacities in vitro. Exploratory findings hint at increased TGF-β1 signaling after irradiation. On top, we found a marginal upregulation of MMP9 mRNA, which was inhibited by TRAM-34. Last, infiltration of CD3+, CD8+ or FoxP3+ T cells was not impacted by either irradiation or KCa3.1 targeting and we found no evidence of adverse events of the combined treatment. We conclude that concomitant irradiation and TRAM-34 treatment is efficacious in this preclinical glioma model.

Ca2+ -activated K+ channels regulate cell volume in human glioblastoma cells

Glioblastoma (GBM), the most lethal form of brain tumors, bases its malignancy on the strong ability of its cells to migrate and invade the narrow spaces of healthy brain parenchyma. Cell migration and invasion are both critically dependent on changes in cell volume and shape driven by the transmembrane transport of osmotically important ions such as K+ and Cl- . However, while the Cl- channels participating in cell volume regulation have been clearly identified, the precise nature of the K+ channels involved is still uncertain. Using a combination of electrophysiological and imaging approaches in GBM U87-MG cells, we found that hypotonic-induced cell swelling triggered the opening of Ca2+ -activated K+ (KCa ) channels of large and intermediate conductance (BKCa and IKCa , respectively), both highly expressed in GBM cells. The influx of Ca2+ mediated by the hypotonic-induced activation of mechanosensitive channels was found to be a key step for opening both the BKCa and the IKCa channels. Finally, the activation of both KCa channels mediated by mechanosensitive channels was found to be essential for the development of the regulatory volume decrease following hypotonic shock. Taken together, these data indicate that KCa channels are the main K+ channels responsible for the volume regulation in U87-MG cells.

Insights into the mechanisms governing P01 scorpion toxin effect against U87 glioblastoma cells oncogenesis

The emerging concept of small conductance Ca²⁺-activated potassium channels (SK_Ca) as pharmacological target for cancer treatment has significantly increased in recent years. In this study, we isolated the P01 toxin from Androctonus australis (Aa) scorpion venom and investigated its effect on biological properties of glioblastoma U87, breast MDA-MB231 and colon adenocarcinoma LS174 cancer cell lines. Our results showed that P01 was active only on U87 glioblastoma cells. It inhibited their proliferation, adhesion and migration with IC₅₀ values in the micromolar range. We have also shown that P01 reduced the amplitude of the currents recorded in HEK293 cells expressing SK2 channels with an IC₅₀ value of 3 pM, while it had no effect on those expressing SK3 channels. The investigation of the SK_Ca channels expression pattern showed that SK2 transcripts were expressed differently in the three cancer cell lines. Particularly, we highlighted the presence of SK2 isoforms in U87 cells, which could explain and rely on the specific activity of P01 on this cell line. These experimental data highlighted the usefulness of scorpion peptides to decipher the role of SK_Ca channels in the tumorigenesis process, and develop potential therapeutic molecules targeting glioblastoma with high selectivity.

Potassium Ion Channels in Glioma: From Basic Knowledge into Therapeutic Applications

Ion channels, specifically those controlling the flux of potassium across cell membranes, have recently been shown to exhibit an important role in the pathophysiology of glioma, the most common primary central nervous system tumor with a poor prognosis. Potassium channels are grouped into four subfamilies differing by their domain structure, gating mechanisms, and functions. Pertinent literature indicates the vital functions of potassium channels in many aspects of glioma carcinogenesis, including proliferation, migration, and apoptosis. The dysfunction of potassium channels can result in pro-proliferative signals that are highly related to calcium signaling as well. Moreover, this dysfunction can feed into migration and metastasis, most likely by increasing the osmotic pressure of cells allowing the cells to initiate the "escape" and "invasion" of capillaries. Reducing the expression or channel blockage has shown efficacy in reducing the proliferation and infiltration of glioma cells as well as inducing apoptosis, priming several approaches to target potassium channels in gliomas pharmacologically. This review summarizes the current knowledge on potassium channels, their contribution to oncogenic transformations in glioma, and the existing perspectives on utilizing them as potential targets for therapy.

Aggressive migration in acidic pH of a glioblastoma cancer stem cell line in vitro is independent of ASIC and KCa3.1 ion channels, but involves phosphoinositide 3-kinase

The microenvironment of proliferative and aggressive tumours, such as the brain tumour glioblastoma multiforme (GBM), is often acidic, hypoxic, and nutrient deficient. Acid-sensing ion channels (ASICs) are proton-sensitive Na⁺ channels that have been proposed to play a role in pH sensing and in modulation of cancer cell migration. We previously reported that primary glioblastoma stem cells (GSCs), which grow as multicellular tumour spheroids, express functional ASIC1a and ASIC3, whereas ASIC2a is downregulated in GSCs. Using a 2.5D migration assay, here we report that acidic pH dramatically increased migration of GSCs of the pro-neural subtype. Pharmacological blockade as well as CRISPR-Cas9-mediated gene knock-out of ASIC1a or stable overexpression of ASIC2a, however, revealed that neither ASIC1a nor ASIC3, nor downregulation of ASIC2a, mediated the aggressive migration at acidic pH. Therefore, we tested the role of two other proteins previously implicated in cancer cell migration: the Ca²⁺-activated K⁺ channel KCa3.1 (KCNN4) and phosphoinositide 3-kinase (PI3K). While pharmacological blockade of K_Ca3.1 did also not affect migration, blockade of PI3K decreased migration at acidic pH to control levels. In summary, our study reveals a strongly enhanced migration of GSCs at acidic pH in vitro and identifies PI3K as an important mediator of this effect.

Autonomous rhythmic activity in glioma networks drives brain tumour growth

Diffuse gliomas, particularly glioblastomas, are incurable brain tumours¹. They are characterized by networks of interconnected brain tumour cells that communicate via Ca²⁺ transients^2-6. However, the networks' architecture and communication strategy and how these influence tumour biology remain unknown. Here we describe how glioblastoma cell networks include a small, plastic population of highly active glioblastoma cells that display rhythmic Ca²⁺ oscillations and are particularly connected to others. Their autonomous periodic Ca²⁺ transients preceded Ca²⁺ transients of other network-connected cells, activating the frequency-dependent MAPK and NF-κB pathways. Mathematical network analysis revealed that glioblastoma network topology follows scale-free and small-world properties, with periodic tumour cells frequently located in network hubs. This network design enabled resistance against random damage but was vulnerable to losing its key hubs. Targeting of autonomous rhythmic activity by selective physical ablation of periodic tumour cells or by genetic or pharmacological interference with the potassium channel KCa3.1 (also known as IK1, SK4 or KCNN4) strongly compromised global network communication. This led to a marked reduction of tumour cell viability within the entire network, reduced tumour growth in mice and extended animal survival. The dependency of glioblastoma networks on periodic Ca²⁺ activity generates a vulnerability⁷ that can be exploited for the development of novel therapies, such as with KCa3.1-inhibiting drugs.

Tumoricidal, Temozolomide- and Radiation-Sensitizing Effects of KCa3.1 K+ Channel Targeting In Vitro Are Dependent on Glioma Cell Line and Stem Cell Fraction

Reportedly, the intermediate-conductance Ca²⁺-activated potassium channel K_Ca3.1 contributes to the invasion of glioma cells into healthy brain tissue and resistance to temozolomide and ionizing radiation. Therefore, K_Ca3.1 has been proposed as a potential target in glioma therapy. The aim of the present study was to assess the variability of the temozolomide- and radiation-sensitizing effects conferred by the K_Ca3.1 blocking agent TRAM-34 between five different glioma cell lines grown as differentiated bulk tumor cells or under glioma stem cell-enriching conditions. As a result, cultures grown under stem cell-enriching conditions exhibited indeed higher abundances of mRNAs encoding for stem cell markers compared to differentiated bulk tumor cultures. In addition, stem cell enrichment was paralleled by an increased resistance to ionizing radiation in three out of the five glioma cell lines tested. Finally, TRAM-34 led to inconsistent results regarding its tumoricidal but also temozolomide- and radiation-sensitizing effects, which were dependent on both cell line and culture condition. In conclusion, these findings underscore the importance of testing new drug interventions in multiple cell lines and different culture conditions to partially mimic the in vivo inter- and intra-tumor heterogeneity.

Potassium Ion Channels in Malignant Central Nervous System Cancers

Malignant central nervous system (CNS) cancers are among the most difficult to treat, with low rates of survival and a high likelihood of recurrence. This is primarily due to their location within the CNS, hindering adequate drug delivery and tumour access via surgery. Furthermore, CNS cancer cells are highly plastic, an adaptive property that enables them to bypass targeted treatment strategies and develop drug resistance. Potassium ion channels have long been implicated in the progression of many cancers due to their integral role in several hallmarks of the disease. Here, we will explore this relationship further, with a focus on malignant CNS cancers, including high-grade glioma (HGG). HGG is the most lethal form of primary brain tumour in adults, with the majority of patient mortality attributed to drug-resistant secondary tumours. Hence, targeting proteins that are integral to cellular plasticity could reduce tumour recurrence, improving survival. This review summarises the role of potassium ion channels in malignant CNS cancers, specifically how they contribute to proliferation, invasion, metastasis, angiogenesis, and plasticity. We will also explore how specific modulation of these proteins may provide a novel way to overcome drug resistance and improve patient outcomes.

Potassium Channels as a Target for Cancer Therapy: Current Perspectives

Potassium (K⁺) channels are highly regulated membrane proteins that control the potassium ion flux and respond to different cellular stimuli. These ion channels are grouped into three major families, Kv (voltage-gated K⁺ channel), Kir (inwardly rectifying K⁺ channel) and K2P (two-pore K⁺ channels), according to the structure, to mediate the K⁺ currents. In cancer, alterations in K⁺ channel function can promote the acquisition of the so-called hallmarks of cancer – cell proliferation, resistance to apoptosis, metabolic changes, angiogenesis, and migratory capabilities – emerging as targets for the development of new therapeutic drugs. In this review, we focus our attention on the different K⁺ channels associated with the most relevant and prevalent cancer types. We summarize our knowledge about the potassium channels structure and function, their cancer dysregulated expression and discuss the K⁺ channels modulator and the strategies for designing new drugs.

Ion Channel Drugs Suppress Cancer Phenotype in NG108-15 and U87 Cells: Toward Novel Electroceuticals for Glioblastoma

Glioblastoma is a lethal brain cancer that commonly recurs after tumor resection and chemotherapy treatment. Depolarized resting membrane potentials and an acidic intertumoral extracellular pH have been associated with a proliferative state and drug resistance, suggesting that forced hyperpolarization and disruption of proton pumps in the plasma membrane could be a successful strategy for targeting glioblastoma overgrowth. We screened 47 compounds and compound combinations, most of which were ion-modulating, at different concentrations in the NG108-15 rodent neuroblastoma/glioma cell line. A subset of these were tested in the U87 human glioblastoma cell line. A FUCCI cell cycle reporter was stably integrated into both cell lines to monitor proliferation and cell cycle response. Immunocytochemistry, electrophysiology, and a panel of physiological dyes reporting voltage, calcium, and pH were used to characterize responses. The most effective treatments on proliferation in U87 cells were combinations of NS1643 and pantoprazole; retigabine and pantoprazole; and pantoprazole or NS1643 with temozolomide. Marker analysis and physiological dye signatures suggest that exposure to bioelectric drugs significantly reduces proliferation, makes the cells senescent, and promotes differentiation. These results, along with the observed low toxicity in human neurons, show the high efficacy of electroceuticals utilizing combinations of repurposed FDA approved drugs.

Patient-individual phenotypes of glioblastoma stem cells are conserved in culture and associate with radioresistance, brain infiltration and patient prognosis

Identification of prognostic or predictive molecular markers in glioblastoma resection specimens may lead to strategies for therapy stratification and personalized treatment planning. Here, we analyzed in primary glioblastoma stem cell (pGSC) cultures the mRNA abundances of 7 stem cell (MSI1, Notch1, nestin, Sox2, Oct4, FABP7, ALDH1A3), and 3 radioresistance or invasion markers (CXCR4, IK_Ca , BK_Ca ). From these abundances, an mRNA signature was deduced which describes the mesenchymal-to-proneural expression profile of an individual GSC culture. To assess its functional significance, we associated the GSC mRNA signature with the clonogenic survival after irradiation with 4 Gy and the fibrin matrix invasion of the GSC cells. In addition, we compared the molecular pGSC mRNA signature with the tumor recurrence pattern and the overall survival of the glioblastoma patients from whom the pGSC cultures were derived. As a result, the molecular pGSC mRNA signature correlated positively with the pGSC radioresistance and matrix invasion capability in vitro. Moreover, patients with a mesenchymal (> median) mRNA signature in their pGSC cultures exhibited predominantly a multifocal tumor recurrence and a significantly (univariate log rank test) shorter overall survival than patients with proneural (≤ median mRNA signature) pGSCs. The tumors of the latter recurred predominately unifocally. We conclude that our pGSC cultures induce/select those cell subpopulations of the heterogeneous brain tumor that determine disease progression and therapy outcome. In addition, we further postulate a clinically relevant prognostic/predictive value for the 10 mRNAs-based mesenchymal-to-proneural signature of the GSC subpopulations in glioblastoma.

Chimeric Stimuli-Responsive Liposomes as Nanocarriers for the Delivery of the Anti-Glioma Agent TRAM-34

Nanocarriers are delivery platforms of drugs, peptides, nucleic acids and other therapeutic molecules that are indicated for severe human diseases. Gliomas are the most frequent type of brain tumor, with glioblastoma being the most common and malignant type. The current state of glioma treatment requires innovative approaches that will lead to efficient and safe therapies. Advanced nanosystems and stimuli-responsive materials are available and well-studied technologies that may contribute to this effort. The present study deals with the development of functional chimeric nanocarriers composed of a phospholipid and a diblock copolymer, for the incorporation, delivery and pH-responsive release of the antiglioma agent TRAM-34 inside glioblastoma cells. Nanocarrier analysis included light scattering, protein incubation and electron microscopy, and fluorescence anisotropy and thermal analysis techniques were also applied. Biological assays were carried out in order to evaluate the nanocarrier nanotoxicity in vitro and in vivo, as well as to evaluate antiglioma activity. The nanosystems were able to successfully manifest functional properties under pH conditions, and their biocompatibility and cellular internalization were also evident. The chimeric nanoplatforms presented herein have shown promise for biomedical applications so far and should be further studied in terms of their ability to deliver TRAM-34 and other therapeutic molecules to glioblastoma cells.

Mechanisms of Invasion in Glioblastoma: Extracellular Matrix, Ca2+ Signaling, and Glutamate

Glioblastoma (GBM) is the most common and malignant form of primary brain tumor with a median survival time of 14–16 months in GBM patients. Surgical treatment with chemotherapy and radiotherapy may help increase survival by removing GBM from the brain. However, complete surgical resection to eliminate GBM is almost impossible due to its high invasiveness. When GBM cells migrate to the brain, they interact with various cells, including astrocytes, neurons, endothelial cells, and the extracellular matrix (ECM). They can also make their cell body shrink to infiltrate into narrow spaces in the brain; thereby, they can invade regions of the brain and escape from surgery. Brain tumor cells create an appropriate microenvironment for migration and invasion by modifying and degrading the ECM. During those processes, the Ca²⁺ signaling pathway and other signaling cascades mediated by various ion channels contribute mainly to gene expression, motility, and invasion of GBM cells. Furthermore, GBM cells release glutamate, affecting migration via activation of ionotropic glutamate receptors in an autocrine manner. This review focuses on the cellular mechanisms of glioblastoma invasion and motility related to ECM, Ca²⁺ signaling, and glutamate. Finally, we discuss possible therapeutic interventions to inhibit invasion by GBM cells.

Potassium Channels in Cancer

Neoplastic transformation is reportedly associated with alterations of the potassium transport across plasma and intracellular membranes. These alterations have been identified as crucial elements of the tumourigenic reprogramming of cells. Potassium channels may contribute to cancer initiation, malignant progression and therapy resistance of tumour cells. The book chapter focusses on (oncogenic) potassium channels frequently upregulated in different tumour entities, upstream and downstream signalling of these channels, their contribution to the maintenance of cancer stemness and the formation of an immunosuppressive tumour microenvironment. In addition, their role in adaptation to tumour hypoxia, metabolic reprogramming, as well as tumour spreading and metastasis is discussed. Finally, we discuss how (oncogenic) potassium channels may confer treatment resistance of tumours against radiation and chemotherapy and thus might be harnessed for new therapy strategies, for instance, by repurposing approved drugs known to target potassium channels.

Deciphering the Role of Ca2+ Signalling in Cancer Metastasis: From the Bench to the Bedside

Metastatic cancer is one of the major causes of cancer-related mortalities. Metastasis is a complex, multi-process phenomenon, and a hallmark of cancer. Calcium (Ca2+) is a ubiquitous secondary messenger, and it has become evident that Ca2+ signalling plays a vital role in cancer. Ca2+ homeostasis is dysregulated in physiological processes related to tumour metastasis and progression-including cellular adhesion, epithelial-mesenchymal transition, cell migration, motility, and invasion. In this review, we looked at the role of intracellular and extracellular Ca2+ signalling pathways in processes that contribute to metastasis at the local level and also their effects on cancer metastasis globally, as well as at underlying molecular mechanisms and clinical applications. Spatiotemporal Ca2+ homeostasis, in terms of oscillations or waves, is crucial for hindering tumour progression and metastasis. They are a limited number of clinical trials investigating treating patients with advanced stages of various cancer types. Ca2+ signalling may serve as a novel hallmark of cancer due to the versatility of Ca2+ signals in cells, which suggests that the modulation of specific upstream/downstream targets may be a therapeutic approach to treat cancer, particularly in patients with metastatic cancers.

Featuring how calcium channels and calmodulin affect glioblastoma behavior. A review article

Glioblastoma (GBM) is considered to be the most aggressive primary brain tumor with an extremely bad prognosis. Recurrence after treatment is a major problem with a survival rate for one year ranging about 39.7%. Ideal outcomes are still difficult to be achieved despite the recent treatment combinations. The ultimate capacity to regrow after resection is considered to be related to the availability of self-regenerating populations of stem cells. We made a literature review interpreting how calcium channels and calcium-regulated proteins mechanistically elaborate glioblastoma virulence in different ways. Calcium channels, and calcium-regulated proteins have shown diverse interconnected roles in shaping different aspects of GBM biology as indicated in some experimental studies. The beneficial prospective of those roles granting GBM different aggressive potentials pose variable applications in targeted therapy whether it is experimental or clinical trials.

Ion Channels and Their Role in the Pathophysiology of Gliomas

Malignant gliomas are the most common primary central nervous system tumors and their prognosis is very poor. In recent years, ion channels have been demonstrated to play important roles in tumor pathophysiology such as regulation of gene expression, cell migration, and cell proliferation. In this review, we summarize the current knowledge on the role of ion channels on the development and progression of gliomas. Cell volume changes through the regulation of ion flux, accompanied by water flux, are essential for migration and invasion. Signaling pathways affected by ion channel activity play roles in cell survival and cell proliferation. Moreover, ion channels are involved in glioma-related seizures, sensitivity to chemotherapy, and tumor metabolism. Ion channels are potential targets for the treatment of these lethal tumors. Despite our increased understanding of the contributions of ion channels to glioma biology, this field remains poorly studied. This review summarizes the current literature on this important topic.

The voltage-gated proton channel hHv1 is functionally expressed in human chorion-derived mesenchymal stem cells

The voltage-gated proton channel Hv1 is widely expressed, among others, in immune and cancer cells, it provides an efficient cytosolic H⁺extrusion mechanism and regulates vital functions such as oxidative burst, migration and proliferation. Here we demonstrate the presence of human Hv1 (hHv1) in the placenta/chorion-derived mesenchymal stem cells (cMSCs) using RT-PCR. The voltage- and pH-dependent gating of the current is similar to that of hHv1 expressed in cell lines and that the current is blocked by 5-chloro-2-guanidinobenzimidazole (ClGBI) and activated by arachidonic acid (AA). Inhibition of hHv1 by ClGBI significantly decreases mineral matrix production of cMSCs induced by conditions mimicking physiological or pathological (inorganic phosphate, Pi) induction of osteogenesis. Wound healing assay and single cell motility analysis show that ClGBI significantly inhibits the migration of cMSCs. Thus, seminal functions of cMSCs are modulated by hHv1 which makes this channel as an attractive target for controlling advantages/disadvantages of MSCs therapy.

The Long Non-Coding RNA-14327.1 Promotes Migration and Invasion Potential of Endometrial Carcinoma Cells by Stabilizing the Potassium Channel Kca3.1

Background

The intermediate-conductance Ca²⁺-activated potassium channel (Kca3.1) plays a key role in maintaining intracellular Ca²⁺ homeostasis and is involved with the carcinogenesis of many human tumors including endometrial carcinoma. However, the underlying mechanism is still remained to be further elucidated.

Methods

The relationship between Kca3.1 and the clinicopathological characteristics of endometrial carcinoma was analyzed using UALCAN cancer database, and its expression was determined by immunohistochemistry. The Kca3.1 binding candidate lncRNAs were screened using RNA immunoprecipitation sequencing assay in the endometrial carcinoma cell line. MTT assay and transwell assay were used to confirm the cell proliferation migration and invasion, respectively. FACS was used to determine the cell cycle distribution. The overexpression efficiency of the lncRNAs was detected by qRT-PCR. The expression of EMT related proteins and the stability of Kca3.1 were analyzed by Western blot assay.

Results

Kca3.1 is related to clinicopathological characteristics of endometrial carcinoma, such as tumor stages. Several Kca3.1 binding lncRNAs were obtained from RNA immunoprecipitation sequencing assay. Stable expression of lncRNA-14327.1, one of the candidate lncRNAs, led to significant upregulation of Kca3.1 protein level, cell migration and invasion abilities, but suppressed cell proliferation and induced cell cycle arrest. Additionally, our data also demonstrated that Lenti-lncRNA-14327.1 could stabilize the protein of Kca3.1 and subsequently increase intracellular Ca²⁺ concentration. Transfection of siRNA-Kca3.1 significantly inhibited cell migration and invasion, and attenuated the EMT in Lenti-lncRNA-14327.1 stably expressed endometrial carcinoma cells.

Conclusion

Taken together, our results demonstrated that the lncRNA-14327.1 promoted cell migration and invasion potential of endometrial carcinoma cells by stabilizing Kca3.1 protein, implying that the lncRNA-14327.1/Kca3.1 might be a promising therapeutic target in endometrial carcinoma, particularly the metastatic one.

GABRP regulates chemokine signalling, macrophage recruitment and tumour progression in pancreatic cancer through tuning KCNN4-mediated Ca2+ signalling in a GABA-independent manner

BACKGROUND AND AIMS

Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer-related death worldwide. Neurotransmitter-initiated signalling pathway is profoundly implicated in tumour initiation and progression. Here, we investigated whether dysregulated neurotransmitter receptors play a role during pancreatic tumourigenesis.

METHODS

The Cancer Genome Atlas and Gene Expression Omnibus datasets were used to identify differentially expressed neurotransmitter receptors. The expression pattern of gamma-aminobutyric acid type A receptor pi subunit (GABRP) in human and mouse PDAC tissues and cells was studied by immunohistochemistry and western blot analysis. The in vivo implications of GABRP in PDAC were tested by subcutaneous xenograft model and lung metastasis model. Bioinformatics analysis, transwell experiment and orthotopic xenograft model were used to identify the in vitro and in vivo effects of GABRP on macrophages in PDAC. ELISA, co-immunoprecipitation, proximity ligation assay, electrophysiology, promoter luciferase activity and quantitative real-time PCR analyses were used to identify molecular mechanism.

RESULTS

GABRP expression was remarkably increased in PDAC tissues and associated with poor prognosis, contributed to tumour growth and metastasis. GABRP was correlated with macrophage infiltration in PDAC and pharmacological deletion of macrophages largely abrogated the oncogenic functions of GABRP in PDAC. Mechanistically, GABRP interacted with KCNN4 to induce Ca²⁺ entry, which leads to activation of nuclear factor κB signalling and ultimately facilitates macrophage infiltration by inducing CXCL5 and CCL20 expression.

CONCLUSIONS

Overexpressed GABRP exhibits an immunomodulatory role in PDAC in a neurotransmitter-independent manner. Targeting GABRP or its interaction partner KCNN4 may be an effective therapeutic strategy for PDAC.

KCa3.1 Channels Confer Radioresistance to Breast Cancer Cells

K_Ca3.1 K⁺ channels reportedly contribute to the proliferation of breast tumor cells and may serve pro-tumor functions in the microenvironment. The putative interaction of K_Ca3.1 with major anti-cancer treatment strategies, which are based on cytotoxic drugs or radiotherapy, remains largely unexplored. We employed K_Ca3.1-proficient and -deficient breast cancer cells derived from breast cancer-prone MMTV-PyMT mice, pharmacological K_Ca3.1 inhibition, and a syngeneic orthotopic mouse model to study the relevance of functional K_Ca3.1 for therapy response. The K_Ca3.1 status of MMTV-PyMT cells did not determine tumor cell proliferation after treatment with different concentrations of docetaxel, doxorubicin, 5-fluorouracil, or cyclophosphamide. K_Ca3.1 activation by ionizing radiation (IR) in breast tumor cells in vitro, however, enhanced radioresistance, probably via an involvement of the channel in IR-stimulated Ca²⁺ signals and DNA repair pathways. Consistently, K_Ca3.1 knockout increased survival time of wildtype mice upon syngeneic orthotopic transplantation of MMTV-PyMT tumors followed by fractionated radiotherapy. Combined, our results imply that K_Ca3.1 confers resistance to radio- but not to chemotherapy in the MMTV-PyMT breast cancer model. Since K_Ca3.1 is druggable, K_Ca3.1 targeting concomitant to radiotherapy seems to be a promising strategy to radiosensitize breast tumors.

Cancer-Associated Intermediate Conductance Ca2+-Activated K⁺ Channel KCa3.1

Several tumor entities have been reported to overexpress K_Ca3.1 potassium channels due to epigenetic, transcriptional, or post-translational modifications. By modulating membrane potential, cell volume, or Ca²⁺ signaling, K_Ca3.1 has been proposed to exert pivotal oncogenic functions in tumorigenesis, malignant progression, metastasis, and therapy resistance. Moreover, K_Ca3.1 is expressed by tumor-promoting stroma cells such as fibroblasts and the tumor vasculature suggesting a role of K_Ca3.1 in the adaptation of the tumor microenvironment. Combined, this features K_Ca3.1 as a candidate target for innovative anti-cancer therapy. However, immune cells also express K_Ca3.1 thereby contributing to T cell activation. Thus, any strategy targeting K_Ca3.1 in anti-cancer therapy may also modulate anti-tumor immune activity and/or immunosuppression. The present review article highlights the potential of K_Ca3.1 as an anti-tumor target providing an overview of the current knowledge on its function in tumor pathogenesis with emphasis on vasculo- and angiogenesis as well as anti-cancer immune responses.

Pharmacological modulation of mitochondrial ion channels

The field of mitochondrial ion channels has undergone a rapid development during the last three decades, due to the molecular identification of some of the channels residing in the outer and inner membranes. Relevant information about the function of these channels in physiological and pathological settings was gained thanks to genetic models for a few, mitochondria-specific channels. However, many ion channels have multiple localizations within the cell, hampering a clear-cut determination of their function by pharmacological means. The present review summarizes our current knowledge about the ins and outs of mitochondrial ion channels, with special focus on the channels that have received much attention in recent years, namely, the voltage-dependent anion channels, the permeability transition pore (also called mitochondrial megachannel), the mitochondrial calcium uniporter and some of the inner membrane-located potassium channels. In addition, possible strategies to overcome the difficulties of specifically targeting mitochondrial channels versus their counterparts active in other membranes are discussed, as well as the possibilities of modulating channel function by small peptides that compete for binding with protein interacting partners. Altogether, these promising tools along with large-scale chemical screenings set up to identify new, specific channel modulators will hopefully allow us to pinpoint the actual function of most mitochondrial ion channels in the near future and to pharmacologically affect important pathologies in which they are involved, such as neurodegeneration, ischaemic damage and cancer. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Role of KCa3.1 Channels in Modulating Ca2+ Oscillations during Glioblastoma Cell Migration and Invasion

Cell migration and invasion in glioblastoma (GBM), the most lethal form of primary brain tumors, are critically dependent on Ca²⁺ signaling. Increases of [Ca²⁺]_i in GBM cells often result from Ca²⁺ release from the endoplasmic reticulum (ER), promoted by a variety of agents present in the tumor microenvironment and able to activate the phospholipase C/inositol 1,4,5-trisphosphate PLC/IP₃ pathway. The Ca²⁺ signaling is further strengthened by the Ca²⁺ influx from the extracellular space through Ca²⁺ release-activated Ca²⁺ (CRAC) currents sustained by Orai/STIM channels, meant to replenish the partially depleted ER. Notably, the elevated cytosolic [Ca²⁺]_i activates the intermediate conductance Ca²⁺-activated K (KCa3.1) channels highly expressed in the plasma membrane of GBM cells, and the resulting K⁺ efflux hyperpolarizes the cell membrane. This translates to an enhancement of Ca²⁺ entry through Orai/STIM channels as a result of the increased electromotive (driving) force on Ca²⁺ influx, ending with the establishment of a recurrent cycle reinforcing the Ca²⁺ signal. Ca²⁺ signaling in migrating GBM cells often emerges in the form of intracellular Ca²⁺ oscillations, instrumental to promote key processes in the migratory cycle. This has suggested that KCa3.1 channels may promote GBM cell migration by inducing or modulating the shape of Ca²⁺ oscillations. In accordance, we recently built a theoretical model of Ca²⁺ oscillations incorporating the KCa3.1 channel-dependent dynamics of the membrane potential, and found that the KCa3.1 channel activity could significantly affect the IP₃ driven Ca²⁺ oscillations. Here we review our new theoretical model of Ca²⁺ oscillations in GBM, upgraded in the light of better knowledge of the KCa3.1 channel kinetics and Ca²⁺ sensitivity, the dynamics of the Orai/STIM channel modulation, the migration and invasion mechanisms of GBM cells, and their regulation by Ca²⁺ signals.

Glioblastoma quo vadis: Will migration and invasiveness reemerge as therapeutic targets?

PURPOSE

The purpose of the current review is to highlight, on one hand, the fact that the migratory pattern of glioma cells is the major obstacle to combat them with chemotherapy, and on the other one, the new treatment strategies to overcome this obstacle.

METHODS

This review surveys several membrane and extracellular molecules involved in glioma cell migration, invasiveness and resistance to apoptosis.

RESULTS

This review focuses on signaling pathways implicated in the positive regulation of glioblastoma cell migration, including glutamate and ion channel networks, microtubes and membrane-derived extracellular vesicles (EV) containing microRNAs. Glioma cells release glutamate to the extracellular matrix, inducing neuronal cell death, which may facilitate glioma growth and invasion. Glioma cell migration and invasion are further facilitated through ion channels and transporters that modify cellular volume. Microtubes and EV promote connections and communication among glioma cells and with the microenvironment and are associated with progression and resistance to therapy. Potential therapies linked to these pathways for glioblastoma are being developed.

CONCLUSION

Our view is evolving from an intracellular view of the complex intracellular signaling pathways to one of orchestral machinery, including connections between heterogeneous tumoral and nontumoral cells and with the microenvironment through channels, microtubes, and extracellular miRNA, generating different signals at different times. All of these elements give rise to a new perspective for the treatment of glioblastoma.

KCNJ3 is a new independent prognostic marker for estrogen receptor positive breast cancer patients

Numerous studies showed abnormal expression of ion channels in different cancer types. Amongst these, the potassium channel gene KCNJ3 (encoding for GIRK1 proteins) has been reported to be upregulated in tumors of patients with breast cancer and to correlate with positive lymph node status. We aimed to study KCNJ3 levels in different breast cancer subtypes using gene expression data from the TCGA, to validate our findings using RNA in situ hybridization in a validation cohort (GEO ID GSE17705), and to study the prognostic value of KCNJ3 using survival analysis. In a total of > 1000 breast cancer patients of two independent data sets we showed a) that KCNJ3 expression is upregulated in tumor tissue compared to corresponding normal tissue (p < 0.001), b) that KCNJ3 expression is associated with estrogen receptor (ER) positive tumors (p < 0.001), but that KCNJ3 expression is variable within this group, and c) that ER positive patients with high KCNJ3 levels have worse overall (p < 0.05) and disease free survival probabilities (p < 0.01), whereby KCNJ3 is an independent prognostic factor (p <0.05). In conclusion, our data suggest that patients with ER positive breast cancer might be stratified into high risk and low risk groups based on the KCNJ3 levels in the tumor.

KCa3.1 Channels and Glioblastoma: In Vitro Studies

BACKGROUND

Several tumor entities including brain tumors aberrantly overexpress intermediate conductance Ca2+ activated KCa3.1 K+ channels. These channels contribute significantly to the transformed phenotype of the tumor cells.

METHOD

PubMed was searched in order to summarize our current knowledge on the molecular signaling upstream and downstream and the effector functions of KCa3.1 channel activity in tumor cells in general and in glioblastoma cells in particular. In addition, KCa3.1 expression and function for repair of DNA double strand breaks was determined experimentally in primary glioblastoma cultures in dependence on the abundance of proneural and mesenchymal stem cell markers.

RESULTS

By modulating membrane potential, cell volume, Ca2+ signals and the respiratory chain, KCa3.1 channels in both, plasma and inner mitochondrial membrane, have been demonstrated to regulate many cellular processes such as migration and tissue invasion, metastasis, cell cycle progression, oxygen consumption and metabolism, DNA damage response and cell death of cancer cells. Moreover, KCa3.1 channels have been shown to crucially contribute to resistance against radiotherapy. Futhermore, the original in vitro data on KCa3.1 channel expression in subtypes of glioblastoma stem(-like) cells propose KCa3.1 as marker for the mesenchymal subgroup of cancer stem cells and suggest that KCa3.1 contributes to the therapy resistance of mesenchymal glioblastoma stem cells.

CONCLUSION

The data suggest KCa3.1 channel targeting in combination with radiotherapy as promising new tool to eradicate therapy-resistant mesenchymal glioblastoma stem cells.

Mesenchymal stem cell differentiation: Control by calcium-activated potassium channels

Mesenchymal stem cells (MSCs) are widely used in modern medicine for which understanding the mechanisms controlling their differentiation is fundamental. Ion channels offer novel insights to this process because of their role in modulating membrane potential and intracellular milieu. Here, we evaluate the contribution of calcium-activated potassium (K_Ca ) channels to the three main components of MSC differentiation: initiation, proliferation, and migration. First, we demonstrate the importance of the membrane potential (V_m ) and the apparent association of hyperpolarization with differentiation. Of K_Ca subtypes, most evidence points to activity of big-conductance channels in inducing initiation. On the other hand, intermediate-conductance currents have been shown to promote progression through the cell cycle. While there is no information on the role of K_Ca channels in migration of MSCs, work from other stem cells and cancer cells suggest that intermediate-conductance and to a lesser extent big-conductance channels drive migration. In all cases, these effects depend on species, tissue origin and lineage. Finally, we present a conceptual model that demonstrates how K_Ca activity could influence differentiation by regulating V_m and intracellular Ca²⁺ oscillations. We conclude that K_Ca channels have significant involvement in MSC differentiation and could potentially enable novel tissue engineering approaches and therapies.

Kca3.1 Activation Via P2y2 Purinergic Receptors Promotes Human Ovarian Cancer Cell (Skov-3) Migration

Disorders in cell signaling mediated by ATP or histamine, activating specific membrane receptors, have been frequently associated with tumorigenesis. Among the elements of response to purinergic (and histaminergic) signaling, ion channel activation controls essential cellular processes in cancer, such as cell proliferation, motility, and death. Here, we studied the effects that ATP had on electrical properties of human ovarian adenocarcinoma cells named SKOV-3. ATP caused increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and, concurrently, it evoked a complex electrical response with a conspicuous outward component. This current was generated through P2Y₂ receptor activation and opening of K⁺ channels, K_Ca3.1, as indicated by electrophysiological and pharmacological analysis, as well as by immunodetection and specific silencing of P2Y₂ or K_Ca3.1 gene by esiRNA transfection. Low µM ATP concentration increased SKOV-3 cell migration, which was strongly inhibited by K_Ca3.1 channel blockers and by esiRNA-generated P2Y₂ or K_Ca3.1 downregulation. Finally, in human ovarian tumors, the P2Y₂ and K_Ca3.1 proteins are expressed and co-localized in neoplastic cells. Thus, stimulation of P2Y₂ receptors expressed in SKOV-3 cells promotes motility through K_Ca3.1 activation. Since P2Y₂ and K_Ca3.1 are co-expressed in primary tumors, our findings suggest that they may play a role in cancer progression.

Overexpression of Large-Conductance Calcium-Activated Potassium Channels in Human Glioblastoma Stem-Like Cells and Their Role in Cell Migration

Glioblastomas (GBMs) are brain tumors characterized by diffuse invasion of cancer cells into the healthy brain parenchyma, and establishment of secondary foci. GBM cells abundantly express large-conductance, calcium-activated potassium (BK) channels that are thought to promote cell invasion. Recent evidence suggests that the GBM high invasive potential mainly originates from a pool of stem-like cells, but the expression and function of BK channels in this cell subpopulation have not been studied. We investigated the expression of BK channels in GBM stem-like cells using electrophysiological and immunochemical techniques, and assessed their involvement in the migratory process of this important cell subpopulation. In U87-MG cells, BK channel expression and function were markedly upregulated by growth conditions that enriched the culture in GBM stem-like cells (U87-NS). Cytofluorimetric analysis further confirmed the appearance of a cell subpopulation that co-expressed high levels of BK channels and CD133, as well as other stem cell markers. A similar association was also found in cells derived from freshly resected GBM biopsies. Finally, transwell migration tests showed that U87-NS cells migration was much more sensitive to BK channel block than U87-MG cells. Our data show that BK channels are highly expressed in GBM stem-like cells, and participate to their high migratory activity. J. Cell. Physiol. 232: 2478-2488, 2017. © 2016 Wiley Periodicals, Inc.

Intermediate-Conductance-Ca2-Activated K Channel IKCa1 Is Upregulated and Promotes Cell Proliferation in Cervical Cancer

BACKGROUND Accumulating data point to intermediate-conductance calcium-activated potassium channel (IKCa1) as a key player in controlling cell cycle progression and proliferation of human cancer cells. However, the role that IKCa1 plays in the growth of human cervical cancer cells is largely unexplored. MATERIAL AND METHODS In this study, Western blot analysis, immunohistochemical staining, and RT-PCR were first used for IKCa1protein and gene expression assays in cervical cancer tissues and HeLa cells. Then, IKCa1 channel blocker and siRNA were employed to inhibit the functionality of IKCa1 and downregulate gene expression in HeLa cells, respectively. After these treatments, we examined the level of cell proliferation by MTT method and measured IKCa1 currents by conventional whole-cell patch clamp technique. Cell apoptosis was assessed using the Annexin V-FITC/Propidium Iodide (PI) double-staining apoptosis detection kit. RESULTS We demonstrated that IKCa1 mRNA and protein are preferentially expressed in cervical cancer tissues and HeLa cells. We also showed that the IKCa1 channel blocker, clotrimazole, and IKCa1 channel siRNA can be used to suppress cervical cancer cell proliferation and decrease IKCa1 channel current. IKCa1 downregulation by specific siRNAs induced a significant increase in the proportion of apoptotic cells in HeLa cells. CONCLUSIONS IKCa1 is overexpressed in cervical cancer tissues, and IKCa1 upregulation in cervical cancer cell linea enhances cell proliferation, partly by reducing the proportion of apoptotic cells.

Regulation of voltage-gated potassium channels attenuates resistance of side-population cells to gefitinib in the human lung cancer cell line NCI-H460

BACKGROUND

Side-population (SP) cells that exclude anti-cancer drugs have been found in various tumor cell lines. Moreover, SP cells have a higher proliferative potential and drug resistance than main population cells (Non-SP cells). Also, several ion channels are responsible for the drug resistance and proliferation of SP cells in cancer.

METHODS

To confirm the expression and function of voltage-gated potassium (Kv) channels of SP cells, these cells, as well as highly expressed ATP-binding cassette (ABC) transporters and stemness genes, were isolated from a gefitinib-resistant human lung adenocarcinoma cell line (NCI-H460), using Hoechst 33342 efflux.

RESULTS

In the present study, we found that mRNA expression of Kv channels in SP cells was different compared to Non-SP cells, and the resistance of SP cells to gefitinib was weakened with a combination treatment of gefitinib and Kv channel blockers or a Kv7 opener, compared to single-treatment gefitinib, through inhibition of the Ras-Raf signaling pathway.

CONCLUSIONS

The findings indicate that Kv channels in SP cells could be new targets for reducing the resistance to gefitinib.

Expression Profiling of Clinical Specimens Supports the Existence of Neural Progenitor-Like Stem Cells in Basal Breast Cancers

BACKGROUND

We previously characterized in salivary adenoid cystic carcinoma (ACC) a novel population of cancer stem cells (CSCs) marked by coexpression of 2 stemness genes, sex-determining region Y (SRY)-related HMG box-containing factor 10 (SOX10) and CD133. We also reported that in ACC and basal-like breast carcinoma (BBC), a triple-negative breast cancer subtype, expression of SOX10 similarly demarcates a highly conserved gene signature enriched with neural stem cell genes. On the basis of these findings, we hypothesized that BBC might be likewise driven by SOX10-positive (SOX10⁺)/CD133⁺ cells with neural stem cell properties.

MATERIALS AND METHODS

To validate our hypothesis on clinical data, we used a novel approach to meta-analysis that merges gene expression data from independent breast cancer studies and ranks genes according to statistical significance of their coexpression with the gene of interest. Genes that showed strong association with CD133/PROM1 as well as SOX10 were validated across different platforms and data sets and analyzed for enrichment with genes involved in neurogenesis.

RESULTS

We identified in clinical breast cancer data sets a highly conserved SOX10/PROM1 gene signature that contains neural stem cell markers common for Schwann cells, ACC, BBC, and melanoma. Identification of tripartite motif-containing 2 (TRIM2), TRIM29, MPZL2, potassium calcium-activated channel subfamily N member 4 (KCNN4), and V-set domain containing T cell activation inhibitor 1 (VTCN1)/B7 homolog 4 (B7H4) within this signature provides insight into molecular mechanisms of CSC maintenance.

CONCLUSION

Our results suggest that BBC is driven by SOX10⁺/CD133⁺ cells that express neural stem cell-specific markers and share molecular similarities with CSCs of neural crest origin. Our study provides clinically relevant information on possible drivers of these cells that might facilitate development of CSC-targeting therapies against this cancer distinguished with poor prognosis and resistance to conventional therapies.

Critical evaluation of KCNJ3 gene product detection in human breast cancer: mRNA in situ hybridisation is superior to immunohistochemistry

Increased expression levels of KCNJ3 have been correlated with lymph node metastases and poor prognosis in patients with breast cancer, suggesting a prognostic role of KCNJ3. We aimed to establish protocols for the detection of KCNJ3 in formalin-fixed, paraffin-embedded (FFPE) breast cancer tissue. Several antibodies were tested for sensitivity and specificity by western blot, followed by optimisation of the immunohistochemistry (IHC) procedure and establishment of KCNJ3 mRNA in situ hybridisation (ISH). Methods were validated by processing 15 FFPE breast cancer samples for which microarray data were available. Spearman's rank correlation analysis resulted in borderline significant correlation for IHC versus ISH (r_S: 0.625; p<0.05) and IHC versus microarray (r_S: 0.668; p<0.01), but in significant correlation for ISH versus microarray (r_S: 0.861; p<0.001). The ISH method was superior to IHC, regarding robustness, sensitivity and specificity and will aid to further study expression levels of KCNJ3 in both malignant and physiological conditions.

Ion channel blockers and glioblastoma risk and outcome: a nested case-control and retrospective cohort studies

PURPOSE

Mutations in ion channels are common among patients with glioblastoma multiforme (GBM) and promote cell migration and invasion. We sought to evaluate the association between the use of specific ion channel blockers such as digoxin, amiodarone, diltiazem and verapamil and GBM risk and survival.

METHODS

We conducted a nested case-control study in a large primary care database from the UK. Cases were defined as all individuals with incident diagnosis of GBM during follow-up. For each case, up to four controls were selected using incidence density sampling. The primary exposure of interest was active treatment with each of the four ion channel blockers. We used conditional logistic regression to estimate odds ratios and 95% confidence interval (CI) for the association between ion channel blocker use and GBM risk. We then performed a Cox regression analysis among those diagnosed with GBM in order to evaluate the association between use of ion channel blockers and overall survival. Both analyses were adjusted to common confounders.

RESULTS

The study included 1076 cases and 4253 matched controls. There was no statistically significant difference between cases and controls in cardiac and metabolic risk factors. There was no change in GBM risk in active users of ion channel blockers compared with non-users. Among patients with GBM, active users of amiodarone had worse survival compared with never users with an HR of 4.41 (95%CI 1.95-9.96). There was no statistically significant change in survival among diltiazem, verapamil or digoxin users.

CONCLUSION

Treatment with specific ion channel blockers was not associated with the risk of GBM but was associated with worse survival in patients with GBM. Copyright © 2016 John Wiley & Sons, Ltd.

K+ channel signaling in irradiated tumor cells

K⁺ channels crosstalk with biochemical signaling cascades and regulate virtually all cellular processes by adjusting the intracellular K⁺ concentration, generating the membrane potential, mediating cell volume changes, contributing to Ca²⁺ signaling, and directly interacting within molecular complexes with membrane receptors and downstream effectors. Tumor cells exhibit aberrant expression and activity patterns of K⁺ channels. The upregulation of highly "oncogenic" K⁺ channels such as the Ca²⁺-activated IK channel may drive the neoplastic transformation, malignant progression, metastasis, or therapy resistance of tumor cells. In particular, ionizing radiation in doses used for fractionated radiotherapy in the clinic has been shown to activate K⁺ channels. Radiogenic K⁺ channel activity, in turn, contributes to the DNA damage response and promotes survival of the irradiated tumor cells. Tumor-specific overexpression of certain K⁺ channel types together with the fact that pharmacological K⁺ channel modulators are already in clinical use or well tolerated in clinical trials suggests that K⁺ channel targeting alone or in combination with radiotherapy might become a promising new strategy of anti-cancer therapy. The present article aims to review our current knowledge on K⁺ channel signaling in irradiated tumor cells. Moreover, it provides new data on molecular mechanisms of radiogenic K⁺ channel activation and downstream signaling events.

Inhibition of SK4 Potassium Channels Suppresses Cell Proliferation, Migration and the Epithelial-Mesenchymal Transition in Triple-Negative Breast Cancer Cells

Treatments for triple-negative breast cancer (TNBC) are limited; intermediate-conductance calcium-activated potassium (SK4) channels are closely involved in tumor progression, but little is known about these channels in TNBC. We aimed to investigate whether SK4 channels affect TNBC. First, by immunohistochemistry (IHC) and western blotting (WB), increased SK4 protein expression in breast tumor tissues was detected relative to that in non-tumor breast tissues, but there was no apparent expression difference between various subtypes of breast cancer (p>0.05). Next, functional SK4 channels were detected in the TNBC cell line MDA-MB-231 using WB, real-time PCR, immunofluorescence and patch-clamp recording. By employing SK4 specific siRNAs and blockers, including TRAM-34 and clotrimazole, in combination with an MTT assay, a colony-formation assay, flow cytometry and a cell motility assay, we found that the suppression of SK4 channels significantly inhibited cell proliferation and migration and promoted apoptosis in MDA-MB-231 cells (p<0.05). Further investigation revealed that treatment with epidermal growth factor (EGF)/basic fibroblast growth factor (bFGF) caused MDA-MB-231 cells to undergo the epithelial-mesenchymal transition (EMT) and to show increased SK4 mRNA expression. In addition, the down-regulation of SK4 expression inhibited the EMT markers Vimentin and Snail1. Collectively, our findings suggest that SK4 channels are expressed in TNBC and are involved in the proliferation, apoptosis, migration and EMT processes of TNBC cells.

Ca2+-Activated IK K+ Channel Blockade Radiosensitizes Glioblastoma Cells

Ca(2+)-activated K(+) channels, such as BK and IK channels, have been proposed to fulfill pivotal functions in neoplastic transformation, malignant progression, and brain infiltration of glioblastoma cells. Here, the ionizing radiation (IR) effect of IK K(+) channel targeting was tested in human glioblastoma cells. IK channels were inhibited pharmacologically by TRAM-34 or genetically by knockdown, cells were irradiated with 6 MV photons and IK channel activity, Ca(2+) signaling, cell cycling, residual double-strand breaks, and clonogenic survival were determined. In addition, the radiosensitizing effect of TRAM-34 was analyzed in vivo in ectopic tumors. Moreover, The Cancer Genome Atlas (TCGA) was queried to expose the dependence of IK mRNA abundance on overall survival (OS) of patients with glioma. Results indicate that radiation increased the activity of IK channels, modified Ca(2+) signaling, and induced a G2-M cell-cycle arrest. TRAM-34 decreased the IR-induced accumulation in G2-M arrest and increased the number of γH2AX foci post-IR, suggesting that TRAM-34 mediated an increase of residual DNA double-strand breaks. Mechanistically, IK knockdown abolished the TRAM-34 effects indicating the IK specificity of TRAM-34. Finally, TRAM-34 radiosensitized ectopic glioblastoma in vivo and high IK mRNA abundance associated with shorter patient OS in low-grade glioma and glioblastoma.

IMPLICATIONS

Together, these data support a cell-cycle regulatory function for IK K(+) channels, and combined therapy using IK channel targeting and radiation is a new strategy for anti-glioblastoma therapy.

Epigenetic dysregulation of KCa 3.1 channels induces poor prognosis in lung cancer

Epigenomic changes are an important feature of malignant tumors. How tumor aggressiveness is affected by DNA methylation of specific loci is largely unexplored. In genome-wide DNA methylation analyses, we identified the KCa 3.1 channel gene (KCNN4) promoter to be hypomethylated in an aggressive non-small-cell lung carcinoma (NSCLC) cell line and in patient samples. Accordingly, KCa 3.1 expression was increased in more aggressive NSCLC cells. Both findings were strong predictors for poor prognosis in lung adenocarcinoma. Increased KCa 3.1 expression was associated with aggressive features of NSCLC cells. Proliferation and migration of pro-metastatic NSCLC cells depended on KCa 3.1 activity. Mechanistically, elevated KCa 3.1 expression hyperpolarized the membrane potential, thereby augmenting the driving force for Ca(2+) influx. KCa 3.1 blockade strongly reduced the growth of xenografted NSCLC cells in mice as measured by positron emission tomography-computed tomography. Thus, loss of DNA methylation of the KCNN4 promoter and increased KCa 3.1 channel expression and function are mechanistically linked to poor survival of NSCLC patients.