KCa3.1 channels are involved in the infiltrative behavior of glioblastoma in vivo

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.

KCa channel targeting impairs DNA repair and invasiveness of patient-derived glioblastoma stem cells in culture and orthotopic mouse xenografts which only in part is predictable by KCa expression levels

Prognosis of glioblastoma patients is still poor despite multimodal therapy. The highly brain-infiltrating growth in concert with a pronounced therapy resistance particularly of mesenchymal glioblastoma stem-like cells (GSCs) has been proposed to contribute to therapy failure. Recently, we have shown that a mesenchymal-to-proneural mRNA signature of patient derived GSC-enriched (pGSC) cultures associates with in vitro radioresistance and gel invasion. Importantly, this pGSC mRNA signature is prognostic for patients' tumor recurrence pattern and overall survival. Two mesenchymal markers of the mRNA signature encode for IKCa and BKCa Ca2+-activated K+ channels. Therefore, we analyzed here the effect of IKCa- and BKCa-targeting concomitant to (fractionated) irradiation on radioresistance and glioblastoma spreading in pGSC cultures and in pGSC-derived orthotopic xenograft glioma mouse models. To this end, in vitro gel invasion, clonogenic survival, in vitro and in vivo residual DNA double strand breaks (DSBs), tumor growth, and brain invasion were assessed in the dependence on tumor irradiation and K+ channel targeting. As a result, the IKCa- and BKCa-blocker TRAM-34 and paxilline, respectively, increased number of residual DSBs and (numerically) decreased clonogenic survival in some but not in all IKCa- and BKCa-expressing pGSC cultures, respectively. In addition, BKCa- but not IKCa-blockade slowed-down gel invasion in vitro. Moreover, systemic administration of TRAM-34 or paxilline concomitant to fractionated tumor irradiation increased in the xenograft model(s) residual number of DSBs and attenuated glioblastoma brain invasion and (numerically) tumor growth. We conclude, that KCa-blockade concomitant to fractionated radiotherapy might be a promising new strategy in glioblastoma therapy.

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.

KCNK1 promotes proliferation and metastasis of breast cancer cells by activating lactate dehydrogenase A (LDHA) and up-regulating H3K18 lactylation

Breast cancer is the most prevalent malignancy and the most significant contributor to mortality in female oncology patients. Potassium Two Pore Domain Channel Subfamily K Member 1 (KCNK1) is differentially expressed in a variety of tumors, but the mechanism of its function in breast cancer is unknown. In this study, we found for the first time that KCNK1 was significantly up-regulated in human breast cancer and was correlated with poor prognosis in breast cancer patients. KCNK1 promoted breast cancer proliferation, invasion, and metastasis in vitro and vivo. Further studies unexpectedly revealed that KCNK1 increased the glycolysis and lactate production in breast cancer cells by binding to and activating lactate dehydrogenase A (LDHA), which promoted histones lysine lactylation to induce the expression of a series of downstream genes and LDHA itself. Notably, increased expression of LDHA served as a vicious positive feedback to reduce tumor cell stiffness and adhesion, which eventually resulted in the proliferation, invasion, and metastasis of breast cancer. In conclusion, our results suggest that KCNK1 may serve as a potential breast cancer biomarker, and deeper insight into the cancer-promoting mechanism of KCNK1 may uncover a novel therapeutic target for breast cancer treatment.

Repurposing the KCa3.1 Blocker Senicapoc for Ischemic Stroke

Senicapoc, a small molecule inhibitor of the calcium-activated potassium channel KCa3.1, was safe and well-tolerated in clinical trials for sickle cell anemia. We previously reported proof-of-concept data suggesting that both pharmacological inhibition and genetic deletion of KCa3.1 reduces infarction and improves neurologic recovery in rodents by attenuating neuroinflammation. Here we evaluated the potential of repurposing senicapoc for ischemic stroke. In cultured microglia, senicapoc inhibited KCa3.1 currents with an IC50 of 7 nM, reduced Ca2+ signaling induced by the purinergic agonist ATP, suppressed expression of pro-inflammatory cytokines and enzymes (iNOS and COX-2), and prevented induction of the inflammasome component NLRP3. When transient middle cerebral artery occlusion (tMCAO, 60 min) was induced in male C57BL/6 J mice, twice daily administration of senicapoc at 10 and 40 mg/kg starting 12 h after reperfusion dose-dependently reduced infarct area determined by T2-weighted magnetic resonance imaging (MRI) and improved neurological deficit on day 8. Ultra-high-performance liquid chromatography/mass spectrometry analysis of total and free brain concentrations demonstrated sufficient KCa3.1 target engagement. Senicapoc treatment significantly reduced microglia/macrophage and T cell infiltration and activation and attenuated neuronal death. A different treatment paradigm with senicapoc started at 3 h and MRI on day 3 and day 8 revealed that senicapoc reduces secondary infarct growth and suppresses expression of inflammation markers, including T cell cytokines in the brain. Lastly, we demonstrated that senicapoc does not impair the proteolytic activity of tissue plasminogen activator (tPA) in vitro. We suggest that senicapoc could be repurposed as an adjunctive immunocytoprotective agent for combination with reperfusion therapy for ischemic stroke.

Pan-cancer ion transport signature reveals functional regulators of glioblastoma aggression

Ion channels, transporters, and other ion-flux controlling proteins, collectively comprising the "ion permeome", are common drug targets, however, their roles in cancer remain understudied. Our integrative pan-cancer transcriptome analysis shows that genes encoding the ion permeome are significantly more often highly expressed in specific subsets of cancer samples, compared to pan-transcriptome expectations. To enable target selection, we identified 410 survival-associated IP genes in 33 cancer types using a machine-learning approach. Notably, GJB2 and SCN9A show prominent expression in neoplastic cells and are associated with poor prognosis in glioblastoma, the most common and aggressive brain cancer. GJB2 or SCN9A knockdown in patient-derived glioblastoma cells induces transcriptome-wide changes involving neuron projection and proliferation pathways, impairs cell viability and tumor sphere formation in vitro, perturbs tunneling nanotube dynamics, and extends the survival of glioblastoma-bearing mice. Thus, aberrant activation of genes encoding ion transport proteins appears as a pan-cancer feature defining tumor heterogeneity, which can be exploited for mechanistic insights and therapy development.

Microglia in Glioma

Myeloid cells are fundamental constituents of the brain tumor microenvironment. In this chapter, we describe the state-of-the-art knowledge on the role of microglial cells in the cross-talk with the most common and aggressive brain tumor, glioblastoma. We report in vitro and in vivo studies related to glioblastoma patients and glioma models to outline the symbiotic interactions that microglia develop with tumoral cells, highlighting the heterogeneity of microglial functions in shaping the brain tumor microenvironment.

Hypoxia, Ion Channels and Glioblastoma Malignancy

The malignancy of glioblastoma (GBM), the most aggressive type of human brain tumor, strongly correlates with the presence of hypoxic areas within the tumor mass. Oxygen levels have been shown to control several critical aspects of tumor aggressiveness, such as migration/invasion and cell death resistance, but the underlying mechanisms are still unclear. GBM cells express abundant K+ and Cl- channels, whose activity supports cell volume and membrane potential changes, critical for cell proliferation, migration and death. Volume-regulated anion channels (VRAC), which mediate the swelling-activated Cl- current, and the large-conductance Ca2+-activated K+ channels (BK) are both functionally upregulated in GBM cells, where they control different aspects underlying GBM malignancy/aggressiveness. The functional expression/activity of both VRAC and BK channels are under the control of the oxygen levels, and these regulations are involved in the hypoxia-induced GBM cell aggressiveness. The present review will provide a comprehensive overview of the literature supporting the role of these two channels in the hypoxia-mediated GBM malignancy, suggesting them as potential therapeutic targets in the treatment of GBM.

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.

Interdependencies of the Neuronal, Immune and Tumor Microenvironment in Gliomas

Gliomas are the most common primary brain malignancy and are universally fatal. Despite significant breakthrough in understanding tumor biology, treatment breakthroughs have been limited. There is a growing appreciation that major limitations on effective treatment are related to the unique and highly complex glioma tumor microenvironment (TME). The TME consists of multiple different cell types, broadly categorized into tumoral, immune and non-tumoral, non-immune cells. Each group provides significant influence on the others, generating a pro-tumor dynamic with significant immunosuppression. In addition, glioma cells are highly heterogenous with various molecular distinctions on the cellular level. These variations, in turn, lead to their own unique influence on the TME. To develop future treatments, an understanding of this complex TME interplay is needed. To this end, we describe the TME in adult gliomas through interactions between its various components and through various glioma molecular phenotypes.

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.

Insights into the Peritumoural Brain Zone of Glioblastoma: CDK4 and EXT2 May Be Potential Drivers of Malignancy

Despite the efforts made in recent decades, glioblastoma is still the deadliest primary brain cancer without cure. The potential role in tumour maintenance and progression of the peritumoural brain zone (PBZ), the apparently normal area surrounding the tumour, has emerged. Little is known about this area due to a lack of common definition and due to difficult sampling related to the functional role of peritumoural healthy brain. The aim of this work was to better characterize the PBZ and to identify genes that may have role in its malignant transformation. Starting from our previous study on the comparison of the genomic profiles of matched tumour core and PBZ biopsies, we selected CDK4 and EXT2 as putative malignant drivers of PBZ. The gene expression analysis confirmed their over-expression in PBZ, similarly to what happens in low-grade glioma and glioblastoma, and CDK4 high levels seem to negatively influence patient overall survival. The prognostic role of CDK4 and EXT2 was further confirmed by analysing the TCGA cohort and bioinformatics prediction on their gene networks and protein-protein interactions. These preliminary data constitute a good premise for future investigations on the possible role of CDK4 and EXT2 in the malignant transformation of PBZ.

Aquaporins and Ion Channels as Dual Targets in the Design of Novel Glioblastoma Therapeutics to Limit Invasiveness

Current therapies for Glioblastoma multiforme (GBM) focus on eradicating primary tumors using radiotherapy, chemotherapy and surgical resection, but have limited success in controlling the invasive spread of glioma cells into a healthy brain, the major factor driving short survival times for patients post-diagnosis. Transcriptomic analyses of GBM biopsies reveal clusters of membrane signaling proteins that in combination serve as robust prognostic indicators, including aquaporins and ion channels, which are upregulated in GBM and implicated in enhanced glioblastoma motility. Accumulating evidence supports our proposal that the concurrent pharmacological targeting of selected subclasses of aquaporins and ion channels could impede glioblastoma invasiveness by impairing key cellular motility pathways. Optimal sets of channels to be selected as targets for combined therapies could be tailored to the GBM cancer subtype, taking advantage of differences in patterns of expression between channels that are characteristic of GBM subtypes, as well as distinguishing them from non-cancerous brain cells such as neurons and glia. Focusing agents on a unique channel fingerprint in GBM would further allow combined agents to be administered at near threshold doses, potentially reducing off-target toxicity. Adjunct therapies which confine GBM tumors to their primary sites during clinical treatments would offer profound advantages for treatment efficacy.

Development of a Novel KCNN4-Related ceRNA Network and Prognostic Model for Renal Clear Cell Carcinoma

Background. Clear cell renal cell carcinoma (ccRCC) accounts for more than 80% of renal cell carcinomas. Yet, it has not been fully understood about the derivation and progression of the tumor, as well as the long-term benefits from multimodality therapy. Therefore, reliable and applicable molecular markers are urgently needed for the prediction of diagnosis and prognosis of ccRCC patients. Methods. Genetic and clinical information of 533 ccRCC patients from The Cancer Genome Atlas database was collected for comprehensive bioinformatic analyses. UALCAN was used to detect gene expression in paired tumor samples. Two data sets from Gene Expression Omnibus database were analyzed to identify differentially expressed genes (DEGs), and Gene Set Enrichment Analysis was applied for the functional enrichment of DEGs. Tumor Immune Single Cell Hub and Tumor IMmune Estimation Resource databases were separately used for analyses of single-immune cell and immune cell infiltration. Encyclopedia of RNA Interactomes database was explored to predict targeted microRNAs (miRNAs) and corresponding long non-coding RNAs (lncRNAs). Cox regression analysis was performed for the construction of risk signature and prognosis model. Finally, quantitative real-time polymerase chain reaction and western blot were conducted for KCNN4 expression detection in cell lines and clinical samples. Small interfering RNA was employed to knock down KCNN4, and corresponding functional experiments were conducted on ccRCC cells as well. Results. KCNN4 showed elevated expression in tumors and prominent clinical correlation in ccRCC. In total, 41 KCNN4-related genes were enriched, and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses showed they were intimately related to immune-related signaling pathways. Spearman’s analysis revealed the significantly positive correlation of KCNN4 with immune cell infiltration. By integrating hub miRNA-let-7e-5p and four critical lncRNA, a competitive endogenous RNA network-based risk signature was constructed. The prognosis model derived from it showed considerable predictive value for survival of ccRCC patients. Finally, in vitro experiments confirmed the remarkable tumor-promoting role of KCNN4 in ccRCC cells. Conclusion. KCNN4 significantly affected the immune status of tumor microenvironment and immunotherapy elements, through which it promoted tumor progression in ccRCC, and it could be a potential biomarker for prognosis and immunotherapy effects of ccRCC patients.

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.

CRAC and SK Channels: Their Molecular Mechanisms Associated with Cancer Cell Development

Cancer represents a major health burden worldwide. Several molecular targets have been discovered alongside treatments with positive clinical outcomes. However, the reoccurrence of cancer due to therapy resistance remains the primary cause of mortality. Endeavors in pinpointing new markers as molecular targets in cancer therapy are highly desired. The significance of the co-regulation of Ca²⁺-permeating and Ca²⁺-regulated ion channels in cancer cell development, proliferation, and migration make them promising molecular targets in cancer therapy. In particular, the co-regulation of the Orai1 and SK3 channels has been well-studied in breast and colon cancer cells, where it finally leads to an invasion-metastasis cascade. Nevertheless, many questions remain unanswered, such as which key molecular components determine and regulate their interplay. To provide a solid foundation for a better understanding of this ion channel co-regulation in cancer, we first shed light on the physiological role of Ca²⁺ and how this ion is linked to carcinogenesis. Then, we highlight the structure/function relationship of Orai1 and SK3, both individually and in concert, their role in the development of different types of cancer, and aspects that are not yet known in this context.

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.

In vivo morphological alterations of TAMs during KCa3.1 inhibition-by using in vivo two-photon time-lapse technology

Tumor associated macrophages (TAMs) are the mostprevalent cells recruited in the tumor microenvironment (TME). Once recruited, TAMs acquire a pro-tumor phenotype characterized by a typical morphology: ameboid in the tumor core and with larger soma and thick branches in the tumor periphery. Targeting TAMs by reverting them to an anti-tumor phenotype is a promising strategy for cancer immunotherapy. Taking advantage of Cx3cr1^GFP/WT heterozygous mice implanted with murine glioma GL261-RFP cells we investigated the role of Ca²⁺-activated K⁺ channel (KCa3.1) on the phenotypic shift of TAMs at the late stage of glioma growth through in vivo two-photon imaging. We demonstrated that TAMs respond promptly to KCa3.1 inhibition using a selective inhibitor of the channel (TRAM-34) in a time-dependent manner by boosting ramified projections attributable to a less hypertrophic phenotype in the tumor core. We also revealed a selective effect of drug treatment by reducing both glioma cells and TAMs in the tumor core with no interference with surrounding cells. Taken together, our data indicate a TRAM-34-dependent progressive morphological transformation of TAMs toward a ramified and anti-tumor phenotype, suggesting that the timing of KCa3.1 inhibition is a key point to allow beneficial effects on TAMs.

Microglial ion channels: Key players in non-cell autonomous neurodegeneration

Neuroinflammation is a critical pathophysiological hallmark of neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and traumatic brain injury (TBI). Microglia, the first responders of the brain, are the drivers of this neuroinflammation. Microglial activation, leading to induction of pro-inflammatory factors, like Interleukin 1-β (IL-1β), Tumor necrosis factor-α (TNFα), nitrites, and others, have been shown to induce neurodegeneration. Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of developing PD, but the mechanism underlying the microglial activation is still under active research. Recently, microglial ion channels have come to the forefront as potential drug targets in multiple neurodegenerative disorders, including AD and PD. Microglia expresses a variety of ion channels, including potassium channels, calcium channels, chloride channels, sodium channels, and proton channels. The diversity of channels present on microglia is responsible for the dynamic nature of these immune cells of the brain. These ion channels regulate microglial proliferation, chemotaxis, phagocytosis, antigen recognition and presentation, apoptosis, and cell signaling leading to inflammation, among other critical functions. Understanding the role of these ion channels and the signaling mechanism these channels regulate under pathological conditions is an active area of research. This review will be focusing on the roles of different microglial ion channels, and their potential role in regulating microglial functions in neurodegenerative disorders.

Bioactive peptides from venoms against glioma progression

Venoms are complex mixtures of different molecules and ions. Among them, bioactive peptides have been found to affect cancer hallmarks, such as cell proliferation, cell invasion, cell migration, and can also modulate the immune response of normal and cancer-bearing organisms. In this article, we review the mechanisms of action on these cancer cell features, focusing on bioactive peptides being developed as potential therapeutics for one of the most aggressive and deadly brain tumors, glioblastoma (GB). Novel therapeutic approaches applying bioactive peptides may contribute to multiple targeting of GB and particularly of GB stem cells. Bioactive peptides selectively target cancer cells without harming normal cells. Various molecular targets related to the effects of bioactive peptides on GB have been proposed, including ion channels, integrins, membrane phospholipids and even immunomodulatory treatment of GB. In addition to therapy, some bioactive peptides, such as disintegrins, can also be used for diagnostics or are used as labels for cytotoxic drugs to specifically target cancer cells. Given the limitations described in the last section, successful application in cancer therapy is rather low, as only 3.4% of such peptides have been included in clinical trials and have passed successfully phases I to III. Combined approaches of added bioactive peptides to standard cancer therapies need to be explored using advanced GB in vitro models such as organoids. On the other hand, new methods are also being developed to improve translation from research to practice and provide new hope for GB patients and their families.

Polyisocyanide hydrogels with tunable nonlinear elasticity mediate liver carcinoma cell functional response

Hepatocellular carcinoma development is closely related to the changes in tissue mechanics induced by excess collagen deposition and crosslinking, which leads to liver fibrosis and malignant progression. The role of matrix stiffness has been widely assessed using various linearly elastic materials. However, the liver, like many soft tissues, also exhibits nonlinear elasticity by strain-stiffening, allowing cells to mechanically interact with their micromilieus which has attracted much attention in cellular processes recently. Here, we use a biomimetic hydrogel grafting of GRGDS peptide with tunable nonlinear mechanical properties, polyisocyanides (PIC), to investigate the influence of strain-stiffening on HepG2 liver cancer cell behavior by tuning PIC polymer length. Compared to short PIC polymer with lower critical stress, PIC hydrogels composed of long polymer with higher critical stress promote the motility and invasiveness of HepG2 cells, and induce more actin stress fibers and higher expression level of mechanotransducer YAP and its nuclear translocation. Strikingly, the expression of calcium-activated potassium channel KCa3.1, an important biomarker in hepatocellular carcinoma, is also affected by the mechanical property of PIC hydrogels. It was also shown that downregulating the KCa3.1 channel can be achieved by inhibiting the formation of actin fibers. Our findings imply that the strain-stiffening property of PIC hydrogels affects the expression of KCa3.1 potassium channel via mediating cytoskeletal stress fiber formation, and ultimately influences the liver carcinoma cell functional response. STATEMENT OF SIGNIFICANCE: The effect of nonlinear elasticity by strain-stiffening, is assessed in HepG2 liver cancer cell behavior by using a biomimetic hydrogel with tunable mechanical properties, polyisocyanides (PIC). PIC gels with higher critical stress promote the motility and invasiveness of HepG2 cells and induce upregulated expression levels of KCa3.1 potassium channel and YAP, but which can be suppressed by inhibiting the formation of actin fibers. Our findings imply that the strain-stiffening property of PIC gels influences the expression of KCa3.1 potassium channel via mediating cytoskeletal stress fiber formation and, ultimately affects the liver carcinoma cell functional response.

Potassium channel-driven bioelectric signalling regulates metastasis in triple-negative breast cancer

BACKGROUND

There is a critical need to better understand the mechanisms that drive local cell invasion and metastasis to develop new therapeutics targeting metastatic disease. Bioelectricity is an important mediator of cellular processes and changes in the resting membrane potential (RMP) are associated with increased cancer cell invasion. However, whether the RMP can be used to target invading cancer cells is unknown.

METHODS

We employed both genetic and pharmacological manipulation of potassium channel activity and characterized the effects on breast cancer cell migration and invasion in vitro, and metastasis in an animal model of breast cancer.

FINDINGS

Our data demonstrate that altering the RMP of triple-negative breast cancer (TNBC) cells by manipulating potassium channel expression increases in vitro invasion, in vivo tumour growth and metastasis, and is accompanied by changes in gene expression associated with cell adhesion.

INTERPRETATION

We describe a novel mechanism for RMP-mediated cell migration involving cadherin-11 and the MAPK pathway. Importantly, we identify a new strategy to target metastatic TNBC in vivo by repurposing an FDA-approved potassium channel blocker. Our results demonstrate that bioelectricity regulates cancer cell invasion and metastasis which could lead to a new class of therapeutics for patients with metastatic disease.

FUNDING

This work was supported by the National Institutes of Health (R00-CA207866 to M.J.O.), Tufts University (Start-up funds from the School of Engineering to M.J.O., Tufts Collaborates Award to M.J.O. and M.L.), Allen Discovery centre program (Paul G. Allen Frontiers Group (12,171) to M.L.), and Breast Cancer Alliance Young Investigator Grant to M.J.O, Laidlaw Scholar funding to D.S. M.L. also gratefully acknowledges support of the Barton Family Foundation.

Microglial Potassium Channels: From Homeostasis to Neurodegeneration

The growing interest in the role of microglia in the progression of many neurodegenerative diseases is developing in an ever-expedited manner, in part thanks to emergent new tools for studying the morphological and functional features of the CNS. The discovery of specific biomarkers of the microglia phenotype could find application in a wide range of human diseases, and creates opportunities for the discovery and development of tailored therapeutic interventions. Among these, recent studies highlight the pivotal role of the potassium channels in regulating microglial functions in physiological and pathological conditions such as Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis. In this review, we summarize the current knowledge of the involvement of the microglial potassium channels in several neurodegenerative diseases and their role as modulators of microglial homeostasis and dysfunction in CNS disorders.

The feeding behaviour of Amyotrophic Lateral Sclerosis mouse models is modulated by the Ca2+ -activated KCa 3.1 channels

BACKGROUND AND PURPOSE

Amyotrophic lateral sclerosis (ALS) patients exhibit dysfunctional energy metabolism and weight loss, which is negatively correlated with survival, together with neuroinflammation. However, the possible contribution of neuroinflammation to deregulations of feeding behaviour in ALS has not been studied in detail. We here investigated if microglial K_Ca 3.1 is linked to hypothalamic neuroinflammation and affects feeding behaviours in ALS mouse models.

EXPERIMENTAL APPROACH

hSOD1^G93A and TDP43^A315T mice were treated daily with 120 mg·kg^-1 of TRAM-34 or vehicle by intraperitoneal injection from the presymptomatic until the disease onset phase. Body weight and food intake were measured weekly. The later by weighing food provided minus that left in the cage. RT-PCR and immunofluorescence analysis were used to characterize microglia phenotype and the main populations of melanocortin neurons in the hypothalamus of hSOD1^G93A and age-matched non-tg mice. The cannabinoid-opioid interactions in feeding behaviour of hSOD1^G93A mice were studied using an inverse agonist and an antagonist of the cannabinoid receptor CB₁ (rimonabant) and μ-opioid receptors (naloxone), respectively.

KEY RESULTS

We found that treatment of hSOD1^G93A mice with the K_Ca 3.1 inhibitor TRAM-34 (i), attenuates the pro-inflammatory phenotype of hypothalamic microglia, (ii) increases food intake and promotes weight gain, (iii) increases the number of healthy pro-opiomelanocortin (POMC) neurons and (iv), changes the expression of cannabinoid receptors involved in energy homeostasis.

CONCLUSION AND IMPLICATIONS

Using ALS mouse models, we describe defects in the hypothalamic melanocortin system that affect appetite control. These results reveal a new regulatory role for K_Ca 3.1 to counteract weight loss in ALS.

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.

Inhibitory effect of terfenadine on Kir2.1 and Kir2.3 channels

Terfenadine is a second-generation H1-antihistamine that despite potentially can produce severe side effects it has recently gained attention due to its anticancer properties. Lately, the subfamily 2 of inward rectifier potassium channels (Kir2) has been implicated in the progression of some tumoral processes. Hence, we characterized the effects of terfenadine on Kir2.x channels expressed in HEK-293 cells. Terfenadine inhibited Kir2.3 channels with a strikingly greater potency (IC50 = 1.06 ± 0.11 μmol L-1) compared to Kir2.1 channels (IC50 = 27.8 ± 4.8 μmol L-1). The Kir2.3(I213L) mutant, possessing a larger affinity for phosphatidylinositol 4,5-bisphosphate (PIP2) than the wild-type Kir2.3, was less sensitive to terfenadine inhibition (IC50 = 13.0 ± 2.9 μmol L-1). Additionally, the PIP2 intracellular application had largely reduced the inhibition of Kir2.1 channels by terfenadine. Our data support that Kir2.x channels are targets of terfena-dine by affecting their interaction with PIP2, which could be regarded as a mechanism of the antitumor properties of terfenadine.

First Tandem Repeat of a Potassium Channel KCNN4 Minisatellite Folds into a V-Loop G-Quadruplex Structure

The KCNN4 gene encoding a potassium channel protein whose expression has been correlated with tumor progression was found to comprise a guanine-rich minisatellite region with the ability to form a putative G-quadruplex (G4). Given the suggested regulatory role of G4s in gene expression, G-quadruplex formation for the polymorphic first repeat of the minisatellite was studied by nuclear magnetic resonance spectroscopy. A stable G-quadruplex of a truncated mutant sequence was shown to represent one of several coexisting species of the wild-type sequence. The high-resolution structure features a noncanonical G4 with a broken G-column and a V-shaped loop. The presence of a 3'-flanking thymidine interacting with the lateral loop preceding the V loop seems to be critical for the formation of this G4 topology. On the contrary, an additional 5'-flanking residue disfavored but still allowed folding into the V-loop structure. The latter may therefore serve as a putative therapeutic target in strategies for G4-based modulation of KCNN4 expression.

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.

SK4 oncochannels regulate calcium entry and promote cell migration in KRAS-mutated colorectal cancer

BACKGROUND

Colorectal cancer (CRC) metastases are the main cause of CRC mortality. Intracellular Ca2+ regulates cell migration and invasion, key factors for metastases. Ca2+ also activates Ca2+-dependent potassium channels which in turn affect Ca2+ driving force. We have previously reported that the expression of the Ca2+ activated potassium channel KCNN4 (SK4) is higher in CRC primary tumors compared to normal tissues. Here, we aimed to investigate the role of SK4 in the physiology of CRC.

RESULTS

SK4 protein expression is enhanced in CRC tissues compared to normal colon tissues, with a higher level of KCNN4 in CRC patients with KRAS mutations. At the cellular level, we found that SK4 regulates the membrane potential of HCT116 cells. We also found that its inhibition reduced store operated Ca2+ entry (SOCE) and constitutive Ca2+ entry (CCE), while reducing cell migration. We also found that the activity of SK4 is linked to resistance pathways such as KRAS mutation and the expression of NRF2 and HIF-1α. In addition, the pharmacological inhibition of SK4 reduced intracellular reactive oxygen species (ROS) production, NRF2 expression and HIF1α stabilization.

CONCLUSION

Our results suggest that SK4 contributes to colorectal cancer cell migration and invasion by modulating both Ca2+ entry and ROS regulation. Therefore, SK4 could be a potential target to reduce metastasis in KRAS-mutated CRC.

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.

KCa3.1-dependent uptake of the cytotoxic DNA-binding dye Hoechst 33258 into cancerous but not healthy cervical cells

The poor and nonselective penetration of current chemotherapeutics across the plasma membranes of cancer cells, which is necessary for the targeted disruption of the intracellular machinery, remains a major pharmaceutical challenge. In several cell types, including mast cells and macrophages, exposure to extracellular ATP is known to stimulate passive entry of large and otherwise membrane impermeable cationic dyes, which is usually attributed to conduction through ionotropic P2X receptors. Here, we report that elevations in cytosolic Ca2+ stimulate the rapid uptake and nuclear accumulation of a DNA-binding fluorescent cation, Hoechst 33258 (H33258), in cervical cancer cells. The H33258 uptake was dependent on activation of intermediate conductance Ca2+-activated K+ channels (KCa3.1), and direct stimulation of the channel with the activators SKA 31 and DCEBIO was sufficient to induce cellular uptake of H33258 directly. In contrast to the results from cancerous cervical cells, KCa3.1-dependent H33258 uptake was rarely observed in epithelial cells derived from the ectocervix and transformation zone of healthy cervical tissue. Furthermore, whole-cell patch clamp experiments and assessment of membrane potential using the slow voltage-sensitive dye bis-(1,3-diethylthiobarbituric acid)trimethine oxonol revealed a significant difference in functional KCa3.1 activity between cancerous and healthy cervical epithelial cells, which correlated strongly with the incidence of KCa3.1-dependent H33258 uptake. Finally, we show that activation of KCa3.1 channels caused a modest but significant sensitization of cancer cells to the growth suppressant effects of H33258, lending plausibility to the idea of using KCa3.1 channel activators to enhance cell penetration of small cationic toxins into cancer cells expressing these channels.

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.

Inhibition of Radiation and Temozolomide-Induced Glioblastoma Invadopodia Activity Using Ion Channel Drugs

Simple Summary

Glioblastoma accounts for approximately 40–50% of all primary brain cancers and is a highly aggressive cancer that rapidly disseminates within the surrounding normal brain. Dynamic actin-rich protrusions known as invadopodia facilitate this invasive process. Ion channels have also been linked to a pro-invasive phenotype and may contribute to facilitating invadopodia activity in cancer cells. The aim of our study was to screen ion channel-targeting drugs for their cytotoxic efficacy and potential anti-invadopodia properties in glioblastoma cells. We demonstrated that the targeting of ion channels in glioblastoma cells can lead to a reduction in invadopodia activity and protease secretion. Importantly, the candidate drugs exhibited a significant reduction in radiation and temozolomide-induced glioblastoma cell invadopodia activity. These findings support the proposed pro-invasive role of ion channels via invadopodia in glioblastoma, which may be ideal therapeutic targets for the treatment of glioblastoma patients.

Abstract

Glioblastoma (GBM) is the most prevalent and malignant type of primary brain cancer. The rapid invasion and dissemination of tumor cells into the surrounding normal brain is a major driver of tumor recurrence, and long-term survival of GBM patients is extremely rare. Actin-rich cell membrane protrusions known as invadopodia can facilitate the highly invasive properties of GBM cells. Ion channels have been proposed to contribute to a pro-invasive phenotype in cancer cells and may also be involved in the invadopodia activity of GBM cells. GBM cell cytotoxicity screening of several ion channel drugs identified three drugs with potent cell killing efficacy: flunarizine dihydrochloride, econazole nitrate, and quinine hydrochloride dihydrate. These drugs demonstrated a reduction in GBM cell invadopodia activity and matrix metalloproteinase-2 (MMP-2) secretion. Importantly, the treatment of GBM cells with these drugs led to a significant reduction in radiation/temozolomide-induced invadopodia activity. The dual cytotoxic and anti-invasive efficacy of these agents merits further research into targeting ion channels to reduce GBM malignancy, with a potential for future clinical translation in combination with the standard therapy.

KCNN4 induces multiple chemoresistance in breast cancer by regulating BCL2A1

Multidrug chemoresistance is a major clinical obstacle in breast cancer treatment. We aimed to elucidate the sensitivity to therapeutics in gemcitabine-resistant breast cancer models. Pooled library screening combined with RNA-seq was conducted to explore the potential targets involved in gemcitabine resistance in breast cancer cells. Cytotoxicity and tumor xenograft assays were used to evaluate the effect of calcium-activated channel subfamily N member 4 (KCNN4) inhibitors on the cellular sensitivity of breast cancer cells to chemotherapeutic drugs both in vitro and in vivo. We found that KCNN4 is an important determinant for the cytotoxicity of gemcitabine. Elevated KCNN4 expression enhanced resistance to chemotherapeutic antimetabolites and promoted cell proliferation. Conversely, silencing KCNN4 or chemical inhibition of KCNN4 by the specific inhibitor TRAM-34 inhibited the chemoresistance and cell proliferation. Mechanistically, KCNN4 upregulated BCL2-related protein A1 (BCL2A1) to suppress apoptosis by activating RAS-MAPK and PI3K-AKT signaling. Moreover, high expression levels of KCNN4 and BCL2A1 were associated with shortened disease-free survival in the cohort studies. Collectively, our findings showed that KCNN4 is a key modulator of progression and drug resistance in breast cancer, indicating that targeting KCNN4 may serve as a promising therapeutic strategy to overcome multidrug chemoresistance in this disease.

Prazosin inhibits the proliferation, migration and invasion, but promotes the apoptosis of U251 and U87 cells via the PI3K/AKT/mTOR signaling pathway

Prazosin, an α-adrenergic receptor antagonist, is used to treat mild to moderate hypertension. It has recently been discovered that α-adrenergic receptors may have potential antitumor properties. Therefore, in the present study, the effect of prazosin on human glioblastoma and the underlying mechanism were investigated. Human glioblastoma U251 and U87 cells were treated with different concentrations of prazosin, and a Cell Counting Kit-8 assay was performed to investigate the effects of prazosin on cell proliferation. Transwell migration and invasion assays were used to assess the effects of prazosin on cell migration and invasion. Prazosin-induced apoptosis in U251 and U87 cells was detected by flow cytometry, and the protein expression levels of anti-apoptotic proteins and proteins related to the PI3K/AKT/mTOR signaling pathway were detected by western blotting. The results suggested that following treatment with prazosin, the proliferation, migration and invasion of U251 and U81 cells were decreased. By contrast, U251 and U81 cell apoptosis, as well as the protein expression levels of Bax and active Caspase-3 were increased after prazosin treatment (P<0.05). Bcl-2 levels were also decreased after prazosin treatment (P<0.05). Additionally, the expression of phosphorylated (p)-AKT and p-mTOR, P70 and cyclin D1 were decreased in U251 and U81 cells following prazosin treatment (P<0.05). The present study suggested that prazosin may suppress glioblastoma progression by downregulating the activity of the PI3K/AKT/mTOR signaling pathway.

Coronin 3 Promotes the Development of Oncogenic Properties in Glioma Through the Wnt/β-Catenin Signaling Pathway

PURPOSE

Evidence indicates that the actin-binding protein Coronin 3, which is aberrantly expressed in various cancers, is associated with cancer development and progression. However, little is known about the role of Coronin 3 in glioma tumorigenesis. Here, we aimed to explore the biological function and regulatory mechanism of Coronin 3 in glioblastoma (GBM).

MATERIALS AND METHODS

Coronin 3 level in human GBM clinical samples and cell lines was investigated. The shRNA knockdown strategy was used to assess the tumor characteristics of GBM cell lines. The role of β-catenin in Coronin 3-mediated oncogenic phenotypes was evaluated.

RESULTS

Coronin 3 was found to be highly upregulated in glioma cell lines. Furthermore, knockdown of Coronin 3 significantly inhibited the growth of glioma cells both in vivo and in vitro and suppressed the expression of Wnt/β-catenin pathway genes, including β-catenin, Cyclin D1, and c-Myc. Moreover, we demonstrated that Coronin 3 regulates the expression of β-catenin in glioma. Our results revealed that Coronin 3-stimulated tumor growth was β-catenin-dependent.

CONCLUSION

Our study reveals a new molecular mechanism of Coronin 3 in promoting glioma growth and development through regulating the Wnt/β-catenin signaling pathway.

The versatile Kv channels in the nervous system: actions beyond action potentials

Voltage-gated K+ (Kv) channel opening repolarizes excitable cells by allowing K+ efflux. Over the last two decades, multiple Kv functions in the nervous system have been found to be unrelated to or beyond the immediate control of excitability, such as shaping action potential contours or regulation of inter-spike frequency. These functions include neuronal exocytosis and neurite formation, neuronal cell death, regulation of astrocyte Ca2+, glial cell and glioma proliferation. Some of these functions have been shown to be independent of K+ conduction, that is, they suggest the non-canonical functions of Kv channels. In this review, we focus on neuronal or glial plasmalemmal Kv channel functions which are unrelated to shaping action potentials or immediate control of excitability. Similar functions in other cell types will be discussed to some extent in appropriate contexts.

Potassium channels and their role in glioma: A mini review

K⁺ channels regulate a multitude of biological processes and play important roles in a variety of diseases by controlling potassium flow across cell membranes. They are widely expressed in the central and peripheral nervous system. As a malignant tumor derived from nerve epithelium, glioma has the characteristics of high incidence, high recurrence rate, high mortality rate, and low cure rate. Since glioma cells show invasive growth, current surgical methods cannot completely remove tumors. Adjuvant chemotherapy is still needed after surgery. Because the blood-brain barrier and other factors lead to a lower effective concentration of chemotherapeutic drugs in the tumor, the recurrence rate of residual lesions is extremely high. Therefore, new therapeutic methods are needed. Numerous studies have shown that different K⁺ channel subtypes are differentially expressed in glioma cells and are involved in the regulation of the cell cycle of glioma cells to arrest them at different stages of the cell cycle. Increasing evidence suggests that K⁺ channels express in glioma cells and regulate glioma cell behaviors such as cell cycle, proliferation and apoptosis. This review article aims to summarize the current knowledge on the function of K⁺ channels in glioma, suggests K⁺ channels participating in the development of glioma.

Conditional KCa3.1-transgene induction in murine skin produces pruritic eczematous dermatitis with severe epidermal hyperplasia and hyperkeratosis

Ion channels have recently attracted attention as potential mediators of skin disease. Here, we explored the consequences of genetically encoded induction of the cell volume-regulating Ca2+-activated KCa3.1 channel (Kcnn4) for murine epidermal homeostasis. Doxycycline-treated mice harboring the KCa3.1+-transgene under the control of the reverse tetracycline-sensitive transactivator (rtTA) showed 800-fold channel overexpression above basal levels in the skin and solid KCa3.1-currents in keratinocytes. This overexpression resulted in epidermal spongiosis, progressive epidermal hyperplasia and hyperkeratosis, itch and ulcers. The condition was accompanied by production of the pro-proliferative and pro-inflammatory cytokines, IL-β1 (60-fold), IL-6 (33-fold), and TNFα (26-fold) in the skin. Treatment of mice with the KCa3.1-selective blocker, Senicapoc, significantly suppressed spongiosis and hyperplasia, as well as induction of IL-β1 (-88%) and IL-6 (-90%). In conclusion, KCa3.1-induction in the epidermis caused expression of pro-proliferative cytokines leading to spongiosis, hyperplasia and hyperkeratosis. This skin condition resembles pathological features of eczematous dermatitis and identifies KCa3.1 as a regulator of epidermal homeostasis and spongiosis, and as a potential therapeutic target.

Role of Infiltrating Microglia/Macrophages in Glioma

In this chapter we describe the state of the art knowledge of the role played by myeloid cells in promoting and supporting the growth and the invasive properties of a deadly brain tumor, glioblastoma. We provide a review of the works describing the intercellular communication among glioma and associated microglia/macrophage cells (GAMs) using in vitro cellular models derived from mice, rats and human patients and in vivo animal models using syngeneic or xenogeneic experimental systems. Special emphasis will be given to 1) the timing alteration of brain microenvironment under the influence of glioma, 2) the bidirectional communication among tumor and GAMs, 3) possible approaches to interfere with or to guide these interactions, with the aim to identify molecular and cellular targets which could revert or delay the vicious cycle that favors tumor biology.

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.

Pharmacology of Small- and Intermediate-Conductance Calcium-Activated Potassium Channels

The three small-conductance calcium-activated potassium (K_Ca2) channels and the related intermediate-conductance K_Ca3.1 channel are voltage-independent K⁺ channels that mediate calcium-induced membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. K_Ca2 and K_Ca3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of K_Ca channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule K_Ca2 and K_Ca3.1 modulators. Finally, we describe the progress that has been made in advancing K_Ca3.1 blockers and K_Ca2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.

KCa3.1 Transgene Induction in Murine Intestinal Epithelium Causes Duodenal Chyme Accumulation and Impairs Duodenal Contractility

The epithelial intermediate-conductance calcium/calmodulin-regulated KCa3.1 channel is considered to be a regulator of intestine function by controlling chloride secretion and water/salt balance. Yet, little is known about the functional importance of KCa3.1 in the intestinal epithelium in vivo. Our objective was to determine the impact of epithelial-specific inducible overexpression of a KCa3.1 transgene (KCa3.1+) and of inducible suppression (KCa3.1−) on intestinal homeostasis and function in mice. KCa3.1 overexpression in the duodenal epithelium of doxycycline (DOX)-treated KCa3.1+ mice was 40-fold above the control levels. Overexpression caused an inflated duodenum and doubling of the chyme content. Histology showed conserved architecture of crypts, villi, and smooth muscle. Unaltered proliferating cell nuclear antigen (PCNA) immune reactivity and reduced amounts of terminal deoxynucleotide transferase mediated X-dUTP nick end labeling (TUNEL)-positive apoptotic cells in villi indicated lower epithelial turnover. Myography showed a reduction in the frequency of spontaneous propulsive muscle contractions with no change in amplitude. The amount of stool in the colon was increased and the frequency of colonic contractions was reduced in KCa3.1+ animals. Senicapoc treatment prevented the phenotype. Suppression of KCa3.1 in DOX-treated KCa3.1− mice caused no overt intestinal phenotype. In conclusion, inducible KCa3.1 overexpression alters intestinal functions by increasing the chyme content and reducing spontaneous contractions and epithelial apoptosis. Induction of epithelial KCa3.1 can play a mechanistic role in the process of adaptation of the intestine.

Radiation Increases Functional KCa3.1 Expression and Invasiveness in Glioblastoma

Glioblastoma (GBM) is a deadly brain tumor, with fast recurrence even after surgical intervention, radio- and chemotherapies. One of the reasons for relapse is the early invasion of surrounding brain parenchyma by GBM, rendering tumor eradication difficult. Recent studies demonstrate that, in addition to eliminate possible residual tumoral cells after surgery, radiation stimulates the infiltrative behavior of GBM cells. The intermediate conductance of Ca²⁺-activated potassium channels (KCa3.1) play an important role in regulating the migration of GBM. Here, we show that high dose radiation of patient-derived GBM cells increases their invasion, and induces the transcription of key genes related to these functions, including the IL-4/IL-4R pair. In addition, we demonstrate that radiation increases the expression of KCa3.1 channels, and that their pharmacological inhibition counteracts the pro-invasive phenotype induced by radiation in tumor cells. Our data describe a possible approach to treat tumor resistance that follows radiation therapy in GBM patients.

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.

Ion Channels in Cancer: Are Cancer Hallmarks Oncochannelopathies?

Genomic instability is a primary cause and fundamental feature of human cancer. However, all cancer cell genotypes generally translate into several common pathophysiological features, often referred to as cancer hallmarks. Although nowadays the catalog of cancer hallmarks is quite broad, the most common and obvious of them are 1) uncontrolled proliferation, 2) resistance to programmed cell death (apoptosis), 3) tissue invasion and metastasis, and 4) sustained angiogenesis. Among the genes affected by cancer, those encoding ion channels are present. Membrane proteins responsible for signaling within cell and among cells, for coupling of extracellular events with intracellular responses, and for maintaining intracellular ionic homeostasis ion channels contribute to various extents to pathophysiological features of each cancer hallmark. Moreover, tight association of these hallmarks with ion channel dysfunction gives a good reason to classify them as special type of channelopathies, namely oncochannelopathies. Although the relation of cancer hallmarks to ion channel dysfunction differs from classical definition of channelopathies, as disease states causally linked with inherited mutations of ion channel genes that alter channel's biophysical properties, in a broader context of the disease state, to which pathogenesis ion channels essentially contribute, such classification seems absolutely appropriate. In this review the authors provide arguments to substantiate such point of view.

Ca2+-activated K+ channels modulate microglia affecting motor neuron survival in hSOD1G93A mice

Recent studies described a critical role for microglia in amyotrophic lateral sclerosis (ALS), where these CNS-resident immune cells participate in the establishment of an inflammatory microenvironment that contributes to motor neuron degeneration. Understanding the mechanisms leading to microglia activation in ALS could help to identify specific molecular pathways which could be targeted to reduce or delay motor neuron degeneration and muscle paralysis in patients. The intermediate-conductance calcium-activated potassium channel KCa3.1 has been reported to modulate the "pro-inflammatory" phenotype of microglia in different pathological conditions. We here investigated the effects of blocking KCa3.1 activity in the hSOD1G93AALS mouse model, which recapitulates many features of the human disease. We report that treatment of hSOD1G93A mice with a selective KCa3.1 inhibitor, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), attenuates the "pro-inflammatory" phenotype of microglia in the spinal cord, reduces motor neuron death, delays onset of muscle weakness, and increases survival. Specifically, inhibition of KCa3.1 channels slowed muscle denervation, decreased the expression of the fetal acetylcholine receptor γ subunit and reduced neuromuscular junction damage. Taken together, these results demonstrate a key role for KCa3.1 in driving a pro-inflammatory microglia phenotype in ALS.

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.