Expression and function of calcium-activated potassium channels in human glioma cells

The therapeutic potential of bee venom-derived Apamin and Melittin conjugates in cancer treatment: A systematic review

The therapeutic potential of bee venom-derived peptides, particularly apamin and melittin, in cancer treatment has garnered significant attention as a promising avenue for advancing oncology. This systematic review examines preclinical studies highlighting the emerging role of these peptides in enhancing cancer therapies. Melittin and apamin, when conjugated with other therapeutic agents or formulated into novel delivery systems, have demonstrated improved efficacy in targeting tumor cells. Key findings indicate that melittin-based conjugates, such as polyethylene glycol (PEG)ylated versions, show potential in enhancing therapeutic outcomes and minimizing toxicity across various cancer models. Similarly, apamin-conjugated formulations have improved the efficacy of established anti-cancer drugs, contributing to enhanced targeting and reduced systemic toxicity. These developments underscore a growing interest in leveraging bee venom-derived peptides as adjuncts in cancer therapy. The integration of these peptides into treatment regimens offers a promising strategy to address current limitations in cancer treatment, such as drug resistance and off-target effects. However, comprehensive validation through clinical trials is essential to confirm their safety and effectiveness in human patients. This review highlights the global emergence of bee venom-derived peptides in cancer treatment, advocating for continued research and development to fully realize their therapeutic potential.

Central nervous system regulation of diffuse glioma growth and invasion: from single unit physiology to circuit remodeling

PURPOSE

Understanding the complex bidirectional interactions between neurons and glioma cells could help to identify new therapeutic targets. Herein, the techniques and application of novel neuroscience tools implemented to study the complex interactions between brain and malignant gliomas, their results, and the potential therapeutic opportunities were reviewed.

METHODS

Literature search was performed on PubMed between 2001 and 2023 using the keywords "glioma", "glioblastoma", "circuit remodeling", "plasticity", "neuron networks" and "cortical networks". Studies including grade 2 to 4 gliomas, diffuse midline gliomas, and diffuse intrinsic pontine gliomas were considered.

RESULTS

Glioma cells are connected through tumour microtubes and form a highly connected network within which pacemaker cells drive tumorigenesis. Unconnected cells have increased invasion capabilities. Glioma cells are also synaptically integrated within neural circuitry. Neurons promote tumour growth via paracrine and direct electrochemical mechanisms, including glutamatergic AMPA-receptors. Increased glutamate release in the tumor microenvironment and loss of peritumoral GABAergic inhibitory interneurons result in network hyperexcitability and secondary epilepsy. Functional imaging, local field potentials and subcortical mapping, performed in awake patients, have defined patterns of malignant circuit remodeling. Glioma-induced remodeling is frequent in language and even motor cortical networks, depending on tumour biological parameters, and influences functional outcomes.

CONCLUSION

These data offer new insights into glioma tumorigenesis. Future work will be needed to understand how tumor intrinsic molecular drivers influence neuron-glioma interactions but also to integrate these results to design new therapeutic options for patients.

The Pentameric Ligand-Gated Ion Channel Family: A New Member of the Voltage Gated Ion Channel Superfamily?

In this report we present seven lines of bioinformatic evidence supporting the conclusion that the Pentameric Ligand-gated Ion Channel (pLIC) Family is a member of the Voltage-gated Ion Channel (VIC) Superfamily. In our approach, we used the Transporter Classification Database (TCDB) as a reference and applied a series of bioinformatic methods to search for similarities between the pLIC family and members of the VIC superfamily. These include: (1) sequence similarity, (2) compatibility of topology and hydropathy profiles, (3) shared domains, (4) conserved motifs, (5) similarity of Hidden Markov Model profiles between families, (6) common 3D structural folds, and (7) clustering analysis of all families. Furthermore, sequence and structural comparisons as well as the identification of a 3-TMS repeat unit in the VIC superfamily suggests that the sixth transmembrane segment evolved into a re-entrant loop. This evidence suggests that the voltage-sensor domain and the channel domain have a common origin. The classification of the pLIC family within the VIC superfamily sheds light onto the topological origins of this family and its evolution, which will facilitate experimental verification and further research into this superfamily by the scientific community.

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.

Oxidative stress and ion channels in neurodegenerative diseases

Numerous neurodegenerative diseases result from altered ion channel function and mutations. The intracellular redox status can significantly alter the gating characteristics of ion channels. Abundant neurodegenerative diseases associated with oxidative stress have been documented, including Parkinson's, Alzheimer's, spinocerebellar ataxia, amyotrophic lateral sclerosis, and Huntington's disease. Reactive oxygen and nitrogen species compounds trigger posttranslational alterations that target specific sites within the subunits responsible for channel assembly. These alterations include the adjustment of cysteine residues through redox reactions induced by reactive oxygen species (ROS), nitration, and S-nitrosylation assisted by nitric oxide of tyrosine residues through peroxynitrite. Several ion channels have been directly investigated for their functional responses to oxidizing agents and oxidative stress. This review primarily explores the relationship and potential links between oxidative stress and ion channels in neurodegenerative conditions, such as cerebellar ataxias and Parkinson's disease. The potential correlation between oxidative stress and ion channels could hold promise for developing innovative therapies for common neurodegenerative diseases.

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.

KCa 2.2 (KCNN2): A physiologically and therapeutically important potassium channel

One group of the K+ ion channels, the small-conductance Ca2+ -activated potassium channels (KCa 2.x, also known as SK channels family), is widely expressed in neurons as well as the heart, endothelial cells, etc. They are named small-conductance Ca2+ -activated potassium channels (SK channels) due to their comparatively low single-channel conductance of about ~10 pS. These channels are insensitive to changes in membrane potential and are activated solely by rises in the intracellular Ca2+ . According to the phylogenic research done on the KCa 2.x channels family, there are three channels' subtypes: KCa 2.1, KCa 2.2, and KCa 2.3, which are encoded by KCNN1, KCNN2, and KCNN3 genes, respectively. The KCa 2.x channels regulate neuronal excitability and responsiveness to synaptic input patterns. KCa 2.x channels inhibit excitatory postsynaptic potentials (EPSPs) in neuronal dendrites and contribute to the medium afterhyperpolarization (mAHP) that follows the action potential bursts. Multiple brain regions, including the hippocampus, express the KCa 2.2 channel encoded by the KCNN2 gene on chromosome 5. Of particular interest, rat cerebellar Purkinje cells express KCa 2.2 channels, which are crucial for various cellular processes during development and maturation. Patients with a loss-of-function of KCNN2 mutations typically exhibit extrapyramidal symptoms, cerebellar ataxia, motor and language developmental delays, and intellectual disabilities. Studies have revealed that autosomal dominant neurodevelopmental movement disorders resembling rodent symptoms are caused by heterozygous loss-of-function mutations, which are most likely to induce KCNN2 haploinsufficiency. The KCa 2.2 channel is a promising drug target for spinocerebellar ataxias (SCAs). SCAs exhibit the dysregulation of firing in cerebellar Purkinje cells which is one of the first signs of pathology. Thus, selective KCa 2.2 modulators are promising potential therapeutics for SCAs.

SPAK-dependent cotransporter activity mediates capillary adhesion and pressure during glioblastoma migration in confined spaces

The invasive potential of glioblastoma cells is attributed to large changes in pressure and volume, driven by diverse elements, including the cytoskeleton and ion cotransporters.  However, how the cell actuates changes in pressure and volume in confinement, and how these changes contribute to invasive motion is unclear. Here, we inhibited SPAK activity, with known impacts on the cytoskeleton and cotransporter activity and explored its role on the migration of glioblastoma cells in confining microchannels to model invasive spread through brain tissue. First, we found that confinement altered cell shape, inducing a transition in morphology that resembled droplet interactions with a capillary vessel, from "wetting" (more adherent) at low confinement, to "nonwetting" (less adherent) at high confinement. This transition was marked by a change from negative to positive pressure by the cells to the confining walls, and an increase in migration speed. Second, we found that the SPAK pathway impacted the migration speed in different ways dependent upon the extent of wetting. For nonwetting cells, SPAK inhibition increased cell-surface tension and cotransporter activity. By contrast, for wetting cells, it also reduced myosin II and YAP phosphorylation. In both cases, membrane-to-cortex attachment is dramatically reduced. Thus, our results suggest that SPAK inhibition differentially coordinates cotransporter and cytoskeleton-induced forces, to impact glioblastoma migration depending on the extent of confinement.

Potassium channels in behavioral brain disorders. Molecular mechanisms and therapeutic potential: A narrative review

Potassium channels (K+-channels) selectively control the passive flow of potassium ions across biological membranes and thereby also regulate membrane excitability. Genetic variants affecting many of the human K+-channels are well known causes of Mendelian disorders within cardiology, neurology, and endocrinology. K+-channels are also primary targets of many natural toxins from poisonous organisms and drugs used within cardiology and metabolism. As genetic tools are improving and larger clinical samples are being investigated, the spectrum of clinical phenotypes implicated in K+-channels dysfunction is rapidly expanding, notably within immunology, neurosciences, and metabolism. K+-channels that previously were considered to be expressed in only a few organs and to have discrete physiological functions, have recently been found in multiple tissues and with new, unexpected functions. The pleiotropic functions and patterns of expression of K+-channels may provide additional therapeutic opportunities, along with new emerging challenges from off-target effects. Here we review the functions and therapeutic potential of K+-channels, with an emphasis on the nervous system, roles in neuropsychiatric disorders and their involvement in other organ systems and diseases.

KCa2 and KCa3.1 Channels in the Airways: A New Therapeutic Target

K⁺ channels are involved in many critical functions in lung physiology. Recently, the family of Ca²⁺-activated K⁺ channels (K_Ca) has received more attention, and a massive amount of effort has been devoted to developing selective medications targeting these channels. Within the family of K_Ca channels, three small-conductance Ca²⁺-activated K⁺ (K_Ca2) channel subtypes, together with the intermediate-conductance K_Ca3.1 channel, are voltage-independent K⁺ channels, and they mediate Ca²⁺-induced membrane hyperpolarization. Many K_Ca2 channel members are involved in crucial roles in physiological and pathological systems throughout the body. In this article, different subtypes of K_Ca2 and K_Ca3.1 channels and their functions in respiratory diseases are discussed. Additionally, the pharmacology of the K_Ca2 and K_Ca3.1 channels and the link between these channels and respiratory ciliary regulations will be explained in more detail. In the future, specific modulators for small or intermediate Ca²⁺-activated K⁺ channels may offer a unique therapeutic opportunity to treat muco-obstructive lung diseases.

Role of Calcium-Activated Potassium Channels in Proliferation, Migration and Invasion of Human Chronic Myeloid Leukemia K562 Cells

Calcium-activated potassium channels (KCa) are important participants in calcium signaling pathways due to their ability to be activated by an increase in intracellular free calcium concentration. KCa channels are involved in the regulation of cellular processes in both normal and pathophysiological conditions, including oncotransformation. Previously, using patch-clamp, we registered the KCa currents in the plasma membrane of human chronic myeloid leukemia K562 cells, whose activity was controlled by local Ca²⁺ entry via mechanosensitive calcium-permeable channels. Here, we performed the molecular and functional identification of KCa channels and have uncovered their role in the proliferation, migration and invasion of K562 cells. Using a combined approach, we identified the functional activity of SK2, SK3 and IK channels in the plasma membrane of the cells. Selective SK and IK channel inhibitors, apamin and TRAM-34, respectively, reduced the proliferative, migratory and invasive capabilities of human myeloid leukemia cells. At the same time, the viability of K562 cells was not affected by KCa channel inhibitors. Ca²⁺ imaging showed that both SK and IK channel inhibitors affect Ca²⁺ entry and this could underlie the observed suppression of pathophysiological reactions of K562 cells. Our data imply that SK/IK channel inhibitors could be used to slow down the proliferation and spreading of chronic myeloid leukemia K562 cells that express functionally active KCa channels in the plasma membrane.

Co-dependent regulation of p-BRAF and potassium channel KCNMA1 levels drives glioma progression

BRAF mutations have been found in gliomas which exhibit abnormal electrophysiological activities, implying their potential links with the ion channel functions. In this study, we identified the Drosophila potassium channel, Slowpoke (Slo), the ortholog of human KCNMA1, as a critical factor involved in dRafGOF glioma progression. Slo was upregulated in dRafGOF glioma. Knockdown of slo led to decreases in dRafGOF levels, glioma cell proliferation, and tumor-related phenotypes. Overexpression of slo in glial cells elevated dRaf expression and promoted cell proliferation. Similar mutual regulations of p-BRAF and KCNMA1 levels were then recapitulated in human glioma cells with the BRAF mutation. Elevated p-BRAF and KCNMA1 were also observed in HEK293T cells upon the treatment of 20 mM KCl, which causes membrane depolarization. Knockdown KCNMA1 in these cells led to a further decrease in cell viability. Based on these results, we conclude that the levels of p-BRAF and KCNMA1 are co-dependent and mutually regulated. We propose that, in depolarized glioma cells with BRAF mutations, high KCNMA1 levels act to repolarize membrane potential and facilitate cell growth. Our study provides a new strategy to antagonize the progression of gliomas as induced by BRAF mutations.

Ion Channels in Gliomas-From Molecular Basis to Treatment

Ion channels provide the basis for the nervous system's intrinsic electrical activity. Neuronal excitability is a characteristic property of neurons and is critical for all functions of the nervous system. Glia cells fulfill essential supportive roles, but unlike neurons, they also retain the ability to divide. This can lead to uncontrolled growth and the formation of gliomas. Ion channels are involved in the unique biology of gliomas pertaining to peritumoral pathology and seizures, diffuse invasion, and treatment resistance. The emerging picture shows ion channels in the brain at the crossroads of neurophysiology and fundamental pathophysiological processes of specific cancer behaviors as reflected by uncontrolled proliferation, infiltration, resistance to apoptosis, metabolism, and angiogenesis. Ion channels are highly druggable, making them an enticing therapeutic target. Targeting ion channels in difficult-to-treat brain tumors such as gliomas requires an understanding of their extremely heterogenous tumor microenvironment and highly diverse molecular profiles, both representing major causes of recurrence and treatment resistance. In this review, we survey the current knowledge on ion channels with oncogenic behavior within the heterogeneous group of gliomas, review ion channel gene expression as genomic biomarkers for glioma prognosis and provide an update on therapeutic perspectives for repurposed and novel ion channel inhibitors and electrotherapy.

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.

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.

Relevance of Abnormal KCNN1 Expression and Osmotic Hypersensitivity in Ewing Sarcoma

Ewing sarcoma (EwS) is a rare and highly malignant bone tumor occurring mainly in childhood and adolescence. Physiologically, the bone is a central hub for Ca2+ homeostasis, which is severely disturbed by osteolytic processes in EwS. Therefore, we aimed to investigate how ion transport proteins involved in Ca2+ homeostasis affect EwS pathophysiology. We characterized the expression of 22 candidate genes of Ca2+-permeable or Ca2+-regulated ion channels in three EwS cell lines and found the Ca2+-activated K+ channel KCa2.1 (KCNN1) to be exceptionally highly expressed. We revealed that KCNN1 expression is directly regulated by the disease-driving oncoprotein EWSR1-FL1. Due to its consistent overexpression in EwS, KCNN1 mRNA could be a prognostic marker in EwS. In a large cohort of EwS patients, however, KCNN1 mRNA quantity does not correlate with clinical parameters. Several functional studies including patch clamp electrophysiology revealed no evidence for KCa2.1 function in EwS cells. Thus, elevated KCNN1 expression is not translated to KCa2.1 channel activity in EwS cells. However, we found that the low K+ conductance of EwS cells renders them susceptible to hypoosmotic solutions. The absence of a relevant K+ conductance in EwS thereby provides an opportunity for hypoosmotic therapy that can be exploited during tumor surgery.

Calcium-Related Gene Signatures May Predict Prognosis and Level of Immunosuppression in Gliomas

Gliomas are the most common primary brain cancer. While it has been known that calcium-related genes correlate with gliomagenesis, the relationship between calcium-related genes and glioma prognosis remains unclear. We assessed TCGA datasets of mRNA expressions with differentially expressed genes (DEGs) and enrichment analysis to specifically screen for genes that regulate or are affected by calcium levels. We then correlated the identified calcium-related genes with unsupervised/supervised learning to classify glioma patients into 2 risk groups. We also correlated our identified genes with immune signatures. As a result, we discovered 460 calcium genes and 35 calcium key genes that were associated with OS. There were 13 DEGs between Clusters 1 and 2 with different OS. At the same time, 10 calcium hub genes (CHGs) signature model were constructed using supervised learning, and the prognostic risk scores of the 3 cohorts of samples were calculated. The risk score was confirmed as an independent predictor of prognosis. Immune enrichment analysis revealed an immunosuppressive tumor microenvironment with upregulation of checkpoint markers in the high-risk group. Finally, a nomogram was generated with risk scores and other clinical prognostic independent indicators to quantify prognosis. Our findings suggest that calcium-related gene expression patterns could be applicable to predict prognosis and predict levels of immunosuppression.

TRPC6 interacted with KCa1.1 channels to regulate the proliferation and apoptosis of glioma cells

Malignant glioma is the most aggressive and deadliest brain malignancy. TRPC6 and K_Ca1.1, two ion channels, have been considered as potential therapeutic targets for malignant glioma treatment. TRPC6, a Ca²⁺-permeable channel, plays a vital role in promoting tumorigenesis and the progression of glioma. K_Ca1.1, a large-conductance Ca²⁺-activated channel, is also involved in growth and migration of glioma. However, the underlying mechanism by which these two ion channels promote glioma progression was unclear. In our study, we found that TRPC6 upregulated the expression of K_Ca1.1, while the immunoprecipitation analysis also showed that TRPC6 interacts with K_Ca1.1 channels in glioma cells. The currents of K_Ca1.1 recorded by the whole-cell patch clamp technique were increased by TRPC6 in glioma cells, suggesting that TRPC6 can provide a Ca²⁺ source for the activation of K_Ca1.1 channels. It was also suggested that TRPC6 regulates the proliferation and apoptosis of glioma cells through K_Ca1.1 channels in vitro. Therefore, C6-bearing glioma rats were established to validate the results in vitro. After the administration of paxilline (a specific inhibitor of K_Ca1.1 channels), TRPC6-dependent growth of glioma was inhibited in vivo. We also found that TRPC6 enhanced co-expression with K_Ca1.1 in glioma. These all suggested that TRPC6/K_Ca1.1 signal plays a role in promoting the growth of glioma. Our results provided new evidence for TRPC6 and K_Ca1.1 as potential targets for glioma treatment.

Alterations of Ion Homeostasis in Cancer Metastasis: Implications for Treatment

We have previously reported that metastases from all malignancies are characterized by a core program of gene expression that suppresses extracellular matrix interactions, induces vascularization/tissue remodeling, activates the oxidative metabolism, and alters ion homeostasis. Among these features, the least elucidated component is ion homeostasis. Here we review the literature with the goal to infer a better mechanistic understanding of the progression-associated ionic alterations and identify the most promising drugs for treatment. Cancer metastasis is accompanied by skewing in calcium, zinc, copper, potassium, sodium and chloride homeostasis. Membrane potential changes and water uptake through Aquaporins may also play roles. Drug candidates to reverse these alterations are at various stages of testing, with some having entered clinical trials. Challenges to their utilization comprise differences among tumor types and the involvement of multiple ions in each case. Further, adverse effects may become a concern, as channel blockers, chelators, or supplemented ions will affect healthy and transformed cells alike.

Therapeutic targeting of membrane-associated proteins in central nervous system tumors

The activity of the most complex system, the central nervous system (CNS) is profoundly regulated by a huge number of membrane-associated proteins (MAP). A minor change stimulates immense chemical changes and the elicited response is organized by MAP, which acts as a receptor of that chemical or channel enabling the flow of ions. Slight changes in the activity or expression of these MAPs lead to severe consequences such as cognitive disorders, memory loss, or cancer. CNS tumors are heterogeneous in nature and hard-to-treat due to random mutations in MAPs; like as overexpression of EGFRvIII/TGFβR/VEGFR, change in adhesion molecules α5β3 integrin/SEMA3A, imbalance in ion channel proteins, etc. Extensive research is under process for developing new therapeutic approaches using these proteins such as targeted cytotoxic radiotherapy, drug-delivery, and prodrug activation, blocking of receptors like GluA1, developing viral vector against cell surface receptor. The combinatorial approach of these strategies along with the conventional one might be more potential. Henceforth, our review focuses on in-depth analysis regarding MAPs aiming for a better understanding for developing an efficient therapeutic approach for targeting CNS tumors.

Minor Allele Frequencies and Molecular Pathways Differences for SNPs Associated with Amyotrophic Lateral Sclerosis in Subjects Participating in the UKBB and 1000 Genomes Project

Amyotrophic lateral sclerosis (ALS) is a complex disease with a late onset and is characterized by the progressive loss of muscular and respiratory functions. Although recent studies have partially elucidated ALS's mechanisms, many questions remain such as what the most important molecular pathways involved in ALS are and why there is such a large difference in ALS onset among different populations. In this study, we addressed this issue with a bioinformatics approach, using the United Kingdom Biobank (UKBB) and the European 1000 Genomes Project (1KG) in order to analyze the most ALS-representative single nucleotide polymorphisms (SNPs) that differ for minor allele frequency (MAF) between the United Kingdom population and some European populations including Finnish in Finland, Iberian population in Spain, and Tuscans in Italy. We found 84 SNPs associated with 46 genes that are involved in different pathways including: "Ca²⁺ activated K⁺ channels", "cGMP effects", "Nitric oxide stimulates guanylate cyclase", "Proton/oligopeptide cotransporters", and "Signaling by MAPK mutants". In addition, we revealed that 83% of the 84 SNPs can alter transcription factor-motives binding sites of 224 genes implicated in "Regulation of beta-cell development", "Transcription-al regulation by RUNX3", "Transcriptional regulation of pluripotent stem cells", and "FOXO-mediated transcription of cell death genes". In conclusion, the genes and pathways analyzed could explain the cause of the difference of ALS onset.

Identification of CRYAB+ KCNN3+ SOX9+ Astrocyte-Like and EGFR+ PDGFRA+ OLIG1+ Oligodendrocyte-Like Tumoral Cells in Diffuse IDH1-Mutant Gliomas and Implication of NOTCH1 Signalling in Their Genesis

Simple Summary

Diffuse grade II IDH-mutant gliomas are rare brain tumors mainly affecting young patients. These tumors are composed of different populations of tumoral cells. Little is known of these cells and how they are generated. These different cells may show different sensitivity to treatments, so our aim was to study them in detail by directly using patient resections. We identified two clearly distinct tumoral populations and defined reliable markers for them. We also uncovered part of the molecular mechanisms that generate them. Finally, we found that the two cell types have different electrical activity. This article provides unique data and new issues on these rare tumors, which need to be further investigated to develop innovative treatments.

Abstract

Diffuse grade II IDH-mutant gliomas are slow-growing brain tumors that progress into high-grade gliomas. They present intratumoral cell heterogeneity, and no reliable markers are available to distinguish the different cell subtypes. The molecular mechanisms underlying the formation of this cell diversity is also ill-defined. Here, we report that SOX9 and OLIG1 transcription factors, which specifically label astrocytes and oligodendrocytes in the normal brain, revealed the presence of two largely nonoverlapping tumoral populations in IDH1-mutant oligodendrogliomas and astrocytomas. Astrocyte-like SOX9⁺ cells additionally stained for APOE, CRYAB, ID4, KCNN3, while oligodendrocyte-like OLIG1⁺ cells stained for ASCL1, EGFR, IDH1, PDGFRA, PTPRZ1, SOX4, and SOX8. GPR17, an oligodendrocytic marker, was expressed by both cells. These two subpopulations appear to have distinct BMP, NOTCH1, and MAPK active pathways as stainings for BMP4, HEY1, HEY2, p-SMAD1/5 and p-ERK were higher in SOX9⁺ cells. We used primary cultures and a new cell line to explore the influence of NOTCH1 activation and BMP treatment on the IDH1-mutant glioma cell phenotype. This revealed that NOTCH1 globally reduced oligodendrocytic markers and IDH1 expression while upregulating APOE, CRYAB, HEY1/2, and an electrophysiologically-active Ca²⁺-activated apamin-sensitive K⁺ channel (KCNN3/SK3). This was accompanied by a reduction in proliferation. Similar effects of NOTCH1 activation were observed in nontumoral human oligodendrocytic cells, which additionally induced strong SOX9 expression. BMP treatment reduced OLIG1/2 expression and strongly upregulated CRYAB and NOGGIN, a negative regulator of BMP. The presence of astrocyte-like SOX9⁺ and oligodendrocyte-like OLIG1⁺ cells in grade II IDH1-mutant gliomas raises new questions about their role in the pathology.

Cilostazol eliminates radiation-resistant glioblastoma by re-evoking big conductance calcium-activated potassium channel activity

In spite of radio- and chemotherapy, glioblastoma (GBM) develops therapeutic resistance leading to recurrence and poor prognosis. Therefore, understanding the underlying mechanisms of resistance is important to improve the treatment of GBM. To this end, we developed a radiation-resistant cell model by exposure to consecutive periods of irradiation. Simultaneously, single high-dose irradiation was introduced to determine "when" GBM developed consecutive irradiation-induced resistance (CIIR). We found that CIIR promoted TGF-β secretion, activated pro-survival Akt, and downregulated p21 in a p53-independent manner. Furthermore, CIIR upregulated multidrug-resistant proteins, resulting in temozolomide resistance. CIIR GBM also enhanced cell mobility and accelerated cell proliferation. The big-conductance calcium-activated potassium channel (BK channel) is highly expressed and activated in GBM. However, CIIR diminishes BK channel activity in an expression-independent manner. Cilostazol is a phosphodiesterase-3 inhibitor for the treatment of intermittent claudication and was able to reverse CIIR-induced BK channel inactivation. Paxilline, a BK channel blocker, promoted cell migration and proliferation in parental GBM cells. In contrast, Cilostazol inhibited CIIR-induced cell motility, proliferation, and the ability to form tumor spheres. Moreover, we established a radiation-resistant GBM in vivo model by intracranially injecting CIIR GBM cells into the brains of NOD/SCID mice. We found that Cilostazol delayed tumor in vivo growth and prolonged survival. As such, inactivation of the BK channel assists GBM in developing radiation resistance. Accordingly, restoring BK channel activity may be an effective strategy to improve therapeutic efficacy, and cilostazol could be repurposed to treat GBM.

Deeper and Deeper on the Role of BK and Kir4.1 Channels in Glioblastoma Invasiveness: A Novel Summative Mechanism?

In the last decades, increasing evidence has revealed that a large number of channel protein and ion pumps exhibit impaired expression in cancers. This dysregulation is responsible for high proliferative rates as well as migration and invasiveness, reflected in the recently coined term oncochannelopathies. In glioblastoma (GBM), the most invasive and aggressive primary brain tumor, GBM cells modify their ionic equilibrium in order to change their volume as a necessary step prior to migration. This mechanism involves increased expression of BK channels and downregulation of the normally widespread Kir4.1 channels, as noted in GBM biopsies from patients. Despite a large body of work implicating BK channels in migration in response to an artificial intracellular calcium rise, little is known about how this channel acts in GBM cells at resting membrane potential (RMP), as compared to other channels that are constitutively open, such as Kir4.1. In this review we propose that a residual fraction of functionally active Kir4.1 channels mediates a small, but continuous, efflux of potassium at the more depolarized RMP of GBM cells. In addition, coinciding with transient membrane deformation and the intracellular rise in calcium concentration, brief activity of BK channels can induce massive and rapid cytosolic water loss that reduces cell volume (cell shrinkage), a necessary step for migration within the brain parenchyma.

Molecular Choreography and Structure of Ca2+ Release-Activated Ca2+ (CRAC) and KCa2+ Channels and Their Relevance in Disease with Special Focus on Cancer

Ca2+ ions play a variety of roles in the human body as well as within a single cell. Cellular Ca2+ signal transduction processes are governed by Ca2+ sensing and Ca2+ transporting proteins. In this review, we discuss the Ca2+ and the Ca2+-sensing ion channels with particular focus on the structure-function relationship of the Ca2+ release-activated Ca2+ (CRAC) ion channel, the Ca2+-activated K+ (KCa2+) ion channels, and their modulation via other cellular components. Moreover, we highlight their roles in healthy signaling processes as well as in disease with a special focus on cancer. As KCa2+ channels are activated via elevations of intracellular Ca2+ levels, we summarize the current knowledge on the action mechanisms of the interplay of CRAC and KCa2+ ion channels and their role in cancer cell development.

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 transporters in microglial function in physiology and brain diseases

Microglial cells interact with all components of the central nervous system (CNS) and are increasingly recognized to play essential roles during brain development, homeostasis and disease pathologies. Functions of microglia include maintaining tissue integrity, clearing cellular debris and dead neurons through the process of phagocytosis, and providing tissue repair by releasing anti-inflammatory cytokines and neurotrophic factors. Changes of microglial ionic homeostasis (Na⁺, Ca²⁺, K⁺, H⁺, Cl^-) are important for microglial activation, including proliferation, migration, cytokine release and reactive oxygen species production, etc. These are mediated by ion channels and ion transporters in microglial cells. Here, we review the current knowledge about the role of major microglial ion channels and transporters, including several types of Ca²⁺ channels (store-operated Ca²⁺ entry (SOCE) channels, transient receptor potential (TRP) channels and voltage-gated Ca²⁺ channels (VGCCs)) and Na⁺ channels (voltage-gated Na⁺ channels (Nav) and acid-sensing ion channels (ASICs)), K⁺ channels (inward rectifier K⁺ channels (K_ir), voltage-gated K⁺ channels (K_V) and calcium-activated K⁺ channels (K_Ca)), proton channels (voltage-gated proton channel (Hv1)), and Cl^- channels (volume (or swelling)-regulated Cl^- channels (VRCCs) and chloride intracellular channels (CLICs)). In addition, ion transporter proteins such as Na⁺/Ca²⁺ exchanger (NCX), Na⁺-K⁺-Cl^- cotransporter (NKCC1), and Na⁺/H⁺ exchanger (NHE1) are also involved in microglial function in physiology and brain diseases. We discussed microglial activation and neuroinflammation in relation to the ion channel/transporter stimulation under brain disease conditions and therapeutic aspects of targeting microglial ion channels/transporters for neurodegenerative disease, ischemic stroke, traumatic brain injury and neuropathic pain.

Dynamical diversity of mitochondrial BK channels located in different cell types

Mitochondrial large-conductance voltage- and Ca²⁺-activated potassium channels (mitoBK) exhibit substantial similarities in their physiology regardless of the channel's location. Nevertheless, depending on the cell type, composition of membranes can vary, and mitoBK channels can be expressed in different splice variants as well as they can be co-assembled with different types of auxiliary β subunits. These factors can modulate their voltage- and Ca²⁺-sensitivity, and single-channel current kinetics. It is still an open question to what extent the mentioned factors can affect the complexity of the conformational dynamics of the mitoBK channel gating. In this work the dynamical diversity of mitoBK channels from different cell types was unraveled by the use of nonlinear methods of analysis: multifractal detrended fluctuation analysis (MFDFA) and multiscale entropy (MSE). These techniques were applied to the experimental series of single channel currents. It turns out that the differences in the mitoBK expression systems influence gating machinery by changing the scheme of switching between the stable channel conformations, and affecting the average number of available channel conformations (this effect is visible for mitoBK channels in glioblastoma cells). The obtained results suggest also that a pathological dynamics can be represented by signals of relatively low complexity (low MSE of the mitoBK channel gating in glioblastoma).

Ion Channels as Therapeutic Targets in High Grade Gliomas

Simple Summary

Glioblastoma multiforme is an aggressive grade IV lethal brain tumour with a median survival of 14 months. Despite surgery to remove the tumour, and subsequent concurrent chemotherapy and radiotherapy, there is little in terms of effective treatment options. Because of this, exploring new treatment avenues is vital. Brain tumours are intrinsically electrically active; expressing unique patterns of ion channels, and this is a characteristic we can exploit. Ion channels are specialised proteins in the cell’s membrane that allow for the passage of positive and negatively charged ions in and out of the cell, controlling membrane potential. Membrane potential is a crucial biophysical signal in normal and cancerous cells. Research has identified that specific classes of ion channels not only move the cell through its cell cycle, thus encouraging growth and proliferation, but may also be essential in the development of brain tumours. Inhibition of sodium, potassium, calcium, and chloride channels has been shown to reduce the capacity of glioblastoma cells to grow and invade. Therefore, we propose that targeting ion channels and repurposing commercially available ion channel inhibitors may hold the key to new therapeutic avenues in high grade gliomas.

Abstract

Glioblastoma multiforme (GBM) is a lethal brain cancer with an average survival of 14–15 months even with exhaustive treatment. High grade gliomas (HGG) represent the leading cause of CNS cancer-related death in children and adults due to the aggressive nature of the tumour and limited treatment options. The scarcity of treatment available for GBM has opened the field to new modalities such as electrotherapy. Previous studies have identified the clinical benefit of electrotherapy in combination with chemotherapeutics, however the mechanistic action is unclear. Increasing evidence indicates that not only are ion channels key in regulating electrical signaling and membrane potential of excitable cells, they perform a crucial role in the development and neoplastic progression of brain tumours. Unlike other tissue types, neural tissue is intrinsically electrically active and reliant on ion channels and their function. Ion channels are essential in cell cycle control, invasion and migration of cancer cells and therefore present as valuable therapeutic targets. This review aims to discuss the role that ion channels hold in gliomagenesis and whether we can target and exploit these channels to provide new therapeutic targets and whether ion channels hold the mechanistic key to the newfound success of electrotherapies.

Differences in Gating Dynamics of BK Channels in Cellular and Mitochondrial Membranes from Human Glioblastoma Cells Unraveled by Short- and Long-Range Correlations Analysis

The large-conductance voltage- and Ca2+-activated K+ channels (BK) are encoded in humans by the Kcnma1 gene. Nevertheless, BK channel isoforms in different locations can exhibit functional heterogeneity mainly due to the alternative splicing during the Kcnma1 gene transcription. Here, we would like to examine the existence of dynamic diversity of BK channels from the inner mitochondrial and cellular membrane from human glioblastoma (U-87 MG). Not only the standard characteristics of the spontaneous switching between the functional states of the channel is discussed, but we put a special emphasis on the presence and strength of correlations within the signal describing the single-channel activity. The considered short- and long-range memory effects are here analyzed as they can be interpreted in terms of the complexity of the switching mechanism between stable conformational states of the channel. We calculate the dependencies of mean dwell-times of (conducting/non-conducting) states on the duration of the previous state, Hurst exponents by the rescaled range R/S method and detrended fluctuation analysis (DFA), and use the multifractal extension of the DFA (MFDFA) for the series describing single-channel activity. The obtained results unraveled statistically significant diversity in gating machinery between the mitochondrial and cellular BK channels.

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.

In silico and in vitro analysis of cation-activated potassium channels in human corneal endothelial cells

The corneal endothelium is the inner cell monolayer involved in the maintenance of corneal transparence by the generation of homeostatic dehydration. The glycosaminoglycans of the corneal stroma develop a continuous swelling pressure that should be counteracted by the corneal endothelial cells through active transport mechanisms to move the water to the anterior chamber. Protein transporters for sodium (Na⁺), potassium (K⁺), chloride (Cl^-) and bicarbonate (HCO₃^-) are involved in this endothelial "pump function", however despite its physiological importance, the efflux mechanism is not completely understood. There is experimental evidence describing transendothelial diffusion of water in the absence of osmotic gradients. Therefore, it is important to get a deeper understanding of alternative models that drive the fluid transport across the endothelium such as the electrochemical gradients. Three transcriptomic datasets of the corneal endothelium were used in this study to analyze the expression of genes that encode proteins that participate in the transport and the reestablishment of the membrane potential across the semipermeable endothelium. Subsequently, the expression of the identified channels was validated in vitro both at mRNA and protein levels. The results of this study provide the first evidence of the expression of KCNN2, KCNN3 and KCNT2 genes in the corneal endothelium. Differences among the level of expression of KCNN2, KCNT2 and KCNN4 genes were found in a differentially expressed gene analysis of the dataset. Taken together these results underscore the potential importance of the ionic channels in the pathophysiology of corneal diseases. Moreover, we elucidate novel mechanisms that might be involved in the pivotal dehydrating function of the endothelium and in others physiologic functions of these cells using in silico pathways analysis.

Multifractal Properties of BK Channel Currents in Human Glioblastoma Cells

Potassium channels play an important physiological role in glioma cells. In particular, voltage- and Ca2+-activated large-conductance BK channels (gBK in gliomas) are involved in the intensive growth and extensive migrating behavior of the mentioned tumor cells; thus, they may be considered as a drug target for the therapeutic treatment of glioblastoma. To enable appropriate drug design, molecular mechanisms of gBK channel activation by diverse stimuli should be unraveled as well as the way that the specific conformational states of the channel relate to its functional properties (conducting/nonconducting). There is an open debate about the actual mechanism of BK channel gating, including the question of how the channel proteins undergo a range of conformational transitions when they flicker between nonconducting (functionally closed) and conducting (open) states. The details of channel conformational diffusion ought to have its representation in the properties of the experimental signal that describes the ion-channel activity. Nonlinear methods of analysis of experimental nonstationary series can be useful for observing the changes in the number of channel substates available from geometrical and energetic points of view at given external conditions. In this work, we analyze whether the multifractal properties of the activity of glioblastoma BK channels depend on membrane potential, and which states, conducting or nonconducting, affect the total signal to a larger extent. With this aim, we carried out patch-clamp experiments at different levels of membrane hyper- and depolarization. The obtained time series of single channel currents were analyzed using the multifractal detrended fluctuation analysis (MFDFA) method in a standard form and incorporating focus-based multifractal (FMF) formalism. Thus, we show the applicability of a modified MFDFA technique in the analysis of an experimental patch-clamp time series. The obtained results suggest that membrane potential strongly affects the conformational space of the gBK channel proteins and the considered process has nonlinear multifractal characteristics. These properties are the inherent features of the analyzed signals due to the fact that the main tendencies vanish after shuffling the data.

SK channel activation potentiates auranofin-induced cell death in glio- and neuroblastoma cells

Brain tumours are among the deadliest tumours being highly resistant to currently available therapies. The proliferative behaviour of gliomas is strongly influenced by ion channel activity. Small-conductance calcium-activated potassium (SK/K_Ca) channels are a family of ion channels that are associated with cell proliferation and cell survival. A combined treatment of classical anti-cancer agents and pharmacological SK channel modulators has not been addressed yet. We used the gold-derivative auranofin to induce cancer cell death by targeting thioredoxin reductases in combination with CyPPA to activate SK channels in neuro- and glioblastoma cells. Combined treatment with auranofin and CyPPA induced massive mitochondrial damage and potentiated auranofin-induced toxicity in neuroblastoma cells in vitro. In particular, mitochondrial integrity, respiration and associated energy generation were impaired. These findings were recapitulated in patient-derived glioblastoma neurospheres yet not observed in non-cancerous HT22 cells. Taken together, integrating auranofin and SK channel openers to affect mitochondrial health was identified as a promising strategy to increase the effectiveness of anti-cancer agents and potentially overcome resistance.

Potassium and Sodium Channels and the Warburg Effect: Biophysical Regulation of Cancer Metabolism

Ion channels are progressively emerging as a novel class of membrane proteins expressed in several types of human cancers and regulating the different aspects of cancer cell behavior. The metabolism of cancer cells, usually composed by a variable proportion of respiration, glycolysis, and glutaminolysis, leads to the excessive production of acidic metabolic products. The presence of these acidic metabolites inside the cells results in intracellular acidosis, and hinders survival and proliferation. For this reason, tumor cells activate mechanisms of pH control that produce a constitutive increase in intracellular pH (pHi) that is more acidic than the extracellular pH (pHe). This condition forms a perfect microenvironment for metastatic progression and may be permissive for some of the acquired characteristics of tumors. Recent analyses have revealed complex interconnections between oncogenic activation, ion channels, hypoxia signaling and metabolic pathways that are dysregulated in cancer. Here, we summarize the molecular mechanisms of the Warburg effect and hypoxia and their association. Moreover, we discuss the recent findings concerning the involvement of ion channels in various aspects of the Warburg effect and hypoxia, focusing on the role of Na+ and K+ channels in hypoxic and metabolic reprogramming in cancer.

The role of caveolin-1 in tumors of the brain - functional and clinical implications

BACKGROUND

Caveolin-1 (cav-1) is the major structural protein of caveolae, the flask-shaped invaginations of the plasma membrane mainly involved in cell signaling. Today, cav-1 is believed to play a role in a variety of disease processes including cancer, owing to the variations of its expression in association with tumor progression, invasive behavior, metastasis and therapy resistance. Since first detected in the brain, a number of studies has particularly focused on the role of cav-1 in the various steps of brain tumorigenesis. In this review, we discuss the different roles of cav-1 and its contributions to the molecular mechanisms underlying the pathobiology and natural behavior of brain tumors including glial, non-glial and metastatic subtypes. These contributions could be attributed to its co-localization with important players in tumorigenesis within the lipid-enriched domains of the plasma membrane. In that regard, the ability of cav-1 to interact with various cell signaling molecules as well as the impact of caveolae depletion on important pathways acting in brain tumor pathogenesis are noteworthy. We also discuss conversant causes hampering the treatment of malignant glial tumors such as limited transport of chemotherapeutics across the blood tumor barrier and resistance to chemoradiotherapy, by focusing on the molecular fundamentals involving cav-1 participation.

CONCLUSIONS

Cav-1 has the potential to pivot the molecular basis underlying the pathobiology of brain tumors, particularly the malignant glial subtype. In addition, the regulatory effect of cav-1-dependent and caveola-mediated transcellular transport on the permeability of the blood tumor barrier could be of benefit to overcome the restricted transport across brain barriers when applying chemotherapeutics. The association of cav-1 with tumors of the brain other than malignant gliomas deserves to be underlined, as well given the evidence suggesting its potential in predicting tumor grade and recurrence rates together with determining patient prognosis in oligodendrogliomas, ependymomas, meningiomas, vestibular schwannomas and brain metastases.

Mechanosensitivity of the BK Channels in Human Glioblastoma Cells: Kinetics and Dynamical Complexity

BK channels are potassium selective and exhibit large single-channel conductance. They play an important physiological role in glioma cells: they are involved in cell growth and extensive migrating behavior. Due to the fact that these processes are accompanied by changes in membrane stress, here, we examine mechanosensitive properties of BK channels from human glioblastoma cells (gBK channels). Experiments were performed by the use of patch-clamp method on excised patches under membrane suction (0-40 mmHg) at membrane hyper- and depolarization. We have also checked whether channel's activity is affected by possible changes of membrane morphology after a series of long impulses of suction. Unconventionally, we also analyzed internal structure of the experimental signal to make inferences about conformational dynamics of the channel in stressed membranes. We examined the fractal long-range memory effect (by R/S Hurst analysis), the rate of changes in information by sample entropy, or correlation dimension, and characterize its complexity over a range of scales by the use of Multiscale Entropy method. The obtained results indicate that gBK channels are mechanosensitive at membrane depolarization and hyperpolarization. Prolonged suction of membrane also influences open-closed fluctuations-it decreases channel's activity at membrane hyperpolarization and, in contrary, increases channel's activity at high voltages. Both membrane strain and its "fatigue" reduce dynamical complexity of channel gating, which suggest decrease in the number of available open conformations of channel protein in stressed membranes.

Functional Roles of the Ca2+-activated K+ Channel, KCa3.1, in Brain Tumors

BACKGROUND

Glioblastoma is the most aggressive and deadly brain tumor, with low disease-free period even after surgery and combined radio and chemotherapies. Among the factors contributing to the devastating effect of this tumor in the brain are the elevated proliferation and invasion rate, and the ability to induce a local immunosuppressive environment. The intermediateconductance Ca2+-activated K+ channel KCa3.1 is expressed in glioblastoma cells and in tumorinfiltrating cells.

METHODS

We first describe the researches related to the role of KCa3.1 channels in the invasion of brain tumor cells and the regulation of cell cycle. In the second part we review the involvement of KCa3.1 channel in tumor-associated microglia cell behaviour.

RESULTS

In tumor cells, the functional expression of KCa3.1 channels is important to substain cell invasion and proliferation. In tumor infiltrating cells, KCa3.1 channel activity is required to regulate their activation state. Interfering with KCa3.1 activity can be an adjuvant therapeutic approach in addition to classic chemotherapy and radiotherapy, to counteract tumor growth and prolong patient's survival.

CONCLUSION

In this mini-review we discuss the evidence of the functional roles of KCa3.1 channels in glioblastoma biology.

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.

BK channels blockage inhibits hypoxia-induced migration and chemoresistance to cisplatin in human glioblastoma cells

Glioblastoma (GBM) cells express large-conductance, calcium-activated potassium (BK) channels, whose activity is important for several critical aspects of the tumor, such as migration/invasion and cell death. GBMs are also characterized by a heavy hypoxic microenvironment that exacerbates tumor aggressiveness. Since hypoxia modulates the activity of BK channels in many tissues, we hypothesized that a hypoxia-induced modulation of these channels may contribute to the hypoxia-induced GBM aggressiveness. In U87-MG cells, hypoxia induced a functional upregulation of BK channel activity, without interfering with their plasma membrane expression. Wound healing and transwell migration assays showed that hypoxia increased the migratory ability of U87-MG cells, an effect that could be prevented by BK channel inhibition. Toxicological experiments showed that hypoxia was able to induce chemoresistance to cisplatin in U87-MG cells and that the inhibition of BK channels prevented the hypoxia-induced chemoresistance. Clonogenic assays showed that BK channels are also used to increase the clonogenic ability of U87-MG GBM cells in presence, but not in absence, of cisplatin. BK channels were also found to be essential for the hypoxia-induced de-differentiation of GBM cells. Finally, using immunohistochemical analysis, we highlighted the presence of BK channels in hypoxic areas of human GBM tissues, suggesting that our findings may have physiopathological relevance in vivo. In conclusion, our data show that BK channels promote several aspects of the aggressive potential of GBM cells induced by hypoxia, such as migration and chemoresistance to cisplatin, suggesting it as a potential therapeutic target in the treatment of GBM.

Expression of KATP channels in human cervical cancer: Potential tools for diagnosis and therapy

Various ion channels, including ATP-sensitive potassium (K_ATP) channels, are expressed in cancer and have been suggested as potential tumor markers and therapeutic targets. K_ATP channels are composed of at least two types of subunit, an inwardly rectifying K⁺ channel (Kir6.x) and a sulfonylurea receptor (SUR). However, the association between K_ATP channels and cervical cancer remains elusive. The present study determined that the Kir6.2, SUR1 and SUR2 subunits are expressed in cervical cancer cell lines and/or human biopsies. The potential association of subunit expression with tumor differentiation and invasion was analyzed. The effect of the K_ATP channel blocker glibenclamide on the proliferation of cervical cancer cell lines was also studied. Five cervical cancer cell lines, two primary cultures of cervical cancer cells, one normal keratinocyte cell line and 74 human biopsies were used in the experiments. The mRNA and protein levels of the Kir6.2 subunit were assessed by reverse transcription-polymerase chain reaction and immunochemistry, respectively. Cell proliferation was evaluated by MTT assay. Kir6.2 subunit overexpression compared with control, was observed in some cervical cancer cell lines and cervical tumor tissues. Additionally, increased K_ATP channel expression was observed in high-grade, poorly differentiated and invasive human cervical cancer biopsies. Kir6.2 subunit expression was not observed in the majority of the non-cancerous cervical tissues. The effect of the K_ATP channel blocker glibenclamide on the proliferation of five different cervical cancer cell lines was studied, revealing that as Kir6.2 mRNA expression increased, the inhibitory effect of glibenclamide also increased. The results of the present study suggest, for the first time to the best of our knowledge, that the K_ATP channel subunits, Kir6.2 and SUR2, could potentially represent tools for diagnosing and treating cervical cancer.

miR-497-5p inhibits cell proliferation and invasion by targeting KCa3.1 in angiosarcoma

Angiosarcoma is a rare malignant mesenchymal tumor with poor prognosis. We aimed to identify malignancy-associated miRNAs and their target genes, and explore biological functions of miRNA and its target in angiosarcoma. By miRNA microarrays and reverse transcription polymerase chain reaction, we identified 1 up-regulated miRNA (miR-222-3p) and 3 down-regulated miRNAs (miR-497-5p, miR-378-3p and miR-483-5p) in human angiosarcomas compared with human capillary hemangiomas. The intermediate-conductance calcium activated potassium channel KCa3.1 was one of the putative target genes of miR-497-5p, and marked up-regulation of KCa3.1 was detected in angiosarcoma biopsy specimens by immunohistochemistry. The inverse correlation of miR-497-5p and KCa3.1 also was observed in the ISO-HAS angiosarcoma cell line at the mRNA and protein levels. The direct targeting of KCa3.1 by miR-497-5p was evidenced by reduced luciferase activity due to complementary binding of miR-497-5p to KCa3.1 mRNA 3′ untranslated region. For the functional role of miR-497-5p/KCa3.1 pair, we showed that application of TRAM-34, a specific KCa3.1 channel blocker, or transfection of ISO-HAS cells with KCa3.1 siRNA or miR-497-5p mimics inhibited cell proliferation, cell cycle progression, and invasion by down-regulating cell-cycle related proteins including cyclin D1, surviving and P53 and down-regulating matrix metallopeptidase 9. In an in vivo angiosarcoma xenograft model, TRAM-34 or miR-497-5p mimics both inhibited tumor growth. In conclusion, the tumor suppressor miR-497-5p down-regulates KCa3.1 expression and contributes to the inhibition of angiosarcoma malignancy development. The miR-497-5p or KCa3.1 might be potential new targets for angiosarcoma treatment.

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.

Voltage-gated K+ channels promote BT-474 breast cancer cell migration

Objective

A variety of ion channels have been implicated in breast cancer proliferation and metastasis. Voltage-gated K⁺ (Kv) channels not only cause repolarization in excitable cells, but are also involved in multiple cellular functions in non-excitable cells. In this study we investigated the role of Kv channels in migration of BT474 breast cancer cells.

Methods

Transwell technique was used to separate migratory cells from non-migratory ones and these two groups of cells were subject to electrophysiological examinations and microfluorimetric measurements for cytosolic Ca²⁺. Cell migration was examined in the absence or presence of Kv channel blockers.

Results

When compared with non-migratory cells, migratory cells had much higher Kv current densities, but rather unexpectedly, more depolarized membrane potential and reduced Ca²⁺ influx. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed the presence of Kv1.1, Kv1.3, Kv1.5, Kv2.1, Kv3.3, Kv3.4 and Kv4.3 channels. Cell migration was markedly inhibited by tetraethylammonium (TEA), a delayed rectifier Kv channel blocker, but not by 4-aminopyridine, an A-type Kv channel blocker.

Conclusions

Taken together, our results show that increased Kv channel expression played a role in BT474 cell migration, and Kv channels could be considered as biomarkers or potential therapeutic targets for breast cancer metastasis. The mechanism(s) by which Kv channels enhanced migration appeared unrelated to membrane hyperpolarization and Ca²⁺ influx.

KCa3.1 channel inhibition sensitizes malignant gliomas to temozolomide treatment

Malignant gliomas are among the most frequent and aggressive cerebral tumors, characterized by high proliferative and invasive indexes. Standard therapy for patients, after surgery and radiotherapy, consists of temozolomide (TMZ), a methylating agent that blocks tumor cell proliferation. Currently, there are no therapies aimed at reducing tumor cell invasion. Ion channels are candidate molecular targets involved in glioma cell migration and infiltration into the brain parenchyma. In this paper we demonstrate that: i) blockade of the calcium-activated potassium channel KCa3.1 with TRAM-34 has co-adjuvant effects with TMZ, reducing GL261 glioma cell migration, invasion and colony forming activity, increasing apoptosis, and forcing cells to pass the G2/M cell cycle phase, likely through cdc2 de-phosphorylation; ii) KCa3.1 silencing potentiates the inhibitory effect of TMZ on glioma cell viability; iii) the combination of TMZ/TRAM-34 attenuates the toxic effects of glioma conditioned medium on neuronal cultures, through a microglia dependent mechanism since the effect is abolished by clodronate-induced microglia killing; iv) TMZ/TRAM-34 co-treatment increases the number of apoptotic tumor cells, and the mean survival time in a syngeneic mouse glioma model (C57BL6 mice implanted with GL261 cells); v) TMZ/TRAM-34 co-treatment reduces cell viability of GBM cells and cancer stem cells (CSC) freshly isolated from patients.Taken together, these data suggest a new therapeutic approach for malignant glioma, targeting both glioma cell proliferating and migration, and demonstrate that TMZ/TRAM-34 co-treatment affects both glioma cells and infiltrating microglia, resulting in an overall reduction of tumor cell progression.

Functional BKCa channel in human resident cardiac stem cells expressing W8B2

Recently, a new population of resident cardiac stem cells (CSCs) positive for the W8B2 marker has been identified. These CSCs are considered to be an ideal cellular source to repair myocardial damage after infarction. However, the electrophysiological profile of these cells has not been characterized yet. We first establish the conditions of isolation and expansion of W8B2⁺ CSCs from human heart biopsies using a magnetic sorting system followed by flow cytometry cell sorting. These cells display a spindle-shaped morphology, are highly proliferative, and possess self-renewal capacity demonstrated by their ability to form colonies. Besides, W8B2⁺ CSCs are positive for mesenchymal markers but negative for hematopoietic and endothelial ones. RT-qPCR and immunostaining experiments show that W8B2⁺ CSCs express some early cardiac-specific transcription factors but lack the expression of cardiac-specific structural genes. Using patch clamp in the whole-cell configuration, we show for the first time the electrophysiological signature of BKCa current in these cells. Accordingly, RT-PCR and western blotting analysis confirmed the presence of BKCa at both mRNA and protein levels in W8B2⁺ CSCs. Interestingly, BKCa channel inhibition by paxilline decreased cell proliferation in a concentration-dependent manner and halted cell cycle progression at the G0/G1 phase. The inhibition of BKCa also decreased the self-renewal capacity but did not affect migration of W8B2⁺ CSCs. Taken together, our results are consistent with an important role of BKCa channels in cell cycle progression and self-renewal in human cardiac stem cells.