ATP-sensitive potassium channels control glioma cells proliferation by regulating ERK activity

The Functional Interaction of KATP and BK Channels with Aquaporin-4 in the U87 Glioblastoma Cell

K+ channels do play a role in cell shape changes observed during cell proliferation and apoptosis. Research suggested that the dynamics of the aggregation of Aquaporin-4 (AQP4) into AQP4-OAP isoforms can trigger cell shape changes in malignant glioma cells. Here, we investigated the relationship between AQP4 and some K+ channels in the malignant glioma U87 line. The U87 cells transfected with the human M1-AQP4 and M23-AQP4 isoforms were investigated for morphology, the gene expression of KCNJ8, KCNJ11, ABCC8, ABCC9, KCNMA1, and Cyclin genes by RT-PCR, recording the whole-cell K+ ion currents by patch-clamp experiments. AQP4 aggregation into OAPs increases the plasma membrane functional expression of the Kir6.2 and SUR2 subunits of the KATP channels and of the KCNMA1 of the BK channels in U87 cells leading to a large increase in inward and outward K+ ion currents. These changes were associated with changes in morphology, with a decrease in cell volume in the U87 cells and an increase in the ER density. These U87 cells accumulate in the mitotic and G2 cell cycle. The KATP channel blocker zoledronic acid reduced cell proliferation in both M23 AQP4-OAP and M1 AQP4-tetramer-transfected cells, leading to early and late apoptosis, respectively. The BK channel sustains the efflux of K+ ions associated with the M23 AQP4-OAP expression in the U87 cells, but it is downregulated in the M1 AQP4-tetramer cells. The KATP channels are effective in the M1 AQP4-tetramer and M23 AQP4-OAP cells. Zoledronic acid can be effective in targeting pathogenic M1 AQP4-tetramer cell phenotypes inhibiting KATP channels and inducing early apoptosis.

Potassium rhythms couple the circadian clock to the cell cycle

Circadian (~24 h) rhythms are a fundamental feature of life, and their disruption increases the risk of infectious diseases, metabolic disorders, and cancer1-6. Circadian rhythms couple to the cell cycle across eukaryotes7,8 but the underlying mechanism is unknown. We previously identified an evolutionarily conserved circadian oscillation in intracellular potassium concentration, [K+]i9,10. As critical events in the cell cycle are regulated by intracellular potassium11,12, an enticing hypothesis is that circadian rhythms in [K+]i form the basis of this coupling. We used a minimal model cell, the alga Ostreococcus tauri, to uncover the role of potassium in linking these two cycles. We found direct reciprocal feedback between [K+]i and circadian gene expression. Inhibition of proliferation by manipulating potassium rhythms was dependent on the phase of the circadian cycle. Furthermore, we observed a total inhibition of cell proliferation when circadian gene expression is inhibited. Strikingly, under these conditions a sudden enforced gradient of extracellular potassium was sufficient to induce a round of cell division. Finally, we provide evidence that interactions between potassium and circadian rhythms also influence proliferation in mammalian cells. These results establish circadian regulation of intracellular potassium levels as a primary factor coupling the cell- and circadian cycles across diverse organisms.

Exploring Regorafenib Responsiveness and Uncovering Molecular Mechanisms in Recurrent Glioblastoma Tumors through Longitudinal In Vitro Sampling

Glioblastoma, a deadly brain tumor, shows limited response to standard therapies like temozolomide (TMZ). Recent findings from the REGOMA trial underscore a significant survival improvement offered by Regorafenib (REGO) in recurrent glioblastoma. Our study aimed to propose a 3D ex vivo drug response precision medicine approach to investigate recurrent glioblastoma sensitivity to REGO and elucidate the underlying molecular mechanisms involved in tumor resistance or responsiveness to treatment. Three-dimensional glioblastoma organoids (GB-EXPs) obtained from 18 patients' resected recurrent glioblastoma tumors were treated with TMZ and REGO. Drug responses were evaluated using NAD(P)H FLIM, stratifying tumors as responders (Resp) or non-responders (NRs). Whole-exome sequencing was performed on 16 tissue samples, and whole-transcriptome analysis on 13 GB-EXPs treated and untreated. We found 35% (n = 9) and 77% (n = 20) of tumors responded to TMZ and REGO, respectively, with no instances of TMZ-Resp being REGO-NRs. Exome analysis revealed a unique mutational profile in REGO-Resp tumors compared to NR tumors. Transcriptome analysis identified distinct expression patterns in Resp and NR tumors, impacting Rho GTPase and NOTCH signaling, known to be involved in drug response. In conclusion, recurrent glioblastoma tumors were more responsive to REGO compared to TMZ treatment. Importantly, our approach enables a comprehensive longitudinal exploration of the molecular changes induced by treatment, unveiling promising biomarkers indicative of drug response.

Exploring the Role of Surface and Mitochondrial ATP-Sensitive Potassium Channels in Cancer: From Cellular Functions to Therapeutic Potentials

ATP-sensitive potassium (KATP) channels are found in plasma membranes and mitochondria. These channels are a type of ion channel that is regulated by the intracellular concentration of adenosine triphosphate (ATP) and other nucleotides. In cell membranes, they play a crucial role in linking metabolic activity to electrical activity, especially in tissues like the heart and pancreas. In mitochondria, KATP channels are involved in protecting cells against ischemic damage and regulating mitochondrial function. This review delves into the role of KATP channels in cancer biology, underscoring their critical function. Notably responsive to changes in cellular metabolism, KATP channels link metabolic states to electrical activity, a feature that becomes particularly significant in cancer cells. These cells, characterized by uncontrolled growth, necessitate unique metabolic and signaling pathways, differing fundamentally from normal cells. Our review explores the intricate roles of KATP channels in influencing the metabolic and ionic balance within cancerous cells, detailing their structural and operational mechanisms. We highlight the channels' impact on cancer cell survival, proliferation, and the potential of KATP channels as therapeutic targets in oncology. This includes the challenges in targeting these channels due to their widespread presence in various tissues and the need for personalized treatment strategies. By integrating molecular biology, physiology, and pharmacology perspectives, the review aims to enhance the understanding of cancer as a complex metabolic disease and to open new research and treatment avenues by focusing on KATP channels. This comprehensive approach provides valuable insights into the potential of KATP channels in developing innovative cancer treatments.

A Novel Cell Volume Sensor for Real-Time Analysis of Ca2+-Activated K+ Channel

Potassium channels play a vital role in cell volume regulation. A cell volume sensor was constructed by integrating regulatory volume decrease (RVD) with quartz-crystal microbalance (QCM) for studying potassium channels and their expression. The sensor successfully monitored the K+ channel's activities during RVD by sensitive and noninvasive means. It showed that Ca2+ activated the K+ channel (KCa) and enhanced the RVD level. The inhibition of blockers on K+ channels exhibited an obvious difference in RVD level between normal and cancerous nasopharyngeal cells, suggesting that the KCa channel contributes a dominant role to the RVD function and provides an approach to identify the activation of various K+ channels.

Exploitation of ATP-sensitive potassium ion (KATP) channels by HPV promotes cervical cancer cell proliferation by contributing to MAPK/AP-1 signalling

Persistent infection with high-risk human papillomaviruses (HPVs) is the causal factor in multiple human malignancies, including >99% of cervical cancers and a growing proportion of oropharyngeal cancers. Prolonged expression of the viral oncoproteins E6 and E7 is necessary for transformation to occur. Although some of the mechanisms by which these oncoproteins contribute to carcinogenesis are well-characterised, a comprehensive understanding of the signalling pathways manipulated by HPV is lacking. Here, we present the first evidence to our knowledge that the targeting of a host ion channel by HPV can contribute to cervical carcinogenesis. Through the use of pharmacological activators and inhibitors of ATP-sensitive potassium ion (KATP) channels, we demonstrate that these channels are active in HPV-positive cells and that this activity is required for HPV oncoprotein expression. Further, expression of SUR1, which forms the regulatory subunit of the multimeric channel complex, was found to be upregulated in both HPV+ cervical cancer cells and in samples from patients with cervical disease, in a manner dependent on the E7 oncoprotein. Importantly, knockdown of SUR1 expression or KATP channel inhibition significantly impeded cell proliferation via induction of a G1 cell cycle phase arrest. This was confirmed both in vitro and in in vivo tumourigenicity assays. Mechanistically, we propose that the pro-proliferative effect of KATP channels is mediated via the activation of a MAPK/AP-1 signalling axis. A complete characterisation of the role of KATP channels in HPV-associated cancer is now warranted in order to determine whether the licensed and clinically available inhibitors of these channels could constitute a potential novel therapy in the treatment of HPV-driven cervical cancer.

Gender Differences in Oxidative Stress in Relation to Cancer Susceptibility and Survival

Genetic, developmental, biochemical, and environmental variables interact intricately to produce sex differences. The significance of sex differences in cancer susceptibility is being clarified by numerous studies. Epidemiological research and cancer registries have revealed over the past few years that there are definite sex variations in cancer incidence, progression, and survival. However, oxidative stress and mitochondrial dysfunction also have a significant impact on the response to treatment of neoplastic diseases. Young women may be more protected from cancer than men because most of the proteins implicated in the regulation of redox state and mitochondrial function are under the control of sexual hormones. In this review, we describe how sexual hormones control the activity of antioxidant enzymes and mitochondria, as well as how they affect several neoplastic diseases. The molecular pathways that underlie the gender-related discrepancies in cancer that have been identified may be better understood, which may lead to more effective precision medicine and vital information on treatment options for both males and females with neoplastic illnesses.

Immunohistochemical, pharmacovigilance, and omics analyses reveal the involvement of ATP-sensitive K+ channel subunits in cancers: role in drug-disease interactions

Background: ATP-sensitive-K+ channels (KATP) are involved in diseases, but their role in cancer is poorly described. Pituitary macroadenoma has been observed in Cantu' syndrome (C.S.), which is associated with the gain-of-function mutations of the ABCC9 and KCNJ8 genes. We tested the role of the ABCC8/Sur1, ABCC9/Sur2A/B, KCNJ11/Kir6.2, and KCNJ8/Kir6.1 genes experimentally in a minoxidil-induced renal tumor in male rats and in the female canine breast cancer, a spontaneous animal model of disease, and in the pharmacovigilance and omics databases. Methods: We performed biopsies from renal tissues of male rats (N = 5) following a sub-chronic high dosing topical administration of minoxidil (0.777-77.7 mg/kg/day) and from breast tissues of female dogs for diagnosis (N = 23) that were analyzed by immunohistochemistry. Pharmacovigilance and omics data were extracted from EudraVigilance and omics databases, respectively. Results: An elevated immunohistochemical reactivity to Sur2A-mAb was detected in the cytosol of the Ki67+/G3 cells other than in the surface membrane in the minoxidil-induced renal tumor and the breast tumor samples. KCNJ11, KCNJ8, and ABCC9 genes are upregulated in cancers but ABCC8 is downregulated. The Kir6.2-Sur2A/B-channel opener minoxidil showed 23 case reports of breast cancer and one case of ovarian cancer in line with omics data reporting, respectively, and the negative and positive prognostic roles of the ABCC9 gene in these cancers. Sulfonylureas and glinides blocking the pancreatic Kir6.2-Sur1 subunits showed a higher risk for pancreatic cancer in line with the positive prognostic role of the ABCC8 gene but low risks for common cancers. Glibenclamide, repaglinide, and glimepiride show a lower cancer risk within the KATP channel blockers. The Kir6.2-Sur1 opener diazoxide shows no cancer reactions. Conclusion: An elevated expression of the Sur2A subunit was found in proliferating cells in two animal models of cancer. Immunohistochemistry/omics/pharmacovigilance data reveal the role of the Kir6.1/2-Sur2A/B subunits as a drug target in breast/renal cancers and in C.S.

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.

Glioma epileptiform activity and progression are driven by IGSF3-mediated potassium dysregulation

Seizures are a frequent pathophysiological feature of malignant glioma. Recent studies implicate peritumoral synaptic dysregulation as a driver of brain hyperactivity and tumor progression; however, the molecular mechanisms that govern these phenomena remain elusive. Using scRNA-seq and intraoperative patient ECoG recordings, we show that tumors from seizure patients are enriched for gene signatures regulating synapse formation. Employing a human-to-mouse in vivo functionalization pipeline to screen these genes, we identify IGSF3 as a mediator of glioma progression and dysregulated neural circuitry that manifests as spreading depolarization (SD). Mechanistically, we discover that IGSF3 interacts with Kir4.1 to suppress potassium buffering and found that seizure patients exhibit reduced expression of potassium handlers in proliferating tumor cells. In vivo imaging reveals that dysregulated synaptic activity emanates from the tumor-neuron interface, which we confirm in patients. Our studies reveal that tumor progression and seizures are enabled by ion dyshomeostasis and identify SD as a driver of disease.

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.

Functionalized Fluorescent Nanodiamonds for Simultaneous Drug Delivery and Quantum Sensing in HeLa Cells

Here, we present multifunctional fluorescent nanodiamonds (FNDs) for simultaneous drug delivery and free radical detection. For this purpose, we modified FNDs containing nitrogen vacancy (NV) centers with a diazoxide derivative. We found that our particles enter cells more easily and are able to deliver this cancer drug into HeLa cells. The particles were characterized by infrared spectroscopy, dynamic light scattering, and secondary electron microscopy. Compared to the free drug, we observe a sustained release over 72 h rather than 12 h for the free drug. Apart from releasing the drug, with these particles, we can measure the drug's effect on free radical generation directly. This has the advantage that the response is measured locally, where the drug is released. These FNDs change their optical properties based on their magnetic surrounding. More specifically, we make use of a technique called relaxometry to detect spin noise from the free radical at the nanoscale with subcellular resolution. We further compared the results from our new technique with a conventional fluorescence assay for the detection of reactive oxygen species. This provides a new method to investigate the relationship between drug release and the response by the cell via radical formation or inhibition.

Potassium Channels as a Target for Cancer Therapy: Current Perspectives

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

Extracellular Adenosine Triphosphate Binding to P2Y1 Receptors Prevents Glutamate-Induced Excitotoxicity: Involvement of Erk1/2 Signaling Pathway to Suppress Autophagy

Glutamate-induced neuroexcitotoxicity could be related to the pathophysiology of some neurodegenerative diseases including Parkinson’s disease and Alzheimer’s disease. Extracellular ATP exerts a wide variety of functions, such as attenuating Aβ-mediated toxicity, inhibiting N-Methyl-D-Aspartate (NMDA) receptor subunit combinations, and aggravating ischemic brain injury. However, the effect of extracellular ATP on glutamate-induced neuroexcitotoxicity remains largely unknown. Herein, we showed that extracellular ATP prevented the glutamate-induced excitotoxicity via binding to its P2Y1 receptors. We found that excessive glutamate triggered cellular reactive oxygen species (ROS) overproduction and mitochondrial membrane potential damage, which were significantly attenuated by extracellular ATP. Besides, glutamate activated autophagy, as illustrated by the increased protein level of autophagic marker LC3II and decreased level of p62, and glutamate-induced neuroexcitotoxicity could be completely abolished by autophagy inhibitor chloroquine. In addition, we revealed that extracellular ATP activated Erk1/2 signaling to suppress autophagy and to exert its neuroprotective effects, which was further reduced by autophagy agonist rapamycin and the selective Erk1/2 inhibitor PD0325901. Taken together, our findings suggest that extracellular ATP binding to P2Y1 receptors protected against glutamate-induced excitotoxicity via Erk1/2-mediated autophagy inhibition, implying the potential of ATP for the treatment of neurodegenerative disorders.

Glycomaterials to Investigate the Functional Role of Aberrant Glycosylation in Glioblastoma

Glioblastoma (GBM) is a stage IV astrocytoma that carries a dismal survival rate of ≈10 months postdiagnosis and treatment. The highly invasive capacity of GBM and its ability to escape therapeutic challenges are key factors contributing to the poor overall survival rate. While current treatments aim to target the cancer cell itself, they fail to consider the significant role that the GBM tumor microenvironment (TME) plays in promoting tumor progression and therapeutic resistance. The GBM tumor glycocalyx and glycan-rich extracellular matrix (ECM), which are important constituents of the TME have received little attention as therapeutic targets. A wide array of aberrantly modified glycans in the GBM TME mediate tumor growth, invasion, therapeutic resistance, and immunosuppression. Here, an overview of the landscape of aberrant glycan modifications in GBM is provided, and the design and utility of 3D glycomaterials are discussed as a tool to evaluate glycan-mediated GBM progression and therapeutic efficacy. The development of alternative strategies to target glycans in the TME can potentially unveil broader mechanisms of restricting tumor growth and enhancing the efficacy of tumor-targeting therapeutics.

ABCC9 Is Downregulated and Prone to Microsatellite Instability on ABCC9tetra in Canine Breast Cancer

Tumorigenesis is associated with metabolic abnormalities and genomic instability. Microsatellite mutations, including microsatellite instability (MSI) and loss of heterozygosity (LOH), are associated with the functional impairment of some tumor-related genes. To investigate the role of MSI and LOH in sporadic breast tumors in canines, 22 tumors DNA samples and their adjacent normal tissues were evaluated using polyacrylamide gel electrophoresis and silver staining for 58 microsatellites. Quantitative real-time polymerase chain reaction, promoter methylation analysis and immunohistochemical staining were used to quantify gene expression. The results revealed that a total of 14 tumors (6 benign tumors and 8 breast cancers) exhibited instability as MSI-Low tumors. Most of the microsatellite loci possessed a single occurrence of mutations. The maximum number of MSI mutations on loci was observed in tumors with a lower degree of differentiation. Among the unstable markers, FH2060 (4/22), ABCC9tetra (4/22) and SCN11A (6/22) were high-frequency mutation sites, whereas FH2060 was a high-frequency LOH site (4/22). The ABCC9tetra locus was mutated only in cancerous tissue, although it was excluded by transcription. The corresponding genes and proteins were significantly downregulated in malignant tissues, particularly in tumors with MSI. Furthermore, the promoter methylation results of the adenosine triphosphate binding cassette subfamily C member 9 (ABCC9) showed that there was a high level of methylation in breast tissues, but only one case showed a significant elevation compared with the control. In conclusion, MSI-Low or MSI-Stable is characteristic of most sporadic mammary tumors. Genes associated with tumorigenesis are more likely to develop MSI. ABCC9 protein and transcription abnormalities may be associated with ABCC9tetra instability.

Altered Elemental Distribution in Male Rat Brain Tissue as a Predictor of Glioblastoma Multiforme Growth-Studies Using SR-XRF Microscopy

Glioblastoma multiforme (GBM) is a particularly malignant primary brain tumor. Despite enormous advances in the surgical treatment of cancer, radio- and chemotherapy, the average survival of patients suffering from this cancer does not usually exceed several months. For obvious ethical reasons, the search and testing of the new drugs and therapies of GBM cannot be carried out on humans, and for this purpose, animal models of the disease are most often used. However, to assess the efficacy and safety of the therapy basing on these models, a deep knowledge of the pathological changes associated with tumor development in the animal brain is necessary. Therefore, as part of our study, the synchrotron radiation-based X-ray fluorescence microscopy was applied for multi-elemental micro-imaging of the rat brain in which glioblastoma develops. Elemental changes occurring in animals after the implantation of two human glioma cell lines as well as the cells taken directly from a patient suffering from GBM were compared. Both the extent and intensity of elemental changes strongly correlated with the regions of glioma growth. The obtained results showed that the observation of elemental anomalies accompanying tumor development within an animal's brain might facilitate our understanding of the pathogenesis and progress of GBM and also determine potential biomarkers of its extension. The tumors appearing in a rat's brain were characterized by an increased accumulation of Fe and Se, whilst the tissue directly surrounding the tumor presented a higher accumulation of Cu. Furthermore, the results of the study allow us to consider Se as a potential elemental marker of GBM progression.

The Anti-diabetic Drug Gliquidone Modulates Lipopolysaccharide-Mediated Microglial Neuroinflammatory Responses by Inhibiting the NLRP3 Inflammasome

The sulfonylurea drug gliquidone is FDA approved for the treatment of type 2 diabetes. Binding of gliquidone to ATP-sensitive potassium channels (SUR1, Kir6 subunit) in pancreatic β-cells increases insulin release to regulate blood glucose levels. Diabetes has been associated with increased levels of neuroinflammation, and therefore the potential effects of gliquidone on micro- and astroglial neuroinflammatory responses in the brain are of interest. Here, we found that gliquidone suppressed LPS-mediated microgliosis, microglial hypertrophy, and proinflammatory cytokine COX-2 and IL-6 levels in wild-type mice, with smaller effects on astrogliosis. Importantly, gliquidone downregulated the LPS-induced microglial NLRP3 inflammasome and peripheral inflammation in wild-type mice. An investigation of the molecular mechanism of the effects of gliquidone on LPS-stimulated proinflammatory responses showed that in BV2 microglial cells, gliquidone significantly decreased LPS-induced proinflammatory cytokine levels and inhibited ERK/STAT3/NF-κB phosphorylation by altering NLRP3 inflammasome activation. In primary astrocytes, gliquidone selectively affected LPS-mediated proinflammatory cytokine expression and decreased STAT3/NF-κB signaling in an NLRP3-independent manner. These results indicate that gliquidone differentially modulates LPS-induced microglial and astroglial neuroinflammation in BV2 microglial cells, primary astrocytes, and a model of neuroinflammatory disease.

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

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

Comparison of Elemental Anomalies Following Implantation of Different Cell Lines of Glioblastoma Multiforme in the Rat Brain: A Total Reflection X-ray Fluorescence Spectroscopy Study

Glioblastoma multiforme (GBM) is a primary brain tumor with a very high degree of malignancy and is classified by WHO as a glioma IV. At present, the treatment of patients suffering from GBM is based on surgical resection of the tumor with maximal protection of surrounding tissues followed by radio- and pharmacological therapy using temozolomide as the most frequently recommended drug. This strategy, however, does not guarantee success and has devastating consequences. Testing of new substances or therapies having potential in the treatment of GBM as well as detection of their side effects cannot be done on humans. Animal models of the disease are usually used for these purposes, and one possibility is the implantation of human tumor cells into rodent brains. Such a solution was used in the present study the purpose of which was comparison of elemental anomalies appearing in the brain as a result of implantation of different glioblastoma cell lines. These were two commercially available cell lines (U87MG and T98G), as well as tumor cells taken directly from a patient diagnosed with GBM. Using total reflection X-ray fluorescence we determined the contents of P, S, K, Ca, Fe, Cu, Zn, and Se in implanted-left and intact-right brain hemispheres. The number of elemental anomalies registered for both hemispheres was positively correlated with the invasiveness of GBM cells and was the highest for animals subjected to U87MG cell implantation, which presented significant decrease of P, K, and Cu levels and an increase of Se concentration within the left hemisphere. The abnormality common for all three groups of animals subjected to glioma cell implantation was increased Fe level in the brain, which may result from higher blood supply or the presence of hemorrhaging regions. In the case of the intact hemisphere, elevated Fe concentration may also indicate higher neuronal activity caused by taking over some functions of the left hemisphere impaired as a result of tumor growth.

Communication of Glioma cells with neuronal plasticity: What is the underlying mechanism?

There has been a significantly rising discussion on how neuronal plasticity communicates with the glioma growth and invasion. This literature review aims to determine which neurotransmitters, ion channels and signaling pathways are involved in this context, how information is transferred from synaptic sites to the glioma cells and how glioma cells apply established mechanics of synaptic plasticity for their own increment. This work is a compilation of some outstanding findings related to the influence of the glutamate, calcium, potassium, chloride and sodium channels and other important brain plasticity molecules over the glioma progression. These topics also include the relevant molecular signaling data which could prove to be helpful for an effective clinical management of brain tumors in the future.

Combined Inhibition of SHP2 and MEK Is Effective in Models of NF1-Deficient Malignant Peripheral Nerve Sheath Tumors

Loss of the RAS GTPase-activating protein (RAS-GAP) NF1 drives aberrant activation of RAS/MEK/ERK signaling and other effector pathways in the majority of malignant peripheral nerve sheath tumors (MPNST). These dysregulated pathways represent potential targets for therapeutic intervention. However, studies of novel single agents including MEK inhibitors (MEKi) have demonstrated limited efficacy both preclinically and clinically, with little advancement in overall patient survival. By interrogation of kinome activity through an unbiased screen and targeted evaluation of the signaling response to MEK inhibition, we have identified global activation of upstream receptor tyrosine kinases (RTK) that converges on activation of RAS as a mechanism to limit sensitivity to MEK inhibition. As no direct inhibitors of pan-RAS were available, an inhibitor of the protein tyrosine phosphatase SHP2, a critical mediator of RAS signal transduction downstream of multiple RTK, represented an alternate strategy. The combination of MEKi plus SHP099 was superior to MEKi alone in models of NF1-MPNST, including those with acquired resistance to MEKi. Our findings have immediate translational implications and may inform future clinical trials for patients with MPNST harboring alterations in NF1. SIGNIFICANCE: Combined inhibition of MEK and SHP2 is effective in models of NF1-MPNST, both those naïve to and those resistant to MEKi, as well as in the MPNST precursor lesion plexiform neurofibroma.

Membrane Transporters and Channels in Melanoma

Recent research has revealed that ion channels and transporters can be important players in tumor development, progression, and therapy resistance in melanoma. For example, members of the ABC family were shown to support cancer stemness-like features in melanoma cells, while several members of the TRP channel family were reported to act as tumor suppressors.Also, many transporter proteins support tumor cell viability and thus suppress apoptosis induction by anticancer therapy. Due to the high number of ion channels and transporters and the resulting high complexity of the field, progress in understanding is often focused on single molecules and is in total rather slow. In this review, we aim at giving an overview about a broad subset of ion transporters, also illustrating some aspects of the field, which have not been addressed in detail in melanoma. In context with the other chapters in this special issue on "Transportome Malfunctions in the Cancer Spectrum," a comparison between melanoma and these tumors will be possible.

Novel Therapeutic Approaches of Ion Channels and Transporters in Cancer

The expression and function of many ion channels and transporters in cancer cells display major differences in comparison to those from healthy cells. These differences provide the cancer cells with advantages for tumor development. Accordingly, targeting ion channels and transporters have beneficial anticancer effects including inhibition of cancer cell proliferation, migration, invasion, metastasis, tumor vascularization, and chemotherapy resistance, as well as promoting apoptosis. Some of the molecular mechanisms associating ion channels and transporters with cancer include the participation of oxidative stress, immune response, metabolic pathways, drug synergism, as well as noncanonical functions of ion channels. This diversity of mechanisms offers an exciting possibility to suggest novel and more effective therapeutic approaches to fight cancer. Here, we review and discuss most of the current knowledge suggesting novel therapeutic approaches for cancer therapy targeting ion channels and transporters. The role and regulation of ion channels and transporters in cancer provide a plethora of exceptional opportunities in drug design, as well as novel and promising therapeutic approaches that may be used for the benefit of cancer patients.

Role of ion channels during cell division

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

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.

KCNK levels are prognostic and diagnostic markers for hepatocellular carcinoma

Two-pore-domain (KCNK, K2P) K⁺ channels are transmembrane protein complexes that control the flow of ions across biofilms, which underlie many essential cellular functions. Because KCNK family members are known to contribute to tumorigenesis in various types of cancer, we hypothesized that they might be differentially expressed in hepatocellular carcinoma (HCC) cells as compared to healthy tissue and serve as diagnostic or prognostic biomarkers. We tested this hypothesis through bioinformatic analyses of publicly available data for the expression of various KCNK subunits in HCC. We observed reduced expression of KCNK2, KCNK15, and KCNK17 in liver cancer, as well as overexpression of KCNK9, all of which correlated with a better prognosis for HCC patients per survival analyses. Moreover, ROC curves indicated that KCNK2, KCNK9, KCNK15, and KCNK17 levels could be used as a diagnostic biomarker for HCC. Finally, our western blot and qRT-PCR results were consistent with those obtained from bioinformatic analyses. Taken together, these results suggest that KCNK2, KCNK9, KCNK15, and KCNK17 could serve as potential diagnostic and prognostic biomarkers of HCC.

Sulfonylurea derivatives and cancer, friend or foe?

Type 2 diabetes mellitus (T2DM) is associated with a higher risk of cancer and cancer-related mortality. Increased blood glucose and insulin levels in T2DM patients may be, at least in part, responsible for this effect. Indeed, lowering glucose and/or insulin levels pharmacologically appears to reduce cancer risk and progression, as has been demonstrated for the biguanide metformin in observational studies. Studies investigating the influence of sulfonylurea derivatives (SUs) on cancer risk have provided conflicting results, partly due to comparisons with metformin. Furthermore, little attention has been paid to within-class differences in systemic and off-target effects of the SUs. The aim of this systematic review is to discuss the available preclinical and clinical evidence on how the different SUs influence cancer development and risk. Databases including PubMed, Cochrane, Database of Abstracts on Reviews and Effectiveness, and trial registries were systematically searched for available clinical and preclinical evidence on within-class differences of SUs and cancer risk. The overall preclinical and clinical evidence suggest that the influence of SUs on cancer risk in T2DM patients differs between the various SUs. Potential mechanisms include differing affinities for the sulfonylurea receptors and thus differential systemic insulin exposure and off-target anti-cancer effects mediated for example through potassium transporters and drug export pumps. Preclinical evidence supports potential anti-cancer effects of SUs, which are of interest for further studies and potentially repurposing of SUs. At this time, the evidence on differences in cancer risk between SUs is not strong enough to guide clinical decision making.

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.

Upregulation of phosphatase and tensin homolog is essential for the effect of 4-aminopyridine on A549/CDDP cells

4-aminopyridine (4-AP), a voltage-gated potassium channel blocker, was revealed to possess pro‑apoptotic properties in various types of cancer cells. The present study aimed to explore the effect of 4‑AP on a cisplatin (DDP) resistant lung cancer cell line A549/CDDP and the underlying mechanism by which it had an effect. In the present study, an MTT assay and cell cycle analysis were used to determine that 4‑AP inhibited cell growth in vitro and a tumorigenesis assay in nude mice determined that 4‑AP also inhibited cell growth in vivo. 4‑AP induced cell apoptosis of A549/CDDP cells observed by electron microscopy and Annexin V‑APC/7‑ADD analysis. In addition, 4‑AP enhanced the sensitivity of A549/CDDP cells to DDP as revealed by an MTT assay. Mechanistically, 4‑AP upregulated the phosphatase and tensin homolog (PTEN) and modulated the phosphoinositide 3‑kinase/protein kinase B signaling pathway and its downstream cell cycle factors, including cyclin D1, cyclin‑dependent kinase 4 and p21, as well as apoptosis‑associated proteins B‑cell lymphoma 2, pro‑caspase 9, pro‑caspase 3, cleaved caspase 9 and cleaved caspase 3. The effects of 4‑AP on cell growth and apoptosis were reversed by PTEN silencing. In conclusion, the results indicated that 4‑AP inhibited cell growth, induced apoptosis and sensitized A549/CDDP cells to DDP via the upregulation of PTEN. 4‑AP may be a potential therapeutic agent for patients with DDP resistance.

Collagen type 1 promotes survival of human breast cancer cells by overexpressing Kv10.1 potassium and Orai1 calcium channels through DDR1-dependent pathway

Collagen type 1 is among the tumor microenvironment (TM) factors, that regulates proliferation, survival, migration and invasion. Ion channels are key players in interactions between tumor cells and TM. Kv10.1 has been shown to play an essential role in breast cancer cell proliferation and migration by permitting Ca²⁺ influx notably via Orai1. Here, we show that human breast cancer (BC) cells growing, in culture media completely devoid of the serum and seeded on collagen 1 coating, exhibited less apoptotic rate and a decrease in Bax expression when compared to those grown on plastic. The survival conferred by collagen 1 was completely abolished by removing extracellular Ca²⁺ from the culture medium. In addition, Ca²⁺ entry was increased in collagen 1 condition along with increased Kv10.1 and Orai1 expressions. Moreover, collagen 1 was able to increase co-localization of Kv10.1 and Orai1 on the plasma membrane. Interestingly, silencing of Kv10.1 and Orai1 reduced survival and Ca²⁺influx without any additive effect. This calcium-dependent survival is accompanied by the activation of ERK1/2, and its pharmacological inhibition completely abolished the increase in Kv10.1 and Orai1 expressions, activities, and the cell survival induced by collagen 1. Moreover, both Kv10.1 and Orai1 knockdown reduced ERK1/2 activation but not Akt. Finally, DDR1 silencing but not β1-integrin reduced the collagen induced survival, ERK1/2 phosphorylation and the expression of Kv10.1 and Orai1. Together these data show that the Kv10.1/Orai1 complex is involved in BC cell survival and this is dependent on collagen 1/DDR1 pathway. Therefore, they represent a checkpoint of tumor progression induced by the tumor microenvironment.

Dietary and pharmacological modification of the insulin/IGF-1 system: exploiting the full repertoire against cancer

As more and more links between cancer and metabolism are discovered, new approaches to treat cancer using these mechanisms are considered. Dietary restriction of either calories or macronutrients has shown great potential in animal studies to both reduce the incidence and growth of cancer, and to act synergistically with other treatment strategies. These studies have also shown that dietary restriction simultaneously targets many of the molecular pathways that are targeted individually by anticancer drugs. The insulin/insulin-like growth factor-1 (IGF-1) system has thereby emerged as a key regulator of cancer growth pathways. Although lowering of insulin levels with diet or drugs such as metformin and diazoxide seems generally beneficial, some practitioners also utilize strategic elevations of insulin levels in combination with chemotherapeutic drugs. This indicates a broad spectrum of possibilities for modulating the insulin/IGF-1 system in cancer treatment. With a specific focus on dietary restriction, insulin administration and the insulin-lowering drug diazoxide, such modifications of the insulin/IGF-1 system are the topic of this review. Although preclinical data are promising, we point out that insulin regulation and the metabolic response to a certain diet often differ between mice and humans. Thus, the need for collecting more human data has to be emphasized.

MiR-126 Regulates the ERK Pathway via Targeting KRAS to Inhibit the Glioma Cell Proliferation and Invasion

The activity of some constitutive contained in the extracellular signal-regulated kinase (ERK) pathway plays crucial roles in glioma cell growth and proliferation. Emerging studies have reported that microRNA (miRNA) could regulate the ERK signal pathway by directly targeting various oncogenes. This study enabled us to discover that the average miR-126 expression was significantly decreased in glioblastoma tissues, and this significant decrease was related to high histopathological grades. Our experiment also demonstrated that the over-expression of miR-126 suppressed glioma cell proliferation and invasion in vitro. Kirsten rat sarcoma viral oncogene (KRAS) which is involved in ERK pathway was directly targeted by miR-126 in glioma through binding to two sites in the 3' untranslated region (3'-UTR) of KRAS mRNA. Notably, the expression level of KRAS was positively correlated to the activity of ERK pathway and its downstream regulators (phosphorylation level of ERK (pERK) and c-Fos). Furthermore, the over-expression of KRAS expression vector without the 3'-UTR partially reverses the tumor-suppressive effects of miR-126. Moreover, the up-regulation of miR-126 contributes to the aberrant activation of the ERK signaling and inhibits cell proliferation and invasion through targeting KRAS. Therefore, it was suspected that miR-126 may be a potential therapeutic target for high-grade glioma.

The Regulation and Function of Lactate Dehydrogenase A: Therapeutic Potential in Brain Tumor

There are over 120 types of brain tumor and approximately 45% of primary brain tumors are gliomas, of which glioblastoma multiforme (GBM) is the most common and aggressive with a median survival rate of 14 months. Despite progress in our knowledge, current therapies are unable to effectively combat primary brain tumors and patient survival remains poor. Tumor metabolism is important to consider in therapeutic approaches and is the focus of numerous research investigations. Lactate dehydrogenase A (LDHA) is a cytosolic enzyme, predominantly involved in anaerobic and aerobic glycolysis (the Warburg effect); however, it has multiple additional functions in non‐neoplastic and neoplastic tissues, which are not commonly known or discussed. This review summarizes what is currently known about the function of LDHA and identifies areas that would benefit from further exploration. The current knowledge of the role of LDHA in the brain and its potential as a therapeutic target for brain tumors will also be highlighted. The Warburg effect appears to be universal in tumors, including primary brain tumors, and LDHA (because of its involvement with this process) has been identified as a potential therapeutic target. Currently, there are, however, no suitable LDHA inhibitors available for tumor therapies in the clinic.

Xyloketal B suppresses glioblastoma cell proliferation and migration in vitro through inhibiting TRPM7-regulated PI3K/Akt and MEK/ERK signaling pathways

Glioblastoma, the most common and aggressive type of brain tumors, has devastatingly proliferative and invasive characteristics. The need for finding a novel and specific drug target is urgent as the current approaches have limited therapeutic effects in treating glioblastoma. Xyloketal B is a marine compound obtained from mangrove fungus Xylaria sp. (No. 2508) from the South China Sea, and has displayed antioxidant activity and protective effects on endothelial and neuronal oxidative injuries. In this study, we used a glioblastoma U251 cell line to (1) explore the effects of xyloketal B on cell viability, proliferation, and migration; and (2) investigate the underlying molecular mechanisms and signaling pathways. MTT assay, colony formation, wound healing, western blot, and patch clamp techniques were employed. We found that xyloketal B reduced cell viability, proliferation, and migration of U251 cells. In addition, xyloketal B decreased p-Akt and p-ERK1/2 protein expressions. Furthermore, xyloketal B blocked TRPM7 currents in HEK-293 cells overexpressing TRPM7. These effects were confirmed by using a TRPM7 inhibitor, carvacrol, in a parallel experiment. Our findings indicate that TRPM7-regulated PI3K/Akt and MEK/ERK signaling is involved in anti-proliferation and migration effects of xyloketal B on U251 cells, providing in vitro evidence for the marine compound xyloketal B to be a potential drug for treating glioblastoma.

Cancer as a channelopathy: ion channels and pumps in tumor development and progression

Increasing evidence suggests that ion channels and pumps not only regulate membrane potential, ion homeostasis, and electric signaling in excitable cells but also play important roles in cell proliferation, migration, apoptosis and differentiation. Consistent with a role in cell signaling, channel proteins and ion pumps can form macromolecular complexes with growth factors, and cell adhesion and other signaling molecules. And while cancer is still not being cataloged as a channelopathy, as the non-traditional roles of ion pumps and channels are being recognized, it is increasingly being suggested that ion channels and ion pumps contribute to cancer progression. Cancer cell migration requires the regulation of adhesion complexes between migrating cells and surrounding extracellular matrix (ECM) proteins. Cell movement along solid surfaces requires a sequence of cell protrusions and retractions that mainly depend on regulation of the actin cytoskeleton along with contribution of microtubules and molecular motor proteins such as mysoin. This process is triggered and modulated by a combination of environmental signals, which are sensed and integrated by membrane receptors, including integrins and cadherins. Membrane receptors transduce these signals into downstream signaling pathways, often involving the Rho GTPase protein family. These pathways regulate the cytoskeletal rearrangements necessary for proper timing of adhesion, contraction and detachment of cells in order to find their way through extracellular spaces. Migration and adhesion involve continuous modulation of cell motility, shape and volume, in which ion channels and pumps play major roles. Research on cancer cells suggests that certain ion channels may be involved in aberrant tumor growth and channel inhibitors often lead to growth arrest. This review will describe recent research into the role of ion pumps and ion channels in cell migration and adhesion, and how they may contribute to tumor development.

Voltage‑gated K+ channel blocker quinidine inhibits proliferation and induces apoptosis by regulating expression of microRNAs in human glioma U87‑MG cells

Accumulating evidence has proved that potassium channels (K+ channels) are involved in regulating cell proliferation, cell cycle progression and apoptosis of tumor cells. However, the precise cellular mechanisms are still unknown. In the present study, we investigated the effect and mechanisms of quinidine, a commonly used voltage-gated K+ channel blocker, on cell proliferation and apoptosis of human glioma U87-MG cells. We found that quinidine significantly inhibited the proliferation of U87-MG cells and induced apoptosis in a dose-dependent manner. The results of caspase colorimetric assay showed that the mitochondrial pathway was the main mode involved in the quinidine-induced apoptotic process. Furthermore, the concentration range of quinidine, which inhibited voltage-gated K+ channel currents in electrophysiological assay, was consistent with that of quinidine inhibiting cell proliferation and inducing cell apoptosis. In U87-MG cells treated with quinidine (100 µmol/l), 11 of 2,042 human microRNAs (miRNAs) were upregulated and 16 were downregulated as detected with the miRNA array analysis. The upregulation of miR-149-3p and downregulation of miR-424-5p by quinidine treatment were further verified by using quantitative real-time PCR. In addition, using miRNA target prediction program, putative target genes related to cell proliferation and apoptosis for two differentially expressed miRNAs were predicted. Taken together, these data suggested that the anti-proliferative and pro-apoptosis effect of voltage-gated K+ channel blocker quinidine in human glioma cells was mediated at least partly through regulating expression of miRNAs, and provided further support for the mechanisms of voltage-gated K+ channels in mediating cell proliferation and apoptosis.

Mitochondrial KATP Channels Control Glioma Radioresistance by Regulating ROS-Induced ERK Activation

Malignant glioma is the most prevalent form of malignant brain tumor. Although radiotherapy is widely used in glioma treatment, the radioresistance of glioma cells limits the success of the glioma treatment. The lack of effective targets and signaling pathways to reverse glioma radioresistance is the critical obstacle in successful treatment. In this study, we demonstrate that mitochondrial ATP-sensitive potassium channels (mtK(ATP) channels) are overexpressed in glioma cells and are closely related to the malignancy grade and the overall survival of the patients. Importantly, we showed that mtK(ATP) channels could control glioma radioresistance by regulating reactive oxygen species (ROS)-induced ERK activation. The inhibition of mtK(ATP) channels suppresses glioma radioresistance by inhibiting ERK activation both in vitro and in vivo. These findings reveal the important roles of the mitochondria and mtK(ATP) channels as key regulators in the radioresistance of glioma cells, and suggest that mtK(ATP) channel blockers and MAPK/ERK kinase (MEK) inhibitors are potential targets for drug development of glioma treatments.

Nuclear BK channels regulate gene expression via the control of nuclear calcium signaling

Ion channels are essential for the regulation of neuronal functions. The significance of plasma membrane, mitochondrial, endoplasmic reticulum and lysosomal ion channels in the regulation of Ca(2+) is well established. In contrast, surprisingly little is known about the function of ion channels on the nuclear envelope (NE). Here we demonstrate the presence of functional large-conductance, calcium-activated potassium channels (BK channels) on the NE of rodent hippocampal neurons. Functionally, blockade of nuclear BK channels (nBK channels) induces NE-derived Ca(2+) release, nucleoplasmic Ca(2+) elevation and cyclic AMP response element binding protein (CREB)-dependent transcription. More importantly, blockade of nBK channels regulates nuclear Ca(2+)-sensitive gene expression and promotes dendritic arborization in a nuclear Ca(2+)-dependent manner. These results suggest that the nBK channel functions as a molecular link between neuronal activity and nuclear Ca(2+) to convey signals from synapse to nucleus and is a new modulator, operating at the NE, of synaptic activity-dependent neuronal functions.

Ion channels in cancer: future perspectives and clinical potential

Ion transport across the cell membrane mediated by channels and carriers participate in the regulation of tumour cell survival, death and motility. Moreover, the altered regulation of channels and carriers is part of neoplastic transformation. Experimental modification of channel and transporter activity impacts tumour cell survival, proliferation, malignant progression, invasive behaviour or therapy resistance of tumour cells. A wide variety of distinct Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels have been implicated in tumour growth and metastasis. Further experimental information is, however, needed to define the specific role of individual channel isoforms critically important for malignancy. Compelling experimental evidence supports the assumption that the pharmacological inhibition of ion channels or their regulators may be attractive targets to counteract tumour growth, prevent metastasis and overcome therapy resistance of tumour cells. This short review discusses the role of Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels in tumour growth and metastasis and the therapeutic potential of respective inhibitors.

Cl- and K+ channels and their role in primary brain tumour biology

Profound cell volume changes occur in primary brain tumours as they proliferate, invade surrounding tissue or undergo apoptosis. These volume changes are regulated by the flux of Cl(-) and K(+) ions and concomitant movement of water across the membrane, making ion channels pivotal to tumour biology. We discuss which specific Cl(-) and K(+) channels are involved in defined aspects of glioma biology and how these channels are regulated. Cl(-) is accumulated to unusually high concentrations in gliomas by the activity of the NKCC1 transporter and serves as an osmolyte and energetic driving force for volume changes. Cell volume condensation is required as cells enter M phase of the cell cycle and this pre-mitotic condensation is caused by channel-mediated ion efflux. Similarly, Cl(-) and K(+) channels dynamically regulate volume in invading glioma cells allowing them to adjust to small extracellular brain spaces. Finally, cell condensation is a hallmark of apoptosis and requires the concerted activation of Cl(-) and Ca(2+)-activated K(+) channels. Given the frequency of mutation and high importance of ion channels in tumour biology, the opportunity exists to target them for treatment.

Identification of KvLQT1 K+ channels as new regulators of non-small cell lung cancer cell proliferation and migration

K+ channels, which are overexpressed in several cancers, have been identified as regulators of cell proliferation and migration, key processes in cancer development/propagation. Their role in lung cancer has not been studied extensively; but we showed previously that KvLQT1 channels are involved in cell migration, proliferation and repair of normal lung epithelial cells. We now investigated the role of these channels in lung cancer cell lines and their expression levels in human lung adenocarcinoma (AD) tissues. First, we observed that the wound-healing rates of A549 lung adenocarcinoma cell monolayers were reduced by clofilium and chromanol or after silencing with KvLQT1-specific siRNA. Dose-dependent decrease of A549 cell growth and cell accumulation in G0/G1 phase were seen after KvLQT1 inhibition. Clofilium also affected 2D and 3D migration of A549 cells. Similarly, H460 cell growth, migration and wound healing were diminished by this drug. Because K+ channel overexpression has been encountered in some cancers, we assessed KvLQT1 expression levels in tumor tissues from patients with lung AD. KvLQT1 protein expression in tumor samples was increased by 1.5- to 7-fold, compared to paired non-neoplastic tissues, in 17 of 26 patients. In summary, our data reveal that KvLQT1 channel blockade efficiently reduces A549 and H460 cell proliferation and migration. Moreover, KvLQT1 overexpression in AD samples suggests that it could be a potential therapeutic target in lung cancer.

CGRP in the trigeminovascular system: a role for CGRP, adrenomedullin and amylin receptors?

The neuropeptide calcitonin gene-related peptide (CGRP) is reported to play an important role in migraine. It is expressed throughout the trigeminovascular system. Antagonists targeting the CGRP receptor have been developed and have shown efficacy in clinical trials for migraine. However, no CGRP antagonist is yet approved for treating this condition. The molecular composition of the CGRP receptor is unusual because it comprises two subunits; one is a GPCR, the calcitonin receptor-like receptor (CLR). This associates with receptor activity-modifying protein (RAMP) 1 to yield a functional receptor for CGRP. However, RAMP1 also associates with the calcitonin receptor, creating a receptor for the related peptide amylin but this also has high affinity for CGRP. Other combinations of CLR or the calcitonin receptor with RAMPs can also generate receptors that are responsive to CGRP. CGRP potentially modulates an array of signal transduction pathways downstream of activation of these receptors, in a cell type-dependent manner. The physiological significance of these signalling processes remains unclear but may be a potential avenue for refining drug design. This complexity has prompted us to review the signalling and expression of CGRP and related receptors in the trigeminovascular system. This reveals that more than one CGRP responsive receptor may be expressed in key parts of this system and that further work is required to determine their contribution to CGRP physiology and pathophysiology.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Altered expression of two-pore domain potassium (K2P) channels in cancer

Potassium channels have become a focus in cancer biology as they play roles in cell behaviours associated with cancer progression, including proliferation, migration and apoptosis. Two-pore domain (K_2P) potassium channels are background channels which enable the leak of potassium ions from cells. As these channels are open at rest they have a profound effect on cellular membrane potential and subsequently the electrical activity and behaviour of cells in which they are expressed. The K_2P family of channels has 15 mammalian members and already 4 members of this family (K_2P2.1, K_2P3.1, K_2P9.1, K_2P5.1) have been implicated in cancer. Here we examine the expression of all 15 members of the K_2P family of channels in a range of cancer types. This was achieved using the online cancer microarray database, Oncomine (www.oncomine.org). Each gene was examined across 20 cancer types, comparing mRNA expression in cancer to normal tissue. This analysis revealed all but 3 K_2P family members (K_2P4.1, K_2P16.1, K_2P18.1) show altered expression in cancer. Overexpression of K_2P channels was observed in a range of cancers including breast, leukaemia and lung while more cancers (brain, colorectal, gastrointestinal, kidney, lung, melanoma, oesophageal) showed underexpression of one or more channels. K_2P1.1, K_2P3.1, K_2P12.1, were overexpressed in a range of cancers. While K_2P1.1, K_2P3.1, K_2P5.1, K_2P6.1, K_2P7.1 and K_2P10.1 showed significant underexpression across the cancer types examined. This analysis supports the view that specific K_2P channels may play a role in cancer biology. Their altered expression together with their ability to impact the function of other ion channels and their sensitivity to environmental stimuli (pO2, pH, glucose, stretch) makes understanding the role these channels play in cancer of key importance.

K(+) channels and cell cycle progression in tumor cells

K⁺ ions play a major role in many cellular processes. The deregulation of K⁺ signaling is associated with a variety of diseases such as hypertension, atherosclerosis, or diabetes. K⁺ ions are important for setting the membrane potential, the driving force for Ca²⁺ influx, and regulate volume of growing cells. Moreover, it is increasingly recognized that K⁺ channels control cell proliferation through a novel signaling mechanisms triggered and modulated independently of ion fluxes. In cancer, aberrant expression, regulation and/or sublocalization of K⁺ channels can alter the downstream signals that converge on the cell cycle machinery. Various K⁺ channels are involved in cell cycle progression and are needed only at particular stages of the cell cycle. Consistent with this idea, the expression of Eag1 and HERG channels fluctuate along the cell cycle. Despite of acquired knowledge, our understanding of K⁺ channels functioning in cancer cells requires further studies. These include identifying the molecular mechanisms controlling the cell cycle machinery. By understanding how K⁺ channels regulate cell cycle progression in cancer cells, we will gain insights into how cancer cells subvert the need for K⁺ signal and its downstream targets to proliferate.

Hydrogen sulphide suppresses human atrial fibroblast proliferation and transformation to myofibroblasts

Cardiac fibroblasts are crucial in pathophysiology of the myocardium whereby their aberrant proliferation has significant impact on cardiac function. Hydrogen sulphide (H₂S) is a gaseous modulator of potassium channels on cardiomyocytes and has been reported to attenuate cardiac fibrosis. Yet, the mechanism of H₂S in modulating proliferation of cardiac fibroblasts remains poorly understood. We hypothesized that H₂S inhibits proliferative response of atrial fibroblasts through modulation of potassium channels. Biophysical property of potassium channels in human atrial fibroblasts was examined by whole-cell patch clamp technique and their cellular proliferation in response to H₂S was assessed by BrdU assay. Large conductance Ca²⁺-activated K⁺ current (BK_Ca), transient outward K⁺ current (I_to) and inwardly rectifying K⁺ current (IK_ir) were found in human atrial fibroblasts. Current density of BK_Ca (IC₅₀ = 69.4 μM; n = 6), I_to (IC₅₀ = 55.1 μM; n = 6) and IK_ir (IC₅₀ = 78.9 μM; n = 6) was significantly decreased (P < 0.05) by acute exposure to NaHS (a H₂S donor) in atrial fibroblasts. Furthermore, NaHS (100–500 μM) inhibited fibroblast proliferation induced by transforming growth factor-β1 (TGF-β1; 1 ng/ml), Ang II (100 nM) or 20% FBS. Pre-conditioning of fibroblasts with NaHS decreased basal expression of Kv4.3 (encode I_to), but not KCa1.1 (encode BK_Ca) and Kir2.1 (encode IK_ir). Furthermore, H₂S significantly attenuated TGF-β1–stimulated Kv4.3 and α-smooth muscle actin expression, which coincided with its inhibition of TGF-β–induced myofibroblast transformation. Our results show that H₂S attenuates atrial fibroblast proliferation via suppression of K⁺ channel activity and moderates their differentiation towards myofibroblasts.

Functional coupling between large-conductance potassium channels and Cav3.2 voltage-dependent calcium channels participates in prostate cancer cell growth

It is strongly suspected that potassium (K⁺) channels are involved in various aspects of prostate cancer development, such as cell growth. However, the molecular nature of those K⁺ channels implicated in prostate cancer cell proliferation and the mechanisms through which they control proliferation are still unknown. This study uses pharmacological, biophysical and molecular approaches to show that the main voltage-dependent K⁺ current in prostate cancer LNCaP cells is carried by large-conductance BK channels. Indeed, most of the voltage-dependent current was inhibited by inhibitors of BK channels (paxillin and iberiotoxin) and by siRNA targeting BK channels. In addition, we reveal that BK channels constitute the main K⁺ channel family involved in setting the resting membrane potential in LNCaP cells at around −40 mV. This consequently promotes a constitutive calcium entry through T-type Cav3.2 calcium channels. We demonstrate, using single-channel recording, confocal imaging and co-immunoprecipitation approaches, that both channels form macromolecular complexes. Finally, using flow cytometry cell cycle measurements, cell survival assays and Ki67 immunofluorescent staining, we show that both BK and Cav3.2 channels participate in the proliferation of prostate cancer cells.