Voltage-gated K+ channels support proliferation of colonic carcinoma cells

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.

The in vitro anticancer effects of FS48 from salivary glands of Xenopsylla cheopis on NCI-H460 cells via its blockage of voltage-gated K+ channels

Voltage-gated K⁺ (K_v) channels play a role in the cellular processes of various cancer cells, including lung cancer cells. We previously identified and reported a salivary protein from the Xenopsylla cheopis, FS48, which exhibited inhibitory activity against K_v1.1-1.3 channels when assayed in HEK 293T cells. However, whether FS48 has an inhibitory effect on cancer cells expressing Kv channels is unclear. The present study aims to reveal the effects of FS48 on the K_v channels and the NCI-H460 human lung cancer cells through patch clamp, MTT, wound healing, transwell, gelatinase zymography, qRT-PCR and WB assays. The results demonstrated that FS48 can be effective in suppressing the K_v currents, migration, and invasion of NCI-H460 cells in a dose-dependent manner, despite the failure to inhibit the proliferation. Moreover, the expression of K_v1.1 and K_v1.3 mRNA and protein were found to be significantly reduced. Finally, FS48 decreases the mRNA level of MMP-9 while increasing TIMP-1 mRNA level. The present study highlights for the first time that blood-sucking arthropod saliva-derived protein can inhibit the physiological activities of tumour cells via the Kv channels. Furthermore, FS48 can be taken as a hit compound against the tumour cells expressing K_v channels.

A potent ion channel blocker, hydroquinidine, exhibits strong anti-cancer activity on colon, pancreatic, and hepatocellular cancer cells

BACKGROUND

Despite recent advances in drug discovery, cancer is still one of the most lethal health problems worldwide. In most cases, standard therapy methods and multi-modal treatments fail, and new therapeutic approaches are required. Ion channels are essential in multiple cellular processes regulating cell division, differentiation, and death. Recent studies on ion-channel modulators emphasize their potential to suppress tumor growth. In that regard, we reasoned that an underinvestigated potassium channel modulator, Hydroquinidine (HQ), may exhibit an anti-carcinogenic activity.

METHODS AND RESULTS

HQ's potential as an anti-neoplastic compound was examined using colony formation assay, wound healing assay, soft agar assay, and Annexin-V assay in the colon, pancreatic, and hepatocellular carcinomas. Our findings unveiled a remarkable anti-cancer activity of HQ by decreasing colony-forming ability, migration capacity, tumorigenicity, and proliferation and stimulating cellular death. HQ significantly reduced the formed colonies and tumorigenicity for all cells. It displayed a significant anti-migrative effect on hepatocellular carcinoma cells and promoted apoptosis in pancreatic and liver cancer cells. The altered gene expression profile upon HQ treatment was in accordance with observed cellular effects. Cells incubated with HQ downregulated the genes acting in cell division and survival, whereas the expression level of genes functioning in cell cycle arrest and apoptosis was elevated.

CONCLUSION

Our data indicate HQ's competency to limit cancer growth and suggest its utilization as a novel potent anti-carcinogenic agent. Future studies are necessary to provide new insights into the HQ action mechanism and to evaluate its capacity in in-vivo.

The distinguishing electrical properties of cancer cells

In recent decades, medical research has been primarily focused on the inherited aspect of cancers, despite the reality that only 5-10% of tumours discovered are derived from genetic causes. Cancer is a broad term, and therefore it is inaccurate to address it as a purely genetic disease. Understanding cancer cells' behaviour is the first step in countering them. Behind the scenes, there is a complicated network of environmental factors, DNA errors, metabolic shifts, and electrostatic alterations that build over time and lead to the illness's development. This latter aspect has been analyzed in previous studies, but how the different electrical changes integrate and affect each other is rarely examined. Every cell in the human body possesses electrical properties that are essential for proper behaviour both within and outside of the cell itself. It is not yet clear whether these changes correlate with cell mutation in cancer cells, or only with their subsequent development. Either way, these aspects merit further investigation, especially with regards to their causes and consequences. Trying to block changes at various levels of occurrence or assisting in their prevention could be the key to stopping cells from becoming cancerous. Therefore, a comprehensive understanding of the current knowledge regarding the electrical landscape of cells is much needed. We review four essential electrical characteristics of cells, providing a deep understanding of the electrostatic changes in cancer cells compared to their normal counterparts. In particular, we provide an overview of intracellular and extracellular pH modifications, differences in ionic concentrations in the cytoplasm, transmembrane potential variations, and changes within mitochondria. New therapies targeting or exploiting the electrical properties of cells are developed and tested every year, such as pH-dependent carriers and tumour-treating fields. A brief section regarding the state-of-the-art of these therapies can be found at the end of this review. Finally, we highlight how these alterations integrate and potentially yield indications of cells' malignancy or metastatic index.

Cancer as a Channelopathy—Appreciation of Complimentary Pathways Provides a Different Perspective for Developing Treatments

Simple Summary

While improvements in technology have improved our ability to treat many forms of cancer when diagnosed at an early stage of the disease, the ability to improve survival and quality of life for patients with late stage disease has been limited, largely due to the ability of cancer cells to evade destruction when treatments block preferred paths for survival. Here, we review the role that ions and ion channels play in normal cell function, the development of disease and their role in the life and death of a cell. It is hoped that viewing cancer from the perspective of altered ion channel expression and ion balance may provide a novel approach for developing more effective treatments for this devastating disease.

Abstract

Life depends upon the ability of cells to evaluate and adapt to a constantly changing environment and to maintain internal stability to allow essential biochemical reactions to occur. Ions and ion channels play a crucial role in this process and are essential for survival. Alterations in the expression of the transmembrane proteins responsible for maintaining ion balance that occur as a result of mutations in the genetic code or in response to iatrogenically induced changes in the extracellular environment is a characteristic feature of oncogenesis and identifies cancer as one of a constellation of diseases known as channelopathies. The classification of cancer as a channelopathy provides a different perspective for viewing the disease. Potentially, it may expand opportunities for developing novel ways to affect or reverse the deleterious changes that underlie establishing and sustaining disease and developing tolerance to therapeutic attempts at treatment. The role of ions and ion channels and their interactions in the cell’s ability to maintain ionic balance, homeostasis, and survival are reviewed and possible approaches that mitigate gain or loss of ion channel function to contribute to new or enhance existing cancer therapies are discussed.

Pleiotropic Roles of Atrial Natriuretic Peptide in Anti-Inflammation and Anti-Cancer Activity

Simple Summary

The relationship between inflammation and carcinogenesis, as well as the response to anti-tumor therapy, is intimate. Atrial natriuretic peptides (ANPs) play a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance. In addition, ANPs exert immune-modulatory effects in the tissue microenvironment, thus exhibiting a fascinating ability to prevent inflammation-related tumorigenesis and cancer recurrence. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs have potential therapeutic value in tumors. Here, we summarized the roles of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs, contributing to the development of ANP-based anti-cancer agents.

Abstract

The atrial natriuretic peptide (ANP), a cardiovascular hormone, plays a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance and is approved to treat congestive heart failure. In addition, there is a growing realization that ANPs might be related to immune response and tumor growth. The anti-inflammatory and immune-modulatory effects of ANPs in the tissue microenvironment are mediated through autocrine or paracrine mechanisms, which further suppress tumorigenesis. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs act on several hallmarks of cancer, such as inflammation, angiogenesis, sustained tumor growth, and metastasis. In this review, we summarized the contributions of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs.

The Kv10.1 Channel: A Promising Target in Cancer

Carcinogenesis is a multistage process involving the dysregulation of multiple genes, proteins, and pathways that make any normal cell acquire a cancer cell phenotype. Therefore, it is no surprise that numerous ion channels could be involved in this process. Since their discovery and subsequent cloning, ion channels have been established as therapeutic targets in excitable cell pathologies (e.g., cardiac arrhythmias or epilepsy); however, their involvement in non-excitable cell pathologies is relatively recent. Among all ion channels, the voltage-gated potassium channels Kv10.1 have been established as a promising target in cancer treatment due to their high expression in tumoral tissues compared to low levels in healthy tissues.

Small molecule-based detection of non-canonical RNA G-quadruplex structures that modulate protein translation

Tandem repeats of guanine-rich sequences in RNA often form thermodynamically stable four-stranded RNA structures. Such RNA G-quadruplexes have long been considered to be linked to essential biological processes, yet their physiological significance in cells remains unclear. Here, we report a approach that permits the detection of RNA G-quadruplex structures that modulate protein translation in mammalian cells. The approach combines antibody arrays and RGB-1, a small molecule that selectively stabilizes RNA G-quadruplex structures. Analysis of the protein and mRNA products of 84 cancer-related human genes identified Nectin-4 and CapG as G-quadruplex-controlled genes whose mRNAs harbor non-canonical G-quadruplex structures on their 5′UTR region. Further investigations revealed that the RNA G-quadruplex of CapG exhibits a structural polymorphism, suggesting a possible mechanism that ensures the translation repression in a KCl concentration range of 25–100 mM. The approach described in the present study sets the stage for further discoveries of RNA G-quadruplexes.

The Effectiveness of Isoplumbagin and Plumbagin in Regulating Amplitude, Gating Kinetics, and Voltage-Dependent Hysteresis of erg-mediated K+ Currents

Isoplumbagin (isoPLB, 5-hydroxy-3-methyl-1,4-naphthoquinone), a naturally occurring quinone, has been observed to exercise anti-inflammatory, antimicrobial, and antineoplastic activities. Notably, whether and how isoPLB, plumbagin (PLB), or other related compounds impact transmembrane ionic currents is not entirely clear. In this study, during GH3-cell exposure to isoPLB, the peak and sustained components of an erg (ether-à-go-go related gene)-mediated K+ current (IK(erg)) evoked with long-lasting-step hyperpolarization were concentration-dependently decreased, with a concomitant increase in the decaying time constant of the deactivating current. The presence of isoPLB led to a differential reduction in the peak and sustained components of deactivating IK(erg) with effective IC50 values of 18.3 and 2.4 μM, respectively, while the KD value according to the minimum binding scheme was estimated to be 2.58 μM. Inhibition by isoPLB of IK(erg) was not reversed by diazoxide; however, further addition of isoPLB, during the continued exposure to 4,4'-dithiopyridine, did not suppress IK(erg) further. The recovery of IK(erg) by a two-step voltage pulse with a geometric progression was slowed in the presence of isoPLB, and the decaying rate of IK(erg) activated by the envelope-of-tail method was increased in its presence. The strength of the IK(erg) hysteresis in response to an inverted isosceles-triangular ramp pulse was diminished by adding isoPLB. A mild inhibition of the delayed-rectifier K+ current (IK(DR)) produced by the presence of isoPLB was seen in GH3 cells, while minimal changes in the magnitude of the voltage-gated Na+ current were demonstrated in its presence. Moreover, the IK(erg) identified in MA-10 Leydig tumor cells was blocked by adding isoPLB. Therefore, the effects of isoPLB or PLB on ionic currents (e.g., IK(erg) and IK(DR)) demonstrated herein would be upstream of our previously reported perturbations on mitochondrial morphogenesis or respiration. Taken together, the perturbations of ionic currents by isoPLB or PLB demonstrated herein are likely to contribute to the underlying mechanism through which they, or other structurally similar compounds, result in adjustments in the functional activities of different neoplastic cells (e.g., GH3 and MA-10 cells), presuming that similar in vivo observations occur.

Regulatory role of Non-canonical DNA Polymorphisms in human genome and their relevance in Cancer

DNA has the ability to form polymorphic structures like canonical duplex DNA and non-canonical triplex DNA, Cruciform, Z-DNA, G-quadruplex (G4), i-motifs, and hairpin structures. The alteration in the form of DNA polymorphism in the response to environmental changes influences the gene expression. Non-canonical structures are engaged in various biological functions, including chromatin epigenetic and gene expression regulation via transcription and translation, as well as DNA repair and recombination. The presence of non-canonical structures in the regulatory region of the gene alters the gene expression and affects the cellular machinery. Formation of non-canonical structure in the regulatory site of cancer-related genes either inhibits or dysregulate the gene function and promote tumour formation. In the current article, we review the influence of non-canonical structure on the regulatory mechanisms in human genome. Moreover, we have also discussed the relevance of non-canonical structures in cancer and provided information on the drugs used for their treatment by targeting these structures.

Roles of non-canonical structures of nucleic acids in cancer and neurodegenerative diseases

Cancer and neurodegenerative diseases are caused by genetic and environmental factors. Expression of tumour suppressor genes is suppressed by mutations or epigenetic silencing, whereas for neurodegenerative disease-related genes, nucleic acid-based effects may be presented through loss of protein function due to erroneous protein sequences or gain of toxic function from extended repeat transcripts or toxic peptide production. These diseases are triggered by damaged genes and proteins due to lifestyle and exposure to radiation. Recent studies have indicated that transient, non-canonical structural changes in nucleic acids in response to the environment can regulate the expression of disease-related genes. Non-canonical structures are involved in many cellular functions, such as regulation of gene expression through transcription and translation, epigenetic regulation of chromatin, and DNA recombination. Transcripts generated from repeat sequences of neurodegenerative disease-related genes form non-canonical structures that are involved in protein transport and toxic aggregate formation. Intracellular phase separation promotes transcription and protein assembly, which are controlled by the nucleic acid structure and can influence cancer and neurodegenerative disease progression. These findings may aid in elucidating the underlying disease mechanisms. Here, we review the influence of non-canonical nucleic acid structures in disease-related genes on disease onset and progression.

New Insights into the Functions of Nucleic Acids Controlled by Cellular Microenvironments

The right-handed double-helical B-form structure (B-form duplex) has been widely recognized as the canonical structure of nucleic acids since it was first proposed by James Watson and Francis Crick in 1953. This B-form duplex model has a monochronic and static structure and codes genetic information within a sequence. Interestingly, DNA and RNA can form various non-canonical structures, such as hairpin loops, left-handed helices, triplexes, tetraplexes of G-quadruplex and i-motif, and branched junctions, in addition to the canonical structure. The formation of non-canonical structures depends not only on sequence but also on the surrounding environment. Importantly, these non-canonical structures may exhibit a wide variety of biological roles by changing their structures and stabilities in response to the surrounding environments, which undergo vast changes at specific locations and at specific times in cells. Here, we review recent progress regarding the interesting behaviors and functions of nucleic acids controlled by molecularly crowded cellular conditions. New insights gained from recent studies suggest that nucleic acids not only code genetic information in sequences but also have unknown functions regarding their structures and stabilities through drastic structural changes in cellular environments.

The Role of pHi in Intestinal Epithelial Proliferation-Transport Mechanisms, Regulatory Pathways, and Consequences

During the maturation of intestinal epithelial cells along the crypt/surface axis, a multitude of acid/base transporters are differentially expressed in their apical and basolateral membranes, enabling processes of electrolyte, macromolecule, nutrient, acid/base and fluid secretion, and absorption. An intracellular pH (pHi)-gradient is generated along the epithelial crypt/surface axis, either as a consequence of the sum of the ion transport activities or as a distinctly regulated entity. While the role of pHi on proliferation, migration, and tumorigenesis has been explored in cancer cells for some time, emerging evidence suggests an important role of the pHi in the intestinal stem cells (ISCs) proliferative rate under physiological conditions. The present review highlights the current state of knowledge about the potential regulatory role of pHi on intestinal proliferation and differentiation.

Sexual Dimorphism in Colon Cancer

A higher incidence of colorectal cancer (CRC) is found in males compared to females. Young women (18-44 years) with CRC have a better survival outcome compared to men of the same age or compared to older women (over 50 years), indicating a global incidence of sexual dimorphism in CRC rates and survival. This suggests a protective role for the sex steroid hormone estrogen in CRC development. Key proliferative pathways in CRC tumorigenesis exhibit sexual dimorphism, which confer better survival in females through estrogen regulated genes and cell signaling. Estrogen regulates the activity of a class of Kv channels (KCNQ1:KCNE3), which control fundamental ion transport functions of the colon and epithelial mesenchymal transition through bi-directional interactions with the Wnt/β-catenin signalling pathway. Estrogen also modulates CRC proliferative responses in hypoxia via the novel membrane estrogen receptor GPER and HIF1A and VEGF signaling. Here we critically review recent clinical and molecular insights into sexual dimorphism of CRC biology modulated by the tumor microenvironment, estrogen, Wnt/β-catenin signalling, ion channels, and X-linked genes.

pH-Channeling in Cancer: How pH-Dependence of Cation Channels Shapes Cancer Pathophysiology

Tissue acidosis plays a pivotal role in tumor progression: in particular, interstitial acidosis promotes tumor cell invasion, and is a major contributor to the dysregulation of tumor immunity and tumor stromal cells. The cell membrane and integral membrane proteins commonly act as important sensors and transducers of altered pH. Cell adhesion molecules and cation channels are prominent membrane proteins, the majority of which is regulated by protons. The pathophysiological consequences of proton-sensitive ion channel function in cancer, however, are scarcely considered in the literature. Thus, the main focus of this review is to highlight possible events in tumor progression and tumor immunity where the pH sensitivity of cation channels could be of great importance.

Kv10.1 Regulates Microtubule Dynamics during Mitosis

Kv10.1 (potassium voltage-gated channel subfamily H member 1, known as EAG1 or Ether-à-go-go 1), is a voltage-gated potassium channel, prevailingly expressed in the central nervous system. The aberrant expression of Kv10.1 is detected in over 70% of all human tumor tissues and correlates with poorer prognosis. In peripheral tissues, Kv10.1 is expressed almost exclusively during the G2/M phase of the cell cycle and regulates its progression-downregulation of Kv10.1 extends the duration of the G2/M phase both in cancer and healthy cells. Here, using biochemical and imaging techniques, such as live-cell measurements of microtubule growth and of cytosolic calcium, we elucidate the mechanisms of Kv10.1-mediated regulation at the G2/M phase. We show that Kv10.1 has a dual effect on mitotic microtubule dynamics. Through the functional interaction with ORAI1 (calcium release-activated calcium channel protein 1), it modulates cytosolic calcium oscillations, thereby changing microtubule behavior. The inhibition of either Kv10.1 or ORAI1 stabilizes the microtubules. In contrast, the knockdown of Kv10.1 increases the dynamicity of mitotic microtubules, resulting in a stronger spindle assembly checkpoint, greater mitotic spindle angle, and a decrease in lagging chromosomes. Understanding of Kv10.1-mediated modulation of the microtubule architecture will help to comprehend how cancer tissue benefits from the presence of Kv10.1, and thereby increase the efficacy and safety of Kv10.1-directed therapeutic strategies.

Inhibition of voltage-gated K+ channels mediates docosahexaenoic acid-stimulated insulin secretion in rat pancreatic β-cells

Kv channels play a vital role in DHA-augmented insulin secretion through GPR40/AC/cAMP/PLC signaling pathway in rat pancreatic β-cells.

Expression of potassium channel genes predicts clinical outcome in lung cancer

Lung cancer is the most common cause of cancer deaths worldwide and several molecular signatures have been developed to predict survival in lung cancer. Increasing evidence suggests that proliferation and migration to promote tumor growth are associated with dysregulated ion channel expression. In this study, by analyzing high-throughput gene expression data, we identify the differentially expressed K⁺ channel genes in lung cancer. In total, we prioritize ten dysregulated K⁺ channel genes (5 up-regulated and 5 down-regulated genes, which were designated as K-10) in lung tumor tissue compared with normal tissue. A risk scoring system combined with the K-10 signature accurately predicts clinical outcome in lung cancer, which is independent of standard clinical and pathological prognostic factors including patient age, lymph node involvement, tumor size, and tumor grade. We further indicate that the K-10 potentially predicts clinical outcome in breast and colon cancers. Molecular signature discovered through K⁺ gene expression profiling may serve as a novel biomarker to assess the risk in lung cancer.

The Maxi-K (BK) Channel Antagonist Penitrem A as a Novel Breast Cancer-Targeted Therapeutic

Breast cancer (BC) is a heterogeneous disease with different molecular subtypes. The high conductance calcium-activated potassium channels (BK, Maxi-K channels) play an important role in the survival of some BC phenotypes, via membrane hyperpolarization and regulation of cell cycle. BK channels have been implicated in BC cell proliferation and invasion. Penitrems are indole diterpene alkaloids produced by various terrestrial and marine Penicillium species. Penitrem A (1) is a selective BK channel antagonist with reported antiproliferative and anti-invasive activities against multiple malignancies, including BC. This study reports the high expression of BK channel in different BC subtypes. In silico BK channel binding affinity correlates with the antiproliferative activities of selected penitrem analogs. 1 showed the best binding fitting at multiple BK channel crystal structures, targeting the calcium-sensing aspartic acid moieties at the calcium bowel and calcium binding sites. Further, 1 reduced the levels of BK channel expression and increased expression of TNF-α in different BC cell types. Penitrem A (1) induced G1 cell cycle arrest of BC cells, and induced upregulation of the arrest protein p27. Combination treatment of 1 with targeted anti-HER drugs resulted in synergistic antiproliferative activity, which was associated with reduced EGFR and HER2 receptor activation, as well as reduced active forms of AKT and STAT3. Collectively, the BK channel antagonists represented by penitrem A can be novel sensitizing, chemotherapeutics synergizing, and therapeutic agents for targeted BC therapy.

Voltage-gated potassium channel blocker 4-aminopyridine induces glioma cell apoptosis by reducing expression of microRNA-10b-5p

Accumulating evidence has demonstrated that voltage-gated potassium channels (Kv channels) were associated with regulating cell proliferation and apoptosis in tumor cells. Our previous study proved that the Kv channel blocker 4-aminopyridine (4-AP) could inhibit cell proliferation and induce apoptosis in glioma. However, the precise mechanisms were not clear yet. MicroRNAs (miRNAs) are small noncoding RNAs that act as key mediators in the progression of tumor, so the aim of this study was to investigate the role of miRNAs in the apoptosis-promoting effect of 4-AP in glioma cells. Using a microRNA array, we found that 4-AP altered the miRNA expression in glioma cells, and the down-regulation of miR-10b-5p induced by 4-AP was verified by real-time PCR. Transfection of miR-10b-5p mimic significantly inhibited 4-AP-induced caspases activation and apoptosis. Moreover, we verified that apoptosis-related molecule Apaf-1 was the direct target of miR-10b-5p. Furthermore, miR-10b-5p mimic significantly inhibited 4-AP-induced up-regulation of Apaf-1 and its downstream apoptosis-related proteins, such as cleaved caspase-3. In conclusion, Kv channel blocker 4-AP may exert its anti-tumor effect by down-regulating the expression of miR-10b-5p and then raised expression of Apaf-1 and its downstream apoptosis-related proteins. Current data provide evidence that miRNAs play important roles in Kv channels-mediated cell proliferation and apoptosis.

Plasma membrane depolarization and permeabilization due to electric pulses in cell lines of different excitability

In electroporation-based medical treatments, excitable tissues are treated, either intentionally (irreversible electroporation of brain cancer, gene electrotransfer or ablation of the heart muscle, gene electrotransfer of skeletal muscles), or unintentionally (excitable tissues near the target area). We investigated how excitable and non-excitable cells respond to electric pulses, and if electroporation could be an effective treatment of the tumours of the central nervous system. For three non-excitable and one excitable cell line, we determined a strength-duration curve for a single pulse of 10ns-10ms. The threshold for depolarization decreased with longer pulses and was higher for excitable cells. We modelled the response with the Lapicque curve and the Hodgkin-Huxley model. At 1μs a plateau of excitability was reached which could explain why high-frequency irreversible electroporation (H-FIRE) electroporates but does not excite cells. We exposed cells to standard electrochemotherapy parameters (8×100μs pulses, 1Hz, different voltages). Cells behaved similarly which indicates that electroporation most probably occurs at the level of lipid bilayer, independently of the voltage-gated channels. These results could be used for optimization of electric pulses to achieve maximal permeabilization and minimal excitation/pain sensation. In the future, it should be established whether the in vitro depolarization correlates to nerve/muscle stimulation and pain sensation in vivo.

The hidden potential of lysosomal ion channels: A new era of oncogenes

Lysosomes serve as the control centre for cellular clearance. These membrane-bound organelles receive biomolecules destined for degradation from intracellular and extracellular pathways; thus, facilitating the production of energy and shaping the fate of the cell. At the base of their functionality are the lysosomal ion channels which mediate the function of the lysosome through the modulation of ion influx and efflux. Ion channels form pores in the membrane of lysosomes and allow the passage of ions, a seemingly simple task which harbours the potential of overthrowing the cell's stability. Considered the master regulators of ion homeostasis, these integral membrane proteins enable the proper operation of the lysosome. Defects in the structure or function of these ion channels lead to the development of lysosomal storage diseases, neurodegenerative diseases and cancer. Although more than 50 years have passed since their discovery, lysosomes are not yet fully understood, with their ion channels being even less well characterized. However, significant improvements have been made in the development of drugs targeted against these ion channels as a means of combating diseases. In this review, we will examine how Ca²⁺, K⁺, Na⁺ and Cl^- ion channels affect the function of the lysosome, their involvement in hereditary and spontaneous diseases, and current ion channel-based therapies.

The combined activation of KCa3.1 and inhibition of Kv11.1/hERG1 currents contribute to overcome Cisplatin resistance in colorectal cancer cells

Background:

Platinum-based drugs such as Cisplatin are commonly employed for cancer treatment. Despite an initial therapeutic response, Cisplatin treatment often results in the development of chemoresistance. To identify novel approaches to overcome Cisplatin resistance, we tested Cisplatin in combination with K⁺ channel modulators on colorectal cancer (CRC) cells.

Methods:

The functional expression of Ca²⁺-activated (K_Ca3.1, also known as KCNN4) and voltage-dependent (K_v11.1, also known as KCNH2 or hERG1) K⁺ channels was determined in two CRC cell lines (HCT-116 and HCT-8) by molecular and electrophysiological techniques. Cisplatin and several K⁺ channel modulators were tested in vitro for their action on K⁺ currents, cell vitality, apoptosis, cell cycle, proliferation, intracellular signalling and Platinum uptake. These effects were also analysed in a mouse model mimicking Cisplatin resistance.

Results:

Cisplatin-resistant CRC cells expressed higher levels of K_Ca3.1 and K_v11.1 channels, compared with Cisplatin-sensitive CRC cells. In resistant cells, K_Ca3.1 activators (SKA-31) and K_v11.1 inhibitors (E4031) had a synergistic action with Cisplatin in triggering apoptosis and inhibiting proliferation. The effect was maximal when K_Ca3.1 activation and K_v11.1 inhibition were combined. In fact, similar results were produced by Riluzole, which is able to both activate K_Ca3.1 and inhibit K_v11.1. Cisplatin uptake into resistant cells depended on K_Ca3.1 channel activity, as it was potentiated by K_Ca3.1 activators. K_v11.1 blockade led to increased K_Ca3.1 expression and thereby stimulated Cisplatin uptake. Finally, the combined administration of a K_Ca3.1 activator and a K_v11.1 inhibitor also overcame Cisplatin resistance in vivo.

Conclusions:

As Riluzole, an activator of K_Ca3.1 and inhibitor of K_v11.1 channels, is in clinical use, our results suggest that this compound may be useful in the clinic to improve Cisplatin efficacy and overcome Cisplatin resistance in CRC.

Gestational high-fat diet and bisphenol A exposure heightens mammary cancer risk

In utero exposure to bisphenol A (BPA) increases mammary cancer susceptibility in offspring. High-fat diet is widely believed to be a risk factor of breast cancer. The objective of this study was to determine whether maternal exposure to BPA in addition to high-butterfat (HBF) intake during pregnancy further influences carcinogen-induced mammary cancer risk in offspring, and its dose-response curve. In this study, we found that gestational HBF intake in addition to a low-dose BPA (25 µg/kg BW/day) exposure increased mammary tumor incidence in a 50-day-of-age chemical carcinogen administration model and altered mammary gland morphology in offspring in a non-monotonic manner, while shortening tumor-free survival time compared with the HBF-alone group. In utero HBF and BPA exposure elicited differential effects at the gene level in PND21 mammary glands through DNA methylation, compared with HBF intake in the absence of BPA. Top HBF + BPA-dysregulated genes (ALDH1B1, ASTL, CA7, CPLX4, KCNV2, MAGEE2 and TUBA3E) are associated with poor overall survival in The Cancer Genomic Atlas (TCGA) human breast cancer cohort (n = 1082). Furthermore, the prognostic power of the identified genes was further enhanced in the survival analysis of Caucasian patients with estrogen receptor-positive tumors. In conclusion, concurrent HBF dietary and a low-dose BPA exposure during pregnancy increases mammary tumor incidence in offspring, accompanied by alterations in mammary gland development and gene expression, and possibly through epigenetic reprogramming.

Silencing of voltage-gated potassium channel KV9.3 inhibits proliferation in human colon and lung carcinoma cells

Voltage-gated potassium (K_v) channels are known to be involved in cancer development and cancer cell proliferation. K_V9.3, an electronically silent subunit, forms heterotetramers with K_V2.1 in excitable cells and modulates its electrophysiological properties. However, the role of K_V9.3 alone in non-excitable cancer cells has not been studied. Here, we evaluated the effect of silencing K_V9.3 on cancer cell proliferation in HCT15 colon carcinoma cells and A549 lung adenocarcinoma cells. We confirmed the expression of K_V9.3 mRNA in HCT15 and A549 cells and showed that silencing K_V9.3 using small interfering RNA caused G0/G1 cell cycle arrest and alterations in cell cycle regulatory proteins in both HCT15 and A549 cells without affecting apoptosis. Also, stable knockdown of K_V9.3 expression using short-hairpin RNA inhibited tumor growth in SCID mouse xenograft model. Using a bioinformatics approach, we identified Sp1 binding sites in the promoter region of the gene encoding K_V9.3. We further found that Sp1 bound to this region and showed that the Sp1 inhibitor, mithramycin A, induced a concentration-dependent decrease in K_V9.3 expression. Taken together, these data suggest that knockdown of K_V9.3 inhibits proliferation in colon carcinoma and lung adenocarcinoma cell lines and may be regulated by Sp1.

The Role of KV7.3 in Regulating Osteoblast Maturation and Mineralization

KCNQ (KV7) channels are voltage-gated potassium (KV) channels, and the function of KV7 channels in muscles, neurons, and sensory cells is well established. We confirmed that overall blockade of KV channels with tetraethylammonium augmented the mineralization of bone-marrow-derived human mesenchymal stem cells during osteogenic differentiation, and we determined that KV7.3 was expressed in MG-63 and Saos-2 cells at the mRNA and protein levels. In addition, functional KV7 currents were detected in MG-63 cells. Inhibition of KV7.3 by linopirdine or XE991 increased the matrix mineralization during osteoblast differentiation. This was confirmed by alkaline phosphatase, osteocalcin, and osterix in MG-63 cells, whereas the expression of Runx2 showed no significant change. The extracellular glutamate secreted by osteoblasts was also measured to investigate its effect on MG-63 osteoblast differentiation. Blockade of KV7.3 promoted the release of glutamate via the phosphorylation of extracellular signal-regulated kinase 1/2-mediated upregulation of synapsin, and induced the deposition of type 1 collagen. However, activation of KV7.3 by flupirtine did not produce notable changes in matrix mineralization during osteoblast differentiation. These results suggest that KV7.3 could be a novel regulator in osteoblast differentiation.

Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders

Members of the electrically silent voltage-gated K(+) (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K(+) channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments.

Voltage-gated ion channels in cancer cell proliferation

Changes of the electrical charges across the surface cell membrane are absolutely necessary to maintain cellular homeostasis in physiological as well as in pathological conditions. The opening of ion channels alter the charge distribution across the surface membrane as they allow the diffusion of ions such as K+, Ca++, Cl.

Targeting ion channels for cancer therapy by repurposing the approved drugs

Ion channels have been shown to be involved in oncogenesis and efforts are being poured in to target the ion channels. There are many clinically approved drugs with ion channels as "off" targets. The question is, can these drugs be repurposed to inhibit ion channels for cancer treatment? Repurposing of drugs will not only save investors' money but also result in safer drugs for cancer patients. Advanced bioinformatics techniques and availability of a plethora of open access data on FDA approved drugs for various indications and omics data of large number of cancer types give a ray of hope to look for possibility of repurposing those drugs for cancer treatment. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Potassium channels in pancreatic duct epithelial cells: their role, function and pathophysiological relevance

Pancreatic ductal epithelial cells play a fundamental role in HCO3 (-) secretion, a process which is essential for maintaining the integrity of the pancreas. Although several studies have implicated impaired HCO3 (-) and fluid secretion as a triggering factor in the development of pancreatitis, the mechanism and regulation of HCO3 (-) secretion is still not completely understood. To date, most studies on the ion transporters that orchestrate ductal HCO3 (-) secretion have focussed on the role of Cl(-)/HCO3 (-) exchangers and Cl(-) channels, whereas much less is known about the role of K(+) channels. However, there is growing evidence that many types of K(+) channels are present in ductal cells where they have an essential role in establishing and maintaining the electrochemical driving force for anion secretion. For this reason, strategies that increase K(+) channel function may help to restore impaired HCO3 (-) and fluid secretion, such as in pancreatitis, and therefore provide novel directions for future pancreatic therapy. In this review, our aims are to summarize the types of K(+) channels found in pancreatic ductal cells and to discuss their individual roles in ductal HCO3 (-) secretion. We will also describe how K(+) channels are involved in pathophysiological conditions and discuss how they could act as new molecular targets for the development of therapeutic approaches to treat pancreatic diseases.

CACNA2D2 promotes tumorigenesis by stimulating cell proliferation and angiogenesis

In the present study, we have assessed whether a putative calcium channel α2δ2 auxiliary subunit (CACNA2D2 gene) could be involved in prostate cancer (PCA) progression. We therefore carried out experiments to determine whether this protein is expressed in PCA LNCaP cells and in PCA tissues, and whether its expression may be altered during cancer development. In addition, we evaluated the influence on cell proliferation of overexpressing or downregulating this subunit. In vitro experiments show that α2δ2 subunit overexpression is associated with increased cell proliferation, alterations of calcium homeostasis and the recruitment of a nuclear factor of activated T-cells pathway. Furthermore, we carried out in vivo experiments on immuno-deficient nude mice in order to evaluate the tumorigenic potency of the α2δ2 subunit. We show that α2δ2-overexpressing PCA LNCaP cells are more tumorigenic than control LNCaP cells when injected into nude mice. In addition, gabapentin, a ligand of α2δ2, reduces tumor development in LNCaP xenografts. Finally, we show that the action of α2δ2 on tumor development occurs not only through a stimulation of proliferation, but also through a stimulation of angiogenesis, via an increased secretion of vascular endothelial growth factor in cells overexpressing α2δ2.

Ion channel expression as promising cancer biomarker

Cancer is a disease with marked heterogeneity in both response to therapy and survival. Clinical and histopathological characteristics have long determined prognosis and therapy. The introduction of molecular diagnostics has heralded an explosion in new prognostic factors. Overall, histopathology, immunohistochemistry and molecular biology techniques have described important new prognostic subgroups in the different cancer categories. Ion channels and transporters (ICT) are a new class of membrane proteins which are aberrantly expressed in several types of human cancers. Besides regulating different aspect of cancer cell behavior, ICT can now represent novel cancer biomarkers. A summary of the data obtained so far and relative to breast, prostate, lung, colorectal, esophagus, pancreatic and gastric cancers are reported. Special emphasis is given to those studies aimed at relating specific ICT or a peculiar ICT profile with current diagnostic methods. Overall, we are close to exploit ICTs for diagnostic, prognostic or predictive purposes in cancer. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Involvement of potassium channels in the progression of cancer to a more malignant phenotype

Potassium channels are a diverse group of pore-forming transmembrane proteins that selectively facilitate potassium flow through an electrochemical gradient. They participate in the control of the membrane potential and cell excitability in addition to different cell functions such as cell volume regulation, proliferation, cell migration, angiogenesis as well as apoptosis. Because these physiological processes are essential for the correct cell function, K+ channels have been associated with a growing number of diseases including cancer. In fact, different K+ channel families such as the voltage-gated K+ channels, the ether à-go-go K+ channels, the two pore domain K+ channels and the Ca2+-activated K+ channels have been associated to tumor biology. Potassium channels have a role in neoplastic cell-cycle progression and their expression has been found abnormal in many types of tumors and cancer cells. In addition, the expression and activity of specific K+ channels have shown a significant correlation with the tumor malignancy grade. The aim of this overview is to summarize published data on K+ channels that exhibit oncogenic properties and have been linked to a more malignant cancer phenotype. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Big Potassium (BK) ion channels in biology, disease and possible targets for cancer immunotherapy

The Big Potassium (BK) ion channel is commonly known by a variety of names (Maxi-K, KCNMA1, slo, stretch-activated potassium channel, KCa1.1). Each name reflects a different physical property displayed by this single ion channel. This transmembrane channel is found on nearly every cell type of the body and has its own distinctive roles for that tissue type. The BKα channel contains the pore that releases potassium ions from intracellular stores. This ion channel is found on the cell membrane, endoplasmic reticulum, Golgi and mitochondria. Complex splicing pathways produce different isoforms. The BKα channels can be phosphorylated, palmitoylated and myristylated. BK is composed of a homo-tetramer that interacts with β and γ chains. These accessory proteins provide a further modulating effect on the functions of BKα channels. BK channels play important roles in cell division and migration. In this review, we will focus on the biology of the BK channel, especially its role, and its immune response towards cancer. Recent proteomic studies have linked BK channels with various proteins. Some of these interactions offer further insight into the role that BK channels have with cancers, especially with brain tumors. This review shows that BK channels have a complex interplay with intracellular components of cancer cells and still have plenty of secrets to be discovered.

Tumor-associated macrophage-derived IL-6 and IL-8 enhance invasive activity of LoVo cells induced by PRL-3 in a KCNN4 channel-dependent manner

Background

Tumor-associated macrophages (TAMs) are known to promote cancer progression and metastasis through the release of a variety of cytokines. Phosphatase of regenerating liver (PRL-3) has been considered as a marker of colorectal cancer (CRC) liver metastasis. Our previous research suggests that PRL-3 can enhance the metastasis of CRC through the up-regulation of intermediate-conductance Ca²⁺-activated K⁺ (KCNN4) channel, which is dependent on the autocrine secretion of tumor necrosis factor-alpha (TNF-α). However, whether TAMs participate in the progression and metastasis of CRC induced by PRL-3 remains unknown.

Methods

We used flow cytometry, coculture, western blotting, invasion assays, real-time quantitative PCR, chromatin immunoprecipitation, luciferase reporter assays, and immunofluorescence staining to determine the effect of TAMs on the ability of PRL-3 to promote invasiveness of CRC cells.

Results

In this study, we found that TAMs facilitated the metastasis of CRC induced by PRL-3. When TAMs were cocultured with CRC cells, the expression of KCNN4 was increased in TAMs and the invasion of CRC cells was enhanced. Furthermore, cytokines that were secreted by TAMs, such as IL-6 and IL-8, were also significantly increased. This response was attenuated by treating TAMs with the KCNN4 channel-specific inhibitor, 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34), which suggested that KCNN4 channels may be involved in inducing the secretion of IL-6 and IL-8 by TAMs and improving CRC cell invasiveness. Moreover, the expression of KCNN4 channels in TAMs was regulated through the NF-κB signal pathway, which is activated by TNF-α from CRC cells. Immunofluorescence analysis of colorectal specimens indicated that IL-6 and IL-8 double positive cells in the stroma showed positive staining for the TAM marker CD68, suggesting that TAMs produce IL-6 and IL-8. Increased numbers of these cells correlated with higher clinical stage.

Conclusions

Our findings suggested that TAMs participate in the metastasis of CRC induced by PRL-3 through the TNF-α mediated secretion of IL-6 and IL-8 in a paracrine manner.

Radiation-induced bystander effects in the Atlantic salmon (salmo salar L.) following mixed exposure to copper and aluminum combined with low-dose gamma radiation

Very little is known about the combined effects of low doses of heavy metals and radiation. However, such "multiple stressor" exposure is the reality in the environment. In the work reported in this paper, fish were exposed to cobalt 60 gamma irradiation with or without copper or aluminum in the water. Doses of radiation ranged from 4 to 75 mGy delivered over 48 or 6 h. Copper doses ranged from 10 to 80 μg/L for the same time period. The aluminum dose was 250 μg/L. Gills and skin were removed from the fish after exposure and explanted in tissue culture flasks for investigation of bystander effects of the exposures using a stress signal reporter assay, which has been demonstrated to be a sensitive indicator of homeostatic perturbations in cells. The results show complex synergistic interactions of radiation and copper. Gills on the whole produce more toxic bystander signals than skin, but the additivity scores show highly variable results which depend on dose and time of exposure. The impacts of low doses of copper and low doses of radiation are greater than additive, medium levels of copper alone have a similar level of effect of bystander signal toxicity to the low dose. The addition of radiation stress, however, produces clear protective effects in the reporters treated with skin-derived medium. Gill-derived medium from the same fish did not show protective effects. Radiation exposure in the presence of 80 μg/L led to highly variable results, which due to animal variation were not significantly different from the effect of copper alone. The results are stressor type, stressor concentration and time dependent. Clearly co-exposure to radiation and heavy metals does not always lead to simple additive effects.

Ion channels and apoptosis in cancer

Humans maintain a constant cell number throughout their lifespan. This equilibrium of cell number is accomplished when cell proliferation and cell death are kept balanced, achieving a steady-state cell number. Abnormalities in cell growth or cell death can lead to an overabundance of cells known as neoplasm or tumours. While the perception of cancer is often that of an uncontrollable rate of cell growth or increased proliferation, a decrease in cell death can also lead to tumour formation. Most cells when detached from their normal tissue die. However, cancer cells evade cell death, tipping the balance to an overabundance of cell number. Therefore, overcoming this resistance to cell death is a decisive factor in the treatment of cancer. Ion channels play a critical role in cancer in regards to cell proliferation, malignant angiogenesis, migration and metastasis. Additionally, ion channels are also known to be critical components of apoptosis. In this review, we discuss the modes of cell death focusing on the ability of cancer cells to evade apoptosis. Specifically, we focus on the role ion channels play in controlling and regulating life/death decisions and how they can be used to overcome resistance to apoptosis in the treatment of cancer.

Serum starvation-induced voltage-gated potassium channel Kv7.5 expression and its regulation by Sp1 in canine osteosarcoma cells

The KCNQ gene family, whose members encode Kv7 channels, belongs to the voltage-gated potassium (Kv) channel group. The roles of this gene family have been widely investigated in nerve and muscle cells. In the present study, we investigated several characteristics of Kv7.5, which is strongly expressed in the canine osteosarcoma cell line, CCL-183. Serum starvation upregulated Kv7.5 expression, and the Kv7 channel opener, flupirtine, attenuated cell proliferation by arresting cells in the G₀/G₁ phase. We also showed that Kv7.5 knockdown helps CCL-183 cells to proliferate. In an effort to find an endogenous regulator of Kv7.5, we used mithramycin A to reduce the level of the transcription factor Sp1, and it strongly inhibited the induction of Kv7.5 in CCL-183 cells. These results suggest that the activation of Kv7.5 by flupirtine may exert an anti-proliferative effect in canine osteosarcoma. Therefore, Kv7.5 is a possible molecular target for canine osteosarcoma therapy.

Up-regulation of Kv7.1 channels in thromboxane A2-induced colonic cancer cell proliferation

Thromboxane A2 (TXA2) is known to stimulate colonic cancer cell proliferation, although the mechanism has not been clarified. In this study, we compared the expression levels of Kv7.1 K(+) channels between human colorectal cancer tissue and the accompanying non-tumor mucosa. Kv7.1 proteins were found to be consistently up-regulated in the cancer tissues from different patients. Kv7.1 was also expressed in human colonic cancer cell lines. Treatment of colonic cancer cells with 9,11-epithio-11,12-methano-thromboxane A2 (STA2), a stable analogue of TXA2, significantly increased whole-cell K(+) currents sensitive to chromanol 293B, an inhibitor of Kv7.1 channels, in parallel with an increased expression of Kv7.1 proteins. In contrast, TXB2, an inactive metabolite of TXA2, had no effects on expression level and function of Kv7.1. A TXA2 receptor antagonist (SQ29548) and an inhibitor of cAMP-dependent protein kinase (Rp-8-Br-MB-cAMPS) inhibited STA2-induced increases in both Kv7.1 expression and chromanol 293B-sensitive K(+) currents. Interestingly, STA2-stimulated proliferation of colonic cancer cells was inhibited by chromanol 293B. These results suggest that Kv7.1 channels are involved in the TXA2-induced cancer cell proliferation and that they are up-regulated by the TXA2 receptor-mediated cAMP pathway.

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.

Atrial natriuretic peptide modulates the proliferation of human gastric cancer cells via KCNQ1 expression

Atrial natriuretic peptide (ANP) and brain NP (BNP) belong to the NP family that regulates mammalian blood volume and blood pressure. ANP signaling through NP receptor A (NPR-A)/cyclic guanosine 3′5′-monophosphate (cGMP)/ cGMP-dependent protein kinase (PKG) activates various downstream effectors involved in cell growth, apoptosis, proliferation and inflammation. Evidence has shown the critical role of plasma K⁺ channels in the regulation of tumor cell proliferation. However, the role of ANP in the proliferation of gastric cancer cells is not clear. In the present study, the expression of NPR-A in the human gastric cancer cell line, AGS, and the effect of ANP on the proliferation of AGS cells were investigated using western blotting, immunofluorescence, qPCR and patch clamp assays. The K⁺ current was also analyzed in the effect of ANP on the proliferation of AGS cells. NPR-A was expressed in the human gastric cancer AGS cell line. Lower concentrations of ANP promoted the proliferation of the AGS cells, although higher concentrations decreased their proliferation. Significant increases in the levels of cGMP activity were observed in the AGS cells treated with 10⁻¹⁰, 10⁻⁹ and 10⁻⁸ M ANP compared with the controls, but no significant differences were observed in the 10⁻⁷ and 10⁻⁶ M ANP groups. The patch clamp results showed that 10⁻⁹ M ANP significantly increased the tetraethylammonium (TEA)- and 293B-sensitive K⁺ current, while 10⁻⁶ M ANP significantly decreased the TEA- and 293B-sensitive K⁺ current. The results showed that 10⁻¹⁰ and 10⁻⁹ M ANP significantly upregulated the expression of potassium voltage-gated channel, KQT-like subfamily, member 1 (KCNQ1) at the protein and mRNA levels, although 10⁻⁷ and 10⁻⁶ M ANP significantly downregulated the expression of KCNQ1. The data indicated that lower and higher concentrations of ANP have opposite effects on the proliferation of AGS cells through cGMP-dependent or -independent pathways. KCNQ1 upregulation and downregulation by lower and higher concentrations of ANP, respectively, have separate effects on the promotion and inhibition of proliferation.

Kv3.4 potassium channel-mediated electrosignaling controls cell cycle and survival of irradiated leukemia cells

Aberrant ion channel expression in the plasma membrane is characteristic for many tumor entities and has been attributed to neoplastic transformation, tumor progression, metastasis, and therapy resistance. The present study aimed to define the function of these "oncogenic" channels for radioresistance of leukemia cells. Chronic myeloid leukemia cells were irradiated (0-6 Gy X ray), ion channel expression and activity, Ca(2+)- and protein signaling, cell cycle progression, and cell survival were assessed by quantitative reverse transcriptase-polymerase chain reaction, patch-clamp recording, fura-2 Ca(2+)-imaging, immunoblotting, flow cytometry, and clonogenic survival assays, respectively. Ionizing radiation-induced G2/M arrest was preceded by activation of Kv3.4-like voltage-gated potassium channels. Channel activation in turn resulted in enhanced Ca(2+) entry and subsequent activation of Ca(2+)/calmodulin-dependent kinase-II, and inactivation of the phosphatase cdc25B and the cyclin-dependent kinase cdc2. Accordingly, channel inhibition by tetraethylammonium and blood-depressing substance-1 and substance-2 or downregulation by RNA interference led to release from radiation-induced G2/M arrest, increased apoptosis, and decreased clonogenic survival. Together, these findings indicate the functional significance of voltage-gated K(+) channels for the radioresistance of myeloid leukemia cells.

Expression of an electrically silent voltage-gated potassium channel in the human placenta

Human placental expression of K(V)9.3, a voltage-gated K channel linked to tissue oxygenation responses, has been suggested at the messenger RNA level but tissue localisation has not been described. We aimed to: (1) produce an antibody to human K(V)9.3 and (2) assess channel expression and distribution in human placental tissue. We determined human placental protein expression and localisation using an antibody to K(V)9.3. Antibody specificity was confirmed by Western blotting. Staining was observed in syncytiotrophoblast microvillous membrane, endothelial cells (in intermediate, stem villi and chorionic plate blood vessels) and vascular smooth muscle cells (large diameter vessels only) by immunohistochemistry. Expression was unchanged in tissue from women with small-for-gestational age babies. It was concluded that K(V)9.3 is localised to human placental vascular tissues and syncytiotrophoblast.

Kcnh1 voltage-gated potassium channels are essential for early zebrafish development

The Kcnh1 gene encodes a voltage-gated potassium channel highly expressed in neurons and involved in tumor cell proliferation, yet its physiological roles remain unclear. We have used the zebrafish as a model to analyze Kcnh1 function in vitro and in vivo. We found that the kcnh1 gene is duplicated in teleost fish (i.e. kcnh1a and kcnh1b) and that both genes are maternally expressed during early development. In adult zebrafish, kcnh1a and kcnh1b have distinct expression patterns but share expression in brain and testis. Heterologous expression of both genes in Xenopus oocytes revealed a strong conservation of characteristic functional properties between human and fish channels, including a unique sensitivity to intracellular Ca²⁺/calmodulin and modulation of voltage-dependent gating by extracellular Mg²⁺. Using a morpholino antisense approach, we demonstrate a strong kcnh1 loss-of-function phenotype in developing zebrafish, characterized by growth retardation, delayed hindbrain formation, and embryonic lethality. This late phenotype was preceded by transcriptional up-regulation of known cell-cycle inhibitors (p21, p27, cdh2) and down-regulation of pro-proliferative factors, including cyclin D1, at 70% epiboly. These results reveal an unanticipated basic activity of kcnh1 that is crucial for early embryonic development and patterning.