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

IK Channel-Independent Effects of Clotrimazole and Senicapoc on Cancer Cells Viability and Migration

Many studies highlighted the importance of the IK channel for the proliferation and the migration of different types of cancer cells, showing how IK blockers could slow down cancer growth. Based on these data, we wanted to characterize the effects of IK blockers on melanoma metastatic cells and to understand if such effects were exclusively IK-dependent. For this purpose, we employed two different blockers, namely clotrimazole and senicapoc, and two cell lines: metastatic melanoma WM266-4 and pancreatic cancer Panc-1, which is reported to have little or no IK expression. Clotrimazole and senicapoc induced a decrease in viability and the migration of both WM266-4 and Panc-1 cells irrespective of IK expression levels. Patch-clamp experiments on WM266-4 cells revealed Ca2+-dependent, IK-like, clotrimazole- and senicapoc-sensitive currents, which could not be detected in Panc-1 cells. Neither clotrimazole nor senicapoc altered the intracellular Ca2+ concentration. These results suggest that the effects of IK blockers on cancer cells are not strictly dependent on a robust presence of the channel in the plasma membrane, but they might be due to off-target effects on other cellular targets or to the blockade of IK channels localized in intracellular organelles.

Potassium channels as novel molecular targets in hepatocellular carcinoma (Review)

Hepatocellular carcinoma (HCC) poses a serious health burden worldwide. It is often not diagnosed until the patient is at an advanced stage of the disease, when treatment options are limited and the prognosis is poor. Therefore, novel treatment strategies are urgently required. Potassium (K+) channels have an important role in HCC, including regulating the proliferation, migration, invasion and drug resistance of HCC cells. The aim of the present review was therefore to survey the relevant publications that have investigated K+ channels not only as markers for the early diagnosis of HCC, but also as potential therapeutic targets for the treatment of HCC. Several of these channels have been indicated to be the sites of action for natural products previously known to inhibit HCC; however, more systematic studies are required to determine which K+ channels may be utilized for the clinical treatment of HCC, particularly in the advanced stages of the disease and in cases where patients are resistant to the existing drugs.

Molecular mechanism of HNTX-I activates the intermediate-conductance Ca2+-activated K+ (IK) channels

The IK channel, a potassium ion channel regulated by calcium ions and voltages in a bidirectional manner, has been implicated in a range of diseases. However, there are currently few compounds available that can target the IK channel with high potency and specificity. Hainantoxin-I (HNTX-I) is the first peptide activator of IK channel discovered so far, but its activity is not ideal, and the underlying mechanism interaction between HNTX-I toxin and IK channel remains unclear. Thus, our study aimed to enhance the potency of IK channel activating peptides derived from HNTX-I and elucidate the molecular mechanism underlying the interaction between HNTX-I and the IK channel. By employing virtual alanine scanning mutagenesis, we generated 11 HNTX-I mutants using site-directed mutagenesis to pinpoint specific residues crucial for the HNTX-I and IK channel interaction. Subsequently, we identified key residues on the IK channel that are involved in the interaction with HNTX-I. Additionally, molecular docking was employed to guide the molecular engineering process and clarify the binding interface between HNTX-I and the IK channel. Our results demonstrate that HNTX-I primarily acts on the IK channel via the N-terminal amino acid, and its interaction with the IK channel is mediated by electrostatic and hydrophobic interactions, specifically the amino acid residues at positions 1, 3, 5, and 7 on HNTX-I. This study provides valuable insights into the peptide toxins that may serve as potential templates for the development of activators with enhanced potency and selectivity for the IK channel.

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

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

Estrogenic Modulation of Ionic Channels, Pumps and Exchangers in Airway Smooth Muscle

To preserve ionic homeostasis (primarily Ca²⁺, K⁺, Na⁺, and Cl^-), in the airway smooth muscle (ASM) numerous transporters (channels, exchangers, and pumps) regulate the influx and efflux of these ions. Many of intracellular processes depend on continuous ionic permeation, including exocytosis, contraction, metabolism, transcription, fecundation, proliferation, and apoptosis. These mechanisms are precisely regulated, for instance, through hormonal activity. The lipophilic nature of steroidal hormones allows their free transit into the cell where, in most cases, they occupy their cognate receptor to generate genomic actions. In the sense, estrogens can stimulate development, proliferation, migration, and survival of target cells, including in lung physiology. Non-genomic actions on the other hand do not imply estrogen's intracellular receptor occupation, nor do they initiate transcription and are mostly immediate to the stimulus. Among estrogen's non genomic responses regulation of calcium homeostasis and contraction and relaxation processes play paramount roles in ASM. On the other hand, disruption of calcium homeostasis has been closely associated with some ASM pathological mechanism. Thus, this paper intends to summarize the effects of estrogen on ionic handling proteins in ASM. The considerable diversity, range and power of estrogens regulates ionic homeostasis through genomic and non-genomic mechanisms.

Pancreatic KCa3.1 channels in health and disease

Ion channels play an important role for regulation of the exocrine and the endocrine pancreas. This review focuses on the Ca²⁺-regulated K⁺ channel K_Ca3.1, encoded by the KCNN4 gene, which is present in both parts of the pancreas. In the islets of Langerhans, K_Ca3.1 channels are involved in the regulation of membrane potential oscillations characterizing nutrient-stimulated islet activity. Channel upregulation is induced by gluco- or lipotoxic conditions and might contribute to micro-inflammation and impaired insulin release in type 2 diabetes mellitus as well as to diabetes-associated renal and vascular complications. In the exocrine pancreas K_Ca3.1 channels are expressed in acinar and ductal cells. They are thought to play a role for anion secretion during digestion but their physiological role has not been fully elucidated yet. Pancreatic carcinoma, especially pancreatic ductal adenocarcinoma (PDAC), is associated with drastic overexpression of K_Ca3.1. For pharmacological targeting of K_Ca3.1 channels, we are discussing the possible benefits K_Ca3.1 channel inhibitors might provide in the context of diabetes mellitus and pancreatic cancer, respectively. We are also giving a perspective for the use of a fluorescently labeled derivative of the K_Ca3.1 blocker senicapoc as a tool to monitor channel distribution in pancreatic tissue. In summary, modulating K_Ca3.1 channel activity is a useful strategy for exo-and endocrine pancreatic disease but further studies are needed to evaluate its clinical suitability.

Activated fibroblasts in cardiac and cancer fibrosis: An overview of analogies and new potential therapeutic options

Heart disease and cancer are two major causes of morbidity and mortality in the industrialized countries, and their increasingly recognized connections are shifting the focus from single disease studies to an interdisciplinary approach. Fibroblast-mediated intercellular crosstalk is critically involved in the evolution of both pathologies. In healthy myocardium and in non-cancerous conditions, resident fibroblasts are the main cell source for synthesis of the extracellular matrix (ECM) and important sentinels of tissue integrity. In the setting of myocardial disease or cancer, quiescent fibroblasts activate, respectively, into myofibroblasts (myoFbs) and cancer-associated fibroblasts (CAFs), characterized by increased production of contractile proteins, and by a highly proliferative and secretory phenotype. Although the initial activation of myoFbs/CAFs is an adaptive process to repair the damaged tissue, massive deposition of ECM proteins leads to maladaptive cardiac or cancer fibrosis, a recognized marker of adverse outcome. A better understanding of the key mechanisms orchestrating fibroblast hyperactivity may help developing innovative therapeutic options to restrain myocardial or tumor stiffness and improve patient prognosis. Albeit still unappreciated, the dynamic transition of myocardial and tumor fibroblasts into myoFbs and CAFs shares several common triggers and signaling pathways relevant to TGF-β dependent cascade, metabolic reprogramming, mechanotransduction, secretory properties, and epigenetic regulation, which might lay the foundation for future antifibrotic intervention. Therefore, the aim of this review is to highlight emerging analogies in the molecular signature underlying myoFbs and CAFs activation with the purpose of identifying novel prognostic/diagnostic biomarkers, and to elucidate the potential of drug repositioning strategies to mitigate cardiac/cancer fibrosis.

Role of organellar Ca2+-activated K+ channels in disease development

The organellar Ca2+-activated K+ channels share a similar ability to transfer the alteration of Ca2+ concentration to membrane conductance of potassium. Multiple effects of Ca2+-activated K+ channels on cell metabolism and complex signaling pathways during organ development have been explored. The organellar Ca2+-activated K+ channels are able to control the ionic equilibrium and are always associated with oxidative stress in different organelles and the whole cells. Some drugs targeting Ca2+-activated K+ channels have been tested for various diseases in clinical trials. In this review, the known roles of organellar Ca2+-activated K+ channels were described, and their effects on different diseases, particularly on diabetes, cardiovascular diseases, and neurological diseases were discussed. It was attempted to summarize the currently known operational modes with the involvement of organellar Ca2+-activated K+ channels. This review may assist scholars to more comprehensively understand organellar Ca2+-activated K+ channels and related diseases.

Potassium channels: Novel targets for tumor diagnosis and chemoresistance

In recent years, the role of potassium channels in tumors has been intensively studied. Potassium channel proteins are widely involved in various physiological and pathological processes of cells. The expression and dysfunction of potassium channels are closely related to tumor progression. Potassium channel blockers or activators present antitumor effects by directly inhibiting tumor growth or enhancing the potency of classical antitumor agents in combination therapy. This article reviews the mechanisms by which potassium channels contribute to tumor development in various tumors in recent years, introduces the potential of potassium channels as diagnostic targets and therapeutic means for tumors, and provides further ideas for the proper individualized treatment of tumors.

QCM sensor provides insight into the role of pivotal ions in cellular regulatory volume decrease

All vertebrate cells generally self-regulate for sustaining homeostasis and cell functions. As a major regulatory mechanism, regulatory volume decrease (RVD) occurs in hypotonicity-induced cell swelling, and then shrinking by the efflux of intracellular osmolytes and water, in which the ions K⁺, Cl^-, and Ca²⁺ play a key role in the RVD process. We observed that these pivotal ions could result in novel RVD behaviors under repeatedly hypotonic stimulation. However, there is a lack of valid means for assessing the effect of pivotal ions on RVD. In this work, we proposed an effective measurement process based on a quartz crystal microbalance (QCM) combined with cell function of RVD for revealing acute variations in cell volume regulation induced by the pivotal ions. A QCM sensor was implemented by adhering MCF-7 cells to a poly-l-lysine-modified gold chip and cyclic stimulation with hypotonic NaCl medium, in which a frequency shift (Δf) showed the superior feasibility of the technique in exhibiting RVD behaviors. With the increase in the number of cycles, the RVD values decreased progressively under three stimulation cycles with hypotonic NaCl alone. Compared with the first cycle, the RVD level in the second and third cycles declined by 60.7±1.7% and 82.1±1.6% (n=3), respectively; conversely, it recovered in NaCl-KCl solution, but was significantly enhanced by 52.2±0.8% in NaCl-CaCl₂ solution. Moreover, the inhibition of chloride channels to block Cl^- efflux also decreased the RVD level by 56.2±3.0%. The results indicate that these ions (K⁺, Cl^-, Ca²⁺) are all able to affect the function of RVD, among which intracellular Cl^- depletion reduced RVD during measurement, but which recovered with K⁺ supplement, and Ca²⁺ enhanced RVD due to activation of ion channels. Therefore, this work provides a comprehensive assessment of cellular behavior and offers an innovative method for gaining insight into cellular functions and mechanisms. A novel strategy was conducted by integrating a quartz crystal microbalance (QCM) with the function of cell volume regulation for analyzing the role of the pivotal ions ( K⁺, Cl^-, Ca²⁺) in NaCl media on the behaviors of regulatory cell volume decrease (RVD).

Pharmacological targeting of the mitochondrial calcium-dependent potassium channel KCa3.1 triggers cell death and reduces tumor growth and metastasis in vivo

Ion channels are non-conventional, druggable oncological targets. The intermediate-conductance calcium-dependent potassium channel (K_Ca3.1) is highly expressed in the plasma membrane and in the inner mitochondrial membrane (mitoK_Ca3.1) of various cancer cell lines. The role mitoK_Ca3.1 plays in cancer cells is still undefined. Here we report the synthesis and characterization of two mitochondria-targeted novel derivatives of a high-affinity K_Ca3.1 antagonist, TRAM-34, which retain the ability to block channel activity. The effects of these drugs were tested in melanoma, pancreatic ductal adenocarcinoma and breast cancer lines, as well as in vivo in two orthotopic models. We show that the mitochondria-targeted TRAM-34 derivatives induce release of mitochondrial reactive oxygen species, rapid depolarization of the mitochondrial membrane, fragmentation of the mitochondrial network. They trigger cancer cell death with an EC₅₀ in the µM range, depending on channel expression. In contrast, inhibition of the plasma membrane K_Ca3.1 by membrane-impermeant Maurotoxin is without effect, indicating a specific role of mitoK_Ca3.1 in determining cell fate. At sub-lethal concentrations, pharmacological targeting of mitoK_Ca3.1 significantly reduced cancer cell migration by enhancing production of mitochondrial reactive oxygen species and nuclear factor-κB (NF-κB) activation, and by downregulating expression of Bcl-2 Nineteen kD-Interacting Protein (BNIP-3) and of Rho GTPase CDC-42. This signaling cascade finally leads to cytoskeletal reorganization and impaired migration. Overexpression of BNIP-3 or pharmacological modulation of NF-κB and CDC-42 prevented the migration-reducing effect of mitoTRAM-34. In orthotopic models of melanoma and pancreatic ductal adenocarcinoma, the tumors at sacrifice were 60% smaller in treated versus untreated animals. Metastasis of melanoma cells to lymph nodes was also drastically reduced. No signs of toxicity were observed. In summary, our results identify mitochondrial K_Ca3.1 as an unexpected player in cancer cell migration and show that its pharmacological targeting is efficient against both tumor growth and metastatic spread 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.

Calcium signaling: A therapeutic target to overcome resistance to therapies in cancer

Innate and acquired resistances to therapeutic agents are responsible for the failure of cancer treatments. Due to the multifactorial nature of resistance, the identification of new therapeutic targets is required to improve cancer treatment. Calcium is a universal second messenger that regulates many cellular functions such as proliferation, migration, and survival. Calcium channels, pumps and exchangers tightly regulate the duration, location and magnitude of calcium signals. Many studies have implicated dysregulation of calcium signaling in several pathologies, including cancer. Abnormal calcium fluxes due to altered channel expression or activation contribute to carcinogenesis and promote tumor development. However, there is limited information on the role of calcium signaling in cancer resistance to therapeutic drugs. This review discusses the role of calcium signaling as a mediator of cancer resistance, and assesses the potential value of combining anticancer therapy with calcium signaling modulators to improve the effectiveness of current treatments.

IK(Ca) channels control breast cancer metabolism including AMPK-driven autophagy

Ca²⁺-activated K⁺ channels of intermediate conductance (IK) are frequently overexpressed in breast cancer (BC) cells, while IK channel depletion reduces BC cell proliferation and tumorigenesis. This raises the question, of whether and mechanistically how IK activity interferes with the metabolic activity and energy consumption rates, which are fundamental for rapidly growing cells. Using BC cells obtained from MMTV-PyMT tumor-bearing mice, we show that both, glycolysis and mitochondrial ATP-production are reduced in cells derived from IK-deficient breast tumors. Loss of IK altered the sub-/cellular K⁺- and Ca²⁺- homeostasis and mitochondrial membrane potential, ultimately resulting in reduced ATP-production and metabolic activity. Consequently, we find that BC cells lacking IK upregulate AMP-activated protein kinase activity to induce autophagy compensating the glycolytic and mitochondrial energy shortage. Our results emphasize that IK by modulating cellular Ca²⁺- and K⁺-dynamics contributes to the remodeling of metabolic pathways in cancer. Thus, targeting IK channel might disturb the metabolic activity of BC cells and reduce malignancy.

Relevance of Abnormal KCNN1 Expression and Osmotic Hypersensitivity in Ewing Sarcoma

Simple Summary

The main oncogene in Ewing sarcoma directly drives a high expression of a previously unknown variant KCNN1 (encoding the K_Ca2.1 channel) that we also verified in samples from >200 patients. Yet, we found that the channel is not functional and does not modulate Ewing sarcoma cell behavior. We could explain this lack of functional impact by the surprising absence of any K_Ca2.1-carried K⁺ current in Ewing sarcoma cells. However, we show in a proof-of-principle study that the essential lack of a K⁺ conductance can be exploited by applying hypoosmotic stress and effectively and selectively killing the Ewing sarcoma cells.

Abstract

Ewing sarcoma (EwS) is a rare and highly malignant bone tumor occurring mainly in childhood and adolescence. Physiologically, the bone is a central hub for Ca²⁺ homeostasis, which is severely disturbed by osteolytic processes in EwS. Therefore, we aimed to investigate how ion transport proteins involved in Ca²⁺ homeostasis affect EwS pathophysiology. We characterized the expression of 22 candidate genes of Ca²⁺-permeable or Ca²⁺-regulated ion channels in three EwS cell lines and found the Ca²⁺-activated K⁺ channel K_Ca2.1 (KCNN1) to be exceptionally highly expressed. We revealed that KCNN1 expression is directly regulated by the disease-driving oncoprotein EWSR1-FL1. Due to its consistent overexpression in EwS, KCNN1 mRNA could be a prognostic marker in EwS. In a large cohort of EwS patients, however, KCNN1 mRNA quantity does not correlate with clinical parameters. Several functional studies including patch clamp electrophysiology revealed no evidence for K_Ca2.1 function in EwS cells. Thus, elevated KCNN1 expression is not translated to K_Ca2.1 channel activity in EwS cells. However, we found that the low K⁺ conductance of EwS cells renders them susceptible to hypoosmotic solutions. The absence of a relevant K⁺ conductance in EwS thereby provides an opportunity for hypoosmotic therapy that can be exploited during tumor surgery.

Effects of KCa channels on biological behavior of trophoblasts

The Ca²⁺-activated potassium (KCa) channels are involved in many cellular functions, but their roles in trophoblasts are unclear. This study aimed to clarify the effects of KCa channels on the biological behavior of trophoblasts. The localization and expression of the three types of KCa channels, including large-conductance KCa channels (BKCa), intermediate-conductance KCa channels (IKCa), and small-conductance KCa channels (SKCa), were detected in human chorionic villi taken from pregnant women between 5 and 8 weeks of gestation (n = 15) and HTR-8/SVneo cells. The effects of KCa channels on proliferation, apoptosis, and migration of HTR-8/SVneo cells were examined by using the activators or inhibitors of KCa channels. Results showed that KCa channels were mainly localized on the membrane and in the cytoplasm of trophoblasts in human chorionic villi and HTR-8/SVneo cells. The proliferation and migration of HTR-8/SVneo cells were inhibited by activating KCa channels. Apoptosis of trophoblasts was promoted through activating BKCa channels but was not affected by neither activating nor inhibiting IKCa and SKCa channels. This study substantiated the abovementioned biological roles of KCa channels in trophoblast cells, which is fundamental to further research on whether dysfunction of KCa channels is involved in the pathogenesis of pregnancy-related complications.

Monitoring extracellular ion and metabolite dynamics with recombinant nanobody-fused biosensors

Ion and analyte changes in the tumor microenvironment (TME) alter the metabolic activity of cancer cells, promote tumor cell growth, and impair anti-tumor immunity. Consequently, accurate determination and visualization of extracellular changes of analytes in real time is desired. In this study, we genetically combined FRET-based biosensors with nanobodies (Nbs) to specifically visualize and monitor extracellular changes in K⁺, pH, and glucose on cell surfaces. We demonstrated that these Nb-fused biosensors quantitatively visualized K⁺ alterations on cancer and non-cancer cell lines and primary neurons. By implementing a HER2-specific Nb, we generated functional K⁺ and pH sensors, which specifically stained HER2-positive breast cancer cells. Based on the successful development of several Nb-fused biosensor combinations, we anticipate that this approach can be readily extended to other biosensors and will open new opportunities for the study of extracellular analytes in advanced experimental settings.

•

Generation of recombinant nanobody-fused FRET biosensors

•

Nb-fused biosensors specifically bind targets on the outer surface of various cells

•

Cellular bound Nb-biosensors visualize extracellular analyte changes in real time

KCNN4 Promotes the Stemness Potentials of Liver Cancer Stem Cells by Enhancing Glucose Metabolism

The presence of liver cancer stem cells (LCSCs) is one of the reasons for the treatment failure of hepatocellular carcinoma (HCC). For LCSCs, one of their prominent features is metabolism plasticity, which depends on transporters and ion channels to exchange metabolites and ions. The K⁺ channel protein KCNN4 (Potassium Calcium-Activated Channel Subfamily N Member 4) has been reported to promote cell metabolism and malignant progression of HCCs, but its influence on LCSC stemness has remained unclear. Here, we demonstrated that KCNN4 was highly expressed in L-CSCs by RT-PCR and Western blot. Then, we illustrated that KCNN4 promoted the stemness of HC-C cells by CD133⁺CD44⁺ LCSC subpopulation ratio analysis, in vitro stemness transcription factor detection, and sphere formation assay, as well as in vivo orthotopic liver tumor formation and limiting dilution tumorigenesis assays. We also showed that KCNN4 enhanced the glucose metabolism in LCSCs by metabolic enzyme detections and seahorse analysis, and the KCNN4-promoted increase in LCSC ratios was abolished by glycolysis inhibitor 2-DG or OXPHOS inhibitor oligomycin. Collectively, our results suggested that KCNN4 promoted LCSC stemness via enhancing glucose metabolism, and that KCNN4 would be a potential molecular target for eliminating LCSCs in HCC.

Assessing K+ ions and K+ channel functions in cancer cell metabolism using fluorescent biosensors

Cancer represents a leading cause of death worldwide. Hence, a better understanding of the molecular mechanisms causing and propelling the disease is of utmost importance. Several cancer entities are associated with altered K⁺ channel expression which is frequently decisive for malignancy and disease outcome. The impact of such oncogenic K⁺ channels on cell patho-/physiology and homeostasis and their roles in different subcellular compartments is, however, far from being understood. A refined method to simultaneously investigate metabolic and ionic signaling events on the level of individual cells and their organelles represent genetically encoded fluorescent biosensors, that allow a high-resolution investigation of compartmentalized metabolite or ion dynamics in a non-invasive manner. This feature of these probes makes them versatile tools to visualize and understand subcellular consequences of aberrant K⁺ channel expression and activity in K⁺ channel related cancer research.

Reciprocal Relationship between Ca2+ Signaling and Ca2+-Gated Ion Channels as a Potential Target for Drug Discovery

Cellular Ca²⁺ signaling functions as one of the most common second messengers of various signal transduction pathways in cells and mediates a number of physiological roles in a cell-type dependent manner. Ca²⁺ signaling also regulates more general and fundamental cellular activities, including cell proliferation and apoptosis. Among ion channels, Ca²⁺-permeable channels in the plasma membrane as well as endo- and sarcoplasmic reticulum membranes play important roles in Ca²⁺ signaling by directly contributing to the influx of Ca²⁺ from extracellular spaces or its release from storage sites, respectively. Furthermore, Ca²⁺-gated ion channels in the plasma membrane often crosstalk reciprocally with Ca²⁺ signals and are central to the regulation of cellular functions. This review focuses on the physiological and pharmacological impact of i) Ca²⁺-gated ion channels as an apparatus for the conversion of cellular Ca²⁺ signals to intercellularly propagative electrical signals and ii) the opposite feedback regulation of Ca²⁺ signaling by Ca²⁺-gated ion channel activities in excitable and non-excitable cells.

Targeting ion channels for the treatment of lung cancer

Lung cancer is caused by several environmental and genetic variables and is globally associated with elevated morbidity and mortality. Among these variables, membrane-bound ion channels have a key role in regulating multiple signaling pathways in tumor cells and dysregulation of ion channel expression and function is closely related to proliferation, migration, and metastasis of lung cancer. This work reviews and summarizes current knowledge about the role of ion channels in lung cancer, focusing on the changes in the expression and function of various ion channels in lung cancer and how these changes affect lung cancer cell biology both in vitro and in vivo as evidenced by both genetic and pharmacological studies. It can help understand the molecular mechanisms of various ion channels influencing the initiation and progression of lung cancer and shed new insights into their roles in the development and treatment of this deadly disease.

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

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

Potential rules of anesthetic gases on glioma

Glioma is one of the most frequent primary brain tumors. Currently, the most common therapeutic strategy for patients with glioma is surgical resection combined with radiotherapy or/and adjuvant chemotherapy. However, due to the metastatic and invasive nature of glioma cells, the recurrence rate is high, resulting in poor prognosis. In recent years, gas therapy has become an emerging treatment. Studies have shown that the proliferation, metastasis and invasiveness of glioma cells exposed to anesthetic gases are obviously inhibited. Therefore, anesthetic gas may play a special therapeutic role in gliomas. In this review, we aim to collect existing research and summarize the rules of using anesthetic gases on glioma, providing potential strategies for further clinical treatment.

Mitochondrial K+ channels and their implications for disease mechanisms

The field of mitochondrial ion channels underwent a rapid development during the last decade, thanks to the molecular identification of some of the nuclear-encoded organelle channels and to advances in strategies allowing specific pharmacological targeting of these proteins. Thereby, genetic tools and specific drugs aided definition of the relevance of several mitochondrial channels both in physiological as well as pathological conditions. Unfortunately, in the case of mitochondrial K⁺ channels, efforts of genetic manipulation provided only limited results, due to their dual localization to mitochondria and to plasma membrane in most cases. Although the impact of mitochondrial K⁺ channels on human diseases is still far from being genuinely understood, pre-clinical data strongly argue for their substantial role in the context of several pathologies, including cardiovascular and neurodegenerative diseases as well as cancer. Importantly, these channels are druggable targets, and their in-depth investigation could thus pave the way to the development of innovative small molecules with huge therapeutic potential. In the present review we summarize the available experimental evidence that mechanistically link mitochondrial potassium channels to the above pathologies and underline the possibility of exploiting them for therapy.

Potassium Channels in Cancer

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

KCa3.1 Mediates Dysregulation of Mitochondrial Quality Control in Diabetic Kidney Disease

Mitochondrial dysfunction is implicated in the pathogenesis of diabetic kidney disease. Mitochondrial quality control is primarily mediated by mitochondrial turnover and repair through mitochondrial fission/fusion and mitophagy. We have previously shown that blockade of the calcium-activated potassium channel KCa3.1 ameliorates diabetic renal fibrosis. However, the mechanistic link between KCa3.1 and mitochondrial quality control in diabetic kidney disease is not yet known. Transforming growth factor β1 (TGF-β1) plays a central role in diabetic kidney disease. Recent studies indicate an emerging role of TGF-β1 in the regulation of mitochondrial function. However, the molecular mechanism mediating mitochondrial quality control in response to TGF-β1 remains limited. In this study, mitochondrial function was assessed in TGF-β1-exposed renal proximal tubular epithelial cells (HK2 cells) transfected with scrambled siRNA or KCa3.1 siRNA. In vivo, diabetes was induced in KCa3.1+/+ and KCa3.1−/− mice by low-dose streptozotocin (STZ) injection. Mitochondrial fission/fusion-related proteins and mitophagy markers, as well as BCL2 interacting protein 3 (BNIP3) (a mitophagy regulator) were examined in HK2 cells and diabetic mice kidneys. The in vitro results showed that TGF-β1 significantly inhibited mitochondrial ATP production rate and increased mitochondrial ROS (mtROS) production when compared to control, which was normalized by KCa3.1 gene silencing. Increased fission and suppressed fusion were found in both TGF-β1-treated HK2 cells and diabetic mice, which were reversed by KCa3.1 deficiency. Furthermore, our results showed that mitophagy was inhibited in both in vitro and in vivo models of diabetic kidney disease. KCa3.1 deficiency restored abnormal mitophagy by inhibiting BNIP3 expression in TGF-β1-induced HK2 cells as well as in the diabetic mice. Collectively, these results indicate that KCa3.1 mediates the dysregulation of mitochondrial quality control in diabetic kidney disease.

ATP-evoked intracellular Ca2+ transients shape the ionic permeability of human microglia from epileptic temporal cortex

Background

Intracellular Ca²⁺ modulates several microglial activities, such as proliferation, migration, phagocytosis, and inflammatory mediator secretion. Extracellular ATP, the levels of which significantly change during epileptic seizures, activates specific receptors leading to an increase of intracellular free Ca²⁺ concentration ([Ca²⁺]_i). Here, we aimed to functionally characterize human microglia obtained from cortices of subjects with temporal lobe epilepsy, focusing on the Ca²⁺-mediated response triggered by purinergic signaling.

Methods

Fura-2 based fluorescence microscopy was used to measure [Ca²⁺]_i in primary cultures of human microglial cells obtained from surgical specimens. The perforated patch-clamp technique, which preserves the cytoplasmic milieu, was used to measure ATP-evoked Ca²⁺-dependent whole-cell currents.

Results

In human microglia extracellular ATP evoked [Ca²⁺]_i increases depend on Ca²⁺ entry from the extracellular space and on Ca²⁺ mobilization from intracellular compartments. Extracellular ATP also induced a transient fivefold potentiation of the total transmembrane current, which was completely abolished when [Ca²⁺]_i increases were prevented by removing external Ca²⁺ and using an intracellular Ca²⁺ chelator. TRAM-34, a selective K_Ca3.1 blocker, significantly reduced the ATP-induced current potentiation but did not abolish it. The removal of external Cl⁻ in the presence of TRAM-34 further lowered the ATP-evoked effect. A direct comparison between the ATP-evoked mean current potentiation and mean Ca²⁺ transient amplitude revealed a linear correlation. Treatment of microglial cells with LPS for 48 h did not prevent the ATP-induced Ca²⁺ mobilization but completely abolished the ATP-mediated current potentiation. The absence of the Ca²⁺-evoked K⁺ current led to a less sustained ATP-evoked Ca²⁺ entry, as shown by the faster Ca²⁺ transient kinetics observed in LPS-treated microglia.

Conclusions

Our study confirms a functional role for K_Ca3.1 channels in human microglia, linking ATP-evoked Ca²⁺ transients to changes in membrane conductance, with an inflammation-dependent mechanism, and suggests that during brain inflammation the K_Ca3.1-mediated microglial response to purinergic signaling may be reduced.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02096-0.

Ion Channels Orchestrate Pancreatic Ductal Adenocarcinoma Progression and Therapy

Pancreatic ductal adenocarcinoma is a devastating disease with a dismal prognosis. Therapeutic interventions are largely ineffective. A better understanding of the pathophysiology is required. Ion channels contribute substantially to the "hallmarks of cancer." Their expression is dysregulated in cancer, and they are "misused" to drive cancer progression, but the underlying mechanisms are unclear. Ion channels are located in the cell membrane at the interface between the intracellular and extracellular space. They sense and modify the tumor microenvironment which in itself is a driver of PDAC aggressiveness. Ion channels detect, for example, locally altered proton and electrolyte concentrations or mechanical stimuli and transduce signals triggered by these microenvironmental cues through association with intracellular signaling cascades. While these concepts have been firmly established for other cancers, evidence has emerged only recently that ion channels are drivers of PDAC aggressiveness. Particularly, they appear to contribute to two of the characteristic PDAC features: the massive fibrosis of the tumor stroma (desmoplasia) and the efficient immune evasion. Our critical review of the literature clearly shows that there is still a remarkable lack of knowledge with respect to the contribution of ion channels to these two typical PDAC properties. Yet, we can draw parallels from ion channel research in other fibrotic and inflammatory diseases. Evidence is accumulating that pancreatic stellate cells express the same "profibrotic" ion channels. Similarly, it is at least in part known which major ion channels are expressed in those innate and adaptive immune cells that populate the PDAC microenvironment. We explore potential therapeutic avenues derived thereof. Since drugs targeting PDAC-relevant ion channels are already in clinical use, we propose to repurpose those in PDAC. The quest for ion channel targets is both motivated and complicated by the fact that some of the relevant channels, for example, KCa3.1, are functionally expressed in the cancer, stroma, and immune cells. Only in vivo studies will reveal which arm of the balance we should put our weights on when developing channel-targeting PDAC therapies. The time is up to explore the efficacy of ion channel targeting in (transgenic) murine PDAC models before launching clinical trials with repurposed drugs.

Depressive effectiveness of vigabatrin (γ-vinyl-GABA), an antiepileptic drug, in intermediate-conductance calcium-activated potassium channels in human glioma cells

BACKGROUND

Vigabatrin (VGB) is an approved non-traditional antiepileptic drug that has been revealed to have potential for treating brain tumors; however, its effect on ionic channels in glioma cells remains largely unclear.

METHODS

With the aid of patch-clamp technology, we investigated the effects of VGB on various ionic currents in the glioblastoma multiforme cell line 13-06-MG.

RESULTS

In cell-attached configuration, VGB concentration-dependently reduced the activity of intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channels, while DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) counteracted the VGB-induced inhibition of IK_Ca channels. However, the activity of neither large-conductance Ca²⁺-activated (BK_Ca) nor inwardly rectifying K⁺ (K_IR) channels were affected by the presence of VGB in human 13-06-MG cells. However, in the continued presence of VGB, the addition of GAL-021 or BaCl₂ effectively suppressed BK_Ca and K_IR channels.

CONCLUSIONS

The inhibitory effect of VGB on IK_Ca channels demonstrated in the current study could be an important underlying mechanism of VGB-induced antineoplastic (e.g., anti-glioma) actions.

The N and C-termini of SPCA2 regulate differently Kv10.1 function: role in the collagen 1-induced breast cancer cell survival

It's now clearly established that the tumor microenvironment participates to tumor development. Among the different actors contributing to these processes, ion channels, located at the cancer cell surface, play a major role. We recently demonstrated that the association of Kv10.1, Orai1 and SPCA2 is crucial to promote the collagen-induced survival of MCF-7 breast cancer cells. By using siRNA directed against SPCA2, we shown that this protein is involved in the regulation of the activity, the expression and the sub-cellular localization of Kv10.1. In addition, it has been demonstrated that SPCA2 is involved in SICE in MCF-7 cells and that the N- and the C-terminal parts of this protein are necessary to interact and to produce Ca2+ entry. However, no information is available about the necessary SPCA2's important region to regulate Kv10.1. The aim of our work is to evaluate how SPCA2 could interact with Kv10.1 channel to induce survival promotion. By using different SPCA2 mutants, we evaluate the role of the N- and C-terminal sections on the expression and the activity of Kv10.1 channels. In addition, we analyzed the impact of these deletions on the collagen 1-induced cell survival. Our results bring out new information about the regulation of Kv10.1 channel through SPCA2. More specifically how the N- and C-terminus of this Ca2+ transporter regulate Kv10.1 expression, trafficking, and function suggesting new opportunities to target Kv10.1 channels in cancer progression.

Co-staining of KCa 3.1 Channels in NSCLC Cells with a Small-Molecule Fluorescent Probe and Antibody-Based Indirect Immunofluorescence

The Ca2+ activated potassium channel 3.1 (KCa 3.1) is involved in critical steps of the metastatic cascade, such as proliferation, migration, invasion and extravasation. Therefore, a fast and efficient protocol for imaging of KCa 3.1 channels was envisaged. The novel fluorescently labeled small molecule imaging probes 1 and 2 were synthesized by connecting a dimethylpyrrole-based BODIPY dye with a derivative of the KCa 3.1 channel inhibitor senicapoc via linkers of different length. Patch-clamp experiments revealed the inhibition of KCa 3.1 channels by the probes confirming interaction with the channel. Both probes 1 and 2 were able to stain KCa 3.1 channels in non-small-cell lung cancer (NSCLC) cells following a simple, fast and efficient protocol. Pre-incubation with unlabeled senicapoc removed the punctate staining pattern showing the specificity of the new probes 1 and 2. Staining of the channel with the fluorescently labeled senicapoc derivatives 1 or 2 or with antibody-based indirect immunofluorescence yielded identical or very similar densities of stained KCa 3.1 channels. However, co-staining using both methods did not lead to the expected overlapping punctate staining pattern. This observation was explained by docking studies showing that the antibody used for indirect immunofluorescence and the probes 1 and 2 label different channel populations. Whereas the antibody binds at the closed channel conformation, the probes 1 and 2 bind within the open channel.

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

Ca²⁺ ions play a variety of roles in the human body as well as within a single cell. Cellular Ca²⁺ signal transduction processes are governed by Ca²⁺ sensing and Ca²⁺ transporting proteins. In this review, we discuss the Ca²⁺ and the Ca²⁺-sensing ion channels with particular focus on the structure-function relationship of the Ca²⁺ release-activated Ca²⁺ (CRAC) ion channel, the Ca²⁺-activated K⁺ (K_Ca2+) ion channels, and their modulation via other cellular components. Moreover, we highlight their roles in healthy signaling processes as well as in disease with a special focus on cancer. As K_Ca2+ channels are activated via elevations of intracellular Ca²⁺ levels, we summarize the current knowledge on the action mechanisms of the interplay of CRAC and K_Ca2+ ion channels and their role in cancer cell development.

ClC-3/SGK1 regulatory axis enhances the olaparib-induced antitumor effect in human stomach adenocarcinoma

Currently, only a few available targeted drugs are considered to be effective in stomach adenocarcinoma (STAD) treatment. The PARP inhibitor olaparib is a molecularly targeted drug that continues to be investigated in BRCA-mutated tumors. However, in tumors without BRCA gene mutations, particularly in STAD, the effect and molecular mechanism of olaparib are unclear, which largely restricts the use of olaparib in STAD treatment. In this study, the in vitro results showed that olaparib specifically inhibited cell growth and migration, exerting antitumor effect in STAD cell lines. In addition, a ClC-3/SGK1 regulatory axis was identified and validated in STAD cells. We then found that the down-regulation of ClC-3/SGK1 axis attenuated olaparib-induced cell growth and migration inhibition. On the contrary, the up-regulation of ClC-3/SGK1 axis enhanced olaparib-induced cell growth and migration inhibition, and the enhancement effect could be attenuated by SGK1 knockdown. Consistently, the whole-cell recorded chloride current activated by olaparib presented the same variation trend. Next, the clinical data showed that ClC-3 and SGK1 were highly expressed in human STAD tissues and positively correlated (r = 0.276, P = 0.009). Furthermore, high protein expression of both ClC-3 (P = 0.030) and SGK1 (P = 0.006) was associated with poor survival rate in STAD patients, and positive correlations between ClC-3/SGK1 and their downstream molecules in STAD tissues were demonstrated via the GEPIA datasets. Finally, our results suggested that olaparib inhibited the PI3K/AKT pathway in STAD cells, and up-regulation of ClC-3/SGK1 axis enhanced olaparib-induced PI3K/AKT pathway inhibition. The animal experiments indicated that olaparib also exerted antitumor effect in vivo. Altogether, our findings illustrate that olaparib exerts antitumor effect in human STAD, and ClC-3/SGK1 regulatory axis enhances the olaparib-induced antitumor effect. Up-regulation of the ClC-3/SGK1 axis may provide promising therapeutic potential for the clinical application of olaparib in STAD treatment.

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.

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.

Synthesis of Small-Molecule Fluorescent Probes for the In Vitro Imaging of Calcium-Activated Potassium Channel KCa 3.1

Small-molecule probes for the in vitro imaging of KCa 3.1 channel-expressing cells were developed. Senicapoc, showing high affinity and selectivity for the KCa 3.1 channels, was chosen as the targeting component. BODIPY dyes 15-20 were synthesized and connected by a CuI -catalyzed azide-alkyne [3+2]cycloaddition with propargyl ether senicapoc derivative 8, yielding fluorescently labeled ligands 21-26. The dimethylpyrrole-based imaging probes 25 and 26 allow staining of KCa 3.1 channels in NSCLC cells. The specificity was shown by removing the punctate staining pattern by pre-incubation with senicapoc. The density of KCa 3.1 channels detected with 25 and by immunostaining was identical. The punctate structure of the labeled channels could also be observed in living cells. Molecular modeling showed binding of the senicapoc-targeting component towards the binding site within the ion channel and orientation of the linker with the dye along the inner surface of the ion channel.

Design and evaluation of self-nanoemulsifying drug delivery systems (SNEDDSs) for senicapoc

Senicapoc (SEN), a potent antisickling agent, shows poor water solubility and poor oral bioavailability. To improve the solubility and cell permeation of SEN, self-nanoemulsifying drug delivery systems (SNEDDSs) were developed. Capryol PGMC®, which showed the highest solubilization capacity, was selected as the oil. The self-emulsification ability of two surfactants, viz., Cremophor-EL® and Tween® 80, was compared. Based on a solubility study and ternary phase diagrams, three optimized nanoemulsions with droplet sizes less than 200 nm were prepared. An in vitro dissolution study demonstrated the superior performance of the SNEDDS over the free drug. During in vitro lipolysis, 80% of SEN loaded in the SNEDDS remained solubilized. An in vitro cytotoxicity study using the Caco-2 cell line indicated the safety of the formulations at 1 mg/mL. The transport of SEN-SNEDDSs across Caco-2 monolayers was enhanced 115-fold (p < 0.01) compared to that of the free drug. According to these results, SNEDDS formulations could be promising tools for the oral delivery of SEN.

Ion Channels in Lung Cancer

Ion channels are a major class of membrane proteins that play central roles in signaling within and among cells, as well as in the coupling of extracellular events with cellular responses. Dysregulated ion channel activity plays a causative role in many diseases including cancer. Here, we will review their role in lung cancer. Lung cancer is one of the most frequently diagnosed cancers, and it causes the highest number of deaths of all cancer types. The overall 5-year survival rate of lung cancer patients is only 19% and decreases to 5% when patients are diagnosed with stage IV. Thus, new therapeutical strategies are urgently needed. The important contribution of ion channels to the progression of various types of cancer has been firmly established so that ion channel-based therapeutic concepts are currently developed. Thus far, the knowledge on ion channel function in lung cancer is still relatively limited. However, the published studies clearly show the impact of ion channel inhibitors on a number of cellular mechanisms underlying lung cancer cell aggressiveness such as proliferation, migration, invasion, cell cycle progression, or adhesion. Additionally, in vivo experiments reveal that ion channel inhibitors diminish tumor growth in mice. Furthermore, some studies give evidence that ion channel inhibitors can have an influence on the resistance or sensitivity of lung cancer cells to common chemotherapeutics such as paclitaxel or cisplatin.

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

Background

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

Methods

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

Results

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

Conclusion

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

[Ca2+-activated K+ channels as cancer therapeutic targets]

Similar to calcium (Ca²⁺) and chloride (Cl^-) ion channels/transporters, potassium (K⁺) channels have been recognized as a crucial cancer treatment target. Recent studies have provided convincing evidences of positive correlation between elevated expression levels of Ca²⁺-activated K⁺ (K_Ca) channels and cancer proliferation, metastasis, and poor patient prognosis. In cancer cells, K_Ca1.1 and K_Ca3.1 K_Ca channels are co-localized with Ca²⁺-permeable Orai/TRP channels to provide a positive-feedback loop for Ca²⁺ entry. They are responsible for the promotion of cell growth and metastasis in the different types of cancer, and are therefore potential therapeutic targets and biomarkers for cancer. We determined the epigenetic and post-transcriptional dysregulation of K_Ca3.1 by class I histone deacetylase inhibitors in breast and prostate cancer cells. We further determined the transcriptional repression and protein degradation of K_Ca1.1 by vitamin D receptor agonists and androgen receptor antagonists, which are expected as potential therapeutic drugs for triple-negative breast cancer. The anti-inflammatory cytokine, interleukin-10 (IL-10) is an immunosuppressive factor involved in tumorigenesis, and plays a crucial role in escape from tumor immune surveillance. We determined K_Ca3.1 activators are a possible therapeutic option to suppress the tumor-promoting activities of IL-10. These results may provide new insights into cancer treatment focused on Ca²⁺-activated K⁺ channels.

KCa3.1 Channels Confer Radioresistance to Breast Cancer Cells

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

Expression Profiling of Calcium Channels and Calcium-Activated Potassium Channels in Colorectal Cancer

Background: Colorectal cancer (CRC) is a highly devastating cancer. Ca²⁺-dependent channels are now considered key regulators of tumor progression. In this study, we aimed to investigate the association of non-voltage gated Ca²⁺ channels and Ca²⁺-dependent potassium channels (KCa) with CRC using the transcriptional profile of their genes. Methods: We selected a total of 35 genes covering KCa channels KCNN1–4, KCNMA1 and their subunits KCNMB1–4, endoplasmic reticulum (ER) calcium sensors STIM1 and STIM2, Ca²⁺ channels ORAI1–3 and the family of cation channels TRP (TRPC1–7, TRPA1, TRPV1/2,4–6 and TRPM1–8). We analyzed their expression in two public CRC datasets from The Cancer Genome Atlas (TCGA) and GSE39582. Results: KCNN4 and TRPM2 were induced while KCNMA1 and TRPM6 were downregulated in tumor tissues comparing to normal tissues. In proximal tumors, STIM2 and KCNN2 were upregulated while ORAI2 and TRPM6 were downregulated. ORAI1 decreased in lymph node metastatic tumors. TRPC1 and ORAI3 predicted poor prognosis in CRC patients. Moreover, we found that ORAI3/ORAI1 ratio is increased in CRC progression and predicted poor prognosis. Conclusions: KCa and Ca²⁺ channels could be important contributors to CRC initiation and progression. Our results provide new insights on KCa and Ca²⁺ channels remodeling in CRC.

Mechanosensitive ion channels push cancer progression

In many cases, the mechanical properties of a tumor are different from those of the host tissue. Mechanical cues regulate cancer development by affecting both tumor cells and their microenvironment, by altering cell migration, proliferation, extracellular matrix remodeling and metastatic spread. Cancer cells sense mechanical stimuli such as tissue stiffness, shear stress, tissue pressure of the extracellular space (outside-in mechanosensation). These mechanical cues are transduced into a cellular response (e. g. cell migration and proliferation; inside-in mechanotransduction) or to a response affecting the microenvironment (e. g. inducing a fibrosis or building up growth-induced pressure; inside-out mechanotransduction). These processes heavily rely on mechanosensitive membrane proteins, prominently ion channels. Mechanosensitive ion channels are involved in the Ca²⁺-signaling of the tumor and stroma cells, both directly, by mediating Ca²⁺ influx (e. g. Piezo and TRP channels), or indirectly, by maintaining the electrochemical gradient necessary for Ca²⁺ influx (e. g. K_2P, K_Ca channels). This review aims to discuss the diverse roles of mechanosenstive ion channels in cancer progression, especially those involved in Ca²⁺-signaling, by pinpointing their functional relevance in tumor pathophysiology.