Contribution of functional voltage-gated Na+ channel expression to cell behaviors involved in the metastatic cascade in rat prostate cancer: I. Lateral motility

Voltage-gated sodium channel as a target for metastatic risk reduction with re-purposed drugs

Objective: To determine the exact role of sodium channel proteins in migration, invasion and metastasis and understand the possible anti-invasion and anti-metastatic activity of repurposed drugs with voltage gated sodium channel blocking properties.

Material and methods: A review of the published medical literature was performed searching for pharmaceuticals used in daily practice, with inhibitory activity on voltage gated sodium channels. For every drug found, the literature was reviewed in order to define if it may act against cancer cells as an anti-invasion and anti-metastatic agent and if it was tested with this purpose in the experimental and clinical settings.

Results: The following pharmaceuticals that fulfill the above mentioned effects, were found: phenytoin, carbamazepine, valproate, lamotrigine, ranolazine, resveratrol, ropivacaine, lidocaine, mexiletine, flunarizine, and riluzole. Each of them are independently described and analyzed.

Conclusions: The above mentioned pharmaceuticals have shown anti-metastatic and anti-invasion activity and many of them deserve to be tested in well-planned clinical trials as adjunct therapies for solid tumors and as anti-metastatic agents. Antiepileptic drugs like phenytoin, carbamazepine and valproate and the vasodilator flunarizine emerged as particularly useful for anti-metastatic purposes.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

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

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

Inhibitory effects of dunning rat prostate tumor fluid on proliferation of the metastatic MAT-LyLu cell line

Tumor fluid accumulation occurs in both human cancer and experimental tumor models. Solid tumors show a tendency to tumor fluid accumulation because of their anatomical and physiological features and this may be influenced by molecular factors. Fluid accumulation in the peri-tumor area also occurs in the Dunning model of rat prostate cancer as the tumor grows. In this study, the effects of tumor fluids that were obtained from Dunning prostate tumor-bearing Copenhagen rats on the strongly metastatic MAT-LyLu cell line were investigatedby examining the cell's migration and tumor fluid's toxicity and the kinetic parameters such as cell proliferation, mitotic index, and labelling index. In this research, tumor fluids were obtained from rats injected with 25105 MAT- LyLu cells and treated with saline solution, and 200 nM tetrodotoxin (TTX), highly specific sodium channel blocker was used. Sterilized tumor fluids were added to medium of MAT-LyLu cells with the proportion of 20% in vitro. Consequently, it was demonstrated that Dunning rat prostate tumor fluid significantly inhibited proliferation (up to 50%), mitotic index, and labeling index of MAT-LyLu cells (up to 75%) (p<0.05) but stimulated the motility of the cells in vitro.

The sodium channel-blocking antiepileptic drug phenytoin inhibits breast tumour growth and metastasis

Background

Voltage-gated Na⁺ channels (VGSCs) are heteromeric protein complexes containing pore-forming α subunits and smaller, non-pore-forming β subunits. VGSCs are classically expressed in electrically excitable cells, e.g. neurons. VGSCs are also expressed in tumour cells, including breast cancer (BCa) cells, where they enhance cellular migration and invasion. However, despite extensive work defining in detail the molecular mechanisms underlying the expression of VGSCs and their pro-invasive role in cancer cells, there has been a notable lack of clinically relevant in vivo data exploring their value as potential therapeutic targets.

Findings

We have previously reported that the VGSC-blocking antiepileptic drug phenytoin inhibits the migration and invasion of metastatic MDA-MB-231 cells in vitro. The purpose of the present study was to establish whether VGSCs might be viable therapeutic targets by testing the effect of phenytoin on tumour growth and metastasis in vivo. We found that expression of Na_v1.5, previously detected in MDA-MB-231 cells in vitro, was retained on cells in orthotopic xenografts. Treatment with phenytoin, at a dose equivalent to that used to treat epilepsy (60 mg/kg; daily), significantly reduced tumour growth, without affecting animal weight. Phenytoin also reduced cancer cell proliferation in vivo and invasion into surrounding mammary tissue. Finally, phenytoin significantly reduced metastasis to the liver, lungs and spleen.

Conclusions

This is the first study showing that phenytoin reduces breast tumour growth and metastasis in vivo. We propose that pharmacologically targeting VGSCs, by repurposing antiepileptic or antiarrhythmic drugs, should be further studied as a potentially novel anti-cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-014-0277-x) contains supplementary material, which is available to authorized users.

Exposure to sodium channel-inhibiting drugs and cancer survival: protocol for a cohort study using the QResearch primary care database

INTRODUCTION

Metastasis from solid tumours is associated with significant morbidity and mortality, and is the leading cause of cancer-related deaths. Voltage-gated sodium channels (VGSCs) are drug targets for the treatment of epilepsy. VGSCs are also present in cancer cells, where they regulate metastatic cell behaviours, including cellular movement and invasion. Treating cancer cells with the VGSC-inhibiting anticonvulsant phenytoin reduces cellular invasion and migration. Together, these suggest that VGSCs may be useful targets for inhibiting metastasis. The purpose of this study is to test the hypothesis that use of VGSC-inhibiting drugs will reduce metastasis, and therefore increase survival time in patients with cancer.

METHODS AND ANALYSIS

A cohort study based on primary care data from the QResearch database will include patients with one of the three common tumours: breast, bowel and prostate. The primary outcome will be overall survival from the date of cancer diagnosis. Cox proportional hazards regression will be used to compare the survival of patients with cancer taking VGSC-inhibiting drugs (including anticonvulsants and class I antiarrhythmic agents) with patients with cancer not exposed to these drugs, adjusting for age and sex. Exposure to VGSC-inhibiting drugs will be defined as having at least one prescription for these drugs prior to cancer diagnosis. High and low exposure groups will be identified based on the length of use. A number of sensitivity and secondary analyses will be conducted.

ETHICS AND DISSEMINATION

The protocol has been independently peer-reviewed and approved by the QResearch Scientific Board. The project has also been approved by the University of York Ethical Review Process. The results will be presented at international conferences and published in an open access peer-reviewed journal, in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria.

Voltage-gated sodium channel Nav 1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+ /Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage-gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB-R7943, at a dose that blocks reverse mode of the Na(+) /Ca(2+) exchanger (NCX), and by knockdown of Nav 1.5 mRNA. We also show that astrocytes display a robust [Ca(2+) ]i transient after mechanical injury and demonstrate that this [Ca(2+) ]i response is also attenuated by TTX, KB-R7943, and Nav 1.5 mRNA knockdown. Our results suggest that Nav 1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca(2+) ]i .

Scorpion venoms as a potential source of novel cancer therapeutic compounds

Scorpions and their venoms have been used in traditional medicine for thousands of years in China, India and Africa. The scorpion venom is a highly complex mixture of salts, nucleotides, biogenic amines, enzymes, mucoproteins, as well as peptides and proteins (e.g. neurotoxins). One of the recently observed biological properties of animal venoms and toxins is that they possess anticancer potential. An increasing number of studies have shown that scorpion venoms and toxins can decrease cancer growth, induce apoptosis and inhibit cancer progression and metastasis in vitro and in vivo. Several active molecules with anticancer activities, ranging from inhibition of proliferation and cell cycle arrest to induction of apoptosis and decreasing cell migration and invasion, have been isolated from scorpion venoms. These observations have shed light on the application of scorpion venoms and toxins as potential novel cancer therapeutics. This mini-review focuses on the anticancer potential of scorpion venoms and toxins and the possible mechanisms for their antitumor activities.

Regulation of voltage-gated sodium channel expression in cancer: hormones, growth factors and auto-regulation

Although ion channels are increasingly being discovered in cancer cells in vitro and in vivo, and shown to contribute to different aspects and stages of the cancer process, much less is known about the mechanisms controlling their expression. Here, we focus on voltage-gated Na⁺ channels (VGSCs) which are upregulated in many types of carcinomas where their activity potentiates cell behaviours integral to the metastatic cascade. Regulation of VGSCs occurs at a hierarchy of levels from transcription to post-translation. Importantly, mainstream cancer mechanisms, especially hormones and growth factors, play a significant role in the regulation. On the whole, in major hormone-sensitive cancers, such as breast and prostate cancer, there is a negative association between genomic steroid hormone sensitivity and functional VGSC expression. Activity-dependent regulation by positive feedback has been demonstrated in strongly metastatic cells whereby the VGSC is self-sustaining, with its activity promoting further functional channel expression. Such auto-regulation is unlike normal cells in which activity-dependent regulation occurs mostly via negative feedback. Throughout, we highlight the possible clinical implications of functional VGSC expression and regulation in cancer.

A highly predictive 3D-QSAR model for binding to the voltage-gated sodium channel: design of potent new ligands

A comprehensive comparative molecular field analysis (CoMFA) model for the binding of ligands to the neuronal voltage-gated sodium channel was generated based on 67 diverse compounds. Earlier published CoMFA models for this target provided μM ligands, but the improved model described here provided structurally novel compounds with low nM IC₅₀. For example, new compounds 94 and 95 had IC₅₀ values of 129 and 119 nM, respectively.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

Role of ion channels and transporters in cell migration

Cell motility is central to tissue homeostasis in health and disease, and there is hardly any cell in the body that is not motile at a given point in its life cycle. Important physiological processes intimately related to the ability of the respective cells to migrate include embryogenesis, immune defense, angiogenesis, and wound healing. On the other side, migration is associated with life-threatening pathologies such as tumor metastases and atherosclerosis. Research from the last ≈ 15 years revealed that ion channels and transporters are indispensable components of the cellular migration apparatus. After presenting general principles by which transport proteins affect cell migration, we will discuss systematically the role of channels and transporters involved in cell migration.

Arrhythmogenesis toxicity of aconitine is related to intracellular ca(2+) signals

Aconitine is a well-known arrhythmogenic toxin and induces triggered activities through cardiac voltage-gated Na(+) channels. However, the effects of aconitine on intracellular Ca(2+) signals were previously unknown. We investigated the effects of aconitine on intracellular Ca(2+) signals in rat ventricular myocytes and explored the possible mechanism of arrhythmogenic toxicity induced by aconitine. Ca(2+) signals were evaluated by measuring L-type Ca(2+) currents, caffeine-induced Ca(2+) release and the expression of NCX and SERCA2a. Action potential and triggered activities were recorded by whole-cell patch-clamp techniques. In rat ventricular myocytes, the action potential duration was significantly prolonged by 1 µM aconitine. At higher concentrations (5 µM and 10 µM), aconitine induced triggered activities and delayed after-depolarizations (6 of 8 cases), which were inhibited by verapamil. Aconitine (1 µM) significantly increased the ICa-L density from 12.77 ± 3.12 pA/pF to 18.98 ± 3.89 pA/pF (n=10, p<0.01). The activation curve was shifted towards more negative potential, while the inactivation curve was shifted towards more positive potential by 1 μM aconitine. The level of Ca(2+) release induced by 10 mM caffeine was markedly increased. Aconitine (1 µM) increased the expression of NCX, while SERCA2a expression was reduced. In conclusion, aconitine increased the cytosolic [Ca(2+)]i by accelerating ICa-L and changing the expression of NCX and SERCA2a. Then, the elevation of cytosolic [Ca(2+)]i induced triggered activities and delayed after-depolarizations. Arrhythmogenesis toxicity of aconitine is related to intracellular Ca(2+) signals.

Voltage-gated sodium channels and metastatic disease

Voltage-gated Na (+) channels (VGSCs) are macromolecular protein complexes containing a pore-forming α subunit and smaller non-pore-forming β subunits. VGSCs are expressed in metastatic cells from a number of cancers. In these cells, Na (+) current carried by α subunits enhances migration, invasion and metastasis in vivo. In contrast, the β subunits mediate cellular adhesion and process extension. The prevailing hypothesis is that VGSCs are upregulated in cancer, in general favoring an invasive/metastatic phenotype, although the mechanisms are still not fully clear. Expression of the Nav 1.5 α subunit associates with poor prognosis in clinical breast cancer specimens, suggesting that VGSCs may have utility as prognostic markers for cancer progression. Furthermore, repurposing existing VGSC-blocking therapeutic drugs may provide a new strategy to improve outcomes in patients suffering from metastatic disease, which is the major cause of cancer-related deaths, and for which there is currently no cure.

Overexpression of the VSSC-associated CAM, β-2, enhances LNCaP cell metastasis associated behavior

BACKGROUND

Prostate cancer (PCa) is the second-leading cause of cancer death in American men. This is due largely to the "silent" nature of the disease until it has progressed to a highly metastatic and castrate resistant state. Voltage sensitive sodium channels (VSSCs) are multimeric transmembrane protein complexes comprised of a pore-forming α subunit and one or two β subunits. The β-subunits modulate surface expression and gating kinetics of the channels but also have inherent cell adhesion molecule (CAM) functions. We hypothesize that PCa cells use VSSC β-subunits as CAMs during PCa progression and metastasis.

METHODS

We overexpressed the beta-2 isoform as a C-terminal fusion protein with enhanced cyan fluorescence protein (ECFP) in the weakly metastatic LNCaP cells. The effect of beta-2 overexpression on cell morphology was examined using confocal microscopy while metastasis-associated behavior was tested by performing several in vitro metastatic functional assays and in vivo subcutaneous tumor studies.

RESULTS

We found that cells overexpressing beta-2 (2BECFP) converted to a bipolar fibroblastic morphology. 2BECFP cells were more adhesive than control (ECFP) to vitronectin (twofold) and Matrigel® (1.3-fold), more invasive through Matrigel® (3.6-fold in 72 hr), and had enhanced migration (2.1-fold in 96 hr) independent of proliferation in wound-healing assays. In contrast, 2BECFP cells have a reduced tumor-take and tumor volume in vivo even though the overexpression of beta-2 was maintained.

CONCLUSIONS

Functional overexpression of VSSC β-subunits in PCa may be one mechanism leading to increased metastatic behavior while decreasing the ability to form localized tumor masses.

Therapeutic potential for phenytoin: targeting Na(v)1.5 sodium channels to reduce migration and invasion in metastatic breast cancer

Voltage-gated Na(+) channels (VGSCs) are heteromeric membrane protein complexes containing pore-forming α subunits and smaller, non-pore-forming β subunits. VGSCs are classically expressed in excitable cells, including neurons and muscle cells, where they mediate action potential firing, neurite outgrowth, pathfinding, and migration. VGSCs are also expressed in metastatic cells from a number of cancers. The Na(v)1.5 α subunit (encoded by SCN5A) is expressed in breast cancer (BCa) cell lines, where it enhances migration and invasion. We studied the expression of SCN5A in BCa array data, and tested the effect of the VGSC-blocking anticonvulsant phenytoin (5,5-diphenylhydantoin) on Na(+) current, migration, and invasion in BCa cells. SCN5A was up-regulated in BCa samples in several datasets, and was more highly expressed in samples from patients who had a recurrence, metastasis, or died within 5 years. SCN5A was also overexpressed as an outlier in a subset of samples, and associated with increased odds of developing metastasis. Phenytoin inhibited transient and persistent Na(+) current recorded from strongly metastatic MDA-MB-231 cells, and this effect was more potent at depolarized holding voltages. It may thus be an effective VGSC-blocking drug in cancer cells, which typically have depolarized membrane potentials. At a concentration within the therapeutic range used to treat epilepsy, phenytoin significantly inhibited the migration and invasion of MDA-MB-231 cells, but had no effect on weakly metastatic MCF-7 cells, which do not express Na(+) currents. We conclude that phenytoin suppresses Na(+) current in VGSC-expressing metastatic BCa cells, thus inhibiting VGSC-dependent migration and invasion. Together, our data support the hypothesis that SCN5A is up-regulated in BCa, favoring an invasive/metastatic phenotype. We therefore propose that repurposing existing VGSC-blocking therapeutic drugs should be further investigated as a potential new strategy to improve patient outcomes in metastatic BCa.

Voltage-gated sodium channel activity promotes prostate cancer metastasis in vivo

Epigenetic upregulation of voltage-gated sodium channels (VGSCs) has been reported in a number of carcinoma cell lines and tissues. Furthermore, a large body of experimental evidence suggested that functional VGSC expression enhances various in vitro cell behaviours, such as directional motility, that would be involved in the metastatic cascade. However, it is not known if VGSC activity promotes metastasis in vivo. Here, using the Copenhagen rat model of prostate cancer and blocking VGSC activity in primary tumours with tetrodotoxin, we show (1) that the number of lung metastasis is reduced by >40% and (2) that lifespan is significantly improved.

Sodium channels and microglial function

Microglia are resident immune cells that provide continuous surveillance within the central nervous system (CNS) and respond to perturbations of brain and spinal cord parenchyma with an array of effector functions, including proliferation, migration, phagocytosis, secretions of multiple cytokines/chemokines and promotion of repair. To sense alterations within their environment, microglia express a large number of cell surface receptors, ion channels and adhesion molecules, which activate complex and dynamic signaling pathways. In the present chapter, we review studies that demonstrate that microglia in vivo and in vitro express specific voltage-gated sodium channel isoforms, and that blockade of sodium channel activity can attenuate several effector functions of microglia. These studies also provide strong evidence that Nav1.6 is the predominant sodium channel isoform expressed in microglia and that its activity contributes to the response of microglia to multiple activating signals.

Ion channnels and transporters in cancer. 5. Ion channels in control of cancer and cell apoptosis

Ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. The involvement of ion channels in regulation of programmed cell death, or apoptosis, has been known for at least three decades based on observation that classical blockers of ion channels can influence cell death rates, prolonging or shortening cell survival. Identification of the central role of these channels in regulation of cell cycle and apoptosis as well as the recent discovery that the expression of ion channels is not limited solely to the plasma membrane, but may also include membranes of internal compartments, has led researchers to appreciate the pivotal role of ion channels plays in development of cancer. This review focuses on the aspects of programmed cell death influenced by various ion channels and how dysfunctions and misregulations of these channels may affect the development and progression of different cancers.

Angiogenic functions of voltage-gated Na+ Channels in human endothelial cells: modulation of vascular endothelial growth factor (VEGF) signaling

Voltage-gated sodium channel (VGSC) activity has previously been reported in endothelial cells (ECs). However, the exact isoforms of VGSCs present, their mode(s) of action, and potential role(s) in angiogenesis have not been investigated. The main aims of this study were to determine the role of VGSC activity in angiogenic functions and to elucidate the potentially associated signaling mechanisms using human umbilical vein endothelial cells (HUVECs) as a model system. Real-time PCR showed that the primary functional VGSC α- and β-subunit isoforms in HUVECs were Nav1.5, Nav1.7, VGSCβ1, and VGSCβ3. Western blots verified that VGSCα proteins were expressed in HUVECs, and immunohistochemistry revealed VGSCα expression in mouse aortic ECs in vivo. Electrophysiological recordings showed that the channels were functional and suppressed by tetrodotoxin (TTX). VGSC activity modulated the following angiogenic properties of HUVECs: VEGF-induced proliferation or chemotaxis, tubular differentiation, and substrate adhesion. Interestingly, different aspects of angiogenesis were controlled by the different VGSC isoforms based on TTX sensitivity and effects of siRNA-mediated gene silencing. Additionally, we show for the first time that TTX-resistant (TTX-R) VGSCs (Nav1.5) potentiate VEGF-induced ERK1/2 activation through the PKCα-B-RAF signaling axis. We postulate that this potentiation occurs through modulation of VEGF-induced HUVEC depolarization and [Ca(2+)](i). We conclude that VGSCs regulate multiple angiogenic functions and VEGF signaling in HUVECs. Our results imply that targeting VGSC expression/activity could be a novel strategy for controlling angiogenesis.

Natural antibodies against nerve growth factor inhibit in vitro prostate cancer cell metastasis

Prostate cancer is a major cause of death in older men, and bone metastasis is the primary cause of morbidity and mortality in prostate cancer. Prostate is an abundant source of nerve growth factor (NGF) that is secreted by malignant epithelial cells and utilized as an important autocrine factor for growth and metastasis. We previously showed that intravenous gammaglobulin (IVIg) contains natural antibodies against NGF, which inhibit growth and differentiation of the NGF-dependent cell line PC-12. In the present study, we examined the effects of these natural antibodies on in vitro migration or metastasis of two prostate cancer cell lines namely DU-145 and PC-3. Cancer cell migration was assessed using these cell lines in the upper chambers of Matrigel invasion chambers. The effects of IVIg and affinity-purified anti-NGF antibodies on cell migration through membrane into the lower chamber were assessed in dose/response experiments by a colorimetric method. Affinity-purified natural IgG anti-NGF antibody inhibited DU-145 migration by 38% (p = 0.01) and PC-3 migration by 25% (p = 0.02); whereas, a monoclonal anti-NGF antibody inhibited DU-145 migration by 40% (p = 0.01) and PC-3 migration by 37% (p = 0.02), at the same concentration. When IVIg was depleted of NGF-specific IgG by affinity chromatography, there was no significant inhibition of migration of the DU-145 and PC-3 cells at a concentration of 1 mg/well. Removal of the NGF-specific antibody from the IVIg was also demonstrated by a lack of effect on PC-12 cell differentiation. Therefore, IVIg is able to inhibit the migration of prostate cancer cell lines, through Matrigel chambers in vitro, only when the natural NGF-specific antibodies actively are present in IVIg.

Estrogen and non-genomic upregulation of voltage-gated Na(+) channel activity in MDA-MB-231 human breast cancer cells: role in adhesion

External (but not internal) application of beta-estradiol (E2) increased the current amplitude of voltage-gated Na(+) channels (VGSCs) in MDA-MB-231 human breast cancer (BCa) cells. The G-protein activator GTP-gamma-S, by itself, also increased the VGSC current whilst the G-protein inhibitor GDP-beta-S decreased the effect of E2. Expression of GPR30 (a G-protein-coupled estrogen receptor) in MDA-MB-231 cells was confirmed by PCR, Western blot and immunocytochemistry. Importantly, G-1, a specific agonist for GPR30, also increased the VGSC current amplitude in a dose-dependent manner. Transfection and siRNA-silencing of GPR30 expression resulted in corresponding changes in GPR30 protein expression but only internally, and the response to E2 was not affected. The protein kinase A inhibitor, PKI, abolished the effect of E2, whilst forskolin, an adenylate cyclase activator, by itself, increased VGSC activity. On the other hand, pre-incubation of the MDA-MB-231 cells with brefeldin A (a trans-Golgi protein trafficking inhibitor) had no effect on the E2-induced increase in VGSC amplitude, indicating that such trafficking ('externalisation') of VGSC was not involved. Finally, acute application of E2 decreased cell adhesion whilst the specific VGSC blocker tetrodotoxin increased it. Co-application of E2 and tetrodotoxin inhibited the effect of E2 on cell adhesion, suggesting that the effect of E2 was mainly through VGSC activity. Pre-treatment of the cells with PKI abolished the effect of E2 on adhesion, consistent with the proposed role of PKA. Potential implications of the E2-induced non-genomic upregulation of VGSC activity for BCa progression are discussed.

Repression of SHP-1 expression by p53 leads to trkA tyrosine phosphorylation and suppression of breast cancer cell proliferation

The nerve growth factor (NGF) receptor, trkA, the tumour suppressor p53 and the phosphatase SHP-1 are critical in cell proliferation and differentiation. SHP-1 is a trkA phosphatase that dephosphorylates trkA at tyrosines (Y) 674 and 675. p53 can induce trkA activation and tyrosine phosphorylation in the absence of NGF stimulation. In breast cancer tumours trkA expression is associated with increased patient survival. TrkA protein expression is higher in breast-cancer cell lines than in normal breast epithelia. In cell lines (but not in normal breast epithelia) trkA is functional and can be NGF-stimulated to promote cell proliferation. This study investigates the functional relationship between trkA, p53 and SHP-1 in breast-cancer, and reveals that in wild-type (wt) trkA expressing breast-cancer cells both endogenous wtp53, activated by therapeutic agents, and transfected wtp53 repress expression of SHP-1 through the proximal CCAAT sequence of the SHP-1-P1-promoter and the transcription factor NF-Y. In these cells trkA-Y674/Y675 phosphorylation is detected when SHP-1 protein levels decrease in a wtp53-dependent manner. Proliferation and cell-cycle assays, with cells expressing endogenous or transfected wt-trkA and a temperature-sensitive p53 grown at 32 degrees C (when p53 is in the wt configuration), show suppressed cell proliferation. Suppression is not detected when grown at 37 degrees C (when p53 is in the mutant configuration). A release from suppression is observed when these cells are transiently transfected with wt-SHP-1 and grown at 32 degrees C. Suppression is also detected when, as control, wt-trkA-expressing cells are transiently transfected with SHP-1-siRNA, but not when a dominant-negative (DN) mutant trkA is used to abolish wt-trkA activity. Importantly, suppression is not seen with control trkA-negative breast-cancer cells (expressing wtp53, wt-SHP-1 and undetectable trkA), transfected with Y674F/Y675F mutant-trkA. BrdU-incorporation experiments reveal lack of incorporation in cells expressing wt-trkA and wtp53, or wt-trkA and SHP-1-siRNA. However, BrdU is incorporated in the presence of Y674F/Y675F mutant trkA or DN mutant trkA. These results indicate that p53 repression of SHP-1 expression leads to trkA-Y674/Y675 phosphorylation and trkA-dependent suppression of breast-cancer cell proliferation. These data provide an explanation as to why high trkA levels are associated with favourable prognosis.

Sodium channel activity modulates multiple functions in microglia

Microglia provide surveillance in the central nervous system and become activated following tissue insult. Detailed mechanisms by which microglia detect and respond to their environment are not fully understood, but it is known that microglia express a number of surface receptors and ion channels, including voltage-gated sodium channels, that participate in transduction of external stimuli to intra-cellular responses. To determine whether activated microglia are affected by the activity of sodium channels, we examined the expression of sodium channel isoforms in cultured microglia and the action of sodium channel blockade on multiple functions of activated microglia. Rat microglia in vitro express tetrodotoxin (TTX)-sensitive sodium channels Nav1.1 and Nav1.6 and the TTX-resistant channel Nav1.5, but not detectable levels of Nav1.2, Nav1.3, Nav1.7, Nav1.8, and Nav1.9. Sodium channel blockade with phenytoin (40 microM) and TTX (0.3 microM) significantly reduced by 50-60% the phagocytic activity of microglia activated with lipopolysaccharide (LPS); blockade with 10 microM TTX did not further reduce phagocytic activity. Phenytoin attenuated by approximately 50% the release of IL-1 alpha, IL-1 beta, and TNF-alpha from LPS-stimulated microglia, but had minimal effects on the release of IL-2, IL-4, IL-6, IL-10, MCP-1, and TGF-alpha. TTX (0.3 microM) reduced, but to a smaller extent, the release of IL-1 alpha, IL-1 beta, and TNF-alpha from activated microglia. Phenytoin and TTX also significantly decreased by approximately 50% adenosine triphosphate-induced migration by microglia; studies with microglia cultured from med mice (which lack Nav1.6) indicate that Nav1.6 plays a role in microglial migration. The results demonstrate that the activity of sodium channels contributes to effector roles of activated microglia.

A novel adhesion molecule in human breast cancer cells: voltage-gated Na+ channel beta1 subunit

Voltage-gated Na(+) channels (VGSCs), predominantly the 'neonatal' splice form of Na(v)1.5 (nNa(v)1.5), are upregulated in metastatic breast cancer (BCa) and potentiate metastatic cell behaviours. VGSCs comprise one pore-forming alpha subunit and one or more beta subunits. The latter modulate VGSC expression and gating, and can function as cell adhesion molecules of the immunoglobulin superfamily. The aims of this study were (1) to determine which beta subunits were expressed in weakly metastatic MCF-7 and strongly metastatic MDA-MB-231 human BCa cells, and (2) to investigate the possible role of beta subunits in adhesion and migration. In both cell lines, the beta subunit mRNA expression profile was SCN1B (encoding beta1)>>SCN4B (encoding beta4)>SCN2B (encoding beta2); SCN3B (encoding beta3) was not detected. MCF-7 cells had much higher levels of all beta subunit mRNAs than MDA-MB-231 cells, and beta1 mRNA was the most abundant. Similarly, beta1 protein was strongly expressed in MCF-7 and barely detectable in MDA-MB-231 cells. In MCF-7 cells transfected with siRNA targeting beta1, adhesion was reduced by 35%, while migration was increased by 121%. The increase in migration was reversed by tetrodotoxin (TTX). In addition, levels of nNa(v)1.5 mRNA and protein were increased following beta1 down-regulation. Stable expression of beta1 in MDA-MB-231 cells increased functional VGSC activity, process length and adhesion, and reduced lateral motility and proliferation. We conclude that beta1 is a novel cell adhesion molecule in BCa cells and can control VGSC (nNa(v)1.5) expression and, concomitantly, cellular migration.

Eicosapentaenoic acid inhibits voltage-gated sodium channels and invasiveness in prostate cancer cells

BACKGROUND AND PURPOSE

The voltage-gated Na(+) channels (Na(v)) and their corresponding current (I(Na)) are involved in several cellular processes, crucial to metastasis of cancer cells. We investigated the effects of eicosapentaenoic (EPA), an omega-3 polyunsaturated fatty acid, on I(Na) and metastatic functions (cell proliferation, endocytosis and invasion) in human and rat prostate cancer cell lines (PC-3 and Mat-LyLu cells).

EXPERIMENTAL APPROACH

The whole-cell voltage clamp technique and conventional/quantitative real-time reverse transcriptase polymerase chain reaction analysis were used. The presence of Na(v) proteins was shown by immunohistochemical methods. Alterations in the fatty acid composition of phospholipids after treatment with EPA and metastatic functions were also examined.

KEY RESULTS

A transient inward Na(+) current (I(Na)), highly sensitive to tetrodotoxin, and Na(V) proteins were found in these cells. Expression of Na(V)1.6 and Na(V)1.7 transcripts (SCN8A and SCN9A) was predominant in PC-3 cells, while Na(V)1.7 transcript (SCN9A) was the major component in Mat-LyLu cells. Tetrodotoxin or synthetic small interfering RNA targeted for SCN8A and SCN9A inhibited metastatic functions (endocytosis and invasion), but failed to inhibit proliferation in PC-3 cells. Exposure to EPA produced a rapid and concentration-dependent suppression of I(Na). In cells chronically treated (up to 72h) with EPA, the EPA content of cell lipids increased time-dependently, while arachidonic acid content decreased. Treatment of PC-3 cells with EPA decreased levels of mRNA for SCN9A and SCN8A, cell proliferation, invasion and endocytosis.

CONCLUSION AND IMPLICATIONS

Treatment with EPA inhibited I(Na) directly and also indirectly, by down-regulation of Na(v) mRNA expression in prostate cancer cells, thus inhibiting their metastatic potential.

Regulation of podosome formation in macrophages by a splice variant of the sodium channel SCN8A

Voltage-gated sodium channels initiate electrical signaling in excitable cells such as muscle and neurons. They also are expressed in non-excitable cells such as macrophages and neoplastic cells. Previously, in macrophages, we demonstrated expression of SCN8A, the gene that encodes the channel NaV1.6, and intracellular localization of NaV1.6 to regions near F-actin bundles, particularly at areas of cell attachment. Here we show that a splice variant of NaV1.6 regulates cellular invasion through its effects on podosome and invadopodia formation in macrophages and melanoma cells. cDNA sequence analysis of SCN8A from THP-1 cells, a human monocyte-macrophage cell line, confirmed the expression of a full-length splice variant that lacks exon 18. Immunoelectron microscopy demonstrated NaV1.6-positive staining within the electron dense podosome rosette structure. Pharmacologic antagonism with tetrodotoxin (TTX) in differentiated THP-1 cells or absence of functional NaV1.6 through a naturally occurring mutation (med) in mouse peritoneal macrophages inhibited podosome formation. Agonist-mediated activation of the channel with veratridine caused release of sodium from cationic vesicular compartments, uptake by mitochondria, and mitochondrial calcium release through the Na/Ca exchanger. Invasion by differentiated THP-1 and HTB-66 cells, an invasive melanoma cell line, through extracellular matrix was inhibited by TTX. THP-1 invasion also was inhibited by small hairpin RNA knockdown of SCN8A. These results demonstrate that a variant of NaV1.6 participates in the control of podosome and invadopodia formation and suggest that intracellular sodium release mediated by NaV1.6 may regulate cellular invasion of macrophages and melanoma cells.

The pharmacology of voltage-gated sodium channels in sensory neurones

Voltage-gated sodium channels (VGSCs) are vital for the normal functioning of most excitable cells. At least nine distinct functional subtypes of VGSCs are recognized, corresponding to nine genes for their pore-forming alpha-subunits. These have different developmental expression patterns, different tissue distributions in the adult and are differentially regulated at the cellular level by receptor-coupled cell signalling systems. Unsurprisingly, VGSC blockers are found to be useful as drugs in diverse clinical applications where excessive excitability of tissue leads to pathological dysfunction, e.g. epilepsy or cardiac tachyarrhythmias. The effects of most clinically useful VGSC blockers are use-dependent, i.e. their efficacy depends on channel activity. In addition, many natural toxins have been discovered that interact with VGSCs in complex ways and they have been used as experimental probes to study the structure and function of the channels and to better understand how drugs interact with the channels. Here we have attempted to summarize the properties of VGSCs in sensory neurones, discuss how they are regulated by cell signalling systems and we have considered briefly current concepts of their physiological function. We discuss in detail how drugs and toxins interact with archetypal VGSCs and where possible consider how they act on VGSCs in peripheral sensory neurones. Increasingly, drugs that block VGSCs are being used as systemic analgesic agents in chronic pain syndromes, but the full potential for VGSC blockers in this indication is yet to be realized and other applications in sensory dysfunction are also possible. Drugs targeting VGSC subtypes in sensory neurones are likely to provide novel systemic analgesics that are tissue-specific and perhaps even disease-specific, providing much-needed novel therapeutic approaches for the relief of chronic pain.

Voltage-gated Na+ channels: potential for beta subunits as therapeutic targets

BACKGROUND

Voltage gated Na(+) channels (VGSCs) contain a pore-forming alpha subunit and one or more beta subunits. VGSCs are involved in a wide variety of pathophysiologies, including epilepsy, cardiac arrhythmia, multiple sclerosis, periodic paralysis, migraine, neuropathic and inflammatory pain, Huntington's disease and cancer. Increasing evidence implicates the beta subunits as key players in these disorders.

OBJECTIVE

To review the recent literature describing the multifunctional roles of VGSC beta subunits in the context of their role(s) in disease.

METHODS

An extensive review of the literature on beta subunits.

RESULTS/CONCLUSION

beta subunits are multifunctional. As components of VGSC complexes, beta subunits mediate signaling processes regulating electrical excitability, adhesion, migration, pathfinding and transcription. beta subunits may prove useful in disease diagnosis and therapy.

An emerging role for voltage-gated Na+ channels in cellular migration: regulation of central nervous system development and potentiation of invasive cancers

Voltage-gated Na(+) channels (VGSCs) exist as macromolecular complexes containing a pore-forming alpha subunit and one or more beta subunits. The VGSC alpha subunit gene family consists of 10 members, which have distinct tissue-specific and developmental expression profiles. So far, four beta subunits (beta1-beta4) and one splice variant of beta1 (beta1A, also called beta1B) have been identified. VGSC beta subunits are multifunctional, serving as modulators of channel activity, regulators of channel cell surface expression, and as members of the immunoglobulin superfamily, cell adhesion molecules (CAMs). beta subunits are substrates of beta-amyloid precursor protein-cleaving enzyme (BACE1) and gamma-secretase, yielding intracellular domains (ICDs) that may further modulate cellular activity via transcription. Recent evidence shows that beta1 regulates migration and pathfinding in the developing postnatal CNS in vivo. The alpha and beta subunits, together with other components of the VGSC signaling complex, may have dynamic interactive roles depending on cell/tissue type, developmental stage, and pathophysiology. In addition to excitable cells like nerve and muscle, VGSC alpha and beta subunits are functionally expressed in cells that are traditionally considered nonexcitable, including glia, vascular endothelial cells, and cancer cells. In particular, the alpha subunits are up-regulated in line with metastatic potential and are proposed to enhance cellular migration and invasion. In contrast to the alpha subunits, beta1 is more highly expressed in weakly metastatic cancer cells, and evidence suggests that its expression enhances cellular adhesion. Thus, novel roles are emerging for VGSC alpha and beta subunits in regulating migration during normal postnatal development of the CNS as well as during cancer metastasis.

PRL PTPs: mediators and markers of cancer progression

Aberrant protein tyrosine phosphorylation resulting from the altered activity of protein tyrosine phosphatases (PTPs) is increasingly being implicated in the genesis and progression of human cancer. Accumulating evidence indicates that the dysregulated expression of members of the phosphatase of regenerating liver (PRL) subgroup of PTPs is linked to these processes. Enhanced expression of the PRLs, notably PRL-1 and PRL-3, promotes the acquisition of cellular properties that confer tumorigenic and metastatic abilities. Up-regulation of PRL-3 is associated with the progression and eventual metastasis of several types of human cancer. Indeed, PRL-3 shows promise as a biomarker and prognostic indicator in colorectal, breast, and gastric cancers. However, the substrates and molecular mechanisms of action of the PRLs have remained elusive. Recent findings indicate that PRLs may function in regulating cell adhesion structures to effect epithelial-mesenchymal transition. The identification of PRL substrates is key to understanding their roles in cancer progression and exploiting their potential as exciting new therapeutic targets for cancer treatment.

The Notch pathway in prostate development and cancer

The Notch family of transmembrane receptors are important mediators of cell fate determination. Accordingly, Notch signaling is intimately involved in the development of numerous tissues. Recent findings have highlighted a critical role for Notch signaling in normal prostate development. Notch signaling is required for embryonic and postnatal prostatic growth and development, for proper cell lineage specification within the prostate, as well as for adult prostate maintenance and regeneration following castration and hormone replacement. Evidence for Notch as a regulator of prostate cancer development, progression, and metastasis has also emerged. This review summarizes our current understanding of the role of Notch pathway elements, including members of the Jagged, Delta-like, hairy/enhancer-of-split, and hairy/enhancer-of-split related with YRPW motif families, in prostate development and tumorigenesis. Data supporting Notch pathway elements as oncogenes and tumor suppressors in prostate tumors, as well as data implicating Notch receptors and ligands as potential markers of normal prostate stem/progenitor cells and prostate cancer stem/initiating cells, are also presented.

Biochemical constitution of extracellular medium is critical for control of human breast cancer MDA-MB-231 cell motility

Although voltage-gated sodium channel (VGSC) activity, upregulated significantly in strongly metastatic human breast cancer cells, has been found to potentiate a variety of in vitro metastatic cell behaviors, the mechanism(s) regulating channel expression/activity is not clear. As a step toward identifying possible serum factors that might be responsible for this, we tested whether medium in which fetal bovine serum (FBS) was substituted with a commercial serum replacement agent (SR-2), comprising insulin and bovine serum albumin, would influence the VGSC-dependent in vitro metastatic cell behaviors. Human breast cancer MDA-MB-231 cells were used as a model. Measurements of lateral motility, transverse migration and adhesion showed consistently that the channel's involvement in metastatic cell behaviors depended on the extracellular biochemical conditions. In normal medium (5% FBS), tetrodotoxin (TTX), a highly specific blocker of VGSCs, suppressed these cellular behaviors, as reported before. In contrast, in SR-2 medium, TTX had opposite effects. However, blocking endogenous insulin/insulin-like growth factor receptor signaling with AG1024 eliminated or reversed the anomalous effects of TTX. Insulin added to serum-free medium increased migration, and TTX increased it further. In conclusion, (1) the biochemical constitution of the extracellular medium had a significant impact upon breast cancer cells' in vitro metastatic behaviors and (2) insulin, in particular, controlled the mode of the functional association between cells' VGSC activity and metastatic machinery.

Epidermal growth factor upregulates motility of Mat-LyLu rat prostate cancer cells partially via voltage-gated Na+ channel activity

The main aim of this investigation was to determine whether a functional relationship existed between epidermal growth factor (EGF) and voltage-gated sodium channel (VGSC) upregulation, both associated with strongly metastatic prostate cancer cells. Incubation with EGF for 24 h more than doubled VGSC current density. Similar treatment with EGF significantly and dose-dependently enhanced the cells' migration through Transwell filters. Both the patch clamp recordings and the migration assay suggested that endogenous EGF played a similar role. Importantly, co-application of EGF and tetrodotoxin, a highly selective VGSC blocker, abolished 65% of the potentiating effect of EGF. It is suggested that a significant portion of the EGF-induced enhancement of migration occurred via VGSC activity.

Identification and characterization of the promoter region of the Nav1.7 voltage-gated sodium channel gene (SCN9A)

The Nav1.7 sodium channel plays an important role in pain and is also upregulated in prostate cancer. To investigate the mechanisms regulating physiological and pathophysiological Nav1.7 expression we identified the core promoter of this gene (SCN9A) in the human genome. In silico genomic analysis revealed a putative SCN9A 5' non-coding exon approximately 64,000 nucleotides from the translation start site, expression of which commenced at three very closely-positioned transcription initiation sites (TISs), as determined by 5' RACE experiments. The genomic region around these TISs possesses numerous core elements of a TATA-less promoter within a well-defined CpG island. Importantly, it acted as a promoter when inserted upstream of luciferase in a fusion construct. Moreover, the activity of the promoter-luciferase construct ostensibly paralleled endogenous Nav1.7 mRNA levels in vitro, with both increased in a quantitatively and qualitatively similar manner by numerous factors (including NGF, phorbol esters, retinoic acid, and Brn-3a transcription factor over-expression).

Involvement of voltage-gated K+ and Na+ channels in gastric epithelial cell migration

Epithelial cell migration plays an important role in gastrointestinal mucosal repair. We previously reported that multiple functional ion channels, including a Ba(2+)-sensitive K(+) inward rectifier K(ir)1.2, 4-aminopyridine (4-AP)-sensitive voltage-gated K(+) channels K(v)1.1, K(v)1.6 and K(v)2.1, and a nifedipine-sensitive, tetrodotoxin (TTX)-insensitive voltage-gated Na(+) channel Na(v)1.5 were expressed in a non-transformed rat gastric epithelial cell line (RGM-1). In the present study, we further investigated whether these ion channels are involved in the modulation of gastric epithelial cell migration. Cell migration was determined by monolayer wound healing assay. Results showed that blockade of K(v) with 4-AP or Na(v)1.5 with nifedipine inhibited RGM-1 cell migration in the absence or presence of epidermal growth factor (EGF), which effectively stimulated RGM-1 cell migration. Moreover, high concentration of TTX mimicked the action of nifedipine, suggesting that the action of nifedipine was mediated through specific blockade of Na(v)1.5. In contrast, inhibition of K(ir)1.2 with Ba(2+), either in basal or EGF-stimulated condition, had no effect on RGM-1 cell migration. In conclusion, the present study demonstrates for the first time that voltage-gated K(+) and Na(+) channels are involved in the modulation of gastric epithelial cell migration.

β-Subunits of voltage-gated sodium channels in human prostate cancer: quantitative in vitro and in vivo analyses of mRNA expression

We previously identified high levels of Na(v)1.7 voltage-gated sodium channel alpha-subunit (VGSCalpha) mRNA and protein in human prostate cancer cells and tissues. Here, we investigated auxillary beta-subunit (VGSCbetas) expression. In vitro, the combined expression of all four VGSCbetas was significantly (approximately 4.5-fold) higher in strongly compared to weakly metastatic cells. This was mainly due to increased beta1-expression, which was under androgenic control. In vivo, beta1-beta4 mRNAs were detectable and their expression in CaP vs non-CaP tissues generally reflected the in vitro levels in relation to metastatic potential. The possible role(s) of VGSCbetas (VGSCalpha-associated and VGSCalpha-independent) in prostate cancer are discussed.

Single cell adhesion measuring apparatus (SCAMA): application to cancer cell lines of different metastatic potential and voltage-gated Na+ channel expression

We have developed a simple yet effective apparatus, based upon negative pressure directed to the tip of a micro-pipette, to measure the adhesiveness of single cells. The "single cell adhesion measuring apparatus" (SCAMA) could differentiate between the adhesion of strongly versus weakly metastatic cancer cells as well as normal cells. Adhesion was quantified as "detachment negative pressure" (DNP) or "DNP relative to cell size" (DNPR) where a noticeable difference in cell size was apparent. Thus, for rat and human prostate and human breast cancer cell lines, adhesiveness (DNPR values) decreased in line with increased metastatic potential. Using the SCAMA, we investigated the effect of tetrodotoxin (TTX), a specific blocker of voltage-gated Na(+) channels (VGSCs), on the adhesion of rat and human prostate cancer cell lines of markedly different metastatic potential. Following pretreatment with TTX (48 h with 1 microM), the adhesion values for the Mat-LyLu cells increased significantly 4.3-fold; there was no effect on the AT-2 cells. For the strongly metastatic PC-3M cells, TTX treatment caused a significant (approximately 30%) increase in adhesion. The adhesion of PNT2-C2 ("normal") cells was not affected by the TTX pretreatment. The TTX-induced increase in the adhesiveness of the strongly metastatic cells was consistent with the functional VGSC expression in these cells and the proposed role of VGSC activity in metastatic cell behaviour. In conclusion, the SCAMA, which can be constructed easily and cheaply, offers a simple and effective method to characterise single-cell adhesion and its modulation.

Ion channels in death and differentiation of prostate cancer cells

Plasma membrane ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. Enhanced proliferation, aberrant differentiation, and impaired ability to die are the prime reasons for abnormal tissue growth, which can eventually turn into uncontrolled expansion and invasion, characteristic of cancer. Prostate cancer (PCa) cells express a variety of plasma membrane ion channels. By providing the influx of essential signaling ions, perturbing intracellular ion concentrations, regulating cell volume, and maintaining membrane potential, PCa cells are critically involved in proliferation, differentiation, and apoptosis. PCa cells of varying metastatic ability can be distinguished by their ion channel characteristics. Increased malignancy and invasiveness of androgen-independent PCa cells is generally associated with the shift to a 'more excitable' phenotype of their plasma membrane. This shift is manifested by the appearance of voltage-gated Na(+) and Ca(2+) channels which contribute to their enhanced apoptotic resistance together with downregulated store-operated Ca(2+) influx, altered expression of different K(+) channels and members of the Transient Receptor Potential (TRP) channel family, and strengthened capability for maintaining volume constancy. The present review examines channel types expressed by PCa cells and their involvement in metastatic behaviors.

Voltage-sensitive ion channels and cancer

Plasma membrane voltage-sensitive ion channels classically have been associated with a variety of inherited diseases or "channelopathies" that range in the severity of symptoms from mild to lethal. Ion channels are found throughout the body and are responsible for facilitated diffusion of ions down the electrochemical gradient across cells membranes in various tissues. Voltage-sensitive ion channels open in response to changes in the membrane potential and are primarily found in excitable cells and tissues. Potassium, calcium, and sodium channels play critical roles in the development of major diseases, such as hyperkalemia, epilepsy, congenital myotonia and several cardiac arrythmias. Recently, cancer studies have begun to define the role of voltage-sensitive ion channels in the progression of cancer to a more malignant phenotype. In cancer, the increased expression or increased kinetics of voltage-sensitive ion channels is associated with an increasing malignant potential as evinced by their role in cell proliferation, migration and survival; as such, these channels are becoming the targets of significant drug development efforts to block or reduce voltage-sensitive ion channel activity in order to prevent or combat malignant disease.

Nerve growth factor enhances voltage-gated Na+ channel activity and Transwell migration in Mat-LyLu rat prostate cancer cell line

The highly dynamic nature of voltage-gated Na+ channel (VGSC) expression and its controlling mechanism(s) are not well understood. In this study, we investigated the possible involvement of nerve growth factor (NGF) in regulating VGSC activity in the strongly metastatic Mat-LyLu cell model of rat prostate cancer (PCa). NGF increased peak VGSC current density in a time- and dose-dependent manner. NGF also shifted voltage to peak and the half-activation voltage to more positive potentials, and produced currents with faster kinetics of activation; sensitivity to the VGSC blocker tetrodotoxin (TTX) was not affected. The NGF-induced increase in peak VGSC current density was suppressed by both the pan-trk antagonist K252a, and the protein kinase A (PKA) inhibitor KT5720. NGF did not affect the Nav1.7 mRNA level, but the total VGSC alpha-subunit protein level was upregulated. NGF potentiated the cells' migration in Transwell assays, and this was not affected by TTX. We concluded that NGF upregulated functional VGSC expression in Mat-LyLu cells, with PKA as a signaling intermediate, but enhancement of migration by NGF was independent of VGSC activity.

Hypothesis of the cause and development of neoplasms

Cancer, in general, is considered a disease of genetic mutation. Many questions are, however, unanswered. How exactly do mutations occur in the cells? How do gene mutations interface with the cell microenvironment and macroenvironment to create cancer phenotypes? Is mutation the cause of cancer or the consequence of special adaptive responses to aging; hormonal imbalance; physical, chemical and biologic stresses and damage? What makes cancer spread in the body and invade other organs causing death to the patient? In this paper, we hypothesize that the cellular hyperexcitability via stimulation of mineral channels (e.g. sodium voltage-gated channels) and ligand excitatory receptors (e.g. glutamate and other neuron and non-neuronal excitatory receptors) could be a significant causative and pathogenic factor of cancer. Managing hyperexcitatory states of the cells through lifestyle, nutritional changes, phytochemical and pharmaceutical medications theoretically could be a prospective direction in cancer prevention and therapy.