Voltage-gated sodium channels potentiate the invasive capacities of human non-small-cell lung cancer cell lines

Expression of neonatal Nav1.5 in human brain astrocytoma and its effect on proliferation, invasion and apoptosis of astrocytoma cells

In the present study, we designed and conducted a series of assays to determine the expression of voltage-gated sodium channel (VGSC) neonatal isoform Nav1.5 (nNav1.5) in human brain astrocytoma and its effect on the proliferation, migration, invasion and apoptosis of astrocytoma U251 cells. The results showed that nNav1.5 mRNA and protein were expressed in both human brain astrocytoma and normal brain tissues, but their expression levels in astrocytoma were significantly higher (P<0.05). In astrocytomas, nNav1.5 mRNA and protein levels were also different (P<0.05) and were correlated with pathological grades. The immunofluorescence confocal microscopy observations demonstrated that nNav1.5 protein was expressed in the nucleus, cytoplasm and membrane of the astrocytoma cells. After transfection, the small interfering RNA (siRNA) targeted to nNav1.5 significantly reduced the expression levels of SCN5A/nNav1.5 mRNA and protein by 57.2% (P<0.05) and 66.6% (P<0.05), respectively. The MTT, wound healing, Matrigel invasion and flow cytometric assays confirmed that following siRNA downregulation of the expression of the SCN5A/nNav1.5 gene, the in vitro proliferation and in vitro invasiveness of the U251 cells were significantly reduced (P<0.05 for both comparisons), and the apoptosis rate was significantly increased (P<0.05). These results revealed that nNav1.5 expression in human brain astrocytoma was upregulated, and its expression was positively correlated with the degree of malignancy. Additionally, reduced nNav1.5 expression significantly suppressed the proliferation and invasiveness of astrocytoma cells, indicating a new target in the molecular diagnosis and therapy of astrocytoma.

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.

Ion channel gene expression in lung adenocarcinoma: potential role in prognosis and diagnosis

Ion channels are known to regulate cancer processes at all stages. The roles of ion channels in cancer pathology are extremely diverse. We systematically analyzed the expression patterns of ion channel genes in lung adenocarcinoma. First, we compared the expression of ion channel genes between normal and tumor tissues in patients with lung adenocarcinoma. Thirty-seven ion channel genes were identified as being differentially expressed between the two groups. Next, we investigated the prognostic power of ion channel genes in lung adenocarcinoma. We assigned a risk score to each lung adenocarcinoma patient based on the expression of the differentially expressed ion channel genes. We demonstrated that the risk score effectively predicted overall survival and recurrence-free survival in lung adenocarcinoma. We also found that the risk scores for ever-smokers were higher than those for never-smokers. Multivariate analysis indicated that the risk score was a significant prognostic factor for survival, which is independent of patient age, gender, stage, smoking history, Myc level, and EGFR/KRAS/ALK gene mutation status. Finally, we investigated the difference in ion channel gene expression between the two major subtypes of non-small cell lung cancer: adenocarcinoma and squamous-cell carcinoma. Thirty ion channel genes were identified as being differentially expressed between the two groups. We suggest that ion channel gene expression can be used to improve the subtype classification in non-small cell lung cancer at the molecular level. The findings in this study have been validated in several independent lung cancer cohorts.

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.

NaV1.5 Na⁺ channels allosterically regulate the NHE-1 exchanger and promote the activity of breast cancer cell invadopodia

The degradation of the extracellular matrix by cancer cells represents an essential step in metastatic progression and this is performed by cancer cell structures called invadopodia. NaV1.5 (also known as SCN5A) Na(+) channels are overexpressed in breast cancer tumours and are associated with metastatic occurrence. It has been previously shown that NaV1.5 activity enhances breast cancer cell invasiveness through perimembrane acidification and subsequent degradation of the extracellular matrix by cysteine cathepsins. Here, we show that NaV1.5 colocalises with Na(+)/H(+) exchanger type 1 (NHE-1) and caveolin-1 at the sites of matrix remodelling in invadopodia of MDA-MB-231 breast cancer cells. NHE-1, NaV1.5 and caveolin-1 co-immunoprecipitated, which indicates a close association between these proteins. We found that the expression of NaV1.5 was responsible for the allosteric modulation of NHE-1, rendering it more active at the intracellular pH range of 6.4-7; thus, it potentially extrudes more protons into the extracellular space. Furthermore, NaV1.5 expression increased Src kinase activity and the phosphorylation (Y421) of the actin-nucleation-promoting factor cortactin, modified F-actin polymerisation and promoted the acquisition of an invasive morphology in these cells. Taken together, our study suggests that NaV1.5 is a central regulator of invadopodia formation and activity in breast cancer cells.

Gender-specific profiling in SCN1A polymorphisms and time-to-recurrence in patients with stage II/III colorectal cancer treated with adjuvant 5-fluoruracil chemotherapy

This study was designed to analyze the gender-related association between SCN1A polymorphisms (voltage-gated sodium channels; α-subunit) and time-to-recurrence (TTR) in patients with colorectal cancer (CRC) treated with 5-fluoruracil (5-FU)-based adjuvant chemotherapy. We enrolled from a prospective database patients with stage II and III CRC treated with adjuvant 5-FU-based chemotherapy. Genotypes for SCN1A rs3812718 and rs229877 were determined by direct DNA sequencing. One hundred twenty-seven males and 107 females were included in the study. In the univariate and multivariate analysis, the shortest TTR was associated with female patients carrying the rs3812718-TT genotype (hazard ratio (HR): 2.26 (95% confidence interval (CI): 0.89, 5.70), P=0.039) but with male patients carrying the rs3812718-CC genotype (HR: 0.49 (95% CI: 0.18, 1.38), P=0.048). For rs229877 the CT genotype was associated with a trend for shorter TTR in both gender populations. The study validated gender-dependent association between genomic SCN1A rs3812718 polymorphism and TTR in CRC patients treated with adjuvant 5-FU-based chemotherapy. This study confirms that voltage-gated Na+ channels may be a potential therapeutic target and a useful predictive biomarker before 5-FU infusion.

Transmembrane voltage potential is an essential cellular parameter for the detection and control of tumor development in a Xenopus model

Understanding mechanisms that orchestrate cell behavior into appropriately patterned tissues and organs within the organism is an essential element of preventing, detecting and treating cancer. Bioelectric signals (resting transmembrane voltage potential gradients in all cells) underlie an important and broadly conserved set of control mechanisms that regulate pattern formation. We tested the role of transmembrane potential in tumorigenesis mediated by canonical oncogenes in Xenopus laevis. Depolarized membrane potential (V_mem) was a characteristic of induced tumor-like structures (ITLSs) generated by overexpression of Gli1, Kras^G12D, Xrel3 or p53^Trp248. This bioelectric signature was also present in precursor ITLS sites. V_mem is a bioelectric marker that reveals ITLSs before they become histologically and morphologically apparent. Moreover, voltage was functionally important: overexpression of hyperpolarizing ion transporters caused a return to normal V_mem and significantly reduced ITLS formation in vivo. To characterize the molecular mechanism by which V_mem change regulates ITLS phenotypes, we performed a suppression screen. V_mem hyperpolarization was transduced into downstream events via V_mem-regulated activity of SLC5A8, a sodium-butyrate exchanger previously implicated in human cancer. These data indicate that butyrate, a histone deacetylase (HDAC) inhibitor, might be responsible for transcriptional events that mediate suppression of ITLSs by hyperpolarization. V_mem is a convenient cellular parameter by which tumors induced by human oncogenes can be detected in vivo and represents a new diagnostic modality. Moreover, control of resting membrane potential is functionally involved in the process by which oncogene-bearing cells depart from normal morphogenesis programs to form tumors. Modulation of V_mem levels is a novel and promising strategy for tumor normalization.

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.

Functional expression of the voltage-gated sodium channel, Nav1.7, underlies epidermal growth factor-mediated invasion in human [R1.S1] non-small cell lung cancer cells

Various ion channels are expressed in human cancers where they are intimately involved in proliferation, angiogenesis, invasion and metastasis. Expression of functional voltage-gated sodium channels (Nav) is implicated in the metastatic potential of breast, prostate, lung and colon cancer cells. However, the cellular mechanisms that regulate Nav expression in cancer remain largely unknown. Growth factors are attractive candidates; they not only play crucial roles in cancer progression but are also key regulators of ion channel expression and activity in non-cancerous cells. Here, we examine the role of epidermal growth factor receptor (EGFR) signalling and Nav in non-small cell lung carcinoma (NSCLC) cell lines. We show unequivocally, that functional expression of Nav1.7 promotes invasion in H460 NSCLC cells. Inhibition of Nav1.7 activity (tetrodotoxin), or, expression (small interfering RNA), reduces H460 cell invasion by up to 50%. Crucially, non-invasive wild type A549 cells lack functional Nav whereas exogenous over-expression of Nav1.7 is sufficient to promote TTX-sensitive invasion of these cells. EGF/EGFR signalling enhances proliferation, migration and invasion of H460 cells but we find that EGFR-mediated up-regulation of Nav1.7 specifically, is necessary for invasive behaviour in these cells. Examination of Nav1.7 expression at the mRNA, protein and functional levels further reveals that EGF/EGFR signalling via the ERK1/2 pathway controls transcriptional regulation of channel expression to promote cellular invasion. Immunohistochemistry of patient biopsies confirms the clinical relevance of Nav1.7 expression in NSCLC. Thus, Nav1.7 has significant potential as a novel target for therapeutic intervention and/or as a diagnostic/prognostic marker in NSCLC.

Antimetastatic potential of amide-linked local anesthetics: inhibition of lung adenocarcinoma cell migration and inflammatory Src signaling independent of sodium channel blockade

BACKGROUND

Retrospective analysis of patients undergoing cancer surgery suggests the use of regional anesthesia may reduce cancer recurrence and improve survival. Amide-linked local anesthetics have antiinflammatory properties, although the mechanism of action in this regard is unclear. As inflammatory processes involving Src tyrosine protein kinase and intercellular adhesion molecule-1 are important in tumor growth and metastasis, we hypothesized that amide-linked local anesthetics may inhibit inflammatory Src-signaling involved in migration of adenocarcinoma cells.

METHODS

NCI-H838 lung cancer cells were incubated with tumor necrosis factor-α in absence/presence of ropivacaine, lidocaine, or chloroprocaine (1 nM-100 μM). Cell migration and total cell lysate Src-activation and intercellular adhesion molecule-1 phosphorylation were assessed. The role of voltage-gated sodium-channels in the mechanism of local anesthetic effects was also evaluated.

RESULTS

Ropivacaine treatment (100 μM) of H838 cells for 20 min decreased basal Src activity by 62% (P=0.003), and both ropivacaine and lidocaine coadministered with tumor necrosis factor-α statistically significantly decreased Src-activation and intercellular adhesion molecule-1 phosphorylation, whereas chloroprocaine had no such effect. Migration of these cells at 4 h was inhibited by 26% (P=0.005) in presence of 1 μM ropivacaine and 21% by 1 μM lidocaine (P=0.004). These effects of ropivacaine and lidocaine were independent of voltage-gated sodium-channel inhibition.

CONCLUSIONS

This study indicates that amide-, but not ester-linked, local anesthetics may provide beneficial antimetastatic effects. The observed inhibition of NCI-H838 cell migration by lidocaine and ropivacaine was associated with the inhibition of tumor necrosis factor-α-induced Src-activation and intercellular adhesion molecule-1 phosphorylation, providing the first evidence of a molecular mechanism that appears to be independent of their known role as sodium-channel blockers.

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.

Expression of Voltage-Gated Sodium Channel Nav1.8 in Human Prostate Cancer is Associated with High Histological Grade

Voltage-gated sodium (Na_v) channels are required for impulse conductance in excitable tissues. Na_vs have been linked to human cancers, including prostate. The expression and distribution of Na_v isoforms (Na_v1.1-Na_v1.9) in human prostate cancer are not well established. Here, we evaluated the expression of these isoforms and investigated the expression of Na_v1.8 in human prostate cancer tissues. Na_v1.8 was highly expressed in all examined cells. Expression of Na_v1.1, Na_v1.2, and Na_v1.9 were high in DU-145, PC-3 and PC-3M cells compared to LNCaP (hormone-dependent), C4-2, C4-2B, and CWR22Rv-1 cells. Na_v1.5 and Na_v1.6 were expressed in all cells examined. Na_v1.7 expression was absent in PC-3M and CWR22Rv-1, but expressed in the other cells examined. Immunohistochemistry revealed intensive Na_v1.8 staining correlated with more advanced pathologic stage of disease. Increased intensity of nuclear Na_v1.8 correlated with increased Gleason grade. Our results revealed that Na_v1.8 is universally expressed in human prostate cancer cells. Na_v1.8 expression statistically correlated with pathologic stage (P=0.04) and Gleason score (P=0.01) of human prostate tissue specimens. The aberrant nuclear localization of Na_v1.8 with advanced prostate cancer tissues warrant further investigation into use of Na_v1.8 as a potential biomarker to differentiate between early and advanced disease.

Na Channel β Subunits: Overachievers of the Ion Channel Family

Voltage-gated Na⁺ channels (VGSCs) in mammals contain a pore-forming α subunit and one or more β subunits. There are five mammalian β subunits in total: β1, β1B, β2, β3, and β4, encoded by four genes: SCN1B–SCN4B. With the exception of the SCN1B splice variant, β1B, the β subunits are type I topology transmembrane proteins. In contrast, β1B lacks a transmembrane domain and is a secreted protein. A growing body of work shows that VGSC β subunits are multifunctional. While they do not form the ion channel pore, β subunits alter gating, voltage-dependence, and kinetics of VGSCα subunits and thus regulate cellular excitability in vivo. In addition to their roles in channel modulation, β subunits are members of the immunoglobulin superfamily of cell adhesion molecules and regulate cell adhesion and migration. β subunits are also substrates for sequential proteolytic cleavage by secretases. An example of the multifunctional nature of β subunits is β1, encoded by SCN1B, that plays a critical role in neuronal migration and pathfinding during brain development, and whose function is dependent on Na⁺ current and γ-secretase activity. Functional deletion of SCN1B results in Dravet Syndrome, a severe and intractable pediatric epileptic encephalopathy. β subunits are emerging as key players in a wide variety of physiopathologies, including epilepsy, cardiac arrhythmia, multiple sclerosis, Huntington’s disease, neuropsychiatric disorders, neuropathic and inflammatory pain, and cancer. β subunits mediate multiple signaling pathways on different timescales, regulating electrical excitability, adhesion, migration, pathfinding, and transcription. Importantly, some β subunit functions may operate independently of α subunits. Thus, β subunits perform critical roles during development and disease. As such, they may prove useful in disease diagnosis and therapy.

Ion channels and transporters [corrected] in cancer. 2. Ion channels and the control of cancer cell migration

A hallmark of high-grade cancers is the ability of malignant cells to invade unaffected tissue and spread disease. This is particularly apparent in gliomas, the most common and lethal type of primary brain cancer affecting adults. Migrating cells encounter restricted spaces and appear able to adjust their shape to accommodate to narrow extracellular spaces. A growing body of work suggests that cell migration/invasion is facilitated by ion channels and transporters. The emerging concept is that K(+) and Cl(-) function as osmotically active ions, which cross the plasma membrane in concert with obligated water thereby adjusting a cell's shape and volume. In glioma cells Na(+)-K(+)-Cl(-) cotransporters (NKCC1) actively accumulate K(+) and Cl(-), establishing a gradient for KCl efflux. Ca(2+)-activated K(+) channels and voltage-gated Cl(-) channels are largely responsible for effluxing KCl promoting hydrodynamic volume changes. In other cancers, different K(+) or even Na(+) channels may function in concert with a variety of Cl(-) channels to support similar volume changes. Channels involved in migration are frequently regulated by Ca(2+) signaling, most likely coupling extracellular stimuli to cell migration. Importantly, the inhibition of ion channels and transporters appears to be clinically relevant for the treatment of cancer. Recent preclinical data indicates that inhibition of NKCC1 with an FDA-approved drug decreases neoplastic migration. Additionally, ongoing clinical trials demonstrate that an inhibitor of chloride channels may be a therapy for the treatment of gliomas. Data reviewed here strongly indicate that ion channels are a promising target for the development of novel therapeutics to combat cancer.

P2X(7) receptor activation enhances SK3 channels- and cystein cathepsin-dependent cancer cells invasiveness

ATP-gated P2X(7) receptors (P2X(7)R) are unusual plasma membrane ion channels that have been extensively studied in immune cells. More recently, P2X(7)R have been described as potential cancer cell biomarkers. However, mechanistic links between P2X(7)R and cancer cell processes are unknown. Here, we show, in the highly aggressive human breast cancer cell line MDA-MB-435s, that P2X(7) receptor is highly expressed and fully functional. Its activation is responsible for the extension of neurite-like cellular prolongations, of the increase in cell migration by 35% and in cell invasion through extracellular matrix by 150%. The change in cancer cell morphology and the increased migration appeared to be due to the activation of Ca(2+)-activated SK3 potassium channels. The enhanced invasion through the extracellular matrix was related to the increase of mature forms of cysteine cathepsins in the extracellular medium, which was independent of SK3 channel activity and not associated with cell death. Pharmacological targeting of P2X(7)R in vivo was crucial for cell invasiveness in a zebrafish model of metastases. Our results demonstrate a novel mechanistic link between P2X(7)R functionality in cancer cells and invasiveness, a key parameter in tumour growth and in the development of metastases. They also suggest a potential therapeutic role for the newly developed P2X(7)R antagonists.

Voltage-gated Na+ channel SCN5A is a key regulator of a gene transcriptional network that controls colon cancer invasion

Voltage-gated Na(+) channels (VGSC) have been implicated in the metastatic potential of human breast, prostate, and lung cancer cells. Specifically, the SCN5A gene encoding the VGSC isotype Na(v)1.5 has been defined as a key driver of human cancer cell invasion. In this study, we examined the expression and function of VGSCs in a panel of colon cancer cell lines by electrophysiologic recordings. Na(+) channel activity and invasive potential were inhibited pharmacologically by tetrodotoxin or genetically by small interfering RNAs (siRNA) specifically targeting SCN5A. Clinical relevance was established by immunohistochemistry of patient biopsies, with strong Na(v)1.5 protein staining found in colon cancer specimens but little to no staining in matched-paired normal colon tissues. We explored the mechanism of VGSC-mediated invasive potential on the basis of reported links between VGSC activity and gene expression in excitable cells. Probabilistic modeling of loss-of-function screens and microarray data established an unequivocal role of VGSC SCN5A as a high level regulator of a colon cancer invasion network, involving genes that encompass Wnt signaling, cell migration, ectoderm development, response to biotic stimulus, steroid metabolic process, and cell cycle control. siRNA-mediated knockdown of predicted downstream network components caused a loss of invasive behavior, demonstrating network connectivity and its function in driving colon cancer invasion.

Structure and function of splice variants of the cardiac voltage-gated sodium channel Na(v)1.5

Voltage-gated sodium channels mediate the rapid upstroke of the action potential in excitable tissues. The tetrodotoxin (TTX) resistant isoform Na(v)1.5, encoded by the SCN5A gene, is the predominant isoform in the heart. This channel plays a key role for excitability of atrial and ventricular cardiomyocytes and for rapid impulse propagation through the specific conduction system. During recent years, strong evidence has been accumulated in support of the expression of several Na(v)1.5 splice variants in the heart, and in various other tissues and cell lines including brain, dorsal root ganglia, breast cancer cells and neuronal stem cell lines. This review summarizes our knowledge on the structure and putative function of nine Na(v)1.5 splice variants detected so far. Attention will be paid to the distinct biophysical properties of the four functional splice variants, to the pronounced tissue- and species-specific expression, and to the developmental regulation of Na(v)1.5 splicing. The implications of alternative splicing for SCN5A channelopathies, and for a better understanding of genotype-phenotype correlations, are discussed.

Ion channels and the hallmarks of cancer

Plasma membrane (PM) ion channels contribute to virtually all basic cellular processes and are also involved in the malignant phenotype of cancer cells. Here, we review the role of ion channels in cancer in the context of their involvement in the defined hallmarks of cancer: 1) self-sufficiency in growth signals, 2) insensitivity to antigrowth signals, 3) evasion of programmed cell death (apoptosis), 4) limitless replicative potential, 5) sustained angiogenesis and 6) tissue invasion and metastasis. Recent studies have indicated that the contribution of specific ion channels to these hallmarks varies for different types of cancer. Therefore, to determine the importance of ion channels as targets for cancer diagnosis and treatment their expression, function and regulation must be assessed for each cancer.

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.

Voltage-gated Sodium Channel Activity Promotes Cysteine Cathepsin-dependent Invasiveness and Colony Growth of Human Cancer Cells

Voltage-gated sodium channels (Na(V)) are functionally expressed in highly metastatic cancer cells derived from nonexcitable epithelial tissues (breast, prostate, lung, and cervix). MDA-MB-231 breast cancer cells express functional sodium channel complexes, consisting of Na(V)1.5 and associated auxiliary beta-subunits, that are responsible for a sustained inward sodium current at the membrane potential. Although these channels do not regulate cellular multiplication or migration, their inhibition by the specific blocker tetrodotoxin impairs both the extracellular gelatinolytic activity (monitored with DQ-gelatin) and cell invasiveness leading to the attenuation of colony growth and cell spreading in three-dimensional Matrigel-composed matrices. MDA-MB-231 cells express functional cysteine cathepsins, which we found play a predominant role ( approximately 65%) in cancer invasiveness. Matrigel invasion is significantly decreased in the presence of specific inhibitors of cathepsins B and S (CA-074 and Z-FL-COCHO, respectively), and co-application of tetrodotoxin does not further reduce cell invasion. This suggests that cathepsins B and S are involved in invasiveness and that their proteolytic activity partly depends on Na(V) function. Inhibiting Na(V) has no consequence for cathepsins at the transcription, translation, and secretion levels. However, Na(V) activity leads to an intracellular alkalinization and a perimembrane acidification favorable for the extracellular activity of these acidic proteases. We propose that Na(v) enhance the invasiveness of cancer cells by favoring the pH-dependent activity of cysteine cathepsins. This general mechanism could lead to the identification of new targets allowing the therapeutic prevention of metastases.

Non-anti-mitotic concentrations of taxol reduce breast cancer cell invasiveness

Taxol is widely used in breast cancer chemotherapy. Its effects are primarily attributed to its anti-mitotic activity. Microtubule perturbators also exert antimetastatic activities which cannot be explained solely by the inhibition of proliferation. Voltage-dependent sodium channels (Na(V)) are abnormally expressed in the highly metastatic breast cancer cell line MDA-MB-231 and not in MDA-MB-468 cell line. Inhibiting Na(V) activity with tetrodotoxin is responsible for an approximately 0.4-fold reduction of MDA-MB-231 cell invasiveness. In this study, we focused on the effect of a single, 2-h application of 10 nM taxol on the two cell lines MDA-MB-231 and MDA-MB-468. At this concentration, taxol had no effect on proliferation after 7 days and on migration in any cell line. However it led to a 40% reduction of transwell invasion of MDA-MB-231 cells. There was no additive effect when taxol and tetrodotoxin were simultaneously applied. Na(V) activity, as assessed by patch-clamp, indicates that it was changed by taxol pre-treatment. We conclude that taxol can exert anti-tumoral activities, in cells expressing Na(V), at low doses that have no effect on cell proliferation. This effect might be due to a modulation of signalling pathways involving sodium channels.

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.

Potassium Channels Keep Mobile Cells on the Go

Cell motility is a prerequisite for the creation of new life, and it is required for maintaining the integrity of an organism. Under pathological conditions, “too much” motility may cause premature death. Studies over the past few years have revealed that ion channels are essential for cell motility. This review highlights the importance of K+ channels in regulating cell motility.

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.