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Background: Human Apolipoprotein (APOE) has three isoforms, ε2, ε3, and ε4 among which ε4 (APOE4) confers the highest risk for late‐onset Alzheimer's disease (AD). APOE4 is also the most prone to aggregate among APOE isoforms. Current evidence strongly suggests that APOE aggregation leads to neuronal dysfunction and eventually to AD. APOE4 increases amyloid plaques and neurofibrillary tangles and decreases synapses and neuronal survival. These phenotypes are alleviated by decreasing APOE4 aggregation. Method: We analyzed APOE aggregation using fluorescence lifetime imaging microscopy (FLIM) in combination with Forster resonance energy transfer (FRET). APOE isoforms tagged with E2GFP or mRuby2 were within 10 nm or less, i.e. in an aggregate the fluorescence lifetime of the donor was shortened and signal intensity was diminished which was monitored using FLIM‐FRET and analyzed using the Phasor approach. APOE aggregation was also confirmed by using small‐angle X‐ray scattering (SAXS) of the Sarkosyl extracts of the cells. Secreted APOE‐Tdtomato was isolated from BHK cell media and analyzed by ion mobility assay. Human neurons were incubated with APOE‐Tdtomato isolated from the media. Results: APOE4 aggregated more than APOE3 in living BHK cells as shown via FLIM‐FRET microscopy. APOE4 aggregated less when its lipidation was induced by ABCA1 expression in line with data published by us and others. These results were confirmed via SAXS. APOE was secreted in HDL particles from BHK cells both in the presence or absence of ABCA1 while ABCA1 increased secretion for both APOE3 and APOE4. Finally, tagged‐APOE secreted to the media was endocytosed by human neurons. Conclusions: FLIM‐FRET is a feasible method to analyze APOE aggregation in living cells. Isolated APOE can be used to study APOE endocytosis in human neurons. [ABSTRACT FROM AUTHOR]

Background and Purpose: Voltage-gated sodium (NaV ) channels are expressed de novo in carcinomas where their activity promotes invasiveness. Breast and colon cancer cells express the neonatal splice variant of NaV 1.5 (nNaV 1.5), which has several amino acid substitutions in the domain I voltage-sensor compared with its adult counterpart (aNaV 1.5). This study aimed to determine whether nNaV 1.5 channels could be distinguished pharmacologically from aNaV 1.5 channels.Experimental Approach: Cells expressing either nNaV 1.5 or aNaV 1.5 channels were exposed to low MW inhibitors, an antibody or natural toxins, and changes in electrophysiological parameters were measured. Stable expression in EBNA cells and transient expression in Xenopus laevis oocytes were used. Currents were recorded by whole-cell patch clamp and two-electrode voltage-clamp, respectively.Key Results: Several clinically used blockers of NaV channels (lidocaine, procaine, phenytoin, mexiletine, ranolazine, and riluzole) could not distinguish between nNaV 1.5 or aNaV 1.5 channels. However, two tarantula toxins (HaTx and ProTx-II) and a polyclonal antibody (NESOpAb) preferentially inhibited currents elicited by either nNaV 1.5 or aNaV 1.5 channels by binding to the spliced region of the channel. Furthermore, the amino acid residue at position 211 (aspartate in aNaV 1.5/lysine in nNaV 1.5), that is, the charge reversal in the spliced region of the channel, played a key role in the selectivity, especially in antibody binding.Conclusion and Implications: We conclude that the cancer-related nNaV 1.5 channel can be distinguished pharmacologically from its nearest neighbour, aNaV 1.5 channels. Thus, it may be possible to design low MW compounds as antimetastatic drugs for non-toxic therapy of nNaV 1.5-expressing carcinomas. [ABSTRACT FROM AUTHOR]

Anti‐invasive effects of riluzole and ranolazine, a neuro‐protectant and an anti‐anginal drug, respectively, on Mat‐LyLu rat prostate cancer (PCa) cells were tested in vitro (a) at non‐toxic doses and (b) under both normoxic and hypoxic conditions, the latter common to growing tumours. Tetrodotoxin (TTX) was used as a positive control. Hypoxia had no effect on cell viability but reduced growth at 48 hours. Riluzole (5 μmol/L) or ranolazine (20 μmol/L) had no effect on cell viability or growth under normoxia or hypoxia over 24 hours. Matrigel invasion was not affected by hypoxia but inhibited by TTX, ranolazine and riluzole under a range of conditions. The expression of Nav1.7 mRNA, the prevailing, pro‐invasive voltage‐gated sodium channel α‐subunit (VGSCα), was up‐regulated by hypoxia. Riluzole had no effect on Nav1.7 mRNA expression in normoxia but significantly reduced it in hypoxia. VGSCα protein expression in plasma membrane was reduced in hypoxia; riluzole increased it but only under hypoxia. It was concluded (a) that riluzole and ranolazine have anti‐invasive effects on rat PCa cells and (b) that Nav1.7 mRNA and protein expression can be modulated by riluzole under hypoxia. Overall, therefore, riluzole and ranolazine may ultimately be "repurposed" as anti‐metastatic drugs against PCa. [ABSTRACT FROM AUTHOR]

The MDA‐MB‐231 cell line was used as a model of triple negative breast cancer to investigate the interaction of β‐adrenergic receptor (β‐AR) and voltage‐gated sodium channel (VGSC). There was significant (86%) overlap in their expression. Short‐term (acute) application of the β‐AR antagonist propranolol (25 μM) led to reduction of peak current and quickening of current inactivation (the latter occurred only in 5% fetal bovine serum). Long‐term (48 hr) incubation with propranolol (25 μM) resulted in several changes in VGSC characteristics: shifts in (a) current‐voltage relationship and (b) steady‐state inactivation, both to more negative potentials and (c) the slowing of recovery from inactivation. We then investigated the effects of propranolol and ranolazine, a blocker of VGSC activity, alone and in combination, on lateral motility and Matrigel invasion. These assays were carried out under hypoxic conditions more representative of tumor progression. Propranolol (2.5 and 25 μM) and ranolazine (5 μM), and their combination inhibited lateral motility. Also, propranolol (25 μM) and ranolazine (5 μM), and their combination inhibited invasion. However, no synergy was observed in the pharmacological combinations for both assays. Propranolol also significantly decreased total neonatal Nav1.5 protein expression, the predominant VGSC subtype expressed in these cells. We conclude (a) that β‐AR and VGSC are functionally coupled in MDA‐MB‐231 cells; (b) that propranolol has direct blocking action on the VGSC; (c) that the action of propranolol is modulated by serum; and (d) that the antimetastatic cellular effects of propranolol and ranolazine are not additive. [ABSTRACT FROM AUTHOR]

Functional expression of voltage‐gated Na+ channels (VGSCs) occurs in human carcinomas and promotes invasiveness in vitro and metastasis in vivo. Both neonatal and adult forms of Nav1.5 (nNav1.5 and aNav1.5, respectively) have been reported to be expressed at messenger RNA (mRNA) level in colorectal cancer (CRCa) cells. Here, three CRCa cell lines (HT29, HCT116 and SW620) were studied and found to express nNav1.5 mRNA and protein. In SW620 cells, adopted as a model, effects of gene silencing (by several small interfering RNAs [siRNAs]) selectively targeting nNav1.5 or aNav1.5 were determined on (a) channel activity and (b) invasiveness in vitro. Silencing nNav1.5 made the currents more "adult‐like" and suppressed invasion by up to 73%. Importantly, subsequent application of the highly specific, general VGSC blocker, tetrodotoxin (TTX), had no further effect. Conversely, silencing aNav1.5 made the currents more "neonatal‐like" but suppressed invasion by only 17% and TTX still induced a significant effect. Hypoxia increased invasiveness and this was also blocked completely by siRNA targeting nNav1.5. The effect of hypoxia was suppressed dose dependently by ranolazine, but its effect was lost in cells pretreated with nNav1.5‐siRNA. We conclude that (a) functional nNav1.5 expression is common to human CRCa cells, (b) hypoxia increases the invasiveness of SW620 cells, (c) the VGSC‐dependent invasiveness is driven predominantly by nNav1.5 under both normoxic and hypoxic conditions and (d) the hypoxia‐induced increase in invasiveness is likely to be mediated by the persistent current component of nNav1.5. The 'neonatal' splice variant of Nav1.5 is shown to drive the invasiveness of human colorectal cancer cells under normoxic and hypoxic conditions. Ranolazine, an inhibitor of the persistent current of the channel, inhibits the hypoxia‐induced increase in invasiveness. [ABSTRACT FROM AUTHOR]

External (but not internal) application of β-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-γ-S, by itself, also increased the VGSC current whilst the G-protein inhibitor GDP-β-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. J. Cell. Physiol. 224: 527–539, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The prostate is a highly specialized mammalian organ that produces and releases large amounts of citrate. However, the citrate release mechanism is not known. Here, we present the results of molecular cloning of a citrate transporter from human normal prostate epithelial PNT2-C2 cells shown previously to express such a mechanism. By using rapid amplification of cDNA ends PCR, we determined that the prostatic carrier is an isoform of the mitochondrial transporter SLC25A1 with a different first exon. We confirmed the functionality of the clone by expressing it in human embryonic kidney cells and performing radiotracer experiments and whole-cell patch-clamp recordings. By using short interfering RNAs targeting different parts of the sequence, we confirmed that the cloned protein is the main prostatic transporter responsible for citrate release. We also produced a specific antibody and localized the cloned transporter protein to the plasma membrane of the cells. By using the same antibody, we have shown that the cloned transporter is expressed in non-malignant human tissues. [ABSTRACT FROM AUTHOR]

In developmentally regulated D1:S3 splicing of Nav1.5, there are 31 nucleotide differences between the 5′-exon (‘neonatal’) and the 3′-exon (‘adult’) forms, resulting in 7 amino acid differences in D1:S3-S3/S4 linker. In particular, splicing replaces a conserved negative aspartate residue in the ‘adult’ with a positive lysine. Here, ‘neonatal’ and ‘adult’ Nav1.5 α-subunit splice variants were stably transfected into EBNA-293 cells and their electrophysiological properties investigated by whole-cell patch-clamp recording. Compared with the ‘adult’ isoform, the ‘neonatal’ channel exhibited (1) a depolarized threshold of activation and voltage at which the current peaked; (2) much slower kinetics of activation and inactivation; (3) 50% greater transient charge (Na+) influx; (4) a stronger voltage dependence of time to peak; and (5) a slower recovery from inactivation. Tetrodotoxin sensitivity and VGSCβ1-4 mRNA expression levels did not change. The significance of the charge-reversing aspartate to lysine substitution was investigated by mutating the lysine in the ‘neonatal’ channel back to aspartate. In this ‘neonatal K211D’ mutant, the electrophysiological parameters studied strongly shifted back towards the ‘adult’, that is the lysine residue was primarily responsible for the electrophysiological effects of Nav1.5 D1:S3 splicing. Taken together, these data suggest that the charge reversal in ‘neonatal’ Nav1.5 would (1) modify the channel kinetics and (2) prolong the resultant current, allowing greater intracellular Na+ influx. Developmental and pathophysiological consequences of such differences are discussed. J. Cell. Physiol. 216: 716–726, 2008, © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Whole-cell patch-clamp recordings showed that a sub-population (10%) of Jurkat cells, a model of human T-cells, expressed a functional voltage-gated sodium channel, which was tetrodotoxin (TTX)-resistant. Expression of voltage-gated sodium channel protein was confirmed by western blots. Semi-quantitative PCR analysis revealed that mRNAs for the α-subunits of multiple voltage-gated sodium channel subtypes were present but indicated that Nav1.5 was the predominant subtype, consistent with the TTX-resistant nature of the recorded currents. Importantly, 10 μM TTX reduced the number of Jurkat cells invading a Matrigel basement membrane by 93.0 ± 5.5%. Since similar sodium channels have also been detected in normal human T-lymphocytes, it is concluded that the activity of voltage-gated sodium channels could represent a novel mechanism potentiating the invasive capacity of these cells. [Copyright &y& Elsevier]