K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity

Potassium channel Kv1.3 is highly expressed by microglia in human Alzheimer's disease

Recent genetic studies suggest a central role for innate immunity in Alzheimer's disease (AD) pathogenesis, wherein microglia orchestrate neuroinflammation. Kv1.3, a voltage-gated potassium channel of therapeutic relevance in autoimmunity, is upregulated by activated microglia and mediates amyloid-mediated microglial priming and reactive oxygen species production in vitro. We hypothesized that Kv1.3 channel expression is increased in human AD brain tissue. In a blinded postmortem immunohistochemical semi-quantitative analysis performed on ten AD patients and ten non-disease controls, we observed a significantly higher Kv1.3 staining intensity (p = 0.03) and Kv1.3-positive cell density (p = 0.03) in the frontal cortex of AD brains, compared to controls. This paralleled an increased number of Iba1-positive microglia in AD brains. Kv1.3-positive cells had microglial morphology and were associated with amyloid-β plaques. In immunofluorescence studies, Kv1.3 channels co-localized primarily with Iba1 but not with astrocyte marker GFAP, confirming that elevated Kv1.3 expression is limited to microglia. Higher Kv1.3 expression in AD brains was also confirmed by western blot analysis. Our findings support that Kv1.3 channels are biologically relevant and microglia-specific targets in human AD.

Microbes taming mast cells: Implications for allergic inflammation and beyond

There is increasing awareness of a relationship between our microbiota and the pathogenesis of allergy and other inflammatory diseases. In investigating the mechanisms underlying microbiota modulation of allergy the focus has been on the induction phase; alterations in the phenotype and function of antigen presenting cells, induction of regulatory T cells and shifts in Th1/Th2 balance. However there is evidence that microbes can influence the effector phase of disease, specifically that certain potentially beneficial bacteria can attenuate mast cell activation and degranulation. Furthermore, it appears that different non-pathogenic bacteria can utilize distinct mechanisms to stabilize mast cells, acting locally though direct interaction with the mast cell at mucosal sites or attenuating systemic mast cell dependent responses, likely through indirect signaling mechanisms. The position of mast cells on the frontline of defense against pathogens also suggests they may play an important role in fostering the host-microbiota relationship. Mast cells are also conduits of neuro-immuo-endocrine communication, suggesting the ability of microbes to modulate cell responses may have implications for host physiology beyond immunology. Further investigation of mast cell regulation by non-pathogenic or symbiotic bacteria will likely lead to a greater understanding of host microbiota interaction and the role of the microbiome in health and disease.

Monozygotic twins discordant for common variable immunodeficiency reveal impaired DNA demethylation during naïve-to-memory B-cell transition

Common variable immunodeficiency (CVID), the most frequent primary immunodeficiency characterized by loss of B-cell function, depends partly on genetic defects, and epigenetic changes are thought to contribute to its aetiology. Here we perform a high-throughput DNA methylation analysis of this disorder using a pair of CVID-discordant MZ twins and show predominant gain of DNA methylation in CVID B cells with respect to those from the healthy sibling in critical B lymphocyte genes, such as PIK3CD, BCL2L1, RPS6KB2, TCF3 and KCNN4. Individual analysis confirms hypermethylation of these genes. Analysis in naive, unswitched and switched memory B cells in a CVID patient cohort shows impaired ability to demethylate and upregulate these genes in transitioning from naive to memory cells in CVID. Our results not only indicate a role for epigenetic alterations in CVID but also identify relevant DNA methylation changes in B cells that could explain the clinical manifestations of CVID individuals.

Tweeters, Woofers and Horns: The Complex Orchestration of Calcium Currents in T Lymphocytes

Elevation of intracellular calcium ion (Ca²⁺) levels is a vital event that regulates T lymphocyte homeostasis, activation, proliferation, differentiation, and apoptosis. The mechanisms that regulate intracellular Ca²⁺ signaling in lymphocytes involve tightly controlled concinnity of multiple ion channels, membrane receptors, and signaling molecules. T cell receptor (TCR) engagement results in depletion of endoplasmic reticulum (ER) Ca²⁺ stores and subsequent sustained influx of extracellular Ca²⁺ through Ca²⁺ release-activated Ca²⁺ (CRAC) channels in the plasma membrane. This process termed store-operated Ca²⁺ entry (SOCE) involves the ER Ca²⁺ sensing molecule, STIM1, and a pore-forming plasma membrane protein, ORAI1. However, several other important Ca²⁺ channels that are instrumental in T cell function also exist. In this review, we discuss the role of additional Ca²⁺ channel families expressed on the plasma membrane of T cells that likely contribute to Ca²⁺ influx following TCR engagement, which include the TRP channels, the NMDA receptors, the P2X receptors, and the IP₃ receptors, with a focus on the voltage-dependent Ca²⁺ (Ca_V) channels.

Toxins Targeting the Kv1.3 Channel: Potential Immunomodulators for Autoimmune Diseases

Autoimmune diseases are usually accompanied by tissue injury caused by autoantigen-specific T-cells. K_V1.3 channels participate in modulating calcium signaling to induce T-cell proliferation, immune activation and cytokine production. Effector memory T (T_EM)-cells, which play major roles in many autoimmune diseases, are controlled by blocking K_V1.3 channels on the membrane. Toxins derived from animal venoms have been found to selectively target a variety of ion channels, including K_V1.3. By blocking the K_V1.3 channel, these toxins are able to suppress the activation and proliferation of T_EM cells and may improve T_EM cell-mediated autoimmune diseases, such as multiple sclerosis and type I diabetes mellitus.

N-Terminally extended analogues of the K⁺ channel toxin from Stichodactyla helianthus as potent and selective blockers of the voltage-gated potassium channel Kv1.3

The voltage-gated potassium channel Kv1.3 is an important target for the treatment of autoimmune diseases and asthma. Blockade of Kv1.3 by the sea anemone peptide K⁺-channel toxin from Stichodactyla helianthus (ShK) inhibits the proliferation of effector memory T lymphocytes and ameliorates autoimmune diseases in animal models. However, the lack of selectivity of ShK for Kv1.3 over the Kv1.1 subtype has driven a search for Kv1.3-selective analogues. In the present study, we describe N-terminally extended analogues of ShK that contain a negatively-charged Glu, designed to mimic the phosphonate adduct in earlier Kv1.3-selective analogues, and consist entirely of common protein amino acids. Molecular dynamics simulations indicated that a Trp residue at position [-3] of the tetrapeptide extension could form stable interactions with Pro377 of Kv1.3 and best discriminates between Kv1.3 and Kv1.1. This led to the development of ShK with an N-terminal Glu-Trp-Ser-Ser extension ([EWSS]ShK), which inhibits Kv1.3 with an IC₅₀ of 34 pm and is 158-fold selective for Kv1.3 over Kv1.1. In addition, [EWSS]ShK is more than 2900-fold more selective for Kv1.3 over Kv1.2 and KCa3.1 channels. As a highly Kv1.3-selective analogue of ShK based entirely on protein amino acids, which can be produced by recombinant expression, this peptide is a valuable addition to the complement of therapeutic candidates for the treatment of autoimmune diseases.

K⁺-channel inhibition reduces portal perfusion pressure in fibrotic rats and fibrosis associated characteristics of hepatic stellate cells

BACKGROUND & AIMS

In liver fibrosis, activated hepatic stellate cells (HSC) secrete excess extracellular matrix, thus, represent key targets for antifibrotic treatment strategies. Intermediate-conductance Ca(2) (+) -activated K(+) -channels (KCa3.1) are expressed in non-excitable tissues affecting proliferation, migration and vascular resistance rendering KCa3.1 potential targets in liver fibrosis. So far, no information about KCa3.1 expression and their role in HSC exists. Aim was to quantify the KCa3.1 expression in HSC depending on HSC activation and investigation of antifibrotic properties of the specific KCa3.1 inhibitor TRAM-34 in vitro and in vivo.

METHODS

KCa3.1 expression and functionality were studied in TGF-β1-activated HSC by quantitative real time PCR, western-blot and patch-clamp analysis respectively. Effects of TRAM-34 on HSC proliferation, cell cycle and fibrosis-related gene expression were assessed by [(3) H]-thymidine incorporation, FACS-analysis and RT-PCR respectively. In vivo, vascular resistance and KCa3.1 gene and protein expression were determined in bile duct ligated rats by in situ liver perfusion, Taqman PCR and immunohistochemistry respectively.

RESULTS

Fibrotic tissues and TGF-β1-activated HSC exhibited higher KCa3.1-expressions than normal tissue and untreated cells. KCa3.1 inhibition with TRAM-34 reduced HSC proliferation by induction of cell cycle arrest and reduced TGF-β1-induced gene expression of collagen I, alpha-smooth muscle actin and TGF-β1 itself. Furthermore, TRAM-34 blocked TGF-β1-induced activation of TGF-β signalling in HSC. In vivo, TRAM-34 reduced the thromboxane agonist-induced portal perfusion pressure.

CONCLUSION

Inhibition of KCa3.1 with TRAM-34 downregulates fibrosis-associated gene expression in vitro, and reduces portal perfusion pressure in vivo. Thus, KCa3.1 may represent novel targets for the treatment of liver fibrosis.

Inhibition of antigen receptor-dependent Ca(2+) signals and NF-AT activation by P2X7 receptors in human B lymphocytes

One of the first intracellular signals after antigen binding by the antigen receptor of B lymphocytes is the increased intracellular Ca(2+) concentration ([Ca(2+)]i), which is followed by several intracellular signaling events like the nuclear translocation of the transcription factor NF-AT controlling the fate of B lymphocytes after their activation. Extracellular ATP, which is released from cells under several pathological conditions, is considered a danger-associated signal serving as an immunomodulator. We investigated the interaction of antigen receptor (BCR) and P2X7 receptor (P2X7R) activation on [Ca(2+)]i signaling and on nuclear translocation of the transcription factor NF-AT in human B lymphocytes. Although the P2X7R is an ATP-gated Ca(2+)-permeable ion channel, P2X7R activation inhibits the BCR-mediated [Ca(2+)]i responses. This effect is mimicked by cell membrane depolarization induced by an increase in the extracellular K(+) concentration or by application of the Na(+) ionophore gramicidin, but is abolished by stabilization of the membrane potential using the K(+) ionophore valinomycin, by extracellular Mg(2+), which is known to inhibit P2X7R-dependent effects, or by replacing Na(+) by the less P2X7R-permeable Tris(+) ion. Furthermore, P2X7R activation by ATP inhibits the BCR-dependent translocation of the transcription factor NF-ATc1 to the nucleus. We therefore conclude that extracellular ATP via the P2X7R mediates inhibitory effects on B cell activation. This may be of relevance for understanding of the activation of the BCR under pathological conditions and for the development of therapeutic strategies targeting human B lymphocytes or P2X7 receptors.

Ion channels in innate and adaptive immunity

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.

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

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

Loureirin B, an essential component of Sanguis Draxonis, inhibits Kv1.3 channel and suppresses cytokine release from Jurkat T cells

Sanguis draxonis (SD), also known as “Dragon’s Blood”, is a traditional herb medicine that has been used to treat a variety of complications with unknown mechanisms. Recent studies show that SD displays immunosuppressive activities and improves symptoms of type I diabetes in animal models. However, the mechanisms underlying SD’s immunosuppressive actions are not completely understood. The voltage-gated Kv1.3 channel plays a critical role in the pathogenesis of autoimmune diseases by regulating the functions of both T cells and B cells. Here we investigated the effect of SD and one of its active components loureirin B (LrB) on Kv1.3. Both SD and LrB inhibited Kv1.3-mediated currents, produced a membrane depolarization, and reduced Ca²⁺ influx in Jurkat T cells. In addition, application of LrB inhibited phytohemagglutinin (PHA)-induced IL-2 release from activated Jurkat T cells. Furthermore, point mutations in the selective filter region significantly reduced the inhibitory effect of LrB on Kv1.3. The results of these experiments provide evidence that LrB is a channel blocker of Kv1.3 by interacting with amino acid residues in its selective filter region. Direct inhibition of Kv1.3 in T cells by SD and LrB might be the cellular and molecular basis of SD-mediated immunosuppression.

NMDA-receptor antagonists block B-cell function but foster IL-10 production in BCR/CD40-activated B cells

BACKGROUND

B cells are important effectors and regulators of adaptive and innate immune responses, inflammation and autoimmunity, for instance in anti-NMDA-receptor (NMDAR) encephalitis. Thus, pharmacological modulation of B-cell function could be an effective regimen in therapeutic strategies. Since the non-competitive NMDAR antagonist memantine is clinically applied to treat advanced Alzheimer`s disease and ketamine is supposed to improve the course of resistant depression, it is important to know how these drugs affect B-cell function.

RESULTS

Non-competitive NMDAR antagonists impaired B-cell receptor (BCR)- and lipopolysaccharide (LPS)-induced B-cell proliferation, reduced B-cell migration towards the chemokines SDF-1α and CCL21 and downregulated IgM and IgG secretion. Mechanistically, these effects were mediated through a blockade of Kv1.3 and KCa3.1 potassium channels and resulted in an attenuated Ca(2+)-flux and activation of Erk1/2, Akt and NFATc1. Interestingly, NMDAR antagonist treatment increased the frequency of IL-10 producing B cells after BCR/CD40 stimulation.

CONCLUSIONS

Non-competitive NMDAR antagonists attenuate BCR and Toll-like receptor 4 (TLR4) B-cell signaling and effector function and can foster IL-10 production. Consequently, NMDAR antagonists may be useful to target B cells in autoimmune diseases or pathological systemic inflammation. The drugs' additional side effects on B cells should be considered in treatments of neuronal disorders with NMDAR antagonists.

Aromatic-aromatic interactions between residues in KCa3.1 pore helix and S5 transmembrane segment control the channel gating process

Interactions between aromatic amino acid residues in the pore helix and S5 transmembrane domain control gating of the Ca²⁺-activated potassium channel KCa3.1.

The Ca²⁺-activated potassium channel KCa3.1 is emerging as a therapeutic target for a large variety of health disorders. One distinguishing feature of KCa3.1 is that the channel open probability at saturating Ca²⁺ concentrations (Pomax) is low, typically 0.1–0.2 for KCa3.1 wild type. This observation argues for the binding of Ca²⁺ to the calmodulin (CaM)–KCa3.1 complex, promoting the formation of a preopen closed-state configuration leading to channel opening. We have previously shown that the KCa3.1 active gate is most likely located at the level of the selectivity filter. As Ca²⁺-dependent gating of KCa3.1 originates from the binding of Ca²⁺ to CaM in the C terminus, the hypothesis of a gate located at the level of the selectivity filter requires that the conformational change initiated in the C terminus be transmitted to the S5 and S6 transmembrane helices, with a resulting effect on the channel pore helix directly connected to the selectivity filter. A study was thus undertaken to determine to what extent the interactions between the channel pore helix with the S5 and S6 transmembrane segments contribute to KCa3.1 gating. Molecular dynamics simulations first revealed that the largest contact area between the pore helix and the S5 plus S6 transmembrane helices involves residue F248 at the C-terminal end of the pore helix. Unitary current recordings next confirmed that modulating aromatic–aromatic interactions between F248 and W216 of the S5 transmembrane helical segment and/or perturbing the interactions between F248 and residues in S6 surrounding the glycine hinge G274 cause important changes in Pomax. This work thus provides the first evidence for a key contribution of the pore helix in setting Pomax by stabilizing the channel closed configuration through aromatic–aromatic interactions involving F248 of the pore helix. We propose that the interface pore helix/S5 constitutes a promising site for designing KCa3.1 potentiators.

HIF-1α-mediated upregulation of TASK-2 K⁺ channels augments Ca²⁺ signaling in mouse B cells under hypoxia

The general consensus is that immune cells are exposed to physiological hypoxia in vivo (PhyO2, 2-5% P(O2)). However, functional studies of B cells in hypoxic conditions are sparse. Recently, we reported the expression in mouse B cells of TASK-2, a member of pH-sensitive two-pore domain K(+) channels with background activity. In this study, we investigated the response of K(+) channels to sustained PhyO2 (sustained hypoxia [SH], 3% P(O2) for 24 h) in WEHI-231 mouse B cells. SH induced voltage-independent background K(+) conductance (SH-K(bg)) and hyperpolarized the membrane potential. The pH sensitivity and the single-channel conductance of SH-K(bg) were consistent with those of TASK-2. Immunoblotting assay results showed that SH significantly increased plasma membrane expressions of TASK-2. Conversely, SH failed to induce any current following small interfering (si)TASK-2 transfection. Similar hypoxic upregulation of TASK-2 was also observed in splenic primary B cells. Mechanistically, upregulation of TASK-2 by SH was prevented by si hypoxia-inducible factor-1α (HIF-1α) transfection or by YC-1, a pharmacological HIF-1α inhibitor. In addition, TASK-2 current was increased in WEHI-231 cells overexpressed with O2-resistant HIF-1α. Importantly, [Ca(2+)]c increment in response to BCR stimulation was significantly higher in SH-exposed B cells, which was abolished by high K(+)-induced depolarization or by siTASK-2 transfection. The data demonstrate that TASK-2 is upregulated under hypoxia via HIF-1α-dependent manner in B cells. This is functionally important in maintaining the negative membrane potential and providing electrical driving force to control Ca(2+) influx.

Low-dose photon irradiation alters cell differentiation via activation of hIK channels

To understand the impact of ionizing irradiation from diagnostics and radiotherapy on cells, we examined K(+) channel activity before and immediately after exposing cells to X-rays. Already, low dose in the cGy range caused in adenocarcinoma A549 cells within minutes a hyperpolarization following activation of the human intermediate-conductance Ca(2+)-activated K(+) channel (hIK). The response was specific for cells, which functionally expressed hIK channels and in which hIK activity was low before irradiation. HEK293 cells, which do not respond to X-ray irradiation, accordingly develop a sensitivity to this stress after heterologous expression of hIK channels. The data suggest that hIK activation involves a Ca(2+)-mediated signaling cascade because channel activation is suppressed by a strong cytosolic Ca(2+) buffer. The finding that an elevation of H2O2 causes an increase in the concentration of cytosolic Ca(2+) suggests that radicals, which emerge early in response to irradiation, trigger this Ca(2+) signaling cascade. Inhibition of hIK channels by specific blockers clotrimazole and TRAM-34 slowed cell proliferation and migration in "wound" scratch assays; ionizing irradiation, in turn, stimulated the latter process presumably via its activation of the hIK channels. These data stress an indirect radiosensitivity of hIK channels with an impact on cell differentiation.

Kv1.3 channel-blocking immunomodulatory peptides from parasitic worms: implications for autoimmune diseases

The voltage-gated potassium (Kv) 1.3 channel is widely regarded as a therapeutic target for immunomodulation in autoimmune diseases. ShK-186, a selective inhibitor of Kv1.3 channels, ameliorates autoimmune diseases in rodent models, and human phase 1 trials of this agent in healthy volunteers have been completed. In this study, we identified and characterized a large family of Stichodactyla helianthus toxin (ShK)-related peptides in parasitic worms. Based on phylogenetic analysis, 2 worm peptides were selected for study: AcK1, a 51-residue peptide expressed in the anterior secretory glands of the dog-infecting hookworm Ancylostoma caninum and the human-infecting hookworm Ancylostoma ceylanicum, and BmK1, the C-terminal domain of a metalloprotease from the filarial worm Brugia malayi. These peptides in solution adopt helical structures closely resembling that of ShK. At doses in the nanomolar-micromolar range, they block native Kv1.3 in human T cells and cloned Kv1.3 stably expressed in L929 mouse fibroblasts. They preferentially suppress the proliferation of rat CCR7(-) effector memory T cells without affecting naive and central memory subsets and inhibit the delayed-type hypersensitivity (DTH) response caused by skin-homing effector memory T cells in rats. Further, they suppress IFNγ production by human T lymphocytes. ShK-related peptides in parasitic worms may contribute to the potential beneficial effects of probiotic parasitic worm therapy in human autoimmune diseases.

Blocking KV1.3 channels inhibits Th2 lymphocyte function and treats a rat model of asthma

Allergic asthma is a chronic inflammatory disease of the airways. Of the different lower airway-infiltrating immune cells that participate in asthma, T lymphocytes that produce Th2 cytokines play important roles in pathogenesis. These T cells are mainly fully differentiated CCR7(-) effector memory T (TEM) cells. Targeting TEM cells without affecting CCR7(+) naïve and central memory (TCM) cells has the potential of treating TEM-mediated diseases, such as asthma, without inducing generalized immunosuppression. The voltage-gated KV1.3 potassium channel is a target for preferential inhibition of TEM cells. Here, we investigated the effects of ShK-186, a selective KV1.3 channel blocker, for the treatment of asthma. A significant proportion of T lymphocytes in the lower airways of subjects with asthma expressed high levels of KV1.3 channels. ShK-186 inhibited the allergen-induced activation of peripheral blood T cells from those subjects. Immunization of F344 rats against ovalbumin followed by intranasal challenges with ovalbumin induced airway hyper-reactivity, which was reduced by the administration of ShK-186. ShK-186 also reduced total immune infiltrates in the bronchoalveolar lavage and number of infiltrating lymphocytes, eosinophils, and neutrophils assessed by differential counts. Rats with the ovalbumin-induced model of asthma had elevated levels of the Th2 cytokines IL-4, IL-5, and IL-13 measured by ELISA in their bronchoalveolar lavage fluids. ShK-186 administration reduced levels of IL-4 and IL-5 and induced an increase in the production of IL-10. Finally, ShK-186 inhibited the proliferation of lung-infiltrating ovalbumin-specific T cells. Our results suggest that KV1.3 channels represent effective targets for the treatment of allergic asthma.

Ion channels and anti-cancer immunity

The outcome of a malignant disease depends on the efficacy of the immune system to destroy cancer cells. Key steps in this process, for example the generation of a proper Ca(2+) signal induced by recognition of a specific antigen, are regulated by various ion channel including voltage-gated Kv1.3 and Ca(2+)-activated KCa3.1 K(+) channels, and the interplay between Orai and STIM to produce the Ca(2+)-release-activated Ca(2+) (CRAC) current required for T-cell proliferation and function. Understanding the immune cell subset-specific expression of ion channels along with their particular function in a given cell type, and the role of cancer tissue-dependent factors in the regulation of operation of these ion channels are emerging questions to be addressed in the fight against cancer disease. Answering these questions might lead to a better understanding of the immunosuppression phenomenon in cancer tissue and the development of drugs aimed at skewing the distribution of immune cell types towards killing of the tumour cells.

Development of a QPatch automated electrophysiology assay for identifying KCa3.1 inhibitors and activators

The intermediate-conductance Ca(2+)-activated K(+) channel KCa3.1 (also known as KCNN4, IK1, or the Gárdos channel) plays an important role in the activation of T and B cells, mast cells, macrophages, and microglia by regulating membrane potential, cellular volume, and calcium signaling. KCa3.1 is further involved in the proliferation of dedifferentiated vascular smooth muscle cells and fibroblast and endothelium-derived hyperpolarization responses in the vascular endothelium. Accordingly, KCa3.1 inhibitors are therapeutically interesting as immunosuppressants and for the treatment of a wide range of fibroproliferative disorders, whereas KCa3.1 activators constitute a potential new class of endothelial function preserving antihypertensives. Here, we report the development of QPatch assays for both KCa3.1 inhibitors and activators. During assay optimization, the Ca(2+) sensitivity of KCa3.1 was studied using varying intracellular Ca(2+) concentrations. A free Ca(2+) concentration of 1 μM was chosen to optimally test inhibitors. To identify activators, which generally act as positive gating modulators, a lower Ca(2+) concentration (∼200 nM) was used. The QPatch results were benchmarked against manual patch-clamp electrophysiology by determining the potency of several commonly used KCa3.1 inhibitors (TRAM-34, NS6180, ChTX) and activators (EBIO, riluzole, SKA-31). Collectively, our results demonstrate that the QPatch provides a comparable but much faster approach to study compound interactions with KCa3.1 channels in a robust and reliable assay.

Blocking KCa3.1 channels increases tumor cell killing by a subpopulation of human natural killer lymphocytes

Natural killer (NK) cells are large granular lymphocytes that participate in both innate and adaptive immune responses against tumors and pathogens. They are also involved in other conditions, including organ rejection, graft-versus-host disease, recurrent spontaneous abortions, and autoimmune diseases such as multiple sclerosis. We demonstrate that human NK cells express the potassium channels Kv1.3 and KCa3.1. Expression of these channels does not vary with expression levels of maturation markers but varies between adherent and non-adherent NK cell subpopulations. Upon activation by mitogens or tumor cells, adherent NK (A-NK) cells preferentially up-regulate KCa3.1 and non-adherent (NA-NK) cells preferentially up-regulate Kv1.3. Consistent with this different phenotype, A-NK and NA-NK do not display the same sensitivity to the selective KCa3.1 blockers TRAM-34 and NS6180 and to the selective Kv1.3 blockers ShK-186 and PAP-1 in functional assays. Kv1.3 block inhibits the proliferation and degranulation of NA-NK cells with minimal effects on A-NK cells. In contrast, blocking KCa3.1 increases the degranulation and cytotoxicity of A-NK cells, but not of NA-NK cells. TRAM-34, however, does not affect their ability to form conjugates with target tumor cells, to migrate, or to express chemokine receptors. TRAM-34 and NS6180 also increase the proliferation of both A-NK and NA-NK cells. This results in a TRAM-34-induced increased ability of A-NK cells to reduce in vivo tumor growth. Taken together, our results suggest that targeting KCa3.1 on NK cells with selective blockers may be beneficial in cancer immunotherapy.

The voltage-dependent K(+) channels Kv1.3 and Kv1.5 in human cancer

Voltage-dependent K⁺ channels (Kv) are involved in a number of physiological processes, including immunomodulation, cell volume regulation, apoptosis as well as differentiation. Some Kv channels participate in the proliferation and migration of normal and tumor cells, contributing to metastasis. Altered expression of Kv1.3 and Kv1.5 channels has been found in several types of tumors and cancer cells. In general, while the expression of Kv1.3 apparently exhibits no clear pattern, Kv1.5 is induced in many of the analyzed metastatic tissues. Interestingly, evidence indicates that Kv1.5 channel shows inversed correlation with malignancy in some gliomas and non-Hodgkin's lymphomas. However, Kv1.3 and Kv1.5 are similarly remodeled in some cancers. For instance, expression of Kv1.3 and Kv1.5 correlates with a certain grade of tumorigenicity in muscle sarcomas. Differential remodeling of Kv1.3 and Kv1.5 expression in human cancers may indicate their role in tumor growth and their importance as potential tumor markers. However, despite of this increasing body of information, which considers Kv1.3 and Kv1.5 as emerging tumoral markers, further research must be performed to reach any conclusion. In this review, we summarize what it has been lately documented about Kv1.3 and Kv1.5 channels in human cancer.

Targeting ion channels for the treatment of autoimmune neuroinflammation

Pharmacological targeting of ion channels has long been recognized as an attractive strategy for the treatment of various diseases. Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system with a prominent neurodegenerative component. A multitude of different cell types are involved in the complex pathophysiology of this disorder, including cells of the immune system (e.g. T and B lymphocytes and microglia), the neurovascular unit (e.g. endothelial cells and astrocytes) and the central nervous system (e.g. astrocytes and neurons). The pleiotropic expression and function of ion channels gives rise to the attractive opportunity of targeting different players and pathophysiological aspects of MS by the modulation of ion channel function in a cell-type and context-specific manner. We discuss the emerging knowledge about ion channels in the context of autoimmune neuroinflammation. While some pharmacological targets are at the edge of clinical translation, others have only recently been discovered and are still under investigation. Special focus is given to those candidates that could be attractive novel targets for future therapeutic approaches in neuroimmune autoinflammation.

Novel Kv1.3 blockers for immunosuppression: WO2012155199

A recent patent application from Bionomics/Merck Serono describes novel compounds as blockers of the voltage-gated Kv1.3 ion channel. The blockade of this channel shows great promise as a new therapeutic target for the treatment of autoimmune disorders such as multiple sclerosis, psoriasis, diabetes and rheumatoid arthritis. The generic claim of this patent refers to a new chemotype of Kv1.3 blockers based on an amide core with potent IC50's which are potentially within the nanomolar range. This article briefly reviews the chemistry and biology found in the patent and compares it with previous discoveries in the field.

Endothelial small-conductance and intermediate-conductance KCa channels: an update on their pharmacology and usefulness as cardiovascular targets

Most cardiovascular researchers are familiar with intermediate-conductance KCa3.1 and small-conductance KCa2.3 channels because of their contribution to endothelium-derived hyperpolarization. However, to immunologists and neuroscientists, these channels are primarily known for their role in lymphocyte activation and neuronal excitability. KCa3.1 is involved in the proliferation and migration of T cells, B cells, mast cells, macrophages, fibroblasts, and dedifferentiated vascular smooth muscle cells and is, therefore, being pursued as a potential target for use in asthma, immunosuppression, and fibroproliferative disorders. In contrast, the 3 KCa2 channels (KCa2.1, KCa2.2, and KCa2.3) contribute to the neuronal medium afterhyperpolarization and, depending on the type of neuron, are involved in determining firing rates and frequencies or in regulating bursting. KCa2 activators are accordingly being studied as potential therapeutics for ataxia and epilepsy, whereas KCa2 channel inhibitors like apamin have long been known to improve learning and memory in rodents. Given this background, we review the recent discoveries of novel KCa3.1 and KCa2.3 modulators and critically assess the potential of KCa activators for the treatment of diabetes and cardiovascular diseases by improving endothelium-derived hyperpolarizations.

Contribution of the KCa3.1 channel-calmodulin interactions to the regulation of the KCa3.1 gating process

The Ca(2+)-activated potassium channel of intermediate conductance, KCa3.1, is now emerging as a therapeutic target for a large variety of health disorders. The Ca(2+) sensitivity of KCa3.1 is conferred by the Ca(2+)-binding protein calmodulin (CaM), with the CaM C-lobe constitutively bound to an intracellular domain of the channel C terminus. It was proposed on the basis of the crystal structure obtained for the C-terminal region of the rat KCa2.2 channel (rSK2) with CaM that the binding of Ca(2+) to the CaM N-lobe results in CaM interlocking the C-terminal regions of two adjacent KCa3.1 subunits, leading to the formation of a dimeric structure. A study was thus undertaken to identify residues of the CaM N-lobe-KCa3.1 complex that either contribute to the channel activation process or control the channel open probability at saturating Ca(2+) (Pomax). A structural homology model of the KCa3.1-CaM complex was first generated using as template the crystal structure of the C-terminal region of the rat KCa2.2 channel with CaM. This model was confirmed by cross-bridging residues R362 of KCa3.1 and K75 of CaM. Patch-clamp experiments were next performed, demonstrating that the solvation energy of the residue at position 367 in KCa3.1 is a key determinant to the channel Pomax and deactivation time toff. Mutations of residues M368 and Q364 predicted to form anchoring points for CaM binding to KCa3.1 had little impact on either toff or Pomax. Finally, our results show that channel activation depends on electrostatic interactions involving the charged residues R362 and E363, added to a nonpolar energy contribution coming from M368. We conclude that electrostatic interactions involving residues R362 and E363 and hydrophobic effects at M368 play a prominent role in KCa3.1 activation, whereas hydrophobic interactions at S367 are determinant to the stability of the CaM-KCa3.1 complex throughout gating.

Weft, warp, and weave: the intricate tapestry of calcium channels regulating T lymphocyte function

Calcium (Ca(2+)) is a universal second messenger important for T lymphocyte homeostasis, activation, proliferation, differentiation, and apoptosis. The events surrounding Ca(2+) mobilization in lymphocytes are tightly regulated and involve the coordination of diverse ion channels, membrane receptors, and signaling molecules. A mechanism termed store-operated Ca(2+) entry (SOCE), causes depletion of endoplasmic reticulum (ER) Ca(2+) stores following T cell receptor (TCR) engagement and triggers a sustained influx of extracellular Ca(2+) through Ca(2+) release-activated Ca(2+) (CRAC) channels in the plasma membrane. The ER Ca(2+) sensing molecule, stromal interaction molecule 1 (STIM1), and a pore-forming plasma membrane protein, ORAI1, have been identified as important mediators of SOCE. Here, we review the role of several additional families of Ca(2+) channels expressed on the plasma membrane of T cells that likely contribute to Ca(2+) influx following TCR engagement, particularly highlighting an important role for voltage-dependent Ca(2+) channels (CaV) in T lymphocyte biology.

NS6180, a new K(Ca) 3.1 channel inhibitor prevents T-cell activation and inflammation in a rat model of inflammatory bowel disease

BACKGROUND AND PURPOSE

The K(Ca) 3.1 channel is a potential target for therapy of immune disease. We identified a compound from a new chemical class of K(Ca) 3.1 inhibitors and assessed in vitro and in vivo inhibition of immune responses.

EXPERIMENTAL APPROACH

We characterized the benzothiazinone NS6180 (4-[[3-(trifluoromethyl)phenyl]methyl]-2H-1,4-benzothiazin-3(4H)-one) with respect to potency and molecular site of action on K(Ca) 3.1 channels, selectivity towards other targets, effects on T-cell activation as well as pharmacokinetics and inflammation control in colitis induced by 2,4-dinitrobenzene sulfonic acid, a rat model of inflammatory bowel disease (IBD).

KEY RESULTS

NS6180 inhibited cloned human K(Ca) 3.1 channels (IC(50) = 9 nM) via T250 and V275, the same amino acid residues conferring sensitivity to triarylmethanes such as like TRAM-34. NS6180 inhibited endogenously expressed K(Ca) 3.1 channels in human, mouse and rat erythrocytes, with similar potencies (15-20 nM). NS6180 suppressed rat and mouse splenocyte proliferation at submicrolar concentrations and potently inhibited IL-2 and IFN-γ production, while exerting smaller effects on IL-4 and TNF-α and no effect on IL-17 production. Antibody staining showed K(Ca) 3.1 channels in healthy colon and strong up-regulation in association with infiltrating immune cells after induction of colitis. Despite poor plasma exposure, NS6180 (3 and 10 mg·kg(-1) b.i.d.) dampened colon inflammation and improved body weight gain as effectively as the standard IBD drug sulfasalazine (300 mg·kg(-1) q.d.).

CONCLUSIONS AND IMPLICATIONS

NS6180 represents a novel class of K(Ca) 3.1 channel inhibitors which inhibited experimental colitis, suggesting K(Ca) 3.1 channels as targets for pharmacological control of intestinal inflammation.

The intermediate conductance calcium-activated potassium channel KCa3.1 regulates vascular smooth muscle cell proliferation via controlling calcium-dependent signaling

The intermediate conductance calcium-activated potassium channel KCa3.1 contributes to a variety of cell activation processes in pathologies such as inflammation, carcinogenesis, and vascular remodeling. We examined the electrophysiological and transcriptional mechanisms by which KCa3.1 regulates vascular smooth muscle cell (VSMC) proliferation. Platelet-derived growth factor-BB (PDGF)-induced proliferation of human coronary artery VSMCs was attenuated by lowering intracellular Ca(2+) concentration ([Ca(2+)]i) and was enhanced by elevating [Ca(2+)]i. KCa3.1 blockade or knockdown inhibited proliferation by suppressing the rise in [Ca(2+)]i and attenuating the expression of phosphorylated cAMP-response element-binding protein (CREB), c-Fos, and neuron-derived orphan receptor-1 (NOR-1). This antiproliferative effect was abolished by elevating [Ca(2+)]i. KCa3.1 overexpression induced VSMC proliferation, and potentiated PDGF-induced proliferation, by inducing CREB phosphorylation, c-Fos, and NOR-1. Pharmacological stimulation of KCa3.1 unexpectedly suppressed proliferation by abolishing the expression and activity of KCa3.1 and PDGF β-receptors and inhibiting the rise in [Ca(2+)]i. The stimulation also attenuated the levels of phosphorylated CREB, c-Fos, and cyclin expression. After KCa3.1 blockade, the characteristic round shape of VSMCs expressing high l-caldesmon and low calponin-1 (dedifferentiation state) was maintained, whereas KCa3.1 stimulation induced a spindle-shaped cellular appearance, with low l-caldesmon and high calponin-1. In conclusion, KCa3.1 plays an important role in VSMC proliferation via controlling Ca(2+)-dependent signaling pathways, and its modulation may therefore constitute a new therapeutic target for cell proliferative diseases such as atherosclerosis.

Proton channels in non-phagocytic cells of the immune system

Proton channels are expressed in all cells of the immune system to various degrees. While their function in phagocytic cells, immune cells that engulf bacteria and cell debris for clearance, has been the object of extensive research, the function of proton channels in non-phagocytic cells has remained more elusive until recently. Further studies have been helped by the discovery of the gene coding for the mammalian proton channel, HVCN1, which has prompted a new wave of research in this area. Recent findings show how proton channels regulate cell function in non-phagocytic cells of the immune system such as basophils and lymphocytes.

Targeting potassium channels Kv1.3 and KC a 3.1: routes to selective immunomodulators in autoimmune disorder treatment?

The Kv1.3 and KC a 3.1 potassium channels are promising targets for the treatment of autoimmune disorders. Many Kv1.3 and KC a 3.1 blockers have a more favorable adverse event profiles than existing immunosuppressants, suggesting the selectivity of Kv1.3 and KC a 3.1 blockade. The Kv1.3 and KC a 3.1 blockers exert differential effects in different autoimmune diseases. The Kv1.3 inhibitors or gene deletion have been shown to have benefits in multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis, and rapidly progressive glomerulonephritis. The KC a 3.1 blockers have demonstrated efficacy in human primary biliary cirrhosis and showed protective effects in animal models of severe colitis, allergic encephalomyelitis, inflammatory bowel disease, and multiple sclerosis. The KC a 3.1 blockers are not considered candidates for treatment of multiple sclerosis. The selective immunosuppressive effects of the Kv1.3 and KC a 3.1 blockers are due to the differences in their distribution on autoimmune-related immune cells and tissues and β1 integrin (very late activating antigen)-Kv1.3 channel cross-talk.

The potassium channel KCa3.1 as new therapeutic target for the prevention of obliterative airway disease

BACKGROUND

The calcium-activated potassium channel KCa3.1 is critically involved in T-cell activation as well as in the proliferation of smooth muscle cells and fibroblasts. We sought to investigate whether KCa3.1 contributes to the pathogenesis of obliterative airway disease (OAD) and whether knockout or pharmacologic blockade would prevent the development of OAD.

METHODS

Tracheas from CBA donors were heterotopically transplanted into the omentum of C57Bl/6J wild-type or KCa3.1 mice. C57Bl/6J recipients were either left untreated or received the KCa3.1 blocker TRAM-34 (120 mg/kg/day). Histopathology and immunologic assays were performed on postoperative day 5 or 28.

RESULTS

Subepithelial T-cell and macrophage infiltration on postoperative day 5, as seen in untreated allografts, was significantly reduced in the KCa3.1 and TRAM-34 groups. Also, systemic Th1 activation was significantly and Th2 mildly reduced by KCa3.1 knockout or blockade. After 28 days, luminal obliteration of tracheal allografts was reduced from 89%±21% in untreated recipients to 53%±26% (P=0.010) and 59%±33% (P=0.032) in KCa3.1 and TRAM-34-treated animals, respectively. The airway epithelium was mostly preserved in syngeneic grafts, mostly destroyed in the KCa3.1 and TRAM-34 groups, and absent in untreated allografts. Allografts triggered an antibody response in untreated recipients, which was significantly reduced in KCa3.1 animals. KCa3.1 was detected in T cells, airway epithelial cells, and myofibroblasts. TRAM-34 dose-dependently suppressed proliferation of wild-type C57B/6J splenocytes but did not show any effect on KCa3.1 splenocytes.

CONCLUSIONS

Our findings suggest that KCa3.1 channels are involved in the pathogenesis of OAD and that KCa3.1 blockade holds promise to reduce OAD development.

Angiotensin II upregulates K(Ca)3.1 channels and stimulates cell proliferation in rat cardiac fibroblasts

The proliferation of cardiac fibroblasts is implicated in the pathogenesis of myocardial remodeling and fibrosis. Intermediate-conductance calcium-activated K⁺ channels (K(Ca)3.1 channels) have important roles in cell proliferation. However, it is unknown whether angiotensin II (Ang II), a potent profibrotic molecule, would regulate K(Ca)3.1 channels in cardiac fibroblasts and participate in cell proliferation. In the present study, we investigated whether K(Ca)3.1 channels were regulated by Ang II, and how the channel activity mediated cell proliferation in cultured adult rat cardiac fibroblasts using electrophysiology and biochemical approaches. It was found that mRNA, protein, and current density of K(Ca)3.1 channels were greatly enhanced in cultured cardiac fibroblasts treated with 1 μM Ang II, and the effects were countered by the angiotensin type 1 receptor (AT₁R) blocker losartan, the p38-MAPK inhibitor SB203580, the ERK1/2 inhibitor PD98059, and the PI3K/Akt inhibitor LY294002. Ang II stimulated cell proliferation and the effect was antagonized by the K(Ca)3.1 blocker TRAM-34 and siRNA targeting K(Ca)3.1. In addition, Ang II-induced increase of K(Ca)3.1 expression was attenuated by transfection of activator protein-1 (AP-1) decoy oligodeoxynucleotides. These results demonstrate for the first time that Ang II stimulates cell proliferation mediated by upregulating K(Ca)3.1 channels via interacting with the AT₁R and activating AP-1 complex through ERK1/2, p38-MAPK and PI3K/Akt signaling pathways in cultured adult rat cardiac fibroblasts.

A microarray platform-independent classification tool for cell of origin class allows comparative analysis of gene expression in diffuse large B-cell lymphoma

Cell of origin classification of diffuse large B-cell lymphoma (DLBCL) identifies subsets with biological and clinical significance. Despite the established nature of the classification existing studies display variability in classifier implementation, and a comparative analysis across multiple data sets is lacking. Here we describe the validation of a cell of origin classifier for DLBCL, based on balanced voting between 4 machine-learning tools: the DLBCL automatic classifier (DAC). This shows superior survival separation for assigned Activated B-cell (ABC) and Germinal Center B-cell (GCB) DLBCL classes relative to a range of other classifiers. DAC is effective on data derived from multiple microarray platforms and formalin fixed paraffin embedded samples and is parsimonious, using 20 classifier genes. We use DAC to perform a comparative analysis of gene expression in 10 data sets (2030 cases). We generate ranked meta-profiles of genes showing consistent class-association using ≥6 data sets as a cut-off: ABC (414 genes) and GCB (415 genes). The transcription factor ZBTB32 emerges as the most consistent and differentially expressed gene in ABC-DLBCL while other transcription factors such as ARID3A, BATF, and TCF4 are also amongst the 24 genes associated with this class in all datasets. Analysis of enrichment of 12323 gene signatures against meta-profiles and all data sets individually confirms consistent associations with signatures of molecular pathways, chromosomal cytobands, and transcription factor binding sites. We provide DAC as an open access Windows application, and the accompanying meta-analyses as a resource.

Curcumin serves as a human kv1.3 blocker to inhibit effector memory T lymphocyte activities

Curcumin, the principal active component of turmeric, has long been used to treat various diseases in India and China. Recent studies show that curcumin can serve as a therapeutic agent for autoimmune diseases via a variety of mechanisms. Effector memory T cells (T(EM), CCR7⁻ CD45RO⁺ T lymphocyte) have been demonstrated to play a crucial role in the pathogenesis of T cell-mediated autoimmune diseases, such as multiple sclerosis (MS) or rheumatoid arthritis (RA). Kv1.3 channels are predominantly expressed in T(EM) cells and control T(EM) activities. In the present study, we examined the effect of curcumin on human Kv1.3 (hKv1.3) channels stably expressed in HEK-293 cells and its ability to inhibit proliferation and cytokine secretion of T(EM) cells isolated from patients with MS or RA. Curcumin exhibited a direct blockage of hKv1.3 channels in a time-dependent and concentration-dependent manner. Moreover, the activation curve was shifted to a more positive potential, which was consistent with an open-channel blockade. Paralleling hKv1.3 inhibition, curcumin significantly inhibited proliferation and interferon-γ secretion of T(EM) cells. Our findings demonstrate that curcumin is able to inhibit proliferation and proinflammatory cytokine secretion of T(EM) cells probably through inhibition of hKv1.3 channels, which contributes to the potency of curcumin for the treatment of autoimmune diseases. This is probably one of pharmacological mechanisms of curcumin used to treat autoimmune diseases.

Systemic effects of ingested Lactobacillus rhamnosus: inhibition of mast cell membrane potassium (IKCa) current and degranulation

Exposure of the intestine to certain strains lactobacillus can have systemic immune effects that include the attenuation of allergic responses. Despite the central role of mast cells in allergic disease little is known about the effect of lactobacilli on the function of these cells. To address this we assessed changes in rat mast cell activation following oral treatment with a strain of Lactobacillus known to attenuate allergic responses in animal models. Sprague Dawley rats were fed with L. rhamnosus JB-1 (1×10(9)) or vehicle control for 9 days. Mediator release from peritoneal mast cells (RPMC) was determined in response to a range of stimuli. Passive cutaneous anaphylaxis (PCA) was used to assess mast cell responses in vivo. The Ca(2+) activated K(+) channel (KCa3.1) current, identified as critical to mast cell degranulation, was monitored by whole cell patch-clamp. L. rhamnosus JB-1 treatment lead to significant inhibition of mast cell mediator release in response to a range of stimuli including IgE mediated activation. Furthermore, the PCA response was significantly reduced in treated rats. Patch-clamp studies revealed that RPMC from treated animals were much less responsive to the KCa3.1 opener, DCEBIO. These studies demonstrate that Ingestion of L. rhamnosus JB-1 leads to mast cell stabilization in rats and identify KCa3.1 as an immunomodulatory target for certain lactobacilli. Thus the systemic effects of certain candidate probiotics may include mast cell stabilization and such actions could contribute to the beneficial effect of these organisms in allergic and other inflammatory disorders.

Microglial KCa3.1 Channels as a Potential Therapeutic Target for Alzheimer's Disease

There exists an urgent need for new target discovery to treat Alzheimer's disease (AD); however, recent clinical trials based on anti-Aβ and anti-inflammatory strategies have yielded disappointing results. To expedite new drug discovery, we propose reposition targets which have been previously pursued by both industry and academia for indications other than AD. One such target is the calcium-activated potassium channel KCa3.1 (KCNN4), which in the brain is primarily expressed in microglia and is significantly upregulated when microglia are activated. We here review the existing evidence supporting that KCa3.1 inhibition could block microglial neurotoxicity without affecting their neuroprotective phagocytosis activity and without being broadly immunosuppressive. The anti-inflammatory and neuroprotective effects of KCa3.1 blockade would be suitable for treating AD as well as cerebrovascular and traumatic brain injuries, two well-known risk factors contributing to the dementia in AD patients presenting with mixed pathologies. Importantly, the pharmacokinetics and pharmacodynamics of several KCa3.1 blockers are well known, and a KCa3.1 blocker has been proven safe in clinical trials. It is therefore promising to reposition old or new KCa3.1 blockers for AD preclinical and clinical trials.

The antibody targeting the E314 peptide of human Kv1.3 pore region serves as a novel, potent and specific channel blocker

Selective blockade of Kv1.3 channels in effector memory T (T(EM)) cells was validated to ameliorate autoimmune or autoimmune-associated diseases. We generated the antibody directed against one peptide of human Kv1.3 (hKv1.3) extracellular loop as a novel and possible Kv1.3 blocker. One peptide of hKv1.3 extracellular loop E3 containing 14 amino acids (E314) was chosen as an antigenic determinant to generate the E314 antibody. The E314 antibody specifically recognized 63.8KD protein stably expressed in hKv1.3-HEK 293 cell lines, whereas it did not recognize or cross-react to human Kv1.1(hKv1.1), Kv1.2(hKv1.2), Kv1.4(hKv1.4), Kv1.5(hKv1.5), KCa3.1(hKCa3.1), HERG, hKCNQ1/hKCNE1, Nav1.5 and Cav1.2 proteins stably expressed in HEK 293 cell lines or in human atrial or ventricular myocytes by Western blotting analysis and immunostaining detection. By the technique of whole-cell patch clamp, the E314 antibody was shown to have a directly inhibitory effect on hKv1.3 currents expressed in HEK 293 or Jurkat T cells and the inhibition showed a concentration-dependence. However, it exerted no significant difference on hKv1.1, hKv1.2, hKv1.4, hKv1.5, hKCa3.1, HERG, hKCNQ1/hKCNE1, L-type Ca(2+) or voltage-gated Na(+) currents. The present study demonstrates that the antibody targeting the E314 peptide of hKv1.3 pore region could be a novel, potent and specific hKv1.3 blocker without affecting a variety of closely related K(v)1 channels, KCa3.1 channels and functional cardiac ion channels underlying central nervous system (CNS) disorders or drug-acquired arrhythmias, which is required as a safe clinic-promising channel blocker.

Charybdotoxin and margatoxin acting on the human voltage-gated potassium channel hKv1.3 and its H399N mutant: an experimental and computational comparison

The effect of the pore-blocking peptides charybdotoxin and margatoxin, both scorpion toxins, on currents through human voltage-gated hK(v)1.3 wild-type and hK(v)1.3_H399N mutant potassium channels was characterized by the whole-cell patch clamp technique. In the mutant channels, both toxins hardly blocked current through the channels, although they did prevent C-type inactivation by slowing down the current decay during depolarization. Molecular dynamics simulations suggested that the fast current decay in the mutant channel was a consequence of amino acid reorientations behind the selectivity filter and indicated that the rigidity-flexibility in that region played a key role in its interactions with scorpion toxins. A channel with a slightly more flexible selectivity filter region exhibits distinct interactions with scorpion toxins. Our studies suggest that the toxin-channel interactions might partially restore rigidity in the selectivity filter and thereby prevent the structural rearrangements associated with C-type inactivation.

Intermediate-conductance calcium-activated potassium channels participate in neurovascular coupling

BACKGROUND AND PURPOSE

Controlling vascular tone involves K(+) efflux through endothelial cell small- and intermediate-conductance calcium-activated potassium channels (K(Ca)2.3 and K(Ca)3.1, respectively). We investigated the expression of these channels in astrocytes and the possibility that, by a similar mechanism, they might contribute to neurovascular coupling.

EXPERIMENTAL APPROACH

Transgenic mice expressing enhanced green fluorescent protein (eGFP) in astrocytes were used to assess K(Ca)2.3 and K(Ca)3.1 expression by immunohistochemistry and RT-PCR. K(Ca) currents in eGFP-positive astrocytes were determined in situ using whole-cell patch clamp electrophysiology. The contribution of K(Ca)3.1 to neurovascular coupling was investigated in pharmacological experiments using electrical field stimulation (EFS) to evoke parenchymal arteriole dilatation in FVB/NJ mouse brain slices and whisker stimulation to evoke changes in cerebral blood flow in vivo, measured by laser Doppler flowmetry.

KEY RESULTS

K(Ca)3.1 immunoreactivity was restricted to astrocyte processes and endfeet and RT-PCR confirmed astrocytic K(Ca)2.3 and K(Ca)3.1 mRNA expression. With 200 nM [Ca(2+)](i) , the K(Ca)2.1-2.3/K(Ca)3.1 opener NS309 increased whole-cell currents. CyPPA, a K(Ca)2.2/K(Ca)2.3 opener, was without effect. With 1 µM [Ca(2+)](i) , the K(Ca)3.1 inhibitor TRAM-34 reduced currents whereas apamin (K(Ca)2.1-2.3 blocker) had no effect. CyPPA also inhibited currents evoked by NS309 in HEK293 cells expressing K(Ca)3.1. EFS-evoked Fluo-4 fluorescence confirmed astrocyte endfoot recruitment into neurovascular coupling. TRAM-34 inhibited EFS-evoked arteriolar dilatation by 50% whereas charybdotoxin, a blocker of K(Ca)3.1 and the large-conductance K(Ca) channel, K(Ca)1.1, inhibited dilatation by 82%. TRAM-34 reduced the cortical hyperaemic response to whisker stimulation by 40%.

CONCLUSION AND IMPLICATIONS

Astrocytes express functional K(Ca)3.1 channels, and these contribute to neurovascular coupling.

Modafinil inhibits K(Ca)3.1 currents and muscle contraction via a cAMP-dependent mechanism

Modafinil has been used as a psychostimulant for the treatment of narcolepsy. However, its primary mechanism of action remains elusive. Therefore, we examined the effects of modafinil on K(Ca)3.1 channels and vascular smooth muscle contraction. K(Ca)3.1 currents and channel activity were measured using a voltage-clamp technique and inside-out patches in mouse embryonic fibroblast cell line, NIH-3T3 fibroblasts. Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration was measured, and the phosphorylation of K(Ca)3.1 channel protein was examined using western blotting in NIH-3T3 fibroblasts and/or primary cultured mouse aortic smooth muscle cells (SMCs). Muscle contractions were recorded from mouse aorta and rat pulmonary artery by using a myograph developed in-house. Modafinil was found to inhibit K(Ca)3.1 currents in a concentration-dependent manner, and the half-maximal inhibition (IC(50)) of modafinil for the current inhibition was 6.8 ± 0.7 nM. The protein kinase A (PKA) activator forskolin also inhibited K(Ca)3.1 currents. The inhibitory effects of modafinil and forskolin on K(Ca)3.1 currents were blocked by the PKA inhibitors PKI(14-22) or H-89. In addition, modafinil relaxed blood vessels (mouse aorta and rat pulmonary artery) in a concentration-dependent manner. Modafinil increased cAMP concentrations in NIH-3T3 fibroblasts or primary cultured mouse aortic SMCs and phosphorylated K(Ca)3.1 channel protein in NIH-3T3 fibroblasts. However, open probability and single-channel current amplitudes of K(Ca)3.1 channels were not changed by modafinil. From these results, we conclude that modafinil inhibits K(Ca)3.1 channels and vascular smooth muscle contraction by cAMP-dependent phosphorylation, suggesting that modafinil can be used as a cAMP-dependent K(Ca)3.1 channel blocker and vasodilator.

Therapeutic potential of KCa3.1 blockers: recent advances and promising trends

The Ca(2+)-activated K(+) channel K(Ca)3.1 regulates membrane potential and calcium signaling in erythrocytes, activated T and B cells, macrophages, microglia, vascular endothelium, epithelia, and proliferating vascular smooth muscle cells and fibroblasts. K(Ca)3.1 has therefore been suggested as a potential therapeutic target for diseases such as sickle cell anemia, asthma, coronary restenosis after angioplasty, atherosclerosis, kidney fibrosis and autoimmunity, where activation and excessive proliferation of one or more of these cell types is involved in the pathology. This article will review the physiology and pharmacology of K(Ca)3.1 and critically examine the available preclinical and clinical data validating K(Ca)3.1 as a therapeutic target.

Rituximab inhibits Kv1.3 channels in human B lymphoma cells via activation of FcγRIIB receptors

Kv1.3 channels play an important role in modulating lymphocyte proliferation and apoptosis. We hypothesized that Kv1.3 channels in B lymphocytes might be regulated by rituximab, an antibody to CD20, a drug for treatments of B-cell lymphomas and autoimmune diseases. Using both whole-cell and cell-attached patch-clamp techniques, we found that rituximab inhibited Kv1.3 channels in Daudi human B lymphoma cells by promoting the channel inactivation at a concentration which was much greater than that required for activation of CD20. The effect of rituximab on Kv1.3 channels was abolished after selective blockade of FcγRIIB receptors with anti-FcγRIIB antibody. Western blot experiments showed that Daudi B cells expressed both Kv1.3 channel and the low affinity Fc receptor, FcγRIIB, which could be activated by the Fc region of rituximab. In contrast, normal lymphocytes expressed less Kv1.3 channels with faster inactivation. Confocal microscopy and flow cytometry data showed that rituximab induced apoptosis of Daudi B cells and that the effect was attenuated by blockade of FcγRIIB receptors and partially mimicked by inhibition of Kv1.3 channels. These results suggest that in addition to previously described complement-dependent cytotoxicity, rituximab also induces apoptosis of malignant B lymphocyte by stimulating FcγRIIB receptors and inhibiting Kv1.3 channels.

The KCa3.1 blocker TRAM-34 reduces infarction and neurological deficit in a rat model of ischemia/reperfusion stroke

Microglia and brain infiltrating macrophages significantly contribute to the secondary inflammatory damage in the wake of ischemic stroke. Here, we investigated whether inhibition of KCa3.1 (IKCa1/KCNN4), a calcium-activated K(+) channel that is involved in microglia and macrophage activation and expression of which increases on microglia in the infarcted area, has beneficial effects in a rat model of ischemic stroke. Using an HPLC/MS assay, we first confirmed that our small molecule KCa3.1 blocker TRAM-34 effectively penetrates into the brain and achieves micromolar plasma and brain concentrations after intraperitoneal injection. Then, we subjected male Wistar rats to 90 minutes of middle cerebral artery occlusion (MCAO) and administered either vehicle or TRAM-34 (10 or 40 mg/kg intraperitoneally twice daily) for 7 days starting 12 hours after reperfusion. Both compound doses reduced infarct area by ≈ 50% as determined by hematoxylin & eosin staining on day 7 and the higher dose also significantly improved neurological deficit. We further observed a significant reduction in ED1(+)-activated microglia and TUNEL-positive neurons as well as increases in NeuN(+) neurons in the infarcted hemisphere. Our findings suggest that KCa3.1 blockade constitutes an attractive approach for the treatment of ischemic stroke because it is still effective when initiated 12 hours after the insult.

Cooperativity between inhibition of cytosolic K+ efflux and AMPK activation during suppression of hypoxia-induced cellular apoptosis

Cellular potassium homeostasis has recently emerged as a critical regulator of apoptosis in response to variety of stimuli. However, functional hierarchy of this phenomenon in the apoptotic cascade and therefore, its significance as a pathway for intervention is not fully established. Chronic hypoxia, a known threat to cell survival, also modulates cellular potassium homeostasis. In this study, we tested if hypoxia-induced apoptosis in lymphocytes can be prevented by modulating cellular K+ homeostasis. We observed that chronic hypoxia accelerated the rate of apoptosis in resting murine splenocytes concomitant with cytosolic K+ efflux. We tested several modalities including elevated extracellular potassium besides various K+ channel inhibitors to curtail hypoxia-induced K+ efflux and interestingly, established that the supplementation of KCl in extracellular medium was most effective in preventing hypoxia-induced apoptosis in these cells. Subsequent mechanistic dissection of pathways underlying this phenomenon revealed that besides effectively inhibiting hypoxia-induced efflux of K+ ion and its downstream cell-physiological consequences; elevated extracellular KCl modulated steady state levels of cellular ATP and culminated in stabilization of AMPKα with pro-survival consequences. Also, interestingly, global gene expression profiling revealed that KCl supplementation down regulated a distinct p53-regulated cellular sub-network of genes involved in regulation of DNA replication. Additionally, we present experimental evidence for the functional role of AMPK and p53 activation during suppression of hypoxia-induced apoptosis. In conclusion, our study highlights a novel bimodal effect wherein cooperativity between restoration of K+ homeostasis and a sustainable 'metabolic quiescence' induced by AMPK activation appeared indispensible for curtailing hypoxia-induced apoptosis.

The Lymphocyte Potassium Channels Kv1.3 and KCa3.1 as Targets for Immunosuppression

The voltage-gated Kv1.3 and the calcium-activated KCa3.1 potassium channel modulate many calcium-dependent cellular processes in immune cells, including T-cell activation and proliferation, and have therefore been proposed as novel therapeutic targets for immunomodulation. Kv1.3 is highly expressed in CCR7(-) effector memory T cells and is emerging as a target for T-cell mediated diseases like multiple sclerosis, rheumatoid arthritis, type-1 diabetes mellitus, allergic contact dermatitis, and psoriasis. KCa3.1 in contrast is expressed in CCR7(+) naïve and central memory T cells, as well as in mast cells, macrophages, dedifferentiated vascular smooth muscle cells, fibroblasts, vascular endothelium, and airway epithelium. Given this expression pattern, KCa3.1 is a potential therapeutic target for conditions ranging from inflammatory bowel disease, multiple sclerosis, arthritis, and asthma to cardiovascular diseases like atherosclerosis and post-angioplasty restenosis. Results from animal studies have been supportive of the therapeutic potential of both Kv1.3 and KCa3.1 blockers and have also not shown any toxicities associated with pharmacological Kv1.3 and KCa3.1 blockade. To date, two compounds targeting Kv1.3 are in preclinical development but, so far, no Kv1.3 blocker has advanced into clinical trials. KCa3.1 blockers, on the other hand, have been evaluated in clinical trials for sickle cell anemia and exercise-induced asthma, but have so far not shown efficacy. However, the trial results support KCa3.1 as a safe therapeutic target, and will hopefully help enable clinical trials for other medical conditions that might benefit from KCa3.1 blockade.