Calcium signaling in B cells: regulation of cytosolic Ca2+ increase and its sensor molecules, STIM1 and STIM2

Effect of a scramblase activator upon lipid and probe scrambling and membrane domain formation in HEK 293T cells

Lipid asymmetry, a difference between the lipid composition of the inner and outer leaflets (monolayers) of a membrane, is a characteristic of mammalian plasma membranes. In artificial lipid vesicles, asymmetry can either suppress or induce the formation of coexisting ordered and disordered lipid domains depending on lipid composition. In mammalian plasma membrane preparations, loss of asymmetry induces the formation of ordered domains. In this report, we studied the effect of a scramblase activator, the ionophore BrA23187 (BrA) plus Ca2+, upon ordered domain (lipid raft) formation in human embryonic kidney 293T cells. Addition of BrA induced a decrease in FRET between the plasma membrane outer leaflet probe TMADPH, which partly associates with ordered domains, and ODRB, which localizes largely in liquid disordered domains. This is consistent with the formation of coexisting ordered and disordered domains in the plasma membrane. In addition, upon BrA addition, the plasma membrane outer leaflet probe Pro12A exhibited a decrease in the generalized polarization (GP) suggesting a decrease in outer leaflet membrane order, perhaps due to a decrease in outer leaflet cholesterol However, there are other explanations for these observations. To test if BrA induced scrambling of fluorescent membrane probes, which would complicate interpretation of the experiments described above, we measured the effect of BrA upon extractability of outer leaflet probes with MβCD (in most cases, MβCD was more effective for extraction than BSA). These experiments showed that at most a small fraction of probes migrate to the inner leaflet upon addition of BrA. Other experiments raise the possibility that BrA binding to membranes may directly influence ordered domain formation and properties or alter fluorescence by direct interactions with TMADPH, and thus not reflect changes in domain formation.

Regulation of BCR-mediated Ca2+ mobilization by MIZ1-TMBIM4 safeguards IgG1+ GC B cell-positive selection

The transition from immunoglobulin M (IgM) to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential maintenance of IgG+ B cells over IgM+ B cells. However, it is not known whether the positive selection of the different Ig isotypes within GCs is dependent on specific transcriptional mechanisms. Here, we explored IgG1+ GC B cell transcription factor dependency using a CRISPR-Cas9 screen and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1+ GC B cell survival during positive selection, whereas IgM+ GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor (IP3R)-mediated calcium (Ca2+) mobilization downstream of B cell receptor (BCR) signaling in IgG1+ B cells. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1+ GC cell death caused by excessive Ca2+ accumulation. This study uncovers a unique Ig isotype-specific dependency on a hitherto unidentified mechanism in GC-positive selection.

STIM-mediated calcium influx regulates maintenance and selection of germinal center B cells

Positive selection of high-affinity germinal center (GC) B cells is driven by antigen internalization through their B cell receptor (BCR) and presentation to follicular helper T cells. However, the requirements of BCR signaling in GC B cells remain poorly understood. Store-operated Ca2+ entry, mediated by stromal interacting molecule 1 (STIM1) and STIM2, is the main Ca2+ influx pathway triggered by BCR engagement. Here, we showed that STIM-deficient B cells have reduced B cell competitiveness compared with wild-type B cells during GC responses. B cell-specific deletion of STIM proteins decreased the number of high-affinity B cells in the late phase of GC formation. STIM deficiency did not affect GC B cell proliferation and antigen presentation but led to the enhancement of apoptosis due to the impaired upregulation of anti-apoptotic Bcl2a1. STIM-mediated activation of NFAT was required for the expression of Bcl2a1 after BCR stimulation. These findings suggest that STIM-mediated survival signals after antigen capture regulate the optimal selection and maintenance of GC B cells.

LBD: a manually curated database of experimentally validated lymphoma biomarkers

Lymphoma is a heterogeneous disease caused by malignant proliferation of lymphocytes, resulting in significant mortality worldwide. While more and more lymphoma biomarkers have been identified with the advent and development of precision medicine, there are currently no databases dedicated to systematically gathering these scattered treasures. Therefore, we developed a lymphoma biomarker database (LBD) to curate experimentally validated lymphoma biomarkers in this study. LBD consists of 793 biomarkers extracted from 978 articles covering diverse subtypes of lymphomas, including 715 single and 78 combined biomarkers. These biomarkers can be categorized into molecular, cellular, image, histopathological, physiological and other biomarkers with various functions such as prognosis, diagnosis and treatment. As a manually curated database that provides comprehensive information about lymphoma biomarkers, LBD is helpful for personalized diagnosis and treatment of lymphoma.

Database URL

http://bis.zju.edu.cn/LBD

Interleukin-10 in the Vasculature: Pathophysiological Implications

Interleukin-10 (IL-10) is an important immunomodulatory cytokine, initially characterized as an anti-inflammatory agent released by immune cells during infectious and inflammatory processes. IL-10 exhibits biological functions that extend to the regulation of different intracellular signaling pathways directly associated with vascular function. This cytokine plays a vital role in vascular tone regulation through the change of important proteins involved in vasoconstriction and vasodilation. Numerous investigations covered here have shown that therapeutic strategies inducing IL-10 result in anti-inflammatory, anti-hypertrophic, antihyperplastic, anti-apoptotic and antihypertensive effects. This non-systematic review summarizes the modulating effects mediated by IL-10 in vascular tissue, particularly on vascular tone, and the intracellular pathway induced by this cytokine. We also highlight the advances in IL-10 manipulation as a therapeutic target in different cardiovascular pathophysiologies, including the physiological implications in animals and humans. Finally, the review illustrates current and potential future perspectives of the potential use of IL-10 in clinical trials, based on the clinical evidence.

Re-Expression of Poly/Oligo-Sialylated Adhesion Molecules on the Surface of Tumor Cells Disrupts Their Interaction with Immune-Effector Cells and Contributes to Pathophysiological Immune Escape

Glycans linked to surface proteins are the most complex biological macromolecules that play an active role in various cellular mechanisms. This diversity is the basis of cell-cell interaction and communication, cell growth, cell migration, as well as co-stimulatory or inhibitory signaling. Our review describes the importance of neuraminic acid and its derivatives as recognition elements, which are located at the outermost positions of carbohydrate chains linked to specific glycoproteins or glycolipids. Tumor cells, especially from solid tumors, mask themselves by re-expression of hypersialylated neural cell adhesion molecule (NCAM), neuropilin-2 (NRP-2), or synaptic cell adhesion molecule 1 (SynCAM 1) in order to protect themselves against the cytotoxic attack of the also highly sialylated immune effector cells. More particularly, we focus on α-2,8-linked polysialic acid chains, which characterize carrier glycoproteins such as NCAM, NRP-2, or SynCam-1. This characteristic property correlates with an aggressive clinical phenotype and endows them with multiple roles in biological processes that underlie all steps of cancer progression, including regulation of cell-cell and/or cell-extracellular matrix interactions, as well as increased proliferation, migration, reduced apoptosis rate of tumor cells, angiogenesis, and metastasis. Specifically, re-expression of poly/oligo-sialylated adhesion molecules on the surface of tumor cells disrupts their interaction with immune-effector cells and contributes to pathophysiological immune escape. Further, sialylated glycoproteins induce immunoregulatory cytokines and growth factors through interactions with sialic acid-binding immunoglobulin-like lectins. We describe the processes, which modulate the interaction between sialylated carrier glycoproteins and their ligands, and illustrate that sialic acids could be targets of novel therapeutic strategies for treatment of cancer and immune diseases.

SLC39A10 Upregulation Predicts Poor Prognosis, Promotes Proliferation and Migration, and Correlates with Immune Infiltration in Hepatocellular Carcinoma

Background

Recent evidence has shown that Solute Carrier Family 39 Member 10 (SLC39A10) promoted tumor progression in several cancer types. The study intended to explore the expression and function of SLC39A10 in hepatocellular carcinoma (HCC).

Methods

Multiple bioinformatics analyses were used to evaluate SLC39A10 expression and potential role in HCC. Quantitative real-time polymerase chain reaction and immunohistochemistry were used to confirm SLC39A10 expression. Intro studies were performed to assess the effects of SLC39A10 on HCC cells proliferation and migration. Furthermore, flow cytometry was conducted to identify its specific function in apoptosis of HCC.

Results

SLC39A10 was significantly over-expressed in HCC samples from both bioinformatic databases and our cohort. Survival analyses suggested patients with high expression of SLC39A10 had poor overall survival and disease-free survival (P-value <0.01). Further, the expression of SLC39A10 was positively correlated with tumor-infiltrating lymphocytes and some immune checkpoints like CTLA4, TIM3 and TGFB1. In HCC cell lines, SLC39A10 knockdown inhibited cells proliferation and migration, but promoted apoptosis.

Conclusion

An increased SLC39A10 expression was found and served as an unfavorable indicator of survival in HCC. Further studies suggested SLC39A10 promotes tumor aggressiveness and may provide a novel target for HCC therapy.

Intravital quantification reveals dynamic calcium concentration changes across B cell differentiation stages

Calcium is a universal second messenger present in all eukaryotic cells. The mobilization and storage of Ca²⁺ ions drives a number of signaling-related processes, stress-responses, or metabolic changes, all of which are relevant for the development of immune cells and their adaption to pathogens. Here, we introduce the Förster resonance energy transfer (FRET)-reporter mouse YellowCaB expressing the genetically encoded calcium indicator TN-XXL in B lymphocytes. Calcium-induced conformation change of TN-XXL results in FRET-donor quenching measurable by two-photon fluorescence lifetime imaging. For the first time, using our novel numerical analysis, we extract absolute cytoplasmic calcium concentrations in activated B cells during affinity maturation in vivo. We show that calcium in activated B cells is highly dynamic and that activation introduces a persistent calcium heterogeneity to the lineage. A characterization of absolute calcium concentrations present at any time within the cytosol is therefore of great value for the understanding of long-lived beneficial immune responses and detrimental autoimmunity.

To B, or not to B: Is calcium the answer?

B lymphocytes are an important component of the adaptive and innate immune system because of their ability to secrete antibodies and to present antigens to T cells, which is critical for immune responses to many pathogens. Abnormal B cell function is the cause of diseases including autoimmune, paraneoplastic, and immunodeficiency disorders. The development, survival, and function of B cells depend on signaling through the B cell receptor (BCR) and costimulatory receptors. One of the signaling pathways induced by antigen binding to the BCR is store-operated Ca2+ entry (SOCE), which depends on the Ca2+ channel ORAI1 and its activators stromal interaction molecule (STIM) 1 and 2. A recent study by Berry et al. [1] reports that B cells lacking STIM1 and STIM2 fail to survive and proliferate because abolished SOCE results in impaired expression of two key anti-apoptotic genes and blunted activation of mTORC1 and c-Myc signaling. The associated Ca2+ regulated checkpoints of B cell survival and proliferation can be bypassed, at least partially, by costimulation through CD40 or TLR9. This study provides important new insights on how SOCE controls B cell function.

Carbohydrate-dependent B cell activation by fucose-binding bacterial lectins

Bacterial lectins are typically multivalent and bind noncovalently to specific carbohydrates on host tissues to facilitate bacterial adhesion. Here, we analyzed the effects of two fucose-binding lectins, BambL from Burkholderia ambifaria and LecB from Pseudomonas aeruginosa, on specific signaling pathways in B cells. We found that these bacterial lectins induced B cell activation, which, in vitro, was dependent on the cell surface expression of the B cell antigen receptor (BCR) and its co-receptor CD19, as well as on spleen tyrosine kinase (Syk) activity. The resulting release of intracellular Ca²⁺ was followed by an increase in the cell surface abundance of the activation marker CD86, augmented cytokine secretion, and subsequent cell death, replicating all of the events that are observed in vitro upon canonical and antigen-mediated B cell activation. Moreover, injection of BambL in mice resulted in a substantial, BCR-independent loss of B cells in the bone marrow with simultaneous, transient enlargement of the spleen (splenomegaly), as well as an increase in the numbers of splenic B cells and myeloid cells. Together, these data suggest that bacterial lectins can initiate polyclonal activation of B cells through their sole capacity to bind to fucose.

Induction of endoplasmic reticulum calcium pump expression during early leukemic B cell differentiation

Background

Endoplasmic reticulum (ER) calcium storage and release play important roles in B lymphocyte maturation, survival, antigen-dependent cell activation and immunoglobulin synthesis. Calcium is accumulated in the endoplasmic reticulum (ER) by Sarco/Endoplasmic Reticulum Calcium ATPases (SERCA enzymes). Because lymphocyte function is critically dependent on SERCA activity, it is important to understand qualitative and quantitative changes of SERCA protein expression that occur during B lymphoid differentiation and leukemogenesis.

Methods

In this work we investigated the modulation of SERCA expression during the pharmacologically induced differentiation of leukemic precursor B lymphoblast cell lines that carry the E2A-PBX1 fusion oncoprotein. Changes of SERCA levels during differentiation were determined and compared to those of established early B lymphoid differentiation markers. SERCA expression of the cells was compared to that of mature B cell lines as well, and the effect of the direct inhibition of SERCA-dependent calcium transport on the differentiation process was investigated.

Results

We show that E2A-PBX1⁺ leukemia cells simultaneously express SERCA2 and SERCA3-type calcium pumps; however, their SERCA3 expression is markedly inferior to that of mature B cells. Activation of protein kinase C enzymes by phorbol ester leads to phenotypic differentiation of the cells, and this is accompanied by the induction of SERCA3 expression. Direct pharmacological inhibition of SERCA-dependent calcium transport during phorbol ester treatment interferes with the differentiation process.

Conclusion

These data show that the calcium pump composition of the ER is concurrent with increased SERCA3 expression during the differentiation of precursor B acute lymphoblastic leukemia cells, that a cross-talk exists between SERCA function and the control of differentiation, and that SERCA3 may constitute an interesting new marker for the study of early B cell phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0556-7) contains supplementary material, which is available to authorized users.

Chloroquine inhibits Ca2+ permeable ion channels-mediated Ca2+ signaling in primary B lymphocytes

BACKGROUND

Chloroquine, a bitter tastant, inhibits Ca²⁺ signaling, resulting in suppression of B cell activation; however, the inhibitory mechanism remains unclear.

RESULTS

In this study, thapsigargin (TG), but not caffeine, induced sustained intracellular Ca²⁺ increases in mouse splenic primary B lymphocytes, which were markedly inhibited by chloroquine. Under Ca²⁺-free conditions, TG elicited transient Ca²⁺ increases, which additionally elevated upon the restoration of 2 mM Ca²⁺. The former were from release of intracellular Ca²⁺ store and the latter from Ca²⁺ influx. TG-induced release was inhibited by 2-APB (an inhibitor of inositol-3-phosphate receptors, IP₃Rs) and chloroquine, and TG-caused influx was inhibited by pyrazole (Pyr3, an inhibitor of transient receptor potential C3 (TRPC3) and stromal interaction molecule (STIM)/Orai channels) and chloroquine. Moreover, chloroquine also blocked Ca²⁺ increases induced by the engagement of B cell receptor (BCR) with anti-IgM.

CONCLUSIONS

These results indicate that chloroquine inhibits Ca²⁺ elevations in splenic B cells through inhibiting Ca²⁺ permeable IP₃R and TRPC3 and/or STIM/Orai channels. These findings suggest that chloroquine would be a potent immunosuppressant.

Store-operated calcium entry is required for sustained contraction and Ca2+ oscillations of airway smooth muscle

KEY POINTS

Airway hyper-responsiveness in asthma is driven by excessive contraction of airway smooth muscle cells (ASMCs). Agonist-induced Ca²⁺ oscillations underlie this contraction of ASMCs and the magnitude of this contraction is proportional to the Ca²⁺ oscillation frequency. Sustained contraction and Ca²⁺ oscillations require an influx of extracellular Ca²⁺ , although the mechanisms and pathways mediating this Ca²⁺ influx during agonist-induced ASMC contraction are not well defined. By inhibiting store-operated calcium entry (SOCE) or voltage-gated Ca²⁺ channels (VGCCs), we show that SOCE, rather than Ca²⁺ influx via VGCCs, provides the major Ca²⁺ entry pathway into ASMCs to sustain ASMCs contraction and Ca²⁺ oscillations. SOCE may therefore serve as a potential target for new bronchodilators to reduce airway hyper-responsiveness in asthma.

ABSTRACT

Asthma is characterized by airway hyper-responsiveness: the excessive contraction of airway smooth muscle. The extent of this airway contraction is proportional to the frequency of Ca²⁺ oscillations within airway smooth muscle cells (ASMCs). Sustained Ca²⁺ oscillations require a Ca²⁺ influx to replenish Ca²⁺ losses across the plasma membrane. Our previous studies implied store-operated calcium entry (SOCE) as the major pathway for this Ca²⁺ influx. In the present study, we explore this hypothesis, by examining the effects of SOCE inhibitors (GSK7975A and GSK5498A) as well as L-type voltage-gated Ca²⁺ channel inhibitors (nifedipine and nimodipine) on airway contraction and Ca²⁺ oscillations and SOCE-mediated Ca²⁺ influx in ASMCs within mouse precision-cut lung slices. We found that both GSK7975A and GSK5498A were able to fully relax methacholine-induced airway contraction by abolishing the Ca²⁺ oscillations, in a manner similar to that observed in zero extracellular Ca²⁺ ([Ca²⁺ ]_e ). In addition, GSK7975A and GSK5498A inhibited increases in intracellular Ca²⁺ ([Ca²⁺ ]_i ) in ASMCs with depleted Ca²⁺ -stores in response to increased [Ca²⁺ ]_e , demonstrating a response consistent with the inhibition of SOCE. However, GSK7975A and GSK5498A did not reduce Ca²⁺ release via IP₃ receptors stimulated with IP₃ released from caged-IP₃ . By contrast, nifedipine and nimodipine only partially reduced airway contraction, Ca²⁺ oscillation frequency and SOCE-mediated Ca²⁺ influx. These data suggest that SOCE is the major Ca²⁺ influx pathway for ASMCs with respect to sustaining agonist-induced airway contraction and the underlying Ca²⁺ oscillations. The mechanisms of SOCE may therefore form novel targets for new bronchodilators.

Treatment of ongoing autoimmune encephalomyelitis with activated B-cell progenitors maturing into regulatory B cells

The influence of signals perceived by immature B cells during their development in bone marrow on their subsequent functions as mature cells are poorly defined. Here, we show that bone marrow cells transiently stimulated in vivo or in vitro through the Toll-like receptor 9 generate proB cells (CpG-proBs) that interrupt experimental autoimmune encephalomyelitis (EAE) when transferred at the onset of clinical symptoms. Protection requires differentiation of CpG-proBs into mature B cells that home to reactive lymph nodes, where they trap T cells by releasing the CCR7 ligand, CCL19, and to inflamed central nervous system, where they locally limit immunopathogenesis through interleukin-10 production, thereby cooperatively inhibiting ongoing EAE. These data demonstrate that a transient inflammation at the environment, where proB cells develop, is sufficient to confer regulatory functions onto their mature B-cell progeny. In addition, these properties of CpG-proBs open interesting perspectives for cell therapy of autoimmune diseases.

Evidence of how functional Bregs develop in vivo has been lacking. Here the authors show that proB cells exposed in vivo to CpG differentiate into distinct Breg subsets that inhibit autoimmunity by arresting T cells in the lymph nodes via CCL19 and by producing IL-10 at the site of immunopathology.

Altered expression of stromal interaction molecule (STIM)-calcium release-activated calcium channel protein (ORAI) and inositol 1,4,5-trisphosphate receptors (IP3Rs) in cancer: will they become a new battlefield for oncotherapy?

The stromal interaction molecule (STIM)-calcium release-activated calcium channel protein (ORAI) and inositol 1,4,5-trisphosphate receptors (IP₃Rs) play pivotal roles in the modulation of Ca²⁺-regulated pathways from gene transcription to cell apoptosis by driving calcium-dependent signaling processes. Increasing evidence has implicated the dysregulation of STIM–ORAI and IP₃Rs in tumorigenesis and tumor progression. By controlling the activities, structure, and/or expression levels of these Ca²⁺-transporting proteins, malignant cancer cells can hijack them to drive essential biological functions for tumor development. However, the molecular mechanisms underlying the participation of STIM–ORAI and IP₃Rs in the biological behavior of cancer remain elusive. In this review, we summarize recent advances regarding STIM–ORAI and IP₃Rs and discuss how they promote cell proliferation, apoptosis evasion, and cell migration through temporal and spatial rearrangements in certain types of malignant cells. An understanding of the essential roles of STIM–ORAI and IP₃Rs may provide new pharmacologic targets that achieve a better therapeutic effect by inhibiting their actions in key intracellular signaling pathways.

Changing calcium: CRAC channel (STIM and Orai) expression, splicing, and posttranslational modifiers

A wide variety of cellular function depends on the dynamics of intracellular Ca(2+) signals. Especially for relatively slow and lasting processes such as gene expression, cell proliferation, and often migration, cells rely on the store-operated Ca(2+) entry (SOCE) pathway, which is particularly prominent in immune cells. SOCE is initiated by the sensor proteins (STIM1, STIM2) located within the endoplasmic reticulum (ER) registering the Ca(2+) concentration within the ER, and upon its depletion, cluster and trap Orai (Orai1-3) proteins located in the plasma membrane (PM) into ER-PM junctions. These regions become sites of highly selective Ca(2+) entry predominantly through Orai1-assembled channels, which, among other effector functions, is necessary for triggering NFAT translocation into the nucleus. What is less clear is how the spatial and temporal spread of intracellular Ca(2+) is shaped and regulated by differential expression of the individual SOCE genes and their splice variants, their heteromeric combinations and pre- and posttranslational modifications. This review focuses on principle mechanisms regulating expression, splicing, and targeting of Ca(2+) release-activated Ca(2+) (CRAC) channels.

Pathophysiological significance of the two-pore domain K(+) channel K2P5.1 in splenic CD4(+)CD25(-) T cell subset from a chemically-induced murine inflammatory bowel disease model

The alkaline pH-activated, two-pore domain K(+) channel K2P5.1 (also known as TASK2/KCNK5) plays an important role in maintaining the resting membrane potential, and contributes to the control of Ca(2+) signaling in several types of cells. Recent studies highlighted the potential role of the K2P5.1 K(+) channel in the pathogenesis of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. The aim of the present study was to elucidate the pathological significance of the K2P5.1 K(+) channel in inflammatory bowel disease (IBD). The degrees of colitis, colonic epithelial damage, and colonic inflammation were quantified in the dextran sulfate sodium-induced mouse IBD model by macroscopic and histological scoring systems. The expression and functional activity of K2P5.1 in splenic CD4(+) T cells were measured using real-time PCR, Western blot, and fluorescence imaging assays. A significant increase was observed in the expression of K2P5.1 in the splenic CD4(+) T cells of the IBD model. Concomitant with this increase, the hyperpolarization response induced by extracellular alkaline pH was significantly larger in the IBD model with the corresponding intracellular Ca(2+) rises. The expression of K2P5.1 was higher in CD4(+)CD25(-) T cells than in CD4(+)CD25(+) regulatory T cells. The knockout of K2P5.1 in mice significantly suppressed the disease responses implicated in the IBD model. Alternations in intracellular Ca(2+) signaling following the dysregulated expression of K2P5.1 were associated with the disease pathogenesis of IBD. The results of the present study suggest that the K2P5.1 K(+) channel in CD4(+)CD25(-) T cell subset is a potential therapeutic target and biomarker for IBD.

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.

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.

Divalent cation signaling in immune cells

Divalent cations of two alkaline earth metals Ca(2+) and Mg(2+) and the transition metal Zn(2+) play vital roles in the immune system, and several immune disorders are associated with disturbances of their function. Until recently only Ca(2+) was considered to serve as a second messenger. However, signaling roles for Mg(2+) and Zn(2+) have been recently described, leading to a reevaluation of their role as potential second messengers. We review here the roles of these cations as second messengers in light of recent advances in Ca(2+), Mg(2+), and Zn(2+) signaling in the immune system. Developing a better understanding of these signaling cations may lead to new therapeutic strategies for immune disorders.

Genetic polymorphisms of ORAI1 and chronic kidney disease in Taiwanese population

Taiwan has very high incidence and prevalence of chronic kidney disease (CKD), which easily progresses to end-stage renal disease (ESRD). The association between inflammation and CKD has been explored in several studies. ORAI1 functions as a pore-forming subunit of the store-operated calcium channels which are involved in the regulation of immune system. Hence, we conducted a case-control study to determine whether the genetic polymorphisms of ORAI1 gene is a susceptibility factor to CKD and its clinical features in a Taiwanese population. Five hundred seventy-nine CKD patients from a hospital-based CKD care program were included in the study. Five tagging single nucleotide polymorphisms (tSNPs) of ORAI1 were selected from the genotyping data of the Han Chinese population from the HapMap project. Among these polymorphisms, rs12313273 was found to be significantly associated with elevated serum calcium levels, which has been linked to increased risk of death in CKD patients. To have a better management of serum calcium, we suggest that ORAI1 polymorphisms might be used as a potential biomarker for initiating non-calcium-based phosphate binder in CKD patients in the future.

Activating mutations in STIM1 and ORAI1 cause overlapping syndromes of tubular myopathy and congenital miosis

Signaling through the store-operated Ca(2+) release-activated Ca(2+) (CRAC) channel regulates critical cellular functions, including gene expression, cell growth and differentiation, and Ca(2+) homeostasis. Loss-of-function mutations in the CRAC channel pore-forming protein ORAI1 or the Ca(2+) sensing protein stromal interaction molecule 1 (STIM1) result in severe immune dysfunction and nonprogressive myopathy. Here, we identify gain-of-function mutations in the cytoplasmic domain of STIM1 (p.R304W) associated with thrombocytopenia, bleeding diathesis, miosis, and tubular myopathy in patients with Stormorken syndrome, and in ORAI1 (p.P245L), associated with a Stormorken-like syndrome of congenital miosis and tubular aggregate myopathy but without hematological abnormalities. Heterologous expression of STIM1 p.R304W results in constitutive activation of the CRAC channel in vitro, and spontaneous bleeding accompanied by reduced numbers of thrombocytes in zebrafish embryos, recapitulating key aspects of Stormorken syndrome. p.P245L in ORAI1 does not make a constitutively active CRAC channel, but suppresses the slow Ca(2+)-dependent inactivation of the CRAC channel, thus also functioning as a gain-of-function mutation. These data expand our understanding of the phenotypic spectrum of dysregulated CRAC channel signaling, advance our knowledge of the molecular function of the CRAC channel, and suggest new therapies aiming at attenuating store-operated Ca(2+) entry in the treatment of patients with Stormorken syndrome and related pathologic conditions.