Production of Ins(1,3,4,5)P4 mediated by the kinase Itpkb inhibits store-operated calcium channels and regulates B cell selection and activation

DNA methyltransferase 1 (DNMT1) promotes cyst growth and epigenetic age acceleration in autosomal dominant polycystic kidney disease

Alteration of DNA methylation leads to diverse diseases, and the dynamic changes of DNA methylation (DNAm) on sets of CpG dinucleotides in mammalian genomes are termed "DNAm age" and "epigenetic clocks" that can predict chronological age. However, whether and how dysregulation of DNA methylation promotes cyst progression and epigenetic age acceleration in autosomal dominant polycystic kidney disease (ADPKD) remains elusive. Here, we show that DNA methyltransferase 1 (DNMT1) is upregulated in cystic kidney epithelial cells and tissues and that knockout of Dnmt1 and targeting DNMT1 with hydralazine, a safe demethylating agent, delays cyst growth in Pkd1 mutant kidneys and extends life span of Pkd1 conditional knockout mice. With methyl-CpG binding domain (MBD) protein-enriched genome sequencing (MBD-seq), DNMT1 chromatin immunoprecipitation (ChIP)-sequencing and RNA-sequencing analysis, we identified two novel DNMT1 targets, PTPRM and PTPN22 (members of the protein tyrosine phosphatase family). PTPRM and PTPN22 function as mediators of DNMT1 and the phosphorylation and activation of PKD-associated signaling pathways, including ERK, mTOR and STAT3. With whole-genome bisulfide sequencing in kidneys of patients with ADPKD versus normal individuals, we found that the methylation of epigenetic clock-associated genes was dysregulated, supporting that epigenetic age is accelerated in the kidneys of patients with ADPKD. Furthermore, five epigenetic clock-associated genes, including Hsd17b14, Itpkb, Mbnl1, Rassf5 and Plk2, were identified. Thus, the diverse biological roles of these five genes suggest that their methylation status may not only predict epigenetic age acceleration but also contribute to disease progression in ADPKD.

Substrate promiscuity of inositol 1,4,5-trisphosphate kinase driven by structurally-modified ligands and active site plasticity

D-myo-inositol 1,4,5-trisphosphate (InsP3) is a fundamental second messenger in cellular Ca2+ mobilization. InsP3 3-kinase, a highly specific enzyme binding InsP3 in just one mode, phosphorylates InsP3 specifically at its secondary 3-hydroxyl group to generate a tetrakisphosphate. Using a chemical biology approach with both synthetised and established ligands, combining synthesis, crystallography, computational docking, HPLC and fluorescence polarization binding assays using fluorescently-tagged InsP3, we have surveyed the limits of InsP3 3-kinase ligand specificity and uncovered surprisingly unforeseen biosynthetic capacity. Structurally-modified ligands exploit active site plasticity generating a helix-tilt. These facilitated uncovering of unexpected substrates phosphorylated at a surrogate extended primary hydroxyl at the inositol pseudo 3-position, applicable even to carbohydrate-based substrates. Crystallization experiments designed to allow reactions to proceed in situ facilitated unequivocal characterization of the atypical tetrakisphosphate products. In summary, we define features of InsP3 3-kinase plasticity and substrate tolerance that may be more widely exploitable.

Evidence that inositol 1,4,5-trisphosphate 3-kinase and inositol 1,3,4,5-tetrakisphosphate are negative regulators of platelet function

Background

Inositol 1,3,4,5-tetrakisphosphate (IP4) is formed from inositol 1,4,5-trisphosphate (IP3) by IP3 3-kinase (ITPK) in most cells. Its function is unknown but has been suggested to be involved in Ca2+ entry, IP3 regulation, and phosphoinositide 3-kinase antagonism.

Objectives

To better elucidate a function for IP4, we tested a specific inhibitor of ITPK (GNF362) on platelets, the effects of IP4 directly in permeabilized platelets and its effect on phosphatidylinositol 3,4,5-trisphosphate (PIP3) binding to pleckstrin-homology (PH) domain-containing proteins in platelets.

Methods

Human platelets were utilized in whole blood for thrombus formation, in platelet-rich plasma and washed suspensions for aggregation, and for Ca2+ studies, or resuspended in high K+ and low Na+ buffers for permeabilization experiments. Phosphorylation of AKT-Ser473 and Rap1-GTP formation were measured by Western blotting and PIP3 binding using PIP3 beads.

Results

GNF362-enhanced platelet aggregation stimulated by low concentrations of ADP, collagen, thrombin, U46619, and thrombus formation in collagen-coated capillaries. GNF362 induced a transient elevation of Ca2+ concentration, elevated basal levels of IP3, and enhanced the peak height of Ca2+ elevated by agonists. In permeabilized platelets, IP4 inhibited GTPγS induced formation of AKT-Ser473 phosphorylation and platelet aggregation. IP4 reduced GTPγS-stimulated Rap1-GTP levels and potently reduced extraction of RASA3 and BTK by PIP3 beads.

Conclusion

ITPK and IP4 are negative regulators of platelet function. IP4 regulation of PH domain-containing proteins may represent a pathway by which platelet activation may be controlled during thrombosis.

Increased Levels of the Parkinson's Disease-Associated Gene ITPKB Correlate with Higher Expression Levels of α-Synuclein, Independent of Mutation Status

Autosomal dominant mutations in the gene encoding α-synuclein (SNCA) were the first to be linked with hereditary Parkinson's disease (PD). Duplication and triplication of SNCA has been observed in PD patients, together with mutations at the N-terminal of the protein, among which A30P and A53T influence the formation of fibrils. By overexpressing human α-synuclein in the neuronal system of Drosophila, we functionally validated the ability of IP3K2, an ortholog of the GWAS identified risk gene, Inositol-trisphosphate 3-kinase B (ITPKB), to modulate α-synuclein toxicity in vivo. ITPKB mRNA and protein levels were also increased in SK-N-SH cells overexpressing wild-type α-synuclein, A53T or A30P mutants. Kinase overexpression was detected in the cytoplasmatic and in the nuclear compartments in all α-synuclein cell types. By quantifying mRNAs in the cortex of PD patients, we observed higher levels of ITPKB mRNA when SNCA was expressed more (p < 0.05), compared to controls. A positive correlation was also observed between SNCA and ITPKB expression in the cortex of patients, which was not seen in the controls. We replicated this observation in a public dataset. Our data, generated in SK-N-SH cells and in cortex from PD patients, show that the expression of α-synuclein and ITPKB is correlated in pathological situations.

Differentiation and homeostasis of effector Treg cells are regulated by inositol polyphosphates modulating Ca2+ influx

Activated Foxp3⁺ regulatory T (Treg) cells differentiate into effector Treg (eTreg) cells to maintain peripheral immune homeostasis and tolerance. T cell receptor (TCR)-mediated induction and regulation of store-operated Ca²⁺ entry (SOCE) is essential for eTreg cell differentiation and function. However, SOCE regulation in Treg cells remains unclear. Here, we show that inositol polyphosphate multikinase (IPMK), which generates inositol tetrakisphosphate and inositol pentakisphosphate, is a pivotal regulator of Treg cell differentiation downstream of TCR signaling. IPMK is highly expressed in TCR-stimulated Treg cells and promotes a TCR-induced Treg cell program. IPMK-deficient Treg cells display aberrant T cell activation and impaired differentiation into RORγt⁺ Treg cells and tissue-resident Treg cells. Mechanistically, IPMK controls the generation of higher-order inositol phosphates, thereby promoting Ca²⁺ mobilization and Treg cell effector functions. Our findings identify IPMK as a critical regulator of TCR-mediated Ca²⁺ influx and highlight the importance of IPMK in Treg cell-mediated immune homeostasis.

Small RNA-Seq Analysis Reveals miRNA Expression of Short Distance Transportation Stress in Beef Cattle Blood

Simple Summary

In this study, three miRNA modules were identified in a cattle short-distance transportation stress model, and the turquoise module showed key miRNA sets according to their correlation with hub genes. Further, hub miRNAs were identified based on their targeting relationship with hub genes in our previous study. This finding provides the potential utility for predicting and treatment of short-distance transportation stress in beef cattle.

Abstract

Transportation is a crucial phase in the beef cattle industry, and the annual losses caused by beef cattle transport stress are substantial. Because of its huge economic losses, such as lower growth rate and even death, long-distance transportation stress has attracted more attention from beef production practitioners because of its huge economic losses. Compared with the long-distance transportation stress, the short-distance transportation stress was ignored for the reason of no obvious symptoms in cattle. Our previous study showed that the disorder of B cell function could be a potential health risk after short-distance transportation. However, the transcriptome details of the changes in the cattle blood after short-distance transportation and the molecular mechanisms for the regulation of the developmental process are not clearly known. In this study, a total of 10 Qinchuan cattle were used to compare the molecular characteristics of blood before and after short-distance transportation. The miRNA-seq showed that 114 differentially expressed miRNAs (DEMs) were found (40 upregulated and 74 downregulated) between two groups before and after transportation. Furthermore, more than 90% of the miRNAs with counts of more than 10 were used to construct a co-expression network by weighted correlation network analysis (WGCNA), and four independent modules were identified. According to their relationship with 30 hub genes, the turquoise module was the key module in this study. The regulator network of hub genes and miRNAs in the turquoise module was constructed by miRNAs targeting genes predicting, and the miRNAs had targeting sites within hub genes that could be identified as hub-miRNAs. Further, it showed that CD40 and ITPKB had the same targeting miRNAs (miR-339a/b), and the newly discovered hub miRNAs filled the gaps in our previous study about the relationship between hub genes in short-distance transportation stress and provided the potential utility for predicting and treatment of short-distance transportation stress in beef cattle.

Inositol 1,4,5-trisphosphate 3-kinase B promotes Ca2+ mobilization and the inflammatory activity of dendritic cells

Innate immune responses to Gram-negative bacteria depend on the recognition of lipopolysaccharide (LPS) by a receptor complex that includes CD14 and TLR4. In dendritic cells (DCs), CD14 enhances the activation not only of TLR4 but also that of the NFAT family of transcription factors, which suppresses cell survival and promotes the production of inflammatory mediators. NFAT activation requires Ca²⁺ mobilization. In DCs, Ca²⁺ mobilization in response to LPS depends on phospholipase C γ2 (PLCγ2), which produces inositol 1,4,5-trisphosphate (IP₃). Here, we showed that the IP₃ receptor 3 (IP₃R3) and ITPKB, a kinase that converts IP₃ to inositol 1,3,4,5-tetrakisphosphate (IP₄), were both necessary for Ca²⁺ mobilization and NFAT activation in mouse and human DCs. A pool of IP₃R3 was located on the plasma membrane of DCs, where it colocalized with CD14 and ITPKB. Upon LPS binding to CD14, ITPKB was required for Ca²⁺ mobilization through plasma membrane-localized IP₃R3 and for NFAT nuclear translocation. Pharmacological inhibition of ITPKB in mice reduced both LPS-induced tissue swelling and the severity of inflammatory arthritis to a similar extent as that induced by the inhibition of NFAT using nanoparticles that delivered an NFAT-inhibiting peptide specifically to phagocytic cells. Our results suggest that ITPKB may represent a promising target for anti-inflammatory therapies that aim to inhibit specific DC functions.

Clinical, Immunological, and Functional Characterization of Six Patients with Very High IgM Levels

Very high IgM levels represent the hallmark of hyper IgM (HIGM) syndromes, a group of primary immunodeficiencies (PIDs) characterized by susceptibility to infections and malignancies. Other PIDs not fulfilling the diagnostic criteria for HIGM syndromes can also be characterized by high IgM levels and susceptibility to malignancies. The aim of this study is to characterize clinical phenotype, immune impairment, and pathogenic mechanism in six patients with very high IgM levels in whom classical HIGM syndromes were ruled out. The immunological analysis included extended B-cell immunophenotyping, evaluation of class switch recombination and somatic hypermutation, and next generation sequencing (NGS). Recurrent or severe infections and chronic lung changes at the diagnosis were reported in five out of six and two out of six patients, respectively. Five out of six patients showed signs of lymphoproliferation and four patients developed malignancies. Four patients showed impaired B-cell homeostasis. Class switch recombination was functional in vivo in all patients. NGS revealed, in one case, a pathogenic mutation in PIK3R1. In a second case, the ITPKB gene, implicated in B- and T-cell development, survival, and activity was identified as a potential candidate gene. Independent of the genetic basis, very high IgM levels represent a risk factor for the development of recurrent infections leading to chronic lung changes, lymphoproliferation, and high risk of malignancies.

Beyond the CRAC: Diversification of ion signaling in B cells

Although calcium signaling and the important role of calcium release–activated calcium channels is well recognized in the context of immune cell signaling, there is a vast diversity of ion channels and transporters that regulate the entry of ions beyond calcium, including magnesium, zinc, potassium, sodium, and chloride. These ions play a critical role in numerous metabolic and cellular processes. The importance of ions in human health and disease is illustrated by the identification of primary immunodeficiencies in patients with mutations in genes encoding ion channels and transporters, as well as the immunological defects observed in individuals with nutritional ion deficiencies. Despite progress in identifying the important role of ions in immune cell development and activation, we are still in the early stages of exploring the diversity of ion channels and transporters and mechanistically understanding the role of these ions in immune cell biology. Here, we review the biology of ion signaling in B cells and the identification of critical ion channels and transporters in B‐cell development, activation, and differentiation into effector cells. Elucidating the role of ion channels and transporters in immune cell signaling is critical for expanding the repertoire of potential therapeutics for the treatment of immune disorders. Moreover, increased understanding of the role of ions in immune cell function will enhance our understanding of the potentially serious consequences of ion deficiencies in human health and disease.

Inhibition of inositol kinase B controls acute and chronic graft-versus-host disease

T-cell activation releases inositol 1,4,5-trisphosphate (IP3), inducing cytoplasmic calcium (Ca2+) influx. In turn, inositol 1,4,5-trisphosphate 3-kinase B (Itpkb) phosphorylates IP3 to negatively regulate and thereby tightly control Ca2+ fluxes that are essential for mature T-cell activation and differentiation and protection from cell death. Itpkb pathway inhibition increases intracellular Ca2+, induces apoptosis of activated T cells, and can control T-cell-mediated autoimmunity. In this study, we employed genetic and pharmacological approaches to inhibit Itpkb signaling as a means of controlling graft-versus-host disease (GVHD). Murine-induced, Itpkb-deleted (Itpkb-/-) T cells attenuated acute GVHD in 2 models without eliminating A20-luciferase B-cell lymphoma graft-versus-leukemia (GVL). A highly potent, selective inhibitor, GNF362, ameliorated acute GVHD without impairing GVL against 2 acute myeloid leukemia lines (MLL-AF9-eGFP and C1498-luciferase). Compared with FK506, GNF362 more selectively deleted donor alloreactive vs nominal antigen-responsive T cells. Consistent with these data and as compared with FK506, GNF362 had favorable acute GVHD and GVL properties against MLL-AF9-eGFP cells. In chronic GVHD preclinical models that have a pathophysiology distinct from acute GVHD, Itpkb-/- donor T cells reduced active chronic GVHD in a multiorgan system model of bronchiolitis obliterans (BO), driven by germinal center reactions and resulting in target organ fibrosis. GNF362 treatment reduced active chronic GVHD in both BO and scleroderma models. Thus, intact Itpkb signaling is essential to drive acute GVHD pathogenesis and sustain active chronic GVHD, pointing toward a novel clinical application to prevent acute or treat chronic GVHD.

Inositol polyphosphates promote T cell-independent humoral immunity via the regulation of Bruton's tyrosine kinase

T cell-independent (TI) B cell response is critical for the early protection against pathogen invasion. The regulation and activation of Bruton's tyrosine kinase (Btk) is known as a pivotal step of B cell antigen receptor (BCR) signaling in TI humoral immunity, as observed in patients with X-linked agammaglobulinemia (XLA) experiencing a high incidence of encapsulated bacterial infections. However, key questions remain as to whether a well-established canonical BCR signaling pathway is sufficient to regulate the activity of Btk. Here, we find that inositol hexakisphosphate (InsP6) acts as a physiological regulator of Btk in BCR signaling. Absence of higher order inositol phosphates (InsPs), inositol polyphosphates, leads to an inability to mount immune response against TI antigens. Interestingly, the significance of InsP6-mediated Btk regulation is more prominent in IgM+ plasma cells. Hence, the present study identifies higher order InsPs as principal components of B cell activation upon TI antigen stimulation and presents a mechanism for InsP-mediated regulation of the BCR signaling.

Proestrus Differentially Regulates Expression of Ion Channel and Calcium Homeostasis Genes in GnRH Neurons of Mice

In proestrus, the changing gonadal hormone milieu alters the physiological properties of GnRH neurons and contributes to the development of the GnRH surge. We hypothesized that proestrus also influences the expression of different ion channel genes in mouse GnRH neurons. Therefore, we performed gene expression profiling of GnRH neurons collected from intact, proestrous and metestrous GnRH-GFP transgenic mice, respectively. Proestrus changed the expression of 37 ion channel and 8 calcium homeostasis-regulating genes. Voltage-gated sodium channels responded with upregulation of three alpha subunits (Scn2a1, Scn3a, and Scn9a). Within the voltage-gated potassium channel class, Kcna1, Kcnd3, Kcnh3, and Kcnq2 were upregulated, while others (Kcna4, Kcnc3, Kcnd2, and Kcng1) underwent downregulation. Proestrus also had impact on inwardly rectifying potassium channel subunits manifested in enhanced expression of Kcnj9 and Kcnj10 genes, whereas Kcnj1, Kcnj11, and Kcnj12 subunit genes were downregulated. The two-pore domain potassium channels also showed differential expression with upregulation of Kcnk1 and reduced expression of three subunit genes (Kcnk7, Kcnk12, and Kcnk16). Changes in expression of chloride channels involved both the voltage-gated (Clcn3 and Clcn6) and the intracellular (Clic1) subtypes. Regarding the pore-forming alpha-1 subunits of voltage-gated calcium channels, two (Cacna1b and Cacna1h) were upregulated, while Cacna1g showed downregulation. The ancillary subunits were also differentially regulated (Cacna2d1, Cacna2d2, Cacnb1, Cacnb3, Cacnb4, Cacng5, Cacng6, and Cacng8). In addition, ryanodine receptor 1 (Ryr1) gene was downregulated, while a transient receptor potential cation channel (Trpm3) gene showed enhanced expression. Genes encoding proteins regulating the intracellular calcium homeostasis were also influenced (Calb1, Hpca, Hpcal1, Hpcal4, Cabp7, Cab 39l, and Cib2). The differential expression of genes coding for ion channel proteins in GnRH neurons at late proestrus indicates that the altering hormone milieu contributes to remodeling of different kinds of ion channels of GnRH neurons, which might be a prerequisite of enhanced cellular activity of GnRH neurons and the subsequent surge release of the neurohormone.

Inositol-triphosphate 3-kinase B confers cisplatin resistance by regulating NOX4-dependent redox balance

How altered metabolism contributes to chemotherapy resistance in cancer cells remains unclear. Through a metabolism-related kinome RNAi screen, we identified inositol-trisphosphate 3-kinase B (ITPKB) as a critical enzyme that contributes to cisplatin-resistant tumor growth. We demonstrated that inositol 1,3,4,5-tetrakisphosphate (IP4), the product of ITPKB, plays a critical role in redox homeostasis upon cisplatin exposure by reducing cisplatin-induced ROS through inhibition of a ROS-generating enzyme, NADPH oxidase 4 (NOX4), which promotes cisplatin-resistant tumor growth. Mechanistically, we identified that IP4 competes with the NOX4 cofactor NADPH for binding and consequently inhibits NOX4. Targeting ITPKB with shRNA or its small-molecule inhibitor resulted in attenuation of NOX4 activity, imbalanced redox status, and sensitized cancer cells to cisplatin treatment in patient-derived xenografts. Our findings provide insight into the crosstalk between kinase-mediated metabolic regulation and platinum-based chemotherapy resistance in human cancers. Our study also suggests a distinctive signaling function of IP4 that regulates NOX4. Furthermore, pharmaceutical inhibition of ITPKB displayed synergistic attenuation of tumor growth with cisplatin, suggesting ITPKB as a promising synthetic lethal target for cancer therapeutic intervention to overcome cisplatin resistance.

Effect of the actin- and calcium-regulating activities of ITPKB on the metastatic potential of lung cancer cells

Inositol-1,4,5-trisphosphate 3-kinase-A (ITPKA) exhibits oncogenic activity in lung cancer cells by regulating Ins(1,4,5)P3-mediated calcium release and cytoskeletal dynamics. Since, in normal cells, ITPKA is mainly expressed in the brain, it is an excellent target for selected therapy of lung cancer. However, ITPKB is strongly expressed in normal lung tissues, but is down-regulated in lung cancer cells by miR-375, assuming that ITPKB might have tumor suppressor activity. In addition, ITPKB binds to F-actin making it likely that, similar to ITPKA, it controls actin dynamics. Thus, the treatment of ITPKA-expressing lung cancer with ITPKA inhibitors simultaneously inhibiting ITPKB may counteract the therapy. Based on these considerations, we analyzed if ITPKB controls actin dynamics and if the protein reduces aggressive progression of lung cancer cells. We found that ITPKB bundled F-actin in cell-free systems. However, the stable expression of ITPKB in H1299 lung cancer cells, exhibiting very low endogenous ITPKB expression, had no significant effect on the actin structure. In addition, our data show that ITPKB negatively controls transmigration of H1299 cells in vitro by blocking Ins(1,4,5)P3-mediated calcium release. On the other hand, colony formation was stimulated by ITPKB, independent of Ins(1,4,5)P3-mediated calcium signals. However, dissemination of H1299 cells from the skin to the lung in NOD scid gamma mice was not significantly affected by ITPKB expression. In summary, ITPKB does not affect the cellular actin structure and does not suppress dissemination of human lung cancer cells in mice. Thus, our initial hypotheses that ITPKB exhibits tumor suppressor activity could not be supported.

Regulation of Hematopoietic Cell Development and Function Through Phosphoinositides

One of the most paramount receptor-induced signal transduction mechanisms in hematopoietic cells is production of the lipid second messenger phosphatidylinositol(3,4,5)trisphosphate (PIP₃) by class I phosphoinositide 3 kinases (PI3K). Defective PIP₃ signaling impairs almost every aspect of hematopoiesis, including T cell development and function. Limiting PIP₃ signaling is particularly important, because excessive PIP₃ function in lymphocytes can transform them and cause blood cancers. Here, we review the key functions of PIP₃ and related phosphoinositides in hematopoietic cells, with a special focus on those mechanisms dampening PIP₃ production, turnover, or function. Recent studies have shown that beyond “canonical” turnover by the PIP₃ phosphatases and tumor suppressors phosphatase and tensin homolog (PTEN) and SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1/2), PIP₃ function in hematopoietic cells can also be dampened through antagonism with the soluble PIP₃ analogs inositol(1,3,4,5)tetrakisphosphate (IP₄) and inositol-heptakisphosphate (IP₇). Other evidence suggests that IP₄ can promote PIP₃ function in thymocytes. Moreover, IP₄ or the kinases producing it limit store-operated Ca²⁺ entry through Orai channels in B cells, T cells, and neutrophils to control cell survival and function. We discuss current models for how soluble inositol phosphates can have such diverse functions and can govern as distinct processes as hematopoietic stem cell homeostasis, neutrophil macrophage and NK cell function, and development and function of B cells and T cells. Finally, we will review the pathological consequences of dysregulated IP₄ activity in immune cells and highlight contributions of impaired inositol phosphate functions in disorders such as Kawasaki disease, common variable immunodeficiency, or blood cancer.

Dietary myo-inositol deficiency decreased intestinal immune function related to NF-κB and TOR signaling in the intestine of young grass carp (Ctenopharyngodon idella)

In this study, we investigated the effects of dietary myo-inositol on the intestinal immune barrier function and related signaling pathway in young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp (221.33 ± 0.84 g) were fed six diets containing graded levels of myo-inositol (27.0, 137.9, 286.8, 438.6, 587.7 and 737.3 mg/kg) for 10 weeks. After the growth trial, fish were challenged with Aeromonas hydrophila. The results indicated that compared with the optimal dietary myo-inositol level, myo-inositol deficiency (27.0 mg/kg diet): (1) decreased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) contents in the proximal intestine (PI), middle intestine (MI) and distal intestine (DI) of young grass carp (P < 0.05). (2) down-regulated the mRNA levels of anti-microbial substance: liver expressed antimicrobial peptide (LEAP) 2A, LEAP-2B, hepcidin, β-defensin-1 and mucin2 in the PI, MI and DI of young grass carp (P < 0.05). (3) up-regulated pro-inflammatory cytokines [IL-1β (not in DI), TNF-α and IL-8], nuclear factor kappa B P65 (not NF-κB P52), c-Rel, IκB kinaseα (IKKα), IKKβ and IKKγ mRNA levels in the PI, MI and DI of young grass carp (P < 0.05); and down-regulated pro-inflammatory cytokines IL-15 (not in DI) and inhibitor of κBα (IκBα) mRNA levels (P < 0.05). (4) down-regulated the mRNA levels of anti-inflammatory cytokines [IL-10 (not in DI), IL-11, IL-4/13B (not IL-4/13A), TGF-β1 and TGF-β2], target of rapamycin (TOR), eIF4E-binding proteins 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6k1) in the PI, MI and DI of young grass carp (P < 0.05). All data indicated that myo-inositol deficiency could decrease fish intestine immunity and cause inflammation under infection of A. hydrophila. Finally, the optimal dietary myo-inositol levels for the ACP and LZ activities in the DI were estimated to be 415.1 and 296.9 mg/kg diet, respectively.

Conformational sampling of membranes by Akt controls its activation and inactivation

The protein kinase Akt controls myriad signaling processes in cells, ranging from growth and proliferation to differentiation and metabolism. Akt is activated by a combination of binding to the lipid second messenger PI(3,4,5)P3 and its subsequent phosphorylation by phosphoinositide-dependent kinase 1 and mechanistic target of rapamycin complex 2. The relative contributions of these mechanisms to Akt activity and signaling have hitherto not been understood. Here, we show that phosphorylation and activation by membrane binding are mutually interdependent. Moreover, the converse is also true: Akt is more rapidly dephosphorylated in the absence of PIP3, an autoinhibitory process driven by the interaction of its PH and kinase domains. We present biophysical evidence for the conformational changes in Akt that accompany its activation on membranes, show that Akt is robustly autoinhibited in the absence of PIP3 irrespective of its phosphorylation, and map the autoinhibitory PH-kinase interface. Finally, we present a model for the activation and inactivation of Akt by an ordered series of membrane binding, phosphorylation, dissociation, and dephosphorylation events.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Non-canonical antagonism of PI3K by the kinase Itpkb delays thymocyte β-selection and renders it Notch-dependent

β-selection is the most pivotal event determining αβ T cell fate. Here, surface-expression of a pre-T cell receptor (pre-TCR) induces thymocyte metabolic activation, proliferation, survival and differentiation. Besides the pre-TCR, β-selection also requires co-stimulatory signals from Notch receptors - key cell fate determinants in eukaryotes. Here, we show that this Notch-dependence is established through antagonistic signaling by the pre-TCR/Notch effector, phosphoinositide 3-kinase (PI3K), and by inositol-trisphosphate 3-kinase B (Itpkb). Canonically, PI3K is counteracted by the lipid-phosphatases Pten and Inpp5d/SHIP-1. In contrast, Itpkb dampens pre-TCR induced PI3K/Akt signaling by producing IP₄, a soluble antagonist of the Akt-activating PI3K-product PIP₃. Itpkb^-/- thymocytes are pre-TCR hyperresponsive, hyperactivate Akt, downstream mTOR and metabolism, undergo an accelerated β-selection and can develop to CD4⁺CD8⁺ cells without Notch. This is reversed by inhibition of Akt, mTOR or glucose metabolism. Thus, non-canonical PI3K-antagonism by Itpkb restricts pre-TCR induced metabolic activation to enforce coincidence-detection of pre-TCR expression and Notch-engagement.

DOI:http://dx.doi.org/10.7554/eLife.10786.001

T cells defend our body against cancer and infectious agents such as viruses. However, they can also cause rheumatoid arthritis and other autoimmune diseases by attacking healthy tissue. T cells recognize target cells via receptor proteins on their surface. To maximize the variety of infections and cancers our immune system can recognize, we generate millions of T cells with different T cell receptors every day.

To ensure T cells work correctly, T cell receptors are tested at various checkpoints. The first checkpoint involves a process called beta (β) selection, during which T cells produce their first T cell receptor – the so-called pre-T cell receptor. This receptor causes T cells to divide and mature, and sets their future identity or “fate”. To complete β-selection, T cells must also receive signals from another surface receptor – one that belongs to the Notch family, which determines cell fate in many different tissues.

The Notch receptor and the pre-T cell receptor both activate an enzyme called PI3K – a key mediator of β-selection. But the pre-T cell receptor also activates another enzyme called Itpkb that is required for T cell development. Westernberg, Conche et al. have now investigated how these different proteins and signaling processes work and interact during β-selection, using mice that lack several immune genes, including the gene that produces Itpkb.

The results of the experiments show that during β-selection, Itpkb limits the ability of PI3K to activate some of its key target proteins. This “dampened” PI3K signaling ensures that both the pre-T cell receptor and the Notch receptor must be activated to trigger T cell maturation. Without Itpkb, β-selection can occur in the absence of Notch signaling.

As Notch signaling is important for determining the fate of many different cell types, Westernberg, Conche et al.’s findings raise the possibility that Itpkb might also regulate cell fate determination in other tissues. Moreover, Itpkb may suppress tumor development, because excessive PI3K signaling drives many cancers.

DOI:http://dx.doi.org/10.7554/eLife.10786.002

Common variable immunodeficiency associated with microdeletion of chromosome 1q42.1-q42.3 and inositol 1,4,5-trisphosphate kinase B (ITPKB) deficiency

Common variable immunodeficiency (CVID) is a heterogenous disorder characterized by hypogammaglobulinemia and impaired specific antibody response and increased susceptibility to infections, autoimmunity and malignancies. A number of gene mutations, including ICOS, TACI and BAFF-R, and CD19, CD20, CD21, CD81, MSH5 and LRBA have been described; however, they account for approximately 20–25% of total cases of CVID. In this study, we report a patient with CVID with an intrinsic microdeletion of chromosome 1q42.1-42.3, where gene for inositol 1,3,4, trisphosphate kinase β (ITPKB) is localized. ITPKB has an important role in the development, survival and function of B cells. In this subject, the expression of ITPKB mRNA as well as ITKPB protein was significantly reduced. The sequencing of ITPKB gene revealed three variants, two of them were missense variants and third was a synonymous variant; the significance of each of them in relation to CVID is discussed. This case suggests that a deficiency of ITPKB may have a role in CVID.

Whole exome sequencing of relapsed/refractory patients expands the repertoire of somatic mutations in diffuse large B-cell lymphoma

Despite the many efforts already spent to enumerate somatic mutations in diffuse large B-cell lymphoma (DLBCL), previous whole-genome and whole-exome studies conducted on patients of mixed outcomes failed at characterizing the 30% of patients who will relapse or resist current immunochemotherapies. To address this issue, we performed whole-exome sequencing of normal/tumoral DNA pairs in 14 relapsed/refractory (R/R) patients subclassified by full-transcriptome arrays (six activated B-cell like, three germinal center B-cell like, and five primary mediastinal B-cell lymphomas), from the LNH-03 LYSA clinical trial program. Aside from well-known DLBCL features, gene and pathway level recurrence analyses proposed several interesting leads including TBL1XR1 and activating mutations in IRF4 or in the insulin regulation pathway. Sequencing-based copy number analysis defined 23 short recurrently altered regions involving genes such as REL, CDKN2A, HYAL2, and TP53. Moreover, it highlighted mutations in genes such as GNA13, CARD11, MFHAS1, and PCLO as associated with secondary variant allele amplification events. The five primary mediastinal B-cell lymphomas (PMBL), while unexpected in a R/R cohort, showed a significantly higher mutation rate (P = 0.003) and provided many insights on this classical Hodgkin lymphoma related subtype. Novel genes such as XPO1, MFHAS1, and ITPKB were found particularly mutated, along with various cytokine-based signaling pathways. Among these analyses, somatic events in the NF-κB pathway were found preponderant in the three DLBCL subtypes, confirming its major implication in DLBCL aggressiveness and pinpointing several new candidate genes.

Inhibition of the Inositol Kinase Itpkb Augments Calcium Signaling in Lymphocytes and Reveals a Novel Strategy to Treat Autoimmune Disease

Emerging approaches to treat immune disorders target positive regulatory kinases downstream of antigen receptors with small molecule inhibitors. Here we provide evidence for an alternative approach in which inhibition of the negative regulatory inositol kinase Itpkb in mature T lymphocytes results in enhanced intracellular calcium levels following antigen receptor activation leading to T cell death. Using Itpkb conditional knockout mice and LMW Itpkb inhibitors these studies reveal that Itpkb through its product IP4 inhibits the Orai1/Stim1 calcium channel on lymphocytes. Pharmacological inhibition or genetic deletion of Itpkb results in elevated intracellular Ca²⁺ and induction of FasL and Bim resulting in T cell apoptosis. Deletion of Itpkb or treatment with Itpkb inhibitors blocks T-cell dependent antibody responses in vivo and prevents T cell driven arthritis in rats. These data identify Itpkb as an essential mediator of T cell activation and suggest Itpkb inhibition as a novel approach to treat autoimmune disease.

The impact of phosphorus on the immune system and the intestinal microbiota with special focus on the pig

There is increasing interest in dietary ingredients that are appropriate to support digestive and immune functions, but also maintain a stable microbial ecosystem in the gastrointestinal tract (GIT), particularly in weaned pigs. P is an essential nutrient for both microbes and their host, as it is involved, for example, in bone formation, energy metabolism, cellular signalling and stabilisation of cell membranes. Non-ruminant animals have limited access to phytate, the main storage form of P in plant seeds. The release of P bound to phytate requires phytase activity of plant or microbial origin, resulting in the formation of variable phosphorylated inositol phosphates (InsPs). The present review focuses on interactions between variations in dietary P supply, the immune system of the host, and the intestinal microbial ecosystem. Although results on the interaction between P and the immune system are inconsistent, several studies in different species have shown a positive impact of dietary P and phytase addition on the adaptive immune response. Recent studies with pigs suggest that P supply may influence intestinal microbial composition and activity. Individual InsPs or phosphate may also affect properties of pathogenic micro-organisms, such as metabolism or virulence. In conclusion, P may be considered as part of an integrated approach to support immune functions and maintain a stable microbial ecosystem in the GIT, thereby providing a barrier against potential pathogens. Within this regard, differences in phytate-P content and intrinsic phytase activity of plant feedstuffs, as well as the formation of individual InsPs, have to be taken into account.

Regulation of NGF-driven neurite outgrowth by Ins(1,4,5)P3 kinase is specifically associated with the two isoenzymes Itpka and Itpkb in a model of PC12 cells

Four inositol phosphate kinases catalyze phosphorylation of the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3 ] to inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4 ]: these enzymes comprise three isoenzymes of inositol 1,4,5-trisphosphate 3-kinase (Itpk), referred to as Itpka, Itpkb and Itpkc, and the inositol polyphosphate multikinase (IPMK). The four enzymes that act on Ins(1,4,5)P3 are all expressed in rat pheochromocytoma PC12 cells, a model that is used to study neurite outgrowth induced by nerve growth factor (NGF). We compared the effect of over-expression of the four GFP-tagged kinases on NGF-induced neurite outgrowth. Our data show that over-expression of the Itpka and Itpkb isoforms inhibits NGF-induced neurite outgrowth, but over-expression of Itpkc and IPMK does not. Surprisingly, over-expression of the N-terminal F-actin binding domain of Itpka, which lacks catalytic activity, was as effective at inhibiting neurite outgrowth as the full-length enzyme. Neurite length was also significantly decreased in cells over-expressing Itpka and Itpkb but not Itpkc or IPMK. This result did not depend on the over-expression level of any of the kinases. PC12 cells over-expressing GFP-tagged kinase-dead mutants Itpka/b have shorter neurites than GFP control cells. The decrease in neurite length was never as pronounced as observed with wild-type GFP-tagged Itpka/b. Finally, the percentage of neurite-bearing cells was increased in cells over-expressing the membranous type I Ins(1,4,5)P3 5-phosphatase. We conclude that Itpka and Itpkb inhibit neurite outgrowth through both F-actin binding and localized Ins(1,4,5)P3 3-kinase activity. Itpkc and IPMK do not influence neurite outgrowth or neurite length in this model.

hCD2-iCre and Vav-iCre mediated gene recombination patterns in murine hematopoietic cells

Cre-recombinase mediated conditional deletion of Lox-P site flanked ("floxed") genes is widely used for functional gene annotation in mice. Many different Cre-transgenic mouse lines have been developed for cell-type specific gene disruption. But often, the precise tissue-patterns of Cre activity remain incompletely characterized. Two widely used transgenes for conditional gene recombination in hematopoietic cells are Vav-iCre driven from the murine Vav1 promotor, and hCD2-iCre driven from the human CD2 promotor. Vav-iCre expresses active Cre in fetal and adult hematopoietic stem cells and all descendants, hCD2-iCre in immature and mature B and T lymphocytes. To better characterize which hematopoietic cells contain hCD2-iCre activity, we compared EYFP fluorescence in hCD2-iCre+/- R26-stop-EYFP+/- and Vav-iCre+/- R26-stop-EYFP+/-mice. R26-stop-EYFP ubiquitously encodes EYFP preceded by a floxed stop cassette. By removing it, Cre activity induces measurable EYFP expression. Our results confirm the known activity patterns for both Cre transgenes and unveil additional hCD2-iCre mediated reporter gene recombination in common lymphoid progenitors, in natural killer cells and their progenitors, and in plasmacytoid and conventional dendritic cells. This supports previously proposed common lymphoid origins for natural killer cells and subsets of dendritic cells, and indicates the need to consider pleiotropic effects when studying hCD2-iCre mediated conditional knockout mice. Vav-iCre+/- R26-stop-EYFP+/-mice did not show the non-hematopoietic recombination in vascular endothelial cells seen in other Vav-Cre mouse lines, but displayed an unexpected Vav-iCre mediated recombination in a bone cell subset lacking hematopoietic markers. This pinpoints the need to consider stromal cell contributions to phenotypes of Vav-iCre mediated conditional knockout mice. Altogether, our data provide the first detailed assessment of hCD2-iCre and Vav-iCre mediated deletion of floxed genes during lymphocyte development from hematopoietic stem cells and open up novel applications for either Cre-transgenic mouse line.

IP3 3-kinase B controls hematopoietic stem cell homeostasis and prevents lethal hematopoietic failure in mice

Tight regulation of hematopoietic stem cell (HSC) homeostasis ensures lifelong hematopoiesis and prevents blood cancers. The mechanisms balancing HSC quiescence with expansion and differentiation into hematopoietic progenitors are incompletely understood. Here, we identify Inositol-trisphosphate 3-kinase B (Itpkb) as an essential regulator of HSC homeostasis. Young Itpkb(-/-) mice accumulated phenotypic HSC, which were less quiescent and proliferated more than wild-type (WT) controls. Itpkb(-/-) HSC downregulated quiescence and stemness associated, but upregulated activation, oxidative metabolism, protein synthesis, and lineage associated messenger RNAs. Although they had normal-to-elevated viability and no significant homing defects, Itpkb(-/-) HSC had a severely reduced competitive long-term repopulating potential. Aging Itpkb(-/-) mice lost hematopoietic stem and progenitor cells and died with severe anemia. WT HSC normally repopulated Itpkb(-/-) hosts, indicating an HSC-intrinsic Itpkb requirement. Itpkb(-/-) HSC showed reduced colony-forming activity and increased stem-cell-factor activation of the phosphoinositide-3-kinase (PI3K) effectors Akt/mammalian/mechanistic target of rapamycin (mTOR). This was reversed by treatment with the Itpkb product and PI3K/Akt antagonist IP4. Transcriptome changes and biochemistry support mTOR hyperactivity in Itpkb(-/-) HSC. Treatment with the mTOR-inhibitor rapamycin reversed the excessive mTOR signaling and hyperproliferation of Itpkb(-/-) HSC without rescuing colony forming activity. Thus, we propose that Itpkb ensures HSC quiescence and function through limiting cytokine-induced PI3K/mTOR signaling and other mechanisms.

Lipid and Protein Co-Regulation of PI3K Effectors Akt and Itk in Lymphocytes

The phosphoinositide 3-kinase (PI 3-kinase, PI3K) pathway transduces signals critical for lymphocyte function. PI3K generates the phospholipid PIP₃ at the plasma membrane to recruit proteins that contain pleckstrin homology (PH) domains – a conserved domain found in hundreds of mammalian proteins. PH domain–PIP₃ interactions allow for rapid signal propagation and confer a spatial component to these signals. The kinases Akt and Itk are key PI3K effectors that bind PIP₃ via their PH domains and mediate vital processes – such as survival, activation, and differentiation – in lymphocytes. Here, we review the roles and regulation of PI3K signaling in lymphocytes with a specific emphasis on Akt and Itk. We also discuss these and other PH domain-containing proteins as they relate more broadly to immune cell function. Finally, we highlight the emerging view of PH domains as multifunctional protein domains that often bind both lipid and protein substrates to exert their effects.

Molecular control of PtdIns(3,4,5)P3 signaling in neutrophils

Neutrophils play critical roles in innate immunity and host defense. However, excessive neutrophil accumulation or hyper-responsiveness of neutrophils can be detrimental to the host system. Thus, the response of neutrophils to inflammatory stimuli needs to be tightly controlled. Many cellular processes in neutrophils are mediated by localized formation of an inositol phospholipid, phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3), at the plasma membrane. The PtdIns(3,4,5)P3 signaling pathway is negatively regulated by lipid phosphatases and inositol phosphates, which consequently play a critical role in controlling neutrophil function and would be expected to act as ideal therapeutic targets for enhancing or suppressing innate immune responses. Here, we comprehensively review current understanding about the action of lipid phosphatases and inositol phosphates in the control of neutrophil function in infection and inflammation.

Role of Calcium Signaling in B Cell Activation and Biology

Increase in intracellular levels of calcium ions (Ca2+) is one of the key triggering signals for the development of B cell response to the antigen. The diverse Ca2+ signals finely controlled by multiple factors participate in the regulation of gene expression, B cell development, and effector functions. B cell receptor (BCR)-initiated Ca2+ mobilization is sourced from two pathways: one is the release of Ca2+ from the intracellular stores, endoplasmic reticulum (ER), and other is the prolonged influx of extracellular Ca2+ induced by depleting the stores via store-operated calcium entry (SOCE) and calcium release-activated calcium (CRAC) channels. The identification of stromal interaction molecule 1(STIM1), the ER Ca2+ sensor, and Orai1, a key subunit of the CRAC channel pore, has now provided the tools to understand the mode of Ca2+ influx regulation and physiological relevance. Herein, we discuss our current understanding of the molecular mechanisms underlying BCR-triggered Ca2+ signaling as well as its contribution to the B cell biological processes and diseases.

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.

Late stages of hematopoiesis and B cell lymphopoiesis are regulated by α-synuclein, a key player in Parkinson's disease

α-Synuclein plays a crucial role in Parkinson's disease and dementias defined as synucleinopathies. α-Synuclein is expressed in hematopoietic and immune cells, but its functions in hematopoiesis and immune responses are unknown. We utilized α-synuclein(-/-) (KO) mice to investigate its role in hematopoiesis and B cell lymphopoiesis. We demonstrated hematologic abnormalities including mild anemia, smaller platelets, lymphopenia but relatively normal early hematopoiesis in KO mice compared to wild-type (WT) as measured in hematopoietic stem cells and progenitors of the different cell lineages. However, the absolute number of B220(+)IgM(+) B cells in bone marrow was reduced by 4-fold in KO mice (WT: 104±23×10(5) vs. KO: 27±5×10(5)). B cells were also reduced in KO spleens associated with effacement of splenic and lymph node architecture. KO mice showed reduced total serum IgG but no abnormality in serum IgM was noted. When KO mice were challenged with a T cell-dependent antigen, production of antigen specific IgG1 and IgG2b was abolished, but antigen specific IgM was not different from WT mice. Our study shows hematologic abnormalities including anemia and smaller platelets, reduced B cell lymphopoiesis and defects in IgG production in the absence of α-synuclein. This is the first report to show an important role of α-synuclein late in hematopoiesis, B cell lymphopoiesis and adaptive immune response.

Modulation of Epidermal Growth Factor Stimulated ERK Phosphorylation and Cell Motility by Inositol Trisphosphate Kinase

Epidermal growth factor [EGF] mediated stimulation of its receptor in endothelial cell [EC] is accompanied by phosphorylation of the EGF-receptor [EGFR] and activation of phospholipase C-γ, resulting in the breakdown of phosphatidylinositol(4,5)-bisphosphate and generating inositol (1,4,5)-trisphosphate [IP₃] and diacylglycerol. IP₃ thus formed can be further converted to inositol (1,3,4,5)-tetrakisphosphate [IP₄] by an enzyme called IP₃-kinase [IP₃K]. In this study we have investigated the effect of modulation of intracellular IP₃K activity by the use of an inhibitor, 2-trifluoromethyl [6-(4-nitrobenzyl)-purine] [IP₃KI] and siRNA against IP₃KB on EGF-induced ERK-phosphorylation and cell motility. EGF stimulated ERK-phosphorylation that has been implicated in EGF-stimulated cell migration was inhibited by both IP₃KI and siRNA against IP₃KB. Inhibition of ERK-phosphorylation was accompanied by decreased cell migration in the presence of IP₃KI.

Inositol 1,4,5-trisphosphate 3-kinase B (Itpkb) controls survival, proliferation and cytokine production in mouse peripheral T cells

Mice genetically-deficient for the B isoform of the inositol 1,4,5-trisphosphate 3-kinase (or Itpkb) have a severe defect in thymocytes differentiation and thus lack peripheral T cells. In order to study the functional role of Itpkb in peripheral T cells, we constructed a new mouse where a transgene encoding mouse Itpkb is specifically and transiently expressed in thymocytes of Itpkb(-)(/)(-) mice. This allows a partial rescue of mature thymocyte/T cell differentiation and thus the functional characterization of peripheral T cells lacking Itpkb. We show here that Itpkb(-)(/)(-) CD4(+) and CD8(+) peripheral T cells present important functional alterations. Indeed, an increased activated/memory phenotype as well as a decreased proliferative capacity and survival were detected in these T cells. These Itpkb-deficient peripheral T cells have also an increased capacity to secrete cytokines upon stimulation. Together, our present results define the important role of Itpkb in peripheral mature T cell fate and function in mouse, suggesting a potential role for Itpkb in autoimmunity.

The intramembrane protease Sppl2a is required for B cell and DC development and survival via cleavage of the invariant chain

B cell development requires tight regulation to allow for the generation of a diverse repertoire while preventing the development of autoreactive cells. We report, using N-ethyl-N-nitrosourea (ENU)-induced mutagenesis, the identification of a mutant mouse (chompB) with a block in early B cell development. The blockade occurs after the transitional 1 (T1) stage and leads to a decrease in mature B cell subsets and deficits in T cell-dependent antibody responses. Additionally, chompB mice have decreases in myeloid dendritic cells (DCs). The mutation was mapped to the intramembrane protease signal peptide peptidase-like 2a (Sppl2a), a gene not previously implicated in immune cell development. Proteomic analysis identified the invariant chain (CD74) as a key substrate of Sppl2a and suggests that regulated intramembrane proteolysis of CD74 by Sppl2a contributes to B cell and DC survival. Moreover, these data suggest that modulation of Sppl2a may be a useful therapeutic strategy for treatment of B cell dependent autoimmune disorders.

Inositol tetrakisphosphate limits NK cell effector functions by controlling PI3K signaling

Natural killer (NK) cells have important functions in cancer immunosurveillance, BM allograft rejection, fighting infections, tissue homeostasis, and reproduction. NK cell-based therapies are promising treatments for blood cancers. Overcoming their currently limited efficacy requires a better understanding of the molecular mechanisms controlling NK cell development and dampening their effector functions. NK cells recognize the loss of self-antigens or up-regulation of stress-induced ligands on pathogen-infected or tumor cells through invariant NK cell receptors (NKRs), and then kill such stressed cells. Two second-messenger pathways downstream of NKRs are required for NK cell maturation and effector responses: PIP(3) generation by PI3K and generation of diacylglycerol and IP(3) by phospholipase-Cγ (PLCγ). In the present study, we identify a novel role for the phosphorylated IP(3) metabolite inositol (1,3,4,5)tetrakisphosphate (IP(4)) in NK cells. IP(4) promotes NK cell terminal differentiation and acquisition of a mature NKR repertoire. However, in mature NK cells, IP(4) limits NKR-induced IFNγ secretion, granule exocytosis, and target-cell killing, in part by inhibiting the PIP(3) effector-kinase Akt. This identifies IP(4) as an important novel regulator of NK cell development and function and expands our understanding of the therapeutically important mechanisms dampening NK cell responses. Our results further suggest that PI3K regulation by soluble IP(4) is a broadly important signaling paradigm.

IP3 3-kinase opposes NGF driven neurite outgrowth

The inositol (1,4,5) trisphosphate 3-kinases comprise a family of enzymes (A, B, and C) that phosphorylate the calcium mobilising molecule inositol (1,4,5) trisphosphate (IP₃) to generate inositol (1,3,4,5) tetrakisphosphate. This molecule can function as a second messenger, but its roles are not completely understood. The A isoform of inositol (1,4,5) trisphosphate 3-kinase localises to filamentous actin within dendritic spines in the hippocampus and is implicated in the regulation of spine morphology and long term potentiation, however the mechanisms through which it signals in neuronal cells are not completely understood. We have used NGF driven neurite outgrowth from PC12 cells as a platform to examine the impact of signaling via inositol (1,4,5) trisphosphate 3-kinase activity in a neuronal cell. We have found that the catalytic activity of the enzyme opposes neurite outgrowth, whilst pharmacological inhibition of inositol (1,4,5) trisphosphate 3-kinase leads to a significant increase in neurite outgrowth, and we show that the reduction in neurite outgrowth in response to inositol (1,4,5) trisphosphate 3-kinase activity correlates with reduced ERK activity as determined by western blotting using phosphorylation-specific antibodies. Our findings suggest a novel neuronal signaling pathway linking metabolism of IP₃ to signaling via ERK.

Defining signal transduction by inositol phosphates

Ins(1,4,5)P(3) is a classical intracellular messenger: stimulus-dependent changes in its levels elicits biological effects through its release of intracellular Ca(2+) stores. The Ins(1,4,5)P(3) response is "switched off" by its metabolism to a range of additional inositol phosphates. These metabolites have themselves come to be collectively described as a signaling "family". The validity of that latter definition is critically examined in this review. That is, we assess the strength of the hypothesis that Ins(1,4,5)P(3) metabolites are themselves "classical" signals. Put another way, what is the evidence that the biological function of a particular inositol phosphate depends upon stimulus dependent changes in its levels? In this assessment, examples of an inositol phosphate acting as a cofactor (i.e. its function is not stimulus-dependent) do not satisfy our signaling criteria. We conclude that Ins(3,4,5,6)P(4) is, to date, the only Ins(1,4,5)P(3) metabolite that has been validated to act as a second messenger.

Tripartite motif containing protein 27 negatively regulates CD4 T cells by ubiquitinating and inhibiting the class II PI3K-C2β

The K(+) channel KCa3.1 is required for Ca(2+) influx and the subsequent activation of CD4 T cells. The class II phosphatidylinositol 3 kinase C2β (PI3KC2β) is activated by the T-cell receptor (TCR) and is critical for KCa3.1 channel activation. Tripartite motif containing protein 27 (TRIM27) is a member of a large family of proteins that function as Really Interesting New Gene (RING) E3 ubiquitin ligases. We now show that TRIM27 functions as an E3 ligase and mediates lysine 48 polyubiquitination of PI3KC2β, leading to a decrease in PI3K enzyme activity. By inhibiting PI3KC2β, TRIM27 also functions to negatively regulate CD4 T cells by inhibiting KCa3.1 channel activity and TCR-stimulated Ca(2+) influx and cytokine production in Jurkat, primary human CD4 T cells, and Th0, Th1, and Th2 CD4 T cells generated from TRIM27(-/-) mice. These findings provide a unique mechanism for regulating class II PI3Ks, and identify TRIM27 as a previously undescribed negative regulator of CD4 T cells.

Age-related changes in gene expression are accelerated in Alzheimer's disease

In the normal brain, age is associated with changes in gene expression. Age is also a prominent risk factor for Alzheimer's disease (AD), where clinical features are similar to age-related decreases in cognitive performance. We hypothesized that some age-related changes in gene expression are accelerated in AD patients. To study this, we selected 10 candidate genes earlier shown by microarray analysis to be differentially expressed in AD (Emilsson et al., [2006] Neurobiol Dis 21:618-625). Using real-time PCR analysis and a control based statistical model, we investigated age-related changes in mRNA levels in a large collection of human brain postmortem tissues from AD patients and controls. Our results demonstrate that the age-related changes in gene expression are manifested earlier in AD. Furthermore, five of the genes (ITPKB, RGS4, RAB3A, STMN1, SYNGR3) have in common an involvement in neuronal calcium dependent signaling, a cellular process previously related to both AD and aging. These observations suggest that coordinated transcriptional changes associated with ageing and calcium homeostasis in the human brain are accelerated in patients with AD. Our results point to the possibility that the activity of these genes can be used in the future as a palette of biomarkers for predicting disease risk in young individuals.

Human inositol 1,4,5-trisphosphate 3-kinase isoform B (IP3KB) is a nucleocytoplasmic shuttling protein specifically enriched at cortical actin filaments and at invaginations of the nuclear envelope

Recent studies have shown that inositol 1,4,5-trisphosphate 3-kinase isoform B (IP3KB) possesses important roles in the development of immune cells. IP3KB can be targeted to multiple cellular compartments, among them nuclear localization and binding in close proximity to the plasma membrane. The B isoform is the only IP3K that is almost ubiquitously expressed in mammalian cells. Detailed mechanisms of its targeting regulation will be important in understanding the role of Ins(1,4,5)P(3) phosphorylation on subcellular calcium signaling and compartment-specific initiation of pathways leading to regulatory active higher phosphorylated inositol phosphates. Here, we identified an exportin 1-dependent nuclear export signal ((134)LQRELQNVQV) and characterized the amino acids responsible for nuclear localization of IP3KB ((129)RKLR). These two targeting domains regulate the amount of nuclear IP3KB in cells. We also demonstrated that the localization of IP3KB at the plasma membrane is due to its binding to cortical actin structures. Intriguingly, all three of these targeting activities reside in one small polypeptide segment (amino acids 104-165), which acts as a multitargeting domain (MTD). Finally, a hitherto unknown subnuclear localization of IP3KB could be demonstrated in rapidly growing H1299 cells. IP3KB is specifically enriched at nuclear invaginations extending perpendicular between the apical and basal surface of the nucleus of these flat cells. Such nuclear invaginations are known to be involved in Ins(1,4,5)P(3)-mediated Ca(2+) signaling of the nucleus. Our findings indicate that IP3KB not only regulates cytoplasmic Ca(2+) signals by phosphorylation of subplasmalemmal and cytoplasmic Ins(1,4,5)P(3) but may also be involved in modulating nuclear Ca(2+) signals generated from these nuclear envelope invaginations.

Inhibitor and activator: dual functions for SHIP in immunity and cancer

SHIP1 is at the nexus of intracellular signaling pathways in immune cells that mediate bone marrow (BM) graft rejection, production of inflammatory and immunosuppressive cytokines, immunoregulatory cell formation, the BM niche that supports development of the immune system, and immune cancers. This review summarizes how SHIP participates in normal immune physiology or the pathologies that result when SHIP is mutated. This review also proposes that SHIP can have either inhibitory or activating roles in cell signaling that are determined by whether signaling pathways distal to PI3K are promoted by SHIP's substrate (PI(3,4,5)P(3) ) or its product (PI(3,4)P(2) ). This review also proposes the "two PIP hypothesis" that postulates that both SHIP's product and its substrate are necessary for a cancer cell to achieve and sustain a malignant state. Finally, due to the recent discovery of small molecule antagonists and agonists for SHIP, this review discusses potential therapeutic settings where chemical modulation of SHIP might be of benefit.

Lipid signaling in T-cell development and function

Second messenger molecules relay, amplify, and diversify cell surface receptor signals. Two important examples are phosphorylated D-myo-inositol derivatives, such as phosphoinositide lipids within cellular membranes, and soluble inositol phosphates. Here, we review how phosphoinositide metabolism generates multiple second messengers with important roles in T-cell development and function. They include soluble inositol(1,4,5)trisphosphate, long known for its Ca(2+)-mobilizing function, and phosphatidylinositol(3,4,5)trisphosphate, whose generation by phosphoinositide 3-kinase and turnover by the phosphatases PTEN and SHIP control a key "hub" of TCR signaling. More recent studies unveiled important second messenger functions for diacylglycerol, phosphatidic acid, and soluble inositol(1,3,4,5)tetrakisphosphate (IP(4)) in immune cells. Inositol(1,3,4,5)tetrakisphosphate acts as a soluble phosphatidylinositol(3,4,5)trisphosphate analog to control protein membrane recruitment. We propose that phosphoinositide lipids and soluble inositol phosphates (IPs) can act as complementary partners whose interplay could have broadly important roles in cellular signaling.

Regulation of B cell survival, development and function by inositol 1,4,5-trisphosphate 3-kinase B (Itpkb)

In mammals, Ins(1,4,5)P3, the well known calcium mobilization messenger, is phosphorylated in the cytosol at the 3-position of the inositol ring to yield Ins(1,3,4,5)P4 by Ins(1,4,5)P3 3-kinases A, B and C isoforms as well as by inositol polyphosphate multikinase (Ipmk). Studies in gene-deficient mice have revealed that these enzymes and Ins(1,3,4,5)P4, their reaction product, play essential role in multiple physiological processes, ranging from synaptic plasticity, hematopoietic cell survival, development and function, to mRNA export, transcriptional regulation and chromatin remodelling. Rather than to provide an unique and “universal” mechanism of Ins(1,3,4,5)P4 action, these studies in genetically-modified mice point for a role of this inositide in the control of calcium mobilization, of the subcellular localisation of PH domain-containing target proteins, and of higher inositol phosphate production. Mice deficient for the B isoform of inositol 1,4,5-trisphosphate 3-kinase (Itpkb) develop profound alterations in T and B cells as well as in neutrophils and mast cells. Our recent studies indicate that the 3-kinase Itpkb and Ins(1,3,4,5)P4 are important for the survival of naïve mature B cells and the control of proapoptotic Bim protein expression, rather than for the control of B cell transition from one developmental stage to another. They also suggest that Itpkb is an important component in the control of B cell anergy.

Tonic BCR signaling represses receptor editing via Raf- and calcium-dependent signaling pathways

Light chain receptor editing is an important mechanism that prevents B cell self-reactivity. We have previously shown that tonic signaling through the BCR represses RAG expression at the immature B cell stage, and that initiation of light chain rearrangements occurs in the absence of these tonic signals in an in vitro model of B cell development. To further test our hypothesis we studied the effect of itpkb deficiency (itpkb(-/-) mice) or Raf hyper-activation (Raf-CAAX transgenic mice), two mutations that enhance BCR signaling, on receptor editing in an in vivo model. This model relies on transferring bone marrow from wild-type or mutant mice into mice expressing an anti-kappa light chain transgene. The anti-kappa transgene induces receptor editing of all kappa light chain expressing B cells, leading to a high frequency of lambda light chain expressing B cells. Anti-κ transgenic recipients of bone marrow from itpkb(-/-) or Raf-CAAX mice showed lower levels of editing to λ light chain than did non-transgenic control recipients. These results provide evidence in an in vivo model that enhanced BCR signaling at the immature B cell stage of development suppresses light chain receptor editing.