Non-radioactive, isomer-specific inositol phosphate mass determinations: high-performance liquid chromatography-micro-metal-dye detection strongly improves speed and sensitivity of analyses from cells and micro-enzyme assays

Isomer-selective analysis of inositol phosphates with differential isotope labelling by phosphate methylation using liquid chromatography with tandem mass spectrometry

Inositol phosphates belong to a family of structurally diverse signaling molecules playing crucial role in Ca²⁺ release from intracellular storage vesicles. There are many possibilities of phosphorylation, including their degree and position. Inositol (1,4,5) trisphosphate has been well recognized as the most important second messenger among this family. It remains a challenge to analyse the entire inositol phosphate metabolite family due to its structural complexity, high polarity, and high phosphate density. In this study, we have established an improved UHPLC-ESI-MS/MS method based on a differential isotope labelling methylation strategy. An SPE extraction kit composed of TiO2 and PTFE filter was employed for sample preparation which provided good extraction performance. Samples were methylated (light label) to neutralize the phosphate groups and give better performance in liquid chromatography. Regioisomers and inositol phosphates differing in their number of phosphate residues were successfully separated after optimization on a core-shell cholesterylether-bonded RP-type column (Cosmocore 2.6Cholester) using methanol as organic modifier. Triple quadrupole MS detection was based on selected reaction monitoring (SRM) acquisition with characteristic fragments. Stable isotope labeling methylation was performed to generate internal standards (heavy label). Limits of quantification from 0.32 to 0.89 pmol on column was achieved. This method was validated to be suitable for inositol phosphate profiling in biological samples. After application in cultured HeLa cells, NIST SRM1950 plasma, and human platelets, distinct inositol profiles were obtained. This newly established method exhibited improved analytical performance, holding the potential to advance the understanding of inositol phosphate signaling.

Mechanisms and functions of calcium microdomains produced by ORAI channels, d-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors

With the discovery of local Ca²⁺ signals in the 1990s the concept of 'elementary Ca²⁺ signals' and 'fundamental Ca²⁺ signals' was developed. While 'elementary Ca²⁺signals' relate to optical signals gained by activity of small clusters of Ca²⁺channels, 'fundamental signals' describe such optical signals that arise from opening of single Ca²⁺channels. In this review, we discuss (i) concepts of local Ca²⁺ signals and Ca²⁺ microdomains, (ii) molecular mechanisms underlying Ca²⁺ microdomains, (iii) functions of Ca²⁺ microdomains, and (iv) mathematical modelling of Ca²⁺ microdomains. We focus on Ca²⁺ microdomains produced by ORAI channels, D-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors. In summary, research on local Ca²⁺ signals in different cell models aims to better understand how cells use the Ca²⁺ toolkit to produce Ca²⁺ microdomains as relevant signals for specific cellular responses, but also how local Ca²⁺ signals as building blocks merge into global Ca²⁺ signaling.

Analytical Methods for Determination of Phytic Acid and Other Inositol Phosphates: A Review

From the early precipitation-based techniques, introduced more than a century ago, to the latest development of enzymatic bio- and nano-sensor applications, the analysis of phytic acid and/or other inositol phosphates has never been a straightforward analytical task. Due to the biomedical importance, such as antinutritional, antioxidant and anticancer effects, several types of methodologies were investigated over the years to develop a reliable determination of these intriguing analytes in many types of biological samples; from various foodstuffs to living cell organisms. The main aim of the present work was to critically overview the development of the most relevant analytical principles, separation and detection methods that have been applied in order to overcome the difficulties with specific chemical properties of inositol phosphates, their interferences, absence of characteristic signal (e.g., absorbance), and strong binding interactions with (multivalent) metals and other biological molecules present in the sample matrix. A systematical and chronological review of the applied methodology and the detection system is given, ranging from the very beginnings of the classical gravimetric and titrimetric analysis, through the potentiometric titrations, chromatographic and electrophoretic separation techniques, to the use of spectroscopic methods and of the recently reported fluorescence and voltammetric bio- and nano-sensors.

Chemical tools for interrogating inositol pyrophosphate structure and function

The inositol pyrophosphates (PP-InsPs) are a unique group of intracellular messengers that represent some of the most highly phosphorylated molecules in nature. Genetic perturbation of the PP-InsP biosynthetic network indicates a central role for these metabolites in maintaining cellular energy homeostasis and in controlling signal transduction networks. However, despite their discovery over two decades ago, elucidating their physiologically relevant isomers, the biochemical pathways connecting these molecules to their associated phenotypes, and their modes of signal transduction has often been stymied by technical challenges. Many of the advances in understanding these molecules to date have been facilitated by the total synthesis of the various PP-InsP isomers and by the development of new methods that are capable of identifying their downstream signalling partners. Chemical tools have also been developed to distinguish between the proposed PP-InsP signal transduction mechanisms: protein binding, and a covalent modification of proteins termed protein pyrophosphorylation. In this article, we review these recent developments, discuss how they have helped to illuminate PP-InsP structure and function, and highlight opportunities for future discovery.

Frontrunners of T cell activation: Initial, localized Ca2+ signals mediated by NAADP and the type 1 ryanodine receptor

The activation of T cells is the fundamental on switch for the adaptive immune system. Ca(2+) signaling is essential for T cell activation and starts as initial, short-lived, localized Ca(2+) signals. The second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) forms rapidly upon T cell activation and stimulates early Ca(2+) signaling. We developed a high-resolution imaging technique using multiple fluorescent Ca(2+) indicator dyes to characterize these early signaling events and investigate the channels involved in NAADP-dependent Ca(2+) signals. In the first seconds of activation of either primary murine T cells or human Jurkat cells with beads coated with an antibody against CD3, we detected Ca(2+) signals with diameters close to the limit of detection and that were close to the activation site at the plasma membrane. In Jurkat cells in which the ryanodine receptor (RyR) was knocked down or in primary T cells from RyR1(-/-) mice, either these early Ca(2+) signals were not detected or the number of signals was markedly reduced. Local Ca(2+) signals observed within 20 ms upon microinjection of Jurkat cells with NAADP were also sensitive to RyR knockdown. In contrast, TRPM2 (transient receptor potential channel, subtype melastatin 2), a potential NAADP target channel, was not required for the formation of initial Ca(2+) signals in primary T cells. Thus, through our high-resolution imaging method, we characterized early Ca(2+) release events in T cells and obtained evidence for the involvement of RyR and NAADP in such signals.

Preferential Coupling of the NAADP Pathway to Exocytosis in T-Cells

A cytotoxic T-lymphocyte (CTL) kills an infected or tumorigenic cell by Ca2+-dependent exocytosis of cytolytic granules at the immunological synapse formed between the two cells. However, these granules are more than reservoirs of secretory cytolytic proteins but may also serve as unique Ca2+ signaling hubs that autonomously generate their own signals for exocytosis. This review discusses a selective role for the Ca2+-mobilizing messenger, nicotinic acid adenine dinucleotide phosphate (NAADP) and its molecular targets, two-pore channels (TPCs), in stimulating exocytosis. Given that TPCs reside on the exocytotic granules themselves, these vesicles generate as well as respond to NAADP-dependent Ca2+ signals, which may have wider implications for stimulus-secretion coupling, vesicular fusion, and patho-physiology.

Calcium Signalling Triggered by NAADP in T Cells Determines Cell Shape and Motility During Immune Synapse Formation

Nicotinic acid adenine dinucleotide phosphate (NAADP) has been implicated as an initial Ca2+ trigger in T cell Ca2+ signalling, but its role in formation of the immune synapse in CD4+ effector T cells has not been analysed. CD4+ T cells are activated by the interaction with peptide-MHCII complexes on the surface of antigen-presenting cells. Establishing a two-cell system including primary rat CD4+ T cells specific for myelin basic protein and rat astrocytes enabled us to mirror this activation process in vitro and to analyse Ca2+ signalling, cell shape changes and motility in T cells during formation and maintenance of the immune synapse. After immune synapse formation, T cells showed strong, antigen-dependent increases in free cytosolic calcium concentration ([Ca2+] i ). Analysis of cell shape and motility revealed rounding and immobilization of T cells depending on the amplitude of the Ca2+ signal. NAADP-antagonist BZ194 effectively blocked Ca2+ signals in T cells evoked by the interaction with antigen-presenting astrocytes. BZ194 reduced the percentage of T cells showing high Ca2+ signals thereby supporting the proposed trigger function of NAADP for global Ca2+ signalling. Taken together, the NAADP signalling pathway is further confirmed as a promising target for specific pharmacological intervention to modulate T cell activation.

Adenine Dinucleotide Second Messengers and T-lymphocyte Calcium Signaling

Calcium signaling is a universal signal transduction mechanism in animal and plant cells. In mammalian T-lymphocytes calcium signaling is essential for activation and re-activation and thus important for a functional immune response. Since many years it has been known that both calcium release from intracellular stores and calcium entry via plasma membrane calcium channels are involved in shaping spatio-temporal calcium signals. Second messengers derived from the adenine dinucleotides NAD and NADP have been implicated in T cell calcium signaling. Nicotinic acid adenine dinucleotide phosphate (NAADP) acts as a very early second messenger upon T cell receptor/CD3 engagement, while cyclic ADP-ribose (cADPR) is mainly involved in sustained partial depletion of the endoplasmic reticulum by stimulating calcium release via ryanodine receptors. Finally, adenosine diphosphoribose (ADPR) a breakdown product of both NAD and cADPR activates a plasma membrane cation channel termed TRPM2 thereby facilitating calcium (and sodium) entry into T cells. Receptor-mediated formation, metabolism, and mode of action of these novel second messengers in T-lymphocytes will be reviewed.

A Plasmodium multi-domain protein possesses multiple inositol phosphate kinase activities

The synchronization of intraerythrocytic maturation of Plasmodium parasites is an important factor in the malaria infection process. Synchronization is mediated by inositol phosphate (InsP(x))-induced Ca(2+)-release from internal stores. To further investigate the InsP(x) metabolism in these parasites a Plasmodium protein possessing inositol phosphate kinase (IPK) activity was recombinantly expressed, purified and enzymatically characterized for the first time. Its main activity is the conversion of the Ca(2+)-releasing second messenger Ins(1,4,5)P(3) to Ins(1,3,4,5)P(4), an important factor in chromatin remodeling and also in Ca(2+)-release. This protein possesses several additional IPK activities pointing to a potential role as inositol phosphate multikinase. Interestingly, we have also identified three putative subdomains of histone deacetylase in this protein possibly linking InsP(x)- and acetylation-mediated transcription regulation. Furthermore, we examined the inhibitory potential of >40 polyphenolic substances against its kinase activity. Because of the important role of InsP(x)-induced Ca(2+)-release in the development of Plasmodium parasites, IPKs are interesting targets for novel antimalarial approaches.

A novel Entamoeba histolytica inositol phosphate kinase catalyzes the formation of 5PP-Ins(1,2,3,4,6)P(5)

The parasitic protozoan Entamoeba histolytica is able to invade human tissues by secreting proteolytic enzymes. This secretion is regulated by inositol phosphate-mediated Ca(2+) release from internal stores. To further investigate the inositol phosphate metabolism of Entamoeba histolytica four putative inositol phosphate kinase genes (ehipk1-4) were identified and their expression analyzed by real-time quantitative PCR using RNA of trophozoites. Furthermore inositol phosphate kinase EhIPK1 was recombinantly expressed, purified and enzymatically characterized. Its main activity is the conversion of InsP(6) to 5PP-Ins(1,2,3,4,6)P(5), one of the main inositol phosphates found in Entamoeba histolytica. Remarkably, EhIPK1 possesses several additional enzymatic activities, e.g. the phosphorylation of the Ca(2+)-releasing second messenger Ins(1,4,5)P(3).We were able to identify several compounds with inhibitory potential against EhIPK1. Because of the important role of inositol phosphates in the invasion of human tissues by Entamoeba histolytica, inositol phosphate metabolizing enzymes are interesting targets for novel therapeutic approaches.

Trifluoromethylated cyclic-ADP-ribose mimic: synthesis of 8-trifluoromethyl-N(1)-[(5''-O-phosphorylethoxy)methyl]-5'-O-phosphorylinosine-5',5''-cyclic pyrophosphate (8-CF(3)-cIDPRE) and its calcium release activity in T cells

A convenient trifluoromethylation method was firstly applied to the synthesis of 8- CF(3)-purine nucleosides. On the basis of this method, new protection and deprotection strategies were developed for the successful synthesis of the trifluoromethylated cyclic-ADP-ribose mimic, 8-CF(3)-cIDPRE 1. Using intact, fura-2-loaded Jurkat T cells compound 1 and 2',3'-O-isopropylidene 8-CF(3)-cIDPRE 14 were characterized as membrane-permeant cADPR agonists. Contrary to the 8-substituted cADPR analogues that mainly act as antagonists of cADPR in cells, 8-substituted cIDPRE derivatives were shown to be Ca(2+) mobilizing agonists. Here we report that even compound 1, the 8-substituted cIDPRE with the strong electron withdrawing CF(3) group, behaves as an agonist in T cells. Interestingly, also the partially protected 2',3'-O-isopropylidene 8-CF(3)-cIDPRE activated Ca(2+) signaling indicating only a minor role for the hydroxyl groups of the southern ribose of cADPR for its biological activity. To our knowledge 8-CF(3)-cIDPRE 1 is the first reported fluoro substituted cADPR mimic and 8-CF(3)-cIDPRE 1 and compound 14 are promising molecular probes for elucidating the mode of action of cADPR.

Genetic control of lithium sensitivity and regulation of inositol biosynthetic genes

Lithium (Li(+)) is a common treatment for bipolar mood disorder, a major psychiatric illness with a lifetime prevalence of more than 1%. Risk of bipolar disorder is heavily influenced by genetic predisposition, but is a complex genetic trait and, to date, genetic studies have provided little insight into its molecular origins. An alternative approach is to investigate the genetics of Li(+) sensitivity. Using the social amoeba Dictyostelium, we previously identified prolyl oligopeptidase (PO) as a modulator of Li(+) sensitivity. In a link to the clinic, PO enzyme activity is altered in bipolar disorder patients. Further studies demonstrated that PO is a negative regulator of inositol(1,4,5)trisphosphate (IP(3)) synthesis, a Li(+) sensitive intracellular signal. However, it was unclear how PO could influence either Li(+) sensitivity or risk of bipolar disorder. Here we show that in both Dictyostelium and cultured human cells PO acts via Multiple Inositol Polyphosphate Phosphatase (Mipp1) to control gene expression. This reveals a novel, gene regulatory network that modulates inositol metabolism and Li(+) sensitivity. Among its targets is the inositol monophosphatase gene IMPA2, which has also been associated with risk of bipolar disorder in some family studies, and our observations offer a cellular signalling pathway in which PO activity and IMPA2 gene expression converge.

Nicotinic acid adenine dinucleotide phosphate-mediated calcium signalling in effector T cells regulates autoimmunity of the central nervous system

Nicotinic acid adenine dinucleotide phosphate represents a newly identified second messenger in T cells involved in antigen receptor-mediated calcium signalling. Its function in vivo is, however, unknown due to the lack of biocompatible inhibitors. Using a recently developed inhibitor, we explored the role of nicotinic acid adenine dinucleotide phosphate in autoreactive effector T cells during experimental autoimmune encephalomyelitis, the animal model for multiple sclerosis. We provide in vitro and in vivo evidence that calcium signalling controlled by nicotinic acid adenine dinucleotide phosphate is relevant for the pathogenic potential of autoimmune effector T cells. Live two photon imaging and molecular analyses revealed that nicotinic acid adenine dinucleotide phosphate signalling regulates T cell motility and re-activation upon arrival in the nervous tissues. Treatment with the nicotinic acid adenine dinucleotide phosphate inhibitor significantly reduced both the number of stable arrests of effector T cells and their invasive capacity. The levels of pro-inflammatory cytokines interferon-gamma and interleukin-17 were strongly diminished. Consecutively, the clinical symptoms of experimental autoimmune encephalomyelitis were ameliorated. In vitro, antigen-triggered T cell proliferation and cytokine production were evenly suppressed. These inhibitory effects were reversible: after wash-out of the nicotinic acid adenine dinucleotide phosphate antagonist, the effector T cells fully regained their functions. The nicotinic acid derivative BZ194 induced this transient state of non-responsiveness specifically in post-activated effector T cells. Naïve and long-lived memory T cells, which express lower levels of the putative nicotinic acid adenine dinucleotide phosphate receptor, type 1 ryanodine receptor, were not targeted. T cell priming and recall responses in vivo were not reduced. These data indicate that the nicotinic acid adenine dinucleotide phosphate/calcium signalling pathway is essential for the recruitment and the activation of autoaggressive effector T cells within their target organ. Interference with this signalling pathway suppresses the formation of autoimmune inflammatory lesions and thus might qualify as a novel strategy for the treatment of T cell mediated autoimmune diseases.

Phosphoinositide and inositol phosphate analysis in lymphocyte activation

Lymphocyte antigen receptor engagement profoundly changes the cellular content of phosphoinositide lipids and soluble inositol phosphates. Among these, the phosphoinositides phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3) play key signaling roles by acting as pleckstrin homology (PH) domain ligands that recruit signaling proteins to the plasma membrane. Moreover, PIP2 acts as a precursor for the second messenger molecules diacylglycerol and soluble inositol 1,4,5-trisphosphate (IP3), essential mediators of PKC, Ras/Erk, and Ca2+ signaling in lymphocytes. IP3 phosphorylation by IP3 3-kinases generates inositol 1,3,4,5-tetrakisphosphate (IP4), an essential soluble regulator of PH domain binding to PIP3 in developing T cells. Besides PIP2, PIP3, IP3, and IP4, lymphocytes produce multiple other phosphoinositides and soluble inositol phosphates that could have important physiological functions. To aid their analysis, detailed protocols that allow one to simultaneously measure the levels of multiple different phosphoinositide or inositol phosphate isomers in lymphocytes are provided here. They are based on thin layer, conventional and high-performance liquid chromatographic separation methods followed by radiolabeling or non-radioactive metal-dye detection. Finally, less broadly applicable non-chromatographic methods for detection of specific phosphoinositide or inositol phosphate isomers are discussed. Support protocols describe how to obtain pure unstimulated CD4+CD8+ thymocyte populations for analyses of inositol phosphate turnover during positive and negative selection, key steps in T cell development.

8-Bromo-cyclic inosine diphosphoribose: towards a selective cyclic ADP-ribose agonist

cADPR (cyclic ADP-ribose) is a universal Ca²⁺ mobilizing second messenger. In T-cells cADPR is involved in sustained Ca²⁺ release and also in Ca²⁺ entry. Potential mechanisms for the latter include either capacitative Ca²⁺ entry, secondary to store depletion by cADPR, or direct activation of the non-selective cation channel TRPM2 (transient receptor potential cation channel, subfamily melastatin, member 2). Here we characterize the molecular target of the newly-described membrane-permeant cADPR agonist 8-Br-N¹-cIDPR (8-bromo-cyclic IDP-ribose). 8-Br-N¹-cIDPR evoked Ca²⁺ signalling in the human T-lymphoma cell line Jurkat and in primary rat T-lymphocytes. Ca²⁺ signalling induced by 8-Br-N¹-cIDPR consisted of Ca²⁺ release and Ca²⁺ entry. Whereas Ca²⁺ release was sensitive to both the RyR (ryanodine receptor) blocker RuRed (Ruthenium Red) and the cADPR antagonist 8-Br-cADPR (8-bromo-cyclic ADP-ribose), Ca²⁺ entry was inhibited by the Ca²⁺ entry blockers Gd³⁺ (gadolinium ion) and SKF-96365, as well as by 8-Br-cADPR. To unravel a potential role for TRPM2 in sustained Ca²⁺ entry evoked by 8-Br-N¹-cIDPR, TRPM2 was overexpressed in HEK (human embryonic kidney)-293 cells. However, though activation by H₂O₂ was enhanced dramatically in those cells, Ca²⁺ signalling induced by 8-Br-N¹-cIDPR was almost unaffected. Similarly, direct analysis of TRPM2 currents did not reveal activation or co-activation of TRPM2 by 8-Br-N¹-cIDPR. In summary, the sensitivity to the Ca²⁺ entry blockers Gd³⁺ and SKF-96365 is in favour of the concept of capacitative Ca²⁺ entry, secondary to store depletion by 8-Br-N¹-cIDPR. Taken together, 8-Br-N¹-cIDPR appears to be the first cADPR agonist affecting Ca²⁺ release and secondary Ca²⁺ entry, but without effect on TRPM2.

NAADP-mediated Ca2+ signaling via type 1 ryanodine receptor in T cells revealed by a synthetic NAADP antagonist

The nucleotide NAADP was recently discovered as a second messenger involved in the initiation and propagation of Ca(2+) signaling in lymphoma T cells, but its impact on primary T cell function is still unknown. An optimized, synthetic, small molecule inhibitor of NAADP action, termed BZ194, was designed and synthesized. BZ194 neither interfered with Ca(2+) mobilization by d-myo-inositol 1,4,5-trisphosphate or cyclic ADP-ribose nor with capacitative Ca(2+) entry. BZ194 specifically and effectively blocked NAADP-stimulated [(3)H]ryanodine binding to the purified type 1 ryanodine receptor. Further, in intact T cells, Ca(2+) mobilization evoked by NAADP or by formation of the immunological synapse between primary effector T cells and astrocytes was inhibited by BZ194. Downstream events of Ca(2+) mobilization, such as nuclear translocation of "nuclear factor of activated T cells" (NFAT), T cell receptor-driven interleukin-2 production, and proliferation in antigen-experienced CD4(+) effector T cells, were attenuated by the NAADP antagonist. Taken together, specific inhibition of the NAADP signaling pathway constitutes a way to specifically and effectively modulate T-cell activation and has potential in the therapy of autoimmune diseases.

Simultaneous determination of inositol and inositol phosphates in complex biological matrices: quantitative ion-exchange chromatography/tandem mass spectrometry

myo-Inositol (Ins) and myo-inositol phosphates (InsPs) are widely distributed in plants and animals. The evaluation of the distribution of Ins and InsPs in cells and plant sources can impact the understanding of their role in nutrition, cellular processes and diseases, and how they may be modulated by diet. We developed an anion-exchange chromatography/tandem mass spectrometry (HPLC/ESI-MS/MS) method for the separation and simultaneous quantitation of Ins and different naturally occurring phosphorylated inositol compounds. Chromatographic separation was achieved in 30 min on a commercial anion-exchange column (0.5 x 150 mm) using a gradient of 200 mM ammonium carbonate buffer (pH 9.0) and 5% methanol in H(2)O. Analytes were identified by selective reaction monitoring using a triple quadrupole mass spectrometer in negative ion electrospray ionization mode. Adenosine 5'-monophosphate was used as a general internal standard for quantitation. Detection is linear in the range of 0.25-400 pmol for Ins, InsP(1), InsP(4), and InsP(5), 40-400 pmol for InsP(2) and InsP(3), and 60-400 pmol for InsP(6), with a minimum r(2) > 0.994. The limit of detection is 0.25 pmol with a signal-to-noise ratio of 10:1 for all analytes. The intra-day and inter-day variations were within 17% at three concentration levels. Recovery values for the seven analytes spiked into extraction solution or different matrices were between 63 and 121%. Using this approach, Ins and InsPs were measured in three different plant samples and in cultured cells, illustrating significant differences in the distribution of inositol compounds in food samples compared to cells and between cell types.

Ins(1,4,5)P3 3-kinase-A overexpression induces cytoskeletal reorganization via a kinase-independent mechanism

In the present study, effects of increased IP3K-A [Ins(1,4,5)P3 3-kinase-A] expression were analysed. H1299 cells overexpressing IP3K-A formed branching protrusions, and under three-dimensional culture conditions, they exhibited a motile fibroblast-like morphology. They lost the ability to form actin stress fibres and showed increased invasive migration in vitro. Furthermore, expression levels of the mesenchymal marker proteins vimentin and N-cadherin were increased. The enzymatic function of IP3K-A is to phosphorylate the calcium-mobilizing second messenger Ins(1,4,5)P3 to (Ins(1,3,4,5)P4. Accordingly, cells overexpressing IP3K-A showed reduced calcium release and altered concentrations of InsPs, with decreasing concentrations of Ins(1,4,5)P3, InsP6 and Ins(1,2,3,4,5)P5, and increasing concentrations of Ins(1,3,4,5)P4. However, IP3K-A-induced effects on cell morphology do not seem to be dependent on enzyme activity, since a protein devoid of enzyme activity also induced the formation of branching protrusions. Therefore we propose that the morphological changes induced by IP3K-A are mediated by non-enzymatic activities of the protein.

Intracellular localization of human Ins(1,3,4,5,6)P5 2-kinase

InsP6 is an intracellular signal with several proposed functions that is synthesized by IP5K [Ins(1,3,4,5,6)P5 2-kinase]. In the present study, we overexpressed EGFP (enhanced green fluorescent protein)-IP5K fusion proteins in NRK (normal rat kidney), COS7 and H1299 cells. The results indicate that there is spatial microheterogeneity in the intracellular localization of IP5K that could also be confirmed for the endogenous enzyme. This may facilitate changes in InsP6 levels at its sites of action. For example, overexpressed IP5K showed a structured organization within the nucleus. The kinase was preferentially localized in euchromatin and nucleoli, and co-localized with mRNA. In the cytoplasm, the overexpressed IP5K showed locally high concentrations in discrete foci. The latter were attributed to stress granules by using mRNA, PABP [poly(A)-binding protein] and TIAR (TIA-1-related protein) as markers. The incidence of stress granules, in which IP5K remained highly concentrated, was further increased by puromycin treatment. Using FRAP (fluorescence recovery after photobleaching) we established that IP5K was actively transported into the nucleus. By site-directed mutagenesis we identified a nuclear import signal and a peptide segment mediating the nuclear export of IP5K.

Inositol phosphate metabolomics: Merging genetic perturbation with modernized radiolabeling methods

Recent discoveries that provide a link between inositol phosphate (IP) signaling and fundamental cellular processes evoke many exciting new hypotheses about IP function, and underscore the importance of understanding how IP synthesis is regulated. Central to studies of IP metabolism is the essential development of efficient, fast, and reproducible methods for quantitative analysis of IPs in systems ranging from simple cell cultures to more complex tissues and whole organisms. Additionally, in many cases there is a need to pharmacologically and/or genetically alter IP kinase and phosphatase activities in order to visualize low abundance inositol signaling messengers. Here, we describe updated methods for rapid analysis of IP metabolism in normal and genetically manipulated Saccharomyces cerevisiae, Arabidopsis thaliana, Drosophila melanogaster, Mus musculus, and Homo sapiens.

Second messenger function of nicotinic acid adenine dinucleotide phosphate revealed by an improved enzymatic cycling assay

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent activator of Ca2+ release from intracellular stores known today. Although recent reports have suggested an important function of NAADP in human T lymphocytes, direct evidence for receptor-induced formation of NAADP is yet missing in these cells. Thus, we developed a highly sensitive and specific enzyme assay capable of quantifying low fmol amounts of NAADP. In unstimulated T cells, the NAADP concentration amounted to 4.4 +/- 1.6 nm (0.055 +/- 0.028 pmol/mg of protein). Stimulation of the cells via the T cell receptor/CD3 complex resulted in biphasic elevation kinetics of cellular NAADP levels and was characterized by a bell-shaped concentration-response curve for NAADP. In contrast, the NAADP concentration was elevated neither upon activation of the ADP-ribose/TRPM2 channel Ca2+ signaling system nor by an increase of the intracellular Ca2+ concentration upon thapsigargin stimulation. T cell receptor/CD3 complex-mediated NAADP formation was dependent on the activity of tyrosine kinases because genistein completely blocked NAADP elevation. Thus, we propose a regulated formation of NAADP upon specific stimulation of the T cell receptor/CD3 complex, suggesting a function of NAADP as a Ca2+-mobilizing second messenger during T cell activation.

An optimized fixation and extraction technique for high resolution of inositol phosphate signals in rodent brain

Members of lower and higher inositol phosphates distinctly participate in signal transduction (1). Relatively little is known regarding possible biological functions of inositol phosphates in functionally different areas of the intact brain. A detailed study on the regional distribution of biologically important inositol phosphates may help elucidate their physiological functions in different brain regions in the regional tissue context. We now show a novel technique which allows fixation and subsequent dissection of whole rat brains into small volume elements for mapping of the whole range of inositol phosphates from Ins(1,4,5)P3 to InsP6. The method has been successfully applied to investigate regional differences of a broader spectrum of inositol phosphates in microdissected brain tissue and to construct 3D-maps of these signaling compounds. The technique can be particularly well employed to investigate regional changes in the spectrum of higher inositol phosphates and phosphoinositides upon neuronal stimulation induced by motor activity or drug treatment.

Amplification and propagation of pacemaker Ca2+ signals by cyclic ADP-ribose and the type 3 ryanodine receptor in T cells

Ligation of the T-cell receptor/CD3 complex results in global Ca(2+) signals that are essential for T-cell activation. We have recently reported that these global Ca(2+) signals are preceded by localized pacemaker Ca(2+) signals. Here, we demonstrate for the first time for human T cells that an increase in signal frequency of subcellular pacemaker Ca(2+) signals at sites close to the plasma membrane, in the cytosol and in the nucleus depends on the type 3 ryanodine receptor (RyR) and its modulation by cyclic ADP-ribose. The spatial distribution of D-myo-inositol 1,4,5-trisphosphate receptors and RyRs indicates a concerted action of both of these receptors/Ca(2+) channels in the generation of initial pacemaker signals localized close to the plasma membrane. Inhibition or knockdown of RyRs resulted in significant decreases in (1) the frequency of initial pacemaker signals localized close to the plasma membrane, and (2) the frequency of localized pacemaker Ca(2+) signals in the inner cytosol. Moreover, upon microinjection of cyclic ADP-ribose or upon extracellular addition of its novel membrane-permeant mimic N-1-ethoxymethyl-substituted cyclic inosine diphosphoribose, similarly decreased Ca(2+) signals were observed in both type 3 RyR-knockdown cells and in control cells microinjected with the RyR antagonist Ruthenium Red. Taken together, our results show that, under physiological conditions in human T cells, RyRs play crucial roles in the local amplification and the spatiotemporal development of subcellular Ca(2+) pacemaker signals.

Rat inositol 1,4,5-trisphosphate 3-kinase C is enzymatically specialized for basal cellular inositol trisphosphate phosphorylation and shuttles actively between nucleus and cytoplasm

The calcium-liberating second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) is converted to inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) by Ins(1,4,5)P3 3-kinases (IP3Ks) that add a fourth phosphate group to the 3-position of the inositol ring. Two isoforms of IP3Ks (named A and B) from different vertebrate species have been well studied. Recently the cloning and examination of a human full-length cDNA encoding a novel isoform, termed human IP3K-C (HsIP3K-C), has been reported. In the present study we report the cloning of a full-length cDNA encoding a rat homologue of HsIP3K-C with a unique mRNA expression pattern, which differs remarkably from the tissue distribution of HsIP3K-C. Of the rat tissues examined, rat IP3K-C (RnIP3K-C) is mainly present in heart, brain, and testis and shows the strongest expression in an epidermal tissue, namely tongue epithelium. RnIP3K-C has a calculated molecular mass of approximately 74.5 kDa and shows an overall identity of approximately 75% with HsIP3K-C. A bacterially expressed, enzymatically active and Ca2+-calmodulin-regulated fragment of this isoform displays remarkable enzymatic properties like a very low Km for Ins(1,4,5)P3 ( approximately 0.2 microm), substrate inhibition by high concentrations of Ins(1,4,5)P3, allosteric product activation by Ins(1,3,4,5)P4 in absence of Ca2+-calmodulin (Ka(app) 0.52 microm), and the ability to efficiently phosphorylate a second InsP3 substrate, inositol 2,4,5-trisphosphate, to inositol 2,4,5,6-tetrakisphosphate in the presence of Ins(1,3,4,5)P4. Furthermore, the RnIP3K-C fused with a fluorescent protein tag is actively transported into and out of the nucleus when transiently expressed in mammalian cells. A leucine-rich nuclear export signal and an uncharacterized nuclear import activity are localized in the N-terminal domain of the protein and determine its nucleocytoplasmic shuttling. These findings point to a particular role of RnIP3K-C in nuclear inositol trisphosphate phosphorylation and cellular growth.

Aberrant 3H in Ehrlich mouse ascites tumor cell nucleotides after in vivo labeling with myo-[2-3H]- and L-myo-[1-3H]inositol: implications for measuring inositol phosphate signaling

After in vivo radiolabeling of Ehrlich cells for 24h with conventional myo-[2-3H]inositol we previously demonstrated an aberrant 3H-labeling of ATP that interfered in the HPLC analysis of inositol trisphosphates. This aberrant 3H-labeling was accounted for by the extensive kidney catabolism of myo-[2-3H] inositol with delivery of 3H-labeled metabolites to extrarenal tissues. As expected, the aberrant labeling of ATP is markedly reduced with the use of 3H-myo-inositol labeled at L-C1 rather than at C2, reflecting that the 3H at L-C1 disappears in the first step of the myo-inositol catabolism: the oxidative conversion to D-glucuronate. In contrast, with the 3H at C2 of myo-inositol, the 3H-C2 passes into the pentose phosphate conversions with resulting labeling of nucleotides. The extent of catabolism to 3H-labeled water, the cellular accumulation of 3H-myo-inositol, the incorporation into cellular inositol phospholipids, and the labeling pattern of cellular phosphoinositides were all found to be similar for the two labeled myo-inositol moieties. With the use of L-myo-[1-3H]inositol an aberrant 3H-labeling at about 25% remained, for which a presumptive mechanism is proposed. L-myo-[1-3H]Inositol appears nevertheless to be a preferable alternative to myo-[2-3H]inositol for tracing the intact myo-inositol molecule after in vivo labeling, with minimized interference from aberrant 3H-labeling of nucleotides.

The human homologue of yeast ArgRIII protein is an inositol phosphate multikinase with predominantly nuclear localization

The function of the transcription regulator ArgRIII in the expression of several genes involved in the metabolism of arginine in yeast has been well studied. It was previously reported that it is also an inositol phosphate multikinase and an important factor of the mRNA export pathway [reviewed by Shears (2000) Bioessays 22, 786-789]. In the present study we report the cloning of a full-length 1248-bp cDNA encoding a human inositol phosphate multikinase (IPMK). This protein has a calculated molecular mass of 47.219 kDa. Functionally important motifs [inositol phosphate-binding site, ATP-binding site, catalytically important SSLL (Ser-Ser-Leu-Leu) domain] are conserved between the human IPMK and yeast ArgRIII. Bacterially expressed protein demonstrated an inositol phosphate multikinase activity similar to that of yeast ArgRIII. Ins(1,4,5)P3 is phosphorylated at positions 3 and 6 up to Ins(1,3,4,5,6)P5. The human IPMK fused with a fluorescent protein tag is localized predominantly in the nucleus when transiently expressed in mammalian cells. A basic cluster in the protein's C-terminus is positively involved in nuclear targeting. These findings are consistent with the concept of a nuclear inositol phosphate signalling and phosphorylation pathway in mammalian cells.

Inositol phosphates in the environment

The inositol phosphates are a group of organic phosphorus compounds found widely in the natural environment, but that represent the greatest gap in our understanding of the global phosphorus cycle. They exist as inositols in various states of phosphorylation (bound to between one and six phosphate groups) and isomeric forms (e.g. myo, D-chiro, scyllo, neo), although myo-inositol hexakisphosphate is by far the most prevalent form in nature. In terrestrial environments, inositol phosphates are principally derived from plants and accumulate in soils to become the dominant class of organic phosphorus compounds. Inositol phosphates are also present in large amounts in aquatic environments, where they may contribute to eutrophication. Despite the prevalence of inositol phosphates in the environment, their cycling, mobility and bioavailability are poorly understood. This is largely related to analytical difficulties associated with the extraction, separation and detection of inositol phosphates in environmental samples. This review summarizes the current knowledge of inositol phosphates in the environment and the analytical techniques currently available for their detection in environmental samples. Recent advances in technology, such as the development of suitable chromatographic and capillary electrophoresis separation techniques, should help to elucidate some of the more pertinent questions regarding inositol phosphates in the natural environment.

A straightforward method for analysis of highly phosphorylated inositols in blood cells by high-performance liquid chromatography

Soluble inositol polyphosphates are found in many cells. The trisphosphate isomers, mainly inositol-1,4,5-trisphosphate, have been extensively studied because of their involvement in signal transduction. However, higher phosphorylated inositols are less frequently studied and their physiological role is poorly understood. Among these, only the myo-inositol-1,3,4,5,6-pentakisphosphate (Ins1,3,4,5,6P5), an important component of bird erythrocytes, has been intensively studied in comparative studies because it is a potent allosteric effector of hemoglobin and decreases its affinity to oxygen. We have developed a procedure for the analysis of inositol polyphosphates and other phosphate compounds in vertebrate blood cells based on a quick and accurate HPLC separation coupled to metal-dye detection. The procedure includes acid extraction of cellular phosphates, acid elimination and concentration of the extract, HPLC separation of phosphate compounds, and quantification by coupled highly sensitive metal-dye detection. The method is especially useful for analyses of highly phosphorylated inositols and for red cell comparative studies. Using the described method we have quantified Ins1,3,4,5,6P5 and the low quantities of InsP6 found in bird erythrocytes. We also identified traces of Ins3,4,5,6P4 and Ins1,3,4,6P4. Moreover, by applying the method in cultured murine macrophages, we have found changes of highly phosphorylated inositols when these cells are activated by lipopolysaccharide.

Sensitive fluorescent quantitation of myo-inositol 1,2-cyclic phosphate and myo-inositol 1-phosphate by high-performance thin-layer chromatography

A non-radioactive micro-assay for the cyclic phosphodiesterase reaction catalyzed by Bacillus cereus phosphatidylinositol-specific phospholipase C is described. The assay involves high-performance thin-layer chromatography on silica gel to resolve the substrate (myo-inositol 1,2-cyclic phosphate) and the product (myo-inositol 1-phosphate), followed by detection with a lead tetraacetate-fluorescein stain. The quantitation of these inositol phosphates in sample spots relative to a series of standards is accomplished by analysis of the fluorescent plate image with a commercial phosphoimager and associated software. The experimental considerations for reliable quantitation of inositol monophosphates in the range of 0.1 to 50 nmol are presented.

Inositol phosphates from barley low-phytate grain mutants analysed by metal-dye detection HPLC and NMR

Inositol phosphates from barley low-phytate grain mutants and their parent variety were analysed by metal-dye detection HPLC and NMR. Compound assignment was carried out by comparison of retention times using a chemical hydrolysate of phytate [Ins(1,2,3,4,5,6)P(6)] as a reference. Co-inciding retention times indicated the presence of phytate, D/L-Ins(1,2,3,4,5)P(5), Ins(1,2,3,4,6)P(5), D/L-(1,2,4,5,6)P(5), D/L-(1,2,3,4)P(4), D/L-Ins(1,2,5,6)P(4) and D/L-Ins(1,4,5,6)P(4) in PLP1B mutants as well as the parent variety. In grain extracts from mutant lines PLP1A, PLP2A and PLP3A unusual accumulations of D/L-Ins(1,3,4,5)P(4) were observed whereas phytate and the above-mentioned inositol phosphates were present in relatively small amounts. Assignment of D/L-Ins(1,3,4,5)P(4) was corroborated by precise co-chromatography with a commercial Ins(1,3,4,5)P(4) standard and by NMR spectroscopy. Analysis of inositol phosphates during grain development revealed accumulation of phytate and D/L-Ins(1,3,4,5)P(4), which suggested the tetrakisphosphate compound to be an intermediate of phytate synthesis. This assumption was strengthened further by phytate degradation assays showing that D/L-Ins(1,3,4,5)P(4) did not belong to the spectrum of degradation products generated by endogenous phytase activity. Metabolic scenarios leading to accumulation of D/L-Ins(1,3,4,5)P(4) in barley low-phytate mutants are discussed.

Nicotinic acid adenine dinucleotide phosphate (NAADP(+)) is an essential regulator of T-lymphocyte Ca(2+)-signaling

Microinjection of human Jurkat T-lymphocytes with nicotinic acid adenine dinucleotide phosphate (NAADP(+)) dose-dependently stimulated intracellular Ca(2+)-signaling. At a concentration of 10 nM NAADP(+) evoked repetitive and long-lasting Ca(2+)-oscillations of low amplitude, whereas at 50 and 100 nM, a rapid and high initial Ca(2+)-peak followed by trains of smaller Ca(2+)-oscillations was observed. Higher concentrations of NAADP(+) (1 and 10 microM) gradually reduced the initial Ca(2+)-peak, and a complete self-inactivation of Ca(2+)-signals was seen at 100 microM. The effect of NAADP(+) was specific as it was not observed with nicotinamide adenine dinucleotide phosphate. Both inositol 1,4, 5-trisphosphate- and cyclic adenosine diphosphoribose-mediated Ca(2+)-signaling were efficiently inhibited by coinjection of a self-inactivating concentration of NAADP(+). Most importantly, microinjection of a self-inactivating concentration of NAADP(+) completely abolished subsequent stimulation of Ca(2+)-signaling via the T cell receptor/CD3 complex, indicating that a functional NAADP(+) Ca(2+)-release system is essential for T-lymphocyte Ca(2+)-signaling.

High-performance thin-layer chromatography method for inositol phosphate analysis

A simple and inexpensive high-performance thin-layer chromatography (HPTLC) method for the analysis of inositol mono- to hexakisphosphates on cellulose precoated plates is described. Plates were developed in 1-propanol-25% ammonia solution-water (5:4:1) and substance quantities as low as 100-200 pmol were detected by molybdate staining. Chromatographic mobilities of nucleotides and phosphorylated carbohydrates were also characterized. Charcoal treatment was employed to separate nucleotides from inositol phosphates with similar R(F) values prior to HPTLC analysis. Practical application of the HPTLC system is demonstrated by analysis of grain extracts from wild type and low-phytate mutant barley as well as phytate degradation products resulting from barley phytase activity.

Enhanced Hippocampal CA1 LTP but Normal Spatial Learning in Inositol 1,4,5-trisphosphate 3-kinase(A)-Deficient Mice

To define the physiological role of IP33-kinase(A) in vivo, we have generated a mouse strain with a null mutation of the IP33-kinase(A) locus by gene targeting. Homozygous mutant mice were fully viable, fertile, apparently normal, and did not show any morphological anomaly in brain sections. In the mutant brain, the IP4 level was significantly decreased whereas the IP3 level did not change, demonstrating a major role of IP33-kinase(A) in the generation of IP4. Nevertheless, no significant difference was detected in the hippocampal neuronal cells of the wild-type and the mutant mice in the kinetics of Ca2+ regulation after glutamate stimulation. Electrophysiological analyses carried out in hippocampal slices showed that the mutation significantly enhanced the LTP in the hippocampal CA1 region, but had no effect on the LTP in dentate gyrus (DG). No difference was noted, however, between the mutant and the wild-type mice in the Morris water maze task. Our results indicate that IP33-kinase(A) may play an important role in the regulation of LTP in hippocampal CA1 region through the generation of IP4, but the enhanced LTP in the hippocampal CA1 does not affect spatial learning and memory.

Vicinal thiols are involved in inositol 1,2,3,5,6-pentakisphosphate 5-phosphatase activity from fetal calf thymus

Inositol 1,2,3,5,6-pentakisphosphate (Ins(1,2,3,5,6)P5) 5-phosphatase present in fetal calf thymus has been partially purified. This enzyme was inhibited dose-dependently by different thiol modifiers like N-ethylmaleimide (NEM), p-chloromercuribenzene sulfonate (PCMBS), diamide, and phenylarsine oxide (PAO). The inhibition by PCMBS and diamide was protected by preincubation with dithiothreitol (DTT) and the phosphatase substrate, Ins(1,2,3,5,6)P5. Diamide, a compound that specifically modifies vicinal thiol groups, also blocked the 5-phosphatase dose-dependently. Specificity of this blockade was proven by using dimercaptopropanol (DMP), a compound known to protect vicinal thiol groups. DMP prevented the enzyme from inhibition by diamide. These data suggest that vicinal thiols are involved in Ins(1,2,3,5,6)P5 5-phosphatase activity.

Biological variability in the structures of diphosphoinositol polyphosphates in Dictyostelium discoideum and mammalian cells

Previous structural analyses of diphosphoinositol polyphosphates in biological systems have relied largely on NMR analysis. For example, in Dictyostelium discoideum, diphosphoinositol pentakisphosphate was determined by NMR to be 4- and/or 6-PPInsP5, and the bisdiphosphoinositol tetrakisphosphate was found to be 4, 5-bisPPInsP4 and/or 5,6-bisPPInsP4 [Laussmann, Eujen, Weisshuhn, Thiel and Vogel (1996) Biochem. J. 315, 715-720]. We now describe three recent technical developments to aid the analysis of these compounds, not just in Dictyostelium, but also in a wider range of biological systems: (i) improved resolution and sensitivity of detection of PPInsP5 isomers by microbore metal-dye-detection HPLC; (ii) the use of the enantiomerically specific properties of a rat hepatic diphosphatase; (iii) chemical synthesis of enantiomerically pure reference standards of all six possible PPInsP5 isomers. Thus we now demonstrate that the major PPInsP5 isomer in Dictyostelium is 6-PPInsP5. Similar findings obtained using the same synthetic standards have been published [Laussmann, Reddy, Reddy, Falck and Vogel (1997) Biochem. J. 322, 31-33]. In addition, we show that 10-25% of the Dictyostelium PPInsP5 pool is comprised of 5-PPInsP5. The biological significance of this new observation was reinforced by our demonstration that 5-PPInsP5 is the predominant PPInsP5 isomer in four different mammalian cell lines (FTC human thyroid cancer cells, Swiss 3T3 fibroblasts, Jurkat T-cells and Chinese hamster ovary cells). The fact that the cellular spectrum of diphosphoinositol polyphosphates varies across phylogenetic boundaries underscores the value of our technological developments for future determinations of the structures of this class of compounds in other systems.