Nicotinic acid adenine dinucleotide phosphate (NAADP) degradation by alkaline phosphatase

T cell Ca2+ microdomains through the lens of computational modeling

Cellular Ca2+ signaling is highly organized in time and space. Locally restricted and short-lived regions of Ca2+ increase, called Ca2+ microdomains, constitute building blocks that are differentially arranged to create cellular Ca2+ signatures controlling physiological responses. Here, we focus on Ca2+ microdomains occurring in restricted cytosolic spaces between the plasma membrane and the endoplasmic reticulum, called endoplasmic reticulum-plasma membrane junctions. In T cells, these microdomains have been finely characterized. Enough quantitative data are thus available to develop detailed computational models of junctional Ca2+ dynamics. Simulations are able to predict the characteristics of Ca2+ increases at the level of single channels and in junctions of different spatial configurations, in response to various signaling molecules. Thanks to the synergy between experimental observations and computational modeling, a unified description of the molecular mechanisms that create Ca2+ microdomains in the first seconds of T cell stimulation is emerging.

Enzymology of Ca2+-Mobilizing Second Messengers Derived from NAD: From NAD Glycohydrolases to (Dual) NADPH Oxidases

Nicotinamide adenine dinucleotide (NAD) and its 2'-phosphorylated cousin NADP are precursors for the enzymatic formation of the Ca²⁺-mobilizing second messengers adenosine diphosphoribose (ADPR), 2'-deoxy-ADPR, cyclic ADPR, and nicotinic acid adenine dinucleotide phosphate (NAADP). The enzymes involved are either NAD glycohydrolases CD38 or sterile alpha toll/interleukin receptor motif containing-1 (SARM1), or (dual) NADPH oxidases (NOX/DUOX). Enzymatic function(s) are reviewed and physiological role(s) in selected cell systems are discussed.

NAADP-Evoked Ca2+ Signaling: The DUOX2-HN1L/JPT2-Ryanodine Receptor 1 Axis

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca²⁺ mobilizing second messenger known to date. Major steps elucidating metabolism and Ca²⁺ mobilizing activity of NAADP are reviewed, with emphasis on a novel redox cycle between the inactive reduced form, NAADPH, and the active oxidized form, NAADP. Oxidation from NAADPH to NAADP is catalyzed in cell free system by (dual) NADPH oxidases NOX5, DUOX1, and DUOX2, whereas reduction from NAADP to NAADPH is catalyzed by glucose 6-phosphate dehydrogenase. Using different knockout models for NOX and DUOX isozymes, DUOX2 was identified as NAADP forming enzyme in early T-cell activation.Recently, receptors or binding proteins for NAADP were identified: hematological and neurological expressed 1-like protein (HN1L)/Jupiter microtubule associated homolog 2 (JPT2) and Lsm12 are small cytosolic proteins that bind NAADP. In addition, they interact with NAADP-sensitive Ca²⁺ channels, such as ryanodine receptor type 1 (RYR1) or two-pore channels (TPC).Due to its role as Ca²⁺ mobilizing second messenger in T cells, NAADP's involvement in inflammation is also reviewed. In the central nervous system (CNS), NAADP regulates autoimmunity because NAADP antagonism affects a couple of T-cell migration and re-activation events, e.g. secretion of the pro-inflammatory cytokine interleukin-17. Further, the role of NAADP in transdifferentiation of IL-17-producing Th17 cells into T regulatory type 1 cells in vitro and in vivo is discussed.

NAADP-Mediated Ca2+ Signalling

The discovery of NAADP-evoked Ca²⁺ release in sea urchin eggs and then as a ubiquitous Ca²⁺ mobilizing messenger has introduced several novel paradigms to our understanding of Ca²⁺ signalling, not least in providing a link between cell stimulation and Ca²⁺ release from lysosomes and other acidic Ca²⁺ storage organelles. In addition, the hallmark concentration-response relationship of NAADP-mediated Ca²⁺ release, shaped by striking activation/desensitization mechanisms, influences its actions as an intracellular messenger. There has been recent progress in our understanding of the molecular mechanisms underlying NAADP-evoked Ca²⁺ release, such as the identification of the endo-lysosomal two-pore channel family of cation channels (TPCs) as their principal target and the identity of NAADP-binding proteins that complex with them. The NAADP/TPC signalling axis has gained recent prominence in pathophysiology for their roles in such disease processes as neurodegeneration, tumorigenesis and cellular viral entry.

NAADP Signaling: New Kids on the Block

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a universal Ca²⁺ mobilizing second messenger essential for initiation of Ca²⁺ signaling. Recently, novel molecular mechanisms of both its rapid formation upon receptor stimulation and its mode of action were discovered. Dual NADPH oxidase 2 (DUOX2) and hematological and neurological expressed 1-like protein (HN1L)/Jupiter microtubule-associated homolog 2 (JPT2) were discovered as NAADP-forming enzyme and NAADP receptor/binding protein—the new kids on the block. These novel aspects are reviewed and integrated into the previous view of NAADP signaling.

Novel ratiometric fluorescent probe for real-time detection of alkaline phosphatase and its application in living cells

A novel ratiometric fluorescent probe has been developed through a simple synthetic route for the detection of alkaline phosphatase(ALP) in aqueous media and for fluorescence imaging in living cells. The introduction of a spontaneous-degradation spacer in the design of the fluorescent probe is beneficial for the ratio detection method and allows the selection of a fluorophore with an amino group. Under catalysis by ALP, the phosphate monoester bond breaks; this is followed by 1,4-elimination, decomposition of the carbamate moiety, and subsequent formation of the 4-amine-1,8-naphthalimide fluorophore. The probe APN shows a significant fluorescence colour change from blue to green in response to ALP, and the fluorescence intensity ratio of the probe solution (F₅₅₀/F₄₈₀) has a good linear relationship with the ALP concentration in the range of 0 to 100 U L^-1. Our studies have demonstrated that APN exhibits high accuracy in recognising ALP, with a detection limit as low as 0.16 U L^-1. Furthermore, the probe shows very good biocompatibility, which is beneficial for its application in biological systems.

HN1L/JPT2: A signaling protein that connects NAADP generation to Ca2+ microdomain formation

NAADP-evoked Ca²⁺ release through type 1 ryanodine receptors (RYR1) is a major mechanism underlying the earliest signals in T cell activation, which are the formation of Ca²⁺ microdomains. In our characterization of the molecular machinery underlying NAADP action, we identified an NAADP-binding protein, called hematological and neurological expressed 1-like protein (HN1L) [also known as Jupiter microtubule-associated homolog 2 (JPT2)]. Gene deletion of Hn1l/Jpt2 in human Jurkat and primary rat T cells resulted in decreased numbers of initial Ca²⁺ microdomains and delayed the onset and decreased the amplitude of global Ca²⁺ signaling. Photoaffinity labeling demonstrated direct binding of NAADP to recombinant HN1L/JPT2. T cell receptor/CD3-dependent coprecipitation of HN1L/JPT2 with RYRs and colocalization of these proteins suggest that HN1L/JPT2 connects NAADP formation with the activation of RYR channels within the first seconds of T cell activation. Thus, HN1L/JPT2 enables NAADP to activate Ca²⁺ release from the endoplasmic reticulum through RYR.

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.

Fluorogenic probes for imaging cellular phosphatase activity

The ability to visualize enzyme activity in a cell, tissue, or living organism can greatly enhance our understanding of the biological roles of that enzyme. While many aspects of cellular signaling are controlled by reversible protein phosphorylation, our understanding of the biological roles of the protein phosphatases involved is limited. Here, we provide an overview of progress toward the development of fluorescent probes that can be used to visualize the activity of protein phosphatases. Significant advances include the development of probes with visible and near-infrared (near-IR) excitation and emission profiles, which provides greater tissue and whole-animal imaging capabilities. In addition, the development of peptide-based probes has provided some selectivity for a phosphatase of interest. Key challenges involve the difficulty of achieving sufficient selectivity for an individual member of a phosphatase enzyme family and the necessity of fully validating the best probes before they can be adopted widely.

NAADP Receptors

Of the established Ca²⁺-mobilizing messengers, NAADP is arguably the most tantalizing. It is the most potent, often efficacious at low nanomolar concentrations, and its receptors undergo dramatic desensitization. Recent studies have identified a new class of calcium-release channel, the two-pore channels (TPCs), as the likely targets for NAADP regulation, even though the effect may be indirect. These channels localized at endolysosomes, where they mediate local Ca²⁺ release, and have highlighted a new role of acidic organelles as targets for messenger-evoked Ca²⁺ mobilization. Three distinct roles of TPCs have been identified. The first is to effect local Ca²⁺ release that may play a role in endolysosomal function including vesicular fusion and trafficking. The second is to trigger global calcium release by recruiting Ca²⁺-induced Ca²⁺-release (CICR) channels at lysosomal-endoplasmic reticulum (ER) junctions. The third is to regulate plasma membrane excitability by the targeting of Ca²⁺ release from appropriately positioned subplasma membrane stores to regulate plasma membrane Ca²⁺-activated channels. In this review, I discuss the role of nicotinic acid adenine nucleotide diphosphate (NAADP)-mediated Ca²⁺ release from endolysosomal stores as a widespread trigger for intracellular calcium signaling mechanisms, and how studies of TPCs are beginning to enhance our understanding of the central role of lysosomes in Ca²⁺ signaling.

Integration of nicotinic acid adenine dinucleotide phosphate (NAADP)-dependent calcium signalling

Nicotinic acid adenine dinucleotide phosphate (NAADP) is currently the most potent endogenous Ca²⁺ mobilizing second messenger. Upon specific extracellular stimulation, rapid production of NAADP has been observed in different cell types from sea urchin eggs to mammalian cells. More than 20 years after the discovery of NAADP, there is still controversy surrounding its metabolism and target receptors/ion channels and organelles. This article briefly reviews recent developments in the NAADP field. Besides the metabolism of NAADP, this review focuses on assumed organelles and putative targets, e.g. ion channels, with special emphasis on ryanodine receptor type 1 (RyR1) and two-pore channels (TPCs). The role of NAADP as a Ca²⁺ trigger is also discussed and the importance of NAADP in the formation of initial Ca²⁺ microdomains is highlighted.

Integrated omics-analysis reveals Wnt-mediated NAD+ metabolic reprogramming in cancer stem-like cells

Abnormal tumor cell metabolism is a consequence of alterations in signaling pathways that provide critical selective advantage to cancer cells. However, a systematic characterization of the metabolic and signaling pathways altered in cancer stem-like cells (CSCs) is currently lacking. Using nuclear magnetic resonance and mass spectrometry, we profiled the whole-cell metabolites of a pair of parental (P-231) and stem-like cancer cells (S-231), and then integrated with whole transcriptome profiles. We identified elevated NAAD⁺ in S-231 along with a coordinated increased expression of genes in Wnt/calcium signaling pathway, reflecting the correlation between metabolic reprogramming and altered signaling pathways. The expression of CD38 and ALP, upstream NAAD⁺ regulatory enzymes, was oppositely regulated between P- and S-231; high CD38 strongly correlated with NAADP in P-231 while high ALP with NAAD⁺ levels in S-231. Antagonizing Wnt activity by dnTCF4 transfection reversed the levels of NAAD⁺ and ALP expression in S-231. Of note, elevated NAAD⁺ caused a decrease of cytosolic Ca²⁺ levels preventing calcium-induced apoptosis in nutrient-deprived conditions. Reprograming of NAD⁺ metabolic pathway instigated by Wnt signaling prevented cytosolic Ca²⁺ overload thereby inhibiting calcium-induced apoptosis in S-231. These results suggest that “oncometabolites” resulting from cross talk between the deranged core cancer signaling pathway and metabolic network provide a selective advantage to CSCs.

Enzyme-instructed self-assembly leads to the activation of optical properties for selective fluorescence detection and photodynamic ablation of cancer cells

An aggregation-induced emission luminogen (AIEgen)-based probe with both fluorescence and photoactivity activatable characteristics is developed for cancer theranostics.

2'-Deoxyadenosine 5'-diphosphoribose is an endogenous TRPM2 superagonist

Transient receptor potential melastatin 2 (TRPM2) is a ligand-gated Ca²⁺-permeable nonselective cation channel. Whereas physiological stimuli, such as chemotactic agents, evoke controlled Ca²⁺ signals via TRPM2, pathophysiological stimuli such as reactive oxygen species and genotoxic stress result in prolonged TRPM2-mediated Ca²⁺ entry and, consequently, apoptosis. To date, adenosine 5'-diphosphoribose (ADPR) has been assumed to be the main agonist for TRPM2. Here we show that 2'-deoxy-ADPR was a significantly better TRPM2 agonist, inducing 10.4-fold higher whole-cell currents at saturation. Mechanistically, this increased activity was caused by a decreased rate of inactivation and higher average open probability. Using high-performance liquid chromatography (HPLC) and mass spectrometry, we detected endogenous 2'-deoxy-ADPR in Jurkat T lymphocytes. Consistently, cytosolic nicotinamide mononucleotide adenylyltransferase 2 (NMNAT-2) and nicotinamide adenine dinucleotide (NAD)-glycohydrolase CD38 sequentially catalyzed the synthesis of 2'-deoxy-ADPR from nicotinamide mononucleotide (NMN) and 2'-deoxy-ATP in vitro. Thus, 2'-deoxy-ADPR is an endogenous TRPM2 superagonist that may act as a cell signaling molecule.

Reaction-Based Off-On Near-infrared Fluorescent Probe for Imaging Alkaline Phosphatase Activity in Living Cells and Mice

Alkaline phosphatases are a group of enzymes that play important roles in regulating diverse cellular functions and disease pathogenesis. Hence, developing fluorescent probes for in vivo detection of alkaline phosphatase activity is highly desirable for studying the dynamic phosphorylation in living organisms. Here, we developed the very first reaction-based near-infrared (NIR) probe (DHXP) for sensitive detection of alkaline phosphatase activity both in vitro and in vivo. Our studies demonstrated that the probe displayed an up to 66-fold fluorescence increment upon incubation with alkaline phosphatases, and the detection limit of our probe was determined to be 0.07 U/L, which is lower than that of most of alkaline phosphatase probes reported in literature. Furthermore, we demonstrated that the probe can be applied to detecting alkaline phosphatase activity in cells and mice. In addition, our probe possesses excellent biocompatibility and rapid cell-internalization ability. In light of these prominent properties, we envision that DHXP will add useful tools for investigating alkaline phosphatase activity in biomedical research.

ADP-ribosyl cyclases regulate early development of the sea urchin

ADP-ribosyl cyclases are multifunctional enzymes involved in the metabolism of nucleotide derivatives necessary for Ca2+ signalling such as cADPR and NAADP. Although Ca2+ signalling is a critical regulator of early development, little is known of the role of ADP-ribosyl cyclases during embryogenesis. Here we analyze the expression, activity and function of ADP-ribosyl cyclases in the embryo of the sea urchin - a key organism for study of both Ca2+ signalling and embryonic development. ADP-ribosyl cyclase isoforms (SpARC1-4) showed unique changes in expression during early development. These changes were associated with an increase in the ratio of cADPR:NAADP production. Over-expression of SpARC4 (a preferential cyclase) disrupted gastrulation. Our data highlight the importance of ADP-ribosyl cyclases during embryogenesis.

Ca(2+) microdomains, NAADP and type 1 ryanodine receptor in cell activation

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a Ca(2+) mobilizing second messenger that belongs to the superfamily of regulatory adenine nucleotides. Though NAADP has been known since 20 years, several aspects of its metabolism and molecular mode of action are still under discussion. Though the importance of the type 1 ryanodine receptor was discovered and published already in 2002 Hohenegger et al. (2002 Oct 15), recent data re-emphasize these original findings in pancreatic acinar cells and in T-lymphocytes. Here we review recent developments in NAADP formation and metabolism, putative target Ca(2+) channels for NAADP with special emphasis on the type 1 ryanodine receptor, and NAADP binding proteins. The latter are basis for a unifying hypothesis for NAADP action. Finally, the role of NAADP in T cell Ca(2+) signaling and activation is discussed. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen.

A primer of NAADP-mediated Ca(2+) signalling: From sea urchin eggs to mammalian cells

Since the discovery of the Ca(2+) mobilizing effects of the pyridine nucleotide metabolite, nicotinic acid adenine dinucleotide phosphate (NAADP), this molecule has been demonstrated to function as a Ca(2+) mobilizing intracellular messenger in a wide range of cell types. In this review, I will briefly summarize the distinct principles behind NAADP-mediated Ca(2+) signalling before going on to outline the role of this messenger in the physiology of specific cell types. Central to the discussion here is the finding that NAADP principally mobilizes Ca(2+) from acidic organelles such as lysosomes and it is this property that allows NAADP to play a unique role in intracellular Ca(2+) signalling. Lysosomes and related organelles are small Ca(2+) stores but importantly may also initiate a two-way dialogue with other Ca(2+) storage organelles to amplify Ca(2+) release, and may be strategically localized to influence localized Ca(2+) signalling microdomains. The study of NAADP signalling has created a new and fruitful focus on the lysosome and endolysosomal system as major players in calcium signalling and pathophysiology.

The enzymatic activities of CD38 enhance CLL growth and trafficking: implications for therapeutic targeting

The ecto-enzyme CD38 is gaining momentum as a novel therapeutic target for patients with hematological malignancies, with several anti-CD38 monoclonal antibodies in clinical trials with promising results. In chronic lymphocytic leukemia (CLL) CD38 is a marker of unfavorable prognosis and a central factor in the pathogenetic network underlying the disease: activation of CD38 regulates genetic pathways involved in proliferation and movement. Here we show that CD38 is enzymatically active in primary CLL cells and that its forced expression increases disease aggressiveness in a xenograft model. The effect is completely lost when using an enzyme-deficient version of CD38 with a single amino-acid mutation. Through the enzymatic conversion of NAD into ADPR (ADP-ribose) and cADPR (cyclic ADP-ribose), CD38 increases cytoplasmic Ca(2+) concentrations, positively influencing proliferation and signaling mediated via chemokine receptors or integrins. Consistently, inhibition of the enzymatic activities of CD38 using the flavonoid kuromanin blocks CLL chemotaxis, adhesion and in vivo homing. In a short-term xenograft model using primary cells, kuromanin treatment traps CLL cells in the blood, thereby increasing responses to chemotherapy. These results suggest that monoclonal antibodies that block the enzymatic activities of CD38 or enzyme inhibitors may prove therapeutically useful.

NAADP and the two-pore channel protein 1 participate in the acrosome reaction in mammalian spermatozoa

A TPCN1 gene–deficient mouse strain is used to show that two convergent working NAADP-dependent pathways with nonoverlapping activation and self-inactivation profiles for distinct NAADP concentrations drive acrosomal exocytosis, by which TPC1 is central for the pathway activated by low-micromolar NAADP concentrations.

The functional relationship between the formation of hundreds of fusion pores during the acrosome reaction in spermatozoa and the mobilization of calcium from the acrosome has been determined only partially. Hence, the second messenger NAADP, promoting efflux of calcium from lysosome-like compartments and one of its potential molecular targets, the two-pore channel 1 (TPC1), were analyzed for its involvement in triggering the acrosome reaction using a TPCN1 gene–deficient mouse strain. The present study documents that TPC1 and NAADP-binding sites showed a colocalization at the acrosomal region and that treatment of spermatozoa with NAADP resulted in a loss of the acrosomal vesicle that showed typical properties described for TPCs: Registered responses were not detectable for its chemical analogue NADP and were blocked by the NAADP antagonist trans-Ned-19. In addition, two narrow bell-shaped dose-response curves were identified with maxima in either the nanomolar or low micromolar NAADP concentration range, where TPC1 was found to be responsible for activating the low affinity pathway. Our finding that two convergent NAADP-dependent pathways are operative in driving acrosomal exocytosis supports the concept that both NAADP-gated cascades match local NAADP concentrations with the efflux of acrosomal calcium, thereby ensuring complete fusion of the large acrosomal vesicle.

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a second messenger in muscarinic receptor-induced contraction of guinea pig trachea

Nicotinic acid adenine dinucleotide phosphate (NAADP) is increasingly being demonstrated to be involved in calcium signaling in many cell types and species. Although it has been shown to play a role in smooth muscle cell contraction in several tissues, nothing is known about its possible role in tracheal smooth muscle, a muscle type that is clinically relevant to asthma. To determine whether NAADP functions as a second messenger in tracheal smooth muscle contraction, we used the criteria set out by Sutherland for a molecule to be designated a second messenger. We report that NAADP satisfies all five criteria as follows. First, the NAADP antagonist Ned-19 inhibited contractions in tracheal rings and calcium increases in isolated smooth muscle cells induced by the muscarinic agonist carbachol. Second, NAADP increased cytosolic calcium in isolated cells when microinjected and was blocked by Ned-19. Third, tracheal homogenates could synthesize NAADP by base exchange from exogenous NADP and nicotinic acid and metabolize exogenous NAADP to nicotinic acid adenine dinucleotide by a 2'-phosphatase. Fourth, carbachol induced a rapid and transient increase in endogenous NAADP levels. Fifth, tracheal homogenates contained NAADP-binding sites of high affinity. Taken together, these data demonstrate that NAADP functions as a second messenger in tracheal smooth muscle, and therefore, steps in the NAADP signaling pathway might provide possible new drug targets.

Calcium pathway machinery at fertilization in echinoderms

Calcium signaling in cells directs diverse physiological processes. The calcium waves triggered by fertilization is a highly conserved calcium signaling event essential for egg activation, and has been documented in every egg tested. This activity is one of the few highly conserved events of egg activation through the course of evolution. Echinoderm eggs, as well as many other cell types, have three main intracellular Ca(2+) mobilizing messengers - IP3, cADPR and NAADP. Both cADPR and NAADP were identified as Ca(2+) mobilizing messengers using the sea urchin egg homogenate, and this experimental system, along with the intact urchin and starfish oocyte/egg, continues to be a vital tool for investigating the mechanism of action of calcium signals. While many of the major regulatory steps of the IP3 pathway are well resolved, both cADPR and NAADP remain understudied in terms of our understanding of the fundamental process of egg activation at fertilization. Recently, NAADP has been shown to trigger Ca(2+) release from acidic vesicles, separately from the ER, and a new class of calcium channels, the two-pore channels (TPCs), was identified as the likely targets for this messenger. Moreover, it was found that both cADPR and NAADP can be synthesized by the same family of enzymes, the ADP-rybosyl cyclases (ARCs). In this context of increasing amount of information, the potential coupling and functional roles of different messengers, intracellular stores and channels in the formation of the fertilization calcium wave in echinoderms will be critically evaluated.