ADP ribosyl cyclase activity of a novel bone marrow stromal cell surface molecule, BST-1

Molecular characterization of a novel cell surface ADP-ribosyl cyclase from the sea urchin

The sea urchin is an extensively used model system for the study of calcium signalling by the messenger molecules NAADP and cyclic ADP-ribose. Both are synthesized by ADP-ribosyl cyclases but our molecular understanding of these enzymes in the sea urchin is limited. We have recently reported the cloning of an extended family of sea urchin ADP-ribosyl cyclases and shown that one of these enzymes (SpARC1) is active within the endoplasmic reticulum lumen. These studies suggest that production of messengers is compartmentalized. Here we characterize the properties of SpARC2. SpARC2 catalyzed both NAADP and cyclic ADP-ribose production. Unusually, the NAD surrogate, NGD was a poor substrate. In contrast to SpARC1, heterologously expressed SpARC2 localized to the plasma membrane via a glycosylphosphatidylinositol (GPI)-anchor. Transcripts for SpARC2 were readily detectable in sea urchin eggs and a majority of the endogenous membrane bound activity was found to be GPI-anchored. Our data reveal striking differences in the properties of sea urchin ADP-ribosyl cyclases and provide further evidence that messenger production may occur outside of the cytosol.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

Sperm express a Ca2+-regulated NAADP synthase

NAADP (nicotinic acid-adenine dinucleotide phosphate), the most potent Ca2+-mobilizing second messenger, is active in a wide range of organisms and cell types. Until now, all NAADP-producing enzymes have been thought to be members of the ADP-ribosyl cyclase family. ADP-ribosyl cyclases exhibit promiscuous substrate selectivity, synthesize a variety of products and are regulated in a limited manner, which may be non-physiological. In the present paper, we report the presence of an enzyme on the surface of sea urchin sperm that exhibits bell-shaped regulation by Ca2+ over a range (EC(50) of 10 nM and IC(50) of 50 microM) that is physiologically relevant. Uniquely, this surface enzyme possesses complete selectivity for nucleotides with a 2'-phosphate group and exhibits only base-exchange activity without any detectable cyclase activity. Taken together, these findings indicate that this novel enzyme should be considered as the first true NAADP synthase.

Molecular characterization of a novel intracellular ADP-ribosyl cyclase

Background

ADP-ribosyl cyclases are remarkable enzymes capable of catalyzing multiple reactions including the synthesis of the novel and potent intracellular calcium mobilizing messengers, cyclic ADP-ribose and NAADP. Not all ADP-ribosyl cyclases however have been characterized at the molecular level. Moreover, those that have are located predominately at the outer cell surface and thus away from their cytosolic substrates.

Methodology/Principal Findings

Here we report the molecular cloning of a novel expanded family of ADP-ribosyl cyclases from the sea urchin, an extensively used model organism for the study of inositol trisphosphate-independent calcium mobilization. We provide evidence that one of the isoforms (SpARC1) is a soluble protein that is targeted exclusively to the endoplasmic reticulum lumen when heterologously expressed. Catalytic activity of the recombinant protein was readily demonstrable in crude cell homogenates, even under conditions where luminal continuity was maintained.

Conclusions/Significance

Our data reveal a new intracellular location for ADP-ribosyl cyclases and suggest that production of calcium mobilizing messengers may be compartmentalized.

CD38 and CD157 as receptors of the immune system: a bridge between innate and adaptive immunity

This paper reviews some of the results and the speculations presented at the Torino CD38 Meeting in June, 2006 and focused on CD38 and CD157 seen as a family of molecules acting as surface receptors of immune cells. This partisan view was adopted in the attempt to combine the enzymatic functions with what the immunologists consider key functions in different cell models. At the moment, it is unclear whether the two functions are correlated, indifferent, or independent. Here we present conclusions inferred exclusively on human cell models, namely T and B lymphocytes, dendritic cells, and granulocytes. As an extra analytical tool, we try to follow in the history of life when the enzymatic and receptorial functions were generated, mixing ontogeny, membrane localization, and cell anchorage.

CD38 and CD157 as receptors of the immune system: a bridge between innate and adaptive immunity

This paper reviews some of the results and the speculations presented at the Torino CD38 Meeting in June, 2006 and focused on CD38 and CD157 seen as a family of molecules acting as surface receptors of immune cells. This partisan view was adopted in the attempt to combine the enzymatic functions with what the immunologists consider key functions in different cell models. At the moment, it is unclear whether the two functions are correlated, indifferent, or independent. Here we present conclusions inferred exclusively on human cell models, namely T and B lymphocytes, dendritic cells, and granulocytes. As an extra analytical tool, we try to follow in the history of life when the enzymatic and receptorial functions were generated, mixing ontogeny, membrane localization, and cell anchorage.

CD157 plays a pivotal role in neutrophil transendothelial migration

Paracellular diapedesis, a key step in leukocyte recruitment to the site of inflammation, occurs at endothelial junctions and is regulated by highly coordinated interactions between leukocytes and endothelium. We found that CD157, a glycosylphosphatidylinositol-anchored ectoenzyme belonging to the NADase/ADP-ribosyl cyclase family, plays a crucial role for neutrophil diapedesis, because its ligation with specific monoclonal antibodies (both on neutrophils or endothelial cells) results in altered neutrophil movement on the apical surface of endothelium and, ultimately, in loss of diapedesis. Real-time microscopy revealed that CD157 behaves as a sort of compass during the interaction between neutrophils and endothelial cells; indeed, following CD157 ligation, neutrophils appear disoriented, meandering toward junctions where they eventually stop without transmigrating. These findings are relevant in vivo because CD157-deficient neutrophils obtained from patients with paroxysmal nocturnal hemoglobinuria are characterized by a severely impaired diapedesis.

NAD+ metabolism in health and disease

Nicotinamide adenine dinucleotide (NAD(+)) is both a coenzyme for hydride-transfer enzymes and a substrate for NAD(+)-consuming enzymes, which include ADP-ribose transferases, poly(ADP-ribose) polymerases, cADP-ribose synthases and sirtuins. Recent results establish protective roles for NAD(+) that might be applicable therapeutically to prevent neurodegenerative conditions and to fight Candida glabrata infection. In addition, the contribution that NAD(+) metabolism makes to lifespan extension in model systems indicates that therapies to boost NAD(+) might promote some of the beneficial effects of calorie restriction. Nicotinamide riboside, the recently discovered nucleoside precursor of NAD(+) in eukaryotic systems, might have advantages as a therapy to elevate NAD(+) without inhibiting sirtuins, which is associated with high-dose nicotinamide, or incurring the unpleasant side-effects of high-dose nicotinic acid.

Redesign of Schistosoma mansoni NAD+ catabolizing enzyme: active site H103W mutation restores ADP-ribosyl cyclase activity

Schistosoma mansoni NAD(P)+ catabolizing enzyme (SmNACE) is a new member of the ADP-ribosyl cyclase family. In contrast to all the other enzymes that are involved in the production of metabolites that elicit Ca2+ mobilization, SmNACE is virtually unable to transform NAD+ into the second messenger cyclic ADP-ribose (cADPR). Sequence alignments revealed that one of four conserved residues within the active site of these enzymes was replaced in SmNACE by a histidine (His103) instead of the highly conserved tryptophan. To find out whether the inability of SmNACE to catalyze the canonical ADP-ribosyl cyclase reaction is linked to this change, we have replaced His103 with a tryptophan. The H103W mutation in SmNACE was indeed found to restore ADP-ribosyl cyclase activity as cADPR amounts for 7% of the reaction products (i.e., a value larger than observed for other members of this family such as CD38). Introduction of a Trp103 residue provides some of the binding characteristics of mammalian ADP-ribosyl cyclases such as increased affinity for Cibacron blue and slow-binding inhibition by araF-NAD+. Homology modeling of wild-type and H103W mutant three-dimensional structures, and docking of substrates within the active sites, provides new insight into the catalytic mechanism of SmNACE. Both residue side chains share similar roles in the nicotinamide-ribose bond cleavage step leading to an E.ADP-ribosyl reaction intermediate. They diverge, however, in the evolution of this intermediate; His103 provides a more polar environment favoring the accessibility to water and hydrolysis leading to ADP-ribose at the expense of the intramolecular cyclization pathway resulting in cADPR.

Different expression patterns of TRP genes in murine B and T lymphocytes

A prolonged increase in the intracellular calcium concentration ([Ca2+]i) is essential for lymphocyte activation that includes cell proliferation and differentiation. This increase in [Ca2+]i results from Ca2+ release from the intracellular store and the subsequent Ca2+ influx from the extracellular environment via calcium channels located on the plasma membrane. Although transient receptor potential (TRP) channels have been reported to play important roles in the [Ca2+]i increase in lymphocytes, the function of these channels in lymphocyte activation remains unknown. Here, we report the comprehensive expression profile of TRP channel gene families including TRPC, TRPV, and TRPM in the murine immune system. RT-PCR analysis revealed different expression patterns of the TRP channel genes in B and T lymphocytes isolated from the spleen. Therefore, our results provide an appropriate reference of TRP gene expression in murine lymphocytes.

The CD38/CD157 mammalian gene family: An evolutionary paradigm for other leukocyte surface enzymes

Human CD38 is the mammalian prototype of a family of phylogenetically conserved proteins which share structural similarities and enzymatic activities involved in the production of an intracellular second messenger with calcium mobilizing effects. Engagement of CD38 by agonistic monoclonal antibodies and the CD31 ligand initiates a cytoplasmic signaling cascade involving tyrosine phosphorylation of the proto-oncogene c-cbl and of the extracellular regulated kinase 1 of 2 complex. Further requirements for signal transduction include a privileged localization within the cholesterol-rich areas of the plasma membrane and physical association with specialized surface receptors. CD38-mediated signals are crucial in heterotypic cell adhesion and migration as well as in the activation of proliferation/survival programs by normal and neoplastic cells. Here we review the most recent literature on this complex topic and attempt to formulate a single model reconciling the enzymatic and receptorial activities of CD38.

The CD38-independent ADP-ribosyl cyclase from mouse brain synaptosomes: a comparative study of neonate and adult brain

cADPR (cADP-ribose), a metabolite of NAD+, is known to modulate intracellular calcium levels and to be involved in calcium-dependent processes, including synaptic transmission, plasticity and neuronal excitability. However, the enzyme that is responsible for producing cADPR in the cytoplasm of neural cells, and particularly at the synaptic terminals of neurons, remains unknown. In the present study, we show that endogenous concentrations of cADPR are much higher in embryonic and neonate mouse brain compared with the adult tissue. We also demonstrate, by comparing wild-type and Cd38-/- tissues, that brain cADPR content is independent of the presence of CD38 (the best characterized mammalian ADP-ribosyl cyclase) not only in adult but also in developing tissues. We show that Cd38-/- synaptosome preparations contain high ADP-ribosyl cyclase activities, which are more important in neonates than in adults, in line with the levels of endogenous cyclic nucleotide. By using an HPLC method and adapting the cycling assay developed initially to study endogenous cADPR, we accurately examined the properties of the synaptosomal ADP-ribosyl cyclase. This intracellular enzyme has an estimated K(m) for NAD+ of 21 microM, a broad optimal pH at 6.0-7.0, and the concentration of free calcium has no major effect on its cADPR production. It binds NGD+ (nicotinamide-guanine dinucleotide), which inhibits its NAD+-metabolizing activities (K(i)=24 microM), despite its incapacity to cyclize this analogue. Interestingly, it is fully inhibited by low (micromolar) concentrations of zinc. We propose that this novel mammalian ADP-ribosyl cyclase regulates the production of cADPR and therefore calcium levels within brain synaptic terminals. In addition, this enzyme might be a potential target of neurotoxic Zn2+.

Boric acid inhibits adenosine diphosphate-ribosyl cyclase non-competitively

Adenosine diphosphate-ribosyl cyclase (ADP-ribosyl cyclase) is a ubiquitous enzyme in eukaryotes that converts NAD+ to cyclic-ADP-ribose (cADPR) and nicotinamide. A quantitative assay for cADPR was developed using capillary electrophoresis to separate NAD+, cADPR, ADP-ribose, and ADP with UV detection (254 nm). Using this assay, the apparent Km and Vmax for Aplysia ADP-ribosyl cyclase were determined to be 1.24+/-0.05 mM and 131.8+/-2.0 microM/min, respectively. Boric acid inhibited ADP-ribosyl cyclase non-competitively with a Ki of 40.5+/-0.5 mM. Boric acid binding to cADPR, determined by electrospray ionization mass spectrometry, was characterized by an apparent binding constant, KA, of 655+/-99 L/mol at pH 10.3.

The Ca2+-releasing messenger NAADP, a new player in the nervous system

Many physiological processes are controlled by a great diversity of Ca2+ signals. Within cell, Ca2+ signals depend upon Ca2+ entry and/or Ca2+ release from internal Ca2+ stores. The control of Ca2+-store mobilization is ensured by a family of messengers comprising inositol 1,4,5 trisphosphate, cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate (NAADP). From recent works, new concepts have emerged where activation of the cells by outside stimuli, acting at the plasma membrane, results in the synthesis of multiple Ca2+-releasing messengers which may interact and shape complex Ca2+ signals in the cytosol as well as in the nucleus. This contribution will cover the most recent advances on NAADP signalling with some emphasis on neurons.

Pyridine nucleotides and calcium signalling in arterial smooth muscle: from cell physiology to pharmacology

It is generally accepted that the mobilisation of intracellular Ca2+ stores plays a pivotal role in the regulation of arterial smooth muscle function, paradoxically during both contraction and relaxation. However, the spatiotemporal pattern of different Ca2+ signals that elicit such responses may also contribute to the regulation of, for example, differential gene expression. These findings, among others, demonstrate the importance of discrete spatiotemporal Ca2+ signalling patterns and the mechanisms that underpin them. Of fundamental importance in this respect is the realisation that different Ca2+ storing organelles may be selected by the discrete or coordinated actions of multiple Ca2+ mobilising messengers. When considering such messengers, it is generally accepted that sarcoplasmic reticulum (SR) stores may be mobilised by the ubiquitous messenger inositol 1,4,5 trisphosphate. However, relatively little attention has been paid to the role of Ca2+ mobilising pyridine nucleotides in arterial smooth muscle, namely, cyclic adenosine diphosphate-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). This review will therefore focus on these novel mechanisms of calcium signalling and their likely therapeutic potential.

Calcium signalling by nicotinic acid adenine dinucleotide phosphate (NAADP)

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a recently described Ca2+ mobilizing messenger, and probably the most potent. We briefly review its unique properties as a Ca2+ mobilizing agent. We present arguments for its action in targeting acidic calcium stores rather than the endoplasmic reticulum. Finally, we discuss possible biosynthetic pathways for NAADP in cells and candidates for its target Ca2+ release channel, which has eluded identification so far.

Production of calcium-mobilizing metabolites by a novel member of the ADP-ribosyl cyclase family expressed in Schistosoma mansoni

ADP-ribosyl cyclases are structurally conserved enzymes that are best known for catalyzing the production of the calcium-mobilizing metabolite, cyclic adenosine diphosphate ribose (cADPR), from nicotinamide adenine dinucleotide (NAD(+)). However, these enzymes also produce adenosine diphosphate ribose (ADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP(+)), both of which have been shown to modulate calcium mobilization in vitro. We have now characterized a new member of the cyclase family from Schistosoma mansoni, a member of the Platyhelminthes phylum. We show that the novel NAD(P)(+) catabolizing enzyme (NACE) expressed by schistosomes is structurally most closely related to the cyclases cloned from Aplysia but also shows significant homology with the mammalian cyclases, CD38 and CD157. NACE expression is developmentally regulated in schistosomes, and the GPI-anchored protein is localized to the outer tegument of the adult schistosome. Importantly, NACE, like all members of the cyclase family, is a multifunctional enzyme and catalyzes NAD(+) glycohydrolase and base-exchange reactions to produce ADPR and NAADP(+). However, despite being competent to generate a cyclic product from NGD(+), a nonphysiologic surrogate substrate, NACE is so far the only enzyme in the cyclase family that is unable to produce significant amounts of cADPR (<0.02% of reaction products) using NAD(+) as the substrate. This suggests that the other calcium-mobilizing metabolites produced by NACE may be more important for calcium signaling in schistosomes. Alternatively, the function of NACE may be to catabolize extracellular NAD(+) to prevent its use by host enzymes that utilize this source of NAD(+) to facilitate immune responses.

T-cell suppression mediated by mesenchymal stem cells is deficient in patients with severe aplastic anemia

OBJECTIVE

To compare the suppressive effect of mesenchymal stem cells (MSC), derived from normal individuals or severe aplastic anemia patients (SAA), on T-cell activation.

PATIENTS AND METHODS

We studied bone marrow MSC from 19 healthy donors and 23 SAA patients in different phases of the disease: at diagnosis (n = 3), following immunosuppressive therapy (IS) (n = 16), or after a bone marrow transplant (BMT) (n = 4). MSC were tested for T-cell suppression in the following assays: mixed lymphocyte reaction (MLR), phytohemaglutinin (PHA)-primed cultures, activation surface markers, gamma-IFN production, hematopoietic colony formation (CFC), production of cyclic ADP-ribose (cADPR).

RESULTS

The abnormalities of SAA MSC included: 1) significantly lower suppression of T-cell proliferation induced by alloantigens (p = 0.009) or PHA (p = 0.006); 2) impaired capacity to suppress CD38 expression on PHA-primed T cells (p = 0.001); 3) impaired ability to suppress gamma-IFN production in PHA cultures, resulting in an 11-fold higher gamma-IFN concentration; 4) no preventive effect on T cell-mediated inhibition of CFC; and 5) significantly reduced (p = 0.009) production of cADPR, a universal calcium mobilizer. MSC-mediated suppression of PHA-induced T-cell proliferation was restored to control levels in 3 of 4 patients post-BMT.

CONCLUSION

The ability of MSC to downregulate T-cell priming, proliferation, and cytokine release is deficient in patients with SAA, persists indefinitely after immunosuppressive therapy, but seems to be restored after BMT. Whether these abnormalities are relevant to the pathogenesis of aplastic anemia remains to be determined.

Generation of potent antitumor CTL from patients with multiple myeloma directed against HM1.24

PURPOSE

The purpose of this work was to test the suitability of the HM1.24 antigen as a CTL target for immunotherapy of patients with multiple myeloma.

EXPERIMENTAL DESIGN

Antigen-specific T cells were generated from patients with multiple myeloma using stimulation with protein-pulsed dendritic cells and tested in ELISPOT and CTL assays.

RESULTS

HM1.24-primed T cells responded selectively to HM1.24-loaded autologous peripheral blood mononuclear cells (PBMC) in an IFN-gamma ELISPOT assay (median, 342; range, 198-495 IFN-gamma-producing cells/10(5) cf. unloaded PBMC median, 98; range, 7-137; P < 0.05, n = 5) and also to autologous malignant plasma cells (MPC; median, 227; range, 153-335; P < 0.05 when compared with the response to allogeneic MPC median, 57; range, 22-158; n = 5). HM1.24-primed T cells lysed autologous MPC (at 20:1 E/T ratio: median, 48% specific killing; range, 23-88%; at 10:1 E/T ratio: median, 43%; range, 15-80%; n = 12) but not allogeneic MPC. Lysis of autologous MPC was inhibited by anti-MHC class I but not anti-MHC class II antibodies and was blocked by Concanamycin A. Lysis of autologous MPC was blocked by competition with autologous HM1.24-transfected dendritic cells (10:1 ratio with autologous MPC). Unmanipulated, or control plasmid-transfected dendritic cells had no effect on lysis of autologous MPC.

CONCLUSION

Our results indicate that HM1.24 is a promising target for immunotherapy of multiple myeloma.

ADP-ribosyl cyclase couples to cyclic AMP signaling in the cardiomyocytes

ADP-ribosyl cyclase (ADPR-cyclase) produces a Ca(2+)-mobilizing second messenger cyclic ADP-ribose (cADPR) from beta-NAD(+). In this study, we examined the molecular basis of which beta-adrenergic receptor (betaAR) stimulation induces cADPR formation and characterized cardiac ADPR-cyclase. The results revealed that isoproterenol-mediated increase of [Ca(2+)](i) in rat cardiomyocytes was blocked by pretreatment with a cADPR antagonistic derivative 8-Br-cADPR, a PKA inhibitor H89 or high concentration of ryanodine. Moreover, incubation of ventricular lysates with isoproterenol, forskolin or cAMP resulted in activation of ADPR-cyclase that was inhibited by pretreatment with H89. Supporting the observations, the cADPR antagonist and H89 blocked 8-CPT-cAMP, a cell-permeant cAMP analog-induced increase in [Ca(2+)](i) but not cGMP-mediated increase. Characterization of partially purified cardiac ADPR-cyclase showed a molecular mass of approximately 42 kDa and no cross-activity with CD38 antibodies, and the enzyme activity was inhibited by Zn(2+) but not dithiothreitol. Microinjection of the enzyme into rat cardiomyocytes increased the level of [Ca(2+)](i) in a concentration-dependent manner. The enzyme-mediated increase of [Ca(2+)](i) was blocked by the cADPR antagonist. These findings suggest that betaAR-mediated regulation of [Ca(2+)](i) in rat cardiomyocytes is primed by activation of cardiac ADPR-cyclase via cAMP/PKA signaling and that cardiac ADPR-cyclase differs from CD38 in biochemical and immunological properties.

CD38/cyclic ADP-ribose signaling: role in the regulation of calcium homeostasis in airway smooth muscle

The contractility of airway smooth muscle cells is dependent on dynamic changes in the concentration of intracellular calcium. Signaling molecules such as inositol 1,4,5-trisphosphate and cyclic ADP-ribose play pivotal roles in the control of intracellular calcium concentration. Alterations in the processes involved in the regulation of intracellular calcium concentration contribute to the pathogenesis of airway diseases such as asthma. Recent studies have identified cyclic ADP-ribose as a calcium-mobilizing second messenger in airway smooth muscle cells, and modulation of the pathway involved in its metabolism results in altered calcium homeostasis and may contribute to airway hyperresponsiveness. In this review, we describe the basic mechanisms underlying the dynamics of calcium regulation and the role of CD38/cADPR, a novel pathway, in the context of airway smooth muscle function and its contribution to airway diseases such as asthma.

Concentrative uptake of cyclic ADP-ribose generated by BST-1+ stroma stimulates proliferation of human hematopoietic progenitors

Cyclic ADP-ribose (cADPR) is an intracellular calcium mobilizer generated from NAD(+) by the ADP-ribosyl cyclases CD38 and BST-1. cADPR, both exogenously added and paracrinally produced by a CD38(+) feeder layer, has recently been demonstrated to stimulate the in vitro proliferation of human hemopoietic progenitors (HP) and also the in vivo expansion of hemopoietic stem cells. The low density of BST-1 expression on bone marrow (BM) stromal cells and the low specific activity of the enzyme made it unclear whether cADPR generation by a BST-1(+) stroma could stimulate HP proliferation in the BM microenvironment. We developed and characterized two BST-1(+) stromal cell lines, expressing an ectocellular cyclase activity similar to that of BST-1(+) human mesenchymal stem cells, the precursors of BM stromal cells. Long term co-culture of cord blood-derived HP over these BST-1(+) feeders determined their expansion. Influx of paracrinally generated cADPR into clonogenic HP was mediated by a concentrative, nitrobenzylthioinosine- and dipyridamole-inhibitable nucleoside transporter, this providing a possible explanation to the effectiveness of the hormone-like concentrations of the cyclic nucleotide measured in the medium conditioned by BST-1(+) feeders. These results suggest that the BST-1-catalyzed generation of extracellular cADPR, followed by the concentrative uptake of the cyclic nucleotide by HP, may be physiologically relevant in normal hemopoiesis.

Altered airway responsiveness in CD38-deficient mice

Cyclic ADP-ribose (cADPR) mobilizes calcium from intracellular stores and contributes to agonist-induced intracellular calcium elevation in airway smooth muscle (ASM). In this study we determined the functional role of CD38/cADPR signaling in the regulation of airway tone using CD38 deficient (cd38(-/-)) mice. The responsiveness to different doses of methacholine, as determined by changes in lung resistance and dynamic compliance, was significantly (P < or = 0.05) lower in cd38(-/-) mice compared with wild-type controls. To determine the mechanism responsible for the reduced responsiveness, we measured the intracellular calcium responses to contractile agonists in ASM cells. In ASM cells isolated from cd38(-/-) mice, the intracellular calcium responses to acetylcholine and endothelin-1 were significantly lower than in controls. Pretreatment of ASM cells with a cADPR antagonist resulted in attenuated intracellular calcium responses to endothelin-1 in cells isolated from wild-type mice, but not in those isolated from the cd38(-/-) mice. Very low cADPR levels and no detectable ADP-ribosyl cyclase activity were observed in lung tissue from cd38(-/-) mice, suggesting that CD38 is a critical source for cADPR synthesis. The results of the present study demonstrate that CD38/cADPR contributes to airway smooth muscle tone and responsiveness through its effects on agonist-induced elevation of intracellular calcium in ASM cells.

CD157 is an important mediator of neutrophil adhesion and migration

CD157, a glycosylphosphatidylinositol (GPI)-anchored protein encoded by a member of the CD38 NADase/ADP-ribosyl cyclase gene family, is expressed on the surface of most human circulating neutrophils. This work demonstrates that CD157 is a receptor that induces reorganization of the cytoskeleton and significant changes in cell shape, and that signals mediated by CD157 act through modulation of cytosolic Ca(2+) concentration. These signals are independent of the products of CD157's enzymatic activities (ie, cyclic adenosine diphosphate [ADP]-ribose and ADP-ribose). Indeed, the enzymatic activities of CD157 in circulating neutrophils as well as in dimethyl sulfoxide (DMSO)-differentiated (CD157(+)/CD38(-)) HL-60 cells, are hardly detectable. This work also shows that the receptorial activity relies on cross-talk between CD157 and beta(2) integrin. CD157 localizes in GM1-enriched lipid rafts and, upon activation, it migrates to the uropod, a structure specialized in motility and adhesive functions. Indeed, CD157 is involved in adhesion to extracellular matrix proteins and in chemotaxis induced in vitro by formyl-methionyl-leucyl-phenylalanine (fMLP). These findings were consistent with the results obtained in neutrophils from patients with paroxysmal nocturnal hemoglobinuria (PNH), in which CD157 is deficient. These neutrophils showed constant defects in adhesion and migration. Our data attribute specific and crucial roles to CD157 in the regulation of innate immunity during inflammation.

Concentrative influx of functionally active cyclic ADP-ribose in dimethyl sulfoxide-differentiated HL-60 cells

Native human HL-60 cells do not express CD38, a multifunctional ectoenzyme, which generates cyclic ADP-ribose (cADPR), a potent calcium mobilizer. However, when HL-60 cells are induced to differentiate to granulocytes by treatment with retinoic acid (RA), they express CD38 and accumulate cADPR. Both processes play a causal role in RA-induced differentiation. Other granulocyte differentiation-inducers, including dimethyl sulfoxide (Me(2)SO), fail to induce CD38 expression. We investigated whether treatment of HL-60 cells with Me(2)SO involves any changes in the cADPR/intracellular calcium ([Ca(2+)](i)) signaling system and, specifically, whether Me(2)SO affects those nucleoside transporters (NT) (both equilibrative (ENT) and concentrative (CNT)) that mediate influx of extracellular cADPR. Semiquantitative polymerase chain reaction analysis of transcripts, binding of [(3)H]nitrobenzylthioinosine (NBMPR) to intact cells, and influx experiments of extracellular cADPR (with selective inhibitors of NT as NBMPR or in specific conditions) were performed in native and Me(2)SO-differentiated HL-60 cells. The native cells showed uptake of cADPR across ENT2, whereas influx of cADPR into the Me(2)SO-differentiated cells occurred mostly by concentrative processes mediated by CNT3 and by an NBMPR-inhibitable concentrative NT designated cs-csg. Me(2)SO-differentiated, but not native HL-60 cells, accumulated cADPR and showed increased [Ca(2+)](i) levels when grown in a transwell co-culture setting over CD38-transfected 3T3 fibroblasts where nanomolar cADPR concentrations are present in the medium. NBMPR inhibited both responses of Me(2)SO-induced cells. Thus, concentrative influx of extracellular cADPR across CNT3 and cs-csg NT could substitute in the absence of CD38 in eliciting cADPR-dependent [Ca(2+)](i) increases in granulocyte-differentiated HL-60 cells, as well as in other CD38(-) cells.

A bivalent single-chain Fv fragment against CD47 induces apoptosis for leukemic cells

We constructed a single-chain antibody fragment (scFv) of murine monoclonal antibody, MABL, which specifically bound to human CD47 (hCD47) and induced apoptosis of the leukemic cells. The scFv of MABL antibody with a 15-residue linker (MABL scFv-15) formed both dimer (Mr 50 kDa) and monomer (Mr 25 kDa). Both MABL scFv-15 dimer and monomer had binding activity for hCD47. MABL scFv-15 dimer strongly induced apoptosis of hCD47-introduced mouse leukemic cells in vitro and exhibited anti-tumor effect in a myeloma transplanted mice model. However, MABL scFv-15 monomer scarcely exhibited these activities. These results strongly demonstrate that the ligation of CD47 antigen by two antigen-binding sites of MABL dimer is needed for inducing apoptosis. The parent MABL antibody caused hemagglutination due to the CD47 expressed on erythrocytes. Interestingly, MABL scFv-15 dimer did not cause hemagglutination. This apoptosis-inducing dimer appears to be a lead candidate for novel leukemic therapy.

A Family of Leukemia Inhibitory Factor-Binding Peptides that Can Act as Antagonists When Conjugated to Poly(ethylene glycol)

A panel of six naïve 14-residue random peptide libraries displayed polyvalently on M13 phage was pooled and sorted against human leukemia inhibitory factor (LIF). After four rounds of selection, a single large family of peptides with the consensus sequence XCXXXXG(A/S)(D/E)(W/F)WXCF was found to bind specifically to LIF. Peptides within this family did not bind related members of the interleukin-6 family of cytokines, nor to murine LIF that has 80% sequence identity with human LIF. A representative peptide from this family was synthesized and found to bind to LIF with an affinity of approximately 300 nM. The phage-displayed form of this peptide was able to compete with the LIF receptor alpha chain (LIFR) for binding to LIF; however, the free synthetic peptide was unable to inhibit LIF-LIFR binding or inhibit LIF bioactivity in vitro. Using a panel of human/murine chimeric LIF molecules, the peptide-binding site on LIF was mapped to a groove located between the B and the C helices of the LIF structure, which is distinct from the surfaces involved in binding to receptor. To mimic the effect of the phage particle and convert the free peptide into an antagonist of LIFR binding, a 40 kDa poly(ethylene glycol) (PEG) moiety was conjugated to the synthetic LIF-binding peptide. This PEG-peptide conjugate was found to be both an antagonist of LIF-LIFR binding and of LIF signaling in engineered Ba/F3 cells expressing LIFR and the gp130 coreceptor.

Evidence for an intracellular ADP-ribosyl cyclase/NAD+-glycohydrolase in brain from CD38-deficient mice

Cyclic ADP-ribose, a metabolite of NAD+, is known to modulate intracellular calcium levels and signaling in various cell types, including neural cells. The enzymes responsible for producing cyclic ADP-ribose in the cytoplasm of mammalian cells remain unknown; however, two mammalian enzymes that are capable of producing cyclic ADP-ribose extracellularly have been identified, CD38 and CD157. The present study investigated whether an ADP-ribosyl cyclase/NAD+-glycohydrolase independent of CD38 is present in brain tissue. To address this question, NAD+ metabolizing activities were accurately examined in developing and adult Cd38-/- mouse brain protein extracts and cells. Low ADP-ribosyl cyclase and NAD+-glycohydrolase activities (in the range of pmol of product formed/mg of protein/min) were detected in Cd38-/- brain at all developmental stages studied. Both activities were found to be associated with cell membranes. The activities were significantly higher in Triton X-100-treated neural cells compared with intact cells, suggesting an intracellular location of the novel cyclase. The cyclase and glycohydrolase activities were optimal at pH 6.0 and were inhibited by zinc, properties which are distinct from those of CD157. Both activities were enhanced by guanosine 5'-O-(3-thiotriphosphate), a result suggesting that the novel enzyme may be regulated by a G protein-dependent mechanism. Altogether our results indicate the presence of an intracellular membrane-bound ADP-ribosyl cyclase/NAD+-glycohydrolase distinct from CD38 and from CD157 in mouse brain. This novel enzyme, which is more active in the developing brain than in the adult tissue, may play an important role in cyclic ADP-ribose-mediated calcium signaling during brain development as well as in adult tissue.

CD157, the Janus of CD38 but with a unique personality

CD157 is a pleiotropic ectoenzyme which belongs to the CD38 family and to the growing number of leukocyte surface molecules known to act independently as both receptors and enzymes. A 45-kDa surface structure with a GPI anchor, the CD157 molecule displays two distinct domains in its extracellular component. The first is implicated in the enzymic activities of the molecule and the second features adhesion/signalling properties. CD157 shares several characteristics with CD38, including a similar amino acid sequence and enzymic functions. Both molecules are involved in the metabolism of NAD(+), and the CD157 gene is synthenic on 4p15 with CD38, with which it also shares a unique genomic organization. Their conservation in phylogeny is striking evidence for their relevance in the life and death cycle of the cell.

CD157 undergoes ligand-independent dimerization and colocalizes with caveolin in CHO and MCA102 fibroblasts

CD157, a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, has recently been shown to induce protein tyrosine phosphorylation in monocytes differentiated from HL-60 cells (mHL-60) in a ligand-dependent manner, but in a ligand-independent manner in stable CD157-transfected CHO (CHO/CD157) and MCA102 (MCA/CD157) fibroblasts [Cell Signal. 11 (1999) 891-897.]. Many GPI-anchored proteins need to be clustered by their ligands or antibodies to induce redistribution to caveolae and a concomitant activation of the associated signal-transducing proteins [Nature 387 (1997) 569-572.]. Here, we demonstrate that CD157, independent of antibody crosslinking, undergoes dimerization with disulfide bond formation and localization in caveolae in CHO/CD157 and MCA/CD157 fibroblasts. However, the native CD157 induced in mHL-60 cells remains a monomer form. The structural integrity of caveolae is required for the association of CD157 with caveolin and CD157-mediated tyrosine kinase signalling in the fibroblasts. We propose that an overexpression of CD157 could lead to its dimerization and relocation to caveolae and to further result in the initiation of signalling processes.

Crystallographic studies on human BST-1/CD157 with ADP-ribosyl cyclase and NAD glycohydrolase activities

cADPR is the novel second messenger that elicits calcium release from intracellular calcium stores and works independently of IP(3). In mammals, the ADP-ribosyl cyclase function is found in two membrane proteins, CD38 and BST-1/CD157. These enzymes, exposed extracellularly, bear cADPR hydrolase and NAD glycohydrolase activities. In spite of its functional importance, the structural basis of these enzymatic reactions remains elusive. We determined the crystal structures of the extracellular region of human BST-1 at atomic resolution in the free form and in complexes with five substrate analogues: nicotinamide, NMN, ATPgammaS, ethenoNADP, and ethenoNAD. The three-dimensional structural views of the reaction centre with these ligands revealed the mode of substrate binding and the catalytic mechanism of the multifunctional enzymatic reactions. In each catalytic cleft of the dimeric enzyme, substrates are recognized predominantly through van der Waals interactions with two tryptophan residues, and thereby the N-glycosidic bond of NAD is correctly exposed near a catalytic glutamate residue. Its carboxyl side-chain stabilizes the catalytic intermediate of the S(N)-1 type reaction. This conformation of the catalytic cleft also implies the mechanism of cyclization between the adenine base and the ribose. The three key residues are invariant among the sequences of BST-1, CD38, and Aplysia cyclase, and hence this substrate recognition mode and catalytic scheme appear to be common in the cyclase family.

Extracellular nicotinamide adenine dinucleotide induces t cell apoptosis in vivo and in vitro

Incubation of mouse T cells expressing the cell surface enzyme ADP ribosyltransferase with nicotinamide adenine dinucleotide (NAD) had been reported to cause ADP ribosylation of cell surface molecules, inhibition of transmembrane signaling, and suppression of immune responses. In this study, we analyze the reasons for these effects and report that contact of T cells with NAD causes cell death. Naive T cells when incubated with NAD and adoptively transferred into semiallogeneic mice fail to cause graft-vs-host disease, and when injected into syngeneic, T cell-deficient recipients do not reconstitute these mice. Rather, they accumulate in the liver, leading to an increase of apoptotic lymphocytes in this organ. Similar effects are induced by injection of NAD, shown to cause a dramatic increase of apoptotic CD3(+), CD4(+), and CD8(+) cells in the liver. Consistent with this, in vitro incubation of naive T cells with NAD is shown to induce apoptosis. In contrast, no cell death is demonstrable when T cells are activated before incubation with NAD. It is concluded that ecto-NAD, as substrate of ADP ribosyltransferase, acts on naive, but not on activated CD69(+) T cells.

Signalling of GPI-anchored CD157 via focal adhesion kinase in MCA102 fibroblasts

CD157, a glycosylphosphatidylinositol-anchored protein, has previously been shown to mediate tyrosine phosphorylation of a 130 kDa protein (p130) in several cell lines. In this study, we have identified the p130 protein to be focal adhesion kinase (FAK or pp125(FAK)). FAK undergoes phosphorylation at Tyr-397 and Tyr-861 in intact MCA102 cells stably transfected with CD157 (MCA/CD157). MCA/CD157 cells, which displayed a rounded and compact cell morphology, exhibited a dispersed distribution, in contrast to a more closely associated and elongated spindle cell shape in the vector-transfected cells. MCA/CD157 cells proliferated at a rate 20-25% slower than the control cells. Our results demonstrate, for the first time, that FAK is a downstream signalling molecule of CD157.

An immature rat lymphocyte marker CD157: striking differences in the expression between mice and rats

We have established a novel monoclonal antibody that recognises mouse and rat CD157, and uncovered striking differences in both the level and stage of expression of this antigen in the primary lymphoid organs between these two species. Unlike mouse, the majority of rat thymocytes express CD 157. SHR and WKY rats were the exception, having unusually low levels (similar to those of the mouse) of these cells. However, in both species, a subset of CD3- CD4- CD8- thymocytes exhibited high levels of CD157. Surprisingly, these CD157high cells temporarily upregulated MHC class I molecules in both species. Furthermore, a third of CD157high rat thymocytes were CD45RC+, a marker found on immature thymocytes with regenerative capacity. Examination of the bone marrow lymphoid population shows that the expression of rat CD157 is largely observed at the CD45R+ IgM- pre-B-II cell stage, and unlike mouse, extension of expression into the IgM+ immature B cell stage was marginal. Similar to CD157high immature thymocytes, these immature B cells also expressed high levels of MHC class I. With the exception of the LEC, SHR and WKY rat strains, which have three- to four-fold less CD157+ bone marrow myeloid cells, percentages of these cells are similar between these two species. Thus, marked differences in the level and stage(s) of CD157 expression on lymphoid cells in mouse and rat indicate that CD157 may not, as previously thought, have a direct role in T or B cell differentiation.

Coordination of Ca2+ signalling by NAADP

Nicotinic acid adenine dinucleotide phosphate (NAADP) mobilizes intracellular Ca2+ stores in several cell types. Ample evidence suggests that NAADP activates intracellular Ca2+ channels distinct from those that are sensitive to inositol trisphosphate and ryanodine/cyclic ADP-ribose. Recent studies in intact cells have demonstrated functional coupling ('channel chatter') between Ca2+ release pathways mediated by NAADP, inositol trisphosphate and cyclic ADP-ribose. Thus, NAADP is probably an important determinant in shaping cytosolic Ca2+ signals.

Site-directed removal of N-glycosylation sites in BST-1/CD157: effects on molecular and functional heterogeneity

Cyclic ADP ribose (cADPR) is a novel second messenger that releases calcium from intracellular calcium stores, but works independently of inositol 1,4,5-trisphosphate. In mammals ADP-ribosyl cyclase function is found in two membrane proteins, CD38 and bone marrow stromal cell antigen 1 (BST-1)/CD157. These enzymes are exposed extracellularly and also possess cADPR hydrolase activity, but an intracellular soluble ADP-ribosyl cyclase has been reported in human T-cells. Previously, a soluble form of BST-1/CD157 (sBST-1), which lacked the glycosylphosphatidylinositol-anchored portion, was expressed by a baculovirus-insect-cell system. In this study, we have purified the sBST-1, and it migrated as two major bands by SDS/PAGE, suggesting that it is post-translationally modified. BST-1 contains four putative N-glycosylation sites. Tunicamycin treatment reduced sBST-1 expression in the culture medium, indicating that N-glycosylation is essential for secretion. Site-directed mutagenesis was performed to generate sBST-1 mutants (N1-N4), each preserving a single N-glycosylation site. N1, N3 and N4 were well secreted into the medium, and were each detected as a single band. Although N3 and N4 retained the ADP-ribosyl cyclase activity, the cADPR-hydrolase activity was retained only in N4. We conclude that N-glycosylation of sBST-1 facilitates the folding of the nascent polypeptide chain into a conformation that is conductive for intracellular transport and enzymic activity. Furthermore a crystal has been obtained using the N4 mutant, but not the wild-type sBST-1. Thus the artificial engineering of N-glycosylation sites could be an effective method to generate homogeneous material for structural studies.

cADP-ribose/ryanodine channel/Ca2+-release signal transduction pathway in mesangial cells

Signaling via release of Ca2+ from intracellular stores is mediated by several systems, including the inositol 1,4,5-trisphosphate (IP3) and cADP-ribose (cADPR) pathway. We recently discovered a high capacity for cADPR synthesis in rat glomeruli and cultured mesangial cells (MC). We sought to determine whether 1) cADPR synthesis in MC is regulated by cytokines and hormones, 2) ryanodine receptors (RyRs) are expressed in MC, and 3) Ca2+ is released through RyRs in response to cADPR. We found that ADP-ribosyl cyclase, a CD38-like enzyme that catalyzes cADPR synthesis, is upregulated in MC by tumor necrosis factor-alpha, interleukin-1beta, and all-trans retinoic acid (atRA). [3H]ryanodine binds to microsomal fractions from MC with high affinity in a Ca2+-dependent manner; binding is enhanced by specific RyR agonists and blocked by ruthenium red and cADPR. Western blot analysis confirmed the presence of RyR in MC. Release of 45Ca2+ from MC microsomes was stimulated by cADPR; release was blocked by ruthenium red and 8-bromo-cADPR. ADPR (non-cyclic) was without effect. In MC, TNF-alpha and atRA amplified the increment of cytoplasmic Ca2+ elicited by vasopressin. We conclude that MC possess elements of a novel ADP-ribosyl cyclase-->cADPR-->RyR-->Ca2+-release signaling pathway subject to regulation by proinflammatory cytokines and steroid superfamily hormones.

Specific Ca2+ signaling evoked by cholecystokinin and acetylcholine: the roles of NAADP, cADPR, and IP3

In order to control cell functions, hormones and neurotransmitters generate an amazing diversity of Ca2+ signals such as local and global Ca2+ elevations and also Ca2+ oscillations. In pancreatic acinar cells, cholecystokinin (CCK) stimulates secretion of digestive enzyme and promotes cell growth, whereas acetylcholine (ACh) essentially triggers enzyme secretion. Pancreatic acinar cells are a classic model for the study of CCK- and ACh-evoked specific Ca2+ signals. In addition to inositol 1,4,5 trisphosphate (IP3), recent studies have shown that cyclic ADPribose (cADPr) and nicotinic acid adenine dinucleotide phosphate (NAADP) release Ca2+ in pancreatic acinar cells. Moreover, it has also been shown that both ACh and CCK trigger Ca2+ spikes by co-activation of IP3 and ryanodine receptors but by different means. ACh uses IP3 and Ca2+, whereas CCK uses cADPr and NAADP. In addition, CCK activates phospholipase A2 and D. The concept emerging from these studies is that agonist-specific Ca2+ signals in a single target cell are generated by combination of different intracellular messengers.

Human CD38: a (r)evolutionary story of enzymes and receptors

Human CD38 is the mammalian prototype of a family of proteins which share structural similarities and an ectoenzymatic activity involved in the production of calcium mobilizing compounds. Besides the enzymatic activity, the molecule performs as a receptor, ruling adhesion and signaling in leukocytes. These functions are exerted through the interaction with surface ligands, one of which was identified as CD31. Recently, CD38 has gained attention as a prognostic marker and a pathogenetic agent in leukemias and in other diseases. Together these insights have produced a model of an as yet unique family of molecules, which act independently as receptors and enzymes.

Modulation of CD157 expression in multi-lineage myeloid differentiation of promyelocytic cell lines

CD157/BST-1 is expressed on mature myeloid cells but not on their precursors in vivo. Also CD38, a homologous gene to CD157, is upregulated in promyelocytic HL-60 cells by the monocyte and granulocyte differentiation-inducing 1alpha,25dihydroxyvitamin D3 (VD3) and all-trans retinoic acid (ATRA), respectively. We have examined whether CD157 expression is upregulated when the promyeloid HL-60 and/or U937 cells are induced to differentiate into mature phenotypes in vitro. VD3 treatment irreversibly upregulated the expression of CD157 in HL-60 cells but not in U937 cells in a time- and concentration-dependent manner when analyzed by flow cytometry, immunoblotting and/or RT-PCR. Different monocyte and granulocyte lineage inducers induced CD157 expression to varying extents while the macrophage differentiation-inducing phorbol 12-myristate 13-acetate (PMA) induced its down-regulation. Time-kinetics of VD3 treatment of HL-60 cells showed that the appearance of CD157 and CD11b (a differentiation marker) antigens were not substantial up to 24 hours but increased subsequently although the appearance of CD38 became significant within 6 hours. Two-color staining of VD3-treated HL-60 cells displayed an apparently linear correlation between CD157 and CD11b expression. Dibutyryl cAMP (cAMP agonist) and forskolin (cAMP-increasing agent) augmented the VD3-dependent induction of CD157 and CD11b expression while PGE1 (cAMP-decreasing agent) inhibited it, suggesting the involvement of a cAMP-dependent mechanism in VD3-induced CD157 upregulation. Co-treatment of HL-60 cells with VD3 plus TNF-alpha or ara-C produced an additive effect on CD157 upregulation. The upregulated CD157 in the VD3-differentiated HL-60 cells was able to activate CD157-dependent tyrosine kinase signal when cross-linked with anti-CD157 antibody.

ADP-Ribosyl cyclase in rat vascular smooth muscle cells: properties and regulation

We investigated whether ADP-ribosyl cyclase (ADPR-cyclase) in rat vascular smooth muscle cells (VSMCs) has enzymatic properties that differ from the well-characterized CD38-antigen ADPR-cyclase, expressed in HL-60 cells. ADPR-cyclase from VSMCs, but not CD38 ADPR-cyclase from HL-60 cells, was inhibited by gangliosides (10 micromol/L) GT(1B), GD(1), and GM(3). Preincubation of membranes from CD38 HL-60 cells, but not from VSMCs, with anti-CD38 antibodies increased ADPR-cyclase activity; CD38 antigen was detected both in VSMCs and in HL-60 cells. ADPR-cyclase in VSMC membranes was more sensitive than CD38 HL-60 ADPR-cyclase to inactivation by N-endoglycosidase F and to thermal inactivation at 45 degrees C. The specific activity of ADPR-cyclase in membranes from VSMCs was >20-fold higher than in membranes from CD38 HL-60 cells. Most importantly, VSMC ADPR-cyclase was inhibited by Zn(2+) and Cu(2+) ions; the inhibition by Zn(2+) was dose dependent, noncompetitive, and reversible by EDTA. In contrast, Zn(2+) stimulated the activity of CD38 HL-60 ADPR-cyclase and other known types of ADPR-cyclases. Retinoids act either via the nuclear receptor retinoic acid receptor or retinoid X receptor, including all-trans retinoic acid (atRA), and panagonist 9-cis-retinoic acid-upregulated VSMC ADPR-cyclase; the stimulatory effect of atRA was blocked by actinomycin D and cycloheximide. 1,25(OH)(2)-Vitamin D(3) (calciferol) stimulated VSMC ADPR-cyclase dose dependently at subnanomolar concentrations (ED(50) congruent with 56 pmol/L). Oral administration of atRA to rats resulted in an increase of ADPR-cyclase activity in aorta ( congruent with+60%) and, to a lesser degree, in myocardium of left ventricle (+18%), but atRA had no effect on ADPR-cyclases in lungs, spleen, intestinal smooth muscle, skeletal muscle, liver, or testis. Administration of 3,5,3'-triiodothyronine (T(3)) to rats resulted in an increase of ADPR-cyclase activity in aorta ( congruent with+89%), but not in liver or brain. We conclude the following: (1) ADPR-cyclase in VSMCs has enzymatic properties distinct from "classic" CD38 ADPR-cyclase, especially sensitivity to inhibition by Zn(2+) and Cu(2+); (2) ADPR-cyclase in VSMCs is upregulated by various retinoids, calcitriol, and T(3) in vitro; and (3) administration of atRA and T(3) increases ADPR-cyclase in aorta in vivo. We suggest that the cADPR signaling system plays an important role in the regulation of VSMC functions in response to steroid superfamily hormones.

ADP-Ribosyl cyclase in rat salivary glands

Both the Ca(2+)-releasing mechanism induced by cyclic ADP-ribose (cADPR) and the ADP-ribosyl cyclase (ADPRC) activity that converts NAD(+) to cADPR were observed in a variety of cell types. We studied the ADPRC activity in rat major salivary glands that include parotid gland (PG), submandiblar gland (SMG), and sublingual gland (SLG). The enzyme activity responsible for cADPR synthesis was detected by spectrofluorometric assay using NGD(+) as a substrate. The enzyme activities in SLG, SMG, and PG were about 400, 30, and 40 nmol/min/g tissue, respectively, in 5-week-old rats. The highest value was observed in SLG and this value was higher than those in other tissues; e.g., spleen (200 nmol/min/g tissue). The enzyme activity in SLG increased gradually after birth and showed a maximum value at 3 weeks. On the other hand, the enzyme activities almost did not change in both PG and SMG between 0 and 9 weeks. In spite of the high ADPRC activity in SLG, we could not detect the cADPR-induced Ca(2+)-release from SLG microsomes. These results suggest that the ADPRC in SLG does not function through Ca(2+)-release observed in various tissues.

Extracellular cyclic ADP-ribose increases intracellular free calcium concentration and stimulates proliferation of human hemopoietic progenitors

Cyclic ADP-ribose (cADPR) is a universal second messenger that regulates many calcium-related cellular events by releasing calcium from intracellular stores. Since these events include enhanced cell proliferation and since the bone marrow harbors both ectoenzymes that generate cADPR from NAD(+) (CD38 and BST-1), we investigated the effects of extracellular cADPR on human hemopoietic progenitors (HP). Exposure of HP to 100 microM cADPR for 24 h induced a significant increase in colony output (P<0.01) and colony size (P<0.003). A horizontal expansion of HP, as demonstrated by a markedly increased replating efficiency in semisolid medium (up to 700 times compared to controls), was also observed, indicating that cADPR priming can affect cell growth for multiple generations over several weeks after exposure. Influx of extracellular cADPR into the cells was demonstrated, and a causal relationship between the functional effects and the increase of intracellular free calcium concentration induced by cADPR on HP was established through the use of specific antagonists. Similar effects on HP were produced by nanomolar concentrations of the nonhydrolyzable cADPR analog 3-deaza-cADPR. These data demonstrate that extracellular cADPR behaves as a cytokine enhancing the proliferation of human HP, a finding that may have biomedical applications for the ex vivo expansion of hemopoietic cells.

Novel kinetics, behaviour and cell-type specificity of CD157-mediated tyrosine kinase signalling

CD157, a recently characterized leukocyte surface antigen, has recently been shown to induce tyrosine phosphorylation of a 130-kDa protein (p130) when cross-linked with its antibody (ligand). We have further investigated the detailed kinetics, behaviour and cell-type specificity of this CD157-stimulated p130 phosphorylation. We demonstrate that CD157-mediated p130 phosphorylation is ligand independent in recombinant CD157-expressing CHO, MCA102 and COS-7 cells but is ligand dependent in HL-60-differentiated monocytes (mHL-60) having enhanced CD157 expression. This p130 phosphorylation is activated only at lower temperatures (0-4 degrees C) in MCA102, COS-7 and mHL-60 cells but is temperature insensitive in CHO cells. We further demonstrate that the CHO/CD157 cell clones have approximately 22-28% slower rates of proliferation than that of a CHO/mock clone. But the MCA102 cell proliferation remains unaffected by CD157 expression. We postulate that the difference in the temperature sensitivity of p130 phosphorylation can be responsible for the discrepancy in the rates of MCA102/CD157 and CHO/CD157 cell proliferation.

Synthesis of NAADP and cADPR in mitochondria

Here we investigated whether cADPR and NAADP are synthesized in mitochondria. We found that ADPR-cyclase activity is present in mitochondria. In addition, we describe for the first time synthesis of NAADP in this intracellular organelle. ADPR-cyclase activities (V(MAX)) and NAADP synthesis in mitochondria were about 4-fold lower than that in plasma membranes. Otherwise, ADPR-cyclases in mitochondria and in plasma membranes have similar catalytic properties in terms of apparent K(m) for the substrate NGD and K(i) values for inhibition by dithiotreitol, beta-NAD, and nicotinamide. ADPR-cyclase in plasma membranes and to a lesser degree mitochondrial enzyme, was inhibited by Zn(2+) and Cu(2+); ADPR-cyclase from mitochondria was more stable upon thermal inactivation. CD38 antigen, determined by Western blot, was well-expressed in plasma membranes but was far less so (17-fold less) in mitochondria. The major difference between ADPR-cyclase activity in mitochondria and plasma membranes is that mitochondrial cyclase activity was increased by incubation with nonionic detergents. Conversely, the incubation with phosphatidylinositol-specific phosphodiesterase C (PI-PLC) released ADPR-cyclase activity from plasma membranes, but not from mitochondria. We conclude that ADPR-cyclase in mitochondria and in plasma membranes are both multifunctional enzymes with similar catalytic properties; however, the two ADPR-cyclases differ in the mode of anchoring to the membrane: by glycosylphosphoinositol anchor in plasma membranes and by hydrophobic interactions in mitochondria. In addition, synthesis of NAADP can also be found in intracellular organelles via mitochondria. We propose that independent mitochondrial cADPR and NAADP systems may have an intracrine signaling function that is not dependent on direct input by extracellular hormonal stimuli, but rather responds to changes of intermediary cellular metabolism.

Characterization of the active site of ADP-ribosyl cyclase

ADP-ribosyl cyclase synthesizes two Ca(2+) messengers by cyclizing NAD to produce cyclic ADP-ribose and exchanging nicotinic acid with the nicotinamide group of NADP to produce nicotinic acid adenine dinucleotide phosphate. Recombinant Aplysia cyclase was expressed in yeast and co-crystallized with a substrate, nicotinamide. x-ray crystallography showed that the nicotinamide was bound in a pocket formed in part by a conserved segment and was near the central cleft of the cyclase. Glu(98), Asn(107) and Trp(140) were within 3.5 A of the bound nicotinamide and appeared to coordinate it. Substituting Glu(98) with either Gln, Gly, Leu, or Asn reduced the cyclase activity by 16-222-fold, depending on the substitution. The mutant N107G exhibited only a 2-fold decrease in activity, while the activity of W140G was essentially eliminated. The base exchange activity of all mutants followed a similar pattern of reduction, suggesting that both reactions occur at the same active site. In addition to NAD, the wild-type cyclase also cyclizes nicotinamide guanine dinucleotide to cyclic GDP-ribose. All mutant enzymes had at least half of the GDP-ribosyl cyclase activity of the wild type, some even 2-3-fold higher, indicating that the three coordinating amino acids are responsible for positioning of the substrate but not absolutely critical for catalysis. To search for the catalytic residues, other amino acids in the binding pocket were mutagenized. E179G was totally devoid of GDP-ribosyl cyclase activity, and both its ADP-ribosyl cyclase and the base exchange activities were reduced by 10,000- and 18,000-fold, respectively. Substituting Glu(179) with either Asn, Leu, Asp, or Gln produced similar inactive enzymes, and so was the conversion of Trp(77) to Gly. However, both E179G and the double mutant E179G/W77G retained NAD-binding ability as shown by photoaffinity labeling with [(32)P]8-azido-NAD. These results indicate that both Glu(179) and Trp(77) are crucial for catalysis and that Glu(179) may indeed be the catalytic residue.

Inhibitor peptide SNP-1 binds to a soluble form of BST-1/CD157 at a 2:2 stoichiometry

Recently we have identified a 15-mer peptide, SNP-1, by a random phage library that can bind to bone marrow stromal cell antigen-1 (BST-1)/CD157 [Sato, A., Yamamoto, S., Ishihara, K., Hirano, T. & Jingami, H. (1999) Biochem. J. 337, 491-496]. SNP-1 inhibits BST-1 ADP-ribosyl cyclase activity uncompetitively with a Ki value of 180 +/- 40 nM. In this study we analysed biophysically the SNP-1 binding to a soluble form of BST-1 (sBST-1). Equilibrium binding data of wild-type SNP-1 from surface plasmon resonance studies gave a Kd value of 500 +/- 35 nM. Titration calorimetry analysis showed that the binding reaction is exothermic at 20 degrees C. The values of Kd = 211 nM, enthalpy change, DeltaH = -18.68 kcal.mol-1, and saturated molar ratio of bound SNP-1 per sBST-1, N = 0.8 mol.mol-1 were obtained. On the basis of the molecular masses of SNP-1 and sBST-1 calculated by analytical ultracentrifugation, the stoichiometry of the binding was determined to be 2 : 2. Electron microscopy also revealed the dimer form of sBST-1. To delineate the core residue of SNP-1 responsible for binding, each amino acid residue has been replaced by alanine. A region from amino acid residues 7-12 appeared to be critical for the SNP-1 binding to sBST-1. The substitution of the first residue, His, to Ala led to a reduction in binding, suggesting that the N-terminal residue is also crucial.

Molecular cloning and characterization of a surface antigen preferentially overexpressed on multiple myeloma cells

HM1.24 antigen has been identified as a surface molecule preferentially expressed on terminally differentiated B cells, and its overexpression is observed in multiple myeloma cells. The HM1.24 antigen is, therefore, expected as a most potent target molecule for antibody-based immunotherapy for multiple myeloma. Here, we have identified the cDNA for human HM1.24 antigen and also analyzed its gene structure including the promoter region. The HM1.24 antigen is a type II membrane glycoprotein, which has been reported as a bone marrow stromal cell surface antigen BST2, and may exist as a homodimer on myeloma cell surface. Although a reason for the overexpression in myeloma cells is not understood, very interestingly, the promoter region of the HM1.24 gene has a tandem repeat of three cis elements for a transcription factor, STAT3, which mediates interleukin-6 (IL-6) response gene expression. Since IL-6 is a differentiation factor for B cells, and known as a paracrine/autocrine growth factor for multiple myeloma cells, the expression of HM1.24 antigen may be regulated by the activation of STAT3. Importantly, a humanized anti-HM1.24 antibody effectively lysed the CHO transformants which expressed HM1.24 antigen as high as human multiple myeloma cells, but not the cells with lower antigen expression. This evaluation shows that ADCC heavily depends on the expression level of target antigens and, therefore, the immunotherapy targeting the HM1.24 antigen should have a promising potential in clinical use.

Cyclic ADP-ribose: a novel Ca2+-mobilising second messenger

Cyclic ADP-ribose (cADPR) was discovered as a potent Ca2+-mobilising natural compound in sea urchin eggs. Recently, cADPR was reported to stimulate Ca2+ signalling in several higher eukaryotic cell systems (e.g., smooth and cardiac muscle cells, neuronal cells, adrenal chromaffin cells, macrophages, pancreatic acinar cells and T-lymphocytes). The following aspects of the role of cADPR as a Ca2+-mobilising second messenger are reviewed: coupling of metabolism of cADPR to stimulation of receptors in the plasma membrane, properties and pharmacology of Ca2+ release by cADPR and the involvement of cADPR in Ca2+ entry.