Quantification of intracellular levels of cyclic ADP-ribose by high-performance liquid chromatography

25 Years of Collaboration with A Genius: Deciphering Adenine Nucleotide Ca2+ Mobilizing Second Messengers Together with Professor Barry Potter

Ca²⁺-mobilizing adenine nucleotide second messengers cyclic adenosine diphosphoribose, (cADPR), nicotinic acid adenine dinucleotide phosphate (NAADP), adenosine diphosphoribose (ADPR), and 2'deoxy-ADPR were discovered since the late 1980s. They either release Ca²⁺ from endogenous Ca²⁺ stores, e.g., endoplasmic reticulum or acidic organelles, or evoke Ca²⁺ entry by directly activating a Ca²⁺ channel in the plasma membrane. For 25 years, Professor Barry Potter has been one of the major medicinal chemists in this topical area, designing and contributing numerous analogues to develop structure-activity relationships (SAR) as a basis for tool development in biochemistry and cell biology and for lead development in proof-of-concept studies in disease models. With this review, I wish to acknowledge our 25-year-long collaboration on Ca²⁺-mobilizing adenine nucleotide second messengers as a major part of Professor Potter's scientific lifetime achievements on the occasion of his retirement in 2020.

Does Cyclic ADP-Ribose (cADPR) Activate the Non-selective Cation Channel TRPM2?

TRPM2 is a non-selective, Ca²⁺-permeable cation channel widely expressed in immune cells. It is firmly established that the channel can be activated by intracellular adenosine 5′-diphosphoribose (ADPR). Until recent cryo-EM structures have exhibited an additional nucleotide binding site in the N-terminus of the channel, this activation was thought to occur via binding to a C-terminal domain of the channel that is highly homologous to the ADPR pyrophosphatase NudT9. Over the years it has been controversially discussed whether the Ca²⁺ mobilizing second messenger cyclic ADP ribose (cADPR) might also directly activate Ca²⁺ entry via TRPM2. Here we will review the status of this discussion.

Endocytosis-mediated mitochondrial transplantation: Transferring normal human astrocytic mitochondria into glioma cells rescues aerobic respiration and enhances radiosensitivity

Emerging evidence indicates that reprogramming of energy metabolism involving disturbances in energy production from a defect in cellular respiration with a shift to glycolysis is a core hallmark of cancer. Alterations in cancer cell energy metabolism are linked to abnormalities in mitochondrial function. Mitochondrial dysfunction of cancer cells includes increased glycolysis, decreased apoptosis, and resistance to radiotherapy. The study was designed for two main points: firstly, to investigate whether exogenous functional mitochondria can transfer into glioma cells and explore the underlying molecular mechanisms from the perspective of endocytosis; secondly, to further verify whether the mitochondrial transplantation is able to rescue aerobic respiration, attenuate the Warburg effect and enhance the radiosensitivity of gliomas.

Methods: Mitochondria were isolated from normal human astrocytes (HA) and immediately co-incubated with starved human glioma cells (U87). Confocal microscopy and gene sequencing were performed to evaluate the ability of isolated mitochondria internalization into U87 cells. The interaction between endocytosis and isolated mitochondria transfer were captured by 3D tomographic microscopy and transmission electron microscopy. NAD⁺, CD38, cADPR and Ca²⁺ release were determined by commercial kits, western blot, HLPC-MS and Fluo-3 AM respectively. PCR array expression profiling and Seahorse XF analysis were used to evaluate the effect of mitochondrial transplantation on energy phenotypes of U87 cells. U87 cells and U87 xenografts were both treated with mitochondrial transplantation, radiation, or a combination of mitochondrial transplantation and radiation. Apoptosis in vitro and in vivo were detected by cytochrome C, cleaved caspase 9 and TUNEL staining.

Results: We found that mitochondria from HA could be transferred into starved U87 cells by simple co-incubation. Starvation treatment slowed the rate of glycolysis and decreased the transformation of NAD⁺ to NADH in U87 cells. A large amount of accumulated NAD⁺ was released into the extracellular space. CD38 is a member of the NAD⁺ glycohydrolase family that catalyzes the cyclization of extracellular NAD⁺ to intracellular cADPR. cADPR triggered release of Ca²⁺ to promote cytoskeleton remodeling and plasma membrane invagination. Thus, endocytosis involving isolated mitochondria internalization was mediated by NAD⁺-CD38-cADPR-Ca²⁺ signaling. Mitochondrial transfer enhanced gene and protein expression related to the tricarboxylic acid (TCA) cycle, increased aerobic respiration, attenuated glycolysis, reactivated the mitochondrial apoptotic pathway, inhibited malignant proliferation of U87 cells. Isolated mitochondria injected into U87 xenograft tumors also entered cells, and inhibited glioma growth in nude mice. Mitochondrial transplantation could enhance the radiosensitivity of gliomas in vitro and in vivo.

Conclusion: These findings suggested that starvation-induced endocytosis via NAD⁺-CD38-cADPR-Ca²⁺ signaling could be a new mechanism of mitochondrial transplantation to rescue aerobic respiration and attenuate the Warburg effect. This mechanism could be a promising approach for radiosensitization.

Cyclic ADP-ribose and IP3 mediate abscisic acid-induced isoflavone accumulation in soybean sprouts

In this study, the roles of ABA-cADPR-Ca2+ and ABA-IP3-Ca2+ signaling pathways in UV-B-induced isoflavone accumulation in soybean sprouts were investigated. Results showed that abscisic acid (ABA) up regulated cyclic ADP-ribose (cADPR) and inositol 1,4,5-trisphosphate (IP3) levels in soybean sprouts under UV-B radiation. Furthermore, cADPR and IP3, as second messengers of UV-B-triggered ABA, induced isoflavone accumulation by up-regulating proteins and genes expression and activity of isoflavone biosynthetic-enzymes (chalcone synthase, CHS; isoflavone synthase, IFS). After Ca2+ was chelated by EGTA, isoflavone content decreased. Overall, ABA-induced cADPR and IP3 up regulated isoflavone accumulation which was mediated by Ca2+ signaling via enhancing the expression of proteins and genes participating in isoflavone biosynthesis in soybean sprouts under UV-B radiation.

Adenine Dinucleotide Second Messengers and T-lymphocyte Calcium Signaling

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

Alteration of enzymatic properties of cell-surface antigen CD38 by agonistic anti-CD38 antibodies that prolong B cell survival and induce activation

Leukocyte cell-surface antigen CD38 is a single-transmembrane protein. CD38 ligation by anti-CD38 antibodies triggers the growth or apoptosis of immune cells. Although the extracellular domain of CD38 has multifunctional catalytic activities including NAD(+) glycohydrolase and cyclase, the CD38-mediated cell survival or death appears to be independent of its catalytic activity. It is proposed that a conformational change of CD38 triggers the signalling. The conformational change of CD38 could influence its catalytic activity. However, the agonistic anti-CD38 antibody that alters the catalytic activity of CD38 has not been reported so far. In the present study, we demonstrated that two agonistic anti-mouse CD38 mAbs (CS/2 and clone 90) change the catalytic activities of CD38. CS/2 was clearly more potent than clone 90 in prolonging B cell survival and activation. CS/2 inhibited the NAD(+) glycohydrolase activity of both the isolated extracellular domain of CD38 (FLAG-CD38) and cell-surface CD38. Kinetic analysis suggested a non-competitive inhibition. On the other hand, clone 90 stimulated the NAD(+) glycohydrolase activity of FLAG-CD38 and had little effect on the NAD(+) glycohydrolase activity of cell-surface CD38. CS/2 and clone 90 had no effect on the cyclase activity of FLAG-CD38 and inhibited the cyclase activity of cell-surface CD38. Accordingly, these agonistic antibodies probably induce the conformational changes of CD38 that are evident in the distinct alterations of the catalytic site. The antibodies will be useful tools to analyze the conformational change of CD38 in the process of triggering B cell survival and the activation signal.

Refinement of a radioreceptor binding assay for nicotinic acid adenine dinucleotide phosphate

The measurement of changes in nicotinic acid adenine dinucleotide phosphate (NAADP) levels in cells has been, and remains, key to the investigation of the functions of NAADP as a Ca²⁺-releasing second messenger. Here we provide details of how to isolate NAADP from cells by extraction with perchloric acid and then measure the NAADP using a radioreceptor assay. We demonstrate that NAADP is neither generated nor broken down during sample processing conditions and that radioreceptor assay is highly selective for the detection of NAADP under cell extract conditions. Furthermore, a number of improvements, such as solid-state detection of the radioactivity, are incorporated to enhance the safety of the procedure. Finally, we have developed a new method to prevent the endogenous metabolism of NAADP by chelating Ca²⁺ with bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), thereby reducing the difficulty of catching a small transient rise in NAADP levels. In summary, we have refined and improved a method for measuring NAADP levels and presented it in a manner accessible to a wide range of laboratories. It is expected that this will enhance research in the NAADP field.

Altered CD38 expression in thioacetamide-induced rat model of liver cirrhosis

BACKGROUND

Cirrhosis is a gradually developing, chronic disease which involves the whole liver. Here, we have shown that CD38 undergoes altered expression upon thioacetamide-induced cirrhosis in rats. CD38 is a type II transmembrane glycoprotein that exhibits ADP-ribosyl cyclase and cADPR hydrolase activities. In this study, the gene and protein expressions of CD38 were investigated in a thioacetamide-induced rat model of cirrhosis.

METHODS

CD38 expression was studied by using real-time RT-PCR, immunohistochemistry, and immunoblotting. cADPR content in liver was measured using cycling assay.

RESULTS

There was a significant increase in CD38 mRNA and protein expressions as well as ADP-ribosyl cyclase activity in cirrhotic liver compared to the control liver. cADPR level was found to be modestly but significantly augmented in cirrhotic liver.

CONCLUSIONS

These results raised the possibility that altered CD38 expression and a concomitant elevation of the enzymatic activity as well as cADPR may be involved in the pathogenesis of liver cirrhosis.

Activation of T cell calcium influx by the second messenger ADP-ribose

Stimulation of Jurkat T cells by high concentrations of concanavalin A (ConA) induced an elevation of the endogenous adenosine diphosphoribose (ADPR) concentration and an inward current significantly different from the Ca2+ release-activated Ca2+ current (I(CRAC)). Electrophysiological characterization and activation of a similar current by infusion of ADPR indicated that the ConA-induced current is carried by TRPM2. Expression of TRPM2 in the plasma membrane of Jurkat T cells was demonstrated by reverse transcription-PCR, Western blot, and immunofluorescence. Inhibition of ADPR formation reduced ConA-mediated, but not store-operated, Ca2+ entry and prevented ConA-induced cell death of Jurkat cells. Moreover, gene silencing of TRPM2 abolished the ADPR- and ConA-mediated inward current. Thus, ADPR is a novel second messenger significantly involved in ConA-mediated cell death in T cells.

Altered Ca2+ homeostasis in human uremic skeletal muscle: possible involvement of cADPR in elevation of intracellular resting [Ca2+]

BACKGROUND

Patients with chronic renal failure may develop muscle weakness and fatigability due to disorders of skeletal muscle function, collectively known as the uremic myopathy. Cyclic adenosine diphosphate-ribose (cADPR), an endogenous metabolite of beta-NAD+, activates Ca2+ release from intracellular stores in vertebrate and invertebrate cells. The current study investigated the possible role of cADPR in uremic myopathy.

METHODS

We have examined the effect of cADPR on myoplasmic resting Ca2+ concentration ([Ca2+]i) in skeletal muscle obtained from control subjects and uremic patients (UP). [Ca2+]i was measured using double-barreled Ca2+-selective microelectrodes in muscle fibers, prior to and after microinjections of cADPR.

RESULTS

Resting [Ca2+]i was elevated in UP fibers compared with fibers obtained from control subjects. Removal of extracellular Ca2+, or incubation of cells with nifedipine, did not modify [Ca2+]i in UP or control fibers. Microinjection of cADPR produced an elevation of [Ca2+]i in both groups of cells. This elevation was not mediated by Ca2+ influx, or inhibited by heparin or ryanodine. [cADPR]i was determined to be higher in muscle fibers from UP compared to those from the control subjects. Incubation of cells with 8-bromo-cADPR, a cADPR antagonist, partially reduced [Ca2+]i in UP muscle fibers and blocked the cADPR-elicited elevation in [Ca2+]i in both groups of muscle cells.

CONCLUSION

Skeletal muscles of the UP exhibit chronic elevation of [Ca2+]i that can be partially reduced by application of 8-bromo-cADPR. cADPR was able to mobilize Ca2+ from intracellular stores, by a mechanism that is independent of ryanodine or inositol trisphosphate receptors. It can be postulated that an alteration in the cADPR-signaling pathway may exist in skeletal muscle of the patients suffering from uremic myopathy.

Release of beta-nicotinamide adenine dinucleotide upon stimulation of postganglionic nerve terminals in blood vessels and urinary bladder

Chemical signaling in autonomic neuromuscular transmission involves agents that function as neurotransmitters and/or neuromodulators. Using high performance liquid chromatography techniques with fluorescence and electrochemical detection we observed that, in addition to ATP and norepinephrine (NE), electrical field stimulation (EFS, 4-16 Hz, 0.1-0.3 ms, 15 V, 60-120 s) of isolated vascular and non-vascular preparations co-releases a previously unidentified compound with apparent nucleotide or nucleoside structure. Extensive screening of more than 25 nucleotides and nucleosides followed by detailed peak identification revealed that beta-nicotinamide adenine dinucleotide (beta-NAD) is released in tissue superfusates upon EFS of canine mesenteric artery (CMA), canine urinary bladder, and murine urinary bladder in the amounts of 7.1 +/- 0.7, 26.5 +/- 4.5, and 15.1 +/- 3.2 fmol/mg of tissue, respectively. Smaller amounts of the beta-NAD metabolites cyclic adenosine 5'-diphosphoribose (cADPR) and ADPR were also present in the superfusates collected during EFS of CMA (2.5 +/- 0.9 and 5.8 +/- 0.8 fmol/mg of tissue, respectively), canine urinary bladder (1.8 +/- 0.5 and 9.0 +/- 6.0 fmol/mg of tissue, respectively), and murine urinary bladder (1.4 +/- 0.1 and 6.2 +/- 2.4 fmol/mg of tissue, respectively). The three nucleotides were also detected in the samples collected before EFS (0.2-1.6 fmol/mg of tissue). Exogenous beta-NAD, cADPR, and ADPR (all 100 nm) reduced the release of NE in CMA at 16 Hz from 27.8 +/- 6.0 fmol/mg of tissue to 15.5 +/- 5.0, 12 +/- 3.0, and 10.0 +/- 4.0 fmol/mg of tissue, respectively. In conclusion, we detected constitutive and nerve-evoked overflow of beta-NAD, cADPR, and ADPR in vascular and non-vascular smooth muscles, beta-NAD being the prevailing compound. These substances modulate the release of NE, implicating novel nucleotide mechanisms of autonomic nervous system control of smooth muscle.

ABA activates ADPR cyclase and cADPR induces a subset of ABA-responsive genes in Arabidopsis

Cyclic ADP-ribose (cADPR) was previously shown to activate transient expression of two abscisic acid (ABA)-responsive genes in tomato cells. Here, we show that the activity of the enzyme responsible for cADPR synthesis, ADP-ribosyl (ADPR) cyclase, is rapidly induced by ABA in both wild-type (WT) and abi1-1 mutant Arabidopsis plants in the absence of protein synthesis. Furthermore, in transgenic Arabidopsis plants, induced expression of the Aplysia ADPR cyclase gene resulted in an increase in ADPR cyclase activity and cADPR levels, as well as elevated expression of ABA-responsive genes KIN2, RD22, RD29a, and COR47 (although to a lesser extent than after ABA induction). Genome-wide profiling indicated that about 28% of all ABA-responsive genes in Arabidopsis are similarly up- and downregulated by cADPR and contributed to the identification of new ABA-responsive genes. Our results suggest that activation of ADPR cyclase is an early ABA-signaling event partially insensitive to the abi1-1 mutation and that an increase in cADPR plays an important role in downstream molecular and physiological ABA responses.

Hormonal control of ADP-ribosyl cyclase activity in pancreatic acinar cells from rats

Cyclic ADP-ribose, a metabolite of NAD+ evokes Ca2+ release from intracellular stores in different cells. We have determined the activity of cADPr-producing enzymes (ADP-ribosyl cyclases) in different cellular fractions prepared from isolated pancreatic acinar cells by measuring the conversion of the beta-NAD+ analogs 1,N6-etheno-NAD and nicotinamide guanine dinucleotide to the fluorescent products 1,N6-etheno-cADPr and cyclic GDP-ribose, respectively. Substrate/product analyses were carried out by reverse-phase high pressure liquid chromatography. In all subcellular fractions examined (cytosol, mitochondria, plasma, and intracellular membranes), ADP-ribosyl cyclase activity was detected except in zymogen granular membranes. Western blot analysis and immunoprecipitation experiments revealed the presence of the ADP-ribosyl cyclase CD38 in both plasma membranes and mitochondria but not in the cytosol. Hormonal stimulation of intact acinar cells for 1 min with acetylcholine (ACh), cholecystokinin (CCK), or a membrane-permeant analog of cGMP increased ADP-ribosyl cyclase activity in the cytosol by 1.8-, 1.6-, and 1.9-fold, respectively, as compared with the control but had no effect in any other fraction. Both ACh and CCK also increased accumulation of cGMP in the cells by about 2-fold. Bombesin had no significant effect on either ADP-ribosyl cyclase activity or cGMP accumulation within this short period of stimulation. We conclude that at least two types of ADP-ribosyl cyclases are present in pancreatic acinar cells: membrane-bound CD38 and a cytosolic enzyme different from CD38. Stimulation of pancreatic acinar cells with CCK or ACh results in exclusive activation of the cytosolic ADP-ribosyl cyclase activity, most likely mediated by cGMP.

High-performance liquid chromatographic technique for detection of a fluorescent analogue of ADP-ribose in isolated blood vessel preparations

Analysis of endogenous nucleotides in biologic media is hampered by rapid degradation and low final concentrations that are difficult to detect. A reversed-phase high-performance liquid chromatographic (HPLC) technique is described that efficiently detects a stable fluorescence derivative of adenosine 5'-diphosphoribose (ADPR), 1,N6-etheno-ADPR (epsilon-ADPR), at low femtomolar concentration range in vascular tissue superfusates. epsilon-ADPR was formed by the reaction of ADPR with chloroacetaldehyde at 80 degrees C and pH 4.0. Gradient elution with 0.1 M KH2PO4 (pH 6.0), increasing methanol (0-35% over 18 min), and a 25-cm by 4.5-mm (5 microm) silica ODS-AM column were employed. epsilon-ADPR was detected by fluorescence at an excitation wavelength of 230 nm and an emission wavelength of 410 nm. The detection sensitivity for epsilon-ADPR was approximately 10 fmol. Linearity of the HPLC detection method was demonstrated in the range from 0.0125 to 1 pmol epsilon-ADPR. The method was validated in terms of within-day and between-day reproducibility of retention times and peak areas of standard nucleotide. Matrix-assisted laser desorption/ionization mass spectrometry measurements confirmed the presence of an etheno ring after reaction of ADPR with chloroacetaldehyde. The method was applied to quantitate the overflow of ADPR upon electrical field stimulation (8 Hz, 0.3 ms, 15 V, 1-2 min) of both canine and guinea-pig isolated mesenteric artery segments.

A novel cycling assay for cellular cADP-ribose with nanomolar sensitivity

cADP-ribose (cADPR) is a novel cyclic nucleotide derived from NAD(+) that has now been established as a general Ca(2+) messenger in a wide variety of cells. Despite the obvious importance of monitoring its cellular levels under various physiological conditions, its measurement has been technically difficult and requires specialized reagents. In this study a widely applicable high-sensitivity assay for cADPR is described. ADP-ribosyl cyclase normally catalyses the synthesis of cADPR from NAD(+), but the reaction can be reversed in the presence of high concentrations of nicotinamide, producing NAD(+) from cADPR stoichiometrically. The resultant NAD(+) can then be coupled to a cycling assay involving alcohol dehydrogenase and diaphorase. Each time NAD(+) cycles through these coupled reactions, a molecule of highly fluorescent resorufin is generated. The reaction can be conducted for hours, resulting in more than a thousand-fold amplification of cADPR. Concentrations of cADPR in the nanomolar range can be measured routinely. The unique ability of ADP-ribosyl cyclase to catalyse the reverse reaction provides the required specificity. Using this assay, it is demonstrated that cADPR is present in all tissues tested and that the levels measured are directly comparable with those obtained using a radioimmunoassay. All the necessary reagents are widely available and the assay can be performed using a multiwell fluorescence plate reader, providing a high-throughput method for monitoring cADPR levels. This assay should be valuable in elucidating the messenger role of cADPR in cells.

Assay for ADP-ribosyl cyclase by reverse-phase high-performance liquid chromatography

Cyclic ADP-ribose (cADPR), a natural metabolite of beta-NAD(+), is a second messenger for Ca(2+) signaling in T cells. As a tool for purification and identification of ADP-ribosyl cyclase(s) in T cells, a sensitive and specific enzymatic assay using 1,N(6)-etheno-NAD(+) as substrate was developed. A major problem-the sensitivity of 1,N(6)-etheno-cADPR toward the extraction medium perchloric acid-was solved by replacing the perchloric acid extraction procedure of nucleotides by a filtration step. Standard compounds for the HPLC analysis of ADP-ribosyl cyclases and NAD(+)-glycohydrolases, e.g., 1,N(6)-etheno-cADPR, 1,N(6)-etheno-ADPR, and 1,N(6)-etheno-AMP, were produced by ADP-ribosyl cyclase from Aplysia californica and dinucleotide pyrophosphatase. The assay was applied to subcellular fractions prepared from human Jurkat T cells. As a result ADP-ribosyl cyclase and NAD(+)-glycohydrolase activity could be detected and precisely quantified in different subcellular fractions indicating the presence of different isoenzymes in T cells.

Mechanisms involved in alpha6beta1-integrin-mediated Ca(2+) signalling

Contact of Jurkat T-lymphocytes with the extracellular matrix (ECM) protein laminin resulted in long-lasting alpha6beta1-integrin-mediated Ca(2+) signalling. Both Ca(2+) release from thapsigargin-sensitive Ca(2+) stores and capacitative Ca(2+) entry via Ca(2+) channels sensitive to SKF 96365 constitute important parts of this process. Inhibition of alpha6beta1-integrin-mediated Ca(2+) signalling by (1) the src kinase inhibitor PP2, (2) the PLC inhibitor U73122, and (3) the cyclic adenosine diphosphoribose (cADPR) antagonist 7-deaza-8-Br-cADPR indicate the involvement of src tyrosine kinases and the Ca(2+)-releasing second messengers D-myo-inositol 1,4,5-trisphosphate (InsP3) and cADPR.

NAD degradation and regulation of CD38 expression by human monocytes/macrophages

In recent years, evidence has accumulated that NAD+ serves as a precursor of metabolites that are involved in a number of regulatory processes. In this work we show that extracellularly added NAD+ was rapidly degraded by intact human monocytes to nicotinamide and ADP-ribose. Besides these main products, minor amounts of AMP, ADP and cADP-ribose were formed. Expression of CD38, which has been identified as NAD+-glycohydrolase (EC 3.2.2.6) degrading NAD+ into nicotinamide and ADP-ribose, was determined on freshly isolated human monocytes by flow cytometry and RT-PCR. Upon ligation with anti-CD38 mAb, CD38 underwent internalization, shedding and new expression. As monocytes possess an intracellular CD38 pool, it could serve as a source for newly expressed CD38. Differentiation of monocytes to macrophages resulted in down-regulation of surface expression of CD38. This decrease correlates with a reduction in NADase activity, indicating that the amount of functional active CD38 molecules decrease during differentiation. As CD38 mRNA was found to be diminished in macrophages, regulation of the gene product seems to occur at the level of transcription or mRNA stability.

Paracrine roles of NAD+ and cyclic ADP-ribose in increasing intracellular calcium and enhancing cell proliferation of 3T3 fibroblasts

CD38 is a bifunctional ectoenzyme synthesizing from NAD(+) (ADP-ribosyl cyclase) and degrading (hydrolase) cyclic ADP-ribose (cADPR), a powerful universal calcium mobilizer from intracellular stores. Recently, hexameric connexin 43 (Cx43) hemichannels have been shown to release cytosolic NAD(+) from isolated murine fibroblasts (Bruzzone, S., Guida, L., Zocchi, E., Franco, L. and De Flora, A. (2001) FASEB J. 15, 10-12), making this dinucleotide available to the ectocellular active site of CD38. Here we investigated transwell co-cultures of CD38(+) (transfected) and CD38(-) 3T3 cells in order to establish the role of extracellular NAD(+) and cADPR on [Ca(2+)](i) levels and on proliferation of the CD38(-) target cells. CD38(+), but not CD38(-), feeder cells induced a [Ca(2+)](i) increase in the CD38(-) target cells which was comparable to that observed with extracellular cADPR alone and inhibitable by NAD(+)-glycohydrolase or by the cADPR antagonist 8-NH(2)-cADPR. Addition of recombinant ADP-ribosyl cyclase to the medium of CD38(-) feeders induced sustained [Ca(2+)](i) increases in CD38(-) target cells. Co-culture on CD38(+) feeders enhanced the proliferation of CD38(-) target cells over control values and significantly shortened the S phase of cell cycle. These results demonstrate a paracrine process based on Cx43-mediated release of NAD(+), its CD38-catalyzed conversion to extracellular cADPR, and influx of this nucleotide into responsive cells to increase [Ca(2+)](i) and stimulate cell proliferation.

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

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

Cyclic ADP ribose as a calcium-mobilizing messenger

This Perspective by Galione and Churchill is one in a series on intracellular calcium release mechanisms. The authors review the evidence for cyclic adenosine diphosphate ribose (cADPR) being a second messenger involved in regulating intracellular calcium. In addition, the physiological stimuli and responses mediated by cADPR are discussed. The Perspective is accompanied by a movie showing a calcium wave triggered by cADPR.

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.

Simultaneous determination of deoxyribonucleoside in the presence of ribonucleoside triphosphates in human carcinoma cells by high-performance liquid chromatography

Simultaneous determination of ribonucleoside and deoxyribonucleoside triphosphates in cells by HPLC is an analytical challenge since the concentration of dNTP present in mammalian cells is several orders of magnitude lower than the corresponding NTP. Hence, the quantitation of dNTP in cells is generally performed after selective oxidation or removal of the major NTP. The procedures reported so far are lengthy and cumbersome and do not enable the simultaneous determination of NTP. We report the development of a simple, direct HPLC method for the simultaneous determination of dNTP and NTP in colon carcinoma WiDr cell extracts using a stepwise gradient elution ion-pairing HPLC with uv detection at 260 nm and with a minimal chemical manipulation of cells. Exponentially growing WiDr cells were harvested by centrifugation, rinsed with phosphate-buffered saline, and carefully counted. The pellets were suspended in a known volume of ice-cold water and deproteinized with an equal volume of 6% trichloroacetic acid. The acid cell extracts (corresponding to 2. 5 x 10(6) cells/100 microl) were centrifuged at 13,000g for 10 min at 4 degrees C. The resulting supernatants were stored at -80 degrees C prior to analysis. Aliquots (100 microl) were neutralized with 4.3 microl saturated Na2CO3 solution prior the injection of 40 microl onto the HPLC column (injection speed 250 microl/min). Chromatographic separations were performed using two Symmetry C18 3. 5-microm (2 x 3.9 x 150 mm) columns (Waters), connected in series equipped with a Sentry guard column (3.9 x 20 mm i.d.) filled with the same packing material. The HPLC columns were kept at 30 degrees C. The mobile phase was delivered at a flow rate of 0.5 ml/min, with the following stepwise gradient elution program: % solvent A/solvent B, 100/0 at 0 min --> 100/0 at 1 min --> 36/64 at 5 min --> 31/69 at 90 min --> 31/69 at 105 min --> 0/100 at 106 min --> 0/100 at 120 min; 50/50 MeOH/solvent B from 121 to 130 min; 100% solvent A from 131 to 160 min. Solvent A contained 0.01 M KH2PO4, 0.01 M tetrabutylammonium chloride, and 0.25% MeOH and was adjusted to pH 7. 0 (550 microl 10 N NaOH for 1 liter solvent A). Solvent B consisted of 0.1 M KH2PO4, 0.028 M tetrabutylammonium chloride, and 30% MeOH and was neutralized to pH 7.0 (1.4 ml 10 N NaOH for 1 liter solvent B). Even though dNTPs are minor components of cell extracts, satisfactory regression coefficients were obtained for their calibration curves (r2 > 0.99) established with the addition-calibration methods up to 120 pmol/40-microl injection. The applicability of the method was demonstrated by in vitro studies of the modulation of NTP and dNTP pools in WiDr colon carcinoma cell lines exposed to various pharmacological concentrations of cytostatic drugs (i.e., FMdC, IUdR, gemcitabine). In conclusion, this optimized, simplified, analytical method enables the simultaneous quantitation of NTP and dNTP and may represent a valuable tool for the detection of minute alterations of cellular dNTP/NTP pools induced by anticancer/antiviral drugs and diseases.

Regulation of calcium signalling in T lymphocytes by the second messenger cyclic ADP-ribose

Cyclic ADP-ribose (cADPR) is a natural compound that mobilizes calcium ions in several eukaryotic cells. Although it can lead to the release of calcium ions in T lymphocytes, it has not been firmly established as a second messenger in these cells. Here, using high-performance liquid chromatography analysis, we show that stimulation of the T-cell receptor/CD3 (TCR/CD3) complex results in activation of a soluble ADP-ribosyl cyclase and a sustained increase in intracellular levels of cADPR. There is a causal relation between increased cADPR concentrations, sustained calcium signalling and activation of T cells, as shown by inhibition of TCR/CD3-stimulated calcium signalling, cell proliferation and expression of the early- and late-activation markers CD25 and HLA-DR by using cADPR antagonists. The molecular target for cADPR, the type-3 ryanodine receptor/calcium channel, is expressed in T cells. Increased cADPR significantly and specifically stimulates the apparent association of [3H]ryanodine with the type-3 ryanodine receptor, indicating a direct modulatory effect of cADPR on channel opening. Thus we show the presence, causal relation and biological significance of the major constituents of the cADPR/calcium-signalling pathway in human T cells.

Ectocellular CD38-catalyzed synthesis and intracellular Ca2+-signalling activity of cyclic ADP-ribose in T-lymphocytes are not functionally related

Cyclic ADP-ribose (cADPR) is a natural metabolite of beta-NAD+ with a potent Ca2+-mobilizing activity in different cell types, including T-lymphocytes. We investigated (i) whether stimulation of T-lymphocytes with different agonists affects the intracellular concentration of cADPR, and (ii) whether the lymphocyte antigen CD38, through its ectocellular ADP-ribosyl cyclase and cADPR-hydrolase enzymatic activities, can account for the regulation of the intracellular levels of cADPR and the Ca2+-mobilizing effects of this nucleotide in Jurkat and HPB.ALL T-lymphocytes. The anti-CD3 antibody OKT3, the sphingolipid sphingosine and lysophosphatidic acid induced an increase in intracellular cADPR with concomitant increases in the intracellular Ca2+ concentration ([Ca2+]i). In contrast, activation of an ectocellular ADP-ribosyl cyclase by preincubation of cells with beta-NAD+ led to a dose-dependent increase in cADPR, but no changes in [Ca2+]i were observed. However, extensive washing of the cells following preincubation with NAD+ demonstrated that the increases in cADPR were not intracellular but due to cell surface-associated nucleotide. Accordingly, measurements of ADP-ribosyl cyclase activity in intact T-cells showed ectocellular synthesis of cADPR, but no evidence was obtained for a shift of this activity into the cells which could account for intracellular accumulation of cADPR. Taken together, the results indicate no direct involvement of the ADP-ribosyl cyclase activity of CD38 on the regulation of the cADPR-mediated intracellular Ca2+-signalling in T-lymphocytes.