Ca2+ entry induced by cyclic ADP-ribose in intact T-lymphocytes

Ca2+ signalling and membrane current activated by cADPr in starfish oocytes

Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+](i)) in a variety of cell types, including immature oocytes from the starfish Astropecten auranciacus. In this study, we employed confocal laser scanning microscopy and voltage clamp techniques to investigate the source of the cADPr-elicited Ca2+ wave originating from the cortical Ca2+ patches we have described previously. The Ca2+ swing was accompanied by a membrane current with a reversal potential of approximately +20 mV. Decreasing external Na+ almost abolished the current without affecting the Ca2+ response. Removal of extracellular Ca2+ altered neither the Ca2+ transient nor the ionic current, nor did the holding potential exert any effect on the Ca2+ wave. Both the Ca2+ response and the membrane current were abolished when BAPTA, ruthenium red or 8-NH(2)-cADPr were preinjected into the oocytes, while perfusion with ADPr did not elicit any [Ca2+](i) increase or ionic current. However, elevating [Ca2+](i) by uncaging Ca2+ from nitrophenyl- (NP-EGTA) or by photoliberating inositol 1,4,5-trisphosphate (InsP(3)) induced an ionic current with biophysical properties similar to that elicited by cADPr. These results suggest that cADPr activates a Ca2+ wave by releasing Ca2+ from intracellular ryanodine receptors and that the rise in [Ca2+](i) triggers a non-selective monovalent cation current that does not seem to contribute to the global Ca2+ elevation.

Analysis of subcellular calcium signals in T-lymphocytes

Subcellular Ca(2+) signals were analysed in Jurkat and peripheral human T-lymphocytes by confocal Ca(2+) imaging employing an off-line deconvolution method. Stimulation of the TCR/CD3 complex in T-lymphocytes resulted in a series of subcellular pacemaker Ca(2+) signals preceding the first global Ca(2+) signal. The pacemaker signals occurred in a cytosolic "trigger" zone, which is localised close to the plasma membrane. The pacemaker signals were almost independent of extracellular Ca(2+) as shown by measurements in the absence of extracellular Ca(2+), or in the presence of the Ca(2+) channel blocker SK-F 96365. Analysis of the confocal Ca(2+) images revealed characteristic amplitudes of 82 +/- 30 to 109 +/- 21 nM, signal diameters between 2.5 +/- 0.9 and 3.5 +/- 1.5 microm and frequencies between 0.235 and 0.677 s(-1). Taken together, our data constitute the first analysis of subcellular Ca(2+) signals in T cells and indicate that the pacemaker Ca(2+) release events, which are necessary for the development of the global Ca(2+) signal, are composed of Ca(2+) release both from inositol 1,4,5-trisphosphate- and ryanodine receptors.

Knock-down of the type 3 ryanodine receptor impairs sustained Ca2+ signaling via the T cell receptor/CD3 complex

In Jurkat T cells, the type 3 ryanodine receptor (RyR) was knocked-down by stable integration of plasmid expressing type 3 ryanodine receptor antisense RNA. Stable integration of the antisense plasmid in individual clones was demonstrated by PCR of genomic DNA, expression of antisense RNA by reverse transcriptase PCR, and efficiently reduced expression of type 3 ryanodine receptor protein by Western blot. Selected clones were successfully used to analyze T cell receptor/CD3 complex-mediated Ca(2+) signaling. Reduced expression of the type 3 RyR resulted in (i) significantly decreased Ca(2+) signaling in the sustained phase and (ii) in permeabilized cells in a significantly impaired response toward cyclic ADP-ribose but not to d-myo-inositol 1,4,5-trisphosphate. For the first time, the role of the type 3 RyR in sustained Ca(2+) signaling was directly visualized by confocal Ca(2+) imaging as a significant contribution to the number and the magnitude of subcellular Ca(2+) signals. These data suggest that the type 3 ryanodine receptor is essential in the sustained Ca(2+) response in T cells.

Extracellular NAD+: a novel autocrine/paracrine signal in osteoblast physiology

Intercellular communication allows co-ordination of cell metabolism and sensitivity to extracellular stimuli. In bone cells, paracrine stimulation and cell-to-cell coupling through gap junctions induce the formation of complex intercellular networks, which favours the intercellular exchange of nutrients and second messengers, ultimately controlling the process of bone remodelling. The importance of local factors in bone remodelling is known since many years. Bone cells secrete and respond to a variety signals, among which include prostaglandins, cytokines, growth factors, and ATP. We here report evidence that extracellular NAD(+) is a novel extracellular signal stimulating osteoblast differentiation. We found that HOBIT human osteoblastic cells, which are known to express ADP-ribosyl cyclase/CD38 activity, respond to micromolar concentrations of extracellular NAD(+) with oscillatory increases of the cytosolic Ca(2+) concentration. The initial Ca(2+) response was followed by a time-dependent inhibition of cell growth, the appearance of an epithelial morphology, and by an increase of alkaline phosphatase and osteocalcin expression. Under resting condition HOBIT cells release NAD(+) in the extracellular medium and the release is significantly potentiated by mechanical stimulation. Taken together these results point to NAD(+) as a novel autocrine/paracrine factor involved in stimulation and maintenance of the osteoblast differentiated phenotype.

Calcium signaling mechanisms in T lymphocytes

Elevation of intracellular free Ca(2+) is one of the key triggering signals for T-cell activation by antigen. A remarkable variety of Ca(2+) signals in T cells, ranging from infrequent spikes to sustained oscillations and plateaus, derives from the interactions of multiple Ca(2+) sources and sinks in the cell. Following engagement of the T cell receptor, intracellular channels (IP3 and ryanodine receptors) release Ca(2+) from intracellular stores, and by depleting the stores trigger prolonged Ca(2+) influx through store-operated Ca(2+) (CRAC) channels in the plasma membrane. The amplitude and dynamics of the Ca(2+) signal are shaped by several mechanisms, including K(+) channels and membrane potential, slow modulation of the plasma membrane Ca(2+)-ATPase, and mitochondria that buffer Ca(2+) and prevent the inactivation of CRAC channels. Ca(2+) signals have a number of downstream targets occurring on multiple time scales. At short times, Ca(2+) signals help to stabilize contacts between T cells and antigen-presenting cells through changes in motility and cytoskeletal reorganization. Over periods of minutes to hours, the amplitude, duration, and kinetic signature of Ca(2+) signals increase the efficiency and specificity of gene activation events. The complexity of Ca(2+) signals contains a wealth of information that may help to instruct lymphocytes to choose between alternate fates in response to antigenic stimulation.

Extracellular NAD(+) induces calcium signaling and apoptosis in human osteoblastic cells

ADP-ribosyl cyclase/CD38 is a bifunctional enzyme that catalyzes at its ectocellular domain the synthesis from NAD(+) (cyclase) and the hydrolysis (hydrolase) of the calcium-mobilizing second messenger cyclic ADP ribose (cADPR). Furthermore, CD38 mediates cADPR influx inside a number of cells, thereby inducing Ca(2+) mobilization. Intracellularly, cADPR releases Ca(2+) from ryanodine-sensitive pools, thus activating several Ca(2+)-dependent functions. Among these, the inhibition of osteoclastic-mediated bone resorption has been demonstrated. We found that HOBIT human osteoblastic cells display ADP-ribosyl cyclase activity and we examined the effects of CD38 stimulation on osteoblasts function. Extracellular NAD(+) induced elevation of cytosolic calcium due to both Ca(2+) influx from the extracellular medium and Ca(2+) release from ryanodine-sensitive intracellular stores. Culturing these cells in the presence of NAD(+) caused a complete growth arrest with a time-dependent decrease of cell number and the appearance of apoptotic nuclei. The first changes could be observed after 24 h of treatment and became fully evident after 72-96 h. We propose a role of extracellular NAD(+) in bone homeostatic control.

Physiological functions of cyclic ADP-ribose and NAADP as calcium messengers

Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) are two Ca(2+) messengers derived from NAD and NADP, respectively. Although NAADP is a linear molecule, structurally distinct from the cyclic cADPR, it is synthesized by similar enzymes, ADP-ribosyl cyclase and its homolog, CD38. The crystal structure of the cyclase has been solved and its active site identified. These two novel nucleotides have now been shown to be involved in a wide range of cellular functions including: cell cycle regulation in Euglena, a protist; gene expression in plants; and in animal systems, from fertilization to neurotransmitter release and long-term depression in brain. A battery of pharmacological reagents have been developed, providing valuable tools for elucidating the physiological functions of these two novel Ca(2+) messengers. This article reviews these recent results and explores the implications of the existence of multiple Ca(2+) messengers and Ca(2+) stores in cells.

Intracellular Ca(2+) release mechanisms: multiple pathways having multiple functions within the same cell type?

The elevation of the cytosolic and nuclear Ca(2+) concentration is a fundamental signal transduction mechanism in almost all eukaryotic cells. Interestingly, three Ca(2+)-mobilising second messengers, D-myo-inositol 1,4,5-trisphosphate (InsP(3)), cyclic adenosine diphosphoribose (cADPR), and nicotinic acid adenine dinucleotide phosphate (NAADP(+)) were identified in a phylogenetically wide range of different organisms. Moreover, in an as yet very limited number of cell types, sea urchin eggs, mouse pancreatic acinar cells, and human Jurkat T-lymphocytes, all three Ca(2+)-mobilising ligands have been shown to be involved in the generation of Ca(2+) signals. This situation raises the question why during evolution all three messengers have been conserved in the same cell type. From a theoretical point of view the following points may be considered: (i) redundant mechanisms ensuring intact Ca(2+) signalling even if one system does not work, (ii) the need for subcellularly localised Ca(2+) elevations to obtain a certain physiological response of the cell, and (iii) tight control of a physiological response of the cell by a temporal sequence of Ca(2+) signalling events. These theoretical considerations are compared to the current knowledge regarding the three messengers in sea urchin eggs, mouse pancreatic acinar cells, and human Jurkat T lymphocytes.

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.

myo-inositol 1,4,6-trisphosphorothioate and myo-inositol 1,3, 6-trisphosphorothioate: partial agonists with very low intrinsic activity at the platelet myo-inositol 1,4,5-trisphosphate receptor

Racemic mixtures and enantiomerically pure D-isomers of both myo-inositol 1,3,6-trisphosphorothioate [Ins(1,3,6)PS(3)] and myo-inositol 1,4,6-trisphosphorothioate [Ins(1,4,6)PS(3)], prepared by total synthesis, were examined in Ca(2+) flux and binding assays. Both D-Ins(1,3,6)PS(3) and D-Ins(1,4,6)PS(3) were shown to be low intrinsic activity partial agonists at the platelet myo-inositol 1,4, 5-trisphosphate [Ins(1,4,5)P(3)] receptor, releasing less than 20% of the Ins(1,4,5)P(3)-sensitive Ca(2+) store. D-Ins(1,4,6)PS(3) displaced specifically bound [(3)H]Ins(1,4,5)P(3) from rat cerebellar membranes, although displacement was some 34-fold weaker than by D-Ins(1,4,5)P(3). D-Ins(1,4,6)PS(3) displaced [(3)H]Ins(1,4, 5)P(3) from cerebellar membranes with roughly twice the affinity of DL-Ins(1,4,6)PS(3) (IC(50) value = 1.4 +/- 0.35 microM compared with 2.15 +/- 0.13 microM), whereas D-Ins(1,3,6)PS(3) displaced [(3)H]Ins(1,4,5)P(3) with roughly twice the affinity of DL-Ins(1,3, 6)PS(3) (IC(50) value = 17.5 +/- 5.8 microM compared with 34 +/- 10 microM), confirming that the activity of both these phosphorothioates resides in their D-enantiomers. Increasing concentrations of either D-Ins(1,3,6)PS(3) or D-Ins(1,4,6)PS(3) were able to partially antagonize Ca(2+) release induced by submaximal concentrations of Ins(1,4,5)P(3), an inhibition that could be overcome by increasing the concentration of Ins(1,4,5)P(3), suggesting competition for binding at the Ins(1,4,5)P(3)-R. The only low-efficacy partial agonists at the Ins(1,4,5)P(3)-R discovered to date have been phosphorothioates; the novel D-Ins(1,3,6)PS(3) and D-Ins(1,4,6)PS(3) can now be added to this small group of analogs. However, D-Ins(1,4,6)PS(3) has a relatively high affinity for the Ins(1,4,5)P(3)-R but maintains the lowest efficacy of all the partial agonists thus far identified. As such, it may be a useful tool for pharmacological intervention in the polyphosphoinositide pathway and an important lead compound for the development of further Ins(1,4,5)P(3)-R antagonists.

Cyclic 3-deaza-adenosine diphosphoribose: a potent and stable analog of cyclic ADP-ribose

Cyclic 3-deaza-adenosine diphosphoribose (3-deaza-cADPR), an analog of cyclic adenosine diphosphoribose (cADPR) was synthesized. 3-deaza-cADPR differs from cADPR by only the substitution of carbon for nitrogen at the 3-position of the purine ring. Similar to cADPR, the analog has potent calcium releasing activity in sea urchin egg homogenates and was able to induce calcium release at concentrations as low as 0.3 nM. The EC(50) value for 3-deaza-cADPR-induced calcium release was 1 nM, which is about 70 times more potent than cADPR. The properties of calcium release induced by 3-deaza-cADPR in all other respects were similar to those of cADPR. Thus, 3-deaza-cADPR and cADPR were capable of cross-desensitizing each other and their calcium releasing activities were potentiated by Sr(2+) as well as caffeine. 8-amino-cADPR, a selective antagonist of cADPR, was also able to inhibit 3-deaza-cADPR induced calcium release. Taken together, these data suggest that 3-deaza-cADPR releases calcium through the same mechanism as cADPR. 3-deaza-cADPR was found to be resistant to both heat and enzymatic hydrolysis. Only 15% of 3-deaza-cADPR was destroyed after boiling this compound for 2 h. No loss of 3-deaza-cADPR was observed when treated with CD38 under conditions where cADPR was completely hydrolyzed. Thus, 3-deaza-cADPR is a potent and stable analog of cADPR. These properties should make 3-deaza-cADPR a useful probe in studies focused on the mechanism of cADPR action.

Pharmacological activation of the ryanodine receptor in Jurkat T-lymphocytes

1 Recently, we provided evidence for cyclic adenosine 5'-diphosphate-ribose, cADP-ribose, as a second messenger in Jurkat T-lymphocytes upon stimulation of the T-cell receptor/CD3- complex (Guse et al., 1999). cADP-ribose mobilizes Ca2+ from an intracellular Ca2+ store which is sensitive to caffeine and gated by the ryanodine receptor/Ca2+ release channel. In the present study we investigated the ability of the trypanocidal drug, suramin, to activate the ryanodine receptor of T-cells. Since suramin cannot permeate the plasma membrane, it was necessary to microinject the drug into Fura-2 loaded T-lymphocytes. 2 In a dose dependent manner suramin increased the intracellular Ca2+ concentration. The dose-response curve is very steep and calculates for an EC50 of 7. 6+/-2.9 mM suramin in the injection pipette. 3 Co-injection of the selective ryanodine receptor inhibitor ruthenium red completely abolished the suramin induced Ca2+ transient. This finding allows for the conclusion that the IP3-receptor sensitive Ca2+ pool is not the primary target of the suramin induced Ca2+ transient. 4 Furthermore, Ins(1,4,6)PS3, an antagonist of the InsP3-receptor could not suppress the suramin-induced Ca2+ signal. The suramin induced Ca2+ transients declined very slowly; however, in the presence of Ins(1,4,6)PS3 this decay was accelerated. In addition, suramin did not interact with the cADP-ribose binding site of the ryanodine receptor of T-cells. 5 In conclusion, suramin is found to be an agonist for the T-cell ryanodine receptor as previously found for the cardiac and skeletal muscle isoform. Therefore, suramin can be designated a universal ryanodine receptor agonist.

Beta1-integrins mediate Ca2+-signalling and T cell spreading via divergent pathways

Interaction of Jurkat T-lymphocytes with two extracellular matrix (ECM) proteins of the basement membrane, laminin or collagen type IV, combined with poly-L-lysine resulted in a strong adhesion, a highly increased intracellular Ca2+-concentration ([Ca2]i), as compared to cells on laminin or collagen type IV alone and in spreading of the cells. The strong adhesion was independent of an increase in [Ca2+]i, was not mediated by a beta1-integrin, and was due to charge interaction between the positively charged polyaminoacid and the negatively charged cell surface. The latter was confirmed by substitution of poly-L-lysine by other positively charged polyaminoacids. In contrast, Ca+-signalling and spreading of the cells adhering to laminin or collagen type IV combined with poly-L-lysine was completely blocked by anti-beta1 mAb. However, spreading of the cells was independent of an increase in [Ca2+]i suggesting divergent signal transduction pathways leading to Ca2+-signalling and spreading of the cells. We elucidated these signal transduction pathways by inhibition of key enzymes involved. The tyrosine kinase inhibitor genistein blocked Ca2+-signalling as well as spreading, whereas inhibitors of PKC (calphostin C, GF109203x), PLCgamma (U73122) and PLA2 (bromophenacyl-bromide (BPB), 3-[4-octadecyl)benzoyl]acrylic acid (OBAA)) selectively blocked spreading of the cells.

A unified mechanism of enzymatic synthesis of two calcium messengers: cyclic ADP-ribose and NAADP

Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) mobilize Ca2+ from two different types of intracellular stores and through completely independent mechanisms. The two Ca2+ messengers are also structurally distinct. cADPR is a cyclic nucleotide derived from NAD, while NAADP is a linear metabolite of NADP. Systems responsive to these two novel signaling molecules are widespread among eukaryotes and include protozoan, plant, invertebrate, mammalian as well as human cells. Despite their functional and structural differences, cADPR and NAADP are sibling messengers synthesized by a single enzyme, ADP-ribosyl cyclase. In this article the recent progress in understanding the physiological roles of cADPR and NAADP is briefly reviewed. A unified mechanism of catalysis is also proposed, which takes into consideration the crystallographic structure of ADP-ribosyl cyclase and accounts for its novel multi-functionality.

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.

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.

Lipid-assisted microinjection: introducing material into the cytosol and membranes of small cells

The microinjection of synthetic molecules, proteins, and nucleic acids into the cytosol of living cells is a powerful technique in cell biology. However, the insertion of a glass micropipette into the cell is a potentially damaging event, which presents significant problems, especially for small mammalian cells (spherical diameter = 2-15 micron), especially if they are only loosely adherent. The current technique is therefore limited to cells that are both sufficiently large or robust and firmly attached to a substrate. We describe here a modification of the standard technique that overcomes some of the problems associated with conventional microinjection but that does not involve the insertion of a micropipette deep into the cell cytoplasm. Instead, this method depends on lipid fusion at the micropipette tip to form a continuous but temporary conductance pathway between the interiors of the micropipette and cell. This technique thus also provides a novel method of transferring lipids and lipid-associated molecules to the plasma membrane of cells.

Calcium signaling by cyclic ADP-ribose, NAADP, and inositol trisphosphate are involved in distinct functions in ascidian oocytes

ADP-ribosyl cyclase catalyzes the synthesis of two structurally and functionally different Ca2+ releasing molecules, cyclic ADP-ribose (cADPR) from beta-NAD and nicotinic acid-adenine dinucleotide phosphate (NAADP) from beta-NADP. Their Ca2+-mobilizing effects in ascidian oocytes were characterized in connection with that induced by inositol 1,4,5-trisphosphate (InsP3). Fertilization of the oocyte is accompanied by a decrease in the oocyte Ca2+ current and an increase in membrane capacitance due to the addition of membrane to the cell surface. Both of these electrical changes could be induced by perfusion, through a patch pipette, of nanomolar concentrations of cADPR or its precursor, beta-NAD, into unfertilized oocytes. The changes induced by beta-NAD showed a distinctive delay consistent with its enzymatic conversion to cADPR. The cADPR-induced changes were inhibited by preloading the oocytes with a Ca2+ chelator, indicating the effects were due to Ca2+ release induced by cADPR. Consistently, ryanodine (at high concentration) or 8-amino-cADPR, a specific antagonist of cADPR, but not heparin, inhibited the cADPR-induced changes. Both inhibitors likewise blocked the membrane insertion that normally occurred at fertilization consistent with it being mediated by a ryanodine receptor. The effects of NAADP were different from those of cADPR. Although NAADP induced a similar decrease in the Ca2+ current, no membrane insertion occurred. Moreover, pretreatment of the oocytes with NAADP inhibited the post-fertilization Ca2+ oscillation while cADPR did not. A similar Ca2+ oscillation could be artificially induced by perfusing into the oocytes a high concentration of InsP3 and NAADP could likewise inhibit such an InsP3-induced oscillation. This work shows that three independent Ca2+ signaling pathways are present in the oocytes and that each is involved in mediating distinct changes associated with fertilization. The results are consistent with a hierarchical organization of Ca2+ stores in the oocyte.

Modulation of transcription factor NF-kappaB by enantiomers of the nonsteroidal drug ibuprofen

1. The nonsteroidal drug ibuprofen exists as an R(-)- and S(+)-enantiomer. Only the S(+)-enantiomer is an effective cyclo-oxygenase inhibitor, while the R(-)-enantiomer is inactive in this respect. Thus the molecular mechanism by which R(-)-ibuprofen exerts its anti-inflammatory and antinociceptive effects remains unknown. 2. In this study the effects of the enantiomers of ibuprofen on modulation of transcription factors have been examined with electrophoretic mobility-shift assay (EMSA), transient transfection experiments, confocal immunofluorescence and nuclear import experiments, to determine their selectivity and potency as inhibitors of the activation of transcription factor nuclear factor-kappaB (NF-kappaB). 3. R(-)-ibuprofen (IC50: 121.8 microM) as well as the S(+)-enantiomer (IC50: 61.7 microM) inhibited the activation of NF-kappaB in response to T-cell stimulation. The effect of ibuprofen was specific because, at concentrations up to 10 mM, ibuprofen did not affect the heat shock transcription factor (HSF) and the activation of NF-kappaB by prostaglandin E2 (PGE2). Very high concentrations of ibuprofen (20 mM) did not prevent NF-kappaB binding to DNA in vitro. Immunofluorescence and nuclear import experiments indicate that the site of ibuprofen action appeared to be upstream of the dissociation of the NF-kappaB-IkappaB-complex. 4. Our data raise the possibility that R(-)-ibuprofen exerts some of its effects by inhibition of NF-kappaB activation.

Does a decrease in subplasmalemmal Ca2+ explain how store-operated Ca2+ channels are opened?

The phenomenon of store-activated Ca2+ inflow (capacitative Ca2+ entry) in which the depletion of Ca2+ in the endoplasmic reticulum (ER) increases the probability of opening of store-operated Ca2+ channels (SOCs) located in the plasma membrane is ubiquitous in 'non-excitable' animal cells and is also found in some 'excitable' cells. At present, neither the structures of SOCs nor the mechanism(s) by which a decrease in Ca2+ in the lumen of the ER activates SOCs are well understood. This paper discusses the hypothesis that a decrease in the concentration of Ca2+ in restricted regions of the subplasmalemmal space (bounded by the plasma membrane and peripheral regions of the ER) is responsible for the activation of SOCs. The hypothesis rests on observations made by others that Ca2+ is a strong feed-back inhibitor of SOCs and of the endoplasmic reticulum (Ca(2+)+Mg2+)-ATPases (SERCAs), and on the concepts (developed previously by others) of a subplasmalemmal space and the directed flow of Ca2+ through SOCs into the lumen of the ER and from there to the deep cytoplasmic space. The way in which the hypothesis might explain the actions of agonists (acting via inositol 1,4,5-trisphosphate) and thapsigargin (an inhibitor of SERCAs) in activating SOCs under physiological conditions is described. The proposed involvement of thapsigargin-insensitive SERCAs, and possible limitations of the hypothesis are discussed.

Cyclic ADP-ribose enhances coupling between voltage-gated Ca2+ entry and intracellular Ca2+ release

Ca2+ release from intracellular stores can be activated in neurons by influx of Ca2+ through voltage-gated Ca2+ channels. This process, called Ca2+-induced Ca2+ release, relies on the properties of the ryanodine receptor and represents a mechanism by which Ca2+ influx during neuronal activity can be amplified into large intracellular Ca2+ signals. In a differentiated neuroblastoma cell line, we show that caffeine, a pharmacological activator of the ryanodine receptor, released Ca2+ from intracellular stores in a Ca2+-dependent and ryanodine-sensitive manner. The pyridine nucleotide, cyclic ADP-ribose, thought to be an endogenous modulator of ryanodine receptors also amplified Ca2+-induced Ca2+ release in these neurons. Cyclic ADP-ribose enhanced the total cytoplasmic Ca2+ levels during controlled Ca2+ influx through voltage gated channels, in a concentration-dependent and ryanodine-sensitive manner and also increased the sensitivity with which a small amount of Ca2+ influx could trigger additional release from the ryanodine-sensitive intracellular Ca2+ stores. Single cell imaging showed that following the Ca2+ influx, cyclic ADP-ribose enhanced the spatial spread of the Ca2+ signal from the edge of the cell into its center. These powerful actions suggest a role for cyclic ADP-ribose in the functional coupling of neuronal depolarization, Ca2+ entry, and global intracellular Ca2+ signaling.