A pivotal role for cADPR-mediated Ca2+ signaling: regulation of endothelin-induced contraction in peritubular smooth muscle cells. (57/314)

cADPR, a potent calcium-mobilizing intracellular messenger synthesized by ADP-ribosyl cyclases regulates openings of ryanodine receptors (RyR). Here we report that in the rat testis, a functional cADPR Ca2+ release system is essential for the contractile response of peritubular smooth muscle cells (PSMC) to endothelin (ET). We previously showed that this potent smooth muscle agonist elicits intracellular Ca2+ release in PSMC and seminiferous tubule contraction via activation of ETA and ETB receptors. ETB-R induces the mobilization of a thapsigargin-sensitive but IP3-independent intracellular Ca2+ pool. Stimulation of permeabilized PSMC with cADPR was found to elicit large Ca2+ releases blocked by either a selective antagonist of cADPR or a RyR blocker, but not by heparin. Western blotting and confocal fluorescence microscopy indicated the specific expression of type 2 RyR in perinuclear localization. ET was found to stimulate the activity of ADP-ribosyl cyclase. Microinjection of the selective cADPR antagonist 8NH2-cADPR completely abolished subsequent stimulation of Ca2+ signaling via ETA and ETB receptors. cADPR therefore appears to have an obligatory role for ETA-R and ETB-R-mediated calcium signaling in PSMC. However, ETB-R seem to be coupled exclusively to cADPR whereas ETA-R activation may be linked to IP3 and cADPR signaling pathways.  (+info)

Pancreatic beta-cell death, regeneration and insulin secretion: roles of poly(ADP-ribose) polymerase and cyclic ADP-ribose. (58/314)

In the early 1980s, we proposed a unifying model for beta-cell damage (The OKAMOTO model), in which poly(ADP-ribose) synthetase/polymerase (PARP) activation plays an essential role in the consumption of NAD+, which leads to energy depletion and necrotic cell death. In 1984, we demonstrated that the administration of PARP inhibitors to 90% depancreatized rats induces islet regeneration. From the regenerating islet-derived cDNA library we isolated Reg (Regenerating Gene) and demonstrated that Reg protein induces beta-cell replication via the Reg receptor and ameliorates experimental diabetes. More recently, we showed that the combined addition of IL-6 and dexamethasone induces the Reg gene expression in beta-cells and that PARP inhibitors enhance the expression. In 1993, we found that cyclic ADP-ribose (cADPR), a product synthesized from NAD+, is a second messenger for intracellular Ca2+ mobilization for insulin secretion by glucose, and proposed a novel mechanism of insulin secretion, the CD38-cADPR signal system. Therefore, PARP inhibitors prevent beta-cell necrosis, induce beta-cell replication and maintain insulin secretion.  (+info)

Interactions between intracellular Ca2+ stores: Ca2+ released from the NAADP pool potentiates cADPR-induced Ca2+ release. (59/314)

Cells possess multiple intracellular Ca2+-releasing systems. Sea urchin egg homogenates are a well-established model to study intracellular Ca2+ release. In the present study the mechanism of interaction between three intracellular Ca2+ pools, namely the nicotinic acid adenine dinucleotide phosphate (NAADP), the cyclic ADP-ribose (cADPR) and the inositol 1',4',5'-trisphosphate (IP3)-regulated Ca2+ stores, is explored. The data indicate that the NAADP Ca2+ pool could be used to sensitize the cADPR system. In contrast, the IP3 pool was not affected by the Ca2+ released by NAADP. The mechanism of potentiation of the cADPR-induced Ca2+ release, promoted by Ca2+ released from the NAADP pool, is mediated by the mechanism of Ca2+-induced Ca2+ release. These data raise the possibility that the NAADP Ca2+ store may have a role as a regulator of the cellular sensitivity to cADPR.  (+info)

Nicotinic acid-adenine dinucleotide phosphate activates the skeletal muscle ryanodine receptor. (60/314)

Calcium is a universal second messenger. The temporal and spatial information that is encoded in Ca(2+)-transients drives processes as diverse as neurotransmitter secretion, axonal outgrowth, immune responses and muscle contraction. Ca(2+)-release from intracellular Ca(2+) stores can be triggered by diffusible second messengers like Ins P (3), cyclic ADP-ribose or nicotinic acid-adenine dinucleotide phosphate (NAADP). A target has not yet been identified for the latter messenger. In the present study we show that nanomolar concentrations of NAADP trigger Ca(2+)-release from skeletal muscle sarcoplasmic reticulum. This was due to a direct action on the Ca(2+)-release channel/ryanodine receptor type-1, since in single channel recordings, NAADP increased the open probability of the purified channel protein. The effects of NAADP on Ca(2+)-release and open probability of the ryanodine receptor occurred over a similar concentration range (EC(50) approximately 30 nM) and were specific because (i) they were blocked by Ruthenium Red and ryanodine, (ii) the precursor of NAADP, NADP, was ineffective at equimolar concentrations, (iii) NAADP did not affect the conductance and reversal potential of the ryanodine receptor. Finally, we also detected an ADP-ribosyl cyclase activity in the sarcoplasmic reticulum fraction of skeletal muscle. This enzyme was not only capable of synthesizing cyclic GDP-ribose but also NAADP, with an activity of 0.25 nmol/mg/min. Thus, we conclude that NAADP is generated in the vicinity of type 1 ryanodine receptor and leads to activation of this ion channel.  (+info)

Calcium signalling: calcium goes global. (61/314)

Recent evidence suggests that multiple calcium-releasing messengers might be activated simultaneously to regulate patterns of intracellular calcium signalling. In this way, agonists might use different messenger cocktails to encode specific signals and target selected processes.  (+info)

Equilibrative and concentrative nucleoside transporters mediate influx of extracellular cyclic ADP-ribose into 3T3 murine fibroblasts. (62/314)

In mammals cyclic ADP-ribose (cADPR), a universal calcium mobilizer from intracellular stores, is generated from NAD(+) at the outer cell surface by the multifunctional ectoenzyme CD38 and by related ADP-ribosyl cyclases. Recently, influx of extracellular cADPR has been observed in 3T3 murine fibroblasts, where it elicits Ca(2+)-mediated enhancement of proliferation. Here we addressed the nature and the properties of cADPR influx into CD38(-) 3T3 cells, which showed pleiotropic mechanisms of both equilibrative and concentrative transport. Based on selective inhibitors or experimental conditions (e.g. abrogation of Na(+)-dependent active symport processes and transient transfection experiments) and on reverse transcriptase-polymerase chain reaction analysis of transcripts in 3T3 fibroblasts and comparatively in HeLa cells, we identified cADPR-transporting activities with specific nucleoside transporters (NT), both equilibrative (ENT2) and concentrative (CNT2 and a nitrobenzylthioinosine (NBMPR)-inhibitable NT). A reciprocal inhibition relationship was observed between inosine and cADPR fluxes across these NT species. Concentrative (but not equilibrative) transport of nanomolar extracellular cADPR took place in CD38(-) 3T3 cells co-cultured for 48 h in transwells on feeders of CD38-transfected, cADPR-generating 3T3 fibroblasts. These results suggest possible, hitherto unrecognized, correlations between ectocellular metabolism of nucleotides/nucleosides and cADPR-mediated regulation of intracellular calcium homeostasis.  (+info)

Evidence for a causal role of CD38 expression in granulocytic differentiation of human HL-60 cells. (63/314)

Granulocytic differentiation of human HL-60 cells can be induced by retinoic acid and is accompanied by a massive expression of CD38, a multi-functional enzyme responsible for metabolizing cyclic ADP-ribose (cADPR), a Ca(2+) messenger. Immunofluorescence staining showed that CD38 was expressed not only on the surface of intact HL-60 cells but also intracellularly, which was revealed after permeabilization with Triton. Concomitant with CD38 expression was the accumulation of cADPR, and both time courses preceded the onset of differentiation, suggesting a causal role for CD38. Consistently, treatment of HL-60 cells with a permeant inhibitor of CD38, nicotinamide, inhibited both the CD38 activity and differentiation. More specific blockage of CD38 expression was achieved by using morpholino antisense oligonucleotides targeting its mRNA, which produced a corresponding inhibition of differentiation as well. Similar inhibitory effects were observed when CD38 expression was reduced by the RNA interference technique targeting two separate regions of the coding sequence of CD38. Further support came from transfecting HL-60 cells with a Tet-On expression vector containing a full-length CD38. Subsequent treatments with doxycycline induced both CD38 expression and differentiation in the absence of retinoic acid. These results provide the first evidence that CD38 expression and the consequential accumulation of cADPR play a causal role in mediating cellular differentiation.  (+info)

Regulation of intracellular Ca2+ stores by multiple Ca2+-releasing messengers. (64/314)

Although glucose-elicited insulin secretion depends on Ca(2+) entry through voltage-gated Ca(2+) channels in the surface cell membrane of the pancreatic beta-cell, there is also ample evidence for an important role of intracellular Ca(2+) stores, particularly in relation to hormone- or neurotransmitter-induced insulin secretion. There is now direct evidence for Ca(2+) entry-induced release of Ca(2+) from the endoplasmic reticulum in neurons, but with regard to glucose stimulation of beta-cells, there is conflicting evidence about the operation of such a process. This finding suggests that the sensitivity of the Ca(2+) release channels in the endoplasmic reticulum membrane varies under different conditions and therefore is regulated. Recent evidence from studies of pancreatic acinar cells has revealed combinatorial roles of multiple messengers in setting the sensitivity of the endoplasmic reticulum for Ca(2+) release. Here we focus on the possible combinatorial roles of inositol 1,4,5-trisphosphate, cyclic ADP-ribose, and nicotinic acid adenine dinucleotide phosphate in beta-cell function.  (+info)