The Ca2+-activated polyphosphoinositide phosphodiesterase of human and rabbit neutrophil membranes.
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ABSTRACT:
SUBMITTER: Cockcroft S
PROVIDER: S-EPMC1144062 | biostudies-other | 1984 Jul
REPOSITORIES: biostudies-other
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Project description:The requirement for Ca2+ for the activation of polyphosphoinositide phosphodiesterase was studied with the guanine nucleotide analogue guanosine 5'-[gamma-thio]triphosphate (GTP gamma S). Levels of Ca2+ that pertain in unstimulated neutrophils (100 nM) are obligatory for the full expression of enzyme activity stimulated with GTP gamma S. Reduction of Ca2+ to 1 nM leads to inhibition. Increasing the level of Ca2+ from 100 nM to 1000 nM does not alter enzyme activity. Guanosine 5'-[beta-thio]diphosphate (GDP beta S) does not stimulate the phosphodiesterase but is an effective inhibitor of activation by GTP gamma S. Ca2+ in the millimolar range can also activate the phosphodiesterase alone and this is not inhibited by GDP beta S. It is also shown that Sr2+ in the millimolar range can stimulate enzyme activity similarly to Ca2+.
| S-EPMC1147444 | biostudies-other
Project description:1. A new assay procedure has been devised for measurement of the Ca(2+)-activated polyphosphoinositide phosphodiesterase (phosphatidylinositol polyphosphate phosphodiesterase) activity of erythrocyte ghosts. The ghosts are prepared from cells previously incubated with [(32)P]P(i). They are incubated under appropriate conditions for activation of the phosphodiesterase and the released (32)P-labelled inositol bisphosphate and inositol trisphosphate are separated by anion-exchange chromatography on small columns of Dowex-1 (formate form). When necessary, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate can be deacylated and the released phosphodiesters separated on the same columns. 2. The release of both inositol bisphosphate and inositol trisphosphate was rapid in human ghosts, with half of the labelled membrane-bound phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate broken down in only a few minutes in the presence of 0.5mm-Ca(2+). For both esters, optimum rates of release were seen at pH6.8-6.9. Mg(2+) did not provoke release of either ester. 3. Ca(2+) provoked rapid polyphosphoinositide breakdown in rabbit erythrocyte ghosts and a slower breakdown in rat ghosts. Erythrocyte ghosts from pig or ox showed no release of inositol phosphates when exposed to Ca(2+). 4. In the presence of Mg(2+), the inositol trisphosphate released from phosphatidylinositol 4,5-bisphosphate was rapidly converted into inositol bisphosphate by phosphomonoesterase activity. 5. Neomycin, an aminoglycoside antibiotic that interacts with polyphosphoinositides, inhibited the breakdown of both phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate, with the latter process being appreciably more sensitive to the drug. Phenylmethanesulphonyl fluoride, an inhibitor of serine esterases that is said to inhibit phosphatidylinositol phosphodiesterase, had no effect on the activity of the erythrocyte polyphosphoinositide phosphodiesterase. 6. These observations are consistent with the notion that human, and probably rabbit and rat, erythrocyte membranes possess a single polyphosphoinositide phosphodiesterase that is activated by Ca(2+) and that attacks phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate with equal facility. Inhibition of this activity by neomycin seems likely to be due to interactions between neomycin and the polyphosphoinositides, with the greater inhibition of phosphatidylinositol 4,5-bisphosphate breakdown consistent with the greater affinity of the drug for this lipid. In addition, erythrocyte membranes possess Mg(2+)-dependent phosphomonoesterase that converts inositol 1,4,5-triphosphate into inositol bisphosphate.
| S-EPMC1163219 | biostudies-other
Project description:1. Both the Ca(2+)-pump ATPase and the polyphosphoinositide phosphodiesterase of the erythrocyte membrane can, when assayed under appropriate conditions, be activated by Ca(2+) in the micromolar range. We have therefore compared the mechanisms and affinities for Ca(2+) activation of the two enzymes in human erythrocyte membranes, to see whether the polyphosphoinositide phosphodiesterase would be active in normal healthy erythrocytes. 2. At physiological ionic strength and in the presence of calmodulin, the Ca(2+)-pump ATPase was activated by Ca(2+) in a highly co-operative manner, with half-maximal activation occurring at about 0.3mum-Ca(2+). At an optimal Ca(2+) concentration, calmodulin stimulated the Ca(2+)-sensitive ATPase activity about 10-fold. 3. Ca(2+) activated the polyphosphoinositide phosphodiesterase in a non-co-operative manner. The Ca(2+) requirements for breakdown of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate were identical, which supports our previous conclusion that Ca(2+) activates a single polyphosphoinositide phosphodiesterase that degrades both lipids with equal facility. Added calmodulin did not affect the activity of the polyphosphoinositide phosphodiesterase. 4. At low ionic strength in the absence of Mg(2+), half-maximal activation of the phosphodiesterase was at about 3mum-Ca(2+). The presence of 1mm-Mg(2+) shifted the Ca(2+) activation curve to the right, as did elevation of the ionic strength. When the Ca(2+)-pump ATPase and the polyphosphoinositide phosphodiesterase were assayed in the same incubations and under conditions of intracellular ionic strength and Mg(2+) concentration, the ATPase was fully activated at 3mum-Ca(2+), whereas no polyphosphoinositide phosphodiesterase activity was detected below 100mum-Ca(2+). 5. The Ca(2+)-pump ATPase of the erythrocyte membrane normally maintains the Ca(2+) concentration of healthy erythrocytes below approx. 0.1mum. It therefore seems unlikely that the polyphosphoinositide phosphodiesterase of the erythrocyte membrane ever expresses its activity in a healthy erythrocyte.
| S-EPMC1158073 | biostudies-other
Project description:Stimulated hydrolysis of the inositol phospholipids phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] was investigated by studying the phosphoinositides produced in a suspended preparation of plasma membranes by transference of 32P from [gamma-32P]ATP. At basal Ca2+ concentration (calculated free Ca2+, 150 nM) phospholipid hydrolysis was stimulated either by the muscarinic agonists carbamoylcholine and bethanecol or by the addition of the non-hydrolysable analogue of GTP, guanosine 5'-[beta gamma-imido]triphosphate [p(NH)ppG]. GTP was without effect on basal hyrolysis. Both GTP and p(NH)ppG enhanced the rapid (within 10 s) hydrolysis of PtdIns4P and PtdIns(4,5)P2 induced by carbamoylcholine in a dose-dependent manner. A rightward shift in the competition curve of carbamoylcholine for bound L-[3H]quinuclidinyl benzilate was seen on addition of GTP or p(NH)ppG (100 microM) under phosphorylating conditions. Pretreatment of intact islet cells with Bordetella pertussis toxin, islet-activating protein (IAP) or treatment of membranes with IAP under conditions which elicited ADP-ribosylation of a protein of Mr 41,000 was without effect on muscarinic binding, phosphoinositide phosphorylation or subsequent hydrolysis by carbamoylcholine. The findings indicate the involvement of a GTP-binding protein in the coupling of the muscarinic receptor to phosphoinositide hydrolysis in the islet cell and suggest that this is distinct from the GTP-binding regulatory component of adenylate cyclase which is covalently modified by IAP.
| S-EPMC1147480 | biostudies-other
Project description:One of the earliest actions of thrombin in fibroblasts is stimulation of a phospholipase C (PLC) that hydrolyses phosphatidylinositol 4,5-bisphosphate (PIP2) to inositol 1,4,5-trisphosphate (IP3) and diacylglycerol. In membranes prepared from WI-38 human lung fibroblasts, thrombin activated an inositol-lipid-specific PLC that hydrolysed [32P]PIP2 and [32P]phosphatidylinositol 4-monophosphate (PIP) to [32P]IP3 and [32P]inositol 1,4-bisphosphate (IP2) respectively. Degradation of [32P]phosphatidylinositol was not detected. PLC activation by thrombin was dependent on GTP, and was completely inhibited by a 15-fold excess of the non-hydrolysable GDP analogue guanosine 5'-[beta-thio]diphosphate (GDP[S]). Neither ATP nor cytosol was required. Guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) also stimulated polyphosphoinositide hydrolysis, and this activation was inhibited by GDP[S]. Stimulation of PLC by either thrombin or p[NH]ppG was dependent on Ca2+. Activation by thrombin required Ca2+ concentrations between 1 and 100 nM, whereas stimulation of PLC activity by GTP required concentrations of Ca2+ above 100 nM. Thus the mitogen thrombin increased the sensitivity of PLC to concentrations of free Ca2+ similar to those found in quiescent fibroblasts. Under identical conditions, another mitogen, platelet-derived growth factor, did not stimulate polyphosphoinositide hydrolysis. It is concluded that an early post-receptor effect of thrombin is the activation of a Ca2+- and GTP-dependent membrane-associated PLC that specifically cleaves PIP2 and PIP. This result suggests that the cell-surface receptor for thrombin is coupled to a polyphosphoinositide-specific PLC by a GTP-binding protein that regulates PLC activity by increasing its sensitivity to Ca2+.
| S-EPMC1148081 | biostudies-other
Project description:Constitutive Ca(2+)/calmodulin (CaM)-activation of adenylyl cyclases (ACs) types 1 and 8 in sinoatrial nodal cells (SANC) generates cAMP within lipid-raft-rich microdomains to initiate cAMP-protein kinase A (PKA) signaling, that regulates basal state rhythmic action potential firing of these cells. Mounting evidence in other cell types points to a balance between Ca(2+)-activated counteracting enzymes, ACs and phosphodiesterases (PDEs) within these cells. We hypothesized that the expression and activity of Ca(2+)/CaM-activated PDE Type 1A is higher in SANC than in other cardiac cell types. We found that PDE1A protein expression was 5-fold higher in sinoatrial nodal tissue than in left ventricle, and its mRNA expression was 12-fold greater in the corresponding isolated cells. PDE1 activity (nimodipine-sensitive) accounted for 39% of the total PDE activity in SANC lysates, compared to only 4% in left ventricular cardiomyocytes (LVC). Additionally, total PDE activity in SANC lysates was lowest (10%) in lipid-raft-rich and highest (76%) in lipid-raft-poor fractions (equilibrium sedimentation on a sucrose density gradient). In intact cells PDE1A immunolabeling was not localized to the cell surface membrane (structured illumination microscopy imaging), but located approximately within about 150nm inside of immunolabeling of hyperpolarization-activated cyclic nucleotide-gated potassium channels (HCN4), which reside within lipid-raft-rich microenvironments. In permeabilized SANC, in which surface membrane ion channels are not functional, nimodipine increased spontaneous SR Ca(2+) cycling. PDE1A mRNA silencing in HL-1 cells increased the spontaneous beating rate, reduced the cAMP, and increased cGMP levels in response to IBMX, a broad spectrum PDE inhibitor (detected via fluorescence resonance energy transfer microscopy). We conclude that signaling via cAMP generated by Ca(2+)/CaM-activated AC in SANC lipid raft domains is limited by cAMP degradation by Ca(2+)/CaM-activated PDE1A in non-lipid raft domains. This suggests that local gradients of [Ca(2+)]-CaM or different AC and PDE1A affinity regulate both cAMP production and its degradation, and this balance determines the intensity of Ca(2+)-AC-cAMP-PKA signaling that drives SANC pacemaker function.
| S-EPMC5054686 | biostudies-literature
Project description:Preterm birth is a major contributor to neonatal mortality and morbidity, and infection is a major risk factor. Chorioamnionitis, inflammation of the placenta, and fetal membranes (FMs) are commonly observed in preterm birth and are characterized by neutrophil infiltration. However, interactions between FMs and neutrophils remain incompletely understood. The objectives of this study were to determine how FMs, with or without bacterial LPS stimulation, affect neutrophil recruitment, activation, and the formation of neutrophil extracellular traps (NETs) and to elucidate the signaling mechanisms involved. Using a combination of in vitro, ex vivo, and in vivo approaches, we show that human resting FMs can directly recruit neutrophils and induce them to produce proinflammatory factors. Furthermore, neutrophils release vital NETs in response to FM-derived factors. LPS-stimulated FMs further augmented neutrophil recruitment, inflammatory cytokine/chemokine secretion, and vital NET release and also induced reactive oxygen species production and degranulation. We demonstrate a role for FM-derived TNF-? in mediating these effects through activation of neutrophil p38 MAPK. We propose that, during infection, neutrophil recruitment and activation may neutralize pathogens, vital NET formation, and prolonged neutrophil viability, and in combination with degranulation, reactive oxygen species production and inflammatory chemokine/cytokine production may contribute to tissue injury at the maternal/fetal interface.
| S-EPMC6616008 | biostudies-literature
Project description:Neutrophil activation is an integral process to acute inflammation and is associated with adverse clinical sequelae. Identification of neutrophil activation in real time in the lungs of patients may permit biological stratification of patients in otherwise heterogenous cohorts typically defined by clinical criteria. No methods for identifying neutrophil activation in real time in the lungs of patients currently exist. We developed a bespoke molecular imaging probe targeting three characteristic signatures of neutrophil activation: pinocytosis, phagosomal alkalinisation, and human neutrophil elastase (HNE) activity. The probe functioned as designed in vitro and ex vivo. We evaluated optical endomicroscopy imaging of neutrophil activity using the probe in real-time at the bedside of healthy volunteers, patients with bronchiectasis, and critically unwell mechanically ventilated patients. We detected a range of imaging responses in vivo reflecting heterogeneity of condition and severity. We corroborated optical signal was due to probe function and neutrophil activation.
| S-EPMC7806726 | biostudies-literature
Project description:Fura-2-loaded human platelets were used to study Ca2+ release from intracellular compartments, as well as Ca2+ influx from the extracellular space. We investigated the response towards the endoperoxide/thromboxane-receptor agonist. U46619, and the inhibitor of the endoplasmic-reticulum Ca(2+)-ATPase, thapsigargin. U46619 dose-dependently depleted intracellular Ca2+ stores, followed by active sequestration of released Ca2+. Ca2+ influx induced by U46619 largely relies on receptor occupancy. Removing the thromboxane analogue from its receptor by using the endoperoxide/thromboxane-receptor antagonist BM 13177 largely blunted U46619-mediated Ca2+ influx. The Ca(2+)-ATPase inhibitor thapsigargin evoked a gradual rise in intracellular Ca2+, which was potentiated by a preceding activation of platelets with the receptor agonist U46619. This agonist-sensitizing effect also depends on receptor occupancy. Removing U46619 from its receptor by addition of the endoperoxide/thromboxane-receptor antagonist BM13177 suppressed the sensitizing effect completely. Furthermore, interrupting downstream receptor signalling events by raising intracellular levels of cyclic nucleotides (cyclic AMP, cyclic GMP) again suppressed the U46619-sensitizing effect on thapsigargin-induced Ca2+ release. This study indicates that the process of Ca2+ release followed by resequestration in response to a platelet agonist by its own is not sufficient to produce the sensitizing effect. Rather, a continuously occupied receptor triggering sustained downstream signalling events seems to be required for sensitization. The presence of a receptor agonist may induce an increased cycling of Ca2+ between the agonist-responsive and the thapsigargin-dischargeable compartment, leading to faster and more intense accumulation of Ca2+ in the cytosolic compartment after inhibition of the Ca(2+) ATPase. Suggestively, receptor occupancy increases the Ca(2+)-releasing potency of thapsigargin by coupling the thapsigargin-sensitive Ca(2+)-storing compartments with an agonist-responsive compartment that exhibits a high leakage rate in stimulated platelets.
| S-EPMC1137430 | biostudies-literature
Project description:Sensory photoreceptors elicit vital physiological adaptations in response to incident light. As light-regulated actuators, photoreceptors underpin optogenetics, which denotes the noninvasive, reversible, and spatiotemporally precise perturbation by light of living cells and organisms. Of particular versatility, naturally occurring photoactivated adenylate cyclases promote the synthesis of the second messenger cAMP under blue light. Here, we have engineered a light-activated phosphodiesterase (LAPD) with complementary light sensitivity and catalytic activity by recombining the photosensor module of Deinococcus radiodurans bacterial phytochrome with the effector module of Homo sapiens phosphodiesterase 2A. Upon red-light absorption, LAPD up-regulates hydrolysis of cAMP and cGMP by up to sixfold, whereas far-red light can be used to down-regulate activity. LAPD also mediates light-activated cAMP and cGMP hydrolysis in eukaryotic cell cultures and in zebrafish embryos; crucially, the biliverdin chromophore of LAPD is available endogenously and does not need to be provided exogenously. LAPD thus establishes a new optogenetic modality that permits light control over diverse cAMP/cGMP-mediated physiological processes. Because red light penetrates tissue more deeply than light of shorter wavelengths, LAPD appears particularly attractive for studies in living organisms.
| S-EPMC4066486 | biostudies-literature