Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Implant surface roughness influences osteoblast proliferation, differentiation, and local factor production. Moreover, the responsiveness of osteoblasts to systemic hormones such as 1, 25-(OH)(2)D(3) is altered by the effects of surface roughness; on the roughest Ti surfaces the effects of roughness and 1, 25-(OH)(2)D(3) are synergistic. Prostaglandin E(2) (PGE(2)) appears to be involved in mediating the effects of surface roughness on the cells, as well as in the response to 1,25-(OH)(2)D(3). However, it is not yet known through which signaling pathways surface roughness exerts its effects on the response of osteoblasts to 1, 25-(OH)(2)D(3). The present study examined the potential role of protein kinase A (PKA), phospholipase A(2)(PLA(2)), and protein kinase C (PKC) in this process. MG63 osteoblast-like human osteosarcoma cells were cultured on cpTi disks with R(a) values of 0. 54 microm (PT), 4.14 microm (SLA), or 4.92 microm (TPS). PKA was inhibited by adding H8 to the cultures; similarly, PLA(2) was inhibited with quinacrine or activated with melittin, and PKC was inhibited with chelerythrine. Inhibitors or activators were included in the culture media through the entire culture period or for the last 24 h of culture. In addition, cultures were treated for 24 h with inhibitors or activators in the presence of 1,25-(OH)(2)D(3). The effects on cell number and alkaline phosphatase specific activity were determined after 24 h; PKC activity was determined after 9 min and at 24 h. Cell number was reduced on rough surfaces, and alkaline phosphatase activity was increased. 1,25-(OH)(2)D(3) had a synergistic effect with surface roughness on alkaline phosphatase. However, neither surface roughness nor 1,25-(OH)(2)D(3) had an effect on PKC. H8 treatment for 24 h inhibited cell number and alkaline phosphatase on all surfaces; however, when it was present throughout the culture period, the PKA inhibitor had no effect on cell number, but decreased alkaline phosphatase-specific activity. H8 reduced the 1,25-(OH)(2)D(3)-mediated effect on cell number and alkaline phosphatase. Quinacrine inhibited cell proliferation and alkaline phosphatase on all surfaces and further reduced the 1,25-(OH)(2)D(3)-dependent decreases in both parameters. Melittin had no effect when applied for 24 h and did not modify the 1,25-(OH)(2)D(3) effect; however, when present throughout the culture period, it caused a decrease in proliferation and an increase in enzyme activity. Chelerythrine, the PKC inhibitor, only inhibited cell proliferation when it was present throughout the entire culture period. However, it decreased alkaline phosphatase in cultures treated for 24 h, but increased enzyme activity when it was present for the entire culture period. The results indicate that surface roughness and 1,25-(OH)(2)D(3) both mediate their effects through PLA(2) which catalyzes the rate-limiting step in PGE(2) production. Further downstream, PGE(2) activates PKA. Surface roughness-dependent effects are also mediated through PKC, but only after the cells have reached confluence and are undergoing phenotypic maturation. The effect of surface roughness on responsiveness to 1,25-(OH)(2)D(3) is mediated through PLA(2)/PKA and not through PKC.
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PMID:Surface roughness modulates the response of MG63 osteoblast-like cells to 1,25-(OH)(2)D(3) through regulation of phospholipase A(2) activity and activation of protein kinase A. 1044 25

Mammalian secretory phospholipase A(2)s (sPLA(2)s) are classified into several groups according to molecular structure and the localization of intramolecular disulfide bridges. Among them, group IIA sPLA(2) has been thought to be one of the key enzymes in the pathogenesis of inflammatory diseases owing to its augmented expression under various inflammatory conditions. However, in a number of inbred mouse strains, the group IIA sPLA(2) gene is naturally disrupted by a frameshift mutation. Here, we report the cloning of a cDNA encoding a novel sPLA(2) expressed in the spleen of group IIA sPLA(2)-deficient mouse. We also cloned its human homolog and mapped its gene location on chromosome 1p36.12 near the loci of group IIA and V sPLA(2) genes. The human mature sPLA(2) protein consists of 125 amino acids (M(r) = 14,500) preceded by a 20-residue prepeptide and is most similar to group IIA sPLA(2) with respect to the number and positions of cysteine residues as well as overall identity (48%). Based on these structural properties, the novel sPLA(2) should be categorized into group II, called group IID to follow the already identified IIA to IIC sPLA(2)s. When the cDNA was expressed in COS-7 cells, PLA(2) activity preferentially accumulated in the culture medium. It is maximally active at neutral to alkaline pH and with 2 mM Ca(2+). In assays with individual substrates, L-alpha-1-palmitoyl-2-linoleoyl phosphatidylethanolamine was more efficiently hydrolyzed than the other phospholipids examined. An RNA blot hybridized with the cDNA exhibited two transcripts (2.0 and 1.0 kb) in human spleen, thymus, and colon. The expression of a novel sPLA(2) mRNA was elevated in the thymus after treatment with endotoxin in rats as well as in group IIA sPLA(2)-deficient mice, suggesting its functional role in the progression of the inflammatory process.
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PMID:Cloning and characterization of novel mouse and human secretory phospholipase A(2)s. 1045 75

Extraction with Tris-citrate or Tris-NaCl-EGTA improved the yield of phospholipase A2 (PLA2) from ram semen by 40-50 fold over the previously recommended method of extraction by dilute (0.18 N) sulphuric acid. The enzyme activity in the citrate extract deteriorated more rapidly than in Tris-NaCl-EGTA. The semen PLA2 activity was optimum at pH 8.0, heat sensitive at 70 degrees C for 30 min, activated by Ca2+ (although approximately 60% activity was also found in the absence of calcium) and did not exist as a pro-enzyme. The semen PLA2 activity was equally distributed among the sperm and seminal plasma (SP) components of ram semen. However, the low levels of PLA2 activity in the SP of vasectomised rams tend to suggest that PLA2 in the SP fraction may have originated from testicular or epididymal secretions or leakage, from sperm. PLA, in sperm exists as a large molecular weight aggregate, whereas in SP it is present as a smaller aggregate. In addition to PLA2, semen also contained PLA2 inhibitor activities. Inhibition was observed against PLA2s from bee venom, pig pancreas and oviductal extracts. The inhibitory activity is presumed to be due to a large molecular weight protein as the inhibitor activity was not extracted in a chloroform:methanol (2:1; v/v) mixture, it was non-dialysable, precipitated by 10% trichloroacetic acid and destroyed by proteases. The inhibitor activity was distributed in various molecular weight fractions of sperm, SP and SP from vasectomised rams.
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PMID:Studies on the measurement of phospholipase A2 (PLA2) and PLA2 inhibitor activities in ram semen. 1046 98

The presence of a lipoprotein profile with abundance of small, dense low density lipoproteins (LDL), low levels of high density lipoproteins (HDL), and elevated levels of triglyceride-rich very low density lipoproteins is associated with an increased risk for coronary heart disease. The atherogenicity of small, dense LDL is believed to be one of the main reasons for this association. This particle contains less phospholipids (PL) and unesterified cholesterol than large LDL, and the apoB-100 appears to occupy a more extensive area at its surface. Although there are experiments that suggest a metabolic pathway leading to the overproduction of small, dense LDL, no clear molecular model exists to explain its association with atherogenesis. A current hypothesis is that small, dense LDL, because of its higher affinity for proteoglycans, is entrapped in the intima extracellular matrix and is more susceptible to oxidative modifications than large LDL. Here we describe how a specific reduction of approximately 50% of the PL of a normal buoyant LDL by immobilized phospholipase A(2) (PLA(2)) (EC 3.1.1.4) produces smaller and denser particles without inducing significant lipoprotein aggregation (<5%). These smaller LDL particles display a higher tendency to form nonsoluble complexes with proteoglycans and glycosaminoglycans than the parent LDL. Binding parameters of LDL and glycosaminoglycans and proteoglycans produced by human arterial smooth muscle cells were measured at near to physiological conditions. The PLA(2)-modified LDL has about 2 times higher affinity for the sulfated polysaccharides than control LDL. In addition, incubation of human plasma in the presence of PLA(2) generated smaller LDL and HDL particles compared with the control plasma incubated without PLA(2). These in vitro results indicate that the reduction of surface PL characteristic of small, dense LDL subfractions, besides contributing to its small size and density, may enhance its tendency to be retained by proteoglycans.
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PMID:Phospholipase A(2) modification of low density lipoproteins forms small high density particles with increased affinity for proteoglycans and glycosaminoglycans. 1046 35

Activation of mitogen-activated protein kinase (MAPK) results in pleiotropic effects such as modulation of the transcription and activation of enzymes involved in signal transduction. One such enzyme is the cytoplasmic phospholipase A(2) (cPLA(2)), which releases arachidonic acid (AA). AA is the precursor of prostaglandins and leukotrienes, two inflammatory mediators, which regulate gene expression and protein kinase (PK) activity. Fumonisin B(1) (FB(1)) was shown to increase PKC translocation and stimulate MAPK. We have investigated the effect of FB(1) on the AA cascade in a human epithelial cell line and the signal transduction pathway regulating PLA(2) activation. We observed that FB(1) stimulated cPLA(2) activity and increased AA release by a mechanism independent of PKC activation and that the activation of cPLA(2) is a two-step process: the first is phosphorylation of cPLA(2) by MAPK; the second is a consequence of the increase in sphingosine inside and outside the cells after 2 h, which is known to induce a rise in intracellular free calcium. Overall, this suggests that the effect of FB(1) on cells is partially dependent on the action of FB(1) on the enzymes involved in the cell cycle, such as MAPK and PKA, and on bioactive fatty acids, such as the prostaglandins and leukotrienes, and also on disruption of sphingolipid metabolism. In addition, we have observed down-regulation of cPLA(2) activity and AA metabolism by a mechanism involving prostaglandin production, cAMP synthesis and PKA activation.
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PMID:Activation of mitogen-activated protein kinase by fumonisin B(1) stimulates cPLA(2) phosphorylation, the arachidonic acid cascade and cAMP production. 1046 11

The differential activation of different members of the phospholipase A(2) (PLA(2)) superfamily and their regulation are important as one or more of them regulates the production of eicosanoids and others may contribute to the formation of other lipid mediators. We previously reported the existence of two forms of secretory or sPLA(2) in mouse keratinocytes, namely type I and type II sPLA(2). We show here that mouse keratinocyte sPLA(2)s were potently activated by protease treatment and inhibited by protease inhibitors. We also observed that G protein effectors induced substantial release of oleic acid (OA) from prelabeled mouse keratinocytes. A G(i)/G(0) protein activator significantly enhanced the hydrolysis of OA and this increase was not responsive to either pertussis toxin or cholera toxin treatment. Although there was a significant negative correlation between intracellular cAMP levels and OA hydrolysis, experimentally increasing cAMP with forskolin treatment had no effect on sPLA(2) activity. Arachidonic acid but not its metabolites was also shown to marginally activate keratinocyte sPLA(2) by 1.5-fold. These results lead to the conclusion that mouse keratinocyte sPLA(2)s can be regulated primarily by proteolytic activation and a G protein pathway.
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PMID:Mechanism(s) of activation of secretory phospholipase A(2)s in mouse keratinocytes. 1048 18

Mammalian group IIA phospholipase A(2) (PLA(2)) is believed to play important roles in inflammation, cell injury, and tumor resistance. However, the cellular site of action has not been clearly defined as it has long been recognized that group IIA PLA(2) is both a secretory and mitochondrial protein. The purpose of this study was to determine the subcellular target of the group IIA PLA(2) and its role in apoptosis stimulated by growth factor withdrawal. Cloning of the rat liver group IIA PLA(2) demonstrated a typical secretory signal and no alternative splicing of the primary transcript. When a sequence including the signal peptide and first 8 residues in the mature enzyme or the entire PLA(2) (including the signal peptide) was fused to enhanced green fluorescent protein, the fusion protein was directed to the secretory pathway rather than mitochondria in baby hamster kidney (BHK) cells. To examine the role of group IIA PLA(2) in cell injury, wild type (wt) rat group IIA PLA(2) and a mutant group IIA PLA(2) containing a His-47 --> Gln mutation (at the catalytic center) were transfected into BHK cells and cells stably expressing these constructs were isolated. After deprivation of growth factors, both normal BHK cells and BHK cells expressing mutant PLA(2) underwent massive apoptosis, while BHK cells expressing wt PLA(2) showed considerable resistance to growth factor withdrawal-induced apoptosis. The secretory PLA(2) inhibitors 12-epi-scalaradial and aristolochic acid abrogated resistance to apoptosis in the wt PLA(2) expressing cells. These two inhibitors did not induce cell death in the presence of fetal bovine serum, suggesting that they induce cell death by blocking PLA(2) generated survival signals. This study demonstrates that group IIA PLA(2) generates anti-apoptotic survival signals in BHK cells targeting the secretory pathway, and suggests that high levels of group IIA PLA(2) accumulated at inflammatory sites may not only regulate inflammation, but also may protect cells from unnecessary death induced by pro-inflammatory agents.
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PMID:Secretory group IIA phospholipase A(2) generates anti-apoptotic survival signals in kidney fibroblasts. 1048 15

Group IIA secretory phospholipase A(2) (sPLA(2)) has been implicated in a variety of inflammatory diseases including acute lung injury (ALI); however, the role of sPLA(2) in this disorder remains unclear. The aim of the present investigation was to examine the role of this enzyme in a model of ALI induced by oleic acid (OA) in rabbits by testing human group IIA phospholipase A(2) (PLA(2)) inhibitor, S-5920/LY315920Na. Experimental groups consisted of a saline control group (n = 8), an OA control group (n = 10) infused intravenously with OA (0.1 ml/kg/h for 2 h), and three groups given OA + S-5920/LY315920Na (three different doses, n = 8, respectively). Infusion of OA provoked pulmonary hemorrhage and edema formation, protein leakage, and massive neutrophil infiltration, resulting in severe hypoxemia and impaired lung compliance. PLA(2) activity was detected in the bronchoalveolar lavage fluid (BALF), but not plasma, which correlated well with severity of lung injury in this model. Pretreatment with S-5920/LY315920Na diminished the OA-induced PLA(2) activity in the BALF and dose-dependently attenuated the previously described lung injury induced by OA, accompanied by protection against lung surfactant degradation and production of thromboxane A(2) (TXA(2)) and leukotriene B(4) (LTB(4)). S-5920/LY315920Na also inhibited the OA-induced production of interleukin-8 (IL-8), both in plasma and BALF. Thus, sPLA(2) appears to play a key role in OA-induced lung injury, suggesting that the group IIA PLA(2) inhibitor may be a promising agent for patients with acute respiratory distress syndrome (ARDS).
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PMID:Crucial role of group IIA phospholipase A(2) in oleic acid-induced acute lung injury in rabbits. 1050 21

The Papuan taipan (Oxyuranus scutellatus canni) is the third most venomous terrestrial snake in the world, however, little is know about the pharmacology of the venom. In the chick biventer cervicis muscle, venom (10 microg/ml) abolished nerve-mediated twitches (time to 90% inhibition (t90) 44+/-5 min, n = 9). This inhibition was unaffected by prior incubation of the venom with the phospholipase A inhibitor 4-bromophenacyl bromide (4-BPB; 0.72 mM) (t90 48+/-7 min, n = 8). The mouse phrenic nerve diaphragm preparation displayed greater sensitivity to venom (10 microg/ml) (t90 25+/-1 min, n = 6). In the chick biventer muscle, venom (10 microg/ml) significantly inhibited responses to acetylcholine (1 mM) and carbachol (20 microM), but not KCI (40 mM), indicating activity at post-synaptic nicotinic receptors. Venom (10 microg/ ml) did not affect direct muscle stimulation. Venom (3-30 microg/ml) produced dose-dependant contractions of the guinea-pig ileum. Contractile responses were significantly inhibited by indomethacin (1 microM) or prior incubation of the venom with 4-BPB (0.72 mM) indicating involvement of a PLA component. In rat phenylephrine (0.3 microM) precontracted aortae, venom (3-100 microg/ml) produced endothelium-independent relaxation which was unaffected by prior incubation of venom (30 microg/ml) with 4-BPB (0.72 mM). In anaesthetised rats, 10 microg/kg (i.v.) venom produced rapid respiratory and cardiovascular collapse while 5 microg/kg (i.v.) venom produced only a small transient decrease in mean arterial blood pressure. Prior administration of 5 microg/kg (i.v.) venom enabled subsequent administration of 10 and 100 microg/kg (i.v.) venom without respiratory or cardiovascular collapse. Further work is required to identify specific toxins with the above pharmacological activity.
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PMID:A pharmacological examination of venom from the Papuan taipan (Oxyuranus scutellatus canni). 1051 50

The regulation of peroxisomal motility was investigated both in CHO cells and in cells derived from human umbilical vein endothelium (HUE). The cells were transfected with a construct encoding the green fluorescent protein bearing the C-terminal peroxisomal targeting signal 1. Kinetic analysis following time-lapse imaging revealed that CHO cells respond to simultaneous stimulation with ATP and lysophosphatidic acid (LPA) by reducing peroxisomal movements. When Ca(2+) was omitted from the extracellular medium or the cells were incubated with inhibitors for heterotrimeric G(i)/G(o) proteins, phospholipase C, classical protein kinase C isoforms (cPKC), mitogen-activated protein kinase kinase (MEK) or phospholipase A(2) (PLA(2)), this signal-mediated motility block was abolished. HUE cells grown to confluency on microporous membranes responded similarly to ATP-LPA receptor co-stimulation, but only when the ligands had access to the basolateral membrane region. These data demonstrate that peroxisomal motility is subject to specific modulation from the extracellular environment and suggest a receptor-mediated signaling cascade comprising Ca(2+) influx, G(i)/G(o) proteins, phospholipase C, cPKC isoforms, MEK and PLA(2) being involved in the regulation of peroxisomal arrest.
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PMID:Receptor-mediated regulation of peroxisomal motility in CHO and endothelial cells. 1052 92


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