Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peripheral lymphocytes treated with phospholipase C (phosphatidylcholine cholin phosphohydrolase E [3.1.4.3]) were examined for their response to mitogen and rosette formations. High levels of phospholipase C (greater than 0.01 unit) showed significant toxic effects on the peripheral lymphocytes as examined by the trypan blue exclusion test. This was attributable to "impurities" in the Cl. perfringens phospholipase C preparation since recovery of the mitogen responses were incomplete after heat inactivation of the enzyme. Active phospholipase C at 0.005 unit significantly (50%) suppressed the PHA response with little or no effect on the PWM stimulation. Similarly, a significant suppression of E rosette formation occurred with phospholipase C (0.005 u) treated lymphocytes. Suppression of similarly treated lymphocytes to EAC rosette was slight. It is suggested that the removal of phosphorylated amines from membrane surfaces affects T-cells more than B-cells and that the use of phospholipase C is a useful means of examining membrane functions of the lymphoid system.
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PMID:Effect of phospholipase C on lymphocyte responses to mitogen. 95 57

JMH is a high-frequency human erythrocyte blood group antigen. Previous work has shown that JMH is absent from complement-sensitive erythrocytes of patients with paroxysmal nocturnal hemoglobinuria (PNH); such cells have a broad defect in expression of phosphatidylinositol (PI)-linked proteins. Using both human JMH antisera and a JMH-like murine monoclonal antibody, we have identified a 76-Kd membrane protein present in JMH-positive but not JMH-negative erythrocytes. A similar 76-Kd JMH protein was also identified on a human lymphoid T-cell line, HSB-2. Using PI-specific phospholipase C, a small amount of JMH antigen could be cleaved from intact erythrocytes and immunoprecipitated from the supernate of treated erythrocytes, thus confirming that the protein bearing the JMH antigen is anchored by a PI-linkage to the erythrocyte membrane. This protein was further shown not to be identical to decay accelerating factor (70 Kd), a previously identified PI-anchored protein of somewhat similar molecular weight.
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PMID:Isolation of the JMH antigen on a novel phosphatidylinositol-linked human membrane protein. 137 90

The specificity and properties of a novel IgA receptor expressed on the surface of a tissue culture-adapted B cell lymphoma, T560, that originated in murine gut-associated lymphoid tissue, have been explored. Like the IgA receptors of murine T and splenic B cells studied by others, the T560 IgA receptor is trypsin sensitive and neuraminidase resistant and is up-regulated on T560 cells by exposing them overnight to high concentrations of polymeric IgA. Unlike them, the T560 IgA receptor is inhibited by low concentrations of IgM and high concentrations of IgG2a and IgG2b, binds at pH 4.0 but not at pH 8.0, is down-regulated by activation of protein kinase C and is sensitive to phosphatidylinositol-specific phospholipase C, indicating that it is glycosyl phosphatidylinositol-linked to the cell membrane. It is not a cell-bound form of galactosyl transferase, does not appear to bind to Ig through carbohydrate residues and does not react specifically with antibody to secretory component. It may be a completely new, cross-reactive receptor, perhaps related in some way to the polymeric Ig receptor or to the receptor for IgA expressed on the apical surface of Peyer's patch M cells, which is known to cross-react with IgG. Alternatively, it may be homologous to the highly IgA-specific Fc alpha R of T cells but, perhaps because of its glycosyl phosphatidylinositol linker, may have an ability to move and interact with other Ig receptors on the cell surface such that Ig bound to them are cross-inhibitory.
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PMID:A novel IgA receptor expressed on a murine B cell lymphoma. 137 46

The TCR is a multimeric structure comprised of distinct Ag recognition and signal transduction components. Although none of the molecules that make up the TCR possess intrinsic protein tyrosine kinase (PTK) activity, stimulation of T cells via the TCR results in the rapid appearance of newly tyrosine phosphorylated proteins in cell lysates. Evidence suggests ligation of the TCR induces activation of a PTK that may be a member of the src family. One early consequence of this TCR-mediated PTK activation is the phosphorylation of the gamma 1 isoform of phospholipase C. This phosphorylation event is associated with increased enzymatic activity resulting in the hydrolysis of phosphatidylinositol 4,5 bisphosphate into two second messengers, inositol 1,4,5 trisphosphate and diacylglycerol. Recently, our laboratory and others have isolated mutant T cells that lack surface expression of CD45, the major surface tyrosine phosphatase expressed on lymphoid cells. Stimulation of the TCR on these cells fails to result in the expected activation events. We demonstrate that reconstitution of surface expression of the 180-kDa isoform of CD45 by gene transfer into a CD45-deficient mutant of the Jurkat T cell leukemic line restores the ability of the TCR to couple fully to its signal transduction machinery. These results support the role of CD45 tyrosine phosphatase activity in regulating the TCR-activated PTK.
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PMID:Restoration of T cell receptor-mediated signal transduction by transfection of CD45 cDNA into a CD45-deficient variant of the Jurkat T cell line. 138 33

An improved method allowing incorporation of [3H]myo-inositol into the phosphoinositide pool of human lymphoid cells is described. The procedure devised involves cell permeabilization with a thiol-activated membranolytic toxin, alveolysin, and optimization of the phosphoinositide labeling and extraction. In these conditions 4 to 10% of the added [3H]myo-inositol is found intracellularly and half of this amount (2-5%) is incorporated into the phosphoinositide pool in only 1 h as compared to the classical 0.2 to 0.3% incorporation obtained after 10 to 20 h. The integrity of coupling between receptors and phospholipase C was assessed by the inositol phosphate production after cell stimulation by various agonists.
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PMID:The phosphoinositide pathway of lymphoid cells: labeling after permeabilization by alveolysin, a bacterial sulfhydryl-activated cytolysin. 142 73

Although the translocation of protein kinase C and phospholipase A2 are well documented, no information is available about the possible down-modulation of transmembrane phospholipase C. We found that TPA induced a dose-dependent (10-200 nM) and time-dependent (15 min-6 h) down-modulation of transmembrane phosphoinositidase C (PLC-PI) on lymphoid cells (CEM-CM3 and WIL2-NS) and epitheloid carcinoma cells (HeLa S3) but not on human fibroblasts (MRC-5). Cell-surface expression of PLC-PI on intact cells was assayed by flow cytometry using saturating concentrations of polyclonal anti-PLC-PI antibodies and phycoerythrin-conjugate. A control phorbol-ester which does not activate protein kinase C (PKC) had no internalization effect on PLC-PI. PKC inhibitors staurosporine (2.5 nM) and H-7 (10 microM) partially inhibited the TPA effect. Cytochalasin B (40 micrograms/ml) did not modify the TPA-induced PLC-PI down-modulation. The effect of TPA on PLC-PI seems quite specific since no internalization was induced by TPA on transmembrane phosphatidylcholine-preferring PLC expression. These results show that TPA can translocate the membrane-bound PLC-PI, probably by PKC activation.
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PMID:Topological regulation of cell-membrane phosphoinositidase C. 165 Jan 98

The Leu-8 molecule, the human homologue of the murine MEL-14 peripheral lymph node homing receptor, is expressed on neutrophils in both species and may be important in localization of cells to sites of inflammation. Most circulating human neutrophils express the Leu-8 molecule, and activation of neutrophils with phorbol myristate acetate causes a rapid decline in Leu-8 membrane fluorescence staining within 15 minutes. Northern blot analysis of total cellular RNA from neutrophils demonstrated two species of Leu-8 messenger RNA, a major one of 2.4 kb and a minor one of 1.9 kb. Because two different Leu-8 cDNA clones were obtained from human lymphocytes that were predicted to encode both transmembrane and phosphatidylinositol (PI)-anchored forms of the molecule, experiments were conducted to determine whether Leu-8 is anchored to neutrophils by a PI-anchor. There was a slight decrease in expression of Leu-8 on neutrophils when they were treated with PI-specific phospholipase C (PI-PLC). However, Leu-8 was abundant on neutrophils obtained from a patient with paroxysmal nocturnal hemoglobinuria. To determine the fate of the Leu-8 molecule during cell activation, neutrophils were labeled with 125I-anti-Leu-8. During activation antibody was rapidly lost from the cell surface and was not internalized, suggesting that Leu-8 is released from the cell membrane during cell activation. When cell extracts of neutrophils were compared with extracts of lymphoid cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting, the Leu-8 species expressed on neutrophils had a significantly higher and more variable relative mobility (70 to 120 Kd for neutrophils v 70 Kd for Jurkat T cells). In addition, Leu-8 molecules were detected in the supernatants of activated neutrophils. These results indicate that human neutrophils express a high-molecular-weight form of the Leu-8 molecule that has a conventional transmembrane anchor and is rapidly released from the membrane during activation. The loss of the Leu-8 membrane glycoprotein during activation may be a mechanism for rapid alteration of neutrophil adhesion characteristics.
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PMID:Human neutrophils release the Leu-8 lymph node homing receptor during cell activation. 170 70

The murine BP-3 antigen was initially described as a variably glycosylated cell surface protein of Mr 38,000 to 48,000 on lymphoid and myeloid cells. In the present experiments we found that this antigen is released from the surface of pre-B cells and macrophages by treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), suggesting a glycosyl-phosphatidylinositol (GPI) linkage with the plasma membrane. When the tissue distribution of the BP-3-reactive cells was examined by immunohistology, high levels of the antigen were observed on brush borders of the intestinal epithelial cells, within collecting tubules of the kidney and on a subpopulation of reticular cells located on lymph nodes. Peyer's patches and the white pulp areas of the spleen. In contrast, reticular cells located in the thymus, bone marrow and splenic red pulp did not express the BP-3 antigen. Ontogenic studies revealed that BP-3 was expressed by the reticular cells in peripheral lymphoid tissues in the neonatal period near the time of lymphocyte immigration into these organs. BP-3+ reticular cells were observed in the collapsed periarterial lymphatic sheaths of adult mice depleted of T and B cells by cyclophosphamide treatment and in mice with severe combined immunodeficiency (scid), indicating that development of this reticular network is lymphocyte independent. The BP-3 antigen on the splenic reticular cells was also GPI anchored but its glycosylation pattern differed from that of the BP-3 molecules on pre-B cells. A specific subpopulation of reticular cells is thus marked by the BP-3 antigen, and the distribution and biochemical properties of the molecule make it an attractive candidate for a role in lymphocyte-stromal interactions in the peripheral lymphoid tissues.
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PMID:Reticular cells in peripheral lymphoid tissues express the phosphatidylinositol-linked BP-3 antigen. 184 77

We have analyzed the induction and expression of Blast-1 at the mRNA and protein levels and demonstrated its identity with CD48. Blast-1/CD48 is expressed on a wider range of cell types, notably T cells and monocytes, than previously thought, but appears to be restricted to lymphoid and myeloid cells. Resting B and T cells express Blast-1/CD48 molecules at the cell surface; however, they lack the epitope recognized by the 17D6 mAb. Resting B cells express no detectable Blast-1/CD48 mRNA. Induction by EBV infection or stimulation with PMA, IL-4, or PHA results in increased levels of Blast-1/CD48 protein (both 6.28 and 17D6 epitopes) at the cell surface. Detailed analysis of EBV-induced expression revealed that it is due to increased steady-state levels of Blast-1/CD48 mRNA induced by transforming but not nontransforming strains of the virus. Induction by IL-1 beta, ionomycin, or suboptimal levels of PMA plus ionomycin results in increased expression of the 17D6 epitope only. In transfected Cos-7 cells Blast-1/CD48 at the cell surface expresses only the 6.28 epitope, whereas cytoplasmic molecules express both 17D6 and 6.28 epitopes. We suggest that these results are most consistent with the idea that Blast-1/CD48 molecules are complexed at the surface of resting cells and Cos-7 cells, resulting in masking of the 17D6 epitope. Activation causes dissociation of the complex, revealing the 17D6 epitope. The existence of 17D6+6.28- Blast-1/CD48 molecules was demonstrated by immunoprecipitation analysis, which also revealed that, unlike the rest of the molecules, this subset was resistant to digestion with glyosylphosphatidylinositol-specific phospholipase C.
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PMID:Expression of the Blast-1 activation/adhesion molecule and its identification as CD48. 184 79

The scrapie agent protein (Sp33-37 or PrPSc) is the disease-associated isoform of a normal cellular membrane protein (Cp33-37 or PrPC) of unknown function. We report that normal human lymphocytes and lymphoid cell lines, but not erythrocytes or granulocytes, express PrPC mRNA and protein. PrPC is detectable on the surface of lymphocytes; the surface immunoreactivity is sensitive to phosphatidylinositol-specific phospholipase C, indicating glycosyl-phosphatidylinositol membrane anchorage. Lymphocyte PrPC surface abundance is increased by cell activation, and polyclonal antibodies to PrPC suppress mitogen-induced activation. We conclude that PrPC is a lymphocyte surface molecule that may participate in cell activation.
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PMID:Cellular isoform of the scrapie agent protein participates in lymphocyte activation. 196 32


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