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)

B lymphocytes from patients expressing the X chromosome-linked immune deficiency disorder, Wiskott-Aldrich syndrome (WAS), fail to produce antibodies in response to stimulation with polysaccharides and other type-2 T cell-independent antigens. To investigate whether this abnormality reflects a defect in the signal transduction cascade normally triggered by ligation of surface immunoglobulin (sIg) on B cells, we have examined early signaling events induced by anti-Ig antibody stimulation of EBV B lymphoblastoid cell lines from WAS patients and healthy controls. Despite the expression of comparable levels of sIg and sIgM on WAS and control EBV B cells, WAS cells failed to manifest the increased proliferation in response to anti-Ig treatment observed in the control cell lines. WAS and control EBV B cells also differed in the magnitude of the change in cytosolic free calcium ([Ca2+]i) induced by sIg ligation; WAS cells showed either markedly diminished or no changes in [Ca2+]i levels whereas control EBV B cells consistently showed increases in [Ca2+]i. Anti-Ig-induced changes in inositol phosphate release were also markedly reduced in WAS compared with control cells. As protein tyrosine phosphorylation is thought to represent a proximal event in the activation of B cells, inducing increases in [Ca2+]i by virtue of tyrosine phosphorylation of phospholipase C (PLC)-gamma, profiles of protein tyrosine phosphorylation and expression of tyrosine-phosphorylated PLC-gamma 1 were compared between WAS and normal EBV B cells before and after sIg cross-linking. These studies revealed that in addition to defective mobilization of Ca2+, the WAS cells manifested little or no increase in tyrosine phosphorylation of PLC-gamma 1 or other intracellular proteins after sIg ligation. Together these results indicate the association of WAS with a defect in the coupling of sIg to signal transduction pathways considered prerequisite for B cell activation, likely at the level of tyrosine phosphorylation. The abnormalities observed in these early transmembrane signaling events in WAS EBV B cells may play a role not only in the nonresponsiveness of WAS patient B cells to certain T independent antigens, but also in the genesis of some of the other cellular deficits exhibited by these patients.
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PMID:Evidence for defective transmembrane signaling in B cells from patients with Wiskott-Aldrich syndrome. 140 Oct 74

The CD4 molecule, a glycoprotein expressed primarily on the cell surface of specific T lymphocytes, is thought to function in T-cell antigen recognition and activation. In addition, CD4 serves as a receptor for human immunodeficiency virus type 1 (HIV-1) by a direct interaction with the HIV-1 surface glycoprotein (gp120). To further characterize the HIV-1-cell interaction, a HeLa cell line was established that expressed a chimeric molecule of CD4 and decay-accelerating factor (DAF). In the chimeric CD4-DAF molecule the transmembrane and cytoplasmic domains of CD4 were deleted and replaced with the carboxy-terminal 37 amino acids of DAF. This resulted in the anchoring of the extracellular domain of CD4 to the cell membrane via a glycophospholipid linkage. The glycophospholipid-anchored CD4 had a molecular size of approximately 56 to 62 kDa and was released following treatment of the cells with phosphatidylinositol-specific phospholipase C. HeLa cells expressing the CD4-DAF hybrid could be infected with HIV-1, as evidenced by reverse transcriptase activity, p24 core antigen content, and infectious virus production. In addition, transfection of the HeLa CD4-DAF cells with a plasmid that directs the synthesis of HIV-1 envelope glycoproteins or cocultivation with HeLa cells expressing the virus glycoproteins resulted in syncytium formation. These results indicate that the transmembrane and cytoplasmic domains of the CD4 molecule are dispensable for both HIV infection and syncytium formation.
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PMID:Human immunodeficiency virus infection and syncytium formation in HeLa cells expressing glycophospholipid-anchored CD4. 170 1

The influence of Staphylococcus alpha-toxin has been investigated on the duration of S-phase of lymphocyte mitotic cycle and on DNA replication in human fibroblasts in vitro. The duration of the S-phase of lymphocytes was measured by counting labeled metaphases and by making replication curves. Alpha-toxin in a dose of 3 micrograms/ml enhances the onset of S-phase, which is inhibited at a dose of 33 micrograms/ml of alpha-toxin. The action of alpha-toxin resulted in a decreased rate of replication fork and in a progressive activation of replicon groups. This effect was most prominent at 33 micrograms/ml of alpha-toxin. The data obtained allow to suggest that immunodeficiency of the second order, so characteristic of the staphylococcal sepsis, may be due, in many respects, to suppression of DNA replication.
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PMID:[The effect of staphylococcal alpha-toxin on DNA replication in human cells]. 182 1

In a previous paper, we determined that treatment of lymphocytes with nonviable preparations of human immunodeficiency virus type 1 (HIV-1) results in an impairment of the phosphatidylinositol/protein kinase C pathway, most likely due to an inhibition of the cleavage of phosphatidylinositol bisphosphate into inositol trisphosphate and diacylglycerol, mediated by phospholipase C. Here we show that one consequence of these changes is a reduced phosphorylation of nuclear matrix-associated DNA topoisomerase II, resulting in an inhibition of the activity of this enzyme. Antibodies to the viral proteins suppressed the inhibitory effects caused by the HIV-1 preparation. Furthermore, the phytohemagglutinin A-caused augmentation of nuclear matrix-associated DNA polymerase alpha and beta activities was found to be abolished by coincubation with the HIV preparation or with the HIV-1 gp120. The phytohemagglutinin A-enhanced matrix association and processivity of DNA polymerase alpha was determined to be reduced if the lymphocytes were in contact with HIV-1 preparation. These results suggest that the reduced proliferative response of lymphocytes to phytohemagglutinin A in the presence of disrupted HIV-1 preparation is due to inhibition of at least two, perhaps separate, pathways, one involving protein kinase C resulting in a reduced phosphorylation of DNA topoisomerase II and the other changing the state of matrix association of DNA polymerase alpha and beta.
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PMID:Effect of nonviable preparations from human immunodeficiency virus type 1 on nuclear matrix-associated DNA polymerase alpha and DNA topoisomerase II activities. 215 2

Although the human immunodeficiency virus can induce cytopathic changes in human lymphocytes in vitro, the mechanism(s) underlying progressive lymphopenia in patients with AIDS and AIDS-related complex has not been elucidated. To investigate this issue, peripheral blood lymphocytes of AIDS and AIDS-related complex patients and healthy control subjects were examined for their ability to resist homologous complement-mediated lysis. Upon sensitization with monoclonal antibodies to major histocompatibility complex class I antigen, as much as 48% lysis of patients' cells was observed in as little as a 1:32 dilution of human serum compared to 18 +/- 8% (mean +/- SD) lysis of controls' cells even in a 1:8 dilution of human serum. To investigate the mechanism of the abnormal complement sensitivity, AIDS and AIDS-related complex cells were analyzed for expression of decay-accelerating factor (DAF), a complement regulatory protein that functions intrinsically in blood cell membranes to prevent complement activation on their surfaces. Flow cytometric assays using anti-DAF monoclonal antibodies demonstrated that patients' lymphocytes and monocytes were DAF-deficient, in contrast to their polymorphonuclear leukocytes, which showed normal DAF levels. Expression of DAF was diminished on CD4+ as well as CD8+ T-lymphocyte subpopulations as opposed to expression of CD3, which was comparable in patients and controls. Incubation of normal lymphocytes with anti-DAF monoclonal antibodies or phosphatidylinositol-specific phospholipase C, an enzyme that cleaves DAF, enhanced lysis. Conversely, reconstitution of patients' cells with exogenous DAF reduced their lysis. The findings of heightened complement sensitivity and DAF deficiency of patients' lymphocytes in vitro suggest the possibility that the DAF deficit may contribute to the progressive lymphopenia of AIDS in vivo.
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PMID:Heightened complement sensitivity of acquired immunodeficiency syndrome lymphocytes related to diminished expression of decay-accelerating factor. 247 Nov 98

Previously it was established [Pahwa, S., Pahwa, R., Saxinger, C., Gallo, R. C. & Good, R. A. (1985) Proc. Natl. Acad. Sci. USA 82, 8198] that nonviable preparations of human immunodeficiency virus 1 (HIV-1) abolish the proliferative response of human lymphocytes to phytohemagglutinin A. Now we describe that this effect might be, at least partially, due to an impairment of the function of phospholipase C. It was found that addition of HIV-1 preparation to lymphocytes diminished the stimulation of phosphatidylinositol phosphorylation caused by phytohemagglutinin A. Moreover, this preparation completely abolished the phytohemagglutinin-A-stimulated release of inositol trisphosphate and prevented a translocation of protein kinase C from cytosol to membranes. From this data we conclude that nonviable HIV-1 preparations inhibit the intracellular signalling pathway, leading to a reduced mitogenic response to phytohemagglutinin A, at the level of protein kinase C.
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PMID:Inhibitory effect of nonviable preparations from human immunodeficiency virus 1 on inositol phospholipid metabolism. 254 10

CD4 is the major cellular receptor for the human immunodeficiency virus (HIV). A hybrid gene encoding the extracellular domains of CD4, linked to the sequence encoding the membrane attachment region of the glycosylphosphatidylinositol (GPI)-anchored protein decay accelerating factor (DAF) was stably transfected into HeLa cells. The resultant cell line (T4HD) expressed GPI-anchored CD4DAF at high levels and was susceptible to gene transfer with a recombinant HIV vector. In an effort to expand the spectrum of cells susceptible to HIV gene transfer, CD4DAF was released from the surface of the T4HD cell line by detergent lysis, purified by immunoaffinity chromatography, and reincorporated into native HeLa cells. Incorporation occurred via the GPI anchor as evidenced by cleavage with phosphatidylinositol-specific phospholipase C. More than 95% of the CD4DAF-treated HeLa cells were CD4-positive by flow cytometry, and kinetic analysis demonstrated that over 75% of the fusion protein remained anchored to the cell membrane after 90 min at 37 degrees C. The purified protein retained its ability to bind the envelope protein of HIV. When incorporated, it bound fluorescein isothiocyanate (FITC)-conjugated gp120, and in its soluble form blocked transduction of CD4-positive cells incubated with an HIV-derived vector containing the Neo gene. In contrast to the T4HD cells, exposure of CD4DAF-treated cells to the Neo HIV vector yielded only transient neomycin-resistant colonies. These results suggest that endogenous synthesis of the CD4 molecule may be necessary for successful HIV genomic integration.
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PMID:Purified GPI-anchored CD4DAF as a receptor for HIV-mediated gene transfer. 753 2

Antigen receptor-mediated activation of T and B lymphocytes results in activation of phospholipase C-gamma isozymes with subsequent hydrolysis of membrane inositol phospholipids. As a method of screening autoimmune or immunodeficient patients for early receptor signaling defects, we have developed a rapid technique for studying phosphatidylinositol (PI) hydrolysis in cultured cells and fresh clinical specimens resulting from surface receptor crosslinking. Using staphylococcal alpha-toxin, we permeabilized freshly isolated, purified human T lymphocytes to facilitate incorporation of [3H]myoinositol into membrane phospholipids. Aggregation of surface antigen receptors (TCR-CD3 complex and CD28 on T cells) with specific antibodies produced extensive ATP and Mg(2+)-dependent hydrolysis of the membrane inositol phospholipids as measured by release of water soluble inositol phosphates. Anti-human CD3 antibody produced 18.5 +/- 1.6 net % PI hydrolysis and anti-human CD28 antibody produced 4.6 +/- 0.2 net % PI hydrolysis. Simultaneous anti CD3/CD28 crosslinking produced 30.8 +/- 1.2 net % PI hydrolysis, an increase over either stimulus alone (p = 0.0013 two tailed t test). Isotype matched control antibodies produced 11.6 +/- 0.4% PI hydrolysis. The tyrosine phosphatase inhibitor orthovanadate (Na3VO4) was used as a positive control because it induces maximal protein tyrosine kinase-dependent PI hydrolysis in permeabilized cells. Na3VO4 consistently induced hydrolysis of > 50% of the membrane inositol phospholipid pool. These data indicate that costimulation of T cells with antibodies to CD3 and CD28 is synergistic and reinforces the importance of CD28 as an accessory T cell stimulus. This easy technique allows quick evaluation of the integrity of the early signaling cascade in lymphocytes as a screen for autoimmune and immunodeficiency diseases.
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PMID:Phosphatidylinositol hydrolysis in freshly isolated human T lymphocytes. 756 Nov 50

We investigated the effect of extracellular Tat protein of human immunodeficiency virus-type 1 (HIV-1) on the phosphatidylinositol (PI) cycle, which represents a major signal transduction pathway in lymphoid cells. Recombinant Tat, recombinant HIV-1 p24 and cross-linked anti-CD3 monoclonal antibody (mAb) were added in culture for 1-60 min to Jurkat lymphoblastoid CD4+ T cells. The stimulation of T cell receptor by cross-linked anti-CD3 mAb resulted in a rapid increase of the phosphatidylinositol-specific phospholipase C (PI-PLC) activity in whole cell lysates. On the other hand, Tat protein, either alone or in combination with anti-CD3 mAb, showed little effect on the PI turnover of whole cell extracts. Tat, however, selectively stimulated a nuclear-specific PI-PLC with a peak of activity after 30 min from the addition in culture to Jurkat cells. Interestingly, this time corresponded to that required for the uptake and nuclear localization of recombinant Tat protein, as demonstrated by electron microscope immunocytochemistry experiments with anti-Tat mAb. Moreover, exogenous Tat reached the nucleus of Jurkat cells in a bioactive form, as shown in a HIV-1 long terminal repeat-chloramphenicol acetyl transferase transactivation assay. The specific increase of a nuclear PI-PLC activity was further demonstrated by the ability of Tat to stimulate PI turnover also when added directly to isolated nuclei. As a whole, these data demonstrate that Tat selectively stimulates a nuclear polyphosphoinositide hydrolysis, which appears to be independent of the cellular PI turnover. The relevance of these findings for a better understanding of the biological functions of extracellular Tat is discussed.
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PMID:Exogenous human immunodeficiency virus type-1 Tat protein selectively stimulates a phosphatidylinositol-specific phospholipase C nuclear pathway in the Jurkat T cell line. 758 47

Endothelin (ET) produced by endothelial cells has recently been found to be a potent vasoconstricting hormone. In this report, ET is shown to be a potent stimulator of interleukin-6 (IL-6) production by rat bone marrow (BM)-derived stromal cells. It was also shown that ET increased the level of mRNA for IL-6 in these cells. The two types of ET receptor (R), ETAR and ETBR, were shown to be expressed on both BM-derived stromal cells in culture and ex vivo in BM tissue, suggesting that ET works as a physiologic stimulator of IL-6 production in the BM. It was shown that ETAR is coupled to phospholipase C activation, leading to the production of inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG) as second messengers in BM-derived stromal cells. This was corroborated by data showing that IL-6 production in these cells was induced by combined stimulation with ionomycin and phorbol myristate acetate, thereby bypassing the effects of IP3 and DAG, respectively. This is the first report on the hormonal regulation of IL-6 production by BM stromal cells, indicating that hematopoiesis is subject to endocrinologic regulation under physiologic conditions. ET has recently been reported to be produced by macrophages in response to bacterial lipopolysaccharide and human immunodeficiency virus-1 glycoprotein 120. These facts, taken together with our findings, raise the possibility that ET shares the same role of IL-1 as a local cytokine, mediating an intercellular signal between macrophages and BM stromal cells in response to bacterial or viral stimulation.
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PMID:Stimulation of interleukin-6 production by endothelin in rat bone marrow-derived stromal cells. 791 71


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