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)

T150R1 is a synthetic copolymer with Na+ ionophore activity. We demonstrated previously that T150R1, when injected into mice, produces rapid thymic involution with depletion of cortical thymocytes. Elevated serum ACTH and corticosterone levels, as well as abrogation of the effects of T150R1 on the thymus by adrenalectomy and hypophysectomy, suggested a pituitary-mediated mechanism. In this work, we investigated the ability of T150R1, and of the related ionophore copolymer T130R2, to stimulate ACTH in vitro from the mouse anterior pituitary cell line AtT-20. Copolymer-induced ACTH release was dose-, time-, and temperature-dependent. Hormone induction peaked at 30 degrees C for T150R1 and 37 degrees C for T130R2. The temperature dependence of ACTH release paralleled that of ionophore activity measured in red blood cells, providing evidence that the ability to induce ACTH is related to the ionophore property of the copolymers. Peak ionophore activity and hormonal release occurred at the temperatures when the copolymers form partially soluble complexes which interact optimally with cell membranes. Cotreatment with exogenous phospholipase C inhibited the effects of T150R1, which suggests that the enzyme either blocks the insertion of T150R1 into the cell membrane or that the phospholipase C-induced increase in intracellular calcium inhibits the ionophore activity of T150R1. These data support an ionophore mechanism for copolymer-induced ACTH release in which changes in the physicochemical structure of the copolymers may affect their interaction with cell membranes. The data also suggest that direct stimulation of pituitary ACTH accounts for at least some of the in vivo immunomodulatory effects of T150R1.
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PMID:Immunomodulatory ionophore copolymers, T150R1 and T130R2, induce corticotropin from anterior pituitary cells. 131 82

Naturally occurring recombinant murine leukemia viruses (MuLVs), termed mink cell focus-inducing (MCF) viruses, are the proximal leukemogens in spontaneous thymic lymphomas of AKR mice. The mechanism by which these viruses transform lymphocytes is not clear. Previous studies have implicated either integrational activation of proto-oncogenes, chronic autocrine immune stimulation, and/or autocrine stimulation of growth factor receptors (e.g., interleukin 2 receptors) via binding of the viral env glycoprotein (gp70) to these receptors. Any one of these events could also involve activation of second messenger signaling pathways in the cell. We examined whether infection with oncogenic AKR-247 MCF MuLV induced transmembrane signaling cascades in thymocytes of AKR mice. Cyclic AMP levels were not changed, but there was enhanced turnover of phosphatidylinositol phosphates, with concomitant increases in diacyglycerol and inositol 1,4,5-triphosphate. Thus, phospholipase C activity was increased. Protein kinase C activity was also elevated in comparison to that in uninfected thymocytes. The above events occurred in parallel with MCF expression in the thymus and were chronically maintained thereafter. No changes in phospholipid turnover occurred in an organ which did not replicate the MCF virus (spleen) or in thymocytes of AKR mice infected with a thymotropic, nononcogenic MCF virus (AKV-1-C36). Therefore, only the oncogenic MCF virus induced phosphatidylinositol signal transduction. Flow cytometric comparison of cell surface gp70 revealed that AKR-247 MCF virus-infected thymocytes expressed more MCF virus gp70 than did thymocytes from AKV-1-C36 MCF virus-infected mice, suggesting that certain threshold quantities of MCF virus env glycoproteins may be involved in this signaling. This type of signal transduction is not induced by stimulation of the interleukin 2 receptor but is involved in certain oncogene systems (e.g., ras and fms). Its chronic induction by oncogenic MCF MuLV may thus initiate thymocyte transformation.
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PMID:Oncogenicity of AKR mink cell focus-inducing murine leukemia virus correlates with induction of chronic phosphatidylinositol signal transduction. 132 63

In order to study the regulatory mechanisms of phospholipase C-gamma (PLC-gamma) via the intrinsic SH2/SH3 region (Z region), two recombinant Z proteins, rP45Z and rP38Z, derived from rat PLC-gamma 1 and PLC-gamma 2, respectively, were purified from the inclusion bodies of Escherichia coli. We examined their direct effects on phosphoinositide hydrolysis induced by four different PLC isoforms purified from bovine brain and thymus, and found that both of these Z proteins suppress the enzyme activity of all four PLC isoforms in a dose-dependent manner. This suppressive effect is very potent and stoichiometric. The kinetics studies indicate that the suppression is non-competitive. This suppression is eliminated by treatment with proteases but is not affected by heat treatment at 95 degrees C for 15 min, indicating that the primary structure might be important for the action of Z proteins. Comparative studies suggested that two Z proteins but not Src and phosphatidylinositol 3-kinase possess, adjacent to their SH2 and SH3 motifs, a phospholipase C inhibitor (PCI) region that strongly suppresses their phosphatidylinositol 4,5-bisphosphate (PIP2)-hydrolyzing activity. A series of synthetic peptides identical with the sequence of the proposed PCI region, including an octamer, YRKMRLRY, inhibited PIP2 hydrolysis induced by four different phospholipase C isoforms. These results demonstrate that both types of phospholipase C-gamma contain the PCI sequence which is responsible for the inhibition of PIP2 hydrolysis, indicating that phospholipase C-gamma is a self-regulating enzyme.
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PMID:Inhibitory effect of src homology (SH) 2/SH3 fragments of phospholipase C-gamma on the catalytic activity of phospholipase C isoforms. Identification of a novel phospholipase C inhibitor region. 132 45

The method of DNA binding to nitrocellulose filters was applied to DNA isolated from mouse liver and Ehrlich ascite carcinoma (EAC), calf thymus, and lymphocytes from patients with chronic lymphoid leukemia. In those and phage PM2 DNA the increase in the DNA binding to the filters with a rise in NaCl concentration from 0.5 up to 4.5 M was sigmoidal being suggestive of a conformational transition. No such activity was found in the case of phage lambda or single-stranded DNA. The binding decreased dramatically after mild cleavage of DNA with DNAase I or treatment with phospholipase C or Eco RI and Hin PI restrictases. Incubation of DNA with ethidium bromide led to decrease in the amount of bound DNA. This effect was enhanced with a rise in the dye concentration. The isotherms of ethidium bromide binding to eukaryotic DNA obtained in Scatchard plots by optic titration had a component with a positive slope at low values of r. Bivalent ions (Mg2+, Zn2+) shifting the equilibrium towards the Z-form increased the proportion of macromolecules retained on the filters at NaCl concentrations of 1-3 M. Local changes in the helix conformation were studied with the help of chemical probes: diethylpyrocarbonate (guanine Z-DNA) and osmium-pyridine reagent (pyrimidines of boundary B-Z sites). These probes incorporation into samples of liver DNA, EAC, and lymphocytes resulted in chemical modification of all these samples. Modification of DNA by osmium-pyridine reagent led to inhibition of subsequent restriction by Eco RI restrictase. The data obtained are suggestive of the presence of Z-regions in the B-helix of eukaryotic DNA. A topological model of Z-site stabilization in small superhelical loops of DNA fixed by protein or lipoprotein molecules is proposed.
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PMID:[Detection of left-helical segments in eukaryotic DNA]. 148 26

In nonobese diabetic (NOD) mice, T cells play a major role in mediating autoimmunity against pancreatic islet beta-cells. We and others previously reported that age-related alterations in the thymic and peripheral T cell repertoire and function occur in prediabetic NOD mice. To study the mechanism responsible for these T cell alterations, we examined whether a defect exists in the thymus of NOD mice at the level of TCR-mediated signaling after activation by Con A and anti-CD3. We found that thymocytes from NOD mice respond weakly to Con A- and anti-CD3-induced proliferation, compared with thymocytes from control BALB/c, BALB.B, (BALB.B x BALB.K)F1, C57BL/6, and nonobese non-diabetic mice. This defect correlates with the onset of insulitis, because it can be detected at 7 to 8 weeks of age, whereas younger mice displayed a normal T cell responsiveness. Thymic T cells from (NOD x BALB/c)F1 mice, which are insulitis- and diabetes-free, exhibit an intermediate stage of unresponsiveness. This T cell defect is not due to a difference in the level of CD3 and IL-2R expression by NOD and BALB/c thymocytes, and both NOD CD4+ CD8- and CD4- CD8+ mature thymic T cells respond poorly to Con A. BALB/c but not NOD thymic T cells respond to Con A in the presence of either BALB/c or NOD thymic APC, suggesting that the thymic T cell defect in NOD mice is intrinsic to NOD thymic T cells and is not due to an inability of NOD APC to provide a costimulatory signal. The defect can be partially reversed by the addition of rIL-2 to NOD thymocytes. To determine whether a defect in signal transduction mediates this NOD thymic T cell unresponsiveness, we tested whether these cells elevate their intracellular free Ca2+ ion concentration in response to Con A. An equivalent Con A-induced increase in Ca2+ ion concentration in both NOD and BALB/c thymocytes was observed, suggesting a normal coupling between the CD3 complex and phospholipase C in NOD thymocytes. In contrast to their low proliferative response to Con A or anti-CD3, NOD thymocytes respond normally (i.e., as do BALB/c thymocytes) to the combinations of PMA plus the Ca2+ ionophore ionomycin and PMA plus Con A but weakly to Con A plus ionomycin. Our data suggest that the age-related NOD thymocyte unresponsiveness to Con A and anti-CD3 results from a defect in the signaling pathway of T cell activation that occurs upstream of protein kinase C activation.
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PMID:Defective thymic T cell activation by concanavalin A and anti-CD3 in autoimmune nonobese diabetic mice. Evidence for thymic T cell anergy that correlates with the onset of insulitis. 182 15

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

Lymphocytes are shown to express a limited number of a unique category of membrane Ag, such as Thy-1, Ly-6, Ly-31, and Qa-2, that are covalently linked to the membrane phosphatidylinositol (PI). We have identified a new glycosyl-phosphatidylinositol (GPI)-anchored lymphocyte Ag, B7, by using a mAb and have determined the primary structure by cDNA cloning. B7 Ag was expressed on the majority, if not all, of the mature lymphocytes of both T and B lineages, including strongly CD3+ thymocytes, most splenic T cells, and approximately 60% of splenic IgM+ B cells, whereas the expression of B7 Ag on bone marrow cells was negligible. The expression of B7 Ag was nearly completely abolished with as little as 2 mU of PI-specific phospholipase C per ml, which did not completely eliminate Ly-6C and Thy-1 expression. Unlike the expression of other GPI-linked lymphocyte Ag, the expression of B7 was rapidly down-regulated upon the activation of T cells by mitogens or IL-2 both in vitro and in vivo. Immunoprecipitation analysis revealed that B7 Ag was an approximately 12-kDa protein. With a CDM8 expression vector, a cDNA encoding B7 Ag was cloned, and it was confirmed that the B7 Ag on cDNA-transfected cells was indeed PI-specific phospholipase C sensitive. The B7 cDNA contained an open reading frame of 222 bp including a typical N-terminal leader sequence and a characteristic sequence at the C terminus encoding hydrophobic amino acids. A computer search revealed no significant homology to any known molecule at both DNA and amino acid sequence levels. Northern blot analysis indicated that the B7 transcript was expressed on lymphohematopoietic tissues, including thymus, spleen, and bone marrow, but not on other organs, such as liver, kidney, and brain. The results indicated that B7 Ag is a new member of the GPI-anchored proteins which is selectively expressed on mature resting but not activated lymphocytes.
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PMID:Identification and gene cloning of a new phosphatidylinositol-linked antigen expressed on mature lymphocytes. Down-regulation by lymphocyte activation. 214 7

The alkaline phosphatase (AP) synthesized by human tumor cells closely resembles human placental AP (PLAP). Little is known about the molecular events that lead to the expression of a placenta-like AP in tumor cells. The complementary DNA encoding the AP expressed by a choriocarcinoma cell line, BeWo, was isolated and characterized. The complementary DNA is the product of the germ cell AP (Nagao isozyme) gene and not of the term PLAP gene. Like placental AP, the tumor AP can be released from the cell membrane by a phosphaditylinositol-specific phospholipase C and has a phosphaditylinositol-glycan (PI-glycan) moiety at the COOH terminus. Immunoprecipitation of phosphaditylinositol-specific phospholipase C-treated AP and analysis by polyacrylamide gel electrophoresis or isoelectric focusing demonstrates that at least 95% of the AP contains PI-glycan. Two-dimensional gel electrophoresis reveals two precursors of the mature AP. One of these does not bind an antibody against the Trypanosoma variable surface glycoprotein cross-reacting determinant and probably does not contain PI-glycan. This precursor had a shorter half-life than the more prominent PI-glycan-containing precursor in pulse-chase experiments, suggesting a precursor-product relationship between the two proteins. These data demonstrate that BeWo AP is the product of a gene normally expressed in testis, thymus, and germ cells, but not in placenta. Thus, the expression of BeWo AP results from the repression of the PLAP gene and derepression of the germ cell AP gene and, as such, the expression is ectopic. The BeWo AP (Nagao isozyme) is modified with PI-glycan that is added soon after translation, not cotranslationally.
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PMID:Expression of a Nagao-type, phosphatidylinositol-glycan anchored alkaline phosphatase in human choriocarcinomas. 216 49

Glucocorticoid-receptor complexes in rat thymus cytosol were characterized by gel-filtration and ion-exchange chromatography and by other procedures. Two forms of non-transformed complex were identified at low ionic strength in the presence of molybdate, with Stokes radii of approx. 8 and 6 nm. The 8 nm molybdate-stabilized form could be converted to the 6 nm form by chromatography on Sephacryl S-300 or Lipidex 1000 or by incubation with charcoal or phospholipase C, but not by chromatography on Sephadex G-25. The dissociation rate of the complex was reduced by treatment with charcoal or Lipidex 1000, but none of the treatments caused transformation to a DNA-binding form. Transformation of the complex, by exposure to elevated temperature or ionic strength in the absence of molybdate, resulted in the appearance of a different 6 nm form, distinguished by an increased affinity for DNA-cellulose and a reduced affinity for DEAE-cellulose. These results suggest that receptor transformation is preceded by structural changes associated with the loss of a lipid factor from the complex. Non-polar steroid antagonists, and lipophilic compounds such as phenothiazines, were found to bind to secondary, hydrophobic sites on the receptor and to exert allosteric effects on the primary steroid-binding site; these and other observations emphasize the importance of hydrophobic interactions as determinants of the structure and properties of glucocorticoid receptors.
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PMID:Influence of hydrophobic interactions on the structure and steroid-binding properties of glucocorticoid receptors. 242 48

T cells of autoimmune-prone mice homozygous for the lpr mutation respond poorly to mitogens in terms of proliferation and of IL-2 production. In a previous study, we have correlated this deficient activation with the inability of mitogens to stimulate hydrolysis of phosphatidylinositol 4,5-bisphosphate in lpr T cells, although these cells bind mitogen and express the TCR/CD3 complex. In order to determine whether activation-deficient lpr T cells contain functional GTP-binding (G) protein(s) and phospholipase C, we examined the effects of the G protein activating agent sodium fluoride plus Al+3 (AlF-4). AlF-4 stimulated phosphatidylinositol turnover, a response characteristic of TCR/CD3 occupancy, in mature L3T4+ and Ly2+ T cells. Second, and more important, AlF-4 stimulated the same biochemical events in L3T4-, Ly2- (double-negative) T cells from the normal thymus or from the enlarged lymph nodes of autoimmune-prone mice homozygous for the lpr mutation. However, these double-negative T cells were unresponsive to receptor-active ligands such as T cell mitogens or anti-CD3-epsilon mAb, despite their ability to bind these ligands. These findings suggest that activation-deficient double negative T cells express the receptors, G protein(s) and effector enzymes necessary for second messenger formation and further suggest that the failure of these cells to generate the relevant second messengers in response to mitogens or anti-CD3-epsilon antibody may be due to inefficient coupling of the TCR/CD3 complex to G proteins.
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PMID:Stimulation of PIP2 hydrolysis by aluminum fluoride in resting T cell subsets of normal and autoimmune-prone lpr mice. 254 77


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