Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cross-linking of Fc gamma RIIIA (CD16) receptor on natural killer (NK) cells induces receptor-associated tyrosine kinase activation and tyrosine phosphorylation of numerous intracellular proteins, including phospholipase C (PLC)-gamma 1, PLC-gamma 2 and the associated zeta chain. Here we report that Vav, a proto-oncogene, also became tyrosine phosphorylated upon stimulation of CD16 in interleukin 2-activated NK cells (LAK-NK) as well as in an NK cell line, NK3.3. In addition, we observed that in LAK-NK cells, Vav was associated with a 70 kDa protein that also became tyrosine phosphorylated upon CD16 cross-linking. The association of this 70 kDa protein with Vav was disrupted by ionic detergent treatment. Tyrosine phosphorylation of Vav was inhibited by herbimycin A, a specific tyrosine kinase inhibitor. In vitro kinase assays with Vav immunoprecipitates derived from NK3.3 cells or LAK-NK cells resulted in the appearance of a phosphorylated 58 kDa protein, suggesting the presence of a kinase within the Vav immunoprecipitates. Cross-linking of CD16 did not enhance this Vav-associated kinase activity. Phosphoamino acid analysis of the 58 kDa protein revealed that it was phosphorylated only on serine and threonine residues, indicating that an unidentified serine/threonine kinase is constitutively associated with Vav. These observations suggest that the downstream signalling events regulated by Vav and its associated proteins are complex involving both tyrosine kinases as well as the yet unidentified serine/threonine kinase in NK cells.
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PMID:Vav in natural killer cells is tyrosine phosphorylated upon cross-linking of Fc gamma RIIIA and is constitutively associated with a serine/threonine kinase. 880 42

The lethal and edema-inducing alpha-toxin from Clostridium novyi causes rounding up of cultured cell lines by redistribution of the actin cytoskeleton. alpha-Toxin belongs to the family of large clostridial cytotoxins that encompasses Clostridium difficile toxin A and B and the lethal toxin from Clostridium sordellii. Toxin A and toxin B have been recently identified as monoglucosyltransferases to modify the low molecular mass GTPases of the Rho subfamily (Just, I., Selzer, J., Wilm, M., Von Eichel-Streiber, C., Mann, M., and Aktories, K. (1995) Nature 375, 500-503 and Just, I., Wilm, M., Selzer, J., Rex, G., Von Eichel-Streiber, C., Mann, M., and Aktories, K. (1995) J. Biol. Chem. 270, 13932-13936). We report here the identification of the alpha-toxin-catalyzed modification of Rho. Using electrospray mass spectrometry, the mass of the modification was determined as 203 Da, consistent with a N-acetyl-hexosamine moiety. UDP-N-acetyl-glucosamine selectively served as cosubstrate for alpha-toxin-catalyzed modification into the Rho subfamily proteins Rho, Rac, Cdc42, and RhoG. The acceptor amino acid of N-acetyl-glucosaminylation was identified by mutagenesis as Thr-37 in Rho (equivalent to Thr-35 in Rac/Cdc42), which is located in the effector domain of the GTPases. C. novyi alpha-toxin seems to mediate its cytotoxic effects on cells by mimicking endogenous post-translational modification of cellular proteins.
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PMID:Clostridium novyi alpha-toxin-catalyzed incorporation of GlcNAc into Rho subfamily proteins. 881 Feb 74

Red/far-red light signal transduction by the phytochrome family of photoreceptors regulates plant growth and development. We investigated the possibility that tyrosine kinases and/or phosphatases are involved in phytochrome-mediated signal transduction using crude extracts of oat seedlings that are grown in the dark. We found that a 124 kDa protein was tyrosine-phosphorylated as determined by Western blotting with a phosphotyrosine-specific monoclonal antibody. The 124 kDa protein was recognized by the anti-phosphotyrosine antibody in anti-phytochrome A immunoprecipitates. The level of anti-phosphotyrosine antibody binding to the 124 kDa protein(s) in phytochrome immunoprecipitates that had been treated with red light prior to immunoprecipitation decreased relative to dark controls. These results suggest that either phytochrome from dark-grown seedlings is tyrosine phosphorylated or that it co-immunoprecipitates with a phosphotyrosine-containing protein of the same molecular weight. The implications of these results in the regulation of (a) the putative Ser/Thr kinase activity of the photoreceptor and (b) the binding of signaling molecules, such as phospholipase C to phytochrome, are discussed.
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PMID:A possible tyrosine phosphorylation of phytochrome. 881 82

We recently demonstrated that epidermal growth factor receptor (EGFR)-mediated signaling of cell motility and mitogenesis diverge at the immediate post-receptor level. How these two mutually exclusive cell responses cross-communicate is not known. We investigated a possible role for a phospholipase C (PLC)-dependent feedback mechanism that attenuates EGF-induced mitogenesis. Inhibition of PLC gamma activation by U73122 (1 microM) augmented the EGF-induced [3H]thymidine incorporation by 23-55% in two transduced NR6 fibroblast lines expressing motility-responsive EGFR; increased cell division and mitosis was observed in parallel. The time dependence of this increase revealed that it was due to an increase in maximal incorporation and not a foreshortened cell cycle. Motility-responsive cell lines expressing a dominant-negative PLC gamma fragment (PLCz) also demonstrated augmented mitogenic responses by 25-68% when compared with control cells. PLCz- or U73122-augmented mitogenesis was not observed in three non-PLC gamma activating, nonmotility-responsive EGFR-expressing cell lines. Protein kinase C (PKC), which may be activated by PLC-generated second messengers, has been proposed as mediating feedback attenuation due to its capacity to phosphorylate EGFR and inhibit the receptor's tyrosine kinase activity. Inhibition of PKC by Calphostin C (0.05 microM) resulted in a 57% augmentation in the fold of EGF-induced thymidine incorporation. To further establish PKC's role in this feedback attenuation mechanism, an EGFR point mutation, in which the PKC target threonine654 was replaced by alanine, was expressed. Cells expressing these PKC-resistant EGFR constructs demonstrated EGF-induced motility comparable to cells expressing the threonine-containing EGFR. However, when these cells were treated with U73122 or Calphostin C, the mitogenic responses are not enhanced. These findings suggest a model in which PKC activation subsequent to triggering of motility-associated PLC gamma activity attenuates the EGFR mitogenic response.
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PMID:Mitogenic signaling from the egf receptor is attenuated by a phospholipase C-gamma/protein kinase C feedback mechanism. 881 94

Erythropoietin regulates the transcription of the protooncogenes c-myc and c-myb by discrete protein kinase C (PKC)-dependent and protein serine/threonine phosphatase-dependent pathways, respectively (Spangler, R., Bailey, S. C., and Sytkowski, A. J. (1991) J. Biol. Chem. 266, 681-684; Patel H. R, Choi H.-S, and Sytkowski A. J. (1992) J. Biol. Chem. 267, 21300-21302). In the present study we demonstrate that up-regulation of c-myc requires the PKC-epsilon isoform and that this pathway is required for erythropoietin-induced DNA synthesis (growth) but apparently not for beta-globin expression (differentiation). Treatment of Rauscher murine erythroleukemia cells resulted in phosphorylation of phospholipase C-gamma1 and activation of PKC-epsilon as evidenced by its translocation from soluble to particulate subcellular fractions. Artificial down-regulation of PKC-epsilon with antisense oligodeoxynucleotides blocked erythropoietin's up-regulation of c-myc in a concentration-dependent manner. In contrast, antisense oligodeoxynucleotides to PKC-alpha, -beta, -gamma, -delta, and -zeta had no effect. Although down-regulation of PKC-epsilon blocked the increase in c-myc expression, it did not inhibit erythropoietin induction of beta-globin expression, a marker of erythroid differentiation. However, down-regulation of PKC-epsilon did block factor-dependent DNA synthesis quantified by measurement of [3H]thymidine incorporation into newly synthesized DNA of normal murine erythroid cells. The results are consistent with discrete intracellular signals regulating erythroid cell growth and differentiation.
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PMID:Protein kinase C-epsilon is necessary for erythropoietin's up-regulation of c-myc and for factor-dependent DNA synthesis. Evidence for discrete signals for growth and differentiation. 890 Jan 91

A mutant toxin (MT) that abolished almost 99% of the hemolytic activity of alpha-toxin was isolated by random polymerase chain reaction (PCR) mutagenesis of the gene for Clostridium perfringens alpha-toxin. In the mutant toxin, the amino acids at Tyr (Y)-62, Thr (T)-74 and Ile (I)-345 were substituted with His, Ile and Met, respectively. Replacement of T-74 with Ile by site-directed mutagenesis resulted in the loss of hemolytic, phospholipase C and sphingomyelinase activities by 1/250-fold of that of the wild-type. The replacement of Y-62 with Ile or I-345 with Met alone did not affect the activities of the toxin. T74I mutant bound to sheep erythrocyte membranes and specifically bound [65Zn]2+ in Tris-buffered saline, in the same manner as the wild-type, and contained 2 mol of zinc ions per mol of protein. These results suggest that the T-74 residue plays a key role in these biological activities of C. perfringens alpha-toxin.
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PMID:Threonine-74 is a key site for the activity of Clostridium perfringens alpha-toxin. 893 72

Until recently, neonatal hyperthyroidism has been considered to be related to the transplacental passage of thyroid-stimulating Ig present in the serum of the mother. We report here the case of a newborn who presented with severe hyperthyroidism, diffuse goiter, and important ocular signs (eyelid retraction and possibly proptosis). However, the absence of thyroid pathology in the parents and the lack of antithyroid antibodies in the mother and in the patient led us to suspect a nonimmune aetiology. Direct genomic sequencing of the last exon of the TSH receptor in the patient revealed a T-->C transversion yielding to a Met453-->Thr heterozygous substitution in the second transmembrane domain of the receptor. The mutation was absent in both parents. Eukaryotic expression analysis in COS-7 cells yielded a mutated receptor that produced constitutive activation of adenylate cyclase without enhancement of phospholipase C activity.
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PMID:A neomutation of the thyroid-stimulating hormone receptor in a severe neonatal hyperthyroidism. 896 21

The aim of the present study was to elucidate events in the plasma membrane (PM) associated with the previously described effect of insulin to rapidly enhance the number of cell surface insulin binding sites in rat adipocytes. [125I]insulin was cross-linked to cell surface insulin receptors of intact cells that had been preincubated with or without insulin. Subsequently prepared PM displayed a approximately 3-fold increase in bound [125I]insulin when cells had been pretreated with 6 nM insulin for 20 min compared to membranes from control cells, and SDS-PAGE with autoradiography showed that this occurred at the insulin receptor alpha-subunit. The magnitude of the effect was similar to that found for insulin binding to intact cells that had been preincubated with insulin. In contrast, the insulin binding capacity in the PM was not affected by prior treatment of cells with insulin when assessed with the addition of [125I]insulin directly to solubilized PM; this suggests an unchanged total number of PM receptors. Thus, the enhancement of cell surface insulin binding capacity produced by insulin is not due to the translocation of receptors, but instead appears to be confined to receptors already present in the PM. The addition of phospholipase C (from Clostridium perfringens), which cleaves PM phospholipids, mimicked the effect of insulin to enhance cell surface binding in adipocytes, and this suggests a pool of cryptic PM receptors. Both the nonmetabolizable cAMP analog N6-monobutyryl cAMP (N6-mbcAMP) and the serine/threonine phosphatase inhibitor okadaic acid abolished the effect of concomitant insulin treatment to increase binding capacity. In contrast, the tyrosine phosphatase inhibitor vanadate increased insulin binding even in the presence of okadaic acid or N6-mbcAMP. The effect of N6-mbcAMP to impair cell surface insulin binding was also evident in the presence of a peptide derived from the major histocompatibility complex type I that effectively impairs receptor internalization, but the amount of PM receptors assessed by immunoblot was unaltered. Taken together, the data suggest that insulin exposure leads to the uncovering of cryptic receptors associated with the PM. It is also suggested that tyrosine phosphorylation promotes this process, whereas enhanced serine phosphorylation, e.g. produced by cAMP, impairs the functional insertion of the receptors, rendering them unable to bind insulin.
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PMID:Insulin promotes and cyclic adenosine 3',5'-monophosphate impairs functional insertion of insulin receptors in the plasma membrane of rat adipocytes: evidence for opposing effects of tyrosine and serine/threonine phosphorylation. 900 93

The neurotrophins are signaling factors that are essential for survival and differentiation of distinct neuronal populations during the development and regeneration of the nervous system. The long-term effects of neurotrophins have been studied in detail, but little is known about their acute effects on neuronal activity. Here we use permeabilized whole-cell patch clamp to demonstrate that neurotrophin-3 (NT-3) and nerve growth factor activate calcium-dependent, paxilline-sensitive potassium channels (BK channels) in cortical neurons. Application of NT-3 or nerve growth factor produced a rapid and gradual rise in BK current that was sustained for 30-50 min; brain-derived neurotrophic factor, ciliary neurotrophic factor, and insulin-like growth factor-1 had no significant effect. The response to NT-3 was blocked by inhibitors of protein kinases, phospholipase C, and serine/threonine protein phosphatase 1 and 2a. Omission of Ca2+ from the extracellular medium prevented the NT-3 effect. Our results indicate that NT-3 stimulates BK channel activity in cortical neurons through a signaling pathway that involves Trk tyrosine kinase, phospholipase C, and protein dephosphorylation and is calcium-dependent. Activation of BK channels may be a major mechanism by which neurotrophins acutely regulate neuronal activity.
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PMID:Activation of calcium-dependent potassium channels in mouse [correction of rat] brain neurons by neurotrophin-3 and nerve growth factor. 902 72

Productive interaction between receptors and G proteins involves multiple intracellular receptor domains, but the role of individual receptor amino acids in directing the selection of specific signaling pathways has not yet been identified. Sequence alignment of several G protein-coupled receptors identified a highly conserved threonine residue in the i2 loop of the 5-hydroxytryptamine 1A (5-HT1A) receptor that is a putative protein kinase C phosphorylation consensus site and is located in a predicted amphipathic alpha-helical domain. To examine the role of this conserved threonine residue in 5-HT1A receptor coupling to Gi/Go proteins, this residue was mutated to alanine (T149A mutant). Wild-type and mutant 5-HT1A receptors were stably transfected into both Ltk- and GH4C1 cells to investigate receptor coupling to multiple signaling pathways. In both cell lines, the T149A mutant displayed similar agonist affinities as the wild-type receptor. In Ltk- cells, the T149A 5-HT1A receptor inhibited cAMP accumulation by 30% compared with wild-type (83%). A 2.6-fold increase in intracellular calcium (due to phospholipase C-mediated calcium mobilization) was observed for the wild-type receptor upon the addition of 100 nM 5-HT; whereas the T149A 5-HT1A receptor failed to mediate a calcium mobilization response at equivalent receptor levels to wild-type. When transfected in GH4C1 cells, the T149A receptor mutant fully inhibited basal cAMP and partially inhibited Gs-stimulated cAMP accumulation compared with wild-type receptor (57 +/- 14% versus 86 +/- 2%). In contrast, the T149A 5-HT1A receptor mutant failed to block the influx of calcium induced by calcium channel agonist (+/-)-Bay K8644, whereas the wild-type 5-HT1A receptor inhibited the calcium influx by 40%. Thus, the Thr149 residue is directly involved in G protein coupling to calcium mobilization (mediated by betagamma subunits of Gi2) and to inhibition of calcium channel activation (mediated by betagamma subunits of Go) but plays a minor role in coupling to alpha1-mediated inhibition of cAMP accumulation. The conserved i2 loop threonine may serve as a G protein contact site to direct the signaling specificity of multiple receptors.
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PMID:A conserved threonine residue in the second intracellular loop of the 5-hydroxytryptamine 1A receptor directs signaling specificity. 922 26


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