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

---

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

Thrombin is by far the most potent platelet agonist. Potentially this reflects multiple intracellular processes involved in transmitting the activation signal from the initial contact with a receptor, or binding site, to the final platelet response. Platelet membranes have two putative receptors: the high affinity glycoprotein Ib, whose function remains to be clarified, and the moderate affinity autoproteolytic receptor. The autoproteolytic receptor is a member of a family of receptors, with seven transmembrane domains, which interact with GTP-binding proteins. Distal to the membrane, several forms of phospholipase C are activated and roles for both heterotrimeric and low molecular mass GTP-binding proteins have been presented. Phospholipase C acts on inositol phospholipids to generate inositol trisphosphate and diacylglycerol, both of which function as second messengers in thrombin-induced platelet activation. Inositol trisphosphate mobilizes internal calcium stores and this is accompanied, and enhanced, by an influx of calcium from the external milieu. Diacylglycerol and calcium both serve to regulate the activity of multiple protein kinases which, in turn, mediate the phosphorylated state of numerous proteins. Phosphorylation can occur on serine, threonine or tyrosine residues of target proteins and the phosphorylated state of these proteins determines the final activation of the platelet.
...
PMID:Post-receptor events associated with thrombin-induced platelet activation. 814 90

Although the importance of protein kinases in platelet activation, particularly protein kinase C (PKC), is well established there remain many problems regarding the various phosphorylation cascades, the role of phosphatases and the importance of other serine/threonine and tyrosine kinases. A particular problem is the mechanism of activation of the fibrinogen receptor, GPIIb/IIIa, a critical step in aggregation. Although GPIIIa is phosphorylated (on threonine) neither the stoichiometry nor the minor changes on activation seem adequate to explain the response. Relatively unspecific inhibitors of PKC such as staurosporine prevent PO4 incorporation into most kinase substrates but only inhibit platelet aggregation partially. However, staurosporine does induce activation and then inhibits several renaturable serine/threonine kinases, probably via phosphatases. Staurosporine did not, however, inhibit the platelet Ca2+ signal in response to thrombin but rather enhanced it. 17-Hydroxywortmannin (HWT), a fungal metabolite, has been shown to inhibit respiratory burst in neutrophils and causes haemorrhages. It was recently reported to be a myosin light chain kinase (MLCK) inhibitor and to inhibit PKC only at much higher concentrations. In platelets, HWT inhibits aggregation and partially inhibits phosphorylation of myosin light chain and P47 in thrombin-activated platelets. It also allows the discrimination of an early and a late phase in the cytoplasmic Ca2+ signal since at lower concentrations it only inhibits the late phase. The late phase of ATP release was also inhibited in a dose-dependent manner. The activation of most of the renaturable serine/threonine kinases was also inhibited by HWT. These results support earlier conclusions that the early phase of the Ca2+ signal is phospholipase C dependent but indicate that other mechanisms must be responsible for the late phase. The relative specificity of HWT for MLCK might indicate that this has an unexpected major role in controlling these late phase reactions including activation of GPIIb/IIIa or its clustering. However, staurosporine completely inhibits phosphorylation of myosin light chain by its kinase (as well as other kinases) and has the opposite effect on Ca2+ signals. Clearly, the interactions and feed-back mechanisms between these kinases are very complex but the results suggest that phosphatases acting together with their complementary kinases should also be considered as important platelet activation regulators. P47, long considered a major PKC substrate, may also be phosphorylated by MLCK.
...
PMID:Serine/threonine kinases in signal transduction in response to thrombin in human platelets. Use of 17-hydroxywortmannin to discriminate signals. 820 81

In order to determine which portion of phosphoinositide-specific phospholipase C (PLC)-beta 1 is required for activation by G alpha q, a series of specific deletions and truncations of PLC-beta 1 cDNA were prepared. After transfection of COS-7 cells with these cDNA clones, the activity and localization of the expressed proteins were determined. Specific deletions in the C-terminal end of the protein did not lead to loss of intrinsic enzymatic activity but did result in loss of the ability to be activated by G alpha q. The region required for activation was localized to the amino acid sequence corresponding to residues 903-1142 of PLC-beta 1. This region was further subdivided into two sequences; one extending from residues Thr-903 to Gln-1030 that was required for particulate fraction association as well as for activation by G alpha q and the other extending from residues Gln-1030 to Leu-1142 that was required for interaction with G alpha subunits. These results were confirmed by the observation that the C-terminal portion of PLC-beta 1, when co-expressed with the muscarinic acetylcholine receptor type 1 or the alpha 1C-adrenergic receptor in COS-7 cells, markedly inhibited ligand-induced release of inositol phosphates. In an in vitro system, two peptides derived from the G-protein interaction region at the C terminus were found to inhibit the guanosine 5'-3-O-(thio)triphosphate-dependent activation of PLC-beta 1 by G alpha q. This further localized the sites on PLC-beta 1 which are involved in interaction with G-protein alpha subunits.
...
PMID:Identification of critical regions on phospholipase C-beta 1 required for activation by G-proteins. 838 37

The molecular events that lead from the interaction of insulin with its receptor to the activation of protein serine/threonine kinases are still unknown. In this study, we have examined the role of GTP-binding proteins in this signaling pathway using differentiated 3T3-L1 adipocytes permeabilized with alpha-toxin from Staphylococcus aureus. Addition of GTP gamma S (guanosine 5'-O-(3-thiotriphosphate)) or insulin to such permeabilized cells markedly increases protein kinase activities in cell lysates using the microtubule-associated protein-2 kinase substrate peptide KRELVE-PLTPSGEAPNQALLR, which contains the threonine 669 phosphorylation site on the epidermal growth factor receptor. Similar stimulations of protein kinase activity by these agents are observed using the peptide KRRRLASLAA, which is selectively phosphorylated by ribosomal protein S6 kinases. The effects of insulin and GTP gamma S are not additive. Importantly, the GTP-binding protein antagonist GDP beta S (guanosine 5'-O-(2-thiodiphosphate)) inhibits the activation of the protein kinase activities by insulin in permeabilized 3T3-L1 adipocytes. These data are consistent with the hypothesis that activation of Ras or other GTP-binding proteins is a key element of the signaling mechanism whereby insulin receptor tyrosine kinase activates the microtubule-associated protein-2 kinase cascade.
...
PMID:Activation of protein kinases by insulin and non-hydrolyzable GTP analogs in permeabilized 3T3-L1 adipocytes. 838 15

The mechanism(s) by which monoclonal antibodies (mAbs) against the epidermal growth factor (EGF) receptor regulate receptor function have been investigated with NIH3T3/HER14 fibroblasts expressing human EGF receptors. Bivalent 225 mAb or monovalent 225 Fab' inhibited transforming growth factor (TGF)-alpha-induced EGF receptor tyrosine phosphorylation and cell proliferation. Culture of HER14 cells with 225 mAb or 225 Fab' did not activate EGF receptor tyrosine kinase when assayed after lysis of cells in SDS sample buffer. However, when cells were cultured with bivalent 225 mAb, but not with monovalent 225 Fab', and were subsequently lysed and further incubated in Triton X-100 lysis buffer containing proteinase and phosphatase inhibitors, receptor phosphorylation was observed. Phosphorylation was confined to tyrosine residues and was inhibited by addition of genistein after lysis, indicating that it was due to the activation of protein tyrosine kinase. The activity of bivalent 225 mAb was unphysiologic, in contrast with TGF-alpha, in that receptor kinase activation occurred only after cell lysis and with delayed kinetics; serine and threonine phosphorylation did not occur; and down-regulation of EGF receptors was slower. Selective mAb-mediated phosphorylation of tyrosine residues on EGF receptors was sufficient to activate phosphorylation of a SH2 group-bearing substrate, phospholipase C-gamma, indicating that serine/threonine phosphorylation is not required for EGF receptor kinase activity. These studies provide novel insights into the capacity of bivalent mAb to modulate EGF receptor function.
...
PMID:Regulation of epidermal growth factor receptor in NIH3T3/HER14 cells by antireceptor monoclonal antibodies. 840 44

Our study describes the production, purification, and properties of alpha-toxin from Clostridium novyi type A 19402. The bacterium produced maximal amounts of alpha-toxin when grown at 37 degrees C for 72 h in dialysis flask cultures containing brain heart infusion supplemented with 0.75% Tween 80 and 2% glycerol. The alpha-toxin was purified by precipitation with polyethylene glycol 6000, followed by chromatography on Q-Sepharose, phenyl-agarose, and Mono-Q. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the toxin exhibited a single band with an M(r) of 200,000. The toxin also exhibited a single immunoprecipitin arc by crossed immunoelectrophoresis with antiserum against crude toxin. It was stable when stored at 4 degrees C and also following exposure to buffers with pHs in the range of 4 to 7. The toxin had a minimum lethal dose in mice of 5 to 10 ng, caused rounding of a variety of cells in tissue culture, and was negative in the rabbit ileal loop assay. The cytotoxic activity was inhibited by agents that affect receptor-mediated processes, and the toxin was less active on a CHO mutant cell line that is defective in endosomal acidification. The analysis of the amino acid composition revealed an unusually high proline content. The N-terminal sequence is Met-Leu-Ile-Thr-Arg-Glu-Gln-Leu-Met-Lys.
...
PMID:Purification and characterization of alpha-toxin produced by Clostridium novyi type A. 851 95

The pp70/85-kDa S6 kinases, collectively referred to as pp70S6k, are thought to participate in transit through the G1 phase of the cell cycle. pp70S6k regulates the phosphorylation of the 40S ribosomal protein S6 and the transcription factor CREM tau. pp70S6k is regulated by serine/threonine phosphorylation, and although 1-phosphatidylinositol 3-kinase and phospholipase C have been implicated as upstream regulators, the mechanism of activation and identity of the upstream pp70S6k kinases remain unknown. To improve our understanding of how this mitogen-stimulated protein kinase is regulated by growth factors and the immunosuppressant rapamycin, we have initiated a structure/function analysis of pp70S6k. Our results indicate that both the N and C termini participate in the complex regulation of pp70S6k activity.
...
PMID:Structural and functional analysis of pp70S6k. 852 31

Tumor Necrosis Factor (TNF) is one of the most potent physiological inducers of the nuclear transcription factor NF-kappa B. In light of the pivotal role of NF-kappa B in the development of immune responses and activation of HIV replication, the identification of TNF signal transduction pathways involved in NF-kappa B activation is of particular interest. Data from our laboratory demonstrate that the TNF signal transduction pathway-mediating NF-kappa B activation involves two phospholipases, a phosphatidylcholine-specific phospholipase C (PC-PLC) and an endosomal acidic sphingomyelinase (aSMase). The aSMase activation by TNF is secondary to the generation of 1,2-diacylglycerol (DAG) produced by a TNF-responsive PC-PLC. SMase and its product ceramide induce degradation of the NF-kappa B inhibitor I kappa B as well as NF-kappa B activation. Besides endosomal acidic SMase, TNF also rapidly activates a plasmamembrane-associated neural SMase (nSMase), that, however is not involved in TNF-induced NF-kappa B activation. NSMase and aSMase are activated by different cytoplasmic domains of the 55 kDa TNF-receptor and are coupled to select pathways of TNF signaling. Ceramide generated by nSMase directs the activation of proline-directed serin/threonine protein kinases and phospholipase A2 and ceramide produced by aSMase triggers the activation of NF-kappa B. No apparent crosstalk was detected between nSMase and aSMase pathways, indicating that ceramide action depends on the topology of its production.
...
PMID:TNF-induced activation of NF-kappa B. 853 Jan 43

Persistent stimulation of specific protein kinase pathways has been proposed as a key feature of receptor tyrosine kinases and intracellular oncoproteins that signal neuronal differentiation of rat pheochromocytoma (PC12) cells. Among the protein serine/threonine kinases identified to date, the p42/44 mitogen-activated protein (MAP) kinases have been highlighted for their potential role in signalling PC12 cell differentiation. We report here that retrovirus-mediated expression of GTPase-deficient, constitutively active forms of the heterotrimeric Gq family members, G alpha qQ209L and G alpha 16Q212L, in PC12 cells induces neuronal differentiation as indicated by neurite outgrowth and the increased expression of voltage-dependent sodium channels. Differentiation was not observed after cellular expression of GTPase-deficient forms of alpha i2 or alpha 0, indicating selectivity for the Gq family of G proteins. As predicted, overexpression of alpha qQ209L and alpha 16Q212L constitutively elevated basal phospholipase C activity approximately 10-fold in PC12 cells. Significantly, little or no p42/44 MAP kinase activity was detected in PC12 cells differentiated with alpha 16Q212L or alpha qQ209L, although these proteins were strongly activated following expression of constitutively active cRaf-1. Rather, a persistent threefold activation of the cJun NH2-terminal kinases (JNKs) was observed in PC12 cells expressing alpha qQ209L and alpha 16Q212L. This level of JNK activation was similar to that achieved with nerve growth factor, a strong inducer of PC12 cell differentiation. Supportive of a role for JNK activation in PC12 cell differentiation, retrovirus-mediated overexpression of cJun, a JNK target, in PC12 cells induced neurite outgrowth. The results define a p42/44 MAP kinase-independent mechanism for differentiation of PC12 cells and suggest that persistent activation of the JNK members of the proline-directed protein kinase family by GTPase-deficient G alpha q and G alpha 16 subunits is sufficient to induce differentiation of PC12 cells.
...
PMID:GTPase-deficient G alpha 16 and G alpha q induce PC12 cell differentiation and persistent activation of cJun NH2-terminal kinases. 855 93

We have used the neurokinin NK-2 receptor as a model to examine how receptor desensitization affects cellular responses. The liganded receptor transiently activates phospholipase C (PLC) and is rapidly phosphorylated on Ser/Thr residues in its C-terminal domain. Mutant receptors lacking this domain mediate persistent activation of PLC. We now show that, in transfected Rat-1 cells, mutant receptor mediates ligand-induced DNA synthesis, morphological transformation and growth in soft agar, whereas wild-type (wt) receptor does not. Wt receptor causes only transient MAP kinase activation. In contrast, MAP kinase activation by mutant receptor is sustained for >4 h. Neither wt nor mutant receptor couples to Ras activation. Downregulation of protein kinase C (PKC) has little effect on MAP kinase activation, DNA synthesis and transformation. Mutant receptors also promote stronger protein tyrosine phosphorylation and stress fibre formation than does wt receptor. Thus, C-terminal truncation allows the NK-2 receptor to signal sustained MAP kinase activation, cell growth and transformation by a Ras- and PKC-independent mechanism. Our results reveal the importance of the C-terminal 'desensitization domain' in suppressing the oncogenic potential of a prototypic PLC-coupled receptor.
...
PMID:Truncated, desensitization-defective neurokinin receptors mediate sustained MAP kinase activation, cell growth and transformation by a Ras-independent mechanism. 867 Aug 36


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---