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:3.4.11.18 (MAP)
7,412 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown that FGF (basic or acidic) is mitogenic for quiescent hamster lung fibroblasts (CCL39 line). It is active alone but is much more efficient in synergistic combinations with G-protein-activating agents. When used alone, FGF appears to exert its mitogenic effects without involving any of the major G-protein-mediated signaling pathways. It causes no significant hydrolysis of phosphoinositides, it does not alter the activity of adenylate cyclase, and its mitogenicity is insensitive to pertussis toxin. It therefore seems likely that all pleiotropic actions of FGF are primarily mediated by the intrinsic protein tyrosine kinase of its receptors. However, FGF, acting through its receptor tyrosine kinase, and thrombin, acting through G-protein-coupled receptors, induce a common set of early responses detected within seconds or minutes at the level of membranes, cytoplasm, and nuclei. Typical examples of early responses are activation of Na/H antiporter and Na/K/Cl cotransporter, phosphorylation of ribosomal protein S6, and increased transcription of early-immediate genes (c-fos, c-jun, and c-myc). Not only various classes of growth factors acting via distinct transducing mechanisms activate common targets, but also their synergistic effects on reinitiation of DNA synthesis is reflected on the early responses. How does the coordination of these signaling events take place? A partial answer to this question is illustrated in Figure 6 in which "switch kinases" play the role of integrators of multiple extracellular signals. Raf and, perhaps more convincingly, MAP kinases that are activated by dual phosphorylation on tyrosine and threonine residues are potential good candidates for this integration. This hypothetical scheme could therefore explain, in part, the coordination and the synergy commonly observed in the mitogenic response. The synergy could be generated at the level of MAP kinases simply by dual activating phosphorylations. With the recent cloning of MAP kinases, these questions will be more easily addressed. Another important gap that will have to be filled in future studies is the identification of all the members of the kinase cascade. When used in synergistic combinations with G-protein-activating agents, FGF does exert in contrast some effects on the G-protein-mediated pathways. It potentiates the G-protein-mediated activations of both PIP2-PLC and adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mitogenic effects of fibroblast growth factors in cultured fibroblasts. Interaction with the G-protein-mediated signaling pathways. 166 81

Treatment of BC3H1 myocytes or 3T3-L1 fibroblasts with fluoroaluminate (AlF4-), a direct activator of G proteins, increased the tyrosine phosphorylation of a 42-kDa cytosolic protein. AlF4- induced a parallel increase in protein kinase activity toward myelin basic protein (MBP) in partially purified cell extracts. To test whether AlF4- was activating the 42-kDa MAP (mitogen-activated protein) kinase, extracts from AlF4--treated cells were taken through the chromatographic steps routinely used to purify MAP kinase from growth factor-stimulated cells. Following phenyl-Superose chromatography, a peak of MBP kinase activity eluted at a position characteristic of MAP kinase. Immunoblotting of the active fractions with anti-phosphotyrosine antibodies revealed a single reactive protein band of Mr 42,000. Stimulation of MAP kinase by AlF4- was rapid, peaking within 15 min and persisting for at least 1 h. In contrast, the activation of MAP kinase by insulin was transient, characteristic of its activation by growth factors in other cell types. Although concentrations of sodium fluoride greater than 1 mM also activated MAP kinase, this effect was shown to be dependent upon the simultaneous presence of aluminum ions in the medium. Activation of MAP kinase by AlF4- was not affected by either cellular depletion of protein kinase C or pretreatment of cells with pertussis toxin. Potential sites of action of AlF4- are discussed. These findings suggest that activation of a G protein(s) in intact cells can initiate events that result in tyrosine phosphorylation and activation of MAP kinase.
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PMID:Activation of mitogen-activated protein kinase in BC3H1 myocytes by fluoroaluminate. 170 25

Signaling via the alpha-beta T cell Ag receptor (Ti)-CD3 complex is a complicated event that implicates several protein kinases, most notably protein kinase C (PKC). We have recently identified a serine kinase in T lymphocytes with the following characteristics: molecular mass 43 kDa, in vitro substrate affinity for microtubule associated protein 2 (MAP-2) with a preference for Mn2+ during the catalytic reaction, and elution from DEAE resin over a salt range 100 to 200 mM NaCl. This kinase is activated in a rapidly reversible fashion during ligation of CD3/Ti by a process which involves prior phosphorylation; in vitro exposure of activated 43-kDa MAP-2 kinase (MAP-K) to an immobilized phosphatase abrogated its kinase activity. We now show that a MAP-2K response could also be obtained during treatment with mAb to Ti and the specific PKC agonist, PMA. Although the kinetics of the former response was rapidly reversible, PMA elicited a more prolonged response. The dose responsiveness for PMA was similar to the requirements for PKC activation in intact lymphocytes. Moreover, as with PKC, we found that the CD3-induced MAP-2K response could be further enhanced by using a second layer cross-linking antibody. The specificity of CD3/Ti in the Jurkat cell response is demonstrated by the fact that OKT-11(CD2) and anti-CD4 mAb did not stimulate a MAP-2K response. It was also not possible to elicit a response in a Jurkat cell mutant that lacks surface expression of CD3 and Ti. The specificity of PKC in these events was further explored with the cell permeant diacylglycerol, 1-oleoyl-2-acetylglycerol, and the nonagonist phorbol ester, 4 alpha-phorbol 12,13-didecanoate: whereas the former was an effective inducer of the MAP-2K response, the latter failed to yield any stimulation. Prior exposure of Jurkat cells to 100 mM PMA for 24 h eliminated greater than 60% of the MAP-2K response during anti-CD3 treatment. This response could also be inhibited in dose-dependent fashion by prior treatment of Jurkat cells with the potent PKC inhibitor 1-(5-isoquinolinesulfonyl) 2-methylpiperazine dihydrochloride. Although a Ca2(+)-ionophore failed to synergize with PMA at inducing a MAP-2K response, depletion of extracellular Ca2+ by EGTA abrogated anti-CD3 responsiveness. The events culminating in MAP-2K activation were slightly inhibited in the presence of cholera toxin but not pertussis toxin.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Stimulation of MAP-2 kinase activity in T lymphocytes by anti-CD3 or anti-Ti monoclonal antibody is partially dependent on protein kinase C. 215 31

Stimulation of Rat-1 fibroblasts, stably transfected with alpha 2C10 receptors, with the specific alpha 2 agonist UK14304 led to the tyrosine phosphorylation and activation of the p42 and p44 isoforms of MAP kinase. Tyrosine phosphorylation of the MAP kinases was prevented by pertussis toxin. In unstimulated cells, there was constitutive tyrosine phosphorylation and activation of the p44 but not the p42 MAP kinase. This effect was not seen in non-transfected parental Rat-1 fibroblasts.
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PMID:Regulation of p42 and p44 MAP kinase isoforms in Rat-1 fibroblasts stably transfected with alpha 2C10 adrenoreceptors. 751 3

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels play important roles in plasticity, neurotransmission, and neurotoxicity in the central nervous system. AMPA, but not N-methyl-D-aspartate (NMDA), receptor signaling in rat cortical neurons was found to involve a G-protein coupled to a protein kinase cascade. While both NMDA and AMPA activated p42 mitogen-activated protein kinase (MAPK) in neurons, only AMPA-induced MAPK was inhibited by pertussis toxin. AMPA, but not NMDA, caused an association of a G-protein beta subunit with a Ras, Raf kinase, and MAP/ERK kinase (MEK)-1 complex. The evidence indicates that AMPA triggers MAPK activation via a novel mechanism in which G-protein beta gamma dimers released from G alpha bind to a Ras protein complex causing the activation of Ras, Raf kinase, MEK-1, and finally MAPK.
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PMID:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, but not N-methyl-D-aspartate, activates mitogen-activated protein kinase through G-protein beta gamma subunits in rat cortical neurons. 755 6

The immunogenic efficacy of multiple antigen peptides, MAPs, i.e. branched molecules in which multiple copies of a given immunogenic peptide are attached on a scaffold of lysine residues via both alpha and epsilon linkages, has been repeatedly demonstrated, but little is known about the structural arrangement of these peptide constructs. A conformational characterization was therefore performed for a known T cell epitope of the S1 subunit of Pertussis toxin, whose sequence is predicted to form alpha-helix. The peptide DNVLDHLTGR, its N-acetylated and C-amidated analogue and a tetrabranched MAP based on the N-acetylated peptide were prepared and studied by CD and two-dimensional 1H-NMR. No evidence of helical structure was obtained in water for the isolated peptides. In contrast, in triflouroethanol, the isolated epitopes fold into a helical structure spanning the segment Val3-Thr8 in the uncapped molecule and encompassing also the N-terminal region in the capped analogue. The mobile C-terminal region tends to adopt a distorted turn arrangement in both peptides due to the folding of Arg10 guanidinium over the backbone. No distortion of the helix structure was observed for the single-copy epitope in the four-branched MAP molecule in trifluoroethanol: each peptide chain is equivalent within the MAP and shows an even more regular helical pattern than the isolated end-blocked sequence. A slight difference was located at the junction with the lysine scaffold: the peptide bond to epsilon NH was found in a much more extended conformation than the corresponding link to alpha NH. These structural results correlate with in vitro T cell stimulatory activity of the three compounds examined and provide arguments supporting the previous suggestion that MAP tetramers are unlikely to elicit an immune response specific for the synthetic template assembly, a feature necessary to retain the advantage of the polymeric epitope presentation.
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PMID:Conformational study of a short Pertussis toxin T cell epitope incorporated in a multiple antigen peptide template by CD and two-dimensional NMR. Analysis of the structural effects on the activity of synthetic immunogens. 769 60

The CXC chemokine, IL-8, is a potent chemoattractant of neutrophils and binds to two distinct receptors, termed IL-8R1 and IL-8R2. These receptors share high affinity for IL-8, however, only IL-8R1 is specific for IL-8 whereas IL-8R2 binds other related chemokines, including GRO alpha with high affinity. Stable Jurkat transfectants were generated expressing either functional IL-8R1 or IL-8R2 (J-IL8R1 and J-IL8R2). Both J-IL8R1 and J-IL8R2 exhibited high affinity IL-8 binding (Kd 3-5 nM) with respective receptor densities of 23,000 +/- 3,000 and 18,500 +/- 1,500. Pre-treatment of both transfectants with 1.0 micrograms/ml B. pertussis toxin (PTx) resulted in inhibition of IL-8 mediated intracellular Ca2+ mobilisation and chemotaxis, without altering the receptor's affinity for its ligand. This indicates that both receptors couple to a PTx-sensitive G-protein. Further studies showed that IL-8R1 and IL-8R2 could mediate time-dependent phosphorylation of p42/p44 MAP-kinase. In both transfectants, phosphorylation was maximal at 1-2 min after IL-8 stimulation and could be inhibited by PTx. Stimulation of J-IL8R1 and J-IL8R2 with GRO alpha revealed that this chemokine was a more potent activator of MAP-kinase in J-IL8R2, an observation reflected in the high affinity binding of GRO alpha to IL-8R2. These studies indicate that chemokines are capable of activating protein kinases and with regards to PTx-sensitivity and MAP-kinase stimulation, no significant differences between IL-8R1 and IL-8R2 post-receptor signalling occur during cell activation by IL-8.
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PMID:A comparison of post-receptor signal transduction events in Jurkat cells transfected with either IL-8R1 or IL-8R2. Chemokine mediated activation of p42/p44 MAP-kinase (ERK-2). 775 May 73

Northern blot analysis and displacement study revealed that the endothelin (ET) receptor functionally expressed in rat primary cultured astrocytes is the ETB receptor. Mitogen-activated protein kinases (MAP kinases) in the cells were activated by 10 nM ET-1, a dose that maximally stimulated phosphoinositide hydrolysis. This activation was potently inhibited by pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA) which leads to protein kinase C (PKC) down-regulation and was slightly inhibited by pretreatment with pertussis toxin (PTX). Pretreatment of the cells with PMA plus PTX completely inhibited the ET-1-augmented MAP kinase activity. Activation of MAP kinases was also induced by 0.1 nM ET-1, which hardly stimulated phosphoinositide hydrolysis. This activation was fully inhibited by pretreatment with PTX but insensitive to pretreatment with PMA. ET-1-stimulated production of inositol phosphates was not affected by pretreatment with PTX. These results suggest that activation of MAP kinases secondary to stimulation of the ETB receptor with ET-1 in rat primary cultured astrocytes was mediated through two independent signalling pathways. PKC-dependent pathway and PTX-sensitive G protein-mediated pathway.
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PMID:Endothelin-1 activates mitogen-activated protein kinases through two independent signalling pathways in rat astrocytes. 798 Jun 11

Rat-1 fibroblasts were transfected with a cDNA encoding the mouse delta opioid receptor. Two separate clones, D2 (which expressed some 6 pmol of the receptor/mg of membrane protein) and DOE (which expressed some 0.2 pmol/mg of membrane protein), were examined in detail. With membranes from both clones, the opioid agonist [D-Ala2]leucine enkephalin (DADLE) caused stimulation of high-affinity GTPase activity and of the binding of guanosine 5'-[gamma-[35S]thio]triphosphate, and inhibition of forskolin-amplified adenylate cyclase activity. DADLE also induced phosphorylation and activation of both the p42MAPK (42 kDa isoform) and p44MAPK (44 kDa isoform) members of the mitogen-activated protein kinase (MAP kinase) family. All of these effects of DADLE were prevented in both clones by pretreatment of the cells with pertussis toxin. The maximal response that could be produced by DADLE in direct assays of G-protein activation were substantially greater in clone D2 than in clone DOE, but in both clones essentially full phosphorylation of both p42MAPK and p44MAPK could be achieved. EC50 values for DADLE stimulation of GTPase activity and for activation of p44MAPK were substantially lower in clone D2 than in clone DOE. Moreover, in both clones the EC50 value for DADLE stimulation of p44MAPK was substantially lower than that for stimulation of GTPase activity, and the Hill coefficients for agonist activation of p44MAPK (h > 1) displayed marked co-operativity whereas those for G-protein activation did not (h 0.8-1.0). DADLE activation of p44MAPK showed more sustained kinetics in clone D2 than in clone DOE. By contrast, lysophosphatidic acid, acting at an endogenously expressed G-protein-coupled receptor, also activated p44MAPK in both clones in a pertussis toxinsensitive manner, but both the kinetics and the concentration-response curve for activation of p44MAPK by this ligand were similar. As with other systems, maintained cellular levels of a cAMP analogue prevented the effects of both G-protein-coupled receptors on activation of p44MAPK. These results demonstrate for the first time that an opioid receptor, at least when expressed in Rat-1 fibroblasts, is able to initiate activation of the MAP kinase cascade in a G1-dependent manner, and show that only a very small proportion of the cellular G1 population is required to be activated to result in full phosphorylation of the p42MAPK and p44MAPK MAP kinases.
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PMID:Agonist activation of p42 and p44 mitogen-activated protein kinases following expression of the mouse delta opioid receptor in Rat-1 fibroblasts: effects of receptor expression levels and comparisons with G-protein activation. 894 92

The influence of aniso-osmolarity on the activity of the MAP kinases Erk-1 and Erk-2 was studied in C6 glioma cells. Hypo-osmotic treatment (205 mosmol/l) led to an increased activity of Erk-1 and Erk-2 within 3 min, which became maximal at 10 min and returned to basal level within 120 min. In contrast, Erk activity was reduced under hyper-osmotic conditions (405 mosmol/l), compared to the normo-osmotic control (305 mosmol/l). Erk activation was accompanied by a mobility shift of Raf-1. Hypo-osmotic exposure increased the cytosolic Ca2+ concentration ([Ca2+]i). Absence of extracellular Ca2+ largely abolished the [Ca2+]i response to hypo-osmolarity, whereas Erk activation following hypo-osmotic stimulation remained unaffected, suggesting a Ca2+ independence of the osmosignalling pathway to the MAP kinases. Both the Ca2+ response as well as the Erk activation following hypo-osmotic exposure were maintained in the presence of the phospholipase C inhibitor U73122. Application of 8-CPT cAMP, forskolin/isobutylmethylxanthine or isoproterenol blocked Erk activation following hypo-osmotic treatment of the cells, suggesting a role of the Ras/Raf pathway upstream from Erk-1 and Erk-2. Protein kinase C (PKC) is unlikely to play a role in the hypo-osmolarity- induced signalling towards MAP kinases, as revealed by inhibition of PKC with Go6850. Inhibition of pertussis- or cholera toxin-sensitive G-proteins as well as inhibition of tyrosine kinases with genistein and of PI3 kinase by wortmannin had no effect on the Erk response to hypo-osmolarity. It is concluded that osmosignalling in C6 glioma cells differs upstream of the MAP kinases from that observed in primary rat astrocytes, H4IIE rat hepatoma cells and isolated rat hepatocytes.
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PMID:Osmosignalling in C6 glioma cells. 900 90


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