Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Madin-Darby canine kidney D1 cells extracellular nucleotides activate P2Y receptors that couple to several signal transduction pathways, including stimulation of multiple phospholipases and adenylyl cyclase. For one class of P2Y receptors, P2Y2 receptors, this stimulation of adenylyl cyclase and increase in cAMP occurs via the conversion of phospholipase A2 (PLA2)-generated arachidonic acid (AA) to prostaglandins (e.g. PGE2). These prostaglandins then stimulate adenylyl cyclase activity, presumably via activation of prostanoid receptors. In the current study we show that agents that increase cellular cAMP levels (including PGE2, forskolin, and the beta-adrenergic agonist isoproterenol) can inhibit P2Y receptor-promoted AA release. The protein kinase A (PKA) inhibitor H89 blocks this effect, suggesting that this feedback inhibition occurs via activation of PKA. Studies with PGE2 indicate that inhibition of AA release is attributable to inhibition of mitogen-activated protein kinase activity and in turn of P2Y receptor stimulated PLA2 activity. Although cAMP/PKA-mediated inhibition occurs for P2Y receptor-promoted AA release, we did not find such inhibition for epinephrine (alpha1-adrenergic) or bradykinin-mediated AA release. Taken together, these results indicate that negative feedback regulation via cAMP/PKA-mediated inhibition of mitogen-activated protein kinase occurs for some, but not all, classes of receptors that promote PLA2 activation and AA release. We speculate that receptor-selective feedback inhibition occurs because PLA2 activation by different receptors in Madin-Darby canine kidney D1 cells involves the utilization of different signaling components that are differentially sensitive to increases in cAMP or, alternatively, because of compartmentation of signaling components.
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PMID:Inhibition of phospholipase A2-mediated arachidonic acid release by cyclic AMP defines a negative feedback loop for P2Y receptor activation in Madin-Darby canine kidney D1 cells. 1018 81

1. Methyl arachidonyl fluorophosphonate (MAFP), an inhibitor of phospholipase A2 (PLA2), has been widely used to assess the roles of PLA2 in various cell functions. Here, we report on a novel action of this compound at concentrations similar to those used for PLA2 inhibition. 2. The murine macrophage J774 released a large amount of prostaglandin E2 (PGE2) by MAFP (1-30 microM), which was abolished by indomethacin and NS-398 but not by valeryl salicylate, and results from increased cyclo-oxygenase-2 (COX-2) protein levels and gene expression. 3. This PGE2 release was blocked by inhibitors of tyrosine kinase (genistein), protein kinase C (PKC) (Ro 31-8220, Go 6976 or LY 379196), mitogen-activated protein kinase kinase (MEK) (PD 098059) or p38 mitogen-activated protein kinase (MAPK) (SB 203580). 4. Consistent with these results, MAFP caused membrane translocation of PKCbetaI and betaII isoforms and activated extracellular signal-regulated kinase (ERK) and p38 MAPK. 5. In accordance with these effects of MAFP, PKC activator phorbol 12-myristate 13-acetate (PMA) increased PGE2 release and caused activation of PKCbeta, ERKs and p38 MAPK. 6. This is the first report that the PLA2 inhibitor, MAFP, can induce COX-2 gene expression and PGE2 synthesis via the PKC-, ERK- and p38 MAPK-dependent pathways. Thus, the use of MAFP as a PLA2 inhibitor should be treated with caution.
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PMID:Induction of cyclo-oxygenase-2 expression by methyl arachidonyl fluorophosphonate in murine J774 macrophages: roles of protein kinase C, ERKs and p38 MAPK. 1021 36

Macrophage migration inhibitory factor (MIF) is an important pro-inflammatory mediator with the unique ability to counter-regulate the inhibitory effects of glucocorticoids on immune cell activation. MIF is released from cells in response to glucocorticoids, certain pro-inflammatory stimuli, and mitogens and acts to regulate glucocorticoid action on the ensuing inflammatory response. To gain insight into the molecular mechanism of MIF action, we have examined the role of MIF in the proliferation and intracellular signaling events of the well characterized, NIH/3T3 fibroblast cell line. Both endogenously secreted and exogenously added MIFs stimulate the proliferation of NIH/3T3 cells, and this response is associated with the activation of the p44/p42 extracellular signal-regulated (ERK) mitogen-activated protein kinases (MAP). The MIF-induced activation of these kinases was sustained for a period of at least 24 h and was dependent upon protein kinase A activity. We further show that MIF regulates cytosolic phospholipase A2 activity via a protein kinase A and ERK dependent pathway and that the glucocorticoid suppression of cytokine-induced cytoplasmic phospholipase A2 activity and arachidonic acid release can be reversed by the addition of recombinant MIF. These studies indicate that the sustained activation of p44/p42 MAP kinase and subsequent arachidonate release by cytoplasmic phospholipase A2 are important features of the immunoregulatory and intracellular signaling events initiated by MIF and provide the first insight into the mechanisms that underlie the pro-proliferative and inflammatory properties of this mediator.
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PMID:Sustained mitogen-activated protein kinase (MAPK) and cytoplasmic phospholipase A2 activation by macrophage migration inhibitory factor (MIF). Regulatory role in cell proliferation and glucocorticoid action. 1036 64

The effect of secretory phospholipase A2 (sPLA2) on intracellular Ca2+ signaling in human astrocytoma cells was studied. sPLA2 increased cytosolic [Ca2+] ([Ca2+]c) in both Ca2+-containing and Ca2+-free medium, thus suggesting Ca2+ release from intracellular stores. The activation by sPLA2 of arachidonate release via cytosolic PLA2 (cPLA2) was also independent of extracellular Ca2+. As sPLA2 requires Ca2+ for activity, these results indicate that both Ca2+ mobilization and cPLA2 activation induced by sPLA2 are unrelated to phospholipase activity but dependent on signaling mechanisms. The sPLA2-induced [Ca2+]c peak was sensitive to Bordetella pertussis toxin and inhibited by caffeine, suggesting its mediation by inositol 1,4,5-trisphosphate (IP3). sPLA2 induced tyrosine phosphorylation and membrane targeting of phospholipase Cgamma-1 (PLCgamma-1). Moreover, the Ca2+ peak was sensitive to protein tyrosine kinase inhibitors. sPLA2 activates two signaling pathways: one leading to the activation of the MAP kinase/cPLA2 cascade and another leading to PLCgamma activation and Ca2+ release.
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PMID:Secretory phospholipase A2 induces phospholipase Cgamma-1 activation and Ca2+ mobilization in the human astrocytoma cell line 1321N1 by a mechanism independent of its catalytic activity. 1038 50

Arachidonic acid (AA) is generated via Rac-mediated phospholipase A2 (PLA2) activation in response to growth factors and cytokines and is implicated in cell growth and gene expression. In this study, we show that AA activates the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in a time- and dose-dependent manner. Indomethacin and nordihydroguaiaretic acid, potent inhibitors of cyclooxygenase and lipoxygenase, respectively, did not exert inhibitory effects on AA-induced SAPK/JNK activation, thereby indicating that AA itself could activate SAPK/JNK. As Rac mediates SAPK/JNK activation in response to a variety of stressful stimuli, we examined whether the activation of SAPK/JNK by AA is mediated by Rac1. We observed that AA-induced SAPK/JNK activation was significantly inhibited in Rat2-Rac1N17 dominant-negative mutant cells. Furthermore, treatment of AA induced membrane ruffling and production of hydrogen peroxide, which could be prevented by Rac1N17. These results suggest that AA acts as an upstream signal molecule of Rac, whose activation leads to SAPK/JNK activation, membrane ruffling and hydrogen peroxide production.
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PMID:Arachidonic acid induces the activation of the stress-activated protein kinase, membrane ruffling and H2O2 production via a small GTPase Rac1. 1038 21

Human platelets are known to contain three forms of mitogen-activated protein kinases; erk1, erk2, and p38MAPK. However the role(s) of mitogen-activated protein kinase cascades in platelet function remains to be determined. Evidence has been presented that suggests that these kinases are involved in the cytoskeleton and in the activation of phospholipase A2; however, other functions seem likely. The object of the present study was to examine the role of the p38MAPK in platelet function using anisomycin, a reported activator of p38MAPK, and SB203580, an inhibitor of p38MAPK. Thrombin and collagen caused the phosphorylation of p38MAPK and this was inhibited by SB203580. Anisomycin did not cause the aggregation of either intact or saponin-permeabilised platelets. In addition anisomycin failed to produce synergistic aggregation responses with submaximal concentrations of collagen, thrombin, the thromboxane mimetic U46619, or the calcium ionophore A23187. There was no detectable phosphorylation of p38MAPK in either intact platelets or platelet lysates incubated with anisomycin. Anisomycin also failed to modulate p38MAPK phosphorylation in response to submaximal concentrations of collagen, thrombin, U46619, or A23187. In contrast anisomycin did cause p38MAPK phosphorylation in rabbit lung and C3 fibroblasts and in rabbit lung fibroblast lysates. These data demonstrate that anisomycin has no detectable effect on either platelet function or p38MAPK phosphorylation and, therefore, that anisomycin has proven to be an ineffective tool to define the role that p38MAPK plays in platelet function.
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PMID:Anisomycin does not activate p38MAPK in human platelets. 1055 82

Oxygen derived free radicals and other reactive oxygen species (ROS) are involved in a variety of disease states, which can have cardiac and vascular implications. The present study was performed to investigate the mechanism of ROS-induced vasoconstriction and the influence of ROS on the functional integrity of isolated rat thoracic aorta. ROS were generated by means of electrolysis (30 mA, during 0.5, 1, 2 or 3 min) of the organ bath fluid. ROS induced a transient (approximately 60 min) vasoconstriction and the maximally induced contraction was dependent on the duration of electrolysis. Dimethyl sulfoxide (DMSO) diminished the ROS-induced vasoconstriction almost completely, indicating a major influence of hydroxyl radicals on contractility. The dual cyclooxygenase/lipoxygenase inhibitor, meclofenamate, completely prevented the ROS-induced vasoconstriction. The phospholipase A2 (PLA2) inhibitor, oleyloxyethyl phosphorylcholine, was able to reduce the vasoconstriction elicited by ROS by approximately 70%. Conversely, the specific cytoplasmic PLA2 inhibitor arachidonyl trifluoromethylketone proved ineffective in this respect. By using the specific mitogen-activated protein kinase (MAPkinase) kinase inhibitor PD98059, it was shown that the activation of extracellular-regulated kinase (ERK) MAPkinase contributes to the ROS-induced vasoconstriction. The effects of ROS on the functional integrity of the aortae were investigated, in particular with respect to receptor (alpha1-adrenoceptor) and non-receptor-mediated contractile responses (high potassium solution). In addition, both the endothelium dependent (methacholine) and endothelium independent (sodium nitroprusside) vasorelaxation were investigated before and after ROS exposure. Electrolysis periods of 0.5 and 1 min induced a modest leftward shift of the concentration response curves for the alpha1-adrenoceptor agonist methoxamine. Longer electrolysis periods of 2 and 3 min additionally decreased the maximal response to (alpha1-adrenoceptor stimulation. Methacholine-induced vasorelaxation proved diminished in aortae subjected to electrolysis (0.5, 1, 2 and 3 min), whereas relaxation to sodium nitroprusside was nearly complete in all groups. KCl-induced contractions proved attenuated only after longer electrolysis periods of 2 and 3 min. This ROS-induced deterioration of functional integrity was almost completely prevented by 0.6% DMSO. From these results we may conclude that ROS induce an eicosanoid and ERK MAPkinase-mediated vasoconstriction in isolated rat thoracic aorta. In addition, exposure to ROS leads to a deterioration of functional integrity characterized by endothelial dysfunction and decreased contractile function.
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PMID:Reactive oxygen species-induced aortic vasoconstriction and deterioration of functional integrity. 1068 67

Recently, a novel peptide (Trp-Lys-Tyr-Met-Val-D-Met, WKYMVm) has been shown to induce superoxide generation in human monocytes. The peptide stimulated phospholipase A2 (PLA2) activity in a concentration- and time-dependent manner. Superoxide generation as well as arachidonic acid (AA) release evoked by treatment with WKYMVm could be almost completely blocked by pretreatment of the cells with cytosolic PLA2 (cPLA2)-specific inhibitors. The involvement of cPLA2 in the peptide-induced AA release was further supported by translocation of cPLA2 to the nuclear membrane of monocytes incubated with WKYMVm. WKYMVm-induced phosphatidylbutanol formation was completely abolished by pretreatment with PKC inhibitors. Immunoblot showed that monocytes express phospholipase D1 (PLD1), but not PLD2. GF109203X as well as butan-1-ol inhibited peptide-induced superoxide generation in monocytes. Furthermore, the interrelationship between the two phospholipases, cPLA2 and PLD1, and upstream signaling molecules involved in WKYMVm-dependent activation was investigated. The inhibition of cPLA2 did not blunt peptide-stimulated PLD1 activation or vice versa. Intracellular Ca2+ mobilization was indispensable for the activation of PLD1 as well as cPLA2. The WKYMVm-dependent stimulation of cPLA2 activity was partially dependent on the activation of PKC and mitogen-activated protein kinase, while PKC activation, but not mitogen-activated protein kinase activation, was an essential prerequisite for stimulation of PLD1. Taken together, activation of the two phospholipases, which are absolutely required for superoxide generation, takes place through independent signaling pathways that diverge from a common pathway at a point downstream of Ca2+.
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PMID:Independent functioning of cytosolic phospholipase A2 and phospholipase D1 in Trp-Lys-Tyr-Met-Val-D-Met-induced superoxide generation in human monocytes. 1075 2

alpha-Adrenoceptors (alpha1AR) are G protein-coupled receptors and include alpha1A, alpha1B, and alpha1D subtypes corresponding to cloned alpha1a, alpha1b, and alpha1d, respectively. alpha1AR mediate several cardiovascular actions of sympathomimetic amines such as vasoconstriction and cardiac inotropy, hypertrophy, metabolism, and remodeling. alpha1AR subtypes are products of separate genes and differ in structure, G protein-coupling, tissue distribution, signaling, regulation, and functions. Both alpha(1A)AR and alpha(1B)AR mediate positive inotropic responses. On the other hand, cardiac hypertrophy is primarily mediated by alpha(1A)AR. The only demonstrated major function of alpha(1D)AR is vasoconstriction. alpha1AR are coupled to phospholipase C, phospholipase D, and phospholipase A2; they increase intracellular Ca2+ and myofibrillar sensitivity to Ca2+ and cause translocation of specific phosphokinase C isoforms to the particulate fraction. Cardiac hypertrophic responses to alpha1AR agonists might involve activation of phosphokinase C and mitogen-activated protein kinase via Gq x alpha1AR subtypes might interact with each other and with other receptors and signaling mechanisms.
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PMID:Cardiovascular alpha1-adrenoceptor subtypes: functions and signaling. 1077 55

Cytosolic group IV phospholipase A2 (cPLA2) is a ubiquitously expressed enzyme with key roles in intracellular signaling. The current paradigm for activation of cPLA2 by stimuli proposes that both an increase in intracellular calcium and mitogen-activated protein kinase-mediated phosphorylation occur together to fully activate the enzyme. Calcium is currently thought to be needed for translocation of the cPLA2 to the membrane via a C2 domain, whereas the role of cPLA2 phosphorylation is less clearly defined. Herein, we report that brief exposure of P388D1 macrophages to UV radiation results in a rapid, cPLA2-mediated arachidonic acid mobilization, without increases in intracellular calcium. Thus, increased Ca2+ availability is a dispensable signal for cPLA2 activation, which suggests the existence of alternative mechanisms for the enzyme to efficiently interact with membranes. Our previous in vitro data suggested the importance of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) in the association of cPLA2 to model membranes and hence in the regulation of cPLA2 activity. Experiments described herein show that PtdInsP2 also serves a similar role in vivo. Moreover, inhibition of PtdInsP2 formation during activation conditions leads to inhibition of the cPLA2-mediated arachidonic acid mobilization. These results suggest that cellular PtdInsP2 levels are involved in the regulation of group IV cPLA2 activation.
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PMID:Cellular regulation of cytosolic group IV phospholipase A2 by phosphatidylinositol bisphosphate levels. 1079 4


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