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:2.7.12.2 (MEK)
18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mammalian group IIA secretory phospholipase A(2) (sPLA(2)) is believed to play an important role in inflammation and cell injury. The present study underlines the importance of group IIA sPLA(2) in the regulation of iNOS. Treatment of cells with sPLA(2) induced protein expression and mRNA accumulation of iNOS in a dose-dependent manner. The pretreatment of cells with rho-BPB or SCA, selective sPLA(2) inhibitors, inhibited sPLA(2)-induced iNOS expression. sPLA(2) stimulated the simultaneous activation of two classes of mitogen-activated protein kinases ERK and JNK, but did not stimulate p38 MAPK. PD98059, a selective MEK inhibitor, inhibited sPLA(2)-induced nitrite production and iNOS expression as well as ERK phosphorylation. In addition, pretreatment of rho-BPB or SCA also resulted in inhibition of sPLA(2)-induced ERK phosphorylation. The sPLA(2) signaling mechanisms involving the activation of transcription factor NF-kappaB were studied in the same cells. That stimulation of cells with sPLA(2) caused NF-kappaB activation in a time-dependent manner was shown by the detection of NF-kappaB-specific DNA-protein binding and by IkappaBalpha degradation. sPLA(2)-induced NF-kappaB activation was prevented in the presence of rho-BPB. Furthermore, the NF-kappaB inhibitor PDTC suppressed sPLA(2)-induced nitrite production and iNOS expression as well as IkappaBalpha degradation. The results strongly suggest that group IIA sPLA(2) induces iNOS in macrophages and that this induction occurs through ERK and NF-kappaB.
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PMID:Group IIA secretory phospholipase A(2) stimulates inducible nitric oxide synthase expression via ERK and NF-kappaB in macrophages. 1153 69

Endotoxin (lipopolysaccharide, LPS) is a component of the outer membrane of Gram-negative bacteria and promotes the activation of macrophages and microglia. Although these cells are highly LPS-responsive, they serve unique tissue-specific functions and exhibit different LPS sensitivities. Accordingly, it was of interest to evaluate whether these biological differences reside in variations within LPS signaling pathways between these two cell types. Because the mitogen-activated protein kinases ERK-1 and ERK-2 have been implicated in the control of many immune responses, we tested the concept that they are a key indicator for differences in cellular LPS sensitivity. We observed that murine RAW 264.7 macrophages and murine BV-2 microglial cells both respond to LPS by exhibiting increased IkappaBalpha degradation, enhanced NF-kappaB DNA binding activity, and elevated nitric oxide and interleukin-1beta production. Although LPS potently stimulates ERK activation in RAW 264.7 macrophages, it does not activate ERK-1/-2 in BV-2 microglia. Moreover, antagonism of the MEK/ERK pathway potentiates LPS-stimulated nitric oxide production, suggesting that LPS-stimulated ERK activation can exert inhibitory effects in macrophage-like cells. These data support the idea that ERK activation is not a required function of LPS-mediated signaling events and illustrate that alternative/additional pathways for LPS action exist in these cell types.
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PMID:A differential role for the mitogen-activated protein kinases in lipopolysaccharide signaling: the MEK/ERK pathway is not essential for nitric oxide and interleukin 1beta production. 1178 32

NF-kappaB is sequestered in the cytoplasm by the inhibitory IkappaB proteins. Stimulation of cells by agonists leads to the rapid phosphorylation of IkappaBs leading to their degradation that results in NF-kappaB activation. IKK-1 and IKK-2 are two direct IkappaB kinases. Two recently identified novel IKKs are IKK-i and TBK-1. We have cloned, expressed, and purified to homogeneity recombinant human (rh)IKK-i and rhTBK-1 and compared their enzymatic properties with those of rhIKK-2. We show that rhIKK-i and rhTBK-1 are enzymatically similar to each other. We demonstrate by phosphopeptide mapping and site-specific mutagenesis that rhIKK-i and rhTBK-1 are phosphorylated on serine 172 in the mitogen-activated protein kinase kinase activation loop and that this phosphorylation is necessary for kinase activity. Also, rhIKK-i and rhTBK-1 have differential peptide substrate specificities compared with rhIKK-2, the mitogen-activated protein kinase kinase activation loop of IKK-2 being a more favorable substrate than the IkappaBalpha peptide. Finally, using analogs of ATP, we demonstrate unique differences in the ATP-binding sites of rhIKK-i, rhTBK-1, and rhIKK-2. Thus, although these IKKs are structurally similar, their enzymatic properties may provide insights into their unique functions.
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PMID:IKK-i and TBK-1 are enzymatically distinct from the homologous enzyme IKK-2: comparative analysis of recombinant human IKK-i, TBK-1, and IKK-2. 1183 43

Human alveolar macrophages (HAM) express FcalphaR receptors for immunoglobulin (Ig)A which could link humoral and cellular branches of lung immunity. Here, we investigate the effects of polymeric (p-IgA) and secretory (S-IgA) IgA interaction with Fc(alpha)R on lipopolysaccharide (LPS)- and phorbol myristate acetate (PMA)-activated respiratory burst and TNF-alpha release by HAM. Activation of HAM with LPS and PMA increases the respiratory burst and TNF-alpha release through activation of the extracellular signal-related protein kinases 1 and 2 (ERK1/2) pathway, because these effects are inhibited by treatment of HAM with PD98059, a selective inhibitor of mitogen-activated protein (MAP)/ERK kinases (MEK) pathway. S-IgA and p-IgA downregulate the LPS-increased respiratory burst in HAM through an inhibition of ERK1/2 activity. In contrast, p- and S-IgA induce an increase in the respiratory burst of PMA-treated HAM. This effect is associated with an upregulation by IgA of the PMA-induced phosphorylation of ERK1/2 and is also inhibited by PD98059. Moreover, p-IgA and S-IgA enhance TNF-alpha release by HAM through an alternative pathway distinct from ERK1/2. Because LPS is known to activate nuclear factor-kappaB (NF-kappaB) in HAM, we evaluate the effect of IgA on NF-kappaB. Treatment of HAM with LPS, p- and S-IgA, but not PMA, induces NF-kappaB activation through IkappaBalpha phosphorylation and subsequent proteolysis. Antioxidants, namely N-acetylcysteine (NAC) and glutathione (GSH), have no effects on IgA-mediated NF-kappaB nuclear translocation and only a minor and late effect on that of LPS, suggesting that reactive oxygen intermediates (ROI) play a minor role in HAM activation through NF-kappaB. TNF-alpha release by LPS-activated HAM is sensitive to NF-kappaB inhibition and only partly to oxidant scavenging. In contrast, TNF-alpha release by IgA-treated HAM is not dependent on oxidants and only partly dependent on NF-kappaB. Our results show a differential HAM regulation by IgA through both dependent and independent modulation of ERK pathway. In addition, IgA activates NF-kappaB and this effect was independent on oxidants. These data may help to understand the role of IgA in both lung protection and inflammation.
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PMID:Effect of IgA on respiratory burst and cytokine release by human alveolar macrophages: role of ERK1/2 mitogen-activated protein kinases and NF-kappaB. 1186 40

We showed previously that epithelial growth factor (EGF) receptor (EGFR) signaling is triggered by metallic compounds associated with ambient air particles. Specifically, we demonstrated that As, Zn, and V activated the EGFR tyrosine kinase and the downstream kinases MEK1/2 and ERK1/2. In this study, we examined the role of Ras in EGFR signaling and the nuclear factor-kappaB (NF-kappaB) activation pathway and the possible interaction between these two signaling pathways in a human airway epithelial cell line (BEAS-2B) exposed to As, V, or Zn ions. Each metal significantly increased Ras activity, and this effect was inhibited by the EGFR tyrosine kinase activity inhibitor PD-153035. Adenoviral-mediated overexpression of a dominant-negative mutant form of Ras(N17) significantly blocked MEK1/2 or ERK1/2 phosphorylation in As-, Zn-, or V-exposed BEAS-2B cells but caused little inhibition of V-, Zn- or EGF-induced EGFR tyrosine phosphorylation. This confirmed Ras as an important intermediate effector in EGFR signaling. Interestingly, V, but not As, Zn, or EGF, induced IkappaBalpha serine phosphorylation, IkappaBalpha breakdown, and NF-kappaB DNA binding. Moreover, PD-153035 and overexpression of Ras(N17) each significantly blocked V-induced IkappaBalpha breakdown and NF-kappaB activation, while inhibition of MEK activity with PD-98059 failed to do so. In summary, exposure to As, Zn, and V initiated EGFR signaling and Ras-dependent activation of MEK1/2 and ERK1/2, but only V induced Ras-dependent NF-kappaB nuclear translocation. EGFR signaling appears to cross talk with NF-kappaB signaling at the level of Ras, but additional signals appear necessary for NF-kappaB activation. Together, these data suggest that, in V-treated BEAS-2B cells, Ras-dependent signaling is essential, but not sufficient, for activation of NF-kappaB.
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PMID:Role of Ras in metal-induced EGF receptor signaling and NF-kappaB activation in human airway epithelial cells. 1194 69

We have shown previously that the transduction of a number of human tumor cell lines with an adenovirus (AV1Y28) expressing a single-chain antibody fragment (scFv) directed against Ras proteins results in radiosensitization. Because Ras is involved in the regulation of a number of transcription factors, we have determined the effects of this adenovirus on the activation of nuclear factor-kappaB (NF-kappaB), a radiation-responsive transcription factor associated with cell survival. In U251 human glioma cells, radiation-induced NF-kappaB was significantly attenuated by prior transduction of the anti-Ras scFv adenovirus. This effect appeared to involve an inhibition of IkappaB kinase activity and IkappaBalpha phosphorylation. Inhibitors to the Ras effectors mitogen-activated protein kinase kinase, phosphatidylinositol 3-kinase, and p38, however, did not reduce radiation-induced NF-kappaB. Whereas AV1Y28 inhibited NF-kappaB activation by hydrogen peroxide and ferricyanide, it had no effect of tumor necrosis factor-alpha-induced NF-kappaB activation. These results are consistent with a novel Ras-dependent, oxidant-specific signaling pathway mediating the activation of NF-kappaB. In additional cell lines radiosensitized by AV1Y28, radiation-induced NF-kappaB activation was also inhibited by the anti-Ras scFv, whereas in cell lines not radiosensitized, radiation did not activate NF-kappaB. This correlation suggested that AV1Y28-mediated radiosensitization involved the inhibition of radiation-induced NF-kappaB activation. However, inhibition of NF-kappaB activation via the expression of a dominant-negative form of IkappaBalpha in U251 cells had no effect on radiation-induced cell killing and did not influence AV1Y28-mediated radiosensitization. Therefore, whereas AV1Y28 inhibits radiation-induced NF-kappaB activation, this process does not appear to play a direct role in its radiosensitizing actions.
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PMID:Inhibition of radiation-induced nuclear factor-kappaB activation by an anti-Ras single-chain antibody fragment: lack of involvement in radiosensitization. 1195 90

We have previously demonstrated that hydrogen peroxide (H(2)O(2)) treatment of murine 70Z/3 pre-B lymphocytes inhibits the immune response to lipopolysaccharide by attenuating signaling through c-Jun N-terminal kinase (JNK) activation. In the present study, we further examined the signaling intermediates responsible for immunosuppression by H(2)O(2), focusing on NF-kappaB, a dimeric transcription factor whose activation is implicated in a number of immune response. Treatment of 70Z/3 pre-B cells with H(2)O(2) caused activation of NF-kappaB in the nuclei by detection of NF-kappaB specific DNA binding, concomitant with phosphorylation of IkappaBalpha. H(2)O(2) stimulation of NF-kappaB occurred within 20 min of treatment, reached maximum level at 60 min, and sustained for 2 h or more. Especially, MEK1 may contribute to H(2)O(2)-induced NF-kappaB activation as shown in the inhibition of NF-kappaB binding activity by the MEK1 inhibitor, PD 98059, and H(2)O(2)-induced MEK1 activation. However, H(2)O(2) exhibited no effect on the activity of Raf-1 kinase, which was an upstream activator of MEK1. Furthermore, B-58l and alpha-hydroxyfarnesylphosphonic acid, two inhibitors of Ras, did not block NF-kappaB activation. In addition, the transient transfection of a dominant negative Ras (RasN17) construct showed a negligible inhibitory effect on the activation of NF-kappaB by H(2)O(2). Instead, treatment of 70Z/3 cells with H(2)O(2) resulted in the activation of MAPK kinase kinase 1 (MEKK1) as well as JNK. Therefore, our data suggest that H(2)O(2) regulates the activity of NF-kappaB by MEK1 activation through MEKK1-dependent but Ras/Raf-independent mechanism.
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PMID:Raf-independent and MEKK1-dependent activation of NF-kappaB by hydrogen peroxide in 70Z/3 pre-B lymphocyte tumor cells. 1253 30

Cell-cell contact between human retinal pigment epithelium (hRPE) cells and monocytes occurs in many retinal diseases involving blood-retinal barrier breakdown. This study investigates chemokine secretion induced by co-culture of hRPE cells and monocytes and illustrates the roles of p38 kinase, ERK, JNK/SAPK and NF-kappaB-inducing kinase signaling pathways for hRPE IL-8 and MCP-1 secretion induced in hRPE by co-culture with monocytes. Co-culture of hRPE cells with monocytes increased steady-state IL-8 and MCP-1 mRNA and protein secretion. Stimulation of hRPE cells by monocytes resulted in prominent increases in p38, ERK1/2 and JNK/SAPK phosphorolation, IkappaBalpha degradation, and NF-kappaB nuclear translocation. The induced IL-8 and MCP-1 proteins were almost completely supporessed by U0126, a specific mitogen-activated protein kinase kinase (MEK) inhibitor, or by SB203580, a selective p38 inhibitor. Chemokine secretion was completely blocked by simultaneous administration of U0126 and SB203580. Induction of IL-8 and MCP-1 was abrogated by Ro318220, an inhibitor of PKC, as well as by genistein or herbimycin A, inhibitors of PTK. In addition, anti-inflammatory drugs dexamethasone (DEX) and cyclosporin A (CSA) both blocked activation of JNKS/SAPK and the cell-cell contact induced production of hRPE IL-8 and MCP-1, while activation of p38 and ERK was only inhibited by DEX, but not by CSA. These results suggest that activation of DEX-sensitive, CSA-resistant MEK/ERK and p38 pathways, and activation of NF-kappaB, PKC, and PTK are essential for IL-8 and MCP-1 expression by hRPE cells.
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PMID:Human RPE-monocyte co-culture induces chemokine gene expression through activation of MAPK and NIK cascade. 1269 21

Recently, there have been considerable efforts to search for naturally occurring substances for the intervention of carcinogenesis. Many components derived from dietary or medicinal plants have been found to possess substantial chemopreventive properties. Curcumin, a yellow coloring ingredient of turmeric (Curcuma longa L., Zingiberaceae), has been shown to inhibit experimental carcinogenesis and mutagenesis, but molecular mechanisms underlying its chemopreventive activities remain unclear. In the present work, we assessed the effects of curcumin on 12-O- tetradecanoylphorbol-13-acetate (TPA)-induced expression of cyclooxygenase-2 (COX-2) in female ICR mouse skin. Topical application of the dorsal skin of female ICR mice with 10 nmol TPA led to maximal induction of cox-2 mRNA and protein expression at approximately 1 and 4 h, respectively. When applied topically onto shaven backs of mice 30 min prior to TPA, curcumin inhibited the expression of COX-2 protein in a dose-related manner. Immunohistochemical analysis of TPA-treated mouse skin revealed enhanced expression of COX-2 localized primarily in epidermal layer, which was markedly suppressed by curcumin pre-treatment. Curcumin treatment attenuated TPA- stimulated NF-kappaB activation in mouse skin, which was associated with its blockade of degradation of the inhibitory protein IkappaBalpha and also of subsequent translocation of the p65 subunit to nucleus. TPA treatment resulted in rapid activation via phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinases, which are upstream of NF-kappaB. The MEK1/2 inhibitor U0126 strongly inhibited NF-kappaB activation, while p38 inhibitor SB203580 failed to block TPA-induced NF-kappaB activation in mouse skin. Furthermore, U0126 blocked the IkappaBalpha phosphorylation by TPA, thereby blocking the nuclear translocation of NF-kappaB. Curcumin inhibited the catalytic activity of ERK1/2 in mouse skin. Taken together, suppression of COX-2 expression by inhibiting ERK activity and NF-kappaB activation may represent molecular mechanisms underlying previously reported antitumor promoting effects of this phytochemical in mouse skin tumorigenesis.
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PMID:Curcumin inhibits phorbol ester-induced expression of cyclooxygenase-2 in mouse skin through suppression of extracellular signal-regulated kinase activity and NF-kappaB activation. 1284 82

We have recently reported that tyrosine kinase, p56(lck) regulates cell motility and nuclear factor kappaB-mediated secretion of urokinase-type plasminogen activator (uPA) through tyrosine phosphorylation of IkappaBalpha following hypoxia/reoxygenation (Mahabeleshwar, G. H., and Kundu, G. C. (2003) J. Biol. Chem. 278, 52598-52612). However, the role of hypoxia/reoxygenation (H/R) on ERK1/2-mediated uPA secretion and cell motility and the involvement of p56(lck) and EGF receptor in these processes in breast cancer cells is not well defined. We provide here evidence that H/R induces Lck kinase activity and Lck-dependent tyrosine phosphorylation of EGF receptor in highly invasive (MDA-MB-231) and low invasive (MCF-7) breast cancer cells. H/R also stimulates MEK-1 and ERK1/2 phosphorylations, and H/R-induced phosphorylations were suppressed by the dominant negative form of Lck (DN Lck, K273R) as well as pharmacological inhibitors of EGF receptor and Lck indicating that EGF receptors and Lck are involved in these processes. Transfection of these cells with wild type Lck or Lck F505 (Y505F) but not with Lck F394 (Y394F) induced phosphorylations of EGF receptor followed by MEK-1 and ERK1/2, suggesting that Lck is upstream of EGF receptor and Tyr-394 of Lck is crucial for these processes. H/R also induced uPA secretion and cell motility in these cells. DN Lck and inhibitors of Lck, EGF receptor, and MEK-1 suppressed H/R-induced uPA secretion and cell motility. To our knowledge, this is the first report that p56(lck) in presence of H/R regulates MEK-1-dependent ERK1/2 phosphorylation and uPA secretion through tyrosine phosphorylation of EGF receptor, and it further demonstrates that all of these signaling molecules ultimately control the motility of breast cancer cells.
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PMID:Tyrosine kinase, p56lck-induced cell motility, and urokinase-type plasminogen activator secretion involve activation of epidermal growth factor receptor/extracellular signal regulated kinase pathways. 1469 20


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