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)

Varicella-zoster virus (VZV) is ultimately dependent upon its host cell for replication. To ensure its reproduction, VZV reorganizes various cellular functions by taking advantage of pre-existing signalling pathways. Recently, it was demonstrated that the activation of stress-related mitogen-activated protein kinase pathways following infection led to increased phosphorylation of cellular transcription factors involved in VZV gene expression. Here, it was shown that members of the extracellular signal-regulated kinase (ERK) pathway are also influenced following VZV infection: c-Raf remained inactive in infected MeWo cells, whereas MEK1/2 and ERK1/2 were phosphorylated transiently, reaching their highest level of phosphorylation at between 10 and 12 h post-infection. Inhibition of this pathway resulted in a severe reduction in viral progeny and in an increased apoptotic response, indicating that the functionality of this cascade is essential for successful high-rate replication. In addition, the activities of Bad, a cytoplasmic target of ERK via ribosomal S6 kinase, and the nuclear-localized target c-Myc were analysed. Bad is a member of the Bcl-2 family and has a key function in regulating apoptosis. Pro-apoptotic functions of Bad are repressed by phosphorylation. A 10-fold increase in Bad phosphorylation at Ser-112 was detected following infection, which was suppressed after inhibition of ERK. The transcription factor c-Myc is involved in the regulation of cell growth and apoptosis. By performing immunoblots and quantitative RT-PCR, suppression of c-Myc expression was demonstrated at both the transcriptional and translational levels in VZV-infected cells. These results suggest that VZV optimizes the conditions for its replication in different ways: upregulation of proviral-acting systems and suppression of potentially antiviral-acting systems.
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PMID:Varicella-zoster virus influences the activities of components and targets of the ERK signalling pathway. 1652 22

In cardiac myocytes, sustained (3 min) intracellular acidosis activates the ERK1/2 (extracellular-signal-regulated kinase 1/2) pathway and, through this pathway, increases sarcolemmal NHE (Na+/H+ exchanger) activity [Haworth, McCann, Snabaitis, Roberts and Avkiran (2003) J. Biol. Chem. 278, 31676-31684]. In the present study, we aimed to determine the time-dependence, pH-dependence and upstream signalling mechanisms of acidosis-induced ERK1/2 activation in ARVM (adult rat ventricular myocytes). Cultured ARVM were subjected to intracellular acidosis for up to 20 min by exposure to NH4Cl, followed by washout with a bicarbonate-free Tyrode solution containing the NHE1 inhibitor cariporide. After the desired duration of intracellular acidosis, the phosphorylation status of ERK1/2 and its downstream effector p90(RSK) (90 kDa ribosomal S6 kinase) were determined by Western blotting. This revealed a time-dependent transient phosphorylation of both ERK1/2 and p90(RSK) by intracellular acidosis (intracellular pH approximately 6.6), with maximum activation occurring at 3 min and a return to basal levels by 20 min. When the degree of intracellular acidosis was varied from approximately 6.8 to approximately 6.5, maximum ERK1/2 phosphorylation was observed at an intracellular pH of 6.64. Inhibition of MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK kinase 1/2) by pre-treatment of ARVM with U0126 or adenoviral expression of dominant-negative D208A-MEK1 protein prevented the phosphorylation of ERK1/2 by sustained intracellular acidosis, as did inhibition of Raf-1 with GW 5074 or ZM 336372. Interference with Ras signalling by the adenoviral expression of dominant-negative N17-Ras protein or with FPT III (farnesyl protein transferase inhibitor III) also prevented acidosis-induced ERK1/2 phosphorylation, whereas inhibiting G-protein signalling [by adenoviral expression of RGS4 or Lsc, the RGS domain of p115 RhoGEF (guanine nucleotide-exchange factor)] or protein kinase C (with bisindolylmaleimide I) had no effect. Our data show that, in ARVM, sustained intracellular acidosis activates ERK1/2 through proximal activation of the classical Ras/Raf/MEK pathway.
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PMID:Ras triggers acidosis-induced activation of the extracellular-signal-regulated kinase pathway in cardiac myocytes. 1683 Nov 26

Klebsiella pneumoniae (KP), an enterobacterium, usually causes urinary tract infection or pneumonia; however, it has caused severe liver abscess in diabetic patients in recent years. How this emerging virulent KP strain causes liver abscess is not known. This study investigates signalling pathways in HepG2 cells infected by virulent KP. Cells were infected with bacteria for various durations and harvested to screen for signalling molecules by Western blotting. Our results showed that phosphorylated mitogen-activated protein kinase (MAPK) kinase (MEK) 1/2, p44/p42 MAPK and p90 ribosomal S6 kinase (p90RSK) were observed and this pathway was inhibited by MEK1/2 inhibitors U0126 and PD98059. Phosphorylation of MEK3/6, p38 kinase and ATF-2 was also observed and this pathway was inhibited by p38 kinase inhibitors SB203850 and SB202190. Toll-like receptor (TLR) 2 and 4 expressions were increased and maximized 2-4 h post infection. The JNK pathway, Elk, MAPKAPK-2 and HSP27 were not activated. These results suggest that KP infections induce signal transduction through TLR2 and TLR4 and activate two downstream MAP kinase pathways, MEK1/2-p44/p42 MAPK-p90RSK and MEK3/6-p38 kinase-ATF-2, but not the JNK pathway in HepG2 cells. The infected HepG2 eventually showed apoptosis and died.
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PMID:Mitogen-activated protein kinase (MAPK) signalling pathways in HepG2 cells infected with a virulent strain of Klebsiella pneumoniae. 1692 65

Evidence is presented that RSK1 (ribosomal S6 kinase 1), a downstream target of MAPK (mitogen-activated protein kinase), directly phosphorylates nNOS (neuronal nitric oxide synthase) on Ser847 in response to mitogens. The phosphorylation thus increases greatly following EGF (epidermal growth factor) treatment of rat pituitary tumour GH3 cells and is reduced by exposure to the MEK (MAPK/extracellular-signal-regulated kinase kinase) inhibitor PD98059. Furthermore, it is significantly enhanced by expression of wild-type RSK1 and antagonized by kinase-inactive RSK1 or specific reduction of endogenous RSK1. EGF treatment of HEK-293 (human embryonic kidney) cells, expressing RSK1 and nNOS, led to inhibition of NOS enzyme activity, associated with an increase in phosphorylation of nNOS at Ser847, as is also the case in an in vitro assay. In addition, these phenomena were significantly blocked by treatment with the RSK inhibitor Ro31-8220. Cells expressing mutant nNOS (S847A) proved resistant to phosphorylation and decrease of NOS activity. Within minutes of adding EGF to transfected cells, RSK1 associated with nNOS and subsequently dissociated following more prolonged agonist stimulation. EGF-induced formation of the nNOS-RSK1 complex was significantly decreased by PD98059 treatment. Treatment with EGF further revealed phosphorylation of nNOS on Ser847 in rat hippocampal neurons and cerebellar granule cells. This EGF-induced phosphorylation was partially blocked by PD98059 and Ro31-8220. Together, these data provide substantial evidence that RSK1 associates with and phosphorylates nNOS on Ser847 following mitogen stimulation and suggest a novel role for RSK1 in the regulation of nitric oxide function in brain.
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PMID:p90 RSK-1 associates with and inhibits neuronal nitric oxide synthase. 1698 26

Multiple stimuli of physiological and pathophysiological significance, including alpha1-adrenoceptor agonists, stimulate the cardiac sarcolemmal Na+/H+ exchanger isoform 1 (NHE1) through activation of the mitogen-activated or extracellular signal-regulated kinase (ERK) kinase (MEK) ERK-90-kDa ribosomal S6 kinase (RSK) signaling cascade. However, the individual contributions of ERK and RSK, which can each phosphorylate the NHE1 regulatory domain, to such stimulation are unknown. In the present study, we have used the novel RSK inhibitor fmk to determine the role of RSK as a direct regulator of NHE1 phosphorylation and activity in response to alpha1-adrenergic stimulation, in ventricular myocytes isolated from the adult rat heart. Initial experiments confirmed that pretreatment of myocytes with fmk before exposure to the alpha1-adrenoceptor agonist phenylephrine inhibited RSK C-terminal kinase activity and thereby RSK N-terminal kinase activation, without affecting MEK or ERK activation. Pretreatment of myocytes with fmk also inhibited phenylephrine-induced increases in NHE1 phosphorylation and the rate of NHE1-mediated H+ efflux under conditions of intracellular acidosis. These findings reveal, for the first time to our knowledge, that RSK is the principal regulator of NHE1 phosphorylation and activity after alpha1-adrenergic stimulation in adult myocardium.
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PMID:Evidence for direct regulation of myocardial Na+/H+ exchanger isoform 1 phosphorylation and activity by 90-kDa ribosomal S6 kinase (RSK): effects of the novel and specific RSK inhibitor fmk on responses to alpha1-adrenergic stimulation. 1714 97

Estradiol prevents neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals. This study investigated whether estradiol modulates the anti-apoptotic signal through the activation of Raf-MEK-ERK and its downstream targets, including 90 ribosomal S6 kinase (p90RSK) and Bad. Adult female rats were ovariectomied and treated with estradiol prior to middle cerebral artery occlusion (MCAO). Brains were collected 24h after MCAO and infarct volumes were analyzed. We confirmed that estradiol significantly reduces infarct volume and decreases the positive cells of TUNEL staining in the cerebral cortex. Estradiol prevents the injury-induced decrease of Raf-1, MEK1/2, and ERK1/2 phosphorylation. Also, it inhibits the injury-induced decrease of p90RSK and Bad phosphorylation. Further, in the presence of estradiol, the interaction of phospho-Bad and 14-3-3 increased, compared with that of oil-treated animals. Our findings suggest that estradiol prevents cell death due to brain injury and that Raf-MEK-ERK cascade activation and its downstream targets, p90RSK, Bad phosphorylation by estradiol mediated these protective effects.
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PMID:Estradiol prevents the injury-induced decrease of 90 ribosomal S6 kinase (p90RSK) and Bad phosphorylation. 1719 35

Activation (phosphorylation) of mitogen-activated protein kinase (MAPK) signal transduction through BRAF and RAS causes a variety of functional effects including cell survival and cell death. In this study, we observed high extracellular signal-regulated kinase (ERK)1/2 phosphorylation levels in clinical melanoma metastases and various melanoma cell lines. Treatment of melanoma cell lines with cisplatin, a potent antitumor agent, increased the level of phosphorylated-ERK (P-ERK)1/2 and enhanced chemoresistance through activation of the cell survival protein 90-kDa ribosomal S6 kinase (RSK)1. The mitogen-activated protein kinase kinase (MEK) inhibitor (U0126) was able to block this effect and reduced cell viability and sensitized cells to cisplatin-induced apoptosis, as shown by PARP cleavage, caspase 3 expression, and annexin-V staining. In conclusion, the MAP kinase-ERK pathway is activated in melanoma and reduces the sensitivity of melanoma to cisplatin. Thus, inhibition of ERK1/2 in combination with selected chemotherapeutic agents may hold promise for more effective therapy of melanoma.
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PMID:ERK1/2 is highly phosphorylated in melanoma metastases and protects melanoma cells from cisplatin-mediated apoptosis. 1750 26

The multidrug resistance gene 1 (MDR1) product, P-glycoprotein (P-gp), pumps out a variety of anticancer agents from the cell, including anthracyclines, Vinca alkaloids, and taxanes. The expression of P-gp therefore confers resistance to these anticancer agents. In our present study, we found that FTI-277 (a farnesyltransferase inhibitor), U0126 [an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)], and 17-allylamino-17-demethoxygeldanamycin (an inhibitor of heat shock protein 90) reduced the endogenous expression levels of P-gp in the human colorectal cancer cells, HCT-15 and SW620-14. In contrast, inhibitors of phosphatidylinositol 3-OH kinase, mammalian target of rapamycin, p38 mitogen-activated protein kinase, and c-Jun NH(2)-terminal kinase did not affect P-gp expression in these cells. We further found that U0126 down-regulated exogenous P-gp expression in the MDR1-transduced human breast cancer cells, MCF-7/MDR and MDA-MB-231/MDR. However, the MDR1 mRNA levels in these cells were unaffected by this treatment. PD98059 (a MEK inhibitor), ERK small interfering RNA, and p90 ribosomal S6 kinase (RSK) small interfering RNA also suppressed P-gp expression. Conversely, epidermal growth factor and basic fibroblast growth factor enhanced P-gp expression, but the MDR1 mRNA levels were unchanged in epidermal growth factor-stimulated cells. Pulse-chase analysis revealed that U0126 promoted P-gp degradation but did not affect the biosynthesis of this gene product. The pretreatment of cells with U0126 enhanced the paclitaxel-induced cleavage of poly(ADP-ribose) polymerase and paclitaxel sensitivity. Furthermore, U0126-treated cells showed high levels of rhodamine123 uptake. Hence, our present data show that inhibition of the MEK-ERK-RSK pathway down-regulates P-gp expression levels and diminishes the cellular multidrug resistance.
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PMID:Inhibition of the mitogen-activated protein kinase pathway results in the down-regulation of P-glycoprotein. 1762 Apr 38

Vitamin A and its metabolite retinoic acid (RA) are essential elements for normal lung development and the differentiation of lung epithelial cells. We previously showed that RA rapidly activated cyclic AMP response element-binding protein (CREB) in a nonclassical manner in normal human tracheobronchial epithelial (NHTBE) cells. In the present study, we further demonstrated that this nonclassical signaling of RA on the activation of CREB plays a critical role in regulating the expression of airway epithelial cell differentiation markers, the MUC2, MUC5AC, and MUC5B genes. We found that RA rapidly activates the protein kinase Calpha isozyme and transmits the activation signal to CREB via the Raf/MEK/extracellular signal-regulated kinase/p90 ribosomal S6 kinase (RSK) pathway. Activated RSK translocated from the cytoplasm to the nucleus, where it phosphorylates CREB. Activated CREB then binds to a cis-acting replication element motif on the promoter (at nucleotides [nt] -878 to -871) of the MUC5AC gene. The depletion of CREB using small interfering RNA abolished not only the RA-induced MUC5AC but also RA-induced MUC2 and MUC5B. Taken together, our findings demonstrate that CREB activation via this nonclassical RA signaling pathway may play an important role in regulating the expression of mucin genes and mediating the early biological effects of RA during normal mucous differentiation in NHTBE cells.
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PMID:Regulation of mucin gene expression by CREB via a nonclassical retinoic acid signaling pathway. 1764 88

Evidence suggests that mitogen-activated protein kinase kinase (MEK) plays a role in cell transformation and tumor development and might be a significant target for chemoprevention. 3,5,4'-Trihydroxy-trans-stilbene (resveratrol), a non-flavonoid polyphenol found in various foods and beverages, including red wines, is reported to be a natural chemopreventive agent. However, the concentrations required to exert these effects might be difficult to achieve by drinking only one or two glasses of red wine a day. On the other hand, the flavonol content of red wine is approximately 30 times higher than that of resveratrol. Here we demonstrated that 3,3',4',5,5',7-hexahydroxyflavone (myricetin), one of the major flavonols in red wine, is a novel inhibitor of MEK1 activity and transformation of JB6 P+ mouse epidermal cells. Myricetin (10 microM) inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA) or epidermal growth factor (EGF)-induced cell transformation by 76 or 72%, respectively, compared with respective reductions of 26 or 19% by resveratrol (20 microM). A combination of myricetin and resveratrol exerted additive but not synergistic effects on either TPA- or EGF-induced transformation. Myricetin, but not resveratrol, attenuated tumor promoter-induced activation of c-fos or activator protein-1. Myricetin strongly inhibited MEK1 kinase activity and suppressed TPA- or EGF-induced phosphorylation of extracellular signal-regulated kinase (ERK) or p90 ribosomal S6 kinase, downstream targets of MEK. Moreover, myricetin inhibited H-Ras-induced cell transformation more effectively than either PD098059, a MEK inhibitor, or resveratrol. Myricetin directly bound with glutathione S-transferase-MEK1 but did not compete with ATP. Overall, these results indicated that myricetin has potent anticancer-promoting activity and mainly targets MEK signaling, which may contribute to the chemopreventive potential of several foods including red wines.
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PMID:Myricetin is a novel natural inhibitor of neoplastic cell transformation and MEK1. 1769 61


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