Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.12.2 (MEK)
 18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

PD98059 [2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one] is a flavonoid and a potent inhibitor of mitogen-activated protein kinase kinase (MEK). Concentrations of PD98059 of </=20 muM were not cytotoxic to cultures of the immortalized human breast epithelial cell line MCF10A. The agent was weakly cytostatic at concentrations of >/=10 microM. In vivo exposure of cultures to </=20 microM PD98059 for 2-22 hr did not affect overall extracellular signal-regulated kinase contents; however, exposure to PD98059 resulted in a rapid loss (>95%) of the dually phosphorylated forms of extracellular signal-regulated kinase (IC50 = 1 muM). Treatment of cultures with PD98059 of >/=1 muM either at the time of addition or up to 48 hr before the addition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suppressed in a concentration-dependent manner the accumulation of induced steady state CYP1A1, CYP1B1, and NQO1 mRNAs. The addition of PD98059 to rat liver cytosol just before the addition of TCDD suppressed TCDD binding (IC50 = 4 muM) and aryl hydrocarbon receptor (AHR) transformation (IC50 = 1 muM), as measured by sucrose gradient centrifugation and electrophoretic mobility shift assays. Flavone and flavanone, two closely related structural analogs of PD98059, inhibited AHR transformation by TCDD with IC50 values similar to that obtained with PD98059. However, neither analog was as potent as PD98059 in inhibiting MEK (IC50 approximately 190 muM for both). These results suggest that PD98059 is a ligand for the AHR and functions as an AHR antagonist at concentrations commonly used to inhibit MEK and signaling processes that entail MEK activation.
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PMID:PD98059 is an equipotent antagonist of the aryl hydrocarbon receptor and inhibitor of mitogen-activated protein kinase kinase. 949 9

The aryl hydrocarbon receptor (AhR) is involved in various processes such as cytochrome P450 (P450) 1A induction after xenobiotic exposure. It is also considered to play a major role in cell proliferation and differentiation. Recent evidences have suggested a cross-talk between AhR functions and the mitogen-activated protein kinase (MAPK) cascade. We now report that 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene (U0126), a specific inhibitor of MAPK kinase (MEK) MEK1/2, elicits a marked increase in CYP1A1 expression at both mRNA and protein levels associated with a significant increase of enzyme activity in primary rat hepatocytes and a human hepatoma cell line. This induction occurred independently of MEK/extracellular signal-regulated kinase (ERK) activation and in the absence of ERK1 and ERK2 expression. The effect of U0126 was mediated by its ability to transactivate xenobiotic responsive element (XRE)-driven genes, as demonstrated by transfection assays with an XRE-driven luciferase construct in the human B16A2 hepatoma cell line. CYP1A1 modulation was abolished by a cotreatment with resveratrol, an established AhR antagonist, arguing for AhR activation by U0126. Such an effect was demonstrated by direct in vitro ligand binding competition assays using rabbit liver cytosol, showing that this compound binds AhR with an EC(50) = 25 x 10(-6) M. Moreover, we demonstrated that U0126 is a substrate for several P450s including human CYP1A2, -1A1, and -1B1. We conclude that the widely used specific inhibitor of MEK/ERK, U0126, also acts as a potent AhR activator and an inducer of related genes. Such effects on the AhR may have an impact on biological functions attributed previously to MAPK inhibition.
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PMID:Aryl hydrocarbon receptor activation and cytochrome P450 1A induction by the mitogen-activated protein kinase inhibitor U0126 in hepatocytes. 1504 23

Hormone (IDMB)-induced adipogenesis in C3H10T1/2 cells is suppressed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the aryl hydrocarbon receptor (AhR). We have previously reported that TCDD addition 48 h before the hormonal stimulation of IDMB suppresses a key mediator of adipogenesis, the peroxisome proliferator-activated receptor (PPARgamma), by a MEK/ERK dependent mechanism. Here we add to previous evidence that this synergism functions after IDMB addition but before increased PPARgamma1 transcription. Suppression remains effective and MEK/ERK dependent when TCDD is added 6-12 h after IDMB addition but not when delayed to 16-24 h, thus preceding the rise in PPARgamma mRNA. TCDD suppression of the number of committed adipocytes and of triglyceride formation is less effective with the delayed addition. TCDD therefore does not directly suppress the expression of the key mediator PPARgamma1. An alternative mediation of adipocyte commitment is apparently less sensitive to the 6-12 h of delayed TCDD addition. TCDD suppression potencies (EC(50) = 50 pM) match the potencies for stimulation of CYP1B1 protein and AhR-sensitive reporters. The AhR antagonist 3'-methoxy-4'-nitroflavone (3-MNF) inhibited both TCDD-mediated CYP1B1 induction and inhibition of PPARgamma protein expression. This antagonism was only effective when 3-MNF was present in the 24-h period after IDMB addition. TCDD activation of AhR in conjunction with MEK/ERK therefore generates PPARgamma1 suppression activity before the increase of PPARgamma1 synthesis. The potency and inhibition data are consistent with induction of one or more gene products that sustain suppression through the extended period of PPARgamma1 transcription.
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PMID:TCDD administration after the pro-adipogenic differentiation stimulus inhibits PPARgamma through a MEK-dependent process but less effectively suppresses adipogenesis. 1505 Apr 17

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces expression of the cytochrome P450 1A1 gene, cyp1a1, by binding to its receptor, aryl hydrocarbon receptor (AhR). TCDD-bound AhR translocates to the nucleus and forms a heterodimer with its partner protein, AhR nuclear translocator (Arnt). The AhR/Arnt heterodimer then binds to the dioxin-response elements (DREs) in the cyp1a1 enhancer and stimulates transcription of cyp1a1. We tested whether kinase pathways are involved in this process by treating Hepa1c1c7 cells with kinase inhibitors. The MEK-1 inhibitor PD98059 reduced TCDD-induced transcription of cyp1a1. TCDD treatment results in phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK), a substrate of MEK-1. Overexpression of dominant negative form of p42 MAPK suppressed TCDD-dependent transcription of a reporter gene controlled by dioxin-response elements (DREs), and pretreatment with PD98059 also blocked this transcription. PD98059 pretreatment also inhibited TCDD-induced DRE binding of the AhR/Arnt heterodimer. Together these results indicate that TCDD activates the MEK-1/p44/p42 MAPK pathway, which in turn activates AhR and so facilitates binding of AhR to the cyp1a1 DRE.
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PMID:Inhibition of the MEK-1/p42 MAP kinase reduces aryl hydrocarbon receptor-DNA interactions. 1531 66

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is the most potent tumor promoter ever tested in rodents. Although it is known that most of the effects of TCDD are mediated by binding to the aryl hydrocarbon receptor (AhR), the mechanisms leading to tumor promotion remain to be elucidated. Loss of contact-inhibition is one characteristic hallmark in tumorigenesis. In WB-F344 cells, TCDD induces a release from contact-inhibition which is manifested by a twofold increase in DNA-synthesis and cell number when TCDD (1 nmol L-1) is given to confluent cells. Because TCDD leads to phosphorylation of the epidermal growth factor receptor and an increase in c-Src-activation in WB-F344 cells, we investigated the functional relevance of this observation. Pharmacological inhibition of c-Src using PP1 (10 micromol L-1) or genistein (10 micromol L-1) did not prevent TCDD-dependent release from contact-inhibition. In accordance, elevation of cyclin A-a previously identified target of TCDD and marker of S-phase entry-was not reduced in the presence of PP1 or genistein. Western blot analysis revealed that phosphorylation of the EGF-receptor downstream target ERK was not induced in response to TCDD. Furthermore, TCDD-dependent increase in DNA-synthesis was not inhibited by the MEK1/2 inhibitor U0126 (10 micromol L-1). Our data show that neither c-Src-activation, nor ERK-activation are required for TCDD-dependent release from contact-inhibition arguing against a functional role of EGF-receptor activation in response to TCDD in WB-F344 cells.
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PMID:Evaluation of the role of c-Src and ERK in TCDD-dependent release from contact-inhibition in WB-F344 cells. 1559 23

An environmental pollutant, tetrachloro dibenzo dioxin (TCDD) is known to illicit the cognitive disability and motor dysfunction in the developing brain. TCDD induced effects leading to neurodevelopmental and neurobehavioral deficit may have been defined, however underlying molecular mechanism and possible intracellular targets remain to be elucidated. In this study, we attempted to analyze TCDD-induced neurotoxic effects in the granule cells from cerebellum where certain cognitive abilities and motor function command are known to be excuted. [3H]PDBu, (phorbol 12,13-dibutyrate) binding assay indicated that TCDD induced a dose-dependent increase of total PKC activity and its induction was the aryl hydrocarbon receptor (AhR) dependent and N-methyl-D-aspartate receptor (NMDAR) independent. TCDD also caused the translocation of both PKC-alpha and -epsilon in a dose-dependent manner but associated with different receptors; PKC-alpha via AhR but not PKC-epsilon indicating an isozyme-specific pattern of the induction. Increase of the ROS formation was also observed in the cells treated with TCDD in a dose-dependent and an AhR-dependent manner. The treatment of the cells with the diamino dicyano-bis(2-aminophenylthio) butadiene (U0126, MEK-1/2 inhibitor), dizocilpine maleate (MK-801, non-competitive N-methyl-D-aspartate glutamate receptor antagonist) and vitamin E attenuated the TCDD-induced ROS production indicating that TCDD-induced ROS formation may be associated with activation of ERK-1/2 in the MAP kinase pathway or the NMDA receptor. TCDD also increased [Ca2+]i, which is associated with ROS formation and PKC activation in the cerebellar granule cells. It is suggested that TCDD activates the NMDA receptor, which may induce a sustained increase of [Ca2+]i in neurons followed by the ROS formation. Our findings may contribute to understanding the mechanism of TCDD-related neurotoxicity, thereby improving the health risk assessment of neurotoxic compounds in humans.
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PMID:Neurotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in cerebellar granule cells. 1576 Dec 53

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a prototypic halogenated aromatic hydrocarbon (HAH), is known as one of the most potent toxicants. At least a part of its toxic effects appears to be derived from its ability to induce TNF-alpha production. However, the signaling pathway of TCDD that leads to TNF-alpha expression has not been elucidated. In this study, we investigated the signaling mechanism of TCDD-induced TNF-alpha expression in PMA-differentiated THP-1 macrophages. TCDD induced both mRNA and protein expression of TNF-alpha in a dose- and time-dependent manner. Alpha-naphthoflavone (NF), an aryl hydrocarbon receptor (AhR) inhibitor, prevented the TCDD-induced expression of TNF-alpha at both mRNA and protein levels. Genistein, a protein tyrosine kinase (PTK) inhibitor, and PD153035, an EGFR inhibitor, also blocked the increase of TNF-alpha expression by TCDD, indicating the role of EGFR in TCDD-induced TNF-alpha expression. On the other hand, PP2, a c-Src specific inhibitor, did not affect TCDD-induced TNF-alpha expression. EGFR phosphorylation was detected as early as 5 min after TCDD treatment. TCDD-induced EGFR activation was AhR-dependent since co-treatment with alpha-NF prevented it. ERK was found to be a downstream effector of EGFR activation in the signaling pathway leading to TNF-alpha production after TCDD stimulation. Activation of ERK was observed from 30 min after TCDD treatment. PD98059, an inhibitor of the MEK-ERK pathway, completely prevented the TNF-alpha mRNA and protein expression induced by TCDD, whereas inhibitors of JNK and p38 MAPK had no effect. PD153035, an EGFR inhibitor, as well as alpha-NF significantly reduced ERK phosphorylation, suggesting that ERK activation by TCDD was mediated by both EGFR and AhR. These results indicate that TNF-alpha production by TCDD in differentiated THP-1 macrophages is AhR-dependent and involves activation of EGFR and ERK, but not c-Src, JNK, nor p38 MAPK. A signaling pathway is proposed where TCDD induces sequential activation of AhR, EGFR and ERK, leading to the increased expression of TNF-alpha.
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PMID:Signaling pathway for 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced TNF-alpha production in differentiated THP-1 human macrophages. 1793 41

Quercetin is an anti-oxidative flavonoid widely distributed in the plant kingdom. Phenolic hydroxyl groups at the B-ring and the 3-position are responsible for its free radical-scavenging activity. Quercetin is commonly present as a glycoside and is converted to glucuronide/sulfate conjugates during intestinal absorption and only conjugated metabolites are therefore found in circulating blood. Although metabolic conversion attenuates its biological effects, active aglycone may be generated from the glucuronide conjugates by enhanced beta-glucuronidase activity during inflammation. With respect to its relationship with molecular targets relevant to cancer prevention, quercetin aglycone has been shown to interact with some receptors, particularly an aryl hydrocarbon receptor, which is involved in the development of cancers induced by certain chemicals. Quercetin aglycone has also been shown to modulate several signal transduction pathways involving MEK/ERK and Nrf2/keap1, which are associated with the processes of inflammation and carcinogenesis. Rodent studies have demonstrated that dietary administration of this flavonol prevents chemically induced carcinogenesis, especially in the colon, whilst epidemiological studies have indicated that an intake of quercetin may be associated with the prevention of lung cancer. Dietary quercetin is, therefore, a promising agent for cancer prevention and further research is warranted.
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PMID:Multitargeted cancer prevention by quercetin. 1846 24

Toxicologic and epidemiologic studies have linked benzo[a]pyrene (B[a]P) exposure with cardiovascular diseases such as atherosclerosis. The mechanisms of action leading to these diseases have not been fully understood. One key step in the development of atherosclerosis is vascular endothelial dysfunction, which is characterized by increased adhesiveness. To determine if B[a]P could lead to increased endothelial adhesiveness, the effects of B[a]P on human endothelial cell intercellular adhesion molecule-1 (ICAM-1) expression was investigated. B[a]P was able to increase ICAM-1 protein only after pretreatment with the aryl hydrocarbon receptor (AhR) agonist beta-naphthoflavone (beta-NF). Knockdown of AhR by siRNA or treatment with AhR antagonist alpha-naphthoflavone (alpha-NF) eliminated the induction of ICAM-1 from B[a]P, confirming the necessity of AhR in this process. Likewise, B[a]P only increased monocyte adhesion to the vascular endothelium when cells were pretreated with beta-NF. Experiments were done to define a signaling mechanism. B[a]P increased phosphorylation of MEK and p38-MAPK, and inhibitors to these proteins blunted the ICAM-1 induction. B[a]P was also able to increase AP-1 DNA binding and phosphorylation of cJun. Phosphorylation of cJun was disrupted by MEK and p38-MAPK inhibitors linking the signaling cascade. Finally, the importance of membrane microdomains, caveolae, was demonstrated by knockdown of the structural protein caveolin-1. Disruption of caveolae eliminated the B[a]P-induced ICAM-1 expression. These data suggest a possible pro-inflammatory mechanism of action of B[a]P involving caveolae, leading to increased vascular endothelial adhesiveness, and this inflammation may be a critical step in the development of B[a]P-induced atherosclerosis.
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PMID:Benzo[a]pyrene induces intercellular adhesion molecule-1 through a caveolae and aryl hydrocarbon receptor mediated pathway. 1867 94

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is known to promote cancer initiation and progression and accumulates in mammary fat tissue. Effects of TCDD are mediated by the aryl hydrocarbon receptor (AhR). Physiological conditions of moderate hypoxia in breast cancer also activate another transcription factor, hypoxia-inducible factor-1 alpha (HIF-1alpha). In addition, the transcription factors p53 and the estrogen receptor alpha (ERalpha) are important key players in breast cancer progression. Here, human breast cancer cells cultured under mild hypoxic conditions were exposed to TCDD and analyzed for regulation of p53 signaling and ERalpha transactivation. Simultaneous exposure to TCDD and hypoxia resulted in a moderate but reproducible inhibition of p53 expression. Both the direct activation of the ERalpha and the transcriptional regulation of Hdm2 mediated this inhibition. As consequence the p53-mediated target gene expression (Dusp5) was reduced. Silencing of Dusp5 by simultaneous exposure of TCDD and hypoxia or by RNAi led to increased phosphorylation of ERK1/2. This increase resulted in transactivation of ERalpha and induction of ERalpha-mediated transcription of Hdm2 and SOCS3. Specificity of ERalpha-transactivation by ERK1/2 was confirmed by treatment with MAPKK-inhibitor PD98059. The combination of inhibition of functional p53 protein and induction of ERalpha signaling could serve as a model for the operational sequence of TCDD effects to prevent cell death and promote breast tumor progression.
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PMID:TCDD mediates inhibition of p53 and activation of ERalpha signaling in MCF-7 cells at moderate hypoxic conditions. 1957 57


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