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

---

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

The activator protein 1 (AP-1) transcription factor is composed of heterodimers of the Fos/activating transcription factor (ATF) and Jun subfamilies of basic-region leucine-zipper (B-ZIP) proteins. In order to determine the identities of individual B-ZIP proteins in various AP-1 complexes we tested the effect of dominant-negative mutants to the B-ZIP proteins c-Fos, ATF2, ATF4 and CCAAT-enhancer-binding protein (C/EBP) on the activities of the collagenase and c-Jun promoters. These dominant-negative mutants inhibit DNA binding of wild-type B-ZIP proteins in a leucine-zipper-dependent fashion. Transcription of a collagenase promoter/reporter gene was induced in HepG2 hepatoma cells by expression of c-Fos and c-Jun, administration of PMA ("TPA") or by expression of a truncated form of MEK (mitogen-activated/extracellular-signal-regulated kinase kinase) kinase-1, MEKK1Delta. In all cases, the dominant-negative mutants A-Fos and A-ATF2 decreased collagenase promoter activity. However, A-ATF4 and A-C/EBP had no effect. A-Fos and A-ATF2 also reduced MEKK1Delta-induced stimulation of the c-Jun promoter. In contrast, constitutive c-Jun promoter activity was blocked solely by A-ATF2, strongly suggesting that ATF2 and/or an ATF2-dimerizing protein are of major importance for c-Jun transcription in unstimulated cells. These results demonstrate that AP-1 transcription factors of different compositions control c-jun gene transcription in resting or stimulated cells.
...
PMID:Regulation and composition of activator protein 1 (AP-1) transcription factors controlling collagenase and c-Jun promoter activities. 1173 49

Transcription factor ATF2 regulates gene expression in response to environmental changes. Upon exposure to cellular stresses, the mitogen-activated proteinkinase (MAPK) cascades including SAPK/JNK and p38 can enhance ATF2's transactivating function through phosphorylation of Thr69 and Thr71. How ever, the mechanism of ATF2 activation by growth factors that are poor activators of JNK and p38 is still elusive. Here, we show that in fibroblasts, insulin, epidermal growth factor (EGF) and serum activate ATF2 via a so far unknown two-step mechanism involving two distinct Ras effector pathways: the Raf-MEK-ERK pathway induces phosphorylation of ATF2 Thr71, whereas subsequent ATF2 Thr69 phosphorylation requires the Ral-RalGDS-Src-p38 pathway. Cooperation between ERK and p38 was found to be essential for ATF2 activation by these mitogens; the activity of p38 and JNK/SAPK in growth factor-stimulated fibroblasts is insufficient to phosphorylate ATF2 Thr71 or Thr69 + 71 significantly by themselves, while ERK cannot dual phosphorylate ATF2 Thr69 + 71 efficiently. These results reveal a so far unknown mechanism by which distinct MAPK pathways and Ras effector pathways cooperate to activate a transcription factor.
...
PMID:Growth factors can activate ATF2 via a two-step mechanism: phosphorylation of Thr71 through the Ras-MEK-ERK pathway and of Thr69 through RalGDS-Src-p38. 1211 May 90

The signal pathway mediating induction of p15(INK4b) and p16(INK4a) during HepG2 growth inhibition triggered by the phorbol ester tumor promoter TPA (12-O-tetradecanoylphorbol 13-acetate) and the Chinese herb Saikosaponin a was investigated. Western blot of three activated forms of mitogen-activated protein kinase (MAPK) (p-ERK, p-JNK and p-p38) demonstrated that phosphorylation of ERK is dramatically induced (11.6-fold ) by TPA during 15 min to 1 h and significantly induced (2.5-fold) by Saikosaponin alpha at 30 min, whereas phosphorylation of JNK was induced only by TPA during 30 min to 1 h. Phosphorylation of p38 was not induced by either drug. During this period, phosphorylation of one of the downstream transcriptional factors of MAPK cascade, ATF2, was 3.2- and 2.0-fold induced by TPA and Saikosaponin a, respectively, whereas that of another transcriptional factor, c-jun, was induced by TPA only. On the other hand, expressions of proto-oncogene c-jun, junB and c-fos were induced by TPA and Saikosaponin a during 30 min to 6 h of treatment. Pretreatment of 20 microg/ml PD98059, an inhibitor of MEK which is the upstream kinase of ERK, prevents the TPA- and Saikosaponin a-triggered HepG2 growth inhibition by 50 and 30%, respectively, accompanied by a 50 - 85% decrease of the p15(INK4b)/p16(INK4a) RNAs and proteins induced by both drugs. Inductions of c-fos RNA by both drugs and c-jun phosphorylation by TPA were also significantly reduced by PD98059 pretreatment. In addition, AP-1 DNA-binding assay using nonisotopic capillary electrophoresis and laser-induced fluorescence (CE/LIF) demonstrated that the AP-1-related DNA-binding activity was significantly induced by TPA and Saikosaponin a, which can be reduced by PD98059 pretreatment. These results suggested that activation of ERK together with its downstream transcriptional machinery mediated p15(INK4b) and p16(INK4a) expression that led to HepG2 growth inhibition.
...
PMID:ERK signaling pathway is involved in p15INK4b/p16INK4a expression and HepG2 growth inhibition triggered by TPA and Saikosaponin a. 1259 82

Specific docking interactions between MAPKs and their activating MAPK kinases (MKKs or MEKs) are crucial for efficient and accurate signal transmission. Here, we report the identification of a MAPK-docking site, or "D-site," in the N terminus of human MKK4/JNKK1. This docking site conforms to the consensus sequence for known D-sites in other MKKs and contains the first of the two cleavage sites for anthrax lethal factor protease that have been found in the N terminus of MKK4. This docking site was both necessary and sufficient for the high affinity binding of the MAPKs JNK1, JNK2, JNK3, p38 alpha, and p38 beta to MKK4. Mutations that altered conserved residues in this docking site reduced JNK/p38 binding. In addition, a peptide version of this docking site, as well as a peptide version of the JNK-binding site of the JIP-1 scaffold protein, inhibited both MKK4/JNK binding and MKK4-mediated phosphorylation of JNK1. These same peptides also inhibited JNK2-mediated phosphorylation of c-Jun and ATF2, suggesting that transcription factors, MKK4, and the JIP scaffold compete for docking to JNK. Finally, the selectivity of the MKK4, MEK1, and MEK2 D-sites for JNK versus ERK was quantified. The MEK1 and MEK2 D-sites displayed a strong selectivity for their cognate MAPK (ERK2) versus a non-cognate MAPK (JNK). In contrast, the MKK4 D-site exhibited only limited selectivity for JNK versus ERK.
...
PMID:A docking site in MKK4 mediates high affinity binding to JNK MAPKs and competes with similar docking sites in JNK substrates. 1278 55

In cells overexpressing active MEKK1 to enhance c-Jun trans-activation, expression of rat cholecystokinin 1 receptor increased the activity of c-Jun while in the same experimental conditions overexpression of mouse cholecystokinin 1 receptor repressed it. This differential trans-activation is specific, since it was not observed for either the other overexpressed kinases (MEK, PKA) or for other transcription factors (ATF2, ELK-1, CREB). This differential behaviour was also detected in a human colon adenocarcinoma cell-line naturally producing high levels of endogenous MEKK1. This differential behaviour between the two receptors on the MEKK1-induced c-Jun trans-activation was independent of the activation state of JNK, of the phosphorylation level of c-Jun and of its ability to bind its specific DNA responsive elements. Two amino acids (Val43 and Phe50 in the mouse cholecystokinin 1 receptor, replaced by Leu43 and Ileu50 in the rat cholecystokinin 1 receptor) localized in the first transmembrane domain were found to play a crucial role in this differential behaviour. MEKK1 probably activates a transcriptional partner of c-Jun whose activity is maintained or increased in the presence of the rat cholecystokinin 1 receptor but repressed in the presence of the mouse cholecystokinin 1 receptor.
...
PMID:Cholecystokinin 1 receptor modulates the MEKK1-induced c-Jun trans-activation: structural requirements of the receptor. 1649 Oct 99

D-sites are a class of MAPK-docking sites that have been found in many MAPK regulators and substrates. A single functional, high affinity D-site has been identified near the N terminus of each of the MAPK kinases (MKKs or MEKs) MEK1, MEK2, MKK3, MKK4, and MKK6. Here we demonstrated that MKK7 recognizes its target JNK by a novel mechanism involving a partially cooperative interaction of three low affinity D-sites in the N-terminal domain of MKK7. Mutations of the conserved residues within any one of the three docking sites (D1, D2, and D3) disrupted the ability of the N-terminal domain of MKK7beta to bind JNK1 by about 50-70%. Moreover, mutation of any two of the three D-sites reduced binding by about 80-90%, and mutation of all three reduced binding by 95%. Full-length MKK7 containing combined D1/D2 mutations was compromised for binding to JNK1 and exhibited reduced JNK1 kinase activity when compared with wild-type MKK7. Peptide versions of the D-sites from MKK4 or the JIP-1 scaffold protein inhibited MKK7-JNK binding, suggesting that all three JNK regulators bind to the same region of JNK. Moreover, peptide versions of any of the three D-sites of MKK7 inhibited the ability of JNK1 and JNK2 to phosphorylate their transcription factor substrates c-Jun and ATF2, suggesting that D-site-containing substrates also compete with MKK7 for docking to JNK. Finally, MKK7-derived D-site peptides exhibited selective inhibition of JNK1 versus ERK2. We conclude that MKK7 contains three JNK-docking sites that interact to selectively bind JNK and contribute to JNK signal transmission and specificity.
...
PMID:Interacting JNK-docking sites in MKK7 promote binding and activation of JNK mitogen-activated protein kinases. 1653 5

Mounting evidence suggests a role for matrix metalloproteinase (MMP)-2 in the malignant progression of breast cancer cells. We showed previously that H-Ras, but not N-Ras, induced invasion of MCF10A human breast epithelial cells through Rac-MKK3/6-p38 pathway resulted in MMP-2 up-regulation. Activation of p38 pathway by MKK6 caused a selective up-regulation of MMP-2. In this study, we aimed to elucidate the transcriptional regulation of MMP-2 by p38 pathway leading to the invasive phenotype of MCF10A cells. By using 5' deletion mutant constructs of MMP-2 promoter, we showed that deletion of the region containing activator protein-1 (AP-1) site caused the greatest reduction of MMP-2 promoter activity both in MKK6- and H-Ras-activated MCF10A cells, suggesting that the AP-1 binding site is critical for the MMP-2 promoter activation. DNA binding and transcriptional activities of AP-1 were increased by MKK6 or H-Ras as evidenced by electrophoretic mobility shift assay and luciferase assay using an AP-1-driven plasmid. By doing immunoinhibition assay and chromatin immunoprecipitation assay, we revealed the activating transcription factor (ATF) 2 as a transcription factor for MMP-2 gene expression through binding to the functional AP-1 site. Activation of ATF2, which depended on p38 activity, was crucial for MMP-2 promoter activity as well as induction of invasive and migrative phenotypes in MCF10A cells. This is the first report revealing ATF2 as an essential transcription factor linking MKK3/6-p38 signaling pathway to MMP-2 up-regulation, providing evidence for a direct role of ATF2 activation in malignant phenotypic changes of human breast epithelial cells.
...
PMID:Activating transcription factor 2 mediates matrix metalloproteinase-2 transcriptional activation induced by p38 in breast epithelial cells. 1707 70

In order to study the role of Phe169 in p38alpha MAP kinase structure and function, wild-type p38alpha and five p38alpha DFG motif mutants were examined in vitro for phosphorylation by MKK6, kinase activity toward ATF2 substrate, thermal stability, and X-ray crystal structure. All six p38alpha variants were efficiently phosphorylated by MKK6. However, only one activated p38alpha mutant (F169Y) possessed measurable kinase activity (1% compared to wild-type). The loss of kinase activity among the DFG mutants may result from an inability to correctly position Asp168 in the activated form of p38alpha. Two mutations significantly increased the thermal stability of p38alpha (F169A DeltaTm = 1.3 degrees C and D168G DeltaTm = 3.8 degrees C), and two mutations significantly decreased the stability of p38alpha (F169R DeltaTm = -3.2 degrees C and F169G DeltaTm = -4.7 degrees C). Interestingly, X-ray crystal structures of two thermally destabilized p38alpha-F169R and p38alpha-F169G mutants revealed a DFG-OUT conformation in the absence of an inhibitor molecule. This DFG-OUT conformation, termed alpha-DFG-OUT, is different from the ones previously identified in p38alpha crystal structures with bound inhibitors and postulated from high-temperature molecular dynamics simulations. Taken together, these results indicate that Phe169 is optimized for p38alpha functional activity and structural dynamics, rather than for structural stability. The alpha-DFG-OUT conformation observed for p38alpha-F169R and p38alpha-F169G may represent a naturally occurring intermediate state of p38alpha that provides access for binding of allosteric inhibitors. A model of the local forces driving the DFG IN-OUT transition in p38alpha is proposed.
...
PMID:Mutagenesis of p38alpha MAP kinase establishes key roles of Phe169 in function and structural dynamics and reveals a novel DFG-OUT state. 1744 92

G protein-coupled receptor kinases (GRKs) are serine/threonine kinases first discovered by its role in receptor desensitization. Phosphorylation of the C-terminal tail of GPCRs by GRKs triggers the docking of beta-arrestins and the functional uncoupling of G proteins and receptors. In addition, we and others have uncovered new direct ways by which GRKs could impinge into intracellular signalling pathways independently of receptor phosphorylation. In particular, we have characterized that elevated GRK2 levels can reduce CCR2-mediated activation of the ERK MAPK route in a manner that is independent of kinase activity and also of G proteins. This inhibition of ERK occurred in the absence of any reduction on MEK phosphorylation, what implicates that GRK2 is acting at the level of MEK or at the MEK-ERK interface to achieve a downregulation of ERK phosphorylation. In fact, we describe here that a direct association between GRK2 and MEK proteins can be detected in vitro. p38 MAPK pathway also appears to be regulated directly by GRK2 in a receptor-independent manner. p38 can be phosphorylated by GRK2 in threonine 123, a residue sitting at the entrance of a docking groove by which this MAPK associates to substrates and upstream activators. The T123phospho-mimetic mutant of p38 shows a reduced ability to bind to MKK6, concomitant with an impaired p38 activation, and a decreased phosphorylation of downstream substrates such as MEF2, MK2 and ATF2. Elevated levels of GRK2 downregulate p38-dependent cellular responses, such as differentiation of preadipocytic cells, while LPS-induced cytokine release is enhanced in macrophages from GRK2 (+/-) mice. In sum, we describe in this article different ways by which GRK2 directly regulates MAPK-mediated cellular events. This regulation of the MAPK modules by GRK2 could be relevant in pathological situations where the levels of this kinase are altered, such as during inflammatory diseases or cardiovascular pathologies.
...
PMID:GRK2-dependent desensitization downstream of G proteins. 1843 30

In response to various environmental stresses, the stress-responsive MAPKs p38 and JNK are activated and phosphorylate ATF2 and c-Jun transcription factors, thereby affecting cell-fate decision. Targeted gene disruption studies have established that JNK-c-Jun signaling plays a vital role in stress-induced apoptosis. The oncogenic phosphatase Wip1 acts as an important regulator in DNA damage pathway by dephosphorylating a spectrum of proteins including p53, p38, Chk1, Chk2, and ATM. In this study we show that Wip1 negatively regulates the activation of MKK4-JNK-c-Jun signaling during stress-induced apoptosis. The loss of Wip1 function sensitizes mouse embryonic fibroblasts to stress-induced apoptosis via the activation of both p38-ATF2 and JNK-c-Jun signaling. Here we reveal that Wip1 has dual roles in alternatively regulating stress- and DNA damage-induced apoptosis through p38/JNK MAPKs and p38/p53-dependent pathways, respectively. Our results point to Wip1 as a general regulator of apoptosis, which further supports its role in tumorigenesis.
...
PMID:Loss of Wip1 sensitizes cells to stress- and DNA damage-induced apoptosis. 1939 78


<< Previous 1 2 3 4 5 Next >>

---