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)

Raf-1 phosphorylates and activates MEK-1, a kinase that activates the extracellular signal regulated kinases (ERK). This kinase cascade controls the proliferation and differentiation of different cell types. Here we describe a Raf-1-interacting protein, isolated using a yeast two-hybrid screen. This protein inhibits the phosphorylation and activation of MEK by Raf-1 and is designated RKIP (Raf kinase inhibitor protein). In vitro, RKIP binds to Raf-1, MEK and ERK, but not to Ras. RKIP co-immunoprecipitates with Raf-1 and MEK from cell lysates and colocalizes with Raf-1 when examined by confocal microscopy. RKIP is not a substrate for Raf-1 or MEK, but competitively disrupts the interaction between these kinases. RKIP overexpression interferes with the activation of MEK and ERK, induction of AP-1-dependent reporter genes and transformation elicited by an oncogenically activated Raf-1 kinase. Downregulation of endogenous RKIP by expression of antisense RNA or antibody microinjection induces the activation of MEK-, ERK- and AP-1-dependent transcription. RKIP represents a new class of protein-kinase-inhibitor protein that regulates the activity of the Raf/MEK/ERK module.
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PMID:Suppression of Raf-1 kinase activity and MAP kinase signalling by RKIP. 1049 27

In rat and human cells, RKIP (previously known as PEBP) was characterized as an inhibitor of the MEK phosphorylation by Raf-1. In Escherichia coli, the genes ybhb and ybcl possibly encode two RKIP homologues while in the genomes of other bacteria and archaebacteria other homologous genes of RKIP have been found. The parallel between the cellular signaling mechanisms in eukaryotes and prokaryotes suggests that these bacterial proteins could be involved in the regulation of protein phosphorylation by kinases as well. We first showed that the proteins YBHB and YBCL were present in the cytoplasm and periplasm of E. coli, respectively, after which we determined their crystallographic structures. These structures verify that YBHB and YBCL belong to the same structural family as mammalian RKIP/PEBP proteins. The general fold and the anion binding site of these proteins are extremely well conserved between mammals and bacteria and suggest functional similarities. However, the bacterial proteins also exhibit some specific structural features, like a substrate binding pocket formed by the dimerization interface and the absence of cis peptide bonds. This structural variety should correspond to the recognition of multiple cellular partners.
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PMID:Crystal structures of YBHB and YBCL from Escherichia coli, two bacterial homologues to a Raf kinase inhibitor protein. 1143 28

Proteins from the PEBP (phosphatidylethanolamine-binding protein) family have been identified in a wide variety of species and are thought to regulate a range of intracellular signalling cascades. The rat homologue (known as RKIP; Raf-1 kinase inhibitor protein) has been shown to negatively regulate the MAP kinase pathway through formation of inhibitory complexes with Raf-1 and MEK. The crystal structure of a new, murine member of the PEBP family, termed mPEBP-2, has been determined. On the basis of amino-acid homology, mPEBP-2 belongs to a distinct subset of the mammalian PEBP proteins. Nonetheless, mPEBP-2 is seen to be very similar in structure to other PEBP proteins from human, bovine and plant sources. Regions of distinctive sequence associated with the PEBP-2 subset are discussed with reference to this structure.
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PMID:The crystal structure of PEBP-2, a homologue of the PEBP/RKIP family. 1203 23

Raf kinase inhibitory protein (RKIP or PEBP) is an inhibitor of the Raf/MEK/MAP kinase signaling cascade and a suppressor of cancer metastasis. We now show that RKIP associates with centrosomes and kinetochores and regulates the spindle checkpoint in mammalian cells. RKIP depletion causes decreases in the mitotic index, the number of metaphase cells, and traversal times from nuclear envelope breakdown to anaphase, and an override of mitotic checkpoints induced by spindle poisons. Raf-1 depletion or MEK inhibition reverses the reduction in the mitotic index, whereas hyperactivation of Raf mimics the RKIP-depletion phenotype. Finally, RKIP depletion or Raf hyperactivation reduces kinetochore localization and kinase activity of Aurora B, a regulator of the spindle checkpoint. These results indicate that RKIP regulates Aurora B kinase and the spindle checkpoint via the Raf-1/MEK/ERK cascade and demonstrate that small changes in the MAP kinase (MAPK) pathway can profoundly impact the fidelity of the cell cycle.
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PMID:Raf kinase inhibitory protein regulates aurora B kinase and the spindle checkpoint. 1691 43

In the present report, we investigated the association between the sustained activation of Src family tyrosine kinases (primarily Src kinase) with the biphasic phosphorylation of extracellular signal-regulated kinase (ERK) induced by ischemia in the rat hippocampal CA3/dentate gyrus subfield. Post-ischemia reperfusion resulted in the phosphorylation of ERK in a Ras-dependent manner; down-regulation of NMDA receptors or Src family protein kinases by ketamine or 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2) potently antagonized the activation of ERK, indicating that NMDA receptors and Src family tyrosine kinases are essential for the up-regulation of ERK activity following ischemic stimuli. Additionally, an ischemia-induced association between RKIP and Raf-1 resulted in the inhibition of the ERK signaling cascade through an inhibition of Src-mediated Raf-1 phosphorylation at Tyr340/341 residues. This ischemia-induced inhibition of ERK was not associated with other downstream pathways involving Raf-1 phosphorylation at Ser 259 elicited by protein kinase B (Akt). Dissociation of Raf-1 from RKIP by 24 h reperfusion or (4S)-3-[(E)-but-2-enoyl]-4-benzyl-2-oxazolidinone (locostatin) influenced the second phase of ERK activation elicited by the Src-Raf cassette. We propose that, following ischemia, the Src family tyrosine kinases are critical for modulation of the Ras/Raf/MEK/ERK cascade, in which RKIP is involved in biphasic phosphorylation of ERK via a blockade of Src-Raf cascades.
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PMID:Sustained activation of Src-family tyrosine kinases by ischemia: a potential mechanism mediating extracellular signal-regulated kinase cascades in hippocampal dentate gyrus. 1700 55

G protein-coupled receptor kinases (GRKs) and arrestins are key participants in the canonical pathways leading to phosphorylation-dependent GPCR desensitization, endocytosis, intracellular trafficking and resensitization as well as in the modulation of important intracellular signaling cascades by GPCR. Novel studies have revealed a phosphorylation-independent desensitization mechanism operating through their RGS-homology (RH) domain and the recent determination of the crystal structures of GRK2 and GRK6 has uncovered interesting details on the structure-function relationships of these kinases. Emerging evidence indicates that the activity of GRKs is tightly modulated by mechanisms including phosphorylation by different kinases and interaction with several cellular proteins such as calmodulin, caveolin or RKIP. In addition, GRKs are involved in multiple interactions with non-receptor proteins (PI3K, Akt, GIT or MEK) that point to novel GRK cellular roles. In this article, our purpose is to describe the ever increasing map of functional interactions for GRK proteins as a basis to better understand its contribution to cellular processes.
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PMID:The G protein-coupled receptor kinase (GRK) interactome: role of GRKs in GPCR regulation and signaling. 1708 6

The Raf kinase inhibitory protein 1 (RKIP-1) and its orthologs are conserved throughout evolution and widely expressed in eukaryotic organisms. In its non-phosphorylated form RKIP-1 negatively regulates the Raf/MEK/ERK pathway by interfering with the activity of Raf-1. In its phosphorylated state, RKIP-1 dissociates from Raf-1 and inhibits GRK-2, a negative regulator of G-protein coupled receptors (GPCRs). Available data indicate that the phosphorylation of RKIP-1 by PKC can stimulate both the Raf/MEK/ERK and GPCR pathways. RKIP-1 has also been implicated as a negative regulator of the NF-kappaB pathway. Recent studies have shown that phosphorylated RKIP-1 binds to the centrosomal and kinetochore regions of metaphase chromosomes, where it may be involved in regulating the partitioning of chromosomes and the progression through mitosis. The collective evidence indicates that RKIP-1 regulates the activity and mediates the crosstalk between several important cellular signaling pathways. A variety of ablative interventions suggest that reduced RKIP-1 function may influence metastasis, angiogenesis, resistance to apoptosis, and genome integrity. Attenuation of RKIP-1 may also affect cardiac and neurological functions, spermatogenesis, sperm decapacitation, and reproductive behavior. In this review, the role of RKIP-1 in cellular signaling, and especially its functions revealed using a mouse knockout model, are discussed.
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PMID:Signaling crossroads: the function of Raf kinase inhibitory protein in cancer, the central nervous system and reproduction. 1770 25

RKIP was first identified as an inhibitor of the Raf-MEK-ERK signaling pathway. RKIP was also found to play an important role in the NF-kappaB pathway. Genetic and biochemical studies demonstrated that RKIP functioned as a scaffold protein facilitating the phosphorylation of IkappaB by upstream kinases. However, contrary to what one would expect of a scaffold protein, our results show that RKIP has an overall inhibitory effect on the NF-kappaB transcriptional activities. Since NF-kappaB target gene expression is subject to negative regulation involving the optimal induction of negative regulators, our data support a hypothesis that RKIP inhibits NF-kappaB activity via the auto-regulatory feedback loop by rapidly inducing the expression and synthesis of inhibitors of NF-kappaB activation.
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PMID:RKIP inhibits NF-kappaB in cancer cells by regulating upstream signaling components of the IkappaB kinase complex. 2004 10

The investigation of the structure and dynamics of signal transduction systems through data-based mathematical models in ordinary differential equations or other paradigms has proven to be a successful approach in recent times. Extending this concept, we here analysed the use of kinetic models based on power-law terms with non-integer kinetic orders in the validation of hypotheses concerning regulatory structures in signalling systems. We integrated pre-existent biological knowledge, hypotheses and experimental quantitative data into a power-law model to validate the existence of certain regulatory loops in the Ras/Raf-1/MEK/ERK pathway, a MAPK pathway involved in the transduction of mitogenic and differentiation signals. Towards this end, samples of a human mammary epithelial cell line (MCF-10A) were used to obtain time-series data, characterising the behaviour of the system after epidermal growth factor stimulation in different scenarios of expression for the critical players of the system regarding the investigated loops (e.g., the inhibitory protein RKIP). The mathematical model was calibrated using a computational procedure that included: analysis of structural identifiability, global ranking of parameters to detect the most sensitivity ones towards the experimental setup, model calibration using global optimization methods to find the parameter values that better fit the data, and practical identifiability analysis to estimate the confidence in the estimated values for the parameters. The obtained model was used to perform computational simulations concerning the role of the investigated regulatory loops in the time response of the signalling pathway. Our findings suggest that the special regularity in the structure of the power-law terms make them suitable for a data-based validation of regulatory loops in signalling pathways. The model-based analysis performed identified RKIP as an actual inhibitor of the activation of the ERK pathway, but also suggested the existence of an intense feedback-loop control of the pathway by the activated ERK that maybe responsible for the damped oscillations we saw in the fraction of activated MEK both in the experiments and simulations. In addition, the model analysis suggested that phosphorylation/deactivation of RKIP during the transient stimulation may have a significant effect on the signalling peaks of both MEK and ERK. This later result suggests that dynamic modulation of signal inhibitors during stimulation may be a regulatory mechanism in ERK signalling and other pathways.
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PMID:Investigating dynamics of inhibitory and feedback loops in ERK signalling using power-law models. 2071 20

RKIP has been shown to regulate the RAS-RAF-MEK-ERK kinase cascade acting as modulator of apoptosis and metastasis in prostate cancer. Our goal was to examine the expression of the RAF (A-RAF, B-RAF and RAF-1) and RKIP genes in urinary bladder cancer. Microarray analysis and qPCR was employed to investigate the expression of RAF and RKIP, in 30 patients with transitional cell carcinoma (TCC) of the urinary bladder vs. the corresponding levels of adjacent normal tissue. Computational analysis was also performed on Gene Expression Omnibus (GEO) datasets, to unravel differences in the expression of RAF or RKIP between tumor and control samples, and between superficial and muscle invasive tumors. Microarray analysis revealed >2-fold expression of BRAF and RKIP in T2, T3, grade III tumors vs. controls. B-RAF over-expression was verified by qPCR in pT1, grade III tumors vs. their normal counterparts (p = 0.016). qPCR revealed a significant RKIP reduction in TCC vs. normal tissue (p = 0.002 and p < 0.001 for T1, grade II and Ta-T1, grade III, respectively); All RAF genes were positively correlated among each other (A-RAF/B-RAF, p = 0.003; A-RAF/RAF-1, p < 0.001; B-RAF/RAF-1, p = 0.050), whereas B-RAF was negatively correlated with RKIP in TCC (p = 0.050). Further computational analysis revealed different expression profiles for the genes of interest, among muscle invasive carcinomas, superficial TCCs, cystectomy specimens and normal tissue. The reduced RKIP mRNA levels in TCC and the elevated levels of B-RAF in pT1, grade III tumors vs. normal tissue, corroborate that these genes are involved in the pathogenesis of urinary bladder cancer.
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PMID:Implication of RAF and RKIP genes in urinary bladder cancer. 2085 79


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