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)

ERYTHROPOIETIN (EPO): Erythropoietin (EPO) is a hormone that promotes the proliferation and differentiation of erythroid progenitor cells and regulates the number of erythrocytes in peripheral blood. EPO is produced mainly by the kidneys, and transcription of the EPO gene is promoted by a reduction in the oxygen concentration in the blood. The existence of EPO was suggested near the end of the 19th century by the discovery that hypoxia increases the production of red blood cells. EPO was identified as a serum factor in the 1950s, and in 1970 Miyake and coworkers succeeded in purifying it by using the urine of patients with aplastic anemia as a starting material. The human EPO gene was cloned in 1985 using a partial amino acid sequence from this purified EPO, and it is well known that recombinant EPO is currently used as a drug to treat anemia associated with chronic renal failure and other illnesses. ACTION OF EPO: When human bone marrow cells are cultured in a semisolid medium containing EPO, they form small erythroblast colonies in five to seven days, and by day 10 large erythroblast colonies appear that resemble fireworks ("burst" colonies). The original cells in the former colonies are called colony forming units-erythroid (CFU-E) or late-stage erythroblast progenitor cells and in the latter colonies they are called burst forming units-erythroid (BFU-E) or early-stage erythroblast progenitor cells. As shown in Figure 1, red blood cells are produced through differentiation from stem cells to BFU-E, CFU-E, and erythroblasts. Although EPO acts on both BFU-E and CFU-E cells, CFU-E cells show greater sensitivity to EPO, and other factors such as stem cell factor (SCF), interleukin (IL)-3, IL-4, and granulocyte macrophage colony-stimulating factor (GM-CSF) must be present together with EPO for BFU-E cell proliferation. In erythroblasts beyond the CFU-E stage, sensitivity to EPO decreases as the cells mature. THE EPO RECEPTOR AND THE CYTOKINE RECEPTOR FAMILY: The EPO receptor gene was cloned by D'Andrea and coworkers in 1989 from murine erythroleukemia cells [1]. It became clear that the EPO receptor belongs to the cytokine receptor family that comprises receptors for the various interleukins, GM-CSF, granulocyte colony-stimulating factor (G-CSF), growth hormone and prolactin. The special characteristic of this family of receptors is that they are switched on (i.e., the receptor is activated) and transduce signals to the interior of the cell by the formation of homo- or hetero-oligomers (dimers or trimers). Moreover, hetero-oligomers of these receptors share a common receptor subunit. As shown in Figure 2, the IL-3, IL-5 and GM-CSF receptors have a common &bgr; subunit, and their ligand specificity is determined by the &agr; subunit. In the same manner, the IL-6, LIF and oncostatin M (OSM) receptors all share gp130, which is the &bgr; subunit of the IL-6 receptor. The IL-2, IL-4 and IL-7 receptors all share the &ggr; subunit of the IL-2 receptor. All the above receptors are activated by the formation of hetero-oligomers, but the G-CSF receptor, EPO receptor, and growth hormone receptor are activated by the formation of homodimers of the same types of molecules [2]. We can see that groups of cytokines such as the interleukins that affect a relatively wide range of cells and have redundant biological activity create this redundancy through the common use of a single receptor subunit. On the other hand, EPO and G-CSF act with high specificity on a relatively limited range of cells, so it was probably unnecessary for their receptors to share one of the subunits. EPO RECEPTOR AND JAK2 KINASE: The signal for cellular proliferation and differentiation into erythroblasts is thought to originate at the EPO receptor. The cytoplasmic domain of the EPO receptor can be divided into two major regions. Roughly half of the cytoplasmic domain, the part lying nearest the plasma membrane, is required for generating the signals for proliferation and differentiation such as the induction of globin synthesis [3, 4]. The remaining half is not required for this signaling, and, conversely, it acts to dampen the signals. It is known that a tyrosine kinase called JAK2 associates with the region near the plasma membrane, undergoes autophosphorylation, and phosphorylates the EPO receptor, and a transcription factor called a STAT [5]. It is thought that JAK2 plays an important role in promoting cellular proliferation. The STAT is activated by the phosphorylation, and it then translocates to the nucleus, recognizes a specific base sequence in the promoter region of its target gene, and initiates transcription. At present, we know that the STAT whose activation is mediated by the EPO receptor is STAT5, and the target genes are CIS [6], which has an SH2 domain (a molecular structure that recognizes a phosphorylated tyrosine) and OSM [7], which is a pleiotropic cytokine. However, activation of STAT5 and activation of the target genes are not unique to the EPO receptor, and they also occur with the IL-2 and IL-3 receptors. Moreover, the JAK2 substrate that is directly linked to cellular proliferation is still unknown. At present, studies are under way to determine the transcription factors specific to EPO and their target genes, as well as the substrates of JAK2. RECEPTOR PHOSPHORYLATION AND CESSATION OF THE SIGNAL: On the other hand, tyrosine phosphorylation of the receptor is necessary at the cytoplasmic tail region far from the plasma membrane, and the signal transduction pathway that originates with this phosphorylated tyrosine and is mediated by proteins with SH2 domains becomes activated. First, a GTP/GDP exchange factor called SOS, which is mediated by Shc and Grb2, migrates to the plasma membrane and converts a ras protein to its GTP form. The activated ras protein then activates the Raf-MAP kinase kinase-MAP kinase cascade, and ultimately initiates the transcription of oncogenes such as c-fos and c-jun. An enzyme called PI3 kinase binds to the tyrosine phosphorylation site of the receptor and a second messenger is born. It is known that this pathway is a requirement for DNA synthesis in certain types of fibroblasts. However, these signal transduction pathways are not unique to the EPO receptor, and they are also activated by most growth factor receptors, so they are not necessarily required for EPO-induced proliferation. Conversely, the tyrosine phosphatase SH-PTP1 (also called HCP) that has an SH2 domain and is specific to blood cells associates with the tyrosine phosphorylation site of the receptor and promotes the dephosphorylation of JAK2. In other words, the role of SH-PTP1 is to stop generation of the signal [8]. Therefore, in mutations lacking this cytoplasmic tail region of the receptor far from the plasma membrane, the receptors do not undergo tyrosine phosphorylation, JAK2 activation continues for a longer period of time, and thus the signal is generated more efficiently. In fact, in one patient with a mild case of familial erythrocytosis a mutation was discovered in which the C-terminus of the EPO receptor was missing 70 amino acids [9]. This was a dominant genetic trait, and the patient's erythroblasts showed an increased sensitivity to EPO. In this family the impairment was not severe enough to be called an illness, and in fact it is said that this patient was proficient enough athletically to compete for a gold medal at the Olympics. More specifically, the reason that athletes undergo training at high altitudes is to boost EPO production because of the lower oxygen partial pressure, and this brings about the desired effect of sustained athletic capability due to a resultant increase in red blood cells. However, the same effect has occurred naturally in this athlete thanks to accelerated receptor capability.
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PMID:Physician Education: The Erythropoietin Receptor and Signal Transduction. 1038 12

The binding of cytokines to the gp130 receptor activates the STAT3, MEK/MAPK, and PI3K/Akt signalling pathways. To assess the relative importance of these pathways in promoting the survival of cytokine-dependent neurons, we conditionally inactivated STAT3 in mice and inhibited MEK, PI3K, and Akt in cultured neurons using pharmacological reagents and by expressing specific inhibitory proteins. Inactivation of STAT3 enhanced the death of the cytokine-dependent sensory neurons of the nodose ganglion in vivo and substantially reduced the response of these neurons to CNTF and LIF in vitro. LY294002, an inhibitor of PI3K, but not PD98059, an inhibitor of MEK, markedly reduced the response of these neurons to CNTF, as did dominant-negative PI3K, dominant-negative Akt, and overexpression of Ruk (a natural PI3K inhibitor). These results demonstrate that STAT3 and PI3K/Akt signalling play major roles in mediating the survival response of neurons to cytokines.
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PMID:Role of STAT3 and PI 3-kinase/Akt in mediating the survival actions of cytokines on sensory neurons. 1159 Nov 28

The IL-6-related cytokines, LIF and cardiotrophin-1, are important growth promoting and cardioprotective agents for cardiomyocytes. However, factors that regulate their actions in the heart are poorly understood. In this study, we tested the hypothesis that endothelin-1, a peptide hormone that produces a pattern of cardiac hypertrophy distinct from LIF and cardiotrophin-1, modulates LIF-induced signaling in cardiomyocytes. Upon binding LIF or cardiotrophin-1, the LIF receptor alpha subunit (LIFRalpha) dimerizes with gp130, leading to activation of constitutively associated Jak1 proteins and LIFRalpha-gp130 tyrosine phosphorylation. We found that pretreatment of neonatal rat ventricular myocytes with endothelin-1 rapidly inhibited LIF-induced LIFRalpha tyrosine phosphorylation and Jak1 activation. This effect of endothelin-1 on LIFalpha and Jak1 was attenuated by the MEK1 inhibitor, PD98059, implicating involvement of the ERK kinases. Radioligand binding studies showed that inhibition of LIF signaling resulted from a reduction in cell surface LlFRalpha levels. Additionally, endothelin-1 was found to reduce LIF-induced STAT3 activation, as indexed by STAT3 Y705 phosphorylation. Finally, endothelin-1 and LIF were shown to induce opposite patterns of STAT3 activation in cardiomyocytes. LIF induced rapid, robust STAT3 Y705 phosphorylation; endothelin-1 produced a delayed, modest increase, and initially decreased STAT3 Y705 phosphorylation. Overall our findings indicate that endothelin-1 acts to temper IL-6-related cytokine signaling in cardiomyocytes, in particular STAT3 activation.
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PMID:Cytokine G-protein signaling crosstalk in cardiomyocytes: attenuation of Jak-STAT activation by endothelin-1. 1248 70

Experiments were performed to define the basis for negative regulation of STAT3 activation (i.e., Tyr705 phosphorylation) by angiotensin II in cardiomyocytes. Treatment of cardiomyocytes with angiotensin II resulted in rapid and sustained phosphorylation of STAT3 on Ser727; in contrast, STAT3 Tyr705 phosphorylation was decreased, with dephosphorylation being most pronounced at 30 minutes. Angiotensin II-induced STAT3 Tyr705 dephosphorylation was not prevented by inhibiting protein synthesis, but was blocked by vanadate or the MEK inhibitor PD98059. PD98059 was found to inhibit angiotensin II-induced Erk activation and STAT3 Ser727 phosphorylation. Angiotensin II also attenuated LIF-induced STAT3 Tyr705 phosphorylation, and this effect could be blocked with PD89059. These results are consistent with Erk-mediated STAT3 Ser727 phosphorylation leading to STAT3 Tyr705 dephosphorylation, and accounting for angiotensin II-mediated STAT3 inhibition in cardiomyocytes. We propose that Erk serves as a scaffolding protein in recruiting either a protein tyrosine or MAP kinase phosphatase to STAT3.
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PMID:Angiotensin II effects on STAT3 phosphorylation in cardiomyocytes: evidence for Erk-dependent Tyr705 dephosphorylation. 1249 67

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.
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PMID:ERK signaling pathway is involved in p15INK4b/p16INK4a expression and HepG2 growth inhibition triggered by TPA and Saikosaponin a. 1259 82

The physiological benefit of the febrile response is poorly understood. Here we show that fever-range thermal stress enhances the function of the L-selectin lymphocyte homing receptor through an interleukin-6 (IL-6)-dependent signaling mechanism. Thermal stimulation of L-selectin adhesion in vitro and in vivo is mediated by engagement of the gp130 signal-transducing chain by IL-6 and a soluble form of the IL-6 receptor-alpha (sIL-6Ralpha) binding subunit. Thermal control of adhesion is maintained in IL-6-deficient mice through a gp130-dependent compensatory mechanism mediated by IL-6-related cytokines (i.e., oncostatin M [OSM], leukemia inhibitory factor [LIF], and IL-11). Combined biochemical and pharmacological inhibitor (PD98059, U0126, SB203580, SP600125) approaches positioned MEK1/ERK1-2, but not p38 MAPK or JNK, in the IL-6/sIL-6Ralpha signaling pathway upstream of activation of L-selectin/cytoskeletal interactions and L-selectin avidity/affinity. These results highlight a role for gp130-linked IL-6/sIL-6Ralpha transsignaling in amplifying lymphocyte trafficking during febrile inflammatory responses.
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PMID:Central role of IL-6 receptor signal-transducing chain gp130 in activation of L-selectin adhesion by fever-range thermal stress. 1473 59

Elevated secretion of glucocorticoids (GCs) or hypersensitivity to GCs has a permissive effect on the development of obesity and leads to abnormalities of body fat distribution. Recent studies demonstrated GCs act as antagonists of leptin in rodents. However, little is known about the interaction between GCs and leptin signaling. In the present study, we investigated the effects of GCs on leptin action in vitro and in vivo. GCs rapidly inhibited the leptin-induced STAT3 phosphorylation in a dose- and time-dependent manner, as assayed by Western blotting using anti-phosphospecific-STAT3 in human hepatoma cell lines (Huh7) transiently expressing long form leptin receptor. GCs also inhibited the leptin-induced JAK2 tyrosine phosphorylation but unaltered the specific binding of (125)I-leptin to the cells. Parallel experiments, however, demonstrated that the inhibitory effects of GCs were not observed in either IL-6- or LIF-induced STAT3 phosphorylation. Furthermore, we examined the feeding behavior and hypothalamic leptin signaling following intracerebroventricular (icv) infusion of GCs prior to icv leptin infusion in Sprague-Dawley rats. The food intake after 24 h of icv leptin injection increased 3-fold in GCs-treated animals. In addition, central infusion of GCs resulted in a marked reduction of hypothalamic STAT3 phosphorylation in response to icv infusion of leptin. To clarify the molecular mechanism by which GCs rapidly reduce leptin-induced JAK/STAT signaling, we examined the intracellular signal transduction pathway potentially mediated by GCs. PD98059, a specific MEK inhibitor, blocked the inhibitory effects of GCs on leptin-induced JAK/STAT activation in Huh7 cells. These results suggest GCs antagonize leptin action by a rapid inhibition of the leptin-induced JAK/STAT pathway partly via MAPK cascade.
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PMID:Rapid inhibition of leptin signaling by glucocorticoids in vitro and in vivo. 1499 17

The standard method for isolation of ES cells from strain 129 mice does not give rise to ES lines of CBA origin. We investigated the effect of inhibition of MEK/ERK signaling in combination with increased stimulation of gp130 signaling on derivation of ES cells from CBA blastocysts. Inhibition of MEKI and MEKII using the drug U0126 and stimulation of gp130 signaling by elevating the level of LIF present gave rise to ES-like lines in 22.6% of explants. No lines arose when MEK was inhibited in the absence of additional LIF stimulation, nor when additional LIF stimulation occurred in the absence of MEK inhibition. Typically for ES cell lines, CBA-derived cells contributed to chimeric mice and differentiated broadly in vitro. Increased levels of gp130 signaling led to similar levels of STAT3 activation in strain 129 and CBA ES cells. We conclude that CBA ES cells have a requirement for additional STAT3 activation.
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PMID:Increased gp130 signaling in combination with inhibition of the MEK/ERK pathway facilitates embryonic stem cell isolation from normally refractory murine CBA blastocysts. 1599 12

We used cytokine protein array to analyze the expression of cytokines from human cord blood-derived mesenchymal stem cells (CB-MSCs). Several cytokines, interleukins (IL), and growth factors, including ENA-78, GM-CSF, GRO, IL-1beta, IL-6, IL-8, MCP-1, OSM, VEGF, FGF-4, FGF-7, FGF-9, GCP-2, IGFBP-1, IGFBP-2, IGFBP-3, IGFBP-4, IP-10, LIF, MIF, MIP-3alpha, osteoprotegerin, PARC, PIGF, TGF-beta2, TGF-beta3, TIMP-1, as well as TIMP-2, were secreted by CB-MSCs, while IL-4, IL-5, IL-7, IL-13, TGF-beta1, TNF-alpha, and TNF-beta were not expressed under normal growth conditions. IL-6, IL-8, TIMP-1, and TIMP-2 were the most abundant interleukins expressed by CB-MSCs. A set of growth factors were selected to evaluate their stimulatory effects on the IL6 secretion for CB-MSCs. IL-1beta was the most important factor inducing CB-MSC to secret IL-6. The mechanism by which IL-1beta promoted IL-6 expression in CB-MSCs was studied. By using various inhibitors of signal transduction, we found that activation of p38 mitogen-activated protein kinases (MAPK) and MAPK kinase (MEK) is essential in the IL-1beta stimulated signaling cascade which leads to the increase in IL-6 synthesis. Additionally, continuous supplement of IL-1beta in the CB-MSCs culture will facilitate adipogenic maturation of CB-MSCs as evidenced by the presence of oil drops in the CB-MSCs and secretion of leptin, a molecule marker of adipocytes. These results strongly suggest that cytokine induction and signal transduction are important for the differentiation of CB-MSCs.
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PMID:Cytokine interactions in mesenchymal stem cells from cord blood. 1637 3

LIF is a cytokine playing a key role in the regulation of self-renewal and maintenance of undifferentiated state in mouse ES cells. The response of pluripotent cells to LIF is mediated mainly by the STAT3 and ERK signalling pathways. Recently, we have shown that LIF potentiated retinoic acid-induced neural differentiation of pluripotent mouse embryonal carcinoma P19 cells. Here we demonstrate that pro-neural effects of LIF and partially also of retinoic acid are abolished by inhibition of the JAK2->STAT3 signalling pathway. In contrast, inhibition of the MEK1->ERK signalling pathway does not exhibit any effect. These results suggest that in neurogenic regions, cooperative action of LIF and other neuro-differentiation-inducing factors, such as retinoic acid, may be mediated by the STAT3 signalling pathway.
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PMID:Neural differentiation potentiated by the leukaemia inhibitory factor through STAT3 signalling in mouse embryonal carcinoma cells. 1797 5


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