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)

JAK2, a member of the Janus kinase superfamily was found to interact functionally with Raf-1, a central component of the ras/mitogen-activated protein kinase signal transduction pathway. Interferon-gamma and several other cytokines that are known to activate JAK2 kinase were also found to stimulate Raf-1 kinase activity toward MEK-1 in mammalian cells. In the baculovirus coexpression system, Raf-1 was activated by JAK2 in the presence of p21ras. Under these conditions, a ternary complex of p21ras, JAK2, and Raf-1 was observed. In contrast, in the absence of p21ras, coexpression of JAK2 and Raf-1 resulted in an overall decrease in the Raf-1 kinase activity. In addition, JAK2 phosphorylated Raf-1 at sites different from those phosphorylated by pp60v-src. In mammalian cells treated with either erythropoietin or interferon-gamma, a small fraction of Raf-1 coimmunoprecipitated with JAK2 in lysates of cells in which JAK2 was activated as judged by its state of tyrosine phosphorylation. Taken together, these data suggest that JAK2 and p21ras cooperate to activate Raf-1.
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PMID:The cytokine-activated tyrosine kinase JAK2 activates Raf-1 in a p21ras-dependent manner. 887 96

Cardiac myocyte survival is of central importance in the maintenance of the function of heart, as well as in the development of a variety of cardiac diseases. To understand the molecular mechanisms that govern this function, we characterized apoptosis in cardiac muscle cells following serum deprivation. Cardiotrophin 1 (CT-1), a potent cardiac survival factor (Sheng, Z., Pennica, D., Wood, W. I., and Chien, K. R. (1996) Development (Camb.) 122, 419-428), is capable of inhibiting apoptosis in cardiac myocytes. To explore the potential downstream pathways that might be responsible for this effect, we documented that CT-1 activated both signal transducer and activator of transcription 3 (STAT3)- and mitogen-activated protein (MAP) kinase-dependent pathways. The transfection of a MAP kinase kinase 1 (MEK1) dominant negative mutant cDNA into myocardial cells blocked the antiapoptotic effects of CT-1, indicating a requirement of the MAP kinase pathway for the survival effect of CT-1. A MEK-specific inhibitor (PD098059) (Dudley, D. T., Pang, L., Decker, S.-J., Bridges, A. J., and Saltiel, A. R. (1995) Proc. Natl. Acad. Sci. USA 92, 7686-7689) is capable of blocking the activation of MAP kinase, as well as the survival effect of CT-1. In contrast, this inhibitor did not block the activation of STAT3, nor did it have any effect on the hypertrophic response elicited following stimulation of CT-1. Therefore, CT-1 promotes cardiac myocyte survival via the activation of an antiapoptotic signaling pathway that requires MAP kinases, whereas the hypertrophy induced by CT-1 may be mediated by alternative pathways, e.g. Janus kinase/STAT or MEK kinase/c-Jun NH2-terminal protein kinase.
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PMID:Cardiotrophin 1 (CT-1) inhibition of cardiac myocyte apoptosis via a mitogen-activated protein kinase-dependent pathway. Divergence from downstream CT-1 signals for myocardial cell hypertrophy. 903 92

In vascular smooth muscle cells, the induction of early growth response genes involves the Janus kinase (JAK)/signal transducer and activators of transcription (STAT) and the Ras/Raf-1/mitogen-activated protein kinase cascades. In the present study, we found that electroporation of antibodies against MEK1 or ERK1 abolished vascular smooth muscle cell proliferation in response to either platelet-derived growth factor or angiotensin II. However, anti-STAT1 or -STAT3 antibody electroporation abolished proliferative responses only to angiotensin II and not to platelet-derived growth factor. AG-490, a specific inhibitor of the JAK2 tyrosine kinase, prevented proliferation of vascular smooth muscle cells, complex formation between JAK2 and Raf-1, the tyrosine phosphorylation of Raf-1, and the activation of ERK1 in response to either angiotensin II or platelet-derived growth factor. However, AG-490 had no effect on angiotensin II- or platelet-derived growth factor-induced Ras/Raf-1 complex formation. Our results indicate that: 1) STAT proteins play an essential role in angiotensin II-induced vascular smooth muscle cell proliferation, 2) JAK2 plays an essential role in the tyrosine phosphorylation of Raf-1, and 3) convergent mitogenic signaling cascades involving the cytosolic kinases JAK2, MEK1, and ERK1 mediate vascular smooth muscle cell proliferation in response to both growth factor and G protein-coupled receptors.
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PMID:Role of Janus kinase/signal transducer and activator of transcription and mitogen-activated protein kinase cascades in angiotensin II- and platelet-derived growth factor-induced vascular smooth muscle cell proliferation. 930 39

Mouse selenocysteine transfer RNA (tRNA) gene transcription-activating factor (mStaf) is a transcriptional activator that enhances RNA polymerase III-dependent mouse selenocysteine tRNA (tRNA(Sec)) gene transcription. The DNA-binding activity of mStaf in mouse mammary gland undergoes developmental changes, reaching a maximal level during the period of lactation. In this study, we employed an organ culture system to examine the hormonal regulation of mStaf binding and its role in the tRNA(Sec) transcription in the mammary gland. The results showed that mStaf binding in mammary explants was stimulated by treatment with the lactogenic hormones, PRL, insulin, and hydrocortisone and that a specific MEK inhibitor, PD98059, inhibited the hormonal stimulation of mStaf binding. Other kinase inhibitors, such as a Janus kinase inhibitor and a calmodulin kinase inhibitor, had no apparent effect. Northern and Western blot analyses revealed that the level of both mStaf messenger RNA and protein was enhanced by the lactogenic hormones and was reduced by the concomitant treatment with PD98059. The mitogen-activated protein kinase activity in cultured explants was rapidly induced and maintained at high levels by the lactogenic hormones. We also found that the lactogenic hormones increased the amount of tRNA(Sec) in a time-dependent manner, which followed the increase in mStaf binding in cultured mammary explants. These results support the view that mStaf plays a key role in the hormonal stimulation of tRNA(Sec) transcription in the mammary gland.
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PMID:Hormonal induction of mouse selenocysteine transfer ribonucleic acid (tRNA) gene transcription-activating factor and its functional importance in the selenocysteine tRNA gene transcription in mouse mammary gland. 992 85

In FDCP2 myeloid cells, IL-4 activated cyclic nucleotide phosphodiesterases PDE3 and PDE4, whereas IL-3, granulocyte-macrophage CSF (GM-CSF), and phorbol ester (PMA) selectively activated PDE4. IL-4 (not IL-3 or GM-CSF) induced tyrosine phosphorylation of insulin-receptor substrate-2 (IRS-2) and its association with phosphatidylinositol 3-kinase (PI3-K). TNF-alpha, AG-490 (Janus kinase inhibitor), and wortmannin (PI3-K inhibitor) inhibited activation of PDE3 and PDE4 by IL-4. TNF-alpha also blocked IL-4-induced tyrosine phosphorylation of IRS-2, but not of STAT6. AG-490 and wortmannin, not TNF-alpha, inhibited activation of PDE4 by IL-3. These results suggested that IL-4-induced activation of PDE3 and PDE4 was downstream of IRS-2/PI3-K, not STAT6, and that inhibition of tyrosine phosphorylation of IRS molecules might be one mechnism whereby TNF-alpha could selectively regulate activities of cytokines that utilized IRS proteins as signal transducers. RO31-7549 (protein kinase C (PKC) inhibitor) inhibited activation of PDE4 by PMA. IL-4, IL-3, and GM-CSF activated mitogen-activated protein (MAP) kinase and protein kinase B via PI3-K signals; PMA activated only MAP kinase via PKC signals. The MAP kinase kinase (MEK-1) inhibitor PD98059 inhibited IL-4-, IL-3-, and PMA-induced activation of MAP kinase and PDE4, but not IL-4-induced activation of PDE3. In FDCP2 cells transfected with constitutively activated MEK, MAP kinase and PDE4, not PDE3, were activated. Thus, in FDCP2 cells, PDE4 can be activated by overlapping MAP kinase-dependent pathways involving PI3-K (IL-4, IL-3, GM-CSF) or PKC (PMA), but selective activation of PDE3 by IL-4 is MAP kinase independent (but perhaps IRS-2/PI3-K dependent).
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PMID:IL-3 and IL-4 activate cyclic nucleotide phosphodiesterases 3 (PDE3) and 4 (PDE4) by different mechanisms in FDCP2 myeloid cells. 1020 31

Limitation of clonal expansion of activated T cells is necessary for immune homeostasis, and is achieved by growth arrest and apoptosis. Growth arrest and apoptosis can occur passively secondary to cytokine withdrawal, or can be actively induced by religation of the T cell receptor (TCR) in previously activated proliferating T cells. TCR-induced apoptosis appears to require prior growth arrest, and is mediated by death receptors such as Fas. We tested whether TCR religation affects T cell responses to interleukin (IL)-2, a major T cell growth and survival factor. TCR ligation in activated primary human T cells blocked IL-2 induction of signal transducer and activator of transcription (STAT)5 DNA binding, phosphorylation of STAT5, Janus kinase (Jak)1, Jak3, and Akt, and kinase activity of Jak1 and Jak3. Inhibition was mediated by the mitogen-activated protein kinase kinase (MEK)-extracellular stimulus-regulated kinase (ERK) signaling pathway, similar to the mechanism of inhibition of IL-6 signaling we have described previously. TCR ligation blocked IL-2 activation of genes and cell cycle regulatory proteins, and suppressed cell proliferation and expansion. These results identify TCR-induced inhibition of IL-2 signaling as a novel mechanism that underlies antigen-mediated feedback limitation of T cell expansion, and suggest that modulation of cytokine activity by antigen receptor signals plays an important role in the regulation of lymphocyte function.
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PMID:Inhibition of interleukin 2 signaling and signal transducer and activator of transcription (STAT)5 activation during T cell receptor-mediated feedback inhibition of T cell expansion. 1054 98

Chronic renal failure in children results in impaired body growth. This effect is so severe in some children that not only does it have a negative impact on their self-image, but it also affects their ability to carry out normal day-to-day functions. Yet the mechanism by which chronic renal failure causes short stature is not well understood. Growth hormone (GH) therapy increases body height in prepubertal children, suggesting that a better understanding of how GH promotes body growth may lead to better insight into the impaired body growth in chronic renal failure and therefore better therapies. This review discusses what is currently known about how GH acts at a cellular level. The review discusses how GH is known to bind to a membrane-bound receptor and activate a cytoplasmic tyrosine kinase called Janus kinase (JAK) 2. The activated JAK2 in turn phosphorylates tyrosines within itself and the associated GH receptor, forming high-affinity binding sites for a variety of signaling molecules. Examples of such signaling molecules include signal transducers and activators of transcription (Stats), which regulate the expression of a variety of GH-dependent genes, and the adapter protein Shc, which leads to activation of the Ras-Raf-MEK-MAP kinase pathway. In response to GH, JAK2 is also known to phosphorylate the insulin receptor substrates, leading to activation of phosphatidyl inositol 3' kinase and most likely other molecules that have been implicated in the regulation of metabolism. Finally, the ability of JAK2 to bind and activate the presumed adapter protein SH2-B is discussed. SH2-B has been shown to be a potent activator of GH-promoted JAK2 activity and downstream signaling events. Presumably these and other pathways initiated by GH combine to result in its ability to regulate body growth and metabolism.
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PMID:Role of the tyrosine kinase JAK2 in signal transduction by growth hormone. 1091 17

Overexpression of the oncogene for ErbB-2 is an unfavorable prognostic marker in human breast cancer. Its oncogenic potential appears to depend on the state of tyrosine phosphorylation. However, the mechanisms by which ErbB-2 is constitutively tyrosine-phosphorylated in human breast cancer are poorly understood. We now show that human breast carcinoma samples with ErbB-2 overexpression have higher proliferative and metastatic activity in the presence of autocrine secretion of prolactin (PRL). By using a neutralizing antibody or dominant negative (DN) strategies or specific inhibitors, we also show that activation of Janus kinase Jak2 by autocrine secretion of PRL is one of the significant components of constitutive tyrosine phosphorylation of ErbB-2, its association with Grb2 and activation of mitogen-activated protein (MAP) kinase in human breast cancer cell lines that overexpress ErbB-2. Furthermore, the neutralizing anti-PRL antibody or erbB-2 antisense oligonucleotide or DN Jak2 or Jak2 inhibitor or DNRas or MAP kinase kinase inhibitor inhibits the proliferation of both untreated and PRL-treated cells. Our results indicate that autocrine secretion of PRL stimulates tyrosine phosphorylation of ErbB-2 by Jak2, provides docking sites for Grb2 and stimulates Ras-MAP kinase cascade, thereby causing unrestricted cellular proliferation. The identification of this novel cross-talk between ErbB-2 and the autocrine growth stimulatory loop for PRL may provide new targets for therapeutic and preventive intervention of human breast cancer.
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PMID:Constitutive tyrosine phosphorylation of ErbB-2 via Jak2 by autocrine secretion of prolactin in human breast cancer. 1093 66

In normal development, embryonic astrocytes progress through their cell lineage by acquiring differentiation, by apoptosis, and by proliferation. In this study, we show that embryonic astrocytes may maintain and make gains in differentiation as they simultaneously progress through one cell cycle when induced by prolactin (PRL). Prolactin induced the majority of astrocytes to incorporate bromodeoxyuridine (BrdU) with a four-fold increase over controls after 18 h of exposure. Investigating possible mitogenic signaling pathways we show for the first time that prolactin is coupled to a sustained phospholipase D (PLD) activation, with an efficacy similar to the phorbol ester and astrocytic mitogen 12-tetradecanoylphorbol-13-acetate (TPA). Both cyclosporine and suramin abolished this activation. Staurosporine and calphostin C also inhibited the PRL effect by 50%, consistent with involvement of protein kinase C-(PKC)-alpha, the major PKC isoform in astrocytes. Genistein and PP1 blocked the activation indicating additional regulation by cytosolic tyrosine kinases. This profile of PLD activation was suggestive of a PLD I isoform and a mitogenic response. Upon completion of the cell cycle, analysis of glia fibrillary acidic protein (GFAP) and vimentin abundance, and glutamine synthetase (GS) activity showed that astrocytes had gained in expression of differentiation markers. Moreover, the intensity of GFAP immunofluorescence was greater per cell, as was the length of the cell processes. In exploring the signaling for prolactin-induced differentiation we found that prolactin activated the tyrosine kinase Janus kinase (JAK) 2 and significantly stimulated tyrosine, phosphorylation of the prolactin receptor. Stat 1 and 3 were also activated presumably downstream to JAK2 activation. A rapid translocation of the cytosolic Stats over the nucleus was seen in nearly every astrocyte corresponding well with the gains in GFAP per cell. The Stats translocation did not depend on MEK-ERK inhibition by PD98059, inhibition of p38 by 1 microm SB203580, or Src kinase family inhibition by PP1. Our results demonstrate the ability of PRL to concurrently induce activation of PLD, a mitogenic signaling pathway in astrocytes, and prolonged stimulation of Stat1, compatible with the increased GFAP upregulation and cell differentiation. Considered together this data may provide an explanation on the fast gain in both numbers and differentiation in the astrocytic population during development (HD 09402, CRF).
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PMID:Prolactin concurrently activates src-PLD and JAK/Stat signaling pathways to induce proliferation while promoting differentiation in embryonic astrocytes. 1097 48

We compared the role of the Raf-1/mitogen-activated protein kinase/extracellular signal-regulated protein kinase (MEK)/extracellular signal-regulated protein kinase (ERK)/p90(RSK) cascade in gp130-mediated cardiac hypertrophy with the contribution of the Janus kinase (JAK)/signal transduction and activation of transcription (STAT) and phosphatidylinositide 3-kinase (PI3-K) pathways. Primary cultured neonatal rat cardiomyocytes were stimulated with leukemia inhibitory factor (LIF). LIF sequentially activated Raf-1, MEK1/2, ERK1/2, and p90(RSK). We used PD-98059 (a specific MEK inhibitor), AG-490 (a JAK2 inhibitor), and wortmannin (a PI3-K inhibitor) to confirm that this cascade was independent of the JAK/STAT and PI3-K/p70 S6 kinase (S6K) pathways. PD-98059, AG-490, and wortmannin suppressed the LIF-induced increase in [(3)H]phenylalanine uptake by 54.7, 21.5, and 25.6%, respectively, and inhibited the increase in cell area by 61.2, 42.8, and 39.2%, respectively. Reorganization of myofilaments was predominantly suppressed by AG-490. LIF-induced expression of c-fos, brain natriuretic peptide, and skeletal alpha-actin mRNA was markedly suppressed by PD-98059 and moderately suppressed by wortmannin and AG-490. Atrial natriuretic peptide was significantly suppressed by AG-490. These findings indicate that this pathway is critically involved in protein synthesis, induction of c-fos, brain natriuretic peptide, and skeletal alpha-actin expression and is partially involved in myofilament reorganization and atrial natriuretic peptide induction in gp130-mediated cardiac hypertrophy.
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PMID:Significance of ERK cascade compared with JAK/STAT and PI3-K pathway in gp130-mediated cardiac hypertrophy. 1100 50


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