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)

The non-angiogenic role of vascular endothelial growth factor (VEGF), and its receptors flt-1 and flk-1, together with downstream signaling pathways were examined in fetal and postnatal rat cerebral cortical organotypic explants. VEGF application in both paradigms caused a significant increase in astroglial proliferation and a dose-dependent increase in GFAP and nestin immunoreactivity. The VEGF receptor flt-1 was observed on most, though not all astrocytes, while flk-1 receptor immunoexpression was absent. Treatment with antisense oligonucleotides (AS-ODNs) to flt-1 resulted in a dramatic decrease in GFAP and nestin immunoreactivity, which further confirmed the role of flt-1 in mediating VEGF's gliotrophic effects, while AS-ODNs to flk-1 had no effect. VEGF-induced gliotrophic effects were found to be mediated by the MAPK/ERK and PI-3 kinase signaling pathways, since the both the MEK1 inhibitor, PD98059 and the PI-3 kinase inhibitor, Wortmannin abolished VEGF-induced astrocytic GFAP(+) expression. Although high dose VEGF application resulted in strong upregulation of both GFAP and nestin immunoreactivity in astrocytes, overlap of the two proteins was not observed in all cells, suggesting that some of the nestin(+) cells might be neural progenitors. Exposure to VEGF resulted in upregulation of both VEGF and bFGF mRNA at the one-day time point, and bFGF protein by 3 days; VEGF activated astrocytes expressed bFGF to a much greater degree than those in untreated explants. The increased expression of bFGF induced by VEGF, may serve in the proliferation of multipotential neural stem/progenitor cells in vitro. VEGF, an established angiogenic factor, appears to play a significant role in the growth and differentiation of astrocytes in the CNS.
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PMID:Astrocyte growth effects of vascular endothelial growth factor (VEGF) application to perinatal neocortical explants: receptor mediation and signal transduction pathways. 1575 57

This study is designed to characterize the signal cascades by which brain-derived neurotrophic factor (BDNF) modulates long-term memory of fear conditioning. Enzyme-linked immunosorbent assay (ELISA) and Western blot analysis of tissue homogenates taken from fear-conditioned rats showed an increase in the amygdala of BDNF protein levels and its receptor TrkB phosphorylation. Bilateral administration of a TrkB ligand scavenger TrkB IgG and a Trk-specific tyrosine kinase inhibitor K252a to the amygdala impaired fear memory, as measured with fear-potentiated startle. Fear conditioning resulted in the association of Shc and TrkB, Shc and Ras, the increase in active Ras and phosphorylation of mitogen-activated protein kinase (MAPK). Treatment of amygdala slices with BDNF for 15 min increased the levels of active Ras, and MAPK and Akt phosphorylation. BDNF-induced MAPK phosphorylation was completely abolished by MEK inhibitors, and was partially inhibited by farnesyltransferase or phosphatidylinositol-3 kinase (PI-3 kinase) inhibitors. On the other hand, BDNF-induced Akt phosphorylation was unaffected by farnesyltransferase or MEK inhibitors, but could be blocked by PI-3 kinase inhibitors. Together, these data suggest a requirement of BDNF for fear learning. The memory-enhancing effect of BDNF involves the activation of MAPK and PI-3 kinase. BDNF-induced MAPK phosphorylation in the amygdala is mediated via TrkB and the Shc-binding site. Shc binding to TrkB leads to activation of Ras, Raf, and MEK. In addition, BDNF could induce phosphorylation of MAPK via activation of PI-3 kinase.
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PMID:Regulation of amygdala-dependent learning by brain-derived neurotrophic factor is mediated by extracellular signal-regulated kinase and phosphatidylinositol-3-kinase. 1603 42

The transcription factor nuclear factor-kappa B (NF-kappaB) subunit p65 is phosphorylated by IkappaB kinase (IKK) at S536 in transactivation domain (TAD) 1. In this study, we investigate the presence of IKK sites in TAD2 of p65. Recombinant IKKbeta, but not IKKalpha, phosphorylated a GST-p65 substrate in which TAD1 was deleted. Mutational analysis revealed S468 as the only IKK site in TAD2. S468 phosphorylation occurred rapidly after TNF-alpha and IL-1beta in T cell, B cell, cervix carcinoma, hepatoma, breast cancer, and astrocytoma lines and in primary hepatic stellate cells as well as peripheral blood mononuclear cells. S468-phosphorylated p65 coimmunoprecipitated with IkappaBalpha, indicating that p65 is phosphorylated while bound to IkappaBalpha. Dominant negative IKKbeta or pharmacological IKK inhibition blocked S468 phosphorylation after TNF-alpha or IL-1beta, whereas dominant negative IKKalpha or inhibitors of MEK, p38, JNK, PI-3 kinase, or GSK-3 had no effect. p65S468A-reconstituted p65-/- mouse embryonic fibroblasts (MEFs) showed a small, but significant, elevation of NF-kappaB-driven luciferase activity and RANTES mRNA levels after TNF-alpha and IL-1beta in comparison to wtp65-reconstituted MEFs. p65 nuclear translocation was not altered in p65S468A-expressing MEFs. In conclusion, our results indicate that 1) IKKbeta phosphorylates multiple p65 sites, 2) IKKbeta phosphorylates p65 in an IkappaB-p65 complex, and 3) S468 phosphorylation slightly reduces TNF-alpha- and IL-1beta-induced NF-kappaB activation.
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PMID:IKKbeta phosphorylates p65 at S468 in transactivaton domain 2. 1604 71

We have previously shown the importance of LTB4 in human pancreatic cancer. LTB4 receptor antagonists block growth and induce apoptosis in pancreatic cancer cells both in vitro and in vivo. Therefore, we investigated the effect of LTB4 on proliferation of human pancreatic cancer cells and the mechanisms involved. LTB4 stimulated DNA synthesis and proliferation of both PANC-1 and AsPC-1 human pancreatic cancer cells, as measured by thymidine incorporation and cell number. LTB4 stimulated rapid and transient activation of MEK and ERK1/2 kinases. The MEK inhibitors, PD98059 and U0126, blocked LTB4-stimulated ERK1/2 activation and cell proliferation. LTB4 also stimulated phosphorylation of p38 MAPK; however, the p38 MAPK inhibitor, SB203580, failed to block LTB4-stimulated growth. The activity of JNK/SAPK was not affected by LTB4 treatment. Phosphorylation of Akt was also induced by LTB4 and this effect was blocked by the PI-3 kinase inhibitor wortmannin, which also partially blocked LTB4-stimulated cell proliferation. In conclusion, LTB4 stimulates proliferation of human pancreatic cancer cells through MEK/ERK and PI-3 kinase/Akt pathways, while p38 MPAK and JNK/SAPK are not involved.
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PMID:LTB4 stimulates growth of human pancreatic cancer cells via MAPK and PI-3 kinase pathways. 1610 64

The aim of the present study was to investigate the effect of transforming growth factor-beta1 (TGF-beta1) on telomerase activity in a panel of human anaplastic thyroid carcinoma (ATC) cell lines. Addition of TGF-beta1 decreased the telomerase activity in HTh 74 and KTC-1 cells, while in C 643 and HTh 7 an increased activity was observed. The decreased telomerase activity appeared to be due to transcriptional repression of the hTERT promoter. Addition of a PI-3 kinase inhibitor (LY294002) abrogated the stimulatory effect of TGF-beta1 on the telomerase activity, indicating the possible involvement of hTERT activation via phosphorylation. Furthermore, the MEK-inhibitor U0126 had similar effects suggesting dual regulatory mechanisms. Interestingly, the cell lines differed genetically in that ATC cell lines responding with increased telomerase activity harbored a p53 mutation. In conclusion, TGF-beta1 exerts opposing effects on telomerase activity in ATC cell lines, possibly reflecting deregulation of TGF-beta1 signaling in a more malignant genotype.
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PMID:Differential effects of TGF-beta1 on telomerase activity in thyroid carcinoma cell lines. 1628 28

A hallmark feature of cancer is resistance to anoikis, apoptosis induced when cells either lose contact with or encounter an inappropriate extracellular matrix. Melanoma is inherently associated with a high degree of resistance to apoptosis. Mutations in B-RAF are prevalent in melanoma and promote constitutive MEK-ERK1/2 signaling and cell transformation. Acquisition of B-RAF mutations correlates with vertical phase growth when melanoma cells invade into the dermis, a collagen-rich environment that also contains fibronectin matrix. In addition, alterations in phosphoinositide-3 kinase (PI-3 kinase) signaling that lead to activation of AKT are detected in advanced melanomas. Here we show that knockdown of B-RAF expression by siRNA or pharmacological inhibition of MEK rendered melanoma cells susceptible to anoikis. Furthermore, adhesion to fibronectin but not collagen protected melanoma cells from anoikis through a PI-3 kinase-dependent pathway. Therefore, melanoma cells require either B-RAF or PI-3 kinase activation for protection from anoikis. Notably, AKT signaling in melanoma cells is substrate specific. These findings demonstrate that melanoma cells utilize multiple signaling pathways to provide resistance to apoptosis.
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PMID:B-RAF and PI-3 kinase signaling protect melanoma cells from anoikis. 1654 95

The objective of this study was to investigate the signal transduction pathways associated with the clonal development of myeloid and erythroid progenitor cells. The contribution of particular signaling molecules of protein tyrosine kinases (PTKs), mitogen-activated protein (MAP) kinase, and PI-3 kinase signaling to the growth of murine bone marrow colony forming unit-granulocyte-macrophage (CFU-GM) and erythroid (burst forming unit-erythroid [BFU-E] and colony forming unit-erythroid [CFU-E]) progenitors was examined in studies performed in the presence or absence of specific signal transduction inhibitors. The results clearly pointed to different signal transducing intermediates that are involved in cell proliferation and differentiation depending on the cell lineage, as well as on the progenitors' maturity. Lineage-specific differences were obtained when chemical inhibitors specific for receptor- or nonreceptor-PTKs, as well as for the main groups of distinctly regulated MAPK cascades, were used because all of these compounds suppressed the growth of erythroid progenitors, with no major effects on myeloid progenitors. At the same time, differential involvement of MEK/extracellular signal-regulated kinase (ERK) MAPK transduction pathway was observed in the proliferation and/or differentiation of early, BFU-E, and late, CFU-E, erythroid progenitor cells. The results also demonstrated that phosphatydylinositol (PI)-3 kinase and nuclear factor kappaB (NF-kappaB) transcriptional factor were required for maintenance of both myeloid and erythroid progenitor cell function. Overall, the data obtained indicated that committed hematopoietic progenitors express a certain level of constitutive signaling activity that participates in the regulation of normal steady-state hematopoiesis and point to the importance of evaluating the impact of signal transduction inhibitors on normal bone marrow when used as potential therapeutic agents.
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PMID:Signaling pathways implicated in hematopoietic progenitor cell proliferation and differentiation. 1720 96

Nitric oxide (NO) in nanomolar (nmol/L) concentrations is consistently detected in tumor microenvironment and has been found to promote tumorigenesis. The mechanism by which NO enhances tumor progression is largely unknown. In this study, we investigated the possible mechanisms and identified cellular targets by which NO increases proliferation of human breast cancer cell lines MDA-MB-231 and MCF-7. DETA-NONOate, a long acting NO donor, with a half-life of 20 h, was used. We found that NO (nmol/L) dramatically increased total protein synthesis in MDA-MB-231 and MCF-7 and also increased cell proliferation. NO specifically increased the translation of cyclin D1 and ornithine decarboxylase (ODC) without altering their mRNA levels or half-lives. Critical components in the translational machinery, such as phosphorylated mammalian target of rapamycin (mTOR) and its downstream targets, phosphorylated eukaryotic translation initiation factor and p70 S6 kinase, were up-regulated following NO treatment, and inhibition of mTOR with rapamycin attenuated NO induced increase of cyclin D1 and ODC. Activation of translational machinery was mediated by NO-induced up-regulation of the Raf/mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase/ERK (Raf/MEK/ERK) and phosphatidylinositol 3-kinase (PI-3 kinase)/Akt signaling pathways. Up-regulation of the Raf/MEK/ERK and PI-3 kinase/Akt pathways by NO was found to be mediated by activation of Ras, which was cyclic guanosine 3',5'-monophosphate independent. Furthermore, inactivation of Ras by farnesyl transferase inhibitor or K-Ras small interfering RNA attenuated NO-induced increase in proliferation signaling and cyclin D1 and ODC translation, further confirming the involvement of Ras activation during NO-induced cell proliferation.
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PMID:Nitric oxide in physiologic concentrations targets the translational machinery to increase the proliferation of human breast cancer cells: involvement of mammalian target of rapamycin/eIF4E pathway. 1721 Jul 10

The MAP kinase pathway inhibitor U0126 in combination with butyrate promotes differentiation in some colon cancer cell lines. We examined several inhibitors of histone deacetylase (HDAC) in combination with U0126 and other protein kinase inhibitors to see if these effects are general properties of HDAC inhibitors or butyrate alone. Alkaline phosphatase and peptidase activities were examined as markers for cellular differentiation in the human colon cancer cell lines Caco-2 and HT29 and the minimally transformed NCM460. Several HDAC inhibitors caused greater increases of alkaline phosphatase in the cancer cells than in NCM460, in which butyrate was the only HDAC inhibitor that caused a consistent increase. Unlike the JNK and PKC inhibitors examined, the MEK 1/2 inhibitor U0126 induced alkaline phosphatase activity in Caco-2 as a single agent and caused additive effects with HDAC inhibitors. The PI-3 kinase inhibitor LY294002 had little effect alone but enhanced the response of most HDAC inhibitors as did the raf inhibitor GW5074. In addition to butyrate, several HDAC inhibitors can induce differentiation in colon cancer cells and the responses may be enhanced by U0126, GW5074 and LY294002.
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PMID:Induction of differentiation of colon cancer cells by combined inhibition of kinases and histone deacetylase. 1746 97

In a previous study, we established that leptin acts synergistically with interferon-gamma in inducing nitric oxide synthase type II in cultured chondrocytes via Janus kinase-2 activation. However, the exact molecular mechanism that accounts for this synergism is not completely understood. The aim of the present study was to further delineate the signalling pathway used by leptin/interferon-gamma in the nitric oxide synthase type II induction in chondrocytes. Consequently, the roles of PI-3 kinase, MEK1 and p38 kinase were investigated using specific pharmacological inhibitors (Wortmannin, LY 294002, PD 098,059 and SB 203580). For this purpose, the amount of stable nitrite, the end product of NO generation by activated chondrocytes, has been evaluated by Griess colorimetric reaction in culture medium of human primary chondrocytes and in the murine ATDC5 cell line stimulated with leptin (400 nM) and interferon-gamma (1 ng/ml), alone or in combination. Specific inhibitors for PI-3K, MEK1 and p38 were added 1 h before stimulation. Nitric oxide synthase type II mRNA was investigated by real-time RT-PCR and NOS type II protein expression has been evaluated by western blot analysis. Our results showed that, as expected, leptin synergizes with IFN-gamma in inducing NO accumulation in the supernatant of co-stimulated cells. Pre-treatment with Wortmannin, LY 294002, PD 098,059 and SB 203580 caused a significant decrease in nitrite production, NOS type II protein expression and NOS type II mRNA expression induced by leptin and interferon-gamma co-stimulation. These findings were confirmed in 15 and 21-day differentiated ATDC5 cells, and in normal human primary chondrocytes. This is the first report showing that NOS type II induction triggered by co-stimulation with leptin and interferon-gamma is mediated by a signaling pathway involving PI-3K, MEK1 and p38.
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PMID:Phosphatidylinositol 3-kinase, MEK-1 and p38 mediate leptin/interferon-gamma synergistic NOS type II induction in chondrocytes. 1793 39


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