Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Basic fibroblast growth factor (bFGF) plays an important role in development of the central nervous system and is neurotropic for a variety of neurons. In this study, we investigated whether bFGF is neurotropic for GT1 GnRH neuronal cell lines and if these cells express functional FGF receptors (FGFRs). The GT1 cell lines generated by genetically targeted tumorigenesis display highly differentiated properties of GnRH neurons. Addition of 2 and 10 ng/ml bFGF increased neurite outgrowth of GT1-7 cells and resulted in a significant increase of GT1 cell survival in serum-free medium. However, bFGF had no effect on [3H]thymidine incorporation at 24 or 48 h. RNase protection assays using riboprobes specific for murine FGFRs 1-3 showed that GT1 cells express FGFRs 1 and 3 but not 2. Occupancy of FGFRs with 10 ng/ml bFGF stimulated the sustained tyrosine phosphorylation of both the 42- and 44-kilodalton mitogen-activated protein kinases (MAPKs) for up to 6 h as shown by Western blot analysis. In addition, phosphorylation of the MAPKs was associated with enzyme activation as shown by an in-gel MAPK assay. GT1-1 and GT1-7 cells also express messenger RNA for bFGF, although the level of bioactive bFGF synthesized by GT1 cells appears suboptimal because GT1 cells can further respond to exogenously added bFGF. Thus, we have demonstrated that bFGF is a neurotropic factor in GT1 GnRh neuronal cell lines, raising the possibility that bFGF may play a role in the neurobiology of GnRH neurons.
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PMID:Basic fibroblast growth factor is a neurotropic factor in GT1 gonadotropin-releasing hormone neuronal cell lines. 764 90

Neurotrophins such as nerve growth factor (NGF) regulate neuronal survival during development and are neuroprotective in certain models of injury to both the peripheral and the central nervous system. Although many effects of neurotrophins involve long-term changes in gene expression, several recent reports have focused on rapid effects of neurotrophins that do not involve synthesis of new gene products. Because enhanced formation of reactive oxygen species (ROS) represents one consequence of many insults that produce neuronal death, we hypothesized that neurotrophins might influence neuronal function and survival through acute alterations in the production of ROS. Using an oxidation-sensitive compound, dihydrorhodamine, we measured ROS formation in a central nervous system-derived neuronal cell line (GT1-1 trk) and in superior cervical ganglion neurons, both of which express the transmembrane NGF receptor tyrosine kinase, trkA. There was enhanced production of ROS in both cell types in the absence of NGF that was rapidly inhibited by application of NGF; complete inhibition of ROS generation in GT1-1 trk cells occurred within 10 min. NGF suppression of ROS formation was prevented by PD 098059, a specific inhibitor of MEK (mitogen/extracellular receptor kinase, which phosphorylates mitogen-activated protein kinase). The observation that NGF acutely blocks ROS formation in neurons through activation of the mitogen-activated protein kinase pathway suggests a novel mechanism for rapid neurotrophin signaling, and has implications for understanding neuroprotective and other effects of neurotrophins.
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PMID:Rapid suppression of free radical formation by nerve growth factor involves the mitogen-activated protein kinase pathway. 910 9

The GT1-1 GnRH neuronal cell lines exhibit highly differentiated properties of GnRH neurons. We have used GT1-1 cells to study the roles of norepinephrine (NE), membrane depolarization, calcium influx, and phorbol esters in the regulation of mitogen-activated protein (MAP) kinase. NE, which is known to stimulate the release of GnRH, induced MAP kinase activity, the tyrosine phosphorylation of MAP kinase, and MAP kinase kinase activity. Forskolin led to activation of MAP kinase comparable with that induced by NE, and a selective inhibitor of cAMP-dependent protein kinase, H8, attenuated the NE-induced activation of MAP kinase. On the other hand, elimination of extracellular calcium by EGTA completely blocked NE-induced tyrosine phosphorylation of MAP kinase, and a selective inhibitor of calcium/calmodulin-dependent protein kinase, KN-62, attenuated the NE-induced activation of MAP kinase. Furthermore, depolarization of GT1-1 cells with 75 mM KCl, 10 microM BayK 8644, or 1 microM calcium ionophore (A23187) induced rapid tyrosine phosphorylation of MAP kinase. The omission of calcium from the extracellular medium completely abolished these effects of tyrosine phosphorylation of MAP kinase. Phorbol 12-myristate 13-acetate (PMA) also induced MAP kinase activity, but pretreatment of the cultured cells with PMA to down-regulate protein kinase C did not abolish the activation of MAP kinase by NE. In addition, although phosphorylation of Raf-1 kinase was stimulated by PMA, this phosphorylation was not induced by either NE or A23187. These results demonstrate that NE activates MAP kinase directly in GT1-1 cells, and that the effect of NE is mediated by increase in the cAMP level and by calcium influx, but not by PMA-sensitive protein kinase C or Raf-1 kinase.
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PMID:Norepinephrine stimulates mitogen-activated protein kinase activity in GT1-1 gonadotropin-releasing hormone neuronal cell lines. 938 11

We identified Ark, the mouse homolog of the receptor tyrosine kinase Axl (Ufo, Tyro7), in a screen for novel factors involved in GnRH neuronal migration by using differential-display PCR on cell lines derived at two windows during GnRH neuronal development. Ark is expressed in Gn10 GnRH cells, developed from a tumor in the olfactory area when GnRH neurons are migrating, but not in GT1-7 cells, derived from a tumor in the forebrain when GnRH neurons are postmigratory. Since Ark (Ax1) signaling protects from programmed cell death in fibroblasts, we hypothesized that it may play an antiapoptotic role in GnRH neurons. Gn10 (Ark positive) GnRH cells were more resistant to serum withdrawal-induced apoptosis than GT1-7 (Ark negative) cells, and this effect was augmented with the addition of Gas6, the Ark (Ax1) ligand. Gas6/Ark stimulated the extracellular signal-regulated kinase, ERK, and the serine-threonine kinase, Akt, a downstream component of the phosphoinositide 3-kinase (PI3-K) pathway. To determine whether ERK or Akt activation is required for the antiapoptotic effects of Gas6/Ark in GnRH neurons, cells were serum starved in the absence or presence of Gas6, with or without inhibitors of ERK and PI3-K signaling cascades. Gas6 rescued Gn10 cells from apoptosis, and this effect was blocked by coincubation of the cells with the mitogen-activated protein/ERK kinase (MEK) inhibitor, PD98059, or wortmannin (but not rapamycin). These data support an important role for Gas6/Ark signaling via the ERK and PI3-K (via Akt) pathways in the protection of GnRH neurons from programmed cell death across neuronal migration.
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PMID:Growth arrest-specific gene 6 (Gas6)/adhesion related kinase (Ark) signaling promotes gonadotropin-releasing hormone neuronal survival via extracellular signal-regulated kinase (ERK) and Akt. 997 50

The processing of the amyloid precursor protein (APP) has become a major focus of research into Alzheimer's disease (AD). Recently, repeated doses of testosterone have been shown to enhance the secretion of the product of the alpha-cleavage pathway of APP (sAPPalpha) over a period of days. Here, the time course of secretion of sAPPalpha after a single physiological dose of testosterone using an immortalized rat hypothalamic cell line (GT1-7) and the signalling pathways involved was analyzed. Testosterone was found to increase the amount of APP secretion rapidly after treatment without effecting the overall amount of cellular APP. The species of APP secreted was found to be predominantly the product of the non-amyloidogenic alpha-secretory pathway. Further, this event is regulated via aromatase-mediated conversion of testosterone to estrogen and the mitogen-activated protein kinase (MAP kinase) signalling pathway. Taken together these data partially elucidates the cellular cascade by which testosterone stimulates sAPP secretion.
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PMID:Testosterone stimulates rapid secretory amyloid precursor protein release from rat hypothalamic cells via the activation of the mitogen-activated protein kinase pathway. 1109 31

The hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH), utilizes multiple signaling pathways to activate extracellularly regulated mitogen-activated protein kinases (ERK1/2) in normal and immortalized pituitary gonadotrophs and transfected cells expressing the GnRH receptor. In immortalized hypothalamic GnRH neurons (GT1-7 cells), which also express GnRH receptors, GnRH, epidermal growth factor (EGF), and phorbol 12-myristate 13-acetate (PMA) caused marked phosphorylation of ERK1/2. This action of GnRH and PMA, but not that of EGF, was primarily dependent on activation of protein kinase C (PKC), and the ERK1/2 responses to all three agents were abolished by the selective EGF receptor kinase inhibitor, AG1478. Consistent with this, both GnRH and EGF increased tyrosine phosphorylation of the EGF receptor. GnRH and PMA, but not EGF, caused rapid phosphorylation of the proline-rich tyrosine kinase, Pyk2, at Tyr(402). This was reduced by Ca(2+) chelation and inhibition of PKC, but not by AG1478. GnRH stimulation caused translocation of PKC alpha and -epsilon to the cell membrane and enhanced the association of Src with PKC alpha and PKC epsilon, Pyk2, and the EGF receptor. The Src inhibitor, PP2, the C-terminal Src kinase (Csk), and dominant-negative Pyk2 attenuated ERK1/2 activation by GnRH and PMA but not by EGF. These findings indicate that Src and Pyk2 act upstream of the EGF receptor to mediate its transactivation, which is essential for GnRH-induced ERK1/2 phosphorylation in hypothalamic GnRH neurons.
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PMID:Dependence of gonadotropin-releasing hormone-induced neuronal MAPK signaling on epidermal growth factor receptor transactivation. 1244 5

In the present study, we investigated the selective role of protein kinase C (PKC) isoforms on neurite outgrowth of the GT1 hypothalamic neurons using several PKC isoform-selective inhibitors and transfection-based expression of enhanced green fluorescence protein (EGFP)-fused PKC isoforms. 12-O-Tetradecanoylphorbol-13-acetate (TPA) induced neurite outgrowth and growth cone formation, effects that were blocked by GF 109203X (a PKC inhibitor), safingolTM(a PKCalpha-selective inhibitor), but not by rottlerinTM (a PKCdelta-selective inhibitor), indicating that PKCalpha may be selectively involved in neurite outgrowth and cytoskeletal changes of filamentous actin and beta-tubulin. To define the differential localization of PKC isoforms, EGFP-tagged PKCalpha, PKCgamma, and PKCdelta were transfected into GT1 neuronal cells. TPA treatment induced relocalization of PKCalpha-EGFP to growth cones and cell-cell adhesion sites, PKCgamma-EGFP to the nucleus, and PKCdelta-EGFP to the membrane ruffle, respectively. An EGFP chimera of the catalytic domain of PKCalpha (PKCalpha-Cat-EGFP), the expression of which was inducible by doxycycline, was employed to directly ascertain the effect of PKCalpha enzymatic activity on neurite outgrowth of GT1 cells. Transient transfection of PKCalpha-Cat-EGFP alone increased the neurite-outgrowth and doxycycline treatment further augmented the number of neurite-containing cells. We also examined the involvement of the extracellular signal-regulated kinase (ERK) MAP kinase in TPA-induced neurite outgrowth. TPA treatment increased phosphorylated ERK MAP kinase, but not p38 MAP kinase. Specific inhibition of PKCalpha with safingol blocked the phosphorylation of ERK induced by TPA. More importantly, both neurite outgrowth and phosphorylation of ERK by TPA were blocked by PD 098059, a specific inhibitor of MEK (MAP kinase/ERK kinase-1), but not by SB203580, a specific inhibitor of p38 MAP kinase. These results demonstrate that PKCalpha isoform-specific activation is involved in neurite outgrowth of GT1 hypothalamic neuronal cells via ERK, but not the p38 MAP kinase signal pathway.
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PMID:Participation of protein kinase C alpha isoform and extracellular signal-regulated kinase in neurite outgrowth of GT1 hypothalamic neurons. 1247 95

The duration as well as the magnitude of mitogen-activated protein kinase activation has been proposed to regulate gene expression and other specific intracellular responses in individual cell types. Activation of ERK1/2 by the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) is relatively sustained in alpha T3-1 pituitary gonadotropes and HEK293 cells but is transient in immortalized GT1-7 neurons. Each of these cell types expresses the epidermal growth factor receptor (EGFR) and responds to EGF stimulation with significant but transient ERK1/2 phosphorylation. However, GnRH-induced ERK1/2 phosphorylation caused by EGFR transactivation was confined to GT1-7 cells and was attenuated by EGFR kinase inhibition. Neither EGF nor GnRH receptor activation caused translocation of phospho-ERK1/2 into the nucleus in GT1-7 cells. In contrast, agonist stimulation of GnRH receptors expressed in HEK293 cells caused sustained phosphorylation and nuclear translocation of ERK1/2 by a protein kinase C-dependent but EGFR-independent pathway. GnRH-induced activation of ERK1/2 was attenuated by the selective Src kinase inhibitor PP2 and the negative regulatory C-terminal Src kinase in GT1-7 cells but not in HEK293 cells. In GT1-7 cells, GnRH stimulated phosphorylation and nuclear translocation of the ERK1/2-dependent protein, p90RSK-1 (RSK-1). These results indicate that the duration of ERK1/2 activation depends on the signaling pathways utilized by GnRH in specific target cells. Whereas activation of the Gq/protein kinase C pathway in HEK293 cells causes sustained phosphorylation and translocation of ERK1/2 to the nucleus, transactivation of the EGFR by GnRH in GT1-7 cells elicits transient ERK1/2 signals without nuclear accumulation. These findings suggest that transactivation of the tightly regulated EGFR can account for the transient ERK1/2 responses that are elicited by stimulation of certain G protein-coupled receptors.
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PMID:Roles of Src and epidermal growth factor receptor transactivation in transient and sustained ERK1/2 responses to gonadotropin-releasing hormone receptor activation. 1264 80

Alzheimer's disease (AD) is characterised by deposition of a 4 kDa amyloid-beta peptide (Abeta) into senile plaques of the affected brain. Abeta is a proteolytic product of the membrane protein, amyloid precursor protein (APP). An alternative cleavage pathway involves alpha-secretase activity and results in secretion of a 100 kDa non-amyloidogenic APP (sAPPalpha) and therefore a potential reduction in Abeta secretion. We have shown that estrogen induces alpha-cleavage and therefore results in the secretion of sAPPalpha. This secretion is signalled via MAP-kinase and PI-3 kinase signal-transduction pathways. These pathways also have the potential to inhibit the activation of glycogen synthase kinase 3beta (GSK), a protein involved in cell death. Therefore, the aim of this work was to further elucidate the estrogen-mediated signaling pathways involved in APP processing, with particular emphasis on GSK activity. By stimulating rat hypothalamic neuronal GT1-7 cells with estradiol, we found that estrogen decreases the activation state of GSK via the MAP kinase pathway. Moreover, the inhibition of GSK activity by LiCl causes enhanced sAPPalpha secretion in a pattern similar to that seen in response to estrogen, suggesting a pivotal role for this deactivation in APP processing. Further, inactivation of GSK by estrogen can be confirmed in an in vivo model. Elucidation of the signaling pathways involved in APP processing may help to understand the pathology of AD and may also prove beneficial in developing therapeutic strategies to combat AD.
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PMID:Estrogen-induced cell signalling in a cellular model of Alzheimer's disease. 1271 Oct 16

The effects of lead on the signal transduction pathways that may be involved in the release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus have not been well defined. Using the GT1-7 cell line, an in vitro model for GnRH-secreting neurons, we examined signal transduction pathways directly affected by lead. We found that lead-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2), as well as p90RSK and cAMP response element-binding protein (CREB), but did not induce IkappaB degradation. MEK1/2 inhibitor (PD98059) suppressed lead-induced ERK and p90RSK activation. Neither PKC inhibitors (Go6983, Go6976) nor CaMKII inhibitor (KN-62) had a pronounced effect on lead-induced ERK1 and ERK2 phosphorylation. However, MEK1/2 inhibitor, CaMKII inhibitor, and PKC inhibitor significantly suppressed lead-induced CREB phosphorylation. These results indicate that lead-activated PKC, CaMKII and MEK/ERK/p90RSK pathways simultaneously, all of which contributed to CREB phosphorylation. Our results also indicate that lead-induced p90RSK and CREB activation does not alter expression of early response genes like c-fos. We conclude that lead activates PKC, CaMKII or MEK-ERK-p90RSK pathways in GT1-7 cells, leading to CREB phosphorylation and modulation of gene expression.
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PMID:Lead-induced cell signaling cascades in GT1-7 cells. 1283 8


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