Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51812 (mitogen-activated protein)
 10,636 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hypothalamic decapeptide gonadotropin-releasing hormone stimulates mobilization of two discrete pools of calcium in clonal (alphaT3-1) and primary pituitary gonadotropes. A multidisciplinary approach was implemented to investigate the effects of discrete calcium fluctuations on the signaling pathways linking the gonadotropin-releasing hormone receptor to activation of mitogen-activated protein kinases and immediate early genes. Blockade of calcium influx through nifedipine-sensitive voltage-gated calcium channels reduced buserelin-induced activation of extracellular signal-regulated kinase (ERK) and c-Fos while activation of c-Jun N-terminal kinase and c-Jun was unaffected. Inhibition of buserelin-stimulated ERK activity by nifedipine was also observed in rat pituitary cells in primary culture. Direct activation of alphaT3-1 cell L-type calcium channels with the agonist Bay-K 8644 resulted in phosphorylation of ERK and induction of c-Fos. However, simple voltage-induced channel activation did not produce a sufficient calcium signal, since depolarization with 35 mM KCl failed to induce activation of ERK. Depletion of intracellular calcium stores with thapsigargin did not affect buserelin-induced ERK activation. An inhibitor of protein kinase C decreased calcium influx through nifedipine-sensitive calcium channels and phosphorylation of ERK induced by buserelin. Pharmacological inhibition of protein kinase C did not block Bay-K 8644-induced ERK activation. These observations suggest that calcium influx through L-type channels is required for GnRH-induced activation of ERK and c-Fos and that the influence of calcium lies downstream of protein kinase C.
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PMID:Calcium influx through L-type channels is required for selective activation of extracellular signal-regulated kinase by gonadotropin-releasing hormone. 1051 57

Although gonadotropin-releasing hormone agonists (GnRHa) have been used in the therapy of the endocrine-dependent cancers, their biological mechanism remained obscure. We have studied the roles of mitogen-activated protein kinase family in the antiproliferative effect of GnRHa on the Caov-3 human ovarian cancer cell line. Reverse transcription-PCR assays confirmed mRNA for GnRH receptor in Caov-3 cells. In the presence of 1 microM GnRHa, the proliferation of cells was significantly reduced to 76% of controls after 24 h, and the effect was sustained up to 4 days. Although GnRHa had no effect on the activation of the Jun N-terminal kinase (JNK), treatment of Caov-3 cells with GnRHa activated extracellular signal-regulated protein kinase (ERK), and its effect was more than that induced by GnRH. Activation of ERK by GnRHa occurred within 5 min, with the maximum occurring at 3 h and sustained until 24 h. GnRHa also activated ERK kinase (mitogen-activated protein/ERK kinase) and resulted in an increase in phosphorylation of son of sevenless (Sos), and Shc. Furthermore, we examined the mechanism by which GnRHa induced ERK activation. Both pertussis toxin (10 ng/ml), which inactivates Gi/Go proteins, and expression of a peptide derived from the carboxyl terminus of the beta-adrenergic receptor kinase I, which specifically blocks signaling mediated by the betagamma subunits of G proteins, blocked the GnRHa-induced ERK activation. Phorbol 12-myristate 13-acetate (PMA) also induced the ERK activity, but pretreatment of the cultured cells with PMA to down-regulate protein kinase C did not abolish the activation of ERK by GnRHa. Elimination of extracellular Ca2+ by EGTA also did not abolish the activation of ERK by GnRHa. To examine the role of ERK cascade in the antiproliferative effect of GnRHa, PD98059, an inhibitor of mitogen-activated protein/ERK kinase, was used. This inhibitor canceled the antiproliferative effect of GnRHa and apparently reversed the GnRH-induced dephosphorylation of the retinoblastoma protein, the hyperphosphorylation of which is a hallmark of G1-S transition in the cell cycle. These results provide evidence that GnRHa stimulation of ERK activity may be mediated by Gbetagamma protein, not by PMA-sensitive protein kinase C nor extracellular Ca2+ in the Caov-3 human ovarian cancer cell line, suggesting that this cascade may play an important role in the antiproliferative effect of GnRHa.
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PMID:Role of mitogen-activated protein kinase/extracellular signal-regulated kinase cascade in gonadotropin-releasing hormone-induced growth inhibition of a human ovarian cancer cell line. 1053 88

Receptors coupled to heterotrimeric G proteins are linked to activation of mitogen-activated protein kinases (MAPKs) via receptor- and cell-specific mechanisms. We have demonstrated recently that gonadotropin-releasing hormone (GnRH) receptor occupancy results in activation of extracellular signal-regulated kinase (ERK) through a mechanism requiring calcium influx through L-type calcium channels in alphaT3-1 cells and primary rat gonadotropes. Further studies were undertaken to explore the signaling mechanisms by which the GnRH receptor is coupled to activation of another member of the MAPK family, c-Jun N-terminal kinase (JNK). GnRH induces activation of the JNK cascade in a dose-, time-, and receptor-dependent manner in clonal alphaT3-1 cells and primary rat pituitary gonadotrophs. Coexpression of dominant negative Cdc42 and kinase-defective p21-activated kinase 1 and MAPK kinase 7 with JNK and ERK indicated that specific activation of JNK by GnRH appears to involve these signaling molecules. Unlike ERK activation, GnRH-stimulated JNK activity does not require activation of protein kinase C and is not blocked after chelation of extracellular calcium with EGTA. GnRH-induced JNK activity was reduced after treatment with the intracellular calcium chelator BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester), whereas activation of ERK was not affected. Chelation of intracellular calcium also reduced GnRH-induced activation of JNK in rat pituitary cells in primary culture. GnRH-induced induction and activation of the JNK target c-Jun was inhibited after chelation of intracellular calcium, whereas induction of c-Fos, a known target of ERK, was unaffected. Therefore, although activation of ERK by GnRH requires a specific influx of calcium through L-type calcium channels, JNK activation is independent of extracellular calcium but sensitive to chelation of intracellular calcium. Our results provide novel evidence that GnRH activates two MAPK superfamily members via strikingly divergent signaling pathways with differential sensitivity to activation of protein kinase C and mobilization of discrete pools of calcium.
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PMID:Divergent signaling pathways requiring discrete calcium signals mediate concurrent activation of two mitogen-activated protein kinases by gonadotropin-releasing hormone. 1079 94

Considering that the action of gonadotropin-releasing hormone (GnRH) may be mediated via different signaling pathways in extrapituitary tissues, in the present study we investigated the role of the human GnRH receptor (GnRHR) in activating mitogen-activated protein kinases (MAPKs), which regulate cell growth, division, and differentiation. The phosphorylation state of p44 and p42 MAPKs was examined using antibodies that distinguish phospho-p44/42 MAPK (P-MAPK, Thr(202)/Tyr(204)) from total p44/42 MAPK (T-MAPK, activated plus inactivated) in human ovarian and placental cells. Cell cultures were treated with various concentrations of a GnRH agonist, (D-Ala(6))-GnRH, for 5 min. (D-Ala(6))-GnRH stimulated a rapid activation of P-MAPK in human granulosa-luteal cells (hGLCs) and immortalized extravillous trophoblast (IEVT) cells. Interestingly, (D-Ala(6))-GnRH treatment of ovarian cancer (OVCAR-3) and placental carcinoma (JEG-3) cells induced a biphasic regulatory pattern in P-MAPK activity. In contrast, no change of T-MAPK levels was observed following addition of the GnRH agonist in the ovarian and placental cells examined. The physiological implication of MAPK activation by GnRH in the ovarian and placental cells was also investigated. Human GLCs were treated with (D-Ala(6))-GnRH for 24 h, and progesterone secretion was measured by an established RIA. (D-Ala(6))-GnRH induced a significant decrease in progesterone secretion with maximum inhibition (a 45% decrease over basal level) at 10(-7) M. This inhibitory effect was completely reversed by pretreatment with MAPK/ERK kinase 1 (MEK1) inhibitor (PD98059), suggesting the involvement of the MAPK pathway in hGLCs. Placental JEG-3 cells were treated with (D-Ala(6))-GnRH for 24 h, and betahCG mRNA level was measured using Northern blot analysis. (D-Ala(6))-GnRH stimulated the expression of betahCG mRNA to 160% of control value in JEG-3 cells. In contrast to the ovarian cells, pretreatment of JEG-3 cells with PD98059 failed to block the stimulatory effect of GnRH on betahCG mRNA level, suggesting that other signaling pathway(s) may play a more dominant role in GnRH-induced betahCG mRNA expression. To our knowledge, this is the first demonstration that (1) GnRH induces activation of the MAPK signaling pathway in normal and carcinoma cells of the human ovary and placenta, and (2) MAPK mediates the direct action of GnRH on progesterone production in hGLCs.
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PMID:Gonadotropin-releasing hormone activates mitogen-activated protein kinase in human ovarian and placental cells. 1116 98

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

Luteinizing hormone (LH) consists of alpha- and beta-subunits, and synthesis and secretion of LH are regulated by gonadotropin-releasing hormone (GnRH). In order to examine the molecular mechanisms by which GnRH regulates LH secretion, we transfected alphaT3-1 cells with rat LHbeta-subunit cDNA under the control of a constitutive promoter and established a stable cell line of LH2 cells which secreted LH in response to GnRH. Pulsatile and continuous GnRH pretreatments increased gene expression of the alpha-subunit and synthesis of LH, and enhanced the LH secretion by brief treatments with GnRH and 56 mM KCl. The LH secretions were partially blocked by elimination of extracellular Ca2+. GnRH-induced LH secretion was completely inhibited by calphostin C (a protein kinase C inhibitor) and 1 microM wortmannin. In contrast to the GnRH induction, high K+-induced LH secretion was inhibited by KN93, a Ca2+/calmodulin-dependent protein kinase II inhibitor, as well as by 1 microM wortmannin. We also confirmed that activation of cAMP-pathway induced LH secretion, but activation of mitogen-activated protein (MAP) kinase pathway was not involved in LH secretion. These results suggest that GnRH directly regulates LH secretion as well as LHbeta-subunit synthesis, and that LH2 cells are a useful model for the study of LH secretion induced by several secretagogues.
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PMID:Characterization of alphaT3-1 cells stably transfected with luteininzing hormone beta-subunit complementary deoxyribonucleic acid. 1294 Apr 64

Defects of either anosmin-1 or fibroblast growth factor receptor 1 (FGFR1) are known to underlie hereditary Kallmann's syndrome (KS), a human disorder of olfactory and gonadotropin-releasing hormone (GnRH) neuronal ontogeny. Here, we report a functional interaction between anosmin-1 and the FGFR1-FGF2-heparan sulfate complex, leading to amplified responses in the FGFR1 signaling pathway. In human embryonic GnRH olfactory neuroblasts, wild-type anosmin-1, but not proteins with loss-of-function KS mutations, induces neurite outgrowth and cytoskeletal rearrangements through FGFR1-dependent mechanisms involving p42/44 and p38 mitogen-activated protein kinases and Cdc42/Rac1 activation. Furthermore, anosmin-1 enhances FGF2 signaling specifically through FGFR1 IIIc in heterologous BaF3 lymphoid cells in a heparan sulfate-dependent manner. Our study provides compelling evidence for anosmin-1 as an isoform-specific co-ligand modulator of FGFR signaling that amplifies and specifies FGFR1 signaling responses during human nervous system development and defines a mechanism underlying the link between autosomal and X-linked KS.
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PMID:Anosmin-1 modulates fibroblast growth factor receptor 1 signaling in human gonadotropin-releasing hormone olfactory neuroblasts through a heparan sulfate-dependent mechanism. 1554 53

Adrenoceptors (ARs) are involved in the regulation of gonadotropin-releasing hormone (GnRH) release from native and immortalized hypothalamic (GT1-7) neurons. However, the AR-mediated signaling mechanisms and their functional significance in these cells are not known. Stimulation of GT1-7 cells with the alpha1-AR agonist, phenylephrine (Phe), causes phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinases that is mediated by protein kinase C (PKC)-dependent transactivation of the epidermal growth factor receptor (EGF-R). Phe stimulation causes shedding of the soluble ligand, heparin-binding EGF (HB-EGF), as a consequence of matrix metalloproteinase (MMP) activation. Phe-induced phosphorylation of the EGF-R, and subsequently of Shc and ERK1/2, was attenuated by inhibition of MMP or HB-EGF with the selective inhibitor, CRM197, or by a neutralizing antibody. In contrast, phosphorylation of the EGF-R, Shc and ERK1/2 by EGF and HB-EGF was independent of PKC and MMP activity. Moreover, inhibition of Src attenuated ERK1/2 responses by Phe, but not by HB-EGF and EGF, indicating that Src acts upstream of the EGF-R. Consistent with a potential role of reactive oxygen species (ROS), Phe-induced phosphorylation of EGF-R was attenuated by the antioxidant, N-acetylcysteine. These data suggest that activation of the alpha1-AR causes phosphorylation of ERK1/2 through activation of PKC, ROS and Src, and shedding of HB-EGF, which binds to and activates the EGF-R.
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PMID:Role of metalloproteinase-dependent EGF receptor activation in alpha-adrenoceptor-stimulated MAP kinase phosphorylation in GT1-7 neurons. 1633 26

Brain-derived neurotrophic factor, which activates the extracellular regulated kinase (ERK) pathway, increases formation of prions in scrapie-infected gonadotropin-releasing hormone (GT1-1) cells. This indicates that conversion of the cellular prion protein PrP(C) to its pathogenic isoform, PrP(Sc), can be regulated by physiological stimuli acting on specific signal transduction pathways. In the present study, we examined the involvement of different mitogen-activated protein (MAP) kinase cascades and the cAMP-PKA pathway in formation of proteinase K-resistant PrP(Sc) (rPrP(Sc)). Long-term depolarization of GT1-1 cells infected with the Rocky Mountain Laboratory strain of scrapie increased the formation of rPrP(Sc). This effect was associated to ERK activation and was blocked by the MAPK/ERK kinase (MEK) inhibitor U0126. Treatment with forskolin caused a similar increase in rPrP(Sc) formation that was prevented by the protein kinase A (PKA) inhibitor H89. Both depolarization and forskolin treatment were accompanied by increased phosphorylation of the S6 ribosomal protein, while phosphorylation of histone H3 occurred only after forskolin treatment. Inhibitors of p38- and c-Jun NH(2)-terminal kinase (JNK) promoted the formation of rPrP(Sc), in contrast to the clearance of rPrP(Sc) produced by inhibitors of the ERK pathway. Thus, the ERK and the p38-JNK MAP kinase pathways appear to exert opposing effects on rPrP(Sc) formation, suggesting that balances between these intracellular signaling cascades may regulate replication of prions.
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PMID:Opposing effects of ERK and p38-JNK MAP kinase pathways on formation of prions in GT1-1 cells. 1882 19

The hypothalamic decapeptide gonadotropin-releasing hormone (GnRH) is well known for its role in the control of pituitary gonadotropin secretion, but the hormone and receptor are also expressed in extrapituitary tissues and tumor cells, including epithelial ovarian cancers. It is hypothesized that they may function as a local autocrine regulatory system in nonpituitary contexts. Numerous studies have demonstrated a direct antiproliferative effect on ovarian cancer cell lines of GnRH and its synthetic analogs. This effect appears to be attributable to multiple steps in the GnRH signaling cascade, such as cell cycle arrest at G(0)/G(1). In contrast to GnRH signaling in pituitary gonadotropes, the involvement of G(alpha q), protein kinase C and mitogen-activated protein kinases is less apparent in neoplastic cells. Instead, in ovarian cancer cells, GnRH receptors appear to couple to the pertussis toxin-sensitive protein G(alpha i), leading to the activation of protein phosphatase, which in turn interferes with growth factor-induced mitogenic signals. Apoptotic involvement is still controversial, although GnRH analogs have been shown to protect cancer cells from doxorubicin-induced apoptosis. Recently, data supporting a regulatory role of GnRH analogs in ovarian cancer cell migration/invasion have started to emerge. In this minireview, we summarize the current understanding of the antiproliferative actions of GnRH analogs, as well as the recent observations of GnRH effects on ovarian cancer cell apoptosis and motogenesis. The molecular mechanisms that mediate GnRH actions and the clinical applications of GnRH analogs in ovarian cancer patients are also discussed.
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PMID:Gonadotropin-releasing hormone and ovarian cancer: a functional and mechanistic overview. 1895 39


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