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

Steel factor (SF), the ligand for the proto-oncogene c-kit, acts synergistically with GM-CSF or IL-3 to support the growth of normal human hematopoietic progenitor cells. We examined the effects of SF on GM-CSF or IL-3 induced proliferation of a human factor-dependent cell line, MO7. SF supported MO7 cell proliferation as well as IL-3 or GM-CSF alone, and its addition dramatically enhanced (three- to sixfold) maximal GM-CSF or IL-3 stimulated proliferation. SF did not increase the number or affinity of cell surface GM-CSF receptors. We examined several early events of signal transduction in an effort to elucidate the biochemical mechanisms of synergy of these factors. Since each of these three cytokines is believed to function in part through activation of a tyrosine kinase, we examined their effects on cellular phosphotyrosine containing proteins. Each cytokine induced rapid, transient, and concentration dependent tyrosine phosphorylation of a number of substrates. For GM-CSF and IL-3, these phosphoproteins were indistinguishable (150, 125, 106, 93, 80, 79, 73, 44, 42, and 36 kDa), while SF induced major or minor tyrosine phosphorylation of 205, 140-150, 116, 106, 94, 90, 80, 79, 73, 44, 42, 39, 36, 32 kDa phosphoproteins. Two other signal transduction intermediates known to be phosphorylated and activated by GM-CSF and IL-3, the 70-75 kDa Raf-1 kinase, and p42 mitogen-activated protein kinase-2 (MAPK), were also phosphorylated by SF. Combinations of GM-CSF or IL-3 with SF did not further increase the phosphorylation of Raf-1 or p42 MAPK when compared to any of the factors alone. In contrast SF, but not GM-CSF or IL-3, induced tyrosine phosphorylation of phospholipase C-gamma (PLC-gamma). These results indicate that SF and GM-CSF/IL-3 have partially overlapping effects on early signal transducing events, as well as striking differences, such as tyrosine phosphorylation of PLC-gamma. This cell line should provide a useful model system to investigate the complicated process of hematopoietic growth factor synergy.
 ...
PMID:Granulocyte-macrophage colony-stimulating factor and steel factor induce phosphorylation of both unique and overlapping signal transduction intermediates in a human factor-dependent hematopoietic cell line. 138 14

Apoptosis of haemopoietic cells can be inhibited by various cytokines, but the specific signalling pathways involved are not well defined. Interleukin (IL)-4 has unique actions since it is unable to activate p21ras or mitogen-activated protein kinase, but can activate PtdIns 3-OH-kinase (PtdIns 3-kinase), the latter effect being shared with most other cytokines. In many cases, IL-4 is able to maintain cell viability by inhibiting apoptosis, but is unable to stimulate continuous proliferation of cells. This led us to investigate the role of PtdIns 3-kinase in inhibition of apoptosis. Two potent inhibitors of PtdIns 3-kinase, wortmannin and LY294002, rapidly induced apoptosis in cells incubated in the presence of IL-4, at concentrations consistent with their ability to inhibit PtdIns 3-kinase activity in whole cells. Interestingly, the same effect was seen in cells in the presence of IL-3 and Steel factor, while cells incubated in the presence of granulocyte-macrophage colony stimulating factor, and to a lesser extent, IL-5 could bypass the effect of wortmannin or LY294002. Therefore, this study suggests that PtdIns 3-kinase activity provides an important, although not a unique signal, required to inhibit apoptosis in haemopoietic cells.
 ...
PMID:Role of phosphatidylinositol 3-OH-kinase activity in the inhibition of apoptosis in haemopoietic cells: phosphatidylinositol 3-OH-kinase inhibitors reveal a difference in signalling between interleukin-3 and granulocyte-macrophage colony stimulating factor. 749 6

Interleukin 3 (IL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) exert their biological functions through acting on a specific receptor which consists of a ligand-specific alpha subunit and the shared common beta subunit. Inhibition by genistein of a subset of IL-3/GM-CSF-mediated signals, including c-myc induction, resulted in the abrogation of DNA synthesis, however, IL-3 still protected cells from apoptotic cell death. Conversely, a C-terminal truncated form of the GM-CSF receptor, which is missing a critical cytoplasmic region required for activation of the Ras/Raf-1/MAP kinase pathway, induced DNA synthesis, but failed to prevent cell death in response to GM-CSF. Consequently, cells died by apoptosis in the presence of GM-CSF, despite displaying a transient mitogenic response. However, expression of activated Ras protein complemented defective signalling through the mutant receptor and supported long-term proliferation in concert with GM-CSF. These results indicate that IL-3 and GM-CSF prevent apoptosis of hematopoietic cells by activating a signalling pathway distinct from the induction of DNA synthesis and that long-term cell proliferation requires the activation of both pathways.
 ...
PMID:Suppression of apoptotic death in hematopoietic cells by signalling through the IL-3/GM-CSF receptors. 783 37

The high affinity receptor for GM-CSF consists of a unique alpha subunit and a beta subunit that is shared with receptors for IL-3 and IL-5. Activation of GM-CSF receptor (GMR) triggers two distinct cytoplasmic signalling pathways, JAK2 and Ras, and is sufficient to maintain proliferation of growth factor-dependent cell lines. Shc proteins are phosphorylated upon activation of GMR and may be involved in the transmission of GM-CSF signals to Ras. To define the role of Shc proteins in cells stimulated with GM-CSF, we investigated both the network of interactions that involve Shc after GM-CSF stimulation and the effects of overexpressing Shc proteins on the proliferative response to GM-CSF. Two cytoplasmic complexes, Grb2/Sos and Grb2/p140 bind through the Grb2 SH2 domain to phosphorylated Shc, and are thereby recruited to the beta subunit. Both complexes are stable, even in the absence of ligand, and depend on the direct association of p140 and Sos respectively with the SH3 domains of Grb2. p140 is an uncharacterized protein constitutively phosphorylated on tyrosine and, in its Grb2-bound form, expressed only in hematopoietic cells, the oligomeric complex formed by phosphorylated beta subunit-phosphorylated Shc-Grb2-SoS-p140 is also induced by IL-3 and L-5 stimulation of growth-factor dependent cell lines. Overexpression of wild-type Shc proteins in growth factor-dependent cells increases both MAP kinase activation and proliferation in response to GM-CSF. These effects require the association of Shc with Grb2. Taken together these results indicate that phosphorylation of Shc proteins is a crucial step in the transmission of GM-CSF proliferative stimuli, since it creates a high affinity binding site for the Grb2/SoS complex, whose function is to activate Ras and, for the Grb2/p140 complex, whose function remains unknown.
 ...
PMID:Overexpression of Shc proteins potentiates the proliferative response to the granulocyte-macrophage colony-stimulating factor and recruitment of Grb2/SoS and Grb2/p140 complexes to the beta receptor subunit. 789 32

The high-affinity receptors for granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 3 (IL-3) and IL-5 consist of two subunits, alpha and beta. The alpha subunits are specific to each cytokine and the same beta subunit (beta c) is shared by these three receptors. Although none of these receptor subunits has intrinsic kinase activity, these cytokines induce protein tyrosine phosphorylation, activation of Ras, Raf-1 and MAP kinase, and transcriptional activation of nuclear proto-oncogenes such as c-myc, c-fos and c-jun. In this paper, we describe a detailed analysis of the signaling potential of the beta c subunit by using a series of cytoplasmic deletion mutants. The human beta c consists of 881 amino acid residues. A C-terminal deletion mutant of beta c at amino acid 763 (beta 763) induced phosphorylation of Shc and activation of Ras, Raf-1, MAP kinase and p70 S6 kinase, whereas a deletion at amino acid 626 (beta 626) induced none of these effects. The beta 763 mutant, as well as the full-length beta c, induced transcription of c-myc, c-fos and c-jun. Deletions at amino acid 517 (beta 517) and 626 (beta 626) induced c-myc and pim-1, but no induction of c-fos and c-jun was observed. GM-CSF increased phosphatidylinositol 3 kinase (PI3-K) activity in anti-phosphotyrosine immunoprecipitates from cells expressing beta 763 as well as beta c, whereas it was only marginally increased from cells expressing beta 517 or beta 626. Thus, there are at least two distinct regions within the cytoplasmic domain of beta c that are responsible for different signals, i.e. a membrane proximal region of approximately 60 amino acid residues upstream of Glu517 is essential for induction of c-myc and pim-1, and a distal region of approximately 140 amino acid residues (between Leu626 and Ser763) is required for activation of Ras, Raf-1, MAP kinase and p70 S6 kinase, as well as induction of c-fos and c-jun.
 ...
PMID:Signal transduction by the high-affinity GM-CSF receptor: two distinct cytoplasmic regions of the common beta subunit responsible for different signaling. 822 33

The newly defined eicosatetraenoates (ETEs), 5-oxoETE and 5-oxo-15(OH)-ETE, share structural motifs, synthetic origins, and bioactions with leukotriene B4 (LTB4). All three eicosanoids stimulate Ca2+ transients and chemotaxis in human neutrophils (PMN). However, unlike LTB4, 5-oxoETE and 5-oxo-15(OH)-ETE alone cause little degranulation and no superoxide anion production. However, we show herein that, in PMN pretreated with granulocyte-macrophage or granulocyte colony-stimulating factor (GM-CSF or G-CSF), the oxoETEs become potent activators of the last responses. The oxoETEs also induce translocation of secretory vesicles from the cytosol to the plasmalemma, an effect not requiring cytokine priming. To study the mechanism of PMN activation in response to the eicosanoids, we examined the activation of mitogen-activated protein kinase (MAPK) and cytosolic phospholipase A2 (cPLA2). PMN expressed three proteins (40, 42, and 44 kDa) that reacted with anti-MAPK antibodies. The oxoETEs, LTB4, GM-CSF, and G-CSF all stimulated PMN to activate the MAPKs and cPLA2, as defined by shifts in these proteins' electrophoretic mobility and tyrosine phosphorylation of the MAPKs. However, the speed and duration of the MAPK response varied markedly depending on the stimulus. 5-OxoETE caused a very rapid and transient activation of MAPK. In contrast, the response to the cytokines was rather slow and persistent. PMN pretreated with GM-CSF demonstrated a dramatic increase in the extent of MAPK tyrosine phosphorylation and electrophoretic mobility shift in response to 5-oxoETE. Similarly, 5-oxoETE induced PMN to release some preincorporated [14C]arachidonic acid, while GM-CSF greatly enhanced the extent of this release. Thus, the synergism exhibited by these agents is prominent at the level of MAPK stimulation and phospholipid deacylation. Pertussis toxin, but not Ca2+ depletion, inhibited MAPK responses to 5-oxoETE and LTB4, indicating that responses to both agents are coupled through G proteins but not dependent upon Ca2+ transients. 15-OxoETE and 15(OH)-ETE were inactive while 5-oxo-15(OH)-ETE and 5(OH)-ETE had 3- and 10-fold less potency than 5-oxoETE, indicating a rather strict structural specificity for the 5-keto group. LY 255283, a LTB4 antagonist, blocked the responses to LTB4 but not to 5-oxoETE. Therefore, the oxoETEs do not appear to operate through the LTB4 receptor. In summary, the oxoETEs are potent activators of PMN that share some but not all activities with LTB4. The response to the oxoETEs is greatly enhanced by pretreatment with cytokines, indicating that combinations of these mediators may be very important in the pathogenesis of inflammation.
 ...
PMID:5-Oxo-eicosanoids and hematopoietic cytokines cooperate in stimulating neutrophil function and the mitogen-activated protein kinase pathway. 866 32

Flt3/flk-2 ligand (Flt3-L) co-stimulates and synergizes with cytokines such as granulocyte-macrophage colony stimulating factor, granulocyte colony stimulating factor (G-CSF), interleukin-3 (IL-3), and erythropoietin in the proliferation of bone marrow and cord blood hematopoietic stem and progenitor cells. To study the biological effects of Flt3-L on the Flt3-L responsive AML5 cell line, the retroviral vector L(Flt3-L)SN was constructed based on the vector LXSN, but containing the human Flt3-L cDNA transcriptionally regulated by the Mo-MLV LTR. High-titer amphotropic producer cells that generated 10(6) cfu/mL after shuttle packaging through ecotropic packaging cells were isolated. AML5 cells were cultured overnight with L(Flt3-L)SN retroviral supernatant, 8 micrograms/mL polybrene, and 100 U/mL G-CSF, and expanded 1 week in medium with G-CSF. Transduced cells were selected in medium containing 0.4 mg/mL G418 and then in medium with 1.0 mg/mL G418. Retroviral mediated gene transfer in G418-resistant cells was confirmed after amplification by PCR of neo-specific sequences in genomic DNA. Northern blot analysis demonstrated L(Flt3-L)SN mRNA expression. Soluble Flt3-L was undetectable (< 100 pg/mL) by ELISA assay of conditioned medium from transduced cells, but Flt3-L was detected on the surface of AML5 cells by FACS analysis. Cells were plated in colony assay with and without 100 ng/mL Flt3-L, 100 U/mL G-CSF, and the combination. Gene transfer or growth factor treatment increased somewhat the clonogenicity of the nontransduced AML5 cells. More strikingly, L(Flt3-L)SN and each growth factor combination greatly increased the size of the resultant colonies such that the size of colonies from AML5/Flt3-L cells without added growth factor approximated that of the AML5 cells stimulated by exogenous soluble Flt3-L. Moreover, MAP kinase activity in L(Flt3-L)SN-transduced cells cultured without soluble Flt3-L was increased to the level induced in control cells by soluble Flt3-L. These results indicate that retroviral mediated gene transfer and autologous expression of the Flt3-L enhances growth and intracellular signaling of AML5 cells, information that should be of value for studying the effects of Flt3-L on immature subsets of primary hematopoietic stem and progenitor cells.
 ...
PMID:Retroviral mediated gene transfer of Flt3 ligand enhances proliferation and MAP kinase activity of AML5 cells. 898 7

Human hematopoietic progenitor cells (TF-1) undergo apoptosis upon deprivation of their dependent cytokine. In this report, we have isolated and characterized some spontaneously derived cytokine-independent variants from TF-1 cells. Analysis of several signaling molecules known to be activated by the GM-CSF pathway revealed that two non-autocrine variants were still responsive to GM-CSF stimulation. However, both variants, without ligand stimulation, already had some activated forms of Raf and MAP kinases. Given current knowledge, the activated Raf/MAP kinase pathway was likely to be responsible for the survival of both variants in the cytokine-free medium. However, the growth of hybrids between wild type and either variant was unexpectedly dependent on GM-CSF. Both variants like the wild type cells were still susceptible to apoptosis induced by other stimuli. These results suggest that either the activated Raf/MAP kinase pathway in both variants is not sufficient to repress the 'two-fold' death signals generated from the hybrids or that there is another mechanism that is responsible for the factor-independent growth of both variants.
 ...
PMID:Characterization of factor-independent variants derived from TF-1 hematopoietic progenitor cells: the role of the Raf/MAP kinase pathway in the anti-apoptotic effect of GM-CSF. 903 80

Loss of functional hematopoietic cell phosphatase (HCP) underlies severe hematopoietic and immunologic abnormalities in mice homozygous for the motheaten and viable motheaten mutations. These mice die from pulmonary accumulation of macrophages that are regulated by macrophage colony-stimulating factor (M-CSF) and granulocyte (G)-M-CSF. We determined the growth response of motheaten macrophages to the two growth factors and looked for potential HCP substrates in these cells. Motheaten macrophages showed increased proliferative responses to GM-CSF but not to M-CSF, demonstrating that HCP plays a critical role in downregulating GM-CSF mitogenic signaling. Despite the heightened growth responses of the motheaten macrophages to GM-CSF, there were no marked differences between motheaten macrophages and normal controls in GM-CSF-induced phosphorylation of GM-CSFR beta, Jak2, STAT5 and MAPK, indicating that these molecules are not major HCP substrates in GM-CSF signaling. Interestingly, several markedly hyperphosphorylated proteins were detected in the motheaten macrophages, including a novel 126-kDa phosphotyrosine protein that associated with the phosphatase via its SH2 domains, suggesting that these proteins depend on HCP for dephosphorylation and may mediate the heightened growth responses to GM-CSF. Our data indicate that macrophage hypersensitivity to GM-CSF may be a major factor in motheaten pathogenesis and that HCP may dephosphorylate novel substrates critical in GM-CSF mitogenic signaling.
 ...
PMID:Macrophages from motheaten and viable motheaten mutant mice show increased proliferative responses to GM-CSF: detection of potential HCP substrates in GM-CSF signal transduction. 921 34

1 Differential HL60 cells have been utilized as a model system to examine the 'priming' of neutrophil phospholipase A2 activity. In control cells activation of phospholipase A2 by a 5 min stimulation with the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (100 nM) was essentially undetectable. When cells were primed by preincubation with 5 microns cytochalasin B for 5 min arachidonate release, a measure of phospholipase A2 activation, was observed within 20 s. 2 Priming by cytochalasin B did not involve or require a change in intracellular free calcium concentration. 3 Priming was associated with an increase in general protein tyrosine phosphorylation and could also be induced by the receptor tyrosine kinase agonist granulocyte macrophage colony-stimulating factor (GM-CSF, 20 ng ml-1) and be mimicked by treatment with the phosphotyrosine phosphatase inhibitor perhydrovanadate (0.5 mM). However, increase in MAP kinase activity was not involved in the priming process. 4 Western blot analysis demonstrated that phospholipase A2 was phosphorylated in both control and primed cells, but that an increase in the amount of membrane associated enzyme was found in the primed cells. 5 Thus priming appears to be due to membrane association of the phospholipase and this may be regulated by tyrosine kinase activities.
 ...
PMID:The regulation by phosphorylation of 'priming' of phospholipase A2 activity in the neutrophil model system, differentiated HL60 cells. 929 23


1 2 3 4 5 6 7 8 9 10 Next >>