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)

We have examined highly purified osteoclasts that were generated in vitro from murine co-culture of marrow precursors with stromal support cells and have found evidence of activation of the MEK/ERK and AKT/NFkappaB survival pathways. Many mature marrow-derived osteoclasts survived for at least 48 h in culture whether or not they are maintained with stromal cells. Moreover, supplementing purified osteoclasts with RANKL and/or M-CSF had no impact on their survival pattern. In addition, spleen-derived osteoclasts generated with RANKL and M-CSF treatment exhibited a similar survival pattern. Blocking MEK, AKT, or NFkappaB activity resulted in apoptosis of many, but not all, of the osteoclasts in purified marrow-derived osteoclasts, marrow-derived osteoclasts co-cultured with stromal cells, and spleen-derived osteoclasts maintained with RANKL and M-CSF. These data support that both the MEK/ERK and AKT/NFkappaB pathways contribute to osteoclast survival. Since PI3K has been shown to activate either of these pathways, we have examined its role in osteoclast survival. PI3K inhibition caused apoptosis of nearly all osteoclasts in purified and co-cultured marrow-derived osteoclasts and spleen-derived osteoclasts maintained with RANKL and M-CSF. Interestingly, in marrow-derived co-cultures, the apoptotic response was restricted to osteoclasts as there was no evidence of stromal support cell apoptosis. PI3K inhibition also blocked MEK1/2, ERK1/2, and AKT phosphorylation and NFkappaB activation in purified osteoclasts. Simultaneous blockage of both AKT and MEK1/2 caused rapid apoptosis of nearly all osteoclasts, mimicking the response to PI3K inhibition. These data reveal that PI3K coordinately activates two distinct survival pathways that are both important in osteoclast survival.
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PMID:Phosphatidylinositol 3-kinase coordinately activates the MEK/ERK and AKT/NFkappaB pathways to maintain osteoclast survival. 1268 17

We have recently reported the identification of a novel member of the leukocyte receptor family, osteoclast-associated receptor (OSCAR), which has two Ig-like domains and functions as a bone-specific regulator of osteoclast differentiation. Here, we have cloned the OSCAR promoter region to examine its regulation by transcription factors. The 1.7-kb promoter region of the mouse OSCAR gene contains two potential E-box elements for microphthalmia transcription factor (MITF) and three putative PU.1 sites. MITF or PU.1 alone activates the OSCAR reporter construct 5-6-fold, and the combination of MITF and PU.1 synergistically activates the OSCAR reporter activity up to 110-fold. The mRNA expression patterns of MITF, PU.1, and OSCAR in TRANCE-treated (RAW 264.7) or TRANCE/M-CSF-treated cells (primary osteoclasts) reveal that MITF mRNA expression is induced at a much earlier time point than OSCAR gene expression. In contrast to MITF, PU.1 mRNA levels remain relatively constant at all time points, suggesting that TRANCE-induced MITF, not PU.1 expression, is one of the critical regulatory mechanisms for optimal OSCAR expression during osteoclastogenesis. In addition, we have shown that the combination of MITF and constitutively active MKK6-expressing plasmids synergistically activates OSCAR reporter activity. Taken together, our results strongly suggest that PU.1 and MITF transcription factors synergistically activate OSCAR gene expression. Moreover, the activation of OSCAR gene expression by PU.1/MITF is further enhanced by the TRANCE-induced MKK6/p38 signaling cascade.
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PMID:Microphthalmia transcription factor and PU.1 synergistically induce the leukocyte receptor osteoclast-associated receptor gene expression. 1269 21

We report here for the first time the detection of the ribosomal p70S6 kinase (p70S6K) in a hematopoietic cell, the neutrophil, and the stimulation of its enzymatic activity by granulocyte macrophage colony-stimulating factor (GM-CSF). GM-CSF modified the Vmax of the enzyme (from 7.2 to 20.5 pmol/min/mg) and induced a time- and dose-dependent phosphorylation on p70S6K residues Thr389 and Thr421/Ser424. The immunosuppressant macrolide rapamycin caused either a decrease in intensity of phospho-Thr389 bands in Western blots, or as a downshift in the relative mobility of phospho-Thr421/Ser424 bands (consistent with the loss of phosphate), but not both simultaneously. The immunosuppressant FK506 failed to inhibit p70S6K activation, but was able to rescue the rapamycin-induced downshift, pointing to a role for the mammalian target of rapamycin (mTOR) kinase. Rapamycin also caused an inhibition (IC50 0.2 nm) of the in vitro enzymatic activity of p70S6K. However, the inhibition of activity was not complete, but only a 40-50%, indicating that neutrophil p70S6K activity has a rapamycin-resistant component. This component was totally inhibited by pre-incubating the cells with the mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD-98059 prior to treatment with rapamycin. This indicated that a kinase from the MEK/MAPK pathway also plays a role in p70S6K activation. Thus, GM-CSF causes the dual activation of a rapamycin-resistant, MAPK-related kinase, that targets Thr421/Ser424 S6K phosphorylation, and a rapamycin-sensitive, mTOR-related kinase, that targets Thr389, both of which are needed in cooperation to achieve full activation of neutrophil p70S6K.
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PMID:Mechanism of ribosomal p70S6 kinase activation by granulocyte macrophage colony-stimulating factor in neutrophils: cooperation of a MEK-related, THR421/SER424 kinase and a rapamycin-sensitive, m-TOR-related THR389 kinase. 1274 Mar 86

Granulocyte/macrophage colony-stimulating factor (GM-CSF) inhibits Fas-induced apoptosis of neutrophils. However, the exact step in the apoptotic pathway blocked by GM-CSF remained unclear. Here, we found that pretreatment of neutrophils with GM-CSF inhibits the recruitment of Fas-associated protein with death domain (FADD) to Fas, abolishing the formation of the death-inducing signaling complex required for Fas-induced apoptosis. Two-dimensional electrophoresis revealed that GM-CSF modifies the ratio of FADD subspecies. These GM-CSF-triggered changes were abrogated, and Fas-induced apoptosis was restored by an inhibitor of classical protein kinase C (PKC), Go6976, and by the combination of a phosphatidylinositol 3-kinase (PI-3K) inhibitor, LY294002, and an inhibitor of mitogen-activated protein kinase kinase (MEK)1, PD98059. Go6976 blocked GM-CSF-elicited phosphorylation of Akt/PKB and extracellular signal-regulated kinase (ERK)1/2. These results indicated that GM-CSF suppresses Fas-induced neutrophil apoptosis by inhibiting FADD binding to Fas, through redundant actions of PI-3K and MEK1-ERK1/2 pathways downstream of classical PKC.
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PMID:Short-term delay of Fas-stimulated apoptosis by GM-CSF as a result of temporary suppression of FADD recruitment in neutrophils: evidence implicating phosphatidylinositol 3-kinase and MEK1-ERK1/2 pathways downstream of classical protein kinase C. 1532 34

Use of all-trans-retinoic acid (ATRA) in combinatorial differentiation therapy of acute promyelocytic leukemia (APL) results in exceptional cure rates. However, potent cell differentiation effects of ATRA are so far largely restricted to this disease and long-term survival rates in non-APL acute myelogeneous leukemia (AML) remain unacceptably poor, requiring development of novel therapeutic strategies. We demonstrate here that myelomonocytic growth factors (granulocyte colony-stimulating factor [G-CSF] and/or granulocyte macrophage colony-stimulating factor [GM-CSF]) potentiate differentiation effects of ATRA in different AML cell lines and primary cells from patients with myeloid leukemia. The ligand-dependent activities of endogenous and transiently expressed retinoic acid receptor alpha (RARalpha) isoforms can be potentiated by G/GM-CSF in U-937 cells and correlate with increased expression of ATRA-inducible RARalpha2 isoform. Specific inhibitors of mitogen mitogen-activated protein kinase (MAPK) (MEK)-1/-2 or p38 extracellular signal-related kinase (ERK) kinase diminish the ATRA as well as ATRA and G/GM-CSF-induced activation of the RARalpha proteins and decreased the differentiation-induced decline in cell numbers. Our data demonstrate that acting, at least in part, via the MAP kinase pathways, myelomonocytic growth factors enhance ATRA-dependent activation of the RARalpha isoforms and maturation of myeloid leukemia cells. These results suggest that combinatorial use of these agents may be effective in differentiation therapy of AML.
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PMID:Retinoids and myelomonocytic growth factors cooperatively activate RARA and induce human myeloid leukemia cell differentiation via MAP kinase pathways. 1533 53

We previously reported that oxidized low-density lipoprotein (Ox-LDL)-induced expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) via PKC, leading to activation of phosphatidylinositol-3 kinase (PI-3K), was important for macrophage proliferation [J Biol Chem 275 (2000) 5810]. The aim of the present study was to elucidate the role of extracellular-signal regulated kinase 1/2 (ERK1/2) and of p38 MAPK in Ox-LDL-induced macrophage proliferation. Ox-LDL-induced proliferation of mouse peritoneal macrophages assessed by [3H]thymidine incorporation and cell counting assays was significantly inhibited by MEK1/2 inhibitors, PD98059 or U0126, and p38 MAPK inhibitors, SB203580 or SB202190, respectively. Ox-LDL-induced GM-CSF production was inhibited by MEK1/2 inhibitors but not by p38 MAPK inhibitors in mRNA and protein levels, whereas recombinant GM-CSF-induced macrophage proliferation was inhibited by p38 MAPK inhibitors but enhanced by MEK1/2 inhibitors. Recombinant GM-CSF-induced PI-3K activation and Akt phosphorylation were significantly inhibited by SB203580 but enhanced by PD98059. Our results suggest that ERK1/2 is involved in Ox-LDL-induced macrophage proliferation in the signaling pathway before GM-CSF production, whereas p38 MAPK is involved after GM-CSF release. Thus, the importance of MAPKs in Ox-LDL-induced macrophage proliferation was confirmed and the control of MAPK cascade could be targeted as a potential treatment of atherosclerosis.
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PMID:Extracellular signal-regulated kinase and p38 mitogen-activated protein kinase mediate macrophage proliferation induced by oxidized low-density lipoprotein. 1538 Apr 45

Several studies have demonstrated that colony-stimulating factors (CSFs) are closely associated with tumor progression, metastasis and invasion through autocrine or paracrine mechanism in lung cancer. However, biologic roles of CSFs are still unknown. Elucidating the biologic roles of CSFs and the regulatory mechanisms of tumor-specific behavior by CSFs raises the possibility of having a new therapeutic approach for lung cancer. We previously established two adenocarcinoma cell lines, A924 and A964 and a large cell carcinoma cell line MI-4. MI-4 and A924 constitutively produced an abundant dose of granulocyte macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF). We examined the effects of GM-CSF and M-CSF on tumor growth, death, and invasion in CSF-producing (A924 and MI-4) and non-producing lung cancer cells (A549 and A964). These cell lines demonstrated both GM-CSF and M-CSF receptor mRNA expression. In our study, GM-CSF seemed to have advantage for tumor proliferation and invasion in lung cancer cells. M-CSF seemed to have advantage for tumor invasion, but not proliferation. The tumor-specific phenotypes (proliferation, invasion and survival) up-regulated by GM-CSF and M-CSF were mediated through MEK/ERK and PI3k/Akt pathways. However, when MEK/ERK was activated by transfection of active form of MEK1 cDNA, the tumor-specific behavior was promoted in CSF-non-producing cells, whereas inhibited in CSF-producing cells though MEK/ERK activation increased constitutive GM-CSF production. MEK/ERK signaling regulated differently tumor-specific behavior between CSF-producing cells and CSF-non-producing cells.
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PMID:Effects of GM-CSF and M-CSF on tumor progression of lung cancer: roles of MEK1/ERK and AKT/PKB pathways. 1682 Sep 47

The immunosuppressor sanglifehrin A (SfA) is a member of a family of immunophilin cyclophilin A-binding molecules and does not inhibit calcineurin activity. Sanglifehrin A inhibits M-CSF-dependent macrophage proliferation by arresting the G1 phase of the cell cycle but does not affect cell viability. This immunosuppressor exerts its action on proliferation by inactivating cyclin-dependent kinase 2 (Cdk2) activity. Moreover, c-myc expression is also repressed. In the early steps of M-CSF signaling, SfA inhibits the phosphorylation of Raf-1 and the external regulated kinases (ERK)1/2 and mitogen-activated protein kinase phosphatase-1, which are required for proliferation. The effects of SfA are not related to a block of the proteosome activity. These data show that immunophilin contributes to M-CSF-dependent proliferation through activation of the Raf-1/MEK/ERK pathway and the regulation of Cdk activities, which is required for cell cycle progression.
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PMID:Cyclophilin A is required for M-CSF-dependent macrophage proliferation. 1690 30

Determining the underlying mechanisms of macrophage colony-stimulating factor (M-CSF)-mediated osteoclast survival may be important in identifying novel approaches for treating excessive bone loss. This study investigates M-CSF-mediated MEK/ERK activation and identifies a downstream effector of this pathway. M-CSF activates MEK/ERK and induces MEK-dependent expression of the immediate early gene Egr2. Inhibition of either MEK1/2 or inhibition of Egr2 increases osteoclast apoptosis. In contrast, wild-type Egr2 or an Egr2 point mutant unable to bind the endogenous repressors Nab1/2 (caEgr2) suppresses basal osteoclast apoptosis and rescues osteoclasts from apoptosis induced by MEK1/2 or Egr2 inhibition. Mechanistically, Egr2 induces pro-survival Blc2 family member Mcl1 while stimulating proteasome-mediated degradation of pro-apoptotic Bim. In addition, Egr2 increased the expression of c-Cbl, the E3 ubiquitin ligase that catalyzes Bim ubiquitination. M-CSF, therefore, promotes osteoclast survival through MEK/ERK-dependent induction of Egr2 to control the Mcl1/Bim ratio, documenting a novel function of Egr2 in promoting survival.
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PMID:Novel pro-survival functions of the Kruppel-like transcription factor Egr2 in promotion of macrophage colony-stimulating factor-mediated osteoclast survival downstream of the MEK/ERK pathway. 1819 76

While M-CSF-mediated MEK/ERK activation promotes osteoclast survival, the signaling pathway by which M-CSF activates MEK/ERK is unresolved. Functions for PI3K, Ras, and Raf have been implicated in support of osteoclast survival, although interaction between these signaling components has not been examined. Therefore, the interplay between PI3K, Ras and Raf in M-CSF-promoted MEK/ERK activation and osteoclast survival was investigated. M-CSF activates Ras to coordinate activation of PI3K and Raf/MEK/ERK, since Ras inhibition decreased PI3K activation and PI3K inhibition did not block M-CSF-mediated Ras activation. As further support for Ras-mediated signaling, constitutively active (ca) Ras promoted MEK/ERK activation and osteoclast survival, which was blocked by inhibition of PI3K or Raf. Moreover, PI3K-selective or Raf-selective caRas were only partially able to promote osteoclast survival when compared to parental caRas. We then examined whether PI3K and Raf function linearly or in parallel downstream of Ras. Expression of caPI3K increased MEK/ERK activation and promoted osteoclast survival downstream of M-CSF, supporting this hypothesis. Blocking Raf did not decrease osteoclast survival and MEK/ERK activation promoted by caPI3K. In addition, PI3K-selective Ras-mediated survival was not blocked by Raf inhibition. Taken together, our data support that Raf signaling is separate from Ras/PI3K signaling and PI3K signaling is separate from Ras/Raf signaling. These data therefore support a role for Ras in coordinate activation of PI3K and Raf acting in parallel to mediate MEK/ERK-promoted osteoclast survival induced by M-CSF.
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PMID:Pathway crosstalk between Ras/Raf and PI3K in promotion of M-CSF-induced MEK/ERK-mediated osteoclast survival. 1827 61


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