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 urokinase-type plasminogen activator receptor (u-PAR) facilitates extracellular matrix degradation in part by accelerating plasmin formation at the cell surface. We previously reported that u-PAR expression is elevated in colon cancer cell lines characterized by their in vitro invasive capacity. Since, u-PAR expression is increased by a variety of growth factors, which signal through the extracellular signal-regulated kinases 1 and 2 (ERK1/ERK2), we determined if these mitogen-activated protein kinases (MAPKs) regulate u-PAR expression in two cultured colon cancer cell lines. An in-gel kinase assay showed that ERK1 activity was considerably higher in RKO cells, which display > or = 10(5) receptors/cell, than the GEO cells which have approximately 10(4) urokinase receptors per cell. The expression of either an ERK-inactivating phosphatase (CL100), or a kinase-defective ERK1, decreased the activity of a u-PAR promoter-driven CAT reporter in RKO cells. Immune complex kinase assays indicated that the constitutive ERK1 activity in RKO cells was largely a result of an activated MEK1. Further, treatment of RKO cells with a specific inhibitor (PD 098059) of MEK1 activation, which diminished ERK1 activity, reduced the amount of urokinase specifically bound to the cell surface and this was associated with reduced laminin degradation. The expression of a dominant negative c-Raf-1 also reduced u-PAR promoter activity suggesting that MEK1 activation involved an activator at, or upstream, of this serine-threonine kinase. Transfection of the u-PAR-deficient GEO cells with a constitutively activated MEK1 expression construct up-regulated u-PAR promoter activity. Similarly treatment of GEO cells with a phosphatase inhibitor (sodium vanadate) caused a dose-dependent increase in ERK1 activity which paralleled increased cell surface binding of urokinase. Taken together, these data suggest that elevated u-PAR expression, in at least a sub-population of colon cancer, is partly a consequence of a constitutively activated ERK-1-dependent signaling cascade.
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PMID:Elevated urokinase-type plasminogen activator receptor expression in a colon cancer cell line is due to a constitutively activated extracellular signal-regulated kinase-1-dependent signaling cascade. 919 Oct 56

UV irradiation leads to severe damage, such as cutaneous inflammation, immunosuppression, and cancer, but it also results in a gene induction protective response termed the UV response. The signal triggering the UV response was thought to originate from DNA damage; recent findings, however, have shown that it is initiated at or near the cell membrane and transmitted via cytoplasmic kinase cascades to induce gene transcription. Urokinase-type plasminogen activator (uPA) was the first protein shown to be UV inducible in xeroderma pigmentosum DNA repair-deficient human cells. However, the underlying molecular mechanisms responsible for the induction were not elucidated. We have found that the endogenous murine uPA gene product is transcriptionally upregulated by UV in NIH 3T3 fibroblast and F9 teratocarcinoma cells. This induction required an activator protein 1 (AP1) enhancer element located at -2.4 kb, since deletion of this site abrogated the induction. We analyzed the contribution of the three different types of UV-inducible mitogen-activated protein (MAP) kinases (ERK, JNK/SAPK, and p38) to the activation of the murine uPA promoter by UV. MEKK1, a specific JNK activator, induced transcription from the uPA promoter in the absence of UV treatment, whereas coexpression of catalytically inactive MEKK1(K432M) and of cytoplasmic JNK inhibitor JIP-1 inhibited UV-induced uPA transcriptional activity. In contrast, neither dominant negative MKK6 (or SB203580) nor PD98059, which specifically inhibit p38 and ERK MAP kinase pathways, respectively, could abrogate the UV-induced effect. Moreover, our results indicated that wild-type N-terminal c-Jun, but not mutated c-Jun (Ala-63/73), was able to mediate UV-induced uPA transcriptional activity. Taken together, we show for the first time that kinases of the JNK family can activate the uPA promoter. This activation links external UV stimulation and AP1-dependent uPA transcription, providing a transcription-coupled signal transduction pathway for the induction of the murine uPA gene by UV.
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PMID:UV irradiation induces the murine urokinase-type plasminogen activator gene via the c-Jun N-terminal kinase signaling pathway: requirement of an AP1 enhancer element. 967 63

The very low density lipoprotein receptor (VLDLr) binds diverse ligands, including urokinase-type plasminogen activator (uPA) and uPA-plasminogen activator inhibitor-1 (PAI-1) complex. In this study, we characterized the effects of the VLDLr on the internalization, catabolism, and function of the uPA receptor (uPAR) in MCF-7 and MDA-MB-435 breast cancer cells. When challenged with uPA.PAI-1 complex, MDA-MB-435 cells internalized uPAR; this process was inhibited by 80% when the activity of the VLDLr was neutralized with receptor-associated protein (RAP). To determine whether internalized uPAR is degraded, we studied the catabolism of [35S]methionine-labeled uPAR. In the absence of exogenous agents, the uPAR catabolism t(1)/(2) was 8.2 h. uPA.PAI-1 complex accelerated uPAR catabolism (t(1)/(2) to 1.8 h), while RAP inhibited uPAR catabolism in the presence (t(1)/(2) of 7.8 h) and absence (t(1)/(2) of 16.9 h) of uPA.PAI-1 complex, demonstrating a critical role for the VLDLr. When MCF-7 cells were cultured in RAP, cell surface uPAR levels increased gradually, reaching a new steady-state in 3 days. The amount of uPA which accumulated in the medium also increased. Culturing in RAP for 3 days increased MCF-7 cell motility by 2.2 +/- 0.1-fold and by 4.4 +/- 0.3-fold when 1.0 nM uPA was added. The effects of RAP on MCF-7 cell motility were entirely abrogated by an antibody which binds uPA and prevents uPA binding to uPAR. MCF-7 cells that were cultured in RAP demonstrated increased levels of activated mitogen-activated protein kinases. Furthermore, the MEK inhibitor, PD098059, decreased the motility of RAP-treated cells without affecting control cultures. These studies suggest a model in which the VLDLr regulates autocrine uPAR-initiated signaling and thereby regulates cellular motility.
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PMID:The very low density lipoprotein receptor regulates urokinase receptor catabolism and breast cancer cell motility in vitro. 1006 6

MDA-MB-231 cells are highly metastatic breast tumor cells. Their high invasiveness is thought to be due to constitutively high levels of urokinase-type plasminogen activator (uPA) and its receptor. Previously (R. Nanbu et al., C. Eur. J. Biochem., 247: 169-174, 1997), we showed that uPA mRNA in these cells is stable and that mRNA degradation mediated by an AU-rich element (ARE) is impaired. Here we report that treatment of MDA-MB-231 cells with SB203580, an inhibitor of the stress-activated p38 mitogen-activated protein (MAP) kinase, strongly destabilized uPA mRNA in an ARE-dependent manner. In contrast, in LLC-PK1 and HeLa cells, uPA mRNA is unstable, and an ARE present in the 3' untranslated region plays a role in its degradation. Enhanced ARE-mediated mRNA destabilization induced by SB203580 was also observed in both LLC-PK1 and HeLa cells with a globin chimeric mRNA harboring two copies of the ARE (globin-2ARE) from uPA mRNA. Overexpression of constitutively active MKK6, a p38 upstream activator kinase, increased the stability of the globin-2ARE message in LLC-PK1 cells, confirming the participation of p38 in the regulation of ARE-mediated mRNA decay. Interestingly, the half-life of the uPA mRNA in the three cell lines studied correlated with the basal levels of active p38. SB203580 treatment of MDA-MB-231 cells decreased cell-associated uPA activity and dramatically reduced in vitro cell invasiveness. These results suggest the participation of p38 in the control of invasiveness through regulation of the stability of uPA and uPA receptor mRNA, which is also destabilized by p38.
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PMID:Regulation by p38 mitogen-activated protein kinase of adenylate- and uridylate-rich element-mediated urokinase-type plasminogen activator (uPA) messenger RNA stability and uPA-dependent in vitro cell invasion. 1053 11

Emerging evidence indicates a prominent role for non-integrin membrane adaptors in the dynamic regulation of integrin signaling. Two such integrin-associated proteins are the glycosylphosphatidyl-inositol (GPI)-linked urokinase receptor (u-PAR) and the cholesterol-binding protein, caveolin-1. Recent studies indicate that caveolin is required for the association of Src-family kinases with beta 1 integrins. Loss of caveolin/beta 1 integrin association results in loss of ligand-induced focal adhesion kinase (FAK) phosphorylation and impaired development of focal adhesion sites. Similarly, fibronectin-dependent fyn signaling through alpha 5/beta 1 leading to mitogen-activated protein (MAP) kinase activation requires the presence of caveolin-1. Caveolin binds Src-family kinases and such binding maintains these kinases in an inactive state. Current evidence favors a model in which ligand-induced integrin clustering, a central event in integrin activation, promotes caveolin oligomerization leading to release and/or activation of Src-family kinases and initiation of integrin signaling. The presence of u-PAR promotes these events because the extracellular domain(s) of u-PAR binds to beta 1 and beta 2 integrins and the GPI anchor of u-PAR, like that of other GPI-anchored proteins, interacts with cholesterol-rich membrane domains enriched in caveolin and tyrosine kinases. Integrins, caveolin, and u-PAR form interdependent functional complexes, promoting the association of integrins with caveolin-rich signaling domains. During states of accelerated cellular migration, such as during inflammation and tumorigenesis, expression of u-PAR may be a key facilitator of integrin signaling. Interruption of u-PAR/integrin interactions may be a strategy to regulate cellular migration in these settings.
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PMID:Role of urokinase receptor and caveolin in regulation of integrin signaling. 1060 16

The monofunctional alkylating agent N-methyl-N-nitro-N-nitrosoguanidine (MNNG) is a widespread environmental carcinogen that causes DNA lesions, leading to cell death. However, MNNG can also trigger a cell-protective response by inducing the expression of DNA repair/transcription-related genes. We demonstrate that the urokinase-type plasminogen activator (uPA) gene product, a broad spectrum extracellular protease to which no DNA repair function has been assigned, is transcriptionally induced by MNNG in C2C12 and NIH3T3 cells. This induction required an AP1-enhancer element located at -2.4 kilobase (kb), because it was abrogated by deletion of this site. MNNG was found to induce the activation of JNK/SAPK and p38 mitogen-activated protein kinases (MAPKs). Accordingly, we attempted to assess the contribution of each of these MNNG-inducible MAPKs to uPA gene induction by this alkylating agent. Coexpression of dominant negative versions of kinases of the JNK pathway, such as catalytically inactive forms of MEKK1, MKK7, and JNKK, and of cytoplasmic JNK-inhibitor JIP-1, as well as treatment of cells with curcumin (which blocks JNK activation by MNNG), inhibited MNNG-induced uPA transcriptional activity. In contrast, neither dominant negative MKK6 nor SB203580, which specifically inhibit p38 MAP kinase activation, abrogated the MNNG-induced effect. Taken together, our results show that the JNK signaling pathway links external MNNG stimulation and AP1-dependent uPA gene expression, providing the first functional dissection of a transcription-coupled signal transduction pathway for MNNG. (Blood. 2000;96:1415-1424)
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PMID:The cJun N-terminal kinase (JNK) signaling pathway mediates induction of urokinase-type plasminogen activator (uPA) by the alkylating agent MNNG. 1094 86

Hypoxia in combination with a growth factor is a strong inducer of angiogenesis. Among several effects, hypoxia can activate endothelial cells directly, but the mechanism by which it acts is not fully elucidated. In vitro, human microvascular endothelial cells (hMVEC) form capillary-like tubules in fibrin solely after stimulation with a combination of fibroblast growth factor (FGF)-2 or vascular endothelial growth factor (VEGF) and the cytokine tumour necrosis factor (TNF)alpha. We show in this paper that in hypoxic conditions, FGF-2-stimulated hMVEC form tube-like structures in a fibrin matrix in the absence of TNFalpha. Hypoxia/FGF-2-stimulated cells express more urokinase-type plasminogen activator (u-PA) receptor than normoxia/FGF-2-stimulated cells and display a slightly higher turnover of u-PA. This small increase in u-PA activation probably cannot fully explain the hypoxia/FGF-2-induced tube formation. Hypoxia activated at least two signal pathways that may contribute to the enhanced angiogenic response. In hypoxia/FGF-2-stimulated hMVEC the transcription factor p65 was activated and translocated to the nucleus, whereas in normoxia/FGF-2-stimulated cells p65 remained inactive. Furthermore, in hypoxic conditions, the amounts of phosphorylated mitogen-activated protein kinases ERK1/2 were increased compared to normoxic conditions. We conclude that hypoxia is able to activate different signal pathways in FGF-2-stimulated human endothelial cells, which may be involved in hypoxia-induced angiogenesis.
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PMID:Hypoxia in combination with FGF-2 induces tube formation by human microvascular endothelial cells in a fibrin matrix: involvement of at least two signal transduction pathways. 1117 87

Plasminogen activator inhibitor 1 (PAI-1) is a major inhibitor of urokinase-type plasminogen activator (uPA). In this study, we explored the role of PAI-1 in cell signaling. In MCF-7 cells, PAI-1 did not directly activate the mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase (ERK) 1 and ERK2, but instead altered the response to uPA so that ERK phosphorylation was sustained. This effect required the cooperative function of uPAR and the very low density lipoprotein receptor (VLDLr). When MCF-7 cells were treated with uPA-PAI-1 complex in the presence of the VLDLr antagonist, receptor-associated protein, or with uPA-PAI-1(R76E) complex, which binds to the VLDLr with greatly decreased affinity, transient ERK phosphorylation (<5 min) was observed, mimicking the uPA response. ERK phosphorylation was not induced by tissue-type plasminogen activator-PAI-1 complex or by uPA-PAI-1 complex in the presence of antibodies that block uPA binding to uPAR. uPA-PAI-1 complex induced tyrosine phosphorylation of focal adhesion kinase and Shc and sustained association of Sos with Shc, whereas uPA caused transient association of Sos with Shc. By sustaining ERK phosphorylation, PAI-1 converted uPA into an MCF-7 cell mitogen. This activity was blocked by receptor-associated protein and not observed with uPA-PAI-1(R76E) complex, demonstrating the importance of the VLDLr. uPA promoted the growth of other cells in which ERK phosphorylation was sustained, including beta3 integrin overexpressing MCF-7 cells and HT 1080 cells. The MEK inhibitor, PD098059, blocked the growth-promoting activity of uPA and uPA-PAI-1 complex in these cells. Our results demonstrate that PAI-1 may regulate uPA-initiated cell signaling by a mechanism that requires VLDLr recruitment. The kinetics of ERK phosphorylation in response to uPAR ligation determine the function of uPA and uPA-PAI-1 complex as growth promoters.
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PMID:Plasminogen activator inhibitor 1 functions as a urokinase response modifier at the level of cell signaling and thereby promotes MCF-7 cell growth. 1126 65

PAI-1 (plasminogen activator inhibitor-1) binds the urokinase-type plasminogen activator (uPA) and causes its degradation via its receptor uPAR and low-density lipoprotein receptor-related protein (LRP). While both uPA and PAI-1 are chemoattractants, we find that a preformed uPA-PAI-1 complex has no chemotactic activity and that PAI-1 inhibits uPA-induced chemotaxis. The inhibitory effect of PAI-1 on uPA-dependent chemotaxis is reversed when uPAR internalization is inhibited by the 39 kDa receptor-associated protein or by anti-LRP antibodies. Under the same conditions, the uPA-PAI-1 complex is turned into a chemoattractant causing cytoskeleton reorganization and extracellular-regulated kinase/mitogen-activated protein kinases activation. Thus, uPAR internalization by PAI-1 regulates cell migration.
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PMID:PAI-1 inhibits urokinase-induced chemotaxis by internalizing the urokinase receptor. 1156 85

The type-I plasminogen activator inhibitor (PAI-1), the primary inhibitor of both tissue-type and urokinase-type plasminogen activators (t-PA, u-PA), is the primary regulator of plasminogen activation and possibly of extracellular proteolysis. In anchorage-dependent cells, the PAI-1 gene is regulated by cell adhesion. PAI-1 gene expression is induced more evidently in cells that adhered to the culture plate than in those that did not adhere. In this study, we further demonstrate that the PAI-1 gene expression associated with cell adhesion is elicited through the activation of MEK and p42/p44 mitogen-activated protein (MAP) kinase (MAPK; ERK) signal pathways. We found that the MEK inhibitors, PD98059 and U0126, inhibited the induction of PAI-1 gene and protein expression during cell adhesion, PD98059 also inhibited the adhesion of cells to the culture plate, and cell adhesion elicited the kinase activities of MEK and ERK. In addition, we illustrate that two transcription response elements, the serum response element (SRE) and the hypoxia response element (HRE), which exist in the PAI-1 promoter, might be correlated with PAI-1 gene expression during cell adhesion. We discovered that the binding ability of nucleoproteins to both SRE and HRE was enhanced by cell adhesion and was dependent on MEK. Based on these results, we suggest that both MEK and ERK are involved in the induction of PAI-1 gene expression during cell adhesion. Furthermore, the subsequent downstream molecules, Elk-1 and HIF-1, may also participate.
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PMID:The plasminogen activator inhibitor-1 gene is induced by cell adhesion through the MEK/ERK pathway. 1463 Nov 13


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