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)

Angiogenesis depends on proper collagen biosynthesis and cross-linking, and type I collagen is an ideal angiogenic scaffold, although its mechanism is unknown. We examined angiogenesis using an assay wherein confluent monolayers of human umbilical vein endothelial cells were overlain with collagen in a serum-free defined medium. Small spaces formed in the cell layer by 2 h, and cells formed net-like arrays by 6-8 h and capillary-like lumens by 24 h. Blocking of alpha2beta1, but not alpha1 or alpha(v)beta3 integrin function halted morphogenesis. We found that a triple-helical, homotrimeric peptide mimetic of a putative alpha2beta1 binding site: alpha1(I)496-507 GARGERGFP*GER (where single-letter amino acid nomenclature is used, P* = hydroxyproline) inhibited tube formation, whereas a peptide carrying another putative site: alpha1(I)127-138 GLP*GERGRP*GAP* or control peptides did not. A chemical inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), SB202190, blocked tube formation, and p38 MAPK activity was increased in collagen-treated cultures, whereas targeting MAPK kinase (MEK), focal adhesion kinase (FAK), or phosphatidylinositol 3-kinase (PI3K) had little effect. Collagen-treated cells had fewer focal adhesions and 3- to 5-fold less activated FAK. Thus capillary morphogenesis requires endothelial alpha2beta1 integrin engagement of a single type I collagen integrin-binding site, possibly signaling via p38 MAPK and focal adhesion disassembly/FAK inactivation.
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PMID:Angiogenesis in collagen I requires alpha2beta1 ligation of a GFP*GER sequence and possibly p38 MAPK activation and focal adhesion disassembly. 1278 34

Adhesion to type 1 collagen can elicit different cellular responses dependent upon whether the collagen is in a fibrillar form (gel) or monomeric form (film). Hepatocytes adherent to collagen film spread extensively, express cyclin D1, and increase DNA synthesis in response to epidermal growth factor, whereas hepatocytes adherent to collagen gel have increased differentiated function, but lower DNA synthesis. The signaling mechanisms by which different forms of type I collagen modulate cell cycle progression are unknown. When ERK MAP kinase activation was analyzed in hepatocytes attached to collagen film, two peaks of ERK activity were demonstrated. Only the second peak, which correlated with an increase of cyclin D1, was required for G1-S progression. Notably, this second peak of ERK activity was absent in cells adherent to collagen gel, but not required in the presence of exogenous cyclin D1. Expression of activated mutants of the Ras/Raf/MEK signaling pathway in cells adherent to collagen gel restored ERK phosphorylation and DNA synthesis, but differentially affected cell shape. Although Ras, Raf, and MEK all increased expression of cyclin D1 on collagen film, only Ras and Raf significantly up-regulated cyclin D1 levels on collagen gel. These results demonstrate that adhesion to polymerized collagen induces growth arrest by inhibiting the Ras/ERK-signaling pathway to cyclin D1 required in late G1.
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PMID:The role of collagen structure in mitogen stimulation of ERK, cyclin D1 expression, and G1-S progression in rat hepatocytes. 1279 85

During liver fibrosis hepatic stellate cells become activated, transforming into proliferative myofibroblastic cells expressing type I collagen and alpha-smooth muscle actin. They become the major producers of the fibrotic neomatrix in injured liver. This study examines if activated stellate cells are a committed phenotype, or whether they can become deactivated by extracellular matrix. Stellate cells isolated from normal rat liver proliferated and expressed mRNA for activation markers, alpha-smooth muscle actin, type I procollagen and tissue inhibitor of metalloproteinases-1 following 5-7 day culture on plastic, but culture on Matrigel suppressed proliferation and mRNA expression. Activated stellate cells were recovered from plastic by trypsinisation and replated onto plastic, type I collagen films or Matrigel. Cells replated on plastic and type I collagen films proliferated and remained morphologically myofibroblastic, expressing alpha-smooth muscle actin and type I procollagen. However, activated cells replated on Matrigel showed <30% of the proliferative rate of these cells, and this was associated with reduced cellular expression of proliferating cell nuclear antigen and phosphorylation of mitogen-activated protein kinase in response to serum. Activated HSC replated on Matrigel for 3-7 days progressively reduced their expression of mRNA for type I procollagen and alpha-smooth muscle actin and both became undetectable after 7 days. We conclude that basement membrane-like matrix induces deactivation of stellate cells. Deactivation represents an important potential mechanism mediating recovery from liver fibrosis in vivo where type I collagen is removed from the liver and stellate cells might re-acquire contact with their normal basement membrane-like pericellular matrix.
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PMID:Basement membrane-like matrix inhibits proliferation and collagen synthesis by activated rat hepatic stellate cells: evidence for matrix-dependent deactivation of stellate cells. 1285 33

TGF-beta1 has been implicated in glomerular extracellular matrix accumulation, although the precise cellular mechanism(s) by which this occurs is not fully understood. The authors have previously shown that the Smad signaling pathway is present and functional in human glomerular mesangial cells and plays a role in activating type I collagen gene expression. It also was determined that TGF-beta1 activates ERK mitogen-activated protein kinase in mesangial cells to enhance Smad activation and collagen expression. Here, it was shown that TGF-beta1 rapidly induces cytoskeletal rearrangement in human mesangial cells, stimulating smooth muscle alpha-actin detection in stress fibers and promoting focal adhesion complex assembly and redistribution. Disrupting the actin cytoskeleton with cytochalasin D (Cyto D) selectively decreased basal and TGF-beta1-induced cell-layer collagen I and IV accumulation. The balance of matrix metalloproteinases (MMP) and inhibitors was altered by Cyto D or TGF-beta1 alone, increasing MMP activity, increasing MMP-1 expression, and decreasing tissue inhibitor of matrix metalloproteinase-2 expression. Cyto D also decreased basal and TGF-beta1-stimulated alpha1(I) collagen mRNA but did not inhibit TGF-beta-stimulated alpha1(IV) mRNA expression. A similar decrease in alpha1(I) mRNA expression caused by the actin polymerization inhibitor latrunculin B was partially blocked by the addition of jasplakinolide, which promotes actin assembly. The Rho-family GTPase inhibitor C. difficile toxin B or the Rho-associated kinase inhibitor Y-27632 also blocked TGF-beta1-stimulated alpha1(I) mRNA expression. Cytoskeletal disruption reduced Smad2 phosphorylation but had little effect on mRNA stability, TGF-beta receptor number, or receptor affinity. Thus, TGF-beta1-mediated collagen I accumulation is associated with cytoskeletal rearrangement and Rho-GTPase signaling.
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PMID:Cytoskeletal rearrangement and signal transduction in TGF-beta1-stimulated mesangial cell collagen accumulation. 1287 50

5-Fluorouracil (5-FU), a pyrimidine analog widely used in cancer chemotherapy and in glaucoma surgery, has recently shown some efficacy in the treatment of keloids, scars that overgrow the boundaries of original wounds. Given the physiopathological importance of transforming growth factor-beta (TGF-beta) in keloid and scar formation, we have examined whether the clinical benefits from 5-FU treatment may result from its capacity to interfere with TGF-beta signaling and resulting activation of type I collagen gene expression. Using various molecular approaches to study the mechanisms underlying 5-FU effects, we have demonstrated that 5-FU antagonizes TGF-beta-driven COL1A2 transcription and associated type I collagen production by dermal fibroblasts. In addition, 5-FU inhibits both SMAD3/4-specific transcription and formation of SMAD/DNA complexes induced by TGF-beta. 5-FU induces c-Jun phosphorylation and activates both AP-1-specific transcription and DNA binding. Overexpression of an antisense c-jun expression vector, or that of a dominant-negative form of MKK4 that interferes with c-Jun N-terminal kinase (JNK) activation, blocks the inhibitory activity of 5-FU on TGF-beta-induced COL1A2 transcription. Furthermore, in a cellular context devoid of JNK activity (i.e., JNK-/- fibroblasts), 5-FU inhibits neither formation of SMAD/DNA complexes nor SMAD-driven COL1A2 transcription in response to TGF-beta. Together, these results identify 5-FU as a potent inhibitor of TGF-beta/SMAD signaling, capable of blocking TGF-beta-induced, SMAD-driven up-regulation of COL1A2 gene expression in a JNK-dependent manner. We thus provide a molecular explanation to the observed clinical benefits of 5-FU in the treatment of keloids and hypertrophic scars.
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PMID:5-fluorouracil blocks transforming growth factor-beta-induced alpha 2 type I collagen gene (COL1A2) expression in human fibroblasts via c-Jun NH2-terminal kinase/activator protein-1 activation. 1292 Feb 8

The Cbfa1/Runx2 transcription factor is essential for osteoblast differentiation. However, levels of Runx2 are often not well correlated with its transcriptional activity suggesting that this factor must be activated either by covalent modification or through interactions with other nuclear components. Runx2 is phosphorylated and activated by the mitogen-activated protein kinase (MAPK) pathway. This pathway is stimulated in at least two ways: by binding of type I collagen to alpha2beta1 integrins on the osteoblast surface and by treatment of cells with the osteogenic growth factor, FGF2. Protein kinase A (PKA) also may phosphorylate/activate Runx2 under certain conditions. Runx2 activity also is enhanced by factors known to stimulate specific signal transduction pathways such as PTH/PTHrP (signals through PKA and PKC pathways) and BMPs (Signal through Smad proteins). Interactions with Runx2 are complex involving both binding of distinct components such as AP-1 factors and Smads to separate sites on DNA, direct interactions between Runx2 and AP-1/Smad factors and MAPK or PKA-dependent Runx2 phosphorylation. These findings suggest that Runx2 plays a central role in coordinating multiple signals involved in osteoblast differentiation.
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PMID:Multiple signaling pathways converge on the Cbfa1/Runx2 transcription factor to regulate osteoblast differentiation. 1295 83

Background/AIMS: Hepatic stellate cells (HSCs) play a key role in the production and degradation of extracellular matrix (ECM) in the liver. In the present study, we investigated the interaction between ECM and HSCs in vitro with emphasis on the modulation of matrix metalloproteinases (MMPs) by ECM. METHODS: Freshly isolated rat HSCs were cultured in several conditions on type I collagen- or matrigel-coated dishes, on thick matrigel or in three-dimensional type I collagen (3D-gel), and MMPs expression in HSCs was examined. In addition, activation and signaling pathway of MMP-9 expression modulated by 3D-gel in HSCs were examined. RESULTS: Increased expression of MMP-3, -9, -13 and -14 was markedly detected only in the 3D-gel-treated HSCs. Zymography demonstrated that only 3D-gel-treated cells showed active gelatinase activity of MMP-9 at 82 kDa. MMP-9 expression was inhibited by neutralizing antibody against integrin alpha2beta1, tyrosine kinase inhibitors, or MEK1,2 inhibitor PD 98059, but not by p38 inhibitor SB 203580. Western blotting also showed phosphorylated p38, ERK1,2, and JUN/SAPK was quickly induced in HSCs by 3D-gel. CONCLUSIONS: MMP-9 expression and activation is induced in HSCs by 3D-gel and this observed collagen-dependent induction of MMP-9 requires ERK1,2 activity.
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PMID:Modulation of matrix metalloproteinase-9 in hepatic stellate cells by three-dimensional type I collagen: its activation and signaling pathway. 1296 32

Maturation of dendritic cells (DCs) is critical for their ability to stimulate resting naive T cells in primary immune responses. Previous studies demonstrated that collagen, such as type I collagen, could facilitate DC maturation; however, the basis of collagen-mediated DC maturation remains unclear. Discoidin domain receptor 1 (DDR1) is a nonintegrin collagen receptor constitutively expressed in a variety of epithelial cells, including tumor cells, and is inducible in leukocytes. In this study, we evaluated the role of DDR1 in DC maturation using human monocyte-derived DCs. Two DDR1 isoforms, DDR1a and DDR1b, were expressed in both immature and mature DCs. Activation of DDR1 on immature DCs resulted in their partial maturation; however, DDR1 activation markedly amplified TNF-alpha- and LPS-induced phenotypic and functional maturation of DCs through activation of p38 mitogen-activated protein kinase (MAPK), suggesting the involvement of DDR1b in this process. Activation of DDR1b on differentiated DDR1b-overexpressing THP-1 cells or DDR1 on mature DCs induced the formation of TNFR associated factor 6 (TRAF6)/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK complex and p38alpha autophosphorylation. Transfection of differentiated DDR1b-overexpressing THP-1 cells with dominant negative TRAF6 completely abrogated DDR1b-mediated p38 MAPK phosphorylation, indicating a critical role of TRAF6 in DDR1b-mediated p38 MAPK activation. Taken together, our data suggest that DDR1b-collagen interaction augments the maturation of DCs in a tissue microenvironment through a unique TRAF6/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK signaling cascade and contributes to the development of adaptive immune responses.
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PMID:Activation of discoidin domain receptor 1 facilitates the maturation of human monocyte-derived dendritic cells through the TNF receptor associated factor 6/TGF-beta-activated protein kinase 1 binding protein 1 beta/p38 alpha mitogen-activated protein kinase signaling cascade. 2066 Mar 62

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the spinal ligaments. Mechanical stress, which acts on the posterior ligaments, is thought to be an important factor in the progression of OPLL. To clarify this mechanism, we investigated the effects of in vitro cyclic stretch (120% peak to peak, at 0.5 Hz) on cultured spinal ligament cells derived from OPLL (OPLL cells) and non-OPLL (non-OPLL cells) patients. The mRNA expressions of Cbfa1 (an osteoblast-specific transcription factor), type I collagen, alkaline phosphatase (ALP), osteocalcin and integrin beta1 (a mechanotransducer) were increased by cyclic stretch in OPLL cells, whereas no change was observed in non-OPLL cells. The effects of cyclic stretch on the spinal ligament tissues derived from OPLL and non-OPLL patients were also analyzed by immunohistochemistry using an antibody against Cbfa1. The expression of Cbfa1 was increased by cyclic stretch at the center of the spinal ligament tissues of OPLL patients, whereas no change was observed in the tissues of non-OPLL patients. Furthermore, U0126, a specific inhibitor of MAPK kinase (MEK), suppressed the stretch-induced mRNA expressions of Cbfa1, ALP and type I collagen in OPLL cells. These results suggest that in OPLL cells, mechanical stress is converted by integrin beta1 into intracellular signaling and that Cbfa1 is activated through the MAP kinase pathway. Therefore, we propose that mechanical stress plays a key role in the progression of OPLL through an increase in Cbfa1 expression.
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PMID:Uni-axial cyclic stretch induces Cbfa1 expression in spinal ligament cells derived from patients with ossification of the posterior longitudinal ligament. 1463 70

Because of its ease of dispersal and high lethality, Bacillus anthracis is one of the most feared biowarfare agents. A better understanding of anthrax pathogenesis is urgently needed to develop new therapies for systemic disease that is relatively unresponsive to antibiotics. Although experimental evidence has implicated a role for macrophages in anthrax pathogenesis, clinical and pathological observations suggest that a direct insult to the host vasculature may also be important. Two bacterial toxins, lethal toxin and edema toxin, are believed to mediate the clinical sequelae of anthrax. Here, I examined whether these toxins are directly toxic to endothelial cells, the cell type that lines the interior of blood vessels. I show for the first time that lethal toxin but not edema toxin reduces the viability of cultured human endothelial cells and induces caspase-dependent endothelial apoptosis. In addition, this toxicity affects both microvascular and large vessel endothelial cells as well as endothelial cells that have differentiated into tubules within a type I collagen extracellular matrix. Finally, lethal toxin induces cleavage of mitogen-activated protein kinase kinases in endothelial cells and inhibits phosphorylation of ERK, p38, and JNK p46. Based on the contributions of these pathways to endothelial survival, I propose that lethal toxin-mediated cytotoxicity/apoptosis results primarily through inhibition of the ERK pathway. I also hypothesize that the observed endothelial toxicity contributes to vascular pathology and hemorrhage during systemic anthrax.
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PMID:Anthrax lethal toxin induces human endothelial cell apoptosis. 1468 24


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