1,721,018 research outputs found
ERK1-2 and p38 MAPK regulate MMP/TIMP balance and function in response to thrombospondin-1 fragments in the microvascular endothelium
No full textWe found that thrombospondin-1 (TSP-1) has opposite functions on angiogenesis depending on the nature of the proteolytic fragment released in vivo by the action of proteases. We studied the effect of the 25 and 140 kDa fragments of TSP-1 generated by its proteolytic cleavage on the cascade of mitogen activated protein kinase (MAPK) activation and matrix-metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) function and expression in microvascular endothelium. Post-capillary endothelial cells (CVEC) isolated from bovine heart were used. The 25 kDa fragment enhanced the upregulation of MMP-2 and -9 and reduced TIMP-2 expression leading to CVEC chemoinvasion. Conversely, the 140 kDa fragment blocked MMP-2 and -9 stimulation and doubled TIMP-2 expression, leading to inhibition of endothelial chemoinvasion induced by fibroblast growth factor-2 (FGF-2). MAPK activity (ERK1-2) was induced by TSP-1 and by the 25 kDa fragment, but not by the 140 kDa fragment which, however, promoted MAPK p38 activation. This evidence indicates that fragments originating from TSP-1 switch the pro- or anti-angiogenic phenotype in endothelium by targeting MAPK cascades with opposite functions on MMP/TIMP balance. © 2004 Elsevier Inc. All rights reserved
Cathepsin B mediates the pH-dependent proinvasive activity of tumor-shed microvesicles
No full textVesicles shed by cancer cells are known to mediate several tumor-host interactions. Tumor microenvironment
may, in turn, influence the release and the activity of tumor-shed microvesicles. In this study, we investigated
the molecular mediators of the pH-dependent proinvasive activity of tumor-shed vesicles. Gelatinase zymography
showed increased microvesicle activity of matrix metalloproteinases 9 and 2 as a result of acid exposure (pH 5.6)
compared to pH 7.4. Thus, we reasoned that the cysteine protease cathepsin B might play a role in mediating the
pH-dependent activation of gelatinases. Cathepsin B expression in tumor-shed microvesicles was confirmed by
Western blot analysis and zymography. The activity of vesicle-associated cathepsin B measured using Z-Arg-
Arg-pNA as substrate was significantly increased at acidic pH values. Inhibition of protease activity by the cysteine
protease inhibitor, E-64, and treatment of ovarian cancer cells with small interfering RNA against cathepsin B suppressed
the ability of tumor-shed microvesicles to stimulate both gelatinase activation and the invasiveness of
endothelial cells observed at low pH values. We conclude that microvesicle shedding is a major secretory pathway
for cathepsin B release from tumor cells. Hence, the acidic microenvironment found in most solid tumors may
contribute to cathepsin B–mediated proinvasive capabilities of tumor-shed vesicle
Shedding of the matrix metalloproteinases MMP-2, MMP-9 and MT1-MMP as membrane vesicles-associated components by endothelial cells
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The heparin binding 25kDa fragment of thrombospondin-1 promotes angiogenesis and modulates gelatinases and TIMP-2 in endothelial cells
No full textThe hypothesis that thrombospondin-1 (TSP-1) can exert opposite effects on angiogenesis
depending on the functional status of its domains/fragments was investigated. In the rabbit
cornea, TSP-1 inhibited angiogenesis induced by fibroblast growth factor-2 (FGF-2).
However, when tested per se, TSP-1 was able to elicit an angiogenic response comparable to
that induced by FGF-2. Induction of angiogenesis was dose-dependent (20 ng - 2 μg/pellet),
was prevented by anti-TSP antibodies or by heat-inactivation of TSP-1, and was not due to
inflammatory mediators, to FGF-2 or to TGF-β. Equimolar concentrations of the 25 kDa
heparin binding fragment of TSP-1 were even more efficient than the whole molecule, and
promoted the angiogenic activity of FGF-2. On the contrary, the 140 kDa fragment of TSP-1
did not induce angiogenesis and turned off the angiogenic response to FGF-2. The 25 kDa
fragment and TSP-1, but not the 140 kDa fragment, increased endothelial cell invasiveness
and stimulated the production and activation of matrix metalloproteinase-2 (MMP-2).
Moreover, the 25 kDa fragment reduced the synthesis of the MMP-2 inhibitor TIMP-2, while
the 140 kDa fragment caused a twofold increase in TIMP-2 production and inhibited MMPs
stimulation by TSP-1 and FGF-2. We conclude that TSP-1 is a source of smaller mediators of
angiogenesis, which affect in an opposite way endothelial cell functions and proteolytic
activity, thus resulting in an opposite final effect on angiogenesis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thrombospondin 1 as a scavenger for matrix-associated fibroblast growth factor 2
No full textThe antiangiogenic factor thrombospondin 1 (TSP-1) binds with high affinity to several heparin-binding angiogenic factors, including fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), and hepatocyte growth factor/scatter factor (HGF/SF). The aim of this study was to investigate whether TSP-1 affects FGF-2 association with the extracellular matrix (ECM) and its bioavailability. TSP-1 prevented the binding of free FGF-2 to endothelial cell ECM. It also promoted the mobilization of matrix-bound FGF-2, generating a TSP-1/FGF-2 complex. The region of TSP-1 responsible for these activities was located within the 140-kDa antiangiogenic and FGF-2 binding fragment, whereas the 25-kDa heparin-binding fragment was inactive. Matrix-released FGF-2/TSP-1 complex had a reduced ability to bind to and induce proliferation of endothelial cells. TSP-1 depleted the ECM laid by FGF-2-overproducing tumor cells of its FGF-2-dependent mitogenic activity for endothelial cells. Besides FGF-2, TSP-1 also inhibited VEGF and HGF/SF binding to the ECM and mobilized them from the ECM. Our study shows that TSP-1 acts as a scavenger for matrix-associated angiogenic factors, affecting their location, bioavailability, and function
The 140-kilodalton antiangiogenic fragment of thrombospondin-1 binds to basic fibroblast growth factor
No full textThrombospondin-1 (TSP) inhibits the angiogenic activity of basic fibroblast growth factor (bFGF). Here we address the hypothesis of a direct interaction between TSP and bFGF. Gel permeation chromatography and cross-linking experiments demonstrated that bFGF binds to TSP in solution. bFGF also bound to immobilized TSP in a solid-phase assay. Binding was dose-dependent, with a Kd in the nanomolar range, and was inhibited by anti-TSP antibodies. The 140-kDa carboxyl-terminal fragment of TSP, but not the 25-kDa heparin-binding fragment, fully retained the bFGF binding capacity. Accordingly, binding was inhibited by monoclonal antibodies directed against this fragment. Heparin completely blocked bFGF binding to TSP and to the 140-kDa fragment. TSP and its 140-kDa fragment inhibited the binding of bFGF to endothelial cells at concentrations (> or = 100 nM) that inhibited endothelial cell proliferation but not motility. Low-affinity binding was inhibited more than high-affinity binding (up to 76 and 41% inhibition, respectively), and the inhibition was reversed by anti-TSP antibodies. Vitronectin and transforming growth factor beta, potentially associated with TSP, did not affect bFGF binding to endothelial cells. Although TSP did not affect the activation of the high-affinity receptors, it reduced the long-term internalization of bFGF. We conclude that TSP binds to bFGF through a domain within its 140-kDa fragment, a mechanism that might affect bFGF interaction with endothelial cells, activity, and association with the extracellular matrix
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