The Experts below are selected from a list of 1110 Experts worldwide ranked by ideXlab platform
Curzio Ruegg - One of the best experts on this subject based on the ideXlab platform.
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radiotherapy suppresses angiogenesis in mice through tgf βri alk5 dependent inhibition of Endothelial Cell Sprouting
PLOS ONE, 2010Co-Authors: Natsuko Imaizumi, Yan Monnier, Monika E Hegi, Reneolivier Mirimanoff, Curzio RueggAbstract:Background: Radiotherapy is widely used to treat cancer. While rapidly dividing cancer Cells are naturally considered the main target of radiotherapy, emerging evidence indicates that radiotherapy also affects Endothelial Cell functions, and possibly also their angiogenic capacity. In spite of its clinical relevance, such putative anti-angiogenic effect of radiotherapy has not been thoroughly characterized. We have investigated the effect of ionizing radiation on angiogenesis using in vivo, ex vivo and in vitro experimental models in combination with genetic and pharmacological interventions.
Tony Pawson - One of the best experts on this subject based on the ideXlab platform.
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downregulation of the ras mitogen activated protein kinase pathway by the ephb2 receptor tyrosine kinase is required for ephrin induced neurite retraction
Molecular and Cellular Biology, 2001Co-Authors: Sabine Elowe, Sacha J Holland, Sarang Kulkarni, Tony PawsonAbstract:External signals that control Cellular behavior in metazoan organisms are often transduced at the Cell surface by receptor tyrosine kinases (RTKs). Eph receptors comprise the largest family of mammalian RTKs, with 14 members. The family has apparently undergone a striking expansion during the evolution of multiCellular animals, since only a single Eph receptor has been identified in Caenorhabditis elegans (30) or Drosophila (65), suggesting that these receptors might be involved in controlling complex Cellular interactions. The ligands for Eph receptors, termed ephrins, are themselves anchored to the plasma membrane, either via a glycosylphosphatidylinositol linkage (A class) or through a transmembrane sequence (B class) (21, 28, 39). Consequently, signaling generally requires direct contact between ephrin- and Eph receptor-expressing Cells. The Eph receptors are also classified into A and B groups on the basis of sequence homology and ephrin-binding ability (27). Although the binding of receptors to ephrins is generally nonselective within a given class, different combinations of receptors and ligands interact with distinct affinities, while EphA4 can bind both classes of ephrins (28). In C. elegans, the VAB-1 Eph receptor and corresponding ephrins regulate a series of morphogenetic Cell movements important for development (14, 30, 72). In mammals, Eph receptors and ephrins are expressed in reciprocal compartments of the developing embryo (28, 33) and are important for axon guidance and topographic map formation in the central nervous system (7, 19, 25, 34, 74), neural crest Cell migration (18), patterning of the hindbrain and paraxial mesoderm (28), and vascular network assembly (1, 29, 31, 71). For both invertebrates and vertebrates, there are data to suggest that Eph receptors have both kinase-dependent and kinase-independent functions, with the latter potentially reflecting either an ability of Eph-ephrin interactions to mediate Cell adhesion or an intrinsic ephrin-signaling activity (13, 22, 23, 37). In the guidance of axons in the nervous system, and in Cell migrations, ephrin-Eph receptor signaling commonly has a repulsive effect on Cell movement (11, 53, 54, 57). In vitro, the activation of Eph receptors in neuronal Cells induces deadhesive responses and collapse of neural growth cones (6), correlating with axon and neural crest Cell repulsion from ephrins displayed on Cells or isolated membranes (53, 54). Although ephrins and Eph receptors clearly activate repellant responses in many Cells, there is increasing evidence that specific ligand-receptor pairs can also initiate an attractive response in some Cell types, for example by eliciting Endothelial Cell Sprouting (1), increased Cellular adhesion (8, 22, 23, 41), neural tube closure (40), and projection of vomeronasal axons (47). This resembles the ability of several other guidance molecules to induce either attraction or repulsion (56). The intraCellular signaling pathways that mediate the biological effects of Eph receptors and ephrins are only starting to emerge. Activated receptors become autophosphorylated at multiple sites, including two absolutely conserved tyrosine residues in the juxtamembrane region and a tyrosine within the activation segment of the kinase domain (6, 44). Interestingly, prior to phosphorylation, the juxtamembrane tyrosines (Y604 and Y610 in EphB2) repress receptor kinase activity, but following phosphorylation they are released to serve as docking sites for SH2 domain proteins (6). RTKs commonly signal through cytoplasmic proteins with SH2 domains, which bind either directly to phosphotyrosine (pTyr) sites on the activated receptor or to phosphorylated docking proteins. Both mechanisms may be used by Eph receptors. A variety of SH2 proteins have been identified as potential Eph receptor-binding partners, including the Fyn and Src tyrosine kinases (15, 26, 35, 75), the p120-Ras GTPase-activating protein (p120-RasGAP) (see interaction ID:123 at www.BIND.ca [35, 38]), the Nck and Crk adaptors (35, 69), SHEP1 (24), the Ras-binding protein AF6 (36), and the Src-like adaptor protein SLAP (58). Which of these targets are relevant to the biological functions of Eph receptors remain uncertain. In addition, we and others have found that activated Eph receptors preferentially phosphorylate the p62dok-1 docking protein in neuronal and Endothelial Cells (4, 38). p62dok-1 has an N-terminal pleckstrin homology (PH) domain followed by a phosphotyrosine-binding (PTB) domain and multiple tyrosine phosphorylation sites which engage the SH2 domains of p120-RasGAP and Nck (73). In NG108 neuronal Cells expressing EphB2 and stimulated with clustered ephrin-B1, p62dok-1 is the most prominently tyrosine-phosphorylated protein other than the receptor itself (38). The Ras-mitogen-activated protein kinase (MAPK) pathway is commonly activated by RTKs, and indeed is viewed as a hallmark of RTK signaling (16). Autophosphorylation of RTKs such as the epidermal growth factor, platelet-derived growth factor (PDGF), or insulin receptors leads to the recruitment (either directly or indirectly) of the Grb2-Sos1 complex, which in turn induces the exchange of GDP for GTP on Ras proteins, and the association of Ras with the Raf serine/threonine protein kinase (59). Raf phosphorylates the dual-specificity protein kinases MEK1 and MEK2, which consequently activate the MAPKs extraCellular signal-related kinases 1 and 2 (ERK1/2). This core biochemical pathway is regulated by many different signals in numerous Cell types, raising the issue of how such a widespread signaling pathway generates distinct biological responses in different Cells or following stimulation by different ligands. In metazoans, each Cell is simultaneously exposed to multiple extraCellular signals and must integrate these inputs to initiate the appropriate outcome. The combined nature of these external signals, together with regulators expressed within the target Cell, may therefore determine the extent and duration of Ras-MAPK activation, which in turn can determine how the Cell responds (51). Unlike other RTKs, Eph receptors appear inefficient at stimulating Cell proliferation in fibroblasts or epithelial Cells (10, 12), and the role of MAPK signaling downstream of activated Eph receptors remains unclear. Here, we show that EphB2 tyrosine kinase activity down regulates Ras and ERK1/2 MAPKs in a neuronal Cell culture system. Our data suggest that p120-RasGAP contributes to Ras inhibition by Eph receptors and indicate that Ras activation interferes with neurite retraction induced by ephrin-B1.
Sarah C Heilshorn - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of vascular Endothelial growth factor-induced pathfinding by Endothelial sprouts in biomaterials.
Tissue Engineering Part A, 2011Co-Authors: Amir Shamloo, Hui Xu, Sarah C HeilshornAbstract:A critical property of biomaterials for use in regenerative medicine applications is the ability to promote angiogenesis, the formation of new vascular networks, to support regenerating tissues. Recent studies have demonstrated that a complex interplay exists between biomechanical and biochemical regulators of Endothelial Cell Sprouting, an early step in angiogenesis. Here, we use a microfluidic platform to study the pathfinding behaviors induced by various stable vascular Endothelial growth factor (VEGF) gradients during Sprouting morphogenesis within biomaterials. Quantitative, time-lapse analysis of Endothelial Sprouting demonstrated that the ability of VEGF to regulate sprout orientation during several stages of Sprouting morphogenesis (initiation, elongation, and turning navigation) was biomaterial dependent. Identical VEGF gradients induced different types of coordinated Cell movements depending on the density of the surrounding collagen/fibronectin matrix. In denser matrices, sprouts were more like...
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matrix rigidity mediates growth factor response during 3d Endothelial Cell Sprouting
Biophysical Journal, 2010Co-Authors: Amir Shamloo, Sarah C HeilshornAbstract:Angiogenesis, the development of complex vascular networks from existing blood vessels, is regulated by multiple biochemical and biomechanical signals acting in concert, although few quantitative systems allow direct measurement and manipulation of these variables. In response, we designed a microfluidic device that produces stable concentration gradients of growth factors within 3D culture matrices and allows independent tuning of the matrix rigidity, soluble growth factor absolute concentration, and concentration gradient steepness within a single experimental platform. Sprout formation of human dermal microvascular Endothelial Cells was studied within collagen gels of varying density (shear moduli from 8-800 Pa) containing stable gradients of soluble VEGF. These experiments revealed that Endothelial Sprouting into multi-Cellular, capillary-like structures is optimized at intermediate collagen matrix rigidities (G′∼100 Pa). In more compliant gels, Cells were unable to maintain coordinated motion and instead migrated as individual Cells through the matrix; while at higher gel rigidities, the Cells formed broad clusters that rarely elongated into a sprout. Sprout thickness directly correlated with matrix rigidity, with thicker sprouts present in gels with the highest shear moduli. Intriguingly, our 3D experiments also found that Endothelial sprouts alter their sensitivity to VEGF depending on the matrix density, suggesting a complex interplay between biochemical and biomechanical factors. As matrix stiffness increases, steeper VEGF gradients and higher VEGF absolute concentrations are required to induce directional Sprouting. In more compliant gels, Endothelial sprouts that originally misaligned were able to turn and properly reorient parallel to the VEGF gradient; however, this turning phenomenon was only rarely observed in stiffer gels. These results demonstrate that matrix stiffness is an effective factor in stabilization and orientation of Endothelial Cells during Sprouting and suggests new anti-angiogenic strategies for potential cancer treatments and pro-angiogenic strategies for regenerative medicine scaffolds.
Jeffrey D Esko - One of the best experts on this subject based on the ideXlab platform.
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3 o sulfation provides high affinity binding to neuropilin 1 and modulates Endothelial Cell Sprouting and neuronal growth cone collapse 607 7
The FASEB Journal, 2014Co-Authors: Bryan E Thacker, Roger Lawrence, Emylie Seamen, Jeffrey D EskoAbstract:Heparan sulfate structural heterogeneity is driven, in part, by the placement of sulfate groups at various positions in the polysaccharide. While many ligands bind to heparan sulfate without strict requirements for the positions of sulfate groups, binding of a small number of known ligands is influenced by the presence of a sulfate at the C3 position of a glucosamine residue. In mammals, seven enzymes can catalyze the addition of 3-O-sulfate groups, suggesting the possibility of other, previously unidentified, ligands whose binding is influenced by 3-O-sulfated sequences. To identify these ligands, affinity matrices were created using CHO-S heparan sulfate, with and without modification by recombinant 3-O-sulfotransferases. Serum was fractionated on the matrices and several proteins binding specifically to the 3-O-sulfated resins were identified by mass spectrometry. Neuropilin-1, a modulator of angiogenesis and axonal guidance, bound specifically to affinity matrices with 3-O-sulfation. In addition, high...
Wolfgang Hiddemann - One of the best experts on this subject based on the ideXlab platform.
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the protein tyrosine kinase inhibitor su5614 inhibits vegf induced Endothelial Cell Sprouting and induces growth arrest and apoptosis by inhibition of c kit in aml Cells
Experimental Hematology, 2002Co-Authors: Karsten Spiekermann, Florian Faber, Robert Voswinckel, Wolfgang HiddemannAbstract:Abstract Objective Angiogenesis, the process of new blood vessel formation, is a critical process during growth and metastasis of solid tumors and might also represent a promising therapeutical target in patients with acute myeloid leukemia (AML). Methods In this study, we analyzed the expression of vascular Endothelial growth factor receptors (VEGFR)-1/2 and its ligand VEGF in AML Cell lines and characterized the inhibitory activity of the protein tyrosine kinase (PTK) inhibitor SU5614 on human Endothelial and leukemic Cells. Results IntraCellular VEGF expression was detected in 9 of 10 leukemic Cell lines. In contrast, VEGFR-1 and VEGFR-2 expression was restricted to 6 and 2 out of 10 Cell lines, respectively. Although SU5614 was a potent inhibitor of the VEGF-induced Endothelial Cell Sprouting in vitro, the sensitivity of leukemic Cells toward the growth inhibitory activity of the compound was determined by the c-kit, but not by the VEGFR-1/2 expression. SU5614 induced growth arrest and apoptosis in c-kit–expressing Kasumi-1, UT-7, and M-07e Cells and inhibited the stem Cell factor (SCF)-induced tyrosine phosphorylation of c-kit. The sensitivity of Kasumi-1 Cells towards the growth inhibitory activity of SU5614 was caused by an autocrine production of SCF, but not by transforming mutations of c-kit. Conclusions Our data provide strong evidence that SU5614 has a dual mode of action, and by direct inhibition of c-kit in AML Cells and by inhibition of VEGFR-2 in Endothelial Cells, it might represent a novel treatment option for patients with c-kit + AML.