Vascular endothelial growth factor (VEGF) provokes angiogenesis in vivo and stimulates growth and differentiation of endothelial cells in vitro. Although VEGF receptor-1 (VEGFR-1) and VEGFR-2 are known to be high affi...
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Vascular endothelial growth factor (VEGF) provokes angiogenesis in vivo and stimulates growth and differentiation of endothelial cells in vitro. Although VEGF receptor-1 (VEGFR-1) and VEGFR-2 are known to be high affinity receptors for VEGF, it is not clear which of the VEGFRs are responsible for the transmission of the diverse biological responses of VEGF. For this purpose we have constructed a chimeric receptor for VEGFR-1 (CTR) and VEGFR-2 (CKR) in which the extracellular domain of each receptor was replaced with the extracellular domain of human colony-stimulating factor-1 receptor (CSF-1R), and these receptors were expressed in pig aortic endothelial (PAE) cells. We show that CHR individually expressed in PAE cells is readily tyrosine-phosphorylated in vivo, autophosphorylated in vitro, and stimulates cell proliferation in a CSF-1-dependent manner. In contrast, CTR individually expressed in PAE cells showed no significant in vivo, in vitro tyrosine phosphorylation and cell growth in response to CSF-1 stimulation. The kinase activity of CKR was essential for its biological activity, since mutation of lysine 866 to arginine abolished its in vivo, in vitro tyrosine phosphorylation and mitogenic signals. Remarkably, activation of CTR repressed CKR-mediated mitogen-activate protein kinase activation and cell proliferation. Similar effects were observed for VEGFR-2 co-expressed with VEGFR-1. Collectively, these findings demonstrate that VEGFR-8 activation plays a positive role in angiogenesis by promoting endothelial cell proliferation In contrast, activation of VEGFR-1 plays a stationary role in angiogenesis by antagonizing VEGFR-2 responses.
Fes is a nonreceptor tyrosine kinase expressed at the highest level in macrophages, We previously showed that the overexpression of c-fes in murine macrophages of the BAC-1.2F5 cell line renders these cells independen...
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Fes is a nonreceptor tyrosine kinase expressed at the highest level in macrophages, We previously showed that the overexpression of c-fes in murine macrophages of the BAC-1.2F5 cell line renders these cells independent of macrophage colony-stimulating factor (MCSF) for survival and proliferation, although no direct relationship could be established between tyrosine-phosphorylated substrates of Fes- and MCSF receptor-dependent signaling and mitogenesis. In this study, we investigated whether the mitogen-activated protein kinase (MAPK) pathway is involved in the growth factor-independent growth of v-fes-overexpressing macrophages, We found a constitutively increased phosphorylation of extracellularly regulated kinase (ERK) in v-fes-overexpressing macrophages as compared with mock-infected cells. This finding was associated with activation of nitrogen/extracellular signal-regulated kinase (MEK) and with constitutive localization of ERK in the nucleus. Treatment of v-fes-overexpressing cells with the MEK-specific inhibitor PD98059 markedly reduced cell growth, hyperphosphorylation, and nuclear localization of ERK, indicating that the MAPK pathway mediates the mitogenic effect of v-fes. (C) 2000 by The American Society of Hematology.
Colony stimulating factor-1 (CSF-1) (or macrophage CSF) is involved in the survival, proliferation, differentiation, and activation of cells of the monocyte/macrophage lineage. Because the mitogen-activated protein ki...
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Colony stimulating factor-1 (CSF-1) (or macrophage CSF) is involved in the survival, proliferation, differentiation, and activation of cells of the monocyte/macrophage lineage. Because the mitogen-activated protein kinase family members extracellular signal-regulated kinases (ERKs), p38, and c-Jun N-terminal kinase are widely implicated in such cellular functions, we measured their activity in growing and growth-arrested cultures of bone marrow-derived macrophages (BMM), as well as their stimulation by saturating concentrations of CSF-1, ERK activity was approximately a-fold higher in cycling BMM compared with growth-arrested BMM;in addition, CSF-l-stimulated BMM DNA synthesis was partially inhibited by PD98059, a specific inhibitor of MEK activation, suggesting a role for a mitogen-activated protein-ERK kinase (MEK)/ERK pathway in the control of DNA synthesis but surprisingly not in the control of cyclin D1 mRNA or c-myc mRNA expression. The suppression of BMM apoptosis by CSF-1, i.e, enhanced survival, was not reversed by PD98059, suggesting that a MEK/ERK pathway is not involved in this process. Using a quantitative kinase assay, it was found that CSF-1 gave a slight increase in BMM p38 activity, supporting prior data that CSF-1 is a relatively weak stimulator of inflammatory cytokine production in monocytes/macrophages, Relatively high concentrations of the p38 inhibitor, SKB202190, suppressed CSF-l-stimulated BMM DNA synthesis. No evidence could be obtained for the involvement of p38 activity in BMM apoptosis following CSF-1 withdrawal. We were not able to show that CSF-1 enhanced BMM JNK-1 activity to a significant extent;again, no role could be found for JNK-1 activity in the BMM apoptosis occurring after CSF-1 removal.
Chronic autoimmune thrombocytopenic purpura (AITP) is an organ specific autoimmune bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in increased pc-mediated p...
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Chronic autoimmune thrombocytopenic purpura (AITP) is an organ specific autoimmune bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in increased pc-mediated platelet destruction by macrophages in the reticuloendothelial system. Although AITP is primarily mediated by IgG autoantibodies, their production is regulated by the influence of T lymphocytes and antigen presenting cells (APC). This review argues that enhanced T helper cell/antigen presenting cell interactions in patients with AITP may be responsible for IgG anti-platelet autoantibody production. Understanding these cellular immune responses in AITP may lead to the development of more immune specific therapies for the management of this disease. (C) 1998 Elsevier Science Ltd. All rights reserved.
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