Two independent mechanisms essential for tumor angiogenesis: inhibition of human melanoma xenograft growth by interfering with either the vascular endothelial growth factor receptor pathway or the Tie-2 pathway.
Protein ligands and receptor tyrosine kinases that specifically regulate endothelial cell function are mainly involved in physiological as well as in disease-related angiogenesis. These ligand/receptor systems include the vascular endothelial growth factor (VEGF) and the angiopoietin (Ang) families, and their receptors, the VEGF receptor family and the tyrosine kinase with immunoglobulin-like and epidermal growth factor homology domains (Tie) family. In the present study, the contribution of these endothelium-specific ligand/receptor systems to tumor angiogenesis was evaluated. A375v human melanoma cells, which express at least the angiogenic growth factors VEGF, VEGF-C, and Ang-1, were stably transfected to overexpress the extracellular ligand-binding domains of the endothelium-specific receptor tyrosine kinases fms-like tyrosine kinase-1 (Flt-1), Flt-4, Tie-1, and Tie-2, respectively. In vitro proliferation and colony formation assays confirmed that expression of the extracellular receptor domains inhibited neither tumor cell mitogenesis nor the ability to produce anchorage-independent growth. Nude mouse xenografts revealed that interference with either the VEGF receptor pathway or the Tie-2 pathway resulted in a significant inhibition of tumor growth and tumor angiogenesis. In contrast, interference with the Flt-4 pathway or the Tie-1 pathway was without significant effect. Our results show that both the VEGF receptor pathway and the Tie-2 pathway are essential for A375v melanoma xenograft growth. The inhibition of the VEGF receptor pathway cannot be compensated by the Tie-2 pathway, nor vice versa. These findings suggest that the VEGF receptor pathway and the Tie-2 pathway have to be considered as two independent mediators essential for the process of in vivo angiogenesis.
Institute of Molecular Medicine, Tumor Biology Center, Frieburg, Germany. gerhard.siemeister@schering.de
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G
Siemeister
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Schirner
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Weindel
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Reusch
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Menrad
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Marmé
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Martiny-Baron
D000818:Animals; D016228:Endothelial Growth Factors / Q000096:biosynthesis; D006801:Humans; D008222:Lymphokines / Q000096:biosynthesis; D008545:Melanoma / Q000098:blood supply* / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D008833:Microcirculation / Q000473:pathology; D009389:Neovascularization, Pathologic / Q000517:prevention & control*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D042787:Receptor, TIE-2; D017978:Receptors, Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D040262:Receptors, Vascular Endothelial Growth Factor; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D008222:Lymphokines; D011518:Proto-Oncogene Proteins; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2; D040262:Receptors, Vascular Endothelial Growth Factor; D040281:Vascular Endothelial Growth Factor Receptor-1