Up-regulation of flk-1/vascular endothelial growth factor receptor 2 by its ligand in a cerebral slice culture system

• Published in: Cancer research (Chicago, Ill.) Ill.), 1997-09, Vol.57 (17), p.3852-3859
• Main Authors: KREMER, C, BREIER, G, RISAU, W, PLATE, K. H
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blood vessels and receptors; Brain - metabolism; Cell Hypoxia; Cells, Cultured; Endothelial Growth Factors - metabolism; Female; Fundamental and applied biological sciences. Psychology; General aspects; Humans; Ligands; Lymphokines - metabolism; Male; Medical sciences; Mice; Mice, Inbred BALB C; Platelet Endothelial Cell Adhesion Molecule-1 - metabolism; Receptor Protein-Tyrosine Kinases - genetics; Receptor Protein-Tyrosine Kinases - metabolism; Receptors, Growth Factor - genetics; Receptors, Growth Factor - metabolism; Receptors, Vascular Endothelial Growth Factor; RNA, Messenger - metabolism; Tumors; Up-Regulation; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors; Vertebrates: cardiovascular system
• ISSN: 0008-5472; 1538-7445

Vascular endothelial growth factor (VEGF) and its tyrosine kinase receptors VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR) are key mediators of physiological and pathological angiogenesis. They are expressed in most tissues during embryonic development but are down-regulated in the adult, when angiogenesis ceases. Up-regulation of VEGFR-2 and of VEGF are observed in many pathological conditions under which angiogenesis is reinduced. A major regulator of VEGF expression is hypoxia. Although the temporal expression pattern of VEGFR-2 parallels VEGF expression to a high extent, little is known about its regulation. Here, we show that VEGFR-2 is highly expressed in early postnatal mouse brain but is down-regulated commencing at postnatal day 15 (P15) of mouse brain development and is hardly detectable in P30 mouse brain. Using P30 mouse brain slices, we observed that hypoxia up-regulates VEGFR-2 in the slices but not in human umbilical vein endothelial cells, suggesting the presence of a hypoxia-inducible factor in the murine neuroectoderm that up-regulates VEGFR-2. To identify the factors involved, normoxic P30 cerebral slices were cultured with growth factors that are either hypoxia-inducible (e.g., PDGF-BB, erythropoietin, and VEGF) and/or are known to act on endothelial cells (e.g., PDGF-BB, VEGF, and PIGF). Exogenously added recombinant VEGF led to an up-regulation of VEGFR-2 expression, which could be inhibited by preincubation with a neutralizing anti-VEGF antibody. Addition of PDGF-BB, PIGF, and erythropoietin had no effect on VEGFR-2 expression. Our results suggest a differential but synergistic regulation by hypoxia of VEGF and VEGFR-2: a direct induction of VEGF that subsequently up-regulates VEGFR-2 in endothelial cells. This autoenhancing system may represent an important mechanism of tumor angiogenesis.