VASCULAR ENDOTHELIAL GROWTH-FACTOR AND GLIOMA ANGIOGENESIS - COORDINATE INDUCTION OF VEGF RECEPTORS, DISTRIBUTION OF VEGF PROTEIN AND POSSIBLE IN-VIVO REGULATORY MECHANISMS

We have previously suggested that tumor angiogenesis in human gliomas is regulated by a paracrine mechanism involving vascular endothelial g rowth factor (VEGF) and flt-1 (VEGF-receptor I), VEGF, an endothelial- cell-specific mitogen, is abundantly expressed in glioma cells which r eside along necrotic areas, whereas flt-1, a tyrosine-kinase receptor for VEGF, is expressed in tumor endothelial cells, but not in endothel ial cells in normal adult brain. Recently, a second tyrosine-kinase re ceptor which binds VEGF with high affinity, designated KDR or flk-1, h as been described, We performed in situ hybridization for VEGF mRNA, f lt-1 mRNA and KDR mRNA on serial sections of normal brain, low-grade a nd high-grade glioma specimens, We show that KDR mRNA is co-expressed with flt-1 in vascular cells in glioblastoma but not in low-grade glio ma. Since fit-1 and KDR are not expressed in endothelial cells in the normal adult brain, the coordinate up-regulation of 2 receptors for VE GF appears to be a critical event which controls tumor angiogenesis. I mmunocytochemistry with a monoclonal anti-VEGF antibody revealed signi ficant amounts of VEGF protein in the same glioma cells that expressed VEGF mRNA. The largest amount of VEGF immunoreactivity, however, was detected on the vasculature of glioblastomas, the site where VEGF exer ts its biological functions. These findings suggest that VEGF is produ ced and secreted by glioma cells and acts on tumor endothelial cells w hich express VEGF receptors. To further characterize VEGF-producer cel ls in vivo, we investigated cellular proliferation, immunoreactivity t o the p53 tumor-suppressor gene product and epidermal-growth-factor-re ceptor(EGFR) expression on serial sections by immunocytochemistry. VEG F-producer cells did not show increased cellular proliferation, p53 im munoreactivity or EGFR immunoreactivity as compared with glioma cells which did not express VEGF, Our studies therefore do not demonstrate e vidence for a growth advantage of VEGF-producer cells in vivo or VEGF induction by p53 mutation or EGFR over-expression. (C) 1994 Wiley-Liss , Inc.