VASCULAR ENDOTHELIAL GROWTH-FACTOR (VEGF) ISOFORMS - DIFFERENTIAL DEPOSITION INTO THE SUBEPITHELIAL EXTRACELLULAR-MATRIX AND BIOACTIVITY OFEXTRACELLULAR MATRIX-BOUND VEGF

Vascular endothelial growth factor (VEGF)mRNA undergoes alternative sp licing events that generate four different homodimeric isoforms, VEGF( 121), VEGF(165), VEGF(189), Or VEGF(206). VEGF(121) is a nonheparin-bi nding acidic protein, which is freely diffusible. The longer forms, VE GF(189) or VEGF(206), are highly basic proteins tightly bound to extra cellular heparin-containing proteoglycans. VEGF(165) has intermediate properties. To determine the localization of VEGF isoforms, transfecte d human embryonic kidney CEN4 cells expressing VEGF(165), VEGF(189), o r VEGF(206) were stained by immunofluorescence with a specific monoclo nal antibody. The staining was found in patches and streaks suggestive of extracellular matrix (ECM). VEGF(165) was observed largely in Golg i apparatus-like structures. Immunogold labeling of cells expressing V EGF(189) or VEGF(206) revealed that the staining was localized to the subepithelial ECM. VEGF associated with the ECM was bioactive, because endothelial cells cultured on ECM derived from cells expressing VEGF( 189) or VEGF(206) were markedly stimulated to proliferate. In addition , ECM-bound VEGF can be released into a soluble and bioactive form by heparin or plasmin. ECM-bound VEGF(189) and VEGF(206) have molecular m asses consistent with the intact polypeptides. The ECM may represent a n important source of VEGF and angiogenic potential.