title: Fibulin-5 antagonizes vascular endothelial growth factor (VEGF) signaling and angiogenic sprouting by endothelial cells.
abstract: Fibulin-5 (FBLN-5) is a widely expressed, integrin-binding extracellular matrix protein that mediates endothelial cell adhesion and scaffolds cells to elastic fibers. It is also a gene target of TGF-beta in fibroblasts and endothelial cells that regulates cell proliferation and motility in a context-specific manner. Whereas FBLN-5 expression is low in adult vasculature, its expression is high in developing and injured vasculature, implicating FBLN-5 in regulating angiogenesis and endothelial cell function. We show here that TGF-beta stimulates FBLN-5 expression in endothelial cells, and that this response was inhibited by coadministration of the proangiogenic factor, VEGF. FBLN-5 expression was downregulated significantly during endothelial cell tubulogenesis, implying that FBLN-5 expression antagonizes angiogenesis. Accordingly, FBLN-5 overexpression in or recombinant FBLN-5 treatment of endothelial cells abrogated their ability to undergo angiogenic sprouting, doing so by inhibiting endothelial cell proliferation and invasion through Matrigel matrices. Moreover, FBLN-5 antagonized VEGF signaling in endothelial cells, as well as enhanced their expression of the antiangiogenic factor, thrombospondin-1. Finally, the ability of FBLN-5 to antagonize angiogenic processes was determined to be independent of its integrin-binding RGD motif. Collectively, our findings establish FBLN-5 as a novel antagonist of angiogenesis and endothelial cell activities, and offer new insights into why tumorigenesis downregulates FBLN-5 expression.
authors.affiliation: Program in Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, Denver, Colorado, USA.
authors.forename: Allan R
authors.initials: AR
authors.lastname: Albig
authors.forename: William P
authors.initials: WP
authors.lastname: Schiemann
mesh_terms: D020533:Angiogenesis Inhibitors / Q000378:metabolism*; D000818:Animals; D016367:Baculoviridae; D015152:Blotting, Northern; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D042783:Endothelial Cells; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D005822:Genetic Vectors; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D018919:Neovascularization, Physiologic / Q000502:physiology*; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D019700:Thrombospondin 1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014316:Tritium; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D020533:Angiogenesis Inhibitors; D017931:DNA Primers; D018076:DNA, Complementary; D016326:Extracellular Matrix Proteins; C492373:FBLN5 protein, human; C120769:Fbln5 protein, mouse; D011994:Recombinant Proteins; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A; D014316:Tritium; D008156:Luciferases