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J. Cell Biol.,
Volume 140, Number 4, February 23, 1998 947-959


* Max Planck Institut für Physiologische und Klinische Forschung, W.G. Kerckhoff Institut, Abteilung Molekulare Zellbiologie,
D-61231 Bad Nauheim; Abstract. Vascular endothelial growth factor (VEGF)
is an important regulator of vasculogenesis, angiogenesis, and vascular permeability. In contrast to its transient expression during the formation of new blood vessels, VEGF and its receptors are continuously and
highly expressed in some adult tissues, such as the kidney glomerulus and choroid plexus. This suggests that
VEGF produced by the epithelial cells of these tissues
might be involved in the induction or maintenance of
fenestrations in adjacent endothelial cells expressing
the VEGF receptors. Here we describe a defined in
vitro culture system where fenestrae formation was induced in adrenal cortex capillary endothelial cells by
VEGF, but not by fibroblast growth factor. A strong induction of endothelial fenestrations was observed in
cocultures of endothelial cells with choroid plexus epithelial cells, or mammary epithelial cells stably transfected with cDNAs for VEGF 120 or 164, but not with untransfected cells. These results demonstrate that, in
these cocultures, VEGF is sufficient to induce fenestrations in vitro. Identical results were achieved when the
epithelial cells were replaced by an epithelial-derived
basal lamina-type extracellular matrix, but not with collagen alone. In this defined system, VEGF-mediated induction of fenestrae was always accompanied by an
increase in the number of fused diaphragmed caveolae-like vesicles. Caveolae, but not fenestrae, were labeled
with a caveolin-1-specific antibody both in vivo and in
vitro. VEGF stimulation led to VEGF receptor tyrosine phosphorylation, but no change in the distribution, phosphorylation, or protein level of caveolin-1
was observed. We conclude that VEGF in the presence
of a basal lamina-type extracellular matrix specifically
induces fenestrations in endothelial cells. This defined
in vitro system will allow further study of the signaling mechanisms involved in fenestrae formation, modification of caveolae, and vascular permeability.
Institut für Pathologie, Universität Tübingen, D-72076 Tübingen; and § Max Delbrück Centrum für
Molekulare Medizin, D-13122 Berlin, Germany
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