Summary
Endothelial barrier function depends on the integrity of intercellular adherens junctions
controlled by the association of VEcadherin/ catenin complex with cortical actin filaments.
Both tyrosine phosphorylation/dephosphorylation of junctional proteins and actin reorganization
mediated by rho-GTPases regulate barrier function but the relationship between these
regulatory mechanisms is unclear. Here we studied the effects of factors increasing
protein tyrosine phosphorylation, pervanadate (PV) and VEGF, on distribution of VE-cadherin,
F-actin polymerization and transendothelial electrical resistance (TER) in human umbilical
vein endothelial cells (HUVECs). Changes in protein tyrosine phosphorylation of cytoplasmic
and junctional proteins, as well as the activity of rho-GTPase rac1, were also measured.
We report for the first time that PV and VEGF induced a rapid transient increase in
endothelial barrier function accompanied by rac1 activation, a differentiated tyrosine
phosphorylation of theVE-cadherin/catenin complex, recruitment of actin filament to
cell junctions and ruffle formation. A sustained decrease in endothelial barrier function
was observed at later times of PV and VEGF treatment. Expression of dominant negative
rac1, N17rac1 abolished the barrier-enhancing effects of PV andVEGF, while the sustained
decrease in barrier function was unaffected. These observations bring into focus early
shortterm effects of protein tyrosine phosphorylation in cells, often overshadowed
by more pronounced and long-lasting later effects and may play an important role in
the regulation of endothelial barrier function.
Keywords
VE-cadherin - catenin - actin - VEGF - pervanadate