Vascular endothelial growth factor induces rapid phosphorylation of tight junction proteins occludin and zonula occluden 1 - A potential mechanism for vascular permeability in diabetic retinopathy and tumors

Vascular endothelial growth factor (VEGF) may have a physiologic role in re gulating vessel permeability and contributes to the pathophysiology of diab etic retinopathy as well as tumor development. We set out to ascertain the mechanism by which VEGF regulates paracellular permeability in rats. Intra ocular injection of VEGF caused a post-translational modification of occlud in as determined by a gel shift from 60 to 62 kDa. This event began by 15 m in post-injection and was maximal by 45 min. Alkaline phosphatase treatment revealed this modification was caused by a change in occludin phosphorylat ion, In addition, the quantity of extracted occludin increased a-fold in th e same time frame, The phosphorylation and increased extraction of occludin was recapitulated in retinal endothelial cells in culture after VEGF stimu lation. The data presented herein are the first demonstration of a change i n the phosphorylation of this transmembrane protein under conditions of inc reased endothelial permeability, In addition, intraocular injection of VEGF also caused tyrosine phosphorylation of ZO-1 as early as 15 min and increa sed phosphorylation ii-fold after 90 min. In conclusion, VEGF rapidly incre ases occludin phosphorylation as well as the tyrosine phosphorylation of ZO -1, Phosphorylation of occludin and ZO-1 likely contribute to regulated end othelial paracellular permeability.