H(2)O(2)-mediated elevation in endothelial solute permeability is associated with pathological events such as ischemia-reperfusion and inflammation. To understand how H(2)O(2) mediates increased permeability, we investigated the effects of H(2)O(2) administration on vascular endothelial barrier properties and tight junction organization and function. We report that H(2)O(2) exposure caused an increase in endothelial solute permeability in a time-dependent manner through extracellularly regulated kinase 1 and 2 (ERK1/ERK2) signal pathways. H(2)O(2) exposure caused the tight junctional protein occludin to be rearranged from endothelial cell-cell junctions. Occludin rearrangement involved redistribution of occludin on the cell surface and dissociation of occludin from ZO-1. Occludin also was heavily phosphorylated on serine residues upon H(2)O(2) administration. H(2)O(2) mediates changes in ERK1/ERK2 phosphorylation, increases endothelial solute permeability, and alters occludin localization and phosphorylation were all blocked by PD-98059, a specific mitogen-activated protein (MAP) or ERK kinase 1 inhibitor. These data strongly suggest that H(2)O(2)-mediated increased endothelial solute permeability involves the loss of endothelial tight junction integrity through increased ERK1/ERK2 activation.

Studies aimed at elucidating the function of the protein synthesis factor eukaryotic initiation factor 4E (elF-4E) have demonstrated that overexpression of this protein results in marked cell phenotypic and proliferative changes, including neoplastic transformation of cells. These data suggest that elF-4E may somehow participate in the development and progression of tumors in vivo. In order to determine how elF-4E exerts its transforming effects, we examined vascular permeability factor (VPF) levels in cells transfected with an elF-4E vector. Cells overexpressing elF-4E showed an increase in intracellular, and an average 130-fold increase in secreted VPF protein levels (CHO 0.13 f 0.12 ng/ml; CHO-4E 20.5 2 12.5 ng/ml) over control cells. HUVEC growth induction revealed these VPF levels to be biologically active. Northern analysis revealed no difference in VPF transcript between the 2 cell lines. Polysome analysis showed that the VPF message in elf-4E-transfected cells was associated with the heavy polysomal regions, whereas the VPF message was associated with light polysomes in control cells. These data strongly suggest that enhanced VPF expression is achieved through translational regulation rather than transcriptional regulation in cells overexpressing elF-4E. This indicates that elf-4E-induced VPF expression may be an important factor in some forms of tumor angiogenesir and development.