Rho and Rac but not Cdc42 regulate endothelial cell permeability

Endothelial permeability induced by thrombin and histamine is accompanied b y actin stress fibre assembly and intercellular gap formation. Here, we inv estigate the roles of the Rho family GTPases Rho1, Rac1 and Cdc42 in regula ting endothelial barrier function, and correlate this with their effects on F-actin organization and intercellular junctions, RhoA, Rac1, and Cdc42 pr oteins were expressed efficiently in human umbilical vein endothelial cells by adenovirus-mediated gene transfer, We show that inhibition of Rho preve nts both thrombin- and histamine-induced increases in endothelial permeabil ity and decreases in transendothelial resistance. Dominant-negative RhoA an d a Rho kinase inhibitor, Y-27632, not only inhibit stress fibre assembly a nd contractility but also prevent thrombin- and histamine-induced disassemb ly of adherens and tight junctions in endothelial cells, providing an expla nation for their effects on permeability, In contrast, dominant-negative Ra d induces permeability in unstimulated cells and enhances thrombin-induced permeability, get inhibits stress fibre assembly, indicating that increased stress fibre formation is not essential for endothelial permeability. Domi nant-negative Cdc42 reduces thrombin-induced stress fibre formation and con tractility but does not affect endothelial cell permeability or responses t o histamine. These results demonstrate that Rho and Rac act in different wa ys to alter endothelial barrier function, whereas Cdc42 does not affect bar rier function.