Endothelial Myosin Light Chain Kinase Regulates Neutrophil Migration Across Human Umbilical Vein Endothelial Cell Monolayer

Although extravasation of neutrophils is a critical step in acute inflammation, the role of the endothelial cytoskeleton in neutrophil transmigration has not been fully investigated. We used an in vitro model of neutrophil transmigration across a monolayer of HUVEC cultured on amniotic membrane. Human neutrophils were allowed to migrate across the HUVEC monolayer in response to a gradient leukotriene B4 and then the number of migrated neutrophils were counted microscopically. We also followed endothelial F-actin and myosin filament formation using rhodamine-phalloidin and anti-myosin Ab staining. Myosin light chain (MLC) phosphorylation in endothelial cells was determined by immunoprecipitation of 32P-labeled HUVEC with anti-myosin polyclonal Ab. Normally, neutrophil migration induced F-actin formation, myosin filament formation, and MLC phosphorylation in HUVEC. When HUVEC was pretreated with the myosin light chain kinase (MLCK) inhibitor, ML-9, neutrophil migration was diminished and F-actin formation, myosin filament formation, and MLC phosphorylation were inhibited. Pretreatments of HUVEC with the intracellular calcium ion chelator, bis-(O-aminophenoxyl)ethane-N, N, N', N'-tetraacetic acid acetoxymethyl ester (BAPTA/AM), and the calmodulin antagonist, trifluoperazine, had similar effects. These results indicate that a calcium/ calmodulin-dependent MLCK in endothelial cells regulates neutrophil transendothelial migration.