We analyzed the effect of IQGAP1 knockdown on actin and MT of confluent EC. The results indicate that IQGAP1 knockdown in EC monolayers decreases MT captured at the interendothelial junctions and decreases lymphocyte diapedesis. Further, drug-induced MT depolymerization decreases paracellular lymphocyte diapedesis. These results indicate that endothelial IQGAP1 tethers MT to interendothelial junctions and participates in junction remodeling during lymphocyte TEM. IQGAP1 has been shown to colocalize with AJ cadherin complex and regulate cadherin-mediated cell–cell

adhesion 24, 26, 27. In EC, we observed IQGAP1 enrichment at the interendothelial junctions (Fig. 1B). To study the role of EC IQGAP1 in lymphocyte TEM, endothelial IQGAP1 expression was inhibited by RNAi. IQGAP1 siRNA transfection of HUVEC consistently reduced IQGAP1 protein expression more than 80% (Fig. 1A–C). However, confluent Tanespimycin solubility dmso IQGAP1-knockdown EC monolayers developed normal AJ, reflected by β-catenin (Fig. 1E) and VE-cadherin (Fig. 2D) localization at the junctions, similar to the control monolayers (Figs. 1D and 2C). Further, analysis of cell surface expression of VE-cadherin and PECAM-1 by flow cytometry identified no change in IQGAP1-knockdown versus control cells (data not shown). Functionally,

electrical impedance across an IQGAP1-knockdown versus the control monolayer was unchanged (data not shown). Dorsomorphin Taken together, these data indicate that IQGAP1 is not required for the surface expression or assembly of endothelial junction components. Next, we sought to characterize the effect of IQGAP1 knockdown on EC cytoskeletal

components since IQGAP1 regulates dynamic filamentous-actin (F-actin) polymerization 23, 35, 36 and MT capture at the cell cortex 21–23. Biochemical analysis of free and polymerized tubulin within EC determined IQGAP1 knockdown decreased the ratio of polymerized tubulin to free tubulin levels in the cytosolic extracts Resveratrol (Fig. 2A and B). Further, measurements of MT density underlying junctions by immunofluorescent double-staining of VE-cadherin and tubulin indicated that tubulin fluorescence intensity per μm2 area adjacent to the VE-cadherin band among IQGAP1 knockdown EC (Fig. 2D and C) decreased by ∼40% (Fig. 2E). These data indicate that IQGAP1 knockdown induced loss of polymerized MT at the interendothelial junctions. To evaluate the effect of IQGAP1 knockdown on the actin cytoskeleton of confluent EC, the population of F-actin and globular-actin (G-actin) in cells was measured. Quantification of results by densitometry did not show any effect in F-actin content by IQGAP1 knockdown (Fig. 2F). Consistent with the biochemical assay, F-actin distribution did not change between IQGAP1 knockdown cells versus control cells by immunofluorescence microscopy (Fig. 2G and H).