Ve decreased Rho and increased Rac and Cdc42 GTPase activities [7]. We first observed that shRNA-mediated caveolin-1 knockdown enhanced Rac1 activity in the basal state and attenuated Rac1 activity decreasing induced by TNF-a in the primary RPMVECs (Fig. 7A). Cav-1 deficient cells showed a significant increase in GTP-bound Rac1 compared with control shRNA cells in the resting state (2.560.2-fold increase, P,0.001) and after TNF-a stimulation (2.760.4-fold increase, P,0.01), suggesting that caveolin-1 acts as a negative modulator of Rac1 inCav-1 Regulates Rac1 Activation and PermeabilityFigure 8. Proposed mechanism for caveolin-1-mediated modulation of endothelial barrier dysfunction induced by TNF-a. TNFa induced the impairment of Rac1 signaling via TNFR-1 which locat in caveolae. This effect was further prevented by 23115181 O-Me-cAMP. Finally, targeted knockdown of caveolin-1 activated Rac1 signaling that resulted in translocation of cortactin from cell cytoplasm to cell membrane, which promote enhancement of adherens junctions and peripheral actin rim and thus increase EC monolayer barrier properties. Therefore, knockdown of caveolin-1 completely abolishes TNF-a-induced barrier dysfunction, indicating that caveolin-1 plays a mechanistic role in TNF-a-induced endothelial cell activation. doi:10.1371/journal.pone.0055213.gprimary RPMVECs, which was consistent with other data [9]. These findings provide a biochemical rationale for our observations using confocal immunofluorescence microscopy (Fig. 6), in which Cav-1-deficient primary RPMVECs were associated with an increase in lamellipodia, translocation of cortactin to cell periphery and an enhancement of cortical actin distribution, all of which are cellular features characteristic of enhanced small GTPase Rac1 activity. However, when Cav-1-deficient cells were treated with TNF-a, the lamellipodia and translocation of cortactin remained obvious, nevertheless, the formation of central stress fibers were not obvious. All these changes were in contrast to control shRNA cells. These phenotypes suggested that PLV-2 custom synthesis downregulation of caveolin-1 can attenuate the decreasing of Rac1 activity and the changing of cells shape induced by TNF-a. Moreover, to investigate whether these variations of Rac1 activity and cell shape correlated with changes in endothelial barrier functions in primary RPMVECs, we measured the ux of FITCBSA across monolayers of control shRNA cells and Cav-1deficient cells. Under resting conditions, the permeability of FITCBSA in Cav-1-deficient cell monolayers was slightly decreased compared with control shRNA cell monolayers, but not significantly different (Fig. 5B). However, when challenged with TNF-a, the permeability of control shRNA cells monolayers significantly increased, whereas the permeability of Cav-1-deficient cells 3-Amino-1-propanesulfonic acid mildly increased. Otherwise, the elevation of Rac1 activity in Cav-1deficient cells could be suppressed by NSC-23766(specific Racinhibitor).Permeability was increased compared with control shRNA cells monolayer in response to TNF-a. These results indicated that the mechanisms by which TNF-a increased permeability involved caveolin-1 and likely implied a reduction of Rac1 activity and Rac1-depended translocation of cortactin followed by endothelial barrier impairment. Mechanistically, we have found that alterations in the signaling of Rac1 and cortactin are responsible for the changes in morphology and permeability in Cav-1-deficient cells. Previous reports have id.Ve decreased Rho and increased Rac and Cdc42 GTPase activities [7]. We first observed that shRNA-mediated caveolin-1 knockdown enhanced Rac1 activity in the basal state and attenuated Rac1 activity decreasing induced by TNF-a in the primary RPMVECs (Fig. 7A). Cav-1 deficient cells showed a significant increase in GTP-bound Rac1 compared with control shRNA cells in the resting state (2.560.2-fold increase, P,0.001) and after TNF-a stimulation (2.760.4-fold increase, P,0.01), suggesting that caveolin-1 acts as a negative modulator of Rac1 inCav-1 Regulates Rac1 Activation and PermeabilityFigure 8. Proposed mechanism for caveolin-1-mediated modulation of endothelial barrier dysfunction induced by TNF-a. TNFa induced the impairment of Rac1 signaling via TNFR-1 which locat in caveolae. This effect was further prevented by 23115181 O-Me-cAMP. Finally, targeted knockdown of caveolin-1 activated Rac1 signaling that resulted in translocation of cortactin from cell cytoplasm to cell membrane, which promote enhancement of adherens junctions and peripheral actin rim and thus increase EC monolayer barrier properties. Therefore, knockdown of caveolin-1 completely abolishes TNF-a-induced barrier dysfunction, indicating that caveolin-1 plays a mechanistic role in TNF-a-induced endothelial cell activation. doi:10.1371/journal.pone.0055213.gprimary RPMVECs, which was consistent with other data [9]. These findings provide a biochemical rationale for our observations using confocal immunofluorescence microscopy (Fig. 6), in which Cav-1-deficient primary RPMVECs were associated with an increase in lamellipodia, translocation of cortactin to cell periphery and an enhancement of cortical actin distribution, all of which are cellular features characteristic of enhanced small GTPase Rac1 activity. However, when Cav-1-deficient cells were treated with TNF-a, the lamellipodia and translocation of cortactin remained obvious, nevertheless, the formation of central stress fibers were not obvious. All these changes were in contrast to control shRNA cells. These phenotypes suggested that downregulation of caveolin-1 can attenuate the decreasing of Rac1 activity and the changing of cells shape induced by TNF-a. Moreover, to investigate whether these variations of Rac1 activity and cell shape correlated with changes in endothelial barrier functions in primary RPMVECs, we measured the ux of FITCBSA across monolayers of control shRNA cells and Cav-1deficient cells. Under resting conditions, the permeability of FITCBSA in Cav-1-deficient cell monolayers was slightly decreased compared with control shRNA cell monolayers, but not significantly different (Fig. 5B). However, when challenged with TNF-a, the permeability of control shRNA cells monolayers significantly increased, whereas the permeability of Cav-1-deficient cells mildly increased. Otherwise, the elevation of Rac1 activity in Cav-1deficient cells could be suppressed by NSC-23766(specific Racinhibitor).Permeability was increased compared with control shRNA cells monolayer in response to TNF-a. These results indicated that the mechanisms by which TNF-a increased permeability involved caveolin-1 and likely implied a reduction of Rac1 activity and Rac1-depended translocation of cortactin followed by endothelial barrier impairment. Mechanistically, we have found that alterations in the signaling of Rac1 and cortactin are responsible for the changes in morphology and permeability in Cav-1-deficient cells. Previous reports have id.
