H2S Signals through VEGFR-PI3K-Rac1-Cofilin Figure 5. Dominant negative Rac1 and Rac1 siRNA both decrease H2S-promoted cell migration and tube formation in HUVECs. Representative micrographs (A) and statistical analysis (B) of scratch wounding assays showing that expression of dominant-negative Rac1 (T17N) and Rac1 siRNA reduced the cell migration rate promoted by 50 mM NaHS. Representative graphs (C) and statistical data (D) of migrated cells in transwell boyden chamber assay indicating that dominant-negative Rac1 (T17N) and Rac1 siRNA affected the cell migration promoted by 50 mM NaHS. Representative pictures (E) and statistical data of tube length (F) and branching points (G) manifesting that dominant-negative Rac1 (T17N) and Rac1 siRNA blunted the microvessel tube formation in three-dimensional culture. Data represent the means 6 SE of five independent experiments. Each experiment was performed in duplicate. *P,0.05. doi:10.1371/journal.pone.0044590.g005 and that H2S-induced Rac1 activation is specifically dependent on the p110a isoform of PI3K. These data provide the first evidence that the H2S-promoted migration of endothelial cells is dependent on Rac1-mediated actin cytoskeleton remodeling and enhance our understanding of the intracellular signaling mechanisms of the small molecule, H2S. Importantly, the present study indicates that H2S induces the formation of typical lamellipodia in endothelial cells, suggesting PLOS ONE | www.plosone.org 8 September 2012 | Volume 7 | Issue 9 | e44590