Gelsolin Induces Cancer Invasion via uPA Cascade Figure 4. Gelsolin modulates the expression of invasion-associated urokinase-type plasminogen activator (uPA) cascade in colorectal cancer cells. (A) uPA was detected by microarray analysis to be differentially regulated by gelsolin overexpression. The average gene expression fold changes in the gelsolin-overexpressing clones compared to vector control clones are shown. The gene expression was verified by real-time PCR, and indicated that increased gelsolin upregulated uPA and uPAR mRNA, and decreased mRNA expression of endogenous inhibitors of uPA and plasmin, PAI-2 and a2-AP, respectively. The relative mRNA levels were normalized to vector control cells. (B) siRNA knockdown of gelsolin reduced uPA levels in colorectal cancer cells. Real-time PCR showing the relative mRNA expression of uPA and uPAR in HCT116, DLD-1 and Caco-2 cells after treatment with gelsolin siRNA as compared to control siRNA. All data shown are the mean 6 standard error of triplicate measurements and are representative of at least three independent experiments. *P,0.05. doi:10.1371/journal.pone.0043594.g004 has been highlighted in a number of studies. Cells at the invasive edge acquire molecular changes such as increased expression of matrix-digesting proteases and integrins for matrix-remodelling [38,39], which may be accompanied by a switch towards a mesenchymal-like, dedifferentiated phenotype. These changes in leading cells at the invasive front drive proteases- and force- mediated matrix remodeling which pave the way for collective cell invasion by non-invasive ‘‘follower cells’’ [39]. Notably, the increased tumor aggressiveness has been associated with increased expression or altered localization of other actin-binding proteins such as b-catenin [30], actinin-4 [40], cortactin [41] and fascin [42] at the invasive region of tumors. We have demonstrated here that gelsolin is crucial for the invasive behavior of colorectal tumor cells. Gelsolin has previously been shown to be important for migration of fibroblasts and invasion of other tumor cells, attributable partly to its actin-depolymerizing effects. However, invasion involves the coordination of multiple mechanisms, which include migration and ECM degradation. It is conceivable that the PLOS ONE | www.plosone.org 7 August 2012 | Volume 7 | Issue 8 | e43594