F., Jr, Pass I., Tesfay L., Gordon R., Woodrow M., Resau J. ECM holes per cell; RNA interference-mediated knockdown of SV decreases these figures. Although SV knockdown alone has no effect, simultaneous down-regulation of SV and the closely related protein gelsolin reduces invasion through ECM. Together, our results show that SV is usually a component of podosomes and invadopodia and that SV plays a role in invadopodial function, perhaps as a mediator of cortactin localization, activation state, and/or dynamics of metalloproteinases at the ventral cell surface. INTRODUCTION During metastasis, tumor cells invade the surrounding extracellular matrix (ECM), migrate into the bloodstream, and traverse endothelial barriers at secondary sites in distant organs (Condeelis assessments. RESULTS SV Promotes Restructuring of the Actin FGF9 Cytoskeleton SV Overexpression Increases F-Actin Punctae.Increased levels of SV decrease the numbers of COS7 cells containing stress fibers (Takizawa tests and with the Student-Newman-Keuls multiple comparison test (*p 0.05, ***p 0.001). SB 202190 Cortactin Increases the Numbers of EGFP-SV F-Actin Punctae.To see whether cortactin is necessary for the formation of EGFP-SVCinduced F-actin punctae, SB 202190 we reduced cortactin levels by 74% of control-treated cells (Figure 6B, CON, lane 1) by using two different cortactin-specific siRNAs (and assessments. (E) Representative micrographs of cells treated with control siRNA (aCc), SV1 siRNA (dCf), or both SV1 and gelsolin (SV1/Gel) siRNAs (gCi) and stained for F-actin (a, d, and g) or sites of matrix degradation (b, e, and h). For merged images (c, f, and i), holes in the matrix were visualized as reddish spots by pseudocoloring the images in b, e, and h after inverting and thresholding their luminosities. Note the sites of matrix degradation at the cell periphery (arrows) and underneath the cell center (arrowheads). Overlaps are yellow or orange. Bar, 20 m. SV Knockdown Does Not Decrease Ventral F-Actin Punctae.Although SV can increase F-actin bundling in vitro and in vivo (Wulfkuhle tests (*p 0.05; n = 3). Conversation We show here SB 202190 that SV reorganizes the cortical actin cytoskeleton, stimulating the formation or redistribution of dynamic basal punctae made up of F-actin, cortactin, and other podosome/invadopodia proteins while decreasing the extents of cortactin and lamellipodin at the cell periphery. SV and cortactin bind directly in vitro and cooperate to redistribute F-actin in vivo. 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