INCREASED BETA-ACTIN EXPRESSION IN AN INVASIVE MOLONEY SARCOMA VIRUS-TRANSFORMED MDCK CELL VARIANT CONCENTRATES TO THE TIPS OF MULTIPLE PSEUDOPODIA

An invasive variant of Moloney sarcoma virus-transformed MDCK cells (M SV-MDCK-INV), which was isolated by the repeated selection of cells th at successfully traversed a Matrigel-coated filter, exhibits increased motile ability and presents an elongated cell shape and numerous pseu dopodia, Although stress fibers are present in both MDCK and MSV-MDCK cells, MSV-MDCK-INV cells contain no stress fibers and exhibit a dense concentration of actin at the tips of pseudopodia, Relative to both M DCK and MSV-MDCK cells, the MSV-MDCK-INV cells exhibit increased expre ssion of beta-actin and redistribution of beta-actin to the tips of ps eudopodia. These actin concentrations are enriched in both F-and G-act in and, thus, represent dynamic regions of actin cytoskeleton remodeli ng. The acquisition of invasive properties by epithelial transformants is, therefore, associated with the increased expression of beta-actin and its concentration in actin-rich domains, which may drive pseudopo dial extension and facilitate tumor cell invasion.