The expression of vinculin, a major component of adhesion plaques and cell-cell junctions, is markedly modulated in cells during growth activation, differentiation, motility and cell transformation. The stimulation of quiescent cells by serum factors and the culturing of cells on highly adhesive matrices induce vinculin gene expression, whereas the transformation of fibroblast and epithelial cells often results in decreased vinculin expression (reviewed in Rodríguez Fernández, J. L., B. Geiger, D. Salomon, I. Sabanay, M. Zöller, and A. Ben-Ze'ev. 1992. J. Cell Biol. 119:427). To study the effect of reduced vinculin expression on cell behavior, 3T3 cells were transfected with an antisense vinculin cDNA construct, and clones displaying decreased vinculin levels down to 10-30% of control levels were isolated. These cells showed a round phenotype with smaller and fewer vinculin-positive plaques localized mostly at the cell periphery. In addition, they displayed an increased motility compared to controls, manifested by a faster closure of "wounds" introduced into the monolayer, and by the formation of longer phagokinetic tracks. Moreover, the antisense transfectants acquired a higher cloning efficiency and produced larger colonies in soft agar than the parental counterparts. The results demonstrate that the regulation of vinculin expression in cells can affect, in a major way, cell shape and motility, and that decreased vinculin expression can induce cellular changes reminiscent of those found in transformed cells.