The morphology and functions of cells and tissues are determined, in a large part, by mechanical forces generated at cell-cell and cell-extracellular matrix (ECM) contacts. At these sites, transmembrane
adhesion receptors of the
integrin and
cadherin families are linked, via their cytoplasmic domain, to the cytoskeleton by submembranal plaque
proteins such as
vinculin,
alpha-actinin and the cell-cell junctional plaque
proteins alpha- and
beta-catenin and
plakoglobin (or
gamma-catenin). Recent studies have implicated this link of structural molecules between the outside and inside of the cell in signal transduction. We have shown that the expression of junctional plaque
proteins is modulated during growth stimulation and differentiation, and is dramatically reduced in certain
tumor cells. To study the functional significance of these changes in expression, we have used
recombinant DNA technologies to overexpress or suppress the levels of junctional plaque
proteins. In addition, we eliminated the expression of
vinculin in embryonal stem (ES) cells and in the
embryonal carcinoma F9 line by gene disruption employing homologous recombination. The results have indicated that moderate overexpression of cell-ECM plaque
proteins results in reduced cell motility. In contrast, suppression of their expression, by antisense transfection, led to enhanced motility and conferred anchorage independent growth and tumorigenicity, upon injection into nude mice. These findings suggest that submembranal plaque
proteins can act as effective
tumor suppressors. In agreement with this notion, we found in several tumor cell lines diminished levels of junctional plaque
proteins. Restoration of their level to that found in normal cells resulted in
tumor suppression after their injection into experimental animals. Here we demonstrate the usefulness of the application of two dimensional (2-D) gel electrophoresis in these studies.