Co-localization of Rac1 and E-cadherin in human epidermal keratinocytes

The Rac1 small GTP-binding protein is known to be involved in reorganization of the actin cytoskeleton and in regulation of intracellular signal transduction. The assembly and maintenance of cadherin-based cell cell junctions in epidermal keratinocytes is thought to be dependent on activity of Rac1. In this study we have generated green fluorescent protein (GFP)-tagged wild type, dominant negative and constitutively active Rac1 expression vectors and analyzed distribution of Rac1 following microinjection of human SCC12F epidermal keratinocytes. Wild type, dominant negative and constitutively active GFP Rac1 proteins distribute to sites of cell cell adhesion and co-localize with E-cadherin and the catenins. Disruption of cadherin-based junctions by reduction in extracellular calcium concentrations, or by use of antibodies to E-cadherin, results in redistribution of Rac1 away from sites of cell cell interaction but the co-localization with E-cadherin is maintained. In addition, expression of constitutively active GFP Rac1 results in formation of membrane ruffles on the apical surface of cells and intracellular vesicles. Interestingly, co-localization of Rac1 with E-cadherin is maintained in these structures. In contrast to previously published work we find that expression of dominant negative Rac1 neither disrupts cell cell adhesion nor prevents assembly of new cadherin-based adhesion structures.