Co-localization of Racl and E-Cadherin in Human Epidermal Keratinocytes

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Abstract
The Racl 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 Racl. In this study we have generated green fluorescent protein (GFP)-tagged wild type, dominant negative and constitutively active Racl expression vectors and analyzed distribution of Racl following microinjection of human SCC12F epidermal keratinocytes. Wild type, dominant negative and constitutively active GFP-Racl 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 Racl away from sites of cell-cell interaction but the co-localization with E-cadherin is maintained. In addition, expression of constitutively active GFP-Racl results in formation of membrane ruffles on the apical surface of cells and intracellular vesicles. Interestingly, co-localization of Racl with E-cadherin is maintained in these structures. In contrast to previously published work we find that expression of dominant negative Racl neither disrupts cell-cell adhesion nor prevents assembly of new cadherin-based adhesion structures.