The small guanosine triphosphatases (GTPases) Cdc42 and Rac1 regulate E- cadherin-mediated cell-cell adhesion. IQGAP1, a target of Cdc42 and Rac1, was localized with E-cadherin and β-catenin at sites of cell-cell contact in mouse L fibroblasts expressing E-cadherin (EL cells), and interacted with E- cadherin and β-catenin both in vivo and in vitro. IQGAP1 induced the dissociation of α-catenin from a cadherin-catenin complex in vitro and in vivo. Overexpression of IQGAP1 in EL cells, but not in L cells expressing an E-cadherin-α-catenin chimeric protein, resulted in a decrease in E-cadherin- mediated cell-cell, adhesive activity. Thus, IQGAP1, acting downstream of Cdc42 and Rac1, appears to regulate cell-cell adhesion through the cadherin- catenin pathway.
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