L cell transfectants stably expressing E-cadherin demonstrate a remarkable increase in adherence to extracellular matrix proteins, such as type IV collagen and fibronectin. This enhanced adhesion is mediated by integrin-type cell surface receptors, as assessed by inhibition with anti-receptor antibodies. Both the rate and efficiency of adhesion were enhanced 4- to 5-fold. In contrast, non-specific adhesion processes, such as cell attachment to polylysine-coated substrata, are unaffected by E-cadherin expression. Thus, integrin-mediated but not non-specific adhesion is modulated by E-cadherin expression. L cells expressing mutant E-cadherin molecules either lacking the cytoplasmic domain or bearing an amino acid substitution in the Ca2+-binding motif did not exhibit enhanced adhesion. The amount of collagen receptor, the α1 and β1 integrin, did not change following expression of E-cadherin. Pull-down assays with the Cdc42/Rac interactive binding (CRIB) domain of the Rac effector, p21-activated kinase, revealed increased Rac-GTP levels in cells expressing wild-type E-cadherin. These results suggest that the activation of Rac is involved in the enhancement of integrin-mediated adhesion induced by E-cadherin expression.
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