| Formatted abstract
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Classical cadherin adhesion molecules belong to a superfamily of cell surface glycoproteins, and are major participants in cell-cell adhesion. E-cadherin, the classical cadherin predominantly expressed in epithelial tissue, is a calcium-dependent, homophilic binding, single pass transmembrane protein that functions in cooperation with the actin cytoskeleton. It is increasingly apparent that E-cadherin operates as an adhesion-activated signalling receptor within the context of a dynamic macromolecular signalling complex. In particular, E-cadherin homophilic ligation can generate intracellular signals that potentially recruit, and activate, membrane or cytosolic proteins at adhesive contacts. The family of small RhoGTPases are one such group of proteins that become activated in direct response to E-cadherin ligation, and appear, in turn, to affect E-cadherin activity. In addition, as major regulators of the actin cytoskeleton, the RhoGTPases are prime candidates to influence E-cadherin and actin co-operativity. However, the molecular basis of an E-cadherin-RhoGTPase signalling pathway has not been elucidated, nor its precise contribution to E-cadherin function clearly understood. This dissertation has examined the contribution of pl20- ctn, a key component of the core cadherin/catenin complex that binds directly to the cadherin-JMD, to E-cadherin function. Using a minimal E-cadherin mutant that uncoupled pl20-ctn binding to the cadherin-JMD, in addition to E-cadherin specific signalling assays, this study reports that pl20-ctn is necessary for E-cadherin signalling to the RhoGTPase, Rac1. Perturbed E-cadherin-Rac signalling was accompanied by profound defects in the capacity for cells to establish cadherin-based contact and in cadherin-mediated adhesion. Therefore, this study provides evidence that pl20-ctn plays a central role in the E-cadherin-Rac signalling pathway.
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