Cadherin Engagement Regulates Rho family GTPases

Abstract

The formation of cell-cell adherens junctions is a cadherin-mediated process associated with reorganization of the actin cytoskeleton. Because Rho family GTPases regulate actin dynamics, we investigated whether cadherin-mediated adhesion regulates the activity of RhoA, Rac1, and Cdc42. Confluent epithelial cells were found to have elevated Rac1 and Cdc42 activity but decreased RhoA activity when compared with low density cultures. Using a calcium switch method to manipulate junction assembly, we found that induction of cell-cell junctions increased Rac1 activity, and this was inhibited by E-cadherin function-blocking antibodies. Using the same calcium switch procedure, we found little effect on RhoA activity during the first hour of junction assembly. However, over several hours, RhoA activity significantly decreased. To determine whether these effects are mediated directly through cadherins or indirectly through engagement of other surface proteins downstream from junction assembly, we used a model system in which cadherin engagement is induced without cell-cell contact. For these experiments, Chinese hamster ovary cells expressing C-cadherin were plated on the extracellular domain of C-cadherin immobilized on tissue culture plates. Whereas direct cadherin engagement did not stimulate Cdc42 activity, it strongly inhibited RhoA activity but increased Rac1 activity. Deletion of the C-cadherin cytoplasmic domain abolished these effects.

Vascular Endothelial-Cadherin Regulates Cytoskeletal Tension, Cell Spreading, and Focal Adhesions by Stimulating RhoA

“…For other cadherins, it has been reported that RhoA is stimulated by N-cadherin engagement in C2C12 myoblasts (Charrasse et al, 2002) and by E-cadherin engagement in keratinocytes (Calautti et al, 2002). However, other investigators have found that cell-cell contact through cadherins inhibits RhoA activity (Noren et al, 2001;Lampugnani et al, 2002), whereas still others detect no changes in RhoA upon cadherin engagement (Nakagawa et al, 2001). The differences among the results reported might be due to differences between the cadherin molecules or cell types studied, or even the specific experimental conditions used, given that RhoA activity is affected by many stimuli in the surrounding microenvironment, including growth factor concentrations and integrin ligation.…”

Src SH3/2 Domain-mediated Peripheral Accumulation of Src and Phospho-myosin Is Linked to Deregulation of E-cadherin and the Epithelial-Mesenchymal Transition

“…Recent work examined the status of cellular RhoA activity upon induction of contact between epithelial cells either at high density or after plating Chinese hamster ovary cells expressing C-cadherin onto the extracellular domain of C- cadherin (Noren et al, 2001). In both cases, substantial reduction of GTP-loading on RhoA was observed, leading Burridge and colleagues to propose that it may be necessary to keep cellular contractility low to avoid tension being applied to the newly formed cell-cell junctions (Noren et al, 2001(Noren et al, , 2003.…”

“…In both cases, substantial reduction of GTP-loading on RhoA was observed, leading Burridge and colleagues to propose that it may be necessary to keep cellular contractility low to avoid tension being applied to the newly formed cell-cell junctions (Noren et al, 2001(Noren et al, , 2003. Indeed, during the process of chicken embryo fibroblast spreading, the rate of spreading is inversely related to myosin activity (Wakatsuki et al, 2003).…”

Metastasis: cell-autonomous mechanisms versus contributions by the tumor microenvironment

“…Moreover, activated Rac1 and Cdc42 promote and consolidate E-cadherinmediated adhesion by sequestering their downstream effector IQGAP1, which in its free form inhibits the interaction of b-catenin with a-catenin/E-cadherin [29]. After an early activation phase, where RhoA is required for Ecadherin clustering, RhoA gets gradually downregulated with a concomitant repression of cell migration [30]. In contrast, forced expression of RhoA (and also RhoC) in tumor cells induces focal adhesions and stress fibers, promoting invasion and metastasis [31,32].…”