Cadherin Engagement Inhibits RhoA via p190RhoGAP

Abstract

Cadherins are transmembrane receptors that mediate cell-cell adhesion in epithelial cells. A number of changes occur during cadherin-mediated junction formation, one of which is a rearrangement of the actin cytoskeleton. Key regulators of actin cytoskeletal dynamics in cells are the Rho family of GTPases. We have demonstrated in previous studies that cadherin signaling suppresses RhoA activity and activates Rac1. The signaling events downstream of cadherins that modulate the activity of Rho family proteins remain unknown. Here we have identified a pathway by which RhoA becomes inactivated by cadherins. To determine whether cadherins regulate RhoA through activation of a GTPase-activating protein (GAP) for RhoA, we used constitutively active RhoA to isolate activated GAPs. Using this assay, we have identified the RhoA-specific GAP, p190RhoGAP, downstream from engaged cadherins. We found that cadherin engagement induced tyrosine phosphorylation of p190RhoGAP and increased its binding to p120RasGAP. The increased precipitation of p190RhoGAP with 63LRhoA was blocked by addition of PP2 suggesting that Src family kinases are required downstream from cadherin signaling. The inhibition of RhoA activity by cadherins was antagonized by expression of a dominant negative p190RhoGAP. Taken together, these data demonstrate that p190RhoGAP activity is critical for RhoA inactivation by cadherins.

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

“…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

“…In epithelial cells, E-cadherin-mediated assembly of adherens junctions recruits and activates Rac1 and Cdc42. Thereby, E-cadherin-bound aand p120-catenin directly interact with Rho family-specific guanine nucleotide exchange factors (GEFs) and with Rho family members [27,28]. 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].…”

Induction of entosis by epithelial cadherin expression

“…We hypothesized that recruitment of a RhoGAP to the epithelial cell junction might restrict the local activity of Rho and contractile myosin, leaving high levels of activity at the cortex oriented away from cell adhesions. To investigate regulators of Rho signaling that could potentially control entosis, we knocked down candidate GAPs that were reported to affect cell-cell junctions [23][24][25][26], including Deleted in Liver Cancer 1 (DLC1), p190A RhoGAP (p190A), and Leukemia-associated RhoGEF (LARG, a GAP for trimeric G proteins 12/13 and q), and examined the effects on entosis. Of these candidates, only the knockdown of p190A with siRNA reduced cell-cell adhesion and induced the scattering of matrix-attached cells ( Figure 5A and 5B), and only p190A knockdown inhibited entosis of cells cultured under matrix-detached conditions ( Figure 5B).…”