E-cadherin Homophilic Ligation Directly Signals through Rac and Phosphatidylinositol 3-Kinase to Regulate Adhesive Contacts

Abstract

Classical cadherins mediate cell recognition and cohesion in many tissues of the body. It is increasingly apparent that dynamic cadherin contacts play key roles during morphogenesis and that a range of cell signals are activated as cells form contacts with one another. It has been difficult, however, to determine whether these signals represent direct downstream consequences of cadherin ligation or are juxtacrine signals that are activated when cadherin adhesion brings cell surfaces together but are not direct downstream targets of cadherin signaling. In this study, we used a functional cadherin ligand (hE/Fc) to directly test whether E-cadherin ligation regulates phosphatidylinositol 3-kinase (PI 3-kinase) and Rac signaling. We report that homophilic cadherin ligation recruits Rac to nascent adhesive contacts and specifically stimulates Rac signaling. Adhesion to hE/Fc also recruits PI 3-kinase to the cadherin complex, leading to the production of phosphatidylinositol 3,4,5-trisphosphate in nascent cadherin contacts. Rac activation involved an early phase, which was PI 3-kinase-independent, and a later amplification phase, which was inhibited by wortmannin. PI 3-kinase and Rac activity were necessary for productive adhesive contacts to form following initial homophilic ligation. We conclude that E-cadherin is a cellular receptor that is activated upon homophilic ligation to signal through PI 3-kinase and Rac. We propose that a key function of these cadherin-activated signals is to control adhesive contacts, probably via regulation of the actin cytoskeleton, which ultimately serves to mediate adhesive cellcell recognition.

Changes in E-cadherin rigidity sensing regulate cell adhesion

“…On Ecad-Fc-functionalized glass, cells were very flat and round, with large focal adhesion-like cadherin plaques at the end of thick radial F-actin bundles around the periphery ( Fig. 1E), similar to observations in previous studies (34)(35)(36)(37). These prominent F-actin and E-cadherin structures were very different from the organization of these proteins in cells adhered to Ecad-Fc PA gels.…”

“…The elastic moduli of the two gel formulations used in this study were verified by atomic force microscopy (AFM): 10%T, 1%C, 27.5-31.8 kPa (median: 29.07 kPa) and 10%T, 2.5% C, 52.6-67.2 kPa (median: 57.34 kPa) (Table S1). We also prepared glass coverslips (with an elastic modulus of ∼100 GPa) coated with Ecad-Fc, which have been used in most other studies (34)(35)(36)(37).…”

“…Previous work showed that cells adhering to a more rigid (95-kPa) N-cadherin-coated PA gel were flat and well spread with large N-cadherin adhesion plaques (21), similar to cells adhered to Ecad-Fc-coated glass coverslips (∼100 GPa) (Fig. 1E) (34)(35)(36)(37). In contrast, cells adhered to a softer (10-kPa) N-cadherin-coated PA gel had a reduced spread area and smaller N-cadherin adhesions (21), similar to small E-cadherin clusters in cells adhering to 2D-supported membranes functionalized with the E-cadherin extracellular domain (58), 30-kPa and 60-kPa Ecad-Fc PA gels (Figs.…”

E-cadherin directly contributes to PI3K/AKT activation by engaging the PI3K-p85 regulatory subunit to adherens junctions of ovarian carcinoma cells

“…Because E-cadh has no catalytic domain, we hypothesize that PI3K activation in ovarian carcinoma cells requires stimuli from adjacent cells to allow ligand and receptor contacts, analogous to what is needed for other ligand and receptor pairs such as ephrin-ephrin receptor-mediated signaling (Himanen et al, 2007). E-cadh homophilic ligation was earlier shown to recruit PI3K complex to the cell membrane through the p85 adapter subunit (Kovacs et al, 2002). Such E-cadhactivated PI3K cascade has a clear impact on cadh function, as it is required for adhesive strengthening and for the efficient assembly of cadh-based adhesive contacts.…”

E-Cadherin Homophilic Ligation Inhibits Cell Growth and Epidermal Growth Factor Receptor Signaling Independently of Other Cell Interactions

“…For example, by manipulating overall cell adhesion and junction assembly, several studies have shown recruitment of phosphatidylinositol 3-kinase (PI3K) to adhesive contacts through a tyrosine kinase activity (Pece et al, 1999;Shinohara et al, 2001) and to signal to the Rho family of GTPase (Braga et al, 1999). Some studies used a functional cadherin ligand to specifically engage cadherins to show that E-cadherin homophilic ligation signals directly through PI3K, Rac, and Src activity (Noren et al, 2001;Kovacs et al, 2002;Lambert et al, 2002;Pang et al, 2005). Moreover, cadherins interact with growth factor receptors at the cell surface, and cell adhesion can modulate growth factor signaling activities (Takahashi and Suzuki, 1996;Pece and Gutkind, 2000;Qian et al, 2004).…”