Similarities between heterophilic and homophilic cadherin adhesion

Abstract

The mechanism that drives the segregation of cells into tissuespecific subpopulations during development is largely attributed to differences in intercellular adhesion. This process requires the cadherin family of calcium-dependent glycoproteins. A widely held view is that protein-level discrimination between different cadherins on cell surfaces drives this sorting process. Despite this postulated molecular selectivity, adhesion selectivity has not been quantitatively verified at the protein level. In this work, molecular force measurements and bead aggregation assays tested whether differences in cadherin bond strengths could account for cell sorting in vivo and in vitro. Studies were conducted with chicken N-cadherin, canine E-cadherin, and Xenopus C-cadherin. Both qualitative bead aggregation and quantitative force measurements show that the cadherins cross-react. Furthermore, heterophilic adhesion is not substantially weaker than homophilic adhesion, and the measured differences in adhesion do not correlate with cell sorting behavior. These results suggest that the basis for cell segregation during morphogenesis does not map exclusively to protein-level differences in cadherin adhesion.cell adhesion ͉ force probe ͉ selectivity ͉ surface forces apparatus B oth the formation of distinct tissues during morphogenesis and the maintenance of adult tissue structure are regulated by adhesive contacts between cells. One family of adhesion proteins, cadherins, is critical to several processes associated with the formation and maintenance of tissues. The genetic regulation of the spatiotemporal expression patterns of cadherins in vivo is believed to play a central role in embryogenesis, cell differentiation, and the maintenance of the multicellular structure of an organism (1-5). One prevalent hypothesis is that differences in adhesion between cells direct cell segregation during morphogenesis, analogous to liquid-liquid phase separation (6). A fundamental unresolved question is whether this sorting out is encoded by protein-specific or cell-specific differences in adhesion. A common hypothesis is that preferential binding between identical cadherins (homophilic) relative to heterophilic binding between dissimilar cadherins induces the cell segregation.Both the adhesive and the selectivity functions of classic cadherins map to the extracellular (EC) region (7), which comprises five tandemly arranged EC domains, EC1-5, numbered from the outermost domain (Fig. 1) (8). Classical cadherins also contain a transmembrane segment and a cytoplasmic domain. Cadherins form multiple bonds that require different EC domains (9-12). A common feature of the classical cadherins is that the N-terminal domains bind by inserting the tryptophan 2 (W2) residue from one protein into a hydrophobic pocket on an opposed N-terminal domain (13-16). However, given the weak adhesion between the outer domains (11, 12), it is questionable whether the tryptophan binding accounts for both cadherin selectivity and robust adhesion.The most extensively ci...

Cadherin Diffusion in Supported Lipid Bilayers Exhibits Calcium-Dependent Dynamic Heterogeneity

“…The soluble, recombinant extracellular domain EC1-5 of Xenopus cleavage stage cadherin with a C-terminal hexahistidine tag was stably expressed in Chinese Hamster Ovary cells (27,28). The soluble, expressed hexahistidinetagged ectodomains were first purified by affinity chromatography on an Affi-Gel column (Bio-Rad, Hercules, CA), as described in Sivasankar et al (28).…”

Modelling condensation and the initiation of chondrogenesis in chick wing bud mesenchymal cells levitated in an ultrasound trap

“…Previous studies of actin reorganisation following cell-cell contact have employed cells grown on an artificial substrate, often using a 'calcium switch' to induce cadherin-mediated cell-cell contact (Ivanov et al, 2004;Zhang et al, 2005). Adhesion molecules such as cadherins (Goodwin and Yap, 2004;Leckband and Prakasam, 2006;Prakasam et al, 2006) and cell adhesion molecules (CAMs) (Crossin and Krushel, 2000;Walmod et al, 2004) (Gao et al, 2006;Modarresi et al, 2005) and coordinate cytoskeletal remodelling (Bamji, 2005;Goodwin and Yap, 2004;Yap and Kovacs, 2003). Both F-actin and E-cadherin are required for strong intercellular adhesion between mouse sarcoma cells brought together using a pair of micropipettes (Chu et al, 2004).…”

Biophysics of Cadherin Adhesion

“…However, adhesion measurements and equilibrium binding studies showed that classical cadherins also form heterophilic bonds [4,9,12,14,15]. Generally, heterophilic affinities and bond energies are intermediate between the homophilic bonds of the two cadherin subtypes [4,9,10,12,14] (Table 2). …”

“…2F, solid line) gave the two-dimensional affinities and dissociation rates for EC1-EC1 bonds (Table 2) [9][10][11]. The relative affinities of homophilic N-and E-cadherin bonds differ from AUC measurements, but the 2D affinities correlated with the segregation of cells that express these proteins and with adhesion measurements [10,12]. The difference may arise from small sequence differences between the proteins studied, because single amino acid differences can alter the K A 's.…”