EpCAM homo-oligomerization is not the basis for its role in cell-cell adhesion

Abstract

Cell-surface tumor marker EpCAM plays a key role in proliferation, differentiation and adhesion processes in stem and epithelial cells. It is established as a cell-cell adhesion molecule, forming intercellular interactions through homophilic association. However, the mechanism by which such interactions arise has not yet been fully elucidated. Here, we first show that EpCAM monomers do not associate into oligomers that would resemble an inter-cellular homo-oligomer, capable of mediating cell-cell adhesion, by using SAXS, XL-MS and bead aggregation assays. Second, we also show that EpCAM forms stable dimers on the surface of a cell with pre-formed cell-cell contacts using FLIM-FRET; however, no inter-cellular homo-oligomers were detectable. Thus, our study provides clear evidence that EpCAM indeed does not function as a homophilic cell adhesion molecule and therefore calls for a significant revision of its role in both normal and cancerous tissues. In the light of this, we strongly support the previously suggested name Epithelial Cell Activating Molecule instead of the Epithelial Cell Adhesion Molecule.

Revisiting the Roles of Pro-Metastatic EpCAM in Cancer

“…The establishment of EpEX crystal structure supports the first model suggesting that EpCAM has cis-dimer orientation, forming trans-tetramer with neighbouring cells [27]. Recent studies however, exerted new evidence in that EpCAM forms neither trans-tetramer nor trans-octamer with another EpCAM molecule on neighbouring cells which is capable of mediating cell-cell adhesion activity [31]. The cis-dimers are the prevalent form and surprisingly, high concentrations of EpCAM dimers tend to resist each other [27,31].…”

“…Recent studies however, exerted new evidence in that EpCAM forms neither trans-tetramer nor trans-octamer with another EpCAM molecule on neighbouring cells which is capable of mediating cell-cell adhesion activity [31]. The cis-dimers are the prevalent form and surprisingly, high concentrations of EpCAM dimers tend to resist each other [27,31]. However, this is not overtly true due to limitations of the techniques used in the study that includes molecular dynamics modelling and chemical cross-linking coupled with mass spectrometry [31].…”

“…The cis-dimers are the prevalent form and surprisingly, high concentrations of EpCAM dimers tend to resist each other [27,31]. However, this is not overtly true due to limitations of the techniques used in the study that includes molecular dynamics modelling and chemical cross-linking coupled with mass spectrometry [31]. These approaches may not detect the presence of cross-linked higher-order oligomers and therefore it is possible that the trans-tetramer structure for example, exist but could not be identified.…”

EPCAMmutation update: Variants associated with congenital tufting enteropathy and Lynch syndrome

“…EpCAM has long been described as a cell adhesion molecule that mediates cell–cell interactions through homooligomerization (Balzar et al., ; Litvinov et al., ). In contrast, recent experiments have not been able to demonstrate EpCAM protein oligomerization in vitro and have not observed a role for EpCAM in the adhesion of carcinoma cell lines (Gaber et al., ; Tsaktanis et al., ). Additionally, EpCAM expression weakens cadherin‐mediated cell adhesion and promotes cell migration and cell invasion in a breast cancer cell line (Osta et al., ; Winter et al., ).…”

Endosomal spatio-temporal modulation of the cortical RhoA zone conditions epithelial cell organization

“…In addition, the loss of EpCAM leads to the development of a rare human disease so-called Congenital Tufting Enteropathy (CTE), characterized by the formation of distinctive lesions in the intestinal epithelium (Patey et al, 1997; Salomon et al, 2014, 2017). However, the conflicting functional interaction of EpCAM with E-cadherin and recent structural analyses tend to challenge its initial function (Litvinov et al, 1997; Winter et al, 2003, 2007; Pavšič et al, 2014; Gaber et al, 2018), and emphasize the need to reconsider its mechanism of action. A link between EpCAM and the actin cytoskeleton was proposed in the 1990’s, with an influence of EpCAM deprivation or overexpression on actin organization (Guillemot et al, 2001), but how it would influence the actin network remained unclear.…”