EpCAM contributes to formation of functional tight junction in the intestinal epithelium by recruiting claudin proteins

Abstract

Tight junctions (TJs) connect epithelial cells and form a semipermeable barrier that only allows selective passage of ions and solutes across epithelia. Here we show that mice lacking EpCAM, a putative cell adhesion protein frequently overexpressed in human cancers, manifest intestinal barrier defects and die shortly after birth as a result of intestinal erosion. EpCAM was found to be highly expressed in the developing intestinal epithelium of wild-type mice and to localize to cell-cell junctions including TJs. Claudin-7 colocalized with EpCAM at cell-cell junctions, and the two proteins were found to associate with each other. Claudins 2, 3, 7, and 15 were down-regulated in the intestine of EpCAM mutant mice, with claudin-7 being reduced to undetectable levels. TJs in the mutant intestinal epithelium were morphologically abnormal with the network of TJ strands scattered and dispersed. Finally, the barrier function of the intestinal epithelium was impaired in the mutant animals. These results suggest that EpCAM contributes to formation of intestinal barrier by recruiting claudins to cell-cell junctions.

Cleavage and Cell Adhesion Properties of Human Epithelial Cell Adhesion Molecule (HEPCAM)

“…Knock-out mice are likewise inconsistent with respect to function(s) of mEpcam in normal cells. Whereas the first published knock-out reported on embryonic lethality (6), following two publications, described a perinatal lethality because of severe intestinal leakage, which resembled congenital tufting enteropathy (7,8). Here again, even similar phenotypes could not be assigned to a unified molecular mechanism.…”

Matriptase-mediated cleavage of EpCAM destabilizes claudins and dysregulates intestinal epithelial homeostasis

“…Mice with germline null mutations in Epcam develop the murine equivalent of CTE and die within 2 weeks after birth (10,11). Consistent with EpCAM's claudin-stabilizing effects (12), intestinal expression of selected claudins, including claudin-7, is markedly decreased in mice and humans with EPCAM mutations (3,10). The strong similarities between the phenotypes of Epcam and Cldn7 knockout mice suggest that EpCAM-claudin interactions are extremely important in the intestine (8,13,14).…”

“…Despite the wide tissue distribution of EpCAM, patients with CTE do not exhibit prominent extraintestinal features (1). Mice with germline null mutations in Epcam develop the murine equivalent of CTE and die within 2 weeks after birth (10,11). Consistent with EpCAM's claudin-stabilizing effects (12), intestinal expression of selected claudins, including claudin-7, is markedly decreased in mice and humans with EPCAM mutations (3,10).…”

Multilabel immunofluorescence and antigen reprobing on formalin-fixed paraffin-embedded sections: novel applications for precision pathology diagnosis

“…To assess visualization of cytoplasmic cell organelles, sections were immunostained for late endosomes/lysosomes (Lamp2), that were localized subapically in duodenal villus enterocytes (Figure 3a). Furthermore, immunostaining for EpCAM, involved in formation of tight junctions, 14 was localized to the basolateral membrane of villus enterocytes (Figure 3b and c). Interestingly, in a case of CTE immunostaining for EpCAM was absent from the basolateral membrane of enterocytes, as previously reported, 7 but in addition was mislocalized to subapical cytoplasmic inclusions that colocalized with Lamp2-positive aggregates representing lysosome-like structures (Figure 3d, e and f).…”