EPCAM and TROP2 share a role in claudin stabilization and development of intestinal and extraintestinal epithelia in mice

Abstract

EPCAM (Epithelial Cell Adhesion Molecule) is a transmembrane glycoprotein expressed on the surface of most epithelial and epithelium-derived tumor cells and reported to regulate stability of epithelial tight junction proteins, claudins. Despite its widespread expression, loss of EPCAM function has so far only been reported to prominently affect intestinal development, resulting in severe early onset enteropathy associated with impaired growth and decreased survival in both humans and mice. In this study, we show that the critical role of EPCAM is not limited to intestinal tissues and that it shares its essential function with its only known homolog, TROP2 (Trophoblast cell surface antigen 2). EPCAM-deficient mice show significant growth retardation and die within four weeks after birth. In addition to changes in small and large intestines, loss of EPCAM results in hyperkeratosis in skin and forestomach, hair follicle atrophy leading to alopecia, nephron hypoplasia in kidney, proteinuria, and altered production of digestive enzymes by pancreas. Expression of TROP2 partially, but not completely, overlaps with EPCAM in a number developing epithelia. Although loss of TROP2 had no gross impact on mouse development and survival, TROP2 deficiency generally compounded developmental defects observed in EPCAM-deficient mice, led to about 60% decrease in embryonic viability, and further shortened postnatal lifespan of born pups. Importantly, TROP2 was able to compensate for the loss of EPCAM in stabilizing claudin-7 expression and cell membrane localization in tissues that co-express both proteins. These findings identify overlapping functions of EPCAM and TROP2 as regulators of epithelial development in both intestinal and extraintestinal tissues.

EpCAM proteolysis and release of complexed claudin-7 repair and maintain the tight junction barrier

“…The malabsorption phenotype of EpCAM -KO mice might be caused by the loss of the TJ-break surveillance and repair mechanism by EpCAM and claudin-7. Double KO mice of EpCAM and its close homolog TROP2 (trophoblast cell surface antigen 2) exhibited more severe phenotypes compared with EpCAM -KO mice, suggesting that TROP2 also contributes to the TJ maintenance ( Szabo et al, 2022 ). Claudin-7 -KO mice exhibit electrolyte wasting and severe dehydration and die within 12 d after birth ( Tatum et al, 2010 ).…”

An EpCAM/Trop2 mechanostat differentially regulates collective behaviour of human carcinoma cells

“…How can one reconcile our results with the apparent redundancy indicated by the normal embryonic development of single knock-out mice, and with the partial compensation observed in tissues where both are expressed (Guerra et al, 2012;Lei et al, 2012;Szabo et al, 2022;Wang et al, 2011)? One piece of explanation may relate to the acute LOFs used in our study (over 2-5 days).…”

“…All properties reported for EpCAM appear to be shared by Trop2, including oligomerization, association with tetraspanin-based domains, with claudins, potential interaction with the cytoskeleton, or matriptase-mediated cleavage (Balzar et al, 2001(Balzar et al, , 1998Fagotto and Aslemarz, 2020;Guerra et al, 2022;Kuhn et al, 2007;Nubel et al, 2009;Pavsic et al, 2014;Pavšič, 2021;Szabo et al, 2022;Wu et al, 2020). Both form homodimers, but structural considerations indicate incompatibility for heterodimers (Pavšič, 2021).…”

“…Additional avenues include association with tetraspanin-based domains (TEM), as well as with members of the claudin family, which are well documented for EpCAM [62,63]. While Trop2 appears to have similar associations [33,64], one could easily imagine some degree of specificity at this level. Various other interactions have been proposed, including with the actin cytoskeleton [6,64,65], although they are in need of further validation.…”

“…We evaluated the impact of EpCAM levels at the cell and tissue scale, and we systematically characterized the effect on myosin contractility and adhesion, using a combination of cellular and biophysical approaches. EpCAM and Trop2 are thought to be at least partly redundant [6,32,33], and Trop2 expression could partially rescue CTE defects [34]. Yet, the conservation of the two genes throughout amniotes argues for distinct functions, but direct experimental comparison at the cellular level has been missing so far.…”