Amelioration of Congenital Tufting Enteropathy in EpCAM (TROP1)-Deficient Mice via Heterotopic Expression of TROP2 in Intestinal Epithelial Cells

Abstract

TROP1 (EpCAM) and TROP2 are homologous cell surface proteins that are widely expressed, and often co-expressed, in developing and adult epithelia. Various functions have been ascribed to EpCAM and TROP2, but responsible mechanisms are incompletely characterized and functional equivalence has not been examined. Adult intestinal epithelial cells (IEC) express high levels of EpCAM, while TROP2 is not expressed. EpCAM deficiency causes congenital tufting enteropathy (CTE) in humans and a corresponding lethal condition in mice. We expressed TROP2 and EpCAM in the IEC of EpCAM-deficient mice utilizing a villin promoter to assess EpCAM and TROP2 function. Expression of EpCAM or TROP2 in the IEC of EpCAM knockout mice prevented CTE. TROP2 rescue (T2R) mice were smaller than controls, while EpCAM rescue (EpR) mice were not. Abnormalities were observed in the diameters and histology of T2R small intestine, and Paneth and stem cell markers were decreased. T2R mice also exhibited enlarged mesenteric lymph nodes, enhanced permeability to 4 kDa FITC-dextran and increased sensitivity to detergent-induced colitis, consistent with compromised barrier function. Studies of IEC organoids and spheroids revealed that stem cell function was also compromised in T2R mice. We conclude that EpCAM and TROP2 exhibit functional redundancy, but they are not equivalent.

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

“…Despite the wide tissue distribution of the two proteins in developing epithelia, TROP2 has been reported to be dispensable for mouse development and survival under normal housing conditions, whereas the effect of EPCAM deficiency has been reported to be largely confined to the intestines (Wang et al, 2011;Guerra et al, 2012;Lei et al, 2012). This unexpected lack of a Biology Open • Accepted manuscript more widespread phenotype has been ascribed to a possible functional compensation between the two proteins (Nakato et al, 2020). To test this hypothesis, especially in light of the rather limited co-expression of EPCAM and TROP2 in several of epithelia (see above), we performed a systematic phenotypic analysis of mice with single or combined EPCAM and TROP2 deficiency.…”

EpCAM (CD326) Regulates Intestinal Epithelial Integrity and Stem Cells via Rho-Associated Kinase

“…EpCAM also modulates tight junction composition and function [ 5 ]. EpCAM and TROP2 are homologous cell surface proteins and exhibit functional redundancy, but they are not equivalent [ 6 ]. In humans and mice, the most prominent feature of mutations in EpCAM is development of congenital tufting enteropathy (CTE) [ 7 , 8 , 9 , 10 , 11 ].…”

TACSTD2 upregulation is an early reaction to lung infection

“…Decreased expression and altered localization of these proteins were also observed in the corneas of GDLD patients (50). Moreover, forced expression of Trop2 can at least partially stabilize claudins and restore epithelial barrier in mouse model of congenital tufting enteropathy (52). Therefore, a possible explanation of TACSTD2 upregulation following infection is that it represents a mechanism that helps maintain/restore the airway epithelial barrier function.…”

“…It should be noted, however, that the long term Trop2 overexpression associated with inflammation may result in hyperplasia of airway epithelium as observed in lungs of COPD patients (41). Although both proteins interact with tight junction proteins (50,69) and participate in maintenance of epithelial barrier (51,70,71), recent study in EpCAM null mice with forced expression of Trop2 revealed that the function of both proteins is similar but not equivalent (52). Interestingly, we did not find a similar pattern of deregulation of TACSTD1 expression in lungs after infection as observed for TACSTD2 (Supplementary Table S3).…”