Knockout of ClC-2 reveals critical functions of adherens junctions in colonic homeostasis and tumorigenicity

Abstract

Adherens junctions (AJs), together with tight junctions (TJs), form an apical junctional complex that regulates intestinal epithelial cell-to-cell adherence and barrier homeostasis. Within the AJ, membrane-bound E-cadherin binds β-catenin, which functions as an essential intracellular signaling molecule. We have previously identified a novel protein in the region of the apical junction complex, chloride channel protein-2 (ClC-2), that we have used to study TJ regulation. In this study, we investigated the possible effects of ClC-2 on the regulation of AJs in intestinal mucosal epithelial homeostasis and tumorigenicity. Mucosal homeostasis and junctional proteins were examined in wild-type (WT) and ClC-2 knockout (KO) mice as well as associated colonoids. Tumorigenicity and AJ-associated signaling were evaluated in a murine colitis-associated tumor model and in a colorectal cancer cell line (HT-29). Colonic tissues from ClC-2 KO mice had altered ultrastructural morphology of intercellular junctions with reduced colonocyte differentiation, whereas jejunal tissues had minimal changes. Colonic crypts from ClC-2 KO mice had significantly higher numbers of less-differentiated forms of colonoids compared with WT. Furthermore, the absence of ClC-2 resulted in redistribution of AJ proteins and increased β-catenin activity. Downregulation of ClC-2 in colorectal cells resulted in significant increases in proliferation associated with disruption of AJs. Colitis-associated tumors in ClC-2 KO mice were significantly increased, associated with β-catenin transcription factor activation. The absence of ClC-2 results in less differentiated colonic crypts and increased tumorigenicity associated with colitis via dysregulation of AJ proteins and activation of β-catenin-associated signaling. NEW & NOTEWORTHY Disruption of adherens junctions in the absence of chloride channel protein-2 revealed critical functions of these junctional structures, including maintenance of colonic homeostasis and differentiation as well as driving tumorigenicity by regulating β-catenin signaling.

E-cadherin Beyond Structure: A Signaling Hub in Colon Homeostasis and Disease

“…Additionally, in a Chloride channel protein-2 (CIC-2; CLCN2 ) null mouse model, recovery from DSS-induced colitis was impaired and the epithelial permeability was decreased [89]. Although these results were firstly attributed to compromised TJ function [89], it was subsequently shown that the AJs were also responsible [90]. E-cadherin and β-catenin distribution as well as the ultrastructural tissue morphology were specifically altered in the colon while it was retained in small intestine [90].…”

“…Although these results were firstly attributed to compromised TJ function [89], it was subsequently shown that the AJs were also responsible [90]. E-cadherin and β-catenin distribution as well as the ultrastructural tissue morphology were specifically altered in the colon while it was retained in small intestine [90]. These observations suggest that CIC-2 is associated with the AJs’ function specifically in the colon [90].…”

“…E-cadherin and β-catenin distribution as well as the ultrastructural tissue morphology were specifically altered in the colon while it was retained in small intestine [90]. These observations suggest that CIC-2 is associated with the AJs’ function specifically in the colon [90]. Polymorphisms in the receptor-type tyrosine-protein phosphatase-S gene ( PTPRS ) that encodes for the PTPσ protein are associated with UC.…”

Interplay Between Ion Channels and the Wnt/β-Catenin Signaling Pathway in Cancers

“…The importance of the chloride channel ClCN2, also called ClC-2, in the regulation of tight junctions' composition in the small intestine has been recently uncovered (Nighot and Blikslager, 2012). As ClCN2 seemed to be an important actor of epithelial integrity and maintenance of the tight junctions, Jin et al questioned its involvement in adherens junctions (AJ) and its interaction with b-catenin (Jin et al, 2018). b-catenin binds E-cadherin in the adherens junctions.…”

“…As ClCN2 seemed to be an important actor of epithelial integrity and maintenance of the tight junctions, Jin et al . questioned its involvement in adherens junctions (AJ) and its interaction with β-catenin ( Jin et al., 2018 ). β-catenin binds E-cadherin in the adherens junctions.…”