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

• Published in: American journal of physiology: Gastrointestinal and liver physiology 2018-12, Vol.315 (6), p.G966-G979
• Main Authors: Jin, Younggeon, Ibrahim, Dina, Magness, Scott T, Blikslager, Anthony T
• Format: Article
• Language: English
• Subjects: Adherens junctions; Adherens Junctions - metabolism; Adherens Junctions - pathology; Animals; beta Catenin - metabolism; Carcinogenesis - genetics; Carcinogenesis - metabolism; Cell proliferation; Chloride Channels - genetics; Chloride Channels - metabolism; Colitis; Colitis, Ulcerative - complications; Colon; Colonic Neoplasms - etiology; Colorectal carcinoma; E-cadherin; Epithelial cells; Homeostasis; HT29 Cells; Humans; Inflammatory bowel disease; Intestinal Mucosa - metabolism; Intestinal Mucosa - pathology; Intestine; Intracellular signalling; Mice; Mice, Inbred C57BL; Mucosa; Proteins; Signal Transduction; Tight junctions; Transcription activation; Tumorigenicity; Tumors; β-catenin
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.00087.2018

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.