Intestinal epithelial CAR-Like Membrane Protein promotes mucosal barrier function and prevents colitis-associated cancer in mice.

CAR-Like Membrane Protein (CLMP) is a transmembrane glycoprotein structurally related to Coxsackie and Adenovirus Receptor. Mutations in CLMP gene have been correlated with the development of an intestinal pediatric disorder termed congenital short bowel syndrome (CSBS). To date, not only is the pathogenesis of CSBS incompletely understood, the role of CLMP in gut homeostasis and disease has not yet been elucidated. We found that CLMP expression is significantly reduced in colorectal cancer (CRC) biopsies and increased in inflammatory bowel disease (IBD) compared to normal mucosa samples. Given the expression pattern of CLMP, we generated mice harboring a tamoxifen inducible intestinal epithelial cell (IEC)-specific deletion of CLMP as well as model human IEC in which CLMP expression was silenced or upregulated. We then assessed the role of CLMP in regulating intestinal mucosal barrier function, the development of chronic inflammation and colitis-associated cancer. In this study we report that CLMP protein expression is abundant in differentiated IEC compared to undifferentiated and highly proliferative IEC. CLMP is associated with tight junction controlling the paracellular permeability to solutes and macromolecules. Epithelial CLMP deficiency resulted in enhanced paracellular permeability in vivo and in vitro.These findings indicate an important role for CLMP in regulating epithelial barrier function. Mechanistically, we found that CLMP is involved in homotypic trans-interactions that facilitate cell-cell cohesion and promotes cell-matrix adhesion through integrin beta 1 activity. Lastly, we observed that loss of CLMP in human and mouse IEC resulted in increased cell proliferation. Conversely, CLMP overexpression in IEC resulted in reduced cell proliferation. These results were corroborated in murine models of cancer that included xenograft experiments with CLMP-deficient tumor cells versus CLMP overexpressing tumor cells and Azoxymethane/Dextran Sulfate Sodium-induced colitis-associated cancer. In these models, CLMP deficiency worsened tumor growth. Biochemical analyses revealed CLMP-dependent regulation of IEC proliferation to be mediated through effects on Akt signaling and beta-catenin transcriptional activity. Collectively, our findings provide the first report of a key role for CLMP in the positive regulation of intestinal epithelial barrier function and prevention of tumor development.