Human intestinal MUC17 mucin augments intestinal cell restitution and enhances healing of experimental colitis

Abstract

The membrane-bound mucins, MUC17 (human) and Muc3 (mouse), are highly expressed on the apical surface of intestinal epithelia and are thought to be cytoprotective. The extracellular regions of these mucins contain EGF-like Cys-rich segments (CRD1 and CRD2) connected by an intervening linker domain (L). The purpose of this study was to determine the functional activity of human MUC17 membrane-bound mucin.Methods-Endogenous MUC17 was inhibited in LS174T colon cells by stable transfection of a small hairpin RNA targeting MUC17 (LSsi cells). The effect of recombinant MUC17-CRD1-L-CRD2 protein on migration, apoptosis, and experimental colitis was determined.Results-Reduced MUC17 expression in LSsi cells was associated with visibly reduced cell aggregation, reduced cell-cell adherence, and reduced cell migration, but no change in tumorigenicity. LSsi cells also demonstrated a 3.7-fold increase in apoptosis rates compared with control cells following treatment with etoposide. Exposure of colonic cell lines to exogenous recombinant MUC17-CRD1-L-CRD2 protein significantly increased cell migration and inhibited apoptosis. As a marker of biologic activity, MUC17-CRD1-L-CRD2 proteins stimulate ERK phosphorylation in colonic cell lines; and inhibition of ERK phosphorylation reduced the antiapoptosis and migratory effect of MUC17-CRD1-L-CRD2. Finally, mice treated with MUC17-CRD1-L-CRD2 protein given per rectum demonstrated accelerated healing in acetic acid and dextran sodium sulfate induced colitis in vivo. These data indicate that both native MUC17 and the exogenous recombinant cysteine-rich domain of MUC17 play a role in diverse cellular mechanisms related to cell restitution, and suggest a potential role for MUC17-CRD1-L-CRD2 recombinant protein in the treatment of mucosal inflammatory diseases.

The MUC13 cell-surface mucin protects against intestinal inflammation by inhibiting epithelial cell apoptosis

“…Polymorphisms in MUC1 have recently been linked to CD by a large genome-wide association study 17. Recombinant Muc3 (murine orthologue of human MUC17) and human MUC17 (highly expressed in the intestine) accelerate the healing of experimental colitis, linking this mucin to wound repair 18 19…”

Mucins and Mucus

“…While many of these studies have been conducted in cultured human cancer cells which often overexpress these mucins, these functions are likely to relate to protecting mucosal epithelia from mucosal cytotoxins including toxins made by pathogens to damage epithelial integrity Sheng et al, 2011). MUC1, MUC3, MUC4, MUC13, and MUC17 also modulate epithelial growth, and some of these mucins have been shown to interact with the c-erb family of growth factor receptors (Schroeder et al, 2001;Carraway et al, 2002;Ho et al, 2006;Luu et al, 2010). MUC1 and MUC13 also modulate inflammatory signaling by mucosal epithelial cells, although interestingly, these mucins have opposing effects, with MUC1 suppressing and MUC13 enhancing inflammatory signaling in response to TLR and NOD ligands (Guang et al, 2010;Sheng et al, 2012b).…”

Keeping bugs in check: The mucus layer as a critical component in maintaining intestinal homeostasis

“…These membrane-bound mucins can be shed from the cell surface in two ways: either by the separation of two subunits at the SEA domain, or by alternative splicing (35)(36)(37). Beyond their role in providing anchor function to secreted mucins to form the mucus layer, transmembrane mucins such as murine Muc3 (38) and human MUC17 (39) inhibit epithelial cell apoptosis and enhance epithelial cell aggregation and migration as demonstrated by the endogenous inhibition of MUC17 (39) and Muc3 expression (38) in epithelial cell lines in vitro. Administration of a recombinant MUC17 fragment consisting of its extracellular portion further accelerated mucosal healing in acetic acid-, and DSS-induced experimental colitis in mice (39).…”

“…Beyond their role in providing anchor function to secreted mucins to form the mucus layer, transmembrane mucins such as murine Muc3 (38) and human MUC17 (39) inhibit epithelial cell apoptosis and enhance epithelial cell aggregation and migration as demonstrated by the endogenous inhibition of MUC17 (39) and Muc3 expression (38) in epithelial cell lines in vitro. Administration of a recombinant MUC17 fragment consisting of its extracellular portion further accelerated mucosal healing in acetic acid-, and DSS-induced experimental colitis in mice (39). These results thus indicate a relevant contribution of these transmembrane mucins in epithelial restitution and mucosal healing.…”