Background & aims: Muc3 intestinal mucin contains an extracellular cysteine-rich domain with 2 epidermal growth factor (EGF)-like motifs. The aim of this study was to determine the functional properties of Muc3 proteins.
Methods: Glutathione S-transferase-fusion proteins containing both Muc3 EGF-like domains (m3EGF1,2) or truncated versions (m3EGF1 and m3EGF2) were purified from Escherichia coli. Mouse colon (young adult mouse colon) and human A431 and LoVo cells were examined for migration and tyrosine phosphorylation in response to recombinant proteins. LoVo cells were transfected with a human MUC3A transmembrane-EGF1,2 construct and a stable clone was isolated (LhM3c14). Endogenous MUC3A in LoVo was inhibited by specific small interfering RNA transfection. Apoptosis was quantitated by nuclear morphology or terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick-end labeling assay. Colitis was induced in mice by oral 5% dextran sodium sulfate or rectal 5% acetic acid, followed by enema treatments.
Results: m3EGF1,2 stimulated cell migration in all cell lines, but did not induce proliferation. Migration was inhibited by a tyrosine phosphorylation inhibitor, genistein, but not by the EGF receptor inhibitor, tyrphostin (AG1478). Inhibition of endogenous MUC3A in LoVo reduced baseline migration. Tyrosine phosphorylation of ErbB receptors was not observed after treatment of cells with m3EGF1,2. LoVo cells pretreated with m3EGF1,2 and transfected LhM3c14 cells showed reduced apoptosis in response to tumor necrosis factor alpha or Fas-receptor stimulation. Administration of m3EGF1,2 per rectum significantly reduced mucosal ulceration and apoptosis in experimental acute colitis. Truncated proteins m3EGF1 and m3EGF2 had no effect.
Conclusions: The Muc3 mucin cysteine-rich domain plays an active role in epithelial restitution, and represents a potential novel therapeutic agent for intestinal wound healing.