Expression of intestinal MUC17 membrane-bound mucin in inflammatory and neoplastic diseases of the colon

Abstract

Aim: To determine the cellular location and expression of MUC17 mucin in specimens of normal, inflamed and neoplastic colon.

Methods: Immunohistochemical analysis of human surgical resection specimens (n=106) was performed with a specific antibody to the MUC17 apomucin protein. A semi-quantitative scoring system was used to measure MUC17 expression. In various colon cancer cell lines, the MUC17 expression was examined by immunoblot analysis and normal RT-PCR.

Results: MUC17 was highly expressed on the surface epithelium and crypts of colonic mucosa. In contrast, the expression of MUC17 was significantly decreased in colonic mucosa of chronic ulcerative colitis (p<0.0001) and ischaemic colitis (p=0.003). Similarly, MUC17 expression was decreased in hyperplastic polyps (p=0.0003), tubular and tubulovillous adenomas (p<0.0001) and colon cancers (p<0.0001). Furthermore, of eight different colon cancer cell lines, MUC17 expression was only detected in LS174T and LS180 cells.

Conclusion: Results indicate that the potential protective effects of this membrane-bound mucin are primarily or secondarily diminished in inflammatory and neoplastic conditions. Further research is needed to determine the specific role of MUC17 in the pathogenesis of these conditions.

Figure 1

The expression of MUC17 in normal and pathological colon tissues (ulcerative colitis, ischaemic colitis, hyperplastic polyp, tubular adenoma and colon cancer) by immunohistochemistry. The colon tissue sections were cut from the paraffin-embedded blocks and stained with anti-MUC17 polyclonal antibody. All sections were examined under a microscope and the immunoreactivity was judged by dark brown staining. Anti-MUC17 antibody showed very faint or no staining in different pathological slides. However, the normal colonic epithelial cells showed a strong staining (arrows). Bar=0.5 inches.

Figure 2

Subcellular localisation of MUC17 in normal and pathological colon tissues (tubular adenoma and colon cancer). Immunohistochemistry showed that in both normal and pathological colons, such as tubular adenoma and colon cancer (in which sporadic staining was found), MUC17 was mostly detected in apical columnar cells, and with a supranuclear pattern of staining (arrow).

Figure 3

(A) RT-PCR analysis of MUC17 expression in various colon cancer cell lines. Actin was used as an internal control. Except for LS174T and LS-180 cells, none of the colon cancer cells have a detectable expression of MUC17. (B) Protein lysates from all the colon cancer cell lines and the AsPC-1 pancreatic cancer cell line (as a positive control), were resolved on 2% agarose gel. The MUC17 protein was only detected in LS174T and LS-180 cells. β-actin was used as a loading control.

Figure 4

Schematic representations of different stages of colitis-associated colon cancer progression, and the status of MUC17 expression in those stages. Colon carcinogenesis mediated trough different colonic inflammatory conditions is a consequence of sequential molecular changes. Inflamed colonic mucosa harbours many altered cancer associated genetic/molecular changes even before any histological evidence of dysplasia or cancer is detected. Among those changes, alteration in the normal expression of mucin (mucin switching) may have functional significance in colitis-associated colon cancer progression. The present study showed that normal colonic MUC17 expression steadily goes down in inflammatory conditions. However, in further advanced stages of cancer progression, MUC17 expression does not differ significantly from inflammatory conditions.