Detection and characterization of sucrase-isomaltase in adult human colon and in colonic polyps.

A panel of monoclonal antibodies specific for sucrase-isomaltase, but differing in their ability to stain the proliferative crypt cells in human jejunum, was used to investigate expression of this enzyme in adult human colon and colonic tumors. Immunofluorescence staining on cryostat sections demonstrated the presence of sucrase-isomaltase in the apical region of normal colonic crypt cells but not on surface epithelium. Colonic sucrase-isomaltase was purified by immunoprecipitation with selected monoclonal antibodies and identified predominantly as high-mannose and complex glycosylated single-chain precursors endowed with relatively low levels of enzyme activities. Most polyps examined (10/16) were also found to express significant amounts of sucrase-isomaltase. In contrast, only 3 of 45 adenocarcinomas were positive by immunofluorescence staining; no correlation was found between enzyme expression and tumor classification either by "Dukes" stage or degree of histological differentiation. These results demonstrate that colonic crypt cells and some benign tumor cells synthesize and express at their cell surface a form of sucrase-isomaltase immunologically distinct from that present in the brush borders of small intestinal villose cells.