Intestinal brush‐border‐associated enzymes: Co‐ordinated expression in colorectal cancer

The brush border of normal small‐intestine epithelial cells is rich in enzymes that are involved in the digestive process. Such molecules can be used as markers to analyze cell lineages and differentiation properties of colorectal cancers. Monoclonal antibodies detecting dipeptidyl peptidase‐IV, aminopeptidase N, endopeptidase F, sucrase‐isomaltase, alkaline phosphatase, maltase‐glucoamylase and lactase have been used to analyze the phenotype of colorectal cancers, adjacent mucosa and histologically normal distant mucosa. The avidin‐biotin peroxidase complex method was used. Expression of dipeptidyl peptidase‐IV, aminopeptidase N, sucrase‐isomaltase and alkaline phosphatase was common in non‐neoplastic mucosa adjacent to, and distant from, the tumor; in contrast, endopeptidase F, maltase‐glucoamylase and lactase were rarely expressed in normal distant mucosa and more frequently expressed in mucosa adjacent to the tumor. Dipeptidyl peptidase‐IV, aminopeptidase N, endopeptidase F, sucrase‐isomaltase and alkaline phosphatase were frequently expressed in colorectal cancers, whereas maltase‐glucoamylase and lactase were rarely expressed. Two general patterns of antibody reactivity were observed: diffuse cytoplasmic and apical; apical reactivity was generally associated with more differentiated tumors. A logistic predictive regression model indicated that enzyme expression in colorectal cancers followed a coordinate pattern, but was unrelated to the location of the tumor, Dukes stage or differentiation grade. In conclusion, expression of brush‐border‐associated enzymes occurs frequently in colorectal cancers and is regulated in a co‐ordinated manner. These markers can be used for the phenotypic sub‐classification of colorectal cancers.