Demonstration of urokinase expression in cancer cells of colon adenocarcinomas by immunohistochemistry and in situ hybridization

The question whether urokinase is expressed in human colon cancer by the ca ncer cells themselves or by surrounding stromal elements such as fibroblast s, macrophages, and leukocytes, which transfer the activator to the recepto rs of the cancer cells, has been a controversial one. In the present study 12 cases of colorectal cancer were investigated by immunohistochemical meth ods using three monoclonal antibodies of different specificity against urok inase. Cytoplasmic staining of strongly varying intensity was observed in a ll cases,with the antigen expressed most strongly in the apical and the bas al regions of the cancer cells. In some cases, staining was also found in s tromal elements surrounding the cancer glands. That the activator was indee d the product of the cancer cells was demonstrated by in situ hybridization using a uPA-cDNA probe, which detected the presence of uPA-mRNA in both th e basal and the apical regions of the cancer cells. A monoclonal antibody a gainst the receptor for uPA showed similar localization. These findings ind icate that the activator is expressed by the cancer cells and is not recrui ted by them from stromal elements.