Localization of plasminogen activators in human colon cancer by immunoperoxidase staining

The immunoperoxidase technique, using antibodies against human urinary urokinase (Mr 55,000), was used for the localization of this enzyme in histological preparations of human colon tumors and normal colon tissue. The localization of tissue (vascular) activator was also investigated using antibodies against enzyme purified from human malignant melanoma. Both the "indirect method" and the peroxidase-antiperoxidase technique were found to be useful. Urokinase-reactive material was found in all tissues examined (33 primary cancers, 11 metastases, and 8 adenomas). In the normal colon, urokinase was found only in some of the goblet cells of the mucosal epithelium. In colon cancer, diffuse specific staining was observed in the cytoplasm, but the most intense staining was localized at the edge of the cancer cells bordering the lumen of the glands. In some cases, intense supranuclear staining could be observed in a location corresponding to the Golgi apparatus. In a few instances, urokinase could be seen associated with fibroblasts near the advancing front of an invading tumor. Adenoma, a benign tumor but often a precursor of cancer, also showed the presence of urokinase. Most significant were the observations showing that, in regions of the mucosal glands where normal epithelial cells were abruptly replaced by cancer cells, the appearance of cytoplasmic urokinase showed strict and exclusive association with the malignant cells, and the same was the case in transitions from normal epithelium to adenoma. In contrast to urokinase, tissue plasminogen activator was not associated with cancer cells, but was consistently present in the stroma which separates the cancer glands and was localized in the endothelium of the blood vessels. This visual evidence was supported by results of extraction of plasminogen activators from tumors, and from the separated mucosal and submucosal layers of the normal colon of the same patients, which showed that urokinase is most abundant in the tumor tissue and least abundant in the submucosa, while tissue activator is most prevalent in the well-vascularized mucosa and submucosa and scarce in the usually poorly vascularized adenocarcinomas.