Secretion of plasminogen activators by human colorectal and gastric tumor explants

Abstract

Conditioned media from explants of human colorectal and gastric tumors in short-term organ culture were analysed for plasminogen activator activity, activity toward the synthetic urokinase substrate, Spectrozyme-UK, and for the presence of urokinase antigen using monospecific goat antibody, by enzyme-linked immunosorbent assay. Comparisons were made between primary tumors, adjacent normal mucosa and metastatic lesions. These analyses were carried out on unfractionated culture fluids and on fractions obtained by fast protein liquid chromatography separation using Superose 6 gels. Plasminogen activator activity, tested by azocaseinolysis in the presence of added plasminogen, was restricted to peaks of 55 kD and 155 kD. These were of the urokinase type as shown by specific immunoinhibition and by absorption by an antiurokinase antibody-Affigel 10 column. Spectrozyme-UK, in addition to these peaks, detected a series of higher molecular weight activities, the largest of which appeared in the void volume, and were therefore of greater than 10(6) molecular weight. These activities were greatly increased by inclusion of trace plasmin indicating that these components were mostly in their proenzyme forms. The characteristics of these very large enzymes were similar to those isolated earlier from a human lung cancer cell line. Comparison of the primary and metastatic tumors confirmed earlier observations showing that urokinase secretion by the metastatic tumors was greatly reduced in comparison with the primary tumors: in the colon carcinomas it was 10 per cent of the value for the primary, in the gastric tumors 3 per cent, whether means or medians were compared (P less than 0.0001). This large difference was characteristic only of plasminogen activator secretion assayable by azocaseinolysis; activities toward Spectrozyme-UK, and antigen reacting with anti-urokinase antibody, were considerably less different in the two groups. In individual tissues, no correlation was found between the amount of extractable plasminogen activator and amounts secreted, or between the latter and the amount of lactic acid released. It is postulated that the greatly reduced plasminogen activator secretion by explants of metastatic tumors may be a phenotypic characteristic of distinct advantage for cancer cells destined to initiate metastatic foci, and may contribute to the ability of circulating cancer cells to lodge in the blood vessels of the target organ.

Urokinase (uPA) and its inhibitor PAI-1 are strong and independent prognostic factors in node-negative breast cancer

“…This hypothesis is consistent with previous findings where a lower proteolytic uPA activity was determined in the metastases compared to primary tumors [37][38][39].…”

Plasminogen activators in human gastric cancers: Correlation with DNA ploidy and immunohistochemical staining

“…Our results confirmed the earlier report of total-and u-PA activity or antigen level being significantly higher in primary gastric cancer tissues than in normal mucosae (Harvey et al, 1988;Nishino etal., 1988). The predominant type of activator in lung, colon and breast cancers was demonstrated by Markus et al (1983) to be of the urokinase type.…”

Overexpression of urokinase-type plasminogen activator in pancreatic adenocarcinoma is regulated by constitutively activated RelA

“…Conversely, inhibition of uPA can reduce the invasion and metastasis in H-ras-transformed NIH3T3 cells (Axelrod et al, 1989;Rao et al, 1993). It has also been reported that inhibition of uPA can reduce the size of prostate cancer tumors or even cause complete remission of cancers in SCID mice (Harvey et al, 1988;Jankun et al, 1997). These ®ndings provide direct evidence for a causal role for uPA in local tumor invasion and metastasis.…”