Secretion of extracellular matrix-degrading proteinases is increased in epithelial ovarian carcinoma

The biochemical events associated with tumor invasion involve localized degradation of the basement membrane by tumor-associated proteinases. In this study, we have characterized the proteinase secretion profiles of 5 ovarian epithelial carcinoma cell lines (DOV 13, OVCA 420, OVCA 429, OVCA 432, OVCA 433) as well as normal ovarian epithelial cells. Immunocapture assays demonstrated that all 5 carcinoma cell lines produce both secreted and surface-associated plasminogen activator. Urinary-type plasminogen activator (u-PA) production was one order of magnitude greater than production of tissue-type plasminogen activator (t-PA). Furthermore, t-PA secretion by normal ovarian epithelial cells was not detectable, whereas u-PA production was 17- to 38-fold lower than in ovarian carcinoma cells. Western-blotting analysis demonstrated that u-PA was secreted as the single chain form (scu-PA) when cells were cultured in serum-free medium. Incubation of plasminogen with ovarian carcinoma cell-conditioned medium resulted in direct activation of the zymogen to plasmin. Furthermore, following incubation of cells with plasminogen, plasmin was eluted from the cell surface, indicating that ovarian carcinoma cells contain binding sites for plasminogen/plasmin which are accessible to surface-associated plasminogen activators. In addition to plasminogen activators, metalloproteinases were also produced by DOV 13, OVCA 429 and OVCA 433 cells. DOV 13 cells produce a 68-kDa metalloproteinase similar to matrix metalloproteinase 2 (MMP-2) whereas a 92-kDa enzyme similar to MMP-9 is secreted by OVCA 429 and 433. Together, ovarian carcinoma-associated plasminogen activators and metalloproteinases catalyze the hydrolysis of the major basement membrane protein components, type-IV collagen, type-IV gelatin, laminin and fibronectin. The enhanced proteolytic capability of ovarian carcinoma cells relative to normal ovarian epithelium suggests a biochemical mechanism by which invasion and spread of ovarian epithelial carcinoma may be mediated.