Tumor invasion through the human amniotic membrane: requirement for a proteinase cascade

To understand the role of proteinases in tumor invasion, the effects of inhibitors of metallo-, serine-, and cysteine-proteinases on this process were studied using 125I-iododeoxyuridine-labeled B16/BL6 cells grown on human amnion basement membrane. Cellular invasion was quantitated by measuring the radioactivity associated with the amniotic membrane after the B16/BL6 cells on the basement membrane were removed by lysis followed by scraping. The results obtained with proteinase inhibitors showed that inhibitors of collagenase and plasmin prevented invasion of the amnion. Tissue invasion was also blocked by antiurokinase antibodies. On the contrary, cysteine-proteinase inhibitors and anti-tissue plasminogen activator antiserum were ineffective. Mersalyl, a compound known to activate collagenase, stimulated invasion under conditions where plasmin formation or activity were inhibited. Evidence for the role of a plasminogen activator-plasmin-collagenase activation cascade in B16 invasion is provided.