Plasminogen activators in normal and malignant oral epithelium in vivo and in vitro.

Urokinase-type (uPA) and tissue-type (tPA) plasminogen activators were identified by fibrinolytic autography in the sulcus epithelium of human gingival mucosa but not in the orthokeratinized gingival epithelium. Fibrinolytic activity was present only over blood vessels in frozen sections of oral squamous cell carcinomas, the malignant epithelial cells showing no plasminogen activator activity. Plasminogen activators could not be demonstrated in either the sulcus or gingival epithelium by immunofluorescence, but both uPA and tPA were found in occasional squamous carcinoma cells. Fibrinolytic activity of culture fluids from epithelial explants grown in vitro from human gingival mucosa showed marked variation, but activity was much higher in the culture supernatants than in the cell lysates. Fibrinolytic activity of culture fluids from epithelial explants of squamous cell carcinomas was low both in supernatants and lysates. Zymogram overlays of sodium dodecyl sulphate-polyacrylamide electrophoretic gels from culture supernatants showed that the low fibrinolytic activity of culture supernatants of oral squamous cell carcinomas was due to the associated presence of plasminogen activator inhibitors. The fibrinolytic activity in the zymogram was due predominantly to uPA but some lysis was due also to tPA.