Proteases in human tumors

We carried on an investigation of proteases associated to human tumors by immunohistological techniques. Most of our work dealt with the plasmin system (plasminogen, its two activators and the two plasmin inhibitors, a 2 antiplasmin and a 2 macroglobulin). We found an antigen reacting with anti plasminogen serum in all the 30 colorectal adenocarcinomas we studied by immunofluorescence. This antigen was mainly plasminogen, as we could not detect active plasmin by a histochemical technique on sections of the same tumors. However it is likely that plasminogen present at the surface of tumor cells and on the contour of tumor foci, mainly in invasive areas, can be converted into plasmin, which in turn plays an important role in the degradation of basement membrane antigens. This makes easier tumor invasiveness and release of isolated tumor cells, ready for metastasizing. Plasmin action is likely of short duration and within short range, as this enzyme is rapidly neutralized by its inhibitors, both present at high concentration in the peritumoral stroma. Cathepsin B was characterized by immunoperoxidase method in many colorectal tumors. However our results are preliminary, so we cannot draw any conclusion on the role of this enzyme in tumor invasiveness.