UROKINASE PLASMINOGEN-ACTIVATOR AND GELATINASES ARE ASSOCIATED WITH MEMBRANE-VESICLES SHED BY HUMAN HT1080 FIBROSARCOMA CELLS

Membrane vesicles are shed by tumor cells both in vivo and in vitro, A lthough their functions are not well understood, it has been proposed that they may play multiple roles in tumor progression, We characteriz ed membrane vesicles from human HT1080 fibrosarcoma cell cultures for the presence of proteinases involved in tumor invasion, By gelatin zym ography and Western blotting, these Vesicles showed major bands corres ponding to the zymogen and active forms of gelatinase B (MMP-9) and ge latinase A (MMP-2) and to the MMP-9.tissue inhibitor of metalloprotein ase 1 complex, Both gelatinases appeared to be associated with the ves icle membrane, HT1080 cell vesicles also showed a strong, plasminogen- dependent fibrinolytic activity in I-125 fibrin assays; this activity was associated with urokinase plasminogen activator, as shown by casei n zymography and Western blotting, Urokinase was bound to its high aff inity receptor on the vesicle membrane, Addition of plasminogen result ed in activation of the progelatinases associated with the vesicles, i ndicating a role of the urokinase-plasmin system in MMP-2 and MMP-9 ac tivation, We propose that vesicles shed by tumor cells may provide a l arge membrane surface for the activation of membrane-associated protei nases involved in extracellular matrix degradation and tissue invasion .