Inhibition of matrix degradation by LIM was more pronounced with PAI inhibiting the release of proline by. With both cell lines, PAI inhibited degradation of sulfatelabeled matrices.In addition, these data suggest that the ability of PAI to completely Riboflavin inhibit the degradation of basement membrane proteoglycans and collagens is lower in cancer cell lines which express both uPA and tPA and that tPA may also play a minor role in invasion.Because cellassociated uPA can recruit proteolytic activity from an enormous pool of the circulating zymogen, plasmin ogen, it was important to determine if the levels of uPA ex pressed on xIO colon cancer cells could be responsible for basement membrane degradation or whether activation of plas min was required.The addition of purified fully Bicalutamide active MT, uPA showed that uPA failed to significantly degrade basement membrane in the absence of plasminogen.Plasmin alone at concentrations as low as g ml caused significant matrix degradation.Under the defined culture conditions of this study, only of the available plasminogen in the culture medium would need to be converted to plasmin to produce similar matrix degradation to that which occurred in the presence of the colon cancer cell line COLO.Although uPA expression in some human tumors or trans formed cell lines is exclusively required for the invasive phenotype, other studies suggest that type IV collagenase is re quired concomitantly with uPA while some studies question any involvement of uPA in the process of tumor metastasis. Basement membranes labeled with serine were prepared as described previously and cultured with, in the presence of PCS in RPMI for hat C,and the percentage of extracellular matrix degraded was determined as outlined previously.PAI AND CANCER CELL EXTRACELLULAR MATRIX DEGRADATION of cellassociated uPA, and the presence of secreted or intracellular endogenous plasminogen activator inhibitors, must be examined before the depth of the involvement of uPA in me tastasis is known.In this study, no degradation of labeled basement membrane was catalyzed by uPA alone.The enhanced rate of matrix degradation by cancer cells illustrates the operation of a cycle of cellassociated plasminogen activation due to low levels of cellbound active uPA which converts the ubiquitous zymogen plasminogen into plasmin which, in turn, catalyzes the activa tion of additional prouPA to active uPA, thereby amplifying the amount of cell surface plasmin present.There was very little plasminogenindependent degradation with either cell line.This shows that the activation of cellasso ciated plasminogen to plasmin is at least one initiating event for the eventual degra dation of a number of extracellular matrix targets, including collagen, proteoglycan, and glycoproteins.Since different ex tracellular matrices have differing macromolecular composi tion, an initiator with broad spectrum protease activity, like plasmin, is a strong candidate to trigger the complex process of cancer invasion.The inability of PAI to completely inhibit extracellular matrix hydrolysis by COLO is in agreement with the previous suggestion that tPA may play a role in invasion, although possibly only a minor role.The ability of COLO to produce high amounts of prouPA and to secrete uPA into serumfree medium has been reported previously.

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