Single-chain, urokinase-type plasminogen activator in a tumor model linked to metastatic potential.

Single-chain urokinase-like plasminogen activators have been determined by an indirect method (after activation to urokinase by plasmin and chromogenic assay with S 2444) in the cytosol of a rat tumor model. Variants of the R 3230 AC rat mammary adenocarcinoma were studied, including a subline with increased metastatic potential established by lung colony assay. The cellular content of the UK precursor was found to be significantly higher in the metastatic variant. Plasminogen activator-mediated invasion and collagenolysis of cells with the metastatic phenotype may be regulated by the release of the precursor which lacks reactivity with inhibitors, its transient activation and subsequent inhibition of the urokinase formed.