Characterization of plasminogen system on rat yolk sac carcinoma (L2) cells.

The plasminogen (Plg) system on rat yolk sac carcinoma (L2) cells was characterized by zymography, Western and immunoprecipitation analysis, reverse-transcriptase polymerase chain reaction, binding, and activity assays. The L2 cells produced tissue Plg activator but not urokinase Plg activator and contained RNA for Plg activator inhibitor 1, but Plg activator inhibitor 1 was not detectable by zymography or Western analysis and contained the receptor for urokinase Plg activator. Plg bound to the cells in a saturable manner when plasmin inhibitors were present with a dissociation constant of 1.34 +/- 0.18 x 10(-6) M and 1.54 +/- 0.25 x 10(7) sites/cell. Immunoprecipitation analysis showed that Plg was binding to gp330, a known Plg receptor. Once bound to the L2 cells, Plg was activated by tissue Plg activator to plasmin in a time- and concentration-dependent manner. Under saturating Plg conditions, most of the plasmin produced was released into the medium. Inhibition of plasmin activation occurred when Plg activator inhibitor 1, anticatalytic tissue Plg activator antibody, or Heymann nephritis autoantibody was present.