Plasminogen carbohydrate side chains in receptor binding and enzyme activation: a study of C6 glioma cells and primary cultures of rat hepatocytes.
The human [Glu1]-plasminogen carbohydrate isozymes, plasminogen type I (Pg 1) and plasminogen type II (Pg 2), were separated by chromatography and studied in cell binding experiments at 4 degrees C with primary cultures of rat hepatocytes and rat C6 glioma cells. In both cell systems, Pg 1 and Pg 2 bound to an equivalent number of receptors, apparently representing the same population of surface molecules. The affinity for Pg 2 was slightly higher. With hepatocytes, the KD for Pg 1 was 3.2 +/- 0.2 microM, and the KD for Pg 2 was 1.9 +/- 0.1 microM, as determined from Scatchard transformations of the binding isotherms. The Bmax was approximately the same for both isozymes. With C6 cells, the KD for Pg 1 was 2.2 +/- 0.1 microM vs. 1.5 +/- 0.2 microM for Pg 2. Again, the Bmax was similar with both isozymes. 125I-Pg 1 and 125I-Pg 2 were displaced from specific binding sites by either nonradiolabeled isozyme. The KI for Pg 2 was slightly lower than the KI for Pg 1 with hepatocytes (0.9 vs. 1.3 microM) and with C6 cells (0.6 vs. 1.1 microM). No displacement was detected with miniplasminogen at concentrations up to 5.0 microM. Activation of Pg 1 and Pg 2 by recombinant two-chain tissue-plasminogen activator (rt-PA) was enhanced by hepatocyte cultures. The enhancing effect was greater with Pg 2. Hepatocyte cultures did not affect the activation of miniplasminogen by rt-PA or the activation of plasminogen by streptokinase. Unlike the hepatocytes, C6 cells did not enhance the activation of plasminogen by rt-PA or streptokinase; however, plasmin generated in the presence of C6 cells reacted less readily with alpha 2-antiplasmin.
Department of Pathology, University of Virginia Health Sciences Center, Charlottesville 22908.
S W
SW
Hall
S R
SR
VandenBerg
S L
SL
Gonias
D000818:Animals; D050260:Carbohydrate Metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D005341:Fibrinolysin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D010958:Plasminogen / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D014407:Tumor Cells, Cultured; D000511:alpha-Macroglobulins / Q000494:pharmacology
D007457:Iodine Radioisotopes; C524898:PLAUR protein, human; C524900:Plaur protein, rat; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D000511:alpha-Macroglobulins; C024668:plasmin-alpha(2)-macroglobulin complex; D010958:Plasminogen; D005341:Fibrinolysin