Interactions between tissue-type plasminogen activator and extracellular matrix-associated plasminogen activator inhibitor type 1 in the human hepatoma cell line HepG2.
Hepatic parenchymal cells contribute to the clearance of circulating tissue-type plasminogen activator (t-PA) in vivo. The hepatocyte extracellular matrix is interposed between the endothelial-lined sinusoids and the parenchymal cell surface and thus may influence t-PA clearance. To test this hypothesis, the well differentiated human hepatoma cell line HepG2 was used to characterize the role of extracellular matrix in t-PA clearance in vitro. Previous studies with these cells demonstrated their capacity for specific catabolism of t-PA in a system modulated by plasminogen activator inhibitor type 1 (PAI-1). In the present study the extracellular matrix growth substratum of HepG2 cells is shown to contain active PAI-1. PAI-1 is distributed in a punctuate pattern throughout the substratum. Components of the substratum confer stability to active PAI-1 for intervals of at least 24 h. Exposing substratum to 125I-t-PA leads rapidly to the formation and release of a sodium dodecyl sulfate-stable 95-kDa 125I-t-PA.PAI-1 complex. In comparison, cell monolayers have the additional capacity for specific binding of the complex. However, PAI-1 is not detected at the surface of HepG2 cells in suspension, suggesting that 125I-t-PA.PAI-1 complexes form in substratum and subsequently bind to cells. Specific binding of performed 125I-t-PA.PAI-1, but not 125I-t-PA, was demonstrated for HepG2 cells in suspension. These results suggest that components of extracellular matrix participate in the clearance of t-PA by hepatocytes.
Owensby
D A
DA
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
Morton
P A
PA
Schwartz
A L
AL
D000873:Anthracenes / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D004705:Endocytosis; D005109:Extracellular Matrix / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008113:Liver Neoplasms; D008962:Models, Theoretical; D015849:Plasminogen Inactivators / Q000378:metabolism*; D011485:Protein Binding; D010959:Tissue Plasminogen Activator / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D000873:Anthracenes; D015849:Plasminogen Inactivators; C061472:9-anthranoylnitrile; D010959:Tissue Plasminogen Activator