Binding of tissue plasminogen activator to cultured human fibroblasts.
The binding of 125I-labeled, one-chain tissue plasminogen activator (t-PA) by WI-38 cultured human lung fibroblasts was investigated. Binding of t-PA to WI-38 monolayers was specific, saturable and temperature dependent. One and two-chain t-PAs were comparable in their ability to compete with 125I-labeled, one-chain t-PA for binding to fibroblasts, while no inhibition of binding was observed with a 500-fold molar excess of urokinase. Studies with various compounds suggest that neither the catalytic site, the fibrin binding site, nor the carbohydrate moieties on t-PA are involved in its binding to WI-38 cells. At higher temperatures, the amount of cell-bound 125I-t-PA that was removed by either incubation in binding buffer containing an excess of unlabeled t-PA, or by brief treatment with acidic buffer, was small (approximately 20%) suggesting that much of the t-PA is internalized. Electrophoretic analysis of extracts prepared from cells that had been incubated with 125I-t-PA revealed the presence of a major band of 70,000 Mr, which corresponds to intact t-PA. Our results suggest that WI-38 fibroblasts are capable of binding and internalizing t-PA, and that these processes involve a receptor site specific for t-PA.
Reilly
T M
TM
E.I. duPont de Nemours and Company, Medical Products Department, Wilmington, DE 19898.
Whitfield
M D
MD
Taylor
D S
DS
Timmermans
P B
PB
D001667:Binding, Competitive; D002450:Cell Communication; D002460:Cell Line; D004705:Endocytosis; D005347:Fibroblasts / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008168:Lung; D011956:Receptors, Cell Surface / Q000032:analysis*; D055293:Receptors, Urokinase Plasminogen Activator; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D010959:Tissue Plasminogen Activator